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I am developing a prototype that connects sensors to a processing unit (an arduino). The sensors reside inside a boot, which is a demanding location: curved, quite tight, and subject to a decent amount of wear and tear. I have incorporated the sensors into a flex pcb that I believe will work in the location, but am having trouble figuring out how to best connect it to the processing unit.

In an idea world, the flex pcb would be a "T" shape, with the T extending outside the boot and connecting to the arduino. But a T-shaped flex pcb will be much more expensive, so at this stage I'd rather use a small PCB and run wires off it.

What is a good way to attach some signaling wires to the flex pcb? I could solder them on directly, but worry about solder taking too much of the mechanical strain. Is there some other simple option that will be secure and not add much thickness to the flex PCB?

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  • \$\begingroup\$ Solder the wires onto the PCB and then get some hotglue on the joint. The result you'll get will be very similar to how handheld machining tools do it with their cords. They however use some soft plastic to hold their cords, not hotglue. \$\endgroup\$
    – Harry Svensson
    Jul 13, 2017 at 23:26
  • \$\begingroup\$ The standard way is to run the traces on the flex circuit to bare pads on the flex circuit. The bare pads then mate with a zero-insertion force connector on a conventional PCB (in your case, the small PCB you mention). Try googling FPC connector. Should find some hits. \$\endgroup\$
    – user57037
    Jul 14, 2017 at 0:50
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    \$\begingroup\$ @HarrySvensson: Is there a "best practices" pcb layout design for the solder and hotglue combo? I'm assuming I should design the board so the wires are soldered somewhat inboard to give me room to put down hotglue. Should I plan to surface solder the wires, or use 1 or 2 sets of holes to make the solder connection more solid? \$\endgroup\$
    – gkavet
    Jul 15, 2017 at 0:40
  • \$\begingroup\$ @mkeith This solution requires the flex to physically touch the conventional pcb, correct? I need a wire between them for spacing reasons. \$\endgroup\$
    – gkavet
    Jul 15, 2017 at 0:42
  • \$\begingroup\$ This is how I would've done it, I'm not an expert, just saying how I personally would do it. I would make a solder joint like 3 cm from the edge of the flex PCB, then I would make two holes with a diameter of 2 mm. One that is 1cm from the solder and another that is 2cm from the solder, towards the edge. Then I would put the wire through the holes and solder the wire, then I would hotglue very thinly on both sides where the wire is visible. It's easy to make the 2 mm hole with a drill. \$\endgroup\$
    – Harry Svensson
    Jul 15, 2017 at 1:06

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This is the kind of stress relief & connection that I would make, how do you like my paint skills? Top notch? Yeah, uhm, the hot glue (green) would also be on the other side if you're pedantic about it.

enter image description here

With the distance (cm) I was talking about, it would look like this: ISH enter image description here

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