prices for discrete capacitors doesnt make much sense at the small scale - Page 1
Forum section: electronics / beginners

author: Capernicus
author_rank: Frequent Contributor
timestamp: October 10, 2021, 01:21:11 am
content: Here 1 picofarad capacitors cost $1https://au.mouser.com/c/passive-components/capacitors/ceramic-capacitors/ceramic-disc-capacitors/?capacitance=1%20pFHere there is a 1 microfarad 50 volt capacitor for 5c. but theres a 100nanofarad capacitor that costs 15c! this doesnt make sense at all.https://www.jameco.com/shop/keyword=.1-Pf-CapacitorSo if you need a low farad capacitor, you pretty much hunt around and get the cheapest one thats above the farad spec you need, either that or get two cm^2 pieces of copper tape and solder a couple of wires to it, and thats the same effect.

author: bob91343
author_rank: Super Contributor
timestamp: October 10, 2021, 02:07:20 am
content: The prices for tiny cheap parts varies all over the place because of the many factors controlling price. There is overhead at the distributor level which has no bearing on the size or value of the part. If demand is small, that overhead gets more cumbersome.Most of these kinds of parts are priced according to the effort required to stock, catalog, ship, and pay to mention a few things. The part cost itself is often dwarfed by these amounts.It was different in the old days when you ambled into a parts store, ran your fingers through a few bins of parts, and took what you wanted to the counter. Then you paid and walked out with the parts. Modern distribution is a far cry from that, and it's anyone's guess as to the specifics for any given part.

author: Kleinstein
author_rank: Super Contributor
timestamp: October 10, 2021, 05:50:32 am
content: For the capacitors there is also more than just capacitance votlage and physical size. Different types can have other less obvious properties that can matter in some applications (e.g. leakage, linearity, TC, reliablity, solderabiltiy) - sometimes it just has to be certain type because of some certification done with that old typ. With the cheap parts the sales effort is a big part and not all prices make sense. With rare values the prices can vary from extra expensive be cause of high stocking costs to very cheap because they want to get rid of them.

author: wraper
author_rank: Unknown
timestamp: October 10, 2021, 06:07:50 am
content: First of all TH MLCC is basically outdated, so way more expensive than SMT counterparts. Also they are just an SMT capacitor with 2 leads soldered on. Secondly, price of 0.1uF capacitor can vary highly, and if you want it with C0G ceramics as small capacitance cap (to have stable parameters), you will pay quite a lot. Especially for more expensive types.MouserBTW producing a very small capacitance with decent tolerance is troublesome and there is not much demand, so price will be higher.

author: tooki
author_rank: Super Contributor
timestamp: October 10, 2021, 01:33:53 pm
content: Quote from: Capernicus on October 10, 2021, 01:21:11 amThe $1+ caps there are 1kV-5kV classic disc caps. (That is, not the multilayer ceramic of the cheap ones you linked; those are a different category.) 1000V to 5000V obviously requires a different construction from a 50V part, not to mention the wildly different economies of scale at play, since so few consumer products use high voltages any more. Secondly, 1pF is an extremely low value that’s not needed nearly as frequently as larger values like 1μF and 100nF, again affecting economies of scale.And then there are all the other parameters that others here have listed.

author: wraper
author_rank: Unknown
timestamp: October 10, 2021, 01:50:53 pm
content: Quote from: tooki on October 10, 2021, 01:33:53 pmYou're right, OP screwed up with search. There are way more 1pF TH caps available at mouserlink

author: Capernicus
author_rank: Frequent Contributor
timestamp: October 10, 2021, 01:59:18 pm
content: A 1pf cap should cost .5c, regardless of the plate distance. you get 1000 for $5 a kilo, that sounds fair to me.

author: HB9EVI
author_rank: Frequent Contributor
timestamp: October 10, 2021, 02:06:39 pm
content: a look at Mouser's capacitor section should clear up, why not every capacitor can cost a few cents only - there are just so many different types - every one of them for its particular purpose.I wouldn't use a simple 50V MLCC cap in a power LPF, where belongs a mica cap; so you pay upto 2 to 3 bucks for a pF mica for a good reason.It'd make sense to dig deeper in to capacitors to learn, which one serves you best - it also gives you the knowledge, why some cost more than others

author: wraper
author_rank: Unknown
timestamp: October 10, 2021, 02:13:03 pm
content: Quote from: Capernicus on October 10, 2021, 01:59:18 pmYou can get both SMD 0.1uF and 1pf for less than that at say qty of 100https://lcsc.com/products/Multilayer-Ceramic-Capacitors-MLCC-SMD-SMT_313.html. But 1pF still will be more expensive because of economies of scale.

