How to dissolve the solder mask on a PCB?

[RuudNL]

I ordered a batch of PCBs, but something went wrong...
Some (5) vital pads on the PCB are covered with the solder mask.
Of course I could scrape the solder mask away, but I am curious if there is a way to dissolve the solder mask.
The PCBs as such are good, so it would be a pity not to use them.
But scraping 5 pads free from the soldermask would be a time consuming job... (50 pcs.)

 

[Vac11]

I used this "pencil"
https://www.conrad.cz/p/rona-811968...confirmation&utm_medium=Email&utm_term=811968
Works suprisingly well and its fast.

Best

M.

 

[JohnRoberts]

A hot iron can help loosen solder mask. For quantity I suspect a wire brush attachment on a Dremel hand grinder might work.

JR

 

[RuudNL]

Thanks for the suggestions! I already started scraping. If you do 5 or 10 at a time, it can be done...

 

[kingcredie]

There is no way to dissolve the solder mask. Scraping 5 pads free from the soldermask is the best way, although it is a time consuming job.

 

[Script]

Flux, solder wick and iron. Pulling the wick while heating does the trick -- on traces/vias at least. Or just scratching with exactor knife.

 

[swpaskett]

Back when I could get it I used methylene chloride based paint stripper.

 

[murrayatuptown]

Depending how much I want to remove, I might use an Xacto/hobby knife if I need better control than 3M ScotchBrite (or similar) pad offers. I use the latter other times if I want to remove a large area, like a portion of a wide trace or similar. SB offers poor control if trying to remove a tiny area's masking without harming another's.

I have also held a small square of ScotchBrite with pliers or hemostats for somewhat better abrasion control than rubbing ScotchBrite with fingers.

I prefer a flat blade for flat hobby knife blade for scraping areas I can do so safely without harming adjacent traces, pads, component leads. I have used these blades for woodworking similar to a woodworking scraper because I don't have a tool hard enough to put a burr back on a dull wood scraper (bought one, not knowing they may have no burr as delivered and are useless until prepared). When a flat hobby blade gets dull, replace it & save the dull one for dull work (can't think of a good example other than removing calibration labels).

 

[gyraf]

While we're at it - do anyone of you know a way to soften epoxy/glassfiber, perhaps temporary, for when I want to bend/mold/form pcb's slightly?

This could have nice applications if possible..

/Jakob E.

 

[Tubetec]

https://www.essentracomponents.com/...onics/your-pcb-substrate-a-guide-to-materialsEpoxy/glass material generally falls into the rigid catergory , so no matter what you do it will want to return to its original shape . The traces on the board might not hold up well under the extra stress over the longer term either .

 

[JohnRoberts]

While we're at it - do anyone of you know a way to soften epoxy/glassfiber, perhaps temporary, for when I want to bend/mold/form pcb's slightly?

This could have nice applications if possible..

/Jakob E.

that would depend on the epoxy,,, fiberglass fibers are strong longitudinally, but can probably bend some.

There is flexible PCB technology (not fiberglass).

JR

 

[kingcredie]

that would depend on the epoxy,,, fiberglass fibers are strong longitudinally, but can probably bend some.

There is flexible PCB technology (not fiberglass).

JR

Hi John,

If it is FPC, the board will probably be damaged since the coverlay is so thin.

Linda

 

[JohnRoberts]

Hi John,

If it is FPC, the board will probably be damaged since the coverlay is so thin.

Linda

Hi Linda,

If FPC stands for flexible printed circuit, shouldn't it be relatively easy to bend and not require heating?

JR

 

[gyraf]

yeah, but I'd like some stuff that temporarily softens the base material, allowing me to form the PCB, then hardening again

Is that too much to ask?

Full disclosure: I'm getting fed up with the 2D'ness of pcb's. Yes, flexprint and aluprint can bend, but that's boring and taking us only to some 2.25D max. I'd like to be able to go at least a bit further, i.e. forming the surface in both directions at once so I at least have 2½D

/Jakob E.

 

[JohnRoberts]

yeah, but I'd like some stuff that temporarily softens the base material, allowing me to form the PCB, then hardening again

Is that too much to ask?

/Jakob E.

There are two part epoxies but I can't imagine fixing a circuit board afterwards by adding the second part somehow.

Would a flexible circuit board help?

[edit] a circuit board that gets soft from heat, might be undesirable for many applications. /edit]

JR

 

[gyraf]

yeah - but it's the surface topology/shape I'd wish to change for mainly-aesthetic reasons, not really in the flex-pcb way. Am well aware that whatever could do this would probably be prohibitively toxic..

/Jakob E.

 

[ccaudle]

do anyone of you know a way to soften epoxy/glassfiber, perhaps temporary,

The substrate material will have a property labeled as TG, the glass transition temperature. At or above that temperature the substrate will soften, so it has to be above normal reflow temperatures, which for modern solders is around 260C. In other words if you can bring the PCB up to around 275C or 280C if might soften enough that you could bend it gently. The problem will be that if the board has multiple layers you may delaminate the construction, and if the board has traces you will risk breaking the traces on the outside of the bend, and rippling or delaminating the traces on the inside of the bend.
Doesn't seem practical to me, but if you want to attempt it then find a way to slowly and evenly heat the PCB so you don't have additional problems from thermal expansion happening too quickly and cracking something else.

 

[cyrano]

Over on the artistic side, epoxy can be bent. They seem to use heat to do it.

Of course, in artwork, there are no copper traces to damage.

 

[JohnRoberts]

yeah - but it's the surface topology/shape I'd wish to change for mainly-aesthetic reasons, not really in the flex-pcb way. Am well aware that whatever could do this would probably be prohibitively toxic..

/Jakob E.

sounds like you could experiment easily enough.

Good luck.

JR

 

[Script]

I have heat-gunned many entire boards for last exit (Bin / Recycle) at up to 350 degrees and the boards never looked too good after that. Maybe the wrong boards.