1 A Comparison of Different Mechanical Testing Techniques on the Reliability of Pb-Free Assemblies By Saurabh N. Athavale May 6 th, 2008 Fahad Mirza, Dr. James Pitarresi, Dr. Eric Cotts and Dr. Daryl Santos

2 Agenda  Introduction / Motivation / Goal / Objective  Literature review  Experimental Methodology  Test Vehicle  Assembly  Mechanical Tests  Test Results (Reliability and Failure Modes)  Findings  References

3 Introduction Portable electronics are very commonly subjected to accidental drops and impacts due to their size and application Increasing consumer electronics (miniaturization, features going up) Consumer Electronics account for more than 50% growth of the electronics industry Miniaturization Time

4 Introduction / Motivation  Lead usage banned due to environmental hazards  Semiconductor industry transitioning to Pb-free components  Limited reliability data available in literature  Different methods used for reliability description such as Ball pull / shear, 4-point Bend, Drop test, etc. Minimizing the use of Drop Test to the final qualification level only by using some other mechanical test to accurately predict the reliability against shock

5 From the literature review going to be discussed later in this presentation Various kinds of test vehicles are used different size different alloys different surface finishes non-symmetrical complicated dynamic response and makes data analysis difficult GOAL Perform a reliability assessment of Pb-free assemblies using a suite of mechanical testing techniques, and to do so on the same test vehicle Introduction contd.

6 Objectives  One kind of Test vehicle subjected to various mechanical tests  Demonstrate the dynamic response of the assembly to shock loading  Statistical reliability analysis of 2 nd level Pb-free solder interconnects  Assessment of the reliability of Pb-free assembly by different mechanical tests  Comparison of cycles to failure and failure modes with regard to drop height and location of components on the board  Determine the comparison between different mechanical tests so as to develop a universal platform

7 Board level drop testing is a effective method to characterize the solder joint reliability performance of handheld products since they experience lot of shocks [Chong et.al., 2006], [Syed et al., 2005], [Pandher R. et al., 2006], [JESD22-B111], [Park S., Pitarresi J., et al., 2007] 1500 g of Input acceleration widely used for drop testing [JESD22-B111], [Pandher R. et al., 2006], [Pandher R., Lewis B., et al., 2007] Test vehicle suggested for drop testing with 15 components [JESD22-B111] A recent study showed in [Chong D., et al., 2006] suggests that the location of packages on the PCB plays an important role in determining reliability during drop testing –In [Chong et al., 2006] the peak input acceleration was 690 g, –Drop testing was done on OSP and ENIG finishes with SAC405 and SnPb solders. It yielded that SnPb shows better performance with both the finishes, though joints were stronger on OSP. –It suggests that drop reliability is affected by component location and thermal aging. It also educates us on the location factor of the components. –Since the PCB is of a rectangular geometry, the length of PCB will be subjected to twisting also in addition to bending. Edge components will undergo deformation constituted by bending and twisting. Center component undergoes maximum deformation due to bending. Components were also placed at the corners which have minimum flexing and twisting but maximum damage due to highest magnitude of stress. Joints on OSP were found to be stronger for SAC as well as for Sn-Pb. It is also mentioned that the joint failure is location dependent [Syed et al., 2005] Literature Review Drop Testing

8 Discussion in Drop test Literature Review [Dongji X., et al., 2006] [Chong et al., 2006] Failure modes obtained Variety of Test Vehicles used Pb-free on OSP Interfacial failure at package side Bulk solder failure at package side Interfacial failure at board side Bulk solder failure at board side [Syed A., et al., 2006] [Lall P., et al., 2006] [Pandher R., et al., 2006]

9 Experimental Methodology

10 Testing Matrix Different Parameters involved Surface Finish (Board Side) SAC Alloys Mechanical testsReflow Conditions ENIG105Drop shock Cu-OSP305Bend TestRSS Im-Sn205Die ShearRTS Im-Ag405Pull Sn-PbShear HS pull HS shear Vibration Dwell Note: proposed testing condition

11 Test Vehicle Board Design & Layout PCB designed as per JEDEC standard JESD22-B111 (units in mm) Holes to mount the board on Drop table Daisy chained components with complementary daisy chains on the board side U4 U8 U12 U14 U O/P Accelerometer Strain Gage Group I (Center) = U8 Group II (Corner) = U2, U4, U12 and U14 CABGA100 I/Os – 10 x 10 (100) Pitch – 0.8mm Ball diameter- 18 mils Surface Finish – ENIG Solder Alloy – SAC 305 Pad geometry – SMD Board- FR4 2 layer board Surface Finish- Cu-OSP Pad diameter-13mils

12 Assembly STENCIL PRINTER REFLOW OVEN PICK & PLACE MACHINE REFLOW PROFILE Soak (Ramp-Soak-Spike) profile with TAL 78 sec, peak 241 o C, soak 140 to 170 o C

13 Drop Test Setup Dynamic response (Input acceleration, Output acceleration and Bending strain) observed in Drop test

14 4-Point Cyclic Bend Test Setup  Both tension and compression in one cycle  Matching displacement /Bending strain at the center component from Drop Test MTS Machine Setup

15 Interconnect Level Test (Ball Shear, Pull)

16 Test Sample Preparation Chip Drop test Bend test Die shear test PCB Stencil printing Sphere placement Reflow Ball shear test Ball pull test

17 Failure Mode Analysis Failure modes for SMD pads Failure modes for NSMD pads

18 Drop Reliability for thermally aged samples at 150 o C up to 1000 hours Sample size: 3 test vehicles on each data point IMC failure on Package side Results

