The superior drop test performance of SAC-Ti solders and its mechanism

Abstract

SAC-Ti alloys exhibited significantly improved drop test performance over not only SAC alloys, but also 63Sn37Pb for ENIG/OSP, NiAu/OSP, and OSP/OSP surface finish systems. The superior performance is attributed to (1) the increased grain size and dendrite size, therefore reduced hardness of solder, (2) inclusion of Ti in the IMC layer, and (3) reduced IMC layer thickness. DSC data indicate that the melting temperature and range were not affected by Ti, but the undercooling was almost completely suppressed. The creep properties of SAC-Ti alloy were comparable with those of SAC alloy, strongly suggesting the gain in drop test performance was not achieved by compromising the thermal fatigue performance. SAC-Mn alloys were also found to outperform SAC alloys and Sn63 for the X/OSP finish combinations studied. In general, SAC-Ti performed equally to or better than SAC-Mn alloys.