author: Capernicus
author_rank: Frequent Contributor
timestamp: October 10, 2021, 02:14:52 pm
content: Some nice cheap ones there. Its wierd that a Pf is more expensive than a nano!

author: Siwastaja
author_rank: Super Contributor
timestamp: October 10, 2021, 02:25:49 pm
content: In what circuit do you think you need 1pF?This is quite specialized value and when it's really needed, design of layout is critical because parasitics easily create another 1pF out of nowhere so must be carefully controlled.

author: Capernicus
author_rank: Frequent Contributor
timestamp: October 10, 2021, 02:31:26 pm
content: you could make a 1pf marx generator, im pretty sure it would still operate, its more of a full auto machine gun with little bullets, instead of a semi - automatic with big ones.About parasitics, probably wouldnt matter. it would only be cross talk capacitance, and i can fix that easy.

author: Siwastaja
author_rank: Super Contributor
timestamp: October 10, 2021, 02:35:50 pm
content: When exact value is non-critical, 1pF is usually arranged by parasitics alone. Cost is zero and availability great.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 10, 2021, 03:00:23 pm
content: Approximately 95% of what you pay is logistics. Probably more?It's the fact that it's been shipped to you, and to the distributor. It's been cataloged by them. Someone designed it (or designed the generator tool that designed it), and materials and process time were allocated to build them. They don't necessarily have to turn a profit for one-offs, but the cost must be designed so that, at whatever power law that product moves at*, they turn a profit overall.*Say 80-20 rule: maybe 80% of all orders are small, while the 20% that are large orders account for 80% of the profit.If you bought them a pallet at a time (a few hundred reels, millions of parts), direct from the manufacturer, the raw material cost would be a noticeable fraction of the total cost. Still far from dominant, but noticeable.In singles, material is essentially irrelevant.The price per capacitance is irrelevant for other reasons, too. This is easiest seen comparing batteries (not usually rated in terms of capacitance, but we can come up with equivalent figures, typically in the ~kF range), to supercaps (same price for ~F), to electrolytics (same price for ~mF), to film and ceramic (nF~uF, depending on voltage). Obviously, the materials change so we shouldn't expect them to cost the same, but the same is true of different types and values of ceramic capacitors as well. In such small values, you aren't even getting much ceramic -- most of the part is metal leads and epoxy dip!Quote from: Siwastaja on October 10, 2021, 02:35:50 pmDownside, parasitics tend to be rather bulky -- 1pF might take up several mm of precious layout area. The tempco is also notoriously bad (FR-4 is, what, +2000 ppm/C? I forget exactly), but you did say "non-critical" after all.Tim

author: tooki
author_rank: Super Contributor
timestamp: October 10, 2021, 03:40:06 pm
content: Quote from: Capernicus on October 10, 2021, 01:59:18 pmThrough the level of knowledge you’ve exhibited throughout your threads, you’ve demonstrated that you are in absolutely no position to be making proclamations about what a given part should and should not cost. Your knowledge level simply isn’t there yet.Quote from: Capernicus on October 10, 2021, 02:14:52 pmThe capacitance is not determined by the amount of material alone. Often it’s the opposite: at the extremes of value ranges (1pF being extremely small), just measuring such extreme values can be difficult. It’s fairly difficult toaccuratelymeasure 1pF (due to the abundance of parasitic capacitance in test leads, etc), so the care needed to set up the manufacturing test systems is nontrivial.And of course, once again your basic premise is wrong anyway. If we look at mouser and look at the price for 1000 pieces, remembering that mouser sells name brand components and not the no-name crap from AliExpress, you find that the price difference between 1pF and 100nF is just 20%: $59 for 1000 vs $49. So it’s not as though all 1pF caps cost a dollar apiece. You went into the wrong category (ceramic, not MLCC) and found a comparatively exotic 1pF that you compared to dirt-cheap MLCCs.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 10, 2021, 04:08:23 pm
content: Quote from: tooki on October 10, 2021, 03:40:06 pmYou could actually give constructive, useful comments, but chose not to.Tim

author: wizard69
author_rank: Super Contributor
timestamp: October 10, 2021, 05:40:02 pm
content: Quote from: Capernicus on October 10, 2021, 01:59:18 pmThat is totally asinine as there are many parameters with respect to cap selection. They don't all cost the same to produce and demand certainly isn't there. that is like saying all 245/70R17 truck tires are alike, when they all vary in capability, design and other specs.

