Fine Pitch Wedge Bonding for High Density Packaging

In today's computers, high pin count packages are required for the high performance, high density silicon being utilized. A significant challenge exists to provide such designs while maintaining a cost effective, high yielding assembly process. This paper discusses Unisys' experience in the development of fine pitch (100/spl mu/m) aluminum wedge bonding for a 591 Pin Grid Array package. Experience and available equipment dictated the package to be die attached using silver glass and wirebonded using 32/spl mu/m aluminum wire. Die attach was well within existing capabilities but the interconnect of over 550 wires on 100/spl mu/m pitch posed a significant challenge. Considerations were given to maximum wire to wire clearance, layer to layer misregistration, wire lengths, bonding tool angles, and fiducials that would provide maximum automatic alignment accuracy. Three dimensional CAD modeling of the bond head and package was followed with an Assembly Test Vehicle (ATV). The ATV was designed to match worst case geometries, and was used to verify concepts developed during 3D modeling. The product was introduced into production in 1993, and has exceeded predicted assembly yields. Although the fine pitch wire bonding was demonstrated on a single chip package, the technology is transportable to multichip applications.