How to remove a big area of soldermask

[Koen]

Hello, would you have any tricks to remove a massive area of soldermask from a PCB ? I forgot to clear it in the gerber. Thank you, Koen

[SteveyG]

I can only think an abrasive would do the job without access to more controlled equipment.

[Fire Doger]

Laser

[Pinkus]

Depending on the quality of the mask lacquer it can be quite difficult. Cheap Chinese PCBs are usually easier, good quality western facilities are often using quite stable lacquer.
At single prototypes I usually scratch it away with a scalpel. Otherwise my tip: throw it away and re-produce it.

Edit: never thought about a laser ... indeed THAT could be a good solution for larger quantities.

[TheHolyHorse]

You probably need a pretty decent later though.

[KaneTW]

Without knowing what soldermask was used, I can just shoot in the dark. Try dichloromethane, acetone, toluene. DCM probably the most likely to work. If that doesn't work, hot 40%  sodium hydroxide solution should work.

https://patents.google.com/patent/US5304252A/en describes a aqueous solution of 5-40% alkali hydroxide and ~15% of softening agent like 2-pyrrolidone or glycol ethers. Read through the thing, or maybe just buy a commercially available stripper.

[T3sl4co1l]

Use DCM very carefully: it swells PCB laminate.

I've seen a stiff fiberglass brush recommended for this, with or without chemicals.

Tim

[eliocor]

https://uk.rs-online.com/web/p/pcb-cleaning-brushes/0514868/
https://uk.rs-online.com/web/p/pcb-cleaning-brushes/0514874/

[SMTech]

https://uk.rs-online.com/web/p/pcb-cleaning-brushes/0514868/
https://uk.rs-online.com/web/p/pcb-cleaning-brushes/0514874/

Certainly work, be prepared for evil glass splinters in your fingers.

[eliocor]

No, the pen (holder) is just done for protecting your fingers and the brushes wear is very little.
I have used such brushes even by hand (no holder) without any problem.
Please take care that, with good soldermask, the brushing process is rather slow!

[mrpackethead]

Depending on the quality of the mask lacquer it can be quite difficult. Cheap Chinese PCBs are usually easier, good quality western facilities are often using quite stable lacquer.
At single prototypes I usually scratch it away with a scalpel. Otherwise my tip: throw it away and re-produce it.

Edit: never thought about a laser ... indeed THAT could be a good solution for larger quantities.

Your basing your comments about chinese PCBs on what?  Actual fact or just the standard china is rubbish mindset?

[Berni]

If you just want to remove all of it then sandpaper is the easiest way.

If you want it in a prceise area then a laser engraver sounds like the best bet. They are plenty powerful enough to burn off most kinds of paint and coatings but don't have nearly enough power to do anything to copper.

[T3sl4co1l]

Your basing your comments about chinese PCBs on what?  Actual fact or just the standard china is rubbish mindset?

Protos often use a cheaper(?), weaker, glossy soldermask.  This is at least true of PCB4U, PCBCart, ALLPCB and ITEAD in my experience, and most likely the other budget services.

My experience with PCBCart full custom has been they use a stronger soldermask.  Most western fabs use a glossy or matte formula with good to excellent strength (e.g., Advanced Circuits, Eagle Electronics, etc.).

It may just be coincidence that these are all Chinese fabs using the formula in question.  More likely, it's simply "you get what you pay for".

Tim

[T3sl4co1l]

It's more about what you're doing.  I would dare consider weaker soldermask a benefit, for proto purposes.  To a point.  Easier to scrape off and make new pads.  Not so weak that it's flaking everywhere, of course.

For production I think matte is better, something about the flow of paste?

Tim

[GerardG]

I have used a CO2 laser to remove big areas of soldermask.
Settings to 60W

After lasering we cleaned the board with IPA.

[HHaase]

Some repair shops I deal with use small bead-blasters to clear large areas,  though they are also usually dealing with clearing off battery corrosion too.

If you go the laser route, definitely keep it in a laser-safe enclosure.  Copper loves to reflect.

[GerardG]

Thank you Blueskull for your reply.

As the CO2 laser removes only the soldermask and reflected from the copper you are not removing any copper.
This was a nice solution for the 12 layer PCB we had to modify.

Do not position the laser on a place without copper as it will ruin your PCB.

[Koen]

Thank you for all your replies. I tried solvents then fiberglass brush then laser. Laser triumphed.

[Fire Doger]

"told ya"
Can you share any pics to complete the topic?