Oxidation: A Cu wirebonding challenge in an interbond connection through SSB (Stand-off Stitch Bond) bonding

Copper wire is now becoming popular that emerge to replace the widely used gold (Au) wire in a semiconductor industry as way of interconnecting the chip to the package. It was well proven that Copper (Cu) wire is better in terms of electrical performance which also maintains same quality & reliability level and most importantly lower in cost. Wirebonding is one of the most critical and complex processes in the whole assembly packaging flow. Demanding market applications can no longer be meet in a single die device packaging alone so a multiple chip packaging either in a “side by side” or multiple “stacked die” configurations are needed. At this condition conventional wirebonding process through “forward bonding” interconnection method cannot simply satisfy but rather opt through SSB (stand-off stitch bond) bonding application which is also known as reverse bonding. This paper will demonstrate the results of the Cu wirebonding process development in a dual die package having interbond connection between die with a challenge faced primarily focus in controlling the inherent “bump” oxidation of Cu wire material.