JP4694251B2 - Copper or copper alloy surface treatment agent for lead-free soldering and use thereof - Google Patents

Description

  The present invention relates to a surface treating agent, a surface treatment method for copper or a copper alloy, a printed wiring board, and a soldering method used when soldering an electronic component or the like to copper or a copper alloy of a printed wiring board.

Recently, surface mounting with improved mounting density has been widely adopted as a method for mounting printed wiring boards. Such surface mounting methods can be classified into double-sided surface mounting in which chip components are joined by cream solder, mixed mounting in which surface mounting by chip solder cream soldering and through-hole mounting of discrete components are combined. In any mounting method, since the printed wiring board is soldered a plurality of times, it is exposed to a high temperature each time and receives a severe thermal history.
As a result, the surface of the copper or copper alloy constituting the circuit portion of the printed wiring board is heated to promote the formation of an oxide film, so that the solderability of the surface of the circuit portion cannot be kept good. .

  In order to protect the copper circuit portion of such a printed wiring board from air oxidation, a treatment for forming a chemical conversion film on the surface of the circuit portion using a surface treatment agent is widely performed. It is required to protect the copper circuit portion without changing (deteriorating) the chemical conversion film even after receiving the heat history of the times, thereby maintaining good solderability.

Conventionally, tin-lead alloy eutectic solder has been widely used for joining electronic components to printed wiring boards, etc., but in recent years there is concern about the harmfulness of the lead contained in the solder alloy to the human body. There is a need to use solder that does not contain lead.
For this purpose, various lead-free solders have been studied. For example, lead-free solders having a metal such as silver, zinc, bismuth, indium, antimony and copper as a base metal have been proposed.

By the way, the conventional tin-lead eutectic solder is excellent in the wettability with respect to the joining base material, especially copper surface, and since it joins firmly with respect to copper, high reliability is acquired.
In contrast, lead-free solder is inferior in wettability to the copper surface compared to conventional tin-lead solder, so solderability is poor, bonding defects such as voids occur, and bonding strength is low Met.
Therefore, when using lead-free solder, selection of a solder alloy with better solderability and a flux suitable for lead-free solder is required, but surface treatment used to prevent oxidation of copper or copper alloy surfaces Also for the agent, a function of improving the wettability of the lead-free solder and improving the solderability is required.
In addition, many lead-free solders have a high melting point, and the soldering temperature is about 20 to 50 ° C. higher than that of conventional tin-lead eutectic solders. Therefore, the surface treatment agent has excellent heat resistance. It is also desired to form a conversion coating.

  Various imidazole compounds have been proposed as active ingredients of such surface treatment agents. For example, Patent Document 1 includes 2-alkylimidazole compounds such as 2-undecylimidazole, and Patent Document 2 includes 2-arylimidazole compounds such as 2-phenylimidazole and 2-phenyl-4-methylimidazole. Patent Document 3 discloses a 2-alkylbenzimidazole compound such as 2-nonylbenzimidazole, and Patent Document 4 discloses a 2-aralkylbenzimidazole compound such as 2- (4-chlorophenylmethyl) benzimidazole. .

  However, when the surface treatment agent containing these imidazole compounds is used, the heat resistance of the chemical conversion film formed on the copper surface has not yet been satisfactory. Also, when soldering, the solder wettability is insufficient, and good solderability cannot be obtained. In particular, in the case where soldering is performed using lead-free solder instead of eutectic solder, the surface treatment agent is difficult to be practically used.

Japanese Patent Publication No.46-17046 JP-A-4-206681 Japanese Patent Laid-Open No. 5-25407 Japanese Patent Laid-Open No. 5-186888

The present invention has been made in view of such circumstances, and copper that constitutes a circuit portion or the like of a printed wiring board when an electronic component or the like is joined to the printed wiring board using eutectic solder or lead-free solder. Another object is to provide a surface treatment agent and a surface treatment method for forming a chemical conversion film having excellent heat resistance on the surface of a copper alloy, improving wettability with solder, and improving solderability. To do.
Further, the printed wiring board in which the surface treatment agent is brought into contact with the surface of copper or copper alloy constituting the copper circuit portion, and the surface of copper or copper alloy in contact with the surface treatment agent, then eutectic solder Another object is to provide a soldering method for performing soldering using lead-free solder.

