The annular ring is the copper area surrounding a drilled hole. It applies to both pads and vias, and it is essential for reliable electrical connections. The resulting diameter of a pad or via equals twice the annular ring width plus the hole diameter.
In Fusion, the annular ring is a design rule. When a pad or via does not meet the rule, Fusion either resizes the object or reports a violation, depending on the object's diameter setting and the Auto Resize option.
Fusion provides separate annular ring rules for different object types:
Inner layer rules for PTH pads, vias, and micro vias include a Match Outer Diameter option. When it is on, inner layer settings follow the outer layer values. When it is off, you can set inner layer values independently.
The Non-Functional Pads rule page has only a Remove All checkbox. When it is on, annular rings do not generate on internal layers.
Whether Fusion adjusts a pad or via depends on how its diameter is defined:
The Parameter Value determines how Fusion sizes the annular ring. Select one of the following:
| Option | Description |
|---|---|
| Absolute | Defines the annular ring as a single minimum value. |
| Calculated | Calculates the annular ring as a percentage of the drill diameter, within an allowable minimum and maximum range. |
Enter the width in the Annular Ring Size field. This field applies to both Absolute and Calculated values.
Calculated scales the annular ring width with the hole diameter and keeps the result within the minimum and maximum values you set. This is useful because a percentage-based width can fall below what your manufacturer can produce on a small hole. When that happens, the minimum value raises the width to a usable size.
The Auto Resize checkbox controls what happens when a pad or via has a library or user-specified diameter that is smaller than the rule minimum:
| State | Behavior |
|---|---|
| On | Fusion resizes the object to meet the rule and reports the change in the Warnings tab of the DRC panel. |
| Off | Fusion keeps the original diameter and reports the violation in the Errors tab of the DRC panel. |
Turn Auto Resize off when you want your library and user-specified diameters to remain fixed and prefer to resolve conflicts yourself.
When pad or via diameter is Auto:
No DRC error or warning appears when Fusion calculates the diameter.
When diameter is user-specified or library-defined, Fusion compares it to the rule. If the value meets the rule, no issue appears. If it violates the rule and Auto Resize is on, Fusion resizes the object and reports a warning. If Auto Resize is off, Fusion keeps your diameter and reports an error.
The Inspector shows the resulting diameter of a pad or via in the outer and inner layers, along with the minimum value the rule applies. When the rule enlarges an object, the resulting diameter is larger than the value you entered. For example:
| Minimum | 0.7 |
| Diameter, outer layers | 0.9 |
| Diameter, inner layers | 0.8 |
Fusion reports annular ring issues in the DRC panel:
Select an entry to see its details and to locate the affected object. You can resolve a violation by changing the object's diameter, editing the annular ring rule, or turning on Auto Resize.