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I am looking for a capacitor with good temperature stability to replace some low value ceramic caps in a bandpass filter. If I understand it correctly, the best types are PPS (poly phenylene sulfide). However, at the values I want, 47p and 82p I cannot find a COTS supplier in 0805 packaging.

What is the next best capacitor type, and how much worse is it than PPS (and how much better than ceramic)?

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  • \$\begingroup\$ can you find silver-mica in 0805? (or at all nowadays?) \$\endgroup\$ – Brian Drummond Oct 28 '15 at 11:18
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Temperature stability of SMT capacitors is typically specified by selecting a type known as a C0G or NP0 capacitor. These Class 1 capacitors are made to be temperature compensating and are made of non ferro-electric materials to yield superior stability.

As far as understanding and comparing various capacitors you really need to download the manufacturers family data sheets and do the specification comparisons yourself to see if any particular type will meet your needs.

Another factor to consider is that if your filter circuit includes other components such as resistors and opamps these may also have performance changes with temperature.

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  • \$\begingroup\$ Other components have stabilities far beyond the ceramic caps being used. For example, I use 10ppm resistors. It seems the ceramic caps are the real weak point. \$\endgroup\$ – Dirk Bruere Oct 28 '15 at 11:10
  • \$\begingroup\$ @DirkBruere - My main point in mentioning other components was that all the tolerances add up. \$\endgroup\$ – Michael Karas Oct 28 '15 at 11:14
  • \$\begingroup\$ @DirkBruere I wouldn't say a 10ppm/degC resistor is "far beyond" the ceramic cap especially if you have four or five resistors compared to say 1 ceramic cap. \$\endgroup\$ – Andy aka Oct 28 '15 at 11:18
  • \$\begingroup\$ I did some calcs on the ceramic chips I originally had in place. Over the temp range I am interested in they are about 500ppm! \$\endgroup\$ – Dirk Bruere Oct 28 '15 at 14:47
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NP0/C0G ceramic caps are pretty good- maximum +/-30 ppm/degree C- to do substantially better would be dramatically bigger and more expensive.

For example you could machine an Invar structure and use dry N2 as the dielectric.

Stray capacitances on FR4 can have high tempco which will affect your total. Careful layout (avoid ground planes) and maybe better $$$ materials such as PTFE.

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