As a result of intensive studies in order to solve the above problems, the present inventors have obtained a surface treatment agent containing a 2-phenyl-4-naphthylimidazole compound represented by the general formula of Chemical Formula 1 as an active ingredient, By treating the printed wiring board having a copper circuit portion, a chemical conversion film having excellent heat resistance, that is, capable of withstanding the soldering temperature of eutectic solder and lead-free solder, can be formed on the surface of the copper circuit portion, and When soldering using eutectic solder or lead-free solder, it is recognized that good solderability can be obtained by improving the wettability of the solder to the surface of copper or copper alloy. It has come.

（式中、Ｒは水素原子又はメチル基を表す。）

(In the formula, R represents a hydrogen atom or a methyl group.)

The surface treatment agent of the present invention can form a chemical conversion film having excellent heat resistance on the surface of copper or copper alloy constituting the circuit portion or the like of a printed wiring board, and eutectic solder and lead-free solder on the surface. Can be improved drastically and solderability can be improved.
In addition, the soldering method of the present invention is useful from the viewpoint of environmental protection because it enables the use of solder that does not contain lead, which is a harmful metal.

Hereinafter, the present invention will be described in detail.
A 2-phenyl-4-naphthylimidazole compound represented by the general formula of Formula 1 suitable for the practice of the present invention is:
2-phenyl-4- (1-naphthyl) imidazole,
2-phenyl-4- (2-naphthyl) imidazole,
2-phenyl-4- (1-naphthyl) -5-methylimidazole and
2-phenyl-4- (2-naphthyl) -5-methylimidazole.

  These imidazole compounds are contained in the surface treatment agent in a proportion of 0.01 to 10% by weight, preferably in a proportion of 0.1 to 5% by weight. When the content ratio of the imidazole compound is less than 0.01% by weight, the film thickness of the chemical conversion film formed on the copper surface becomes thin, and oxidation of the copper surface cannot be prevented. On the other hand, when the amount is more than 10% by weight, the imidazole compound in the surface treatment agent remains undissolved and a uniform aqueous solution cannot be obtained.

  In practicing the present invention, an organic acid or an inorganic acid is used as an acid for making an imidazole compound into an aqueous solution, but a small amount of an organic solvent may be used in combination. Typical organic acids used in this case include formic acid, acetic acid, propionic acid, butyric acid, glyoxylic acid, pyruvic acid, 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, methoxypropionic acid, ethoxypropionic acid, propoxypropionic acid, butoxypropionic acid, benzoic acid, paranitrobenzoic acid, paratoluenesulfonic acid, salicylic acid, picric acid, oxalic acid Succinic acid, maleic acid, fumaric acid, tartaric acid, adipic acid, etc. It is, as the inorganic acid, hydrochloric acid, phosphoric acid, sulfuric acid, and nitric acid. These acids may be added in a proportion of 0.1 to 50% by weight, preferably 1 to 30% by weight, based on the aqueous solution.

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

To the surface treatment agent of the present invention, a copper compound can be added in order to increase the rate of formation of the chemical conversion film on the surface of copper or copper alloy, and zinc can be added to further improve the heat resistance of the formed chemical conversion film. A compound may be added.
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. Typical examples of the zinc compound include zinc oxide, zinc formate, zinc acetate, zinc oxalate, zinc lactate, zinc citrate, zinc sulfate, zinc nitrate, zinc phosphate and the like. Any of these may be added in a proportion of 0.01 to 10% by weight, preferably 0.02 to 5% by weight, based on the surface treatment agent.

  When these copper compounds and zinc compounds are used, in addition to organic or inorganic acids, substances having a buffering action such as ammonia or amines such as monoethanolamine, diethanolamine and triethanolamine are added to the solution. It is desirable to stabilize the pH.

  The surface treatment agent of the present invention contains 0.001 to 1% by weight of a halogen compound, preferably 0.01 to 0.1% by weight, in order to further improve the formation rate of the conversion coating and the heat resistance of the coating. It is desirable to add in proportions. 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. Etc.

  As conditions for treating the surface of copper or copper alloy using the surface treating agent of the present invention, it is appropriate that the liquid temperature of the surface treating agent is 10 to 70 ° C. and the contact time is 1 second to 10 minutes. is there. Examples of the contact method include dipping, spraying, and application methods.

