Unusual pcb corrossion problem

N

N_Cook

Guest
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
 
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
Click to expand...
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
 
Paul Drahn <pdrahn@webformixair.com> wrote in message
news:jf4c7a$okn$1@dont-email.me...
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
Click to expand...
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
 
On 1/18/2012 1:04 AM, N_Cook wrote:
Paul Drahn<pdrahn@webformixair.com> wrote in message
news:jf4c7a$okn$1@dont-email.me...
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
Click to expand...
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
 
[This followup was posted to sci.electronics.repair and a copy was sent
to the cited author.]

In article <jf6qu4$8r5$1@dont-email.me>, pdrahn@webformixair.com 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
Click to expand...
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
 
Michael Karas <mkaras@carousel-design.com> wrote in message
news:MPG.298157d7264c17259896be@news.eternal-september.org...
[This followup was posted to sci.electronics.repair and a copy was sent
to the cited author.]

In article <jf6qu4$8r5$1@dont-email.me>, pdrahn@webformixair.com 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
Click to expand...

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.
 
On Wed, 18 Jan 2012 09:04:56 -0000, "N_Cook" <diverse@tcp.co.uk> wrote:

Paul Drahn <pdrahn@webformixair.com> wrote in message
news:jf4c7a$okn$1@dont-email.me...
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
Click to expand...
Sounds like the now common solder mask, far lower cost the older conformal
coating (usually applied after board assembly).

?-)
 
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