Identification and Predictive Modeling of High Propensity of Defects and Field Failure in Copper-aluminum Wire Bond Interconnect under Exposure to High Temperature and Humidity

Abstract

Semiconductor packaging industry is undergoing a paradigm shift from gold to copper wire bonding. The main driving force behind this shift is the much lower raw material cost of copper compared to gold as well as superior mechanical, thermal, electrical material properties. As fast as the growth of the use of copper wire bond has been since 2008, there are still a few reliability issues which prevent cooper wire bond from mass production. One of the most prominent concerns is the microscopic galvanic corrosion at wire bond interface when being used under high temperature/humidity operational environmental conditions. This study focuses on investigation of micro galvanic corrosion failure mechanism of wire bond and development of a multiphysics finite element model capable of predicting the life span of copper wire bond deployed under various harsh environmental conditions. Butler-Volmer equation and Nernst-Planck equations are used in the FE model to characterize the transport behavior of chlorine contaminant and corrosion behavior of Cu-Al intermetallic compound layers (IMCs). Transport cell are designed to measure chlorine diffusivity and ionic mobility. Chlorine release rate of epoxy molding compounds are quantified using experimental data. Three-electrode electrochemical polarization are used to characterize the Tafel parameters of Cu-Al IMCs. Novel moving boundary approach is implemented in the model to capture the corrosion behavior of Cu-Al IMCs. The developed FE model is used to predict time-to-failure results of cooper wire bond and those results are compared with experimental time-to-failure results to verify the accuracy of model prediction. The study has shown that reducing the chorine contaminant level in epoxy molding compound, lower the transport rate of chlorine will help increase the reliability of copper wire bond under harsh environmental conditions.