Multiphysics Effect of Temperature and Humidity on Copper Wire Bond Degradation via Enthalpy-Based Water-Vapor Energy

In this study, the degradation of copper wire under different temperatures and humidity levels is investigated. High temperature and high humidity accelerated stress tests with a cumulative duration of 960 h are conducted. The stress tests are carried out at temperatures of 85 °C, 110 °C, and 130 °C and relative humidity (RH) of 85%, 50%, and simulated dry conditions. The stress conditions are selected based on the energy level of water vapor based on enthalpy and their relevance to the industrial standards. Ceramic dual in-line packages are used as the test vehicle with and without molding compound encapsulation with bare copper wire bonded directly onto the gold-plated lead frame. In situ electrical testing and failure analysis are carried out to identify the degradation mechanisms. It is found that the oxidation of copper at the wire span contributes to the steady increase in the electrical resistance, while the oxidation of copper at the stitch bond interface leads to open contact failure. The stitch bond formation plays a critical role in the lifetime of the wire bond under accelerated stress test. We propose that the energy level of water vapor based on enthalpy can be used to evaluate the effect of humidity in the copper wire bond degradation during accelerated stress test.