Rheological Evaluation
A rheological test method measures the time-dependent recovery of structured fluids after experiencing high shear forces. The 3itt protocol executes three sequential shear phases to simulate stencil printing conditions on solder paste. Rheometers apply a high-shear destructive phase followed by a low-shear recovery period to capture this rebuild.
Squeegee motion correlates directly with the high-shear phase, whereas the subsequent rest state on the print pad represents the recovery phase. Continuous monitoring of the third phase reveals how quickly the paste rebuilds its internal network.
Structural Recovery
Time-resolved viscosity measurements capture the rate of structural rebuild after stencil squeeze-out. Solder paste relies on the 3itt protocol to ensure the material thins under the squeegee but regains structural body immediately after aperture exit. If the recovery is too slow, the print suffers from slump.
When the recovery is too rapid, the paste fails to wet the pad properly or blocks the stencil.
Defect Correlation
Automated optical inspection verifies print height and pad coverage to link lab measurements with factory performance. Solder paste that exhibits insufficient recovery during the 3itt protocol generates bridging defects between fine-pitch pads. Insufficient viscosity in the final phase allows the deposit to spread laterally under its own weight.
Regular rheological verification reduces line stop occurrences on high-speed assembly lines.
