[SI-LIST] Re: Regarding "unbonded region" in PCB stackup
- From: "Loyer, Jeff" <jeff.loyer@xxxxxxxxx>
- To: <sivakumar_skm@xxxxxxxxx>
- Date: Wed, 19 Feb 2003 14:46:12 -0800
Since no-one else replied, I'll put in my 2cents...
I haven't used this, but I checked with a person here. He says:
"...it is called a "bookbinder" type construction (typically in rigid =
flex, but also multi-layer flex) because the unbonded portions resemble =
the pages of a book bound at the adhered regions.
[Teledyne (probably among others)] markets it.
Modelling would depend on individual flex "page" construction and bend =
of the flexible section. An unbent flex section would have the =
individual "pages" lying relatively flat on top of each other, while =
when bent at say 90 degrees, the inside "pages" would "bulge" forming an =
airgap between "pages" for some distance."
End quote.
As I suspected, it's an attempt to regain the flexibility you lose when =
you laminate the different layers of a flex design together. Simple =
beam physics: the inner layers will have a different bend radius than =
outer layers and if they're laminated together, they are fairly rigid. =
If you don't laminate the layers, you get back some flexibility, but the =
layers have to do something funny between the ends to accomodate the =
different radii (take a pad of paper and staple the bottom of the sheets =
together, bend the pad, and see what funny things the pages do).
Sounds pretty ugly for high speed applications, unless the vendor has =
done something else to allow the layers to accomodate the different =
radii (or perhaps, you "preload" enough bend that you ensure you will =
always have a substantial airgap above your signal).
A Google search on "bookbinder flex" looked pretty promising for more =
explanations.
Jeff Loyer
-----Original Message-----
From: Siva kumar [mailto:sivakumar_skm@xxxxxxxxx]
Sent: Monday, February 17, 2003 5:07 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Regarding "unbonded region" in PCB stackup
Hi Gurus,
When i was going thru' a stackup i came
across a term "UMNBONDED". I searched for some
explanation for this word (UNBONDED) and one appln
note says like this,
" A flex-circuit design technique that involves
providing an insulating layer between every conductive
layer of a flex-circuit, but with no adhesive bonding
between the insulating layers in certain areas of the
circuit. This technique improves circuit flexibility.
"
I couldn't understand this properly.
Could anybody please give me some more explantion on
this topic?..
And also, how would you handle this type of stackup
in simulation. ie. defining stackup in xtk file or in
any other tool.
=20
thanks in advance,
siva
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