Rheological Shift
Rheological monitoring tracks the flow behavior of complex fluids and solder pastes exposed to continuous mechanical shear and thermal fluctuations. Exposure to these factors can lead to viscosity drift, which alters the printability and dispensing accuracy of the material. This shift manifests as a progressive thinning or thickening of the fluid over time.
It can prevent the paste from rolling properly or cause it to slump after deposition.
Print Performance
Changes in paste consistency affect how easily the material fills the stencil apertures and how cleanly it releases. When viscosity drift occurs during a long production run, the deposit heights can become inconsistent, causing volume variations. Thickened paste may fail to fill fine-pitch apertures, resulting in insufficient joints after reflow.
Conversely, thinned paste can bleed under the stencil and cause bridging between adjacent pads. This breakdown in paste structure also increases the risk of component shifting during board transport before they enter the oven.
Environmental Control
Maintaining a stable production environment is the primary method for preventing fluid behavior variations on the line. Since viscosity drift is driven by ambient temperature and humidity, stencil printers are often equipped with climate control units. Monitoring these environmental factors ensures consistent assembly quality.
