Re: [SI-LIST] : Design Note on Right Angle Bends

Scott McMorrow (scottmc@teleport.com)
Fri, 10 Jul 1998 12:04:09 -0700

Mike,

If you follow the curve of the right angle bend you will
find that the width of the trace changes when you measure
from the center. This translates into a change in
characteristic impedance which causes a discontinuity
in the net. This discontinuity is so small that at the usual
edge rates we see on most boards the influence of the
bend is negligible. (It can, however, be seen on a TDR.)

When edge rates get below about 50ps, or frequencies
are above 3GHZ I would begin to worry about the bends.
Then, reflections will occur which can cause EMI.
Otherwise there are much more important sources of EMI
on most pcboards.

Regards,

Scott

Mike Mayer wrote:

> I am puzzled by a design note on the Ultracad web site:
>
> http://www.ultracad.com/tech.htm
>
> It states that:
>
> THE REASON YOU DON'T USE RIGHT ANGLE TURNS ON CIRCUIT BOARDS IS
> THAT RIGHT ANGLE CORNERS BEGIN TO LOOK LIKE ANTENNAS.
>
> There are no references given or any further explanation. Can anyone
> explain what they mean?

--
___________________________
Scott McMorrow
Principal Engineer
SiQual

mailto:scottmc@siqual.com ___________________________

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