[SI-LIST] Re: Dielectric constant for FR4 at above 1Ghz frequency
- From: "David Hoover" <dhoovy@xxxxxxxxxxxxx>
- To: <alexh1@xxxxxxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
- Date: Tue, 25 Nov 2003 20:46:23 -0800
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
> >------------------------------------------------------------------
> >To unsubscribe from si-list:
> >si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
> >
> >or to administer your membership from a web page, go to:
> >//www.freelists.org/webpage/si-list
> >
> >For help:
> >si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
> >
> >List technical documents are available at:
> > http://www.si-list.org
> >
> >List archives are viewable at:
> > //www.freelists.org/archives/si-list
> >or at our remote archives:
> > http://groups.yahoo.com/group/si-list/messages
> >Old (prior to June 6, 2001) list archives are viewable at:
> > http://www.qsl.net/wb6tpu
> >
>
>
> ------------------------------------------------------------------
> To unsubscribe from si-list:
> si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
>
> or to administer your membership from a web page, go to:
> //www.freelists.org/webpage/si-list
>
> For help:
> si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
>
> List technical documents are available at:
> http://www.si-list.org
>
> List archives are viewable at:
> //www.freelists.org/archives/si-list
> or at our remote archives:
> http://groups.yahoo.com/group/si-list/messages
> Old (prior to June 6, 2001) list archives are viewable at:
> http://www.qsl.net/wb6tpu
>
>
>
>
> ------------------------------------------------------------------
> To unsubscribe from si-list:
> si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
>
> or to administer your membership from a web page, go to:
> //www.freelists.org/webpage/si-list
>
> For help:
> si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
>
> List technical documents are available at:
> http://www.si-list.org
>
> List archives are viewable at:
> //www.freelists.org/archives/si-list
> or at our remote archives:
> http://groups.yahoo.com/group/si-list/messages
> Old (prior to June 6, 2001) list archives are viewable at:
> http://www.qsl.net/wb6tpu
>
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List technical documents are available at:
http://www.si-list.org
List archives are viewable at:
//www.freelists.org/archives/si-list
or at our remote archives:
http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
Other related posts:
