Metal treatment – Compositions – Fluxing
Patent
1991-05-15
1992-12-01
Rosenberg, Peter D.
Metal treatment
Compositions
Fluxing
148 24, 148 25, B23K 3534
Patent
active
051677296
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FILED
The present invention relates to a soldering flux.
BACKGROUND ART
In general, to coat a solder on a base metal, oxides and other stains on the surface of the metal are removed, and simultaneously, a re-oxidation of the metal surface during the soldering is prevented, to reduce the surface tension of the solder and improve the wettability of the melted solder with the metal surface, and for this purpose, a soldering flux is used.
As the soldering flux, usually a resin flux formed by incorporating an activator capable of removing an oxide film into a thermoplastic resin having a low softening point, such as rosin, is used.
However, where the soldered portion is exposed to a high-temperature atmosphere, for example, to an atmosphere of 80.degree. C. as in an engine room of an automobile, if the flux comprising a thermoplastic resin having a softening point below about 70.degree. C., such as rosin, the thermoplastic resin is melted and an active ion in the activator held in this thermoplastic resin is released to lower the electrically insulating property and cause a corrosion of the metal surface.
This problem has been resolved by washing and removing the residual flux after the soldering, but since flourocarbon or the like is used as the washing solvent, a problem arises of environmental pollution, and furthermore, the cost is increased by the use of the washing solvent and the washing step.
Therefore, a primary object of the present invention is to provide a soldering flux capable of maintaining the electrically insulating property without washing away the residual flux, i.e., without washing, even if used in a high-temperature atmosphere.
DISCLOSURE OF THE INVENTION
The inventors of the present invention carried out an investigation with a view to attaining the above object, and as a result, found that the above problem can be solved and the above object can be attained if the soldering flux is constructed as described below.
In accordance with the first aspect of the present invention, there is provided a soldering flux comprising at least (a) a thermoplastic resin having a softening point not lower than 80.degree. C. and (b) an activator.
If the soldering flux of the first aspect of the present invention is used, the thermoplastic resin having a softening point not lower than 80.degree. C. is not melted even if exposed to a relatively high temperature such as the temperature of an engine room of an automobile, and therefore, no active ion is released. Furthermore, even if a part of the thermoplastic resin is replaced with rosin, the thermoplastic resin forms a high temperature-resistant film on the surface of the flux and covers the residual rosin after the soldering. Accordingly, the active ion released from the activator, which is formed in a high-temperature atmosphere is enveloped, and a reduction of the electrically insulating property and the occurrence of corrosion can be prevented.
In accordance with the second aspect of the present invention, there is provided a soldering flux comprising (a) at least one member selected from the group consisting of epoxy group-containing compounds, unsaturated double bond-containing compounds and blocked isocyanate group-containing compounds and (b) an activator.
If the soldering flux of the second aspect of the present invention is used, even if the residual flux is not removed by washing, the epoxy group-containing compound, unsaturated double bond-containing compound or blocked isocyanate group-containing compound causes, under heating at the soldering step, an addition reaction with a halogen acid, which is the active ion of the activator contained in the flux residue, with the result that the activator is deactivated and the active ion in the flux residue eliminated, the resistance to reduction of the electrically insulating property and the corrosion resistance are not lowered, and the reliability is improved.
In accordance with the third aspect of the present invention, there is provided a soldering flux comprising (a) a thermoplast
REFERENCES:
patent: 2158984 (1939-05-01), Lytle
patent: 4325754 (1982-04-01), Mizuhara
patent: 4495007 (1985-01-01), Zado
patent: 4919731 (1990-04-01), Iyogi
patent: 4981526 (1991-01-01), Kudo
Aihara Masami
Onishi Tatsushi
Takemoto Masanori
Harima Chemicals Inc.
Nippondenso Co. Ltd.
Rosenberg Peter D.
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