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40 The PCB Design Magazine • October 2014 ods provided information that there was a thermal issue with the LED packages under test; however, only the JESD 51-51 compliant transient test method provided a hint about the loca- tion of the problem. As well as being useful for failure analysis, this method can be used to de- rive an appropriate compact LED model which, when inserted into a simulation tool, can pro- vide better predictions of LED operation. LED system design- ers will be able to rely on real measured component data, al- lowing them to make better judgments on their thermal de- signs. This capability will allow wider adoption and reduced costs with the energy-saving po- tential of LEDs. PCBDESIGN References 1. JEDEC Standard JESD51- 51, "Implementation of the Electrical Test Method for the Measurement of the Real Ther- mal Resistance and Impedance of Light-emitting Diodes with Exposed Cooling Surface," (April 2012). 2. JEDEC Standard JESD51- 52, "Guidelines for Combining CIE 127-2007 Total Flux Mea- surements with Thermal Mea- surements of LEDs with Exposed Cooling Surface," (April 2012). 3. JEDEC Standard JESD51- 14 "Transient Dual Interface Test Method for the Measurement of the Thermal Resistance Junction-To-Case of Semiconductor Devices with Heat Flow Through a Single Path," (November 2010). 4. B. Marovic, "Efficient and Accurate Ther- mal Simulation by Combining Thermal and Radiometric Characterized LEDs with Compu- tational Fluid Dynamics," International Sym- posium on Automotive Lighting, Sept. 2013, Darmstadt, Germany. Figure 4: an example of the calculation done in the CFD simula- tion software using the LED Compact Model of the luminous flux, at operating junction temperature for the LEDs in a luminaire. (Image courtesy of OptimalOptik Ltd. and Budapest university of Technology and Economics, Budapest, Hungary.) ThERMAL ChARACTERIzATION OF LEDS continues Dr. John Parry is electronics industry manager for the mechanical analysis division of Mentor Graphics. He serves on the JEDEC Thermal Standards Committee and on various conference committees and was General Chair of the SEMI-THErM 21 conference. article