capacitors. which are the best? which should be used?

[matrigs]

i realised that there is nowhere mentioned which capacitors to use with the ucapps system if the ones stated in the orderlists aren't in reach.

i also realised that whenever i see a picture of a core or other module, everyone uses different capacitors in different places. mostly the ceramic caps.

the thing is - are all capacitors actually the same or is there a difference appart from the quality of them? can they affect the work of the system?

most of the caps on my core are quite high quality but i used, for example as the 33pf ones for the crystal, those very cheap yellow ones.

what differences can someone expect when using cheaper caps for his projects?

[stryd_one]

So long as you follow the parts list and use the right type (electrolytic/ceramic/etc etc) and you don't get one of those crazy russian-doll-chinese-fake-capacitors you'll be right. Of course you get what you pay for, so you might end up with the occasional dead one. Testing capacitors with a multimeter has been covered before so I won't go there.

[matrigs]

i'm speaking more of the differences between caps of the same type but made with different materials.

this and

http://tme.pl/katalog_pics/7/b/9/7b9c402a32884ba3a82ac99d81d8eb66/cc%20330.jpg

this one are both 330 pf caps. but i mean there is a reason why they make those different ones right ?

[Screaming_Rabbit]

          FILM CAPACITORS

Film includes a variety of polymers, such as polyester, polycarbonate, Teflon, polypropylene, and polystyrene.  Traditional film capacitors were only available in modest sizes, <10 uF.  In recent years, film capacitors have sought to leverage their superior longevity compared to electrolytics, to move into some applications that call for much larger parts, even to thousands of uF.  Film capacitors come in two broad categories, film-foil, and metallized film.  Film-foil capacitors are made of alternating layers of plastic film and metal foil, while metallized film capacitors have the metal vacuum deposited directly on the film.  In general, film-foil is better at handling high current, while metallized film caps are much better at self-healing.  Various hybrid types can also be found. 

              Pros:  The film capacitors mostly have reasonably well behaved electrical properties and offer many tradeoffs of performance and cost for people with precise requirements.  The main parameters of interest include capacitance vs. temperature, dissipation factor, and dielectric absorption. Their main virtues include low leakage and low aging. 

              Cons:  The main drawback of film capacitors is their low dielectric constants (K), which is only partly offset by their relatively good breakdown voltages.  That  means that film capacitors are physically large for their capacitance.  Their Ks vary from a low of about 2.2 for Teflon to about 8 for PVDF (rarely used).  Unfortunately, the rule-of-thumb is that the higher the K (and therefore the smaller the size), the worse the electrical properties tend to be.  Film capacitors have not made an entirely graceful transition into the age of surface mounting.  While some film dielectrics are suitable for surface mounting, most can't withstand the heat of soldering.  Even polyester, the toughest of the traditional films, is barely good enough.  However, capacitor makers have responded by developing several new dielectrics.  SMD film capacitors are not as widely second-sourced as other capacitors however.

          CERAMIC CAPACITORS

          Ceramic capacitors offer a broad range of size vs. performance tradeoffs and are easily the most popular in numbers sold.  Ceramic capacitors are available from < 1 pF to 1000s of uF.

          Pros:  The main virtue of ceramic capacitors are their relatively high dielectric constants.  This can vary from C0G with a K of up to 60, which has excellent electrical properties but is relatively large and expensive, to ceramics with Ks in the tens of thousands but with very poor electrical properties.  Large- value ceramics can replace electrolytic capacitors in high-frequency applications like switch-mode power supplies because of their lower ESR.  Ceramic capacitors are especially suitable for surface mounting due to their heat resistance, mechanical integrity, and the ability to make them in very small packages at low cost, for portable equipment.  This has greatly added to their usage.  To some extent ceramics are slowly displacing other types of capacitors. 

          Cons:  Low breakdown voltage means that the low-K ceramics (Class 1), the ones with the good electrical properties, have poor volumetric efficiency, and are usually found only in small values.  High-K ceramics (Class 2 and higher) have poor electrical properties, which are highly dependent on temperature, voltage, and frequency, plus a significant aging rate.  Unlike many other capacitors, ceramics have no self-healing mechanism.  This means that manufacturers must maintain a high level of quality control over the dielectric.  Ceramics are most cost affective in small sizes at present.  Very large ceramics are a bit of a challenge, especially in SMD. 

