Biased humidity degradation model for Cu-Al wire bonded contacts based on molding compound properties

A large effort is made across the industry to understand the various failure mechanisms involving Cu wire. Component users, not only in the automotive supply chain, are becoming more demanding and critical. They are expecting equal, or higher, quality levels compared to Au. Since corrosion of the Cu-Al system under the influence of moisture and temperature is one of the most widely observed failure mechanisms encountered during development and qualification of Cu wire in microelectronics packaging, several papers have been published on this subject. In a recent publication we have described the failure mechanism in more detail, and proposed a new acceleration model to enable one to make lifetime predictions for (electrically) unbiased conditions. However, one of the major gaps seen in the available literature is the influence of bias as an additional accelerating factor. Therefore, studying in more detail the influence of bias and electrical field strength, especially in relation to molding compound properties, will be the subject of this paper. The existence of an "incubation-time", before the actual corrosion is starting, is also proposed. This study provides two outcomes. On one hand, molding compounds for Cu wire can be selected by determining two key material properties: halide concentration and volume resistivity. On the other hand, these properties are linked to a complete empirical degradation model for the CuAl contact. This model enables lifetime predictions in real life applications where the combined degradation under moisture, temperature and bias may occur, e.g. during standby and switching the component/ application from an off to on stage.