Squeegee Velocity
Deposition of solder paste through a stencil requires a controlled squeegee movement across the stencil surface to fill the apertures uniformly. Setting the correct print speed ensures that the squeegee generates a rolling wave of solder paste ahead of the blade. This roll pushes the paste into the openings of the stencil, filling them from the bottom up.
Squeegee velocities typically range between twenty and one hundred and fifty millimeters per second, depending on the viscosity of the paste and the aperture sizes. If the speed is too low, the cycle time of the production line increases without any benefit to print quality. If the speed is too high, the paste does not have enough time to flow into the small apertures, resulting in incomplete prints and insufficient solder volume.
Paste Behavior
Solder paste behaves as a thixotropic material, meaning its viscosity decreases when shear stress is applied. The rolling action generated by the squeegee provides this shear force, making the paste fluid enough to fill the apertures. Fast squeegee movements apply more shear, but if the velocity exceeds the capability of the paste, the roll becomes turbulent and uneven.
Production Throughput
Optimizing this parameter requires balancing the stencil cleaning cycle and the overall line beat rate. High-speed printing must be matched with appropriate squeegee pressure to ensure the stencil is wiped clean during each stroke. This balance maintains high output without sacrificing print quality.
