The behaviour of solder pastes in stencil printing with electropolishing process

Abstract

PurposeThe 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/approachDuring 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.FindingsThe 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/valueDue 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.