How to remove soldermask and silkscreen - Page 1
Forum section: electronics / projects

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: December 19, 2015, 04:30:48 pm
content: HiSo for a uni project, I designed a PCB that had an antennea and an SMA connector. Usually the project PCB's are produced inhouse and come without and soldermask and/or silkscreen, so I didn't design actual ground pins in either of the two (silly me though I could save a few minutes work - lesson learned). However, it turns out now this time the pcb's will be sent out (because of the time of year, the in-house guys don't work over Christmas and newyears) and now they will get soldermask.The design has been handed in so I can't just go in and add a soldermask keepout or such.This means I will have to remove the solder mask once I have my hands on the actual PCB's. How would I best go about this? I've thought of scratching it off, but was hoping there might be some (simple) chemical methods that would give a better finish, especially since SMA connectors aren't exactly massive, so I don't want to slip while scratching and ruing the center conductor.

author: Christe4nM
author_rank: Unknown
timestamp: December 19, 2015, 06:28:33 pm
content: You could try very high grid sand paper while keeping it wet. Apply very light pressure. At uni we used this method to get the masking of the newly etched PCBs. (Masking here is not soldermask, but the pre-etch masking covering the copper you want to keep during etching)

author: Pjotr
author_rank: Frequent Contributor
timestamp: December 19, 2015, 10:22:37 pm
content: I usually scrape off the mask with a small round scalpel when needed. Some masks weaken with methylene chloride, MEK or acetone which makes scraping off easier. Others do not.

author: Richard Crowley
author_rank: Super Contributor
timestamp: December 19, 2015, 11:17:38 pm
content: Depending on the nature of the materials, you might be able to remove it with cotton swabs and a strong solvent like acetone or MEK.

author: Kjelt
author_rank: Super Contributor
timestamp: December 19, 2015, 11:23:49 pm
content: We used very small iron files, high grid sandpaper on a powerfile also works if you have to do many ocbs, be carefull though.

author: JSnyder
author_rank: Contributor
timestamp: December 19, 2015, 11:45:20 pm
content: Not that I've tried it, but I've heard fiberglass scratch brushes work pretty well for this purpose. If it's just a small amount of solder mask/silk I'd be inclined to use an exacto and light pressure to scrape it off. Commercial solder masks tend to be (intentionally) resistant to most solvents, and require some pretty nasty/expensive chemicals to remove it.

author: Jeroen3
author_rank: Super Contributor
timestamp: December 19, 2015, 11:58:55 pm
content: Such fiberglass pencil has the lowest chance of damaging the tracks. But might be ineffective when dealing with a thick layer.It's worth to have one anyway, go get one and try.I often use a fresh scalpel to scratch it off with the blade 90 degree on the board. But this is inaccurate and also removes copper when you're not careful.Maybe you can mask the area's you don't want removed, go to the workshop and use a fine glass-pearl blaster at low pressure.

author: matseng
author_rank: Frequent Contributor
timestamp: December 20, 2015, 05:38:56 am
content: Quote from: Richard Crowley on December 19, 2015, 11:17:38 pmI once tried immersing in acetone for a day and also boiling in MEK for 15 minutes. Both the silk and mask was totally unaffected by this. :-( Abrasion with a stubby glassfibre brush was the only thing that worked....

author: tonyarkles
author_rank: Regular Contributor
timestamp: December 20, 2015, 05:45:25 am
content: Yup, scalpel has served me well numerous times. Go slow, be gentle, and go slow

author: kayvee
author_rank: Regular Contributor
timestamp: December 20, 2015, 06:32:15 am
content: A scalpel with a No. 15 blade I find is the best solution for this type of thing.

author: SeanB
author_rank: Super Contributor
timestamp: December 20, 2015, 07:13:56 am
content: Abrasive pen eraser works as well, and if you are doing a few use a fine abrasive flap brush in a Dremel or clone.

author: KL27x
author_rank: Super Contributor
timestamp: December 20, 2015, 07:46:08 am
content: Under high enough magnification you can pretty accurately expose a small ground pad with a small, sharp chisel.If you just want quick and dirty, you can always just grind out a convenient spot on the ground plane and wire a jumper to your ground pin.

author: Pjotr
author_rank: Frequent Contributor
timestamp: December 20, 2015, 01:14:10 pm
content: Quote from: matseng on December 20, 2015, 05:38:56 amDepends largely on the make, some do, some do not. The boards from EuroCircuits do, most Chinese do not.

author: Cerebus
author_rank: Super Contributor
timestamp: December 21, 2015, 02:37:22 am
content: I happened to have an etched and masked test board handy that I was testing liquid photoimageable mask* on so it doesn't matter what damage I do to it.I tried scraping with a sharp small straight screwdriver held almost flush to the board, so that the very tip of the screwdriver (the flat bit at the end) was just off vertical. I made two tries, one took the solder resist off cleanly and left the electroless tin underneath intact and the copper under that compeletly untouched. A second try took the mask off cleanly and left the copper undamaged but scratched off the electroless tin. The trick is to keep the screwdriver blade flat so that the corners don't dig in and scratch the copper. It might need refining with a bit of very fine wet and dry or a fibreglass pencil to leave a high solderability surface.* Horrible, messy stuff that is almost impossible to get a decent result with working at home.

author: nanofrog
author_rank: Super Contributor
timestamp: December 21, 2015, 04:28:15 am
content: If MEK, acetone, dichloromethane/methylene chloride (main ingredient of most solvent based paint strippers & dry cleaning fluid*), and a fiberglass scratch brush won't do, then a small ball mill in a die grinder & usedvery gentlywill be your best bet (i.e. last resort really AFAIK). For the die grinder, you need low RPM & high torque, such as a Foredom LX series (+ steady hand and nerves of steel).BTW, can you even get MEK in the EU anymore?* IIRC, Dichloromethane/methylene chloride is no longer available in the EU.

author: Ian.M
author_rank: Super Contributor
timestamp: December 21, 2015, 05:54:30 am
content: If you've got electroless or HASL tin under the solder mask, you may be able to scrape a small spot and enlarge it with some fresh solder + scrubbing with the soldering iron bit.Dichloromethane is now highly regulated, but you might be able to get your supervisor to beg a favour of a technician in the chemistry department to get the use of a fume cupboard and a couple of ml of it. Apply a drop with a glass rod. If you see any wrinkling, scrape while still wet.