SMT Array Tech Note
Contents
1. 5 1 MLP Solder Footprint The solder footprint shown in Figure 6 has been shown to work well for the 8mm MLP parts e g Micro 30035 SMT It consists of four square 1 4mm x 1 4mm pads arranged in a square with a pitch of 1 8mm between pad centres 0 4mm gap between pads Solder footprint information for the TSV parts can be found in the relevant product User Manual mr a n dl Figure 6 5 2 MLP Device Spacing The MLP devices are cut from strips with a cut accuracy of 50um Therefore if the parts were placed with 100um spacing there could be extreme cases where the devices could touch Therefore to ensure that there would always be a minimum spacing of 100um a component spacing of 200UM was chosen Figure 7 shows how this results in a variable gap between the devices ranging from 100um to 8300um Regardless of this variation in outside package size the position of the inner die will be fixed Therefore based on a spacing of 200um the active areas will be 1 04mm apart This gives an array fill factor of 8 16 0 52 3 16 75 Note The minimum spacing of 200um is too small to allow re work Should the user wish to design an array that can be reworked then a minimum of SOOum spacing is recommended Min 100um Ideal 200um Max 300um Min ideal 2 00mm Max 2 05mm Figure 7 SMT Array Design sensl sense light TECH NOTE NOTE The TSV parts are cut with greater accuracy and as a consequence can be2. 0 072 0 077 0 076 0 072 500059 00029 0 006 0 004 Figure 11 SENSL M9 ARRAY SAMPLE 1C ALL SENSORS MEASURED 30 25 a 20 N EE 0 5 UIL GP PS D s oy gy S gy g g O ry kK HPP SR Figure 12 SMT Array Design sensl sense light TECH NOTE 5 5 Solder Paste To avoid significant voiding under the SMT pads it is important to use the correct type of solder paste It was found that using a standard solder paste such as the Qualitek DSP 875 Types resulted in significant solder voids formed under the SMT pads This problem was resolved by using one of two solder pastes Multicore WS300 solder paste Qualitek DSP 875 Type 5 Figure 13 shows how voiding is significantly reduced by using the Qualitek DSP 875 Type 5 solder paste rather than the more standard Type 3 paste iy oe a k Wie Hi a Qualitek DSP 875 Type 3 Qualitek DSP 875 Type 5 Figure 13 SMT Array Design sensl sense light TECH NOTE 6 ARRAY TESTING To test the MLP array the board was connected to a Matrix system and then on to a PC hosting the Matrix system GUI software For these tests the MLP sensors were of type MicroF M 30035 SMT 6 1 Basic Pixel Functionality Test The initial test was carried out to prove that each SIPM pixel in the fabricated array functioned correctly This was carried out using a 3x3x156mm LYSO scintillating crystal and the SensL Matrix system software GUI The crystal was moved from pixe
3. AND TSV SMT DEVICES 2 1 Applicable Documents IPC JEDEC J STD 020 IPC JEDEC J STD 033 2 2 Storage Conditions SMT devices both MLP and TSV are moisture sensitive Moisture can diffuse into the package from atmospheric humidity Surface mount soldering of the SMT packages to PCBs exposes the entire package body to temperatures up to 260 C Rapid expansion of trapped moisture during this process can result in package cracking delamination of critical interfaces within the package or damaged bond wires Parts are shipped in moisture barrier bags MBBs Unopened MBBs shall be stored at temperature below 40 C with humidity below 90 RH After the MBB has been opened the devices must be reflow soldered within a specific time period as defined by the moisture sensitivity level MSL The MSL for SensL parts are shown in Table 1 The parts must be baked according to J STD 033 table 4 1 if any of the following occurs 1 The parts are not reflow soldered within the given time period after opening the MBB 2 The MBB is expired according to the packing date and conditions on the label 3 The humidity indicator card HIC shows the moisture level within the MBB has increased beyond the required level Table 1 MSL values and details More detailed information about storing and handling the SMT parts can be found in the following Tech Note SMT Array Design sensl sense light TECH NOTE 2 3 Solder Reflow Conditions MLP and TSV pro
