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68 SMT007 MAGAZINE I JUNE 2018 Article by Timothy O'Neill, Carlos Tafoya, and Gustavo Ramirez AIM METALS AND ALLOYS Abstract Building upon an earlier study which focused on solder paste powder size, room-temperature aging and PCB pad and aperture designs, this study continues to investigate powder mesh size, but also examines stencil surface treat- ments and stencil foil tension. The goal of the study was to identify and rank the variables that provided the most improvement in repeat- ability, transfer efficiency and print definition for fine pitch printing. The results showed that nanocoating, powder type and tension rank highest to lowest in terms of their effect on print quality, and that high tension should be further studied to better understand where it makes the most significant impact. Introduction Previous work [1] revealed that: a. reducing solder powder mesh size provides a modest improvement in print consistency and transfer efficiency for certain aperture designs b. reducing solder powder mesh size may reduce solder paste useful life and increase process variables under certain conditions c. pad and aperture design are the most significant variables in improving solder paste transfer efficiency when using high-quality, nanocoated stencils at standard mounting tensions This study adds to the database the effect of nanocoating and mounting tension on print quality, bringing a new arm to the experiment by printing unaged Type 4 (T4) and Type 5 (T5) solder pastes with similar stencils; however, one stencil is coated with a commercial poly- mer nanocoating and the other is uncoated and mounted at high tension. For reference, "stan- dard" mounting tension is about 35N/cm, whereas "high" tension is 50N/cm or higher. Theoretically, higher mounting tension should create Smore precise deposits because the foil will not deflect or reverberate as much during the separation phase of the printing process compared to a lower tension foil. Experimental Method Test Vehicle The test vehicle (TV) selected for the print study was the Jabil Solder Paste Evaluation

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