Characterization of the thermal impedance of high–power LED assembly based on innovative printed circuit board technology

We present a method of dynamic thermal characterization of an entire test assembly, consisting of high-power Light Emitting Diodes (LED) and a printed circuit board (PCB) by measuring the thermal response on a power-on-step function and describing the thermal impedance with a Foster RC network. For this purpose, we record temporal temperature functions on test assemblies during pulse load experiments under defined initial and boundary conditions (the assemblies were horizontally positioned under free air in a test chamber), establish the LEDs' junction temperature-versus-time functions for known power functions and calibrate the parameters of the Foster RC network. Moreover, we reveal connections between design parameters (conductor layout, thermal via geometry, and PCB material) and the thermal impedance of the assembly. The method allows the user to predict the LED's junction temperature as transient thermal response on an arbitrary pulse load function (as e.g. flashes with different intensity, duration and repetition rate) with low effort.