JP2561150B2 - Surface treatment method for copper and copper alloys - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for forming a coating film containing alkylimidazole as a main component, which has excellent heat resistance, on the surface of copper and a copper alloy, and particularly to a circuit in a printed wiring board. The present invention provides a suitable method as the pre-flux treatment shown in the figure.

2. Description of the Related Art A surface treatment method for forming a film of a 2-position long-chain alkylimidazole compound on the surface of copper or a copper alloy is disclosed in Japanese Patent Publication No.
46-17046, 48-11454, 48-25621, 49-1
983, 49-26183, 58-22545, 61-41988 and JP-A-61-90492.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention A coating film of a 2-position long-chain alkylimidazole compound formed on the surface of copper or a copper alloy is stable at around room temperature but discolors in a relatively short time at high temperature, and solder on the film surface There is a fear that it will interfere with the attachment. In recent years, a surface mounting method has been widely adopted as a method for joining electronic components to a printed wiring board. According to this method, chip components are temporarily fixed, both sides of a component device are mounted, or chip components and discrete components are mixedly mounted. , Especially printed wiring boards are exposed to high temperatures.

Therefore, in order to obtain good solderability, it is necessary to improve the heat resistance of the alkylimidazole coating used as the preflux.

Means for Solving the Problems As a result of repeating various tests, the inventors of the present invention contacted the surface of copper or a copper alloy with an aqueous solution containing a 2-position long-chain alkylimidazole compound, an organic acid and a zinc compound. The inventors have found that a chemical conversion coating having excellent heat resistance as compared with conventional methods can be obtained, and completed the present invention.

Typical examples of the 2-position long-chain alkylimidazole compound used in the method of the present invention include 2-amylimidazole, 2-heptylimidazole, 2-decylimidazole, 2-undecylimidazole, 2-dodecylimidazole and 2-tridecylimidazole. There are decyl imidazole, 2-tetradecyl imidazole, 2-heptadecyl imidazole, 2-undecyl-4-methyl imidazole, 2-heptadecyl-4-methyl imidazole and salts thereof, particularly 2-undecyl imidazole and 2-undecyl- 4-Methylimidazole and salts thereof are preferred.

In carrying out the method of the present invention, the 2-position long-chain alkylimidazole compound may be added to water in the range of 0.01 to 5%, preferably 0.1 to 2%.

In the practice of the method of the present invention, the 2-chain long-chain alkylimidazole is poorly soluble in water. Therefore, in order to dissolve them in water, the long-chain alkylimidazole is reacted with an organic acid to dissolve it in water. You can use salt.

As the organic acid used in the practice of the method of the present invention, formic acid, acetic acid, propionic acid, capric acid, glycolic acid, acrylic acid, benzoic acid, paranitrobenzoic acid, parabutyl benzoic acid, paratoluene sulfonic acid, picric acid, salicylic acid, m-toluic acid, oxalic acid, succinic acid, maleic acid, fumaric acid, tartaric acid, adipic acid, etc.,
It may be added in the range of 0.01 to 15%, preferably 0.2 to 5% with respect to water.

Suitable zinc compounds for carrying out the method of the present invention include zinc formate, zinc acetate, zinc oxalate, zinc lactate, zinc citrate,
Zinc benzoate, zinc salicylate, zinc chloride, zinc sulfate,
There are zinc nitrate, zinc phosphate, etc., 0.02-5% to water
In the range of 0.1 to 2%, preferably 0.1 to 2%.

In order to carry out the method of the present invention, the surface of copper or a copper alloy may be mechanically polished or acid washed, and then these metals may be immersed in a treatment liquid, or the treatment liquid may be applied or sprayed on the metal surface.

In the method of the present invention, the treatment liquid may be brought into contact with the surface of copper or copper alloy in the temperature range of about 20 ° C. to 60 ° C. for 5 seconds to several minutes.

The working 2-position long-chain alkylimidazole compound dissolves well in an acidic aqueous solution and is ionized. This ionized imidazole has a strong reactivity with copper and forms a monomolecular imidazole film on the copper surface. It is known that the remaining alkyl imidazole in the treatment liquid is further gathered on the monomolecular film due to both the hydrogen bond between long-chain alkyl imidazoles and the Van der Waals force, and the film on the copper surface grows thickly. ing. In this case, the formation rate of the imidazole film depends on the type and amount of the organic acid added.

