Connecting plastic membrane to pc board

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Long time, no post! I've been rather busy with new job. I've actually been making a living for the last 2 years.

Playing with my trains, I'm getting annoyed with how often the silly RC controlers have to go back for repair. "Hey, Dummy," I thought, "You're an Electronics Engineering Tech and you make things that hold up better than this junk all the time."

Does anybody know how to connect these thin plastic membrane traces to a pc board on a hobbiest basis? I'd like to replace the calculator pc board with my own nefarious function :twisted:

The finished gadget might be mounted in my favorite enclosure -- an Altoids box. Unless I can get it small enough to fit in this $1 calculator from Wal*Mart. :)

The largest known prime number: 282589933-1

Without adult supervision.

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Quote:
Does anybody know how to connect these thin plastic membrane traces to a pc board on a hobbiest basis?

You really can't (at least it's REALLY difficult). You need the right socket, which is probably surface mount (again, not a hobbyist thing).

If you try to solder, you'll just melt the flex circuit.

It looks like the flex circuit is connected to a PCB. Can you take the signals off of that?

-Paul

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Search Digi-Key for FFC/FPC connectors. They have several flavors.

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pkafig wrote:
Quote:
Does anybody know how to connect these thin plastic membrane traces to a pc board on a hobbiest basis?

You really can't (at least it's REALLY difficult). You need the right socket, which is probably surface mount (again, not a hobbyist thing).

I've been making PCBs at home for years using surface-mount parts.

Leon

Leon Heller G1HSM

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actually here it looks like it's a glued connection. you might be able to carefully peel the flex circuit off the original PCB, retaining the original adhesive, and then simply press it back against your own PCB. it'll be a compression connection, so if you can add pressure to the connection in the case, it will help maintain connection.

Writing code is like having sex.... make one little mistake, and you're supporting it for life.

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Quote:
FFC/FPC connectors

Ah! The name of those dealies! Hmm. Digikey gets me 997 items, but if I try to narrow it with any of the filters, I get "no matches." That's usually how these search engines work.

There's 28 pins. The pitch looks to be 1mm WM5712CT-ND looks to be the deal! WM5704TR-ND looks to match the keypad, almost. The keypad has 11 contacts.

The largest known prime number: 282589933-1

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not sure what it is called in english but theres a silver solvent you can paint electrical tracks with (used for repairs etc.) you can probably just paint the connection to you board and then throw a big lump of glue on top of it to keep it safe

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I bailed out bought displays with pins to solder :lol:

The largest known prime number: 282589933-1

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For these I sometimes do what pkafig said. If it's an old calculator and you don't need it anyways, just dremel the board right after the flex connector, and solder from the PCB..

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glitch wrote:
actually here it looks like it's a glued connection. you might be able to carefully peel the flex circuit off the original PCB, retaining the original adhesive, and then simply press it back against your own PCB. it'll be a compression connection, so if you can add pressure to the connection in the case, it will help maintain connection.

Tried this method today with a disposed something-o-meter. The glue was somewhat weak, but unfortunately strong enough to destroy the flex cable's contacts; they still remained on the PCB, and the cable was now useless. I guess wires of the flex cable were made from conductive ink of some sort, making them fragile by nature.

It might be possible to soften the glue with heat or chemicals. Of course, if the glue is heat curing this may backfire :D

-Simo (browsing through old postings)

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If the stripes on the flex cable match the tracks on your PCB, it is possible to use the zebra conductive rubber out of a damaged LCD (between the glass and the PCB)with a clamp over the top. It adds some more resistance but can still work. Some flex circuits (eg keyboard matrices) are clamped directly onto graphite plated tracks on the PCB.

C. H.
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