Testing with Stannous

[Exibar]

So if I have a PC board, and I think that there is gold plate under the green enamel cover and I'd like to test to see if it is indeed gold plate would the following be the right way to go?

I'd scrape off the enamel cover with a fiberglass knife, so as not to remove the gold plate underneath.
After mixing up a fresh vial of Stannous Chloride, I'd scratch the suspected gold plate a bit with a sharp stainless knife, not so much to remove all the plating but enough to get some dust.
I'd dip a Q-Tip into th evial of Stannous, and rub it on the scratches.

Now if the Q-tip turns purple, there is gold there. If no purple, no gold.

Is this correct?

Thank you all for the help!

Mike B

 

[lazersteve]

Mike,

You'll need to get the gold into solution for stannous to work.

You should add 1 drop of HCl to the fresh clean exposed trace, then add 1 drop of bleach. Let the HCl-Cl work for about two minutes then soak it up with your swab. Now drip a drop of stannous on the HCl-Cl soaked swab. A purple result is positive for gold.

Steve

 

[Exibar]

Hi Steve!
I knew I had to be missing something in there. Thank you very much for the help!

Is it common that there is gold plate under the enamel in someolder ISA cards? I have a bunch that were made in the late 80's.

thanks again!
Mike B

 

[synthetiklone]

EDIT: heh, here I stand corrected, :lol: see next message! (thx agn steve).

As far as I am aware, gold coatings on pcbs are only used for connectors which are probably exposed. The gold coating providing a non oxidising, good (low resistance/noiseless/clean) electrical connection for where sensitive electron flow is required. There would be usually no point in gold plating and area under an already protected coating if nothing is going to become connected to it.

I'd say in a majority of cases, if you can see its golden, its gold! The exceptions are keeping in mind alot of gold is also hidden inside chips, under pcbs, and inside alot of connector plastic housings.. but these arent pcbs. I even found gold inside a hermetically sealed box on a pcb, it was some sort of rf device which required it. So dig deep.

BUT in the case of pcbs, test away, just in case - I may be wrong in some instance where a manufacturer has decided to plate gold there. Which also leaves me open for correction, please do.

 

[lazersteve]

Synth,

Actually, there are many old and new boards with fully plated gold traces under the solder mask as strange as it sounds.

I have many of these boards and have made several posts concerning their identification.

Here's one such post:

Gold Traces

The entire thread is full of really good information and you should read it start to finish.

Steve