Hello Eric,

It is possible to crease and fold flex circuits provided that it is bonded
and the copper has suffucent ductility. Moreover there are design concerns
that should be address. Since you are going to use double sided flex try to
stagger the conductors on the opposite sides so metal does not lie above
metal. This will avoid the "I-beam effect" which would stengthen the bend
area rather than weaken it. This will also reduce the strain on the copper
on the outer bend surface.

I have in the past folded flat flex circuits for customers bonding the
folded halves permanently in a lamination press. The circuit I remember had
1 oz copper on two sides and no additional platings. It is not the ideal
but it can work. The common "rules of thumb" for minimum bend radius are
3-6 times total thickness for single metal layer flex and 6-10 times
thickness for two metal layers.

Given that you will have a small radius and pot the assembly I think you
will be fine. I would, however, suggest trying it and examining at the
results. Be aware of the fact that if copper is plated up on the bend area
the thickness is no longer 1/2 oz and if the plating is too thick or
brittle, fracture is possible. If you have further interest in flex
circuits, I have writen a text title "Flexible Circuit Technology, 2nd
Edition" it and many of the other fine books on circuit technology
mentioned on TechNet are available on line from Amazon.com or in your case,
Amazon.co.uk  Barnes and Noble has an on-line site as well.

Good luck,
J. Fjelstad


At 04:49 AM 2/17/99 -0800, you wrote:
>We're currently working on a design which entails a leap into the unknown for
>us. I'd like to know if anyone's been here before and what they found.
>
>I've got a very small Flex which needs folded up in order to fit it into a
>tube, Once the flex is inside the tube everything is potted and so the flex
>never moves again. In order to get it into the smallest diameter tube we need
>to put a sharp, permanent bend into the flex. Has anyone done this before and
>did it cause cracking in the tracks - the bend will always be
perpendicular to
>the tracks.
>
>The spec fo the flex is:
>
>double sided
>1/2 oz copper
>0.002" pyrolux (polyimide) substrate
>0.25mm inner bend radius.
>Epoxy coverlay top and bottom.
>
>
>
>
>Eric Christison
>
>################################################################
>TechNet E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c
>################################################################
>To subscribe/unsubscribe, send a message to [log in to unmask] with
following text in the body:
>To subscribe:   SUBSCRIBE TechNet <your full name>
>To unsubscribe:   SIGNOFF TechNet
>################################################################
>Please visit IPC's web site (http://www.ipc.org) "On-Line Services"
section for additional information.
>For technical support contact Hugo Scaramuzza at [log in to unmask] or
847-509-9700 ext.312
>################################################################
>
>
>

################################################################
TechNet E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c
################################################################
To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body:
To subscribe:   SUBSCRIBE TechNet <your full name>
To unsubscribe:   SIGNOFF TechNet 
################################################################
Please visit IPC's web site (http://www.ipc.org) "On-Line Services" section for additional information.
For technical support contact Hugo Scaramuzza at [log in to unmask] or 847-509-9700 ext.312
################################################################