The impact of stencil aperture design for next generation ultra-fine pitch printing

Miniaturisation is pushing the stencil printing process. As features become smaller, solder paste transfer efficiency is becoming more critical. In latest research work, actual paste deposit volumes and transfer efficiency have been monitored and compared for both square and round apertures with area ratio's ranging from 0.20 thru to 1.35. This covers apertures sizes of between 100 and 550 microns in a nominal 100 micron thick stencil foil. In addition, the effect of ultrasonically activated squeegees (ProActiv) has been assessed as part of the same experiment. A further comparison has also been made between type 4 and type 4.5 solder paste aswell. The data presented here will help provide guidelines for stencil aperture designs and strategies for ultra-fille pitch components such as 0.3CSP's.