Journal of SMT Article
A Comprehensive Analysis of the Thermal Fatigue Reliability of SnPb and Pb Free Plastic Ball Grid Arrays (PBGA) Using Backward and Forward Compatible Assembly Processes
Company: Alcatel-Lucent, Texas Instruments, and Flextronics
Date Published: 10/30/2008 Volume: 21-4
This paper presents the results of attachment reliability testing of backward compatible (SnPb paste/Pb free BGA) mixed alloy test boards assembled using parameters that produced both full and partial Pb mixing. The assembled test boards were thermally cycled from 0 °C to 100 °C in accordance with the IPC-9701 industry test guidelines using 10 and 30 minute dwell times. To enable a more comprehensive reliability comparison, additional test cells were incorporated using SnAgCu (SAC) Pb free assembly, SnPb/SnPb assembly, and SAC paste/SnPb BGA assembly (forward compatible).
Post-cycling failure analysis was conducted on representative test samples from each cell including optical metallography and scanning electron microscopy with backscattered electron imaging (BEI) and energy dispersive X-ray spectroscopy (SEM-EDS) to identify the failure mode and evaluate the microstructure. The accelerated temperature cycling (ATC) test data and failure analysis results are discussed in terms of the relationship to the initial and evolving microstructures and mechanical behavior that result from temperature cycling. The thermal fatigue reliability of the mixed alloy assemblies is discussed relative to that of the pure SAC and SnPb assemblies and the results indicate that mixed assemblies can provide acceptable reliability, even when mixing is not complete.
Key words: Pb-free, SnPb, microstructure, mixed alloy soldering, backward compatible process, forward compatible process.
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