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54 SMT Magazine • February 2014 fitted with a ProActiv ultrasonic squeegee sys- tem was used to print a test pattern through an industry standard 100-micron-thick laser-cut stainless steel stencil. Printed deposits were mea- sured for volume using a CyberOptics SE500 fit- ted with a micropad sensor. The test substrates used throughout the investigation were a set of numbered 1.6 mm thick, FR-4 boards. During the print cycle the test substrates were secured in place with a dedicated vacuum tooling plate. The same squeegee assembly together with 170 mm metal blades, with 15 mm overhang, were used for all testing in both the standard and activated print mode. For a standard print process the ultrasonic capability was simply dis- abled. Prior to each test run the squeegees were automatically calibrated. Industry standard lead-free type 4 and type 4.5 solder pastes from a single solder paste ven- dor were used for printing. Test Substrate & Stencil Design An example of the test substrate used is shown in Figure 4. The simple design contains a range of industry standard components. How- ever, for the purpose of this experiment, focus was placed on the four area arrays highlighted in Figure 4. These arrays consist of 0.5 mm di- ameter pads on a 1 mm pitch. With the cor- responding stencil design, a combination of square and circular apertures was incorporated with reducing aperture sizes, ranging between 100 microns and 550 microns (relating to area ratios of between 0.25 and 1.375). The outline of one of these arrays is shown in Figure 5. Each stencil aperture was measured using a semi-au- FEATUrE bIG IDeaS ON MINIaTurISaTION continues Figure 3: Area ratio requirements for current and future component technologies. Figure 4: Test substrate with the four arrays used for the reducing array apertures highlighted.