> From: Mark Radley <[log in to unmask]>
>
> I am thinking of using a long signal trace to control some timing.
> Can someone tell me how much delay will be added to a signal due to the
length of the signal trace on the board?

Propagation delay can take several forms. The most
critical one has to do with the inductance and
capacitance of the trace.  Propagation delay
for a trace that isn't connected to anything
(no load) is

Tpd = [L0 * C0]^0.5

where  L0 = inductance per length (usually inches)
       C0 = capacitance per length (usually inches)

Propagation delay for a trace connected
to something (Loaded condition) is

Tpd' = [L0 * (C0 + Cd)]^0.5

L0 = inductance per unit length
C0 = capacitance per unit length
Cl = capacitance of the load

These are for "ideal" conditions.
Manufacturing techniques will make this vary.

>  The Trace width will be .006  - 1/2 oz copper.
> Is this delay dependent on  internal / external layers ?

Sometimes.

> Is this delay dependent on impedance control ?

Yes.

> What kind of tolerance can be exepcted from one board to the next?

I don't know.  Depends upon how the manufacturing
process is controlled.

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