Reactions and mechanical properties between AuSn20 solders and metalized Al–Si alloys for electronic packaging application

Abstract

AuSn20 (mass fraction) lead-free solder reacting with the Au/Ni-metalized AlSi50 substrate during reflowing and aging processes were investigated in this study. The single lap shear strength, fracture behavior and microstructure evolution characteristics of the joints are detected. It is found that only a thin (Ni,Au)3Sn2 layer forms at the interface between the AuSn20 solder and Ni metalized AlSi50 alloy. But a composite Intermetallic compound (IMC) layer of (Ni,Au)3Sn2 and (Au,Ni)Sn is formed in the aged joints, due to the continuous interfacial reactions during aging process. The growth of the composite IMC layer is governed by the volume diffusion of the constituent elements at 120, 160 and 200 °C. The shear strength decreases with the increasing aging time and temperature, which is caused primarily by the growth of the IMC layer. The presence of faceted structures on the fracture surfaces of these specimens is indicative of a brittle failure mode for the joints.