The Intermetallic Compound Formation for the Wire Bond Between an Al Pad and Ag-xPd Alloy Wire

摘要

Silver-palladium alloy wire has been shown as an economical and reliable substitute for gold wire in various applications in the electronic packaging industry. The success of wire bonding relies on the formation of an interfacial intermetallic compound (IMC). This study is aimed to investigate the formation behavior of IMCs between an Al pad and Ag-Pd alloy wire with various Pd concentrations of 1.0-6.0% for the as-bonded commercial Ag/Al joint. The interfacial IMCs were investigated with scanning electron microscopy and energy-dispersive x-ray spectroscopy. The IMCs formed are separate (Ag, Pd)(2)Al and (Ag, Pd)(3)Al-2 for a Ag6Pd wire bond, while (Ag, Pd)(2)Al and (Ag, Pd)(3)Al-2 are mixed for the other Ag(1-4.5)Pd alloy wire bonds. The thickness of the total IMC layer varies from 0.65 mu m for Ag1Pd to 0.91 mu m for Ag6Pd, yet a minimum of 0.44 mu m exists for Ag3.5Pd. The compound formation behavior was found to correspond with the Ag-Al phase diagram. After pressure cooker tests, a less stable IMC (Ag, Pd)(3)Al formed at the AgxPd/Al interface.