Pd effects on the reliability in the low cost Ag bonding wire

Recently, the application of Ag bonding wires in electronic devices has been attempted as alternative to Au bonding wires to reduce the material cost of Au. Nevertheless, Ag bonding wires have not been applied to devices due to interface corrosion problems between the Ag wire and Al pad during humidity reliability tests, such as the PCT (Pressure Cooker Test). As the technology for alloying Pd element in Ag wire has developed recently, the corrosive failure problem at the interface in the PCT has been improved significantly. This study examined the behavior of IMCs(intermetallic compounds) and interface corrosion between an Ag wire and Al metallization under humidity conditions (100%RH, 121´C). The chemical compositions of the Ag wires tested were pure Ag, Ag — 1wt%Pd and Ag-3%Pd. These wires are bonded to Al and noble metal(Au, Pd) metallization using a thermo-sonic bonder. The interfaces were characterized by FIB(Focused ion beam), HRTEM (High Resolution Transmission Electron Microscope) and EDS (Energy Dispersive X-ray Spectroscopy) The findings show that, (1) the interfacial reliability between the Ag wire and Ag metallization was improved considerably. The interface corrosion was suppressed significantly as the Pd content was increased. (2) Ag wires on a noble metal(Au, Pd) pad have stable reliability in PCT.