# How do you strip PCB's of there solder mask.



## Emil (Nov 28, 2008)

I want to thank the forum for all the information it makes available to novices like me. I couldn't procede without the knowledge and members of this forum.

I am in the process of assembling the equipment and chemicals for a Sulfuric Cell and the AP process. Nitric Acid is not for me now. Maybe when I have a great deal more of experience.

I have 10 pcb's with Gold under the solder mask, and canvased the forum for a method to remove the mask with no results. I did find a suggestion from Steve to use Sodium Hydroxide. I couldn't find a description of how to specificly use SH. I hope that someone will give me the specific method of what to do.

Type of container?

If the solution needs to be heated, if so how hot and how long? 

How many PCB's at one time?

Ventilation?( I'm in the basement of my own home and can install an exhaust fan.)

Safety?

I have two quarts of Drano in sealed plastic containers. I've had them for years and never used them. They contain Sodium Hypochlorite, Sodium Hydroxide, Sodium Chloride, surfactant and water. Will this solution fit the bill.

Looking foward to your response.

Emil


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## Oz (Nov 28, 2008)

You mention that nitric acid is not for you now but maybe when you have much more experience. 

You will find that strong bases that are used for stripping solder mask and the concentrated sulfuric acid used in a cell are more dangerous than nitric. Your choice of AP is an ideal process since it seems that you will be starting with electronic scrap. Follow LaserSteves advice and videos on AP and it will walk you right through.


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## Harold_V (Nov 28, 2008)

Oz said:


> You will find that strong bases that are used for stripping solder mask and the concentrated sulfuric acid used in a cell are more dangerous than nitric.


Yep! What Oz said!

Years ago, late 70's, I got a drop of tech grade nitric acid in my eye. Right out of the bottle! Not diluted in the least, aside from the dilution from my tears. 

Within seconds, the surface of my eye was a yellow color, and shed a few seconds later. I was only a few steps from my sink, so I immediately flushed the eye. I was alone, working in my lab. Susan, my wife, was gone for the afternoon. 

I drove myself to an ophthalmologist, who examined me and told me how lucky I was. His comment was that had I been working with a base solution (sodium hydroxide, for example) I had but 15 seconds to save the sight in that eye. The human body has little ability to neutralize bases, it appears. 

Aside from the symptoms of old age, my eyes are no worse for the experience. In fact, my right eye, the one in question, is far better than my left eye. 

You may not consider a drop of nitric acid in your eye as good fortune----but how fortunate would one be to have it be lye instead?

Harold


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## Emil (Nov 28, 2008)

Oz, Harold, thanks for the response.
Are you saying that if I put the PCB's in to the AP it will disolve the mask and the under lying gold plating.


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## Harold_V (Nov 29, 2008)

Emil said:


> Are you saying that if I put the PCB's in to the AP it will disolve the mask and the under lying gold plating.


I'm not familiar with AP----so you'll have to rely on the comments of others. However, I think AP won't touch the mask. 

Harold


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## lazersteve (Nov 29, 2008)

Eml,

Harold and Oz are both right to a degree.

AP won't touch the solder mask, but it will undermine the mask (very, very, slowly) and eat the copper away, thus freeing the mask. This leaves a lot of trash in the foils. [edit]AP should only be used on unpopulated boards ! (Thanks Oz))[/edit]

It's best to remove the mask first. I did not post the sodium hydroxide technique of removing the mask. I believe that was AgAuPt in this post:

Solder Mask Removal

This entire thread is very informative so read it all, you'll be glad you did.

Also Lou and a few others have discussed methylene chloride solvent as a means to remove the mask. Here's the thread:

More on Solder Mask Removal

Steve


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## Oz (Nov 29, 2008)

You do not want to put whole boards in AP. AP is best used for processing fingers and CPUs that have been removed from PCBs. Putting a whole board in AP will give you a mess and possibly give you some rather hazardous elements in you solution depending on the boards. Please find any post of LazerSteve’s and click on the link at the bottom of his post and watch his free videos and data doing a bit of due diligence before you do anything else. In this way you can stay safe, and it will save you the trouble of asking questions unnecessarily.


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## Emil (Nov 29, 2008)

OZ sorry, pressed the wrong button.

Emil


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## sugush01 (Dec 14, 2008)

what will hapen if nitric acid is 65%? is that will couse any thing??


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## butcher (Dec 14, 2008)

? 65% nitric is very strong, alot of process we dilute it with water.
it usually depends what you are using it for.


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