Metal treatment – Compositions – Fluxing
Patent
1990-06-14
1992-05-26
Rosenberg, Peter D.
Metal treatment
Compositions
Fluxing
148 24, 148 25, B23K 3534
Patent
active
051164329
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a processing method used in the manufacturing of electrical and electronic components. This applies particularly to printed circuits equipped with components which were soft soldered by means of soldering machines and the application of a soft soldering flux based on carboxylic acid. This process is regularly used in the electric and electronic industry.
Soft soldering fluxes containing organic carboxylic acids are already known. Refer to PS EP 0 215 773 for the description of the development of this technology.
The increasing employment of in-circuit-tests and SMT-manufacturing showed, however, that a special kind of flux is required for this purpose, i.e. a flux whose residues needn't be removed after the soldering process and which, nevertheless, can offer incontestable production results when used together with any of the two manufacturing technologies specified above. This can be achieved particularly by means of fluxes which have a drastically reduced amount of solid matter contents as compared to customary ones.
This reduction in solid matter contents is preferably attained by either: cutting down substantially the amount of resins, leaving these out altogether, or substituting these by other products. In this respect, we hereby make reference to PS DE 211497, DE 2832317, DE 1608425, DE 2725701, EP 0184825, EP 090960, EP 0077622, EP 0201150, EP 0219175 and/or U.S. Pat. No. 4,419,146 respectively.
However, the considerable reduction in solid matter contents by reducing or dispensing of the resin components, respectively, diminishes the spreadability and foamability features of the fluxing agent accordingly. An attempt to counteract this negative physical effect was made; it consisted in the addition of tensides (e.g. non-ionic, anionic, cationic, amphoteric ones, etc) as spreading or foaming components, respectively. However, it was soon established that these admixtures impair the electrochemical fatigue strength.
Secondly, the soldering vapors, i.e. the hot flux residues which evaporate after the soldering of the printed circuits until these have cooled down, proved to have a somewhat too strong physiologic activity; this was due to the missing resin, which priorly served to soften this effect. Consequently, the idea was to find a similar substitute for the succinic acid which was basically responsible for the mentioned physiologic effects.
If a halide free soldering flux without any carrying agent is created, which equals the absence of resin (e.g. as described in PS EP 090960), the crystalline nature of the carboxylic acids will leave a white crystalline pattern of flux residues after soldering; this, of course, is optically unpleasant. This phenomenon is avoided (as in the past) by adding resin, although to a considerably diminished extent (see also PS EP 0184825).
If the requirements described above are taken into consideration, for a fluxing agent whose residues needn't be removed after soldering, the optimum amount of solid matter contents is 6%, for it to be adequate for in-circuit-tests and SMT manufacturing. Nevertheless, other amounts of solid matter concentration may also be accepted.
The recently developed soft soldering fluxing agent described below--which is mainly based on PS EP 0215773, offers those features required by electrochemical and production engineering.
In this respect, the use of alicyclic carboxylic acids along with the addition of alcyl-fluoric alcohols of the chemical formula Rf--CH2--CH2--OH, where Rf represents a chain of 6-16 carbon atoms, was found to be an essential basis towards long-term electrochemical stability. Any type of chains may be used for the alcyl-fluoric alcohols.
Alyphatic hydroxy carboxylic acids proved to be suitable substitutes for succinic acid. The use of hydroxy carboxylic acids as flux activators is well known (e.g. PS DE 2344493, PCT SE 850029). Nevertheless, particularly citric acid, a corrosive and thermically instable agent, and tartaric acid, the latter being almost insoluble in commercial solvents, are used for
REFERENCES:
patent: 3734791 (1973-05-01), Poliak
patent: 4342607 (1982-08-01), Zado
patent: 4988395 (1991-01-01), Taguchi
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