What is a via?

Geometry Elements - Vias

The term ”via” commonly refers to a connection from metal on the substrate surface to the groundplate beneath the substrate. However, as used in Sonnet, a via can be used to connect metalization between any substrate or dielectric layer, not just bottom layer to ground. Thus, em’s vias can be used in modeling airbridges, spiral inductors, wire bonds and probes as well as the standard ground via.

Em’s vias use a uniform distribution of current along their height and thus are not intended to be used to model resonant length vertical structures. The height of the via should be a small fraction of a wavelength. The via height is the same as the thickness of the substrate or dielectric layer it penetrates.

If a microstrip substrate is a significant fraction of a wavelength thick, over-moding also becomes a major problem. If vias are used to form, for example, a septum, or an interior wall, you may need to model it with multiple layers to achieve an accurate analysis.

There are two types of vias: edge and polygon. An edge via is added to the edge of an existing metal polygon and is one cell wide along the complete edge. A polygon via is a via created by drawing a polygon. The via is the one cell wide perimeter of the polygon. The picture below shows examples of different types of vias. The top is a rectangular via, the middle is an edge via and the bottom is a polygon via. Note the black outlines; this is the shape drawn by the user, the actual metal fill is displayed in reverse video of the metal type pattern.

For a detailed discussion of vias, see the ''Vias and 3-D Structures'' chapter in the Sonnet User's Guide.