perhaps someone from the laminate industry can explain why if you draw a
straight line graph between all e glass @ 6.28 and all resin @3.6 , the
resulting line is parallel to but not overlaying the Dk graph for your
material.
Dougal Stewart
email [log in to unmask]
telephone +44 1896 822204
mobile +44 7984 629667


-----Original Message-----
From:   Brad Saunders [SMTP:[log in to unmask]]
Sent:   29 November 2001 16:40
To:     [log in to unmask]
Subject:        Re: [TN] Dielectric constant vs degree of cure , FR4

FR4 will not change Er due to cure temp at fabrication,  however the press
cycle may.   Total dielectric constant (Er) is a function of the main
ingredients of Eglass (6.28 Er) and Resin (3.6 for epoxy).  The higher the
Eglass content the higher resultant Er.  Hence, any "above normal" squeeze
out of resin will have the propensity to increase resultant Er for B-stage,
C-stage is a little different.  I say "propensity" for the Er is estimating
averages and empiric data that over time develops a heritage of dependable
predictability.   Sameness is good.

Copper thickness may be a culprit if impedance are varying.  >.0007 and
edges
can start getting ragged.  I introduce this relative to fixed cycles of
press
times and the amount of field support for dielectric materials.  Copper
etching may be more subjective and susceptible to OE (Operator Error).
 Given
that the fabrication is repeatable, which it is, deliverable impedance can
go
significantly below the standard +/-10%, otherwise we couldn't deliver 25
ohm
boards.

Brad
 << File: ATT00002.htm >>

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