Research On Fatigue And Fracture Characteristics Of Power Module Bonding Wire Interface

Wire bonding is a widely used micro-interconnect method in electronic packaging.The reliability of wire bonding has always been the focus of researchers.The failure mode of wire bonding can be mainly divided into two types: the bonding interface lift off and the neck area failure.Many researchers have put forward various empirical formulas to predict fatigue life of the interface.With continuous development of cohesive zone model in recent years,it has been proved to be a useful method to describe the interface failure.Therefore,applying the cohesive zone model to study the interface failure of wire bonding can make a deeper understanding of the interface failure mechanism,and make up for the deficiency of empirical formula in describing fatigue failure.The major work of this thesis is summarized as follows:(1)An interpolation-based cohesive zone model was established,which can describe various different shapes of cohesive zone model.The effect of the shape of cohesive zone model was studied by finite element simulation.A "two-step" parameter inversion method was proposed to determine the parameters of the interpolation-based cohesive zone model.Experimental data and pseudo-experimental data were used to verify the accuracy and efficiency of this method,respectively.The influence of the inversion information on the inversion results was studied.The results show that combining two types of information to carry out the inverse analysis can get a more reliable and uniform result than using a single type of information.(2)The temperature cycling experiment of the power module was carried out,and the failure condition of the power module wire bonding parts was analyzed.The results show that the failure of the bonding part is mainly located at the bonding interface and the neck area.The failure analysis of power module with different packaging materials was carried out through finite element simulation.With the help of sub-model technique,a more realistic model of wire bonding was established,and the cyclic life of power module under temperature cycling was predicted by use of Coffin-Manson theory.(3)A cyclic cohesive zone model was established based on the fatigue damage theory.Bringing the cyclic cohesive zone model into the wire bonding model,the damage evolution of the wire bonding interface under the temperature cycling was studied,and the characteristics of damage evolution of the interface was determined,and the similarities and differences of the interface damage accumulation for various packaging materials were analyzed.Qualitative analysis of fatigue life of the wire bonding model under different packaging materials was carried out.The results show the consistency with the experimental results and make up for the deficiency of the traditional life prediction methods.(4)Both fracture and fatigue failure behaviors of the bonding interface of the power module were simulated by using the cohesive zone model.By comparing these two kinds of simulation results,different failure mechanisms of the interface were disclosed.