HFSS Etch Factor — Ansoft Designer 7.0 在线帮助文档，Ansys Designer 教程

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HFSS Etch Factor

Substrate manufacturing does not create exact geometry. The actual geometry of substrate manufacturing often results in different thicknesses in the dimensions of each geometry within a layer — and that difference is represented by an "etch" or "etch factor". Designer geometry allows for the presence of an etch factor in the design and modelling of different substrate layers. The specific etch factor that applies to a particular layer is usually available from the manufacturer. But in general, the etch factor is calculated by taking the ratio of etch depth to undercut (where undercut is defined as being the portion of the wafer that is etched away under the photoresist):

etch_factor = layer_thickness / (bottom_dimension - top_dimension) / 2

When the bottom dimension of the stackup is larger than the top, the etch factor is positive. When the top dimension is larger than the bottom, the etch factor is negative. For example, with a positive etch factor, a transmission line with a 2mm nominal width will be 2mm wide on the bottom and narrower at the top. While the same transmission line with a negative etch factor will be 2mm wide on the top and narrower at the bottom. An etch factor of 0 means no etch, and the top and bottom dimensions are the same. Also, very large etch factors — both positive and negative — result in little or no etch.

In Designer, only signal layers can have an etch factor, dielectric and ground layers do not. Designer supports an etch ratio that is referred to as the HFSS Etch Factor, and this etch is used when the mesh is created for an HFSS simulation. Note, however, that the etch is not applied to geometry drawings in the 3D layout view. For more information see Stackup Tab Controls.


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