[SI-LIST] Re: PCB Corners - Need help finding research paper
- From: "Lee Ritchey" <leeritchey@xxxxxxxxxxxxx>
- To: "DAVID CUTHBERT" <telegrapher9@xxxxxxxxx>, bdempsey85@xxxxxxxxx
- Date: Tue, 12 Aug 2008 11:18:54 -0700
I've always found it puzzling that many engineers fret over the use of
right angle bends when routing a PCB, but pay no attention to the fact that
there have always been many right angle bends in IC packages which no one
worried about- especially QFP type packages.
Must be a case of looking where the light is good!
Might also be the result of several simulations presented from time to time
that show the field lines at a right angle bend look different from those
of a mitered corner. These simluations are rarely, if ever, validated to
show that the difference is significant.
In any case, agonzing about the effects of right angle bends on digital
signals is misplaced worry and often distracts ones attention form issues
that are important.
Lee Ritchey
> [Original Message]
> From: DAVID CUTHBERT <telegrapher9@xxxxxxxxx>
> To: <bdempsey85@xxxxxxxxx>
> Cc: Yuriy Shlepnev <shlepnev@xxxxxxxxxxxxx>; <Chris.McGrath@xxxxxxxx>;
<si-list@xxxxxxxxxxxxx>
> Date: 8/8/2008 8:16:11 PM
> Subject: [SI-LIST] Re: PCB Corners - Need help finding research paper
>
> Oh,
> the line width is 10 mils and the distance from the trace to the bottom
> reference is 10 mils and 12 mils to the top reference.
>
> Overall it looks pretty minor to me. Now this is just one corner. What if
we
> have ten?
>
> I think a more important thing to focus on would be vias. This can be more
> of a discontinuity than a bend.
>
> Dave Cuthbert
>
> On Fri, Aug 8, 2008 at 6:55 PM, Bill Dempsey <bdempsey85@xxxxxxxxx> wrote:
>
> > Dave,
> > You fail to mention the dimensions you simulated. What were they?
> > Bill
> >
> > > -----Original Message-----
> > > From: si-list-bounce@xxxxxxxxxxxxx
> > > [mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of DAVID CUTHBERT
> > > Sent: Friday, August 08, 2008 6:59 PM
> > > To: Yuriy Shlepnev
> > > Cc: Chris.McGrath@xxxxxxxx; si-list@xxxxxxxxxxxxx
> > > Subject: [SI-LIST] Re: PCB Corners - Need help finding research paper
> > >
> > > Chris,
> > >
> > >
> > > I wouldn't call it a *myth* but an *exaggeration*. I just ran
> > > a SONNET simulation to confirm this. For the case of the
> > > microstrip I just modeled in
> > > FR-4 the non-chamfered bend shows degraded performance above
> > > 15 GHz. This corresponds to a 25 ps edge.
> > >
> > >
> > >
> > > If one wants to account for every systematic effect in a
> > > system (I consider this good practice) I recommend chamfered bends.
> > >
> > >
> > >
> > > Dave Cuthbert
> > >
> > >
> > > On Fri, Aug 8, 2008 at 3:59 PM, Yuriy Shlepnev
> > > <shlepnev@xxxxxxxxxxxxx>wrote:
> > >
> > > > Chris,
> > > >
> > > > Here is another investigation with comparisons of different
> > > 45-deg and
> > > > 90-deg bends - see App. Note #2007_3 at
> > > > http://www.simberian.com/AppNotes.php
> > > >
> > > > Best regards,
> > > > Yuriy Shlepnev
> > > > www.simberian.com
> > > >
> > > >
> > > > -----Original Message-----
> > > > From: si-list-bounce@xxxxxxxxxxxxx
> > > > [mailto:si-list-bounce@xxxxxxxxxxxxx]
> > > > On
> > > > Behalf Of Chris.McGrath@xxxxxxxx
> > > > Sent: Friday, August 08, 2008 11:11 AM
> > > > To: si-list@xxxxxxxxxxxxx
> > > > Subject: [SI-LIST] PCB Corners - Need help finding research paper
> > > >
> > > > I used to have a copy of a public paper that debunked the myth that
> > > > stated the evils of using 90 degree corners when routing
> > > PCB traces.
> > > > I can't seem to find it on the web, so I'm hoping that one
> > > of you may
> > > > either have a copy of it or can point me to the link. Feel free to
> > > > email me directly with the attachment since the SI List
> > > server will block it.
> > > > Thanks!
> > > > Chris
> > > >
> > > >
> > > > -------------------------------------------------------
> > > > Chris McGrath
> > > > Applications Engineer
> > > > chris.mcgrath@xxxxxxxx
> > > > Office: 480.704.7061
> > > > Blackberry: 480.747.3848
> > > > www.smsc.com
> > > > -------------------------------------------------------
> > > >
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