The self-resonance is determined by the parasitics in the structure, and when a manufacturer of a component specifies this value, it's discult to know what they mean! For
instance, for a capacitor, the series inductance is a strong function of how the component
is connected to the board. The consequent geometry will set the parasitic inductance and
hence the self-resonant frequency. One can only guess how the component was characterized.
For instance, if an 0603 capacitor is measured as a two-port circuit using transmission line
interconnect, then inductance is a strong function of the characteristic impedance of the
line's Z0 (see below). It is therefore advisable to measure the self-resonance frequency of the
component for the application at hand by measuring test structures on test boards which
have similar geometry to what you'll use in your final design. RF designers often send out
boards with such structures before they fab their final board designs. This way, parasitics
can be characterized on the test boards, and their effects compensated for in the final design.