B03 ISSE 2012 – Bad Aussee, Austria LED Lamp – Design and Thermal Management Investigations Petko Mashkov, Berkant Gyoch, Hristo Beloev and Stanislav Penchev University of Ruse, Ruse, Bulgaria tgp@uni-ruse.bg Abstract: The aims of this work are connected with development of new method of LEDs’ mounting onto the heat sink in lighting equipment. The technique involves usage of copper pins instead of standard MCPCBs. LEDs are soldered on copper pins. Mounting of LEDs demands boring holes in the heat sink and fixing copper pins into the holes by thermal conductive epoxy resin only. LED lamp is made using new technology and LEDs’ thermal performance investigations are made at various ambient conditions (air temperatures from 20ºC to 45ºC) and different current values through LEDs – up to 600 mA. Temperature regimes of operation of power LEDs soldered on MCPCBs and on copper pins (and mounted on heat sink) are experimentally tested and compared. Experimental results show that utilization of copper pins underneath LED thermal pads ensures good dissipation of heat, good manufacturability, enables varied designs of light equipment and is cost effective. 1. INTRODUCTION Application of power LEDs in light equipment possesses a lot of advantages. Luminaire efficacy of best LEDs is more than 100 lm per watt. LEDs’ efficacy is better than efficacy of CFL (compact fluorescent lamps) more than two times. The lifetime of LED is remarkable long - five to fifty times longer than other light sources before requiring maintenance. Lighting equipment based on LEDs does not fail catastrophically like light bulbs; its useful lifetime is more than 50 000 hours before the light output to degrade below 70% of the initial one. But all these benefits can be realized only by precise thermal management calculations and investigations. During operation of LEDs about 85% of electric power is turned into a heat in the LED chip [1 ÷ 3] and one of the most critical design parameters in LED illumination systems is the ability of system LED – PCB – heat sink to draw heat away from the LED junction. High operating temperatures at the LED junction adversely affect the performance of LEDs, resulting in decreased light output and lifetime. In accordance to life time predictions during operation junction temperatures T j of LEDs must be kept below 80ºC - then lifetime of the light equipment will be over 50 000 hours. Usually LEDs for lighting equipment are soldered on metal core printed circuit boards (MCPCB) which possess low thermal resistance. But assembling of MCPCBs on heat sink demands many hand’s operations and isn’t with good manufacturability. That is why the purpose of these investigations is to find low-cost thermal effective manner for assembling power LEDs on the heat sink in light equipment. Thermal resistance between solder point and heat sink must to be as low as when MCPCB is used, but assembling of LEDs onto heat sink have to be much easier. During investigations non contact measurements by infrared camera are used. The developed method [4] gives a lot of advantages and allows evaluating temperature distribution easily and quickly on all LEDs in the light equipment on the whole area of the heat sink. 2. PROBLEM STATEMENT Experiments using LEDs XLamp XPC–White, CREE Inc., with light output 100 lm at 350 mA are made. Ambient temperature of the LED’s immediate surroundings, power dissipated by the LED and thermal path between the LED junction and surroundings influence strongly on the junction temperature. During operation heat flows from junction of the LED via solder point and PCB to the heat sink by way of conduction. The heat sink diffuses heat to the ambient surroundings mostly by convection [1].