Corrosion reliability of copper wirebond (CuWB) packages-Impact of voltage and corrosive ions from packaging materials

Abstract

Reliability of electronic devices used in extreme and harsh conditions such as in automotive applications is often associated with prevention of corrosion at the interfaces of dissimilar interconnect metals and of metal (Al or Cu) bonding pads. Packaging materials, especially molding compounds, contain several ionic components and can uptake certain level of moisture to provide electrolytic conditions to initiate corrosion processes. Probability of occurrence of corrosion in devices with high voltage applications is of special interest as many analog devices operates at higher voltages and with new CuWB packages there is a higher susceptibility of corrosive failures. This paper examines the impact of voltage on the mold compound compatibility with CuWB packages up to 65 V. Bias HAST reliability evaluation of various mold compounds at different voltages will be described. Corrosion of bonding pad (Al) and at the Al-Cu intermetallic compound interface was observed in the presence of certain ions present in mold compounds. Even though current mold compounds are “green”, the allowable amounts of halide ions can far exceed the ppm limit to prevent CuWB corrosive failures. Bromide ions are known to be very corrosive to metals. Br ions are still present in some mold compounds. The impact of the Br ion on CuWB reliability will be described. Additive impact of Br ions in presence of Cl will be examined. Another corrosive component present in many mold compounds, sulfur compounds, also can be corrosive under certain reliability stress conditions. Difference in corrosion behavior of Cu and Pd –Cu wirebonded packages due to sulfur compounds will be presented. Corrosive impact of high levels of Cl on the Al pad corrosion leading thick aluminum oxide growth and reliability failures will be discussed.