Surface Mount Technology (SMT) involves the
printing of solder paste on to printed circuit board (PCB)
interconnection pads prior to component placement and
reflow soldering. This paper focuses on the solder paste
deposition process. With an approximated cause ratio of
50 – 70% of post assembly defects, solder paste
deposition represents the most significant cause initiator
of the three sub-processes. Paradigmatic cause models,
and associated design rules and effects data are
extrapolated from academic and industrial literature and
formulated into physical models that identify and
integrate the process into three discrete solder paste
deposition events - i.e. (i) stencil / PCB alignment, (ii)
print stroke / aperture filling and (iii) stencil separation /
paste transfer. The project’s industrial partners are
producers of safety-critical products and have recognised
the in-service reliability benefits of electro-mechanical
interface elimination when multiple smaller circuit
designs are assimilated into one larger Printed Circuit
Assembly (PCA). However, increased solder paste
deposition related defect rates have been reported with
larger PCAs and therefore, print process physical models
need to account for size related phenomena
