Ron -

The stack-up of the board can vary between vendors, using different standard
prepregs,  even if the layer to layer distance remains the same.  The change
in the ration of glass to epoxy resin in different prepreg cores will cause
slight shifts in the dielectric constant of the finished PCB.  The range for
dielectric constant for FR-4 will also vary over the frequency spectrum.
Low-end of about 4.0 in the KHz range and 4.8 in the GHz range.
These variances may be the cause problems in your design.  However if the
cause is this little of variance the design is probably marginal to begin
with (just my experience and opinion).

Jeffrey A. McGlaughlin
PCB Designer
Battelle Memorial Institute
Columbus Ohio
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        -----Original Message-----
        From:   Ron Luman [SMTP:[log in to unmask]]
        Sent:   Monday, 27 September, 1999 11:01
        To:     [log in to unmask]
        Subject:        [DC] RF boards

        I am having a problem with the RF engineer saying the board material
        (vendor) is the problem with his circuit not working. In every
formula I
        have looked at the dielectric constant of FR4 is the same.
        My boards are .062 thick FR4 Tg 130. no soldermask no silkscreen.
        Can someone out there explain to me what the differences can be
between two
        vendors when they are both using the same process notes I supply to
make the
        boards??
        And how this might effect the RF circuit?
        Thank You

        Ronny Luman C.I.D.
        SERCEL INC.
        (918) 621-5725
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