Moisture- and Saline-induced Degradation of Silver Wire and Silver-Aluminum Bond Integrity

The use of Ag wires as a substitute material for packages requiring cheaper material compared to Au, or using die technologies that are susceptible to mechanical damage due to the harsh bonding conditions required by Cu, are under vigorous development. Ag wire has the advantages of great workability, high electrical conductivity, and low intermetallic compound (IMC) growth rate at the bonding interface. However, like Cu wires, the integrity of the bonding interface is strongly affected by the presence of moisture and ionic impurities like chloride ions. Herein, we report the systematic study of the effects of moisture and chloride ions (introduced as neutral saline solution) on the bond integrity of Ag wires on Al pads. In addition, the effect of thermal treatment, inducing IMC growth in the absence and in the presence of these contaminants are discussed. The results clearly show that moisture and chloride ions negatively affect the bond integrity by promoting interfacial corrosion leading to lifted ball. Moreover, we show that water has a preferential interaction with the Al/Al
2
O
3
layer, while chloride ions prefer the Ag wire. The presence of chloride ions catalyzes the interfacial corrosion under thermal treatment.