3
\$\begingroup\$

I accidentally tore my Lego EV3's LCD FPC (Flexible Printed Circuit) while opening it. The FPC is a 1.0mm 18-pin-pitch FPC which near the end is converted to a 0.5mm one.

I found this post in the Bricks Stack Exchange of someone a while back having the same issue, however as my tear is smaller I was wondering if it was possible to fix it:

Image of torn 18-pin ribbon cable

Nothing has been taken away from the FPC, and the torn part still fits in with the rest. It is not possible to replace the screen as it was custom made by Lego to fit the EV3.
I have a soldering iron along with a basic kit.

\$\endgroup\$
12
  • 3
    \$\begingroup\$ That's a difficult fix. Not impossible, but I'm not sure you'll have much success if you're not experienced with this kind of work. (Also, what soldering iron? Cheap ones are usually garbage and will cause more problems than they solve.) \$\endgroup\$
    – Hearth
    Commented Sep 7, 2023 at 14:44
  • 1
    \$\begingroup\$ Possible? Yes. But it would require extreme precision repairing something so fine. \$\endgroup\$
    – Simon B
    Commented Sep 7, 2023 at 14:48
  • \$\begingroup\$ @Hearth not sure how high quality my soldering iron is, but I have have a very fine tip and it has adjustable temperature May you suggest alternatives to soldering it? The cable is soldered onto the LCD if that helps. \$\endgroup\$
    – pythoncat
    Commented Sep 7, 2023 at 15:15
  • 5
    \$\begingroup\$ Barring a repair, get a junk unit with a good ribbon and swap it. \$\endgroup\$
    – rdtsc
    Commented Sep 7, 2023 at 16:10
  • 1
    \$\begingroup\$ That is not a ribbon cable. That is an FPC (Flexible Printed Circuit), and it mates to an FFC (flat Flex Cable) socket. \$\endgroup\$
    – Davide Andrea
    Commented Sep 8, 2023 at 12:46

3 Answers 3

Reset to default
4
\$\begingroup\$

Your best bet is to try to scrape off the polyimide covering the copper on both sides of the tear, repair the tear with a bit of fine-gauge wire-wrap wire soldered to it (use leaded solder. Lead-free is not worth the extra trouble, especially here), and then after verifying that you didn't short two pins together, cover the whole thing in a protective coat of lacquer. Nail polish or automotive touch-up paint will probably work as that protective coat.

You'll need a pretty fine tip on your soldering iron. Make sure it's a temperature controlled iron (not necessarily adjustable--just controlled. Note that it can be adjustable and still not be controlled.). I specify because you say you have "a basic kit", and cheap soldering irons that are often included in such kits or bought alongside them cause way more problems than they solve.

\$\endgroup\$
1
  • \$\begingroup\$ Use a small piece of kapton tape to reinforce the tear \$\endgroup\$
    – D Duck
    Commented Sep 8, 2023 at 14:10
3
\$\begingroup\$

I would suggest using a small piece of FPC cable with the same pitch instead of trying to fit any wires there. This way you do not need any special soldering iron or other fine tools.

Remove about 1 mm of polyimide coat on each end of the patch piece and on the edges of damaged cable. Tin with low-temperature solder. Put patch in place and melt the solder straight through the polyimide on the other side. Make sure to use plenty of flux to avoid bridges.

The above works better if you cut off the flapping piece and prepare accurate place for the patch. Alternatively, if the traces are not damaged, you can align them together and solder patch piece with 2mm of film removed on top of a tear, then cut off excess of patch.

There are several methods for removing the insulation, like chemical dissolution, thermal or mechanical. Search the web for whatever is suitable for you. Here is an example. Mechanical seems to be better fit here as it allows you to expose copper traces on one side only.

\$\endgroup\$
1
  • \$\begingroup\$ I agree. Low temperature solder is key to success. It needs to be lower melting point than typical leaded solder. \$\endgroup\$
    – Kuba hasn't forgotten Monica
    Commented Sep 8, 2023 at 14:16
2
\$\begingroup\$

In my experience the key to success is being able to see what you’re doing - a binocular microscope is ideal but anything that aids vision, including good lighting, is better than nothing.

It’s also important to make clean soldered connections; heat the copper, apply solder and let the joint cool. If you need to rework the joint the solder will quickly oxidise so it’s better to scrape the excess off with your iron and start again.

Use lead solder, as this is easier to work with than lead-free. Good luck!

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.