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SMT007-Oct2020

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58 SMT007 MAGAZINE I OCTOBER 2020 Article by Jasbir Bath, Shantanu Joshi, and Noriyoshi Uchida KOKI SOLDER AMERICA AND KOKI COMPANY LIMITED Abstract With the increased use of electronics in new technology areas, flux formulations are being developed to address the new and existing requirements. For sensors and camera mod- ules used for Advanced Driver Assistance Sys- tem (ADAS) and internet of things (IoT) appli- cations, there is a demand for no-clean flux formulations in lead-free solder paste, which can reduce flux splattering during reflow. Development was done on a specially adopted flux chemistry, which helped to reduce solder/flux spattering without the use of a spe- cially developed reflow profile adjustment in an air reflow atmosphere. The flux chemis- try in the Sn3Ag0.5Cu solder paste was devel- oped so that the flux residue layer can cover the molten solder surface during reflow pre- venting splattering. Tests were done on a copper plate printed with solder paste and a copper plate placed slightly above the reflowing solder paste on the test vehicle to measure flux splattering with a variety of reflow profiles evaluated. While the conventional solder pastes required an increase of the preheat temperature to drive off vola- tile flux components to reduce splattering, this developed paste successfully prevented the occurrence of the splatter regardless of the type of preheat and reflow profile used. The results of the work will be reported in this article. Introduction During surface mount assembly with sol- der paste, flux splattering may occur during reflow. Flux splattering occurs as flux compo- nents disperse when gas is generated, which happens when flux components contained in solder paste dissolve and volatilize and are expelled from the solder (Figure 1). Reducing Flux Splatter in Sensors and Camera Modules Figure 1: Flux spattering generation behavior.

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