CarbAl (TM) Based Circuit Board for Power LED Packaging

The primary obstacle to readily implementing energy-saving LED lighting systems in established commercial and municipal lighting networks lies in dealing with the heat that is generated by high power LEDs. To produce the light output that is needed in commercial luminaries, high power LEDs are needed. State-of-the-art LEDs can consume in excess of 10 Watts each, and even at the efficiency levels of todays LEDs, the majority of that power is being converted to heat as a byproduct of the light generated in the semiconductor junction of the device. This heat is generated internal to the structure of the LED chip, so unlike a light bulb that radiates its heat; this heat needs to be mechanically conducted away from the LED junction as efficiently as possible to maintain proper operation of the LED. Rises in junction temperature in the LED result in color shift, reduced light output, and ultimately reduced life of the LED. Also, temperature fluctuation is one of major factors that cause LED color drift. For example, temperature fluctuations from 25 to 70C during operation lead to a color drift of up to uv = 0.03. This is equivalent to a factor of 6 above the perception threshold of the human eye for color differences. One way of reducing the amount of heat and stabilize temperature is to increase the number of LEDs in the array. For a given light output level, a larger number of LEDs allows them to be operated at a lower current level and subsequent power level. This moves the operation of the LED to a more efficient point on the Current vs. Light Output efficiency curve, so the Lumens per Watt increases and the amount of heat for a given level of light output is reduced. The high cost of these leading-edge LEDs makes increasing the LED count the less desirable option in most cases however, in a market with burgeoning competition. Beating the heat and keeping the cost down for a given design is the task of every LED lighting developer. In this DOE program, Applied Nanotech, Inc (ANI) proposes a novel approach to create the advanced high-performance power LED circuit board that can effectively dissipate heat generated by power LEDs and stabilize temperature to minimize color drift. Our approach begins with a highly thermal conductivity graphitic material, CarbAlTM. CarbAl, developed by ANI, can be derivatized using unique surface engineering techniques. These functionalized layers include high-thermal conductivity dielectric materials (printed AlN dielectric layer) as well as direct printed circuits using nano-Cu inks. The combination of high-performance CarbAl and functionalized layers provide considerable reduction in total thermal interfaces in a power LED package, greatly benefitting the heat dispassion, elimination of hot-spot, and temperature stabilization.