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Working with Backdrilling in Allegro PCB Designer: Best Practices
Property
BACKDRILL_MAX_PTH_STUB
Purpose
Identification of nets targeted for backdrilling
Usage
Required
Value
Max allowable stub in length (database units)
Objects
Nets
Backdrill analysis flag
S
Tool Tip – All backdrill application properties begin with a 'BACKDRILL' prefix.
Stub Calculation
A stub is calculated from either the top or bottom side of the board to the adjacent
dielectric layer where the trace enters the PTH. To perform an accurate stub analysis, it
is a prerequisite that all the information pertaining to the conductor and dielectric
thickness be entered in the Cross Section form.
Example – A trace enters a pin on LAYER_5 and exits on LAYER_6, resulting in a
stub from both the top and bottom side. The top side stub includes the conductor and
dielectric thickness from the layer TOP to the surface of the layer LAYER_5. The bottom
side stub includes the conductor and dielectric thickness from the layer BOTTOM to the
surface of the layer LAYER_6. Each side-based stub, not the accumulated total, is
compared individually against the BACKDRILL_MAX_PTH_STUB property value.
