Influence of Solder Mask on PCB's Thermal Radiation

I'm not sure that is entirely true, but you can correct me if I am wrong.

I do know of surface mount components (typically power related) that rely on large pads or copper flooded areas to act as heat sinks.

Signal traces are another matter and typically play no role in thermal dissipation, but these thermal pads do not get a solder mask anyways, so the original question is probably not applicable unless they are doing something extraordinary with their design. In which case consulting a field application engineer for the part in question is the best recourse.

What you say is true, to some extent. That does not mean that solder mask would reduce the thermal radiation of the copper pads by any measurable amount. And, since we don't know if the board is forced air cooled, convection may not be the primary means of heat removal.

We also used to build very large heat sink areas into sub-layers of multilayer boards that were isolated electrically from the heat generating components.

Those boards were also fully coated with some type of conformal coating, often as thick as .005", or thicker.

So, I still say it doesn't matter.

Hi redfred. As AH said (#6), I'm talking about large copper areas instead of small traces. These large areas (pads or planes) are used as "heatsinks" for power components. So, my question was: what if such a copper area is covered with solder mask? Is there any significant influence on the heat transfer from the copper to the environment?

Anyway, it seems that this influence is very small and it can be ignored (and you were right about that).

[Btw, when I use such copper pads for heat transfer, I take care these pads to be exposed (without solder mask) for better results. However, I'm trying to estimate a situation on a PCB which is not my design.]

Answer: No.

However, it is typical to simply leave those areas tinned.

Having been in the PWB equipment and solder mask/resist/etch chemistry business for 10 years and in electronic packaging/vibration and protective coatings for aerospace electronics industry for 15 years, including satellite electronics where there is no convective cooling, I can tell you that it is not an issue I have ever heard discussed before.

You'd need to look at not only thermal conductivity but absorptivity and emissivity in the particular environment.

I'd disregard it, out of hand.

That might be why she can't find it on the internet!

SolarEagle, thank you for the links. Especially the last one is very useful in general.

Indeed, it seems that the solder mask has a very small influence to the heat transfer (convection) from the PCB to the environment (especially for a large PCB area) and it can be ignored.

Agreeing that classic silk screen in PCB has no significant influence on thermal radiation, new, coloured silk screens that can be from reflective white to opaque black, when things get tight thermal-wise as in many... squeezed to fit applications, well, a few degrees could mean problems. And I suppose Solder Mask IR transparency, and reflectivity compared to plain, varnished or shiny tinned copper could give measurable temp differences, up or even down in some cases. S.M.

Thank you all for your answers. I couldn't reply earlier because I couldn't have access to any of the CR4's pages. (A temporary problem of the CR4's server I suppose.)