[SI-LIST] Re: Impedance Mismatch due to neck down
- From: johndp@xxxxxxxx
- To: qazi@xxxxxxxxxx, si-list@xxxxxxxxxxxxx
- Date: Fri, 24 Jun 2005 17:56:09 +0100
Quazi,
Try a web search for impedance matching tapers, there are many methods, 1/4wave
transformers, bessel, expotential, binomial, klopfenstien, some of which can be
designed with widebandwidths.
Regards
John
qazi@xxxxxxxxxx wrote:
> R: [SI-LIST] Impedance Mismatch due to neck downThanks guys for the
> responses.
> One reason for which we do not want to have 4-5 mil traces all the way is
> the resistive loss.
> 5 mils within the DUT and then gradual increase to 8 mils looks like a
> pretty good solution.
> Rgds,
> Qazi Iqbal
> -----Original Message-----
> From: Guasti Giovanni [mailto:Giovanni.Guasti@xxxxxxxxxx]
> Sent: Friday, June 24, 2005 12:41 AM
> To: 'qazi@xxxxxxxxxx'; si-list@xxxxxxxxxxxxx
> Subject: R: [SI-LIST] Impedance Mismatch due to neck down
>
>
> I agree with Paul, a slow signal would not notice the 1-2 cm long trace
> impedance mismatch.
> But you could think to make 5 mils traces ewerywere too. 65 Ohm is not =
> so
> high but there are some simple ways to reduce it further.
>
> If you choose a dieletric thickness around 0.150mm you'll obtain an
> impedance of 50 ohm.
> Isn't er=4 too low? with an er=4.3-4.4 the impedance reduces from 6=
> 5 to
> 60ohm.
> With a 8 mil trace and er=4.4 -> Zo=47ohm. Is it what you would lik=
> e to
> obtain?
> By
> Giovanni
>
> -----Messaggio originale-----
> Da: Qazi Arif Iqbal [mailto:qazi@xxxxxxxxxx]
> Inviato: giovedì 23 giugno 2005 19.59
> A: si-list@xxxxxxxxxxxxx
> Oggetto: [SI-LIST] Impedance Mismatch due to neck down
>
>
>
> Hi Experts,
> The board that I am using is of a stripline setup with 8mil traces (1 o=
> z
> Cu), FR-4 (4.0) and 10 mil dielectric thickness which gives 50ohm
> (relatively low speed). The BGA is tightly pitched and I have to neckdo=
> wn
> traces around 4-5 mils which gives impedance mismatch (65.4 ohm). Neckd=
> own
> is a must but I also want to avoid impedance mismatch, is there any way=
> of
> doing it? Does doubling help? (looks like this would give a parallel of=
> 2
> 65.4ohms = 32.7, worse than what I have).
>
> Thanks in advance,
> Qazi
>
>
>
>
>
>
>
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