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44 SMT Magazine • May 2015 it is possible to implement status-based main- tenance. The reference boards can also be used dur- ing verification and troubleshooting scenarios. A typical troubleshooting example is when there is a quality deviation during the manufac- turing of a product. The methodology can then be used to verify if the printing and inspection process has changed or if the issues are related more to the product design. Once the issues have been identified it often proves useful to use classical 6-sigma methods like Ichikawa and kaizen events to identify and remedy the root- cause of the quality deviation. For the implementation of the process veri- fication, the following guideline (Figure 17) can be used in production in order to increase the process control and ensure that the process does not deviate outside the set limits. IV. Conclusion This paper has presented a methodology for quality assurance of the solder paste print- ing process and its adjacent inspection process. The methodology makes it possible to have immediate feedback from the inspection pro- cess in order to control the printing process. The methodology utilizes reference boards and Figure 15: Box plots of solder paste volume distributions (mm3). Volume 11 is the deposit adjacent to the step edge and volume 1r is the deposit furthest away. all distributions above are from 0.25 x 0.25 mm square stencil apertures. 1 mil step (upper left), 2 mil step (upper right), 4 mil step (lower left) and 5 mil step (lower right). Feature SOLDER PaSTE PRINTING: QUaLITy aSSURaNCE mETHODOLOGy continues