20 April 2006 Multi-chip color variable LED linear modules
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In this paper we report on a multi-chip color variable LED linear module with new concepts of optics design, free encapsulation, mechanical assembly and color control. Six dice are mounted close together on a substrate and combined with a faceted dielectric collimator to shape the light output. To achieve a very slim optical collimator (with minimal thickness), we combine a mechanical reflector with a total intern reflection (TIR) collimator. One of the bottlenecks in LED module design is the very high coefficient of thermal expansion (CTE) for organic optical materials (encapsulant). This material is needed to make good optical contact between LED-chip and surrounding optical system. Therefore, it is important that the design can handle large volume changes of the encapsulant during LED operation whilst maintaining good and stable optical performance. Furthermore, the encapsulant needs to be soft to avoid high stresses on fragile components (e.g. bond wires). These problems are solved in our module. To overcome variations in the color of the light output due to temperature changes and ageing, this module is equipped with a temperature and a light sensor. The signals of these sensors are supplied to a color control algorithm, which changes the power levels to each LED color in the appropriate way. This algorithm is capable of reducing the color error Δu'v' from 0.022 (in open loop) to 0.005 for a temperature change of 50 degrees Celsius. Cooling of the linear module is based on natural convection. The operation temperature of the housing is about 300C above ambient temperature. Variable material combinations in the thermal path from the junction to the house have been modeled in order to minimize the internal thermal resistance. A prototype is made and optical performance is measured as well. The optical efficiency of the module is about 75%.
© (2006) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Lingli Wang, Lingli Wang, Martijn Riemeijer, Martijn Riemeijer, Georges Calon, Georges Calon, Peter Deurenberg, Peter Deurenberg, Theo Treurniet, Theo Treurniet, Edwin van Lier, Edwin van Lier, Johan Ansems, Johan Ansems, Oscar Chao, Oscar Chao, Virginie Mercier, Virginie Mercier, Koen van Os, Koen van Os, Gerard Lijten, Gerard Lijten, "Multi-chip color variable LED linear modules", Proc. SPIE 6183, Integrated Optics, Silicon Photonics, and Photonic Integrated Circuits, 618322 (20 April 2006); doi: 10.1117/12.662666; https://doi.org/10.1117/12.662666


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