How To Repair Broken Trace On Flex Cable

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Repairing flexible pcb connector rail?

Discussion in 'Electronic Repair' started past Ian P, Jul 29, 2022.

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In the form of doing some modifications to a very expensive Sony 3 scrap 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 just the bad
flake is the tracks are only 0.1mm broad on a 0.2mm pitch! Ideally one would
just supplant the flex pcb simply in practice that would involve dismantling the
photographic 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 because abrading off the top mylar blanket to expose the copper
and then bridging the breaks with some very narrow pitch zebra strip. My other
idea is to make my ain miniature insulation displacement/piercing connector
using a stack of razor blade bits sandwiched with insulation layers.

The last option would exist to apply 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 whatsoever thoughts or experiences if anyone has whatever.

Cheers

Ian
This is "not different" fixing a PCB trace. How would you do that?
What nearly globbing some eutectic solder over the traces (even though it
shorts them), and then using "something" to suspension the solder into individual
"strands" while information technology's still liquid?

I'yard wondering whether zebra strip would be conductive enough? Information technology might non
matter over such a curt (ar, ar) altitude.

I wish you success. And if this happened this morning, please put it aside
and relax. Work on something else, something easy, and effort 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 pigment designed to repair
automotive window heaters.
Assuming you're not in a stripline-blazon state of affairs with ground plane/rf
considerations, endeavor plaiting some magnet wire and soldering to the 3 pcb
solder points at either end of the plaited section of "ribbon", you may
take to brand a hole through the pcb though.
Based on my experience of trying to repair adventitious damage to flexiprints
(yes, it happens to united states all no affair how long nosotros've been in the game and how
experienced we are !) I think that y'all are going to struggle to go 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-indicate soldering tip and under a microscope, and using a single strand
from superflex instrument cable, such as is used for meliorate quality meter
leads, for instance.
I don't know whether this is a commercial job, or i for a friend, or maybe
even for yourself, but before y'all commit to whatever strategy that'due south going to
waste a lot of time, and stop up with no fix at the end of it anyway, the job
would probably stand up being left for a solar day or two, before revisiting it with
a articulate head, to await at how hard replacing the flexiprint would *actually*
be. I've often plant that things that look as though they are going to be a
copper-bottomed-gilt-plated bitch to practise, are actually not then bad, when
looked at over again after you've calmed down, and forced a degree of 'san fairy
ann' into your head over it. If you take a re-create of the service transmission or tin
obtain one, a look at the parts listing will tell you if replacement is even an
selection (if you're really unlucky it might be an integral function of the lens
assembly) and if it is available, a look at the exploded view diagram, would
exist helpful to determine how many 'hidden' branches the flexiprint has, and
where they get.

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

Good luck with it, and please post dorsum, and let us know how you go on with
information technology :-\

Arfa
William
I too wondered about how conductive zebra strip is only considered information technology for
this because the tracks are so narrow they are probably only carrying logic
level signals whereas some of the other tracks in this detail flex are
over one.5mm broad.

Information technology 'happened' several days ago so have got over the initial shock and
annoyance with myself. I am non rushing in until feel right.

Ian
Its a newspaper thin flexible pcb, aureate brownish in colour which I remember is made
from Mylar. Because of the narrowness of the tracks and their spacing I
doubtfulness it could be done with paint.
Ian
Its only depression level analogue signals but the break is close to the cease 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 like shooting fish in a barrel!
Ian
It happened several days ago and so have got over the initial stupor Proficient. That means you'll probably come with the "least bad" solution.
Arfa
Thanks for your advice. As you lot postulated this pcb is integral with the lens
and although I accept the total 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 impairment though and I demand to
repair it because there is not actually any alternative.

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

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

Ian
Thanks for your advice. Equally you postulated this pcb is integral with the I'k starting to go the feeling that maybe you should "bite the bullet" and
have Sony do the repair. It'due south going to cost a lot of coin, merely it might exist
worth information technology, simply in the grief saved.
If I tin can repair the broken tracks I will locally stiffen the ribbon so that
information technology will not be discipline to flexing anyway. Your idea of staggering the links
(which I might do with wire and soldering) means that I accept a bit more room
to piece of work with.
Ian
I feel for you lot, it's a serious oops moment to recover from.
Contact Sony for an idea of price of ready, then yous can place importance
of fixing yourself in your mind? If you can afford the gear up at least
at that place'southward a way out.

You've got stuff to practice with, but I tin can't come across how y'all're going to
reliably connect to that fine pitch. Are at that place accessible places where
the cutting tracks get wider? Do the cut tracks terminate to accessible
places where you tin create another, separate cablevision to bridge the
breaks?

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

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

Take it easy, information technology is not a blitz job.

Grant.
I am not certain that Sony would want to repair the camera now considering I was in
the procedure of carrying out electromechanical modifications and then its a bit non
standard.
Ian
The subassembly in question is the lens. Parts of the cable are wrapped
round and glued to the lens trunk, and the simply way to access it is to
completely dismantle the bulk of the photographic camera, more or less reversing the
original manufacturers associates process.
Ian
Another possibility, if you get to the point of 'kill or cure', and
depending on how much space yous've got to play with. I have had considerable
success on remaking the ends of flexiprints, that take failed from bending
at the stiffening film at the connection betoken. Y'all can advisedly knife off
the last few mm of cable, then re-expose the impress 'fingers' by abrading the
plastic. I actually use a edgeless curved scalpel bract. Once the fingers have
been thus exposed, the cable tin be reinserted in the connector, and and so
the original stiffener pushed dorsum in behind to give a good tension on the
connector again. Suppose now that y'all could cut right across where the
harm is, and re-expose connector fingers at each cutting end. If y'all could
then obtain connectors, and solder them back to back, you could so use
this as a joint to remake your cable. I realise that with such a fine pitch,
the soldering would not be easy, merely at least you would be doing it on the
bench, in the open up, and with good light. A strong magnifier would be enough
to exist able to run across what you are doing, and some liquid flux, and desoldering
braid, should make the task do-able.
Along like lines, another possibility might be to over again cut correct across
the cable, and expose the conductors on the upper surface of i end, and
the lower of the other. Then treat it every bit a surface mount soldering job. If
you lot use liquid flux, solder paste, and hot air, and do a good job of lining
upward the tracks and preventing move before you commencement, at that place'south a good
chance of success at making a satisfactory join. Capillary activity will pull
the solder onto the tracks, and providing you lot've been sparing with it, there
shouldn't exist whatsoever shorts between tracks.

Arfa
No, making hole/s through the pcb, to take the plait, so you tin make proper
solder joins to pre-existing solder joints on the ribbon sockets
If heat resistant and then probably kapton tape. If indicate levels and you have a
fairy godmother then anisotropic tape is another possibility , if y'all can
bare back to the underlying condusctors .
Arfa
You have made some very good suggestions there and I can tell you've had
some feel in repairing things others would not even consider! I can
come across no reason why the lapped joint idea wouldn't work, all the same the backside
of the flex is probably the substrate that the copper was plated onto and
scraping that off might exist very tricky.

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

Ian
I wouldn't hesitate to do this, just I'd not effort information technology whatsoever
without a microscope. Can y'all borrow one?

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