Cleaning and liquid contact with solids – Processes – Using sequentially applied treating agents
Patent
1993-12-14
1997-10-21
El-Arini, Zeinab
Cleaning and liquid contact with solids
Processes
Using sequentially applied treating agents
134 30, 134 31, 134 38, 134 40, 134 42, B08B 308, B08B 310, C23G 502, C23G 5024
Patent
active
056791755
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to processes for removing adherent soils from substrates. More specifically, the invention relates to effective cleaning processes which utilize non-azeotropic mixtures of solvating agents and rinsing agents.
The present invention provides cleaning methods having characteristics and features which are highly desirable in numerous and varied commercial applications. For example, most metallic components are treated with an oil or other processing agent during the fabrication process, and this oil must be removed before the component is installed in the finished product. It is also frequently required that excess rosin flux must be removed from printed circuit boards before the boards are acceptable for use. The present processes are adaptable for use in these and many other applications. Thus, although the present invention is described initially herein in connection with its applicability to the cleaning of printed circuit boards, it will be appreciated from a reading of the entire application that the invention has wider application.
Printed circuit boards typically consist of a rigid or flexible sheet of fiberglass-reinforced dielectric plastic having electrical contacts and conductors on one or both sides thereof. Electrical components are electrically connected to these connectors and/or contacts using any one of a number of soldering techniques. Most of the soldering techniques currently used in commercial manufacturing processes include the step of coating the entire circuit side of the printed circuit board, or at least a portion thereof, with a solder flux prior to carrying out the actual soldering step. Rosin flux is commonly used alone or in combination with activating amine-based additives, such as amine hydrochloride, to clean the conductive metal parts and to promote strong mechanical and electrical bond with the solder.
After the soldering process is complete, the presence of residual flux on the printed circuit board is detrimental to the operability of the electrical circuitry and components contained on the board. Accordingly, any residual flux present on the board must be removed.
REPORTED DEVELOPMENTS
The techniques used to remove adherent residues from printed circuit bards are numerous and varied, ranging from simple brushing of the board with solvent to relatively sophisticated emulsion cleaning. See Leonida, Handbook of Printed Circuit Design, Manufacture, Components and Assembly, Chapter 9, pp. 464-489 (1981). One of the most widely used cleaning techniques is known as vapor degreasing or vapor-liquid-vapor cleaning. According to this process, the printed circuit board is contacted in succession by: (1) relatively hot solvent-containing vapors; (2) by relatively cool solvent-containing liquid; and (3) finally by relatively hot solvent-containing vapor.
Equipment typically used in connection with vapor degreasing consists of a two-section tank. The first section of the tank contains boiling solvent and the second section of the tank contains relatively cool, non-boiling solvent. Refrigerated coils are provided in the vapor space above the boiling solvent, and solvent vapor condenses onto the coils and is transferred to the cold solvent in the second section of the tank. A certain portion of the cold liquid solvent is returned to the first section of the tank to maintain a sufficient quantity of boiling liquid solvent. The cleaning process typically proceeds by first introducing a relatively cold, soil-containing circuit board into the vapor space above the boiling solvent. Due to the temperature difference between the circuit board and the solvent vapor, solvent condenses on the printed circuit board and achieves a solvating action on the residual rosin fluxes. The condensed vapors and the rosin fluxes solvated thereby are allowed to return to the first section of the tank. After the desired amount of cleaning action has occurred, the board is then moved to the second section of the tank and immersed in the cold solvent, thereb
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Hayes Michael E.
Hosman Donald P.
Hrebenar Kevin R.
Sell Robert D.
El-Arini Zeinab
Petroferm Inc.
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