Study On Thermal-Mechanical Performance Of PBGA Package Devices Based On Multi-physical Coupling Method

Plastic ball grid array(PBGA)packaging devices are widely used in motion control,medical equipment,Internet of things and other fields,but the heat generated during its working process will cause a variety of thermal-mechanical failure problems.In the past,most of the researchers studied the thermal-mechanical performance and reliability design of PBGA packages based on the assumption of the overall isothermal temperature or the convective heat transfer coefficient of each surface,but paid less attention to the thermal-mechanical performance changes of the package caused by its heat dissipation structure and heat dissipation effect.In order to solve this problem,this paper takes the on-board core(PBGA324 package)of a field programmable gate array(FPGA)demo board as the research object,and uses multi-physical field coupling simulation to study the heat dissipation characteristics of PNGA324 and the effects of different heat dissipation effects on the mechanical properties of the package.Firstly,the effects of the installation angle of the printed circuit board(PCB),the position of the PBGA package,the horizontal thermal conductivity of the PCB and the power consumption of the chip on the package junction temperature,the average surface convective heat transfer coefficient,the proportion of convective heat transfer and the temperature distribution are studied by means of fluid-heat transfer coupling simulation.The results show that:the change rate of junction temperature caused by installation angle is the largest,and the change rate of junction temperature with installation angle is 4.68%.The position change has the smallest effect on the package junction temperature,the maximum change range of the junction temperature caused by it is 0.4 ?,and the corresponding change rate is only0.58%.The average convective heat transfer coefficient of each surface of the package is quite different.When the power consumption is 0.5W and the horizontal thermal conductivity of PCB is 40W/(m·K),the ratio of the maximum value to the minimum value of the average convective heat transfer coefficient of the package surface reaches 3.55.The average convective heat transfer coefficient of each surface increases with the increase of power consumption,but the growth rate decreases with the increase of power consumption.The proportion of convective heat transfer on each surface does not change with power consumption.In the process of moving the package position from the lower side to the upper side,the proportion of convection heat transfer on the upper surface of the PCB increases,with a maximum growth rate of 3.4%,while the proportion of convective heat transfer on the upper surface of the PBGA package decreases,with a maximum reduction rate of 15%.The increase of PCB horizontal thermal conductivity has a great impact on the proportion of convective heat transfer on the upper surface of the package,and its maximum reduction rate is 9.8%.The influence of installation angle on the surface temperature distribution of PBGA packaging can be ignored.The change of package position has a great impact on the temperature distribution of PCB and package.When the package is located on the lower side,the symmetry of temperature distribution between package and PCB is the best.Then,by means of fluid-heat transfer-thermal stress coupling simulation,the effect of heat dissipation on package von mises and displacement is studied when the power consumption is 0.5W.The variation trend of the maximum displacement of the package,the maximum von mises of the chip and the maximum von mises of the solders with the installation angle is the same as that of the junction temperature with the installation angle,but the change rate is higher than that of the junction temperature.When the horizontal thermal conductivity of PCB is 40W/(m · K),the installation angle changes from 90°to 135°.the maximum displacement of the package,the maximum von mises of the chip and the maximum von mises of the solders increase by 8%,8.08% and 7.96%,respectively.The position movement of the package along the center line of the PCB has no effect on the distribution of the package displacement,but changes the maximum von mises of the chip.When the horizontal thermal conductivity of PCB is 40W/(m·K)and the installation angle is 90°,after the package moves up and down from the middle position,the relative growth rate of the maximum von mises of the chip reaches 5.5%.Finally,based on the thermal-mechanical failure form of PBGA package,a comprehensive index for evaluating the thermal-mechanical performance of PBGA package under different heat dissipation design is established,and the influence of package structure on the comprehensive evaluation index is studied by orthogonal experimental design.Orthogonal test results show that the chip size has the greatest impact on the overall package index,followed by the thickness of the substrate,followed by the thickness of the die attach layer,the thickness of the chip and the thickness of the molding layer.When the thickness of the chip is 0.5mm,the size of the chip is 14 mm,the thickness of the substrate is 0.6mm,the thickness of the bonding layer is 0.1mm,and the thickness of the plastic package is 1.4mm,the comprehensive index of the package is the smallest.