Water-soluble preflux, printed circuit board, and method for manufacturing a printed circuit board

Abstract

To provide a water-soluble preflux capable of forming an organic coating with excellent appearance uniformity and repairability. [Solution] A water-soluble preflux containing (A) an imidazole compound, (B) a monocarboxylic acid, (C) a dicarboxylic acid, and (D) water.

Description

Technical Field

[0001] The present invention relates to a water-soluble preflux, a printed wiring board, and a method for manufacturing a printed wiring board.

Background Art

[0002] Printed wiring boards often circulate with a solder resist coating formed. In such cases, most of the printed wiring board is covered by the solder resist coating. However, there is no solder resist coating on the electrode terminals (lands) for mounting electronic components. Therefore, when the printed wiring board is circulated or stored, the surface of the electrode terminals is likely to be oxidized. Thus, the surface of the electrode terminals of the printed wiring board may be subjected to a gold plating process to prevent oxidation of the surface of the electrode terminals. However, there is a problem that the cost increases because a noble metal is used in the gold plating process. Therefore, in printed wiring boards, instead of the gold plating process, a method of forming an organic film on the surface of the electrode terminals with a water-soluble preflux is adopted (for example, Patent Document 1).

[0003] Surface treatment steps for the purpose of protecting copper foil, such as water-soluble preflux (hereinafter sometimes referred to as OSP) and plating treatment, are in the final step of manufacturing a printed wiring board. In particular, for surface treatment including OSP, uniform appearance is required to protect from humidity during transportation of copper foil or to prevent re-oxidation of copper foil from the heat treatment received in the mounting soldering process after delivery. However, OSP forms a very thin coating film of about 0.12 μm to 0.5 μm of an imidazole-based organic material on the copper foil. Also, OSP is processed by an immersion method in an OSP chemical solution whose temperature is adjusted to 40°C to 45°C, for example. Therefore, there is always a liquid draining step, and uneven appearance defects may occur due to variations in the contact time of the chemical solution remaining in the liquid draining step. Therefore, while halogen components were added to secondarily ensure uniform appearance, this came at the cost of poor repairability against release agents. Thus, there is a need for materials other than halogen components that can improve uniform appearance. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 6-322551 [Overview of the project] [Problems that the invention aims to solve]

[0005] The present invention aims to provide a water-soluble preflux capable of forming an organic coating with excellent uniformity of appearance and repairability, a printed circuit board, and a method for manufacturing a printed circuit board. [Means for solving the problem]

[0006] According to the present invention, the following water-soluble preflux, printed circuit board, and method for manufacturing a printed circuit board are provided. [1] (A) an imidazole compound, (B) a monocarboxylic acid, (C) a dicarboxylic acid, and (D) water, The aforementioned component (A) is at least one selected from the group consisting of 2,4-diphenylimidazole, 2-(4-chlorobenzyl)benzimidazole, and 2-(3,4-dichlorobenzyl)benzimidazole. The aforementioned component (C) is glutaric acid. Water-soluble preflux. [2] In the water-soluble preflux described in [1], The amount of component (A) is 0.02% by mass or more and 1% by mass or less, relative to 100% by mass of the water-soluble preflux. The amount of component (C) is 0.03% by mass or more and 1% by mass or less, relative to 100% by mass of the water-soluble preflux. Water-soluble preflux. [3] An organic coating is formed on the electrode terminal by the water-soluble preflux described in [1] or [2]. Printed circuit board. [4] The process includes forming an organic coating on the electrode terminals of a printed circuit board using the water-soluble preflux described in [1] or [2]. A method for manufacturing printed circuit boards. [Effects of the Invention]

[0007] According to one aspect of the present invention, a water-soluble preflux capable of forming an organic coating with excellent uniformity of appearance and repairability, a printed circuit board, and a method for manufacturing a printed circuit board can be provided. [Modes for carrying out the invention]

[0008] [Water-soluble preflux] First, the water-soluble flux composition according to this embodiment will be described. The water-soluble pre-flux according to this embodiment contains (A) an imidazole compound, (B) a monocarboxylic acid, (C) a dicarboxylic acid, and (D) water, which will be described below.

