Rough Metal Model

Many circuit manufacturing processes produce planar metalization with rough surfaces. Depending on how the metalization is formed, one, or both, of the trace metal surfaces could be relatively rough. The Rough Metal type allows you to capture this surface roughness effect in your model. The entry fields are defined below.

Cross Section: There are two variations of this model: Thin and Thick. You select which variation you wish to use by selecting it from the Cross Section drop list.

The Thin option models the metal as a single zero thickness          (2D sheet), like the Normal Metal type, but with the surface roughness effect. With this option, the user must specify a Current Ratio.

The Thick option models the metal as two sheets of current: one for the top surface and one for the bottom surface of the planar metal trace. This is very similar to the Thick Metal model (with 2-sheets), with the surface roughness effect.

Specify Using: You may chose to define your metal loss using Conductvity, Resistivity, or Sheet Resistance at DC. Select which value you wish to use from this drop list. The dialog box is updated to include a text entry box for whichever choice you make in the drop list. The factory default is to use Conductivity with a value of 5.8e7 S/m which corresponds to pure copper. If you wish to use a different metal, then enter its conductivity value.

Thickness: Enter the physical thickness of the metal. The effect of the thickness is determined by the Cross Section option as described above. The units of the thickness are your project units.

Top Roughness: Enter the top surface roughness in RMS microns. Often circuit material suppliers provide this information directly or you can ask the manufacturing group producing your physical parts.

Bottom Roughness: Enter the bottom surface roughness in RMS microns. Often circuit material suppliers provide this information directly or you can ask the manufacturing group producing your physical parts.

Direction: Select "Up" from this drop list if you wish the rough metal to extend upward through the dielectric layer from the level on which the polygon is drawn. If you wish to have the metal extend downward into the dielectric layer underneath the metal level, select "Down" from this drop list. Extending upward is the default. This field only appears if "Thick" is selected for the Cross section.

 For a more detailed discussion of the Rough Metal Model, please see Rough Metal Model in the Sonnet User's Guide.