Comparison of Inelastic Behaviors of Lead-Free and Sn—Pb Solder Joints

Abstract

In this study, finite element analysis is used to investigate the inelastic behaviors of lead-free solders, 96.5Sn—3.5Ag and 95.5Sn—3.9Ag—0.6Cu, and classical 63Sn—37Pb solder-bumped wafer level chip scale package (WLCSP) on printed circuit board (PCB) assemblies subjected to four different temperature cycle tests. The behaviors of equivalent strain range and strain energy density at the outmost corner solder joint adjoining to the upper pad are examined. It is found that: (1) the 95.5Sn—3.9Ag—0.6Cu solder has the best performance on the effect of plastic behavior among these three solder alloys, but it accumulates more plastic strain while the number of temperature cycling increased; (2) the 96.5Sn—3.5Ag solder alloy can sustain more creep than others; (3) the difference exists between using the equivalent total strain range and the strain energy density, respectively, to assess the thermo-mechanical behaviors of the solder-bumped WLCSP on PCB assemblies.