Process optimization approach in fine pitch Cu wire bonding

With SiO₂ dielectric under aluminum pads, a 60 μm bond pad pitch with 52 um bond pad opening Cu wire bonding process was developed in PBGA Hip 7 PGE wafer technology. The critical factors (wire type, capillary, and bonding parameter) and critical responses (bonded ball diameter, bonded ball height, wire pull, ball shear and number of metal lift/peeling and ball lift after wire pull) are affecting bonding quality. Design of experiment and response of surface were used to optimize the bonding parameters. The wire pull and ball shear test at three thermal aging read points were studied.

I. INTRODUCTION

Copper wire has been studied for over 20 years, but only recently has been incorporated in actual volume production. It oxidizes and thus requires an inert atmosphere during electronic flame off (EFO) ball formation. The upward trend in gold base price and lower price of copper has spurred customer interest in copper wire as a gold wire replacement, which can help reduce cost without diminishing conductivity, chip functionality and reliability.