A model for thermal fatigue that accounts for both plastic and elastic strains and a mean strain is developed. The model is based on a combination of the generalized Coffin-Manson Equation and the Goodman diagram for fatigue. This model was applied to two accelerated thermal cycling tests—one was for TAB leads; the other, unfilled PTHs at TCM sites in PC boards. Good agreement between the model and data was found. In addition, an existing industry model, which is based solely on plastic strain, is compared to the proposed model and the observed behavior in these two tests. It was concluded that both the effects of elastic and plastic strains and a mean strain are needed to explain the results of these evaluations.

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