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Does anyone have a good solution for a mechanical connector for flexible printed PCB, like those used for strips of common-cathode RGB LEDs?

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(You can cut the strip across any of the solder pads and scrape back the silicon insulation)

"Just solder" isn't the answer I want to hear (neither is "get better at soldering") as a) I need to do lots of these joins which need to be b) mechanically sound and ideally c) field-repairable, in quite a tough field (on the playa at Burning Man.) The joints need to be mechanically sound as I plan to sew about 30 x 50cm strips into a garment.

Ideally I'd like some kind of screw-terminal. But I don't know what to ask for and can't find one on my own.

Another idea I've come up with is taking 90° header pins and pushing/piercing/drilling little holes for them through the printed track and soldering those in (a much easier task—I've found component-through-hole soldering orders of magnitude easier than wire-to-pad soldering; tracks lift and it's hard to get everything to bloody stay still.) Anyone think this might work and/or tried it?

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  • \$\begingroup\$ Can you give us a bit more information about your application? Is the flex PCB going to be moving around a lot? I could see issues with placing a large rigid connector on the flex pcb and having the solder joints come loose. \$\endgroup\$ – Kellenjb Oct 25 '10 at 19:01
  • \$\begingroup\$ So you are wanting something that will crimp down on the pads marked 12v, g, r, and b and have a screw that loosens/tightens the crimp? \$\endgroup\$ – Kellenjb Oct 27 '10 at 2:12
  • \$\begingroup\$ Precisely. (Then on the other side, either more screw terminals for the connecting wires, or 2.5mm pitch sockets/pins) \$\endgroup\$ – Robert Atkins Oct 28 '10 at 1:38
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How thick is the flexible PCB that you are using? Could you put a flat flex connector on your board and design your flexible pcb to socket into it?

Hmm... As I type this I wonder if this will actually work. I would be interested in what someone who has used flex pcb has to say.

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  • \$\begingroup\$ that is almost right. Generally you have the socket on the rigid pcb and plug (pins) on the end of the flex. Sometimes flex straight into a connector, other time, rigid - flex -rigid combination and a small strip of rigid that goes into the connector on the rigid pcb. \$\endgroup\$ – smashtastic Oct 26 '10 at 6:35
  • \$\begingroup\$ Can you give me a link to a picture of one of these "flat flex connectors" of which you speak? \$\endgroup\$ – Robert Atkins Oct 27 '10 at 10:45
  • \$\begingroup\$ imperial-connect.com/connectors/flat-flex-cable-connector.aspx They come in different pin counts and pin pitch. They usually have a clip that you slide on to lock the cable in place. \$\endgroup\$ – Kellenjb Oct 27 '10 at 15:18
  • \$\begingroup\$ I think I get the idea but I can't quite see how they work from the pictures on that page. Other problem is that supplier seems to carry maximum 1mm pitch, I'd need 2.5mm as that's the spacing on my solder pads. But I'll shop those pictures around Sim Lim Tower and see if anyone bites. \$\endgroup\$ – Robert Atkins Oct 28 '10 at 1:36
  • \$\begingroup\$ That supplier was just found from a google images search. Here is an actual list of different types mouser.com/Interconnects/Rectangular-Connectors/… \$\endgroup\$ – Kellenjb Oct 28 '10 at 2:24
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i'd probably solder some 18-20awg stranded wire to the ends of the flex, after you solder, coat the joint with some decent strength insulating epoxy such that there is a firm physical attachment between the wire and the flex material to remove any stress from the solder joint. The stranded wire should be strong but flexible enough to not break and run back to your controlling box which i assume will be on your belt or something.

The wire shouldn't be too bad on the weight of the clothing if you use some light stuff with thin insulation and loosly stitch it into the cloth so it can slide back and forth a bit. The wire attachment into the control box could be screw terminals, although i'd recommend some sort of quick disconnect with a tension relieving mechanism for the wire, 3m makes a lot of connectors that would work.

Ideally leave enough slack in the wire that the slack doesn't get into the way but there isn't a tension issue on the connection to the box. You can probably stitch a sliding loop of wire into the back of the top of the 'clothing' such that tension on the wire that results from crazy dancing around fires just contracts the loop rather than putting much strain on the wire connectors.

I don't know if that picture you posted is of the actual strips you plan to use but if so i'd go over all the exposed solder joints with epoxy or some other sealing insulator. Between the heat and the shenanigans at Burning Man i wouldn't count on those strips staying dry.

As for field repair, bring a tube of epoxy (an environmentally friendly type highly recommended for Burning Man) and a battery powered solder iron. I imagine you'll have a solar battery charger of some sort with you anyway so that should cover it, maybe a bit of solder. Worst case you can be the town soldering helper, i'm sure you'll find someone in need.

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  • \$\begingroup\$ He specifically says "just solder" is not the answer he is looking for. \$\endgroup\$ – Kellenjb Oct 27 '10 at 6:34
  • \$\begingroup\$ Yeah, sorry—the problem is not connecting the wires to the control box, but connecting the strips to eachother. I'd down vote, but I don't have the required reputation. \$\endgroup\$ – Robert Atkins Oct 27 '10 at 10:40
  • \$\begingroup\$ And yes, the strip pictured is the actual one I'm using. \$\endgroup\$ – Robert Atkins Oct 27 '10 at 10:42
  • \$\begingroup\$ how is soldering then using epoxy for a mechanical connection "just soldering" ? \$\endgroup\$ – Mark Oct 27 '10 at 13:04
  • \$\begingroup\$ Ok, we're talking at crossed purposes: my original sentence was meant to read as "'Just solder [you lazy/incompetent bastard, if you were any good at it the joints would be both mechanically and electrically sound]' isn't the answer I want to hear." I am both lazy and incompetent and I know that out of 120-odd joints I'd have to make, I'd screw at least one of them up and have no chance of finding the fault and repairing it onsite. \$\endgroup\$ – Robert Atkins Oct 27 '10 at 15:30

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