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Li98 Thermally Conductive Adhesive Tape for LED Lighting Applications Slide 5

The efficiency of solid-state lighting devices strongly depends on the junction temperature. A strong argument by solid state lighting advocates is the long life of the LEDs, which results in cheaper and more reliable illumination systems. Current LEDs are more sensitive to temperature than standard solid-state electronic components so more attention must be paid to the thermal architecture. Current high brightness LED designs have begun to migrate away from 5 mm lamp style packaging into custom packages better designed for heat transfer. The required low junction temperature of the LED demands thermally efficient systems design. For example, a 10 W system in a 50°C ambient environment with a design goal of 100°C at the heat sink base requires a 5 K/W heat sink resistance. This resistance normally has to be achieved with low cost, passive, orientation insensitive, and reliable solutions. Typical incandescent lighting systems use both radiation and natural convection to achieve successful thermal management. Due to extremely high filament temperatures, thermal radiation is dominant. On the other hand, solid-state lighting systems are different than conventional lighting systems due to tight junction temperature requirements. Therefore a typical thermal design for an LED system revolves around efficient LED packaging, and an efficient heat transfer to ambient. LED packages must successfully conduct heat away from the chip to the heat sink. Standard heat sink materials with conductivities of 75 to 200 W/m-K are suitable for system level thermal management. Often, if a material with a lower thermal conductivity is used, the design will demand either shortening the length of the path or increasing the heat transfer area. Sometimes the conduction part of the thermal path consists of several parts that are held together in various ways. These joints between parts create solid-to-solid thermal interfaces causing additional thermal contact resistances. Surface finishes of each part and the contact pressures are the primary variables that affect the thermal interface resistances. Silicone based gap-filling, thermally conductive tapes, or phase change materials may be used to create intimate contact.

PTM Published on: 2013-06-07