Investigating the Effect of Viscosity Models on the Stencil Printing by Numerical Modelling

In this paper, the effect of different viscosity models on the numerical results of stencil printing modelling was addressed. The numerical model was established by defining the geometry of the printing squeegee, the stencil, and the shape of the rolling solder paste. The squeegee had a 53 degrees attack angle, which was determined by prior measurements, and the blade height was 20 mm. The output parameters of the model included the shear rate distribution and velocity field within the rolling solder paste, and the pressure profile on the stencil. The material properties of the solder paste were set by measuring the rheological behaviour of Type3 (particle size: 20-45 mu m), Type4 (particle size: 20-38 mu m), Type5 (particle size: 15-25 mu m) solder pastes and by fitting viscosity models onto the measurement results. Two different material models were compared, the Cross and the Carreau-Yasuda models, where the effect of the different models on the numerical results was evaluated The results showed a significant difference in the pressure during stencil printing between the cases using the viscosity of solder pastes in initial state (Cross model) and in steady state (Carreu-Yasuda model). The difference was about 25% in the case of Type-3, Type-4, and Type-5 solder pastes respectively. These differences proved that appropriate material models should be used in the numerical models of the stencil printing, to be able to apply that in early-stage prediction in the concept of Industry 4.0.