Author Topic: Does PCB Mask colour affect thermal performance?  (Read 2211 times)

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Offline equalizor

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Does PCB Mask colour affect thermal performance?
« on: February 08, 2021, 03:58:24 pm »
Hi everyone,

I recently made a video on my channel which was a teardown of a Dual Handle soldering station and someone commented that the reason that Black PCB mask is used on PCB's is because it provides better heat dissipation.

Actual quote :"The black solder mask is more than cosmetic. It is a thermal "heat sink" (or more accurately "Heat Spreader") to mitigate hot spots created by power components. It shows up in many higher quality AC Adapters used to charge mobile phones."

In my mind better heat dissipation on a PCB would be provided using via stitching and copper pours/pads, and that colour doesn't make a whole lot of difference, although I am not an expert in PCB design.

What do you guys think?

Cheers

Rob
 

Offline CJay

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Re: Does PCB Mask colour affect thermal performance?
« Reply #1 on: February 08, 2021, 04:03:36 pm »
Load of rubbish.
 

Offline tszaboo

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Re: Does PCB Mask colour affect thermal performance?
« Reply #2 on: February 08, 2021, 04:35:19 pm »
There is no difference between the materials of solder masks. The color is just an additive, sort of like the food coloring additives.
There will be a miniscule of difference between white and black PCB, for black body radiation. It is really small unless the temperature of the board is very high. Ignore it.
Solder mas is not a heat spreader, it conducts heat very badly.
Via stiching does help, but only in the first mm or so away from the component.
Copper pour helps a lot.
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Offline reboots

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Re: Does PCB Mask colour affect thermal performance?
« Reply #3 on: February 08, 2021, 05:13:47 pm »
Solder mask is an insulator. It will not aid in thermal dissipation. Leaving the copper bare would be more effective. You are correct that via stitching and copper pour will promote heat conduction and dissipation.

Whether color affects mask thickness or density, or if certain colors are more insulating than others, I can't say. Certainly some common mask pigments (e.g. yellow) seem less opaque.
 
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Offline nctnico

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Re: Does PCB Mask colour affect thermal performance?
« Reply #4 on: February 08, 2021, 08:16:49 pm »
Solder mask is an insulator. It will not aid in thermal dissipation. Leaving the copper bare would be more effective. You are correct that via stitching and copper pour will promote heat conduction and dissipation.
That is not necessarily true. The keyword is emissivity:
https://en.wikipedia.org/wiki/Emissivity

Added to that it is entirely possible that something that looks black to the human eye can have a totally different behaviour at different wavelengths. All in all you need to carefully study material properties and 'do the math' before making any final conclusion.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 
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Offline mikeselectricstuff

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Re: Does PCB Mask colour affect thermal performance?
« Reply #5 on: February 08, 2021, 08:52:50 pm »
If your PCB gets so hot  that emissivity of the resist makes a difference, it's probably running way too hot, even with matt black.
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Offline nctnico

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Re: Does PCB Mask colour affect thermal performance?
« Reply #6 on: February 08, 2021, 09:30:09 pm »
If your PCB gets so hot  that emissivity of the resist makes a difference, it's probably running way too hot, even with matt black.
The emissivity of bare metals is actually quite low https://www.engineeringtoolbox.com/emissivity-coefficients-d_447.html where plastics seem to have a much higher emissivity.

And the color of the solder mask can matter:
https://iopscience.iop.org/article/10.1088/1757-899X/734/1/012027/pdf
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline mikeselectricstuff

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Re: Does PCB Mask colour affect thermal performance?
« Reply #7 on: February 08, 2021, 10:41:55 pm »
If your PCB gets so hot  that emissivity of the resist makes a difference, it's probably running way too hot, even with matt black.
The emissivity of bare metals is actually quite low https://www.engineeringtoolbox.com/emissivity-coefficients-d_447.html where plastics seem to have a much higher emissivity.

