Effect of chip die bonding on thermal resistance of high power LEDs

Thermal resistance of high power blue Light Emitting Diode (LED) package is experimentally examined. The LED package consists of eight CREE EZ900 chips. The dimension of each chip is 880 μm×880 μm and the metal board area is 30 mm×32 mm with 3 mm thickness. The LED package is operated at the current of 11 A with 10 % duty cycle. To measure junction temperature, the forward voltage method is used. The metal board temperature is measured by attaching K-type thermocouple. Then, the thermal resistance from junction to metal board is calculated. For comparison, six identical LED packages are examined. Each LED package shows different thermal resistance from 0.4 K/W to 10.3 K/W. To investigate how the chips are well attached on the metal board, X-ray computed tomography (CT) images of the LEDs are taken and air gap areas are evaluated. The result shows that the thermal resistance increases with the increase of air gap area.