Brad's
what brad v. says is what many have said and is the conventional wisdom
however i have made many bds with 3 signal layers and 1 ground plane
well, ok maybe 3 or 4 (that's 'many' isn't it :) )
no one (fabricators) ever complained and they never warped
just put a note:
'ok to add theiving copper on inner signal layer to balance construction'
they sprinkle little dots around, seems to work fine
i can't remember the largest i have done this way but most were probably
roughly 4" x 6"
or as brad v suggests route the inner layer then maybe pour a polygon on
the power net on the innner signal layer and see what it looks like
if there is not a lot of coverage by the polygon the fab's theiving
copper is probably a better bet
Dennis Saputelli
_______________________________________________________________________
Integrated Controls, Inc. Tel: 415-647-0480 EXT 107
2851 21st Street Fax: 415-647-3003
San Francisco, CA 94110 www.integratedcontrolsinc.com
Brad Velander wrote:
Brad,
You would not want to add just a single plane layer and a single signal
layer. It would result in unbalanced copper and quite likely warping of the
board. The golden rule for multi-layer is to keep a symmetrical stack-up. i.e.
Signal, Plane, Plane, Signal. OR Signal, Signal, Signal, Signal. for 4 layer
examples. NOT Signal, Signal, Plane, Signal.
Now without knowing how many signals you may have to route internally, could you do mixed signal/plane(polygon) internal layers? And try to roughly balance the copper coverage between the two internal layers? This works well when you don't need many signal traces on the internal layers.
The key is to always keep your stack-up as perfectly symmetrical (with
regards to copper coverage), about an imaginary central plane through the
middle of the PCB stackup, as much as possible.
Then no matter what, send the Gerbers to your vendor for review prior
to going through all your approvals and any formal documentation. Do this as
early as possible so that it is less work to fix anything they might want
changed.
Sincerely,
Brad Velander
Senior PCB Designer
Northern Airborne Technology
1925 Kirschner Rd.,
Kelowna, BC, V1Y 4N7.
tel (250) 763-2329 ext. 225
fax (250) 762-3374
-----Original Message-----
From: Brad Kosiance [mailto:[EMAIL PROTECTED]
Sent: August 8, 2005 3:14 PM
To: [email protected]
Subject: [PEDA] Multilayer PCB.
I hope this post does not generate the feedback caused by the vias posting.
I have a small dense board with surface mount and through hole on both
sides.
Because it is so dense I want to add some internal layers to assist in the
signal routing.
Is there any recommendation for the internal layers (i.e. one is a ground
plane and the other is a signal layer).
I don't require a power plane.
I have only laid out double sided PCB's thus far.
Thanks,
Brad.
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