Transient Numerical Modelling of the Pin-in-Paste Technology

The pin-in-paste technology is an advancing soldering technology for assembling complex electronic products, which include both surface-mounted and through-hole components. A computational fluid dynamics model was established to investigate the stencil printing step of this technology, where the hole-filling by the solder pastes is the most critical factor for acquiring reliable solder joints. The geometry of the transient numeric model included the printing squeegee, the stencil, and the through-holes of a printed circuit board with different geometries and arrangements. A two-phase fluid model (solder paste + air) was applied, utilizing the Volume of Fluid method (VoF). The rheological properties of the solder paste were addressed by an exhaustive viscosity model. It was found that the set of through-holes affected the flow-field and yielded a decrease in the hole-filling if they were arranged in parallel with the travelling direction of the printing squeegee. Similar disturbance on the flow-field was found for oblong-shaped through-holes if they were arranged in parallel with the squeegee movement. The findings imply that the arrangement of a set of through-holes and the orientation of oblong-shaped through-holes should be optimized even in the early design phase of electronic products and during the set of assembly processes. The soldering failures in pin-in-paste technology can be reduced by these early design-phase considerations, and the first-pass yield of electronic soldering technologies can be enhanced