Flat flex repair ideas

[billclay]

I have a flat flex cable that is torn completely in half.  I want to make a temporary repair, and then discard it.  How would you do it?

The cable is 4mm wide with 12 traces.

[c4757p]

I've fought with messed up FFC a few times before. Never works out. And it was nothing like yours - twelve traces in 4mm?? I'm cringing just hearing about it. Just replace the cable.

[Psi]

I've repair hacked flat flex before the tracks were a mm wide with 1.5mm clearance between them so it was much easier.
I used some sharp copper pins to push through the plastic for each track in the flex.  Then I soldered the pairs together with wire between the pins.
For thin flat flex, like what you have, that isnt going to be possible.

Do you have room to cut and overlap the two ends?
If so, and you can get access to the exposed conductive layers, you might be able to sandwich some of that rubber ZEBRA strip stuff between the ends.

http://en.wikipedia.org/wiki/Elastomeric_connector

[XOIIO]

I've repair hacked flat flex before the tracks were a mm wide with 1.5mm clearance between them so it was much easier.
I used some sharp copper pins to push through the plastic for each track in the flex.  Then I soldered the pairs together with wire between the pins.
For thin flat flex, like what you have, that isnt going to be possible.

Do you have room to cut and overlap the two ends?
If so, and you can get access to the exposed conductive layers, you might be able to sandwich some of that rubber ZEBRA strip stuff between the ends.

http://en.wikipedia.org/wiki/Elastomeric_connector

That would be the best option, not sure if he can find zebra strip that fine, but even if they can be pressed together hard enough it might work for a bit

[FrankenPC]

If you have a microscope and insane patience, you can try electrically conductive epoxy: http://www.amazon.com/AA-CARB-Electrically-Conductive-Temperature-Adhesive/dp/B00EPYBRFE/ref=sr_1_3?ie=UTF8&qid=1404056307&sr=8-3&keywords=electrically+conductive+epoxy

 You would have to scrape the plastic outer layer away then hold down the two halves so they are butted against each other and completely flat.  Using a tiny pin, glob the epoxy on the adjacent copper traces until you've joined them all.  Then, after that has dried, place a layer of normal epoxy over the whole thing it give it strength.  Keep in mind, you can't flex this at all.   

[Tinkerer]

The way flat flex is made, its practically impossible to repair. Like people have said, get a new one.

[senso]

How about sanding the kapton(is it?) insulating layers, and throw a bit of z tape at it, migh work, or not.
I lost my laptop keyboard to a broken connection in the flat flex, and it was a pain in the but to find a new one the the pt layout.

[fluxcapacitor]

heres a flat flex repair video on youtube,ive used this method myself and it does work. The video is in russian but its easy to follow.

[Rasz]

you  can

a/ find replacement

or

b/ find matching connectors, buy two, solder them back to back (on small pcb or line them up in hot glue first), scrape off soldermask from flex ends, insert into connectors

or

c/ cut 1cm, scrape off soldermask in strategic places, find properly sized clamp that looks like:
http://www.proepster.de/Shop/big_pics.php?topic=shop&lang=de&id=388280&pic=produkt_pic/111718.png
+ 1 flat pieces of rubber, line it up with 1cm piece on top to make a connection and press fit together.


d/ make small pcb with patching pitch, solder both flex ends to that pcb back to back using leaded solder and lowest temp you can get away with


e/ be hardcore
https://www.eevblog.com/forum/projects/possible-to-repair-0-2-mm-spacing-flat-flex-cable/msg269379/#msg269379

[What_NZ]

To really answer the question I would need to see some pictures of the cable and the connectors at each end. Also see how the cable is routed through the unit.

[idpromnut]

An alternative to sourcing a replacement part (if you can't fix this part) is to maybe use one of these PCB houses that offer Flexible PCBs, like iTeadStudio and design your own part: http://imall.iteadstudio.com/open-pcb/pcb-prototyping/2layer-flexible-printed-circuits-fpc-5cm-x-5cm-max.html

It ain't cheap, but it might be worth not having to toss the device you're trying to repair if you can't find replacements.

[RetroGameModz]

Hello everyone! First post on the forum.
I used the search function and found this thread, which I thought would be a perfect place for my question.

I am currently trying to take on an impossible repair of a flat flex cable. I say "impossible" because considering the circumstances, most people (including myself) would consider it to be impossible. However, I am not a person who easily gives up without a fight.

First of all, replacing the flat flex cable is not possible. This is because the flat flex cable is not going into a connector at both ends, but only at one end. The other end of it is going into the plasma display panel of a plasma TV that I'm trying to repair. What this means is that either I repair the flat flex cable, or the plasma panel that the cable is attached to will become scrap and end up in the landfill. This will probably happen to the rest of the TV as well since sourcing a new plasma panel for it is not easy.

Since the flat flex is not replaceable, trying to repair it is my only option before giving up.
The pitch of the conductive traces? Trust me, you don't want to know. Actually, I don't have any exact measurement of it, but it's so small that it's near impossible to see the individual traces going parallel to each other inside the flex circuit. The traces can be easily seen under a microscope of course, but the width of the traces are so small that a human hair looks big in comparison. Because of this, using a point-to-point soldering technique to patch up the broken traces is completely impossible, no matter how small the iron tip is. So I have already given up on that idea.

But before scrapping the TV, there is just one more thing I would like to try.
If the whole flat flex cable is cut off right at the problem area (all conductors are going in parallel there), then maybe I could attempt to scrape off the coating on both "ends" of the cable (where it's cut), leaving me with conductive traces on both ends, then lap soldering the whole cable together again.
The pitch of the traces is ridiculously small, but the reason I think this could perhaps work is because of the same principle as with drag soldering; you don't get any bridging between pins/traces because of the reduced surface tension of the flux. Therefore, by aligning the cable ends together so that the conductive traces align up but with a bit of overlap on every trace, maybe I could reattach the conductors and make it all work.

Since the conductors are so incredible small, any physical stress to any conductor will break it off. If that happens it's game over.
The flat flex cable has a COF on it. It's a one layer flex circuit (if it was a two layer, I wouldn't even attempt the repair). The upper side is coated with some green kind of coating acting as a solder mask, and the lower side consists of a brown-orange looking material, quite similar to the color of kapton tape. This acts as the substrate of the flex circuit. (Is it maylar, perhaps?)
I have managed to get the green coating off at one end of the cable, exposing the conductive traces. I managed to to this with only minor damage to some traces, which I think I will be able to repair.
However, I have now gotten stuck and am unsure how to proceed. Because I need to free the conductive traces from the bottom side of the flex circuit as well, leaving nothing but the exposed conductors for a length of 1 mm or so. This is the length that is to be overlapped to the other "end" of the cable that I'm reattaching to.

Now to my question.
How can I get the brown-orange bottom (mylar?) flex substrate to separate from the conductive traces without damaging the traces or accidentally solder the traces together? How are the traces bonded to the bottom flex substrate during manufacture of the flat flex cable? Is there any kind of chemical out there that can dissolve this bonding material, without causing any harm to the conductive traces? Any suggestions?

I do realize that I'm going to fail with this attempt with 99.5% certainty. If the pitch had at least been within reasonable limits, then I might have gotten away with a point-to-point patching technique with a higher chance of success. But because of the fine pitch, I consider my chances being slim to none. Still though, like I mentioned, I don't like to give up without first having a good fight.