Moreover, after performing the surface treatment of this invention, it is also possible to form a double structure with a thermoplastic resin on a chemical conversion film, and to improve heat resistance further.
That is, after forming a chemical conversion film on the surface of copper or copper alloy, rosin derivatives such as rosin and rosin ester, terpene resin derivatives such as terpene resin and terpene phenol resin, aromatic hydrocarbon resin and aliphatic hydrocarbon resin A thermoplastic resin having excellent heat resistance, such as a hydrocarbon resin such as a mixture thereof, is dissolved in a solvent such as toluene, ethyl acetate, isopropyl alcohol, etc., and a thickness of 1 to 30 μm is formed on the chemical conversion film by a roll coater or the like. It may be applied uniformly so as to form a double structure of the chemical conversion film and the thermoplastic resin.

  As solder suitable for the practice of the present invention, Sn-Ag-Cu-based, Sn-Ag-Bi-based, Sn-Bi-based, Sn-Ag in addition to commonly used eutectic solders of tin-lead alloys. Examples include lead-free solders such as -Bi-In, Sn-Zn, and Sn-Cu.

  In addition, the soldering method of the present invention is a flow method in which a printed wiring board is flowed over a solder bath containing heated and melted liquid solder, and soldering is performed on the joint between the electronic component and the printed wiring board, or It can be applied to the reflow method, etc., in which paste-like cream solder is printed on the printed wiring board according to the circuit pattern in advance, electronic components are mounted on the printed wiring board, the printed wiring board is heated to melt the solder, and soldering is performed. Is.

EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention concretely, this invention is not limited to these.
In addition, the imidazole compound used in the Example and the comparative example and the evaluation test method are as follows.

[Imidazole compound]
The imidazole compounds used in Examples 1-8 and Reference Examples 9-14 are shown in Reference Examples 1-8.
[Reference Example 1]
<2- (1-naphthyl) -4-phenylimidazole>
In a solution of 2-acetoxyacetophenone and equimolar 1-naphthaldehyde dissolved in isopropyl alcohol, 2.2-fold mol of copper (II) acetate monohydrate was dissolved in 20-fold mol of 25% aqueous ammonia. The solution was added in small portions under water cooling, then heated to 60 ° C. for 1 hour and further to 78 ° C. over 3 hours. After cooling, the precipitate was collected by filtration, washed with water and dried. The resulting dark green powder was suspended in methanol, added with 0.6 times mole of 70% sodium hydrosulfide, heated to reflux for 1 hour, cooled. The black insoluble material was removed by filtration. The filtrate was dried under reduced pressure, the dried product was dissolved in chloroform, washed with water, chloroform was distilled off under reduced pressure, and the resulting dried product was recrystallized from acetonitrile to give milky white powder 2- (1 -Naphthyl) -4-phenylimidazole was obtained.

[Reference Example 2]
<2- (2-naphthyl) -4-phenylimidazole>
The 1-naphthaldehyde of Reference Example 1 was replaced with 2-naphthaldehyde and synthesized according to the method of Reference Example 1.

[Reference Example 3]
<2-Phenyl-4- (1-naphthyl) imidazole>
Benzamidine hydrochloride and equimolar sodium methylate were heated to reflux in tetrahydrofuran for 1 hour, and after cooling, an equimolar solution of ω-bromo-1-acetonaphthone in tetrahydrofuran was added dropwise so as not to exceed 30 ° C. Mole of sodium methylate was added and heated to reflux for 1 hour. After distilling off the solvent under reduced pressure, the residue was washed with water and recrystallized from acetonitrile to obtain gray-blue crystals of 2-phenyl-4- (1-naphthyl) imidazole.

[Reference Example 4]
<2-Phenyl-4- (2-naphthyl) imidazole>
The ω-bromo-1-acetonaphthone of Reference Example 3 was synthesized according to the method of Reference Example 3 in place of ω-bromo-2-acetonaphthone.

[Reference Example 5]
<2- (1-naphthyl) -4-phenyl-5-methylimidazole>
1-phenyl-1,2-propanedione, equimolar 1-naphthaldehyde and 6-fold molar ammonium acetate were heated to reflux in acetic acid for 3 hours. After completion of the reaction, the vacuum concentrate was poured into a large amount of dilute aqueous ammonia, and the precipitated solid was collected by filtration, washed with water and dried to give a brown solid. This solid was washed with methanol and then with hexane to obtain 2- (1-naphthyl) -4-phenyl-5-methylimidazole as a pale yellow powder.

