The growth of intermetallic compound in Cu/Sn3.5Ag/Au solder joints under current stressing

In this study, the interfacial reactions and polarity effect on intermetallic compounds (IMCs) formation of the Cu/Sn3.5Ag/Au solder joints were investigated under 100 °C, 2.6 × 103 A/cm2 of current stressing. With electron flow from the Cu toward the Au, both Sn and Cu atoms migrated from the cathode to the anode, these phenomena also accompanied with the crack formation at the (Cu,Au)6Sn5/solder interface and the rapid dissolution of Cu consumed. The sequence of Au–Sn IMCs formed at the Au side upon electromigration (EM) is AuSn4/AuSn2/AuSn/Au5Sn while as AuSn4/AuSn2/AuSn for aging. At cathodic Au side, the voids were formed in the AuSn4 and at the AuSn4/solder interface due to the migration of Sn toward the anode. The voids formation in AuSn on both cathode and anode sides is due to the consumption of Sn by transformation of AuSn into Au5Sn.