[SI-LIST] 6 Layer microvia stackup

Hello,

I'm currently designing a really dense PCB and was wondering if anybody has
comments with regards to the signal integrity of the following stack; 


1 GND           
                50um    ER1 3.6
2 SIG 1                                         75um trace for 50 ohm
                50um    ER1
3 SIG 2                                         100um trace for 50 ohm
                100um   ER2 4.2
4 GND
                50um    ER1 3.6
5 PWR
                50um    ER1 3.6
6 MISC


Basically the plan is to do all routing on layers 2 and 3. The top layer is
mostly BGA's and floods to a pretty solid GND plane. All lands on layers 1
and 6 are micro via in pad. So microvias from layers; 1-2, 2-3 . These can
be stacked to create a 1-3 via.

So I have a few worries about this stack;

1. Can't route SIG1+SIG2 orthogonally. The impedance calculations are based
on each layer being calculated as an independent offset stripline. Is this
valid and will there be a lot of cross talk on traces running underneath
each other.

2. Getting controlled impedance on tracks that switch between 2 and 3 could
be tricky.


Lastly I was wondering if anybody knows a good reference for micro via
stack's. It seems that you basically have to throw away the stacks used for
conventional via's. For example if you have 3 micro via layers on each side
(3+n+3) where do your planes go?

Best regards,

Andrew








------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field

or to administer your membership from a web page, go to:
http://www.freelists.org/webpage/si-list

For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field

List FAQ wiki page is located at:
                http://si-list.org/wiki/wiki.pl?Si-List_FAQ

List technical documents are available at:
                http://www.si-list.org

List archives are viewable at:     
                http://www.freelists.org/archives/si-list
or at our remote archives:
                http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
                http://www.qsl.net/wb6tpu

Other related posts: