Hi Susy
Well regarding your question about the multiple PCB thickness on one
board
Sounds scary!, one thing to considered, what is the intend for this?
Is this meant for card guide fitting, Do you required this thickness for
extra layers and still meet required impedance?
What I would suggest is see what the intend is first, and then make the
necessary changes.
If extra routing layers are needed, maybe selecting different materials
with lower Dk could accomplish the layout with an overall thickness of
.062"
Also if impedance is an issue, try to route signals reference to Planes
a few layers away meaning cut copper planes in the area where you need
extra Dielectric thickness.
For example I had to layout a board .093 mils thick containing a total
of 18 layers.
I did have an issue with some of the high speed signals requiring 100
ohms diff impedance. In order to achieve this, my trace width would turn
out to be 4 mils wide. This was unacceptable for loss tangent at high
frequencies (skin effect) we required wider traces, 8 mils wide minimum.
What I did was to route the signals at 8mils wide, and have those
particular signals reference to Planes 2 layers away on each side, Cut
the copper on the adjacent planes this gave the required dialectic
Height to meet my impedance.
Hope this helps
Inkra Networks
Patrick Jabbaz CID
Sr Board Layout Eng.
40971 Encyclopedia Circle
Fremont, CA 94539
Work (510) 249-4835
Mobile (408) 621-6533
[log in to unmask]
-----Original Message-----
From: Susy Webb [mailto:[log in to unmask]]
Sent: Wednesday, February 06, 2002 9:58 AM
To: [log in to unmask]
Subject: [DC] routing the thickness of a board
I've got a good one for the gurus out there!
And engineer just asked me if a rigid board could have an area (an edge
actually) routed such that the overall area of the board is one
thickness
(.125), and the routed area is another (.062) See the side view picture
below...
routed area
\ __________________
_____| |
.062 |_______________________| .125
Other than the obvious issues of controlling routing depth, and I
imagine a
hugh cost, what else should I be concerned about? Can it even be done???
We
were thinking that it might be easier to build two boards and fuse them
into
one, but would the alignment problems kill that idea?
TIA for any help,
Susy
Susy Webb, CID
Sr PCB Designer
Carlo Gavazzi Computer Systens
281-875-1500 x33
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