Scott,

DC means Dielectric Constant?  That is a new one.  The PWB industry likes to call it
"Dk", and the RF Electrical Engineers call it "Er", or epislon-r.  Some people call it
"permittivity".  I am not sure where these people come from.  I have to look really
close at who I am talking to before deciding what to call it.  Both Getek and Nelco
4000-13 materials have Dk's of around 3.9.  Typical FR-4 is 4.5.  PTFE (teflon)
materials range from 2 - 3, depending on lots of other stuff.

The other important factor in RF material is the "Dissipation Factor" (PWB Industry)
aka Loss Tangent (RF EEs).  This is a measurement of how much power gets sucked off the
traces by the material and converted into heat.  It is the same effect present in your
microwave oven.  The ceramic dish holding the food has a low Dissipation Factor, and
does not heat up in the oven, while the water in your food has a very high Dissipation
Factor, and warms up quite nicely.  These materials have Loss Tangents of  .010 at 1
MHz.  FR-4 is about .020, and PTFE is .0012.  The PTFE and High frequency Epoxy
materials will have slightly increasing Loss Tangents as Frequencies increase.  FR-4 on
the other hand, increases very quickly, to the point where you can loose 1 dB/inch of
trace length at a few Gigs.  Using FR-4 at High frequency is kinda like trying to shine
a flash light through a brick.  It can work, but the brick has to be pretty thin.

Call your PWB Board supplier.  They can get you information on materials that THEY know
how to work with.  There are many other materials being used for RF work which fall
between PTFE and FR-4 in RF performance.  They also fall between "nice" and "WOW" in
cost.

If you would like, send me your phone number.
I'll see if I can give you a call, (but first I'll try to arrange for commission
payments from the material suppliers.)

George Franck
"My Opinions are just that."

"Scott D. Shepard" wrote:

> I just had a discussion with engineer about our RF project. He would really like to
> see a lower-loss material. What is the characteristic dielectric constant (DC) for
> Getek and Nelco 4000-13? I haven't used/specified these before. Or if there are
> other common materials, excluding polyimide or teflon, that I could suggest. The
> goal is a DC less than 4.
>
> TIA
>
> Scott
> IDS