Interfacial Characteristics and Dynamic Process of Au- and Cu-Wire Bonding and Overhang Bonding in Microelectronics Packaging

Abstract

Microstructure characteristics of Cu-wire bonding interface are investigated first by using the X-ray microdiffractometer, and the dynamic process of Cu- and Au-wire overhang bonding is recorded first with a high-speed camera system. It was found that the success rate of Cu-wire bonding is lower than that of Au-wire bonding, the formation of Cu-Al intermetallic compounds (IMCs) is more difficult than that of Au-Al IMCs, and the impact and deflection of Cu-wire overhang bonding process are much bigger than those of Au-wire overhang bonding process and affect bonding performance. In order to improve the bondability of Cu-wire bonding and overhang bonding, an approach with thick Al pad on the die which reduces its hardness is more compliant during Cu bonding process; another idea is to activate the formation of Cu-Al IMCs by increasing the energy. The effectiveness of the suggested approach is confirmed. In particular, Al2Cu and Al4Cu9 IMCs can form within 18 ms due to diffusion and reaction activated by high thermal (to 340 ° C) combined with ultrasonic energy at the bonding interface, and the success rate and strength of Cu-wire bonding increased significantly when Cu-Al IMCs form. For overhang bonding, the approach with thick Al layer improves dynamics features of hard Cu-wire overhang bonding process; thereby, it enhances the performance of Cu-wire overhang bonding.