The explosion of SMT and highly-density packages has resulted in more complex and higher density board designs in order to incorporate more features into products while reducing overall package size. This has, in tum, created major challenges for the surface mount manufacturing process, particularly in solder screen printing, component placement, and reflow soldering. Investigation into these areas will contribute to our understanding of the origin of post reflow defects in surface mount assembly and improvement in product quality. The thesis particularly explores empirically the relationship between screen printed paste deposit, the final joint geometry and the fluxing behaviour within the reflowing solder. The thesis also demonstrates the effect of modified screen printing parameters and the lead geometry.