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Working with Backdrilling in Allegro PCB Designer: Best Practices
Net Identification
The first step in the backdrill application is the identification of nets targeted for potential
backdrilling. The word potential is used because, ultimately, backdrilling only affects the
pins and vias on the nets that violate the maximum stub rule. Although a net is
identified, it might be omitted from backdrilling if a required layer pair does not exist and
the stub lengths are within the margin. The net level property,
BACKDRILL_MAX_PTH_STUB, can be applied at the Schematic level, Cadence or third
party, Allegro canvas using Edit Property (Edit > Properties) or within Allegro Constraint
Manager. The value of this property is the maximum allowable PTH stub and is
restricted to the length in database units.
Applying Property in Constraint Manager
The BACKDRILL_MAX_PTH_STUB property can be easily assigned to the nets in
Constraint Manager as follows:
o Open the General Properties worksheet located in the Net Workbook.
o Scroll across the worksheet to the Backdrill column.
o Select relevant cells where backdrill property is to be applied
o RMB > Change.
o Enter the maximum stub value, or enter 0 if no stub is allowed.
o Click OK.
Applying BACKDRILL_MAX_PTH_STUB in Constraint Manager
