Mirka,

Yes.  I would definitely follow the rules for annular ring.  Check out
tables 9.4 & 9.5 in the IPC-2221.  I've found them to be very reliable
when done properly.  

If you haven't used mircrovias before, there are other issues to be
aware of such as cost, spacing, solder mask, via-in-pad, etc.  Let me
know if you need more info.  Also, I know there are some people on this
list who work with Class 3 more than I do and could give you better
specifics.  Plus, I think you really have to look at the particular
environment that the board has to function in.

Cherie

-----Original Message-----
From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of
Mirka Halas
Sent: Thursday, May 28, 2009 8:15 AM
To: [log in to unmask]
Subject: [DC] Class 3 and microvias

Hello all,
           are microvias, buried and blind allowed on class3 board?
If so are the rules for annular ring same as for thru holes?

Thank you

Mirka

------------------------------------------------------------------------
---------
DesignerCouncil Mail List provided as a free service by IPC using
LISTSERV 1.8d
To unsubscribe, send a message to [log in to unmask] with following text
in
the BODY (NOT the subject field): SIGNOFF DesignerCouncil.
To temporarily stop/(restart) delivery of DesignerCouncil send: SET
DesignerCouncil NOMAIL/(MAIL)
Search previous postings at: www.ipc.org > On-Line Resources & Databases
> E-mail Archives
Please visit IPC web site
http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional
information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100
ext.2815
------------------------------------------------------------------------
---------

---------------------------------------------------------------------------------
DesignerCouncil Mail List provided as a free service by IPC using LISTSERV 1.8d
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF DesignerCouncil.
To temporarily stop/(restart) delivery of DesignerCouncil send: SET DesignerCouncil NOMAIL/(MAIL)
Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives
Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
---------------------------------------------------------------------------------