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Repairing silver traces on flexible plastic film

Discussion in 'Electronic Repair' started by Isaac Wingfield, Nov 30, 2004.

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  1. I'm trying to fix a laptop computer keyboard. It's made of three layers
    of thin plastic -- the upper and lower sheets have silver traces (looks
    silkscreened on), and the center sheet is an insulator except that holes
    are punched directly under the keys. When you press a key, the traces on
    the upper and lower sheets are connected.

    Some of the keys don't work and I know exactly where the break is. I
    tried bridging the break using some copper tape with a conductive
    adhesive, but it didn't work. I think soldering will melt the plastic.

    How do I repair this thing?

    Does that conductive-ink pen that Radio Shack sells work reliably? I'm
    reluctant to drop nearly fifteen dollars if it won't do the job, as a
    "new-used" keyboard is only about $50-$60.

    thanks, Isaac
     
  2. NSM

    NSM Guest

    | I'm trying to fix a laptop computer keyboard. It's made of three layers
    | of thin plastic -- the upper and lower sheets have silver traces (looks
    | silkscreened on), and the center sheet is an insulator except that holes
    | are punched directly under the keys. When you press a key, the traces on
    | the upper and lower sheets are connected.
    |
    | Some of the keys don't work and I know exactly where the break is. I
    | tried bridging the break using some copper tape with a conductive
    | adhesive, but it didn't work. I think soldering will melt the plastic.
    |
    | How do I repair this thing?
    |
    | Does that conductive-ink pen that Radio Shack sells work reliably? I'm
    | reluctant to drop nearly fifteen dollars if it won't do the job, as a
    | "new-used" keyboard is only about $50-$60.

    IMO a new keyboard will be your best bet. Most efforts to fix keyboards,
    apart from skilled cleaning, meet with continual failure.

    N
     
  3. Jerry G.

    Jerry G. Guest

    Your best bet is to get a new keyboard. Most of the repairs to these
    keyboards never last very long.

    --

    Jerry G.
    ======

    I'm trying to fix a laptop computer keyboard. It's made of three layers
    of thin plastic -- the upper and lower sheets have silver traces (looks
    silkscreened on), and the center sheet is an insulator except that holes
    are punched directly under the keys. When you press a key, the traces on
    the upper and lower sheets are connected.

    Some of the keys don't work and I know exactly where the break is. I
    tried bridging the break using some copper tape with a conductive
    adhesive, but it didn't work. I think soldering will melt the plastic.

    How do I repair this thing?

    Does that conductive-ink pen that Radio Shack sells work reliably? I'm
    reluctant to drop nearly fifteen dollars if it won't do the job, as a
    "new-used" keyboard is only about $50-$60.

    thanks, Isaac
     
  4. I had this problem on an old IBM Thinkpad. The flex cable was folded
    at one point with the conductors on the outside, and one went open.

    Step 1 was to fix it mechanically. I epoxied a small piece of PCB offcut
    to the back so it became rigid. I folded the cable in a different place
    (and the other way, so the conductors were on the inside of the fold
    which puts them under less stress.)

    To bridge the conductors, I recommend the silver-loaded paint that is sold
    at car places to repair heated rear windows. It's hard to paint in fine
    lines, but one can put too much on and then scrape the excess off.

    Works fine now, though I do try not to take the thing apart too often.

    Mike.
     
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