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Surface Mount Package User`s Manual

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1. 2 6 00 5 Hs e PRENNE 0 6 11 o Z i j 222 ZA S 1 0 10 t CMPAK 4 D CMPAK 5 D 1 3 0 65 0 65 Z 5 122 2 o o 06 B 0 4 T si Z 5 nus VSON 5 0 5 0 5 224 923 0 45 Figure 3 15 Example of Mounting Pad Design for Discrete Packages 4 Note DY in CMPAK 4 D CMPAK 5 D indicates diode packages However is omitted in each product s document HITACHI 3 2 Solder Application As the lead pitch for surface mount packages has become narrower the application process of solder paste has come to have a great influence on the stability of soldering qualities yield and reliability By optimizing the following elements of the application process of solder paste it is possible to stabilize the quality of the soldering e Solder paste materials e Printing mask for the solder paste application e Application equipment of solder paste printer or dispenser 3 2 1 Solder Paste 1 Structure of the Material Solder paste consists of solder powder flux etc a Solder Powder As lead pitches have become narrower solder powder has undergone a sequential miniaturization from irregular shape to spherical shape to fine spherical shape At present the spherical shape solder is used the most in surface mounting applications F
2. e Type 3 375 mil 9 53 Type 6 600 mil 15 24 b Bo a 0 2 or more 2 By 0 2 to 0 5 vi B 0 2 Y 0 3 b 0 76 f L B1 B gt Reference values based on the former EIAJ standard ED 7402 1 Figure 3 8 Example of Mounting Pad Design for SOP HITACHI 13 TSOP 1 Mp j I S Ean Te qum E BRR FRB b l e E b th 2 Units mm 0 1 100 2 By 0 2 to 0 3 Bo 0 2 Y 0 25 fel 0 5 b 0 25 Lo gt L 1 2 Reference values based on the former EIAJ standard ED 7402 3 Figure 3 9 Example of Mounting Pad Design for TSOP I HITACHI TSOP II E Me e e i L X 02 s 1 J Y e b esf Units mm 0 0 1 By 0 2 Bo 0 2 L lo gt L Bi B Q Do b to ej y Reference values based on the former EIAJ standard ED 7402 4A Figure 3 10 Ex
3. x 2 1 o m Moisture o 4L absorption ratio S 85 C 85 RH E Fad bi S gi cane 03w o 9 o o g 0 2 wt e m 0 1 wt 5 lt 0 250 0 Temperature C Figure 3 51 Dependence on Temperature of the Adhesive Strength Mechanical Strength of the Resin and the Generated Stress 3 9 3 Discerning the Package Crack When the cracks are extreme and the cracks extend to the surface of the package it is possible to discern the cracks through an visual inspection The cracks that do not extend to the surface however can be evaluated through the use of an ultrasonic scanning instrument Figure 3 52 shows an overview of this ultrasonic scanning method An ultrasonic beam either 25 MHz or 50 MHz is transmitted from a probe into the package which is immersed in water and the ultrasonic waves that are reflected from the package are picked up by the probe The ultrasonic waves received by the probe are converted into electronic signals and are canceled against the ultrasonic wave signals that are reflected from the surface of the package etc so that only internal signals are subjected to image processing Using this process it is possible to make the comparison shown in Figure 3 53 where an example of a package wherein internal cracks are detected is compared to an example devoid of cracks These internal cracks result when the reflow conditions are relatively harsh The use of this
4. Solder b Single sided mixed mounting Surface mount insertion mount Solder paste Application of solder paste Printed wiring board AA Surface mount package mounting Soldering reflow T The board is turned ove r 1 Application of Solder paste QE gt Solder paste Reflow T The board is turned over reflow flow soldering Solder paste m Printed wiring board MEN DAE Adhesive lt L Application of temporary adhesive Surface mount package mounting Soldering reflow c Double sided surface mounting Surface mount surface mount reflow reflow Surface mount package mounting Adhesive cure c Ultraviolet rays m ee x The board is turned over r s Insertion of insertion type package pany oe a eS Soldering flow soldering d Double sided mixed mounting Surface mount surface mount insei Solder ion mount reflow batch flow soldering Figure 1 1 Types of Surface Mount Package Mounting Configurations HITACHI HITACHI Section 2 Surface Mount Package Assembly Process Flow 2 1 Basic Assembly Process Flow for Surface Mount Packages Figure 2 1 shows the basic assembly process flow for surface mount packages First a solder paste is
5. sese 89 4 4 Reflovv Soldering Conditions eese entente ener nennen enne 90 4 5 Inspecting the Solder Joints After Mounting on the Printed Wiring Board 91 4 6 Removing Method orbe piene Ree deutsch et eee Per ee reete reete crat 92 4 7 Cleaning ie R Y aO epe 93 4 8 StOLage ceti 6i eA RH I RU Gr AE RIA RN haya d bier 94 ii HITACHI Section 1 Types of Package Mounting Configurations Package mounting configurations may include surface mounting and mixed mounting The forms of the various mounting approaches are as shown in Figure 1 1 Because only surface mount devices can be used in double sided surface mounting the double sided surface mounting method provides the highest mounting density Insertion devices and surface mount devices are both used in mixed mounting A flow soldering process is used for the insertion devices Application of solder paste Solder paste Application of solder paste Printed wiring board Solder paste Printed wiring board Surface mount package mounting Soldering reflow a Single sided surface mounting reflow Application of Solder paste Surface mount package mounting Surface mount package mounting A E Ee Reflow Insertion of insertion type package Soldering flow soldering pam E n e
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7. Solder mask pattern accuracy and ease of solder inspection 2o gt L B Be 22 Mounting pad length b lt b s lel r b Mounting pad vvidth y Eliminating solder bridge B4 0 2 mm L Length of flat part of terminal b Terminal width Units mm e 1 0 0 8 0 65 0 5 0 4 0 3 a 0 2 or more 0 1 or more 0 2 0 2 By 0 5 0 2 to 0 3 0 3 0 3 Bo 0 2 0 2 0 2 0 2 Y 0 3 0 25 0 2 0 15 Reference values based on the former EIAJ standard 0 7404 Figure 3 4 Example of Mounting Pad Design for QFP Including TQFP and LQFP 10 HITACHI SOJ B Units mm 1 12 lo 2 0 b2 0 75 Reference values based on the former EIAJ standard ED 7406 Figure 3 5 Example of Mounting Pad Design for SOJ QFJ PLCC 8p g98 1 1 i G T J m
8. 24 V Soldering iron tip Figure 3 47 Example of Grounding for the Soldering Iron 77 HITACHI 3 Countermeasures to Prevent Electrostatic Discharge from the Semiconductors When there is static electrical charge on a package or on the semiconductor die the electrostatic charge by itself does not damage the semiconductor rather it is the terminal coming into contact with a metal object when the semiconductor is charged that causes a discharge which damages the semiconductor In this type of situation grounding the metal will have no effect The countermeasures to be used are as follows a Avoid contact semiconductor with or rubbing semiconductor against insulative materials that will tend to cause triboelectric charging b Avoid handling operations of the semiconductors on metal plates but rather work on ESD protective mats c When there is the chance that the semiconductor is charged static electricity be careful to avoid bringing the semiconductors into direct contact with metal objects 4 Notes and Cautions for Mounting Operations a It is necessary to use a ESD protective mat etc even when mounting the semiconductors on the printed wiring board and to insure that the mat is grounded in advance Special care is required when there is an accumulated charge in the capacitor after operation tests have been performed on the printed wiring board b The printed wiring board will be charg
9. b da isi 1 D or 1 E EE NES ie b 01 l2 T 75 r1 e e D Units mm 1 12 72 2 0 b 0 75 Reference values based on the former EIAJ standard ED 7407 Figure 3 6 Example of Mounting Pad Design for QFJ PLCC HITACHI QFN LCC E i e i 22 Li D I r SHHH nnn gt L Mp lt D 2 x L Mp 2 D 2 x Me lt E 2 x L Mg 2E 2x a bx b lt Je B F LI Mp M b D2 Y Y Do Me Mee Units mm 0 0 2 b 0 3 Reference values based on the former EIAJ standard ED 7412 12 Figure 3 7 Example of Mounting Pad Design for QFN LCC HITACHI SOP ET Do RQ i Y Lo A Eq ER Eq RS RI NY AY SY SY SS SS ES Units mm Type 1 225 mil 5 72 Type 2 300 mil 7 62 Type 4 450 mil 11 43 Type 5 525 mil 13 34
10. device to float e Use LSls with minimal attached to the lead The lead is bent in bend in the leads QFPs SOPs etc Re examine the The amount of solder printing parameters paste printed is not Increase the thickness uniform of the printing layer e There is uneven heating e Re examine the and thus there is a non heating conditions uniformity in the time over which the solder is molten Cleaning defect Despite the fact that flux residue is Use a solder paste Pad the board has been resistant to cleaning that has good cleaning D Lead Powder residue 7 cleaned there is flux residue or vvhite The cleaning solution is not appropriate The cleaning method is not appropriate properties Re examine the cleaning solution and cleaning method Residue The cleaning solution did Perform the cleaning not saturate the residue 85 soon as possible e There is a long time after the reflow delay between the reflow PrOCess process and the cleaning process Wicking There is no solder Inthe VPS method this Insure adequate Lead Solder Pad Printed wiring board between the lead and the pad because the molten solder has been sucked up SOJ QFJ PLCC lead occurs when the heating is done too rapidly HITACHI preheating in the VPS method Perform the soldering in a far infrared reflow furnace 71 3 8 Storage 3 8 1 Moisture proof Packing When the plas
11. dip gt fo lt DN Direction of movement Flow solder Solder bath for surface mounting Figure 3 39 Schematic of Flow Soldering Method Using a SOP as an example 3 5 3 Setting the Soldering Temperature Profile Peak temperature Temperature Temperature ramping Preheating temperature Temperature ramping Preheating Main heating Cooling Reflow e Key Approaches to Setting the Temperature Profile Key considerations in setting the temperature profile for the soldering process include the following Setting temperature conditions that allow effective soldering Setting temperature conditions that do not cause thermal damage to the devices 52 HITACHI e Key Points in Assigning Actual Temperature Profile Settings The key parameters to be set in defining the temperature profile include the following Peak temperature Solder melting time Preheating temperature and time Temperature ramping 1 Setting the Peak Temperature The optimal parameters for the peak temperature should be set after taking the following into consideration a The surface temperature of the devices to be mounted must be less than the thermal durability temperature of those devices b The solder joint temperature must be higher than the solder paste melting point Example 1 63Sn 37Pb eutectic solder paste Generally
12. ed hec 25 3 2 3 Amount of Printed Solder Paste sese 31 3 3 Temporary Adhesive uires eret e Rar 33 3 3 1 Adhesive Strength nies eere e eine ua teet 34 3 322 Conditions OI es ERR banana 35 3 3 3 Amount of Adhesive Applied Height eee 36 34 Mounting Placement kuy as n ee tete ere eere tee s s 37 3 4 1 Mounting Process pete eet e eed eee prt te led toes 37 3 42 Selecting th Munter a s rere t Oper eter teet 39 3 43 Mounting Accuracy seson iae e Ue dI Unete e ed etre 40 3 4 4 Shapes of the Package 1 2 40 3 5 Soldering isset nete remp pp o e epit b iet 44 3 5 1 Soldering Methods 4 cte P te the rer aos 44 3 5 2 Overview of Various Soldering 5 eee 46 3 5 3 Setting the Soldering Temperature Profile sess 52 3 5 4 Soldering Methods for Various Surface Mount Packages 55 3 5 5 Soldering Conditions seeiis orere ir nhu Ps Uh eene nenne nennen 56 32 6 eau oe e RR RUNE E te ve tette i s n 63 3 6 1 Selecting the Cleaning Solution sese 63 3 6 2 leamng Methods s RB t te eie pe mr teneret 64 3 6 3 Cleaning Conditions essere 65 3 6 4 Determining the Cleanliness esee 65 3 65 Other Notes and C
13. following require careful consideration when selecting the mounter e Mounting accuracy Mounting speed e Positioning method e Repeatability accuracy e Set up time High precision equipment is especially important when performing fine pitch mounting for multipin QFP etc with a lead pitch of 0 5 mm or less The key points in selecting the mounter for fine pitch placement are to emphasize the precision of the mounting and the following issues require special attention e The equipment must be able to recognize the printed wiring board e The equipment must have a positional accuracy within 0 1 mm and there must be visual recognition for all devices The equipment must be able to provide control in the vertical direction i e the direction of the Z axis so that that the force with which the leads are inserted can be controlled The equipment must be able to detect bent leads and must have an auto reject function 1 a function that inspects the package and only places packages with the proper external appearance On the IC package side as well it is critical that the packages are shipped in hard trays to prevent bent leads and floating leads thus making it possible to provide high precision mounting capabilities For the lead coplanarity which is an especially critical attribute 0 1 mm is guaranteed for most packages 39 HITACHI 3 4 3 Mounting Accuracy Figure 3 31 shows the fundamental concepts of mo
