SMTA International Conference Proceedings

The Effect Of Pb Mixing Levels On Solder Joint Reliability And Failure Mode Of Backward Compatible, High Density Ball Grid Array Assemblies

Authors: Richard Coyle, Raiyo Aspandiar, Vasu Vasudevan, Steve Tisdale, Iulia Muntele, Richard Popowich, Debra Fleming, and Peter Read
Company: Alcatel Lucent, Intel Corporation, Intel Corporation, Sanmina Corporation,
Date Published: 10/13/2013   Conference: SMTA International

Abstract: Accelerated temperature cycling (ATC) was used to assess the thermal fatigue reliability of a Pb free, 37.5 mm fully populated, 1284 I/O ball grid array (BGA) package assembled with backward compatible, mixed alloy (Pb free BGA/SnPb paste) assembly processes. The surface mount assembly was done using custom SnPb eutectic soldering profiles designed to optimize the complete (full) mixing of the Pb and to create two additional test cells with levels of Pb mixing in the Pb-free BGA balls defined as low and medium. The influence of partial mixing on reliability was evaluated because full Pb mixing is more challenging as the package size and board complexity increase. To complete the reliability comparisons and provide experimental controls, SAC405-SAC405 and SnPb-SnPb assemblies were included. Post-cycling failure analysis was performed on representative test samples. The thermal cycling data and failure analysis are discussed in terms of the initial Pb mixing levels, mixed alloy microstructures, and attachment failure modes. The results indicate that full Pb mixing provides acceptable reliability, but certain cases of partial Pb mixing have measurably lower reliability and may present a reliability risk.

Key Words: 

Pb-free solder backward compatibility, mixed alloy assembly, thermal fatigue, and accelerated temperature cycling

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