How to repair a ribbon cable connection on consumer electronics

It’s not uncommon in cheaper devices to find a ribbon cable soldered directly to the circuit board like the one pictured above. Using a connector would have been a much more resilient approach, but adding parts adds cost. If you take a close look you’ll see things aren’t looking so great anymore. [Chaotic and Random] pulled this board out of his VW Camper Van. Rather than buy an expensive replacement part, he shows us how to repair a soldered ribbon wire connection.

This repair is rather invasive and he suggests trying some hot-air rework (possibly using a heat gun) to fix up any misbehaving connections. But if that has failed it’s time for the knife. The first step is to  cut the ribbon so that the LCD can be removed from the board. From there he peels the remaining scrap off ribbon of the pads. This makes us cringe as it could lift traces from the PCB, but he was gentle enough to avoid it. Now comes the time to start reassembling. After thoroughly cleaning the pads the ribbon is cut straight and resoldered. The trick is to flow the solder without melting the ribbon. He uses tin foil to cover the tip and cools it on a moist sponge just before reflowing solder.

It sounds like more art than science. But when the only alternative is to spend hundreds on a new part it may be worth a try.

Comments

  1. Uky says:

    Nice. The very thin flex ribbons on newer small electronics doesn’t even melt at soldering temps, making it easy to solder.

    • nes says:

      If the substrate melts it means it probably wasn’t soldered in the first place. Glued connections to flexible substrates are quite common and are a royal PITA to fix. 3M make an eye-wateringly expensive top-bottom conductive double-sided sticky tape for this kind of application.

      • Uky says:

        I have had a lot of luck with a conductive trace writer pen to fix breaks, can be used to draw finer lines than solder for even the smallest traces.

      • J. Peterson says:

        I’ve also seen a number of these glued connectors fail. It’s strictly adhesive that’s holding a non-metallic (carbon?) conductor in place. These are very commonly used to attach the LCD glass to a PCB.

      • mundanecat says:

        The eye-wateringly expensive tape to use, I think, would be 3M’s 9705/9706. Not much is needed, but a roll needs to be sourced. In their data sheet, they say to bring the adhesive to 70-100 C to make removal easier. After cleanup, just pressure is needed to adhere the two surfaces (i.e. the ribbon and the PCB). The tape is neat; it is designed to conduct through the two surfaces but not along them–like water through a bunching of drinking straws.

  2. willrandship says:

    This kind of problem is the number one thing that breaks in TI calculators.

  3. Jason says:

    Look into a product called Chip Quik – it’s an alloy that reduces the temperature at which the solder melts, and it makes rework like this very easy.

  4. Andrew B says:

    I have some success with this sort of connection, grab a piece of TO-220 heatsink pad, turn your soldering iron down to about 280C (550F). Put the pad at a start point on the flex connector, side of iron tip nearly parallel to boards on pad, and drag the pad along the connect flex keeping the iron in contact. Doesn’t need much pressure. This can take 15 to 20 passes, it takes a while for the whole setup to warm up, but you don’t want to over do it. In one particular job, a 128×64 LCD, I have found that I can actually have the LCD powered while I go through this process, and can see the results immediately. Has worked with flex to PCB and flex to glass bonds. YMMV

  5. cutandpaste says:

    I repaired a break in a very similar ribbon cable on my old(ish) BMW recently.

    First I stripped off a layer of plastic on one side of each end, and cleaned and tinned the exposed copper.

    After that, I overlapped them by about 1MM, lined things up, taped it in place (clear packing tape on the back side), and applied heat directly through the plastic on the top.

    On each conductor (there were only a half-dozen or so), I also immediately applied pressure to the hot joint after removing the iron, to keep things compressed as it cooled off. (I used a chunk of plastic for this, incidentally from a Radio Shack 1/8″ plug, which worked fine. A wooden implement would also work well.)

    I found that the plastic had a high-enough melting point that I could apply a hot iron directly to it to heat the layers below, and still come back with a good-looking joint instead of a smoldering mess.

    I was amused by how ridiculously easy it was to splice this sort of cable, which looked impossible or not even worth trying until I looked up the cost of even a used replacement part and realized that it was certainly worth a few hours of repair effort, even if it didn’t work.

    But it did work, and I’m happy with that. :)

  6. jaap says:

    Once you have fixed a thin ribbon cable (and its just a strait piece of cable with the same end connectors), it helps to swap the whole cable around, so the parts of the cable that have been stressed most often end up in a location where they don’t move at all.
    Tip for whoever assembled HP designjet 500 plotters: make sure that when the printhead is in its right-most location, the cable is long enough to still make a nice U-bend, and does not kink near the printhead….

  7. Matthew says:

    I had this problem with a Saab 9-5, they used the same thing, alternating carbon strips and adhesive. 3M (I believe) make the cables, and sell a very expensive tool to bond them. There is a specific heat/cool curve that needs to be followed to ensure it bonds and then solidifies properly.

    Quick fixes were usually to jam a rubber band against the contact points and compress it in, or to apply a hot air tool to it and press the ribbon down with the end of a wooden ice lolly stick.

    The design issue with the Saab at least was that you were placing this cable in a box, under a black dashboard, with 8x 1 watt incandescent bulbs for illumination. Then placing it on top of a stereo system that runs hotter than the nose of a shuttle.

    Eventually, a replacement cable which relied on manual pressure was installed, and all was well :)

  8. Webster says:

    No need to cringe over the risk of lifting traces. The component is already dead as you go in. It really can’t get more wrecked. The standard solution is to pay a chunk of cash for a new part. Hacking the dead board is a gamble to win, with nothing to lose.

  9. James says:

    It seems a bit of education is in order. The connector shown is called a heat seal connector. It is attached using both heat and pressure to bond the material to the glass and PCB. My company actually makes a piece of equipment to do this, our main customer being 3M who makes the material. Do not put a hot iron on it directly and do not add any solder. Most usually a quick fix for this type of connection is to just take a soldering iron set to a lower temp and apply heat to the traces through a thin piece of rubber. We call this rubber material an interposer. The bonding temp would be about 180C. The reason this material is used the most is the pitch of the connections. It is hard to find a connector that is .050″ pitch or less and can connect with ITO traces on a piece of glass. The alternative is a zebra connector. Happy to answer question of you have them.

    • dude says:

      Thats exactly how I repair broken original gameboys. You would be amazed how many people throw out or sell off “broken” gameboys. I have saved dozens from getting thrown out this way. Just open it and put something over the end of the ribbon that wont melt and hit it with an soldering iron and pressure. No cutting necessary I do this while it is on to see which lines need more or less heat. They will turn black or clear, then go to normal as they cool. I once bought 8 broken gameboys for 10 bucks and got 7 of them working this way. Not too shabby.

  10. kxbx says:

    Is there any reason a locking connector couldn’t be soldered to the board? It would remove any difficult with registration and avoid having to heat the ribbon cable.

  11. James says:

    The heat seal connector is just to thin and soft to use any sort of off the shelf connector. The HSC we are using right now is 0.002″ thick. It is not a FPC type of material. A FPC cable could be attached to the LCD with ACF and you could put the end of that in a connector but then it is much more costly. ACF=Anisotropic Conductive Film

  12. sunblock says:

    Where exactly did he find an LCD screen on a VW camper van??!

  13. Jon says:

    Hi, I recently managed to repair my ripped flex cable in my Panasonic camcorder, so I thought the video I made of me doing it may be useful to others. It’s on youtube here:

    Regards Jon

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