Measurement Error Series Capacitors

[opaydar]

I'm measuring across two SMD capacitors soldered together in series. When separate from one another, the capacitors both have a nominal value of 1 pF measured to be 970 fF and 920 fF, respectively (with an agilent 4294A and verified by an agilent 4280A). When soldered together, the series capacitance is measured to be 300 fF (although I was expecting to measure ~ 500 fF). As a sanity check, I probed across AB and across BC, both values agree with the previous 970 fF and 920 fF measurement.

What is causing the deviation when the caps are soldered together? I ran phase compensation calibration on the impedance analyzer (agilent 4294A) before making the measurements.

Any and all help will be very much appreciated! Thanks!


A------||--B--||------C

 

[D.A.(Tony)Stewart]

what was the SRF and test frequency?

 

[opaydar]

I swept from 1 kHz to 2 MHz, but the capacitance values above were reported at 1 MHz. Because the sweep stops at 2 MHz, I didn't notice the characteristic dip of impedance at the SRF, therefore I don't know what it is.