An SMT screen printer 100 is disclosed herein. In a described embodiment, the screen printer 100 comprises: i) a stencil 110 with a plurality of apertures; ii) a paste dispenser arranged to dispense a paste material through the plurality of apertures of the stencil to form a print pattern of the stencil to form a print pattern of the paste material on an electronic device; iii) an image capturing device in the form of a fiducial camera 176 arranged to capture at least one image of the plurality of apertures 114 of the stencil 110; iv) a processor 180 arranged to select which of the apertures 114 require cleaning based on the at least one captured image; and v) a cleaning device 138 arranged to clean the selected apertures 114. A method of cleaning a stencil 110 of an SMT screen printer 100 is also disclosed.