Flex Circuit attachment method

Discussion in 'General Electronics Chat' started by SIcam, Aug 14, 2009.

  1. SIcam

    Thread Starter Active Member

    Aug 9, 2008
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    I am doing a hack on an electronic item that has buttons that are attached to a PCB with flex circuits. The I am trying to figure out how to connect to the flex circuit. How do I connect 30 ga wire to the circuits?
     
  2. Wendy

    Moderator

    Mar 24, 2008
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    How perminant does it have to be? Something like grabber clips?

    [​IMG]

    These suckers can be less than 1" long, and are used all the time for mods of existing designs.
     
  3. SIcam

    Thread Starter Active Member

    Aug 9, 2008
    61
    0
    The attachment needs to be permanent.

    I am wanting to attach to the flex circuit on a digital camera. The flex circuit is used for the ON/OFF, zoom +/-, focus, and pic connection to the board. The traces on the board are extra tiny so I was hoping to take a broken camera and tap into the circuit were is spreads apart into larger traces in the flex circuit. Maybe if I use silver epoxy I could glue the trace to an external wire.

    what is the smalled insulated wire I can get? 30 GA?
     
  4. Wendy

    Moderator

    Mar 24, 2008
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    It's gonna be iffy. How're soldering skills? You can use solder, but it is going to take an extra fine touch, and a iron with a small temp controlled tip, and conventional lead/tin solder.

    I don't think you're thinking of going in the flex cable? I'm thinking where it is soldered into its PCB.
     
  5. BillB3857

    Senior Member

    Feb 28, 2009
    2,400
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    Ribbon cable similar to that used for hard disk drives???
    Connectors are available that can be soldered to the circuit board and the cable plugged in.
     
  6. GetDeviceInfo

    Senior Member

    Jun 7, 2009
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    I've often found it easiest to solder onto the device legs.
     
  7. SIcam

    Thread Starter Active Member

    Aug 9, 2008
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    0
    I have soldered to some tiny stuff but the legs on this connector are very very small and narrowed spaced. Since I have a broken camera I thought it would be easier splicing into the pads on the flex connector higher up.
     
  8. rjenkins

    AAC Fanatic!

    Nov 6, 2005
    1,015
    69
    I've done a few mods on gear that uses flex circuit connectors.

    The method I've come up with is:
    Split the flex cable to individual conductors with a very! sharp knife.
    If you use light pressure and pull the blade from, say, 20mm in towards the end, it tends to follow the slight depression in the insulation between conductors.
    Repeat a few times until that conductor is seperated & so on.

    Tin the ends of the conductors. I find putting the iron square on the end of the conductor & steadily feeding solder, it will burn back the insulation. Tin it for 3 - 4 mm.

    Get some very thin, flexible insulated wire. I use 10/0.1mm stripped from thin multicore.

    Strip & tin the ends of that for 3-4 mm.

    Hold the tinned bit against the side of a tinned flex conductor (so you are extending it, not doubled back) and touch with a freshly tinned iron to flow the joint.

    After they are all done, put a 1cm piece of hi-shrink heatshrink sleeve over each joint. The stuff I use is 3:1 ratio, 3mm down to 1mm. Be very careful shrinking the sleeve, if you get a flame too close to the flex circuit you can crozzle it...

    After all the joints are insulated, carefully roll the flex cable side to side to push all the joints into a tight bundle and put a 25mm piece of larger heatshrink over the whole thing as a strain relief. If the flex cable is too short to do this, smother the joint area with quickset epoxy or none-corrosive RTV silicon.

    The individual flex conductors are extremely fragile from where they are split and an overall strain relief is essential to stop them cracking as you move the joined-on wires about, hence the extra sleeve or silicon.

    If you replace a PC CD or DVD drive, the old one is often a good source of (among other items) micro pitch flex cables - they often use them for linking the optical head carriage to the circuit board. Wider ones are available on ebay as ZIF hard drive connecting cables.
     
    Last edited: Aug 17, 2009
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