Cleaning of electronic components has become more difficult in recent years because of the need to eliminate the use of ozone-depleting chlorofluorocarbons. Toxicological studies of hydrochlorofluorocarbon (HCFC), the planned freon replacements, have raised questions about the feasibility of their widespread use for cleaning applications. 1 Unfortunately, the remaining options are few. Among these, vacuum baking works only for a limited number of contaminant/substrate systems, and aqueous solvents require a drying step, leading to a waste-disposal problem. Although water also has a high surface tension in comparison to freons, 2 surfactants added to water to improve its wettability may leave unwanted residues. Finally, various chlorinated solvents used for analytical extraction or cleaning are under scrutiny for health reasons and may generate corrosive hydrochloric acid if overheated during processing.As an alternative, supercritical fluids, compounds existing above their critical temperature and pressure, possess liquid-like solvent and gas-like diffusibility and viscosity properties that enable rapid penetration into crevices and boundary layers and allow for complete removal of organic and inorganic contaminants contained therein. [3][4][5] Moreover, by cycling pressure between supercritical and subcritical values, particles can be effectively dislodged during the expansion phase of the pulsation. 6 Specifically, supercritical CO 2 has the advantage of versatility over other liquid solvents with a minimum of waste. For instance, the solvent properties of CO 2 can be adjusted by manipulating their density via external temperature and pressure application. Small amounts of polar cosolvents can also be added to enhance the solubility of polar materials. 7,8 In addition, the low surface tension of supercritical CO 2 makes it an attractive candidate for cleaning porous materials 9 and possibly removing particles from electronic components. For example, chip resistors are important and commonly used electronic components in PC boards for surface mount technology (SMT). Most of the chip resistors on the market today have wraparound terminations with a barrier of 3-5 m nickel and 6-8 m Sn/Pb solder electroplated by a barrel-plating process. 10 After the Ni and Sn/Pb plating, it is necessary to rinse the chip to take out Ni and Sn/Pb residuals to ensure the quality of solderability during termination soldering application. 11,12 Thus, the termination purity level is the key controlling factor. Applying deionized (DI) water to rinse the electroplated terminations is a conventional method for barrel-plating processes. Such a process generates a mass consumption of DI water and a need for an expensive recycling system for waste treatment. As a result, advanced rinsing methods to improve current disadvantages are expected. We have therefore selected the removal of Ni and Sn/Pb residuals from the terminations of chip resistors as a test for this novel supercritical CO 2 cleaning technique.The main focus of our current work...

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