Design guidelines for ultra fine pitch solder paste printing.

Competitive pressures to reduce equipment size and to maximise circuit performance have resulted in new challenges for ultra fine pitch solder paste printing. The ratio between the open area of the stencil aperture and the area of the aperture wall (AAR) significantly affect the quality of solder paste printing. The AARs for today’s ultra fine pitch components printing are below 0.5, and much lower than that for coarser pitch components such as SOIC (above 1.5). To over come this ratio reduction and to improve printing performance through ultra fine pitch apertures, all aspects of the print process required a great deal of attention to achieve optimisation. The design guidelines for ultra fine pitch solder paste printing are considered, and the effect of stencil type, stencil wall aperture finish, aperture design and paste choice on printing investigated.