Numerical investigation on the effect of the printing force and squeegee geometry on stencil printing

The effects of printing force and different squeegee geometries on the process of stencil printing were investigated in this paper. Numerical models were established, which included squeegees with different geometries (different overhang sizes of 6, 15, 20, 25 mm) and took the printing force (specific value 0.3 N/mm) into account by using loaded squeegee angles instead of unloaded ones. The flow behaviour of the solder paste was captured by utilising non-Newtonian fluid parameters, which were determined by fitting a curve to the prior measurement results of a lead-free solder paste (particle size 20-38 mu m). The effect of different squeegee geometries was characterised by calculating the pressure distribution over the stencil. Results showed a significant difference in the pressure using the unloaded and the loaded squeegee geometries. In the case of unloaded squeegee angle of 60 degrees, the increase was (similar to)22%, (similar to)45% and (similar to)90% for overhang sizes of 15, 20, 25 mm respectively by applying loaded squeegees. In the case of unloaded squeegee angle of 45 degrees, the increase in pressure was even more noticeable; (similar to)45%, (similar to)102% and (similar to)250% for the overhang sizes of 15, 20, 25 mm respectively. This increase in pressure implies that neglecting the printing force and squeegee geometries in numerical investigation of the stencil printing process results in significant calculation errors.