Repairing flexible pcb connector track?

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

Reply to
Ian P
Loading thread data ...

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.

Reply to
William Sommerwerck

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.

Reply to
Meat Plow

HD

the

connector

could

any.

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.

Reply to
N_Cook

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

Reply to
Arfa Daily

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

Reply to
Ian P

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

Reply to
Ian P

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

Reply to
Ian P

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

Reply to
William Sommerwerck

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

Reply to
Ian P

going

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.

Reply to
William Sommerwerck

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.

--
Paul Hovnanian  paul@hovnanian.com
----------------------------------------------------------------------
 Click to see the full signature
Reply to
Paul Hovnanian P.E.

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

Reply to
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.

Reply to
Grant

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

Reply to
Ian P

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

Reply to
Ian P

Look for a dead unit on ebay for parts.

--
Anyone wanting to run for any political office in the US should have to
have a DD214, and a honorable discharge.
Reply to
Michael A. Terrell

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

Reply to
Arfa Daily

chip

would

dismantling

in

copper

of

the

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

Reply to
N_Cook

it

individual

made

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 .

Reply to
N_Cook

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.