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September 1997

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Subject:
From:
Richard MacCutcheon <[log in to unmask]>
Reply To:
TechNet Mail Forum.
Date:
Wed, 3 Sep 1997 15:10:00 -0600
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======== Original Message ========
I am looking for some helpful hints in pursuing a design using Orcad Layout
7.10a  with Blind and Buried Vias.

This particular design is densely populated with SM components on Top &
Bottom.  Probably an 8-10 layer board ( 2 planes )

This will be my first shot at using B&B vias  and I don't want to get too
carried away ( 5 or  6 different drill tapes ) .
I understand that with Orcad, I can just define several vias, assign them to
the nets,  and the Router will select
The appropriate via as needed.

Are there any recommendations/suggestions as to how deep the blind vias
should go? How many layers should the buried vias traverse?  Are there
"good" strategies to approach the definition of the vias?  Or is this
strictly design dependent and 'I'm on my own'?

How about recommendations from the fab point of view ?

Thanks..........

MARK  RADLEY
Rick Pray & Associates
96 Lock Street   Port Crane, New York 13833
607-648-8594  (voice)  //  607-648-2535 (fax)
[log in to unmask]              www.rpaeng.com
======== Fwd by: Richard MacCu ========
From a fab standpoint, the easiest/cheapest way to do blind/buried vias is
to limit the layers they traverse to two if possible.  As you add more
layers you must pay for extra lamination steps to build up the padstacks you
require.  It is relatively easy to create buried vias.   Blind vias are more
difficult whether controlled depth drilling or some other blind via
technique is used.  Each subsequent lamination can impact board price as
much as 30%.
As far as definition of vias.  Having separate drill drawings reflecting the
 via locations and a table showing each drawing's relationship is usually
easy to interpret.  If you use a particular supplier I would suggest having
one of their Manufacturing Engr. types evaluate the docs on a preproduction
basis to get their input.

Good Luck


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