Wetting behavior and vacuum soldering of novel Au-30Ga solder on Ni and Cu substrate

Abstract

As a novel high-temperature solder with suitable eutectic temperature and high thermal conductivity, Au-30Ga solder is expected to be used in high-power device packaging. This research provides a timely and necessary study of its solderability. The wetting behavior and reactivity of Au-30Ga solder on Cu and Ni substrates was investigated through spreading tests in vacuum. The favorable wetting property of Au-30Ga solder on Ni and Cu substrate was observed. However, fundamental differences in the wetting behavior of liquid Au-30Ga alloy in contact with Ni and Cu substrates were immediately apparent. Their behavior changed from reactive wetting, characterized by formation of two thin Ni–Ga compound layers and a wide wetting ring, to dissolutive wetting, characterized by formation of a thick (Au, Cu)9Ga4 interface layer. Moreover, significant signs of solidification shrinkage of liquid solder are observed on the surface of wetting ring for the first time, which provides direct evidence for the formation mechanism of wetting ring. The wetting ring also reveals the microstructure of the Ni–Ga compounds during ripening. In addition, the soldering performance was evaluated by the shear strength of solder joints. The findings presented in this thesis add to understanding of solderability of the high-temperature Au-30Ga solder.