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# thermal design LED PCB

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#### ekozo

##### Newbie level 4
Hi

İ design LED PCB. İ have a question thermal relevant. which material (FR4,CEM1, Aluminum) have to use. Example: i desgn a pcb for 6W each led power dissapation 250mW and my PCB area is 100cm2 What should be material for best cooling. have it rules or formula. i am waiting for your help

Hi,

6W each led power dissapation 250mW
with a 6W LED i expect the power dissipation to be also almost 6W.

Some power will be transformed into light the remainig power will be transformed into heat. This will be the biggest part.
Maybe you have additional parts like LED driver or any resistor.. then these will additionally dissipate power.

Klaus

The losses due to light emission should be negligible, and the power consumption of the LED can be took solely on the current across its terminals against its drop voltage.

Even assuming that the OP is referring to a continuous operation ( not pulsed ), the power density over this sufrace size seems feasible to operate at the standard FR4 PCB if the footprint is properly clear of the solder mask and covered by solder finishing. An additional care to draw several vias spreaded along the die device could also disperse the heat towards the opposite side.

i wonder. how many watt which can i use material at limited area. it should be a formula.

no formula, it depend on the thermal environment, whether fan or water cooling is there, whether or not you have air vent in the enclosure, whether you have nice finned heatsink to sit the fr4 on etc etc.

I agree, formulas and graphs are excellent methods for an ordinary estimation, but nowadays there are tools that can perform thermal analysis taking into account several parameters, such as the geometry involved, heating transfer attributes, etc...providing acceptable results.

No simple formula, but as a starting point 0.5mW per centimeter square per degree celcius is acceptable for flat horizontal plates. Since your board is 100cm sq. the average power handling should be 50mW per degree celcius and a total rise of 6/.05 = 120C.
FR4 boards should be ok if you use thermal vias and a small heat sink at the opposite side of the board.

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