The patent's assignee is
News editors obtained the following quote from the background information supplied by the inventors: "This invention relates to the thermal management of light emitting diode (LED) based lighting systems.
"With higher power LED applications, thermal management is becoming a critical issue. Without adequate thermal management, the temperature of an LED package can rise significantly. This rise in temperature can cause changes in the output wavelength of light, yellowing of lens, breaking of wire bonds, delamination, and internal solder joint detachment. The final outcome may be a catastrophic failure of the LED device.
"There are three mechanisms for dissipating thermal energy from an LED: conduction, radiation, and convection. Conduction occurs when LED chips, the mechanical structure of the LEDs, the LED mounting structure (such as printed circuit boards), and the light fixture housing are placed in physical contact with one another. Physical contact with the LED is generally optimized to provide electrical power and mechanical support. Traditional means of providing electrical and mechanical contact between LEDs and the light fixture provide poor means of conduction between the LEDs and external light fixture surfaces (such as die cast housing). One disadvantage of using a thermally conductive structure within the light fixture envelope is that it allows dissipation of heat into the enclosure, which is generally sealed. This effectively raises the ambient temperature of the air surrounding the LEDs, thus compounding thermal related failures.
"Radiation is the movement of energy from one point to another via electromagnetic propagation. Much of the radiant energy escapes the light fixture through the clear optical elements (light emitting zones, lenses, etc) and reflectors, which are designed to redirect the radiant energy (visible light in particular) out of the light fixture according to the needs of the application. The radiant energy that does not escape through the lenses is absorbed by the various materials within the light fixture and converted into heat.
"Convection occurs at any surface exposed to air, but may be limited by the amount of air movement near the emitting surface, the surface area available for dissipation, and the difference between the temperature of the emitting surface and the surrounding air. In many cases, the light fixture is enclosed further restricting airflow around the LEDs. In the case of an enclosed light fixture, heat generated by the LEDs is transferred by convection to the air within the enclosure, but cannot escape the boundaries of the enclosure. As a result, the air within the enclosure experiences a build up of heat, which elevates lamp and light fixture temperatures and may lead to heat related failures.
"Heat transfer between the LED board and the heat sink is through a fabricated thermal interface pad. Conventional heat sinks are often formed, or stamped from metals including copper and aluminum, in an array of shapes. Normally they have a flat surface or recessed cavity into which the LED board is attached. Prior to attaching the heat sink, a die cut fabricated thermal pad is placed between the heat sink and the LED board.
"This invention pertains to a novel method of thermal management of the LED package. Instead of using a fabricated thermal pad, a thin layer of curable thermal management composition is printed or dispensed directly on the LED board or the heat sink. The thermal management composition can either (1) be pre-cured on the LED board or the heat sink with a room or low temperature cure prior to attaching the LED board and the heat sink or (2) attached to either the LED board or heat sink, followed by attaching the LED board and heat sink and cured over time in between the LED board and the heat sink."
As a supplement to the background information on this patent application, VerticalNews correspondents also obtained the inventors' summary information for this patent application: "This invention is directed to a method for applying a thermal management composition between an LED mounted circuit board and a heat sink, where the LED mounted circuit board comprises a substrate having a first surface with at least one LED mounted thereto and a second surface opposite the first surface, the method comprising the steps of;
"(a) applying a deposit of a thermal management composition onto either the second surface of the LED mounted circuit board or onto a surface of the heat sink, through a deposition tool having at least one aperture, where the at least one aperture has a perimeter surrounded by sidewalls, where the sidewalls have heights, where the heights are reduced around at least a portion of the perimeter of the apertures on the deposition tool as compared to the average height of the deposition tool and
"(b) securing the LED mounted circuit board and the heat sink wherein the thermal management composition resides between the second surface of the LED mounted circuit board and the surface of the heat sink.
"In one embodiment, the thermal management composition is cured after step (b) and in another embodiment, the thermal management composition is cured before step (b).
DESCRIPTION OF THE DRAWINGS
"FIG. 1 is a schematic view of a LED mounted circuit board, a thermal management composition, and a heat sink prior to assembly, according to the present invention;
"FIG. 2 is a view of a LED mounted circuit board.
"FIG. 3 is a view of a heat sink.
"FIG. 4a shows a top view of a down-step stencil useful in the method of this invention.
"FIG. 4b shows a top view of a portion of the stencil in FIG. 4a.
"FIG. 4c is a side cross sectional view taken along line A of the portion of the stencil in FIG. 4b.
"FIG. 4d is a side cross sectional view taken along line B of the portion of the stencil in FIG. 4b."
For additional information on this patent application, see: Becker,
Keywords for this news article include: Electronics, Circuit Board,
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