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

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, Al
₂
Cu and Al
₄
Cu
₉
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.