Effect of Zn Addition on Interfacial Reactions and Mechanical Properties Between Eutectic Sn58Bi Solder and ENIG
Shiqi Zhou1, Siliang He1, Hiroshi Nishikawa1
1Joining and Welding Research Institute, Osaka University, Osaka, 567-0047, Japan.
Abstract:
A comprehensive study of the interfacial reactions between Zn-added Sn58Bi solder alloys and electroless Ni/immersion Au (ENIG) substrates during reflow and solid-state thermal aging was conducted. The shear strengths of these samples were tested before and after aging. Zn first reacted with Au forming AuZn₃ intermetallic compounds (IMCs) that detached in small pieces from the substrate and immediately moved into the solder bulk. A very thin Au-Zn-Ni-Sn IMC layer was observed attached to the substrate. This layer, with a thickness of 0.25 μm, significantly suppressed IMC layer growth during thermal aging, resulting in a thermally stabled joint. By contrast, the thickness of the (Au, Ni)(Sn, Bi)₄ IMC layer on the eutectic Sn58Bi/ENIG interface doubled during aging and, therefore, its shear strength decreased.
