Effect of thermal aging on the interfacial structure of SnAgCu solder joints on Cu

Interfacial structure plays a great role in solder joint reliability. In solder joints on Cu, not only is Kirkendall voiding at the solder/Cu interface a concern, but also the growth of interfacial Cu–Sn intermetallic compounds (IMCs). In this work, evolution of microstructure in the interfacial region was studied after thermal aging at 100–150 °C for up to 1000 h. Special effort was made during sample preparation to reveal details of the interfacial structure. Thickness of the interfacial phases was digitally measured and the activation energy was deduced for the growth of Cu3Sn. Kirkendall voids formed at the Cu/Cu3Sn interface as well as within the Cu3Sn layer. The thickness of Cu3Sn significantly increased with aging time, but that of Cu6Sn5 changed a little. The interfacial Cu3Sn layer was found growing at the expense of Cu6Sn5. Evolution of the interfacial structure during thermal aging is discussed.