Evaluation of bond shear strength of heat treated Cu-Al bonding interface

Abstract

Ball shear strength of the thermosonic wire bond interconnection relates closely to the reliability of the microchip during performance of its function in any application. Concerns regarding the reliability of Cu wired electronic microchips are raised due to formation of void at the copper (Cu) wire- aluminium (Al) bond pad bonding interface, predominantly after high temperature storage (HTS) annealing conditions. The interfacial void formation is suspected originated from a volumetric shrinkage during the growth of the Cu-Al intermetallic compound (IMC) layer in the Cu-Al bonding interface. In this report, the ball shear strength and interfacial microstructure of the thermosonic Cu wire-Al bond pad system bonded at difference temperature (150 °C, 280 °C and 400 °C); and annealed at different HTS durations (as-synthesized, 500 hours and 1000 hours) were studied. It was observed no significant difference in the mean of the ball shear strength of bonds bonded at different temperature before HTS treatment. On the other hand, the ball shear strength increase with the HTS duration. This is due to the fact that higher bonding temperature and longer HTS promoted better growth of the Cu-Al IMC layer. A transmission electron microscopy - energy dispersive X-ray analysis (TEM-EDX) has also been carried out to observe the formation of the Cu-Al IMC layer in the sample.