High‐cycle fatigue testing of Pb‐free solder joints

The research aims to explore the high‐cycle fatigue performance of Pb‐free alloys and compare them to Sn‐Pb. In doing this, it also aims to demonstrate the viability of a new testing method.

The method introduced uses existing test equipment in a novel way to combine the speed and applicability of general vibration testing with the control of single, model specimen testing. Model solder joints are constructed in a repeatable manner and repeated tensile stress cycles are applied until failure.

It is found that in the regime studied, all of the Pb‐free alloys tested show significantly decreased performance compared to Sn‐Pb, at ambient temperatures. No obvious mechanical or microstructural features have been identified as the cause of this discrepancy. The test method employed demonstrates good correlation with existing fatigue test methods despite the known variance of solder mechanical test results.

It is recognised that results pertaining to essentially only a one‐dimensional stress state are obtained, and that practical stresses will vary. The performance difference between Pb and Pb‐free alloys warrants further investigation.

The results obtained are of interest to high‐reliability electronics sectors such as aerospace, defence and automotive, where vibrations in service are encountered. Very little work exists on the subject of solder high‐cycle fatigue performance and to the author's knowledge none comparing Pb to Pb‐free alloys in an objective manner.