[0009] [(A) component] Examples of the (A) imidazole compound used in this embodiment include imidazoles and benzimidazoles. These may be used individually or in combination of two or more. Examples of imidazoles include 2-pentylimidazole, 2-undecyl-4-methylimidazole, 2,4-dimethylimidazole, 2-phenylimidazole, 2-toluylimidazole, 2-phenyl-4-methylimidazole, 2-phenyl-4-benzylimidazole, 2-phenyl-4-methyl-5-benzylimidazole, 2,4-diphenylimidazole, 2,4,5-triphenylimidazole, 2-benzylimidazole, 2-benzyl-4-methylimidazole, 2-phenylethylimidazole, 2-(2-phenylethyl)imidazole, and 2-(2-phenylpentyl)imidazole. Among these, 2,4-diphenylimidazole is preferred from the viewpoint of increasing the thickness of the organic coating film.

[0010] Examples of benzimidazoles include 2-propylbenzimidazole, 2-pentylbenzimidazole, 2-octylbenzimidazole, 2-nonylbenzimidazole, 2-hexyl-5-methylbenzimidazole, 2-(2-methylpropyl)benzimidazole, 2-(1-ethylpropyl)benzimidazole, 2-(1-ethylpentyl)benzimidazole, 2-cyclohexylbenzimidazole, 2-(2-cyclohexylethyl)benzimidazole, 2-(5-cyclohexylpentyl), 2-phenylbenzimidazole, 2-phenyl-5-methylbenzimidazole, 2-benzylbenzimidazole, 2-(2-phenylethyl)benzimidazole, and 2-(5- Examples include phenylpentyl)benzimidazole, 2-(3-phenylpropyl)-5-methylbenzimidazole, 2-(4-chlorobenzyl)benzimidazole, 2-(3,4-dichlorobenzyl)benzimidazole, 2-(2,4-dichlorobenzyl)benzimidazole, 2-(mercaptomethyl)benzimidazole, 2-(2-aminoethyl)benzimidazole, 2,2'-ethylenedibenzimidazole, 2-(1-naphthylmethyl)benzimidazole, 2-(2-pyridyl)benzimidazole, 2-(2-phenylvinyl)benzimidazole, 2-(phenoxymethyl)benzimidazole, and 2-(phenoxymethyl)-5-methylbenzimidazole.

[0011] The amount of component (A) is preferably 0.01% to 5% by mass, more preferably 0.02% to 3% by mass, even more preferably 0.05% to 2% by mass, and particularly preferably 0.1% to 1% by mass, based on 100% by mass of water-soluble preflux. If the amount of component (A) is above the lower limit, it becomes easier to form organic coatings such as rust-preventive films. Furthermore, if the amount of component (A) is below the upper limit, there is no increase in insoluble matter, which is also economically preferable.

[0012] [(B) Component] Examples of (B) monocarboxylic acids used in this embodiment include formic acid, acetic acid, propionic acid, butanoic acid, glycolic acid, lactic acid, chloroacetic acid, dichloroacetic acid, trichloroacetic acid, bromoacetic acid, and methoxyacetic acid. Among these, formic acid or acetic acid is preferred from the viewpoint of making component (A) water-soluble, and acetic acid is particularly preferred. These may be used individually or as a mixture of two or more.

[0013] The amount of component (B) is preferably 1% by mass or more and 40% by mass or less, and more preferably 2% by mass or more and 30% by mass or less, based on 100% by mass of the water-soluble preflux. If the amount of component (B) is within the above range, component (A) can be sufficiently made water-soluble.

[0014] [(C) component] The (C) dicarboxylic acid used in this embodiment is a compound having two carboxyl groups in one molecule. The reason why this (C) component can improve appearance uniformity without reducing repairability is not entirely clear, but the inventors speculate as follows: The inventors speculate that this is because the (C) component changes the surface tension of the resulting organic film or has an auxiliary effect during the formation of the organic film. Of course, the fact that the (C) component can improve appearance uniformity is remarkable and is something that the inventors have discovered for the first time. From the above viewpoint, the number of carbon atoms in the (C) component is preferably 2 to 12, more preferably 4 to 8, and particularly preferably 5 to 6. (C) Examples of component (C) include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, dodecanedioic acid, fumaric acid, maleic acid, phenylsuccinic acid, tartaric acid, malic acid, and diglycolic acid. Among these, succinic acid, glutaric acid, adipic acid, or malic acid are preferred from the viewpoint of uniform appearance, and glutaric acid or adipic acid are particularly preferred. These may be used individually or in combination of two or more.

