[SI-LIST] Re: Controlled impedance PCB question
- From: "Zabinski, Patrick J." <zabinski.patrick@xxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Thu, 19 Jul 2001 14:34:25 -0500
Allan,
"Design" of two impedances is generally straight forward
(easy). It simply requires the use of two different
line widths.
The ease of "fabrication" of two impedances has much to do
with the design. If the 50 and 40 ohm traces are on
the same layer, it can sometimes be difficult to get
both within a reasonable tolerance.
To ease manufacture/fabrication, it works best to
separate the 50 ohm traces onto one metal layer and
the 40 ohm traces onto another with a ground and/or power
plane between them. This will allow the PCB vendor to
tune/tweak the processing of the 50 ohm traces independent
of tuning/tweaking the 40 ohm traces.
Pat
> Hi guys:
> If I wanted a PCB with two different values of controlled
> impedance, say
> some 50 ohm traces and some 40 ohm traces, is this relatively easy to
> design and fabricate, or would I end up paying a lot more for both the
> design of the board and production quantities?
>
> Also, is this fairly common, a board with multiple values of
> controlled
> impedance traces?
>
> Appreciate any insight.
> Thanks, Allan
>
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