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7/02/2020

Removing heat from High-power LEDs

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Removing heat from High-power LEDs can draw over 1 watt in a single LED. Most of the electrical power in a LED generates heat rather than light— approximately 70% heat and 30% light output. If the heat generated is not effectively removed, the LEDs will run at higher temperatures, which lowers their efficiency and decreases their lifespan, making the LED design less reliable. Thus, thermal management of high-power LEDs is a crucial area of the PCB designer’s research and development.

It is necessary to limit the junction temperature to a low enough temperature, typically about 110° C maximum, to ensure that the LED has a long, useful life. Temperature is a measurement of resident heat in an object; if you remove more generated heat, you therefore lower the die temperature. In printed circuits, the difficulty is compounded because we need high-voltage dielectric isolation between the copper traces and the copper or aluminum heat sink. We need a high thermal conductance laminate, and a low thermal impedance, three properties that are present in thermal laminates.

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   “It is necessary to limit the junction temperature to a low enough temperature, typically about 110°C maximum, to ensure that the LED has a long, useful life.”

To make the situation more complex, the physical size of the LED base
is quite small. In thermodynamics, heat removal area is king. To remove
the pinpoint LED heat easier, we need to design a circuit board that
spreads the heat out so the lower thermal impedance insulation laminate
supporting the copper traces can better move the heat to an attached
heat sink. We can use heavy copper traces and through-holes to create
a more efficient thermal spreader area around the LED base.

The heat will flow along the high conductive copper traces, essentially
increasing the effective size of the LED die. The larger heated area will be
more evenly distributed into the thermal insulation laminate below. The
more copper and thermal vias we can put in direct contact with the LED
die and its leads, the lower the LED’s temperature.

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