Description: The Screen Printing process deposits solder paste onto a PCB by means of a stencil with apertures for each pad to be soldered. As a squeegee moves over the stencil (screen), solder paste is pressed through the apertures to the lands on the circuit board. Screen Printing is one of two option for Solder Application, the other being Solder Jetting (see Solder Jetting). Screen Printing is much more common than Solder Jetting and so is ON by default.

Screen Printing Cycle Time is a sum of the time to load the PCB into the machine from the input conveyor, move the PCB to the lock position in the machine and clamp it down, look at the fiducials on the PCB and the corresponding ones on the stencil, make a theta adjustment to the rails to compensate for the fiducial alignment, raise the PCB to the stencil, lower the squeegee to the stencil and swipe across the PCB width to deposit paste, slowly release the PCB from the stencil, lower the screen printer rail, unload the PCB from the screen printer and output rail, and clean the stencil in the screen printer machine.

// Screen printer cycle time is a machine specification. It includes all cycle time to screen print PCB except for fiducial, print & cleaning time. It captures load, raise, adjust theta time.

// Time to look at alignment fiducials or apertures on both PCB and stencil for alignment purposes.

// Time to move squeegee across stencil, therefore depositing solder paste through stencil apertures onto PCB.

// Stencil cleaning time. Not necessarily performed every time.

PSO: Fiducial Quantity (Number of fiducials to be inspected to ensure proper alignment of PCB to stencil.)

PSO: Stencil Clean Frequency (Number of PCBs printed prior to stencil clean.)