# Solder mask removal



## oldtimmer (Feb 18, 2009)

I have read in the forun about using caustic soda (Lye?) to remove solder mask on circuit boards. I have perhaps 50 or so PC boards that I have set aside until I could find an easy way to remove the solder mask. I am still unable to search all of the forun and find the needed method to remove it. What is the procedure?

Thanks,

dave


----------



## Juan Manuel Arcos Frank (Feb 18, 2009)

Dave:

Take a look at the AP process for base metal removal..it is here,in the forum.

Regards.

Manuel


----------



## lazersteve (Feb 18, 2009)

Try this link:

Solder Mask Removal

Be safe!

Steve


----------



## Lou (Feb 18, 2009)

My friend informs me that N-methyl pyrrlidone is a superior solvent for dissolving away the plastics on circuit boards.

It's commercial name is NMP. Great solvent.


----------



## Emil (Feb 18, 2009)

Lou, 

Which is safer to use when removing the solder mask, Sodium Hydroxide or NMP. Is it necessary to heat the NMP.

Emil


----------



## Lou (Feb 19, 2009)

I would go with NMP. It has a certain toxicity, but as I recall, it biodegrades. 

I would rather work with warm NMP than hot lye on any occasion. Hot lye can blind with one splash, NMP, well perhaps it is a suspect carcinogen. 


I have not done sufficient research into it--I was just forwarding what I've been told. Supposedly it is a solvent of choice in industry, because it has a high boiling point (therefore low volatility), great solvent properties, relatively nontoxic, and easily recycled. 



Lou


----------



## Emil (Feb 19, 2009)

Lou, thanks for the reply and I will do a bit of homework on the subject.

Emil


----------



## qst42know (Feb 19, 2009)

Here is some interesting things about NMP. The link is to the rest of the article. 

What polymer is a flat pack chip made of?

"Materials Compatibility: NMP dissolves polyamides, polyimides, polyesters, polystyrenes, polyacrylonitriles, polyvinyl chlorides, polyvinyl acetates, polyurethanes, polycarbonates, polysulfones, polymethylmethacrylate, and many copolymers. Assemblies containing these materials should be tested before using NMP. NMP will dissolve or swell Buna-N rubber, natural rubber, neoprene, and Viton. Assemblies containing these materials should be tested before using NMP.

NMP does not react with most metals, including steels, aluminum, nickel, silver, gold, chromium and chromates, copper, tin, and silicon. However, it should not be used with bronze or brass valves in process piping."

"NMP is resisted by polyethylene, polypropylene, polytetrafluorethyene (Teflon), and butyl rubber. Teflon is recommended for wetted seals and gaskets. Butyl rubber is recommended for personal protective equipment."

http://205.153.241.230/P2_Opportunity_Handbook/5_10.html


----------

