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.
If this is critical, I'd do the experiment and measure the
effect. I
am assuming you know how to measure temperature with a forward
biased
diode on the chip in question. I know when we characterized
"copper"
heatsinks at Maxim, it was without soldermask simply because
board
grinders were used.
Yes, I know how to measure temperature with a diode, and I
occasionally also use Natsem's LM35. But the issue is not really
critical. I'm mounting the ICs on a 3.5 degC/W extruded Al
heatsink which alone should provide adequate cooling for the 10W
(max.) loss. The copper plane is just extra insurance, but I
wanted the info for future applications too.
This thread has received more response than I expected and it has
been enlightening. Looking back, I realise that I should have
been more careful in my choice of terms. When I spoke about
radiation, I meant getting rid of the heat in general. It should
have been obvious even to me that solder mask would enhance heat
radiation rather than hinder it. What I was really concerned
about was the effect of insulating the copper from contact with
circulating air. It has been clearly pointed out that the thin
layer of solder mask won't make much difference. Thanks,
everyone.