Viscosity Transformation
Rheological behavior relies on the reduction of viscosity as the material is subjected to mechanical force. During the printing cycle, flux vehicle shear thinning allows the paste to flow easily through fine stencil apertures. The liquid carrier contains long-chain molecules that align under the pressure of the squeegee.
This alignment lowers the internal resistance to movement.
Printing Mechanism
Transfer efficiency improves when the paste transitions from a thick gel to a fluid state during the stroke. Once the squeegee passes, flux vehicle shear thinning ceases and the material regains its original high viscosity almost instantly. This rapid recovery prevents the paste from bleeding under the stencil or slumping on the pad.
If the recovery is too slow, the print definition is lost and bridging becomes likely. Mechanical energy from the printer head must be sufficient to trigger the change without damaging the delicate chemical bonds.
Material Stability
Consistent temperature prevents the flux from becoming too thin before the stroke begins. Variations in flux vehicle shear thinning can lead to inconsistent deposit volumes across the panel. Modern formulations use synthetic resins to ensure the thinning effect is repeatable.
Proper paste handling and storage preserve these rheological properties.
