| Insulation Gate Bipolar Transistor(IGBT)has become the dominant power device in various medium and high power electronic converter systems due to its fast switching speed,low drive power,reduced through-state voltage and high current carrying capacity.Since the introduction of IGBT,the failure of this device in power electronics devices has been a difficult problem for engineering applications.Currently,the most important failure mode of IGBT modules is bonding failure in the Al wire-Al metallization interface.This form of failure will directly lead to the breakage of the internal current circuit of the IGBT module,which eventually triggers the failure of the IGBT module.pure Al film sputtered on the surface of the IGBT chip,but the Al metallization containing a certain amount of Si elements(1% mass fraction).After the power cycle,the Si element will segregate to the grain boundaries,which will change the mechanical properties of the bonding region and make the wire-metallization interface prone to fracture along the crystal,thus triggering the failure.Therefore,studying the mechanism of Si segregation behavior and the relationship with the mechanical properties of the bonding region is of great value for the reliability estimation of high-power devices.In this thesis,the relationship between microstructure evolution and mechanical property degradation in the wire-metallization interface of IGBT modules under power cycling conditions is systematically analyzed using a combination of experimental observations and molecular dynamics simulations.The research contents are as follows.(1)The construction of the DC power cycle experimental platform is completed,and power cycle experiments are conducted to provide a basis for subsequent microstructure evolution observation experiments of IGBT modules.A sample preparation method for bonding region microstructure observation was proposed to facilitate the observation of wire-metallization interface microstructure.(2)The microstructure of the wire-metallization interface of the module before and after power cycling was observed.The surface morphology of the chip and wiremetallization interface was observed by microscopic morphology analysis technique,and the failure mechanism was analyzed.The evolution of the phase distribution,element concentration changes and grain orientation in the bonding region before and after the power cycle were also studied.The relationship between the microstructure evolution of the wire-metallization interface and Si segregation during the power cycle was established based on experimental observations.(3)The main factors influencing the segregation of Si elements were analyzed.Molecular dynamic(MD)simulations were used to simulate the segregation of Si elements at different temperatures,stresses and grain orientation differences.The results show that both temperature and stress promote Si deviations,while tensile stress causes grain boundary deviations and compressive stress causes grain boundary depletion.(4)The relationship between Si element bias and the degradation of micromechanical properties in the wire-metallization interface was explored.Molecular dynamics simulations were used to develop mechanical models for doping with different concentrations of Si,and simulations of tensile,shear,and fracture behaviors as well as nanoindentation were performed.The results show that all the Si bias behaviors lead to the degradation of mechanical properties such as tensile and shear in the bonded region,and promote the sprouting and extension of cracks on grain boundaries. |
