[SI-LIST] Re: Dielectric constant for FR4 at above 1Ghz frequency

For what it's worth, Nelco has nice tables of dielectric constant at 
1MHz, 1GHz, 2.5GHz and 10GHz for several laminated thicknesses along 
with the constructions (e.g. 2 layers of 2116).  Reference the tables
at http://www.parknelco.com/parknelco/resources.htm and take the link for
"Typical Dielectric Property Tables".  You will need to register for a 
password first.

Isola has some similar information for their FR406 and FR408 products at
http://www.isolalaminatesystems.com/isolaus.nsf/main?OpenFrameset .  See
the spreadsheets under Processing Guide for the respective laminates.

jf
------------------------------------------------------------------------

Jonathan Fasig                      Email:  fasig.jonathan@xxxxxxxx     
Mayo Foundation 
4001 41st Street NW 
MSC Sn 2-132                        Phone:  (507) 538-5464
Rochester, MN 55901                 Fax:    (507) 284-9171


-----Original Message-----
From: David Hoover [mailto:dhoovy@xxxxxxxxxxxxx] 
Sent: Tuesday, November 25, 2003 10:46 PM
To: alexh1@xxxxxxxxxxxxx; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Dielectric constant for FR4 at above 1Ghz frequency


Alex, (it's been awhile) (below is my $.02 from a fabricator)

In the case of FR-4 we typically see a series of variables
that gives us the PCB dielectric properties.
For example:

If we look at the 5 most common (E-Glass) fiberglass styles used in the
U.S.: 1060, 1080, 2113, 2116, and 7628 These yield different thicknesses
within the PCB. The 1060 yields the thinnest all the way up to the 7628
which is (one of ) the thickest. The Dk of the pure resin of FR-4 epoxy is
~3.6 and the pure (E-glass) fiberglass is ~6.6 (@ 1 MHz . That's all I've
found on the raw materials so far). It's the resin to glass ratio that gives
us the variance.

We typically find:
Prepreg        Thickness    Resin                Er
  Style                           Percentage     (@ 1 GHz)
1060             ~.002"           69                3.63
1080             ~.003"           62                3.80
2113             ~.004"           55                4.00
2116             ~.005"           52                4.08
7628             ~.007"           45                4.32

Those values above are used to manufacture the various FR-4 cores. Each is
basically like a building block used to achieve various thicknesses. The
thinner ones typically cost more than the thicker ones. Some PCB fab shops
or OEMs have rules where they require the use of two plys minimum. A key
note to bring up is that even though the 1060 has the lowest Er, it would
not be a good idea to build an entire PCB out of that prepreg. The resin
content is too high and the pressed PCB would flow resin all over the edges
of the lamination templates onto the lamination press. The thinner
material(s) also has the greatest amount of dimensional movement within the
PCB. An entire PCB built of 1060 would cost alot and would experience large
amounts of material shrinkage when pressed. For cost and dimensional
movement reasons we minimize the amount of plies by choosing those different
styles of prepreg to build the various dielectric thickness. (This allows
the pad to hole ratio used today to be maintained)

There is beginning to be a few more choices of fiberglass styles. Nelco has
introduced the "SI" style fiberglass which has a Dk of 4.4. When used to
make prepreg, it yields a substantially lower Er product. If you factor in
lower Dk resin blends (like the "-13") you can achieve a fairly low Er
material (when compared to standard FR-4).

Hitachi and a few others have blends coming on line that have fairly low Er
values. These are all thermoset materials. (Meaning they cure into a hard
rigid state) The thermoplastic materials (like PTFE
based) have Er's that get very low but sometimes are very difficult to build
multilayer PCBs with.

We should start seeing more and more folks starting to test their materials
at various frequencies soon. This is driven by issues such what Stuart,
Andy, and Tom are discussing.

As far as manipulating resins properties to achieve less loss, I havn't
encountered that yet. I have heard of R and D efforts by the laminate
manufacturers working on this, but I have not heard of any production ready
releases.

