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40 SMT Magazine • May 2015 After the basic parameters had been identi- fied, the project continued to optimize the sol- der paste printing process by also investigating other important parameters. Figure 9 depicts the results of varying the separation speed be- tween the board and the stencil after the print- ing process is completed. A clear optimum was identified for the project setup of 2 mm/s sepa- ration speed. Another important parameter that was in- vestigated was how the board support affected the printing quality. In production both fixed and variable board support were used for flex- ibility and cost reasons. The reference board was set up with both types and the separation speed was varied in order to see if there was a significant difference between the different production methods. The results are depicted in Figure 10 and clearly show that the spread between maximum and minimum failure rates has about a 10% difference in favor of a fixed board support. SOLDER PaSTE PRINTING: QUaLITy aSSURaNCE mETHODOLOGy continues Feature figure 9: results for how the misprints vary with the separation speed. figure 10: results for how the spread of the solder paste deposit varies with separation speed and type of board support (40 mm/s print speed, 1.2 bar internal pressure, 2.6 kg squeegee pressure and ±20% acceptance level for the volume).