From: Dan Swanson ([email protected])
Date: Mon Apr 03 2000 - 04:57:18 PDT
Dear Sunil,
1. I don't think there is a formula for capacitance or
inductance for this situation.
2. It's the wrong question. I believe the question should
be: "Is it possible to get a controlled impedance transition
between these to layers with good return loss out
to some specified frequency?"
3. The answer is yes. But I only know how to design these
things on a case by case basis using a field-solver.
4. In general you are doing the right things, removing unused
pads. The antipads may need to be bigger than you are
used to. The actual transition region probably suffers from
excess capacitance, so "tuning" it by narrowing down the
signal traces for a short distance on either side sometimes
helps.
Dan
Dan Swanson EMAIL: [email protected]
Bartley R.F. Systems TEL: (978) 241-1091
38 Water Street FAX: (978) 388-7077
Amesbury, MA 01913
-----Original Message-----
From: Sunil Kumar [SMTP:[email protected]]
Sent: Friday, March 31, 2000 12:34 AM
To: [email protected]
Subject: [SI-LIST] : via capacitance
Dear all SI experts.
I am using a multilayer board having the following stack-up:
LAYER1 TOP LAYER (CONDUCTOR)
LAYER2 GND
LAYER3 CONDUCTOR
LAYER4 CONDUCTOR
LAYER5 VCC
LAYER6 GND
LAYER7 CONDUCTOR
LAYER8 CONDUCTOR
LAYER9 GND
LAYER10 BOTTOM LAYER (CONDUCTOR)
A signal trace is going from layer7 to layer8. A through-hole via is used.
The via is having pads on layers 1,7,8,10. There are antipads on the power
planes. Is there any formula/tools to calculate the exact capacitance of
the via?? How can I measure it in the board??
Sunil Kumar
Research Engineer
C-DOT
INDIA
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