Investigating the effect of squeegee attack angle on the solder paste pressure during stencil printing

In this paper, the effect of the squeegee attack angle on pressure distribution along the stencil surface during the stroke has been investigated. At first, a Finite Element Method (FEM) model has been developed to determine the true attack angle of the squeegee for given printing forces. The model has also been validated with experiments. As a next step, a Finite Volume Model (FVM) has been developed to calculate the pressure distribution along the surface of the stencil, applying non- Newtonian fluid properties for the solder paste. With the aid of this model, the pressure distribution has been determined for unloaded squeegees (attack angle is 60°) as well as for loaded squeegees, where a printing force of 0.32 N/mm resulted in an attack angle of 55°. The results showed that there was a noticeable difference between the pressure distributions, ca. 16 % in average for a change 5° in the angle. Finally, pressure distributions were determined at attack angles of 45, 50, 55, 60°.