The Future of Solder Paste Printing for SMT Reflow Soldering

Abstract

The use of fine‐pitch SMD devices has increased the need for accurate and consistent solder paste deposits for reflow soldering. Continued miniaturisation in PCB and SMD lead sizes is presenting the user, paste supplier and print equipment manufacturer with paste printing challenges. Most of these challenges are user‐driven, and are generally met by enhancing associated print equipment and solder paste materials. Recent developments in fine‐particle pastes, water‐soluble and no‐clean pastes are among the improvements in materials. Vision‐assisted stencil aperture and PCB pad alignment, the use of metal squeegees and new stencil fabrication methods are among the latest developments on the equipment side. Printing tests have shown that there is a physical limit for the solder paste printing process, which is defined partly by the nature of the stencil fabrication process, the physical forces and the stencil's ability to meter a precise volume of paste. The challenge as SMD lead sizes decrease is to improve the printing process to match component lead sizes. There is a fear that we are now operating at the very limits of the solder paste printing process. To meet future component developments, there is a need to develop alternative printing processes for solder reflow.