Aperture Modification
Specialized printing tool features localized areas where the foil thickness is increased to deliver a larger volume of solder paste to specific pads. A step up stencil allows for the simultaneous assembly of standard components and high power devices that require more solder. The transition between the different thicknesses is achieved through a chemical etching or laser milling process on the squeegee side.
SMT Application
Designing these stencils requires careful consideration of the distance between the stepped area and the surrounding fine pitch apertures. If the step up stencil is too close to a small component, the squeegee may not be able to conform to the surface, resulting in poor paste release. This technology solves the problem of meeting different volume requirements on a single board without multiple print cycles.
The ramp area usually requires a clearance of several millimeters to ensure a clean print.
Cleaning Requirement
Maintenance of these tools is more complex than standard flat foils because the recessed areas can trap paste and dried flux. Automated stencil cleaners must be effective at removing debris from the transition zones of the step up stencil to prevent clogging. Inconsistent cleaning leads to variations in the deposited volume and increases the risk of solder balls.
Proper handling is required to prevent bending the thin transition walls of the foil.
