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I have 2 different 100nF capacitors. Let's call them A and B. My dad told me that B is "better" than A. I've tried measuring their capacitance using a Metex multimeter which has the option of measuring capacitors. I connected A and it showed 80nF and then it started slowly rising until it reached about 130nF. What's more, I've tried touching the capacitor (I was careful not to touch the terminals, I've touched only the coating). It influenced the result of the measurement - capacitance decreased. I thought that maybe it is related to the temperature but then I blowed warm air on it and it didn't change anything.

And then I connected capacitor B. It showed 100.5nF. I could touch it as much as I wanted and it didn't influence the measured capacitance. It was rock solid.

At first I thought that A is faulty but I have more capacitors of this type and all of them behave in the same manner. Why is this happening? Can I still use them e.g. as a Vcc buffer in an IC (like Atmega, etc.)?

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  • \$\begingroup\$ What kind of capacitors? \$\endgroup\$ – Majenko Dec 16 '14 at 22:07
  • \$\begingroup\$ Do you have other specs? Like type, ESR, etc? \$\endgroup\$ – Samuel Dec 16 '14 at 22:07
  • \$\begingroup\$ I don't have any specs. I think that A is a standard ceramic capacitor. Not so sure about B. I can make and post a photo if it's of any help. \$\endgroup\$ – rubix_addict Dec 16 '14 at 22:09
  • \$\begingroup\$ It might help. Also, your father seems to know, ask him. \$\endgroup\$ – Samuel Dec 16 '14 at 22:12
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    \$\begingroup\$ @Majenko: Capacitive touch sensors work on a few pF or a few 100 fF. Other than by providing a resistive path, touching isn't going to matter at 100 nF. Also, he said he was careful not to touch the leads (no resistive connection), and the same touching doesn't affect the other type of cap. There are various possible effects going on here, but the principle behind capactive touch sensors isn't one of them. \$\endgroup\$ – Olin Lathrop Dec 16 '14 at 22:57
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Type A might be a Y5V

enter image description here

or a Z5U "semiconductor" capacitor. They're not only bad, they're horrible. Try to avoid ever using them. They're sort of acceptable sometimes as crappy bypass capacitors, but note that they pretty much disappear from the circuit if the temperature reaches extremes.

http://www.avx.com/docs/Catalogs/cz5u.pdf

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  • \$\begingroup\$ +1 for underappreciated information about the wide variety of dielectrics. \$\endgroup\$ – pjc50 May 26 '15 at 14:45
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The high value ceramic capacitors are far from being ideal capacitors. Their capacitance varies with among other things temperature and level of charge. They are also "microphonic", that is sound waves can cause the voltage on a charged ceramic to change.

As Spehro says Y5V and Z5U are horrible and I would avoid them completely unless I was really trying to penny pinch.

X5R and X7R are bit better but still really only suitable for power bypass capacitors and the like, not for any application where stable and predictable capacitance is important.

For stable predictable capacitances in this capacitance range you want film capacitors or possibly C0G/NP0 ceramics. The downside is larger physical size and higher cost.

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