Any truth to the rumor that the whole 90 degree story started back in
the days when the industry was still doing Printed Wiring Boards (PWB).
The story I heard was that there was one PWB supplier whose machines
could not bend the wire to make a clean 90 degree bend. So, in order to
not loose business they started spreading FUD about 90 degree bends.
Anybody else ever here this story?
-----Original Message-----
From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of
Roger Stoops
Sent: Tuesday, September 05, 2006 8:44 AM
To: [log in to unmask]
Subject: Re: [DC] Best routing method- arc or 45deg or 90deg
Hi Nagaraj,
With digital (and some mixed-signal) designs up to a GHz, it may make no
difference as to the type of corner used. If the photoplot output from
your CAD software chooses a round aperture for drawing traces/lines,
then you would not have a sharp corner for a 90 degree bend, but a
rounded corner (trace width at corner would be 1.207w , where w=trace
width).
http://www.ultracad.com/articles/90deg.pdf
http://www.montrosecompliance.com/Technical_papers/corners-Japan.pdf#sea
rch='pcb%2090%20corners'
Unless, of course, you would prefer to believe this from:
http://www.icd.com.au/articles/emc.html
>>>>>snip
Routing
Orthogonal trace corners should be avoided. The debate rages, but as
frequencies and edge rates continue to rise, ninety degree corners
introduce excess capacitance and cause a small change in characteristic
impedance. This becomes disastrous at high frequencies (e.g. 100 MHz)
when electrons virtually fly off the sharp corners of the bend.
Forty-five degree turns, with a minimum segment length of twice the
trace width, are better. Arced corners, with the inside radius of at
least the trace width, are by far the best approach for high-speed
signals.
>>>>>snip
The electrons that "virtually fly off" land where??
Rounded/curved corners and 45 degree angles sure do look pretty though,
do they not? With many CAD systems, 45 is easier than rounded.
Roger
-----Original Message-----
From: ert ert [mailto:[log in to unmask]]
Sent: Monday, September 04, 2006 4:01 AM
Subject: Best routing method- arc or 45deg or 90deg
Hi All,
In design we route with 45deg, 90 deg and also using arcs. I undersand
90deg traces acts as antennas, also adds manufacturing issues like
underetching, overetching. And with 45deg these isses can be reduced.
If arcs are used I feel the manufacturing issues get reduced much and
reduces antenna effects on board.
Just curious to know, Is there any other reasons with respect to
manufacturing /SI aspects for using arcs and 45deg routing? What IPC
designers usually recommends and why? Is there any limitation in arc
routing?
Thanks in advance for your ideas and suggestion.
Nagaraj.
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