"Arfa Daily" wrote in message
news:gcp4o.319800$Yb4.133179@hurricane...


"Ian P" wrote in message
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"Arfa Daily" wrote in message
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"Ian P" wrote in message
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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

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


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