Repairing flexible pcb connector track?

[Ian P]

In the course of doing some modifications to a very expensive Sony 3 chip HD
camcorder I have accidentally cut through 3 tracks on the edge of a mylar?
flexible cable. On the good side the damage is very accessible but the bad
bit is the tracks are only 0.1mm wide on a 0.2mm pitch! Ideally one would
just replace the flex pcb but in practice that would involve dismantling the
camera and lens to get to all the places the pcb branches out to, and in
some places it actually goes into the lens mechanism itself.

I am considering abrading off the top mylar coating to expose the copper
then bridging the breaks with some very narrow pitch zebra strip. My other
idea is to make my own miniature insulation displacement/piercing connector
using a stack of razor blade bits sandwiched with insulation layers.

The last option would be to use wire links and solder but I think this could
only be done with some sort of mechanical micropositioning rig in view of
the small sizes involved.

I would be interested to hear any thoughts or experiences if anyone has any.

Cheers



Ian

 

[William Sommerwerck]

This is "not unlike" fixing a PCB trace. How would you do that?

What about globbing some eutectic solder over the traces (even though it
shorts them), then using "something" to break the solder into individual
"strands" while it's still liquid?

I'm wondering whether zebra strip would be conductive enough? It might not
matter over such a short (ar, ar) distance.

I wish you success. And if this happened this morning, please put it aside
and relax. Work on something else, something easy, and try to forget about
this problem for the time being.

 

[Meat Plow]

This is "not unlike" fixing a PCB trace. How would you do that?

What about globbing some eutectic solder over the traces (even though it
shorts them), then using "something" to break the solder into individual
"strands" while it's still liquid?

I'm wondering whether zebra strip would be conductive enough? It might
not matter over such a short (ar, ar) distance.

I wish you success. And if this happened this morning, please put it
aside and relax. Work on something else, something easy, and try to
forget about this problem for the time being.

Flexible pcb connector as in a ribbon connector? I've had some limited
success repairing these with conductive paint designed to repair
automotive window heaters.

 

[N_Cook]

In the course of doing some modifications to a very expensive Sony 3 chip HD
camcorder I have accidentally cut through 3 tracks on the edge of a mylar?
flexible cable. On the good side the damage is very accessible but the bad
bit is the tracks are only 0.1mm wide on a 0.2mm pitch! Ideally one would
just replace the flex pcb but in practice that would involve dismantling the
camera and lens to get to all the places the pcb branches out to, and in
some places it actually goes into the lens mechanism itself.

I am considering abrading off the top mylar coating to expose the copper
then bridging the breaks with some very narrow pitch zebra strip. My other
idea is to make my own miniature insulation displacement/piercing connector
using a stack of razor blade bits sandwiched with insulation layers.

The last option would be to use wire links and solder but I think this could
only be done with some sort of mechanical micropositioning rig in view of
the small sizes involved.

I would be interested to hear any thoughts or experiences if anyone has any.

Cheers



Ian

Assuming you're not in a stripline-type situation with ground plane/rf
considerations, try plaiting some magnet wire and soldering to the 3 pcb
solder points at either end of the plaited section of "ribbon", you may
have to make a hole through the pcb though.

 

[Arfa Daily]

In the course of doing some modifications to a very expensive Sony 3 chip
HD camcorder I have accidentally cut through 3 tracks on the edge of a
mylar? flexible cable. On the good side the damage is very accessible but
the bad bit is the tracks are only 0.1mm wide on a 0.2mm pitch! Ideally
one would just replace the flex pcb but in practice that would involve
dismantling the camera and lens to get to all the places the pcb branches
out to, and in some places it actually goes into the lens mechanism
itself.

I am considering abrading off the top mylar coating to expose the copper
then bridging the breaks with some very narrow pitch zebra strip. My other
idea is to make my own miniature insulation displacement/piercing
connector using a stack of razor blade bits sandwiched with insulation
layers.

The last option would be to use wire links and solder but I think this
could only be done with some sort of mechanical micropositioning rig in
view of the small sizes involved.

I would be interested to hear any thoughts or experiences if anyone has
any.

Cheers



Ian

Based on my experience of trying to repair accidental damage to flexiprints
(yes, it happens to us all no matter how long we've been in the game and how
experienced we are !) I think that you are going to struggle to get a fix on
one of that tiny pitch. I have had plenty of success with abrading and
soldering ones of a slightly greater pitch, doing it with a tiny
needle-point soldering tip and under a microscope, and using a single strand
from superflex instrument cable, such as is used for better quality meter
leads, for instance.

