Bond stitch on ball for bare copper wire

Abstract

The integration of multiple functions IC into single package including MCM package, 3D stacking, system in package had became a trend in recent year. In addition, demand of thin packages is rapidly gaining momentum with the emerging of advance handheld consumer products. All of these integrations and developments need BSOB bonding for interconnection purpose. Cu wire with lower cost, better reliability and electrical performance is favored in packaging material selection but BSOB in Cu wire is a rare case and inherent its challenges during implementation. For success Cu BSOB bond, bond pad structure design must be robust enough to withstand two time thermosonic impact, perfect integration between bump & stitch must be in place and ball bond had to be firmly bonded on Ag/PPF surface. Success of characterization will be lifmited if these few factors are not considered. In this study, we will discuss challenges encountered during bare Cu BSOB characterization i.e Cu bump formation stability and consistency, interaction of oxidized bump with 2nd bond stitch on Cu oxide surface by mean of stitch pull strength, cross-section analysis with varies bump staging time, BOAC bond pad structure robustness test without failure at extreme condition, and ball bond integrity on uPPF surface. Complete understanding of multiple interacting factors will promise a robust bonding condition with long term stability.