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EMS Specialist MELECS presents efficient thermal management solution as an alternative to expensive Insulated Metal Substrates
High Brightness LEDs on FR4
Especially in the cost-sensitive and safety-conscious automotive business, this new solution could save costs significantly, Gerhard Neumann, Head of R&D of Melecs, is convinced: "Using this method, unsophisticated ancillary lamps like daytime running lights, indicators, fog lamps, etc can be manufactured at very low prices, maybe even below 10 Euro."
Until now, IMS or ceramic substrates are used in order to ensure thermal management for the high power density. However, those materials are very expensive and do have limitations. For cost reasons, driver electronics usually aren't mounted close to the LED on the same board which means separate boards with cables, connectors, SMT jumpers, etc. Assembling HB-LEDs together with their driver circuits on common FR4 substrate avoids all of those difficulties. Mr. Neumann explains: "The aim is achieving an optimal combination of design, performance and thermal management under the constraints of customer specifications".
Daytime running lamps without heat sink
MELECS unites Power-LEDs with driver electronics on a single FR4 board using its steel clamps that connect the printed circuit board to the lamp housing. The manufacturing process is similar to traditional PCB production and the clamps can easily be fitted. This requires very thin boards in order to minimize the thermal path from the LED to the heat sink. Tests have shown thicknesses between 0.7 and 0.8 mm to be optimal. At the same time, the thermal path should be as wide as possible so the extremely localized heat of the LED can dissipate as good as possible. The MELECS solution employs 70 to 105 µm copper on the external layer which allows for heat dissipation on an area of about 15 mm x 15 mm. Then, thermal vias in a 0.8 to 1 mm grid pattern conduct the heat through the FR4. The bottom as well as the top layer consists of thick copper, so there is only a small thermal contact resistance between board and heat sink.
At the same time, the steel clamps ensure safe thermal contact between the PCB copper layer and the thermoplastic resin of the lamp housing. Their elastic force compensates for possible shrinking, flowing, contracting or twisting. Furthermore, the housing material doesn't have to have higher thermal conductivity, so standard materials like PC ABS (polycarbonate acrylonitrile butadiene styrene) are sufficient. Housing and front screen can easily be friction-welded.
"Experiments showed that for example traditional daylight running lamps with four Luxeon Rebel LEDs by Philips Lumileds can even do without an aluminium heat sink", explains Mr. Neumann and remarks: "This even works for environmental temperatures up to 70 °C. MELECS can guarantee for the thermal contact to the steel clamps over the full lifetime of the light source."
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