Effect of a nano-ZnO addition on the wettability and interfacial structure of Sn-based Pb-free solders on aluminum

Abstract

Aluminum soldering with a low-temperature Pb-free solder is very important in electronics and radiator applications. In this paper, a nano-ZnO addition was introduced into the interfacial reaction between a Sn-3.5Ag or Sn-9Zn solder and aluminum to improve the wettability, interfacial structure and mechanical properties of joints. A spreading test showed that the Sn-3.5Ag solder had higher wettability than Sn-9Zn. With the nano-ZnO addition, the wettability of these two solders was obviously improved. An analysis of the interfacial structure showed that the bonding between Sn-Zn and Al was realized with a Zn-Al solid solution, while that between the Sn-3.5Ag solder and Al was realized with an Ag2Al intermetallic layer. The introduction of nano-ZnO obviously accelerated the formation of Ag2Al of Sn-3.5Ag on Al. Finally, a shear test showed that the nano-ZnO addition helped increase the shear strength of Al solder joints.