FreeLists / si-list / [SI-LIST] Re: Impedance control with split ground planes

["Jack C. Olson" <OLSON_JACK_C@xxxxxxx>]

Forgive me for asking such a "newbie" question among so many 
experts, but just reading through this thread has made me curious...
(I have never had to use blind vias before, but I have some experience
with impedance control.)
If the original problem was that routing out from the BGA has to be 
done on layer 2 from blind vias, where did he go wrong?
Do other designs drill through a plane on 2 and route from 3? 
None of the responses ever said what the original mistake was in
designing the stackup, so I am confused.

Jack (aka "the new guy")






steve weir <weirsi@xxxxxxxxxx> 
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04/20/2006 08:28 AM
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[SI-LIST] Re: Impedance control with split ground planes




Caterpillar: Confidential Green Retain Until: 05/20/2006        Retention 
Category:  G90 - General Matters/Administration


Balaji,   I don't think there are any simple fixes.  About the only 
think you have going for you is that SDR 133 is pretty tolerant.  My 
best recommendation is to start with the basics:  Propose a strategy 
and test feasibility.  If it is feasible then work the details.  If 
not, iterate using a different strategy.  I know no other reliable 
way to design.  From your questions, it sounds like you may have 
elected an implementation before determining overall feasibility.  If 
so, it is time to back-up and see where you stand.  If you are lucky 
then the strategy is feasible with some effort and/or changes.

Good luck.

Steve.
At 12:52 AM 4/20/2006, Balaji S wrote:
>Hi Steve,
>A small correction. My high speed signals are routed on S2 ( and not on
>S1. typo).. Still is the design so flawed??
>
>Since due to microvias (aspect ratio 1:1) and cost constraint, we had to
>go 4 that stack-up.
>
>Any suggestions for improvement will definitely be welcome..
>
>Regards
>Balaji S
>




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