Cyclindrical, not flat, circuit boards

Go To Last Post
18 posts / 0 new
Author
Message
#1
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

I'm contemplating a project that would really benefit from a cyclindrical, not a flat, circuit board.

The board would actually just bend 90 degrees, it would not be a full circle.

The arc would be about the size to wrap around a coffee mug, with the heigth of the board being about 3 inches. The length of each of the legs would be about 3 inches and 6 to 8 inches, extending straight out at 90 degrees from each other, after the curved region. It would be SMT and partial TH components.

As a personal project, I'd be looking for 4 - 8 boards, funded by me, not off a project account.

I've used ExpressPCB in the past, and I don't know Eagle, or other board layout software, but I could learn whatever it takes to get the project done.

So, any thoughts on curved surface circuit boards?

Thanks,

JC

edit:
This link to a YouTube Video of a Mini LED Light Bar, (not my video), shows the underlying concept. The boards on this mini-light bar are curved, with LEDs installed around the curved surface.

YouTube Light Bar Video

Last Edited: Tue. Jul 1, 2008 - 10:31 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

I would consider flexible PCB made from thin mylar or other similar material. Never done it, but a friend of mine makes tracking devices for animals and to keep the weight down, he has his boards (the size of a postage stamp) made on a thin material. He buys a sheet and then cuto out what he needs with scissors. Don't know who makes the boards though.

Randy

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

I think I would go with flexible pcb material soldered to each board. The stuff is sometimes called "flat flex" or "FFC" or "FPC". It appears to be available from DigiKey in lengths as short as 2", solder each end.

Eagle is not that hard, but certainly not easy. They have a pretty good walk-through tutorial, and if you really do follow it, its a lot easier. A lot of the challenge of Eagle is really in all the layout software just because of the huge number of options - drill sizes, pad sizes, trace size and spacing, trace geometry, how traces and pads join, etc, etc. Its a mind-boggling array of stuff to deal with but its generally no worse in Eagle,

Jim

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Randy, Jim,
Thank you for your thoughts!
I'll look into those suggestions.

Other thoughts?

JC

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Just some thoughts: from the video you posted, it seems to me (but my eyes are not so good, though) that the LED's in fact are on a flat board, and the 'curved' portion of the light bar in fact are some light guides placed on a curved metacrilate or similar. Or in fact, the light guides are the same metacrilate/policarbonate/whatever.

Google for 'angel eyes', and probably you would find some posts about similar round light bars.

Guillem.
"Common sense is the least common of the senses" Anonymous.

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

You could use regular paper phenolic PCB configured as breakaway strips (row of holes running the entire width of the PCB, so you can break the PCB there). Do the assembly, solder some wire jumpers across the break line, then break the PCB and bend as desired. The jumpers will keep the strips formed the way you want.

Note: glass epoxy PCBs are tough to break in this way.

If you think education is expensive, try ignorance.

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

We do flex pcb's all the time at work. I've never ever seen one where the IC's were soldered to the flexible part. On all of them we add a rigid pcb to the section that has anything soldered to it. The exceptions are connectors and through-hole LED's. The connector section is usually mounted to something so it won't flex and the LEDs are oriented so that the two pads are parallel to the axis of the bend. I can't see how you would flex a pcb that has stuff soldered to it.

Oh and flex pcbs are wicked expensive. The tooling charges will shock you.

Go electric!
Happy electric car owner / builder

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Guillem, Emuler, & Sgomes,

Thank you for the feedback!
I tracked down one of these light bars and got a look at it from the side of the vehicle.
It has a curved board, with LEDs inserted on the outter face of the arc.
Very cool from an optical perspective.
I would have like to see it up closer, or better yet to have popped the case...
Most LED light bars have the usual flat boards mounted at an angle for the corners.
The curved pattern gives better intersection warning, which is a big deal.

Emuler, I can picture your design in my mind. Labor intensive, but certainly an option.

I envision the LED drivers and AVR on either the flat portion of the board, or an a base plate circuit board, with the LEDs, pads, and their traces on the curved portion of the board.

Quote:
flex pcbs are wicked expensive

I guess the old saying applies: "If you have to ask how much, then you can't afford it!"

Thanks for the thoughts, everyone!
JC

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Quote:

Emuler, I can picture your design in my mind. Labor intensive, but certainly an option.

