The engineer should have some general idea of how he or she wants the stackup
configured with respect to ground and power planes, and signal layers. Those
considerations are important for shielding, propagation delay, etc. The
engineer should also know what impedances and tolerances are needed on each
signal layer.

I would suggest then preparing a sketch or table of the proposed stackup and
impedances and giving it to one or more of the potential pcb fabrication shops.
They will be able to determine the detailed stackup in terms of core
thicknesses and prepregs as well as trace widths that should be used. Of
course, different shops will provide slightly different answers; but, you
should be able to either determine a good compromise or just specify the
impedances to the chosen fabricator and let them be responsible for hitting the
target impedance.

An example stackup table to provide the pcb fabricator could look like:

Layer 1 signal 80 ohms
Layer 2 GND
Layer 3 signal 65 ohms
Layer 4 signal 65 ohms
Layer 5 GND
Layer 6 Vcc
Layer 7 signal 65 ohms
Layer 8 signal 65 ohms
Layer 9 GND
Layer 10 Signal 80 ohms

Regards,

Denis Mori
Hewlett-Packard Company
NPSD
Roseville, CA


_______________________________________________________________________
I am currently testing a new e-mail client called Outlook.
If present, please disregard the "winmail.dat" attachment.
_______________________________________________________________________

-----Original Message-----
From: Non-HP-CADpcb2427 /HP-Roseville,[log in to unmask]
Sent: Thursday, August 20, 1998 7:35 AM
To: Non-HP-TechNet /HP-Roseville,[log in to unmask]
Cc: Non-HP-CADpcb2427 /HP-Roseville,[log in to unmask]
Subject: [TN] More Controlled Impedance

Thanks to those who responded to my previous question about trying to find
some information about how to design a board with controlled impedance.
Unfortuneatly, I still haven't been able to find any information on the topic.

I now have an engineer who wants me to design his board with some controlled
impedance. Can anyone tell me what questions I should ask him, and give me
some design considerations that I should pay attention to.

Thanks,

Cameron

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