Deriving lifetime predictions for wire bonds at high temperatures

Abstract

We report a method to predict wire bond lifetimes. Wire bond resistance increase due to thermal stress can be modelled by the Arrhenius equation, permitting prediction of wire bond reliability in a product prior to qualification if sufficient experimental data is collected and statistically analysed. Activation energies for various experiment “legs” are determined by stressing a number of wire bonds at 3 different temperatures, then, using survival analysis techniques for accelerated failure time models, extrapolating results to use conditions. Example lifetime predictions for Cu and PCC wire bonds on Al pads are shown to illustrate the method, using a small number of test dies that incorporate four-wire resistance measurements of wire bond pairs, with two ball bond sizes and two different wire types, stressed at precise temperatures with in-situ resistance monitoring in the University of Waterloo's “mini-oven” reliability test systems. These results show that typical Cu wire bonds on Al bond pads can be highly reliable up to 163 °C without encapsulation or 155 °C with encapsulation, with estimated lifetimes of 12,000 h with <1 ppm failure rate, assuming a failure condition of 10% resistance change.