Bond strength evaluation of heat treated Cu-Al wire bonding

Abstract

Bond strength evaluation of wire bonding in microchips is the key study in any wire bonding mechanism. The quality of the wire bond interconnection relates very closely to the reliability of the microchip during performance of its function in any application. Concerns regarding the reliability of the microchip are raised due to formation of void at the wire-bond pad bonding interface, predominantly after high temperature storage (HTS) annealing conditions. In this paper, the quality of wire bonds prepared at different conditions, specifically annealed at different HTS durations are determined by measurements of the strength of the interface between the bond wire and the bond pad. The samples are tested in ball shear test and wire pull test. A transmission electron microscopy - energy dispersive X-ray analysis (TEM-EDX) has been carried out to observe the formation of the Cu-Al IMC layer in the sample. Results showed that longer duration of HTS increased the bond shear strength. Two-sample T-test analysis concluded that there is a significant difference in the mean ball shear strength of the samples. TEM photograph showed a distinctive thin layer of Cu-Al intermetallic compound whereby increasing thickness of the IMC layer increased the shear strength of the bonds.