No abstract

Time-pressure dispensing has been widely employed in electronics packaging manufacturing, where the fluid (such as encapsulant, epoxy, adhesive, etc.) in a syringe is driven by pressurized air and delivered onto boards or substrates. In such a process, the flow rate dynamics is critical in controlling the amount of fluid dispensed, yet extremely difficult to represent due to its complex behavior. This paper presents the development of a model of the flow rate dynamics in time-pressure dispensing, taking into account both air compressibility and fluid inertia. Experiments have been conducted to verify the effectiveness of the model developed.

Micromixers have better efficiency in terms of both the timescale of chemical kinetics and diffusive transport compared to the conventional macro-mixers. The mixing efficiency in micromixers is an important performance indicator in mixers. This paper presents a numerical study of how the design of a micromixer along with the design of the mixing process affects the mixing efficiency. Specifically, two different types of cross-sections of the channel in micromixers, namely circular and rectangular cross-sections, together with the inlet angle of the channel, were studied. The process parameters, such as the inlet velocity of fluids and diffusion coefficient, were studied as well. The result shows that the circular cross-section can sustain a large pressure difference without undergoing any remarkable distortion and deformation, and it can achieve better performance. The result further indicates that the inlet velocity and diffusion coefficient have significant effects on mixing efficiency; specifically, the low inlet velocity and high diffusion coefficient value can lead to a better mixing performance. However, different input angles alone could not make the mixing efficiency change noticeably. In other words, the mixing performance of such micromixers relies more on the inlet velocity and diffusion coefficient than on the fluid flow angle in the inlet. Keywords Micromixers • COMSOL multiphysics • Pressure drop • Input angles • Mixing efficiency • Cross-section List of symbols A Cross-sectional area (m 2) C Concentration of reagents (mol/m 3) D Diffusion coefficient (m 2 /s) F Force (N) f Mole fraction (-) j Diffusion (mol/s m 2) I Identity matrix (-) L Microchannel length (m) M i Mixing efficiency (%) R Change in concentration rate (mol/s m 3) U Velocity (m/s) Density (kg/m 3) Viscosity (Pa s) Standard deviation (-)

To effectively control the dispensing process by which fluids are delivered onto substrates in electronics packaging, one of the key issues is to understand and characterize the flow behavior of the fluids being dispensed. However, this task has proven to be a demanding one as the fluids used for electronics packaging usually exhibit the time-dependent rheological behavior, which has not been well documented in the literature. In this paper, the characterization of time-dependent rheological behavior of fluids is studied. In particular, a model using the structural theory is proposed and applied to the characterization of the decay and recovery of fluid behavior, which are typically encountered in a dispensing process. Experiments are conducted to validate the proposed model.