1. Home
  2. Electronics Repair
  3. Unusual pcb corrossion problem

Unusual pcb corrossion problem

Remote control about 5 years old, no spillages or abuse. I don't know how they make the pcbs , perhaps something like this. Conformal coating over pcb and tracks, etched back around the button pads or some other process and then laying down the black resistive-conductive tracks.

1mm or so green/blue lump (copper sulphate/carbonate?) in one of these "guard" rings around a pad and neat hole in a track under. Another such lump , similarly placed, but copper not etched through under. Both lumps at the battery end so perhaps outgasing from batteries rather than air pollution. But battery box on the other side of pcb
Reply to
N_Cook
Loading thread data ...

Five years old would mean it was assembled with lead-free solder. That requires very active flux to get the solder to stick to the copper. The board was not properly washed after assembly, so some of the flux is still on the copper. That causes the "lumps" to form.

Conformal coating merely limits the moisture getting to the traces and components, doesn't entirely eliminate it. I doubt your remote control has conformal coating. It's expensive to apply.

I had a similar experience with an electric gate opener. The antenna/receiver part is connected by wire to the main control box. The whole system became erratic. I finally looked in the little receiver/antenna box and found lots of white fuzz on parts of it's circuit board. Carefully cleaned the board with IPA (isopropal alcohol) and all worked properly, again. The board had not been cleaned after the connecting wires were soldered to the board.

Paul

Reply to
Paul Drahn

how

pcb

lump

the

pollution.

I didn't think to check for PbF but more than likely. Another factor could be fibre board pcb and some fibres cross the width of the board and then an easier path for gas from batteries. Green tint lacquer, if not conformal coating, over the board

Reply to
N_Cook

I hope you meant FR4 fiberglass for the board when you wrote "fibre board". If not, then I don't have a clue about how the board was manufactured. Most circuit boards have a green solder mask layer with writing on it showing, at least, the component id and perhaps a board name and revision level. The solder mask is a very thin transparent sheet of fiberglass that is laminated with the board. That is probably what you are seeing.

Paul

Reply to
Paul Drahn

Open up some remote controls. You will find that virtually all of them use phenolic type circuit boards.

Solder mask is not a thin layer of fiberglass. Usually the stuff is a photo sensitive coating that is spread across the board surface. It is then exposed to light through the solder mask artwork layer which changes the material that is exposed to the light. Afterwards a wash process is used to remove the part of the solder mask that is over the pads on the board.

--

Michael Karas
Carousel Design Solutions
http://www.carousel-design.com
Reply to
Michael Karas

Because somewhrre along the way the resistive-conductive black stuff has to be in good reliable electrical contact with the underlying copper and then no coating over those.

Reply to
N_Cook

know

over

and

these

such

at

The

The

alcohol)

the

could

an

Sounds like the now common solder mask, far lower cost the older = conformal coating (usually applied after board assembly).

?-)

Reply to
josephkk

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.