To ensure that at time zero no crack has occurred, solder paste is applied to PCB metal pads using screen printing. The volume of the printed solder paste is determined by the stencil aperture and its thickness. In most cases, the thickness of a stencil must be matched to the needs of all components on the PCB. Stencil apertures should be a circular shape. A laser cutting (mostly made from stainless steel) with nickel blanking is preferred to ensure that both uniform and high-solder paste is transferred to the PCB. The recommended stencil design dimensions are listed in the following table and shown in the image.
| Aperture Shape | Pitch | Diameter | Stencil Thickness |
|---|---|---|---|
| Round | 25 mils and 37.8 mils | 14 mils | 5 mils |
Figure 1. Board to Board Connector Recommended Stencil Design
