In printed circuit boards, thin copper layers are used as current paths. During the thermal loading of printed circuit boards, stresses arise due to the different coefficients of thermal expansion of the used materials. To be able to model the mechanical behavior of printed circuit boards under cyclic thermal loads, cyclic mechanical tests of thin copper foils under changing tensile and compression loads at different temperatures were conducted. From these experiments, the isotropic and kinematic hardening parameters were determined serving as material input data for a nonlinear isotropic/ kinematic hardening model in the finite element analysis-software Abaqus. The kinematic hardening parameters were fitted in an optimization process. The isotropic hardening variables were determined based on the stress versus plastic strain relationship that was constructed incrementally from the available individual cycles. The so-obtained curve was found to be not unique, but to depend on the loading situation. Hence, different approaches for strain range memorization were evaluated. Since these approaches were developed for modeling strain-controlled tests, whereas the experimental data were obtained in a force-controlled way, a phenomenological formulation was developed and applied. The results of curvature measurements during thermal cycling were used for model validation. The experimental results and the numerical predictions are in good agreement.

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Thin AU2Cu6Sn2 solder joints have been identified to provide improved electrical and thermal device performance compared to thicker solder joints [1].Both the material high thermal conductivity and the reduced joint thickness improve the thermal dissipation through the solder joint , making the thin AU2Cu6Sn2 solder layer very attractive for high power devices. In this paper, we establish a material model for the AU2Cu6Sn2 material in order to study solder thermal fatigue using finite element analysis.