Surface Mount Stencil Aperture Sizing Calculations for Fine Pitch Components
Maintain stencil aperture area ratios above 0.66 and aspect ratios above 1.5 to achieve reliable solder paste transfer efficiency on fine pitch components.
Squeegee Separation Speed
Dynamic Lift
Specific rates at which the stencil moves away from the printed circuit board after the paste stroke influence the definition and height of the solder deposits. Setting the squeegee separation speed correctly prevents the paste from being pulled back up with the stencil, which would cause peaked or misshapen prints. The speed is measured in millimeters per second and is a necessary part of the printer program.
Release Mechanics
Fine pitch apertures require a slower separation to allow the paste time to release from the narrow walls. If the movement is too fast, the vacuum created between the foil and the board can distort the solder bricks or cause them to stick to the stencil. A gradual lift ensures that the material stays on the copper pads.
For larger components, a faster speed may be used to increase the overall throughput of the assembly line.
Process Calibration
Optimal settings vary based on the viscosity of the solder paste and the ambient temperature of the factory. Automated systems often allow for a multi stage separation where the initial lift is slow followed by a faster move. The squeegee separation speed directly affects the yield of the printing process.