Dr. Franz Schrank

Tridonic, Head of Research & Technology

Dr. Franz Schrank

Tridonic, Head of Research & Technology

Biography

1979 – 1984   Study of technical chemistry at the TU Graz
1984 – 1989   Ph.D. study at the institute of inorganic chemistry at the TU Graz
1984 – 1990   Assistant professor at the institute of inorganic chemistry at the TU Graz
1990 – 2002   Development engineer at Epcos OHG
2002 – 2012   Head of chemical engineering at Lumitech Produktion und Entwicklung GmbH


Design, Substrates and Processes for the Production of High Performance LED Flip Chip Modules

Due to the fast development of markets for “solid state lighting”, all major producers of lighting systems are competing in terms of efficiency and cost targets. The requirements for next generation of high efficacy and reliable LED modules will expand the current state of the art in terms of illumination density, efficacy and correlated color temperature of 3000K and CRI80 and switching stability up to 250.000 cycles. These requests lead to rising demands on the thermal, mechanical and electrical stability of the whole LED-module. In this paper we report the development of an innovative concept for integrated LED systems. The high performance LED module consists of flip chip LEDs coated with a phosphor conversion layer assembled directly on a PCB via joining technologies, such as silver sintering or soldering. Therefore, materials and processes for contacting the LED chips on the substrates were investigated. Finite element simulations for the thermal management were performed to facilitate and fasten up the development of this innovative LED module design.

There are several suppliers for flip chip LEDs. Criteria for the selection of applicable components was the availability as a series product, the process capability, the light flux, the wall plug efficiency and of course the price. Based on these framework, three different types of chips were used for a performance check, which was carried out on high performance modules with high chip density. The flip chip LEDs were mounted on a fourfold cluster with small gap (less than 200µm) between the LEDs. The substrate was based on the Haeusermann HSMtec technology, which had to be redesigned, regarding the thermal behavior, to fulfill the expanded requirements on increasing chip density. In addition, a screening of thermal interface material (TIM) was performed and evaluated.

Both the radiant power of the blue chips and the light flux of the white light emitting modules are presented as the optical performance data. The de-heating of the color conversion element of the LED module was an issue in terms of its thermal management. Overcoming this challenge, the thickness of the color conversion layer was reduced with a simultaneously increased thermal conductivity. Therefore, three different approaches were proposed: 1) a simple increase of the amount of phosphor particles, 2) an adding of transparent fillers with higher thermal conductivity or 3) a binder material with higher thermal conductivity. Several technologies, considering the phosphor conversion layer, such as screen printing, spraying and jetting were tested, aiming for a thin conformal coating. The impact of the substrates, the bonding technologies and the set-up of the color conversion element was used for the investigation of the developed LED module.

Co-authors: F. Janisch-Lang1, S. Hoerth2, L. Goullon3, M. Hutter3, R. Hammer4, J. Magnien4, L. Mitterhuber4, E. Kraker4

  1. Tridonic Jennersdorf GmbH, Jennersdorf, Austria
  2. Haeusermann GmbH, Gars am Kamp, Austria
  3. Fraunhofer-Gesellschaft, Institut für Zuverlässigkeit und Mikrointegration, Berlin, Germany
  4. Materials Center Leoben Forschung GmbH, Leoben, Austria

Acknowledgement
Financial support by the Austrian Federal Government (in particular from Bundesministerium für Verkehr, Innovation und Technologie) represented by Österreichische Forschungsförderungsgesellschaft mbH within the framework of the „7. Ausschreibung Produktion der Zukunft nat. Projekte“ Programme (project number: 848574 project name: FlipTheLED) is gratefully acknowledged.

All session by Dr. Franz Schrank

Session 2

13:00 - 14:30
SEESTUDIO, SEEFOYER, PROPTER HOMINES
LED professional Symposium +Expo
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