IMC study on Cu wirebond failures under high humidity conditions

The governing factors of copper wirebond failures under high humidity conditions were experimentally elucidated on the basis of the results of intermetallic compound (IMC) analysis using Scanning Transmission Electron Microscope (STEM). The IMC behavior at the bonding interface under high temperature storage (HTS) test and pressure cooker test (PCT) have been examined and compared. The results of HTS and PCT suggested that the main factor causing the Cu wirebond failures under PCT condition is not a growth of brittle IMC but a corrosion of IMC (Cu9Al4), which is mainly produced during assembly processes and susceptible to corrosion. Result of EPMA mapping for the pad-surfaces on the failure chip indicated that the corrosion is induced by halogen (Cl) in the vicinity of the bonding interface under high humidity condition. The effect of Pd coating and characteristics of mold resin are also discussed on the basis of STEM analysis of the IMC formation and FEM analysis of the thermal stress at the bonding interface.