WO2010024472A1

WO2010024472A1 - Surface treating agent for copper or copper alloy and use thereof

Info

Publication number: WO2010024472A1
Application number: PCT/JP2009/065562
Authority: WO
Inventors: Hirohiko Hirao; Noriaki Yamaji; Takayuki Murai
Original assignee: Shikoku Chemicals Corporation
Priority date: 2008-09-01
Filing date: 2009-09-01
Publication date: 2010-03-04
Also published as: TWI448581B; JP2010059445A; TW201011125A; CN102137953B; CN102137953A; KR20110063440A; KR101520992B1; JP5321878B2

Abstract

An object is to provide a surface treating agent, which in mounting electronic parts or the like to a printed wiring board using a lead-free solder, forms a chemical layer having excellent heat resistance on the surface of copper or a copper alloy constituting a circuit part of a printed wiring board or the like and at the same time, improves the wettability to the solder and makes the solderability good, and a surface treatment method. Also, another object is to provide a printed wiring board resulting from bringing the surface of copper or a copper alloy constituting a copper circuit part into contact with the foregoing surface treating agent and to provide a soldering method by bringing the surface of copper or a copper alloy into contact with the foregoing surface treating agent and then performing soldering using a lead-free solder. A surface treating agent for copper or a copper alloy, which contains an imidazole compound represented by the formula (I): wherein R₁, R₂ and R₃ are the same or different and represent a hydrogen atom or an alkyl group having 1 to 8 carbon atoms; and at least one selected from R₁, R₂ and R₃ is an alkyl group having 4 or more carbon atoms.

Description

DESCRIPTION

SURFACE TREATING AGENT FOR COPPER OR COPPER ALLOY AND USE THEREOF

Technical Field

The present invention relates to a surface treating agent which is used during soldering electronic parts or the like to copper or a copper alloy of a printed wiring board, and use thereof.

Background Art

In recent years, surface mount technology with high density has been widely adopted as a mount method of a printed wiring board. Such surface mount technology is classified, among others, into double-sided surface mount technology in which chip type parts are joined with use of solder paste, and hybrid mount technology which is a combination of surface mount technology of chip type parts using solder paste and through-hole mount technology of discrete parts. In either mount process, a printed wiring board is subjected to two or more soldering steps, and thus it is exposed to high temperatures resulting in a severe thermal history.

As a result, oxide film formation is accelerated by heating the surface of copper or copper alloys (hereinafter sometimes simply referred to as copper) constituting the circuit part of a printed wiring board, and thus the surface of the circuit part cannot maintain good solderability .

In order to protect the copper circuit part of the printed wiring board from air oxidation, a chemical layer is generally formed on the surface of the circuit part using a surface treating agent. It is necessary, however, that good solderability be maintained by preventing the chemical layer from degenerating (i.e., being degraded) to protect the copper circuit part even after the copper circuit part has a thermal history of multiple cycles.

Tin-lead alloy eutectic solders have been conventionally used for mounting electronic parts to a printed wiring board, etc. In recent years, however, concerns have developed that the lead contained in the solder alloy adversely affects the human body, and thus the use of a lead-free solder is desired.

Accordingly, various lead-free solders are being considered. For example, lead-free solders have been suggested in which one or more metals, such as silver, zinc, bismuth, indium, antimony, copper, etc. , are added to a base metal of tin .

The conventionally used tin-lead eutectic solder is excellent in wettability on the surface of a substrate, particularly copper, and thus strongly adheres to copper, resulting in high reliability.

In contrast, a lead-free solder is inferior to the conventionally used tin-lead solder in wettability on a copper surface, and thus exhibits poor solderability and low bonding strength due to voids and other bonding defects .

Therefore, when using a lead-free solder, it is necessary to select a solder alloy with superior solderability and a flux which is suitable for use with the lead-free solder. A surface treatment agent for use in preventing oxidation on the surface of copper or a copper alloy is also required to have functions for improving the wettability and solderability of the lead- free solder .

Many lead-free solders have a high melting point, and a soldering temperature that is about 20 to about 50°C higher than that of the conventionally used tin-lead eutectic solder. Thus, the surface treatment agent for use in the process of soldering with the lead-free solder should have the characteristic of being able to form a chemical layer with excellent heat resistance.

As active ingredients of such surface treating agents, various imidazole compounds have been proposed. For example, Patent Document 1 discloses 2-alkγlimidazole compounds such as 2-undecylimidazole; Patent Document 2 discloses 2-arγlimidazole compounds such as 2- phenylimidazole and 2-phenγl-4-methγlimidazole; Patent Document 3 discloses 2-alkγlbenzimidazole compounds such as 2-nonγlbenzimidazole; Patent Document 4 discloses 2- aralkγlbenzimidazole compounds such as 2-(4- chlorophenγlmethyl)benzimidazole; and Patent Document 5 discloses 2-aralkγlimidazole compounds such as 2- (4- chlorophenylmethyl) imidazole and 2- (2 , A- dichlorophenylmethyl) -4 , 5-diphenylimidazole , respectively .

However, in the case where a surface treating agent containing such an imidazole compound is used, the heat resistance of a chemical layer as formed on the copper surface was not satisfactory yet. Also, in soldering, the solder wettability is not sufficient and thus good solderability cannot be obtained. In particular, in the case of performing soldering using a lead-free solder in place of the eutectic solder, it was difficult to put the foregoing surface treating agent into practical use.

Citation List Patent Literature

[PLT 1] JP-B-46-17046 [PLT 2] JP-A-4-206681 [PLT 3] JP-A-5-25407 [PLT 4] JP-A-5-186888 [PLT 5] JP-A-7-243054

Summary of the Invention

In view of the foregoing circumstance, the invention has been made. An object of the invention is to provide a surface treating agent, which in mounting electronic parts or the like to a printed wiring board using a lead-free solder, forms a chemical layer having excellent heat resistance on the surface of copper or a copper alloy constituting a circuit part of a printed wiring board and at the same time, improves the wettability to the solder and makes the solderability good, and a surface treatment method.

Also, another object of the invention is to provide a printed wiring board resulting from bringing the surface of copper or a copper alloy constituting a copper circuit part into contact with the foregoing surface treating agent and to provide a soldering method by bringing the surface of copper or a copper alloy into contact with the foregoing surface treating agent and then performing soldering using a lead-free solder.

In order to solve the foregoing problems, the present inventors made extensive and intensive investigations. As a result, it has been found that by treating a printed wiring board with a surface treating agent containing an imidazole compound represented by the formula (I) , a chemical layer having excellent heat resistance, i.e., capable of resisting soldering temperature of a lead-free solder can be formed on the copper surface of the circuit part of the printed wiring board and at the same time by improving the wettability of a lead-free solder to the surface of copper or a copper alloy in the soldering using the solder, good solderability is obtained, leading to accomplishment of the invention.

That is, the present invention includes the following aspects in its broadest configurations: (1) A surface treating agent for copper or a copper alloy, which comprises an imidazole compound represented by the formula (I) :

(D

wherein Ri, R₂ and R₃ are the same or different and represent a hydrogen atom or an alkyl group having 1 to 8 carbon atoms; and at least one selected from R₁, R₂ and R3 is an alkyl group having 4 or more carbon atoms.

(2) A surface treatment method for copper or a copper alloy, which comprises bringing a surface of the copper or the copper alloy into contact with the surface treating agent according to the above (1) .

(3) A printed wiring board, which comprises copper or a copper alloy constituting a copper circuit part, wherein a surface of the copper or the copper alloy has been brought into contact with the surface treating agent according to the above (1) .

(4) A soldering method, which comprises bringing a surface of copper or a copper alloy into contact with the surface treating agent according to the above (1) and then performing soldering.

The surface treating agent according to the invention is not only able to form a chemical layer having excellent heat resistance on the surface of copper or a copper alloy constituting a circuit part of a printed wiring board but also able to greatly improve the wettability of a lead-free solder to the subject surface and make the solderability good.

Also, since the soldering method according to the invention makes it possible to use a solder not containing lead which is a harmful metal, it is useful from the viewpoint of environmental protection.

Description of Embodiments

The following will describe the invention in detail The imidazole compound for use in the invention is represented by the formula (I) :

wherein Ri, R₂ and R3 are the same as described above.

R₁, R₂ and R₃ in the foregoing formula (I) are a hydrogen atom or an alkyl group and the alkyl group is a linear or branched saturated aliphatic group. Examples of such an alkyl group include a methyl group (1 carbon atom) , an ethyl group (2 carbon atoms) , a propyl group (3 carbon atoms) , an isopropyl group (3 carbon atoms) , a butyl group (4 carbon atoms) , an isobutyl group (4 carbon atoms) , a sec-butyl group (4 carbon atoms) , a tert-butyl group (4 carbon atoms) , a pentyl group (5 carbon atoms) , a hexyl group (6 carbon atoms) , a heptyl group (7 carbon atoms) and an octyl group (8 carbon atoms) .

The imidazole compound for use in carrying out the invention can be synthesized by, for example, adopting the synthetic method shown in the following reaction scheme .

wherein Ri , R₂ and R3 are the same as described above and X represents a chlorine atom, a bromine atom or an iodine atom.

As the imidazole compound represented by the formula (I) employed in carrying out the invention, examples thereof include: - (4-butylbenzγl) -4-phenylimidazole,- (4-tert-butylbenzyl) -4-phenylimidazole,- (2-sec-butylbenzyl) -4-phenylimidazole,- (4-pentylbenzyl) -4-phenylimidazole,- (4-hexylbenzyl) -4-phenylimidazole,- (4-heptylbenzyl) -4-phenylimidazole,- (4-octylbenzyl) -4-phenylimidazole,-benzyl-4- (2-butylphenyl) imidazole, -benzyl-4- (3-butylphenyl) imidazole, -benzyl-4 - (4 -butylphenyl ) imidazole ,-benzyl-4- (4 -isobutylphenyl) imidazole,-benzyl-4- (4-sec-butylphenyl) imidazole, -benzyl-4- (4-tert-butylphenyl) imidazole, -benzyl-4- (4 -pentylphenyl) imidazole, -benzyl-4- (4-isopentylphenyl) imidazole,-benzyl-4- (4-neopentylphenyl) imidazole,-benzyl-4- (2-hexylphenyl) imidazole, -benzyl-4- (3-hexylphenyl) imidazole, -benzyl-4 - (4 -hexylphenyl ) imidazole , -benzyl-4- (4-cyclohexylphenyl) imidazole,-benzyl-4- (4 -heptylphenyl) imidazole, -benzyl-4- (4-octylphenyl) imidazole , -benzyl-5-butyl-4 -phenylimidazole, -benzyl-5-isobutyl-4-phenylimidazole, -benzyl-5-sec-butyl -4 -phenylimidazole, 2-benzyl-5-tert-butyl-4 -phenylimidazole,

2-benzyl-5-pentyl-4 -phenylimidazole ,

2-benzyl-5-isopentyl -4 -phenylimidazole,

2-benzyl-5-neopentyl-4-phenylimidazole,

2-benzyl-5-hexyl-4 -phenylimidazole,

2-benzyl-5-heptyl-4-phenylimidazole ,

2-benzyl-5-octyl-4 -phenylimidazole,

2- (2-butylbenzyl) -4- (2-methylphenyl) imidazole,

2- (4-butylbenzyl) -4- (4-methylphenyl) imidazole,

4- (3-ethylphenyl) -2- (4-hexylbenzyl) imidazole,

2- (3-tert-butylbenzyl) -5-methyl-4- (3- methylphenyl ) imidazole ,

2- (4-hexylbenzyl) -4- (4-isopropylphenyl) -5-methylimidazole,

2- (4-butylbenzyl) -5-methyl -4 -phenylimidazole,

2- (2-isopentγlbenzyl) -4 -phenyl -5-propylimidazole,

2-benzyl-4- (4-butylphenyl) -5-methylimidazole,

2-benzyl-4- (4-tert-butylphenyl) -5-methylimidazole,

2-benzyl-4- (4-hexylphenyl) -5-methylimidazole,

2-benzyl-4- (4-cyclohexylphenyl) -5-methylimidazole,

2-benzyl-5-methyl-4- (4 -octylphenyl) imidazole,

2-benzyl-4 - (4 -isobutylphenyl ) -5-methylimidazole ,

5-ethyl-4- (4-hexylphenyl) -2- (3-methylbenzyl) imidazole,

4- (2-heptylphenyl) -2- (2-isopropylbenzyl) imidazole,

2-benzyl-5-butyl-4- (4-methylphenyl) imidazole,

2-benzyl -5-pentyl -4- (4-propylphenyl) imidazole, 2-benzyl-5-hexγl-4- (4-isopropylphenyl) imidazole,

5-heptyl-2- (4-methylbenzyl) -4- (2-methylphenyl) imidazole,

2- (3-isopropylbenzyl) -5-octyl-4 -phenylimidazole,

4- (4 -tert-butylphenyl) -5-methyl-2- (4- pentylbenzyl ) imidazole ,

2- (4 -butylbenzyl) -4- (4 -hexylphenyl) imidazole,

5-hexyl-4- (4-isobutylphenyl) -2- (4-methylbenzyl) imidazole,

2-benzyl-4- (isopentyl) -5-neopentylimidazole,

2- (4-butylbenzyl) -5-hexyl-4-phenylimidazole,

5-heptyl-4- (4-isopropylphenyl) -2- (4- pentylbenzyl) imidazole,

2- (4-hexylbenzyl) -5-octylimidazole,

5-heptyl-4- (3-hexylphenyl ) -2- (4-isobutylbenzyl) imidazole, and

4- (4-tert-butylphenyl) -2- (4-neopentγlbenzyl) -5- octylimidazole .

The imidazole compound is used as an active ingredient of a surface treating agent prepared by dissolving it in water. The imidazole compound may be contained, for example, in a proportion of from 0.01 to 10% by weight, and preferably from 0.1 to 5% by weight in the surface treating agent. When the content of the imidazole compound is less than 0.01% by weight, the film thickness of the chemical layer as formed on the surface of copper may be too thin, so that the oxidation of the surface of copper cannot be sufficiently prevented. On the other hand, when it exceeds 10% by weight, the imidazole compound in the surface treating agent may fail to be completely dissolved, or there is a concern that the imidazole compound may be reprecipitated even after it has been completely dissolved, and is therefore not preferred.

Incidentally, in carrying out the invention, among the imidazole compounds represented by the formula (I) , only one suitable kind thereof may be used but it is also possible to use a combination of different kinds of the imidazole compounds .

In carrying out the invention, in dissolving the imidazole compound in water (forming an aqueous solution) , an organic acid or an inorganic acid may be generally used as the acid, but a small amount of an organic solvent may be used simultaneously. Representative examples of the organic acid to be used on this occasion include formic acid, acetic acid, propionic acid, butyric acid, glyoxylic acid, pyruvic acic, acetoacetic acid, levulinic acid, heptanoic acid, caprylic acid, capric acid, lauric acid, glycolic acid, glyceric acid, lactic acid, acrylic acid, methoxyacetic acid, ethoxyacetic acid, propoxyacetic acid, butoxyacetic acid, 2- (2- methoxyethoxy) acetic acid, 2- [2- (2- ethoxyethoxy) ethoxy] acetic acid, 2-{2-[2-(2- ethoxyethoxy) ethoxy] ethoxy}acetic acid, 3- methoxypropionic acid, 3-ethoxypropionic acid, 3- propoxypropionic acid, 3-butoxypropionic acid, benzoic acid, p-nitrobenzoic acid, p-toluenesulfonic acid, salicylic acid, picric acid, oxalic acid, succinic acid, maleic acid, fumaric acid, tartaric acid, and adipic acid; and examples of the inorganic acid include hydrochloric acid, phosphoric acid, sulfuric acid, and nitric acid. Such an acid may be added in a proportion of from 0.1 to 50% by weight, and preferably from 1 to 30% by weight in the surface treating agent.

Also, as the organic solvent, suitable are lower alcohols such as methanol, ethanol , and isopropyl alcohol, or acetone, N,N-dimethylformamide, ethylene glycol and the like, which are freely miscible with water.

To the surface treating agent of the invention, a copper compound may be added in order to hasten the formation rate of the chemical layer on the surface of copper or a copper alloy. Also, a zinc compound may be added in order to further enhance the heat resistance of the chemical layer formed.

Representative examples of the copper compound include copper acetate, cuprous chloride, cupric chloride, cuprous bromide, cupric bromide, copper iodide, copper hydroxide, copper phosphate, copper sulfate, and copper nitrate; and representative examples of the zinc compound include zinc oxide, zinc formate, zinc acetate, zinc oxalate, zinc lactate, zinc citrate, zinc sulfate, zinc nitrate, and zinc phosphate. Both of them may be contained in a proportion of from 0.01 to 10% by weight, and preferably from 0.02 to 5% by weight in the surface treating agent.

In the case where such a copper compound or zinc compound is used, it may be desirable to stabilize the pH of the solution by adding a substance having a buffer action, amine compound such as ammonia, monoethanolamine, diethanolamine, or triethanolamine in addition to the organic acid or inorganic acid.

For the purpose of further enhancing the formation rate of the chemical layer and the heat resistance of the layer, a halogen compound (using "halogen" in its more general sense) may be added into the surface treating agent in a proportion of from 0.001 to 1% by weight, and preferably from 0.01 to 0.1% by weight. Examples of the halogen compound include sodium fluoride, potassium fluoride, ammonium fluoride, sodium chloride, potassium chloride, ammonium chloride, sodium bromide, potassium bromide, ammonium bromide, sodium iodide, potassium iodide, and ammonium iodide. With respect to the conditions for treating the surface of copper or a copper alloy using the surface treating agent according to the invention, the liquid temperature of the surface treating agent may be preferably from 10 to 70⁰C, and the contact time may be preferably from 1 second to 10 minutes . Examples of the contact method include dipping, spraying, and coating methods .

Also, after performing the surface treatment according to the invention, it is possible to further enhance the heat resistance by forming a double layer structure comprising the chemical layer coated with a thermoplastic resin.

That is, after forming the chemical layer on the surface of copper or a copper alloy, a double layer structure of the chemical layer and a thermoplastic resin may be formed by dissolving a thermoplastic resin having excellent heat resistance, which may be composed of a rosin derivative (for example, rosin or a rosin ester) , a terpene resin derivative (for example, a terpene resin or a terpene phenol resin) , a hydrocarbon resin (for example, an aromatic hydrocarbon resin or an aliphatic hydrocarbon resin) , or a mixture thereof in a solvent (for example, toluene, ethyl acetate, or isopropyl alcohol) and uniformly coating the solution in a thickness of, for example, from 1 to 30 μm on the chemical layer using a roll coater or the like.

Examples of the lead-free solder which is suitable for carrying out the invention include lead-free solders such Sn-Ag-Cu based, Sn-Ag-Bi based, Sn-Bi based, Sn-Ag- Bi-In based, Sn-Zn based, and Sn-Cu based solders.

The soldering method of the invention is applicable to flow soldering which comprises moving a printed wiring board over a molten liquid-state solder in a solder bath to solder junctions between electronic parts and the printed wiring board or reflow soldering which comprises printing in advance a paste cream solder on the printed wiring board according to a circuit pattern, mounting electronic parts thereon, and heating the whole printed wiring board to melt the solder to complete the soldering.

Examples

The following will specifically describe the present invention with reference to Examples and Comparative Examples but it should not be construed that the invention is limited thereto.

(Imidazole Compounds)

Imidazole compounds used in Examples are as follows . •2- (4-Butylbenzyl) -5-methyl-4-phenγlimidazole (referred to as " IMZ-A" )

•2- (4-Hexylbenzγl) -4-phenγlimidazole (referred to as

"IMZ-B")

•2-Benzγl-4- (4-butylphenyl) imidazole (referred to as

"IMZ-C")

• 2-Benzyl-4- (4-sec-butylphenyl) imidazole (referred to as

"IMZ-D")

•2-Benzyl-5-methyl-4- (4-octylphenyl) imidazole (referred to as "IMZ-E")

•2- (4-Butylbenzyl) -5-hexyl-4-phenylimidazole (referred to as "IMZ-F") .

Imidazole compounds used in Comparative Examples are as follows.

•2- (4 -Methylbenzyl) -4-phenylimidazole (referred to as "IMZ-G")

•2-Benzyl-5-methyl-4- (4-methylphenyl) imidazole (referred to as "IMZ-H")

•2-Phenylimidazole (referred to as "IMZ-I") •2-Nonylbenzimidazole (referred to as "IMZ-J") •2- (4-Chlorobenzyl)benzimidazole (referred to as "IMZ-K")

Chemical formulae of the imidazole compounds used in Examples (IMZ-A to IMZ-F) and the imidazole compounds used in Comparative Examples (IMZ-G to IMZ-K) are shown below.

I MZ-A IMZ-B I MZ-C

Evaluation test methods employed in Examples and Comparative Examples are as follows.

(Evaluation test for solder flow-up rate property)

A printed wiring board made of a glass epoxy resin of 120 mm (length) x 150 mm (width) x 1.6 mm (thickness) and having 300 copper through-holes having an inner diameter of 0.80 mm was used as a test piece. This test piece was degreased, subjected to soft etching, and then washed with water. Thereafter, the test piece was dipped in a surface treating agent kept at a prescribed liquid temperature for a prescribed period of time, washed with water, and then dried to form a chemical layer having a thickness of from about 0.10 to 0.50 μm on the copper surface.

The surface-treated test piece was subjected to two cycles of reflow-heating in which the peak temperature was 240°C using an infrared reflow oven (trade name: MULTI-PRO-306, manufactured by Vetronix Co., Ltd.) and subsequently soldering was performed with a flow soldering device (conveyor speed: 1.0 m/min) .

The solder used was a tin-lead eutectic solder with a composition of 63% tin and 37% lead (% by weight) (trade name: H63A, manufactured by Senju Metal Industry Co., Ltd.) , and the flux used for soldering was JS-64MSS (manufactured by Koki Co., Ltd.). The soldering temperature was 240⁰C.

The test piece surface treated as above was also soldered using a lead-free solder in the same manner as for the tin-lead eutectic solder. The solder used was a lead-free solder (trade name: H705 "ECOSOLDER", manufactured by Senju Metal Industry Co., Ltd.) with a composition of 96.5% tin, 3.0% silver and 0.5% copper (% by weight) , and the flux used for soldering was JS-E-09 (manufactured by Koki Co., Ltd.) . The reflow-heating peak temperature was 245°C, and the soldering temperature was also 245°C.

For the soldered test piece, the proportion (%) of the number of (soldered) copper through-holes in which the solder was filled up to the upper land of the copper through-holes with respect to the total number of copper through-holes (300 holes) was calculated.

When the solder wettability on the copper surface is large, the molten solder penetrates inside each copper through-hole, whereby the molten solder readily fills it to the upper land of the through-hole. That is, when a ratio of the number of through-holes whose upper lands were soldered to the total number of through-holes was large, solder wettability and solderability to the copper would be judged to be excellent.

(Evaluation test for solder spreadability)

A printed wiring board made of a glass epoxy resin of 50 mm (length) x 50 mm (width) x 1.2 mm (thickness) was used as a test piece. This printed wiring board had a circuit pattern in which 10 pieces of a copper-foiled circuit with a conductor width of 0.80 mm and a length of 20 mm were formed in a width direction at intervals of 1.0 mm. The test piece was degreased, subjected to soft etching, and then washed with water. Thereafter, the test piece was dipped in a surface treating agent kept at a prescribed liquid temperature for a prescribed period of time, washed with water, and then dried to form a chemical layer having a thickness of from about 0.10 to 0.50 μm on the copper surface.

The surface-treated test piece was subjected to one cycle of reflow-heating in which the peak temperature was 240⁰C using an infrared reflow oven (trade name: MULTI- PRO-306, manufactured by Vetronix Co., Ltd.) . Thereafter, a tin-lead solder paste was printed on the center of the copper circuit parts using a metal mask having an aperture diameter of 1.2 mm and a thickness of 150 μm, and reflow-heating was conducted under the above- described conditions and soldering was conducted. The tin-lead solder paste used was an eutectic solder (trade name: OZ-63-330F-40-10 , manufactured by Senju Metal Industry Co., Ltd.) composed of 63% tin and 37% lead (% by weight) .

Test pieces surface treated as above were also soldered using a lead-free solder paste in the same manner for the tin-lead solder paste. The lead-free solder used was composed of 96.5% tin, 3.0% silver and 0.5% copper (% by weight) (trade name: M705-221BM5-42-11 , manufactured by Senju Metal Industry Co., Ltd.). The peak temperature of reflow-heating attained before and after the solder paste printing was set to 245°C.

The length (nun) of solder which wet and spread over the copper circuit part of the obtained test piece was measured.

When the length was longer, solder wettability and solderability would be judged to be excellent.

Example 1

After 2- (4-butylbenzyl) -5-methyl-4-phenylimidazole as an imidazole compound, acetic acid and lactic acid as acids, copper acetate and zinc acetate as metal salts, and ammonium bromide as a halogen compound were dissolved in deionized water so as to have a composition as described in Table 1, and the pH was adjusted at 2.7 with ammonia water, thereby preparing a surface treating agent.

Next, a test piece of a printed wiring board was dipped in the surface treating agent as controlled at a temperature of 40⁰C for 120 seconds, washed with water, and then dried, thereby measuring the solder flow-up rate properties and solder spreadability . These test results are shown in Table 2.

Examples 2 to 6

Using imidazole compounds, acids, metal salts and halogen compounds as described in Table 1, surface treating agents each having a composition as described in Table 1 were prepared in the same manner as in Example 1 and subjected to a surface treatment under the treatment conditions as described in Table 2. With respect to the resulting test pieces, the solder flow-up rate properties and solder spreadability were measured. These test results are shown in Table 2.

Comparative Examples 1 to 5

Table 1

ho

Table 2

t\3

According to the test results as shown in Table 1 and Table 2, it is submitted that the wettability of an eutectic solder or a lead-free solder to the surface of copper of a printed wiring board is improved by bringing the surface treating agent according to the invention into contact with the copper circuit part of the printed wire board to form a chemical layer on the surface of copper, and the solderability (solder flow-up rate properties, solder spreadability) of an eutectic solder or a lead-free solder to the surface of copper is greatly improved. The surface treating agent according to the invention can be used, of course, in the soldering using an eutectic solder but can be suitably used in the soldering using a lead-free solder.

Industrial Applicability

While the invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the scope thereof.

This application is based on Japanese patent application No. 2008-223663 filed on September 1, 2008, the entire contents thereof being hereby incorporated by reference .

Claims

1. A surface treating agent for copper or a copper alloy, which comprises an imidazole compound represented by the formula (I) :

wherein Ri , R₂ and R₃ are the same or different and represent a hydrogen atom or an alkyl group having 1 to 8 carbon atoms; and at least one selected from Ri, R₂ and R3 is an alkyl group having 4 or more carbon atoms.

2. A surface treatment method for copper or a copper alloy, which comprises bringing a surface of the copper or the copper alloy into contact with the surface treating agent according to claim 1.

3. A printed wiring board, which comprises copper or a copper alloy constituting a copper circuit part, wherein a surface of the copper or the copper alloy has been brought into contact with the surface treating agent according to claim 1.

4. A soldering method, which comprises bringing a surface of the copper or the copper alloy into contact with the surface treating agent according to claim 1 and then performing soldering.