Publication: Effect of aperture filling parameters of solder paste on stencil printing process
Date
2020-05-01
Authors
Rusdi, Mohd Syakirin
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Abstract
The stage that causes major concern compared to the other stages in Surface Mount Technology (SMT) is known as the stencil printing stage. The study of pre-stencil printing is performed using simulation software to minimize fabrication costs and time. Therefore, this research focuses on the 3D simulation of aperture filling using lead-free solder during the stencil printing process via the usage of CFD simulation. The aperture filling of a solder paste at a varying squeegee pressure, squeegee speed and separation speed were studied using a commercial solder paste printer (DEK 265), and a 3D solder paste scanner (KOH YOUNG Aspire 2). A PCB that measures at 183 mm × 133 mm with 2 mm thickness was used in the experiment. Optimization of the process was done via Response Surface Methodology (RSM) where optimum solder filling volume, solder paste height and solder area coverage were obtained during the printing process. The optimum values suggested by RSM were squeegee pressure = 0.69 MPa, squeegee speed = 35 mm/s, and separation speed = 0.498 mm/s, and the optimal responses were volume = 0.783 mm3, height = 0.121 mm, and area = 6.481 mm2. The optimized parameters then were used as the validating data to carry out other extending studies. Anton Parr Physica MCR 301 Rotary Rheometer machine was used to conduct experiments on solder paste rheology (shear rate and viscosity). Parallel-plate (PP) and Cone-plate (CP) spindle were used to carry out five different tests consisting of different spindle type and setting. The volume filled under different squeegee speeds found that PP of 0.5mm gap exhibited the lowest average discrepancy value at 5.4% while CP1° and PP 0.5mm at 11.6% for different aperture sizes. The average discrepancy was the comparison between experiments and simulations results. Then, the studies were further extended to simulate the stencil printing process by using ANSYS Fluent 19. VOF method with Cross viscosity model was selected to undergo the numerical simulation. The volume filled by the solder paste at different aperture size according to the experiment and simulation results were compared. For different aperture size, all the results showed a similar trend with an average discrepancy of 11.6%. Furthermore, another study was added to investigate the stencil printing process efficiency at different squeegee speed and aperture size. The performance of the solder pastes for stencil printing is then compared with different lead-free solder paste (SAC105, SAC307, SAC305, SAC405 and SN100C). Leaded solder paste (Sn62Pb36Ag2) was also included in the analysis to demonstrate how well the lead-free solder pastes perform in comparison to the leaded solder paste. The research results were analyzed by comparing the effects of different angles, stencil thickness and aperture size. Results showed that the SAC305 gives the best result compared to other lead-free solder pastes and also leaded solder paste.