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Impact of Pb-free Solder Alloy Mixing on Solder Joint Integrity Using BGAs
An investigation was conducted to assess the solder joint integrity (acceptable/nonacceptable) for three different solder alloys on ball grid arrays (BGAs) in a mixed metallurgy configuration as compared to a baseline SAC305 system. Thermal cycle testing using a -55 to +125 ºC range in accordance with the IPC-9701 specification was used. Technical Paper
Tim Pearson, Dave Hillman, Julie Mills, Leela Hereña
Collins Aerospace
IA, USA
Summary
An investigation was conducted to assess the solder joint integrity (acceptable/nonacceptable) for three different solder alloys on ball grid arrays (BGAs) in a mixed metallurgy configuration as compared to a baseline SAC305 system. Thermal cycle testing using a -55 to +125 ºC range in accordance with the IPC-9701 specification was used. Weibull statistical assessment and metallurgical cross-sectioning analysis was completed after 800 total thermal cycles. This paper documents the investigation results.
Conclusions
The investigation produced the following conclusions:
The concern of a “mixed Pb-free metallurgy” BGA configuration for Pb-free soldered products degrading solder joint integrity was not observed with the Pb-free solder alloys tested. BGAs assembled with Senju M794 and the Indalloy 292 solder paste both performed better in thermal cycle testing than the SAC305 solder alloy.
Reflow oven profile development should be reviewed as part of any implementation action for either the Senju 794 or the Indalloy 292 solder alloys in an effort to reduce/eliminate the incidence of solder joint interfacial cracking failure modes.
Further work needs to be done with SEM analysis to determine the if the methods of solder strengthening is consistent with previous work done in pure alloy configurations.
Initially Published in the SMTA Proceedings
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