flexible circuit 'board'

[dadx4]

Has anyone done any playing w/ flexible circuit 'boards'?

Was thinking conductive paint screened onto a flexible substrate. Components attached w/ conductive adhesive (epoxy?).

Just wondering if anyone has toyed w/ anything similar w/ any degree of sucess.

[BeanieBots]

As a reliabilty engineer for many years, my suggestion is don't do it. Almost all failures are where something flexes. Even professionally produced "flexible" PCBS are notoriously unreliable if allowed to actually flex. A permanent "fold" such as those found in compact video cameras and the like is OK so long as normal operation does not cause movement. The break is always a hairline fracture and almost impossible to see with the naked eye making fault finding even harder.
Conductive paint is likely to flake and crack as would any other form of paint that is not specifically designed to flex.
By all means have a play, but be warned.

[Michael 2727]

Camera manufacturers use flexible film quite a bit, I have even seen entire circuits done
this way and mulitlayer also, but as BB said they are not really meant to move once in place.
It's just a way to jam circuits into awkward limited space, they are held together with lots of
double sided tape. Dry solder joints can be hard to find at the best of times they need no
encouragement.

I can almost hear the cogs ticking, over the Tasman, rubberized Bread Board.

Sorry, I hadda doit, ~ ;o)

[dadx4]

Point taken.

I was thinking flexible more for contour matching than movement. My son wants to try
logging the temp *inside* our clothes dryer during different cycles. Wanting to do our best to keep the tumbling clothes from destroying the piece we thought stay as flat against the drum wall as possible...but it's an arc. I'm guessing there are temp issues w/ the picaxe itself to consider, but the flexibility issue was the first we thought of. Are the conductive paints/glues that would be required suitable for a small circuit (adequate conductivity)?

[BeanieBots]

The conductivity is good but the current handling capacity is not. Just about good enough for an LED. It's VERY expensive as well.
Why not try "Stan's Challenge" and fit it all into a 35mm film canister? Then just chuck it in with the wash. Should be water tight and there's plenty of room to fit all the components and a 3v lithium battery. Not sure how hot you get the whole thing before getting problems though.

Edited by - beaniebots on 1/19/2006 9:15:36 PM

[Michael 2727]

I don't know about the conductivity of any of those products, I would never use them.
They must be fairly good, some at least. There are windshield demister repair kits
available to fix damaged tracks, not sure how successful they are though.

Logging clothes in a dryer will be diffucult.
The drum itself will usually be hotter than the clothes inside it, being more heat
conductive and made of metal, as opposed to damp clothing, which while still
fairly damp and due to evaporative effects will cause them initally to chill.
Toward the end of the cycle the drum will probably remain constantly hotter
than its contents.
You really need the logger tumbling around with the clothes and padded to
prevent damage to it and the clothes and the drum and also the front window.
But at the same time still allowing sufficient heat transfer.
The heavier items (in material density and weight) will dry/heat much slower
than the lightweight items also.

I would suggest as lightweight as possible and wrapped in a thick sock or two
and tied up very securely.

Remember dryers are notorious for melting foam rubber and plastics, most
capacitors are only rated to around 85 deg C, some plastic enclosures would
be less than this, batteries may not like the heat either be carefull, and I don't
know the heat specs on the picaxe.
I would hate to see you end up with a very sticky molten ball upon opening
the dryer.

[Michael 2727]

Just another thought,,?

Battery, short curcuit, forced hot air, dry materials,,,, 911.
Keep your battery very small so if it did
have a short or circuit failure the battery
would just go flat.

[Michael 2727]

Edited by - Michael 2727 on 1/19/2006 9:25:45 PM

[premelec]

Historic Note: The first 'integrated' circuit I ever saw described was National Bureau of Standards printing silver conductors and resistor paint onto a subminiature vacuum tube [valve] in the late 1940s. An interesting concept...