Non-Newtonian Flow Dynamics in Thin Prepreg Dielectric Micro-Channels
Non-Newtonian resin flow inside thin prepreg micro-channels governs void formation, trace displacement, and dielectric thickness stability during high-pressure lamination.
Dynamic Shear Stress
Rheological Measurement
Solder paste evaluation under high-speed squeegee movement requires analyzing the resistance to fluid deformation. Measuring dynamic shear stress helps process engineers predict how easily the paste will release from the stencil apertures during printing. This measurement focuses on the transition from a semi-solid to a flowing state.
Assembly Performance
Squeegees apply mechanical force to roll the solder paste across the stencil surface before filling the micro-vias and fine-pitch pads. The dynamic shear stress of the paste must drop rapidly under this applied force to allow complete aperture filling. Once the squeegee passes, the paste must recover its viscosity quickly to prevent slump and bridging.
Rheometers measure this property by rotating a plate or cone against a paste sample at controlled shear rates. If the shear stress is too high, the paste will not roll smoothly, leaving voids in the printed deposits. Conversely, if it is too low, the paste may bleed under the stencil and cause shorts between pads.
Inspection Limit
Solder paste inspection systems verify deposit volume and height after stencil release to catch defects before component placement. When the rheological behavior falls outside the limits, volume reproducibility declines. Regular testing prevents assembly failures on high-density interconnect boards.