Effect of Creep Deformation on Inelastic Deformation of Electroplated Copper Foil

High-density electronic package employs elerctroplated copper foils for micro-wiring. To ensure the reliability of the micro-wiring, the characteristics of deformation of electroplated copper foils must be clarified. Then, in this study, inelastic deformation characteristics of an electroplated copper foil were investigated by conducting tests under several loading conditions. Though all the tests were conducted at room temperature, stress-strain curves in tensile tests were affected by strain rate, and clear creep curves were obtained by creep tests. Moreover, stress relaxation by strain maintenance and ratchetting deformation by cyclic tension-unloading occurred. To discuss the mechanism of these time-dependent deformations, an elasto-plastic-creep constitutive model for the electroplated copper foil was constructed and simulations of the deformations were conducted by employing the model. As a result, the strain rate effect, the creep and the stress relaxation were almost described by the constructed model, and it was found that the creep strain controlled the characteristics of the time-dependent deformation. Meanwhile, the model could not describe the ratchetting deformation well. This suggests that a parameter which expresses damages due to cyclic loading should be considered in the constitutive model for the electroplated copper foil to predict the ratchetting deformation precisely.