And the color of the solder mask can matter:
https://iopscience.iop.org/article/10.1088/1757-899X/734/1/012027/pdf
But in space, radiation is the only way to get heat out, back on earth, convection is going to dominate at normal electronics-friendly sensible temperatures, so differences in emissivity won't make nealy as much difference
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Offline reboots

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Re: Does PCB Mask colour affect thermal performance?
« Reply #8 on: February 09, 2021, 08:19:01 pm »
Solder mask is an insulator. It will not aid in thermal dissipation. Leaving the copper bare would be more effective. You are correct that via stitching and copper pour will promote heat conduction and dissipation.
That is not necessarily true. The keyword is emissivity:
https://en.wikipedia.org/wiki/Emissivity
The emissivity of bare metals is actually quite low https://www.engineeringtoolbox.com/emissivity-coefficients-d_447.html where plastics seem to have a much higher emissivity.

And the color of the solder mask can matter:
https://iopscience.iop.org/article/10.1088/1757-899X/734/1/012027/pdf
I appear to be mistaken, and I accept the correction. This analysis offers additional evidence in favor of solder mask promoting thermal dissipation:

http://www.brysonics.com/pcb-thermal-resistance-some-unexpected-results/

Interestingly, the IOP paper you linked suggests that white solder mask is most effective in a satellite environment; possibly due to its reflectance of albedo radiation? Black, white, green and red were tested.
 

Offline penfold

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Re: Does PCB Mask colour affect thermal performance?
« Reply #9 on: February 09, 2021, 08:55:46 pm »
Even if there was a marginal effect (which I'm not really disputing, I'm just choosing that wording to make my argument sound more profound), I would suggest it would become significantly more marginal when the PCB is installed within an enclosure, the internal surface of which being able to reflect IR back at the board. I wonder if some coating could be applied that would produce a "reverse greenhouse effect"... of course at the detriment to the convection
 

Offline Kleinstein

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Re: Does PCB Mask colour affect thermal performance?
« Reply #10 on: February 09, 2021, 09:08:17 pm »
Most plastics are relatively good absorbers in the thermal IR range. The main parts to avoid are clean metal surfaces, like copper, gold or aluminum. Here the solder mask gives quite some improvement, but likely little difference between the colors. 
Crude estimates for the emissivity are something like 90% for the solder mask and maybe 1% for a clean copper or aluminum and 0.1% for gold.

There is not much one can do to improve the radiative exchange other than getting reasonable good absorbers on both sides - especially avoid the good reflectors. The only way to get higher is getting the parts very close, to less than a some 2 µm. This can give added near field effects.
 

Offline S. Petrukhin

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Re: Does PCB Mask colour affect thermal performance?
« Reply #11 on: February 11, 2021, 08:43:35 am »
When I was in school, I was told that black bodies radiate better.  :)

But this color must be black for the range you want to emit. Black in the visible spectrum appears to a person, but it may not be black for thermal radiation.

The explanation for this phenomenon was given by Planck, who introduced quantum theory.
And sorry for my English.
 
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Offline DaveEmrich

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Re: Does PCB Mask colour affect thermal performance?
« Reply #12 on: October 18, 2021, 05:43:47 am »
Hi there,

Actually that's almost completely wrong. Bare copper is THE WORST thing for _radiating_ away heat. The critical number is "emissivity" (which ranges from 0 to 1, or 0% to 100% if you like) and you want it as high as possible, ideally above 95%.

Yes, you want lots of copper to _conduct_ the heat way from your hot devices, but you want to cover as much as you can of that copper in soldermask to _radiate_ the heat off the board. And matte-black solder mask IS better than shiny green, although we're talking high 80%s to 95% so ...

That's also why the best heatsinks are black-anodized and matte finish, since this radiates as much heat away as possible. If shiny/bare metal was best at radiating heat, then heatsinks would be gold plated...

I am a circuit board engineer designing power-electronics and dealing with thermal dissipation in my day to day job. But in case you don't want to take my word for it  here is some reference material ...

http://www.brysonics.com/pcb-thermal-resistance-some-unexpected-results/

https://www.ti.com/lit/an/snva419c/snva419c.pdf

Cheers, Dave E.



 
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