Thermal Siliconne for mount LED MCPCB

pavithra_uk · Mar 13, 2012

Is it ok to Mount MCPCB to Heat sink using Thermally conductive Siliconne ? It has conductivity of 1.55 W/MK.
LED Power is 2.5W (700mA x 3.3V Vfd)

Best suitable adhesive is Arctic Alumina thermal adhesive. but it unavailable in here. I have above Thermal silicone only.

CKOD · Mar 13, 2012

With only 2.5w on a star, you should be fine with silicone as long as youre screwing it down too so it has good compression to make for a nice thin bondline. Careful not to over-apply, youre just filling in irregularities in the metal, not giving it a cushion to float on

And with 2.5w, dont worry about sillyness like lapping mating surfaces etc either.

pavithra_uk · Mar 13, 2012

CKOD said:
With only 2.5w on a star, you should be fine with silicone as long as youre screwing it down too so it has good compression to make for a nice thin bondline. Careful not to over-apply, youre just filling in irregularities in the metal, not giving it a cushion to float on And with 2.5w, dont worry about sillyness like lapping mating surfaces etc either.

Thanks for your valuable reply

my idea is also same. apply some silicone and press MCPCB gently to form thin layer.

Im going to make small flashlight from 1" Aluminum tube. MCPCB is nearly same diameter as tube. so no room for screws.

AnAppleSnail · Mar 13, 2012

pavithra_uk said:
Thanks for your valuable reply

my idea is also same. apply some silicone and press MCPCB gently to form thin layer.

Im going to make small flashlight from 1" Aluminum tube. MCPCB is nearly same diameter as tube. so no room for screws.

Compression is important with the silicone compound. It's meant to sit between a pressed-down heatsink and a computer CPU, for example. If screws will not fit, perhaps you can deepen two of the cutouts so that the screws fit? Remember to isolate the screws from the contacts on top of the star.

If you can't or don't want to carve up your LED board, then maybe the construction of the light will provide this compression. If the reflector (May need to be electrically isolated from those contacts) is pressed in by the bezel, then that provides adequate protection. If you have an IR thermometer, try running this light as a test, turn it off, and gauge the temperature down the reflector. The light must be off or the photons will heat the sensor thermocouple, giving ludicrous results. If the LED doesn't get too hot, all is well.

pavithra_uk · Mar 13, 2012

AnAppleSnail said:
Compression is important with the silicone compound. It's meant to sit between a pressed-down heatsink and a computer CPU, for example. If screws will not fit, perhaps you can deepen two of the cutouts so that the screws fit? Remember to isolate the screws from the contacts on top of the star.

If you can't or don't want to carve up your LED board, then maybe the construction of the light will provide this compression. If the reflector (May need to be electrically isolated from those contacts) is pressed in by the bezel, then that provides adequate protection. If you have an IR thermometer, try running this light as a test, turn it off, and gauge the temperature down the reflector. The light must be off or the photons will heat the sensor thermocouple, giving ludicrous results. If the LED doesn't get too hot, all is well.

I have no IR thermometer to check temperature. I heard Junction temperature can be determine by forward voltage drop under constant current. so I did following simple test. here results;

LED was driven constant 700mA. I got forward voltage readings as soon as LED turn on and after 10 minutes. with MCPCB screw to heat sink with thermal paste & another one with silicone (same heat sink, LED, MCPCB used)

1. LED with thermal paste
LED Vfd=3.20V / After 10 minutes: 3.17V

2. LED with Silicone
LED Vfd=3.20 / After 10 minutes: 3.14V

Heat sink temperature is around 60-65C degrees. (measured by thermistor that found laptop battery packs

)

(Silicone = 1.55 W/MK, Thermal grease = 4 W/MK)

I have another idea too. Mount MCPCB with thermal paste and press it and apply some silicone or epoxy over MCPCB edge. is it good idea ?

AnAppleSnail · Mar 13, 2012

pavithra_uk said:
I have another idea too. Mount MCPCB with thermal paste and press it and apply some silicone or epoxy over MCPCB edge. is it good idea ?

I've done similar things, but didn't see much improvement. I say it's not worth the mess and trouble.

Thermal Siliconne for mount LED MCPCB

pavithra_uk

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CKOD

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pavithra_uk

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AnAppleSnail

Flashlight Enthusiast

pavithra_uk

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AnAppleSnail

Flashlight Enthusiast

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