Thermal Analysis of LEDs for Liquid Crystal Display's Backlighting

This paper investigated the thermal design of the light emitting diode (LED) onto the board and its packaging. The LED was a 6-lead MultiLED with 3 chips designed for LCD backlighting and other lighting purposes. A 3D finite element model of this LED was built up and thermal analysis was carried out using the multi physics software package, PHYSICA. The modeling results were presented as temperature distributions in each LED, and the predicted junction temperature was used for the thermal resistance calculation. The results for the board structure indicated that (1) removing the foil attach decreased the thermal resistance, (2) Increasing the copper foil thickness reduced the thermal resistance. Package design indicated that the SMT designed LED with integrated slug gave lower thermal resistance. Pb-free solder material gave lower thermal resistance and junction temperature when compared with conductive adhesive.