14. immersing the IC which is not mounted on a board into the solder bath However although this method is both convenient and easy to perform because all surfaces of the package directly contact the molten solder the temperature within the IC will be higher than it would were the IC mounted on a board used as it is in actual practice and thus the stresses exerted on the package will be larger Consequently we would suggest that when thermal durability testing is performed relative to the flow soldering method it should be performed using ICs that are actually mounted on boards in order to insure testing conditions more closely resembling the actual conditions of use 60 HITACHI Figure 3 41 shows a comparison of the temperature profiles for tests using the ICs which are not mounted on boards vs tests where the ICs are mounted on boards Even when the solder temperatures and dip times are held constant whether or not the package cracks is dependent on the temperatures within the package i e the temperature at the die itself or at the die pad etc and we can see from the figure that there is relatively little chance of cracking when the ICs are mounted on boards 300 SOP 32 pins Mounted on board Not mounted on board 10s Board surface temperature H 10s 2501 Solder bath temperature 247 C Package surface e C i 3 2 Package surface V temperature
15. induction Examples of countermeasures to prevent electrostatic discharge include the wearing of ESD protective smocks the use of conductive carrier boxes and the use of air ionizers b In order to avoid electrostatic charge all measurement instruments conveyer belts workbenches floor mats tools soldering irons etc must be grounded The workbenches and the floors should be covered with ESD protective mats with resistance of 10 to 10110 See Figure 3 45 c The workers should be grounded using wrist straps However in order to prevent the risk of electrical shock the grounding for the human beings must be placed in series with a resistor of at least IMQ as shown in Figure 3 46 d Use only soldering irons that are designed for use with semiconductors e g low voltage soldering irons functioning at voltages between 12 V and 24 V Ground the soldering iron tip as shown in Figure 3 47 76 HITACHI Resistance 1 ESD protective mat for grounding Ground the human workers using wrist straps ESD protective floor mat for grounding Humidifier ESD protective smock ESD protected footwear WD Oo Figure 3 45 Examples of Countermeasures to Prevent Static Electricity in Operations Metal or other conductive material Q 7 Coated wire pu MO or more Figure 3 46 Grounding the Human Body Aci vO 12 V to
16. instrument makes it possible to find the optimal reflow conditions and thus develop a high reliability system 83 HITACHI Probe m d XYZ AT Water tank gt Scan Ultrasonic 7 i F beam 2 eflecte wave Package Figure 3 52 Detecting Internal Cracks Using Ultrasonic Scanning Instrument Internal crack Peeling a Product with no cracks b Product with cracks 84 Figure 3 53 Results of an Inspection Using Ultrasonic Scanning Instrument HITACHI 3 9 4 Importance to Measures to Deal with Mechanical Stress Broken Leads Due to Package Resonance In cases where circuit boards with devices using QFP packages or the like mounted on them are stored in a location where there is a significant amount of vibration such as the engine compartment of an automobile there is a danger that mechanical stress due to package resonance could cause the leads the break To prevent this it is important to verify at the design stage for the chassis and circuit boards that the packages do not resonate In addition the leads can be reinforced by applying a coating or an adhesive or under fill can be used to secure the package to the circuit board These can be effective ways to prevent package resonance Note however that careful preliminary evaluation is required before using coatings adhesives or under fills Separated BGA Solder Connections Due to Shock fro
17. method are now used in addition to the conventional etching method for fine pitch printing with pitches of 0 5 mm or less Figure 3 19 supplied by Sonocom Ltd shows the openings of the metal stencils manufactured through both the conventional etching process and the additive process Figure 3 20 combines the various elements and shows the effects of improvements to the number of boards that can be printed continuously Source Data from Hitachi Techno Engineering Ltd Additive stencil Etched stencil Figure 3 19 Cross sectional View of the Metal Stencils Source Sonocom Ltd 27 HITACHI E S 5 E Spherical solder Additive stencil 2 paste O xp A gt Etched stencil S O E 17 6 3F J o Irregular 9 solder E paste S 2 Additive stencil and 4 spherical solder paste E Xl 1r O o a 3 2 4 0 3 0 65 0 5 Lead pitch mm Figure 3 20 Results of Experiments on the Number of Boards That Can Be Printed Continuously Source Hitachi Techno Engineering Ltd Data ii Improving the Solder Paste Removal Properties The solder paste removal properties are influenced by the cross sectional smoothness of the stencil openings Consequently the stencils that are manufactured through the electro forming method an additive method have come to be used because of the excellent smoothness of the side surfaces of the openi
18. reliability of the devices and of the wiring board interconnects Because of this a cleaning or rinsing is performed to remove the residual flux or solder paste must be selected that includes a flux that is compatible to a no clean process i e a flux that leaves little residual material The following must be taken into account when determining whether to use a cleaning process or to use a no clean process e Product reliability level e Environment in which the product will be used e Appearance level e Characteristics of the flux to be used Whether or not there is the need for an in circuit test 3 6 1 Selecting the Cleaning Solution The type of cleaning solution will vary greatly depending on whether the flux to be used is a rosin based or whether the flux to be used is water soluble The cleaning solution must be selected to match the characteristics of the flux residue 1 When a Rosin based Flux is Used a Terpene based solvent A fluid that has components extracted from orange peels b Petroleum based solvent A compound fluid made from a petroleum based solvent and a surface activator c Alcohol based solvent Ethanol methanol etc d Alkaline thinner 2 When a Water soluble Flux is Used a Water including hot water b Water with an alkali neutralizer 3 Cleaning Solutions and Fluxes Compatible With the Anti chlorofluorocarbon Regulations We have investigated the impact on semiconductor pack
19. the Solder Paste Generally the solder paste is applied through either a screen printing method or a dispensing method The application method of solder paste will differ depending on the form of the solder powder in the solder paste Summaries of both methods are presented below 1 Screen Printing Method The screen printing method is a method where a printing mask loaded with solder paste is aligned on top of the printed wiring board a squeegee is used on top of the printing mask to push the solder paste through the mask supplying the solder paste to the pads through the openings in the mask There are mesh screens and metal stencils for the printing masks The characteristics of each are shown in Figure 3 18 The various factors that influence the print quality are listed in Table 3 6 i When a mesh screen is used Squeegee Solder paste Screen gap Printed wiring board ii When a metal stencil is used Printing in direct contact with the printed wiring board Squeegee Solder paste Printed wiring board Figure 3 18 Screen Printing 25 HITACHI Table 3 6 Factor Screen a Density of the mesh b Thickness of the emulsion or the thickness of the metal c Amount of tension d Unbalanced tension Factors That Influence the Quality of Screen Printing Categories of Impact With Details Clarity of pattern resolution Pattern film thi
20. the temperature is 30 C above the solder paste melting point Solder paste melting point 183 C Solder joint temperature 210 to 260 C at leads 210 to 260 C at balls of BGA Note When BGA is used it is necessary to melt the balls as well in order that the shape of the solder joints after reflow soldering should be a uniform barrel shape If the composition of the BGA balls is Sn Ag the solder joint temperature should be between 220 C and 260 C Example 2 Sn Ag solder paste Solder paste melting point Approximately 217 C Solder joint temperature 230 to 260 C at leads 230 to 260 C at balls of BGA Depending on the size of the device there may be differences between the solder joint temperature and the temperature of the surface of the package body While there is a tendency that there is few differences between the lead temperature and the surface temperature of the package in the small TQFP 1414 size the lead temperature tends to be higher than the surface temperature of the package in the larger QFP 2828 size 2 Solder Melting Time When the solder melting time is too short the solder does not adequately melt and spread onto the mounting pads and the leads Conversely if the solder melting time is too long there can be a silver scavenging phenomenon in the Ag and Ag Pd electrodes reducing the strength of the solder joint These factors must be taken into consideration when setting the solder melting time 53
21. 1 Soldering Appearance Inspection Equipment While in the past the primary objective of inspections and tests was to determine whether or not the soldering appearance is acceptable recently the equipment is also able to inspect the device mounting status at the same time 66 HITACHI Table 3 19 Schematic Representations of Inspection Equipment Defects Soldering Appearance Device Mounting Status Incorrect Insufficient Open Misaligned Missing Misaligned Mounting Solder Lead Lead Bridge Device Device Orientation Method Principle L1 z y 7 Multi angular TV camera EPE C O O O Xto O illumination A 216 us Y ee Light cut off im source Ato O O O O O XtoA 27 lens Laser Spot laser O O O O O O XtoA scanning LI Photoreceiver 1 m X ray u Focus O O O O O A x Xray source Image Q Can be inspected X Cannot be inspected A Can be inspected with conditions or the detection rate is low In fine pitch lead packages the coplanarity which has an especially large impact on quality has been standardized at 0 1 mm Efforts are being made to improve technologies in the pursuit of quality improvements of the lead coplanarity 2 Inspection Equipment for Appearance of Solder Paste After Printing The objective of these systems is to prevent in advance the occurrence of soldering defects such as inadequate solder bridging etc by inspecting the shape of the fine pitch
22. 15 0 15 Unit mm 4 3 3 Allowable Mounting Misalignment In BGA there is a great latitude for self alignment and adequate mounting can be performed using a 0 5 mm pitch QFP compatible mounter If the center of the BGA bump is on the edge part of the mounting pad then the soldering occurs at the proper location due to the self alignment effect 89 HITACHI 4 4 Reflow Soldering Conditions Use a common reflow method such as the air reflow far infrared reflow N reflow etc for soldering Perform the soldering by melting the solder balls that are on the rear surface of the BGA package body Considering the thermal durability of the product it is necessary to control the surface temperature of the BGA package Refer to section 3 5 5 Soldering Conditions for specific temperature conditions If there are soldering temperature stipulations in the delivery specifications perform the soldering based on the soldering conditions in the delivery specifications Set the preheating conditions after giving consideration to issues such as driving out the flux from the solder paste the warping of the printed wiring board etc In common cases the settings are the same as for QFP 90 HITACHI 4 5 Inspecting the Solder Joints After Mounting on the Printed Wiring Board The BGA cannot be inspected visually after mounting on the printed wiring board however BGA solder defect rates of several PPM have been reported by various firms and def
23. 247 C Dip time 10 seconds 241 p temperature 241 C Ae Die surface temperature 224 C 200 5 L Die surface 2 Ns temperature 189 C i g 3 j 2 i S 150 i ge E o i 100 i 50 0 L L L 0 60 0 60 120 180 240 300 Time seconds Figure 3 41 Comparative Example of Solder Dip Temperature Profiles For ICs mounted on boards vs ICs not mounted on boards HITACHI 61 Furthermore when the IC has been in the solder dip for 5 seconds or less a small change in the solder dip time will result in a large difference in peak temperature within the IC See Figure 3 42 The thermal stresses on the ICs can be minimized by shortening the duration of the solder dip as much as possible 300 10 seconds 9 seconds 250 8 seconds 7 seconds 6 seconds 5 seconds 200 4 seconds 3 seconds 2 seconds 150 100 1 second Internal Temperature C 50 SOP 28 pins Solder bath temperature 260 2 C Time gt Figure 3 42 Examples of the Relationship Between the Temperature Within the IC and the Duration of the Solder Dip Example taken for a IC not mounted on board 62 HITACHI 3 6 Cleaning When there is residual flux that includes corrosive materials on the printed wiring board after the reflow soldering process is performed this flux may have an influence on the
