Surface Roughness Models in Clarity 3D Simulation

Surface roughness is a component of surface texture. It represents the deviations in the direction of the normal vector of a real surface from its ideal form. Depending on deviations, the surface is defined as either rough or smooth. Surface roughness has a significant impact at higher frequencies due to the skin effect; at lower frequencies, it is less considered. However, it is very significant when considering thermal reliability because it relates to the mechanical strength of the bond between the dielectric and copper layers.

Clarity 3D Solver supports different surface roughness model definitions such as the Huray Model, Modified Hammerstad Model, and Modified Groisse Model.

Key points to remember while using surface roughness models are:  

• The accuracy may depend on the mesh; therefore, the meshing requires extra care. 
• You can set different surface roughness models on different surfaces. The translator does not set aside the surface to be rough in this case. 
• Clarity 3D Solver supports surface roughness modeling on the top and bottom sides of the signal line. The sidewall surface roughness is automatically applied, which is the same as the bottom. There is no “side” concept in Clarity 3D Workbench like Clarity 3D Layout. 
• Surface roughness is only applied to the skin impedance. 
• AC starting frequency is only used on the auto-fitting selection. If auto-fitting is used, the engine will take care of how to model metals. For metal inside or skin impedance, the AC starting frequency will be disabled.
• In Clarity 3D Layout, the definition can be applied in the stack-up for signal lines, whereas in Clarity 3D Workbench (FEM), it can be applied in the boundary conditions.

 More details can be found here.

Team SimTech 

Cadence Design Systems