Thermal and Optical Analyses and Measurements of Multi-chip LED Package

• Main Authors: Shuan Fu Chen, 陳宣甫
• Other Authors: M. Y. Tsai
• Format: Others
• Published: 2009
• Online Access: http://ndltd.ncl.edu.tw/handle/41589017205958552700

碩士 === 長庚大學 === 機械工程研究所 === 97 === The purpose of this study is to investigate the thermal behaviors and candela distributions of multi-chip LED package. This package contains three kinds of LEDs colors (red, green and blue chips), which can be combined to generate colored and white light. In experiment the junction temperature (Tj) of the different chips were measured by “LED Junction Temperature Tester” for only one chip heated and all of three chips heated, and the surface temperatures can be found by thermal couple. In simulation the LED model was built by using finite element method. In addition, the linear superposition method and thermal resistance circuit method were used for predicting the Tj. Then the parametric studies were performed by effective FEM model to find out the key factors to Tj. Finally, the relations about chip position on thermal and optical analyses were discussed by using FEM and TracePro. The results of experiments, FEM, linear superposition method and thermal resistance circuit method indicate that the trends on Tj of the different chips are similar under different input powers. Each parts of thermal resistance between FEM and experiment are consistent. So the FEM method, experiment, linear superposition method and thermal resistance circuit method are proved to be valid. Parametric studies by validated FEM model show that the thermal conductivity coefficient of Ag-epoxy, lead frame and PCB substrate have an obviously effect on Tj. And the best efficiency can be achieved by replacing the substrate material of PCB with aluminum. As aspect of geometry, it can’t affect Tj when varying Ag-epoxy overflow, fillet and number of thermal via. In thermal and optical analyses, changing chip position almost have no effect on Tj and candela distributions. This package includes three kinds of chips which Tj are affected by each other. By linear superposition method, a thermal resistance matrix from experiment was applied to thermal resistance circuit method for estimating the Tj. Besides, because of the lead frame has uniform temperature under low power, the thermal resistance matrix can be adjusted and used to do parametric studies for thermal resistance circuit method.