Cleaning process for electronic and electrical assemblies

Details Cleaning process for electronic and electrical assemblies Cleaning process for electronic and electrical assemblies

1994-01-24

1995-10-10

Simmons, David A.

Cleaning and liquid contact with solids

Processes

Miscellaneous

134 38, 252170, 252171, C23G 502, B08B 308

Patent

active

054567602

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION



STATEMENT OF RELATED ART

This invention relates to water-miscible cleaning agents free from halogenated hydrocarbons for cleaning electronic and electrical assemblies and to the use of the cleaning agent for the removal of flux from circuit boards after soldering.
Basically, fluxes based on rosin are made up of products belonging to two different chemical groups, namely relatively apolar resin-like compounds, for example rosin, and polar compounds, so-called activators. In accordance with the laws of chemistry, the chemical compounds dissolve best in solvents of the same type, i.e. in apolar or polar cleaning agents. Particular problems arise in the prior art when the carboxylic acids used as activators are present in the rosin in concentrations of up to 35% and, in some cases, are insoluble in fluorinated hydrocarbons or chlorinated hydrocarbons and only sparingly soluble in alcohols. This often leads to dissolution of the rosin and to exposure of white residues of the activators which, freed from the insulating effect of the rosin, can become conductive and corrosive under the effect of atmospheric moisture.
Until very recently, fluorinated hydrocarbons were mainly used for cleaning electronic and electrical assemblies, more particularly for removing rosin-containing fluxes from circuit boards after soldering. In view of the problem of destruction of the ozone layer by chlorofluorocarbons, attempts have recently been made to develop alternative cleaning agents.
DE-A 23 16 720 describes a cleaning agent for removing rosin-containing residues from electrical equipment which is said largely to eliminate rosin residues and activators, if any, but which on the other hand does not affect the insulating materials and metals normally used in electrical circuits. The cleaning solution contains in particular a polar, higher alcohol, more particularly butyl glycol or n-butanol, a polar lower alcohol, more particularly methanol or isopropanol, in addition to an apolar hydrocarbon, more particularly trichlorotrifluoroethane or hexane, optionally in the presence of a nonionic wetting agent. Firstly, a water-immiscible cleaning agent is obtained through the use of the polar hydrocarbon. Secondly, the chlorofluorocarbon used should be avoided on account of its ozone-destroying effect. In addition, cleaning agents of the type in question have extremely low flash points without the chlorofluorocarbons so that their practical application requires appropriate explosion-proof equipment.
A cleaning agent containing non-halogenated hydrocarbons, a fluorinated alcohol and, optionally, other polar organic solvents in addition to halogenated hydrocarbons is known from EP-A-0 120 319. In view of the presence of halogenated hydrocarbons, this cleaning agent does not satisfy present-day requirements.
EP-A-0 416 763 describes the cleaning of electronic circuit boards with preparations containing terpenes or other non-halogenated solvents. Unfortunately, these cleaning agents have an extremely low flash point so that appropriate anti-explosion measures have to be taken for their practical application.
EP-A-0 419 089 describes a cleaning agent containing dimethyl cyclooctadiene.
The use of diacetone alcohol for dissolving rosin and many natural and synthetic resins is known from Rompps Chemie-Lexikon [Title in English: Rompps Chemical Dictionary], 9th Edition, Vol. 2 (1990), page 923, keyword "diacetone alcohol".
Water-tree solvent mixtures consisting of chlorofluorocarbons and ketones are known from Chemical Abstracts, Vol. 114 (1991), page 139, Abstract 114:84372 g from JP-A90/202998. In addition to the chlorofluorocarbons mentioned, diacetone alcohol inter alia is used for removing fluxes.


DESCRIPTION OF THE INVENTION



Object of the Invention

By contrast, the problem addressed by the present invention was to provide a water-miscible preparation free from halogenareal hydrocarbons for cleaning electronic and electrical assemblies which would be capable of safely removing the polar and apolar substances

REFERENCES:
patent: 4276186 (1981-06-01), Bakos et al.
patent: 4968447 (1990-11-01), Dixon et al.
patent: 4983224 (1991-01-01), Mombrun et al.
patent: 5116426 (1992-05-01), Asano et al.
patent: 5128057 (1992-07-01), Bixenman
patent: 5183514 (1993-02-01), Marquis et al.
patent: 5238504 (1993-08-01), Henry
patent: 5271775 (1993-12-01), Asano et al.
patent: 5302313 (1994-04-01), Asano et al.
Chemical Abstracts, vol. 114 (1991), p. 139 Abs. 114:84372 g.

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