Definition

Solder Paste Inspection (SPI) systems measure solder paste deposits immediately after stencil printing and before component placement. Using laser or structured light, SPI measures paste volume, height, area, and position for each pad. Catching paste defects early prevents downstream assembly failures - insufficient paste causes open joints, excess paste causes bridges, and offset deposits cause tombstoning. SPI has become standard in quality-focused assembly lines because paste printing accounts for 60-70% of SMT defects. For designers, SPI capability means your assembly house can verify that fine-pitch pads receive adequate paste, enabling confident use of 0.4mm pitch components.