Re: Dielectric Constants of Various Resin/Glass Materials

For background, most Dk values reported in manufacture's literature are either
at 1 MHz or the preferred frequency of 10 GHz.  There will be some variation
in the reported Dk values depending of the frequencies the tests were run at.
For the majority of glass reinforced laminate and prepreg materials the Dk of
the composite is dominated by the glass content.  Glass is around 5.5.-5.9 @ 1
MHz.  Also the majority of resin systems such as epoxy, polyimide, BT and
General Electric's GETEK (Epoxy and PPO-polyphenyloxide) have Dks around
3.4-3.6.  So the ratio of resin to glass becomes a factor...the higher the
glass content, the higher the Dk of the composite. In general, the Dk of these
systems are in the 4.0 -4.6 range.  Other resin systems like cyanate ester and
PTFE (Teflon) have lower dielectic constants, i.e. 2.1 to 2.9, so the Dk of
the composites with glass range from around 3.0 to 3.9, again depending on the
glass or other reinfocement to resin ratio.  There are other PTFE based
materials from Rogers Corp. that have Dk in the 2.3-3.0 range that are
normally used in microwave applications.  The Dk of the Kevlar  non woven
reinforcement used in Thermount is 4.0.
The Gore product is one called "SPEEDBOARD".  It is only a prepreg, not a
laminate and it is not reinforced with glass.  The resin is contained inside
of an expanded PTFE matrix (GORE-TEX).  Two resin systems are available,
SPEEDBOARD N with a 140 Tg epoxy the Dk at 10 GHz is 3.0; SPEEDBOARD C with a
cyanate ester resin system the Dk is 2.6-2.7.  The Gore material is used in
signal layers only as a prepreg and is normally combined with standard glass
reinforced cores in a multilayer since the SPEEDBOARD material is not in
itself reinforced.  Gore does offer a laminate material called GORE-CLAD that
uses two plies of SPEEDBOARD C prepreg with a single ply of 1080 cyanate
glass. The Dk of this composite is 2.9 at 10 GHz with a 10 mil thick core.
I hope this answers your question, if not get to me off line and I can expand
on this topic.

Regards,
Lyle Wallig

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