Publication: High speed solder paste stencil printing using computational fluid dynamics (cfd)
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Date
2023-07-01
Authors
Muhammad Irfan Bin Ishak
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Abstract
The demand for miniaturized consumer electronics and electric vehicles has driven significant growth in the Surface Mount Technology (SMT) market. SMT involves key steps like stencil printing, component placing, and reflow soldering. Stencil printing is particularly crucial, accounting for about 60% of assembly process faults. However, enhancing solder paste deposition alone is not enough; it's essential to reduce cycle time for PCB assemblies. To address this, high stencil printing speeds are used in bottleneck scenarios or when a single printer serves multiple assembly lines. In this paper, a computational fluid dynamics (CFD) model for high-speed stencil printing has been developed by integrating the volume of fluid method and the rheological properties of solder paste. The simulation investigates the impact of squeegee speed (70 mm/s, 95 mm/s, 120 mm/s, and 145 mm/s) and five different aperture types (Tantalum D, 1210, MELF, SOT, and 0603) on the volume transfer efficiency of solder paste. The CFD simulation model was developed using ANSYS Fluent 22, and its accuracy was validated against experimental results obtained from Celestica Malaysia. The volume filled by the solder paste at different aperture size according to the simulation results range from 0.339758 mm3 to 0.75949334 mm3 for large aperture size while at small aperture size the volume range from 0.080432 mm3 to 0.16073 mm3. However, the experimental results demonstrated greater variations in deposition volumes between speeds ranging from 0.320095 mm3 to 0.884774467 mm3 at large aperture and 0.063049 mm3 to 0.170654 mm3 at small aperture size. In terms of volume transfer efficiency, the simulation result shows that SOT aperture recorded the highest efficiency among all aperture ranging from 97.3 % to 98.0 % while the experiment result shows that 1210 aperture recorded the highest efficiency ranging from 97.6% to 129.3%. The simulation findings suggest that an optimal speed of 70 mm/s is suitable for all types of apertures. In contrast, experimental results indicate that a speed of 145 mm/s is optimal for all aperture types. The simulation research reveals that larger apertures generally exhibit higher volume transfer efficiencies, whereas smaller apertures show slightly lower efficiencies. The findings from experiment introduce similar pattern with simulation although the result is quite complex.