Re: Green solder mask and heatsinking


"Phil Hobbs" <pcdhSpamMeSenseless@xxxxxxxxxxxxxxxxxx> wrote in
message news:490CB152.4070302@xxxxxxxxxxxxxxxxxxxxx
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.

Thanks for the confirmation. In that case, I wonder why many
manufacturers leave solder mask off ground planes that double as
heatsinks even when there's neither a clutter of solder points
nor a need to reinforce conductor cross-section with solder.

(The HS is for two 7812 regulators that together will dissipate
about 10W max. The copper plane will be thermally coupled to the
ICs via their ground leads and to a blackened extruded Al
heatsink via mounting bolts. I considered using a switched-mode
PSU but decided against it).


.

Relevant Pages

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  • Re: Green solder mask and heatsinking
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