Estimation of Maximum Operating Temperature for Cu Wire Bonds: Comparison of Epoxy and Silicone Encapsulant Types

摘要

To add to the knowledge of high-temperature reliability of Cu wire bonds, this work reports a method and data for the estimation of maximum operating temperature levels for various Cu wire and encapsulant combinations. An accelerated failure time model based on the Arrhenius equation was used to describe the dependence of the degradation times on the aging temperature and to recommend maximum operating temperature values. Failure was defined as +10 % resistance change. However, due to time constraints, insufficient failure time data was available for model fitting using this failure criterion. Instead, models were fit using a failure criterion of 1 % resistance increase, then extrapolated to the original failure criterion, assuming a linear rate of resistance increase. Using this extrapolation, it was estimated that to keep the failure probability below 1 ppm, the recommended maximum operating temperature levels for a standard lifetime of 12 kilohours with PCC wire are 163 °C, 145 °C, and 141 °C for encapsulants air, epoxy, and silicone, respectively. Corresponding maximum temperatures for bare Cu wire are 159 °C and 125 °C for epoxy and silicone, respectively. Bare Cu wire in air had poor reliability at 225 °C and so was not tested at 200 °C or 175 °C.