Altium Designer Documentation

Max Via Stub Length (Back Drilling)

Modified by Jason Howie on Sep 26, 2019
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Rule Category: High Speed

Rule Classification: Unary

Summary

A stub is the length of via or pad barrel that protrudes beyond the last-used signal layer that the via/pad connects on. Back drilling will be applied to suitable vias/pads in nets targeted by this rule, in accordance with the enabled side-of-board Layer checkboxes, and the back drill [BD] pairs defined in the Drill-Pair Manager dialog.

As well as being used to define which vias/pads are to be considered for back drilling, during design rule checking this rule tests for via and pad stubs longer than the specified Max Stub Length, for all nets targeted by this rule (regardless of whether back drilling has been applied to that via or pad). This rule also specifies how much larger the drill size must be for vias and pads that are back drilled.

Use appropriate rule scoping to target vias/pads in a specific net (or collection of nets), using query expression keywords such as InNet, InNetClass, or In AnyNet.

All design rules are created and managed within the PCB Rules and Constraints Editor dialog. For a high-level view of working with the design rules system, see Constraining the Design - Design Rules. For detailed information regarding how to target the objects that you want a design rule to apply to, see Scoping Design Rules.

Constraints

Default constraints for the Max Stub Length rule.

  • Max Stub Length - the maximum length of stub allowed. This setting is used to test for remaining stubs of this length or longer, it does not define the drill depth used for back drilling.
    • Top Layer - back drill vias/pads, in targeted nets, from the top side of the board.
    • Bottom Layer - back drill vias/pads, in targeted nets, from the bottom side of the board.
  • Back Drill Oversize - the radial increase in size of the drill used for back drilling, over the original via/pad hole size.
    • Tolerance - allowable +ve and -ve tolerance allowed on this drill size, enter both as a positive number.

The drill depth is defined by: the sum of the layer thicknesses of all layers from the surface layer (included) through to the stop layer (not included), defined in the Drill Pair Manager dialog.

How Duplicate Rule Contentions are Resolved

All rules are resolved by the priority setting. The system goes through the rules from highest to lowest priority and picks the first one whose scope expression matches the object(s) being checked.

Rule Application

Batch DRC.

Refer to the Controlled Depth Drilling, or Back Drilling article, to learn more.

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