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.
3d SPI Height Profiling
Volumetric Assessment
Automated metrology of solder paste deposits on circuit boards establishes the necessary feedback for printing parameters before components are placed. Within this inspection sequence, 3d SPI height profiling calculates the Z-axis dimension of each deposit by analyzing the distortion of projected light patterns on the board surface. Accuracy here prevents board defects like solder bridging or starved joints.
Measurement Process
Structured light patterns are projected across the printed board at a known angle to generate a phase-shifted image captured by a high-resolution camera. This optical approach to 3d SPI height profiling avoids any physical contact with the wet solder paste to prevent deformation. The measurement system extracts the height of the paste at millions of points across the board and translates these values into a three-dimensional topographic map.
These processed height measurements are then compared directly against the baseline CAD layout data to confirm correct alignment and volume.
Process Tolerance
Height limits are established within the printer recipe to trigger warnings when deposit dimensions deviate from nominal paste height values. In a typical surface mount technology run, 3d SPI height profiling flags boards that show a height deviation of more than twenty percent from the stencil foil thickness. This measurement acts as a primary control for subsequent reflow success.