I designed a board with six 1 Oz copper layers on flex portion with no book binder. The flexibility was acceptable for assembly and test.

Lr1 - diagonal cross-hatch GND (width 10/ grid 50 in mils)
Lr2 - mostly wide power/GND copper traces
Lr3 - diagonal cross-hatch GND (15/50) staggered 25mils in relationship to L1
Lr4 - signal traces
Lr5 - diagonal cross-hatch GND (15/50) staggered 25mils in relationship to L3 
Lr6 - signal traces staggered in relationship to L4

Material used:
Flex copper clad Adhesiveless polyimide   AP9111 (1 Oz /1 mil THK / 1 Oz)
Bond ply LF0111 (1mil THK adhesive / 1 mil THK kapton / 1mil THK adhesive
Coverlay  LF0110  (1mil THK adhesive / 1 mil THK kapton)

You will want to have the solid reference traces for control impedance.

Veronika Anderson C.I.D | Sr. Electrical/Mechanical Design Engineer | Excelitas Technologies

Office:  +1 626.967.9521 x 236
1330 East Cypress Street, Covina, CA 91724 USA 
[log in to unmask]
www.excelitas.com

-----Original Message-----
From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of David Baldwin
Sent: Friday, April 11, 2014 1:16 PM
To: [log in to unmask]
Subject: [DC] Rigid Flex Plane Cross-Hatching & Impedance

I have a rigid-flex design that is too difficult to bend and form.  We have 100 ohm DP's going across the flex against solid reference planes.  We want to cross hatch the planes in the flex regions in an attempt to make it more flexible (along with other adjustments).

1. What are the guidelines for cross-hatching the copper (50%, diagonal, orthogonal?) 2. How badly will it affect the impedance?  Should I keep the copper solid under the DP's?

Thanks,

Dave


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