Generally you can create a balanced construction by using combinations
of core/prepreg.  When using a blank layer we will request to repeat the
odd layer to provide symmetry from the center line.  If this is not
possible, a single sided core is not used, as you need the venting
pattern/objects in the thief to maintain good resin flow and bonding.  

Jeffrey Bush
Director, Quality Assurance and Technical Support
VERMONT CIRCUITS INCORPORATED 
           76 Technology Drive - POB 1890 
              Brattleboro, Vermont 05302
                Voice - 802.257.4571 ext 21
                    Fax - 802.257.0011
                       <http://www.vtcircuits.com/> 
                           

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Ofer Cohen
Sent: Wednesday, June 14, 2006 2:16 AM
To: [log in to unmask]
Subject: [TN] Odd layers count

Hello all, 
Due to constraints of PCB thickness and routing dead end I was requested
to approve odd layers count (19 metal layers). I checked the stack up -
it is completely symmetrical, except of the center line that is in metal
layer rather than in laminate or prepreg, as we are used to. Did anyone
experience a problem caused by the non symmetry of laminates versus
prepreg count? Is there availability problem of single-sided laminates?
The material is hi-Tg/hiTd regular FR 4.

Regards

Ofer Cohen

Director - Quality Assurance and Reliability

SIEMENS COM FN A SB

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