Non-Newtonian numerical modelling of solder paste viscosity measurement

Abstract

Purpose The purpose of this paper is to present the establishment of a computational fluid dynamics model for investigating different non-Newtonian rheological models of solder pastes by simulating solder paste viscosity measurement. A combined material model was established which can follow the measured, apparent viscosity values with lower error. Design/methodology/approach The model included a parallel plate arrangement of rheometers. The diameter of the plate was 50 mm, whereas the gap between the plates was 0.5 mm. Only one quarter of the plate was modelled to enable using fine enough mesh, while keeping the calculation time low. Non-Newtonian properties were set using user defined function in Ansys, based on the Cross and Carreau–Yasuda material models. The viscosity values predicted by the mathematical models were compared to measured viscosity values of different types of solder pastes. Findings It was found that the Cross model predicts the apparent viscosity with a relatively high error (even approximately 50 per cent) at lower shear rates, whereas the Carerau–Yasuda model has higher errors at higher shear rates. The application of the proposed, combined model can result in a much lower error in the apparent viscosity between the calculated and measured viscosity values. Originality/value The error of Cross and Carreau–Yasuda material models has not been investigated yet in details. The proposed, combined material model can be applied for subsequent simulations via the described UDF, e.g. in the numerical modelling of the stencil printing. This can result in a more accurate modelling of the stencil printing process, which is inevitable considering the printing of solder paste for today fine-pitch, small size components.

Transient Numerical Modelling of the Pin-in-Paste Technology

“…The rheological properties of the solder paste were described by the Al-Ma'aiteh model (3) [19], with parameters valid for a Type-4 solder paste (particle size range is 20-38 µm).…”

“…A transient 3D CFD model was created based on the Volume of Fluid (VOF) method, and the non-Newtonian fluid properties were addressed by Cross's viscosity model [18]. The results of their model match the experimental measurements with an acceptable error at different aperture sizes, though the error might be reduced further by using Al-Ma'aiteh's viscosity model [19].…”