To successfully print solder paste onto circuit boards using stencils, a properly controlled fill-in process must be followed by an efficient snap-off. Due to the non-Newtonian nature of solder paste, its flow behavior during a snap-off is highly complex and difficult to analyze. In this paper, solder paste is modeled as a dense suspension that flows with a slip at the wall boundary. Based on a visualization technique, the wall slip behavior is studied and its influence on the snap-off process is discussed. In particular, it is found that at higher temperatures, wall slip can be enhanced and the snap-off success rate can be improved. Based on the study of wall slip, practical methods for improving snap-off are proposed.

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