JPH08118070A - Water-soluble flux - Google Patents

Abstract

PURPOSE: To obtain a water-soluble flux which does not produce red eyes and has good solderability by using at least one kind of specific sugar alcohols as a base material of the flux. CONSTITUTION: At least one kind of the sugar alcohols selected from sorbitol, mannitol, erythritol, etc., are incorporated into the water-soluble flux to be used for a soldering stage. The sugar alcohols to be used as a base material are usable alone or by mixing these sugar alcohols with glycerols or polyalkylene glycols. Mixing of activators, such as methyl amine and ethyl amine, is possible as well. The specific sugar alcohols are solid at an ordinary temp. and exhibit high solubility in water. The prepn. of the sugar alcohols in the form of an aq. soln. of about 70 to 80% is possible. This thick aq. soln. mixes easily with a water-soluble org. solvent of alcohols, etc.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a water-soluble flux used for soldering. More specifically, the present invention relates to a water-soluble flux having a function of applying to a soldered portion in a soldering process of a printed circuit board or an electronic component and attaching the solder to the soldered portion by contact with molten solder.

[0002]

2. Description of the Related Art As a flux used in a soldering process for printed circuit boards and electronic parts, a base resin such as rosin or acrylic resin is dissolved in an organic solvent such as isopropyl alcohol (IPA), and an amine is halogenated. A non-aqueous flux containing hydrogen salt, organic acid or its derivative as an activator, and a water-soluble liquid containing a water-soluble liquid such as glycols as a main component, a hydrogen halide salt of amine, an organic acid or its derivative And the like are added as an activator to the water-soluble flux.

The water-soluble flux according to the present invention is used for electronic parts such as pre-coating the lead part of an IC with solder, or pre-coating a copper wiring part of a printed circuit board with solder (called leveler flux). It is used to solder the mounted printed circuit board (called water-soluble post flux).

Generally, conventionally used water-soluble fluxes are based on water-soluble liquids such as glycerin and polyalkylene glycol, on which amines, hydrogen halide salts of amino acids, organic acids or their derivatives are added. It is added and, if necessary, its viscosity is adjusted with water-soluble alcohols such as IPA, ethylene glycol, propylene glycol and ethylene glycol monobutyl ether, or water.

In such a water-soluble flux,
In recent high-density mounting boards (boards that have small soldering area sizes and are densely packed), there is a drawback that red eyes (also called copper eyes or areas where solder is not attached) occur due to insufficient solder wetting. there were.

[0006]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a water-soluble flux which is free of red eyes and has excellent solderability.

[0007]

Means for Solving the Problems The inventors of the present invention have made extensive studies to solve the above problems, and as a result, the above problems can be solved by using a specific sugar alcohol as a base material of a water-soluble flux. The present invention has been completed by finding out that. That is, the present invention is a water-soluble flux used in the soldering process, sorbitol,
The problem was solved by using a water-soluble flux containing at least one sugar alcohol selected from mannitol and erythritol.

Considering the requirements to be provided as a base material for the water-soluble flux, the soldering temperature (usually 200 to
At 270 ° C.), the following conditions are desired to be satisfied. 1) Being a liquid 2) Being vaporized in a short period of time 3) Having the ability to reduce and remove solder and copper oxides Conventionally used water-soluble flux is glycerin as described above. , Water-soluble liquids such as polyalkylene glycol are used as the base material.
It was found that the requirement (3) mentioned above was not satisfied or insufficient, and it was confirmed that the requirement (3) was satisfied only by substituting a specific sugar alcohol for these known base materials. Heading The present invention has been completed.

That is, as an experiment, heat treatment was carried out at 130 ° C. for 30 minutes, a surface of a copper plate was placed with a predetermined weight of solder particles, various base materials were placed thereon, and then 250
Placed on a solder bath at ℃. It was cooled for 60 seconds after the solder was melted.

At this stage, the following judgment was made visually. a) Copper oxide reducing ability: Whether the copper oxide covered with the heat-melted sugar alcohol has changed to the color of metallic copper b) Heat resistance: Whether the heat-melted sugar alcohol has not been discolored. Was washed with water and the solubility (washability) was determined. Further, the solder spreading rate was measured according to JIS Z 3197.