Since the imidazole film formed in this way has high reactivity with copper, it easily reacts with metallic copper on the substrate,
It forms an alkyl imidazole metal complex in a short time. This alkylimidazole metal complex gradually undergoes oxidative decomposition at high temperature due to the catalytic action of copper atoms in the molecule.
When this complex is formed on copper metal, it is easily oxidatively decomposed in air at high temperature due to the catalytic action of metallic copper.
Therefore, suppressing the strong catalytic action of copper leads to improvement in heat resistance of the formed film.

The detailed mechanism by which the heat resistance of the coating is improved when zinc ions are present in the treatment liquid is not clear, but one reason is considered to be due to the high ionization engagement of zinc. That is, since the ionization tendency of zinc is higher than that of copper, when the surfaces of copper and copper alloys are treated with an aqueous solution containing an alkylimidazole, an organic acid and a zinc compound, the dissolution of copper ions in the liquid and the film is considerably reduced. It is considered that zinc ions, which are suppressed and are re-entrapped in the film formed, considerably suppress the catalytic action of copper at the time of heating, so that the heat resistance of this chemical conversion film is improved.

In addition, various imidazole-zinc complexes are also used as flux activators (Japanese Patent Application No. 62-222371).
No.), the alkylimidazole zinc complex, which is considered to be present in the formed film, may contribute to the improvement of solderability.

The method of the present invention will be specifically described below with reference to Examples and Comparative Examples.

In these tests, the thickness of the chemical conversion coating on the metal surface was determined by immersing a test piece of a predetermined size in a 0.5% aqueous hydrochloric acid solution to elute the long-chain alkylimidazole and using an ultraviolet spectrophotometer. The concentration of the long-chain alkyl imidazole contained in the solution was measured, and the thickness of the chemical conversion coating was calculated based on the following empirical formula.

Film thickness (μ) = 0.253 x A x y / S Example 1 and Comparative Example 1 2-undecyl-4-methylimidazole (1.0 g) in acetic acid
Add 0.40 ml to dissolve imidazole and
Add 0 ml and stir well to make a uniform solution (pH 4.75),
0.34 g of zinc acetate dihydrate was added to this solution and dissolved with stirring to prepare a treatment liquid.

Then, the copper surface of the 4 cm x 4 cm copper clad laminate was polished with a wet abrasive (trade name "Scotch Bright" manufactured by Sumitomo 3M), immersed in a 0.5% hydrochloric acid aqueous solution for 15 seconds, washed thoroughly with water and dried. It was made into the test piece. The test piece was immersed in the treatment solution at a liquid temperature of 50 ° C. for 1 minute while oscillating, washed with water and dried, and the chemical conversion film of the test piece was 0.65 μm. This test piece was left to stand in a circulating dryer at a temperature of 150 ° C. and 210 ° C. for a predetermined time to perform a heat treatment.

A eutectic solder was used for the heat-treated test piece, and the spread rate of the solder was measured by the method of JIS Z-3197.

The results are as shown in Table 1. In this test, 120 g / dl of isopropyl alcohol solution of w / w rosin was used as post-flux, the measurement was performed 5 times, and the average value was calculated.

For comparison, 1.0 g of 2-undecyl-4-methylimidazole was added to 0.40 ml of acetic acid to dissolve it, and then 10 g of pure water was added.
0 ml was added and well stirred to prepare a treatment liquid having a pH of 4.75.
When a treatment was carried out using this treatment liquid under the same conditions as in Example 1, the thickness of the chemical conversion coating on the surface of the test piece was
It was 0.60μ, and the solder spreading ratio after heating was as shown in the same table.

Example 2 Lactic acid in 1.0 g of 2-undecyl-4-methylimidazole
0.57 g was added to dissolve imidazole, and 100 ml of pure water was added.
Was added and stirred well to form a uniform solution (pH 4.62), and 0.91 g of zinc lactate was added to this solution and dissolved by stirring to prepare a treatment solution.

Then, when the same operation as in Example 1 was performed, the film thickness was
0.55μ, the spread of the solder was 80.9% after heating at 150 ° C. for 3 hours, 67.2% after heating at 150 ° C. for 5 hours, and 51.0% after heating at 210 ° C. for 20 minutes. there were.

Example 3 To 0.2 g of 2-undecylimidazole, 0.29 g of formic acid was added to dissolve imidazole, 100 ml of pure water was added, and the mixture was well stirred to give a uniform solution of pH 4.60, and the solution thus prepared was added. Zinc formate 0.29 g, 0.59 g and 0.88 g were added respectively and dissolved by stirring to prepare three kinds of treatment liquids.

