SMT Rule Types

The design rules of the SMT category are described below.

The SMT category of design rules.

SMD To Corner

Default Rule: not required

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

Constraints

Default constraints for the SMD To Corner rule

Distance - the value for the minimum permissible distance from the SMD pad edge to the start of the first routing corner.

Rule Application

Online DRC and Batch DRC, and Interactive Routing.

Notes

• The interactive router will obey this rule by maintaining a straight pad exit trace emanating from the pad center on any allowed "entry angle" (see SMD Entry rule), at least to the distance specified.

  
  The SMD to Corner rule defines the distance to the first corner. Use the SMD Entry rule to specify where the route is allowed to enter (or exit) the SMD pad.

• 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 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.
• 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.

SMD To Plane

Default Rule: not required

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

Default constraints for the SMD To Plane rule

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

Default Rule: not required

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

Constraints

Default constraints for the SMD Neck-Down rule

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

Default Rule: not required

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

Constraints

Default constraints for the SMD Entry rule

• 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.

Rule Application

Online DRC, Batch DRC, and Interactive Routing.

Notes

• The rule applies to surface mount pads only, that is, a pad defined on a single copper layer.
• The end of the pad is determined from the pad dimensions, the ends are the shorter edges.
• Pads can always be entered from either end (the shorter edge)
• The rule is applied on both routing out of the pad (exit) and into the pad (entry).

• The rule works in harmony with the SMD To Corner design rule, configure both to ensure neat SMD routing.

  
  The SMD Entry rule specifies where the route is allowed to enter/exit the SMD pad, all rule checkboxes are cleared in this example animation. Use the SMD to Corner rule to define the distance to the first corner.

• 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 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.
• 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.