A realtime process control system for solder paste stencil printing

The goal of stencil printing solder paste in surface mount printed circuit board (PCB) assembly is to apply an accurate and repeatable volume of solder paste at precise locations. The causes for a substantial proportion of the problems associated with PCB assembly can be traced back to the solder paste printing process. Control of the stencil printing process has become significantly more important over the years due to the introduction of ultra fine pitch technologies. Three important issues have to be considered in the stencil printing process to obtain a good yield. They are: (i) setting up the process in an efficient way, (ii) monitoring and controlling the process when necessary and (iii) troubleshooting the process when a defect occurs. This research focused on the design and development of software systems that could perform the above-mentioned functions. Three systems were developed in the research discussed in this paper. They are the process advisor, the intelligent control system (or the ICS) and the diagnosis system. The process advisor (the first system) provides for the setup of the stencil printing process. It helps the user to set up a new as well as an existing application. The process advisor also helps the user in estimating the volume of solder paste that would be deposited for a given stencil thickness and aperture dimensions. The ICS (the second system) was developed to control the stencil printing process in real-time. The diagnosis system (the third system) is used to troubleshoot the process, if needed.