The last post provided an introduction to the mechanism of rheology modification using fumed silica.  This post will expand on that discussion and provide more insights into the shear thinning and viscosity recovery process. Figure 1. Viscosity as a function of shear stress for a fumed silica filled epoxy resin.  Figure 1 clearly shows the viscosity decreases ... [Click to Continue...]

The last post introduced the concept of using fumed silica as a rheology modifier to tailor the dispensing of many types of adhesives used in electronic applications.  In the image in the top right in the figure above shows a die attach adhesives dispensed on a PBGA substrate.  After dispensing, the adhesives retain the “snowflake” or “asterisk” dispensing pattern.  The ... [Click to Continue...]

The last post described how to measure the viscosity-shear rate relationship using either a cone-and-plate or a parallel plate rheometer using a shear rate sweep.  An example is shown above.  This post covers how the viscosity profile influences the dispensing process and provides a short introduction to viscosity modifiers used to control the shear thinning and yield ... [Click to Continue...]

The last post described some of the potential pitfalls of the controlled stress measurements.  Controlled stress measurements are good if you require a precise yield point measurement.  An example would be if you were designing the yield point for a particular dispensing application.  The point-to-point creep test would allow the yield point to be measured accurately.  If on ... [Click to Continue...]