Deposition Rate
Lateral speed at which the metal or polyurethane blade moves across the stencil surface dictates the filling time for each aperture. Squeegee velocity is a primary variable in the stencil printing process that influences the volume and consistency of the solder paste. It must be synchronized with the paste rheology to ensure a clean wipe of the stencil top.
High speeds are used for high-volume production, while lower speeds are reserved for complex, fine-pitch assemblies.
Hydraulic Pressure
Downward force and horizontal movement combine to create a hydraulic injection effect. As squeegee velocity increases, the pressure within the solder paste bead rises, forcing the material into the cavities. If the blade moves too fast, the paste may skip over the apertures, leading to insufficient solder.
Conversely, moving too slowly can cause the paste to bleed under the stencil or stick to the blade. Precise control of the motor prevents variations in the print height across the entire board surface.
Throughput Limit
Modern printing machines allow for different speeds in the forward and reverse directions to optimize the cycle time. Squeegee velocity is limited by the maximum shear rate the paste can withstand without losing its structure. Typical values range from 20 to 150 millimeters per second depending on the alloy and flux type.
Consistency in this parameter is essential for maintaining a stable manufacturing process.
