The last post described the controlled stress experiment.  In the image above, a stress was applied to the sample and the deformation as a function of time (strain-rate) was measured at steady state.  There are two measurement modes for controlled stress curves: Manual: a series of creep measurements (which was used above) Automatic: Flow or viscometry mode in a ... [Click to Continue...]

This post will cover the interpretation of a typical controlled stress flow curve for a highly filled uncured material.  In many electronic applications, the adhesive or coating is applied to the substrate using dispensing equipment where the filled material is in a syringe and either air pressure or an auger is used to flow the material through a small needle onto the ... [Click to Continue...]

Rheometers are used to determine the viscosity by measuring the stress at a known shear-rate or measuring the shear rate at a known stress.  There are two types of torsional rheometers: Controlled strain (most common) Controlled stress In the case of the strain controlled rotational rheometer, a typical configuration is shown in the following figure: In this ... [Click to Continue...]

The rheological properties of polymers used in electronic packaging applications spans a wide range of fluid types and viscosity ranges.  In the uncured state, many adhesives, coatings, mold compounds, and underfills have interesting rheological behavior.  Many of these types of materials are highly filled to achieve the desired mechanical properties such as low coefficient of ... [Click to Continue...]