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70 SMT Magazine • December 2017 by Neeta Agarwal, Robert Farrell, and Joe Crudele, BENCHMARK ELECTRONICS INC.; Chrys Shea, SHEA ENGINEERING SERVICES; Ray Whittier, VICOR CORP.; and Chris Tibbetts, ANALOGIC CORP. SMT stencil printing technology continual- ly evolves to keep pace with device miniaturiza- tion technologies. Printed circuit board assem- blers have numerous new technology options to choose from, and need to determine the most effective ones to produce the highest qual- ity and most reliable solder interconnections. The objective of these tests was to identi- fy the best stencil technology for high-volume production of miniaturized SMT components. The solder paste used for this assessment was SAC305 Pb-free no-clean, Type 4 mesh. The specified stencil thickness for all stencils was 4 mils (100µm). EXPERIMENTAL SETUP: Test Vehicle The test vehicle shown in Figure 1 was de- signed in-house for a multitude of PCB assem- bly tests, including new packages, pad designs, solder paste print performance and process evaluation tests. The devices selected for anal- ysis in these tests included 0.3- and 0.4 mm- pitch BGAs and 0201s. Their area ratios ranged from 0.46 to 0.70. Locations and names of the specific devices used in the stencil analysis are shown in Figure 1. The recommended stencil thickness for the 0.3mm microBGA location is 3 mils (75 µm) versus the 4 mil (100 µm) thickness selected for this study. Consistent release for these apertures was not anticipated but relative comparisons of FEATURE Figure 1: Test vehicle and features used in stencil analysis.

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