24. AK products please refer to the delivery specifications 58 HITACHI iii Diode Packages Table 3 15 Soldering Conditions for Diode Packages Using Reflow Soldering Methods Lead plating Sn Pb Sn Bi Sn Cu Solder paste Sn Pb eutectic Sn Ag Sn Pb eutectic Sn Ag Package surface Peak temperature 260 C Peak temperature 260 C temperature upper limit 230 C or greater for 50 seconds or less 230 C or greater for 50 seconds or less 50 seconds or less 50 seconds or less 260 C Max 260 C Max 230 C 230 C Temperature profile 140 to 160 C 150 to 180 C Es 1 to 4 C second N 1 to 4 C second 90 30 Approx seconds 60 seconds 1 to 5 C second Package surface temperature Package surface temperature 1 to 5 C second Time Time b Flow Soldering Conditions Table 3 16 The conditions for the flow soldering method are shown in the table below Table 3 16 Soldering Conditions Using Flow Soldering Method Item Conditions Upper Limit Condition Setting Preheating Temperature 80 to 150 C At the surface of the printed wiring board Time 1 to 3 minutes Solder dip Temperature 230 to 250 C 260 C Solder bath temperature Time 2to4seconds 7 seconds Time during which the package passes through the solder bath Notes 1 For some products of thin packages TQFP TSOP the solder bath temp
25. HITACHI 3 54 Preheating The role of preheating is becoming more important as the mounting density increases The primary roles played by the preheating process include the following a Preventing or minimizing board warping b Evaporating the solvent in the solder paste c Preventing the wicking and the Manhattan phenomena While the preheating process does not affect thermal damage to the devices themselves the process is required for effective soldering When the preheating process is too long the surface of solder paste and the printed wiring board oxidizes which may lead to the formation of solder balls and poor wetting On the other hand if the preheating process is too short the amount of warp in the printed wiring board may increase there may be temperature gaps between the board the IC leads and the surface of the packages and there may be a greater tendency for the wicking and the Manhattan phenomena Taking these factors into consideration we recommend that preheating conditions be set such that the entire printed wiring board is heated to a uniform temperature Thermal Ramping There is the danger of thermal damage to the devices when the temperature ramping i e the rate at which the temperature is increased or decreased is too large in the process however there should be no problems with the 1 to 5 C second temperature ramp recommended by Hitachi On the other hand increasing the thermal ramp with whic
26. Surface Mount Package User s Manual HITACHI ADE 810 007C Rev 4 0 3 15 02 Hitachi Ltd on Hita semiconductor Cautions 1 Hitachi neither warrants nor grants licenses of any rights of Hitachi s or any third party s patent copyright trademark or other intellectual property rights for information contained in this document Hitachi bears no responsibility for problems that may arise with third party s rights including intellectual property rights in connection with use of the information contained in this document 2 Products and product specifications may be subject to change without notice Confirm that you have received the latest product standards or specifications before final design purchase or use 3 Hitachi makes every attempt to ensure that its products are of high quality and reliability However contact Hitachi s sales office before using the product in an application that demands especially high quality and reliability or where its failure or malfunction may directly threaten human life or cause risk of bodily injury such as aerospace aeronautics nuclear power combustion control transportation traffic safety equipment or medical equipment for life support 4 Design your application so that the product is used within the ranges guaranteed by Hitachi particularly for maximum rating operating supply voltage range heat radiation characteristics installation conditions and other characteri
27. action The extracted solvent resistance is 6 x 106 O cm or more 3 Extraction Method Rinse both sides of the printed wiring board with 10 ml 2 54 x 2 54 cm for at least 1 minute 4 Extracted Solvent Resistance Measurement With a conductivity gage Check MIL P 28809A for details on the MIL standards 2 Performance Required by the Solder Paste Requirements for performance of the solder paste are as listed below a Paste can be printed in the appropriate thickness and pattern using a screen printing method Or it is possible to supply a specific amount of paste using a dispenser It may also be dip coated b When there is a preheat process the printed pattern will spread as much as required after printing c There is excellent solderability on the chip electrodes and on the circuit paths d There is high reliability for the flux residual after reflow e Cleaning properties for the residual flux are excellent f There are no remaining solder balls after reflow or after cleaning g There are no changes in viscosity over time and that a specific set of use requirements are maintained h Solder paste remains adhesive even after printing and it is able to adhere the device Materials supplied by Senju Metal Industry Co Ltd The board mounting pad dimensions and operability product reliability and so forth should be thoroughly researched before selecting the solder paste 24 HITACHI 3 2 2 Applying
28. ages of the use of typical cleaning solutions and fluxes that are compatible with anti chlorofluorocarbon regulations The typical materials are given in Table 3 17 below None of these materials have an impact on the semiconductor packages 63 HITACHI Table3 17 Cleaning Solutions and Fluxes Compatible With Anti chlorofluorocarbon Regulations Cleaning Solutions Compatible With Rosin based Fluxes Water Soluble Fluxes EC 7 Lonco 3355 11 Pain a ST 100S Tamura Chemicals TF 33B Clean Through 750H Koki JSW 3F Techno care FPW FPV Filler Metals Japan FW175 35 FW178 The table above lists the common cleaning solutions Select the cleaning solution after considering the impact on the environment and the safety issues etc 3 6 2 Cleaning Methods Cleaning methods include ultrasonic cleaning immersion cleaning spray cleaning and vapor cleaning The respective benefits of these methods are listed below Table 3 18 Various Cleaning Methods Ultrasonic Cleaning This is a method where the cleaning is performed by subjecting the product to ultrasonic vibrations when it is in the solution While this method can make the cleaning solution to enter fine spaces caution is required because it may damage the connections in the product Immersion Cleaning This is a method where the product is submerged in the cleaning fluid requiring the cleaning fluid to be very clean Spray Cleaning This is a method where a high pressure solven
29. ample of Mounting Pad Design for TSOP II SOI gt m e g E WA 21 w 3 1 Units mm b 0 50 i 2 2 00 L ey 9 53 E 0 80 1 b Figure 3 11 Example of Mounting Pad Design for SOI 15 HITACHI Discrete Packages MFPAK SMPAK SMFPAK 6 0 4 aa 0 5 0 5 T LO i 9 13 oja ia o m s S le 7 WA 222 2 M An ZA S 2 i a i t i r 344 1 o 0 4 0 5 0 5 CMPAK CMPAK 4 T CMPAK 5 T 0 65 0 65 0 6 0 65 d hi as pe c e e bad qa 0 6 2 LZ Zs 3 s 77 e P 0 6 10 6 o 1 i lt N 31 22 s ba s o o x 0 6 lt 0 65 0 65 0 65 0 65 CMPAK 6 CMFPAK 6 0 3 0 3 lt 1 1 l OA Cok ZA GA Ue o o 0 65 0 65 Figure 3 12 Example of Mounting Pad Design for Discrete Packages 1 Note T in CMPAK 4 T CMPAK S T indicates transistor packages However T is omitted in each product s document The CMPAK mounting pads are suitable for both transistor
30. applied to the mounting pads on the printed vviring board and the devices are placed thereon and then soldered References Printed uc D a Ps Solder paste 3 2 1 P 20 to Application of 0000000000 322 P25to solder paste m m mE 323 i LSI packages 4 x Mounting 3 4 P 37 to Application of temporary 3 3 P 33 to adhesive Soldering 3 5 P 44 Co Oo CO 1 1 Heating i 1 i gt x i Cleaning 3 6 P 65 3 7 P 68 Figure 2 1 Basic Assembly Process Flow for Surface Mount Packages HITACHI When simultaneous reflow for double sided surface mounting or flow soldering is performed a temporary adhesive is used to affix the devices to the printed wiring board before the soldering is performed A cleaning process is performed to remove the residual flux etc after the soldering process is performed after which an inspection is performed A baking process is performed before the soldering when a moisture removal treatment is required when a plastic package is used See the references in Figure 2 1 for details about the various steps in t
31. autions o n pe n tei e eet 65 3 7 Inspection iR tu ete 0 BE 66 37 1 Inspection Equipment eot tree pide tete 66 3 7 2 Subject of Inspections hi tette AR eth 68 3 8 SLOTA BS EE 72 3 8 1 Moisture proof Packing 000 72 i HITACHI 3 8 2 Storage Before the Moisture proof Bag is Opened 73 3 8 3 Storage and Handling After the Moisture proof Bag is Opened 73 3 8 4 Storage and Handling Without Moisture proof Packing 74 3 85 Baking Process diee n an teed Pee 74 3 9 Notes and Cautions During the Mounting Process sese 76 3 9 Damage from Static Electricity essere 76 3 9 2 Notes and Cautions Before Performing the Reflow Soldering 79 3 9 3 Discerning the Package Crack sss eene 83 3 9 A Importance to Measures to Deal with Mechanical Stress 85 Section 4 Examples of BGA Assembly 1 see 87 41 Assembly Process bete ee nir reet 87 42 Mounting Pad Design suu aaa eet e Rer ee ALMAS ASS EEE E 88 4 3 Applying the Solder Paste toe ee trei Rn 89 431 Solder Paste sis esee ERREUR eee d rds 89 4 3 2 Solder Printing Stencil esset cte feet 89 4 3 3 Allowable Mounting Misalignment
32. bag equals the quantitative value on the spot Y The color sample within the printed frame is lavender Printed Color within the Frame Lavender Figure 3 44 Humidity Indicator Card Specifications HITACHI 75 3 9 Notes and Cautions During the Mounting Process 3 9 1 Damage from Static Electricity Because semiconductors are generally susceptible to damage by electrostatic discharge ESD extreme caution is required when handling the semiconductors and mounting them on the printed wiring boards The cautions and procedures are as described below 1 Operating Environment When the relative humidity is low there is an increased risk of electrostatic charging While it is necessary to store the surface mount packages in a dry ambient in order to prevent them from absorbing water when these packaged are handled and mounted on printed wiring boards etc a relative humidity between 45 and 75 is ideal from the perspective of the accumulation of electrostatic charge 2 Preventing the Accumulation of Electrostatic Charge During Operations a Avoid the use of insulative materials in the assembly process because these materials tend to accumulate electrostatic charge It is especially important to be careful with semiconductors and completed boards even if these semiconductors and boards are not contacted or touched directly when these objects are in the presence of a charged object they will be charged by a phenomenon of static
33. ckness Pattern film thickness Pattern misalignment non uniformity of the film thickness Paste a Viscosity Pattern film thickness Blotting blurring contamination Squeegee a Squeegee hardness b Shape of the squeegee three types flat rectangular or sword like Pattern dimensional precision film thickness Pattern dimensional precision film thickness c Angle of the squeegee when a flat squeegee Pattern dimensional precision film thickness is used Operating Conditions a Screen gap b Squeegee pressure c Squeegee speed d Ambient temperature and humidity Pattern dimensional precision film thickness Blotting blurring contamination Clarity dimensional precision and film thickness of pattern Pattern film thickness Changes in the viscosity of the paste evaporation of the solvent Changes in the board dimensions Changes in the screen tension and the dimensions Mechanical Precision of the Printer a Stability of the squeegee speed speed variation Non uniformity of the pattern film thickness b Stability of the screen frame screen slipping Pattern printing misalignment c Uneven screen gap d Parallelism of the squeegee vis vis the table e Parallelism of the operation of the squeegee f Mechanical strength the force vis vis the squeegee 26 Pattern printing misalignment non uniformity of film thickness Pattern print
34. e u 991JO 501001100 jeuinsuo SesseooJd uound ui pooc 4 xoda jaded odx 1 u4 l lenswoipny AL SessoeooJd uound ui pooc N S UPE YIM oua 9dXXX 2 u4 Soluo4 o 9l JOWUNSUOD Ayyiqeanyoeynuew souedns Joke laddog lous pus dd enaze ese S ON ISNV VW3N suoneorddy sonsuejereuo einjn s 1 eseg HITACHI Table3 2 Characteristics of the Various Types of Resin Laminate Boards Material Characteristics Glass Coefficient Transition of Thermal Tensile Dielectric Coefficient Tempe Expansion Thermal Strength Constant Volume Surface of Water Material Structure rature XY Conductivity XY 1 MHz Resistivity Resistance Absorption Units C PPM C W M C PSI x 10 5 Q cm Q 96 Printed Wiring Board Glass Epoxy FR 4 125 14 18 0 16 2 5 4 8 1012 1013 0 10 High Tg Glass Epoxy 194 8 9 5 1 1015 1014 0 11 New FR 5 Glass Polyimide 250 12 16 0 35 4 8 4 8 1014 1013 0 35 Aramid based Epoxy 125 6 8 0 12 4 4 3 9 1016 1016 0 85 Aramid based 250 5 8 TBD 4 0 3 6 101 101 1 50 Polyimide Glass Teflon Laminate 75 20 0 26 0 2 2 3 1010 1011 1 10 norganic Materials Alumina Beryllia 5107 21 0 44 0 8 0 1014 TBD TBD ceramic Magnetic coated 6107 TBD TBD TBD TBD TBD TBD Copper Laminate Alloy Note TBD Variable to be determined When it comes to the reliability of solder joints it is necessary to take into consideration the matchin
