RE: [SI-LIST] : RF boards

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From: Ron Miller (rmiller@Brocade.COM)
Date: Fri Apr 28 2000 - 16:43:57 PDT


Hi Mike

> -----Original Message-----
> From: Degerstrom, Michael J.
> Sent: Friday, April 28, 2000 1:52 PM
> To: si-list@silab.eng.sun.com
> Subject: RE: [SI-LIST] : RF boards
>
> Ron,
>
> Isn't your statement that PCB dielectric losses dominate above
> 1 Ghz only relavent for your particular line length and line width?
        [Ron Miller]
        Dominate as I understand it means greater than others.
        Below 1 Ghz, scin effect is the greater loss factor,(HP published a
paper on this.)
        at DC resistance is the greatest loss

        These are all relative. Line length multiplied by the loss per
length
        would give total loss.

        Line width? No. The width of your line needs to be correct to
provide
        the desired impedance in the dielectric, and thickness used. For
those
        working at DC line width could effect loss, as could scin effect
which
        might be important below 1 Ghz. Usually practical constraints force
the
        thickness of the layers and meeting the impedance required dictates
the
        trace width, so you do not have much choice.

> For
> example, the few published comparisons of eye closure for various
> laminates
> tend to base their measurement on .012" wide 12" long lines. My
> experience is with .004" wide 2" long lines in FR-4. Simulations
> with a .02 loss tangent and sqrt(freq) skin-effect losses predicted
> 12 Gb/s. I measured 5 Gb/s. I believe the extra loss is attributed
> to surface roughness as I don't think a loss tangent of .06 at 5 Gb/s
> is realistic.
        [Ron Miller]
        I am not sure either way on this. Howevrer, it is will know that
        the loss tangent goes up with frequency on many materials. Teflon
        is fairly flat with frequency, but the epoxy materials often roll
off
        above 1 Ghz.
>
>
> By the way, with the lower loss laminates, how do
> you know that the lower loss is mostly attributed to the lower
> loss tangent? Couldn't the surface metal be smoother and/or of better
> quality than the metal typically used on FR-4 laminates?
        [Ron Miller]
        All I know is that substituting AR350, and a bunch of other
improvements,
        simulating the whole mess with HP MDS I predicted a bandwidth
improvement
        on a board, built the board and was within 0.2 db of the simulated
losses and
        improvement. I dropped my investigation there and went into
production.

        Ron

> Mike
>
> _______________________________________________________________
> Mike Degerstrom Email: degerstrom.michael@mayo.edu
> Mayo Clinic
> 200 1st Street SW
> Gugg. Bldg. RM 1042A Phone: (507) 284-3292
> Rochester, MN 55905 FAX: (507) 284-9171
> WWW: http://www.mayo.edu/sppdg/sppdg_home_page.html
> _______________________________________________________________
>
>
> > -----Original Message-----
> > From: Ron Miller [mailto:rmiller@Brocade.COM]
> > Sent: Friday, April 28, 2000 3:12 PM
> > To: 'si-list@silab.eng.sun.com'
> > Subject: RE: [SI-LIST] : RF boards
> >
> >
> > The dielectric loss tangent dominates high frequency losses
> > at frequencys above 1 Ghz. Since most digital signals these
> > days have edge rates which generate components much higher
> > than 1 Ghz, the edges are distorted if you have lossy material.
> >
> > Roln MIller
> >
> > > -----Original Message-----
> > > From: Sean Murray
> > > Sent: Friday, April 28, 2000 10:31 AM
> > > To: si-list@silab.eng.sun.com
> > > Subject: RE: [SI-LIST] : RF boards
> > > Importance: High
> > >
> > > Ron,
> > > I do not see much of a difference between the nelco 4000 and
> > > Getek. Is there some variable that I'm missing that plays a
> > big part in
> > > the performance at the RF levels other than the DK?
> > >
> > >
> > >
> > > > -----Original Message-----
> > > > From: Ron Miller [mailto:rmiller@Brocade.COM]
> > > > Sent: Friday, April 28, 2000 10:02 AM
> > > > To: 'si-list@silab.eng.sun.com'
> > > > Subject: RE: [SI-LIST] : RF boards
> > > >
> > > >
> > > > Hi Sean
> > > >
> > > > I have done some work substituting Arlon 350(teflon with
> > > > ceramic loading)
> > > > for FR4 and have
> > > > been able to double the bandwidth of previous generations.
> > > > Going from FR4
> > > > to Getek will
> > > > not get you much, but if you go to Nelco 4000-13SI, you can
> > > > expect a big
> > > > improvement in
> > > > the frequency dependent losses.
> > > >
> > > > Good luck
> > > > Ron Miller
> > > >
> > > >
> > > > > -----Original Message-----
> > > > > From: Sean Murray
> > > > > Sent: Friday, April 28, 2000 7:58 AM
> > > > > To: 'si-list@silab.eng.sun.com'
> > > > > Subject: [SI-LIST] : RF boards
> > > > > Importance: High
> > > > >
> > > > > Anyone have any feelings on what subtle differences when
> > > > fabricating a
> > > > > board can do to an RF board. Such as going from FR-4 to
> > > > Getek; 50/200
> > > > > gold/nickle vs. 30/100 gold/nickle. Is there any books out
> > > > there that
> > > > > deal with strictly the layout of RF boards??
> > > > >
> > > > > Regards,
> > > > > Sean Murray
> > > > > Sales Manager
> > > > >
> > > > > M&M Specialties Inc.
> > > > > 1236 W. Southern Ave. #106
> > > > > Tempe, AZ. 85282-4518
> > > > > Phone: (480) 858-0393 x105
> > > > > Cell: (602) 684-7859
> > > > > Fax: (480) 858-1882
> > > > > Email: seandm@mmspec.com
> > > > > WWW.mmspec.com
> > > > >
> > > > >
> > > > >
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