A stress relaxation model for predicting the fatigue life of leaded surface mounted solder joints

Summary form only given. A model that will allow the prediction of fatigue life for leaded SMT components has been developed. The model incorporates the fact that, as plastic creep strain occurs in a solder joint, the driving stress will decrease, resulting in a reduction of the strain rate. The temperature dependence of the creep rate has been included to correct for the different strain rates that would occur at either extreme of a temperature cycle. This results in a more realistic prediction of the strain range, which is then included into a Manson-Coffin fatigue equation to predict mean cycles to failure. The sensitivity of fatigue life to variables such as component type, lead compliance, temperature cycle and temperature extremes, and solder geometry was investigated