4. board and from 2 diagonal lines it calculates the ideal plane The position of the surface of each sensor pixel is then measured and compared with the ideal plane An example result from one of the prototype arrays is shown in Figure 11 It displays a value that tells you how close or the device is from the ideal plane for each pixel For example Pixel 111 is 0 005mm bum above the ideal plane Pixel 80 is 0 0138mm 13um below the ideal plane Blue ve ABOVE Green ve BELOW 4 vd MM Hd R ma Re TE n ii i id 4 i 4 4 7 lip r at di di ie l ee eens aa sd d dd a lt Hi 7 d Tla d J f r F Hy ii 4 1 k eee at ME de dt T oo TY ml mm Oe et de mt rr EA tr jy JH Ji I des Patents ae d ana Las C 14 d ily TE it FT Ed eke fe J H T y wy dar em 4 Figure 9 Figure 10 The graph in Figure 12 shows the 144 values placed in 10um bins from 100 to 100um The results shows the range is 80 to 60 140um SMT Array Design TECH NOTE SENSL sense light 133 134 0 031 0 004 121 122 0 028 0 029 109 110 0 027 0 019 97 98 0 030 0 020 85 86 0 030 0 013 73 74 0 033 0 015 61 62 0 021 0 005 49 50 0 009 0 049 37 38 0 029 0 001 25 26 0 013 0 011 13 14 0 035 0 038 1 2 3 4 5 6 7 8 9 10 11 12 0 Qal7 0 021 0 013 0 04
5. SMT Array Design sensl sense light TE NOTE Building Arrays of SensL SMT Sensors on PCB INTRODUCTION This document focusses on the creation of close packed arrays a of SIPM sensors It describes the design and test of a 12x12 144 ae ities n pixel array using 8mm surface mount SMT SIPM Primarily the ER oat ei adhd design was carried out to investigate the achievable pixel pitch and AE ona Ji planarity when producing arrays using these devices To evaluate fide ar fei el My rika the functionality of the array it was decided to design the board to have the necessary output to be compatible with the Matrix readout system which allowed for performance testing of the array Although the work here uses the MLP type of SMT sensor package all of the information applies equally to the creation of arrays using SensL TSV parts Pm at were ari op bh ma Ta fi 1 SENSL SMT PACKAGES This document contains information necessary for the user to create close packed 1D or 2D arrays of SensL surface mount SMT compatible sensor packages either the micro leadframe package MLP or through silicon via TSV parts The MLP SMT products have a part number with the suffix SMT whereas the TSV SMT is denoted by TSV Figure 1 below shows examples of each package type Figure 1 MLP SMT parts left and TSV SMT parts right SMT Array Design sensl sense light TECH NOTE 2 HANDLING OF MOISTURE SENSITIVE MLP SMT
6. ducts must be mounted according to specified soldering pad patterns Refer to the product User Manual for details e g UM MicroC pdrt Solder paste we recommend using no clean solder paste must be evenly applied to each soldering pad to insure proper bonding and positioning of the component After soldering allow at least three minutes for the component to cool to room temperature before further operations Solder reflow conditions must be in compliance with J STD 20 table 5 2 This is summarized in Figure 2 The number of passes shall not be more than 2 Solder Reflow Profile 300 Max 10sec at 260 C Max 260 C 250 f N ms ZNE K gt O 1 7 180 C _ Aid R 150 oY 7 60 to 120 sec Temperature C N m e O O 0 50 100 150 200 250 300 Time sec Figure 2 Solder reflow profile for the MLP SMT and the TSV SMT parts SMT Array Design sensl sense light TECH NOTE 3 ARRAY BUILD CONSIDERATIONS The following key parameters should be taken into account when seeking a vendor to assemble the MLP or TSV array to ensure the best quality Planarity Minimum gap between sensor parts fill factor e Component placement accuracy Board material Handling to the applicable MSL specifications see page 2 3 1 Planarity The planarity is a measurement of how flat the board is It is the deviation from 2 diagonal points as a percentage of the diagonal measurement For example if two corner
7. l to pixel Each time the GUI was used to verify that the particular pixel was detecting the intrinsic radioactivity from the Lutetium in the LYSO crystal 6 2 Cesium 137 Source Energy Resolution Measurement Using a Cs 137 radioactive source that produces gamma rays of 662keV and a 38x8x15mm LYSO crystal energy resolution measurements were carried out on 9 different pixels Figure 14 shows a typical energy plot using the Matrix system GUI It was found that in all cases it was relatively simple to achieve an energy resolution of 212 0 sensl Technologies Matrix Readout Software Plot Range Plot Quit amp ZoomTo Lowlo E Channel o Array 8 Pixel 15 Save Plots Refresh Halt Zoom Out HGH 1000 Channel 2 Array 2 Pixel 2 Piot Fit Report ENERGY PLOT running Timing Energy Windows Timing Energy Calculation LOW HGH Pair Tolerance o 10 5 nS Singles 1 Pixel 1 250 420 Coincidence Pairs Singles 2 Pixel Z z790 450 Save Range Low 425 Peak Bin No 494 Energy Plot 1 RED Best Fit BLUE Plot Select Smoothing a Q HGH 561 Resolution 12 49 Figure 14 www sensl com N sales sensl com S C S 353 21 240 7110 International i 1 650 641 3278 North America sense light All specifications are subject to change without notice
