AN610 VISHAY
Document overview
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Technical content
www.vishay.com One PCB can accommodate eight PolarPAK pack- ages (see Figure 6). Appendix B covers PCB fabrica- tion details. PCBA characteristics: Surface finish: Immersion silver Board thickness: 3.175 mm [0.125 in.] Board size: 4.5 in. by 5 in. Each PCB side is designed to accommodate two types of parts. PCB Part #SMDTF125T16L_Ver C accommodates PolarPAK and PowerPAK SO-8 sin- gle ext. b) PCB assembly: The test sample build was deter- mined by IPC-9701, which calls for 32 fresh and 10 reworked solder joint assemblies. Seven boards with seven parts on each board gives 49 assembled parts. Reworking two parts from six boards renders 12 reworked parts. Five boards from the reworked group and a seventh non-reworked board for temper- ature cycling were used to meet IPC-9701 criteria. The sixth reworked board was retained as a zero temperature cycle reference board. Using the PCB assembly process developed and described in AppNote AN-xxx titled "Development of Lead-free soldering profile for PolarPAK" [2] seven PCBs were assembled wit h seven PolarPAK parts on each board. Part ID U16 was not assembled. Assembly process parameters: a. Stencil aperture opening: Increase of 10% -- the aperture increase from the original pad size was used b. Aperture shape and size, stencil thickness, and aspect ratio are described in the following table: Aspect ratio (aperture opening / stencil thickness) = 2.5 Minimum area ratio (LxW / 2(L+W)T) = 0.8 Solder pastes: The following solder paste was used: Lead-free solder paste SAC-387 (Tamura TLF-206- 93G) 1. Stencil printing: Machine: EKRA E5 Squeegee size / angle: 450 mm / 60° Front/rear pressure: 40 Newtons Print speed: 8-12 mm/s Snap off: 0 mm Separation speed: 0.5 mm/s Stencil thickness: 5 mils Stencil opening: See Table 1 below Figure: 6 PCB Dimensions Version Aperture shape Aperture opening Stencil thickness (mil) Aspect ratio Area ratio Component shape Width (mils) Length (mils) POLARPAK CA Rectangle 25.2 189.2 5 5.04 2.22 CA Rectangle 21.0 189.2 5 4.20 1.89 CA Rectangle 94.5 189.2 5 18.90 6.30
www.vishay.com Document Number 73507 31-Aug-05 Vishay Siliconix AN610 Table 1 2. Pick and place Machine: Juki 2060E Note: In each board, leave the first location empty (no load/part) 3. Reflow Machine: BTU Pyramax 98 (seven heating zones and two cooling zones) - no nitrogen, air only RSS profile shown in Figure 7 was used for the lead- free solder paste For immediate reference, the reflow process and parameters used for lead-free solder are summa- rized below: Solder joint visual inspection criteria were derived from IPC-A-610D[4]; refer to Appendix D for relevant details. The visual inspection also included looking for any obvious solder joint defects such as a cold joint, solder bumps, bridges, or other flaws. In addition, 2DX X-ray and 5DX X-ray processes were employed to inspect void levels on each solder joint. All images were compared by void level. During 2DX inspection the focus was on number and size of voids. 5DX measurements were sorted and selected based on the percentage of void areas. The first method, 2DX image review, was a qualitative com- parison. The second method, 5DX parametric data, was a quantitative analysis. See Appendix A for best- case/worst-case void leve l X-ray images for Polar- PAK. Using these criteria , good solder assemblies were achieved with void levels less than 25%. c) Rework: Using the worst-case locations from the X- ray inspection results, six PCBs and two locations on each board were selected and marked "X" with in- delegable black ink for re work. The originally sol- dered part was de-soldered and replaced with a new part. Table 2: Rework Locations for Lead-Free Assemblies Rework setup: AirVac DRS24 - BGA rework machine Special rework nozzle Rework steps: 1. Remove components using a hot-air BGA rework machine 2. Clean up pads using a soldering iron 3. Solder bump pads using a soldering iron and sol- der wire SAC 305. 