Ofer

I can assure you that odd layer boards will warp. While you in theory have
the neutral axis coincident with the geometric, in practice there will be
some separation which will cause warp. Since the modulus of elasticity of
the cooper is much greater than that of the prepreg, small changes here
magnify the warp.

Best regards

Lee

J. Lee Parker, Ph.D.
JLP Consultants LLC
804 779 3389

----- Original Message -----
From: "Ofer Cohen" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Wednesday, June 14, 2006 2:16 AM
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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