[SI-LIST] Re: Conductor loss reduction at High Frequency
- From: olaney@xxxxxxxx
- To: eric@xxxxxxxxxxxxxxx
- Date: Wed, 29 Aug 2007 15:59:27 -0700
Quite correct. At high frequencies, everything counts: dielectric, glass
weave, conductor roughness, plating, solder mask. To this add the
statistical variation in trace width created by the etch process. Edge
roughness is about half a thousandth for 1 ounce foil. This tiny profile
of the Alps manifests itself as "noise" in the local impedance, which
increases distributed return loss. Since RF current preferentially
bunches at the trace edges, the importance of this loss contributor is
magnified. Fine lines have edge roughness as a greater fraction of the
total width and suffer proportionately. This suggests that for fine
lines, high frequency loss can be lowered with thinner foil, because the
sloped edges of the trace are shorter and the width uncertainty is
reduced for geometric reasons alone, even for the same etch process
(assuming that etching rather than imaging is setting the resolution
limit). Of course, fine line processes demand thinner foil for a variety
of reasons.
Orin
On Wed, 29 Aug 2007 16:47:28 -0500 "Eric Bogatin" <eric@xxxxxxxxxxxxxxx>
writes:
> I second Scott's important point. Above 1 GHz, skin depth is less
> than 2
> microns in copper. When the RMS surface roughness is larger than the
> skin
> depth, it affects conductor loss.
>
> Above 3 GHz, surface roughness can almost double conductor loss. In
> fact,
> the commonly used approximations for the impact from conductor loss,
> saturate at a factor of 2 increase to the resistance when the
> surface
> roughness is about 3 x skin depth.
>
> This means, even though your line width is 5 mils, it would have the
> conductor loss equivalent of a 2.5 mil wide line. The conductor loss
> can
> easily swamp the dissipation factor of even FR4, negating any
> benefit for
> low loss materials unless you are using very wide lines.
>
> If you want the biggest bang for the buck in evaluating conductors,
> try
> looking at surface treatments that allow smoother copper foils.
>
> --eric
>
> **************************************
> Dr. Eric Bogatin, President
> Bogatin Enterprises, LLC
> Setting the Standard for Signal Integrity Training
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> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx
> [mailto:si-list-bounce@xxxxxxxxxxxxx] On
> Behalf Of Scott McMorrow
> Sent: Wednesday, August 29, 2007 4:11 PM
> To: jeff.loyer@xxxxxxxxx
> Cc: sridharam@xxxxxxxxxx; si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: Conductor loss reduction at High Frequency
>
> Surface roughness is the largest contributor we've measured for
> conductor loss. There are certain low loss materials that are
> constructed with high tooth copper for maximum adhesion, which show
> enough loss to absolutely negate any benefit that the low loss (low
> tan
> delta) material would have had over materials with twice the
> dielectric
> loss.
>
> Interesting stuff.
>
> Scott McMorrow
> Teraspeed Consulting Group LLC
> 121 North River Drive
> Narragansett, RI 02882
> (401) 284-1827 Business
> (401) 284-1840 Fax
>
> http://www.teraspeed.com
>
> TeraspeedR is the registered service mark of
> Teraspeed Consulting Group LLC
>
>
>
> Loyer, Jeff wrote:
> > My 2 cents available in the article below:
> >
> > http://pcdandm.com/cms/content/view/2572/95/
> >
> >
> > Jeff Loyer
> >
> > -----Original Message-----
> > From: si-list-bounce@xxxxxxxxxxxxx
> [mailto:si-list-bounce@xxxxxxxxxxxxx]
> > On Behalf Of M Sridhar
> > Sent: Wednesday, August 29, 2007 5:08 AM
> > To: si-list@xxxxxxxxxxxxx
> > Subject: [SI-LIST] Conductor loss reduction at High Frequency
> >
> > Hi Members,
> >
> > What are the methods by which we can reduce the conductor losses
> at high
> > frequency?(Loss due to skin effect, Dielectric losses etc.)
> > Which is the best conductor at higher frequency? in the range of
> 1-5 GHz
> >
> > Thanks,
> > Sridhar
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