An investigation into the printing characteristics and mechanical dynamics of advanced squeegee mechanisms

The new breed of solder paste deposition systems, such as the DEK ProFlow, incorporate a contained solder paste chamber enabling independent control of machine parameters, pressure, down force and print speed. Previous work by Ekere et al. (1994) and Monaghan et al. (1991-2) have modelled conventional squeegee systems, but only part of this work is applicable to the new mechanism. Practical experimentation has been employed, both to gain an appreciation of the printing characteristics in general and to serve as reference for purely analytical models. Flow visualisation experiments have provided useful indications of flow dynamics within the print head, highlighting dominant flow patterns, velocity profiles and other phenomena such as evidence of air entrapment or cavitation. The FIDAP CFD package is used to perform detailed analysis, providing measures of data not practically obtainable through physical measurement. Pressure, shear and temperature profiles are obtained for a range of operating conditions and their influence on ink/solder paste transfer can be evaluated, leading to the identification of operational limits. Results from the FIDAP model compare very well with the experimental work and have identified the critical areas of the squeegee mechanism. This analysis is now being used to refine the process, to extend its application to lower viscosity materials and to incorporate simpler control systems than have been found to be necessary with conventional squeegee mechanisms (Lofti and Howarth, 1998; Zhuang et al., 1997)