LEDs – everybody wants them
Light-emitting diodes, so-called "LEDs", are the lighting technology of the present – and the future. LEDs can now be found as part of virtually every lighting concept: whether in medical engineering, the automotive sector or furniture lighting and panel lights. The trend now is for ever greater luminosity, longer lifespan and use in extreme environments. LEDs must meet ever higher technological requirements, which may lead to losses in terms of colour stability, efficiency and service life.
When it comes to product life in particular, it is essential to know how the various materials interact when subjected to extreme operating temperatures and temperature fluctuations during switching processes. Mechanical tensions due to interactions between the various materials and resulting damage must be kept to an absolute minimum.
Together with Tridonic Jennersdorf GmbH the MCL explores the thermo-mechanical issues of white light LED modules. A white LED module consists of an LED chip, a transparent plastic capsule and 50 μm contact wires which are about as thin as a human hair. The component heats up during operation. This warming due to the different physical and mechanical properties of the materials does not occur evenly, however, resulting in thermo-mechanical interactions between the materials used, e.g. between the wire and the capsule. The resultant thermo-mechanical "stress zones" can lead to breaking of the contact wires and thus total failure of the LED module.
Greater Output through a new design and new materials
The aim of the project is to apply experimental methods and computer-aided thermomechanical simulation to investigate these critical stress zones in order to prevent potential component failure and thus increase product life. Verifying the reliability of the calculation models presents a particular challenge. The use of high resolution computer tomography (CT) provides a three-dimensional insight into the LED module.
The combination of thermomechanical simulation and high resolution computer tomography opens up new possibilities for developing more robust LED modules in the future. This paves the way for targeted materials development and optimised thermomechanical component design. Further research in this field will be undertaken in a recently launched project under the FFG "Production of the Future" programme in collaboration with the Graz University of Technology and Tridonic Jennersdorf GmbH.
According to a current market analysis, annual growth rates for LEDs are estimated at 5% until 2016 and subsequently 3% until 2020. The cutting-edge methods developed at the MCL provide a detailed understanding of thermomechanical interactions in white LEDs and can therefore be used to identify potential weaknesses within the module. The results of this research help to considerably increase LED lifespan through the improved selection of materials in terms of their thermal and mechanical properties.