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Keywords: LED, Thermal Management, Thermal Pyrolytic Graphite
Light emitting diode (LED) is being rapidly adopted by the automotive headlight sector due to its efficiency, reliability, color and many other advantages. Changing from incandescent or high intensity discharge (HID) lighting to LED presents a new set of design challenges, especially thermal management of the LED junction temperature. Heat sink or heat spreader made of aluminum and copper are commonly used for extracting heat from the LEDs and dissipating it to the surroundings. With their thermal conductivity of 120 to 400 W/m-K, aluminum and copper based thermal management solutions limits the maximal power loading to LEDs and the design options. Typical practices to improve the heat sink efficiency include enlarging cross-section of heat path, increasing heat dissipation area, installing forced air cooling or liquid cooling, etc, which not only adding size and weight, but complexity and cost. On the other hand, Thermal Pyrolytic Graphite (TPG), a unique synthetic material produced by Momentive via chemical vapor deposition, contains millions of layers with highly-oriented stacked graphene planes and exhibits excellent in-plane thermal conductivity (>1500 W/m-K) and very low density (2.25g/cm^3). TPG-metal composites, including TC1050 Heat Spreader, TMP-EX Heat Sink, and TMP-FX Thermal Strap, simultaneously achieve high thermal conductivity from the TPG core and high mechanical strength from the metal shell. The study presented in this paper investigated the benefits of incorporating TPG into LED headlight assembly. Design configuration and power performance of an aftermarket LED headlight replacement kit was used as the baseline. Based on thermal resistance analysis, two components of the LED headlight assembly were highly modified to incorporate TPG solutions. Thermal simulation was conducted in parallel and successfully predicted the performance of each experimental heat sink, which facilitated design choices for subsequent prototypes. Our bench tests on the LED headlight prototypes, which incorporated TPG in various configurations, indicated: I.Replacing aluminum fins with metallized TPG plates (TMP-FX) reduced total system thermal resistance by 27%. II. Inserting a TPG core (TC1050) underneath LED dies achieved another 24% thermal resistance reduction. Our final study demonstrated that 2x of the LED power can be loaded to the assembly with TPG assisted heat dissipation at the two strategic locations. With current TMP product portfolio, Momentive has extended expertise and success from thermal management at the board level with TC1050 Heat Spreaders to the chip level with TMP-EX Heat Sinks and TMP-FX Thermal Straps. Integrating multiple TMP products together presents additional opportunities to maximize the heat dissipation in high power LED assemblies.
Wei Fan, Senior Materials Scientist
Momentive Performance Materials Inc.
Strongsville, OH

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