Thermal Grease Application Method

robincnn

Well-Known Member
TIM is applied to heatsink or cob ? Both or either ?
Saw a bridgelux video for thermal paste application in some thread. Can't find it.

Edit: found it
salmonetin page 42
Heatsinks for DIY LED lamps
 
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Doer

Well-Known Member
There are polished transfer surfaces, like CPUs and there are sadly pitted surfaces like the Cree Ceramic. And we are either concerned with the very lowest impedance possible or we are aren't.

So, dab and smush is likely to get you a burned COB array, if not very lucky. And too much interface material is similar to no interface material and will likely get you a burned COB array, if not very lucky.

What we are discussing then, is throwing away electrons we paid for. Somewhere in the range is a theoretical sweet spot, Momma Bear. Not too much electron loss, with minimized chance of smoking the array. We know heat and electron leakage are related to current, but the hotter the junction the more the energy is lost that did not turn into photons.
 
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stardustsailor

Well-Known Member
Cree CXA 3070 ( 3000K -80Ra ) for 2500 hours at 1.5 A , Ta= 35 C.
Results of Poorly applied TIM
(Arctic silver 5 ) and overtighten IDEAL holder ..

Temperature of LES was well beyond 100 C .
Still none of the COBs chips was fried .
COB WAS fully operational .
Until dissection was done ...


P5242848.JPG

P5242836.JPG


P5242849.JPG

P5242851.JPG
^^^ Epoxy glued chips on the ceramic board.
 

robincnn

Well-Known Member
Cree CXA 3070 ( 3000K -80Ra ) for 2500 hours at 1.5 A , Ta= 35 C.
Results of Poorly applied TIM
(Arctic silver 5 ) and overtighten IDEAL holder ..

Temperature of LES was well beyond 100 C .
Still none of the COBs chips was fried .
COB WAS fully operational .
Until dissection was done ...


View attachment 3426017

View attachment 3426019


View attachment 3426020

View attachment 3426021
^^^ Epoxy glued chips on the ceramic board.
photo.JPG
You can cut a hole in the middle of heatsink. No TIM required, No holder overtighten issue and it works perfectly fine.
But you will need to use this advanced Chinese COB.
led_module_full_color_cob_led_array.jpg
 

Bhookus

Member
So how many tubes of arctic silver 5 should I order for a 24 cob(cxa 3070) build?
 
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robincnn

Well-Known Member
You might try outlining the Cob on the heatsink surface before applying the paste. Done this way you would only need to insure the contact was square with the TIM layer and aim for the circle.
I aligned stencil with back of Vero 29 and marked the position of 4 hole position on stincil. Then aligned the 4 holes in stencil with the 4 holes on heatsink and applied TIM. Then Vero on top and moved it a little back and forth to even out TIM.

IMG_3530.JPG
 

littlejacob

Well-Known Member
Bonjour
When i read all the problems you can get with TIM when you don't use it the good way...I think I should go with thermopads it will be better for a noob like me (and i don't want to fry my 3590's)
Thanks for sharing
 

Tazbud

Well-Known Member
Are pads up to the heat from cobs? Ive got some for my Vero 18's at low power but baulked as I don't see them mentioned or tested?

Is the reflector with 4 contact points and 2 screws a good alternative to putting 2 screws through vero? I can't see why it wouldn't be as good as screwing or taping vero.
 

beodrone

Active Member
So far in my testing the pads work just fine. I don't see any difference in temperatures when comparing with fixtures that I used thermal paste on. The large fixture I am testing has 18 COBS and runs great.

At the end of the day I feel better about using the thermal tape vs misusing TIM paste.
 

Tazbud

Well-Known Member
Ah, right, see the mention of 3m Tape earlier. I thought it was a one sided tape but its TIM.
You'd need to measure the temp increase on the LES to know temp differences.
 

Abiqua

Well-Known Member
I wanna make a stencil using a 3d printer, with a slide, like a silk screen printer, to smooth the TIM inside the stencil to a certain height, then you could also determine, how much you need for each cob ^^^^
Now I just have to buy a 3d printer :)

:peace: :joint:
 

salmonetin

Well-Known Member
Cree CXA 3070 ( 3000K -80Ra ) for 2500 hours at 1.5 A , Ta= 35 C.
Results of Poorly applied TIM
(Arctic silver 5 ) and overtighten IDEAL holder ..

Temperature of LES was well beyond 100 C .
Still none of the COBs chips was fried .
COB WAS fully operational .
Until dissection was done ...


View attachment 3426017

View attachment 3426019


View attachment 3426020

View attachment 3426021
^^^ Epoxy glued chips on the ceramic board.
...decoding... then for my pov the cobs leds needs temp protection against hot temps... driver dimmed or totaly off....external driver temp sensor way... sens leds temps...(maybe thermistor way)...

...maybe similar way to protect fan failure for hot temps....with temp sensor too... ;)

...but the best temp sensor location for cobs its for thermocouples... ...maybe a well calibrated thermistor near the cob not affected for the light helps too... ...from my inexpert pov...;)

...for the rest... aplication method... only needs practice... blade or stencil ... or both... some Silver 5.... sds prefered ;)...and practice... from my pov... ...the good thermal pads are expensive way... silver 5 a blade or one stencil arent not expensives ways...

..ultra thin layer...0.050 mm to 0.150 mm?... ...TIM thicknesses for LED arrays typically range from 0.050 mm to 0.500 mm...

...from my pov ...on both ways pads or grease... better go with a temp protection for leds on it... drivers with auxiliary external temp sensor for monitoring the led temps... some models dimming ....rest go on total off...on high external temps... ...:idea: or one auxiliary digital thermostat controller (not expensive too)...

pd... from my pov ...i recommend thermal grease way...not the thermal pad way....

...Wilson time to shout my mouth ....bros gone...only read method actived... back to the cavern... ...what a summer ehh...:evil:

:peace:

saludos
 
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