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Repairing mylar cable?

Discussion in 'Electronic Repair' started by John E., Apr 9, 2007.

  1. John E.

    John E. Guest

    Cable was damaged by melting several (6) traces worth of conductors. It's
    part of an expensive controller assembly for which no individual replacement
    parts such as this are available. Terminated end is under membrane switch
    panel which is affixed to the front of the controller. Disassembly to reach
    the other end of the cable would be near-destructive.

    So I'm resolved to fix it. The best approach I can think of is to scrape away
    the light protective coating over the conductors (which aren't copper PC, but
    some painted-on conductive substance) but not scrape too deeply (I've found
    by experimenting that this is Not Good )c: ) and affix 30 ga wires via
    conductive epoxy, bridging the damage.

    I dread this approach because of the fine pitch of the conductors, and not
    knowing until I've finished each patch whether 1) there remains enough
    conductor to patch and 2) the epoxy "took".

    There is about 1 inch undamaged conductor on either side of the damage to
    effect a connection, so if any one attempt at bridging a conductor fails I
    can attempt another, if need be.

    It's going to be rough going, I fear.

    Any other suggestions? Maybe find source for this type of cable and graft it
    to the existing one?

    Sources for these cables?

    Thanks,
     
  2. Guest

    What is the pitch of the conductors?

    Printed circuit manufacturers make flexible printed cables - flexies -
    which are patterns of copper on a variety of substrates. They are
    usually supplied with an insulating layer on both sides of the
    conducting traces.

    You define where you want the copper with "Gerber plots" in the same
    way that you describe a rigid printed circuit board you want
    manufactured.

    Tell us where you are, and someone may be able to suggest the name of
    a supplier in your area.
     
  3. John  Larkin

    John Larkin Guest

    3M makes connectors that pierce such flexprint conductors, with spikes
    that fold over and make good contact.

    John
     
  4. John E.

    John E. Guest

    What is the pitch of the conductors?

    20 conductor, 1 mm pitch, "painted" conductor (not copper strip).

    [...]
    SF bay area, N. California, USA.
    Thanks for your suggestions, Bill.

    On further examination the "flexie" seems to be contiguous with the membrane
    switch backplane; it's one piece, so a replacement doesn't sound likely.

    Now, if a means exists for easily (!) and reliably grafting another
    20-conductor flexie to the good stub, I'm all ears!

    Or... other ideas?

    Thanks again,
     
  5. John E.

    John E. Guest

    3M makes connectors that pierce such flexprint conductors, with spikes
    I wonder if they make a splice connector that would simply connect two
    flexies. Man, that would just save my bucket.

    Other possibility with such connectors: crimp on a female flexie connector
    and use another flexie to bridge the gap.

    Can you recall a trade name? P/N, by chance or by prayer? Source? (c:

    Thanks for your assistance, John. It's a glimmer in the dark...
     
  6. N Cook

    N Cook Guest

    Bare back to conductors , cover whole area with silver loaded paint and when
    cured score lines with ruler and scalpel , pairs of close lines and scrape
    off the areas between lines with a slightly blunt needle against ruler.
    You need a magnifier lamp and check with a DVM before and after the process.
     
  7. John E.

    John E. Guest

    Bare back to conductors, cover whole area with silver loaded paint and when
    Not quite clear to me... does this involve any new flexie material? Or just
    paint? Is paint expected to bridge a gap in the flexie?

    This seems a good way to repair breaks in conductive traces, but a damaged
    flexie...?

    If you could explain in a bit more detail...

    Thanks,
     
  8. N Cook

    N Cook Guest

    does it flex in use or just to assemble/disassemble ?
     
  9. John E.

    John E. Guest

    does it flex in use or just to assemble/disassemble ?

    No movement in use. It is just a means of getting membrane switch inputs to
    the PCB.

    Thanks,
     
  10. John Fields

    John Fields Guest

    See my post to seb.
     
  11. PeterD

    PeterD Guest


    John,

    I've done repairs such as you describe. A PITA, but it worked when I
    was done. I figured it would last a few months and that was maybe four
    years ago. It still works, and sees service in a rugged environment
    with lot's of abuse!

    In my case I used a technique such as your initial idea of the
    conductive epoxy and 30 gauge wires...
     
  12. John E.

    John E. Guest

    In my case I used a technique such as your initial idea of the
    Thanks, Peter. If I can't find a connector-cable-connector solution to my
    problem, it's nice to know that someone has blazed this particular trail with
    these particular tools before.

    Thanks again,
     
  13. John Fields

    John Fields Guest

    ---
    Which one? ;)


    Check this out:

    https://portal.fciconnect.com/porta...YPE&ctx_urlparams_list=|categoryNodeName=FLEX

    If the link wraps, go here:

    https://portal.fciconnect.com/portal/page?_pageid=335,1577673&_dad=portal&_schema=PORTAL&language=EN

    and navigate the menu.

    I think AMP (Tyco) also makes essentially the same thing.

    I think you'll have trouble finding mating males, but if you're
    lucky and the conductor pitch is right, (I'm guessing 0.1")
    you'll be able to use two females and insert a male-male
    header between them.
     
  14. Tam/WB2TT

    Tam/WB2TT Guest

    I can't quite visualize your cable, but can you cut it at the bad spot, and
    clamp it between two pieces of PC board, where one or both PC boards have
    traces on them that line up with your conductors? The connection would be
    made by compression.

    Tam
     
  15. John E.

    John E. Guest

    I can't quite visualize your cable,

    It's just a single-sided, translucent mylar flex cable with 20 "printed"
    conductors on 1 mm centers.
    The success of this would depend on how well I could scrape away the
    protective layer above the "painted" conductors without removing the
    conductive material. I'm not so confident to be able to do that 40 times
    reliably such that the resultant bare conductors would all line up nicely
    with the PC traces.
     
  16. jasen

    jasen Guest

    if there's a gap glue a bridge behind it (you'll have to find an adhesive
    that sticks to it and goes hard, )
     
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