Thermal analysis and optimal design of lamp type light-emitting diodes

摘要

The steady-state temperature distribution and the corresponding thermal stresses of packaged light-emitting diodes (LEDs) were investigated numerically via three-dimensional finite element analysis. An LED lamp mounted on a FR-4 printed circuit board was simulated under a natural convection environment. The junction-to-ambient thermal resistance (R-ja) was found to be 335K/W. The maximum thermal stress due to mismatch of thermal expansion coefficients occurred in the interface between silver epoxy and encapsulation. By response surface methodology, 13 design points were established and a regressive model was obtained using the least squares method. The optimal variables, which can effectively reduce the junction-to-ambient thermal resistance, can be determined by increasing the thermal conductivity of lead frame material, by increasing the height of encapsulation, and by widening the cathode by no more than a critical value. The results obtained from the Taguchi method are also discussed.