# Found what is not supposed to exist



## rickbb (Feb 1, 2014)

Was de-populating some boards this afternoon to prep for AP, seems they have gold plating everywhere. Not just what is showing but under the green mask, traces and large areas as well. 

I use a heat gun to loosen the solder and putty knife to scrap off the stuff and some of the mask came off revealing the gold.

Came from some old Motorola hand held bar code scanners with Windows CE, mini PC kind of thing.

So, what is the best way to strip the solder mask? Soak in HCL, NaOH? 

I don't have many of these so I don't want to invest in PCB stripper for a half dozen boards.


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## bmgold2 (Feb 1, 2014)

I just found a post where it discussed using brake fluid to remove the solder mask. I've never tried this so I don't know how/if it works. Read all the post since brake fluid and chlorine can self ignite or explode. Not sure how you clean the brake fluid off the boards. Maybe brake cleaner or parts cleaner and then soap and hot water?

http://goldrefiningforum.com/~goldrefi/phpBB3/viewtopic.php?f=37&t=4701

Another post or two I read but didn't save the links said that scratching the solder mask a bit and then just using AP and a lot of time can eventually get to the copper under the mask and gold. The gold stays attached to the mask but should rub off after the copper is mostly gone. Then the mask is caught in the filter after dissolving the gold.

I never tried any of this but I found one little circuit board from a water softener that appears to have all the traces gold plated but it is mostly under the solder mask and also some rubbery, clear coating. I guess all the salt requires the gold plating and other protection.


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## pattt (Feb 1, 2014)

Hi, 

On Lazersteve"s website there is a video for removing solder mask with NaOH.
Use Gloves and eye protection hot NaOH is dangerous :!: ( do a search about it)
stay save and have fun

Pat


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## Palladium (Feb 1, 2014)

Don't use glass vessels with hot NaOh. Glass dissolves in hot NaOh.


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## lazersteve (Mar 6, 2014)

Aqueous sodium hydroxide used in the video will not harm Pyrex at the lower temperatures (<100C). If one were to melt sodium hydroxide (318C) pellets in a Pyrex beaker, that would be a different story.

Steve


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## Varmint (Mar 11, 2014)

Brake fluid is a form of alcohol, so is very easy to clean up with nothing more than running water.

I know it will attack car paint (all but the poly varieties), so it has a fair chance ofdoing at least some softening of the mask. Trouble is, the mask is formulated to withstand harsh treatment, so you'll just have to give it a try and hope for the best.

DAS


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## rickbb (Mar 11, 2014)

I used 5% NaOH solution heated to approximately 165F and it worked well. 

Had to leave it in a bit longer than if I had used a 20% solution. But I was not in a hurry for it.

Anyway, it softened it up nicely, some of it dissolved away in the bath and the rest wiped right off with a 3M scuff pad.

There was at least 3 times as much gold plating under the mask on those boards than what was showing. 

Too bad I didn't have a ton or two of them instead of just 6 boards.


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