Flexible PCB Blanks for home construction

Hi,

Just throwing this out there.

I’ve been playing with the idea of making flexible PCBs at home.

I’ve managed a rough small one sided quasi flex PCB using one side of a lamination pouch and some copper foil scavenged from the shield of an old camera.

Problems were when doing the toner transfer technique trying to keep the heat correct without melting laminate and releasing the copper…plus I have doubts on the durability of the copper foil.

Does sparkfun have a supply of flex blanks they can put up on the website? Even better would be double sided flex blanks.

Presumably the laminate material will be properly formulated for heat resistance and bonded properly. Also blanks from a proper supplier will have the correct alloy of copper for lots of flexing. Imagine the fun we could have coming up with ideas to use flex materials. Electronics clothes, jewellery, moving parts, less hardware intensive enclosures etc.

Stretching the concept even further, blank laminate with bonded adhesive to make multi layer PCBs…probably only heat dispersion layers would be practical for home users.

Anyway…just an idea. Might get hobbyists into the 21st century.

Phil

There must be some source of this flexible laminate, with a bit of luck pre-sensitised so you can etch it like anyother PCB . I would be interested also if anyone knows a supplier.

Got to say I was a bit sceptical about the robustness but having recently had few hundered flexible led lighting strips, no problems or failures. Even hand soldering on connection leads to the solder pads did not cause frustration. Its wise to be quick with the iron to avoid over heating the laminate.

The product I had seems to use a double sided laminate although it had no via’s or through holes.

Also they have done the smt assembly directly onto the copper foil, no plating or other treatment seems to be apparent.

That’s an interesting concept.

What about using flexible plastic sheeting, and using conductive thread to form the traces? Can that stuff be sewn with a sewing machine? I have no idea if it can, but if possible it would make more complex traces possible (compared to hand sewing). And to make the connection between the thread and the ICs (and other components), could you make small deposits of copper (or similar) foil that can be both soldered to the chip, and connected to the thread?

Note: I have never tried anything like this, or used any of the materials involved. I’m just throwing the idea out there…

Gold Phoenix is doing flex these days, but it’s not cheap. $260 for 75 sq inches, $280 for 100 sq in.

We recently had a rep from our PCB manufacturer come over with flex samples and whatnot and he gave us a bit of info on flex and multilayer boards…I was surprised this sort of thing isn’t all that complex or more expensive to make than normal boards (as long as you have the basic raw materials to begin with).

  • multilayer boards are just double sided boards stacked together. They’re made the same way, vias and everything.

  • when specifying flex boards, you need to decide beforehand on if the flex board will be moving or not. If not moving (say for wrapping around an enclosure) then they use a cheaper more brittle copper. Bendy moving bits (say for a rotating hinge on an LCD panel) needs a more ductile copper.

  • The only difference in designing a flex panel for a commercial manufacturer is to specify an extra layer for stiffening areas, such as under ICs or large components.

everything else is processed (according to the rep) as per a normal board such as reflow, component placement etc.

So presumably if Sparkfun can get blanks in bulk, the price can be made affordable to those of us who want to make them at home using toner transfer or your other favourite methods…

Interesting I found this link

http://www.instructables.com/id/DIY-Fle … -Circuits/

where they just put the flex blanks through a printer (they needed to use solid ink though). I wonder if they’d pass through a laser printer??

Phil

I am now wondering if we are talking about the same thing ?

The flexiable circuit I have is 0.2mm thick, 10mm wide and 300mm long and I can easy wrap it in a spiral around a broom handle, let it go and it will more or less keep its shape. In fact you can stick it on almost any shape using double sided tape.

Is “flex” board this flexabile or is it stiffer ?

Flex circuits are that flexible, however if they are carrying lots of circuitry like large ICs, then you’ll find extra stiffening bits of plastic under the bits you want stiff.

