Effect of thermal conduction path deficiency on thermal properties of LEDs package

•A numerical study is made concerning deficient thermal conduction path of LED lamp.•Deficient thermal path affects LED thermal properties even with efficient heat sink.•Junction temperature exceeds 120°C for an air layer thickness ε>150μm.•No indication from the heat sink temperature about the deficient thermal path.•The deficient path effect is more pronounced for lower effective thermal conductivity. This paper presents the details of a numerical study of the LEDs thermal conduction path deficiency. A three-dimensional numerical modeling using COMSOL Multiphysics® simulation software has been developed. The model was then validated by the literature, showed a good agreement. The effect of the number of LED-chips put on substrate was studied since it can affect the junction temperature and participate severely on the LED degradation. In addition, when there is trouble in the LED package, junction temperature can increase widely with no indication from the heat sink temperature, even with an efficient heat sink design. To justify this fact, a study of the effect of a deficient thermal conduction path between the heat sink and the thermal grease was performed by two methods: adding an air layer between the TIM and the heat sink, and modifying the effective thermal conductivity of the TIM. Its effects on the junction temperature, the heat sink average temperature, the total thermal resistance and the luminous flux was also investigated and it was found that a deficient thermal path affects severely the thermal properties of LED package even with an efficient heat sink.