Effect of temperature on isothermal fatigue of solders

The effect of temperature on isothermal fatigue of low-tin lead-based and lead-tin eutectic solders is discussed. The study was conducted at low strain ranges (0.3-1.0% total strain) in tests without and with hold time in the cycle. While temperature has almost no effect on the fatigue life of eutectic solder, the fatigue life of low-tin lead-based solder is a complex function of temperature. Extrapolation of fatigue data for this older was only possible in a 25-80 degrees C temperature range, using values of apparent activation energy for 25 to 45 kJ/mole depending on strain range, strain rate, and presence of hold time in the cycle. Variation in the values of activation energy was found to be associated with different failure modes under various testing conditions. Higher activation energy for the fatigue of low-tin lead-based solder was associated with mixed transgranular-intergranular failure. Failure in grain boundaries was characterized by lower values of activation energy.<
>