[0015] The blending amount of component (C) is preferably 0.01% by mass or more and 5% by mass or less, more preferably 0.03% by mass or more and 3% by mass or less, still more preferably 0.05% by mass or more and 2% by mass or less, and particularly preferably 0.1% by mass or more and 1% by mass or less, based on 100% by mass of the water-soluble preflux. If the blending amount of component (C) is within the above range, the appearance uniformity can be further improved.

[0016] [Component (D)] The (D) water used in the present embodiment is the remainder other than components (A), (B), and (C) in the water-soluble preflux and other components described below.

[0017] [Chelating agent] The water-soluble preflux according to the present embodiment preferably further contains a chelating agent. According to this chelating agent, problems when using the water-soluble preflux according to the present embodiment on a substrate on which dissimilar metals such as copper lands and gold lands are mixed can be suppressed. That is, in order to maintain the bonding property of the printed wiring board, a substrate on which dissimilar metals such as copper lands and gold lands are mixed may be used for the bonding surface. When attempting to perform water-soluble preflux treatment on such a substrate, a local battery reaction due to dissimilar metals occurs, and the water-soluble preflux is also treated on the gold land surface that is not originally necessary. In such a case, it may cause problems such as discoloration. According to this chelating agent, problems such as discoloration can be suppressed.

[0018] Chelating agents include iminodiacetic acid (IDA), nitrilotriacetic acid (NTA), ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (DTPA), triethylenetetraminehexaacetic acid (TTHA), 1,2-diaminocyclohexanetetraacetic acid (CyDTA), glycol ether diamine tetraacetic acid (GEDTA), N,N-bis(2-hydroxybenzyl)ethylenediamine diacetic acid (HBED), ethylenediamine dipropionic acid (EDDP), ethylenediamine diacetic acid (EDDA), diaminopropanol tetraacetic acid (DPTA-OH), hexamethylenediamine tetraacetic acid (HDTA), hydroxyethyliminodiacetic acid (HIDA), diaminopropane tetraacetic acid (Methyl-EDTA), nitrilotripropionic acid (NTP), ethylenediamine tetrakis(methylenephosphonic acid) (EDTPO), and nitrilotris(methylenephosphonic acid) (NTPO), and metal salts thereof. Among these, from the viewpoint of suppressing problems such as discoloration, iminodiacetic acid, ethylenediaminetetraacetic acid, or metal salts thereof are preferred, and iminodiacetic acid or sodium iron ethylenediaminetetraacetic acid is more preferred.

[0019] The blending amount of the chelating agent is preferably 0.01% by mass or more and 2% by mass or less, more preferably 0.05% by mass or more and 1% by mass or less, and particularly preferably 0.1% by mass or more and 0.5% by mass or less with respect to 100% by mass of the water-soluble preflux. If the blending amount of the chelating agent is within the above range, problems such as discoloration can be more reliably suppressed.

[0020] [Other components] The water-soluble preflux according to the present embodiment may contain an organic solvent, a buffer solution, a pH adjuster, a complex film formation aid, etc., as long as the effects of the present invention are not inhibited. However, the water-soluble preflux according to the present embodiment preferably does not contain a halogen compound. This is because although the appearance uniformity is improved by the halogen compound, the reparability is reduced. Examples of the organic solvent include methanol, ethanol, and acetone. Examples of bases in buffer solutions or pH adjusters include ammonia, diethylamine, triethylamine, diethanolamine, triethanolamine, monoethanolamine, dimethylethanolamine, diethylethanolamine, isopropylethanolamine, sodium hydroxide, and potassium hydroxide. Examples of metal compounds that can be used as complex film-forming aids include copper formate, copper oxalate, copper acetate, copper hydroxide, copper carbonate, copper phosphate, copper sulfate, manganese formate, manganese oxalate, manganese sulfate, zinc acetate, lead acetate, nickel acetate, barium acetate, zinc hydride, ferrous oxide, and ferric oxide. When using these, the amount used is preferably 0.01% by mass or more and 10% by mass or less, and more preferably 0.05% by mass or more and 5% by mass or less, based on 100% by mass of the water-soluble preflux.

