Working with Backdrilling in Allegro PCB Designer: Best Practices
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The layer pair rows for TOP to LAYER_4_P and BOTTOM to LAYER_7_P is not being
reported as an issue because the minimum stub length after backdrill can be achieved,
for example:
• "To Layer (1.20 mils)" + "Dielectric (16.00 mils)" = "17.20 mils"
• Total Thickness is 17.20 mils, which is greater than 10.00 mils stub length.
Selecting the Yellow Cell on the layer pair row from BOTTOM to LAYER_4_P will
produce a dialog to explain the violation:
Note: The fabrication vendor can adjust the To Layer to meet their minimum stub
length after backdrill, which will result in these moving it to LAYER_5 with the stub
spanning the two layers. All Backdrill data will still be generated, even when these
Warnings exist.
Tool Tip – Backdrill Analysis can take into consideration the specified Manufacturing
Stub Length and make adjustments during the creation of the layer pair by setting a
special environmental variable.
• Set the environmental variable BACKDRILL_LAYER_PAIR_ADJUSTMENT.
• Select Layer Pair Initialization button under the Layer Pairs tab.