[Reference Example 6]
<2- (2-naphthyl) -4-phenyl-5-methylimidazole>
The 1-naphthaldehyde of Reference Example 5 was replaced with 2-naphthaldehyde and synthesized according to the method of Reference Example 5.

[Reference Example 7]
<2-Phenyl-4- (1-naphthyl) -5-methylimidazole>
The ω-bromo-1-acetonaphthone of Reference Example 3 was synthesized according to the method of Reference Example 3 in place of 2-bromo-1′-propionnaphthone.

[Reference Example 8]
<2-Phenyl-4- (2-naphthyl) -5-methylimidazole>
The ω-bromo-1-acetonaphthone of Reference Example 3 was synthesized according to the method of Reference Example 3 in place of 2-bromo-2′-propionnaphthone.

The imidazole compounds used in the comparative examples are as follows.
・ 2-Undecylimidazole (manufactured by Shikoku Kasei Kogyo Co., Ltd., trade name “C11Z”)
・ 2-Phenylimidazole (product name “2PZ”, manufactured by Shikoku Kasei Kogyo Co., Ltd.)
・ 2-Phenyl-4-methylimidazole (manufactured by Shikoku Kasei Kogyo Co., Ltd., trade name “2P4MZ”)
・ 2-nonylbenzimidazole (manufactured by SIGMA-ALDRICH, reagent)
2- (4-Chlorophenylmethyl) benzimidazole (synthesized according to the method described in “Science of Synthesis, 12 , 529 (2002)”)

[Evaluation test of solderability]
As a test piece, a printed wiring board made of glass epoxy resin of 120 mm (vertical) × 150 mm (horizontal) × 1.6 mm (thickness) having 300 copper through holes with an inner diameter of 0.80 mm was used. The test piece was degreased, soft-etched and washed with water, then immersed in a surface treatment agent maintained at a predetermined liquid temperature for a predetermined time, then washed with water and dried to a thickness of about 0.10 to 0.00 on the copper surface. A 50 μm conversion coating was formed.
About the test piece which performed this surface treatment, the reflow heating whose peak temperature is 240 degreeC was performed 3 times using the infrared reflow apparatus (product name: MULTI-PRO-306, Vitronics company make), then, flow solder Soldering was performed using an attaching device (conveyor speed: 1.0 m / min).
The solder used was tin-lead eutectic solder (trade name: H63A, manufactured by Senju Metal Industry Co., Ltd.) having a composition of 63 tin-37 lead (weight%), and the flux used for soldering was JS- 64MSS (manufactured by Hiroki). The solder temperature was 240 ° C.
Further, the test piece subjected to the surface treatment was soldered using lead-free solder in the same manner as in the case of tin-lead eutectic solder. The solder used is a lead-free solder (trade name: H705 “Eco Solder”, manufactured by Senju Metal Industry Co., Ltd.) having a composition of 96.5 tin-3.0 silver-0.5 copper (% by weight). The flux used for attaching is JS-E-09 (manufactured by Hiroki). The peak temperature of reflow heating was 245 ° C., and the solder temperature was 245 ° C.
For the soldered test piece, the number of through holes in which the solder went up to the upper land portion of the copper through hole (soldered) was measured, and the ratio (%) to the total number of through holes (300 holes) was calculated. .
The higher the solder wettability with respect to the copper surface, the more easily the molten solder penetrates into the copper through hole and rises to the upper land portion of the through hole. That is, it is determined that the higher the ratio of the number of through holes in which the solder has reached the upper land portion with respect to the total number of through holes, the better the solder wettability with respect to copper and the better the solderability.

