[SI-LIST] Re: Voltage rating of a Ceramic capacitor

I would like to know why you have X7R better than NPO.  I believe=20
the correct order is NPO, X7R, Z5U/Y5V.  The NPO is the more=20
pure ceramic with low dielectric constant.  X7R is the next one in=20
line.  The additives used to get a higher dielectric constant will=20
deteriorate the electrical/mechanical characteristics.  Some
applications can live with this.

X5R is basically the same as X7R.  The X5R will have a capacitance
change of +/- 15% in a temperature range of -55=B0C to 85=B0C while X7R =

will have the same capacitance change but the temperature range is=20
-55=B0C to 125=B0C.

Jose

-----Original Message-----
From: Wilson, Mary [mailto:MWilson@xxxxxxxxxxxxxxx]
Sent: Wednesday, June 20, 2001 1:05 PM
To: 'si-list@xxxxxxxxxxxxx'
Subject: [SI-LIST] Re: Voltage rating of a Ceramic capacitor



I am very interested in why you recommended against the use of
Z5U or Y5V caps.=20

Thanks,
Mary Wilson
EMC Design Engineer
Astral Point Communications
(978) 367-6376


-----Original Message-----
From: HaroldLSJ@xxxxxxx [mailto:HaroldLSJ@xxxxxxx]
Sent: Wednesday, June 20, 2001 1:33 AM
To: si-list@xxxxxxxxxxxxx; ajmani@xxxxxxxxxx
Subject: [SI-LIST] Re: Voltage rating of a Ceramic capacitor


Ravinder,

I must correct the misinformation you have received concerning the =
voltage=20
rating of a ceramic capacitor and in particular for an X7R type =
dielectric.

First, ALL ceramic capacitors are tested to 2.5 times rated voltage so =
your=20
6.3V rating has been 100% tested to 15.75 volts.  Further, the typical =
X7R=20
MLC (multilayer capacitor) will not breakdown until you reach a voltage
above=20
500V!  The typical breakdown voltage I see is in the 500V to 800V =
range!

Second, the voltage coefficient for X7R caps at ten (10V) volts is less =
than

a negative 5% change in capacitance value and at five (5V) volts it is =
less=20
than a negative 2% change in capacitance so this will not be a problem.

Third, the typical temperature coefficient for X7R for this voltage =
range=20
will not change the capacitance value by more than a negative fifteen =
(15%)=20
percent from -55C to +125C and is most likely to be less than -10%.

Fourth, the biggest factor from a SI standpoint is the change in =
capacitance

value with frequency.  This should be qualified on a part by part =
basis.
The=20
typical X7R will drop ten (10%) percent of its value from zero to 1MHz =
so
get=20
a good high frequency gain/phase meter and compare your tantalum and =
the X7R

you plan to use then adjust accordingly.  If your frequency is =
extremely=20
high, consider using a porcelain microwave cap.  An NPO cap has almost =
zero=20
capacitance drop across this same frequency span.

Remember an MLC is a miniature thick film hybrid circuit so test and =
mount=20
the cap with the plates normal (vertical) to the PCB trace.

Finally, ceramic caps like tantalums usually fail by shorting.  If you=20
require high reliability, then request the lot be HALT (highly =
accelerated=20
life testing) qualified which is usually a maximum failure rate of =
between 5

to 8 caps out of 55 tested from the lot you are interested in buying.   =
For=20
extreme high reliability (zero failures), have the caps 100% HALT =
sorted. =20
HALT testing will always find more failures than Mil testing.  X7R will =

always have a higher reliability than NPO and don't use Z5U or Y5V.  =
There
is=20
not enough room here to discuss this further so email me direct if you =
need=20
more info on reliability.

Harold L. Snyder, Jr.
Scientist & Consultant

Begin Included Message:
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D

> Subj: [SI-LIST] Voltage rating of a Ceramic capacitor
> Date: 6/14/2001 5:13:41 PM Central Daylight Time
> From:    ajmani@xxxxxxxxxx (Ravinder Ajmani)
> Sender:    si-list-bounce@xxxxxxxxxxxxx
> Reply-to:    si-list@xxxxxxxxxxxxx
> To:    si-list@xxxxxxxxxxxxx
>=20
>=20
>=20
> I have been asked to replace Tantalum bulk capacitor in a design with =
a
> suitable Ceramic capacitor.  The Ceramic capacitor is X5R type, which =
I
> believe is more stable than Y5V.  However, its voltage rating being =
6.3V,
I
> am not feeling very comfortable to use it in the 5V application.  Can
> anyone advise me about the minimum voltage rating I should have for a =
bulk
> Ceramic capacitor in a 5V application.
>=20
> Regards, Ravinder
> PCB Development and Design Department
> IBM Corporation
> Email: ajmani@xxxxxxxxxx
>
************************************************************************=
***
> Always do right.  This will gratify some people and astonish the =
rest.
> .... Mark Twain
>=20
>=20

=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D
End Included Message.







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