Screen printing apparatus and method including a printing screen having a wave guide driven to induce ultrasonic vibrations in the screen

A printing screen for printing deposits of a print medium onto workpieces,

• the printing screen comprising a sheet in which a pattern of printing apertures are formed to allow for printing of a pattern of deposits onto a workpiece, wherein the sheet can be mounted within a supporting frame, the frame extending around the periphery of the sheet, and
• a waveguide which can be driven to induce an ultrasonic vibration in the sheet, wherein the waveguide comprises an elongate body at a surface of the sheet which surrounds the pattern of printing apertures and is disposed inwardly of the supporting frame, and an actuator node to which an ultrasonic actuator may be coupled,
• wherein the waveguide is a single, continuous element which includes the actuator node in the path of the elongate body.