|
|
| |||||||||||||||
|
PPI 0402BB103 10mil Rogers 4350B Substrate: Scattering Matrix Measurement Conditions and Notes This describes the considerations and measurement conditions used in the creation of the PPI 0402BB103 capacitor series scattering matrices. All comments apply to parts in the series microstrip configuration, i.e. capacitors that span a gap in the center trace of a microstrip transmission line. Scattering parameters of multilayer ceramic capacitors mounted on microstrip substrates depend not only on the dielectric and electrode capacitor structure, but on a number of substrate-related parameters. These include: (1) substrate dielectric constant and thickness; (2) mounting pad and trace dimensions; and (3) capacitor orientation (internal electrode planes relative to the substrate surface), horizontal or vertical. Measurements were made for the 0402BB series by Modelithics, Inc., a specialty vendor contracted by PPI. The measurements employed coplanar probes and coplanar-to-microstrip transitions; these, as well as any other structures between the probes and the capacitor-under-test mounting pad edges, were de-embedded using statistical TRL techniques. Tests were performed on a Vector Network Analyzer from 0.01 to 16 GHz for the 0402BB103 and from 0.01 to 35 GHz for the 0402BB104. The scattering matrix is simply a text file; an example is shown below: # MHz S dB R 50
The first line is a header, designated by the “#” character. Succeeding characters describe respectively the frequency units, parameter, measurement format, and characteristic impedance of the measurement system in Ohms. (Note: for the BB series, the frequency unit is Hertz, not MHz, and the measurement format is magnitude-angle, rather than dB magnitude angle shown in the example.) The data is arranged as follows: The first column is the frequency, in the units specified in the header. The next two columns are S11 magnitude (again, as specified in the header) and S11 phase. Succeeding column pairs represent S21, S12, and S22. It should be noted that some software simulators may require that artificial data -- e.g. 0 dB return losses and very large insertion losses -- be added at zero frequency to avoid passivity or other issues. In general, caution is suggested when using software simulation, since many programs attempt to extrapolate scattering matrix data both below and above the frequencies where it is valid – and often arrive at grossly incorrect results. Parallel resonances in the series microstrip configuration manifest as notches (“suckouts”) in S21 or S12, the insertion loss. It should be noted that some software simulators may require that artificial data -- e.g. 0 dB return losses and very large insertion losses -- be added at zero frequency to avoid passivity or other issues. In general, caution is suggested when using software simulation, since many programs attempt to extrapolate scattering matrix data both below and above the frequencies where it is valid – and often arrive at grossly incorrect results. Fig. 1 depicts a typical capacitor on the mounting pads of a microstrip substrate.
Fig. 1 A multilayer ceramic capacitor in a series configuration on a microstrip substrate Reference planes are always at the pad edges, as shown. The following parameters apply: Series: 0402BB103 The last two parameters, “50-Ohm Trace Width on substrate (mils)” and “Reference plane spacing (mils)” are for reference only. To determine the intrinsic properties and capabilities of a part, it is often valuable to characterize it with minimal exogenous parasitics, in this case, the fewest additional parasitic reactances beyond those of the basic capacitor spanning a gap in a microstrip trace. Generally, two conditions are necessary to accomplish this:
Fig. 2 General equivalent circuit for MLCC on microstrip (left) approximately reduces, for DC block, to lumped equivalent circuit for short length of transmission line (right) PPI has created at least one set of scattering matrices in each series where the reference planes closely coincide with the nominal part edges, and where the 50-Ohm trace width on a particular substrate is close to the nominal part width. Mounting pad dimensional limitations in the models determined to what degree these conditions could be achieved. DISCLAIMER: Passive Plus Inc. (PPI) has made every effort to make this information as accurate as possible. However, no responsibility is assumed by PPI for its use or for any infringements of rights of third parties that may result from its use. PPI reserves the right to revise the content or modify its product line without prior notice. |
|
|