Results of comparative reliability tests on lead-free solder alloys

The use of lead-free solder brings up concerns regarding the reliability of the new alloys to be used. In a European project (LEADFREE) SnAg, SnAgCu, SnAgCuSb, SnZn and SnPbAg have been tested in order to evaluate comparative data of the growth of cracks in solder joints. Reliability tests performed in other projects use accelerated tests proposed for tin-lead solders and showed a superior reliability of lead free solder over tin-lead alloys. The validity of these tests has to be questioned since they do not allow full relaxation of the stresses in solder joints. Thus each alloy is subject to another amount of strain. LEADFREE tests are run with slow temperature ramps and long dwell times to account for this fact. As a result a faster growth of cracks has been observed in lead free solder joints compared to Sn62Pb36Ag2.