On the assessment of the life of SnAgCu solder joints in cycling with varying amplitudes

The long-term reliability of SnAgCu solder joints under actual field service conditions is far from well understood. Most accelerated cycling tests are restricted to constant amplitudes, whereas realistic environments usually involve varying amplitudes and/or more than one type of loading. Thus assessments of life as well as relative comparisons of alternatives in terms of life in service invariably have to rely on the assumption of a damage accumulation rule. This paper focuses on the life of SnAgCu solder joints in isothermal mechanical cycling with varying amplitudes. Test samples use representative solder material and geometry in electronic packaging industry. Experimental results show that the load sequence affects life significantly, reflecting deviations from a linear damage accumulation rule. Hardness and microstructure of solder material are studied after cyclic loading. The effect of load sequence could be explained by the damage evolution path and solder property change, which varied with cycling. Moreover, different levels of initial loading lead to changes in acceleration factors in subsequent shear fatigue cycling.