8. placed with a minimum spacing of 100um although a minimum spacing of 500um is required if the user wishes to allow for rework 5 3 Planarity The vendor used for the array assembly believed that a simple 6 layer FR4 PCB would be acceptable providing good care was taken during the manufacturing process The planarity of the resulting array is very much dependent on the process of soldering the devices to the board It was observed by the vendor that during the re flow process it was important to hold the boards in a rigid frame to avoid any warping due to the heat process By designing a specific frame to hold the boards less than 220um warping diagonally from corner to corner was achieved with relative ease As the diagonal measurement of the board is 71mm see Figure 8 this gives a planarity measurement of Q227 103 This fits well inside the quoted range of 0 09 to 0 53 50 2mm amm OOOOOO0OC H000000E H0000 OOUOOUOCOULL I Length Width 12 x 4mm 11 x 0 2mm 50 2mm 2 2 Diagonal 2A50 2 50 2 1mm Figure 8 SMT Array Design sensl sense light TECH NOTE 5 4 Detailed Planarity Measurements Prototype boards were manufactured as shown in Figure 9 sensor side and Figure 10 rear connector side To fully test the planarity one of the samples was analyzed using a non contact optical instrument specifically designed for this type of measurement The machine first takes the position of each corner of the
9. s of a30mm x 40mm board deviate by 0 4mm then the planarity is O 4 50 0 8 Diagonal of board is 50mm An example of good values for the key parameters are as follows Planarity 0 09 to 0 53 Minimum gap 0 2mm Component placement 25umM SMT Array Design sensl sense light TECH NOTE 4 TEST ARRAY ELECTRONICS DESIGN A test array mounted on PCB was fabricated using SensL MLP packaged sensor parts The array layout was designed to be compatible with the SensL Matrix System that could be used for evaluation PLOO 18 Figure 3 Figure 3 shows one of 9 blocks designed to replicate the function of the 4x4 array used on the Matrix system detector head with each element representing an Micro 30035 SMT sensor The 16 cathodes N of each 4x4 block of devices are connected together to create the 9 ARRAY signal lines The corresponding anode P outputs of each 4x4 block of devices are connected together to create 16 PIXEL signal lines The positive bias is applied to the ARRAY side of the device However with alternative readout electronics other routing of the signals is possible SMT Array Design sensl sense light TECH NOTE AO Al A2 A3 A4 A5 A6 A7 AB OO NP N NN N N NN ME O NDUPUO ND UI OO Og w U145 R10 PLOO 15 DS1822Z Figure 4 Figure 4 shows the ribbon cable connector and thermometer IC This is identical to the circuit used for the Matrix system detector head Hence the board is elec
10. trically identical to the Matrix system detector head SMT Array Design sensl sense light TECH NOTE 5 MANUFACTURING THE TEST ARRAY Figure 5 shows the engineering drawing of the Micro 300385 SMT devices which was used for the test array The MLP package is nominally a 4mm x 4mm square housing the SIPM die of 3 16mm x 3 16mm The information below could also apply to an array based on the TSV parts using CAD and pin out information from the relevant product User Manual The manufacturing challenge for this project was two fold le MLP Device Spacing manufacture a board with the devices as close as possible to ensure the best possible fill factor 2 Planarity manufacture the board with best planarity measurement as possible 4 00 0 1 ve Area U lt T NY OO 2 ioe Pin 11D Table 2 Pad Numbering for the Micro 300XX Cathode 0 6520 05 Figure 5 Fast Output Fast Output Cathode Not Connected Not Connected Common practice would be to ground any floating pins such as the NC pin 4 Grounding the pin helps shielding and keeps noise interference from external sources EMI RF down but it may also be left floating without issue In the production of the PCBs discussed in this document the NC pin was grounded In addition it should be ensured that the assembly of the array board takes into account the MSL specifications of the devices SMT Array Design sensl sense light TECH NOTE
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