Working with Backdrilling in Allegro PCB Designer: Best Practices
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Fabrication Vendor Backdrill requirements (Reference
Only)
• Backdrill size is normally 6 – 10 mils over the primary drill.
• Clearance to backdrill path is normally 16 mils over the backdrill size.
• Inner layer pads in the backdrill path should be removed.
• Outer layer backdrill entry pad is normally reduced so it is slightly larger than the
primary drill, which will be drilled away by the backdrill (Primary Drill + 5 mils).
• Outer layer backdrill solder mask opening is normally 6 – 10 mils over the
backdrill size.
Note: Consult a fabrication vendor to determine which rules are going to work
best and update your library padstacks so each design has consistent backdrill
rules.
The backdrill data being stored in the padstack allows the information to be updated at
the library and design levels to take full advantages of this enhanced backdrill
functionality. No special scripts and SKILL routines are needed to maintain design
integrity.
Tool Tip – Although the backdrill data can be entered in the padstack at either the
library or design level, it is recommended to maintain the backdrill data at the library
level for a consistent set of backdrill rules and guidelines.
