SMTA International Conference Proceedings

Solder Joint Crack Investigations In Real Cases

Authors: Jose M. Servin and Cynthia Gomez
Company: Continental
Date Published: 10/13/2013   Conference: SMTA International

Abstract: During failure analysis, to investigate what happened could be expensive and time-consuming, and in most cases, the urgency to find out the root-cause is very important and critical. Finding out the cause of solder joint crack could be a real challenge especially when it can come from an unknown failure mode. For that, the crack topographic study reveals the crack type and consequently what stress could have caused it.

In this article, the analyses of four real solder joint failure cases are shown. The results cover several situations. In the first unit, it can be seen striation marks and concentration of solder phases and solder was grinded down by stress; this is evidence that the assembly would have suffered thermalstress fatigue. In the second assembly, thermo-vibration fatigue failure had initiated micro cracks which derivates a catastrophic crack and the solder joint fracture, and also we could observe intermetallics clusters and a changes in the distribution of solder phases. In the third assembly, a exposure to high temperature but below solder melting point resulted in a more uniform crack surface compared to the first two; the intermetallics from pin-solder can be seen although some solder plastic deformations are observed. In the last assemble, an exposure to mechanical stress initiated a crack along of intermetallic layer.

All assemblies were investigated in order to find the failure root cause and also in some of them, the failure mode was reproduced to check the consistency of the results. The failure from thermo-vibration fatigue was initiated by a “loose” heat sink causing vibration movement beside the natural fatigue due to unit functionality. In the second case, the failure mode was caused by an external factor; although, the factor was identified but not reproduced. In next two cases, the cause of observed failures was mishandling and steps to mitigate them were implemented.

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