SMT Magazine

SMT-Apr2017

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50 SMT Magazine • April 2017 VAPOR DEGREASING CHEMISTRIES in temperature or humidity. Once the dendrite connects the two leads, the circuit can short and cause failures to the overall system. Needless to say, cleaning quickly became as important to the electronics production process as assembly. At the start of the electronics cleaning frenzy, vapor degreasing reigned dominant thanks to its ease-of-use, quick processing times and spot-free, dry results. One of the most common electronics cleaners of the 1980s was CFC-113 (more com - monly known as Freon 113). Roughly 70% of Freon 113 use was designated to the electronics industry and in 1986 roughly 94 million pounds of Freon 113 was used in electronics manufac- turing 1 . However, FREON's reign was cut short in 1988 when the US ratification of the Montreal Protocol on Substances that Deplete the Ozone Layer forced the cleaning industry to discontin- ue the production of CFCs 2 . The Clean Air Act Amendment of 1990 increased the enforcement of ozone depleting substances and further re- stricted the cleaning industry 3 . At the same time, advancements in flux formulations lead to the development of no-clean and low-residue flux- es. These no-clean flux formulations are intend- ed to remain on the board and leave minimal residues, which allows manufacturers to skip the cleaning process altogether. However, time has shown that these residues are still capable of at - tracting moisture, inhibiting conformal coating uniformity, or simply leaving aesthetically unac- ceptable visual results. During the past decade, the growing demand for smaller electronics has forced circuit board manufacturers to miniaturize circuits, and pack more components into tighter spaces. This min- iaturization causes a greater likelihood for even minor electro-migration to bridge components and result in failures. Figure 2 depicts an exam- ple of a low-standoff integrated circuit compo- nent on a substrate. A very low surface tension liquid would be required to penetrate the small space between the solder bumps and remove any debris, flux, or residues from the compo- nent underside. It is also understandable how even minor dendritic growth or debris could impact such an intricate circuit. Further regulation restrictions have also forced electronics manufacturers to reduce or re- move leaded ingredients from solder; this has forced solder and flux manufacturers to reformu- late to accommodate higher melting-point met- als. These high-temperature soldering jobs often leave burned flux residues, which are more diffi- cult to clean. Although the aqueous cleaning in- dustry has been the superior cleaning guru for the past 10 years, these new soldering hurdles have shed light on the limitations of water . The surfactant formulations are continuously ad - vanced to assist in removing these difficult resi- Figure 1: Dendrite growth between two leads. Figure 2: Integrated circuit on a substrate.

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