[SI-LIST] Re: Inserion loss of fr4 , 50 ohm trace .

  • From: Scott McMorrow <scott@xxxxxxxxxxxxx>
  • To: bala <balaseven@xxxxxxxxx>
  • Date: Sat, 23 Nov 2013 10:37:15 -0500

Immersion silver plating is your friend.  It has almost exactly the same
conductivity as Copper.

On Sat, Nov 23, 2013 at 10:35 AM, bala <balaseven@xxxxxxxxx> wrote:

> So stripline structure is strongly recommended for RF at 2.4Ghz?
>
> Regards
> bala
> On 23 Nov 2013 20:44, "Scott McMorrow" <scott@xxxxxxxxxxxxx> wrote:
>
>> The problem is most likely ENIG gold plating.  2.4 GHz is near the sweet
>> spot for nickel resonance.  Nickel (a component of ENIG plating) has a
>> resonance at approximately 2.7 GHz.
>> Here are slides that Yuriy Shlepnev of Simberian and I created for the EMC
>> conference paper that was presented several years ago  We show a detailed
>> analysis of interconnect losses with Nickel and present a model for it's
>> loss behavior.
>>
>>
>> http://www.simberian.com/Presentations/NickelCharacterizationPresentation_emc2011.pdf
>>
>> Here is the reference for our IEEE paper.
>>
>> Y. Shlepnev, S. McMorrow, “Nickel characterization for interconnect
>> analysis”, Proc. of
>> the 2011 IEEE International Symposium on Electromagnetic Compatibility,
>> Long Beach,
>> CA, USA, August, 2011, p. 524-529.
>>
>>
>>
>> On Sat, Nov 23, 2013 at 9:51 AM, steve weir <weirsi@xxxxxxxxxx> wrote:
>>
>> > Demon nickel barrier could be the culprit.  In that case the simulation
>> > model did not include the surface finish which is an easy way to get
>> > surprised in the lab.
>> >
>> > Best Regards,
>> >
>> >
>> > Steve.
>> > On 11/23/2013 6:32 AM, Scott McMorrow wrote:
>> > > Did you use gold plating on the CPW?  That is one source of potential
>> > > additional loss.  Another is that your are not exciting the CPW mode
>> > > correctly with your measurements and are measuring a different mode.
>> > >
>> > > On Sat, Nov 23, 2013 at 8:44 AM, bala <balaseven@xxxxxxxxx> wrote:
>> > >
>> > >> Sunil,
>> > >> I would recommend to consider copper roughness and double check your
>> via
>> > >> and coplanar modeling in your simulation.I believe you considered the
>> > loss
>> > >> of your measurement cable.or simply generate s-parameter model from
>> VNA,
>> > >> check symmetric and passivity ,put that model in your sim setup and
>> see
>> > >> whats the loss.You shall definitely  get an idea.
>> > >> Regards
>> > >> bala
>> > >> On 23 Nov 2013 18:33, "sunil bharadwaz" <sunil_bharadwaz@xxxxxxxxx>
>> > wrote:
>> > >>
>> > >>> Hi friends ,
>> > >>> We are designing a dual band receiver ( 2.4 Ghz & 5.5 Ghz ) on a Fr4
>> > >>> substrate .
>> > >>>
>> > >>> The length of the 50 ohm RF trace ( CPW - 15 mil trace width & 18
>> mil
>> > >>> spacing to ground ) ,
>> > >>> is approximately 5 cms .We have simulated this 5 cms long CPW trace
>> on
>> > >>> HFSS using DK of
>> > >>>
>> > >>> 4.4 & DF  of 0.018 . The loss reported was about 1.6 dB .
>> > >>>
>> > >>> We have received the actual board , which shows about 6 dB loss for
>> the
>> > >>> same trace (actual measurement on VNA)
>> > >>>
>> > >>> Measured the 50 ohm trace with TDR . It shows about 53 to 54 ohms .
>> The
>> > >>> fab report is also
>> > >>> in sync with the measurement on the impedance front .The test
>> coupon (
>> > >>> from fab  )also shows
>> > >>> the right impedance .
>> > >>>
>> > >>> Why are we seeing such a huge insertion loss ? The DF of 0.018
>> seems to
>> > >> be
>> > >>> correct .
>> > >>> I have double checked this number , with the fab .
>> > >>>
>> > >>> Can some one ( pls ) explain the inconsistency between the
>> simulated &
>> > >>> actual results  ?
>> > >>>
>> > >>> Best Regards
>> > >>> Sunil.Bh
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>> >
>> >
>> > --
>> > Steve Weir
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>> --
>>
>> Scott McMorrow
>> Teraspeed Consulting Group LLC
>> 16 Stormy Brook Rd
>> Falmouth, ME 04105
>>
>> (401) 284-1827 Business
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-- 

Scott McMorrow
Teraspeed Consulting Group LLC
16 Stormy Brook Rd
Falmouth, ME 04105

(401) 284-1827 Business

http://www.teraspeed.com

Teraspeed® is the registered service mark of
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