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| Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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#1
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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 |
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#2
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Unusual pcb corrossion problem
On 1/17/2012 12:46 AM, N_Cook wrote:
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 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 |
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#3
Posted to sci.electronics.repair
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Unusual pcb corrossion problem
Paul Drahn wrote in message
... On 1/17/2012 12:46 AM, N_Cook wrote: 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 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 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 |
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#4
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Unusual pcb corrossion problem
On 1/18/2012 1:04 AM, N_Cook wrote:
Paul wrote in message ... On 1/17/2012 12:46 AM, N_Cook wrote: 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 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 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 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 |
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#6
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Unusual pcb corrossion problem
Michael Karas wrote in message
... [This followup was posted to sci.electronics.repair and a copy was sent to the cited author.] In article , says... 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 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 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. |
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#7
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Unusual pcb corrossion problem
On Wed, 18 Jan 2012 09:04:56 -0000, "N_Cook" wrote:
Paul Drahn wrote in message ... On 1/17/2012 12:46 AM, N_Cook wrote: 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 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 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 Sounds like the now common solder mask, far lower cost the older conformal coating (usually applied after board assembly). ?-) |
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