[Evaluation test of solder spreadability]
As a test piece, a printed wiring board made of glass epoxy resin of 50 mm (vertical) × 50 mm (horizontal) × 1.2 mm (thickness) (as a circuit pattern, a circuit part having a conductor width of 0.80 mm and a length of 20 mm made of copper foil) 10 were formed in the width direction at intervals of 1.0 mm). The test piece was degreased, soft-etched and washed with water, then immersed in a surface treatment agent maintained at a predetermined liquid temperature for a predetermined time, then washed with water and dried to a thickness of about 0.10 to 0.00 on the copper surface. A 50 μm conversion coating was formed.
About the test piece which performed this surface treatment, the reflow heating whose peak temperature is 240 degreeC was performed once using the infrared reflow apparatus (Product name: MULTI-PRO-306, Vitronics company make). After that, using a metal mask having an opening diameter of 1.2 mm and a thickness of 150 μm, tin-lead cream solder was printed at the center of the copper circuit portion, and reflow heating was performed under the previous conditions to perform soldering. The tin-lead cream solder used is a eutectic solder (trade name: OZ-63-330F-40-10, manufactured by Senju Metal Industry Co., Ltd.) composed of 63 tin-37 lead (% by weight).
Moreover, about the test piece which performed the said surface treatment, it soldered using the lead-free cream solder similarly to the case of a tin-lead cream solder. The lead-free cream solder used was a lead-free solder (commercial name: M705-221BM5-42-11, manufactured by Senju Metal Industry Co., Ltd.) composed of 96.5 tin-3.0 silver-0.5 copper (% by weight). ). The reflow heating performed before and after the cream solder printing was set so that the peak temperature was 245 ° C.
About the obtained test piece, the length (mm) of the solder which wet-spreaded on the copper circuit part was measured.
The larger this length, the better the solder wettability and the better the solderability.

[ Reference Example 9 ]
2- (1-naphthyl) -4-phenylimidazole as the imidazole compound, acetic acid and n-heptanoic acid as the acid, copper acetate as the metal salt, and ammonium chloride as the halogen compound so that the composition described in Table 1 is obtained. After dissolving in exchange water, the surface treatment agent was prepared by adjusting to pH 3.1 with aqueous ammonia.
Next, the test piece of the printed wiring board was immersed in a surface treatment agent adjusted to 40 ° C. for 60 seconds, washed with water and dried, and the solder finish and solder spreadability were measured. These test results were as shown in Table 1.

[ Examples 1-8, Reference Examples 10-14 ]
In the same manner as in Reference Example 9 , a surface treatment agent having the composition described in Table 1 was prepared using the phenylnaphthylimidazole compound, acid, metal salt and halogen compound described in Table 1, and the processing conditions described in Table 1 The surface treatment was performed. About the obtained test piece, solder rising property and solder spreading property were measured. These test results were as shown in Table 1.
In addition, 2- (2-methoxyethoxy) acetic acid used as an acid is a reagent manufactured by SIGMA-ALDRICH. Further, regarding 2- [2- (2-ethoxyethoxy) ethoxy] acetic acid and 2- {2- [2- (2-ethoxyethoxy) ethoxy] ethoxy} acetic acid, “Oil Chemical, 32 , 118 (1983)” Those synthesized in accordance with the synthesis method described in 1. were used.

[Comparative Examples 1-7]
In the same manner as in Reference Example 9 , a surface treatment agent having the composition described in Table 2 was prepared using the imidazole compound, acid, metal salt and halogen compound described in Table 2, and the treatment conditions described in Table 2 were used. Surface treatment was performed. About the obtained test piece, solder rising property and solder spreading property were measured. These test results were as shown in Table 2.

According to the test results shown in Tables 1 and 2, a chemical conversion film was formed by bringing the surface treatment agent of the present invention into contact with the copper surface, and soldering was performed using eutectic solder or lead-free solder. In this case, it is recognized that the solder wettability and the solder spreadability are remarkably improved, and the solder wettability of both eutectic solder and lead-free solder is remarkably improved.

Claims (4)

A surface treatment agent for copper or copper alloy for lead-free soldering, comprising a 2-phenyl-4-naphthylimidazole compound represented by the general formula of Chemical Formula 1 as an active ingredient.

(In the formula, R represents a hydrogen atom or a methyl group.) A surface treatment method for copper or copper alloy for lead-free soldering, wherein the surface treatment agent according to claim 1 is brought into contact with the surface of copper or copper alloy.   A printed wiring board, wherein the surface treatment agent according to claim 1 is brought into contact with the surface of copper or copper alloy of the copper circuit portion. After contacting the surface of copper or a copper alloy with a surface treatment agent containing a 2-phenyl-4-naphthylimidazole compound represented by the general formula of Chemical Formula 1 as an active ingredient , soldering is performed using a lead-free solder. A soldering method characterized by that.