THELED - THELED - [Original in Deutsch: Entwicklung neuer thermomechanischer Konzepte für die kosteneffiziente Herstellung von LED-Baugruppen]

Project: Research project

Description

The need for more powerful white light LED devices for illumination purposes is steadily increasing. Luminous flux of 15 lm/mm² represent standard technology, the project targets for 40 lm/mm². However higher light power output is limited due to the onset of higher temperatures in the LED devices, which deteriorate colour stability, efficiency and lifetime. Hence thermal management is of major importance in the functional elements of a LED which is formed by a complex compound of materials (chip, colour conversion layer, electrical connectors, PCBs, packaging). Since the major part of the thermal energy is released in the LEDs junction or in the colour conversion layer (CCL), the CCL (usually a polymer compound) must have a high thermal conductivity. In addition the device experiences numerous switching cycles in its later application which lead to cyclic thermo-mechanic stresses in the device. Without proper adoption of the thermo-mechanical material properties and careful choice of the corresponding design parameters one will have to face damages and complete device failures. Thus important research and reliability activities to complete the project’s targets comprise (i) the synthesis of functionalized filler materials via the “Stöbermethod” to optimize the thermal management, (ii) the formulation of processes for the production of a highly thermal conductive material compound for colour conversion consisting of a matrix material (usually silicone), components containing phosphor compounds for the colour conversion and suitable filler materials. The produced material must fulfill optical, chemical, rheological, thermo-mechanical and process-technological criteria. Optical investigations via spectrometry, thermo-mechanical measurements involving DMA, DSC, rheology, UV-tests for chemical stability and studies for the kinetics of polymerization have to be performed to this purpose.
In the next step follows (iii) the investigation of thermo-mechanical interactions of this material compound and the rest of the system (especially the electrical wiring) using computer aided tools (FEM multiphysics simulation). This will already result in an optimized choice of the materials with respect to thermal and mechanical properties of the later product as well as tuned system design- and process parameters (curing) to minimize residual stresses in the system after production. Further survey focuses on (iv) the thermo-mechanical robustness of the complete material compound (the LED-device) by subjecting it to a thorough dynamic thermo-mechanical analysis. Combined mechanical multimode-testing and synchronously applying cyclic thermal and mechanical stresses will enable qualitative and quantitative conclusions on the onset of possible design weaknesses and reliability problems. The last workpackage (v) finally deals with the cooling efficiency of the product design by applying a thermal impedance analysis. In addition thermal impedance analysis will be used to monitor the stability of critical process- and product parameters by their impact on thermal device performance. Main result of the project is a stable, cost efficient and validated production process for high power LEDs delivering patentable knowledge on the production of specialized material compounds for colour conversion and sound knowledge based design criteria on the construction of new power LED designs shortening time to marketing considerably.
StatusFinished
Effective start/end date1/02/1431/01/16