[0021] [Printed wiring board and its manufacturing method] Next, a printed circuit board and its manufacturing method according to this embodiment will be described. The method for manufacturing a printed circuit board according to this embodiment includes the step of forming an organic coating on the electrode terminals of the printed circuit board using the water-soluble preflux according to this embodiment. Furthermore, the printed circuit board according to this embodiment is obtained by the above manufacturing method. The printed circuit board may be a semiconductor substrate or the like, in addition to a printed circuit board. This printed circuit board may also be a substrate on which dissimilar metals such as copper lands and gold lands are mixed. As a method for forming the organic coating, for example, a pretreatment step can be employed in which the surface of the electrode terminals of the printed circuit board to be processed is degreased, chemically polished (soft etching), pickled, and washed with water, and then, if necessary, pretreated with a pretreatment solution, the printed circuit board is immersed in a water-soluble preflux at 10°C to 60°C for 1 second to 100 minutes (preferably at 20°C to 50°C for 5 seconds to 60 minutes, more preferably at 20°C to 50°C for 10 seconds to 10 minutes). The pretreatment solution may contain an amine compound. Examples of amine compounds include imidazole compounds and alkanolamines. Examples of imidazole compounds include imidazoles and benzimidazoles. Examples of alkanolamines include triisopropanolamine. The pretreatment solution may further contain an organic solvent and an ammonium salt. Examples of organic solvents include isopropanol. Examples of ammonium salts include ammonium acetate. In this way, the imidazole compound adheres to the surface of the electrode terminal, and the amount of adhesion increases with higher processing temperatures and longer processing times. Using ultrasound is preferable during this process. Alternatively, the organic coating may be formed by other coating methods, such as spraying, brushing, or roller application. As described above, an organic coating (such as a rust-preventive film) can be formed on a printed circuit board. The thickness of the organic coating at this time (coating thickness calculated using the conversion formula) is preferably 0.2 μm or more, more preferably 0.25 μm or more, and particularly preferably 0.35 μm or more. [Examples]

[0022] Next, the present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited in any way by these examples. The materials used in the examples and comparative examples are listed below. (Component A) Imidazole compound A: 2,4-diphenylimidazole Imidazole compound B: 2-(4-chlorobenzyl)benzimidazole Imidazole compound C: 2-(3,4-dichlorobenzyl)benzimidazole ((B) component) Monocarboxylic acid:acetic acid ((C) component) Dicarboxylic acid A: Glutaric acid Dicarboxylic acid B: succinic acid Dicarboxylic acid C: adipic acid Dicarboxylic acid D: Malic acid ((D) component) Water: Ion-exchanged water (Other ingredients) Halogen compound A: Zinc chloride Halogen compound B: Sodium iodide pH adjuster: 25% by mass of aqueous ammonia

[0023] [Example 1] A water-soluble preflux was obtained by dissolving 0.5% by mass of imidazole compound A and 0.3% by mass of dicarboxylic acid A in 74.2% by mass of water, 20% by mass of monocarboxylic acid, and 5% by mass of pH adjusting agent. The obtained water-soluble preflux was then pH-adjusted with a pH adjusting agent to obtain a water-soluble preflux treatment solution capable of forming a coating.

[0024] [Examples 2-8] A water-soluble preflux and a water-soluble preflux treatment solution were obtained in the same manner as in Example 1, except that each material was blended according to the composition shown in Table 1. [Comparative Examples 1-3] A water-soluble preflux and a water-soluble preflux treatment solution were obtained in the same manner as in Example 1, except that each material was blended according to the composition shown in Table 1.

