Local Mechanical Testing and Parameter Identification for Modeling of Interconnection Materials
Authors: Falk Naumann, Georg Lorenz, Matthias Petzold Company: Fraunhofer Institute for Mechanics of Materials IWM Date Published: 2/11/2014
Pan Pacific Symposium
Abstract: The reliability properties of almost all interconnection materials used for microelectronic device packaging are affected by the mechanical and thermo-mechanical stresses occurring during fabrication and under operating conditions. Precise knowledge of the respective stress and strain states is one key issue in understanding potential failure modes and enabling reliable life time predictions. Theoretical models, e.g. describing the creep behavior of solder or the plastic deformation of ductile materials like bond wires are based on the assumption of specific constitutive material laws. Various related material parameters have to be determined by suitable mechanical tests. Within this paper, an approach determining the mechanical parameters of heavy bond wires by combined testing and parameter identification methods is presented. Cyclic material tests in a low cycle fatigue regime are used to study the yielding and hardening behavior in relation to the fatigue mechanisms of different wire materials. In particular, kinematic hardening parameters were estimated for a simplified Chaboche model, using optimization algorithms in order to allow the calculation of local loadings during thermo-cycling tests. In addition, temperature-dependent tension testing at an increased strain regime and nano-indentation tests were used to investigate temperature influences on yield and hardening behavior, thus complementing the data base of cyclic tension testing. In order to also get access to local material properties of composite wire materials like aluminum clad copper wires, nano-indentation measurements were applied thus allowing to study the mechanical behavior of the components separately. To extract the required material parameters from indentation testing, numerical simulations of the experiments were coupled with parameter identification routines. In summary, the procedure proposed enables a more accurate modeling of the local loading governing degradation mechanisms in interconnection materials. The results provide an improved basis for advanced life time modelling and reliability predictions of loaded wire bonded interconnects.