35. e Cg RSS 247A ABER 5 35 C HEE 8526 RH LAF 1 Shelf life in sealed bag 24 months at 5 35 C and lt 85 relative 2 BER humidity RH Y7O MB Ny 7 5 EUR EE 235CUF ET CORSI 2 After this bag is opened devices that will be subjected to reflow a AAR 30 C 60 RH ELE O32 168 MLA peak package body temp 235 must be 3 ROWS RRWMICN PMUBMYEBLRVET a Within 168 hours at conditions of less than 30 C 60 RH a HEA 2 2 5 3076 DL b 23C 5 CCIBER Em B Devices require baking before mounting if b Lit 2a OR I amp 73 5 iki a Humidity Indicator Card is gt 30 when read at 23 C 5 C or 4 ZI 22 5 xi 50 S RIT b 2a is not met IYT LX 2 BE BS Fel WELA If baking is required devices may be baked for kun 125T 5 16 2485 60 Sat CoG H EL Baking Temp Baking Time Total Baking Time TSOP TQFP 125 C 5 C 4 2455 f RTI RAA General Products 125 C 5 C 16 24Hr S96Hr FS RULER PARMHBOMEI KS TSOP TQFP 125 C 5 C 4 24Hr 96 Special Products As per the delivery specifications EAR NOSSSIA a3 ESAJVO9 4 22 FESR eae ses Date AG weedy 5 If blank see Weekcode on bar code label TEL RURLAUUIEIPCAIEDEC MERO J STD 020A KAAL TUES Note Level defined by IPC JEDEC Standard J STD 020A Handle packages according to the instructions written on th
36. e surface of the moisture proof bags Figure 3 43 Moisture proof Packing Example taken for Magazines 72 HITACHI 3 8 2 Storage Before the Moisture proof Bag is Opened Before the moisture proof bag is opened it should be stored at the target of between 5 and 35 C at 85 RH or less If the storage duration exceeds 24 months the devices should be checked for solderability corrosion on the leads etc before use 3 8 3 Storage and Handling After the Moisture proof Bag is Opened Table3 21 Standard Storage Conditions After the Moisture proof Bag is Opened Item Condition Notes Temperature 5 to 30 C Humidity 60 RH or less Time 168 hours or less This refers to the total time between opening the moisture proof bag and completing the final reflow soldering process When there is a thermal resistant ranking or storage conditions specified on the label affixed to the moisture proof bag or if there are stipulations in the delivery specifications etc these stipulations take priority over the conditions listed above in Table 3 21 Contact your service representative if the devices are to be stored under any conditions in violation of the storage conditions listed above in Table 3 21 e g in a different environment or for a longer period of time The use of a readily available low moisture storage chamber at less than 3096 RH is recommended if the devices are to be stored for a long period of time after the moisture
37. ecommended values based on the MIL standards for the cleanliness of the board after devices are mounted Table3 4 Structural Components of the Flux and Flux Functions Structure Function Composition Resin To prevent reoxidization Natural or Modified rosin To reduce surface tension WW rosin Polymerized rosin Hydrogenated To provide adhesion rosin Disproportionated rosin Activating To provide a surface cleaning Amine hydrohalide salts Component effect Etylamine hydrobromide Aniline hydrocloride etc Organic acids stearic acid sebacic acid etc Supplementary To supplement the functions Slump prevention material adhesive material Components etc Thixotropic Agent To prevent separation Hardened caster oil etc Solvent To regulate the viscosity Butyl carbitol To provide adhesion Terpineol Materials provided by Senju Metal Industry Co Ltd 23 HITACHI Table3 5 Cleanliness of the Boards after the Devices Have Been Mounted Converted values from the MIL P 28809A specified values Item Standard Cleanliness of the printed Amount of residual Cl 1 u g cm or less wiring board after cleaning The resistivity of the extracted 2 x 106 Q cm or more solvent after extraction Notes 1 Board Area Both sides of the printed wiring board plus the surface area of the devices mounted thereon 2 Extraction Solvent lsopropyl alcohol 75 by volume plus H gt O 25 by volume Before Extr
38. ect rates in the order of about 1 10 to 1 50 have been achieved for 0 5 mm pitch QFP X ray transparency inspection is difficult in mass production situations Because of this process conditions should be set in advance through research before mass production begins 91 HITACHI 4 6 Removing Method As is shown in Figure 4 2 blowing hot air on the package makes it possible to remove the package Note however that some research will be required in advance when setting the conditions for BGA removal because the adjacent devices and the ones on the back surface of the printed wiring board are also heated when the BGA is removed 1 J x HHHHHHHHHHH C2 CU002087 q ep PEG H S HS H S H 3 C2 TIS Figure 4 2 BGA Removing Method 92 HITACHI 4 7 Cleaning Select the cleaning solution and the cleaning conditions after taking into consideration regulations such as environmental regulations when it is necessary to perform a cleaning process after soldering No damage is done to the BGA even when the cleaning is performed with the solutions compatible with the anti chlorofluorocarbon regulations that are used most commonly Investigations are also required in advance to set the parameters for long term cleaning and repetitive brush cleaning operations etc to insure that the markings on the packages are not eras
39. ed 93 HITACHI 4 8 Storage Refer to section 3 8 Storage for information on storing packages prior to soldering 94 HITACHI Surface Moount Package User s Manual Publication Date 1st Edition September 1987 Ath Edition March 2002 Published by Business Planning Division Semiconductor amp Integrated Circuits Hitachi Ltd Edited by Technical Documentation Group Hitachi Kodaira Semiconductor Co Ltd Copyright Hitachi Ltd 1987 All rights reserved Printed in Japan
40. ed by contact rubbing conduction etc To prevent electrostatic discharge by contact during transportation using a carrier box etc it is necessary to use an anti static bag or to innovate ways to isolate the printed wiring boards c For chip components for which taping has been performed and for ICs MPAK SOP etc the electrostatic charge resulting from peeling the cover tape from the carrier tape is larger the faster the peeling is performed Rubbing and rapid peeling should be avoided as much as possible The recommended peeling rate is 10 mm second or less 78 HITACHI 3 9 2 Notes and Cautions Before Performing the Reflow Soldering Because when compared with conventional insertion packages surface mount packages that contain large dies are structurally weaker and because in the reflow processes that are generally used the entire package is heated the handling before the reflow process and the reflow conditions should be set in advance after referencing the characteristics shown below 1 Mechanisms By Which the Packages Crack During Reflow and the Moisture Absorption Characteristics Packages that absorb moisture exhibit the cracking phenomenon during reflow as shown in Figure 3 48 In other words the moisture that is absorbed during storage diffuses throughout the interior of the package and thus becomes moisture content throughout the resin When a package in this state passes through the reflow furnace which heats the en
41. educing Cushioning Material and Changing Packing Materials Before change After change Outside packing box Example of reduced use of cushioning material for devices shipped Air bubbles for packing lt N a gt reduced use of cushioning material for devices shipped in magazines in trays I Inside box Inside box Size of outside box adjusted to match inside box Inside box Inside box carton paper Inside box cardboard Example of Bubble wrap or Styrofoam ndividual packing Example of change in packing materials for devices shipped in tapes Embossed carrier tapes made of polyvinyl chloride Polystyrene no polyvinyl chloride HITACHI 43 3 5 Soldering 3 5 1 Soldering Methods Soldering methods can be divided into partial heating methods where only the parts to be soldered are heated and full heating methods where the entire packages are heated While the influence of temperature on the package is relatively small because of the minimal increase in temperature of the package itself in the partial heating method the range of application of this method is limited because of its unsuitability for high volume production On the other hand even though the superior performance in mass production of the full heating method has caused this method to be employed used the temperature increase of the package as a whole is considerable and thus ample care i
42. eog But eseq 01 pueog BuuiM paud seq E N pueog peiuud sonse douu ul 1luelsis yeay ayeulwe pejo jeddoo ajqixaj4 ejeuiue eseq speuejeul aysodwog ejeuiue pejo Jeddo eseq ouqe4 sse ejeuiue1 pero s ddo seq jedeg SIEH YEVN oiuefiou SIEH YEVN oiueB1o Spieog 4 10 2124 Figure 3 1 Types of Printed Wiring Board Materials HITACHI Types of Copper clad Laminate Board and Their Primary Characteristics and Applications Table 3 1 EL 9 Bd G661 1equieoeq ABojouuoe Puno eoeyuns gAAd Puroejes ui senss speorueu egiuso YOY NSLWESEN N eonos suoyejnoyeo soiuoJjoeje 1euinsuo eoud mo A wld JeiseAog jeuejeul suahe d ewseupy no eNseupe Od3 Idd seJeureo soluono l 1eunsuo edA Kxod3 eui ospe si eju ueuidinbe uoneuoine yupiqeanp soluo1 09l feli snpul jeuueui ysy Zillqix l i Jefejjeddo9 pud Siu uini sul pueul p Avelilul eds sjejnduioo uoneynsul uDiu suogeoiunuiuioo hill res quejsuoo oupejemp mog efeljeddoo euuonjJ s1eKe ejdnnuu E yum juawidinba is hqeli q use eq osje Ae d9 JOjonpuooiuies sjejnduio5 uiu Buoys u
43. erature should not exceed 235 C and the time passing through the solder bath should not exceed 5 seconds Refer to the delivery specifications of the individual product for details 2 For surface mounted transistor products the time passing through the solder bath should not exceed 5 seconds Refer to the delivery specifications of the individual product for details 59 HITACHI 4 seconds SOP 28 pins l lt gt Solder bath 245 G 235 C Dip time 4 seconds The temperature is measured at the surface of the printed wiring board Preheat approximately 60 seconds 1209026553 Board surface temperature Temperature A A Enters the solder Exits the solder Time Figure 3 40 Example Temperature Profile for Flovv Soldering Method Note that the applicability of this process depends on the individual products contact your service representative directly to check the applicability of this process to your products When the flow soldering method is used there are even greater temperature differences within the IC itself depending on the thermal capacity of the packages than there are using reflow methods such as IR reflow This is because the heat that reaches the IC comes from direct thermal transmission from contact with the molten solder One method that is commonly used in experimenting with the thermal durability to flow soldering method is that of
44. esin L o Generated stress N g w a p a Macc NS max Eh Expansion Shape coefficient Young s Modulus of the resin E P Internal pressure Spe PTT 7 a Dimension of the die pad in the oe Wmax short direction Thickness of resin under the die pad Omax gt F T a Omax BOE P Cracks Crack F T Resin strength B Shape coefficient Figure 3 48 Mechanism By Which Package Cracks Occur HITACHI 0 5 No cracks occur Cracks occur Calculated values 0 3 0 2 0 1 Moisture absorption 85 C 85 RH baked at 80 C Moisture desorption Moisture absorption ratio percentage by weight 60 Storage time h 80 100 Figure 3 49 Cracks and Moisture Absorption Ratio During Moisture Absorption and Moisture Desorption HITACHI 81 o 500 o 5 R 2 400 ie oO a 5 o 300 2 Q 25 C E 200 9 7 300 o 100 o D g 0 o 40 60 80 100 2 Relative humidity during storage RH 8 lt Figure 3 50 Example of the Allowable Storage Times After the Moisture proof Bag Has Been Opened 82 HITACHI 10 10 p Fs 8r 48 5 VPS IR a Pi 9 D z 4 EAG ux sat
45. etimes ruined when it is spread after printing or during the preheat process This is normally called slump for solder paste When this slump is increased it can lead to the formation of solder balls and can extremely lead to the bridge and or misaligned devices Figure 3 25 A It is said that by making the surface area of the paste that is printed somewhat smaller than the mounting pads it is possible to avoid the formation of solder balls Figure 3 25 B Solder paste Slump Solder balls Mounting pad gt Es b B uum Printed wiring board Print Preheat Reflow The solder applied is slighted smaller than the size of the mounting pad b gt Eu Figure 3 25 Solder Paste Slump Materials provided by Senju Metal Industry Co Ltd 32 HITACHI 3 3 Temporary Adhesive When the flow soldering method i e the solder dipping method is used the devices must be affixed temporarily before soldering The temporary affixing of the devices is usually performed using an adhesive The temporary adhesives used can be categorized by how they are cured either using thermosetting type or UV curable type Issues such as the following must be taken into account when selecting the temporary adhesive Ease of Applying the Adhesive Will a dispenser be used or will screen printing be used Is high speed dispensing a possibility Adhesive Stre
