1. SAC Aging III Idea Stage Project Richard J. Coyle HDP User Group Member Meeting Host: Engent Atlanta Ga, USA Sept 9, 2015 © HDP User Group International, Inc.

2. 2 Project Background A follow-on to the HDPUG SAC Aging2 project applying lessons learned – SAC Aging2 thermal cycling test results were flawed due to warpage of the test boards. Although flawed, these data indicated that the aging conditions used in the experiment were insufficient to induce decreased reliability – Results from iNEMI Aging study corroborate SAC Aging2, indicating that longer aging times are required to demonstrate aging effects – No acceleration factor exits to allow correlation of aging at the relatively high temperature of 125  C used in the experiment to aging at the lower temperatures such as 30  C typical of storage conditions or 75  C typical of some operating conditions. It is debatable whether high temperature,125  C aging effects are relevant to “real world” applications.

3. 3 Project Background Previously: ATC performance of SAC solder joints is known to be affected by thermal pre-conditioning often simply called aging. – Lower reliability measured by characteristic lifetime and lower Weibull slope of ATC failures sometimes with earlier failures – The effect is not the same or apparent in all cases and likely is dependent on component and strain Microstructural Focus Baseline microstructure without cycling: – ambient aged and elevated temperature isothermally aged – long term isothermal aging. Characterization of cycled joints – microstructural evolution and failure mode.

4. Warpage Discussion PCB warpage corrupted the thermal cycling data from SAC Aging2. What caused the PCB warpage?  We suspect that there was incomplete curing in some regions of some panels. Subsequent thermal exposure in either reflow, pre-aging, or thermal cycling completed the curing and this unbalance caused the warpage. How does warpage affect reliability?  We speculate that out-of-plane tensile stress from warpage interacts with the in-plane shear stress due to CTE mismatch to alter the number of cycles to failure. Tensile stress may reduce the number of cycles to failure and compressive stress may increase the number of cycles to failure.

5. 5 The Effect of Aging Aging, thermal preconditioning, or pre-aging initiates the microstructural evolution process of IMC particle coarsening in advance of the temperature cycling. IMC particle coarsening is the precursor to recrystallization and crack initiation in the bulk solder. If aging “jumpstarts” the particle coarsening process, crack initiation should occur in fewer thermal cycles than in un-aged samples. Thus, we expect aging to reduce the reliability or number of cycles to failure.

6. 6 The Test Vehicle Components 192 CABGA 84 CTGA PCB Developed for iNEMI Alloy project and used in SAC Aging2 project

7. Project Overview Use the existing test board design and components to facilitate the launch of a new SAC Aging Project. – The test board design already exists and the components can be procured easily. – The exact test board is completely compatible with the ALU ATC chamber and rack system. – This testing can address some of the existing gaps in the current SAC Aging project Perform baseline microstructural characterization on ambient (no age) and aged samples. Perform failure mode analysis and characterization on ATC samples to determine extent of microstructural evolution and impact on final failure. Build additional samples for microstructural analysis at different aging times/temperatures – complete plan to be worked out (tentative based on resource availability).

8. 8 Design of Experiment Evaluates SAC305 solder alloy Characterizes PCB board warpage prior to building assemblies or initiating thermal cycling to avoid issues that corrupted the SAC Aging2 data Single precondition aging temperature: 125ºC with three different aging times: 0 days (baseline), 20 days, and 40 days Optional extended low temperature aging at 75  C depending on available resources Evaluates one component type: 192 CABGA. Optional second component (84CTBGA) depending on available resources Cycling temperature range using two different ATC profiles: 0/100  C and -40/125  C

9. 9 Design of Experiment SAC Aging Project Basic Single Component Single ATC Profile Test Cell SAC305 ATC - 0 days (RT aging)32 ATC - 20 days@125 °C32 ATC - 40 days@125 °C32 ATC – xxx days@75 °C32 Baseline (no ATC) 0 days16 Baseline – (ATC) 20 days @125 °C16 Baseline – (ATC) 40 days @125 °C16 Baseline – (ATC) xxx days @75 °C16 Total components192 Evaluates SAC305 solder alloy with single precondition aging temperature of 125ºC with three different aging times: 0 days (baseline), 20 days, and 40 days Optional extended low temperature aging at 75  C depending on available resources Evaluates one component type: 192 CABGA. Optional second component (84CTBGA) depending on available resources Cycling temperature range 0-100ºC. Number of components required roughly doubles with two ATC profiles (0/100  C and -40/125  C )

10. 10 Summary This SAC Aging3 proposal uses lessons learned from previous industry aging projects to design a more focused evaluation plan. Single solder alloy: SAC305 solder alloy Single component type: 192 CABGA. Optional second component (84CTBGA) depending on available resources. The inherent characteristic lifetime of the 192CABGA is much lower than the 84CTBGA, providing shorter test time (fewer cycles to failure). Single precondition aging temperature of 125ºC with three different aging times: 0 days (baseline), 20 days, and 40 days. Longer aging times will emphasize aging effects. Optional extended lower temperature aging at 75  C depending on available resources. Cycling temperature range 0-100ºC. Number of components required roughly doubles with two ATC profiles (0/100  C and -40/125  C ). The - 40/125  C test can be executed in roughly half the number of cycles as the 0/100  C test.

11. 11 Project Schedule PlannedActual _ Design TVCompleteComplete Receive Components11/2015 Receive Boards11/2015 Assembly Complete02/2016 Wire Boards03/2016 Precondition Boards05/2016 Begin Long Term aging05/2016 ATC start (short term aging)05/2016 Begin Microstructure Analysis05/2016 Complete Microstructure Evaluation08/2016 ATC start (long term aging) 11/2016 ATC complete short term aging 12/2016 Interim Report12/2016 ATC complete long term aging 07/2017 ATC Weibull AnalysisOngoing with ATC Final Report2017

12. 12 Project Team (So Far) Alcatel-Lucent* Keysight Nihon-Superior Sanmina (PCB and assembly) Akrometrix Panasonic * project leader