Sodium Hydroxide (NaOH) Dissolved my GOLD?

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electronixredux

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Joined
Apr 3, 2011
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Has anyone experienced this? I was processing some touch pads by soaking them in a NaOH solution to remove the solder mask. I may have either allowed the temp. to get to high or had too concentrated of a solution or let them sit too long, either way the shiny gold boards are now silvery and there is no more gold (or solder mask). My question is, can this be percipitated from the solution and if so with what? Any recommendations would be much appreciated! Also, if anyone has any insight as to why this happened I would love to know so it doesnt happed again.

Thanks
 
Thank you very much for the reply, I would have been chasing my tail for weeks trying to figure this out! That makes total sense; I had assumed what looked like gold, was actually gold. Thanks again!
 
strong bases will discolor gold. did you rub what remained to see if you could find any gold color on the base metal?
 
Thank you Geo, I tried rubbing and a little scraping too but no gold underneath. I have uploaded a photo showing the before and after of removing the mask and you can see that there is still blotches of what looks like a gold plating remaining. I am still scrathing my head!
 

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Geo is right, I have seen gold become discolored in the same way...

I haven't had any problems since I have been using these measurements to mix my de-masking solutions.

I mix about 40 grams to ever liter of water. If you are using gallons, it would be 150 grams per gallon, about.

Scott

Edited:

You might try to do an acid test on both the discolored and gold parts of the touch pads. That should prove any gold content.
 
Scott, I have been using a much more concentrated solution of NaOH and H2O which was presented in a Lasersteve video. There it was sugguested to use a 20% solution or 20g NaOH + 80ml H2O, and for my last batch I used 120g NaOH + 500ml H2O. For any future batches I am going to dilute the solution to your recommendations. When I get a few minutes I will definately perform an acid test to verify what we are looking at. Thanks again for your time.
 
i use hcl to remove tin solder. there are a couple of points on this i want to address. hcl acid alone will not dissolve gold. beginners post often saying " i soaked the boards in hcl and now my gold is gone. what happened to my gold?"

the gold is still there, it didnt dissolve or whatever else one would think may have happened to it. it just doesnt look like gold anymore. it has to do with the polarity of the atoms and the dissolution of the tin. when the tin is dissolved, it takes on a positive charge which make it stick to the gold plate. most people wouldnt know that you can brush it off after it dries and the gold will show through.
 
electronixredux said:
Has anyone experienced this? I was processing some touch pads by soaking them in a NaOH solution to remove the solder mask. I may have either allowed the temp. to get to high or had too concentrated of a solution or let them sit too long, either way the shiny gold boards are now silvery and there is no more gold (or solder mask). My question is, can this be percipitated from the solution and if so with what? Any recommendations would be much appreciated! Also, if anyone has any insight as to why this happened I would love to know so it doesnt happed again.

Thanks
Click to expand...
Bro SAME THING just happened to me!! So happy I found this post!
 
electronixredux said:
Has anyone experienced this? I was processing some touch pads by soaking them in a NaOH solution to remove the solder mask. I may have either allowed the temp. to get to high or had too concentrated of a solution or let them sit too long, either way the shiny gold boards are now silvery and there is no more gold (or solder mask). My question is, can this be percipitated from the solution and if so with what? Any recommendations would be much appreciated! Also, if anyone has any insight as to why this happened I would love to know so it doesnt happed again.

Thanks
Click to expand...
So.... Is the gold still GOLD, or no? It is just discolored???? 🙏🏻🙏🏻🙏🏻
 
There are many different metals on a board. Tin can dissolve in NaOH but it can also plate out onto metal surfaces as part of an electrochemical cell formed by other metals. If you had gold then it is probably just covered under a thin tin film.

Mouse pads looks good but is often very thin. Often just covered with ENIG so when you dissolve the underlying copper the gold comes off in microscopic pieces and it looks like it disappears. But in reality there is a fine dusting of gold particles, easily suspended in the liquid.

I've seen it happening to heavy plated gold fingers where everything was gold plated except a few fingers that turned white.

Göran
 

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