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72 SMT Magazine • December 2014 Print and Inspection results The slit blade was tried first. Excessive paste was left on top of the stencil. The pressure was increased to 4 kgm, but the increased pressure resulted in the slit portion on top of the raised area being bent back at a lower angle without improving the residue paste left on the surface. For the notched and normal straight metal squeegee blades, 2 kgm of pressure was used. No excessive paste residue was left on the sten- cil in either case. Results showed that for all the blades there was paste residue at the edge of the step-up por- tion edges. This was caused by a slight lip at the edge of the step. The data showed that the set of apertures located closest to the step edge (25 mils, 635µm) produced solder bricks with the largest paste volume deviation. Table 1 shows the paste volume and paste volume standard deviation for the four blade types on one of the printed boards. The "measures volume" is the measured volume divided by the aperture volume times 100% giving the % volume of paste transferred. Ten boards were run on the printer. The next five boards were run in the solder paste inspec- tion machine for paste volume measurements. As seen in Table 1, the most consistent results are with the straight metal squeegee blade, which showed the lowest standard deviation. PrINTING TWO-LeveL PcbS IN ONe STeP WITH A 3d eLecTrOFOrm STeNcIL continues ArTiClE Figure 2: paste residue on slit squeegee blade (left); notch squeegee blade (center); metal straight squeegee blade (right). Table 1: Standard Deviation for 4 Blade Types.