Selecting the Best Metal Model for Via Metal Loss

When you create a new via metal type using the Via Metal Editor, you must choose a loss model for the via metal.

There are three loss models for via metal:

Volume: This loss model is the most commonly used because the values you specify are directly related to the physical properties of the via. With the volume model, you enter a conductivity, resistivity, resistivity per via or Sheet Resistance at DC and Volume Properties. This loss model is frequency-dependent when using conductivity, resistivity, or sheet resistance to define the loss, with both a DC loss component and also an RF loss component. The 3D volume characteristics of the via are taken into account to compute skin depth for the RF loss calculations. You may specify a finite value for the wall thickness of the via, or you may set up the via to be solid. If you are defining the loss using resistance per via, the loss is constant with frequency. The resistance per via represents the total resistance of the via polygon in the Z-direction.

Surface: The surface loss model should be used when you know the surface impedance of a via, but not the physical characteristics. Via loss is modeled using a complex sheet impedance in ohms/square. The surface via loss model treats the via as an infinitely thin hollow tube giving it a 2D surface. The complex sheet impedance is applied to this 2D surface.

Array: The Array via loss model is used to represent an array of small solid vias by approximating the entire array as a single large via. This is usually done to reduce the processing resources necessary to analyze the circuit, as having many small vias is computationally expensive. The Array via loss model is most often used for computing the loss of via arrays which have been simplified when translating a circuit into a Sonnet project. If you are entering your circuit manually, it may also be used to model a single via that represents an array in your final design.  Like the Volume model, when using conductivity or resistivity to define the loss, it is a frequency-dependent model which takes into account the 3D characteristics of the via array. The loss is constant with frequency if you are using resistance per via to define the loss.