How to Change Thermal Relief in Altium?

Changing thermal relief settings in Altium Designer is primarily managed through Design Rules, specifically the Power Plane Connect rule. This rule defines how pads and vias connect to polygon pours.

You can customize the thermal relief pattern by adjusting parameters such as the number of conductors (spokes), their width, the air gap, and even the connection angle.

Steps to Modify Thermal Relief Settings

Follow these steps to adjust the thermal relief properties for connections to polygon pours:

1. Access Design Rules: Go to Design > Rules from the main menu in your PCB document.
2. Navigate to Power Plane Connect: In the PCB Rules and Constraints Editor dialog, expand the Plane category and select the Power Plane Connect rule. You can create a new rule if needed or modify the default one (usually Power Plane Connect(All)).
3. Configure Rule Scope: Define which objects the rule applies to using the Where the Object Matches section. By default, it applies to All, but you can specify nets, components, or classes.
4. Adjust Settings: In the Constraints section, select Connect Style: Thermal Relief. Here you will find the key parameters:
   • Conductors:
     • Number: Specify how many spokes connect the pad/via to the polygon. Common values are 2 or 4.
     • Width: Define the width of these spokes.
   • Airgap: Set the distance between the pad/via edge and the polygon pour edge.
   • Connection Angle: You can customize the connection angle. This setting determines the angle at which the thermal spokes are drawn from the center of the pad/via.
5. Apply Changes: After adjusting your settings, press OK in the PCB Rules and Constraints Editor dialog.

Key Thermal Relief Parameters

Here's a summary of the main settings you'll typically adjust:

Setting	Description
Connect Style	Must be set to Thermal Relief.
Conductors - Number	How many spokes connect to the pad/via.
Conductors - Width	The width of each connecting spoke.
Airgap	The distance from the pad/via edge to the polygon pour edge.
Connection Angle	The angle relative to the pad/via origin where spokes are placed.

Important: Repour the Polygon

If you don't see any changes immediately after updating the design rules, make sure to repour the polygon. Altium does not automatically update the polygon pour based on rule changes.

To repour all polygons, go to Tools > Polygon Pours > Repour All.

While Design Rules are the standard method for applying thermal relief settings globally or to classes of objects, you can sometimes override these settings directly on individual pad or polygon pour properties if specific exceptions are needed.