EMC Question of the Week: May 17, 2021

Surface Mount Capacitors on a Circuit Board

The connection inductance of an 0603 SMT decoupling capacitor that is well-mounted to a printed circuit board 2 or 3 layers above the power/ground plane pair is typically a couple

  1. nanohenries
  2. hundred picohenries
  3. picohenries
  4. hundred femtohenries


The best answer is “a.” Despite what the datasheet may say, a well-mounted decoupling capacitor typically has at least 1-2 nanohenries of connection inductance. The inductance values often quoted in datasheets are based on measurements where the fixture inductance is determined by making a measurement with a shorting block. This value is then subtracted from the inductance measured with the capacitor in the fixture. However, the inductance of a loop is not simply the sum of its parts. Subtracting the fixture inductance results in a number that underestimates the actual contribution of the capacitor to the connection inductance.  

In addition, the inductance of the via connections between the planes and the capacitor pads is not negligible. It generally contributes about a nanohenry to the total connection inductance when the vias are optimally spaced and less than a millimeter long. So despite the numbers that appear in the datasheet, a well-connected 0603 capacitor will typically have 1-2 nanohenries of connection inductance. 

Note: Poor via placement or allowing decoupling capacitors to share via connections (as shown in the figure) can effectively result in connection inductances that are significantly higher than 1-2 nanohenries.

Have a comment or question regarding this solution? We'd like to hear from you. Email us at This email address is being protected from spambots. You need JavaScript enabled to view it..