Stress Relaxation and Fatigue Characterisation of Eutectic SnPb Solder Alloy

Abstract

Soldering is the most important joining technology in the semiconductor industry, especially for IC chip packaging. The binary eutectic SnPb alloy had been in used for decades, before regulations and restriction on the usage of lead in solders was imposed. Thus, replacing SnPb solder alloy with Pb-free solders has also been an issue in the electronic industry. The previously used SnPb alloy was in used due to several reasons, namely (a) it has low melting temperature (183oC) and solidified at a single temperature to form eutectoid composition, (b) binary in composition and is readily available commercially and (c) many researches had been undertaken in the previous decades. Creep, stress relaxation and fatigue tests were conducted on eutectic SnPb solder alloy in order to study the alloy mechanical characteristics, and hence a suitable Pb-free solder alloy could be chosen as a replacement alloy. In this study, creep, stress relaxation and fatigue tests were conducted on eutectic SnPb solder alloy at 30oC and 50oC, respectively. The study showed that stress relaxation in the alloy decayed instantaneously to zero-value when cycling was done at R=-1 and that cycling was done at 600 cycle per minute (CPM) which enable fatigue test to be conducted on the bulk solder alloy. A non-zero stress relaxation value will result in the alloy to failed predominantly due to creep and fatigue failure will not be observed.