Microelectronics Reliability 55, pp 582-587, Feb - March 2015, DOI:10.1016/S0026-2714(15)00039-6

An evaluation of dwell time and mean cyclic temperature parameters in the Engelmaier model

Elviz George, Michael Osterman, Michael Pecht
Center for Advanced Life Cycle Engineering, University of Maryland, College Park, MD 20742, United States


The Engelmaier model is a strain-range-based fatigue model for evaluating the life expectancy of solder joints under power and temperature cycling. The model relates cycles to failure to a strain range metric using a power law relationship. In Engelmaier’s original formulation in 1983, the exponent term in the power law relationship was defined to be a function of mean cyclic temperature and cyclic frequency. Engelmaier replaced the cyclic frequency with dwell time in 1988 without explanation. This paper provides a rationale and the implications for changing the formulation of the exponent term of the Engelmaier model. Using non-linear regression, model constants are derived for Engelmaier model formulations with cyclic frequency and dwell time parameters. A t-statistic measure is estimated to quantify the influence of cyclic frequency and dwell time parameters on the cycles to failure. In tin-based lead-free solders, the absolute values of the t-statistic for cyclic frequency are approximately 3–10% higher than that for dwell time. The higher absolute value of a t-statistic identifies a stronger dependence of cycles to failure on cyclic frequency than on dwell time. Then, the feasibility of replacing the mean cyclic temperature parameter in the exponent term with time-averaged cyclic temperature using t-statistic measures is explored. Based on the evaluation of t-statistic measures, the authors recommend the Engelmaier model with cyclic frequency and mean cyclic temperature parameters to be used for solder joint life prediction.

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