Evaluating Step Stencil Keep out Zones for Mixed Pitch Assemblies
Step stencil keep out zones require a 10 to 1 distance ratio per mil of step height difference to prevent squeegee levitation and solder paste bridging.
Laser Milled Step
Subtractive Cavity
Precision stencil modification uses high-energy beams to remove material and create discrete pockets of reduced thickness. The creation of a laser milled step allows paste deposits of different volumes to be printed simultaneously on the same circuit board. This localized reduction accommodates fine-pitch components while maintaining larger volumes for standard components.
Manufacturing Step
Controlled vaporisation of stainless steel or nickel foil is executed with a fiber laser system to carve out the desired cavity depth. Unlike chemical etching, the laser milled step process delivers highly vertical walls and precise depth control down to five microns. The beam sweeps across the designated step area in overlapping paths to achieve a uniform floor thickness.
This mechanical accuracy prevents printing paste from squeezing out during the print stroke. A final polishing step removes any slag or burrs left along the cavity boundaries to ensure a smooth squeegee travel.
Depth Control
Height variations across the stencil surface must stay within a tight range to prevent squeegee damage or paste bleeding. Measurement of the laser milled step depth is performed using white-light interferometry or digital micrometer inspection. A deviation of more than ten percent from the target step depth causes rejection of the stencil.