19 Results

20 Dynamic Response of the PCBs aged at 150 o C up to 1000 Hours

21 Bend Reliability for thermally aged samples at 150 o C up to 1000 hours

22 Comparison of Drop Test and Bend Test

23 Ball Shear on Board-side (0, 200, 500, 1000 Hours) Ball Shear and Pull test on Component-side and Board-side

24 Die Shear Test for Thermally aged samples up to 1000 Hours Sample size: 10 components at each data point

25 Effect of Accelerated Temperature Aging on the Microstructure of Pb-free solders

26  Drop test  Aging decreases the characteristic life of the Pb-free assemblies. Failure mode transitioned from pad cratering (board-side) at 0 and 200 hours aging to IMC failure (component-side) at 500 and 1000 hours of aging  Failure mode was independent of the location of components on the board  The location of the package on the test vehicle has an effect on the drops to failure  Bend test  Significant decrease was seen in the bend test reliability (like-wise drop) till 500 hours of aging. Pad cratering is found together with a crack (diagonally opposite) towards the component-side  Shear test  Average peak ball shear force does not vary significantly with aging  Die shear force consistently decreased with aging time. Likewise drop testing, pad tear-out (board-side) was seen for majority of the solder joints  Pull test  Average Ball pull strength decreased with aging hours on either joints component-side and PCB-side Findings The scaling factor of can be applied to minimize the usage of drop testing

27 References Bukhari S., “Evaluation of the effects of the processing conditions on shear strength in Pb-free surface mount assembly”, Masters Thesis, Binghamton University, 2001 Bukhari S., Santos D., Cotts E., Lehman L., “Evaluation of the effects of the processing conditions on shear strength and Microstructure in Pb-free surface mount assembly”, Journal of Surface Mount Technology, 2004, Vol. 17, No. 2, pp Bukhari S., Santos D., Cotts E., Lehman L., “Continued Evaluation of the effects of the processing conditions and Aging Treatments on shear strength and Microstructure in Pb-free surface mount assembly” Proceedings of the 10th Annual PanPacific Microelectronics Conference, 2005, pp Chatterji I., “Effect of aging on shear force and intermetallic thickness in Lead-free solder alloys”, Masters Thesis, Binghamton University, 2003 Chatterji I., et al., “The Effect of Aging on the shear strength of Pb-free and Pb-bearing BGA solder Spheres” Nepcon West and Fiberoptic Automation Expo-Conference Proceedings, 2002, pp Chong D., et al., “Performance Assessment on Board-level Drop Reliability for Chip Scal Packages (Fine- pitch BGA)”, Electronic Components and Technology Conference, 2006, pp Chouta P., “Evaluation of shear strength of Lead-free solder spheres for BGA applications”, Maters Thesis, Binghamton University, 2000 Chouta P., Santos D., et al., “A Shear Strength study of Lead-free solder spheres for BGA Applications on Different Pad Finishes”, Proceedings of PanPacific Microelectronics Symposium, SMTA, 2001, pp Dongji X., et al., “A Comparative Study on Drop Test Performance of Fine Pitch BGA Assemblies” Electronic Components and Technology Conference, 2006, pp Huang X., et al., “Characterization and Analysis on the solder ball shear testing conditions”, Electronic Components and Technology Conference, 2001 JEDEC standard for Board level Drop test method of components for handheld electronic products: JESD22-B111 JEDEC standard for Monotonic Bend Characterization of Board-level Interconnections IPC/JEDEC-9702

28 JEDEC standard for Board Level Cyclic Bend Test Method for Interconnect Reliability Characterization of Components for Handheld Electronic Products: JESD22B113 Johal K., Roberts H., et al., “Performance and Reliability Evaluation of Alternative Surface Finishes for Wire Bond and Flip Chip BGA Applications”, Pan Pacific Symposium, 2006 Lall P., et al., “High Speed Digital Image Correlation for Transient-Shock Reliability of Electronics”, Electronic Components and Techniligy Conference, 2006, pp Mercado L. L., et al., “Use-Condition-Based Cyclic Bend test Development for Handheld Components”, Electronic Components and Technology Conference, 2004, pp Pandher R., Athavale S., Boureghda M., “High speed Ball pull- A predictor of Brittle solder joints”, Electronic Packaging Technology Conference, 2006 Pandher R., Lewis B., et al., “Drop Shock Reliability of Lead-Free Alloys – Effect of Micro-Additives”, Electronic Components and Technology Conference, 2007, pp Park S., Pitarresi J., et al., “Transient Dynamic Simulation and Full-Field Test Validation for A Slim-PCB Of Mobile Phone under Drop / Impact”, Electronic Components and Technology Conference, 2007, pp Syed A., et al., “Effect of Pb free Alloy Composition on Drop/Impact Reliability of 0.4, 0.5 & 0.8mm Pitch Chip Scale Packages with NiAu Pad Finish”, Electronic Components and Technology Conference, 2006, pp Syed A., et al., “A methodology for Drop Performance Prediction and Application for Design Optimization of Chip Scale Packages”, Electronic Components and Technology Conference, 2005, pp Sykes R., “Pull testing of solder balls on BGA and CSP packages without reflow”, Dage Precision Industries Ltd., England References contd.

29 Future work Phase 2 Quote acquired for smaller sized CVBGA97-.4mm-5mm-DC-LF-305 (10 mil 0.4mm pitch) Daisy chained Area/Perimeter array SAC305 We intend to pursue Phase 2 using COTS dummy packages as above. If non daisy chained: interconnect level tests like shear, pull can be conducted) If daisy chained the whole suite of mechanical tests can be conducted (assuming components and boards are provided) CVBGA97-.4mm-5mm-DC-LF-305

30 Future Work

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