Remove silk screen from board

[Emil]

I got a batch of PCB's where some of the silk screen on the back of the board is not readable. The unreadable silk screen is nothing critical, just the name of the product and the url of my website but it looks very ugly with the unreadable text.

I need a few boards I can ship while waiting for replacement boards, so my question:

Is there some way to remove the silk screen without damaging the solder mask?

[connectTek]

Acetone ?

[Emil]

Acetone ?

I have cleaned boards with acetone before and it didn't damage the silk screen. Maybe if I soak it for a while.

[westfw]

Probably not.  On a "real" board, the same sort of ink is used for both silkscreen and soldermask, and they're both epoxy-like and not very soluble in anything once they've cured.

[BradC]

Yeah, like westfw said they are generally UV cured epoxy and anything that'll attack the silkscreen will likely remove the soldermask as well.

You won't dissolve it or just wipe it away, but a soak in Toluene will probably soften it. Failing that, Chloroform or Dichloromethane (Paint and/or gasket stripper). Neither are particularly fun to be around but DCM even less so.

If it really annoys you I'd use a polishing buff in a dremel with some medium grit compound and buff it off.

[Precipice]

Time for some strategically placed serial number, tested, QC and other stickers?

[Emil]

Time for some strategically placed serial number, tested, QC and other stickers?

I like this idea.

[Legit-Design]

Some people use sugar and it can gently scrub of silkscreen like white printing off of plastic products. Becareful with the pressure as sugar can easily scratch a surface. I tried it on my old camera and the white ink printing came off really easily until I noticed the scratches.(the camera was not particularly new or high end) Just used normal sugar and paper towel no water no liquids.

Quick instructable I found:
http://www.instructables.com/id/How-to-remove-Logos-from-your-PDA--cell-phone-wit/

[T3sl4co1l]

On good quality PCBs it's been my experience that silk can be scraped off, cautiously, with something sharp (like a blade or sharp screwdriver).  Go carefully and avoid digging into the soldermask.

Tim

[Emil]

I found a solution. Edit: Ignore this. Appared to work on the first board I tried, but I can't reproduce the result.

I used an activator spray for cyanoacryalate glue. According to the MSDS it's N,N-dimetyl-p-toluidin. I sprayed some on the board and some on a cotton bud. The silk screen was easily rubbed away.

It was just a quick test, but I didn't notice any damage to the solder mask.

[Falcon69]

what exactly IS cyanoacryalate glue?  I am having same problem and need to get rid of the silkscreen.  I just had some boards made, and the Manufacture mirrored the silk screen on the bottom.  I checked gerbers, it's their fault, not mine.  They wont replace.  So I need to just get rid of the silk screen (because of mirrored, the writing is on/off the board, looks like crap).

[T3sl4co1l]

http://www.sigmaaldrich.com/catalog/product/aldrich/d189006?lang=en&region=US if you can buy from SA and want to pay their prices.

Wouldn't have thought that would have any special properties compared to, say, toluene or trialkylamines.  Maybe the amine is reactive... actually that may be, I recall water also catalyzes cyanoacrylate polymerization, it might be the mild nucleophilicity at work.

Anyway, I wonder if there are other solvents in that activator stuff?  I wonder if something strong like THF or methylene chloride might be doing it?

What is CA glue?  Exactly what it says, cyanoacrylate.  It's a fairly simple organic compound (carbon with hydrogen and oxygen) with some oxygen atoms near a double bond, which tend to activate it towards polymerization.  So, in the tube of glue, you get the monomer, and it sets on exposure -- to ambient moisture, actually.  And, at least as far as I recall, it polymerizes the same way other plastics with double bonds do, like polyethylene, polypropylene, etc., which are just less reactive to the point where they have to be done industrially, so you buy the finished plastic, not the... well, those also start as gasses, which aren't as easy to handle, either.

Tim

[Emil]

Update: The CA activator spray did NOT work well. It seens to soften the silk screen a little, but it still takes a lot of rubbing to remove the silk screen. It seemed to work well on the first board I tried, but I can't reproduce it.

[Falcon69]

Well, the guy at the PCB mnufacturer told me to use NaOH (Sodium Hydroxide, also known as Lye and Caustic Soda), but that didn't seem to work. It got hot, I mean real hot too touch, but, it just didnt work.  I was afraid of sticking the circuit board into the solution.  Didn't want the soldermask taken off, or the gold.

Too bad that spray didn't work Emil.  I would have liked to know.  There's got to be something that takes that crap off.

[T3sl4co1l]

NaOH gets hot when dissolved in water, it has exothermic heat of solution, that's all.

Obviously, don't touch the stuff, it literally turns your hands to soap.

I would be surprised if it did anything, unless the coating is very specific (polyesters are vulnerable to strong bases, for example).  Otherwise, it would be a much more general "fuck shit up" reaction, especially if we're not talking H2O solution but direct molten attack (NaOH melts around soldering temperatures).  Which I see no reason for it to stop at mere soldermask, or anything but elemental copper for that matter (it will also aggressively dissolve glass).

Tim

[Emil]

One observation: It's MUCH harder to remove silk screen from the boards I have reflowed than from the new boards. On a new board I can scrape it off with a piece of plastic, this does not work work on the reflowed boards.

(This is probbaly why the activator seems to work at first, I tested it on a bare board. Then later when testing on a reflowed board it was ineffective.)

[Falcon69]

That is what I was thinking Tim.  That is why I didn't submerge the circuit board into it.  This guy who made my boards from me, I got the idea he was just a middle man, and not an engineer or the actual manufacturer.  Didn't trust him when he told me to buy the NaOH.  But thought I'd give it a try.  At least now when my kitchen sink backs up again, I have some naOH to throw down it now!  LOL

[Falcon69]

Emil,

Someone mentioned earlier that the boards that you reflow are much more likely to have the silkscreen "ink" made out of nearly the same chemical make-up as the soldermask.  I think, for us, We may be out of luck with removing it if that is the case. Removing it will remove the soldermask as well, and for me, that is just not an option.

[PedroDaGr8]

Yeah, like westfw said they are generally UV cured epoxy and anything that'll attack the silkscreen will likely remove the soldermask as well.

You won't dissolve it or just wipe it away, but a soak in Toluene will probably soften it. Failing that, Chloroform or Dichloromethane (Paint and/or gasket stripper). Neither are particularly fun to be around but DCM even less so.

If it really annoys you I'd use a polishing buff in a dremel with some medium grit compound and buff it off.

chloroform and methylene chloride don't work. I know from work experience because I use them to degrease board.

Sent from my LGLS990 using Tapatalk

[BradC]

chloroform and methylene chloride don't work. I know from work experience because I use them to degrease board.

Awesome info, thanks! I'll file that away for future reference.

[T3sl4co1l]

Yikes, methylene chloride will swell epoxy and strip paint!  Don't get that stuff near any kind of boards or components!

Tim

[westfw]

You might have some luck with the paint strippers and "graffiti removers" sold at your local hardware store.  Assume that they will strip soldermask as well as silkscreen, and apply with due care.  (also, don't assume that these products are any safer to use than individual chemicals-with-scary-names, just because they're sold retail to ordinary consumers.)