Evolution of microstructure of Lead free cu/Sn solders and copper oxide phase precipitation in Cu3Sn intermetallic during thermal cycling

Abstract

Intermetallic layers were formed after Solid Liquid Interdiffusion (SLID). Cu-Sn interdiffusion leads to the formation of two intermetallic layers: Cu6Sn5 and Cu3Sn. In this work, Sn solder was subjected to thermal cycling from −65 to +250 °C at 10 °C/min. After few cycles we noticed the appearance of a new –pillar– shaped phase made of copper oxide. The Intermetallic layers were mechanically tested using die-shear testing. The die-shear resistance appears to be increasing when the number of thermal cycles increases. The microstructure was observed using Backscatter Electron detector (BSD) and Scanning Electron Microscopy (SEM). The composition of the phase was measured using Energy Dispersive x-ray spectroscopy (EDX). It appears that a new copper oxide phase forms after few cycles. As the number of cycles increase, the size and the number of the copper oxide phases increase.