4. Apply no-clean gel flux on the pad 5. Place the component using the hot-air BGA rework machine 6. Reflow the component using the hot-air BGA rework machine per profiles shown below in Figure 8 Version Comp Type Buildt Qty Profile Stencil Thickness Aperture Design Drain-Gate (mils) Source CA PolarPAK 7 RSS 5 mils 21 x 189.2 94.5 x 189.2 Figure 7: RSS Profile for Lead-Free Peak Temperature: 237 °C Time above 220 °C: 30 seconds Soak time (120 °C to 200 °C): 115 seconds Board # Side Comp Type Rework Location
29 CA PolarPAK U10, U11
30 CA PolarPAK U11, U15
31 CA PolarPAK U12, U15
32 CA PolarPAK U11, U12
33 CA PolarPAK U13, U14
34 CA PolarPAK No Rework
35 CA PolarPAK U10, U12
www.vishay.com If any solder joint failure occurs, it is detected by com- paring the joint resistance and is recoded with respect to the cycle number in which it occurred. (2) Test setup: A programmable temperature cycling chamber was programmed for the temperature cycle shown in Fig- ure 13. The test chamber had a pre-wired card-cage that could take multiple PCB assemblies conforming to the card-cage form-fact or. Each daisy chain was connected to an analysis-tech event detector sys- tem. The latter device compared, at a preset interval of one cycle time during dwell-time, the resistance with preset value 1 k Ω, and reported/recorded an event any time the daisy chain resistance exceeded the preset value. Thus, even momentarily open cir- cuits were caught and reported. (3) Temperature cycling chamber calibration: The temperature cycle chamber was calibrated for a thermal mass of test load by measuring the actual temperature profile on pertinent locations on the PCB assembly and component. Figure 14 shows the cali- brated profile used during the actual testing. (4) Temperature cycling: The very first and last steps of the temperature cycling test are measurements of daisy chain resis- tance. Appendix E is a tabulated record of each daisy chain resistance before and after the temperature cycling. The first resistance column is initial resis- tance and the second resistance column is the value after 3,000 cycles. PCB assemblies were loaded in the temperature cycling chamber to begin the thermal fatigue test. (5) Test database The final test results are tabulated in the following table: Table 4: 3,000-Cycle Test Data Figure 14: Calibration Profile Vishay Board # 1 0 to 100°C 10 min. ramp and 10 min. dwell -20 -10 100 110 120 18:35 18:40 18:45 18:50 18:55 19:00 19:05 19:10 19:15 19:20 19:25 19:30 19:35 Time Degrees C TC 15 Started 11/17/2004 Terminated 3/2/2005 Board Package Side ID Fail
29 PolarPAK U9
29 PolarPAK U10
29 PolarPAK U11
29 PolarPAK U12
29 PolarPAK U13
29 PolarPAK U14
29 PolarPAK U15
31 PolarPAK U9
31 PolarPAK U10
31 PolarPAK U11
31 PolarPAK U12
31 PolarPAK U13
31 PolarPAK U14
31 PolarPAK U15
32 PolarPAK U9
32 PolarPAK U10
32 PolarPAK U11
32 PolarPAK U12
32 PolarPAK U13
32 PolarPAK U14
32 PolarPAK U15
33 PolarPAK U9
33 PolarPAK U10
33 PolarPAK U11
33 PolarPAK U12
33 PolarPAK U13
33 PolarPAK U14
33 PolarPAK U15
34 PPAK SO8-EXT U1
34 PPAK SO8-EXT U2
34 PPAK SO8-EXT U3
34 PPAK SO8-EXT U4
34 PPAK SO8-EXT U5 t0
34 PPAK SO8-EXT U6
www.vishay.com Document Number 73507 31-Aug-05 Vishay Siliconix AN610 (6) Results summary Table 5: The above results show that the PolarPAK package passes the lead-free solder joint reliability test guide- lines as per IPC-9701 REFERENCE: [1] "Thermal fatigue analysis to study solder joint reliabil- ity for new-generation SMD parts introduced by Vishay Siliconix," by Serge Jaunay and Kandarp Pandya. [2] IPC-9701 Standard for So lder Joint Reliability, an IPC publication. [3] "Voiding: Occurrence and reliability issues with lead- free," by Martin Wickham, NPL. [4] IPC-A-610D Criteria for So lder Joint Quality Inspec- tion.
