Rheology, thick-film viscosity

Thick film preparation and applications involve flow phenomena. The control of rheological behavior of thick-fihn inks is important for the screen printing operation. Print thickness and print resolution are directly affected by paste rheology. Paste viscosity is used as a quality control tool by circuit manufacturers. For the paste manufacturer, understanding the correlation between the paste formulation and rheology is important for reproducible product manufacturing and new product development. 

The 5P4E presents both a high viscosity and an important pressure viscosity coefficient so it can form sufficiently thick films in the contact to obtain spectra with a good signal to noise ratio. Its rheological properties at 25°C and 50 C are given in Table 2. 

An effective viscosity rp has been introduced in the Reynolds equation to describe the non-Newtonian lubricant properties. Ignoring the variation of viscosity across the film thickness, one may evaluate the effective viscosity via the following rheological model that considers a possible shearthinning effect [19],... 

Thin solid films of polymeric materials used in various microelectronic applications are usually commercially produced the spin coating deposition (SCD) process. This paper reports on a comprehensive theoretical study of the fundamental physical mechanisms of polymer thin film formation onto substrates by the SCD process. A mathematical model was used to predict the film thickness and film thickness uniformity as well as the effects of rheological properties, solvent evaporation, substrate surface topography and planarization phenomena. A theoretical expression is shown to provide a universal dimensionless correlation of dry film thickness data in terms of initial viscosity, angular speed, initial volume dispensed, time and two solvent evaporation parameters. 

The theoretical result of Equation 5 provides a universal dimensionless expression for the correlation of experimental dry film thickness data in terms of the four variables initial viscosity, angular speed, initial volume dispensed or film thickness and time and two solvent evaporation parameters. Note that Equation 5 reduces to Equation 3 when there is no solvent evaporation, i.e. OL = o. Also, note the forms of the predicted H dependencies on the four variables, at large dimensionless number t. The parameter i can be determined from Equation 1, estimated from Equation 2 or obtained by a fit of data. The rheological and evaporation parameter a can be obtained from a fit of H (to),... 

In the evaluation of viscosity by tilting the container, panel members indicated that their judgments were based on the rate at which each sample flowed down the side of the beaker, that is, viscosity was judged from the behavior of the apex of the film which flowed down the side of the container when it was first tilted. The major variable was the thickness of the film flowing down the side and its rate of flow, that is, viscosity evaluation by tilting the container depends on the shear rate of (10 —100 s ) developed at a shear stress (6-60 Pa) (Figure 7-4) which varies with the rheological properties of the sample. 

Coalescence of the droplets can only happen if it is possible to break up the thin film. This occurs if surface waves are formed or if external forces are applied. At a certain point, the thickness will fall below the critical value and coalescence occurs (17, 18). The influence of this step is given by the interfacial and surface rheological properties such as interface elasticity, interface viscosity, type of surfactant, etc. (19-25). 

When the film thickness h is sufficiently large, one observes the rheological behavior typical of bulk fluids [201,202]. Flow can be described by the bulk viscosity pg and a shp length 5 at each wall. As in simulations, typical values of S are comparable to molecular dimensions and would be irrelevant at the macroscopic scale. However, a few systems show extremely large slip lengths, particularly at high shear rates [203,204]. 

We have recently reported (6, 7) that those surfactant formulations which yield good oil recovery exhibit both low interfacial tensions and low interfacial viscosities. Our experiments have shown that surfactant formulations which ensure low interfacial viscosity will promote the coalescence of oil droplets and thereby decrease the emulsion stability, thus enhancing the formation of a continuous oil bank. It has been demonstrated that the requirements for emulsion stability are the presence of an interfacial film of high viscosity and a film of considerable thickness. We have observed that the surfactant concentration which minimizes the interfacial tension may not simultaneously minimize the interfacial viscosity. Hence, our results indicate both interfacial tension and interfacial rheology must be considered in selecting surfactant formulations for tertiary oil recovery. 

Adsorbed protein film properties thickness, rheology (viscosity, cohesiveness, elasticity), net charge and its distribution, degree of hydration... 

Flack and co-workers developed a complex model that included the effects of evaporation on the rheological properties of the viscous fluid. Their work established the idea that only fluid viscosity, angular speed, and evaporative effects are important in determining the final film thickness. Dispense volume, dispense rate, and other factors seem not to be particularly critical in determining the final film thickness as long as the wafer is spun for a sufficiently long time. Yet, in spite of evaporative effects, the final thickness /if of the fluid can be fairly well predicted with an inverse power law relationship [Eq. (11.13)], where C is a constant depending on the viscosity and contains the effects of viscous forces. 

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