Study of wire bonding reliability of Ag-Pd-Au alloy wire with flash-gold after chlorination and sulfidation

Abstract

In this study, wire is made of nanometer flash-gold (Au) film deposited onto the surface of Ag-2.5 wt% Pd-1.5 wt% Au wire (APA wire), denoted as AAPA wire. The flash-Au film increases the resistance to chlorination and sulfidation of the silver (Ag) alloy wire, which is susceptible to deterioration in a chlorine- and sulfur-rich environment. In the chlorination test, the mechanical properties of the AAPA wire were better than those of the APA wire. Chloride ions corrode the wire along grain boundaries, resulting in a change from ductile fracture to brittle fracture in the tensile test. Chloride ions preferentially corroded the aluminum (Al) pad, greatly decreasing the reliability of the ball bond. The wedge bond did not fail due to the use of Au pad. In the sulfidation test, the average diameter of the wire increased with increasing sulfidation time. After sulfidation, the electrical conductivity decreased due to the thickening of Ag2S, whose resistance is high, and a decrease in the effective channel of the electric current. In addition, the formation of Ag2S caused a consumption of Ag atoms in the Ag wire, and thus formed voids at the interface between the sulfide layer and the Ag wire. The fracture of the sulfided ball bond was located in the heat-affected zone after the tensile test. The results show that the AAPA wire has better resistance in chlorination and sulfidation environment.