Non-Solder Mask Defined

Registration Tolerance

Because the mask opening is larger than the pad, small misalignments of the solder mask do not affect the size of the solderable area. This reduces the risk of the mask encroaching on the pad and causing a defective joint. The clearance between the pad and the mask edge is typically set to 50 or 75 microns.

Stress Distribution

Mechanical loads are distributed across the entire surface and the sides of the pad. This often results in better fatigue life for solder joints compared to designs where the mask limits the wetting area. It is the standard choice for ball grid array footprints in most high reliability applications.

Copper Adhesion

The copper pad sits on top of the laminate without the mask overlapping the edges. This makes the pad more susceptible to lifting during rework or extreme mechanical stress. Designers must balance the improved solder joint strength against the risk of pad detachment.

The etch quality of the copper traces becomes a critical factor for fine pitch pads.