Review on silver wire bonding

Cu wire bonding has been adopted fast in the past few years in semiconductor industry and has displaced Au wire bonding a significant percentage owing to low cost of Cu wire. However, there are some concerns raised due to high hardness of Cu FAB and corrosion of Cu-Al IMC at HAST reliability test. These drawbacks constrain the application of Cu wire in some area, like stacked-die package, die-to-die wire bonding, and LED assembly. Ag, a softer material in nature, is a good candidate to displace Cu as an alternative low cost bonding wire. There are various compositions of alloyed Ag wire proposed, basically they can be categorized into three groups: (1) Au wire alloyed with Ag, (2) high purity Ag-alloy wire, and (3) low purity Ag-alloy wire. This paper will review the recent researches on the three types of the wires bonded to Al, Au and Pd metal pads, IMC formation, and reliability performance. Comparison to Au wire will be addressed. Effect of Pd addition on the reliability performance and Silver migration will be discussed as well.