Repairing flat flexible cable

[btgc]

This whole thing started as malfunctioning lens and traced down to damaged tracks in flat flexible cable. It consists of semi-rigid brown plastics with tracks inside.
One end is connected to contact plate and two tracks look like torn from being bent (not sure why because there's no movement) very close to solder points.

My plan is to carefully melt plastics over tracks on both ends using small tip soldering iron, make it clean and restore conductivity using wire glue. Damage is at very end of cable right under lens contact plate where it doesn't have any movement and will stay fixed...in fact I wonder how it got damaged....

Some people use conductive pen but that is just ink which can't handle force and will break, but there will be some when installing contact plate back to mount. So I've opted for conductive glue or wire glue as they call it.

Which type of conductive glue can you recommend? I need one which will cure and stay semi rigid so probably no epoxy type, and retain integrity over time. What is general experience with conductive glues?

 

[btgc]

Just talked to repairman I know, his opinion is only soldering under microscope or replacing flex cable. He rejected idea about conductive glue as viable repair option. Hm. At the moment he just can't help me with soldering, for independent from him reasons.

 

[FrozenInTime]

You may be able to bridge the crack with just solder if the joint does not flex.
If it does flex, try Litz wire -which is very flexible . It comes in very thin gauges and consists of many strands of even finer wire each enamel coated - this melts off when dipped into a blob of molten solder on the end of the soldering iron.

To get solder to adhere to the flex traces, you will have to scrape the flex wires clean with a scalpel.

 

[Landshark]

We would use an Xacto knife to scrape the traces clean and use a few strands from ~30ga wire. Used clear nail polish to insulate it.

 

[btgc]

Thanks for your ideas and support.

Yes, that's the whole case - to clear traces covered by plastics, and not damage other traces as damage is at place where ribbon makes turn, next to contact board. I have dealt with tiny things but this is really small.

Another culprit I see is to solder wire to the end which is next to contact on the board, I mean, not to loosen contact in its place - not sure if it is secured in place only by solder from wire end or pressed in tightly (have never dealt with this before).

 

[sevo]

These things are actually fabricated by printing conductive paint onto a flexible base, galvanizing the results before giving it a final coat. Overall, the materials are too thin and fragile to do partial repairs - but it should be feasible to make a replacement. The process does not need mass production to be viable, there ought to be companies that fabricate prototypes and one-of variations of the genre, and perhaps some 3Ds printer capable of printing with a conductive material could even be used to directly print such a flexible PCB.

 

[btgc]

I've read about guy who purchased flex cable to be made for his lens but as one were too costly, he ordered batch of 20 or so. After repairing his lens and selling rest of cables he has covered his expenses and even made some money 🙂
My lens isn't that common and while only two tracks are affected I'd prefer to go repair route as it would be heck of job to reattach contacts at all ends and control chip (I haven't explored if it's soldered to some board or directly to cable, but it's very close to it).

 

[mikemc_photo]

My first thought after many daunting repairs of unique mechanisms is "Can you get a new part?"

It sounds as your trusted repairman has seen the issues and wisely passed.

What is it from? any pictures of your damage?

 

[kzphoto]

There was a thread floating around awhile back which described some type of conductive marker with which one could draw leads or repair circuits. Repairing for cables is a daunting task! Find a skilled repair tech, electronics engineer or anyone with reflow soldering certificates.