There are significant physical and metallurgical differences between SnPb and Pb-free solders, which have a direct effect on thermal cycle performance. There are complications in extending the SnPb behavior to SAC solders as the properties and failure behavior are markedly different. If the outliers identified in Pb-free soldering thermal fatigue studies are a function of the structure/properties, they may not be visible in the relatively small sample size used in thermal cycling tests. If so, the traditional SnPb sample size (32) is inadequate to characterize the reliability of Pb-free solders, and test data using these sample sizes could result in over-estimation of reliability (i.e., small sample size could mask early Pb-free failures).
This new iNEMI effort will be working to determine whether a large sample size will reveal Pb-free early failures in accelerated thermal fatigue testing of Pb-free solder joints. The team plans to develop a unique test vehicle with a large sample size (256 components), to test BGA solder joints. Testing will include two components that tend to fail relatively quickly (to encourage early failure) and a third with a slightly longer life, and will cover four conditions: small sphere joints, large sphere joints, low strain rate, and high strain rate. Real-time analysis will be used so that results are better understood, analyzing at regular intervals as well as at failure events. In order to keep the variables manageable, all testing will be done with a single alloy system and a single ATC profile.
Statement of Work
- Statement of Work (March 11, 2008; Version 3.2)
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