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Capacitor selection, dielectric types, footprints on PCB

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ayeong

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cx7r capacitor murata

Hi,

Anybody got any application note on capacitor selection or an introduction to different type of capacitor ?

Out of the 3 type of dielectric X5R, X7R & CG0 (NP0), which one is the cheapest in term of cost ?

Next, which footprint (0402, 0603, 1210 & etc) is the most common on PCB ?

Thanks a million in advance !

Best Regards
 

I general the footprints are moving against smaller and smaller sizes. I think 0805 have been the most common for some time and before that 1206. But 0603 and 0402 are getting more common. Especially for resistors. The problem with caps is that you can't make very small footprints with big capacity. But size of footprints depends of what they are going to be used for. Portablle devices like cellphones etc. uses smaller footprints in general. When you need big cap sizes you may need to use a bigger footprints for some of your caps.
 

types

The NPO are very stable and linear. They are used in oscillators and filters.
X7R are for power supply bypassing. They are very nonlinear and temperature sensitive.
X5R is in between.

The following links are from the dismally designed AVX web site which can only be found through a google search. Fortunately the AVX products work better than the web site.


**broken link removed**
**broken link removed**
**broken link removed**
**broken link removed** is a good selection guide.
 

I think it is quite easy to navigate through AVX's site.
Here is the link where you can find all the datasheets flaulent linked to: www.avxcorp.com/prodinfo_catlist.asp?ParentID=124
There is also datasheet for the Y5V caps: www.avxcorp.com/docs/catalogs/cy5v.pdf
Here is AVX's Surface Mount Ceramic Capacitor Master Catalog: www.avxcorp.com/docs/masterpubs/smccp.pdf

I think the best is to read these technical infos:
MULTILAYER CERAMIC CAPACITORS – MATERIALS AND MANUFACTURE www.avxcorp.com/docs/techinfo/mlcmat.pdf
Decoupling: Basics www.avxcorp.com/docs/techinfo/dcplbsc.pdf
Introduction to Choosing MLC Capacitors for Bypass/Decoupling Applications www.avxcorp.com/docs/techinfo/mlcbypas.pdf
 

Thanks guys for the input.

Wondering which dielectric material is the cheapest & most expensive ?

And do you guys have any similar links for inductors as well ?

Thanks

Best Regards
 

ayeong said:
Wondering which dielectric material is the cheapest & most expensive?

X7R is the cheapest of the three you mention and NP0 is the most expensive. This makes sense because the most expesive cap. is the most temperature stable cap. If you need caps. for decoupling purposes, there is you should just choose the cheapest one. If you are going to use the caps. for frequency critical circuit like osc. and some filters, you migth consider using one of the more temprature stable dielectrics.
 

In general the Y5V are the cheapest, but their capacitance is typically 1/4 off the specificed value if you run them near full voltage. They are also very unstable with temperature and change value with mechanical vibration quite a bit. They also have very high dissipation factor, which, in general, is good for bypass caps.
I use the 1uf size 0402, the 22uv size 1206, and the 100uf size 1210, mostly the 1uf and 100uf for bypassing. When used with via-in-pad, you can get the size 0402 parts down to about 1nh total mounted inductance
 

Via on Pad

When used with via-in-pad, you can get the size 0402 parts down to about 1nh total mounted inductance

Via on pad is interesting. Is it allowed?
My PCB manufacturer requires .2mm minimum clearance between pad and via. Is he follwing an outdated rule?

Some more comments on pad on via please....
Sibi
 

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