Specify the performance values you need and let the fabricator do the stack
up.  G. Frank is right.  There are too many factors for the designer to
consider that are specific to processes, and materials.

        -----Original Message-----
        From:   Gfranck [SMTP:[log in to unmask]]
        Sent:   Monday, September 27, 1999 11:40 AM
        To:     [log in to unmask]
        Subject:        Re: [DC] RF boards

        Your RF guy might be correct.
        For RF applications using Epoxy blended materials I usually specify
the
        laminate.  Two that come to mind are Getek, and Nelco 4000-13.
There are many
        others which are blended for high-speed, low-loss operations.  There
actually is
        a wide range of materials which can qualify as FR-4, with a wide
range of
        electrical properties at 'higher' frequencies.

        Even with the same resin, the dielectric constant for them material
on 7628
        glass might be 4.6, and on 106 glass might 4.1.  Why?  because the
resin %
        changes from 40% to 75% and the glass has a dielectric constant of
over 6, and
        the resin has a constant of around 3.



        George Franck
        "My Opinions are just that"


        Ron Luman wrote:

        > 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
        > [log in to unmask]
        >