RU2096152C1 - Soldering flux for washingless low-temperature soldering - Google Patents

Abstract

FIELD: soldering. SUBSTANCE: flux contains, wt.-%: mixture of difficultly water-soluble mono- and dibasic C₄-C₁₀-carboxylic acids, 3.5-6.0; natural or synthetic resin, up to 5.0; benzotriazol, 0.1-0.5; monoatomic alcohol or mixture thereof with ethylacetate or triacetyn, the balance. Flux may be supplemented with polyoxyethylated esters of lauric and oleic acids with average molecular weight 596 and 503, respectively, or polyoxyethylated fatty C₁₀-C₁₈-alcohols with molecular weight 1000, up to 0.25. EFFECT: simplified soldering procedure. 2 cl, 1 tbl

Description

 The invention relates to the field of soldering production, in particular to fluxes for mechanized soldering of printed circuit boards with tin-lead solder.

 Known flux for soldering, which does not require washing residues after soldering, containing as an active component ammonium bromide and rosin. This flux has a high fluxing ability and high corrosive effects. To maintain insulation resistance, a high rosin content (18%) is necessary, which contaminates the surfaces of printed circuit boards and solder frames.

 Fluxes are also known that do not require washing of solder residues, containing predominantly adipic acid as an activator.

 Soldered compounds obtained using such fluxes have a gray color and a whitish coating on the metal surface.

 The closest in composition to the claimed is a soldering flux, including a solvent, an activator containing one or more dicarboxylic acids having from 4 to 12 carbon atoms in an amount of not more than 3.5% rosin and / or other additives in an amount of up to 2 wt. and wetting agent in an amount of from 0.2 to 3 wt. moreover, the total amount of solids does not exceed 6 wt. The disadvantages of the known flux are the low quality of soldering, significant corrosive effects on copper, as well as the need to wash the residual flux with water.

 The aim of the invention is to improve the quality of soldering, reducing the corrosive effects on copper and eliminating the need to remove residual flux after soldering.

 The goal is achieved in that the flux comprising an activator containing a mixture of organic acids having from 4 to 10 carbon atoms, a thickener and a solvent further comprises benzotriazole; as a mixture of organic acids, it contains a mixture of mono- and dibasic water-insoluble organic acids; as a thickener, natural or synthetic resin; as a solvent, monohydric alcohol or its mixture with ethyl acetate or triacetin in the following ratio of components, wt.

A mixture of mono- or dibasic, water-insoluble organic acids containing from 4 to 10 carbon atoms 3.5-6.0
Natural or synthetic resin up to 5.0
Benzotriazole 0.1-0.5
Monohydroxy alcohol or its mixture with ethyl acetate or triacetin - Else
It is also possible the additional content of polyoxyethylated esters of lauric, oleic acid with an average molecular weight of 596 and 503, respectively, or polyoxyethylated fatty alcohols fraction C ₁₀ -C ₁₈ with a molecular weight of 1000 in an amount of up to 0.25 wt.

 The use as an activator of a mixture of organic acids, sparingly soluble in water, makes it possible to obtain a sufficiently active flux, the residues of which are slightly hydrolyzed by air moisture, and therefore slightly affect the insulation resistance of printed circuit boards.

 As polyoxyethylated fatty acid esters of the indicated molecular weight, the proposed flux may contain industrial products of laurox-9, oleox-5, syntanol DS-10. The introduction of a surfactant into the flux composition ensures good flux wetting of the places to be soldered, increases the flux activity. The amount of wetting agent up to 0.25 wt. allows to achieve good complete wetting of printed circuit boards with flux Introduction to the composition of the flux of benzotriazole inhibitor composition - allows you to get a non-corrosive flux. As a flux solvent, ethanol is most preferred as a less toxic substance, but isopropanol or a mixture thereof with ethyl acetate or triacetin can also be used.

 As examples of specific performance, you can consider the following compositions, wt.

