The invention relates to apparatus for dispensing flowable material, e.g., for dispensing solder paste for application through a stencil or screen to a substrate such as a circuit board.
Solder pads are often deposited in a desired pattern on a workpiece through a screen or a stencil. Typically a line of solder paste is manually dispensed from a tube onto the screen or stencil, and a squeegee blade is used to spread the solder paste across the stencil and cause it to fill up the holes in the screen or stencil. The solder paste tends to roll in front of the blade, which desirably causes mixing and shearing of the solder paste so as to attain desired viscosity to facilitate filling of the openings in the screen or stencil. The viscosity of the solder paste is also affected by its exposure to the atmosphere and by its temperature.
Fluid pressure affects the flow of material into stencil apertures. The fluid pressure of the solder paste is a function of the speed of the squeegee blade moving across the stencil surface and the angle that the squeegee blade makes with the stencil surface. The blade angle itself is dependent on the speed of the squeegee blade, and the downward preload (which can vary across the stencil surface) deflects the blade, also altering the fluid pressure. The fluid pressure of the solder paste is thus coupled to a number of dependent machine parameters.