Thermal ratcheting of solder-bonded elastic and elastoplastic layers

The cyclically growing deflection of solder-bonded elastic and elastoplastic layers subjected to cyclic thermal loading is Studied. Finite element analysis of a Si/Sn-95Pb/OFHC-Cu layered structure is performed by taking into account the temperature-dependent viscoplastic behavior of Sn-95Pb as well as the uniaxial ratcheting behavior of OFHC-Cu. A temperature-dependent power law is employed for the viscoplasticity of Sn-95Pb, while a combined nonlinear kinematic and isotropic hardening model is assumed for the cyclic plasticity of OFHC-Cu. It is shown that the temperature-dependent viscoplasticity of Sn-95Pb and the uniaxial ratcheting of OFHC-Cu are the controlling factors for the cyclic growth of deflection of the layered structure under temperature cycling. It is also shown that cyclic hardening of OFHC-Cu plays an important role for the cyclic growth of deflection, and that elastic stress in the Si layer cyclically develops noticeably if the cyclic growth of deflection is significant. (C) 2008 Elsevier Ltd. All rights reserved.