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I am doing an SMB soldering project. I Have here 3 ceramic capacitors, 100nF, I test each one after soldering to the board.

enter image description here Oddly, the capacitor at the top of this image is not reading any capcitance at all when soldered. When I desolder it, it reads 100nF.

All other capacitors read 100nF when soldered.

Is this a sign of a problem, or can this be absolutely normal! Please advise.

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Apparently the specific board network of connections interferes with your method of measuring the capacitance. The caps are apparently connected differently. The usual method employed in DMMs for measuring capacitance is to charge caps with short pulses and measure RC reaction to this. Or measure a frequency of some internal generator with the cap under test. If your top cap has a parallel connection to a small resistor, the DMM will have false readings.

In general, there is no reason to check "capacitance" on soldered components, since they might be likely a part of a complex network and can't be characterized by a single "capacitance" parameter.

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  • \$\begingroup\$ Useful knowledge thank you. How can I test that my component is correctly soldered to the board? Ultimately, that is what I want to do. \$\endgroup\$
    – RenegadeAndy
    Commented Nov 10, 2017 at 19:34
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    \$\begingroup\$ @RenegadeAndy, if you follow basic soldering technology (right iron tip temperature, right solder and flux), visual inspection is usually sufficient to ensure connectivity. Measuring the cap actually is useless, it can have "cold joint", show right capacitance, but the circuit will fail to work. \$\endgroup\$
    – Ale..chenski
    Commented Nov 10, 2017 at 19:38
  • \$\begingroup\$ Ok - useful to know. There is no check I can perform on these soldered components until I power the board on in this case \$\endgroup\$
    – RenegadeAndy
    Commented Nov 10, 2017 at 19:39
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    \$\begingroup\$ Depending on the component and how it's soldered, if you know where the trace is connecting to, you can sometimes measure it. If there is any metal on the top without solder on it, you can put one DMM lead on that and put the other lead on the destination trace. Not a super reliable method though \$\endgroup\$
    – BeB00
    Commented Nov 10, 2017 at 21:15

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