Quantifying the improvements in the solder paste printing process from stencil nanocoatings and engineered under wipe solvents

Over the past several years, much research has been performed and published on the benefits of stencil nano-coatings and solvent under wipes. The process improvements are evident and well-documented in terms of higher print and end-of-line yields, in improved print volume repeatability, in extended under wipe intervals, and in photographs of the stencil´s PCB-seating surface under both white and UV light. But quantifying the benefits using automated Solder Paste Inspection (SPI) methods has been elusive at best. SPI results using these process enhancements typically reveal slightly lower paste transfer efficiencies and less variation in print volumes to indicate crisper print definition. However, the improvements in volume data do not fully account for the overall improvements noted elsewhere in both research and in production. This paper and presentation outlines a series of tests performed at three different sites to understand the SPI measurement processes and algorithms, and suggests inspection parameters to better capture and quantify the correlation between nano-coatings and solvent under wipes with overall print quality and process performance.