Christian Herbold

Thermal improvements for high power UV LED clusters

We present a high power density UV LED module for a wavelength of 395 nm with an optical power density of 27.3 W/cm2. The module consists of 98 densely packed LED chips soldered onto an Al2O3 ceramic board. Thermal and optical measurements were conducted. The module was cooled by a forced air heat sink for the characterization experiments. A room temperature liquid gallium alloy was used as thermal interface material between substrate and heat sink with a TiN barrier layer to prevent corrosion. Further a technology to replace Al2O3 ceramics by aluminum as substrate is presented. An initial characterization shows that aluminum with a dielectric layer for electrical insulation is a competitive substrate material for efficient heat removal.

High power UV-LED-clusters on ceramic substrates

We present a high power density UV-LED module for a wavelength of 395 nm with an optical power density of 13.1 W/cm2. The module consists of 98 densely packed LED chips adhesively bonded to an Al2O3-ceramic board. Thermal simulations and measurements as well as optical measurements were conducted. The module was cooled by a forced air heat sink for the characterization experiments. A surface micro cooler with water as a coolant is proposed to improve thermal performance of the module. To drive the LED module, we developed an efficient current source powered directly from AC mains supply with integrated power factor correction using a single switching component.

Index matched fluidic packaging of high power UV LED clusters on aluminum substrates for improved optical output power

We present an improved cooling for a high power density UV LED module for a wavelength of 395 nm. The module consists of 98 LED chips soldered on a thick film printed alumina substrate on an area of 2.11 cm2. We investigated cooling by a commercial water cooler as well as by a surface micro cooler developed by our own. Further we describe a technology to replace alumina by aluminum as substrate material. A module consisting of 25 UV LEDs was optically characterized without and with liquid encapsulation. Finally we conducted numerical studies to develop an easily producible, sufficiently powerful, and robust water cooler. Based on the results we present a water cooler design with cooling channels embedded in the aluminum substrate of an LED module, removing the interface between LED substrate and heat sink.

High power density LED modules with silver sintering die attach on aluminum nitride substrates

Current research studies deal with the investigation of the thermal and optical properties of four LED modules on different substrate materials. The LED modules consist of arrays of 98 blue emitting LEDs with an emission wavelength of 457 nm within an area of 2.11 cm2. The modules are based on aluminum oxide or aluminum nitride substrates and the LED chips are attached by using a soldering or a pressureless silver sintering process. The modules are mounted on a high performance microstructured heat exchanger. By using the water driven cooler a maximum optical power density of 106.2 W/cm2 at a forward current of 2100 mA and 837.5 W electrical input power is achieved. A saturation of the optical power density over the input current due to thermal degradation is not observed.

Very high power density LED modules on aluminum substrates with embedded water cooling

We present optical measurements of an LED module consisting of 98 UV LEDs with an emission wavelength of 395 nm soldered onto a ceramic substrate within an area of 211 mm2. The module is mounted to a high performance mi-crostructured water cooler. This cooler enables a maximum optical power density of 45.9 W/cm2 at a forward current of 1350 mA and 447.9 W electrical input power. Further we describe the development of an LED module based on an aluminum substrate with thick film printed insulator and conductor layers and embedded, meander shaped water cooling channels. Numerical and experimental studies with different channel cross-sections are shown. Finally experimental results for this kind of UV LED module with 98 LED chips are presented and compared to the ceramic based module.

Blue and white light emitting high power density LED modules

We present optical measurements of an optimized LED module consisting of 98 blue light emitting LED chips silver-sintered onto an aluminum nitride ceramic substrate within an area of 211 mm2. The module is cooled by a high performance microstructured water cooler. Using this cooler a maximum optical power density of 111.6 W/cm2 at a forward current of 3003 mA and 1255.6 W electrical input power could be achieved. Placing sintered glass discs doped with yellow phosphor in different concentrations in front of the module, white light with correlated color temperatures between 3600 K and 4200 K was produced.

UV-LED Module Design with Maximum Power Density

We designed an UV-LED module with LEDs mounted as close as possible to each other to achieve the maximum optical output. Resulting from this the heat dissipation density rises up to 61 Wcm-2.