Influence of Bi Addition on Pure Sn Solder Joints: Interfacial Reaction, Growth Behavior and Thermal Behavior

Abstract

The effects of different Bi contents on the properties of Sn solders were studied. The interfacial reaction and growth behavior of intermetallic compounds (IMCs) layer (η-Cu6Sn5 + e-Cu3Sn) for various soldering time and the influence of Bi addition on the thermal behavior of Sn-xBi solder alloys were investigated. The Cu6Sn5 IMC could be observed as long as the molten solder contacted with the Cu substrate. However, with the longer welding time such as 60 and 300 s, the Cu3Sn IMC was formed at the interface between Cu6Sn5 and Cu substrate. With the increase of soldering time, the thickness of total IMCs increased, meanwhile, the grain size of Cu6Sn5 also increased. An appropriate amount of Bi element was beneficial for the growth of total IMCs, but excessive Bi (⩾ 5 wt%) inhibited the growth of Cu6Sn5 and Cu3Sn IMC in Sn-xBi/Cu microelectronic interconnects. Furthermore, with the Bi contents increasing (Sn-10Bi solder in this present investigation), some Bi particles accumulated at the interface between Cu6Sn5 layer and the solder.