[SI-LIST] Re: tolerance on components
- From: steve weir <weirsi@xxxxxxxxxx>
- To: jan.vercammen1@xxxxxxxx
- Date: Fri, 29 Oct 2010 05:56:33 -0700
Jan, the capacitor manufacturers have gotten really good at controlling
their processes. The general observation is that the value distribution
is generally pretty tight as in +/-2% typically for X7R and C0G and runs
at the low-end of the tolerance saving them material. For ultimate
value stability in tuned circuits you should be using C0G/NPO
components. Higher K dielectrics like X5R have temperature and
conditioning variations that make them much more variable off the reel.
Steve
jan.vercammen1@xxxxxxxx wrote:
> hi si-list,
>
> I am looking for information on tolerance of SMD capacitors, to be
> more specific the: the (probability) distribution of component values.
>
> I remember - maybe incorrectly - that this subject has been already
> discussed on the si-list. I have searched the archive, but without succes.
>
> I have been working on a RF matching circuit with lumped components.
> The tolerances on the inductors and capacitorshave been selected as 5%
>
> >From simulations I know that certain capacitors values are more senstive
> than
> others and I use multiple parallel capacitors to improve on the tolerance.
> (the frequency is low enough to allow for parrallel parts).
>
> All capacitors used are generic 0603 generic series 50V, NPO or COG,
> were one can select the the tolerance from 1, 2 or 5%. However, not all
> values
> of 1 or 2% are readily available and we use 5% as a standard in our
> database.
> Our boards are assembled by an external partner and the components
> are acquired from various sources - buying a generic part.
>
> However, I can imagine that capacitor manufacturers select 1 and 2%
> tolerance
> parts and sell the rest as 5% parts (discarding parts or as 10%) . Which
> means that
> the distribution is not necessarily normal, but maybe normal with a gap in
> the middle.
>
> Is my reasoning correct? Has anyone ever observed this kind of
> distributions?
>
>
> Met vriendelijke groet,
> Kind Regards,
>
> Jan Vercammen | Agfa HealthCare
> EMI specialist | HE/A&D / ELEC2
> T +32 3444 6233 | F +32 3 444 6268
>
> Agfa HealthCare NV, Septestraat 27, 2640 Mortsel, Belgium
> http://www.agfa.com/healthcare/
> R.O.: Septestraat 27, B-2640 Mortsel, Belgium | RLE Antwerp | VAT BE
> 0403.003.524 | IBAN Operational Account BE81363012356224 | IBAN Customer
> Account BE20375104592856 | ING Belgium NV, B-1000 Brussels
> Click on link to read important disclaimer:
> http://www.agfa.com/healthcare/maildisclaimer
>
> __________________
>
> hi si-list,
>
>
> I need help on the resistivity of copper tracks of a 2-layer PCB
>
> It concerns a RFID reader with a loop antenna operating at 13.56MHz.
>
> I have measured the loop impedance as 2uH + 7Ohm
>
> I have simulated the loop with FastHeny as 2uH + 4.6Ohm using w=150um and
> t=35um and sigma=30e6
>
> I have been using for the resitivity of copper 34nS/m, the double of the
> textbook value of 17nS/m
> of pure copper (or 50% of the textbook conductivity)
>
> A reference (manual LC Cray) quotes the PCB conductivity as 30-70% of the
> conductivity of pure copper.
>
> If I repeat the simulation with sigma=20e6 (or about 30%) then the result
> match better or about 6.4Ohm.
>
> Next I measured (optically) the track width (there are 4 loops, w=150um
> and separation = 125um):
> - the two outer tracks are consistently thinner, about 120um (at
> the top)
> - the two central tracks are about 140um (at the top)
> - they seem to be trapezoid, the top is less wide than the base,
> the base seems to be right on 150um for the inner tracks
> and about 140um for the outer tracks
> - registration is very good
> With this information and using thinner tracks (average of about 130um)
> the resistance turns out about 6.7Ohm
>
> I assume that the trapezium shape could have more loss than a rectangular
> bar ...
>
> So can I assume that the conductivity of PCB tracks is about 30% of that
> of pure copper or is the variation
> much larger (between PCB manufacturers)?
>
> As the skin effect is completey developped at 13.56MHz I would assume that
> the loop resistance would be proportional to
> the sqaure root of the resistivity because the skin depth is proportional
> to the square root of the resistivity and the resistance
> is proportional to resistivity/skin_depth ... or is this argumentation
> incorrect?
>
> I am asking this because I have to match the RF generator to the loop and
> reading range is very sensitive
> to good matching of both the inductance and the resistance ... the latter
> is a problem because it seems more prone
> to variation
>
> There is also a temperature effect. Can I use the coeff of pure copper as
> an approximation?
>
>
> Met vriendelijke groet,
> Kind Regards,
>
> Jan Vercammen | Agfa HealthCare
> EMI specialist | HE/A&D / ELEC2
> T +32 3444 6233 | F +32 3 444 6268
>
> Agfa HealthCare NV, Septestraat 27, 2640 Mortsel, Belgium
> http://www.agfa.com/healthcare/
> R.O.: Septestraat 27, B-2640 Mortsel, Belgium | RLE Antwerp | VAT BE
> 0403.003.524 | IBAN Operational Account BE81363012356224 | IBAN Customer
> Account BE20375104592856 | ING Belgium NV, B-1000 Brussels
> Click on link to read important disclaimer:
> http://www.agfa.com/healthcare/maildisclaimer
>
> ------------------------------------------------------------------
> To unsubscribe from si-list:
> si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
>
> or to administer your membership from a web page, go to:
> //www.freelists.org/webpage/si-list
>
> For help:
> si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
>
>
> List technical documents are available at:
> http://www.si-list.net
>
> List archives are viewable at:
> //www.freelists.org/archives/si-list
>
> Old (prior to June 6, 2001) list archives are viewable at:
> http://www.qsl.net/wb6tpu
>
>
>
>
--
Steve Weir
IPBLOX, LLC
150 N. Center St. #211
Reno, NV 89501
www.ipblox.com
(775) 299-4236 Business
(866) 675-4630 Toll-free
(707) 780-1951 Fax
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List technical documents are available at:
http://www.si-list.net
List archives are viewable at:
//www.freelists.org/archives/si-list
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
Other related posts:
