JP2834884B2 - Copper and copper alloy surface treatment method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of forming a chemical conversion coating having excellent heat resistance on the surface of copper and a copper alloy, and more particularly to a hard printed wiring board or a flexible printed wiring board. And a method suitable for the pre-flux treatment of the circuit section in the above.

[Conventional technology]

JP-B-46-17046, JP-B-48-11454, JP-B-48-25621, and JP-B-4-25646 disclose surface treatment methods for forming a coating of a 2-position long-chain alkylimidazole compound on the surface of copper or a copper alloy.
No. 9-1983, No. 49-26183, No. 58-22545, No. 61-419
No. 88 and JP-A-61-90492.

As a method of forming a conversion coating of a benzimidazole compound on the surface of copper or a copper alloy, Japanese Patent Application Laid-Open No.
No. 1281 discloses a method using 5-methylbenzimidazole.

In recent years, surface mounting has been widely used as a method of joining electronic components to printed wiring boards. Printed wiring boards have been used by temporarily fixing chip components, mounting both sides of component devices, or mixing chip components and discrete components. Have been exposed to high temperatures.

However, a conventional conversion coating of a long-chain alkylimidazole formed at the 2-position on a copper circuit portion is stable at around room temperature, but discolors at high temperatures, and may sometimes hinder soldering. In addition, the surface treatment method of copper metal using a 5-methylbenzimidazole compound, since these benzimidazole compounds are relatively easily soluble in water, to form a conversion coating of 0.08 μm or more which is recognized as a preferable film thickness. Therefore, it was difficult to perform the role of protecting the underlayer during heating.

In order to cope with such a surface mounting method, the present inventors have proposed a benzimidazole compound (hereinafter, a 2-alkylbenzimidazole compound) having an alkyl group having 3 or more carbon atoms at the 2-position on the surface of copper or a copper alloy. ) And an aqueous solution containing an organic acid to form a pre-flux coating having excellent heat resistance.

[Problems to be solved by the invention]

However, when the method of treating the surface of the copper metal by contacting it with an aqueous solution containing a 2-alkylbenzimidazole compound and an organic acid is carried out, generally, in a pretreatment step of removing stains on the copper metal surface, sodium persulfate is used. A soft etching solution comprising ammonium persulfate or sulfuric acid and hydrogen peroxide is used.

Therefore, when the pretreatment and the formation of the chemical conversion film are continuously performed, the etching solution containing a sulfate group is gradually mixed into the treatment solution containing a 2-alkylbenzimidazole compound, and as a result, copper or a copper alloy is formed. There are various problems such that the chemical conversion film formed on the surface is not uniform, the thickness of the chemical conversion film is significantly reduced, and sometimes a sulfate of an oily 2-alkylbenzimidazole compound is precipitated. It has been found.

[Means for solving the problem]

As a result of repeated studies to solve such a problem, the present inventors have found that the surface of copper or a copper alloy contains a 2-alkylbenzimidazole compound, an organic acid and barium ions or barium ions or barium ions and halogen ions. The inventor has found that the intended purpose can be achieved by contact with an aqueous solution, thereby completing the present invention.

Representative examples of the 2-alkylbenzimidazole compound used in the practice of the method of the present invention include a compound represented by a general formula (Wherein, R ₁ represents an alkyl group having 3 or more carbon atoms) 2-propylbenzimidazole, 2-butylbenzimidazole, 2-pentylbenzimidazole, 2-hexylbenzimidazole, 2-heptylbenzimidazole , 2-octylbenzimidazole,
2-nonylbenzimidazole, 2-undecylbenzimidazole, 2-heptadecylbenzimidazole and salts thereof, general formula (Wherein, R ₁ is the same as described above, and R ₂ , R ₃ and R ₄ represent a lower alkyl group, a halogen atom, a nitro group or a hydrogen atom, and one of them is a lower alkyl group, a halogen atom or a nitro group. 2-propyl-5-methylbenzimidazole, 2-propyl-4,5-dimethylbenzimidazole, 2-butyl-5-chlorobenzimidazole,
2-butyl-5-nitrobenzimidazole, 2-pentyl-4-methylbenzimidazole, 2-pentyl-
5-methyl-benzimidazole, 2-pentyl-5,6
-Dichlorobenzimidazole, 2-hexyl-5,6-
Dimethylbenzimidazole, 2-hexyl-5-nitrobenzimidazole, 2-heptyl-4-methylbenzimidazole, 2-heptyl-5-methylbenzimidazole, 2-heptyl-5-chlorobenzimidazole, 2-octyl-5, 6-dichlorobenzimidazole, 2-octyl-5-chlorobenzimidazole, 2
-Nonyl-4-methylbenzimidazole, 2-nonyl-4,5-dimethylbenzimidazole, 2-nonyl-5
-Nitrobenzimidazole, 2-undecyl-4-methylbenzimidazole, 2-heptadecyl-5-methylbenzimidazole and salts thereof, and 2-propyl-4-methylbenzimidazole and 2-propyl-5
-Methylbenzimidazole mixture, 2-butyl-4
A mixture of -methylbenzimidazole and 2-butyl-5-methylbenzimidazole, a mixture of 2-pentyl-4-methylbenzimidazole and 2-pentyl-5-methylbenzimidazole, 2-hexyl-4-methylbenzimidazole and 2 Mixture of 2-hexyl-5-methylbenzimidazole, mixture of 2-heptyl-4-methylbenzimidazole and 2-heptyl-5-methylbenzimidazole, 2-octyl-4-methylbenzimidazole and 2-octyl-5-methyl A mixture of benzimidazole, a mixture of 2-nonyl-4-methylbenzimidazole and 2-nonyl-5-methylbenzimidazole, a mixture of 2-undecyl-4-methylbenzimidazole and 2-undecyl-5-methylbenzimidazole, 2 −Heptade Mixture and salts of these mixtures-4-methylbenzimidazole and 2-heptadecyl-5-methylbenzimidazole, and the like.

When a benzimidazole compound having an alkyl group having a small number of carbon atoms at the 2-position is used, a part of the chemical conversion film formed on the surface of copper metal tends to elute, and benzimidazole having an alkyl group having a large number of carbon atoms. When a is used, a large amount of an organic acid is required to form a treatment solution, and therefore, an alkyl group at the 2-position having 5 to 9 carbon atoms is particularly preferable.

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

In the practice of the method of the present invention, since 2-alkylbenzimidazoles are hardly soluble in water, to dissolve them in water, alkylbenzimidazole is reacted with an organic acid to form a water-soluble salt. And it is sufficient.

The organic acids used in the practice of the method of the present invention include formic acid, acetic acid, lactic acid, propionic acid, capric acid, glycolic acid, acrylic acid, benzoic acid, paranitrobenzoic acid, parabutylbenzoic acid, paratoluenesulfonic acid,
Picric acid, salicylic acid, metatoluic acid, acid, succinic acid, maleic acid, fumaric acid, tartaric acid, adipic acid, etc., in the range of 0.01 to 15% based on water, preferably 0.2 to
It may be added at a rate of 5%.

The compound used as a barium ion source used in the practice of the method of the present invention is suitably soluble in water or an acidic aqueous solution, and typical examples thereof include barium bromide, barium chloride, barium fluoride, and water. Barium oxide, barium carbonate, barium nitrate, barium phosphate, barium oxide, barium oxide, barium acetate and the like, among which barium bromide, barium chloride and barium hydroxide are particularly preferred.

In the practice of the present invention, the barium compound should be added in such a proportion that the barium ion concentration in the treatment liquid is at least 50 ppm or more, preferably 200 to 5000 ppm.

In the case where barium ions and halogen ions coexist in the treatment liquid, compounds used as a halogen ion supply source include hydrohalic acids such as hydrochloric acid and hydrobromic acid, sodium chloride, potassium chloride, barium chloride, and bromide. Alkali metals such as barium, sodium iodide, sodium fluoride, potassium fluoride, ammonium chloride, ammonium bromide, halides of alkaline earth metals and ammonium ions, chromium chloride, nickel chloride, cupric chloride, zinc chloride, It is a halide of a first transition series metal such as nickel bromide and copper bromide. Of these, ammonium chloride, ammonium bromide, cupric chloride and cupric bromide are particularly preferred.

In this case, the halogen ion concentration in the treatment liquid should be added at a rate of at least 50 ppm or more, preferably 200 to 5000 ppm.If the amount of the halogen ions is too large, the chemical conversion formed on the surface of the copper metal The moisture resistance of the coating tends to decrease.

In the practice of the present invention, a 2-alkylbenzimidazole compound and an organic acid, and an aqueous solution containing barium ions or barium ions and halogen ions,
By adding a copper compound or a zinc compound and bringing it into contact with the surface of copper or a copper alloy, the heat resistance of the chemical conversion film can be further increased.

Representative copper compounds that can be used in these methods include cuprous chloride, cupric chloride, copper bromide,
Copper hydroxide, copper phosphate, etc., typical zinc compounds include zinc oxide, zinc formate, zinc acetate, zinc acid,
Zinc lactate, zinc citrate, zinc benzoate, zinc salicylate, zinc phosphate, etc.
It is desirable to add at a ratio of 0.1 to 5%.

In the practice of the present invention, a copper or copper alloy surface is contacted with an aqueous solution containing a 2-alkylbenzimidazole compound and an organic acid, and a barium ion or a compound that generates a barium ion and a halogen ion. May be brought into contact with an aqueous solution containing the copper compound or the zinc compound.

It is preferable to add a substance having a buffering action such as ammonia water or amines to the treatment liquid to stably maintain the pH of the solution.

In the practice of the present invention, when the treatment is performed for a long time, barium sulfate is precipitated by the sulfate group contained in the soft etching solution gradually brought into the treatment solution and the treatment solution becomes cloudy. It is desirable to pass the treatment liquid through a circulation system equipped with a filter to remove the generated barium sulfate out of the system.

In the method of the present invention, the step of contacting the surface of the copper or copper alloy with an aqueous solution containing a 2-alkylbenzimidazole compound and an organic acid and barium ions or barium ions and halogen ions is carried out at a temperature of the aqueous solution of about 20 ° C.
To 60 ° C. for a contact time of one second to several minutes.

As a means for bringing the treatment liquid into contact with the surface of copper or a copper alloy, any of immersion, coating, and spraying is possible.

In the practice of the method of the present invention, it is also possible to form a two-layer structure of a thermoplastic resin on the chemical conversion film to improve heat resistance.

That is, after forming a chemical conversion film on the surface of copper or copper alloy, rosin, rosin derivative such as rosin ester, terpene resin, terpene resin derivative such as terpene phenol resin and aromatic hydrocarbon resin, aliphatic hydrocarbon resin, oil Dissolve a thermoplastic resin having excellent heat resistance, such as a hydrocarbon resin such as a cyclic hydrocarbon resin, in a solvent such as toluene, ethyl acetate, or IPA, and form a film having a thickness of 1 to 30 μm on the chemical conversion film by a roll coater method or the like. Preferably, the coating may be performed uniformly so as to have a thickness of 2 to 20 μm.

The contact between a 2-alkylbenzimidazole compound and an organic acid and an aqueous solution containing barium ion or barium ion and halogen ion is brought into contact with the surface of copper or a copper alloy to form a complex between the 2-alkylbenzimidazole compound and copper. By the action of both the hydrogen bond between the 2-alkylbenzimidazole compounds and the van der Waals force, a chemical conversion coating of the 2-alkylbenzimidazole compound which locally becomes a copper complex is formed on the copper surface.

When the thus formed chemical conversion coating is left or heated, copper migration from the copper surface occurs, and most of the 2-alkylbenzimidazole compound becomes a 2-alkylbenzimidazole copper complex, and the 2-alkylbenzimidazole compound Since the chemical conversion coating consisting of comprises a conjugated benzene ring, it is considered to be thermally stable.

When contacting the surface of copper or a copper alloy with an aqueous solution containing a 2-alkylbenzimidazole compound, an organic acid and barium ion or a barium ion and a halogen ion or a copper compound or a zinc compound, a conversion coating of the 2-alkylbenzimidazole compound is used. In the process of forming on the metal surface, copper or zinc is taken into the chemical conversion film to form a 2-alkylbenzimidazole zinc complex, so that the heat resistance of the chemical conversion film is considered to be improved.

In forming such a chemical conversion coating, sodium persulfate, ammonium persulfate or sulfuric acid and hydrogen peroxide are used in a soft etching treatment step for removing dirt on a copper metal surface as a pretreatment, and these are 2-alkyl. When mixed and accumulated in a treatment solution containing a benzimidazole compound, the uniformity of the conversion coating formed on the surface of copper or copper alloy is impaired, and the thickness of the conversion coating is extremely reduced. If an appropriate amount of barium ions is present, sulfate groups contained in the soft etching agent brought into the processing solution react with barium ions to form insoluble barium sulfate and precipitate out of the system. The formation of a sulfate of a benzimidazole compound is prevented beforehand, so that the above-mentioned obstacles can be avoided and the properties of the chemical conversion film are not spun.

When barium ions and halogen ions coexist in the treatment liquid, the effect of suppressing troubles caused by the soft etching agent containing sulfate is further enhanced.

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

In these tests, the thickness of the conversion coating on the metal surface was determined by immersing a test piece of a predetermined size in a 0.5% hydrochloric acid aqueous solution to extract a 2-alkylbenzimidazole compound, and using an ultraviolet spectrophotometer. The concentration of the compound contained in this extract was measured and calculated based on the empirical formula shown by the following equation.

