EEVblog Electronics Community Forum

Electronics => Projects, Designs, and Technical Stuff => Topic started by: electronx on December 08, 2023, 11:12:26 am

Title: same capacitance,same class,same voltage rating,different package characteristic
Post by: electronx on December 08, 2023, 11:12:26 am
The same capacitance has the same class at the same voltage rating. However, the capacitor package are different. Will the characteristics be different?
I usually wouldn't pay any attention to this, but I found this information. Is this only valid for class 2 and class 3 caps ?
(https://i.imgur.com/TYU7hJj.jpg)
Title: Re: same capacitance,same class,same voltage rating,different package characteristic
Post by: Kleinstein on December 08, 2023, 12:13:09 pm
This is mainly a thing with class 2 MLCCs. The drop in capacitance with small relatively high capacitance X7R and similar is well known. The smaller 0805 part has thinner dielectric and thus getting the drop earlier. They may also opt. for a higher µr material that is more sucesptible to saturation.

The voltage rating with ceramic caps is sometimes not a really hard limit, but more a test limit on how much testing is done. So the same parts could also be tested a bit stricter and sold with a higher voltage rating (e.g. 16 V) - this could well work with the 1210 size, but for the 0805 size one may have more failing the test.
Title: Re: same capacitance,same class,same voltage rating,different package characteristic
Post by: TimFox on December 08, 2023, 03:00:19 pm
The non-linear behavior of Class-II dielectrics is a property of the material itself, and therefore depends on the E-field (voltage gradient = dV/dx) in the material, not the total voltage across the entire slab of ceramic.
Larger packages can have substantially higher thickness, thus reducing the E-field for a given total voltage.
Title: Re: same capacitance,same class,same voltage rating,different package characteristic
Post by: MarkT on December 08, 2023, 11:19:00 pm
The materials that exhibit super-high dielectric constant (1000's to 10000's) are all ferroelectric (BaTiO4 is the best known), and ferroelectrics are highly non-linear, very sensitive to temperature and microphonic (i.e. piezoelectric).  Ferroelectricity is named by analogy with ferromagnetism and has nothing to do with iron.
Title: Re: same capacitance,same class,same voltage rating,different package characteristic
Post by: aeg on December 08, 2023, 11:36:32 pm
Go to the cap vendor's website and look up the characteristics graph (not the datasheet) for the individual part number.
Title: Re: same capacitance,same class,same voltage rating,different package characteristic
Post by: CosteC on December 10, 2023, 11:03:59 am
Two caps with same capacity and voltage and material may vary in C vs DC and C vs time (ageing) curves. Real voltage withstand will also differ, but this is usually not important.