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I have seen many claims of conformal coating helping for protection against, amongst many other things, extreme temperature. One such claim in here would be: Question regarding PCB coating

My understanding is that such coatings act as a relatively good thermal insulator; is that right? What I do not understand, however, is how they can be effective when the components themselves need to dissipate heat?

We use heat sinks with good thermal conductivity and large surface area to ensure heat can dissipate quickly, so long as the environment's temperature is lower. And if the environment is warm, then I can see how coatings could help insulate the board from the environment.

I'm probably missing something obvious, but how about conditions where we expect the environment and electronic component to warm up beyond its specified operating temperature limits?

In my specific scenario, I'm looking at PIC32MZ, probably the extended temperature range (-40 to 125 deg C), and thinking of having a system-level operation range that gets to about 110 deg C, and want a good tolerance margin. I could also do with using the industrial version of PCB components if I can get away with it.

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    \$\begingroup\$ You misunderstood the Question regarding PCB coating, it does not contain any claims about better thermal dissipation. The question was about durability of coating under high temperatures. Coating will not help to extend your temperature range. \$\endgroup\$ – Ale..chenski Sep 28 '16 at 21:28
  • \$\begingroup\$ I see. But the does conformal coating make thermal dissipation worse? \$\endgroup\$ – mehfoos yacoob Oct 2 '16 at 18:56
  • \$\begingroup\$ I am not sure about this. On one side, the extra layer of plastic on top of chips adds to thermal resistance from top to air. On the other side, adding extra plastic between pins and likely under chips would reduce thermal resistance to board, since plastic is a better conductor than air. So, I don 't know. \$\endgroup\$ – Ale..chenski Oct 2 '16 at 20:20
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They don't want you to know that all plastics are thermal insulators unless they contain metallic particles like alumina oxide and would be grey in colour.

For the automotive market, spray or dip conformal coatings are an essential process.

The epoxy used in IC's cases has better than average heat conduction in [W/m'K] but mainly it is selected for it's moisture seal resistance.

So how do you keep electronics cool in the engine compartment?

  • Well not likely by radiation.
  • More likely by baseplate conduction to the frame.
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  • \$\begingroup\$ So 'No', to the question, I presume? (Thanks for the relevant info) And by that logic, coating act as an insulator, so if applied directly to IC seal can make it warmer? It's meant for just bare PCB? \$\endgroup\$ – mehfoos yacoob Oct 2 '16 at 19:00
  • \$\begingroup\$ If external radiant heat is far greater than self heat, YES, otherwise NO and your PCB better be heatsinked if required to a frame. based on deg/W rise of package loss(W) Rjc plus heatsink resistance \$\endgroup\$ – Sunnyskyguy EE75 Oct 2 '16 at 19:04
  • \$\begingroup\$ Sorry, could you clarify the terminology? By 'Radiant heat' do you mean heat in the environmental? And by 'Self heat' do you mean heat from IC? \$\endgroup\$ – mehfoos yacoob Oct 2 '16 at 19:08
  • \$\begingroup\$ that is correct. ambient heat like an internal combustion engine \$\endgroup\$ – Sunnyskyguy EE75 Oct 2 '16 at 19:14
  • \$\begingroup\$ But even if radiant heat is far greater than self heat, isn't a temperature delta required for heat dissipation? Won't it accumulate and add up otherwise and lead to increase in temperature? I completely agree with conduction to frame, but I don't get how coatings cannot make things worse. \$\endgroup\$ – mehfoos yacoob Oct 2 '16 at 19:17
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Not always the conformal coating is applied just by spraying the entire board with painting. The industrial electronics is coated with different coatings on a CNC machine that sprays only the board, leaving the dissipating elements free.

https://www.youtube.com/watch?v=ZYajcsSralg

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  • \$\begingroup\$ Interesting video, thanks. What is striking that the depicted process is an obvious waste of time. The entire operation could take much less time if a plane regular pattern is used. Again, selective application of coating defies one of main purpose of coating - to provide a moisture-proof product. \$\endgroup\$ – Ale..chenski Oct 3 '16 at 14:59

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