Gordon Elger is a research professor at the university of Applied Science in Ingolstadt for microelectronic packaging and manufacturing technologies. His research team is focusing on LED and high power electronic packaging for automotive application and development of measurement and test methods for reliability and quality insurance. In especially one focus is transient thermal testing and heat management. Gordon Elger made his PhD at the Free University of Berlin and worked afterwards at different companies and institutes in the field of optoelectronic, MEMS, HF and LED packaging (Royal Philips, Hymite GmbH, Fraunhofer IZM).
Automatic Panel Level Transient Thermal Tester
Because degradation of LED is temperature driven, the thermal resistance junction to case (Rth) is an important parameter for LEDs. The dominating test method for the thermal resistance is transient thermal testing. However transient thermal testing is presently still work and time consuming and not automated. In the paper an automatic panel level thermal tester is presented. The tester targets to ease thermal testing during reliability assessment and for production inspection. Typical application are LED dies mounted first level on ceramic tiles or LED packages mounted on printed circuit board panels. The LED panel is placed on the temperature controlled table to keep the LED panel on constant temperature. The measurement electronic with 4-point probes are mounted on an xyz-system. The position of the electrical test pads of the LEDs are read into the machine.
To resolve the thermal resistance between the LED die and the heat spreader the forward voltage of the LEDs after current switching need to be measured as early as possible. The current source allows very fast switching below a microsecond and the detection current is stabilized within 1µs. By the short impedance matched cables the dead time is solely limited by the diffusion capacity of the LEDs. Signal amplifiers have an appropriate bandwidth to allow a sampling with 10MHz sampling frequency. For thermal resistance calculation the k-factor free relative thermal resistance measurement method published in  is applied. Real Rth values are calculated by a set of calibrated reference samples. The measurement signal of the LED under test is normalized to the known calibrated samples and the product of k-factor and thermal load of the sample is calculated.
The automatic tester is demonstrated using LED test board-panels. The thermal resistance of chip size package CSP LEDs and ceramic LED packages is measured automatically. The thermal resistance measured with the automated tester is compared to the thermal resistance obtained by standard measurement, i.e. measuring the k-factor and the optical load.
 Transient thermal analysis as measurement method for IC package structural integrity, A. Hanß, M. Schmid, E Liu, G. Elger, Chinese Physics B 24(6)068105, June 2015