34 PPAK SO8-EXT U7
34 PolarPAK U9
34 PolarPAK U10
34 PolarPAK U11
34 PolarPAK U12
34 PolarPAK U13
34 PolarPAK U14
34 PolarPAK U15
35 PolarPAK U9
35 PolarPAK U10
35 PolarPAK U11
35 PolarPAK U12
35 PolarPAK U13
35 PolarPAK U14
35 PolarPAK U15
Package First Fail # Failed % Failed PolarPAK 0 0% Started 11/17/2004 Terminated 3/2/2005 Board Package Side ID Fail
www.vishay.com Appendix A POLARPAK X-Ray Images After assembly (without rework) Note: The smallest voids are based on signal pins. All images are captured through 5DX. No void measure- ment is available because of too many false calls on this component type. Smallest void Board#: 29 Location: U14 Largest void Board#: 29 Location: U9 Smallest void Board#: 30 Location: U11 Largest void Board#: 30 Location: U15
www.vishay.com Document Number 73507 31-Aug-05 Vishay Siliconix AN610 Smallest void Board#: 31 Location: U11 Largest void Board#: 31 Location: U10 Smallest void Board#: 32 Location: U11 Largest void Board#: 32 Location: U14
www.vishay.com Smallest void Board#: 33 Location: U12 Largest void Board#: 33 Location: U9 Smallest void Board#: 34 Location: U13 Largest void Board#: 34 Location: U14
www.vishay.com Document Number 73507 31-Aug-05 Vishay Siliconix AN610 Smallest void Board#: 35 Location: U12 Largest void Board#: 35 Location: U14
www.vishay.com Appendix B PCB Layout SMD125T16L_Ver C_Side A
www.vishay.com Document Number 73507 31-Aug-05 Vishay Siliconix AN610 Appendix C PCB Fabrication Material: FR-4 Thickness: 3.175 mm [0.125 in.] Number of copper layers: 16 Nominal outer layer (top/bottom) cu thickness: 35 µm [1378 µin.] 0.5 oz. Nominal inner layer cu thickness: 12 µm [472 µin.] 0.5 oz. Nominal FR4 insulation layer thickness: 231.8 µm [7,709 µin.] Even internal layers 2, 4, 5, 7 from each side: Power and ground Cu coverage on power/ground layers:70% Cu coverage on Signal trace: 40% Min. outer layer trace width: 150 µm [5906 µin.] Test pads for each daisy chain to be provided Minimum 15-mm [0.6-in.] clearance around each part for rework and if necessary the removal of the failed part with- out damage to the adjacent part/trace Minimum via for large (drain) land pad:50% Via size: Pitch: 1.0 mm [0.040 in.] Diameter: 0.3 mm [0.012 in.] Solder mask encroachment on the via pad for these via on the bottom side to prevent the solder from spreading on the bottom side. Square test pad size: 1.5 mm [0.060 in.] PTH Drill: 1.0 mm [0.040 in.] Surface finish: (preferred)OSP (Organic Solderability Preservative) Silkscreen or Cu etch to label all components, all test points, and location of pin is mandated.
www.vishay.com Appendix D Performance and Reliability of Solder Joints for Vishay Siliconix SMD Part Package -- PolarPAK Scope of work for temperature cycling Using IPC-9701 guidelines Test sample size distribution: Total number of test vehicles (PCBs): 6 (+1 reference board) Total number of daisy chains: 42 (+7 on reference board) Variety of PCBs - lead-free assemblies: PCB #SMD125T16L Ver_C Side A 6 (+1 reference board) Number of PolarPAK parts on each PCB: 7 Number of PolarPAK daisy chains per PCB: 7 Number of parts reworked: 10 (+2 on reference board) Number of parts reworked per PCB: 2 for 6 out of 7 test boards (including reference board) Temperature cycle definition: TC1 0 °C to 100 °C tolerance +/-5 °C Temperature ramp rate: 20 °C/minutes High temperature dwell: 10 minutes Low temperature dwell: 10 minutes Test duration: Whichever condition occurs first: 50% cumulative failure or Number of thermal cycles: NTC-D 3,000 cycles In case of failure continue testing up to 6,000 cycles or 50% cumulative failures, whichever occurs first. Temp Cycle 100 120 0 5 15 20 30 354 55 0 Time in Min. Temp in Deg.C Ts (max) Ts (min) Time Temp 51 0 0 15 100 20 0 30 0 35 100 45 100 50 0