Lets say your designing a board to fit snugly inside an enclosure like a hand held sensor. Say you have some front panel switches and LEDs, and a micro+support circuitry like voltage regulator or opamps. You might have some sensors you want to route to a convenient place. Lets say you want to wrap these around a battery, sensor or card reader. The micro/ICs etc will be large and you don’t want them to bend, so you’ll put attach some stiffening plastic under these so the ICs don’t pop off when handling. You’ll then have some tracks leading to the switches/LEDs which are nice and flexible so they can wrap. If the switches are large you might stiffen these as well. LEDs are small so you probably won’t stiffen the board under these.

Doing this the conventional way you’d have a board for the micro, another board for the switches/LEDs, plus maybe some wiring to the sensor and connectors or wiring looms between them all, screws to attach them all…fiddly stuff. Using flex circuits you have all the circuitry on one board and just wrap it into place.

If maybe the LED/switches are on a lift out hinge like on a tricorder, to do it the proper commercial way, you’d also have to specify the copper to be suitably ductile. If you don’t need the circuit to flex repeatably you can get away with cheaper less ductile copper.

I’ve been looking everywhere for flexible copper sheets to do flex PCBs and would definately buy a lot if it become available on SF.

Doing research all I can find is flexible copper laminate often called Pyralux, Kapton, DuPont, Polyimide copper-clad or flex copper. However, I cannot find any of it for sale anywhere. The only thing I can find is Kapton tape with single sided copper, but with it being tape it is only 18mm wide, and extreeeemly expensive.

Does anyone know anywhere that sells flexible copper sheets for home production?

Is this too thin for you?

http://cgi.ebay.com.au/KAPTON-COPPER-CL … 35a552875a

This is a great instructable for printing flexible pcb using a Phaser Solid Ink printer…

http://www.instructables.com/id/DIY-Fle … -Circuits/

If you keep your eye out on craigslist, ebay, etc. you can find these older printers pretty cheap.

That size would be fine, however the price at $33 + $55 P&P comes to $88 which personally I think is an crazy price for a slightly larger than A4 sheet. Also its off eBay where as I would prefer to find an actual distributor or stock supplier.

Regarding the printer tutorial… whats wrong with just taping it to A4 paper and running it through a laser printer as normal?

angelsix:
That size would be fine, however the price at $33 + $55 P&P comes to $88 which personally I think is an crazy price for a slightly larger than A4 sheet. Also its off eBay where as I would prefer to find an actual distributor or stock supplier.

Regarding the printer tutorial… whats wrong with just taping it to A4 paper and running it through a laser printer as normal?

It wont work because Laser printers are electrostatic, the copper on the sheet will conduct the electrostatic field away that was deposited to attract the toner, so no toner will stick. This is why they use wax thermal printers to prototype this kind of circuit, they don’t use a static charge to attract the ‘ink’.

Mike

As per the “Instructables”, you either need to use a “solid ink” printer, or use toner-transfer sheets with a laser printer (due to the issue Mike mentioned).

Angel, I’m guessing you’re in USA - the shipping on that Ebay item I mentioned would be $US17 - still expensive, but not as bad as for those of us in Australia. You could always make them an offer with the Ebay “Make Offer” function…

Hi,

What is a reasonable price for flexible PCB these days? I have a few 8x10 sheets of single and double sided left over from a couple projects. Substrate is 5-10 mils. I found it years ago in a surplus store and it was quite expensive; but I needed it…

Regards,

Dennis

I’ve been making flex PCBs for awhile. Check out my post about it at steampunkworkshop.com

If you don’t want to do anything too fine, then membrane keypad manufacturers might be a cheap alternative.

  • They usually don’t get precious about MOQ or tooling. Many are happy to laser cut small quantities.

  • They have heaps of great substrates - different stiffnesses, chemical resistance etc.

  • They can build in switches (obviously) but also LEDs and passives.

  • They can do multilayer and any combination of shapes within the stack.

  • They have clear conductive ink - see through circuits!

  • They can print overlays, colours, pictures on top of the circuit.

BUT…

  • I haven’t seen one do 8mil tracks and spacing!

  • And you may be limited by what pads/connectors they can use.

Just a thought.