Kind Regards,

David Hoover
Sr. Field Application Engineer
Multilayer Technology, Inc.

San Jose, Ca
http://www.multek.com

----- Original Message -----
From: "Alex Horvath" <alexh1@xxxxxxxxxxxxx>
To: <si-list@xxxxxxxxxxxxx>
Sent: Monday, November 24, 2003 3:04 PM
Subject: [SI-LIST] Re: Dielectric constant for FR4 at above 1Ghz frequency


> Exactly, it seems to be fairly common misconception that skin effect
losses always dominate. Dielectric losses are proportional to frequency,
although they start out lower they will always exceed skin effect losses
between 500 and 1Ghz or so. The biggest factor affecting this seems to the
resin content of the PCB.
>
> I'd like to hear more about the properties of the resin, if it can be
manipulated for less loss and what are the tradeoffs. I wasn't able to find
out much about resin properties on the web.
>
> Thanks
> steve weir <weirsp@xxxxxxxxxx> wrote:
> Stuart, for common dielectrics, somewhere in the high hundreds of MHz 
> dielectric loss overtakes loss from skin effect.
>
> Steve.
> At 05:16 PM 11/24/2003 -0500, Stuart Brorson wrote:
> >True enough, but aren't the dielectric losses in FR-4 more or less 
> >frequency independent (i.e. to the <10% level that the dielectric 
> >function is constant)?
> >
> >Anyway, Tom is right: you need to consider the frequency variation of 
> >both Dk (the dielectric function) and Df (the dielectric loss 
> >function). However, both are typically dominated by skin effect 
> >losses, particular in the GHz range.
> >
> >Stuart
> >
> >
> > > To make the answer complete you need also to include dielectric 
> > > losses
> > which
> > > also are frequency dependent.
> > >
> > > Tom Dagostino
> > > Teraspeed Consulting Group LLC Teraspeed Consulting Group LLC 2926 
> > > SE Yamhill St. Device Modeling Division Portland, OR 97214 13610 
> > > SW Harness Lane Beaverton, OR 97008
> > > http://www.teraspeed.com 503-430-1065
> > > tom@xxxxxxxxxxxxx
> > >
> > >
> > > -----Original Message-----
> > > From: si-list-bounce@xxxxxxxxxxxxx 
> > > [mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Stuart Brorson
> > > Sent: Monday, November 24, 2003 1:22 PM
> > > To: andyk@xxxxxxxxxx
> > > Cc: si-list@xxxxxxxxxxxxx
> > > Subject: [SI-LIST] Re: Dielectric constant for FR4 at above 1Ghz 
> > > frequency
> > >
> > >
> > > If I am not mistaken, your question is equivalent to this one: Is 
> > > the dielectric function constant over the 1 MHz -- 1 GHz range? 
> > > The answer is: It is not constant, but varies by several percent 
> > > or more over that range for many FR-4s. (FR-4 is not a single 
> > > material, but is a family of materials, each different depending 
> > > upon your PCB vendor, and whatever batch of materials he was 
> > > shipped on any particular day.)
> > >
> > > However, the bigger problem for you to think about is the loss due 
> > > to the skin effect in your copper traces. The skin effect losses 
> > > vary as the square root of the frequency, IIRC. The 
> > > frequency-dependent loss due to the skin effect dominates over the 
> > > frequency variation of the FR-4's dielectric constant.
> > >
> > > Here are some references:
> > >
> > > http://www.tdasystems.com/library/appnotes/siml0803.pdf
> > > http://signalintegrity.com/Pubs%5Cnews%5C4_5.htm
> > >
> > > Stuart
> > >
> > >
> > > > Hi all,
> > > >
> > > > I am designing a high speed PCB at over 1Ghz frequency using FR4
> > material=
> > > > .
> > > > I am wondering how much the dielectric constant will be affected 
> > > > by
the
> > > > frequency over 1Ghz as compared to 1Mhz?
> > > >
> > > > Thank you
> > > >
> > > > Regards,
> > > > Andy
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