46. f Label C i orrugated cardboar Cardboard Magazine g Label Magazine Tray or Tape Tape IC device kr m s 2 4 Figure 3 32 LSI Package Packing Specifications 41 HITACHI Table3 7 Features and Characteristics of Hitachi s Packing Specifications Characteristic Magazine Standardized at 495 mm or 500 mm long the magazines are used for various types of packages Tray The external tray dimensions are standardized at 315 8 mm L x 185 8 mm W x 7 6 mm T However the trend toward the use of JEDEC trays continues Tape The specifications for the tape conform to the JIS C0806 EIA481 and IEC286 3 2 Environmental Compatibility Hitachi is aggressively pursuing the following measures to reduce waste and to increase the effectiveness of resource utilization m gt Recycling of Packing Materials e To decrease waste and utilize limited resources Hitachi plans to recover and reuse trays promotes marking to indicate the materials used in packing trays magazines reels etc seeks easily recycled alternatives to conventional packing materials di Reducing the Amount of Packing Material and Switching to Different Packing Materials As shown in Table 3 8 Hitachi is reducing the amount of cushioning material used for devices shipped in trays and certain devices shipped in magazines and changing the packing materials for devices shipped in tapes 42 HITACHI Table 3 8 R
47. g of the coefficient of thermal expansion with that of the package when selecting the materials In the electronic circuits LSI packages are soldered on the boards that have different coefficients of thermal expansion Figure 3 2 shows the coefficient of thermal expansion of various materials As is shown in Figure 3 3 changes in temperatures cause repetitive relative thermal displacements which may cause the solder joints to crack and break The thermal displacements A is calculated as shown below and is dependent on the difference in the coefficients in thermal expansion between the board and the package Aq the difference in temperature AT and the package size A Aa x AT x 2 In the thin packages such as typified by TSOP packages that are compatible with the recent demands for smaller and thinner devices the percentage of the package body volume occupied by the silicon dies is increasing and the coefficient of thermal expansion of the overall package has become relatively small In applications requiring high levels of reliability the application of boards with low coefficients of thermal expansion such as the new FR 5 in Table 3 2 are recommended because they are able to reduce the global mismatch of the coefficients of thermal expansion between the package and the board 8 HITACHI Coefficient of Thermal Expansion x 10 2C Device 100 Board High temperature solder 9 1 95 5 50 4 Paper
48. h the printed wiring boards are cooled i e by increasing the speed of cooling can improve the luster of the solder surface of the solder joints However it must be noted when setting the thermal ramping parameters that if the cooling ramp is too fast there will be an increased tendency for the printed wiring board to warp HITACHI 3 5 4 Table 3 10 shows the appropriate soldering methods to be used for the various types of surface mount packages Select the soldering method based on factors such as manufacturing capability thermal damage to devices etc Soldering Methods for Various Surface Mount Packages Table 3 10 Soldering Methods for Various Surface Mount Packages HTSSOP 4 HQFP 4 HLQFP 4 4 5 QFN SSOP TSSOP P VQFN MFPAK HSOP VSSOP BGA SMPAK Other QFP P VSON LFBGA CMFPAK Discrete LQFP HSOI HBGA SMFPAK Packages HQFP TQFP G QFP QFJ HFBGA TSOP 6 Not Listed Soldering Methods HLQFP HTQFP TSOP SIP 3 SOJ G QFJ TFBGA LDPAK S LFPAK RP8P 4 SFP to the Left Partial Soldering O O x O O x x O Mas iron Laser Pulse heater O O O O X X x x x Qo Hot air O O O O O o O Q x O o o Full Infrared reflow O O O O o O O O o O Heating Air reflow Methods Vapor phase O O O O O O O o reflow Flow O O 2 x O x x x x x soldering 5 Soldering is possible using this method on the conditions recommended by Hitachi Ltd X Soldering cannot be performed using this met
49. he assembly process HITACHI Section 3 Overview of the Individual Steps in the Assembly Process 3 1 Designing the Printed Wiring Board and the Mounting Pad In surface mount assembly the materials from which the printed wiring board is manufactured and the design of the mounting pads have an effect on the manufacturability and on the solder joint reliability The section below will discuss the selection of the materials from which to manufacture the printed wiring boards and the design standards for mounting pads 3 1 1 Printed Wiring Board Material Although there are many different types of printed wiring boards these printed wiring boards basically fall into one of two broad categories boards made from organic materials and boards made from inorganic materials See Figure 3 1 Printed wiring boards made from organic materials are the most commonly used today and copper clad laminate boards are the most common Table 3 1 describes the types of copper clad laminate boards and their primary characteristics and applications Because the various board materials can be categorized by the specific applications the materials should be selected after taking required electrical characteristics thermal dissipation characteristics thermal durability mechanical characteristics reliability and so forth into account Table 3 2 shows the types of printed wiring boards used most commonly in the consumer and industrial uses HITACHI
50. here the soldering is performed by melting the solder through irradiating the solder joint with a laser beam Generally Y AG lasers are used most often in this process because of the thermal transfer to the metal surface at the solder joint and because of the level of energy absorption at the printed wiring board Camera 0 Cross line Relay lens i Mirrors for beam axis Dichroic mirror adjustment Illumination Beam expander Focusing lens Material to be soldered Laser beam Figure 3 35 Example of the Optical System for a YAG Laser v Light Beam Heating This is a method where light from a source such as a xenon lamp is concentrated using a parabolic mirror and the soldering is performed by splitting the beam and shining it on the solder joints There is also equipment that splits the beam into four parts making it possible to perform the soldering of the packages with the leads emerged into four sides 2 Full Heating Methods 48 i Infrared Reflow Method This is a method where the solder is melted and the soldering process is thus performed based on radiant heat i e heat that is radiated from infrared light sources such as lamps panel heaters sheath heaters etc This method is used very often because of its superior performance in mass production situations Figure 3 36 shows a schematic of infrared reflow equipment For the reasons listed below it i
51. hod Please avoid using this method Notes 1 Varies depending on the product Contact your sales representative for more details 2 For some products the maximum solder bath temperature is 235 C and the maximum time passing through the solder bath is 5 seconds 3 Only the SP 23TD may be surface mounted 4 Heat spreader exposed type and die pad exposed type 5 With fine pitch packages there is the potential for solder bridges etc Use this method only after the soldering conditions have been confirmed HITACHI 55 3 5 5 Soldering Conditions Control of both the soldering temperature and the humidity during package storage are important in order to prevent the deterioration in surface mount package reliability due to thermal shock during soldering A variety of soldering conditions are described below If there are any points of disagreement the soldering conditions listed in the delivery specifications for the individual products should take priority over the conditions listed below 1 Soldering Conditions Using Partial Heating Methods Table 3 11 The conditions listed below are recommended when using Sn Pb eutectic or Sn Ag solder paste to mount packages with leads QFP etc that are suitable for soldering using partial heating methods Table3 11 Soldering Conditions Using Partial Heating Methods Methods Conditions Soldering iron Maximum lead temperature 260 C for 3 seconds However the temperature of the solde
52. ign Examples Solder ball pitch 0 5 0 65 0 8 1 0 1 27 Solder ball size diameter 0 3 0 4 0 5 0 6 0 76 Over resist type Solder resist 0 25 0 35 0 45 0 50 0 62 opening diameter Copper land 0 35 0 45 0 55 0 60 0 72 diameter Normal type Solder resist 0 28 0 35 0 45 0 50 0 62 opening diameter Copper land 0 18 0 25 0 35 0 40 0 52 diameter Unit mm Note Above values calculated based on a solder resist positioning accuracy of 0 05 mm 50 um 88 HITACHI 4 3 Applying the Solder Paste The printing method is the best way to apply the solder paste Print the paste at the same time for other devices on the printed wiring board 4 3 1 Solder Paste In addition to the tin lead eutectic solder pastes commonly used lead free compounds have started to be used as well Sufficient research should be performed before selecting the composition to be used 4 3 2 Solder Printing Stencil Table 4 2 shows an example of solder printing stencil designs The solder printing stencil opening diameter should have the same dimensions as the solder resist opening diameter Table 4 2 Solder Printing Stencil Design Examples Solder ball pitch 0 5 0 65 0 8 1 0 1 27 Solder ball size diameter 0 3 0 4 0 5 0 6 0 76 Solder printing stencil Over resist type 0 25 0 35 0 45 0 50 0 62 opening diameter mounting pad structure Normal type mounting 0 28 0 35 0 45 0 50 0 62 pad structure Solder printing stencil thickness 0 15 0 15 0 15 0
53. igure 3 16 shows a comparison of solder powder shapes Figure 3 17 shows the relationship between the size of the solder powder grains and the paste printing mask opening dimensions Generally excellent printing results can be obtained when the powder grain diameter is less than about 1 7 of the printing mask opening width and less than about 1 5 of the thickness of the printing mask Generally the printing mask opening dimension when used with a 0 5 mm lead pitch QFP is approximately 0 25 mm and the solder powder average grain diameter is about 0 03 mm 30 um 20 HITACHI Shape of Solder Powder Diameter of Solder Powder Grain 53 to 75 um 25 to 38 um 15 to 25 um Lead Pitch 0 65 mm and above 0 5 to 0 4 mm 0 3 mm Compatibility Figure 3 16 Shape of Solder Powder Materials provided by Senju Metal Industry Co Ltd 3 5 150 o E amp 5 L E 100 o L o Q 50 o o 9 25 o gt lt 0 W 0 15 mm 0 25 mm 0 35 mm 0 76 mm Printing mask opening width Corresponding lead pitch 03mm 0 5mm 0 65 mm 1 27 mm Figure 3 17 Relationship Between the Printing Mask Opening Width and the Average Solder Powder Grain Diameter Table 3 3 shows the types of solder alloys that are used for the primary solder pastes HITACHI 21 Table 3 3 Types of Solder Alloys Used in Major Solder Pastes Alloy Type Composition Characteristics App
54. ing misalignment non uniformity of film thickness Pattern printing misalignment non uniformity of film thickness Pattern printing misalignment non uniformity of film thickness HITACHI Comparing metal stencils to mesh screens the metal stencils are most appropriate in terms of printing precision and durability and in soldering for fine lead pitch the metal stencils are most appropriate The following conditions are required by the metal stencils i Dimensional accuracy the dimensions of the openings and the stencil thickness ii Ease of the solder paste removal iii Positional accuracy This accuracy is more important the finer the pitch of the pads i Improving the Dimensional Accuracy The accuracy of the opening dimensions and of the stencil thickness is greatly influenced by the metal stencil manufacturing process thus the metal stencil manufacturing process must be selected based on the level of accuracy requirements Stencils that are manufactured using the electro forming method an additive method are marked by the shortcomings that they are expensive and that they have poor durability however their removal characteristics are excellent in that the solder paste does not catch on the side surfaces of the openings when the stencil is removed which leads to the strength that this approach can improve the solder paste printing process Because of this metal stencils that have been manufactured using the additive
55. it unit 4 Coolin Preheat Reflow rise chamber chamber I Al z l T 1 i I Cm 112 Ex F TEHen s ur In line equipment structure Source Hitachi Techno Engineering Ltd catalog Figure 3 38 Vapor Phase Reflow Equipment v Flow Soldering Method In this method the devices are temporarily fixed to the printed wiring board using an adhesive the board is inverted so that the devices are on the bottom surface of the board and the bottom surface of the board is then passed through molten solder flow solder Figure 3 39 shows a schematic of the flow soldering process by which soldering is performed using the SOP The flow soldering method usually uses temperatures relatively higher than reflow methods when performing the soldering and thus large thermal shocks are likely limiting the range of products to which this process can be applied Note that this process is not suited to all products please contact your service representative regarding whether or not the flow soldering process can be applied to your products We also recommend that you review Section 3 3 regarding the use of temporary adhesives 51 HITACHI Adhesive Adhesive application Pa Ec SOP placement f Av Mounting pads r SOP Adhesive cure Solder
