Study of the Effects of Zn Content on the Interfacial Reactions Between Sn-Zn Solders and Ni Substrates at 250°C

摘要

The interfacial reactions of Ni with Sn-Zn alloys with 1 wt.% to 9 wt.% Zn at 250°C were examined. The Zn content greatly affected the intermetallic compounds formed and microstructural evolution. A continuous Ni₅Zn₂₁ layer was formed for the Sn-Zn/Ni couples with a Zn content higher than 5 wt.%. A stable reaction layer existed at the interface and grew thicker with time. When decreasing to 3 wt.% Zn, two thin reaction layers of Ni₅Zn₂₁ and (Ni,Zn)₃Sn₄ were simultaneously observed initially, and then an extremely large faceted Ni₅Zn₂₁ phase was formed near the boundary between the Ni₅Zn₂₁ layer and the solder. Furthermore, when the Zn content was lower than 2 wt.%, the dominant phase changed to (Ni,Zn)₃Sn₄. The Zn concentration of the solder gradually decreased with reaction, and thus the interfacial stability was reduced. Subsequently, a large amount of (Ni,Zn)₃Sn₄ grains were dispersed into the molten solder, and finally the reaction product at the interface changed to Ni₃Sn₄.