Bondability of Pd and Au Containing Ag-Alloy Wires on Au Pads for LED Package

This study investigated the mechanism of the interfacial reaction of Ag-alloy wires in the gold bond pad of an LED die after a wire bonding process and their reliability. The results showed that in the as-bonded condition, no intermetallic compounds (IMCs) formed between the Ag-alloy wire and the gold bond pad and that the interfacial reaction mechanism was diffusional solid solution reaction. After 168 h of thermal aging at 200 °C, it was found that adding Pd to the Ag-alloy wire could improve the mechanical properties of the wire, and the bonding strength between the Ag-alloy wires and gold bond pad showed an increasing trend. It was speculated that increasing the thermal aging period allowed sufficient time for the diffusion reaction between the silver alloy and gold bond pad. The gold ball residual area difference indicated that adding Pd to Ag-alloy wire was more helpful than adding Au for boosting bond shear test (BST) strength in the as-bonded condition, while adding Au to a ternary Ag-alloy wire helped the bonding strength in terms of thermal stability. BST and wire pull test (WPT) specifications are suggested for Ag-alloy wire joints in LED packaging products based on tests of the critical quality parameters of Cpk.