Certain vendors have specially constructed caps that are internally asymmetrically built . As frequency increases the electrons do not go to the 'far' plates in the stack. So you can buy caps where the plates are vertically placed , or offset in the body. Take these out of the tape and reel and you better not drop em or you dont know what side is up ....
This is kind of off-topic, but about the symmetry of capacitors: What about regular, symmetrical MLCCs? Does mounting position matter? The smaller values look the same right-side-up or up-side-down, and I have been assuming that it really doesn't matter which way you install them. The larger values, such as an 0805 1uF capacitor, tend to be almost the same size both horizontally and vertically. What happens if you accidentally solder one on with the plates vertical instead of horizontal? Is it all right to do that? Will it lead to less flexibility and thus more cracked capacitors or broken solder joints?
This is silly:
1. The impedance, as measured, is on the graph. Period. Is the impedance low enough for your purposes? Great! You don't even need to know the capacitance, damping factor, voltage rating or anything else. (That is, assuming the impedance curve remains true in your application.)
2. The worst possible case electrical difference would be if all the plates were flat to one side, so that the effective height above the board surface ranges from nearly zero ("face down") to nearly the chip thickness. ...
So What? That makes a loop -- an inductor. The loop area is
maybe a half a nanohenry, for say, 0805 or thereabouts. There is no effect on the capacitance, assuming you're talking about the frequency range where it, well, capacitates... The only difference will occur at extremely high frequencies, where it's inductive either way.
3. All capacitors exhibit skin effect, just as all conductors do. Indeed, radiation of any given wavelength will tend to propagate within the surface of a dielectric -- conductors are not needed at all to illustrate the skin effect. This has applications and examples ranging from dielectric antennas (microwaves) to total internal reflection (arguably, extending up into x-rays). This is independent of construction, limited only by the dielectric constant of the material.
Wound film types are especially notable, due to the relatively large physical construction (the effective roll-off frequency is low enough to be of significance) and the effect of schoopage (end terminal metallization) shorting across the roll (thereby forcing current away from the center at high frequencies).
A good example, from my personal experience, is CDE 940 type snubber caps. They're rated for lots of peak current. Beefy. But not nearly as much RMS as you would expect from their size. (Datasheet for reference:
http://www.cde.com/catalogs/940C.pdf ) Take 1uF 600V for instance. 8.9A RMS, 196A peak. Yet the voltage curve starts rolling off at only 2kHz. (The astute reader will notice 250VAC at 2kHz draws only 3.1A; the voltage curve drops after this, but if you calculate current, you see it rises to 6.3A at 10kHz, then around 10A at 100kHz -- presumably 8.9A from the table. The graph might show more since it says 25C ratings, not 70C.) Now, it's not obvious from the data if the current rating rolls off at all. It seems to climb. In this case, the datasheet doesn't help me illustrate my point, unfortunately!
The reason I give this example
from personal experience is, I've tried them before, and they
get hot. I tried using them at more like 200-400kHz, at somewhat less than rated current, but the losses were real, disproportionately higher. They are definitely better suited to lower frequency use (under 100kHz). Other than the hazy foreboding of data ending at 100kHz, the datasheet doesn't tell you this.
FWIW, that application ended up with Epcos metallized MKP style caps, which worked just fine -- within ratings. Push a smidge past and they'll heat up and melt and puke and burn -- finely engineered down to a price, without a doubt. Other types and brands were also tried, with more and less suitable results.
A better example to illustrate my point:
http://industrial.panasonic.com/www-data/pdf/ABD0000/ABD0000CE47.pdfPage 6, ECWFA, 250V, permissible current. Notice how the larger uF values reach peak current at lower frequencies.
Now, regarding current ratings, let me be clear: I don't mean to assert that skin effect, or in general, eddy current effects, are limiting current capacity of large capacitors at high frequencies. There are many possible reasons, any of which may dominate in a particular case. (A few pages ahead, the higher voltage types show nearly flat current limit curves, at least in the smaller values. Is skin effect a consideration for those parts? Who knows.) I'm no capacitor designer, so I don't know what all goes into them, I only make educated guesses. Skin effect will vary greatly with construction, so blaming it for the unsuitability for a particular application (like the 940s in my example) is only suspicion.
TLDR: ceramic caps are hunks of ceramic with a characterized impedance over frequency. It doesn't matter how you put them in.
Tim