The present article investigated the performance and interfacial behavior between Cu 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 24, 7.6, and 4.3 ppm chlorine contents. The ball bonds were stressed under 130 o C/85%RH with biased voltage of 10V. The interfacial evolution between Cu wire bond and Al pad was investigated in EMC of three chlorine contents after the biased-HAST test. The Cu bonding wires used in the plastic ball grid array (PBGA) package include bare Cu wire (4N Cu) and Pd coated Cu alloy wire (98Cu2Pd). The as bonded wire bond exhibits an average Cu-Al IMC thickness of ~0.12 µm in both types of Cu wire. Two Cu-Al IMC layers, Cu 9 Al 4 and CuAl 2 , analyzed by EDX were formed after 100h of biased-HAST test. The joint failed in 192h and 1296h, respectively, under ultra-high and high chlorine content EMC. The joint lasts longer than 2000h with low chlorine content EMC. The corrosion of IMC formed between Cu wire and Al pad, occurs in the ultra-high and high chlorine molding compound. 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. Al 2 O 3 was formed within the IMC layer. It is believed the existence of Al 2 O 3 accelerates the penetration of the chlorine ion and thus the corrosion.