Crack propagation in ultrasonic-bonded copper wires investigated by power cycling and accelerated mechanical fatigue interconnection test methods

Abstract

The introduction of robust interconnects such as copper wire and metallization, and silver sinter die technology have significantly increased the reliability of insulated gate bipolar transistor (IGBT) power devices. As a result, the reliability testing duration has increased, and it is particularly challenging to investigate the degradation mechanism in the wire bonds. To shorten the testing time, and to test the failure modes in the wire bonds an isothermal accelerated mechanical fatigue interconnect test has been introduced. This mechanical fatigue test attempts to mimic thermomechanical stresses caused during power cycling. In this work, an in-depth microstructure investigation of the failure mode in copper top interconnects after power cycling and after mechanical fatigue testing was carried out. It was found that the crack propagation path for both tests was similar. The mechanical test is seen to alter the microstructure of the wire bond, particularly around the wire and metallization interface.