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I am debugging a power amplifier circuit and trying several capacitors values to fine tune the design to meet the frequency response specifications. All the 0603 and 0805 ceramic capacitors are experiencing the following issue:

I measure the capacitor (this one for example) using this digital LCR meter which reads 360nF (typical value 390nF with 10% tolerance). When I hand-solder the capacitor, it reads 420nF in-circuit, and when I desolder the cap, it still reads 420nF. What caused this big increase in capacitance?!

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    \$\begingroup\$ That's nothing... Did you know that (especially smaller) ceramic capacitors change their effective capacitance based on their biasing voltage? an 0402 0.1uF capacitor rated at 50V isn't a 0.1uF capacitor if you only put 5V across it! \$\endgroup\$ – akohlsmith Jan 11 '14 at 20:14
  • \$\begingroup\$ Could the solder itself account for the capacitance change? When talking Nano, it probably would not take much. \$\endgroup\$ – R Hughes Jan 12 '14 at 7:26
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The only clue I can find might be this: -

enter image description here

It looks like you are seeing a +16% shift in value and X5R is not known for the greatest dielectric so this may be counted as some form of initial aging due to soldering. After all, it started about 8% down and it's gone 8% over. I'd expect X7R dielectric to be better (stabler) and C0G/NP0 to be better again.

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  • \$\begingroup\$ Caps have a maximum soldering temperature listed in their datasheet and usually a thermo profile for the reflow oven. This indeed has to do with changed capacitance after soldering. \$\endgroup\$ – jippie Jan 12 '14 at 9:59
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Check a few by measuring, soldering, desoldering and remeasuring.

Sometimes I put the component above a soldering iron , or in an instant freeze spray to get an idea of it's temperature coefficient.

You didn't say what the capacitor values were; if small, stray capacitance when soldered into the circuit could be a factor.

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    \$\begingroup\$ The question already states "when I desolder the cap, it still reads 420nF", which means they are measuring, soldering, desoldering and measuring again. \$\endgroup\$ – Anindo Ghosh Jan 12 '14 at 6:47
  • \$\begingroup\$ Think he meant check more than one cap in a solder/de-solder cycle to see if that one was just a fluke. \$\endgroup\$ – R Hughes Jan 12 '14 at 7:24

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