Not particularly, unless you'll be drilling all those holes manually. The trick is to solder the jumpers first, when the PCB is in one piece. That way the whole PCB is assembled just like any regular PCB. Then you break it along the dotted lines.

I have done this for some designs where space was tight and the circuit had to be split into two boards, one at right angle to the other. We assembled and tested the boards in one piece, and only broke and bent it at the final fitting stage when it went into the housing. Much cheaper and less trouble (while wave soldering) than connectors.

Don't put the jumpers flat against the PCB surface. Leave them curved a little (loose) so the broken strips can be bent as desired. You even get zero ohm resistors that can be used in place of wire jumpers, which is more convenient for automatic assembly equipment.

If you think education is expensive, try ignorance.

Last Edited: Wed. Jul 2, 2008 - 10:41 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Hi Doc

All Electronics (www.allelectronics.com) used to sell some 0.012 pcb material. I just checked, and they don't list it anymore :(

Just saw abcfab has some 0.014 for sale on ebay (#310038549887) - that should curve to the radius you're talking about.

Randy

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Flexing the PCB is a very good way to end up with broken tracks. Hairline cracks difficult to see with the naked eye, which mysteriously join together when the PCB is un-bent for testing, so the board works when taken out for testing, but doesn't when put back in the housing. Guaranteed to make you pull out your hair. If you do decide to go that route, try to get all the tracks on one side, or break up long tracks into short segments on opposite sides connected with vias.

If you think education is expensive, try ignorance.

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Thanks everyone,

Randy, I'll take a look at the eBay offering.

Emuler, assuming the new Freaks web site still has Avitars you'll see I don't have that much hair left to pull out...your concept is still on the options list!

JC

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Interesting thread...if I had to create a truly flexible PCB I would probably try to do the artwork first and then do a mock-up with card stock. If things went well I would probably try to etch copper foil by putting resist on both sides (not sure if that would work) and then affix the result to a form of backing that was custom shaped (acrylic or similar).

You may also try to use adhesive backed pads and traces from a stencil kit.

re EAGLE: I can say that I have the demo version of EAGLE downloaded and am not a fan. I might be if I could afford the full software suite (the limtations of the demo version are too restrictive for my needs). You might try FreePCB from Allan Wright. It continues to grow and get better with all the user input. After my artwork is done I check the dimensions in a Gerber viewer (I use Viewmate). You can then print the copper layers from your gerber viewer and use them in the mock-up.

Here is a screenshot from FreePCB [I'm telling you guys...this is great software!):

John

Attachment(s): 

Just some guy

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Hi John,

I keep thinking I ought to learn Gerber, but the first system I ever used was ExpressPC, and many boards later I've never had reason, (yet), to change.

There are many more players in the field these days, for small quantity production, and some are significantly less expensive, making me re-think this part of the process. Looking at / for a curved surface board might be just the motivation to learn something new. If, (when ?), I make the jump I will certainly look at FreePCB and Viewmate. I appreciate the guidance and your insight.

Thus far I'm learning that a curved surface board is possible, but quite costly.

JC

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Question is, do you REALLY need to use a curved PCB? If this is just for LEDs, couldn't you get a piece of acrylic or plexiglass bent to whatever shape you need, then drill in the LED holes, and wire everything up to your board with clear-insulator wire?

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Hi UnixWhore,

Good question. That is certainly possible. The biggest concern there being heat dissipation. Most current light bars use low power LEDs. It is hard to get real spec's on their bars. Some of the newer ones might be using 1 W LEDs. I'd like to use 3 W Leds, and now even 5 W LEDs are available, but very costly.

Having a big, thick, copper layer, both sides of the board, and perhaps a metal layer in the middle, would help thermally, and be tougher for me to fabricate at home.

Hand wiring it would make for quite a rat's nest, but I did that in the (remote) past :)

JC

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Quote:
I've never ever seen one where the IC's were soldered to the flexible part.
It can be done but you have to be careful about tolerances and assembly workmanship. For a larger flex board you can have them add stiffener under the area where you are going to put the components. As was mentioned, hairline fractures in components like ceramic caps can really be a PITA so be careful about where you "bend" the board.

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Hello Nanovate,
Thanks for the warning. Intermittant hardware failures can be so difficult to identify. If I go this route I'll put the chips on the straight part of the board, and just LEDs, (and their traices...), on the curved surface.

JC