17.5um thin Cu wire bonding for fragile low-K wafer technology

This paper describes the challenges of a 17.5um thin bare Cu wire bonding on aluminum bond pads for a fragile low-k wafer technology, on a BGA package. Previous evaluations have so far focused on 20um and 25um bare Cu wires as a suitable low cost replacement for Au wires. To improve performance, more fragile low-k wafer technology is being developed. In the past, some key technical challenges experienced are the substantial aluminum splash and potential cracks underneath the bond pads. This paper will focus on using a thin Cu wire of 17.5um diameter to address the smaller BPO of 44um, with very minimal aluminum splash, and prevent any cracks on a fragile low-k construction. As copper is a harder material than aluminum, to make a good bonding interconnect between the two metals and yet addressing these concerns, is critical. Also, the bonded ball bond should have a sufficient amount of remnant aluminum to survive reliability test. As Cu oxidation is rampant, an inert environment of a forming gas of 95N
2
5H
2
is needed to contain this aspect in order to achieve a good wire bond.