Reliability and lifetime evaluation of different wire bonding technologiesfor high power IGBT modules

IGBT modules for power transmission, industrial and traction applications a re operated under severe working conditions and in harsh environments. Ther efore, a consequent design, focused on quality, performance and reliability is essential in order to satisfy the high customer requirements. One of th e main failure mechanisms encountered in high power IGBT modules subjected to thermal cycles is wire bond lift-off, which is due to the large thermal expansion coefficient mismatch between the aluminum wires and the silicon c hips. The paper describes various bonding technologies using different wire materials directly bonded onto chip metallisation as well as the ABB solut ion where the wire is bonded on a thin molybdenum strain buffer soldered on to the chip. We assess in the present paper the potential of these technolo gies to enhance module reliability and lifetime through a power cycling tes t. Failure analysis results are presented and the failure mechanisms relate d to each technology are explained in detail. (C) 1999 Elsevier Science Ltd . All rights reserved.