Backdrill Type

The Backdrill type is used to define the parameters for a backdrilled via.

val bd = Backdrill(
  Bottom,                 ; Side - Top / Bottom
  LayerIndex(4, Bottom),  ; Stop Layer
  0.4                     ; drill diameter, mm
  0.6                     ; starting pad diameter, mm
  0.8                     ; Soldermask Opening diameter, mm
  1.0                     ; Copper Clearance Diameter, mm

The Backdrill can be defined from either the bottom side or the top side. The second parameter defined the stop layer, which is the copper layer that is the drill boundary.

In this example - the drill depth is computed from the sum of the copper and dielectric layers from the Bottom layer to 5 copper layer (zero-indexed value) from the bottom. The 5th copper layer from the bottom is the layer that will conduct signal for this via. The 1-4th copper layers from the bottom will be drilled out and not able to conduct or form a stub.