Silver alloy wire for IC packaging solution

Abstract

In recent years, copper wire especially palladium coated copper wire interconnects has been quite widely proliferated into mass production. However, the hardness of copper wire requires higher ultrasonic power and bonding force, which lead to higher risk of bond pad crack causing electrical test failure or board level reliability failure. In order to mitigate the risk of wire bond failure, device manufacturer usually reengineer the bond pad fabrication structure or adding over pad metallization (OPM) on bond pad to protect the underneath circuit. This approach adds cost to the wafer fabrication. In order to avoid bond pad crack without reengineering the bond pad, silver alloy wire is proposed as an alternative to cu wire bonding due to its softer material property. In this paper, the authors researched into process development of silver alloy wire, including fine tuning of material properties, wire bond and assembly process optimization, and reliability assessment on various wire bond application including BSOB, low loop wire bonding, and evaluated wire bonding performance on different lead finger finishing. Special attention was placed on package and board level reliability since silver alloy wire is still relatively new in some of the IC packaging application. This paper also discussed the economic and cost consideration of mass volume production implementation for silver alloy wire.