          ELECTROLYTIC CAPACITORS

        "Electrolytic" means any capacitor that requires a conductive layer between the dielectric and one electrode.  In the original electrolytic capacitor, the layer was an actual electrolyte, a conductive salt in a solvent.  Some electrolytic capacitors today don´t actually use an electrolyte, but the word is still commonly used, to the annoyance of some.  Electrolytic capacitors are made by growing a oxide film, the dielectric, on a metal, the anode, by electrochemical means.  The films are very thin with fairly high Ks (roughly 10-25) which make for a lot of capacitance in a small package.  The resulting devices pass current much better in one direction than the other, making a rectifier of a sort.  Because of this, the metals are sometimes called "valve" metals.  The metals presently used are aluminum, tantalum, and niobium. 

          Pros:  Electrolytic capacitors are best used when you need a lot of capacitance in a small space and at a reasonable price, such as power supply filtering, or energy storage.  They are available in sizes far beyond that of other capacitors.  Aluminum electrolytics are presently available from 0.1 uF to several F.  I have no idea why someone would use a 0.1 uF electrolytic capacitor however.  Tantalum electrolytics are available from 0.1 uF to a few thousand uF.

          Cons:  Marginal electrical properties means that these capacitors must be applied with care.  The parameters to be watched include leakage, service life vs. temperature, ESR, ESL, and low-temperature performance.  Unlike other capacitors, electrolytic capacitors are not inherently non-polar, but non-polar types are available.  Electrolytics are widely available in SMD packages, at least in moderate sizes, but users complain of more reliability problems than with through-hole styles.

          MISCELLANEOUS  DIELECTRICS

          Miscellaneous capacitors include materials like glass, mica, porcelain, and even gas and vacuum.  A few exotic dielectrics like silicon dioxide and sapphire are used in niche applications like microwave capacitors and trimmers.  Some are available in surface-mount packages.

          Pros:  The electrical properties of the miscellaneous capacitors are generally most similar to film capacitors.  However, they all have electrical properties that make them useful in some special applications.

          Cons:  These materials also have Ks similar to plastic films so they have no advantage in size.  Except for mica, these capacitors are commonly available only in small sizes, <1 uF.  They also tend to be more expensive than other capacitors of similar size. 

http://my.execpc.com/~endlr/

Greets, Roger

[stryd_one]

Yeh ,those pics are not the same type. Same rating in farads, but not the same type. The one not shown but linked, is ceramic. The red one shown is not.

[/tilted/]

For the purposes likely to be encountered in the MBHP, there are basically two types of capacitors:

POLARISED:

These include the types: Electrolytic and Tantalum. Electrolytic are more commonly used in these applications.

NON-POLARISED:

These include the types: Ceramic, Monolithic, MKT, "Greencap" - Polyester.

also, to confuse the issue slightly, there are non-polarised electrolitics available.

There are other, more expensive non-polarised types around, but you are unlikely to use these for a uCApps project.

These are typically the type of thing that guitar boffins and audiophile lunatics will carry on endlessly about.

You should not use a polarised cap where a non-polarised is called for, or vice versa.

Regarding your specific example, the two caps shown are essentially interchangeable as far as MBHP is concerned.

The only exception I would make is to only use ceramic type around the crystal resonator circuit, ie C1 and C2 on the core module. This type of crystal oscillator is best realised with a ceramic, as they have better thermal characteristics.

For the rest of them, you can use ceramic, MKT, whatever you have (and in some cases, you can probably leave them out, but I don't want to start that up again)...

There may be other important examples, but offhand I can't think of them.

[matrigs]

i was just curious because i saw that everyone making his core has his own "way" of using capacitors of different types. everyone uses "better" caps in different places. for example thorsten has this expensive plastic cap in the picture of his sid module - but in a lot of different modules people just use simple ceramic ones...

[nILS]

For the filter caps a lot of people use styroflex caps. See some of Smash's sid boards or seppoman's filter board.

[nebula]

Film capacitors have not made an entirely graceful transition into the age of surface mounting.  While some film dielectrics are suitable for surface mounting, most can't withstand the heat of soldering.

I can attest to this.  At work we used some SMT film capacitors (very tight tolerances) for use in a very precise notch filter.  We found that, unlike ceramic caps, we finally needed to heed the warning we got during our surface mount soldering training:

Surface-mount chip capacitors should not be applied using the same method we usually use for chip resistors.

