Optimization of gold wire bonding on electroless nickel immersion gold for high temperature applications

Conventional gold (Au) wire bonding on aluminum (Al) bond pads leads to the formation of intermetallic compounds. During high temperature exposure, associated Kirkendall voids formed in the intermetallic phases (IMP) can degrade reliability of the interconnect. The advert of green molding compounds has exacerbated the ball bond reliability with Al bond pad. Thus there is a need for alternative bond pad metallization to be investigated for compatibility with new developments in mold compounds and for high temperature automotive applications. The objective of this work is to establish Au wire bonding process on electroless nickel immersion gold (ENIG) capped on Al bond pad and to investigate the reliability of the interconnect. Designed experiments are performed to understand the influence of bond parameters on the ball bond shear and wire pull strength responses and thereby optimize wire bonding parameters. By defining the optimization criteria, a process window for robust wire bonding on ENIG bond pads is established. This paper also reports the reliability performance of Au-Al and Au-ENIG interconnect molded with a green molding compound subjected to high temperature storage (HTS) tests up to 4000 hours at 150degC and 200degC.