Green solder mask and heatsinking

[David L. Jones]

Gold is about as bad as copper an an IR emitter, with emissivity as
close to zero as doesn't matter. It's generally microinches thick
anyhow. But radiation isn't usually a serious pcb cooling mechanism
anyhow.

Yup, I was referring to gold plate more in regards to the
"professional look" the OP is after.

Dave.

 

[David L. Jones]

[...]
Green solder mask is passe, there are many other colours that are much
better looking. Gloss black is nice.
A good cheap place to get your boards made iswww.pcbcart.com

AFAIR even pcbcart charges extra for non-green boards.

Yes they do.
On a 100x100mm board 100qty I just priced 13% more for black solder
mask compared to green which is not hugely significant if you are
after a more professional look.
Immersion gold finish was another 6% extra.

This would look pretty sucky in Green for instance:
http://www.calcwatch.com

Dave.

 

[[email protected]]

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.

 

[legg]

We have a customer who decided to use red mask on "esd sensitive"
boards. Then their QC people argued that all boards are esd sensitive,
so now they are all red.

(I DID get the joke but..)

Is there no consideration for eye strain?

RL

 

[pimpom]

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.

 

[[email protected]]

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.

I've read the responses, and am not 100% sure the solder mask
increases radiation. Granted, some good arguments were made. The mask
is an insulator. When you wear a jacket, does your body radiate heat
better. Theory is fine, but theory always needs to be tested. Once you
make your board, you could order one board without the mask. I've only
done PCBs for prototyping and building a few units of something, so I
can't vouch for how the real world does it. A bit OT, but I recall a
PCB vendor telling me that some customers say the solder mask causes
measurable leakage.

Anyway, theory is good, you test it, then when it doesn't work like
you thought, you refine the theory. Newton thought he was pretty
smart, but Einstein proved him wrong.

 

[krw]

Here's one...

ftp://66.117.156.8/GoldT550.JPG

which is awfully cute in person.

Hmm, that gives me an idea. That's awfully close to orange and navy
(Auburn colors). ;-)

 

[krw]

I saw some of that game. The uniforms are designed to invoke nausea in
the opposing team.

Wouldn't know. I've never watched a game.

 

[krw]

An Auburn game, that is. I turned down sidelines passes (to several
teams) because I didn't feel I knew our equipment well enough to be
of any help. Next year I'll likely go to a few games to help out.

When you're hungry, and the best pizza and beer is at a nearby sports
bar, you go along with it. I'd never watch a football game at home.

I watched perhaps a quarter this year. Too many other things to do
than go to bars, since beer is no longer allowed. I don't know
anyone here so I don't go out with the crowd either.

 

[krw]

I had a contract for the sound system at a high school for their
football games. I had to be available if something quit working, but I
didn't have to be in the press box or watch the game so I modified an
old B&W TV to run of the truck battery and watched TV during the games.

That's what we do (Coach's intercom equipment, and similar sorts of
things). Most of the professional employees went to the first few
games to support our new generation of equipment. No TV in the
truck though.