Then, using the same test piece as in Example 1, the same pretreatment was performed, and after dipping in the treatment liquid at a liquid temperature of 50 ° C. for 30 seconds,
After heating for 4 minutes on a solder bath at 250 ° C., 20 g / dl of isopropyl alcohol solution of w / w rosin was used as post flux to measure the spread rate of solder. As a result, the spread rate of the solder was 0.29 g of zinc formate.
65.3% when adding, and 78 when adding 0.59 g.
8% and 70.0% when 0.8g was added.

Comparative Example 2 0.29 g of formic acid was added to 1.0 g of 2-undecylimidazole to dissolve the imidazole, 100 ml of pure water was further added, and the mixture was stirred well to prepare a treatment liquid having a pH of 4.60, and treated in the same manner as in Example 3 above. After forming a coating film and heat treatment, the spread rate of the solder was measured and found to be 33.8%.

Example 4 0.92 g of lactic acid was added to 1.5 g of 2-undecylimidazole to dissolve the imidazole, 100 ml of pure water was added, and the mixture was stirred well to obtain a uniform solution of pH 4.65, and zinc acetate dihydrate was added to this solution. 0.34 g of the product was added and dissolved by stirring to prepare a treatment liquid.

On the other hand, the surface of deoxidized copper (JIS C-1220) of 10 mm x 50 mm x 0.3 mm was wet-polished with the product name "Scotch Bright" Sumitomo 3M
Manufactured by K.K.], degreased with ethanol, further immersed in a 0.5% hydrochloric acid aqueous solution for 15 seconds, washed well with water and dried to obtain a test piece. This test piece was immersed in the treatment liquid at a liquid temperature of 50 ° C. for 30 seconds, and then left in a circulating dryer at a temperature of 150 ° C. for 90 minutes for heat treatment.

Solder wetting tester after heat treatment (WET-3000, Co., Ltd.)
The time from the start of immersion until the buoyancy due to the surface tension becomes zero was measured using a Resca product.

The test piece is post-flux [trade name "JS-64MS-
1 "(made by Hiroki Co., Ltd.), and the liquid was thoroughly wetted with a filter paper, and then the measurement was performed. The measurement was performed at a dipping depth of 2 mm to a dipping speed of 120 mm / sec.
It was 1.90 seconds.

Comparative Example 3 0.92 g of lactic acid was added to 1.5 g of 2-undecylimidazole to dissolve the imidazole, 100 ml of pure water was added, and the mixture was stirred well to prepare a treatment liquid having a pH of 4.65 and treated in the same manner as in Example 4 above. After forming the coating film and heat treatment, the wetting time was measured by the solder wettability tester.
It was 3.30 seconds.

Example 5 2.0 g of 2-undecylimidazole and 1.30 g of acrylic acid
Was added to dissolve imidazole, 100 ml of pure water was further added, and well stirred to form a uniform solution (pH 4.31). To this solution, 1.0 g of zinc acetate dihydrate was added and stirred to dissolve the treatment liquid. Prepared.

Then as post-flux [Product name "GX-7"
Asahi Kagaku Kenkyusho Co., Ltd. was used and the solder wettability was measured in the same manner as in Example 4, and the wetting time was 0.80 seconds.

Comparative Example 4 2.0 g of 2-undecylimidazole and 1.30 g of acrylic acid
Was added to dissolve imidazole, 100 ml of pure water was further added, and the mixture was stirred well to prepare a treatment solution having a pH of 4.31.

Next, after performing film formation and heat treatment in the same manner as in Example 5, the wetting time was measured by a solder wettability tester, and the result was 1.52 seconds.

EFFECTS OF THE INVENTION According to the method of the present invention, it is possible to form a heat-resistant chemical conversion coating film containing a 2-position long-chain alkylimidazole compound as a main component on the surface of copper or a copper alloy, and in particular, a surface mounting method for a printed wiring board. The good solderability after the heating step can be improved.

Claims (3)

(57) [Claims] 1. A method for surface-treating copper or a copper alloy, which comprises bringing the surface of copper or a copper alloy into contact with an aqueous solution containing a 2-position long-chain alkylimidazole compound, an organic acid and a zinc compound. 2. A 2-undecylimidazole compound is used as the 2-position long-chain alkylimidazole compound.
The method for surface treatment of copper and copper alloy according to. 3. The surface treatment method for copper and copper alloys according to claim 1, wherein 2-undecyl-4-methylimidazole is used as the 2-position long-chain alkylimidazole compound.