56. ive Figure 3 29 Optimization of the Application Height of the Temporary Adhesive Schematic 36 HITACHI 3 4 Mounting Placement 3 4 1 Mounting Process While the actual mounting process may vary in terms of the equipment used or in terms of the devices that are mounted the mounting capability etc when it comes to the mounting process itself the processes used can be categorized as the individual device mounting method the in line mounting method and the batch mounting method depending on whether individual devices are mounted one at a time or whether multiple devices are mounted simultaneously Supplementary equipment for each model type must be provided so that the mounter that will be used for surface mount packages will be able to perform high precision mounting operations and in most cases robots are used in an individual device mounting system The various methods for mounting are as shown in Figure 3 30 37 HITACHI X Y Table 3 Vacuum nozzle Printed wiring board Devices Feeder a Individual Mounting Method Feeder Vacuum nozzle i Pri iring board Devices rinted wiring boar b In line Mounting Method Printed wiring board Magazine c Batch Mounting Method Figure 3 30 Device Mounting Methods 38 HITACHI 3 4 2 Selecting the Mounter As lead pitches become finer there are ever increasing demands for greater accuracy in the mounting process Issues such as the
57. lead solder paste patterns i e the volume shifted patterns the height of the paste bridging slump unevenness etc after the minute patterns are printed At present one of two systems is used either the multi angular illumination method or the laser scanning method 67 HITACHI 3 7 2 Subject of Inspections The inspections of the solder joints inspect the defects shown in Table 3 20 Both the causes and the countermeasures for the various defects are listed in this table This material should be used as a reference when improving the various processes Table3 20 Reflow Soldering Defects Troubleshooting Guide Type of Defect Inadequate reflow This is a situation where Some solder powder is still remaining A i Printed wiring board Mounting pad Description there is still remaining solder powder and either e the solder paste has not been subjected to reflow at all or even though most of the solder paste has been melted in the reflow process there are still those places where soldering has not been performed and solder powder is found on the surface of the solder that has been melted Causes Inadequate heating temperature time Solder paste degradation aging Excessive preheating temperature and time e between beginning heating and melting the solder Countermeasures Re evaluate the heating equipment and method Store the solder paste i
58. lication Eutectic solder 63Sn 37Pb The melting temperature is low 183 C General and thus there is little thermal impact on the electronic components Silver bearing 62Sn 36Pb 2Ag solder Solder joint strength is stronger and Ag electrodes Ag has superior life expectancy patterns Prevents the silver scavenging phenomenon Lead free Sn Ag Sn 3 0Ag 0 5Cu solder etc High soldering temperature General High solder bulk strength Lead free mounting Higher creep strength than Sn Pb eutectic solder Notes When applying solder to metal surfaces that include Ag such as Ag conductors and Ag pads this is a phenomenon where the Ag from the material being soldered diffuses into the solder 22 Materials provided by Senju Metal Industry Co Ltd HITACHI b Flux The flux used in the solder paste performs functions such as preventing reoxidization cleaning the surface providing adhesion etc The compositional structure of the flux is as shown in Table 3 4 Generally halogen is included in activator After the solder is applied then when there is residual activator 1 e where this activator contains halogen etc on the devices or the board then there will be an impact of reliability Consequently regulations should be put in place and enforced regarding cleaning the boards Evaluate the cleanliness of the boards after considering the cleaning conditions when selecting the flux Table 3 5 shows the r
59. livery specifications o and thick QFPs or QFJs is 250 C f the individual product for details HITACHI 57 e BGA Table3 13 Soldering Conditions for BGA Using Reflow Soldering Methods Ball composition Sn Pb eutectic Sn Ag Solder paste Sn Pb eutectic Sn Ag Sn Pb eutectic Sn Ag Package surface temperature upper limit Peak temperature 260 C 230 C or greater for 50 seconds or less Temperature profile 50 seconds or less 260 C Max 230 C 150 to 180 C x 1 to 4 C second 90 30 seconds Package surface temperature 1 to 5 C second Time ii Transistor Packages Table 3 14 Soldering Conditions for Transistor Packages Using Reflow Soldering Methods Temperature profile Package surface temperature Lead plating Sn Pb palladium Sn Bi Sn Cu Solder paste Sn Pb eutectic Sn Ag Sn Pb eutectic Sn Ag Package surface Peak temperature 260 C Peak temperature 260 C temperature upper limit 230 C or greater for 50 seconds or less 230 C or greater for 50 seconds or less 50 seconds or less 50 seconds or less 260 C Max 260 C Max 230 C 230 C 140 to 160 C 150 to 180 C N 1 to 4 C second ES 1 to 4 C second 90 30 Approx seconds 60 seconds 1 to 5 C second 1 to 5 C second Package surface temperature Time Time Note For UPAK DPAK and LDP
60. low soldering of other devices In high density mounting methods such as the VPS method and the air reflow method which tend not to raise the temperature of the package as a whole but which are able to heat the solder joints directly are useful in terms of the thermal conduction methods Infrared reflow Air reflow Radiant heat Convection heat a Lr NE Conducted heat Conducted heat Conducted heat Conducted heat Ed Printed wiring board Figure 3 33 Comparison of Thermal Conduction Methods Schematic 3 5 2 Overview of Various Soldering Methods 1 Partial Heating Methods i Soldering Iron Heating This is a method where the package is affixed to the board using flux or an adhesive and a soldering iron is used to perform the soldering process i e melting the solder In order to avoid reliability degradation from overheating the temperature of the soldering iron should be 350 C or less and the soldering iron should not be in contact with any given pin for more than 3 seconds The temperature of the lead itself should be 260 C or less ii Pulse Heating This is a method where a heat collet is placed on the leads after the package has been placed on the pad and the collet is heated through a pulse current to perform the soldering by melting the solder a While the reflow heating characteristics are determined by the collet temperature because there is gap bet
61. m Dropping Since area array package types such as BGA and CSP have no leads mechanical stress affecting a populated circuit board is applied directly to the solder connections For this reason solder connections becoming separated due to shock from dropping is a concern For example circuit boards can be dropped accidentally after devices are mounted when the boards are divided into smaller sections during in circuit testing or during the assembly process Also mobile equipment containing such devices can be dropped in the marketplace For these reasons it is important to carefully study ways to maintain circuit boards that will prevent them from being exposed to mechanical stress during the assembly process In addition when designing chassis and circuit boards attention needs to be paid to verifying ways to eliminate mechanical stress caused by being dropped in the marketplace Another effective method of reinforcing soldered connections and ameliorating the effects of mechanical stress is to secure the package body to the circuit board using adhesive or under fill Note however that careful preliminary evaluation is required before using adhesives or under fills 85 HITACHI 86 HITACHI Section 4 Examples of BGA Assembly Evaluations The BGA Ball Grid Array assembly method is as described below 4 1 Assembly Process Flow Use a reflow process similar to the process used for conventional packages such as QFPs and SOJs to pe
62. method N5 nitrogen is circulated instead of air when the reflow soldering is performed When the oxygen density is 1000 PPM or less in the circulating chamber when the solder is melted then there are generally effects such as greater control of solder balls and greater control of solder bridges when there is fine pitch placement than is possible when performing the reflow in a normal atmosphere environment iv Vapor Phase Reflow Method VPS Method This is a method where a solvent is heated to create a vapor layer the entire printed wiring board is passed through this solvent vapor layer and the reflow soldering is performed by the latent heat of vaporization Figure 3 38 shows a schematic of the vapor phase reflow equipment The features of this method include the following HITACHI a There is no danger of overheating vis vis the set temperature because the reflow temperature does not exceed the boiling point of the solvent where solvents at the boiling point of 215 C are commonly used b The heating is performed uniformly so that there is little influence of the shape of the devices or of the printed wiring boards c Because the reflow process is performed in an inert atmosphere there is no oxidation of the solder and thus the solder wettability is excellent d There is a decreased tendency for the flux to become burnt on making cleaning relatively easy Exhaust system je Chiller recovery un
63. mity in the solder paste with better There is a different S not uniform paste during printing printability amount of solder on nd the amount of solder 2 i the different pads anait iin tof solder Re examine the paste printed is thus printing parameters non uniform e The solder paste has poor printability e The printing parameters are not set correctly Position slip Device is soldered The devices have been Place the devices so in a misaligned placed with an offset that they are not position I shifted Visi e The devices have shifted m4 in their position due to Minimize the vibration pe vibrations during during transport ea transport Switch to a solder Inadequate adhesive paste with greater strength in the solder adhesive strength paste Reduce the amount of Inadequate force flux included applied to the devices during placement e Shifted due to the flux during reflow Too much flux in the solder paste 70 HITACHI Table3 20 Reflow Soldering Defects Troubleshooting Guide cont Type of Defect Description Causes Countermeasures Open lead The solder paste is AA small shift in the e Print so that there is Lead reflowed cleanly and at position of the device no shift Solder 277 to nane flux in the solder Reduce the amount of connection however paste has caused the flux included the solder is not
64. n a refrigerator Do not use hardened portions of solder paste such as surface areas Not solder There is no solder Mounting there was supposed to be e a Pad soldered There is no solder found on the locations where Solder paste will not print Poor printability of solder paste The printing conditions are not suited to the solder paste properties Select solder paste with good printability Re evaluate the printing parameters including the printing mask thickness and the printing mask size Inadequate spread The spread is not adequate The solder does not spread to adequately cover the mounting pad or the lead Die npe 68 The solder paste printing are smaller when compared to the e pad The pad lead or paste have poor solderability The amount of solder paste used in the printing is inadequate HITACHI Increase the printing area Switch to the pads leads or solder paste with better solderability Plate the pads and leads with solder Print a thicker solder layer Table3 20 Reflow Soldering Defects Troubleshooting Guide cont Type of Defect Bridge Pad 1 Connection Leads Description The gaps between adjacent pads were filled with solder when the reflow process was performed Causes There has been too much solder paste printed and thus a connection is made to the adjacent pads already by
65. ng that is circulated within the furnace chamber after either air or inert gas has been heated using a heater One of two methods can be used either the heating can be performed using hot air alone or the heating can be performed using a combination of hot air and infrared radiation Figure 3 37 shows a schematic of the air reflow equipment 49 HITACHI The strengths of this method have to do with the fact that the heating is performed primarily by thermal transmission from the hot air flow and thus it is possible to have less variability in temperature in the devices and in the printed wiring board than is found using the infrared reflow method with thermal uniformities similar to those of the VPS method When compared to the VPS method the air reflow method has a relative cost advantage because there is no need for any solvent and thus this method is expected to be increasingly popular in the future However when inert gases are not used then the ambient gases will be likely to cause oxidation which could lead to problems such as solder balls Thus care is required when selecting the gas Hot air flow fan Exhaust Fan Heater s ooler A IKE 1 S h le 7s Preheat Preheat Reflow s s cd chamber chamber Figure 3 37 Air Reflow Equipment iii Nz Reflow Method While in principle this method is the same as the air reflovv method in this
