Tarnishing of PCB copper.

[Pimpom]

There's no quick and easy way to order a PCB from where I live
and I make most of my own. For major projects, I persuade local
silk-screen printers to print the solder mask on. For minor ones,
to protect the finished copper areas, I either tin them with
solder or use the old method of painting it over with rosin.
Unless I do this, the bare copper gets visibly tarnished in a
matter of days.

However, when working on years-old company products, I often see
unused solder pads that are still fairly clean and bright and
take solder readily. And I don't mean the gold-plated ones.
What's the trick? If they are covered with an anti-oxidation
coating, it must be quite thin and transparent.

 

[Nico Coesel]

There's no quick and easy way to order a PCB from where I live
and I make most of my own. For major projects, I persuade local
silk-screen printers to print the solder mask on. For minor ones,
to protect the finished copper areas, I either tin them with
solder or use the old method of painting it over with rosin.
Unless I do this, the bare copper gets visibly tarnished in a
matter of days.

However, when working on years-old company products, I often see
unused solder pads that are still fairly clean and bright and
take solder readily. And I don't mean the gold-plated ones.
What's the trick? If they are covered with an anti-oxidation
coating, it must be quite thin and transparent.

They probably coated with protective flux. A product called SK10 is
popular over here:
http://nl.farnell.com/kontakt-chemie/loetlack-sk10-200ml/varnish-pcb-sk10-200ml/dp/800983

 

[Spehro Pefhany]

They probably coated with protective flux. A product called SK10 is
popular over here:
http://nl.farnell.com/kontakt-chemie/loetlack-sk10-200ml/varnish-pcb-sk10-200ml/dp/800983

Generically called "organic coating", I think. Unfortunately, in North
America you'll get hammered for a hazmat fee that exceeds the cost of
the product when you buy any reasonable amount.


Best regards,
Spehro Pefhany

 

[legg]

I clean, then spray home-made boards & protos with ordinary Krylon
clear acrylic spray, available at most any store. It keeps boards new
forever, AFAICT--more than 33 years for some of my samples, with many
of those years spent stored in salt-air environments. They still look
new, and you can solder right through it.

I do the same, after thorough cleaning.

Krylon acrylic is a good moisture barrier, on anything that doesn't
have to suffer from knocking about.

OSP on pcb's doesn't survive past the solder wave - is designed to
break down. If the boards you're looking at were hand soldered, that
might explain the residue on 'unused' pads.

RL

 

[Jamie]

There's no quick and easy way to order a PCB from where I live
and I make most of my own. For major projects, I persuade local
silk-screen printers to print the solder mask on. For minor ones,
to protect the finished copper areas, I either tin them with
solder or use the old method of painting it over with rosin.
Unless I do this, the bare copper gets visibly tarnished in a
matter of days.

However, when working on years-old company products, I often see
unused solder pads that are still fairly clean and bright and
take solder readily. And I don't mean the gold-plated ones.
What's the trick? If they are covered with an anti-oxidation
coating, it must be quite thin and transparent.

http://www.rapidonline.com/Tools-Fa...PCB-Accessories/Printed-circuit-lacquer/30085

Jamie

 

[Pimpom]

There's no quick and easy way to order a PCB from where I live
and I make most of my own. For major projects, I persuade local
silk-screen printers to print the solder mask on. For minor
ones,
to protect the finished copper areas, I either tin them with
solder or use the old method of painting it over with rosin.
Unless I do this, the bare copper gets visibly tarnished in a
matter of days.

However, when working on years-old company products, I often
see
unused solder pads that are still fairly clean and bright and
take solder readily. And I don't mean the gold-plated ones.
What's the trick? If they are covered with an anti-oxidation
coating, it must be quite thin and transparent.

Thanks for all the replies. There's no chance of getting the
particular brands of protective sprays mentioned by various
people, but there *are* acrylic clear finish spray cans available
even here. They're not specifically made for the
electrical/electronics market and are used mostly by people
engaged in decorative work. I'll get one and try it out.

 

[legg]

Thanks for all the replies. There's no chance of getting the
particular brands of protective sprays mentioned by various
people, but there *are* acrylic clear finish spray cans available
even here. They're not specifically made for the
electrical/electronics market and are used mostly by people
engaged in decorative work. I'll get one and try it out.

Krylon spray cans (or something similar) are available at art supply
stores, home craft supply stores, and Canadian Tire (automotive
touch-up), above the 49th parallel.

RL

 

[Rich Grise]

Thanks for all the replies. There's no chance of getting the
particular brands of protective sprays mentioned by various
people, but there *are* acrylic clear finish spray cans available
even here. They're not specifically made for the
electrical/electronics market and are used mostly by people
engaged in decorative work. I'll get one and try it out.

Yes, any lacquer should protect the copper from the air. But of
course, preaching to the choir, be sure that the copper is bright
shiny clean, and the board is bone-dry when you spray it. And,
don't quote me or bet the farm on it, but you could probably
solder through it with barely a puff of smoke from burned lacquer,
and the flux smoke will certainly swamp that out.

Have Fun!
Rich

 

[Rich Grise]

Is acrylic 'lacquer'? I thought 'lacquer' always meant 'lac' as in
'shellac', as in 'made from the shell of the lac beetle.' I read that
as a kid anyhow, and it's stuck with me to this day. Hmmm...

http://en.wikipedia.org/wiki/Lacquer

<read read read .../read>

Nope, it seems lacquer is generic for the modern synthetics, the Diet
Pepsi of wood finishes; shellac is the real thing(tm).

Thanks Rich!

Hey, you're more than welcome! It's just that ISTR seeing a spray can
labeled "acrylic lacquer" or something. But these days, "Acrylic" doesn't
narrow it down much. Plexiglass is acrylic. There are acrylic "hobby"
paints, for artsy-fartsy folks - they're as vivid as tempera, but somehow
better, maybe more durable. It seems like I've heard of even acrylic floor
tile, but I might have dreamed or hallucinated that one. ;-)

Shall we throw it out to the group? Hey - in how many contexts have you
heard the term "acrylic?"

Cheers!
Rich