Re: getting rid of gold on pcb

On Sat, 13 Oct 2007 12:22:40 -0700, D from BC
<myrealaddress@xxxxxxxxx> wrote:

On Sat, 13 Oct 2007 11:06:50 -0700, D from BC
<myrealaddress@xxxxxxxxx> wrote:

On Sat, 13 Oct 2007 10:18:20 -0700, John Larkin
<jjlarkin@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:

On Fri, 12 Oct 2007 21:17:29 -0700, D from BC
<myrealaddress@xxxxxxxxx> wrote:

On Fri, 12 Oct 2007 11:35:02 -0700, a7yvm109gf5d1@xxxxxxxxxxx wrote:

We have boards that inadvertently ended up with hard gold finish. As a
result we have 50 microinches of gold causing all kinds of headaches
at assembly.
We asked to have the extra gold stripped off but I was told it was not
possible.
Is there no way to dissolve the gold off? Otherwise we have to get
another batch made and they're expensive.
Mercury bath? Hot cyanide? Microtome? Have an immersion silver finish
over the gold!!! Argghgghgh anything!!

I have no experience in this area so I'll just rattle off the wacky
ideas:

1) Sandblasting (copper microspheres?)
2) Planar (as with lumbar)
3) Wet abrasive and lapping (mirror polishing)
4) Air blasting at 1063C (Au melting point)
(Cu melts at 1083C and Ni at 1455C..but PCB will burn)
5) EDM engraving
6) 3:1 HCL:HNO3 etching
7) Chlorine gas etching or Chlorine in solution


D from BC


You could probably rub the gold off with a scotchbrite pad and
household cleanser.

John

Yup.. Does sound like that'll work and perhaps worth a try..

Gold is a relatively soft metal. Using a pad that is just harder than
the gold but softer than the copper (or plating on copper) will help
reduce wear on the copper.
I know scotchbrite scuffs copper which means something in the
scotchbrite is harder than copper..

Household cleansers (ex Javex) contain chlorine compounds but I don't
know if that will react with gold.. (I'm not a chemist!)
However chlorine gas will. How fast..I dunno..

It's interesting, it takes only 1% chlorine to saturate water. Max
solubility is at 9.6C.. Anymore and it gases.
This can be a good thing too. I suspect chlorine has much more
reactivity with gold at 9.6C temp than with copper..
So.. chilled water saturated with chlorine and etch the board is my
guess... I have no idea if that'll work..but seems like a start.

Joke...Perhaps you could just plop the pcbs in a chlorinated public
swimming pool for a few days..
(I dunno if that'll work..)
D from BC

I got curious and found a few net references that it's recommended to
remove gold (ex: rings) before going in swimming pools..
"
Remove gold jewelry before entering swimming pools. The chlorine in
the water will erode gold jewelry."


Gold is one of the least reactive metals. The classic reactant is aqua
regia. I doubt that a bit of chlorine in water would have much effect.
And anything that eats through gold will go wild when it hits the
copper.


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

"When Germany invaded Denmark in World War II, the Hungarian chemist
George de Hevesy dissolved the gold Nobel Prizes of Max von Laue and
James Franck into aqua regia to prevent the Nazis from stealing them.
He placed the resulting solution on a shelf in his laboratory at the
Niels Bohr Institute. It was subsequently ignored by the Nazis who
thought the jar?one of perhaps hundreds on the shelving?contained
common chemicals. After the war, de Hevesy returned to find the
solution undisturbed and precipitated the gold out of the acid. The
gold was returned to the Royal Swedish Academy of Sciences and the
Nobel Foundation presented new medals to Laue and Franck."

John


.

Relevant Pages

  • Re: getting rid of gold on pcb
    ... We asked to have the extra gold stripped off but I was told it was not ... Sandblasting (copper microspheres?) ... Chlorine gas etching or Chlorine in solution ... swimming pool for a few days.. ...
    (sci.electronics.design)
  • Re: getting rid of gold on pcb
    ... We asked to have the extra gold stripped off but I was told it was not ... Chlorine gas etching or Chlorine in solution ... ...and do not forget environmentally and people friendly Mercury as well ...
    (sci.electronics.design)
  • Re: getting rid of gold on pcb
    ... We asked to have the extra gold stripped off but I was told it was not ... Chlorine gas etching or Chlorine in solution ... ...and do not forget environmentally and people friendly Mercury as well ...
    (sci.electronics.design)
  • Re: getting rid of gold on pcb
    ... We asked to have the extra gold stripped off but I was told it ... Chlorine gas etching or Chlorine in solution ... How about Aqua Regia? ...
    (sci.electronics.design)
  • Re: getting rid of gold on pcb
    ... We asked to have the extra gold stripped off but I was told it was not ... Chlorine gas etching or Chlorine in solution ... ...and do not forget environmentally and people friendly Mercury as well ...
    (sci.electronics.design)