www.vishay.com Document Number 73507 31-Aug-05 Vishay Siliconix AN610 Test monitoring: Event detector or continuous monitoring of electrical resistance of each daisy chain Temperature chamber characterization: Component temperature to be monitored and recorded at each board location in the chamber during the initial setup. Characterization should be performed using a representative sample load, test board configuration, and fixtures. Failure definition: Event detector 1,000 W, 10 events (maximum), 1 µs duration (maximum), reports first verified as time-to-failure. and/or Data logger/voltmeter: 20% nominal resistance increase (maximum), five readings/scans (maximum) Data documentation: 1. Detailed description of all experimental apparatus, including thermal chamber and data acquisition system 2. Temperature vs. time plots for both the board and cham ber including the chamber setup characterization data 3. Resistance vs. time plot for data logger samples 4. Tabular data for the number of cycles to failure for all failures 5. Weibull analysis
www.vishay.com Appendix E Continuity Test Board#: 029 (Lead-Free) Rev: C / Side: A Comp Ref Package type Res (Ohm) Res (Ohm) Note U16 PolarPAK Open Open No component U15 PolarPAK 0.209 0.229 U14 PolarPAK 0.317 0.336 U13 PolarPAK 0.433 0.451 U12 PolarPAK 0.072 0.088 U11 PolarPAK 0.217 0.229 X’ (Rework) U10 PolarPAK 0.305 0.305 X’ (Rework) U9 PolarPAK 0.406 0.407 Board#: 030 (Lead-Free) Rev: C / Side: A Comp Ref Package type Res (Ohm) Res (Ohm) Note U16 PolarPAK Open Open No component U15 PolarPAK 0.201 0.202 X’ (Rework) U14 PolarPAK 0.303 0.306 U13 PolarPAK 0.425 0.417 U12 PolarPAK 0.065 0.057 U11 PolarPAK 0.213 0.205 X’ (Rework) U10 PolarPAK 0.297 0.317 U9 PolarPAK 0.401 0.413 Board#: 031 (Lead-Free) Rev: C / Side: A Comp Ref Package type Res (Ohm) Res (Ohm) Note U16 PolarPAK Open Open No component U15 PolarPAK 0.206 0.202 X’ (Rework) U14 PolarPAK 0.307 0.302 U13 PolarPAK 0.425 0.422 U12 PolarPAK 0.068 0.066 X’ (Rework) U11 PolarPAK 0.214 0.247 U10 PolarPAK 0.296 0.303 U9 PolarPAK 0.399 0.403 Board#: 032 (Lead-Free) Rev: C / Side: A Comp Ref Package type Res (Ohm) Res (Ohm) Note U16 PolarPAK Open Open No component U15 PolarPAK 0.201 0.239 U14 PolarPAK 0.305 0.344 U13 PolarPAK 0.421 0.456 Board#: 032 (Lead-Free) Rev: C / Side: A Comp Ref Package type Res (Ohm) Res (Ohm) Note U12 PolarPAK 0.061 0.092 X’ (Rework) U11 PolarPAK 0.207 0.233 X’ (Rework) U10 PolarPAK 0.291 0.316 U9 PolarPAK 0.393 0.415 Board#: 033 (Lead-Free) Rev: C / Side: A Comp Ref Package type Res (Ohm) Res (Ohm) Note U16 PolarPAK Open Open No component U15 PolarPAK 0.198 0.229 U14 PolarPAK 0.304 0.336 X’ (Rework) U13 PolarPAK 0.415 0.443 X’ (Rework) U12 PolarPAK 0.059 0.084 U11 PolarPAK 0.207 0.233 U10 PolarPAK 0.293 0.301 U9 PolarPAK 0.391 0.399 Board#: 034 (Lead-Free) Rev: C / Side: A Comp Ref Package type Res (Ohm) Res (Ohm) Note U16 PolarPAK Open Open No component U15 PolarPAK 0.201 0.229 No U14 PolarPAK 0.304 0.321 U13 PolarPAK 0.415 0.438 U12 PolarPAK 0.063 0.086 U11 PolarPAK 0.209 0.228 U10 PolarPAK 0.292 0.309 U9 PolarPAK 0.394 0.410 Board#: 035 (Lead-Free) Rev: C / Side: A Comp Ref Package type Res (Ohm) Res (Ohm) Note U16 PolarPAK Open Open No component U15 PolarPAK 0.205 0.215 U14 PolarPAK 0.312 0.311 U13 PolarPAK 0.426 0.424 U12 PolarPAK 0.066 0.053 X’ (Rework) U11 PolarPAK 0.215 0.214 U10 PolarPAK 0.300 0.295 X’ (Rework) U9 PolarPAK 0.399 0.398