The behaviour of solder pastes in stencil printing with electropolishing process

Purpose - The purpose of this paper is to study the effect of the electropolishing time of stencil manufacturing parameters and solder-mask definition methods of PCB pad design parameters on the performance of solder paste stencil printing process for the assembly of 01005 chip components. Design/methodology/approach - During the study, two types of stencils were manufactured for the evaluations: electroformed stencils and electropolished laser-cut stencils. The electroformed stencils were manufactured using the standard electroforming process and their use in the paste printing process was compared against the use of an electropolished laser-cut stencil. The electropolishing performance of the laser-cut stencil was evaluated twice at the following intervals: 100 s and 200 s. The performance of the laser-cut stencil was also evaluated without electropolishing. An optimized process was established after the polished stencil apertures of the laser-cut stencil were inspected. The performance evaluations were made by visually inspecting the quality of the post-surface finishing for the aperture wall and the quality of that post-surface finishing was further checked using a scanning electron microscope. A test board was used in a series of designed experiments to evaluate the solder paste printing process. Findings - The results demonstrated that the length of the electropolishing time had a significant effect on the small stencil's aperture quality and the solder paste's stencil printing performance. In this study, the most effective electropolishing time was 100 s for a stencil thickness of 0.08 mm. The deposited solder paste thickness was significantly better for the enhanced laser-cut stencil with electropolishing compared to the conventional electroformed stencils. In this printing-focused work, print paste thickness measurements were also found to vary across different solder-mask definition methods of printed circuit board pad designs with no change in the size of the stencil aperture. The highest paste value transfer consistently occurred with solder-mask-defined pads, when an electropolished laser-cut stencil was used. Originality/value - Due to important improvements in the quality of the electropolished laser-cut stencil, and based on the results of this experiment, the electropolished laser-cut stencil is strongly recommended for the solder paste printing of fine-pitch and miniature components, especially in comparison to the typical laser-cut stencil. The advantages of implementing a 01005 chip component mass production assembly process include excellent solder paste release, increased solder volume, good manufacture-ability, fast turnaround time, and greater cost saving opportunities.