Silica Filled Resin Viscosity Minimization during High Pressure Lamination Ramps
Silica-filled resin viscosity minimization requires synchronizing heating ramps with press pressure timing to ensure complete void encapsulation without core shift.
Thixotropic Shear Thinning
Fluid Behavior
A physical property of solder paste describes the temporary drop in viscosity that occurs when the paste is subjected to mechanical shear during the printing stroke. Stencil printing processes rely on thixotropic shear thinning to allow high-viscosity paste to flow like a liquid through the small apertures. This property ensures that the paste flows smoothly under the squeegee and into the stencil openings.
Paste Release
Once the squeegee passes and the shear force is removed, the paste must quickly return to its high-viscosity state. This recovery allows the printed brick to stand on the pad without slumping or running before it enters the reflow oven. This dynamic transition determines the quality of the printed pattern and reduces the rate of bridging defects.
Aperture Design
Designers of fine-pitch boards must choose stencils and paste formulations that utilize this property to maximize transfer efficiency. The behavior must be matched to the aperture dimensions to ensure that the paste leaves the metal foil without leaving residue. This mechanical response is a critical factor in the success of modern surface mount assembly lines.
If the paste is too thick, it will clog the holes, while paste that is too thin will spread and cause short circuits.