RU2347656C2 - Fluxing agent for soft soldering - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: proposed fluxing agent contains components in the following ratio, wt %: technical glycerine 30.5-32.1, triethanolamine 20.2-22.2, carbamide 12.2-13.3, ammonium citrate 11.5-12.2, alcohol - the rest. The chosen quantitative ratio of components enables activation of the process of removing oxide films.

EFFECT: high quality of soldered joints, higher corrosion resistance and reliability of the soldered joints.

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Description

The invention relates to soldering, in particular to soldering fluxes, intended for use when soldering and tinning with soft solders in the technological processes of electronic, radio engineering and other industries, for removing oxide films during soldering and ensuring high quality of the soldered joint.

Currently, rosin fluxes activated by various inorganic or organic compounds are most widely used in the manufacture of electronic equipment for low-temperature soldering [1].

Such fluxes are used for brazing not only copper and its alloys, but also structural and corrosion-resistant steels and other alloys.

Pure rosin as a flux is used less and less, especially in serial and mass production.

Most rosin-containing fluxes do not cause corrosion of the brazed joint, but have weak active fluxing properties.

Organic fluxes have more active fluxing properties. They are made on the basis of low molecular weight organic acids and solvents. The main advantage of these fluxes is their high fluxing activity.

Closest to this technical solution is a paste-like organic flux [2] based on glycerol with the addition of active components, containing, wt.%:

Technical glycerin 45 Ammonium chloride (saturated solution) eighteen Aniline hydrochloride 5 Triethanolamine 2 Alcohol thirty

This composition belongs to the group of active halogen fluxes. However, after soldering in the soldered joint zone, solid solid residues are formed which are poorly removed even in alcohol or alcohol-gasoline mixture. Soldering circuit boards of electronic equipment under tight surface mounting with such a flux is unacceptable, since the flux is poorly removed from under the elements and legs of the microcircuit, and the remaining chlorine in the flux residues under conditions of high humidity and temperature causes corrosion of the soldered joints and, as a result, contact breakdown in places of installation connections.

In addition, in the process of soldering during heating, the decomposition of flux with the release of hydrogen chloride, harmful to health and the environment.

The aim of the proposed technical solution is to create a flux with improved technological properties for manual and mechanized soldering, including printed circuit boards with a high density of installation. The flux must be highly active in removing oxide films, while the minimum corrosive attack on the system is the solder material of the solder joint, and after soldering, its residues are washed off well with distilled water.

The inventive composition of the flux contains components in the following quantitative ratio, wt.%:

Technical glycerin 30.5-32.1 Triethanolamine 20,2-22,2 Urea 12.2-13.3 Ammonium Citrate 11.5-12.2 Alcohol rest

The high fluxing activity of the inventive flux allows the soldering of various materials: copper, nickel, brass, steel, gold, silver, tin-bismuth coatings.

The quantitative content of urea, ammonium citric acid, and glycerol reduces the surface tension of the molten solder at the metal – solder – flux interface, improves the wettability of the brazed surfaces, and thus significantly enhances the removal of oxide films from the brazed surfaces and solder, since the active components of the flux completely react when heated with oxide film.

The quantitative content of triethanolamine and alcohol in the inventive flux provides the necessary flux viscosity, which allows it to be used in manual and mechanized soldering and to avoid the formation of gummy substances at the soldering sites.

The quantitative content of the components in the inventive flux allows you to get a flux, which after soldering is well washed off with water, and its residues do not have a corrosive effect on metals and metal coatings.

With a quantitative content of glycerol of less than 30.5% and an increase in urea of more than 13.3% and ammonium citric acid of more than 12.2%, the flux causes corrosion of the brazed joints, while becoming pasty, which makes it difficult to use in mechanical soldering.

When the glycerol content is more than 32.1% and, accordingly, urea is less than 12.2% and ammonium citric acid is less than 11.5%, its activity decreases and the quality of soldering deteriorates.

When the content of triethanolamine is less than 20.2%, a resinous precipitate precipitates during soldering, which reduces the activity of the flux and is poorly removed from the surface after soldering with water, and when the content is more than 22.2%, the flux becomes more viscous, which makes it difficult to apply, and resinous substances are formed, which are poorly removed after soldering with water.

The method of obtaining flux

The flux is prepared in the following way. In a water bath, glycerin is heated to a temperature of 80-100 ° C, urea and ammonium citrate are successively dissolved in glycerin, then triethanolamine is introduced. The resulting mixture was cooled and diluted with alcohol.

The properties of the inventive flux were investigated on control samples.

The experimental results are shown in table 1.

The experiment was carried out on flat samples of copper, nickel, coated with tin-bismuth and a silver coating. POS-61 was used as solder; soldering was carried out at a heating temperature of 220 ° C and a holding time of 5 s.

After soldering, the samples were cleaned of flux residues:

when using the inventive flux in distilled water;

when using a known flux, in a gasoline-alcohol mixture with preliminary locking.

Flux activity was determined by measuring the spreading coefficient

K _ps = S ₁ / S ₀ ,

where S ₁ and S ₀ - the area of the "sample" of solder before and after melting. The quality of soldering and the reliability of soldered joints were investigated on samples made with an overlap.

The corrosion resistance of soldered joints was evaluated by the mass corrosion index, which was determined by the change in the mass of the sample, referred to unit surface area per unit time. For this, the samples were placed in a humidity chamber of 95% moisture and a temperature of 40 ° C and every 10 days they were removed, washed, dried and weighed.

Table 1 Indicators The inventive flux, wt.% Known flux, wt.%: Ingredients (components) no less no more Technical glycerin - 45 Technical glycerin 30.5 32.1 Ammonium chloride (saturated solution) -18 Triethanolamine 20,2 22.2 Aniline hydrochloride - 5 Urea 12,2 13.3 Triethanolamine - 2 Ammonium Citrate 11.5 12,2 Alcohol - 30 Alcohol rest In this case, the total content of all ingredients should be 100% Spreading Factor K _ps : on copper 6.9-7.4 5,4 nickel 6.6-7.2 5.9 tin bismuth 10.1-10.2 9.8 silver 9.6-9.8 9.6 Quality and reliability soldered joints: shear force (kg / mm ² ) after soldering 4.8-4.9 3.6 3 months after soldering 4.7-4.8 2,8 Corrosion after Corrosive effect Corrosion is observed moisture chambers absent

Thus, the selected quantitative ratio of the components makes it possible to activate the process of removing oxide films and to ensure high quality of brazed joints, to increase their corrosion resistance and reliability, while flux residues can be easily removed with distilled water even from printed circuit boards at high density mounted mounting. In this case, the flux is environmentally friendly, since it does not form toxic compounds, and its use allows not to pollute the water and air environment.

Information sources

1. OST 4GO 033.200 "Solder and fluxes for soldering, grade, composition, properties and scope", 1978.

2. Khryapin V.E. "Handbook of a soldering iron", M., Mechanical Engineering, 1981, p.112.

Claims (1)

Low temperature brazing flux containing glycerin, triethanolamine, ethyl alcohol, characterized in that it additionally contains ammonium citrate and urea in the following ratio, wt.%:
Technical glycerin 30.5-32.1 Triethanolamine 20,2-22,2 Urea 12.2-13.3 Ammonium Citrate 11.5-12.2 Alcohol Rest