Reliability Enhancement of Thick Al–Cu Wire Bonds in IGBT Modules Using Al₂Cu Precipitates

Abstract

The reliability enhancement of Al wire bonds used in the insulated gate bipolar transistor (IGBT) modules is crucial to raise their reliability at the high operating temperatures of the motor vehicles in which the modules are widely used because cracking can occur in the Al. We investigated the bonding reliability of thick Al–0.5 mass% Cu wires, inside of which very fine Al₂Cu phases precipitated in both grain boundaries and the Al matrix. We found the reliability of the aged Al–Cu wire bonds was much better than the reliabilities for Al–Cu wire bonds without aging and conventional Al–Ni wire bonds for temperature change ΔT of 50 K. We also found from thermal cycle test results that Al₂Cu precipitates prevented crack propagation due to thermal expansion mismatch between Al wires and Si substrate.