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In Cadence Allegro the backdrilling table defines for each backdrill type what the end layer will be. Then Allegro calculates the drill-depth from the stackup.
The manufacturer/fabs typically provide manufacturing capability as stub length after backdrill will be 8mil +/-4mil.
How do you use it?
a) for layer-3 signals you define end-layer to be layer-5. Hopefully layer-5 is around 8mil from layer-3.
b) for layer-3 signals you define end-layer to be layer-3, and separately specify stub length. The allegro drill depth will reach layer-3, so it has to be avoided to cut layer-3, by overriding the drill depth. how do you specify?
The manufacturer/fabs typically provide manufacturing capability as stub length after backdrill will be 8mil +/-4mil.
How do you use it?
a) for layer-3 signals you define end-layer to be layer-5. Hopefully layer-5 is around 8mil from layer-3.
b) for layer-3 signals you define end-layer to be layer-3, and separately specify stub length. The allegro drill depth will reach layer-3, so it has to be avoided to cut layer-3, by overriding the drill depth. how do you specify?