Quantifying Shear Degradation and Fiber Breakdown in Mold Tooling
Quantifying shear rates and gate geometry limits prevents fiber length attrition, tool surface erosion, and mechanical strength loss in molded composite parts.
Shear Rate Calculation
Meaning
Mathematical methods for determining the velocity gradient within a flowing fluid provide the data needed to predict the behavior of solder paste and adhesives. The shear rate calculation is used to select the correct nozzle size and pressure for dispensing operations in electronic assembly. This value influences how the viscosity of a non-newtonian fluid changes during application.
Fluid Dynamics
Flow through a narrow tube or a stencil aperture creates a variation in speed from the wall to the center. Performing a shear rate calculation allows engineers to ensure that the paste remains fluid enough to fill the opening but thick enough to hold its shape. The geometry of the dispensing needle is a primary input for this formula.
Solder Application
Automated systems use real time feedback to adjust the speed of the print head based on the calculated values. The shear rate calculation helps in avoiding defects like slumping or bridging between fine pitch pads on a circuit board. Maintaining the correct flow profile is essential for achieving a consistent solder volume across the entire panel.
Viscosity Limit
Measurements of fluid resistance are taken at different speeds to create a rheology profile. A shear rate calculation determines if the material is being stressed beyond its physical limits during a high speed cycle. If the rate is too high the chemical structure of the adhesive might break down and lead to a permanent loss of adhesion.