Re: [SI-LIST] : RE: 2.5 GHz in FR4

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From: Bill Owsley ([email protected])
Date: Mon Apr 30 2001 - 06:38:22 PDT

At 06:56 AM 04/30/2001 -0400, [email protected] wrote:
>After reading all of the replies to the 2.5GHz questiion, I can see the need
>for using stripline to keep phaseshift constant on long runs. In trying to
>make the stubs a part of the transmission line, wouldn't it be advisable to
>utilise most of the via as part of the line by using the stripline located on
>the opposite side of a card from the IC?
>Consider the 8 layer stackup shown here for clarification.
>------- Sig and IC layer
>------------- Plane
>------- Sig
>------------- Plane
>------------- Plane
>------- Sig 2.5 GHz stripline
>------------- Plane
>------ Sig
>The stub resulting from the the unused portion of the via is reduced in
>length. The trick would be to make the vias look like the transmission line
>Another thought--It seems like an imbedded microstrip line would possess
>almost the same qualities of a stripline in terms of dielectric affecting
>phaseshift. Can a card be made so that the vias would go only from the IC

HDI - High density interconnect. Lasers burn thru to the next layer and
then it's plated to make the connection.

>layer to an imbedded microstrip layer directly below? This would get rid of
>any stubs. What do you think?
>Richard Ellison

Bill Owsley, [email protected]
919) 392-8341

Compliance Engineer
Cisco Systems
7025 Kit Creek Road
POB 14987
RTP. NC. 27709

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