I don't know whether this is a commercial job, or one for a friend, or maybe
even for yourself, but before you commit to any strategy that's going to
waste a lot of time, and end up with no fix at the end of it anyway, the job
would probably stand being left for a day or two, before revisiting it with
a clear head, to look at how hard replacing the flexiprint would *really*
be. I've often found that things that look as though they are going to be a
copper-bottomed-gold-plated bitch to do, are actually not so bad, when
looked at again after you've calmed down, and forced a degree of 'san fairy
ann' into your head over it. If you have a copy of the service manual or can
obtain one, a look at the parts list will tell you if replacement is even an
option (if you're really unlucky it might be an integral part of the lens
assembly) and if it is available, a look at the exploded view diagram, would
be helpful to determine how many 'hidden' branches the flexiprint has, and
where they go.

I really feel for you on this one. I've been there many times over the years
....

Good luck with it, and please post back, and let us know how you get on with
it :-\

Arfa

 

[Ian P]

This is "not unlike" fixing a PCB trace. How would you do that?

What about globbing some eutectic solder over the traces (even though it
shorts them), then using "something" to break the solder into individual
"strands" while it's still liquid?

I'm wondering whether zebra strip would be conductive enough? It might not
matter over such a short (ar, ar) distance.

I wish you success. And if this happened this morning, please put it aside
and relax. Work on something else, something easy, and try to forget about
this problem for the time being.

William

I too wondered about how conductive zebra strip is but considered it for
this because the tracks are so narrow they are probably only carrying logic
level signals whereas some of the other tracks in this particular flex are
over 1.5mm wide.

It 'happened' several days ago so have got over the initial shock and
annoyance with myself. I am not rushing in until feel right.

Ian

 

[Ian P]

Flexible pcb connector as in a ribbon connector? I've had some limited
success repairing these with conductive paint designed to repair
automotive window heaters.

Its a paper thin flexible pcb, golden brown in colour which I think is made
from Mylar. Because of the narrowness of the tracks and their spacing I
doubt it could be done with paint.

Ian

 

[Ian P]

Assuming you're not in a stripline-type situation with ground plane/rf
considerations, try plaiting some magnet wire and soldering to the 3 pcb
solder points at either end of the plaited section of "ribbon", you may
have to make a hole through the pcb though.

Its just low level analogue signals but the break is close to the end of the
ribbon where the tracks are gold plated to fit in the board connector. The
copper conductors are encapsulated in the Mylar and drilling through the
track which is only 0.004" wide would not be easy!

Ian

 

[William Sommerwerck]

It happened several days ago so have got over the initial shock

and annoyance with myself. I am not rushing in until feel right.

Good. That means you'll probably come up with the "least bad" solution.

 

[Ian P]

Based on my experience of trying to repair accidental damage to
flexiprints (yes, it happens to us all no matter how long we've been in
the game and how experienced we are !) I think that you are going to
struggle to get a fix on one of that tiny pitch. I have had plenty of
success with abrading and soldering ones of a slightly greater pitch,
doing it with a tiny needle-point soldering tip and under a microscope,
and using a single strand from superflex instrument cable, such as is used
for better quality meter leads, for instance.

I don't know whether this is a commercial job, or one for a friend, or
maybe even for yourself, but before you commit to any strategy that's
going to waste a lot of time, and end up with no fix at the end of it
anyway, the job would probably stand being left for a day or two, before
revisiting it with a clear head, to look at how hard replacing the
flexiprint would *really* be. I've often found that things that look as
though they are going to be a copper-bottomed-gold-plated bitch to do, are
actually not so bad, when looked at again after you've calmed down, and
forced a degree of 'san fairy ann' into your head over it. If you have a
copy of the service manual or can obtain one, a look at the parts list
will tell you if replacement is even an option (if you're really unlucky
it might be an integral part of the lens assembly) and if it is available,
a look at the exploded view diagram, would be helpful to determine how
many 'hidden' branches the flexiprint has, and where they go.

I really feel for you on this one. I've been there many times over the
years ...

Good luck with it, and please post back, and let us know how you get on
with it :-\

Arfa

Arfa

Thanks for your advice. As you postulated this pcb is integral with the lens
and although I have the full service manual for the camera it give no
information at all on the lens which is a bought in item (not removable
though). The job is not really commercial, for a friend or myself but it a
sort of combination of all three. I caused the damage though and I need to
repair it because there is not really any alternative.

