Reliability of Cu wire bonding on active area for automotive applications

Increasing cost of gold (Au) for bonding wires and decreasing die and, therefore, bond pad size raise the demand for alternative bonding wire materials. A cheap alternative with good electrical conductivity is copper. Cu wire is harder than gold and aluminium. The material itself shows a pronounced strain hardening, so that the hardness increases significantly during ball bonding. These mechanical properties of Cu increase the stress on the bond pad and chip compared to Au and Al wires. A sensitive analysis in terms of reliability is required to assess the interconnect performance, especially for the combination of bonding over active area and in automotive applications. We present a reliability study of 50 ¿m Cu wire on a Cu based bond pad for automotive applications. Initial evaluations were done to assess the impact of bonding parameters, floor live time and forming gas flow rate on the process performance. A detailed reliability assessment follows to assess the interconnect performance. Electron Microscopy (transmission TEM, and scanning SEM) and cratering test were used to assess changes in the material after stress test and electrical testing to ensure the functionality of the product. It shows that Cu wire can be used even for critical applications and bonding on active area with good reliability performance.