Relation between Kirkendall voids and intermetallic compound layers in the SnAg/Cu solder joints

Abstract

Several different kinds of intermetallic compound (IMC) layers were fabricated through adding trace elements into the Sn-3.5Ag solder, to investigate the relationship between the Kirkendall void (KV) and the IMC layers. The results show that a considerable amount of KVs were observed at the Cu3Sn/Cu interface in the Sn-3.5Ag/Cu joint after isothermal aging. A proper amount of Zn (0.5 wt%) and Ge (0.1 and 0.3 wt%) were found to effectively suppress the formation of the Cu3Sn layer, and no obvious KVs were observed at the Cu6Sn5/Cu interface, while more Zn induced the formation of the Cu6Sn5 plus Cu–Zn mixed IMC layer, and voids (not KVs) were observed at the Cu6Sn5/Cu–Zn interface. (Cu,Ni)6Sn5 IMC layer replaced the initial Cu6Sn5 at the SnAg-Ni/Cu joints, likewise, the Cu3Sn was suppressed at the thermal aging stage. Moreover, voids were found at the IMC/solder interface, while not at the IMC/Cu. Therefore, the formation of KVs is greatly determined by the characteristic of the IMC layer, this is consistent with the previous reports. On other hand, the KV can be suppressed by controlling the interfacial phase through adding trace elements into the solder.