I have in the past repaired and modified boards and components and used thin
wire just as you described, this cable though has track and spacing widths
that are really challenging, and I don't have any microscope.

I have lots of old bits of similar flexible boards and cables so I am going
to experiment with them.

Ian

 

[William Sommerwerck]

Thanks for your advice. As you postulated this pcb is integral with the

lens and although I have the full service manual for the camera it give no
information at all on the lens which is a bought in item (not removable
though). The job is not really commercial, for a friend or myself but it a
sort of combination of all three. I caused the damage though and I need
to repair it because there is not really any alternative.

I have in the past repaired and modified boards and components and used
thin wire just as you described, this cable though has track and spacing
widths that are really challenging, and I don't have any microscope.

I have lots of old bits of similar flexible boards and cables so I am going
to experiment with them.

I'm starting to get the feeling that maybe you should "bite the bullet" and
have Sony do the repair. It's going to cost a lot of money, but it might be
worth it, simply in the grief saved.

 

[Ian P]

I've had some luck repairing individual breaks with a conductive repair
pen.

Given the pitch you are working with, you might have to expose spots on
each
trace that are separated by a few millimeters along the length of the
traces to prevent bridging them with the ink.

I'm not certain how well the conductive ink stands up to continued
flexing.
Gluing some stiff backing behind the area of the repair might be a good
idea.

If I can repair the broken tracks I will locally stiffen the ribbon so that
it will not be subject to flexing anyway. Your idea of staggering the links
(which I might do with wire and soldering) means that I have a bit more room
to work with.

Ian

 

[Grant]

In the course of doing some modifications to a very expensive Sony 3 chip HD
camcorder I have accidentally cut through 3 tracks on the edge of a mylar?
flexible cable. On the good side the damage is very accessible but the bad
bit is the tracks are only 0.1mm wide on a 0.2mm pitch! Ideally one would
just replace the flex pcb but in practice that would involve dismantling the
camera and lens to get to all the places the pcb branches out to, and in
some places it actually goes into the lens mechanism itself.

I am considering abrading off the top mylar coating to expose the copper
then bridging the breaks with some very narrow pitch zebra strip. My other
idea is to make my own miniature insulation displacement/piercing connector
using a stack of razor blade bits sandwiched with insulation layers.

The last option would be to use wire links and solder but I think this could
only be done with some sort of mechanical micropositioning rig in view of
the small sizes involved.

I would be interested to hear any thoughts or experiences if anyone has any.

I feel for you, it's a serious oops moment to recover from.

Contact Sony for an idea of cost of fix, so you can place importance
of fixing yourself in your mind? If you can afford the fix at least
there's a way out.

You've got stuff to practice with, but I can't see how you're going to
reliably connect to that fine pitch. Are there accessible places where
the cut tracks get wider? Do the cut tracks terminate to accessible
places where you can create another, separate cable to bridge the
breaks?

IOW, sidestep trying to repair the damage by creating an alternate
circuit.

Seems to me it's a cable replacement, but that could be sub-assembly
replacement if the flex also gets glued in place to some smaller parts.

Take it easy, it is not a rush job.

Grant.

 

[Ian P]

I'm starting to get the feeling that maybe you should "bite the bullet"
and
have Sony do the repair. It's going to cost a lot of money, but it might
be
worth it, simply in the grief saved.

I am not sure that Sony would want to repair the camera now because I was in
the process of carrying out electromechanical modifications so its a bit non
standard.

Ian

 

[Ian P]

I feel for you, it's a serious oops moment to recover from.

Contact Sony for an idea of cost of fix, so you can place importance
of fixing yourself in your mind? If you can afford the fix at least
there's a way out.

You've got stuff to practice with, but I can't see how you're going to
reliably connect to that fine pitch. Are there accessible places where
the cut tracks get wider? Do the cut tracks terminate to accessible
places where you can create another, separate cable to bridge the
breaks?

IOW, sidestep trying to repair the damage by creating an alternate
circuit.

Seems to me it's a cable replacement, but that could be sub-assembly
replacement if the flex also gets glued in place to some smaller parts.

Take it easy, it is not a rush job.

Grant.

The subassembly in question is the lens. Parts of the cable are wrapped
round and glued to the lens body, and the only way to access it is to
completely dismantle the bulk of the camera, more or less reversing the
original manufacturers assembly procedure.

