Cu wire bonding: Reliability improvement for high temperature in plastic packages

The request of the electronic market to increase the working temperature of power integrated circuits up to 180-200degC has a big impact on the reliability of standard plastic packages. The joint between bonding ball and pad is mainly affected in conditions of high temperature and high current. Various solutions were tried in order to reach the target with standard interconnection solutions. If Au or Cu wires on Al pad are used, intermetallics growth takes place leading to high increase of electrical resistance and possible ball lift. The insertion of an under bump metallization between wire and pad is known to be a solution for Au wire. In this paper this solution is investigated using Cu wire instead of Au wire. Cu is less expensive than Au and its use reduces the impact of the cost of the UBM.