Backdrilling definition

[buenos]

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?

 

[Linda.guo]

Hello,

i think you mislead the manufacturing capability you supplier offered 8mil+/-4mil.
in fact , it would like to inform you two facts:
1. they can get thinnest stub/remaining thickness after backdrilling 8mil+/-4mil, if you hope to get thinner stub such as 6mil, they can not meet your need.
2. the tolerance of stubs they can control +/4mil.

if you define the depth of backdrilling so that it can avoid the drilling drill through the undesired layer according to the designed stackup.
hope my reply can help you out, if you have any questions related to PCB manufacturing , please contact me .