The solder paste printing process: critical parameters, defect scenarios, specifications, and cost reduction

Purpose - The purpose of this paper is to comprehensively explore the effects of critical parameters on solder deposition and to establish a systematic approach for determining guidelines for solder paste inspection (SPI) workstations. Design/methodology/approach - This study explored the effects of process parameters, stencil and printed circuit board designs on solder deposition and identified the major post-reflow defect scenarios. Through the investigation of correlation between the results of SPI analysis and post-reflow defective scenarios, SPI specifications are suggested for minimizing the total cost of poor quality. Findings - The higher the printing pressure the lower the solder deposition. There was a significant difference in solder deposition between the front squeegee and the rear squeegee. Insufficient distance between the stencil aperture and the initial printing location resulted in irregular solder paste and variations in solder deposition. A stencil with a higher area ratio resulted in greater solder deposition and less variation. Stencil apertures parallel to the direction of printing were superior to a 45 vector print. Further, the nominal solder thickness should take into account the thicknesses of the solder mask and the legend ink. There was an offset in the results of SPI measurements between the solder mask defined (SMD) pads and non-SMD pads. The specifications for solder deposition with irregular stencil apertures need to be adjusted. Originality/value - To address the arbitrariness of existing industry practice, this study was a joint effort with a Taiwan-based electronics manufacturing service company. Real data were taken from a mass production environment and inferences were then made based on a statistical analysis.