How to dissolve the solder mask on a PCB?

[Matador]

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

There are still some paint strippers with methylene chloride that can be found. They can be applied with a Q-tip, left to work for 10-15 minutes, and turn soldermask into a jelly that can be wiped off. The main hitch is that they'll also weaken and remove the copper if left on for too long, so you have to monitor it closely.

 

[gyraf]

Thanks, guys - you made me think. Will report back if I find a good way...

/Jakob E.

 

[ccaudle]

There are still some paint strippers with methylene chloride

What do they do to the epoxy in the substrate?
According to Wikipedia methylene chloride (also dichloromethane) "chemically welds certain plastics." Sounds like you need to be pretty careful with it around typical equipment with e.g. plastic knobs, faceplates, plastic parts in pots, etc.

 

[murrayatuptown]

I am wondering if I missed that the original question was about a flex PCB, or that was a suggestion later. My abuse of PCB's was only on non-flex types.

Subsequent discussion of subjecting PCB's to other chemicals reminded me of situation where a technician request to strip conformal coating from a PCB for troubleshooting was referred to an onsite chemist who surprised the group by saying he needed to check that everything on that board was compatible with the terpene-based stripper, and thanked them for asking instead of just doing it without inquiry. He was concerned that some plastic-body IC's were not permitted due to ingress or absorption of the solvent.

There was such a document already for that board and it was OK. It was a hi-rel product-hence the neurotic level of documentation.

 

[Matador]

What do they do to the epoxy in the substrate?
According to Wikipedia methylene chloride (also dichloromethane) "chemically welds certain plastics." Sounds like you need to be pretty careful with it around typical equipment with e.g. plastic knobs, faceplates, plastic parts in pots, etc.

To be honest I've only used them to remove soldermask on unpopulated boards, and it was to "uncover" vias so I could use them to probe signals that ran on intermediate layers to BGA arrays where the "exits" would be covered by a package. So long as you dab it on, wait for it to 'bubble' up, then you can wipe away the soldermask. I never had any issues with the actual fiberglass or the copper, however I've heard that if you leave it on for a long time, it can cause the copper to delaminate.

And yes, it's really nasty stuff, however paint stripper is less than 1% concentration so it isn't the worst either.

 

[murrayatuptown]

More (impractical) thoughts...there are abrasive processes to remove certain board coatings where solvents aren't OK. I don't know what magical properties powdered walnut husk or shell has, but that is what I saw used. It was not exactly a sandblaster, but that concept. I also don't know how ESD was controlled in that process.

I also can't remember what was used to remove Parylene coating (I can't, or won't, spell the other name), just that you didn't want it where it didn't belong.

But that has nothing to do with shape-shifting a board-sorry...

 

[kingcredie]

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.

Hi,

That's a good idea, but it is hard to implement in practice.
Linda

 

[kingcredie]

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

Hi John,

Even if it is a FPC board, the place that suitable for bending is only the area of pure lines/tracks. The positions of the holes and the components are not suitable bending.

Linda

 

[kingcredie]

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.

Hello,

Usually, the common material can bear about 280 degrees in 5 seconds. 350 degrees is too high.

Linda

 

[Script]

Yes, I too replace SMDs at lower temperatures. Question was whether heat can help shape or bend a board -- and I'd say: definitely not the ones that I decommissioned (at 350).

 

[RoadrunnerOZ]

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.

Heat the board right through above 180F - if you go too high thr fibre/epoxy bonds will deteriorate and the board can buckle permanently and you can melt IC sockets, edge connectors and some capacitors - if you bend more than a few degrees the print will crack or buckle depending on whether you’re stretching or compressing the print - or both if it’s double sided. Large size SMD IC’s will tear the solder pads off the board or shear the tiny print connections to the pads as they won’t flex with the board. Resistors can crack if pulled too hard on the convex side of the board.
If the temp is too high the solder will melt - I have repaired graphics cards by baking at 200C (390F) which partially reflows the solder on the GPU.
Chemically once epoxy is softened by soaking in any form of solvent it never re-hardens. For PCB’s for the epoxy they use it’s likely the softening temp is well above the factory soldering temps.

 

[Matador]

Lots of places are doing aluminum PCB's: I wonder if those meet Gyraf's criterion of bendable while warmed then mostly rigid?

 

[RoadrunnerOZ]

Lots of places are doing aluminum PCB's: I wonder if those meet Gyraf's criterion of bendable while warmed then mostly rigid?

They are already flexible for the LED Strip type - you can bend them to a right angle and the copper doesn’t break because it’s held on with a flexible adhesive resin strip which also compresses around corners. With thicker aluminium I would imagine that once bent it stays bent. Some also have heat sinks glued to the back for heat dissipation with LED’s I doubt you’d be bending those.

 

[kingcredie]

Although the aluminum board can be bent, it is almost one-time. If bend many times, the traces will be damaged.
Linda

 

[murrayatuptown]

I've also used something like Excelta 267/267A fiberglas-tip 'scratch brush' when I have one. Sometimes I can't find a replacement 267A tip after wearing one down to a nub. Dust is nasty, but the tool can be controlled fairly well for 'macro' areas, not so well for 'micro'. About US$12 on Amazon. Made in Germany so I imagine available readily in Europe.

They make other variations (262). I don't know if finer tools have evolved with SMD lead pitch.

 

[RoadrunnerOZ]

Those fibreglass brush pens come with about 10 refills these days and they’re cheap.

 

[gyraf]

..fiberglass brush pens are effective, but the pieces they shred are very, very nasty - please take care when using these..

/Jakob E.

 

[Script]

Yes, should wear gloves and not breath in particles...

 

[RoadrunnerOZ]

For removing PCB mask some automotive degreasers containing methylene chloride will do the job but as soon as the mask is cleared the area needs to be wiped with water and Isopropyl. Also some paint strippers wil do the job.