Issue link: https://iconnect007.uberflip.com/i/989774
JUNE 2018 I SMT007 MAGAZINE 71 area is climate controlled and can be manip- ulated to simulate production environments around the globe. Test conditions were opti- mized at 25.4°C (77.4°F) at 59% RH for these tests and recorded twice daily. The facility is staffed with full-time SMTA- certified process engineers with over 50 years of combined experience in SMT assem- bly processes. Figure 2 shows the laboratory manager preparing the DEK Horizon printer and Parmi Sigma X SPI machine for the test run. The print parameters were as follows: • Squeegee: 14" (355 mm) 60° angle DEK OEM • Squeegee speed: 40 mm/sec (~1.6 in/sec) • Squeegee pressure: 10 kg (~1.5 lb./in on 14" blades) • Separation speed: 1 mm/sec (~0.040 in/sec) • Separation distance: 3 mm (~120 mils) • Under wipe sequence: Wet-Vacuum-Dry (WVD), using DEK EcoRoll wiper paper and AIM DJAW-10 solvent. Stencils were automatically underwiped before the first print of each set of five. A dedicated flat tooling support block was used to provide solid support for the PCB, and new squeegee blades were used for the tests. Automatic Solder Paste Inspection SPI inspection parameters were modified to improve the accuracy of the measurements. Typically, a 30-40 µm measurement threshold is used in production environments to eliminate noise from PCBs' topographical features like silkscreen markings, mask over trace, etc. Because the design of this TV limits topographical feature noise, it enabled a 15 µm measurement threshold, to improve measurement fidelity and aid in detecting subtle variations in print behavior. Solder Paste The solder paste tested included Types 4 and 5 in a modern, no-clean flux medium. The pastes were blended, shipped and stored under recommended condi- tions. The same metal percentage was used for the T4 (88.5%) and T5 (88.3%) as in earlier tests; however, different lots of solder powder and flux medium were used in this test. Experimental Design Input variables in the experiment included: • Paste Type (4, 5) • Stencil nanocoating (Y/N) • Foil mounting tension (std/high) • Pause time between print tests (0, 30, 60 and 90 minutes) • PCB pad size (6–15mil) • PCB pad shape (circular, square, modified square with rounded corners) • PCB pad definition (NSMD, SMD) Output variables included: • Deposit volume • Deposit height • Transfer efficiency (% volume). TE is based on theoretical aperture sizes, not measured aperture sizes. All the stencils were cut from the same material on the same cutter by the same operator, so it is assumed that any systemic error is applied equally to all stencils. Actual aperture sizes were not measured Figure 2: AIM applications laboratory manager reviews test setup.