[0025] <Evaluation of water-soluble preflux> The performance of the water-soluble preflux (film thickness, appearance after application, and repairability) was evaluated using the following method. The results are shown in Table 1. (1) Film thickness A double-sided copper-clad laminate (size: 25mm x 50mm, thickness: 1.6mm, substrate type: FR-4) was degreased, soft-etched, and washed with water to clean the surface. Then, it was immersed in the resulting water-soluble preflux at 40°C for 2 minutes to form a film, washed with water, and dried with hot air to prepare the test substrate. The film thickness measurement was performed using a surface area of ​​25 cm² on both sides. 2 The coating on the test substrate was extracted in 50 mL of 0.5% hydrochloric acid, and the maximum absorbance due to the active ingredients in the coating in the extract was measured. The coating thickness (in μm) was then calculated using a conversion formula. (2) Appearance after application A double-sided copper-clad laminate (size: 25mm x 50mm, thickness: 1.6mm, substrate type: FR-4) and a pattern-forming substrate with land opening diameters of φ0.2mm and φ1.0mm were degreased, soft-etched, and washed with water to clean the surface. Then, the substrates were immersed in the resulting water-soluble preflux at 40°C for 2 minutes to form a coating, washed with water, and dried with hot air to obtain the test substrates. The appearance of the test substrate was then observed under a 40-200x optical microscope to check for color unevenness, and the appearance after coating was evaluated according to the following criteria. ○: No uneven coloring. △: There is slight color unevenness, but it does not affect practical use. ×: There are color inconsistencies. (3) Repairability A double-sided copper-clad laminate (size: 25mm x 50mm, thickness: 1.6mm, substrate type: FR-4) and a pattern-forming substrate with land opening diameters of φ0.2mm and φ1.0mm were degreased, soft-etched, and washed with water to clean the surface. Then, the substrates were immersed in the resulting water-soluble preflux at 40°C for 2 minutes to form a coating, washed with water, and dried with hot air to obtain the test substrates. Next, the test substrate was immersed and agitated in a degreasing agent containing 3% sulfuric acid at room temperature for 2-3 minutes to dissolve and remove the water-soluble preflux coating. Subsequently, the test substrate was soft-etched and washed with water again, following the same procedure as above, to clean the surface. Then, it was immersed in the resulting water-soluble preflux at 40°C for 2 minutes to form a film, washed with water, and dried with hot air to obtain the test substrate. The appearance of the test substrates was then observed under a 40-200x optical microscope to check for color unevenness, and the repairability was evaluated according to the following criteria. In addition, the coating thickness of the test substrates was compared with that of the test substrates before repair, and the coating recovery rate (in %) was calculated. ○: No uneven coloring. △: There is slight color unevenness, but it does not affect practical use. ×: There are color inconsistencies.

[0026] [Table 1]

[0027] As is clear from the results shown in Table 1, the water-soluble prefluxes of the present invention (Examples 1-8) were found to be excellent in all evaluation results, including film thickness, appearance after application, and repairability. Therefore, it was confirmed that the present invention can form an organic coating with excellent appearance uniformity and repairability. [Industrial applicability]

[0028] The water-soluble preflux of the present invention is useful as a manufacturing technology for printed circuit boards or semiconductor substrates.

Claims

1. (A) contains an imidazole compound, (B) a monocarboxylic acid, (C) a dicarboxylic acid, and (D) water. The aforementioned component (A) is at least one selected from the group consisting of 2,4-diphenylimidazole, 2-(4-chlorobenzyl)benzimidazole, and 2-(3,4-dichlorobenzyl)benzimidazole. The above component (C) is glutaric acid. Water-soluble preflux.

2. In the water-soluble preflux according to claim 1, The amount of component (A) is 0.02% by mass or more and 1% by mass or less, relative to 100% by mass of the water-soluble preflux. The amount of component (C) is 0.03% by mass or more and 1% by mass or less, relative to 100% by mass of the water-soluble preflux. Water-soluble preflux.

3. An organic coating is formed on the electrode terminal by the water-soluble preflux according to claim 1 or claim 2. Printed circuit board.

4. The process includes forming an organic coating on the electrode terminals of a printed circuit board using the water-soluble preflux described in claim 1 or claim 2. A method for manufacturing printed circuit boards.

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