Optimization of solder paste printability with laser inspection technique

This paper describes an evaluation technique for solder paste printability using a solder paste inspection system and optimization of printing parameters. In a Surface Mount Assembly (SMA), it is very important to evaluate printability of solder paste precisely, because printability of solder paste directly influences reflow soldering quality. We established quite reliable inspection criteria for print quantity of solder paste. So it was found that about 90% of reflow soldering defects could be reduced by prevention of printing defects. Furthermore, since package types have been varied in a SMA, high soldering quality demands stable printability for all patterns. This paper presents a printability evaluation adopted procedure based on the quality engineering (TAGUCHI method). As a result of optimizing squeegee shape and printer condition by this evaluation method, printability was improved better than 20% in the production process. And optimization of solder paste and stencil added to printer condition resulted in good printability for 0.3 mm pitch patterns on the optimum condition.