Electronic – Attaching wires to flex pcb

connectorpcbsolderingwire

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?

Best Answer

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.

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

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Solder doesn’t stick wires to connectors

175C is pretty low for soldering. Low temperature lead solder ("63/37") melts around 185C, RHoS solder even melts around 250C. You also do not seem to use flux - do it. The solder flows fast and evely if the pads/pins have the right temperature. If you have problems with soldering in general check solderingguide.com, the soldering is easy comic or the tons of videos on youtube.

Electronic – Clamp / pierce into flex PCB

I suggest neither melting nor crimping because the copper is way to thin and fragile (unlike magnet wire, where you melt away the insulation - and unlike a comparatively massive stranded or solid wire used for crimping, the 17, 35 or 70 µm Cu layer on flex "boards" is just way too thin for either method!).

Flex boards are usually composed of a polyimide (PI) substrate below and a coverlayer above the etched copper traces:

xxxxxxxxxxxx coverlayer or flexible soldermask
------------ Cu traces (thin!)
============ PI substrate

PI is heat resistant and as a base material for copper traces to be soldered on, is about as good as good ol' FR4.

Try finding out on which side you have the coverlayer, use something sharp to scratch it off, and try to solder onto the copper that remains on the PI substrate. The best way would be to clean away the coverlayer (or flex soldermask) and put the thing into a ZIF socket, because solder blobs on a flex "board" might not last long under mechanical stress - but I guess for a hobbyist's approach, soldering might do.

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Electronic – Clamp / pierce into flex PCB

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