EAGLE for Flex Circuit Design

"Nicholas Kinar" <n.kinar@usask.ca> wrote in message

news:4A5437D6.2070904@usask.ca...

Hello--

 

Has anyone used Eagle CAD for flex circuit design?  Is this possible or

even recommended?  If so, then what are some basic design aspects that I

should watch out for?

 

 

Nicholas

As with any new project, first find a fab house that can do what you need.

Then look to see what their input requirements are in terms of line width,

spacing, layers... pretty much all the usual except a different substrate. I

have it in mind to make my own specialty membrane keyboards with flex tails

one of these days.

    Oppie

Nicholas Kinar wrote on Wed, 08 July 2009 02:08

Hello--

 

Has anyone used Eagle CAD for flex circuit design?  Is this possible or

even recommended?  If so, then what are some basic design aspects that I

should watch out for?

Hello Nicholas,

I'm just releasing a flex cable design today that I designed with EAGLE.

As Oppie pointed out, the concept is the same from a CAD point of view,

it's just a different material.

There are some additional constraints.  The biggest one being that flex

lines should be perpendicular to traces.  And you'll need a stiffener in

the areas where IC's and vias are going to be to keep them from cracking.

Find a few places to get it manufactured and get their design

suggestions.

Cheers,

James.

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Thanks, Oppie! I need to design a flex circuit so that I can mount the

SCP1000 barometer outside of the circuit board enclosure box.  Here's a

link to the datasheet:

http://www.vti.fi/en/products/pressure-sensors/pressure_sensors/

Apparently, there are no "ready-made" solutions for this, and the

company recommends in an app note to use a flex circuit.

Does anyone know the general cost of producing a flex circuit?  Is it

more expensive than an "ordinary" PCB?  I think that all I would require

is a two-layered flex circuit.

Nicholas

As with any new project, first find a fab house that can do what you

need. Then look to see what their input requirements are in terms of

line width, spacing, layers... pretty much all the usual except a

different substrate. I have it in mind to make my own specialty membrane

keyboards with flex tails one of these days.

   Oppie

Thanks, James!

I'm just releasing a flex cable design today that I designed with EAGLE.

As Oppie pointed out, the concept is the same from a CAD point of view,

it's just a different material.

 

Ah - good luck with your design!

There are some additional constraints.  The biggest one being that flex

lines should be perpendicular to traces.  And you'll need a stiffener in

the areas where IC's and vias are going to be to keep them from cracking.

 

Find a few places to get it manufactured and get their design

suggestions.

How would you delineate the boundary of the PCB in Eagle?  Would this be

the same as an "ordinary" PCB?  I am assuming that the flex circuit is

simply a flexible PCB, so the boundary delineation would be the same.

Nicholas

Nicholas Kinar wrote:

Hello--

 

Has anyone used Eagle CAD for flex circuit design?  Is this possible or

even recommended?  If so, then what are some basic design aspects that I

should watch out for?

 

 

Nicholas

I am just starting a flex design as well.    In reviewing the input

requirements I see that some vendors recommend special pad shapes around

through holes to minimize stress concentrations at the points where the

trace meets a pad.    Another difference from a hard board is the

recommendation to add hold-down tabs around thru-hole pads in some

applications.

You might want to take at look at a design guide ... I found it helpfull!

http://www.minco.com/uploadedFiles/Products/Flex_Circuits/Technical_Specifications/FC302.pdf

Jim

How many of these are you using? If it's just a low quantity, you could most

likely get away with manually soldering a #30 awg (.254mm diameter) wire

directly to the pads. I do this all the time for prototype construction -

just have to use a fine tip iron and stick to decaf coffee     Oppie

Oppie wrote:

just have to use a fine tip iron and stick to decaf

coffee <grin>.

The decaf coffee is the essential part

I took a look at the test adapter board; thank you for pointing this

out!  In my application, there is bound to be some vibration, so I am

kind of leaning toward a flex cable design in lieu of a test carrier

board.  However, if I can use the test carrier, then all the better!

Thanks Opie!

Jim Littlefield wrote:

 

I am just starting a flex design as well.    In reviewing the input

requirements I see that some vendors recommend special pad shapes around

through holes to minimize stress concentrations at the points where the

trace meets a pad.    Another difference from a hard board is the

recommendation to add hold-down tabs around thru-hole pads in some

applications.

 

You might want to take at look at a design guide ... I found it helpfull!

 

http://www.minco.com/uploadedFiles/Products/Flex_Circuits/Technical_Specifications/FC302.pdf

 

 

Jim

Great design guide and recommendations; thanks Jim!

Nicholas

n.kinar@usask.ca

Nicholas Kinar wrote:

Hello--

 

Has anyone used Eagle CAD for flex circuit design?  Is this possible or

even recommended?  If so, then what are some basic design aspects that I

should watch out for?

 

 

Nicholas

Hello Nicholas,

I used Eagle for a flex cable design earlier this year.  It was fairly

straightforward thanks to some fairly specific design rules from the fab

house.

Advanced Circuits has some guidelines for Flex you can use as a starting

point, regardless of what vendor you ultimately select.

http://www.4pcb.com/index.php?load=content&page_id=87

Probably the most important considerations are to avoid sharp bends in

traces and to route perpendicular to the direction of flex.

Probably the hardest part of the design was writing the check to the fab

house - flex is not cheap!  In my case, the cost was more than an order

of magnitude higher than a traditional PCB run.

Jeff

Jeff Keyzer wrote:

Probably the most important considerations are to avoid sharp bends in

traces and to route perpendicular to the direction of flex.

This is, of course, incorrect.  What I meant to say was that you need to

route parallel to the direction of flex.  I suppose this could be

considered perpendicular to the axis of flex, but in short, the traces

should go in the same direction as you plan on bending the flex cable.