The corrosion behavior of Ag alloy wire bond on Al pad in molding compounds of various chlorine contents under biased-HAST

Abstract

The present article investigated the performance and corrosion behavior between Ag alloy wire bond and Al pad under molding compounds of different chlorine contents. The epoxy molding compounds (EMCs) were categorized as ultra-high chlorine, high chlorine and low chlorine, respectively, with 18.3 and 4.1 ppm chlorine contents. The ball bonds were stressed under 130°C/85%RH with biased voltage of 10V. The interfacial evolution between Ag alloy wire bond and Al pad was investigated in EMC of three chlorine contents after the biased-HAST test. The Ag bonding wires used in the plastic ball grid array (PBGA) package include low Ag wire (89wt%) and high Ag alloy wire (97wt%). The as bonded wire bond exhibits an average Ag-Al IMC thickness of ∼0.56 µm in both types of Ag alloy wire. Two Cu-Al IMC layers, AgAl2 and Ag4Al, analyzed by EDX were formed after 96h of biased-HAST test. The joint failed in 96h and 480h, respectively, under high chlorine content EMC. The joint lasts longer than 1056h with low chlorine content EMC. The corrosion of IMC formed between Ag alloy wire and Al pad, occurs in the high Ag content alloy wire. The results of EDX analysis indicate that the chlorine ion diffuses from molding compound to IMC through the crack formed between IMC and Al pad. Al2O3 was formed within the IMC layer. It is believed the existence of Al2O3 accelerates the penetration of the chlorine ion and thus the corrosion.