[SI-LIST] Re: Dielectric constant for FR4 at above 1Ghz frequency
- From: "Chris McGrath" <chris.mcgrath@xxxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Tue, 2 Dec 2003 11:30:36 -0800
This response addresses a couple of mini-threads that started with the
original posting:
1. Frequencies greater than 1 GHz are perfectly fine to run on FR4(-6)
material and we have done a number of 2GHz designs with FR4. As in many
areas of design, the criteria for use depends on your application. =20
2. When trying to determine the Er (vs. frequency) of the material for
use in simulation, the best method is to ask your fab house unless you
are dealing with a specific manufacturer like Nelco. Either way, the
fab house will have this information as it relates to the manufacturers
they regularly use.
-Chris=20
> -----Original Message-----
> From: Fasig, Jonathan L. [mailto:fasig.jonathan@xxxxxxxx]=20
> Sent: Wednesday, November 26, 2003 11:14 AM
> To: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: Dielectric constant for FR4 at above=20
> 1Ghz frequency
>=20
>=20
> For what it's worth, Nelco has nice tables of dielectric constant at=20
> 1MHz, 1GHz, 2.5GHz and 10GHz for several laminated thicknesses along=20
> with the constructions (e.g. 2 layers of 2116). Reference=20
> the tables at=20
> http://www.parknelco.com/parknelco/resources.htm and take the=20
> link for "Typical Dielectric Property Tables". You will need=20
> to register for a=20
> password first.
>=20
> Isola has some similar information for their FR406 and FR408=20
> products at=20
> http://www.isolalaminatesystems.com/isolaus.nsf/main?OpenFrame
> set . See the spreadsheets under Processing Guide for the=20
> respective laminates.
>=20
> jf
> --------------------------------------------------------------
> ----------
>=20
> Jonathan Fasig Email: fasig.jonathan@xxxxxxxx=09
> Mayo Foundation=20
> 4001 41st Street NW=20
> MSC Sn 2-132 Phone: (507) 538-5464
> Rochester, MN 55901 Fax: (507) 284-9171
>=20
>=20
> -----Original Message-----
> From: David Hoover [mailto:dhoovy@xxxxxxxxxxxxx]=20
> Sent: Tuesday, November 25, 2003 10:46 PM
> To: alexh1@xxxxxxxxxxxxx; si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: Dielectric constant for FR4 at above=20
> 1Ghz frequency
>=20
>=20
> Alex, (it's been awhile) (below is my $.02 from a fabricator)
>=20
> In the case of FR-4 we typically see a series of variables
> that gives us the PCB dielectric properties.
> For example:
>=20
> If we look at the 5 most common (E-Glass) fiberglass styles=20
> used in the
> U.S.: 1060, 1080, 2113, 2116, and 7628 These yield different=20
> thicknesses within the PCB. The 1060 yields the thinnest all=20
> the way up to the 7628 which is (one of ) the thickest. The=20
> Dk of the pure resin of FR-4 epoxy is ~3.6 and the pure=20
> (E-glass) fiberglass is ~6.6 (@ 1 MHz . That's all I've found=20
> on the raw materials so far). It's the resin to glass ratio=20
> that gives us the variance.
>=20
> 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
>=20
> Those values above are used to manufacture the various FR-4=20
> cores. Each is basically like a building block used to=20
> achieve various thicknesses. The thinner ones typically cost=20
> more than the thicker ones. Some PCB fab shops or OEMs have=20
> rules where they require the use of two plys minimum. A key=20
> note to bring up is that even though the 1060 has the lowest=20
> Er, it would not be a good idea to build an entire PCB out of=20
> that prepreg. The resin content is too high and the pressed=20
> PCB would flow resin all over the edges of the lamination=20
> templates onto the lamination press. The thinner
> material(s) also has the greatest amount of dimensional=20
> movement within the PCB. An entire PCB built of 1060 would=20
> cost alot and would experience large amounts of material=20
> shrinkage when pressed. For cost and dimensional movement=20
> reasons we minimize the amount of plies by choosing those=20
> different styles of prepreg to build the various dielectric=20
> thickness. (This allows the pad to hole ratio used today to=20
> be maintained)
>=20
> There is beginning to be a few more choices of fiberglass=20
> styles. Nelco has introduced the "SI" style fiberglass which=20
> has a Dk of 4.4. When used to make prepreg, it yields a=20
> substantially lower Er product. If you factor in lower Dk=20
> resin blends (like the "-13") you can achieve a fairly low Er=20
> material (when compared to standard FR-4).
>=20
> Hitachi and a few others have blends coming on line that have=20
> fairly low Er values. These are all thermoset materials.=20
> (Meaning they cure into a hard rigid state) The thermoplastic=20
> materials (like PTFE
> based) have Er's that get very low but sometimes are very=20
> difficult to build multilayer PCBs with.
>=20
> We should start seeing more and more folks starting to test=20
> their materials at various frequencies soon. This is driven=20
> by issues such what Stuart, Andy, and Tom are discussing.
>=20
> As far as manipulating resins properties to achieve less=20
> loss, I havn't encountered that yet. I have heard of R and D=20
> efforts by the laminate manufacturers working on this, but I=20
> have not heard of any production ready releases.
>=20
> Kind Regards,
>=20
> David Hoover
> Sr. Field Application Engineer
> Multilayer Technology, Inc.
>=20
> San Jose, Ca
> http://www.multek.com
>=20
> ----- 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=20
> 1Ghz frequency
>=20
>=20
> > Exactly, it seems to be fairly common misconception that skin effect
> losses always dominate. Dielectric losses are proportional to=20
> frequency, although they start out lower they will always=20
> exceed skin effect losses between 500 and 1Ghz or so. The=20
> 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=20
> it can be
> manipulated for less loss and what are the tradeoffs. I=20
> 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=20
> 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=20
> > >function is constant)?
> > >
> > >Anyway, Tom is right: you need to consider the frequency=20
> variation of
> > >both Dk (the dielectric function) and Df (the dielectric loss=20
> > >function). However, both are typically dominated by skin effect=20
> > >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=20
> Group LLC 2926
> > > > SE Yamhill St. Device Modeling Division Portland, OR=20
> 97214 13610=20
> > > > 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=20
> above 1Ghz=20
> > > > frequency
> > > >
> > > >
> > > > If I am not mistaken, your question is equivalent to=20
> this one: Is
> > > > the dielectric function constant over the 1 MHz -- 1 GHz range?=20
> > > > The answer is: It is not constant, but varies by=20
> several percent=20
> > > > or more over that range for many FR-4s. (FR-4 is not a single=20
> > > > material, but is a family of materials, each different=20
> depending=20
> > > > upon your PCB vendor, and whatever batch of materials he was=20
> > > > shipped on any particular day.)
> > > >
> > > > However, the bigger problem for you to think about is=20
> the loss due
> > > > to the skin effect in your copper traces. The skin=20
> effect losses=20
> > > > vary as the square root of the frequency, IIRC. The=20
> > > > frequency-dependent loss due to the skin effect=20
> dominates over the=20
> > > > 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=20
> frequency using FR4
> > > material=3D
> > > > > .
> > > > > I am wondering how much the dielectric constant will=20
> be affected
> > > > > by
> the
> > > > > frequency over 1Ghz as compared to 1Mhz?
> > > > >
> > > > > Thank you
> > > > >
> > > > > Regards,
> > > > > Andy
> > >------------------------------------------------------------------
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