Thermal impedance measurements of layered Metal Core PCB used in LED lighting

Methods of measuring the thermal impedance of Metal Core PCBs are analyzed. The ASTM D5470 method can measure the thermal conductivity of the insulated layer of MCPCBs, but cannot distinguish the contacting thermal resistance, which introduced during the measuring, and the boundary thermal resistance, arising from the layered structure of MCPCBs. Thus, it cannot measure the whole thermal impedance of MCPCBs, especially when these two thermal resistances are comparable. In principle, ASTM E1461 method is not applicable for measuring heterogeneous materials. Thereafter it should not be used to measure MCPCBs. Using a model based on the theory of heat diffusion across multilayer structure and the data measured by ASTM E1461 method, the whole thermal impedance of MCPCBs can be obtained. This method is quick, convenient and reliable, and there is no contacting with the sample during the measuring.