Modeling the Capacitance of an SMT Capacitor with LCGEN

Geometry and setup

Pad size: 0.5 mm × 0.5 mm × 0.017 mm
Cathode/Anode: 0.5 mm × 0.1 mm × 0.5 mm
Plate: 0.5 mm × 0.7 mm × 0.05 mm
Dielectric: 1.5 mm × 1.8 mm × 0.1 mm
Gap b/w two plates: 0.1 mm
Capacitor size: 1005
Dielectric: εr = 4.4

Setup:
The structure was drawn using the model editor. Then, using the simulation file builder, the model file was opened and the simulation default parameters were utilized. The build file and run option was then selected.

Download input geometry ibm_smtcap.zip

Simulation result

Capacitance: 0.461 pF

Model decisions

  1. Materials
    • Copper modeled as a PEC
    • Capacitor core and PCB dielectric were FR4
  2. Simulation
    • Output charge data selected
    • Disabled inductance solution because it won't work with this setup
    • Ran simulation in the foreground

Comments

  • How difficult was it to input this geometry in LCGEN?

    After becoming comfortable with the model editor in LCGEN this was not difficult at all.
  • Could this model be used as a generic part?

    LCGEN offers a way to input one drawing into another. The SMT capacitor could be drawn and saved as it's own part and then added on top of a PCB model.
Screen shots
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simulation model
Fig. 1. Simulation model
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charge distribution
Fig. 2. Charge distribution