Optimization of flexible substrate for automotive LED rear-lamp

High brightness light-emitting diodes (HB LEDs) for the automotive exterior lighting system are required to maintain the stable light output irrespective of the ambient temperature. We design the flexible substrate with the thick trace layer for heat spreader for the conventional process of printed circuit board (PCB). The performance of flexible PCB substrate with the thick copper layer of 200 um is compared with the conventional substrate attached on aluminum heat spreader of 1.5 mm and 150 W/m-K. The proposed design is analyzed in accordance with the size and thickness of heat spreader, and then the heat emission properties of the proposed substrate laminated with thick copper foil is characterized by using CFD (computational fluid dynamics) technology. The optimization of the substrate is carried out in accordance with the forward current and voltage. The thermal resistance from the top surface of LED to the plastic housing can be decreased over 1.5 times in comparison with the conventional structure while the delta forward voltage is controlled within 0. 04 V.