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

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.