Thermal Stress Analysis of PBGA Using A Fluid-Solid Coupling Method under Steady Convective Heat Transfer

As the power density enhances while package size decreases, thermal management becomes a primary concern of the reliability and performance of the electronic packaging. When the natural convective heat transfer can't meet the thermal budget, a forced convective heat transfer must be employed in order to prevent the inappropriate temperature and thermal induced stress which would cause many problems to the electronic packaging. When it comes to the thermal stress simulation of electronic packaging under forced convective heat transfer condition, many researchers just set a constant heat transfer coefficient on the heat transfer surface according to the empirical formulas, a more extreme case is to just set a heat transfer coefficient randomly. Obviously these approachs may lead to inaccurate results due to that many factors would affect the value of heat transfer coefficient, such as the velocity and direction of the wind, the local temperature, the complex structure of the packaging, and so forth. Moreover, the heat transfer coefficient is not a constant at every location. So a more accurate method such as the fluid-solid coupling method is needed to obtain good results. In this paper, we firstly investigated the temperature and thermal stress of a specific PBGA whose input power was 2W under natural convective heat transfer, and find that the maximal temperature exceeds the normal operation temperature. As the input power increase further, the maximal temperature and thermal stress increase as well. So a forced convective heat transfer will be needed to enhance the thermal dissipation. In the second part, the simulation work of thermal stress of the PBGA under forced convective heat transfer condition using a fluid-solid coupling method was carried out, the results show that the forced convective heat transfer can increase the thermal dissipation sharply, thus reduce the maximal temperature and the resulting stress. Finally, various distributions of temperature and thermal stress were obtained under a range of wind velocity and input power, which provide us a frame of reference to choose the suitable wind velocity while satisfying the temperature and stress requirement.