Stencil opening

The stencil opening is the area of a surface-mount device (SMD) pad through which solder paste is applied. A stencil is a thin metal sheet that deposits solder paste onto the pads before components are placed. Fusion creates the stencil opening by reducing inward from the pad area by the offset value. Stencil openings apply only to SMD pads.

In Fusion, the stencil opening is a design rule. When a pad does not meet the rule, Fusion either adjusts the opening or reports a violation, depending on how the opening is defined and the Auto Resize option. Stencil geometry appears on layer 31 (StencilTop) and layer 32 (StencilBottom). Stencil rules do not include an auto tenting option. The default stencil offset is 0, which matches the stencil opening to the SMD pad size.

Set the stencil opening

The Parameter Value determines how Fusion sizes the opening. Select one of the following:

Option	Description
Absolute	Defines the opening offset as a single minimum value.
Calculated	Calculates the offset as a percentage of the smaller dimension of the pad, within an allowable minimum and maximum range. For Long, Offset, or Slot pads, Fusion uses the smaller dimension.

Stencil offset values are positive and reduce the stencil opening inward. The Minimum and Maximum limits in the rule apply to all calculated and manual values.

How Fusion calculates stencil size

When the stencil property is Auto:

Absolute: Uses the rule Minimum offset.
Calculated: Applies Offset Reduction as a percentage of pad size, then clamps the result to Minimum Offset Reduction and Maximum Offset Reduction.

No DRC error or warning appears when Fusion calculates the size.

When you set a specific Offset Reduction value, 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 adjusts the offset and reports a warning. If Auto Resize is off, Fusion keeps your value and reports an error.

Resize openings automatically with Auto Resize

The Auto Resize checkbox controls what happens when a stencil offset falls outside the range the rule allows:

State	Behavior
On	Fusion adjusts the offset to the nearest valid value and reports the change in the Warnings tab of the DRC panel.
Off	Fusion keeps the offset you entered and reports the violation in the Errors tab of the DRC panel.

Resolve stencil violations

Fusion reports stencil issues in the DRC panel:

A warning appears when a design rule reduces a stencil beyond your specified value.
An error appears when a stencil violates the rule and Auto Resize is off.

Select an entry to see its details and to locate the affected object. You can resolve a violation by changing the pad's opening, editing the stencil rule, or turning on Auto Resize.

Set the stencil opening on individual pads

You can override the rule for a single pad in its command dialog or in the Inspector. Choose one of the following:

Option	Description
Auto	Uses the design rule to set the stencil size.
Offset Reduction	Sets a custom stencil size for the object.
Percentage Reduction	Sets a stencil size to 0-100% coverage of the pad. DRC does not check this option.
Off	Disables the stencil for the pad.