[SI-LIST] Re: Microstrip vs. Stripline
- From: Ravinder.Ajmani@xxxxxxxxxxxxxx
- To: "si-list@xxxxxxxxxxxxx" <si-list@xxxxxxxxxxxxx>
- Date: Mon, 20 Sep 2010 13:37:51 -0700
Hi All,
I am thankful to all who responded to my query. As I indicated in my
earlier response, I do not have any issue at 6 Gbps. I used 35 ps TDR
rise time for my measurements, and was concerned with the impedance
discontinuities with their possible impact on the future designs.
As I understand from the responses, there is no choice winner between
Microstrip and Stripline, and I need to get a better understanding of the
root cause of impedance discontinuity.
Thanks again.
Regards,
Ravinder Ajmani
Server PCB Development
Hitachi Global Storage Technologies
Email: Ravinder.Ajmani@xxxxxxxxxxxxxx
"Loyer, Jeff" <jeff.loyer@xxxxxxxxx>
Sent by: si-list-bounce@xxxxxxxxxxxxx
09/20/2010 07:11 AM
To
"o. laney" <olaney@xxxxxxxx>, "Ravinder.Ajmani@xxxxxxxxxxxxxx"
<Ravinder.Ajmani@xxxxxxxxxxxxxx>
cc
"si-list@xxxxxxxxxxxxx" <si-list@xxxxxxxxxxxxx>
Subject
[SI-LIST] Re: Microstrip vs. Stripline
I agree - the impacts of localized impedance variations due to plating
and/or soldermask should be negligible for the risetimes that come out of
most packages. And, in the last 5 years, most board vendors have made
tremendous progress in controlling those. If you're seeing large
variations, consider another vendor.
As for the weave effect, simply putting 10 degree zig-zags in your routing
can mitigate that effect; see our DesignCon paper "Fiber Weave Effect:
Practical Impact Analysis and Mitigation Strategies". As Wolfgang pointed
out, stripline is prone to the same problem, so that's not an attractive
option.
I'm greatly relieved to find that your 2.5" link wasn't broken at 6Gbps -
that had me wondering! :-)
Jeff Loyer
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of o. laney
Sent: Saturday, September 18, 2010 6:58 PM
To: Ravinder.Ajmani@xxxxxxxxxxxxxx
Cc: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Microstrip vs. Stripline
What is the risetime of your actual signal as compared to the risetime of
the TDR? If the TDR is lots faster, you are looking at artifacts that
might not matter at all for your signal.
Orin Laney
On Fri, 17 Sep 2010 14:28:37 -0700 Ravinder.Ajmani@xxxxxxxxxxxxxx writes:
> Hi Experts,
> I have 2.5" long interconnects running at 6 Gbps. Currently I am
> using
> Microstrip transmission lines, routed over 3.5 mil Prepreg, because
> I am
> able to route them on the Top layer without any vias. However TDR
> shows
> impedance discontinuities perhaps caused by non-uniform plating and
> solder
> mask, and weave effect.
>
> I would like to know if a dual Stripline transmission line will be
> better
> although I will have to use a pair of vias on each trace. My card
> thickness is 0.8 mm and back-drilling of the vias is not an option.
> I
> also have to stay with standard FR-4 for cost reasons. I have tried
>
> simulating both options and the simulation supports the Microstrip
> approach, but I am not able to simulate the effects of non-uniform
> plating
> and solder mask or weave effect.
>
> Any suggestions.
>
> Thanks.
>
> Regards,
> Ravinder Ajmani
> Server PCB Development
> Hitachi Global Storage Technologies
>
>
> Email: Ravinder.Ajmani@xxxxxxxxxxxxxx
>
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