Film thickness (μ) = 0.2579 × A × y ÷ X (where A is the maximum absorbance around 268.5 nm, x is the surface area of copper metal (cm ² ), and y is the amount (ml) of the extract used) In addition, the solder wetting time depends on the treated test piece (5m
(m × 50mm × 0.3mm) is immersed in post flux (trade name “JS-64” manufactured by Hiroki Co., Ltd.) immediately before measurement, and measured with a solder wettability tester (SAT-2000, manufactured by Resca Corporation). The measurement conditions were a solder temperature of 240 ° C., an immersion depth of 2 mm, and an immersion speed of 16 mm / sec.

Examples 1 to 3 and Comparative Examples 1 and 2 A strip-shaped copper plate (length 50 mm, width 5 mm, thickness 0.3 mm) was degreased,
After polishing and washing, a test piece was made.
Each of the test pieces was immersed in a treatment aqueous solution having the composition shown in Table 2 at a given temperature for a given time, washed with water, and dried to form a chemical conversion coating of 0.2 μm (excluding Comparative Example 1 and No. 2) on the surface of each test piece. Was formed.

For comparison, a similar test was performed using a treatment solution containing no barium ion.

After the test piece subjected to the above treatment was visually inspected for the condition of the chemical conversion film, the heat treatment was performed at 120 ° C.
The steps of heating for 5 minutes in an oven for 5 minutes and in a gas phase at 215 ° C. (“Fluorinert FC-70” manufactured by 3M) for 5 minutes were repeated three times, and the solder wettability of the heat-treated test pieces was measured.

The test results are as shown in Table 1. In the case where barium ions were present in the treatment liquid, even if a soft etching agent was added to the treatment liquid, there was no effect on the conversion coating. After the reflow heat treatment,
The solder wettability of the conversion coating was almost unchanged.

Examples 4 to 9 A copper plate test produced by performing the same treatment as in the above example was immersed in a treatment aqueous solution having the composition shown in Table 2 at a predetermined temperature for a predetermined time, washed with water, and dried. A chemical conversion coating was formed on the surface of each test piece.

The conversion coatings of the test pieces thus treated were all uniform and uniform, and the film thickness was as shown in the table.

Next, each test piece was subjected to the same heat treatment in the same reflow furnace as in the above-described example, and the solder wettability of the test piece was measured.

The test results are as shown in Table 2. When barium ions were present in the processing liquid, the processing liquid was almost the same as the processing liquid without the soft etching agent even if the soft etching agent was added. It had the same solder wettability.

Example 10 A brass plate (length 50 mm, width 5 mm, thickness 0.3 mm) was soft-etched in the same manner as in Example 1 to produce a polished surface test piece. When the test piece was immersed in a treatment aqueous solution having the same composition as that of No. 2 at a liquid temperature of 40 ° C. for 30 seconds, washed with water, and dried, a uniform chemical conversion film was formed on the test piece surface without any unevenness. Is
It was 0.31 μm and 0.36 μm.

[Effects of the Invention] According to the method of the present invention, it is possible to form a chemical coating having high heat resistance on the surface of copper and a copper alloy, and at that time, an etching agent containing a sulfate group is mixed in the treatment liquid. Also, since the formation of the chemical conversion film and the characteristics of the film are not affected, the present invention can exert a remarkable effect particularly in improving the soldering work in the surface mounting method of the printed wiring board.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-3-28381 (JP, A) JP-A-3-2383 (JP, A) JP-A-4-80375 (JP, A) JP-A-4- 157174 (JP, A) JP-A-4-99285 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C23C 22/00-22/86

Claims (5)

(57) [Claims] 1. The method according to claim 1, wherein the surface of the copper or copper alloy is at least 2
A surface treatment method for copper and copper alloys, which comprises contacting a benzimidazole compound having an alkyl group having 3 or more carbon atoms at the position with an organic acid and an aqueous solution containing 50 ppm or more of barium ion. 2. The method according to claim 1, wherein the surface of the copper or copper alloy is
A surface treatment method for copper and copper alloys, which comprises contacting a benzimidazole compound having an alkyl group having 3 or more carbon atoms at the position with an organic acid and an aqueous solution containing 50 ppm or more of barium ion and halogen ion. 3. The copper and copper alloy according to claim 1, wherein any one of barium chloride, barium bromide and barium hydroxide is used as a supply source of barium ions. Surface treatment method. 4. The method according to claim 1, wherein the surface of the copper or copper alloy is
A surface treatment method for copper and a copper alloy, comprising contacting an aqueous solution containing a benzimidazole compound having an alkyl group having 3 or more carbon atoms at a position, an organic acid, and 50 ppm or more of barium ion and a copper compound. 5. The method according to claim 5, wherein the surface of the copper or copper alloy is at least 2
A surface treatment method for copper and a copper alloy, comprising contacting an aqueous solution containing a benzimidazole compound having an alkyl group having 3 or more carbon atoms at a position, an organic acid, and 50 ppm or more of barium ion and a zinc compound.