author: Capernicus
author_rank: Frequent Contributor
timestamp: October 10, 2021, 05:51:48 pm
content: caps are all the same to me.

author: tooki
author_rank: Super Contributor
timestamp: October 10, 2021, 06:11:34 pm
content: Quote from: T3sl4co1l on October 10, 2021, 04:08:23 pmCheck yourself before you chastise me. I’ve given him plenty of concrete comments in numerous threads (including this threadand the rest of the message you quoted) and he just ignores it. Look at his posting history and you’ll see why I am going hard on him. He’s either a troll, or a cocky mofo who needs a reality check.

author: bob91343
author_rank: Super Contributor
timestamp: October 11, 2021, 02:51:40 am
content: In the old days, a 1 pF capacitor was made as a gimmick. As much as 5 pF also, although the most common value was around 2 pF. I used those in a few designs back then.https://www.google.com/search?q=gimmick+capacitor&rlz=1C1AVNE_enUS701US725&sxsrf=AOaemvKKp_L5kb8R-2E1QjNUlLihne1CKQ%3A1633920613978&ei=ZaZjYe6ZO7fZytMPhIOj-As&oq=gimmick+capacitor&gs_lcp=Cgdnd3Mtd2l6EAEYADIFCAAQgAQyBggAEBYQHjIGCAAQFhAeOgcIABBHELADOgcIABCwAxBDOgoILhDIAxCwAxBDOgwILhDIAxCwAxAKEEM6EAguEMcBEK8BEMgDELADEEM6DQgAEIAEELEDEEYQ-QE6BQguEIAEOgsILhCABBDHARCvAUoFCDgSATFKBAhBGABQpdwCWPiSA2CsqANoAXACeACAAf0DiAGoCJIBBzAuNC41LTGYAQCgAQHIAQ_AAQE&sclient=gws-wiz

author: Capernicus
author_rank: Frequent Contributor
timestamp: October 11, 2021, 11:29:22 am
content: Thats really cool Bob!It says its 1Pf an inch! so id have to them inch twists, and then all capacitors could just be wires.

author: Siwastaja
author_rank: Super Contributor
timestamp: October 11, 2021, 02:05:09 pm
content: Note that if some circuit really needs 1pF, chances are that the related IC or transistor pins already have 0.5pF of parasitics, so then what to do? Your layout will at least have some 0.1-0.2pF no matter how small you squeeze it or remove the ground plane, so why not accept that and adjust it to another 0.5pF and be done without any component.The answer is, because the capacitance from the PCB layout is poorly controlled, even if you tune it using prototypes to 0.5pF, then in production some unit is 0.7pF and another 0.3pF.But the capacitance between IC or transistor pins is poorly controlled as well. So all in all the circuit should be designed in such way that you "need" significantly more capacitance than the parasitics. This brings the parasitic variation relatively lower. For example, say you need 1pF and your total parasitics vary between 0.3pF and 0.7pF. You will use a perfect ideal 0.5pF capacitor and the sum will vary between 0.8 and 1.2pF. Quite some tolerance. Now if you are able to redesign the circuit to use 10pF instead and control the parasitics to the same accuracy, you'll be using a perfect ideal 9.5pF capacitor and the total will vary between 9.8 and 10.2pF.This also explains why a 1pF capacitor is possibly more expensive: to achieve the same, say 5% tolerance, they need to tune it to 0.05pF accuracy, requiring tiny geometrical changes. 10pF capacitor is easy to manufacture in 5% tolerance, though.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 11, 2021, 03:00:21 pm
content: Indeed, you rarely see percentage tolerances in such low values, more often a capacitance range, sometimes a mix of both.Tim

author: Capernicus
author_rank: Frequent Contributor
timestamp: October 12, 2021, 04:08:39 am
content: Quote from: Siwastaja on October 11, 2021, 02:05:09 pmA cap only qualifies as a cap (even a teeny tiny one) as a TOTAL separation at that point, if there is NO **TOTAL** separation it is not a cap, so PF caps designate a definite break in the circuit at that point, and they are easily separated from parasitics, its an INCH of twisted wire to get to a PF, that doesnt happen by accident, as I see it.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 12, 2021, 02:51:56 pm
content: ...

author: TimFox
author_rank: Super Contributor
timestamp: October 12, 2021, 03:40:27 pm
content: The default tolerance on most small capacitors is +/- 0.5 pF, for practical reasons.Back in the chip-and-wire hybrid days (ca. 1982), I once purchased a lot of 0.5 pF +/- 0.5 pF capacitors (the smallest value available in NP0 from Johanson Dielectrics).