The results are shown in Table 1. Among sugar alcohols, sorbitol (sorbit), mannitol (mannitol) and erythritol (erythritol) have excellent ability to reduce copper oxide by themselves, resulting in soldering. It was revealed that the wettability was excellent. It was also found that these have excellent heat resistance and are difficult to thermally decompose near the soldering temperature. On the other hand, lactitol, which is the same sugar alcohol, has no copper oxide reducing ability, does not wet the solder, and tends to undergo thermal decomposition near the soldering temperature, and it turns out that sugar alcohol does not serve as a base material. It was

Table 1 ─────────────────────────────── Copper oxide reduction capacity Heat resistance Detergency Solder spreading rate ──── ────────────────────────── Sorbitol 〇 〇 〇 80% Mannitol 〇 〇 〇 〇 80 erythritol 〇 〇 〇 〇 83 Lactitol × 〇 to △ 〇 39 ─ ───────────────────────────── Glycerin 〇 〇 〇 77 PEG # 400 △ △ 〇 45 ────────── ─────────────────────

On the other hand, glycerin, which has been conventionally used as a base material for a water-soluble flux, exhibits properties close to those of the above specific sugar alcohol, but has a slightly poor solderability, and polyethylene glycol (a type of polyalkylene glycol) It was revealed that PEG # 400) is considerably inferior in heat resistance and solder wettability. Therefore, the present inventors have completed the present invention by combining at least one base material selected from specific sugar alcohols with an activator.

Here, the specific sugar alcohols are sorbitol (sorbit), mannitol (mannitol),
Erythritol (erythritol). These may be used alone as a base material or may be used as a mixture with glycerin or polyalkylene glycols which have been used as a base material in the past. In this case, the ratio of the specific sugar alcohol to the conventional base material varies depending on the type of the conventional base material, but is generally 5:95 to 10 by weight.
The range of 0: 0, preferably 10:90 to 100: 0 is preferable. If the specific sugar alcohol is less than this ratio,
The heat resistance and copper oxide reducing ability of a specific sugar alcohol cannot be fully exerted.

As the activator, amines such as methylamine, ethylamine, diethylamine, triethylamine, propylamine, butylamine, cyclohexylamine, pyridine, triethanolamine, ethylenediamine and hydrazine, or amino acids such as glutamic acid and hydrogen chloride, Salts with hydrogen halides such as hydrogen bromide, inorganic acids such as hydrochloric acid and hydrobromic acid, and organic acids such as hydroxyacetic acid, tartaric acid, glutaric acid, succinic acid, and maleic acid, used alone or in combination. To be

Here, the mixing ratio of the base material and the activator largely varies depending on the kind of the activator. Generally, in the case of amine and a salt of hydrogen halide or hydrohalic acid,
Generally converted to hydrogen chloride in a weight ratio of 100: 0.5-
100: 5 is preferable.

Below this range, the soldering effect is low and red eyes tend to appear. Further, if it exceeds this range, the soldering effect will be saturated. When the activator is an organic acid, generally, the weight ratio is preferably 100: 1 to 100: 20. Below this range, the soldering effect is low and red eyes tend to appear.
Further, if it exceeds this range, the soldering effect will be saturated.

The specific sugar alcohol used in the present invention is a solid at room temperature, and a solvent is required to convert them into a solution-like flux. Although these are almost insoluble in water-soluble organic solvents such as alcohols, they have high solubility in water and it is easy to form an aqueous solution of about 70 to 80%. Such a concentrated aqueous solution is easily mixed with a water-soluble organic solvent such as alcohols.

As the water-soluble organic solvent, water-soluble alcohols such as methanol, ethanol, IPA, ethylene glycol, propylene glycol and ethylene glycol monobutyl ether may be used alone or in combination.

