SMT Rule Types

Updated: October 18, 2026

At a Glance

This article gives a focused overview of the SMT design rule types available for PCB layout in Altium Designer, with specific attention to what each rule controls, the constraints you can define, and how those rules affect routing and design rule checking. From the example shown, readers can see how a rule like SMD To Corner sets the minimum distance from a surface mount pad to the first routing corner, how it is applied during Online DRC, Batch DRC, and Interactive Routing, and how it works alongside related SMT routing behavior. If you want a clearer understanding of how Altium Designer handles SMT-specific rule settings during layout, this article is a strong place to start, keep reading to build more confidence in your PCB routing decisions.

- A clear summary of the SMT design rule types available in Altium Designer for PCB layout.
- Insight into how rule constraints are defined and enforced during routing and design rule checking.
- A practical understanding of how the SMD To Corner rule influences trace routing near surface mount pads.

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The design rules of the SMT category are described below.

The SMT category of design rules.

SMD To Corner

This rule specifies the minimum distance from the edge of a surface mount pad to the first routing corner.

Constraints

Constraint Manager – default constraints for the SMD To Corner rule.

PCB Rules and Constraint Editor – default constraints for the SMD To Corner rule.

SMD To Corner Constraints

Default Rule	Not required.
Distance	The value for the minimum permissible distance from the SMD pad edge to the start of the first routing corner. The distance is measured from the edge of the pad to the centerpoint of the track end ().
Behavior	The interactive router will obey this rule by: Maintaining a straight pad exit trace emanating from the pad center on any allowed entry edge (see SMD Entry rule), at least to the specified Distance (). Once the pad has been exited, the route is kept away from the pad. The software does not allow the route to re-enter the pad and then re-exit without regard to the SMD rules. SMD rules are ignored if the pad exit is blocked (they are also ignored during pad entry in this situation). Note that if there is a pad exit available that does not violate the SMD to corner rule, that exit will be used. Miters are not created in violation of SMD rules. The software favors the SMD to corner rule over the miter, allowing the miter to collapse to zero if required. Stubs that follow the SMD rules are created in Any Angle routing mode. In this mode, once the first track segment has been placed arcs will be included in the corners. If you need an arc in the first corner, place the exit stub before attempting to create a corner. When using the Interactive Differential Pair Routing tool, note that coupling the differential pair has priority. Therefore, the SMD To Corner and SMD Entry design rules might not work as expected. If strict respect for these rules is required when routing a differential pair, use the Quick Differential Pair Routing tool.
Rule Application	Online DRC and Batch DRC, and Interactive Routing.

SMD To Plane

This rule specifies the maximum routing length from the center of a surface mount pad to the center of the pad/via connecting to a power plane.

Constraints

Constraint Manager – default constraints for the SMD To Plane rule.

PCB Rules and Constraint Editor – default constraints for the SMD To Plane rule.

SMD To Plane Constraints

Default Rule	Not required.
Distance	The value for the maximum permissible distance from SMD pad to pad/via connecting to the power plane.
Rule Application	Online DRC and Batch DRC.

SMD Neck-Down

This rule specifies the maximum ratio of the track width to the SMD pad width, expressed as a percentage.

Constraints

Constraint Manager – default constraints for the SMD Neck-Down rule.

PCB Rules and Constraint Editor – default constraints for the SMD Neck-Down rule.

SMD Neck-Down Constraints

Default Rule	Not required.
Neck-Down	The percentage value for the maximum permissible ratio of track width to SMD pad width. Entering a larger value will allow for the use of greater width track.
Rule Application	Online DRC and Batch DRC.

SMD Entry

This rule specifies the direction(s) a track can enter, or exit, an SMD pad.

Constraints

Constraint Manager – default constraints for the SMD Entry rule.

PCB Rules and Constraint Editor – default constraints for the SMD Entry rule.

SMD Entry Constraints

Default Rule	Not required.
Any Angle	If enabled, the track can enter/exit the pad at any angle, and at any point along its edge.
Corner	If enabled, the track can enter/exit through a pad corner.
Side	If enabled, the track can enter/exit at 90 degrees on either side of the pad. The longer edge of the pad is considered the side. Note that the side option is only applied if the `Side length > 2x End length`. For example, if the pad is `2mm x 1mm` then the side option is ignored (all sides are treated as ends). If the pad is `2.1mm x 1mm` then the side option is applied.
Behavior	The algorithm views the pad: The rule applies to surface mount pads only, that is, a pad defined on a single copper layer. Pads can always be entered from either end (the shorter edge). The end of the pad is determined from the pad dimensions, the ends are the shorter edges, as described above in the Side definition. The rule is applied on both routing out of the pad (exit) and into the pad (entry).
Interaction with other rules	The rule works in harmony with the SMD To Corner design rule, configure both to ensure neat SMD routing (). Once the pad has been exited, the route is kept away from the pad. The software does not allow the route to re-enter the pad and then re-exit without regard to the SMD rules. Miters are not created in violation of SMD rules. The software favors the SMD to corner rule over the miter, allowing the miter to collapse to zero if required. SMD rules are ignored if the pad exit is blocked (they are already ignored during pad entry in this situation). Note that if there is a pad exit available that does not violate the SMD to corner rule, that exit will be used. Stubs that follow the SMD rules are created in Any Angle routing mode. In this mode, once the first track segment has been placed arcs will be included in the corners. If you need an arc in the first corner, place the exit stub before attempting to create a corner. When using the Interactive Differential Pair Routing tool, note that coupling the differential pair has priority. Therefore, the SMD To Corner and SMD Entry design rules might not work as expected. If strict respect for these rules is required when routing a differential pair, use the Quick Differential Pair Routing tool.
Rule Application	Online DRC, Batch DRC, and Interactive Routing.

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SMT Rule Types

At a Glance

SMD To Corner

Constraints

SMD To Plane

Constraints

SMD Neck-Down

Constraints

SMD Entry

Constraints

Contents

Contents