66. ngs See Figure 3 21 When solder paste with higher levels of viscosity is used providing a taper on the side walls of the openings is said to improve the printing characteristics 28 HITACHI A 0 3 mm pitch pattern printed using a stencil A 0 3 mm pitch pattern printed using a stencil manufactured by an additive method manufactured by an etching method Figure 3 21 Print Patterns Using Different Types of Stencils Source Hitachi Techno Engineering Ltd Catalog Select the printing stencil type to be used based on the lead pitch of the ICs to be mounted the costs and so forth in an overall evaluation before making the selection iii Improving the Positional Accuracy It is important to increase the stiffness of the stencil so that there will be no misalignment during printing if there are going to be improvements in the positioning accuracy Furthermore image recognition is required in order to perform high accuracy alignment between the board and the stencil Solder paste application equipment possessing the automatic pattern recognition and positioning methods such as shown in Figure 3 22 is recommended if it is required to perform high yield soldering especially in high pin count or fine pitch applications 29 HITACHI Screen Screen d Screen marks Printing Unit Os recognized after Printing Unit qa
67. ngth How much adhesive strength in terms of kg is required In particular will the adhesive be able to stand up to the flow soldering conditions Curing Conditions What is the maximum temperature and the maximum time to which the IC device and the board can be exposed for curing Reliability What impact will there be on reliability of the products as a whole when it comes to the characteristics of the adhesive after curing for example its electrical isolation characteristics its dielectric constant its coefficient of thermal expansion etc 33 HITACHI 3 3 1 Adhesive Strength Figure 3 26 shows the temporary adhesive strength of typical adhesives in the market place Regardless of the adhesive material used we were able to obtain an adequate adhesive strength However the adhesives with the greater adhesive strengths were the thermosetting types Adhesive strength criteria 0 3 kg mm 1 5 Cured at 150 C T for 60 z seconds o 1 0 Y O E O D O 05 Q o ees ree sas eee 7 2 s A oO 0 o UF1300 NF5000 PD860002 D124F JU 11T Adhesive A Fuji lt Chemicals Somar Heleus Amicon Koki UV curable type Thermosetting type 34 Figure 3 26 Adhesive Strengths of the Temporary Adhesives Examples Using SOP HITACHI 3 3 2 Curing Conditions In adhesive A which was shown in Figure 3 26 an adequate adhesive strength is obtained after cured a
68. oc a test print PAIN i Screen marks 14 5 Camera Recognition k Recognition Unit Printing marks Unit i Test print board Board for 1 printing standby unit a Normal Method b Method Used When Performing Solder Printing Figure 3 22 Reference Mark Recognition Method 2 Dispensing Method The dispensing method is a method that uses air pressure to dispense a specific volume of solder paste from a nozzle The amount of paste dispensed is adjusted by the paste viscosity the nozzle diameter the air pressure and the dispensing time Figure 3 23 presents a schematic diagram of the dispensing method Air pressure 1 oo 570 Regulator Nozzle Solder paste Printed vviring board Mounting pad Figure 3 23 Dispensing Method 30 HITACHI 3 2 3 Amount of Printed Solder Paste The solder paste to be printed is calculated using the method described below Figure 3 24 a When a Mesh Screen Is Used The amount of paste printed screen thickness x proportion of open area emulsion thickness x pattern area lt Screen thickness Emulsion thickness b When a Metal Stencil Is Used The amount of paste printed stencil thickness x pattern area A Eee Soe Solde paste Figure 3 24 Amount of Printed Solder Paste HITACHI 31 The shape of the printed solder paste is som
69. of temperature When there has been no cracking in the reflow soldering after a given heating test then we can obtain the graph shown in Figure 3 50 for the allowable storage time Figure 3 51 shows the relationship between the adhesive strength between the resin and the frame at various temperatures the maximum stress that is generated when the package is heated given various moisture absorption conditions and the bending strength of the resin In this example cracks were formed when the moisture absorption ratio exceeded 0 2 by weight in a VPS process Vapor Phase Soldering process at 215 C The correctness of this model is supported by the fact that crack appears when in practice the absorption ratio within a package is 0 25 by weight Note This graph shows that the length of the allowable storage period changes depending on the storage temperature and the storage humidity When the storage temperature or storage humidity is lower the storage time can be increased Die 2 Resin Storage Moisture absorption we D 55 at ox I c Moisture density within the yo gp xw au cp eG DEL 2 package h ET D Coefficient of diffusion of water Vaporization of a Reflow internal moisture 1 mol H20 soldering content 22 4 latm DV pV 2 nRT Frame I I om gt fad m N Interfacial peeling fad Adhesive strength of the r
70. onejnsur uDIH ougej ssej x s r sioyeyn yeo soluono l Jeuunsuoo utu 01 5 LL 9 3ueuidinbe uoreuiojne 391440 Ayiqeys jeuorsueup 3 9 3 SoIUOJ129J0 eLISNPU yBiy uoneinsur UB H jefepjeddoo vuelo fxod3 ouge ssero JeKe jeddo NS UDpE AUR 6uons ulsed 9 44 l s o sap q SAL 5586 Jaddoo soiuonoojo 2 9oUugejsse YY Jeise Ajod sesn seuineuiog qissod 51 yew SsejD 10 uts 25 in ouqej sse O yew ssero slurensuoo qu uidinb uoljguio ne ss uyoluy Asoyoey qu uidinb uoneulolne uone nsui ufi uiSe1 uuos eJeui 6 soiuoJjoeje peuisnpu 9Uqejsse p fxod3 1 ded ssero Sspieoq J elninui sie e d qO eyeureo oepi SosseooJd yound ul poop Ul puno osiy WW 8 SoIuoJioeje Jeuunsuo Jokejuaddop Jefe jeddo9 391440 uolyejnsu 1 ougejsse p wre Soluo1 l eusnpu ouge ssej5 1442 ulseJ Jaded fxod3 7 Jede s o soluono 1eunsuoo ulsel d 90Uqejsse Mo SesseooJd yound ui poop jKepjeddo 12 2 y TensiA olpne eouejsiseJ Buppoen poo S91U01 99 JOWINSUOD SessoooJd d d ys loci yound ul poog l sisuni 3ueuidinbe uogeuioine aiqissod si Bunejd ejou uBnolu uisoy jed
71. phenol Y In the Y direction Eutectic solder Paper phenol X In the X direction Glass epoxy Y Resin epoxy Copper silver yt Ys m o Gold Glass epoxy X L 10 D Glass c wi Alumina Kovar alloy 42 5 i 7 1 SiC Si Spe E 1 4 A Figure 3 2 Types of Electronic Materials for Surface Mount Assembly and Their Coefficients of Thermal Expansion lt gt Lead Resin Board Thermal displacement A Af AccAT 0 2 y max t Shear strain Y QFP SOP Figure 3 3 Structure of Minute Solder Joint and Thermal Shear Displacement The dotted line represents the deformation by changes in temperature HITACHI 3 1 2 Mounting Pads The geometry of the mounting pad is critical because of its influence on the soldering yield and the solder joint reliability Examples of mounting pad design for various surface mount packages are given below Figures 3 4 to 3 15 The optimum value for mounting pads depends on the board material the solder paste material the soldering method and the precision of the equipment used The actual design of the mounting pads must be suited to the circumstances QFP Including TQFP and LQFP Mip D 2a Hg or Hp 2Bo o Ease of cleaning B4 Solder joint strength
72. proof bag is opened Please insure that the requirements in Table 3 21 are fulfilled when the packages are removed from the low moisture storage chamber just as they are when the packages are removed from the moisture proof bag When the devices are removed from the moisture proof bag for the delivery check etc be sure that the devices are re put into the moisture proof bag as soon as possible at the target of within 60 minutes When multiple soldering processes for up to three multiple soldering processes are performed be sure that the time until the completion of the final process falls within the storage times given in Table 3 21 73 HITACHI 3 8 4 Storage and Handling Without Moisture proof Packing Due to considerations of solderability corrosion on the leads etc the following conditions should be taken as guidelines for storage and handling of devices not in moisture proof bags Temperature 5 to 30 C Humidity 45 to 7576 RH Storage Period 1 year VVhen there are stipulations in delivery specifications etc these stipulations take priority over the conditions listed above 3 8 5 Baking Process VVhen the follovving conditions apply baking process moisture removal process should be performed based on the conditions listed in Table 3 22 e Products provided with a humidity indicator card When the 3046 spot on the card turns pink when the moisture proof bag is opened When there is a difference in color between
73. rform the soldering The flow of the assembly process is shown in Figure 4 1 Printed wiring board Solder paste Metal stencil r mmm Printed wiring board Solder paste Solder printing li Mounting DAS Reflow soldering i em E Cleaning lt Y 1 V Figure 4 1 BGA Assembly Process Flow 87 HITACHI 4 2 Mounting Pad Design Mounting pad designs include the over resist type where the mounting pad is covered with solder resist and the normal type where the solder resist is not placed on the pad Select the type based on considerations of the wiring design on the printed wiring board Over resist type Normal type Mounting pad copper land m Solder resist c The standard alignment accuracy of solder resists is about 0 1 mm An example of a mounting pad design designed based on this specification is shown in Table 4 1 The pad copper land dimension should be designed taking into consideration the solder resist alignment accuracy Whichever pad type is used the opening diameter of the solder resist should be the same as the pad dimension on the BGA side This produces a ball shape with good vertical balance following reflow soldering which helps to moderate the concentration of thermal stress during the heat cycle Table4 1 Mounting Pad Des
74. ring iron itself should not exceed 350 C Pulse heater Hot air Laser Light beam 5 to 10 seconds E 8 230 C to 9 260 C To ea Pack Solder 5 ackage Mounting pad Time Location at which to measure the temperature of the solder joint is marked with the diagonal lines 56 HITACHI 2 Soldering Conditions Using Full Heating Methods We recommend limiting heating to three times within the storage durations indicated in section 3 8 3 a Reflow Soldering Conditions Tables 3 12 to 3 15 i IC Packages Packages with Leads QFP etc Table 3 12 Soldering Conditions for IC Packages with Leads Using Reflow Soldering Methods Lead plating Sn Pb palladium Sn Bi Sn Cu Solder paste Sn Pb eutectic Sn Ag Sn Pb eutectic Sn Ag Package surface temperature upper limit Peak temperature 260 C 230 C or greater for 50 seconds or less Peak temperature 260 C 230 C or greater for 50 seconds or less Temperature profile Package surface temperature 50 seconds or less 260 C Max 230 C 140 to 160 C N 1 to 4 C second Approx 60 seconds 1 to 5 C second Time 50 seconds or less 230 C 150 to 180 C p 1 to 4 C second 90 30 seconds Package surface temperature 1 to 5 C second Time 260 C Max Note The maximum temperature for large Refer to the de
75. s Determine the cleanliness based on Table 3 5 of Section 3 2 1 discussed above Cleanliness of the Boards after the Devices Have Been Mounted 3 6 5 Other Notes and Cautions 1 Be aware that exposure to excessive cleaning may cause the markings on the package to fade for disappear check the process under actual use conditions 2 Cleaning Using Organic Solvents a Because of flammability concerns fire prevention equipment must be used when terpene based solvents alcohol or petroleum based solvents are used b When the cleaning is done by rinsing with water it is necessary to give adequate consideration to processing the effluent 3 Rinsing with Water Care must be taken to follow all regulations pertaining to waste water processing 65 HITACHI 3 7 Inspection 3 7 1 Inspection Equipment As the soldering connection pitch becomes finer and the solder joints are miniaturized the amount of solder per joint and the area of joint both become smaller and thus the inspections in each process through the completion of soldering are ever more important While in the past visual inspections have been the primary means by which these inspections have been performed recently a variety of automated inspection equipment has been developed and has appeared on the market At present the inspection equipment is primarily soldering appearance inspection equipment and solder paste post printing appearance inspection equipment
76. s and diodes 16 HITACHI MPAK MPAK 4 0 95 0 95 BY aw Te 18 8 0 8 I 1 9 0 8 MPAK 5 MPAK 6 0 95 0 95 0 95 0 95 0 8 si 10 4 44 02 Z 1 9 TSOP 6 UPAK 2 0 0 5 ptt I H e NNUS inf S T7 1 0 11 0 1 0 2 Y nius 1 10 10 e a P Figure 3 13 Example of Mounting Pad Design for Discrete Packages 2 Note The MPAK and MPAK 5 mounting pads are suitable for both transistors and diodes HITACHI LDPAK S DPAK S 11 2 6 0 2 5 lt 1 0 j 1 01 1 5 5 5 oo 79 bi 4 0 E 88 2 0 2 2 0 2 0 lt lt wo 3 Y Y 2 54 2 54 2 3 2 3 LFPAK LLD 4 57 7 7 l 2 px 12 22 12 x s SRP 0 76 z 4 R 15 20 15 127 mu 457 4 2 ge mm Figure 3 14 Example of Mounting Pad Design for Discrete Packages 3 HITACHI UFP SFP MOP
77. s likely that there will be a temperature gap even within a given package HITACHI a There will be locations that are illuminated directly by the infrared radiation the top surfaces of the devices etc along with places that are not illuminated such as the bottom surfaces of the devices b The level of absorption of infrared radiation will vary depending on the material being used e g the resin lead materials solder paste etc As a result when this method is used the surface temperature of the package body will be higher than the temperature of the leads when the reflow temperature profile is set for the lead parts which are to be soldered which in some cases may cause thermal stresses and cracks in the package There are especially large thermal stresses on the ICs when the near infrared rays are used wherein resin is quite transparent and thus at present the far infrared rays are usually used In either case the surface temperature of the package body must be checked when the temperature profile is set Section 3 9 2 should also be referenced for the information regarding the prevention of package cracking Exhaust Heaters Heaters or lamps Preheating Main nesting Cooling O O O Of DBD coi om N P Conveyor O Figure 3 36 Infrared Reflow Equipment ii Air Reflow Method In the air reflow method the solder is melted through a hot gas convection heati