Further, if necessary, the water-soluble flux of the present invention may be added to the base resin such as an antioxidizing agent, a surfactant, a icing inhibitor, a matting agent, a corrosion inhibitor, a preservative, a thixotropic agent, and a fragrance. , A colorant and the like can be added. As antioxidizing agents, tocopherol, nordihydroguaiaretinic acid, N, N′-diphenyl-p-phenylenediamine, N-phenylene-N′-isopropyl-p-phenylenediamine, dilaurylthiodipropionate, 2-mercaptobenzothiazole, Hydroquinone dimethyl ether, dibenzothiazine, trilauryl trithiophosphite, diphenylol propane,
Cyclohexylphenol, butylhydroxyanisole, 2,2′-methylene-bis (4-methyl-6-t-butyl-phenol), propyl gallate and the like are used.

[0021]

EXAMPLES The present invention will be described in detail based on examples. (Example 1) Formulation examples 1 to 1 of the present invention as shown below
3. The water-soluble fluxes of Conventional Formulation Examples 1 and 2 were prepared. Formulation Example 1 Mannitol 350 g Ethylene glycol 150 g Diethylamine hydrochloride 50 g Water 50 g Butyl cellosolve 200 g Formulation example 2 Sorbitol 50% aqueous solution 500 g Polyethylene glycol # 400 100 g Ethylene glycol 150 g Propylene glycol 150 g Butyl cellosolve 70 g 35% Hydrochloric acid 30 g

Comparative Formulation Example 1 Polyethylene glycol # 400 350 g Ethylene glycol 150 g Propylene glycol 150 g Butylcellosolve 70 g Water 250 g 35% Hydrochloric acid 30 g Comparative formulation example 2 Polyethylene glycol # 400 550 g Diethylamine hydrochloride 50 g Butylcellosolve 200 g Water 200 g

Formulation Example 3 Mannitol 150 g Erythritol 150 g Ethylamine hydrochloride 30 g Glycolic acid 30 g Propylene glycol 240 g Isopropyl alcohol 150 g Water 250 g

On one side of a 30 × 21 cm copper-clad laminate (glass-epoxy base material), a thermosetting solder (CCR-2000S-3, manufactured by Asahi Chemical Laboratory) was used.
A test board having 1000 copper patterns of 1.0 mm square was formed. After applying each flux shown above to a thickness of about 0.1 mm, it was immersed in a solder bath at 240 ° C. for 4 seconds, and excess solder was removed by high temperature (250 ° C.) air. After this substrate was brush-cleaned with water at 40 ° C., the soldering state was observed.

Table 2 shows the results of averaging the results of five experiments with each flux. Table 2 shows that red eye (non-soldered portion) was generated in the conventional example, but red eye was not generated in the case of the present invention. It was There was no difference in the cleanability after soldering.

[0026]

Example 2 A water-soluble flux was used as a base material, a 70% aqueous solution of sorbitol, diethylamine hydrochloride and glycolic acid as an activator, ethylene glycol and butyl cellosolve as a diluent, and nordihydroguaiaretinic acid as an antioxidant. A mixture of polyoxyethylene nonylphenyl ether as a surfactant, sodium benzoate as a corrosion inhibitor, sorbic acid as a preservative, and colloidal silica as a thixotropic agent was mixed and prepared in the following composition. With this formulation, as in the case of the present invention shown in Example 1, no red eye was observed in a soldering experiment using a solder leveler.

70% aqueous sorbitol solution 600 g ethylene glycol 200 g butyl cellosolve 70 g diethylamine hydrochloride 50 g glycolic acid 15 g polyoxyethylene nonylphenyl ether 50 g nordihydroguaiaretinic acid 1 g sodium benzoate 3 g sorbic acid 1 g colloidal silica 10 g

[0029]

INDUSTRIAL APPLICABILITY The present invention provides a water-soluble flux which contains at least one sugar alcohol selected from sorbitol, mannitol, erythritol, etc., and has a very good solderability without red eyes. Provided.

Claims (1)

[Claims] 1. A water-soluble flux used in a soldering process, wherein at least one sugar alcohol selected from sorbitol, mannitol, erythritol and the like is used.
A water-soluble flux characterized by containing a seed.