Standard practice for a chip resistor is like this:  heat up one of the pads with your iron and put a bit of solder on it.  Apply a small drop of flux on top of the hardened solder.  Then place the chip with one side on the pad you soldered, so that it is partly immersed in flux.  Using your iron, apply heat and allow the solder to bond to the chip.  As you pull your iron away, the chip will centre itself correctly over the pad.  You can then solder the other side.

The problem is that a capacitor can be damaged by this uneven application of heat.  We always ignored this warning, because we never had that problem with the ceramic caps we used.  But with these film caps, they ended up having a different value after they were soldered, and our filter frequency was going off as a result!

The solution:  first apply solder to both pads.  Regular solder works here, but solder "paste" (a suspension of tiny solder pellets in a thick flux) works better.  Unfortunately this paste is dispensed from a special syringe using a metered, compressed-air paste dispenser.  If you use regular solder, you must then apply a drop of flux to each pad. Place your chip capacitor, then use the hot-air blower from your ultra-expensive SMT rework station to blow a little jet of air (at about 850 degrees F) over the component until the solder melts and flows over the joints. (The paste really works best for this, because it helps to hold the component in place while the hot air is blown over the capacitor, preventing it from flying off the work surface like a single piece of confetti).

The solution works because it ensures the entire capacitor heats up evenly, so the metal layers expand evenly and do not crack.

[nebula]

Does anybody have a rule of thumb over whether you use tantalum vs aluminum electrolytics?

My understanding is that it's generally better to use aluminum across a DC line for filtering, but for most other applications, tantalum is often preferred.

I came across this article which discusses the issue some, but I'm curious about how the experienced MIDIboxers practice this: 

http://www.electro-tech-online.com/general-electronics-chat/26407-electrolytic-caps-vs-tantalum-caps.html

[m00dawg]

Why do you think aluminum is better for DC filtering? I was under the impression that aluminum electrolytics were rather poor at filtering HF noise. Seems like tantalum is quite good at that and gives you larger capacitance. Given that the ones that can handle higher voltages are somewhat expensive (and their intolerance to voltage spikes), I wouldn't put them before a regulator. They might be good after, though.

Anyone have any further thoughts about these guys? Been thinking of replacing my 47uF cap on my PSU design with a tantalum in hopes I can get better HF filtering (the PSU will be powering an MB-SID).

[/tilted/]

aluminium electrolytic capacitors are better for DC filtering, because the basic usecase here is for removing the AC component, following rectification. Their HF performance is limited largely by the fundamental design, which has relatively high internal resistance / inductance. They make up for this shortcoming by being relatively cheap, and being available to higher voltage ratings. They are also a liiiittle bit more robust when these ratings are exceeded, compared to tantalum. (Tantalum caps have something of a reputation for exploding...)

In a linear DC supply, the electrolytics are usually used in concert with other caps of lower value, down to around 100-350nF. These caps are there to filter out the HF noise, leaving the electrolytics as your main storage caps.

If you want to use a tantalum in a power supply, there's no great reason why you shouldn't. (I'm assuming the 47uF is not the only filter cap in there...)

[m00dawg]

If you want to use a tantalum in a power supply, there's no great reason why you shouldn't. (I'm assuming the 47uF is not the only filter cap in there...)

Yep, the 47uF between two 100nF caps after the regulator output. That was suggested in the multi-tap psu discussion. I don't have this setup on my current power board (which is on a protoboard) but plan on getting a nice printed board out of this and have plenty of room for caps if I needed them.

I figured that tantalum here might be better at filtering here, either in addition, or even to replace one of the 100nF caps. Having it explode could be bad, though :) However, since it's after the regulator, something would have to go seriously wrong to get the voltage up to 25V I'm guessing. That said, if I can get the same filtering ability (or better) using other caps, I'm find with that. Tantalum seemed to sort of kill two birds with one stone.

[/tilted/]

I think I understand what you're saying now.

The 100nf/330nF caps are not there so much to make up for a shortcoming of the electrolytic cap, but rather to filter a different area of the spectrum.

I think off hand (feel free anyone to correct me) that having a tantalum cap doesn't mean you won't need the 100/330nF caps anymore.

What the caps are doing here is providing a low pass filter for your PSU.

Adding more caps of different sizes is akin to changing the slope of your filter.