Re: Green solder mask and heatsinking
- From: Phil Hobbs <pcdhSpamMeSenseless@xxxxxxxxxxxxxxxxxx>
- Date: Sat, 01 Nov 2008 15:43:14 -0400
pcw1.cad@xxxxxxxxxxxx wrote:
On Nov 1, 7:24 pm, "pimpom" <pim...@xxxxxxxxxxxxxxx> wrote:Does anyone know something or point me to a web resource about
the heat radiating/insulating property of green solder mask?
I'm making two PCBs for a custom-built project and want the
finished boards to have a professional look. I've done the screen
printing and etching. One of the PCBs has a large (~8 sq.in.)
plain copper area to supplement the separate finned heatsink. All
soldering will be done by hand and from experience, I find it
difficult to get a nice finish covering even a couple of sq.in.
with a thin film of solder by hand (for corrosion protection).
The alternative would be to cover the heatsink area with green
solder mask along with the rest of the PCB. But I would like to
be able to estimate the loss of heat radiation. I'm not really
expecting precise figures as there are many variables, but I'll
be grateful for some indication other than a wild guess.
(Note: Without going into details at this time, let me assure you
that I don't have the alternative of ordering the PCBs from a
manufacturer. I'm doing everything myself).
Thanks in advance for any help.
Loss of radiation will be miniscule. I always cover my gound planes/
heat blocks with solder mask.
Heat *radiation* will be greatly improved, because the organic solder mask is highly absorbing in the thermal IR (say 5-15 microns wavelength) and therefore is an efficient emitter. (The second law of thermodynamics requires that the absorptivity and emissivity of any surface be the same at all wavelengths, because otherwise you could have heat spontaneously flowing from cold to hot, which can't happen.) Shiny metal is a very poor infrared radiator.
Heat transfer by convection, i.e. conduction to the air followed by mass motion of the heated air, won't be changed much, just as pcw1.cad says. (Puke one cad? What kind of name is that?) The reason is that natural convection is so lousy that a mil or two of plastic won't hurt it much.
Cheers,
Phil Hobbs
.
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