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

摘要

The interfacial reactions of Ni with Sn-Zn alloys with 1 wt.percent to 9 wt.percent Zn at 250 deg C were examined. The Zn content greatly affected the intermetallic compounds formed and microstructural evolution. A continuous Ni_(5)Zn_(21) layer was formed for the Sn-Zn/Ni couples with a Zn content higher than 5 wt.percent. A stable reaction layer existed at the interface and grew thicker with time. When decreasing to 3 wt.percent Zn, two thin reaction layers of Ni_(5)Zn_(21) and (Ni,Zn)_(3)Sn_(4) were simultaneously observed initially, and then an extremely large faceted Ni_(5)Zn_(21) phase was formed near the boundary between the Ni_(5)Zn_(21) layer and the solder. Furthermore, when the Zn content was lower than 2 wt.percent, the dominant phase changed to (Ni,Zn)_(3)Sn_(4). The Zn concentration of the solder gradually decreased with reaction, and thus the interfacial stability was reduced. Subsequently, a large amount of (Ni,Zn)_(3)Sn_(4) grains were dispersed into the molten solder, and finally the reaction product at the interface changed to Ni_(3)Sn_(4).