[SI-LIST] Re: PCB tracks
- From: "gurunath vinayakrao kulkarni" <gurunath.kulkarni@xxxxxxxxx>
- To: <PhilippeR@xxxxxxxxxxxx>, "SI-LIST" <si-list@xxxxxxxxxxxxx>
- Date: Thu, 8 Aug 2002 17:45:38 +0530
Hi all,
I agree with Philippe Robert as I have not seen the PCB with curved traces
usually 45 deg is O.K
GVK
----- Original Message -----
From: "Philippe Robert" <PhilippeR@xxxxxxxxxxxx>
To: "SI-LIST" <si-list@xxxxxxxxxxxxx>
Sent: Thursday, August 08, 2002 4:20 PM
Subject: [SI-LIST] Re: PCB tracks
> Hi all,
>
> The on-board maximum frequency won't exceed 200 MHz and it is all digital.
I
> know now why I have never seen any PCb with curved traces ! I think that I
> will keep 45-degree angles for the traces, as it would not make any real
> difference.
>
> Thanks a lot for your help.
>
>
> Kind Regards.
> Philippe.
>
>
> -----Original Message-----
> From: john lipsius [mailto:johnlipsius@xxxxxxxxx]
> Sent: 07 August 2002 12:48
> To: SI-LIST
> Subject: [SI-LIST] Re: PCB tracks
>
>
>
> Philippe,
>
> For a detailed answer, you should find it in a textbook.
> There's been much prior discussion on this; see the si-list archives
> //www.freelists.org/archives/si-list/ .
> Or see perhaps www.signalintegrity.com or www.gigatest.com .
>
> I assume your problem area is current digital technology.
>
> 1. For digital boards, even dealing with 10Gbps, 90 deg. is fine.
> There's just not a significant effect requiring even 45 deg., much less
> curved traces.
>
> 2. That said, why is 45 is "better" than 90 deg., and curvilinear is best?
> All for the same reason: with sudden geometry changes, the TEM
> (transverse electromagnetic) wave sets up "evanescent modes" other
> than the main one to compensate for the change. Why? Remember,
> the EM field is a solution to partial differential equations with both
> space and time as variables. Therefore, sudden spatial boundary changes
> force different boundary conditions, forcing different local micro field
> changes, thus local impedance changes. The locus of these changes is
> so much less than the wavelengths of importance that the signal
> integrity effect is unimportant. The energy loss in these evanescent
modes
> is, likewise, minimal in the overall noise budget. This assumes you have
a
> limited number of trace bends.
>
> That's my $.02. Due to inflation and the passing of time, it may now be
> $.015 or less.
>
> ---
>
>
> ----- Original Message -----
> From: "Philippe Robert" <PhilippeR@xxxxxxxxxxxx>
> To: <si-list@xxxxxxxxxxxxx>
> Sent: Wednesday, August 07, 2002 2:22 AM
> Subject: [SI-LIST] PCB tracks
>
>
> > Hi there,
> >
> > I am currently in the process of doing a new PCB, at the routing stage.
In
> > the router that I am using, there is an option to have 90-degree or
> > 45-degree angles on the tracks. I know that it is better to have the
> option
> > set to 45 to avoid changing too much the impedance of the tracks. I
> designed
> > few board using that option.
> >
> > In the router, there is an other option to have curves instead of angles
> on
> > the tracks. Theoretically, it should be better in terms of impedance as
> the
> > width of the track vary even less.
> >
> > Could someone tell me if curves are better than 45-degree angles and why
?
> >
> > Best regards.
> > Philippe.
> >
> >
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>
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