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'[EE] Flexible Circuits?'
2005\08\24@112731 by Harold Hallikainen

face picon face
Anyone have any experience with flexible circuits? Who have you used to
make them? Can they work from the typical gerber and drill files, same as
a typical board house? In this product, a flex circuit is being considered
due to the curved shape and required thinness of the product. However,
there are lots of parts (chips, LEDs, resistors) that go on the board. Can
you solder parts to a flex circuit without melting the whole thing? I've
generally seen flex circuits used as connecting cables without parts
soldered to them. Can they be used the same as regular boards? If so, how
are parts attached? So far we've used .020 inch thick FR4 board, but that
may be too thick and not flexible enough. Any other ideas? We're using
Advanced Circuits for our normal circuit boards. I see they do flex
(http://www.4pcb.com/quickturn_pcb_flex_design_guidelines.htm), but would
appreciate any comments piclisters may have.

THANKS!

Harold


--
FCC Rules Updated Daily at http://www.hallikainen.com

2005\08\24@114853 by Alan B. Pearce

face picon face
>In this product, a flex circuit is being considered due to the
>curved shape and required thinness of the product. However, there
>are lots of parts (chips, LEDs, resistors) that go on the board. Can
>you solder parts to a flex circuit without melting the whole thing?

Sounds like you are really after what is known as "flexi-rigid" circuit,
where there is a flexible portion connecting two rigid portions. These are
typically built up the same way a multi-layer rigid PCB is, by taking a thin
layer (in this case the flexible portion) and etching that as required, then
building up the ends to the required thickness in normal manner, and etching
those as appropriate.

Often done where the flexible portion is going to have normal connectors
soldered on the ends, but there is no reason to limit it to connectors.

However if you are looking to have a flexible portion with components on
because it needs to flow around other items, it may be worth having a look
inside an old camera from the early days of electronic cameras (such as a
Canon EF) and have a look in there for ideas/techniques. These used flexible
circuits with components on quite extensively.

2005\08\24@130719 by Bob Axtell

face picon face
Alan's got it.

The normal application is to eliminate tiny connectors and their attendant
unreliability. As long as the components are actually installed on the rigid
portions of the circuit, all will be well, but mounting them anywhere on the
flex part is a prescription for disaster. Done in this way, the design
is quite
reliable.

On one camera, I have seen one circuit open up like a flower into 3 rigid
parts, and it worked very well. It eliminated the need for bottom-side
SMD mounting, saving the client a lot of manufacturing money as well
as easing repair and/or rework.

--Bob

Alan B. Pearce wrote:

{Quote hidden}

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2005\08\24@134526 by Spehro Pefhany

picon face
At 10:06 AM 8/24/2005 -0700, you wrote:
>Alan's got it.
>
>The normal application is to eliminate tiny connectors and their attendant
>unreliability. As long as the components are actually installed on the rigid
>portions of the circuit, all will be well, but mounting them anywhere on the
>flex part is a prescription for disaster. Done in this way, the design is
>quite
>reliable.
>
>On one camera, I have seen one circuit open up like a flower into 3 rigid
>parts, and it worked very well. It eliminated the need for bottom-side
>SMD mounting, saving the client a lot of manufacturing money as well
>as easing repair and/or rework.
>
>--Bob

Last time I looked at small production quantities, we went with connectors,
cables and rigid boards because the tooling costs were fairly high
(thousands).

>Best regadrs,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
.....speffKILLspamspam@spam@interlog.com             Info for manufacturers: http://www.trexon.com
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2005\08\24@154424 by Bob Axtell

face picon face
Yes, the tooling costs ARE higher than standard PCBs. But lots of connectors
can add weight and a LOT of grief. I've done 3 over the years, and all
three were
a $wash against standard connectors/cables/PCBs _if_ the qtys are high
(above
500), but the product's reliablity was higher; in one case dramatically
higher (product
subject to severe vibration in normal operation).

But the main problem is PROVING that to management. That is normally
done with
a prototype- and, as noted- they are very expensive.

--Bob

Spehro Pefhany wrote:

{Quote hidden}

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attachments must be sent to
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2005\08\24@161452 by Spehro Pefhany

picon face
At 12:43 PM 8/24/2005 -0700, you wrote:
>Yes, the tooling costs ARE higher than standard PCBs. But lots of connectors
>can add weight and a LOT of grief. I've done 3 over the years, and all
>three were
>a $wash against standard connectors/cables/PCBs _if_ the qtys are high (above
>500), but the product's reliablity was higher; in one case dramatically
>higher (product
>subject to severe vibration in normal operation).
>
>But the main problem is PROVING that to management. That is normally done with
>a prototype- and, as noted- they are very expensive.
>
>--Bob

The proto makers now seem to have laser or water-cutting techniques
(soft tooling) that knock the prototype cost down.

I really like the rigid-flex technique for things like panels, but have not
had a chance to spec it yet (you have to consider things like heat sealed
polyimide flex cables plus two rigid boards instead).

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
EraseMEspeffspam_OUTspamTakeThisOuTinterlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
->> Inexpensive test equipment & parts http://search.ebay.com/_W0QQsassZspeff


2005\08\24@192218 by Tim N9PUZ

picon face
> From: piclist-bouncesspamspam_OUTmit.edu
> [@spam@piclist-bouncesKILLspamspammit.edu] On Behalf Of Harold Hallikainen

> Anyone have any experience with flexible circuits? Who have
> you used to make them? Can they work from the typical gerber
> and drill files, same as a typical board house?

I worked at a facility that manufactured one product that had a flex circuit
board. We placed no parts on the unsupported portions of the flex circuit
and then had two larger areas that were bonded to the outside of the case
for heatsinking purposes. The enclosure was folded together much like you
would fold a single slice of bread into a "C" shape to make a small
sandwich.

The board was laid out using conventional type tools and gerbers were
produced. The product was for an agricultural application where the device
needed to be very reliable with as few connectors as possible. In our case
there was 1 multi-pin connector.

Sorry, I wasn't close enough to the project to know who made the actual
circuit boards.

Tim

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