Example 1
Sebacic acid 3.0
Salicylic Acid 3.0
Rosin 2.0
Syntanol 0.2
Benzotriazole 0.1
Ethanol Else up to 100.0
The flux is prepared by dissolving the dry components in ethanol by heating to 60-70 ^o C and stirring until a homogeneous, transparent, light yellow liquid is formed.

Flux is tested in the technical process of mechanized "wave" soldering. The quality of soldering of printed units is determined visually in 100% of soldered joints by the presence of nepropae, fistulas, icicles, the shape of the meniscus and the luster of the solder. The percentage of solvable defects to be repaired is calculated. The effect of flux residues on the dielectric properties of printed circuit boards is judged by the value of insulation resistance (R _out ) after holding them in a heat and climate chamber at a temperature of t (40 ± 2) ^o C and relative humidity Φ _rel (93 ± 3)% for 21 days

The corrosion effect of fluxes and their residues after soldering on copper is determined in accordance with GOST 9.076-77 in terms of corrosion after holding samples with fluxes at t (4 ± 2) ^o C and Φ _rel (93 ± 3)% for 56 days.

The number of removable soldering defects obtained by soldering the print units using the flux according to Example 1 is 3%; the form of the soldered joint is flooded, the solder is brilliant. Insulation resistance after 21 days 7x10 ⁶ Ohms.

 The corrosive effect of the flux of Example 1 on copper, evaluated in terms of corrosion on a 10-point scale (GOST 9.076-77), is 1 point, flux residues are also 1 point, which means no corrosion.

 As a prototype, a flux of the following composition was tested, wt.

Adipic acid 1.5
Sebacic acid 0.5
Polyoxyethylated Lauric Acid 1.2
Rosin 0.8
Ethanol Else up to 100.0
The prototype and fluxes for the remaining examples were prepared and tested analogously to example 1. The compositions of the fluxes and the results of their tests are shown in the table.

 The flux according to example 6 has insufficient activity, therefore, the quality of the soldering of printed units with it is unsatisfactory. The absence of a corrosion inhibitor contributes to the appearance of traces of salt-like corrosion, which we rated at 3 points. Flux residues are non-corrosive.

 The flux according to example 7 has a high fluxing activity, however, a large amount of solids after soldering becomes visible, which spoils the appearance of soldered printing units.

 The test results of the fluxes in examples 6 and 7 show that the limits of the change in the content of flux components are selected correctly.

 The proposed soldering flux, which does not require washing of the residues after soldering, allows to obtain high-quality soldered skeletal joints with a low number of solvable soldering defects (up to 8%). Flux and its residues after soldering do not have a corrosive effect on copper (and even more so on PIC) during tests for 56 days in tropical conditions.

 When applying the proposed flux, a significant economic effect is expected, expressed in the elimination of the washing process.

Claims (1)

 1. Flux for low-temperature brazing, including an activator containing a mixture of organic acids having 4 to 10 carbon atoms, a thickener and a solvent, characterized in that it additionally contains benzotriazole, as a mixture of organic acids, it contains a mixture of mono- and dibasic water-insoluble organic acids, as a thickener - natural or synthetic resin, and as a solvent, monohydroxy alcohol or its mixture with ethyl acetate or triacetin in the following ratio of components, wt. A mixture of monobasic and dibasic water-insoluble organic acids containing from 4 to 10 carbon atoms 3.5 6.0
Natural or synthetic resin Up to 5
Benzotriazole 0.1 0.5
Monohydroxy alcohol or its mixture with ethyl acetate or triacetin - Else
2. The flux according to claim 1, characterized in that it further comprises polyoxyethylated esters of lauric, oleic acid with an average mol.m. 596 and 503, respectively, or polyoxyethylene fatty alcohols of the fraction C _{1 0} C _{1 8} with mol.m. 1000 in an amount of up to 0.25 wt.

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