Thermal Stress Simulation And Structure Improvement Of Copper Clip Bonding Package Based On Finite Element Method

With the miniaturization and thin design of power devices,the size has continued to shrink,and the energy density inside the module has grown exponentially.Thermal loads that cannot be effectively dispersed can cause thermal and mechanical failure,which can lead to material fatigue and reduce service life.Therefore,more and more power devices abandon the traditional wire bonding technology and adopt the copper clip bonding technology witch with lower thermal resistance,better heat dissipation performance and higher mechanical reliability.However,due to the mismatching of thermal expansion coefficient between different materials in the device,the copper clip bonding package still faces with the problem of large thermal stress under working conditions.In this paper,ANSYS finite element analysis software is used as a platform to perform steady-state thermo-mechanical simulation of a typical copper clip-bonding package.The study of thermal stress distribution under high-power working conditions is carried out.It is found that in the interior of the package,stress concentration occurs on the solder layers between the copper chip and the die,and between the chip and lead frame.Stress concentration will also occur on the die.The stress concentration point is easy to develop into a failure point to affect the operational reliability.After revealing the main cause and failure location that affect the reliability of the copper clip bonding package,in this paper,four new copper clip-bonding package structures are proposed by mechanical analysis based on elastic mechanics and the commonly used mechanical design method to improve stress concentration.The structural optimization was carried out by using design of experiment method and response surface analysis method based on MOGA algorithm to reduce the maximum thermal stress.After optimization,four optimized copper clip bonding package structures are output.Through finite element simulation to verify its effectiveness,the thermal stress on the two solder layers and the die of the copper clip bonding package with step in clip is reduced by 49.88%,38.36%and 35.54%,respectively,compared with the typical copper clip bonding package.The thermal stress in the solder layer and die of the copper clip bonding package that has depression on surface is reduced by 41.79% and 48.37%,respectively,compared with the original clip package.For the copper clip bonding package with load reduction groove,the thermal stress on die is 48.95% lower than the original structure.