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Why are good capacitors so expensive, and why don't they make these any more?

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MathWizard:
It's time for me to stock up on some parts, and I'll get a bunch of Polyester/Mylar caps, for audio-RF type projects. Why don't they make them down into the pF level, I mainly see 1nF as the smallest?

And I see polypropylene capacitors are better, and maybe 10x more expensive (at least where I'm shopping). And I read polycarbonate caps are better again, so are polystyrene and polytetrafluorethylene caps. But already with polypropylene caps, there's less values commonly available, and hardly anything under 1nF (maybe the big retailers, but I bet it's expensive).

So for quality through hole caps under 1nF, for low RF/radio work, what do people use these days (if they aren't rich)?

But some of these hardly anyone makes anymore, so why not? and what do they use now then? Is it since everything is SMD these days and they use something else for all that ?

And why is this stuff so expensive anyways ? Is it just lack of competition or is it that hard and expensive to make the chemicals, or make the capacitors ? My memory of organic chemistry would say it's easy and cheap to make these chemicals now a-days.

tom66:
Depends on the application. For RF work ceramic is plenty fine - and you can get down to sub-pF with ceramics.  And it's fine for many audio applications if you're careful with how you use them.  You generally only need other types of capacitors when you have high stability requirements (limited drift in capacitance with temperature/voltage), reliability requirements (ceramic can be vulnerable to shock often failing short), or specific anti-microphonic requirements.

I suspect that since ceramics can fulfill almost every niche now besides a few very specific ones, there is much less commercial incentive to produce other types of capacitor.  The market moves with technology.  For the few cases where specialist caps are needed the cost will obviously be higher, because there's much higher overheads to produce lower quantities of these things.

Kleinstein:
For the small values COG ceramic capacitors are working very well. The average C0G cap is more stable than the film capacitors and the losses are about on par with PP or PS. Good ones can even get lower loss - on par with exotic PTFE capacitors.  If the larger TC of the film caps is wanted, there are special ceramis ones with positive and negative TC.
The C0G ceramic is essentially not microphonic - possibly less than film types.
MLCC C0G caps up to some 10 nF are still affordadble and hardly a need for small film capacitors anymore. Very low leakage (sup pA) may be an exotic exception, where one may still want PS capacitors.
For the RF use the size matters and SMD is big plus and for the high frequencies THT is a no go - even in the 1970s they used a kind of SMD (or in plane mount), even with germanium transistors (e.g. AF379) .

The PP and PS film materials are not compatible with the high temperatures of SMD soldering. SMD film capacitors are mainly limited to PPS.
Polycarbonate was OK with a relatively low TC, but otherwise not especially good. AFAIK the essentially olny manufacturer of the foils stopped quite some time ago and hardly any such caps after that.

T3sl4co1l:
Don't use polyester at RF, the Q is poor.  They're fine as bypass/coupling caps, but mind the current ratings, which are relatively low for the same reason.

That leaves PP as the most likely candidate, which, it is quite good, so that's fine.

Small values are occasionally available, but you may find C0G ceramic the better option.  C0G is essentially ideal; typical parts can have Q over 3000.  It's so high it's hard to measure.  Available down to fractional pF, which, you'd have a hard time even making a film cap as such at those values (it'd be mostly body/lead capacitance, not the dielectric as such).

Values 1nF and up, I use a mix of types, as C0G starts going up in price compared to X7R that remains flat until 100s nF (in low voltages), and, it's nice to have film around when breadboarding (cheap like X7R, none of the nonlinearity; good for audio purposes).  PE or PP is fine for signal purposes, again unless you need high Q.

Large values simply get expensive, no matter the voltage; C0Gs can't be made in low voltages (50V ratings basically mean 10s or 100s nm dielectric thicknesses I think?), and the same is true of film caps.  Yield and production rate suffer; extreme surface area means high chance of dielectric breakdown, and lots of layers means more time spent in production.  Films up to a couple uF and 50 or 100V are still reasonable, but good luck with like 10s or 100s of uF.

Larger values, consider using one of the "poorer" types, as a compromise.  For example, electrolytic can be used at AC by using a bipolar type, or pairs in anti-series (with clamp diodes or a bias supply); tantalum are excellent timing / sampling capacitors for LF/DC purposes (well behaved within rated voltage range, lowish leakage); etc.  Adjust circuit impedances to suit the ratings; for example, electrolytics aren't bad as coupling capacitors, even at fairly high frequencies (MHz) as long as you don't mind the modest and variable impedance (some ohms ESR + ESL; negligible in something like a wideband RF preamp).  Or for LF highpass applications like signal coupling, the nonlinearity of electrolytic isn't much of a problem as significant (AC) voltage is developed across the capacitor only around the cutoff frequency.

Ironically, ceramic are quite good for large values at very low voltages, simply because e.g. 47uF 6.3V (or even 4V) X7R and X5R, say in 1210 chip size, are a commodity item -- used en masse in cellphones, PCs, etc.  Production probably sucks (very thin layers of dielectric, and very many of them), but because it's competitive and at scale, that's just part of the process.

Also mind that, you won't find something cheaper than whatever the minimum material plus production plus amortized capital cost is; but you can always find something more expensive, whether because it's a boutique part, specialized purpose (especially certain approvals?), low production volume, going obsolete (or gone, even -- old stock), or etc.  Compare modest-size ceramic chips (0805 to 1210 package, say) to large-chip or lead-frame types; I don't know the economics of the lead-frame kind, but I assume they're low production and therefore just stupendously expensive in general.  Maybe they come down in quantity, or from China, I don't know.  See also, most anything for military purposes: wet-slug tantalum, hermetically sealed electrolytic; or oddities like poled ceramics.

I suppose there's also the trifecta of large, low-quantity and boutique, for applications like induction heating, power factor correction and pulse generation; the catch with these is, because they're so large, the economics work out better in general -- you're buying a few thousand bucks worth of capacitor anyway, so the fact that it's sealed with love into a hermetically welded metal can isn't the most expensive part of it anymore.  And you occasionally see them come up for cheap on auction, if you need to snag one say for that quarter shrinker project you've always drooled over.

Tim

TimFox:
Polyester/Mylar vs. polypropylene:
Polyester has a higher dielectric constant than polypropylene, therefore less material and winding are needed than with polypropylene, and the result is physically smaller, all other things being equal.
Unfortunately, polyester is mediocre in dielectric loss and dielectric absorption compared with polypropylene (which is one of the best dielectrics), so polypropylene is preferred for critical applications.
Polystyrene is also good, but melts easily.  Teflon is great, but expensive and hard to find.
Ceramics: NP0/C0G dielectric is also excellent, but the other common materials have higher loss and are non-linear (capacitance decreases with applied voltage).  Those other dielectrics have higher dielectric constant than C0G, so larger C values can be had in small packages, if the higher loss, etc. can be tolerated in the application: read the data sheet for the specific part number (it’s quite interesting).

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