Analysis of thermal spreading resistance in high power LED package and its design optimization

Thermal spreading resistance has a great influence on thermal resistance of LED chip especially in flip chip, and there exists a need for a thermal design optimization of LED package. In this paper, we analyze thermal spreading effect in both flip chip and face-up chip, and get a thermal design optimization of LED package. Firstly, thermal spreading resistance is calculated, and then thermal simulation is done using finite element method. Influencing factors in thermal spreading are analyzed by these two methods and the results are matched quite well. An optimal thickness of heat sink is found, and the minimal thermal resistance of heat sink is attained in this thickness value. The optimal thickness decreases after increasing area of heat source. In flipchip LED, thermal resistance decreases after increasing area of Au bumps and the thickness of PN junction available at the present technology. At the same Au usage, reduce the area of each bump and increase the number of bumps could effectively decrease thermal resistance of PN junction and have good temperature evenness. It is important to consider thermal spreading effect in LED packaging.