Research On The Interface Delamination Of Solder Layer And Sintered Layer Of IGBT Chip

In recent years,IGBT power modules have been developing towards high power,high integration and high reliability.IGBT power modules are made of plastic encapsulation of various materials.Due to the differences in Young’s modulus,thermal expansion coefficient and thermal conductivity coefficient of different materials,resulting in different mechanical and thermal stress of each material,so during the production or use of IGBT power devices,delamination failure between interfaces will occur between interfaces of different materials.Aiming at the problem of interface delamination failure of IGBT power module,this paper takes the heterogeneous interface composed of IGBT chip welding layer and sintering layer as the research object,and studies the mechanical behavior during the interface delamination process by means of simulation.The purpose is to establish A cohesive force model parameter that can characterize the interface delamination and expansion of the solder layer and sintered layer of an IGBT chip.The research content includes the following aspects:(1)Using ANSYS finite element analysis software,the stress and strain distributions of IGBT modules without solder crack defects and IGBT modules with solder crack defects were analyzed under temperature cycling conditions.The simulation results show that the thermal stress is mainly concentrated in the four corners where the chip and the solder layer are in contact and the four corners where the chip and the plastic package are in contact.When the nano-silver welding layer has crack defects,stress concentration will occur at the crack tip,which increases the stress value of the welding layer;under extremely low or high temperature conditions,the crack area is most likely to expand and extend.(2)Based on the cohesion model,the generation and propagation of spalling at the homogenous interface are studied.The simulations were carried out with different tensile strengths as variables respectively,and the cohesive force element sizes of different sizes were set to observe the simulation results.The results show that the maximum demand force to reach the spall demand point increases with the increase of tensile strength,and the growth slope of the curve represented by the force-load-displacement curve is consistent.The accuracy of the simulation and the efficiency during calculation are also different.In order to obtain the size of a single mesh element that is relatively convergent,the calculation can be performed according to the calculation criterion of cohesion,so as to realize the consideration of element mesh refinement and simulation calculation efficiency.(3)Based on the cohesive force model,the heterogeneous interface composed of the welding layer and the sintering layer of the IGBT chip is studied.The effect of shear stress on the stress change at the initiation point of interfacial spalling was studied.The results show that it is found that changing the ultimate shear stress in the simulation setting has no effect on all the loading point-force-displacement curves of the simulation results;with the setting of the ultimate tensile strength value,the positive contact of the interface delamination initiation process The stress shows a linear growth trend,and the value reaches the ultimate tensile force value set during the simulation modeling.(4)The parameters of the cohesive force model to characterize the initiation and propagation of interfacial layer cracks between the solder layer and the sintered layer of the IGBT chip.The interface spall propagation curve is obtained through the interface spall propagation test;in pure tensile mode,the critical energy release rate is calculated through virtual crack closure simulation;according to the energy release rate,a set of IGBT chip welding layers and Cohesion model parameters for spall propagation at the interface of the sintered layer.Based on this model,set different ultimate tensile strength values,then simulate the mechanical test experiment of simulating interface spalling,compare the simulation results with the experimental results,and select the ultimate tensile strength.