Fatigue life prediction of solder material: effect of ramp time, hold time and temperature

The influence of factors such as ramp time, hold time, and temperature on isothermal fatigue of low-tin lead-based solder is investigated. Ways to extrapolate fatigue life are demonstrated. Decrease of frequency below 10/sup -2/ Hz is shown to lead to the reduction in the number of cycles to failure. The relation between N/sub f/ and frequency may be described by Eckel's relation. The effect of frequency is a function of strain range; therefore, the frequency-modified Coffin-Manson relation is not applicable to this solder at strains studied. Hold time dramatically reduces the number of cycles to failure and leads to the saturation in the N/sub f/. The method to calculate this limit is developed. The activation energy is a function of cycling conditions. High strain rates and high strain ranges lead to mixed transgranular-intergranular fracture. Activation energy, which is 24-26 kJ/mol. at low strain ranges and at all strain ranges with low strain rates (slow cycling or hold time in the cycle), can be used for isothermal fatigue data extrapolation of this solder.<
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