78. s required regarding the thermal shock to the packages Table 3 9 shows the primary soldering methods used for surface mount packages 44 HITACHI Table 3 9 Soldering Methods Used for Surface Mount Packages Summary of Soldering Temperature Thermal Method Illustration Productivity Uniformity Shock Solderability Cost Partial Soldering iron Soldering iron O Heating lt Methods Pulse heater Pulse current O Heater Hot air 1e Hot air AIM JN Laser O S7 Laser Light beam pen Parabolic mirror Printed wiring board Full Infrared reflow OOO raed O O Heating uu Methods LL Cooling coil O O O Saturated vapor Vapor phase reflow VPS method Inert liquid Heater Air reflow Heater Hot air Q O O N reflow Heater Nitrogen O O O ULZ Flow solderin RO 9 C A a m O O po Flow solder Solder bath for surface mounting Note The circle mark indicates a comparative advantage over the other methods VPS Vapor Phase reflow Soldering 45 HITACHI Although full heating methods are seen as advantageous for mass production for devices that are particularly sensitive to the heat associated with soldering we recommend using a partial heating method e g soldering iron heating following ref
79. stics Hitachi bears no responsibility for failure or damage when used beyond the guaranteed ranges Even within the guaranteed ranges consider normally foreseeable failure rates or failure modes in semiconductor devices and employ systemic measures such as fail safes so that the equipment incorporating Hitachi product does not cause bodily injury fire or other consequential damage due to operation of the Hitachi product 5 This product is not designed to be radiation resistant No one is permitted to reproduce or duplicate in any form the whole or part of this document without written approval from Hitachi 7 Contact Hitachi s sales office for any questions regarding this document or Hitachi semiconductor products Contents Section 1 Types of Package Mounting Configurations sees 1 Section 2 Surface Mount Package Assembly Process Flow 3 2 1 Basic Assembly Process Flow for Surface Mount Packages 3 Section 3 Overview of the Individual Steps in the Assembly Process 5 3 1 Designing the Printed Wiring Board and the Mounting Pad esses 3 3 1 1 Printed Wiring Board Material sess eene 5 3 1 2 Mounting Pads ot rmt e E reete 10 32 Solder Application ooi a t repr meer 20 B21 Solder Paste oen re teh tert A R AT eR IR RE 20 32 2 Applying the Solder Paste nre Rep
80. t a sufficiently high temperature As is shown in Figure 3 27 generally the adhesive which is applied to the bottom surface of the package body is cooler than the surface of the board Be sure to obtain adequate adhesive strength by controlling the curing conditions at the adhesive Temperature on the surface of the board Temperature 150 C N Scie 135 C Temperature at the adhesive Time Figure 3 27 Example of the Temperature Profile When Curing the Temporary Adhesive HITACHI 35 3 3 3 Amount of Adhesive Applied Height The dependence of the adhesive strength on the area adhesion is substantial and it is necessary to investigate the coating spread of the adhesive so that the optimal strength can be obtained Figure 3 28 Moreover the stand off heights are different depending on the packages The amount of adhesive applied and especially the height of the application must be optimized for each package Figure 3 29 20 O For a 32 pin SOP T E RE 2 15 5 O D 10 o o 2 0 o 5 5 o 0 10 20 30 40 Adhesive area after curing mm Figure 3 28 Relationship Between the Adhesive Area and the Adhesive Strength Using Adhesive NF5000 The adhesive layer is not thick enough for an SOJ and thus does not reach SOP SOJ F ZI Sur m L 77 Temporary adhes
81. t spray is sprayed against the product Spraying at an angle may increase the effectiveness of cleaning when there is little clearance between the devices and the printed wiring board Vapor Cleaning This is a method where the cleaning is performed by solvent vapors This method is often used as a final cleaning method because it is possible to clean using a solvent that contains no impurities The selection of the cleaning solution the cleaning method the cleaning equipment and so forth depends on the structure of the printed wiring board and on the configuration of devices on the board Select an appropriate cleaning method based on an evaluation that takes all of these factors into account 64 HITACHI 3 6 3 Cleaning Conditions The following conditions are presented as an example of ultrasonic cleaning However care is required in selecting the applied frequency power especially the peak power and time Also be sure devices do not resonate a Frequency 28 kHz to 29 kHz selected so that the device does not resonate b Ultrasonic output 15W liter once c Time 30 seconds or less d Other The oscillator shall not contact the device or the printed wiring board directly This is especially true for ceramic packages such as QFN LCC and QFP Ceramic because they are cavity packages and the ultrasonic cleaning will cause the connection wires to resonate thus breaking the wires 3 6 4 Determining the Cleanlines
82. the indicator card and the silica gel then make the decision based on the color of the indicator card Products not provided with a humidity indicator card When the silica gels turn pink when the moisture proof bag is opened e When the storage conditions exceed the stipulation in Table 3 21 after the moisture proof bag is opened See Figure 3 44 regarding the specifications of the humidity indicator card Table 3 22 Recommended Baking Conditions Baking Temperature Baking Time Repetitive Baking General products 125 C 5 C 16 to 24 hours Total of 96 hours or less Thin packages with a mounting 125 C 5 C 4to 24 hours Total of 96 hours or less height of 1 20 mm or less Special products As per the delivery specifications Be sure to use heatproof trays etc when performing the baking process Heatproof trays are marked HEAT PROOF or carry an indication of their maximum temperature rating Confirm these markings before performing the baking process 74 HITACHI 76 0 1 0mm Characteristics of the Humidity Indicator Card HUMIDITY INDICATOR While the color of the spot becomes blue when it is dry as it becomes moist the color PIE CALIVESHMIDITYOBEBGENTAGE shifts from blue to lavender and then shifts further to pink Qo When the card is removed from the moisture proof bag the presence of a lavender spot indicates that the relative humidity within the 50 0 1 0mm Spot
83. the time of the preheat process The solder paste is printed bridging several pads Countermeasures Reduce the amount of solder both the printed area and the thickness Change the printing method Solder balls Pad TZ Solder balls Pad M Solder balls Solder balls are found e around the pads or around the devices The solder paste has melted in places aside from the pad The reason for this might be Shift during printing the solder paste or blotting during printing Slump of solder paste during the heating Capillary effect of solder paste between the device and the board Align the printing position Print a somewhat smaller pattern on the pads Switch to a solder paste that is less likely to slump Solder balls are found e on the surface of the solder which has been subjected to a reflow process Inadequate heating temperature time Solder paste degradation aging Solder paste degradation due to excessive preheating HITACHI Re evaluate the heating equipment and method Store the solder paste in a refrigerator Switch to a solder paste that does not degrade as much over time 69 Table 3 20 Reflow Soldering Defects Troubleshooting Guide cont Type of Defect Description Causes Countermeasures Uneven amount of The amount of solder e There is a lack of e Switch to a solder solder on the mounting pads unifor
84. tic packages are stored in a high moisture location the resin absorbs the moisture When soldering is performed while the resin contains this absorbed moisture the high temperature will vaporize the water content and cause reflow cracks Those devices that are sensitive to moisture should be provided with moisture proof packing to prevent the absorption of moisture before soldering See Figure 3 43 m Stopper Magazine LSI This card is not applied to some devices 1 Magazine CAUTION ELECTROSTATIC THESE DEVICES ARE A SENSITIVE MOISTURE SENSITIVE DEVICES M DO NOT OPEN OR HANDLE am ES EXCEPT ATA Band 1 Humidity BB SE SER STATIC FREE WORKSTATION d indicator AERA d BRRR vv 77 2212002 3 5 VID RRRA YT 72 7 v 7 BRE d 5 Belt U 7 MEARE ii amp 5 30 C COXRHUFORET REL 168HRUNICU PA RREELTUKLKE lt K KOBER BU EY Moisture proof bag 13 Silica gel WARNING aluminium laminated ONCE DRY PACK IS OPENED DEVICES MUST BE STORED AT LESS THAN 60 RH AND 5 30 C AND MUST BE REFLOW SOLDERED WITHIN 168 HOURS OTHERWISE PACKAGE Moisture CRACKING COULD OCCUR DURING REFLOW SOLDERING proof packing CL 2 There is also the following specification which is based on the JEDEC standard Inside box ELECTROSTATIC SENSITIVE DEVICES This bag Contains DO NOT OPEN OR HANDLE CAUTION MOISTURE SENSITIVE A EXCEPT AT A DEVICES STATIC FREE WORKSTATION SRW WARNING 1 Bii
85. tire package the adhesive strength at the interface between the resin and the frame is reduced by the high temperature while at the same time differences in the coefficient of thermal expansion produce a sheer force Because of this minute interfacial peeling appears at the interface between the resin and the frame and the water content within the resin near the frame vaporizes due to the heat and is expelled to the interface accelerating the peeling at this interface In this region the internal pressure increases and the resin warps eventually resulting in cracks Using the Fick diffusion model we can calculate the diffusion of the moisture within the resin as follows 5 C x t 82 C x t x t D x t t 62X2 x The distance from the back surface of the package in the direction of the center of the package t Storage time D Diffusion coefficient Furthermore Q 0 C x t dx indicates the total moisture content in the package Consequently due to the storage time and environment of the package there will be situations where the amount of moisture in the package has the opposite effect on the cracking See Figure 3 49 Because of this it is important to control the moisture content by focusing on the amount of moisture in the vicinity of the frame 79 HITACHI The diffusion coefficient D shown above is a function of temperature and thus the amount of moisture in the vicinity of the frame is also a function
86. unting accuracy Lead L X Allovvable misalignment Mounting pad E E b Allowable protrusion Mounting accuracy x Total placement accuracy Board accuracy QFP lead accuracy Total placement accuracy the amount of allowable misalignment X Example Example for a 0 4 mm pitch QFP where the allowable protrusions are 1 3 of lead width W Total placement accuracy allowable misalignment X W x 1 3 b W x 1 2 0 17 mm 3 0 22 mm 0 17 mm 2 0 0817 mm When we assume that the board pattern accuracy 0 01 mm QFP lead accuracy 0 03 mm Mounting accuracy 0 0817 0 01 0 03 0 075 mm Figure 3 31 QFP Mounting Accuracy 3 4 4 Shapes of the Package Packing 1 Specifications and Characteristics of the Package Packing At Hitachi Ltd products are shipped in one of three forms magazines trays and embossed taping See Chapter 4 of the Hitachi Semiconductor Package Data Book published by Hitachi Ltd regarding the form in which the packages are shipped and regarding the external dimensions of the various packing types Figure 3 32 shows the general packing specifications used at Hitachi Table 3 7 lists the features and characteristics of the packing characteristics at Hitachi 40 HITACHI Outside Cardboard Packing Box Carton tape blue PP band Inside Box Corrugated cardboard
87. ween the collet temperature and the actual temperature at the 46 HITACHI solder joints it is likely that the actual temperature at the solder joints will be lower than the temperature setting for the collet b When there is a large amount of variability within the temperature distribution within the heat collet or when the heat collet is lacking adequate thermal capacity the soldering temperature will differ depending on the actual soldering process performed For these reasons it is necessary to carefully consider the following when setting the reflow conditions a Setting the reflow temperature conditions in terms of the actual solder joint temperature b Setting the reflow temperature at a target of approximate 50 C higher than the solder melting point iii Hot Air Heating This is a process where the reflow heating makes use of a jet of hot gas from a nozzle where this gas air nitrogen etc is heated using a heater Because the thermal conduction and thermal capacity of the gaseous medium used in this method are low an extremely large volume of heated air must be supplied and it is difficult to insure uniformity and stability in the processing conditions Heater Air or nitrogen Quartz glass tube air Solder paste 4 Printed wiring board Mounting pad Figure 3 34 Schematic Diagram of the Hot Air Heating Method 47 HITACHI iv Laser Heating This is a method w

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