Ian

 

[Arfa Daily]

Arfa

Thanks for your advice. As you postulated this pcb is integral with the
lens and although I have the full service manual for the camera it give no
information at all on the lens which is a bought in item (not removable
though). The job is not really commercial, for a friend or myself but it a
sort of combination of all three. I caused the damage though and I need to
repair it because there is not really any alternative.

I have in the past repaired and modified boards and components and used
thin wire just as you described, this cable though has track and spacing
widths that are really challenging, and I don't have any microscope.

I have lots of old bits of similar flexible boards and cables so I am
going to experiment with them.

Ian

Another possibility, if you get to the point of 'kill or cure', and
depending on how much space you've got to play with. I have had considerable
success on remaking the ends of flexiprints, that have failed from bending
at the stiffening film at the connection point. You can carefully knife off
the last few mm of cable, then re-expose the print 'fingers' by abrading the
plastic. I actually use a blunt curved scalpel blade. Once the fingers have
been thus exposed, the cable can be reinserted in the connector, and then
the original stiffener pushed back in behind to give a good tension on the
connector again. Suppose now that you could cut right across where the
damage is, and re-expose connector fingers at each cut end. If you could
then obtain connectors, and solder them back to back, you could then use
this as a joint to remake your cable. I realise that with such a fine pitch,
the soldering would not be easy, but at least you would be doing it on the
bench, in the open, and with good light. A strong magnifier would be enough
to be able to see what you are doing, and some liquid flux, and desoldering
braid, should make the job do-able.

Along similar lines, another possibility might be to again cut right across
the cable, and expose the conductors on the upper surface of one end, and
the lower of the other. Then treat it as a surface mount soldering job. If
you use liquid flux, solder paste, and hot air, and do a good job of lining
up the tracks and preventing movement before you start, there's a good
chance of success at making a satisfactory join. Capillary action will pull
the solder onto the tracks, and providing you've been sparing with it, there
shouldn't be any shorts between tracks.

Arfa

 

[N_Cook]

Its just low level analogue signals but the break is close to the end of the
ribbon where the tracks are gold plated to fit in the board connector. The
copper conductors are encapsulated in the Mylar and drilling through the
track which is only 0.004" wide would not be easy!

Ian

No, making hole/s through the pcb, to take the plait, so you can make proper
solder joins to pre-existing solder joints on the ribbon sockets

 

[N_Cook]

Its a paper thin flexible pcb, golden brown in colour which I think is made
from Mylar. Because of the narrowness of the tracks and their spacing I
doubt it could be done with paint.

Ian

If heat resistant then probably kapton tape. If signal levels and you have a
fairy godmother then anisotropic tape is another possibility , if you can
bare back to the underlying condusctors .

 

[Ian P]

Another possibility, if you get to the point of 'kill or cure', and
depending on how much space you've got to play with. I have had
considerable success on remaking the ends of flexiprints, that have failed
from bending at the stiffening film at the connection point. You can
carefully knife off the last few mm of cable, then re-expose the print
'fingers' by abrading the plastic. I actually use a blunt curved scalpel
blade. Once the fingers have been thus exposed, the cable can be
reinserted in the connector, and then the original stiffener pushed back
in behind to give a good tension on the connector again. Suppose now that
you could cut right across where the damage is, and re-expose connector
fingers at each cut end. If you could then obtain connectors, and solder
them back to back, you could then use this as a joint to remake your
cable. I realise that with such a fine pitch, the soldering would not be
easy, but at least you would be doing it on the bench, in the open, and
with good light. A strong magnifier would be enough to be able to see what
you are doing, and some liquid flux, and desoldering braid, should make
the job do-able.

Along similar lines, another possibility might be to again cut right
across the cable, and expose the conductors on the upper surface of one
end, and the lower of the other. Then treat it as a surface mount
soldering job. If you use liquid flux, solder paste, and hot air, and do a
good job of lining up the tracks and preventing movement before you start,
there's a good chance of success at making a satisfactory join. Capillary
action will pull the solder onto the tracks, and providing you've been
sparing with it, there shouldn't be any shorts between tracks.

Arfa

Arfa

You have made some very good suggestions there and I can tell you've had
some experience in repairing things others would not even consider! I can
see no reason why the lapped joint idea wouldn't work, however the backside
of the flex is probably the substrate that the copper was plated onto and
scraping that off might be very tricky.

I'm leaning towards fine wire soldered jumpers across the breaks.

Ian

 

[Smitty Two]

I'm leaning towards fine wire soldered jumpers across the breaks.

I wouldn't hesitate to do this, but I'd not attempt it whatsoever
without a microscope. Can you borrow one?