RE: [SI-LIST] : Searching For Equations Governing Serpentine Trac

Mellitz, Richard (richard.mellitz@intel.com)
Mon, 18 Jan 1999 11:12:29 -0800

.. .Rich Mellitz
Intel

-----Original Message-----
From: Hall, Stephen H [mailto:stephen.h.hall@intel.com]
Sent: Monday, January 18, 1999 12:31 PM
To: 'Abe Riazi'
Cc: 'si-list@silab.eng.sun.com'
Subject: RE: [SI-LIST] : Searching For Equations
Governing Serpentine Trac es

I typically use a rule of thumb that says the edge-to-edge
spacing between
the parallel sections of the serpentine must be at least 3x
to 5x the height
above the ground plane. This will ensure that the trace is
heavily coupled
to the ground plane and minimally coupled to the adjacent
serpentine
sections of the trace. On a recent design, the 3x rule of
thumb produced a
timing skew impact due to increased velocity of
approximately 40ps on a 5
inch long heavily serpentined line. This was a 55 ohm trace
on typical FR4.
These rule of thumbs produce minimum timing problems,
although, it sometimes
causes layout issues.

I hope that this helps.

-- Steve Hall
Intel

-----Original Message-----
From: Abe Riazi [mailto:ariazi@anigma.com]
Sent: Sunday, January 17, 1999 9:03 PM
To: 'si-list@silab.eng.sun.com'
Subject: [SI-LIST] : Searching For Equations Governing
Serpentine Traces

Dear Si-List Members,

Serpentine traces are frequently employed in design of
high speed
digital PCBs to increase propagation time of certain signal
lines.
These wavy shaped tracks provide an effective means for
matching trace
lengths and flight times of various signals.

I am searching for equations and rules of thumb which
allow
determination of magnitude of crosstalk and changes in
signal
propagation delay (or velocity) as a function of serpentine
geometry
(dimensions and separation of adjacent trace segments).

Thank you in advance for your suggestions regarding laws
or formulas
which govern serpentine traces..

Best Regards,

Abe Riazi
email: ariazi@anigma.com

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