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.
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.
