When designing PCBs with Altium Designer, in addition to basic rules such as electrical clearance, rules like trace width, solder mask, internal plane connection, and copper pour settings are equally important. These configurations not only affect routing efficiency but also determine the manufacturability and reliability of the finished board.
Today, we will go into detail on how to configure these key rules in Altium, including trace width, vias, solder mask, internal planes, and copper pour connections, with a full practical walkthrough and illustrations that correspond to the user interface.
01
Short Circuit Rule Setting
Function: Defines whether short-circuit connections are allowed. By default, Altium does not allow short circuits (the “Allow Short Circuit” option is unchecked). If a short is required (e.g., test points on the same net), this option can be enabled. Recommendation: Keep the default unchecked unless there is a special requirement, to avoid accidental shorts.
02
Routing Rule Settings
✅ Trace Width Rule
Altium provides three width parameters:
- Max Width: Maximum allowed trace width
- Preferred Width: Recommended width (used preferentially by the system during routing)
- Min Width: Minimum allowed trace width (to avoid issues due to overly thin traces)
Path: Design → Rules → Routing → Width
You can apply different width settings to different nets or net classes for more precise routing control.
✅ Routing Via Style Rule
This rule configures the via dimensions used during routing:
- Via Diameter: Outer diameter of the via
- Via Hole Size: Inner diameter (drill size)
Supports setting maximum, minimum, and preferred values to accommodate different scenarios.
⚠️ Note: The difference between outer and inner diameter should not be too small; otherwise, it may increase manufacturing difficulty or affect soldering reliability.
03
Solder Mask Rule Setting
Used to define the clearance between pads and the solder mask (i.e., solder mask opening size):
- Solder Mask Expansion: Recommended value is 2.5 mil
This prevents the solder mask from covering pads, which can lead to soldering issues. A solder mask opening that is too large or too small can cause problems, so it is advised to follow your PCB manufacturer’s recommended values.
04
Plane (Internal Power Layer) Rule Settings
✅ Power Plane Connect Style
Defines how pads or vias connect to the power plane:
- Relief Connect: Thermal relief (recommended)
- Direct Connect: Solid connection
- No Connect: No connection
Other parameters:
- Conductors: Number of connecting spokes (2 or 4)
- Conductor Width: Width of the connecting spokes
- Air-Gap: Spacing between spokes
- Expansion: Distance from the via edge to the spokes
▶️ Recommendation: Use “Thermal Relief” for typical power nets for better heat dissipation and easier soldering.
✅ Power Plane Clearance
Defines the minimum safe clearance (commonly called isolation ring or anti-pad) between the power plane and the traces/vias passing through it:
- Recommended value: 9–12 mil
Too small can risk shorts; too large wastes space and isn’t suitable for high-density designs.
05
Polygon Connect Style (Copper Pour Connection) Rule Settings
This rule defines how polygon copper pours connect to pads/vias:
- Options: Thermal Relief, Direct Connect, or No Connect
- Allows control over connection line count, width, etc. (similar to internal plane settings)
▶️ General Recommendations:
- Pads: Use “Thermal Relief” connection
- Vias: Use “Direct Connect” (for more stable conductivity)
Example: To add a rule for vias to fully connect to copper pours
Set the via connection in “Polygon Connect Style” to “Direct Connect” and assign a higher priority to this rule so it applies preferentially when copper pours connect to vias.
06
Other Notes
- Most unlisted rules can remain as default settings, which are sufficient for general designs;
- For high-reliability or high-speed signal designs, additional rules like differential pair routing, impedance control, and length matching should be configured;
- All rules can be exported as .rul files for reuse and can also be used to generate report documents for review.
07
Conclusion
This is the full procedure for setting trace width, vias, solder mask, copper pour connections, and other essential rules in Altium Designer. These detailed rules ensure design quality and should never be overlooked.
Rule setting is not a burden—it is a crucial step to ensure your design is standardized, efficient, and reliable.
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