Electroless gold plating solution

Abstract

[The technical problem to be solved] The objective of this invention is to provide an electroless gold plating solution that minimizes the leaching of copper from copper raw materials during the formation of a gold plating film on a substrate such as a nickel film, or a method for manufacturing an electroless gold plating film using the same electroless gold plating solution or a method for manufacturing electronic components. Technical means to solve the problem The present invention addresses the aforementioned problem by providing an electroless gold plating solution containing a water-soluble gold salt and a condensed ring compound having a nitrogen atom in the ring. Examples of condensed ring compounds include condensed ring compounds having two or more non-carbon atoms in the ring, or condensed ring compounds formed by the condensation of a benzene ring or a pyridine ring with a heterocyclic five-membered ring having a nitrogen atom. The condensed ring compound may have substituents such as alkyl, mercapto, hydroxyl, carboxyl, nitro, or halogen groups having 1 to 6 carbon atoms.

Description

Technical Field

[0001] This invention relates to an electroless gold plating solution. Furthermore, this invention relates to an electroless gold plating solution preparation composition for formulating the electroless gold plating solution, or a method for manufacturing an electroless gold plating film using the electroless gold plating solution, or a method for manufacturing electronic components. Prior Technology

[0002] In the plating of connectors and other parts used in electronic components such as printed circuit boards, as a process to prevent corrosion of the connectors and to perform wire bonding, solder bonding, etc., the method of depositing a gold film on an electroless nickel plating film on a copper base material uses the following processes: a process of applying displacement gold plating on an electroless nickel plating film (ENIG, also known as Electroless Nickel Immersion Gold); a process of applying displacement gold plating on an electroless nickel plating film with an electroless palladium film in between (ENEPIG, also known as Electroless Nickel Electroless Palladium Immersion Gold); a process of applying displacement gold plating on an electroless nickel plating film and further applying reduction gold plating on top to increase the gold film thickness (ENEAG, also known as Electroless Nickel Electroless Autocatalytic Gold), etc.

[0003] The substitution gold plating used in the above processes involves the metal substrate becoming ions and dissolving in the gold plating solution. The electrons released are then transferred to the gold ions, causing the gold ions to become gold and precipitate on the surface of the substrate metal to form a gold film. Since gold deposition in displacement gold plating involves the substitution of gold ions with the substrate metal, the gold will not react further once the substrate metal surface is covered with gold, making it difficult to achieve a thick gold film. Therefore, it is known to add a reducing agent to a displacement-type electroless gold plating solution to induce a gold reduction reaction in the solution and form a gold plating film, thereby reducing the rate of gold film formation caused by the displacement reaction (displacement-reduction gold plating) (e.g., Patent Document 1, Patent Document 2).

[0004] To achieve good bonding strength in wire bonding and solder bonding, the adhesion between the gold plating film and the substrate metal must be excellent. Various improvements are made to the gold plating solution based on this principle.

[0005] Patent Document 3 describes a displacement gold plating solution applicable to the surface of a nickel film on a copper surface for displacement gold plating (ENIG process). This displacement gold plating solution contains nitrogen-containing aliphatic compounds or nitrogen-containing heterocyclic compounds as gold deposition inhibitors. The gold deposition inhibitor in Patent Document 3 suppresses partial and excessive etching or corrosion of the substrate metal caused by the displacement reaction with the substrate metal (nickel) during gold plating. The gold plating film formed by the displacement gold plating solution in Patent Document 3 is considered to have excellent adhesion to the substrate metal.

[0006] Patent document 4 describes a displacement gold plating solution containing polyethylene glycol, amidosulfuric acid, and amidosulfonate as corrosion inhibitors and applicable to the ENEPIG process. It is considered to have a fast gold deposition rate and minimal variation in the thickness of the deposited film.

[0007] In processes such as ENIG, ENEPIG, and ENEAG, a nickel or palladium film is formed on top of the copper substrate, and a replacement gold plating film is then formed on top of it. Ideally, the copper will not be exposed on the substrate with the gold plating film, and there will be no copper dissolving into the replacement gold plating solution. However, in actual mass production of printed circuit boards, the presence of undeposited portions of nickel and palladium films on the substrate, or structural problems (such as poor dry film formation), means that although the exposed portion of copper is small, it still exists, and thus copper gradually accumulates in the gold plating solution. Because copper accumulates in the gold plating solution, problems such as reduced corrosion resistance and peeling of the gold film can occur due to increased plating speed and decreased gold film coverage. These issues can sometimes hinder mass production. In such cases, the gold plating solution must be replaced frequently, leading to increased costs.

[0008] With the increasing complexity and density of printed circuit boards, copper accumulation is becoming more likely to occur. Therefore, it is hoped that a technology can be developed to suppress copper accumulation. [Previous Technical Documents] [Patent Literature]

[0009] [Patent Document 1] Japanese Patent Application Publication No. 2001-107259 [Patent Document 2] Japanese Patent Application Publication No. 2000-219973 [Patent Document 3] Japanese Patent Application Publication No. 2000-144441 [Patent Document 4] Japanese Patent Publication No. 6521553 Summary of the Invention Problems to be Solved by the Invention

[0010] The present invention was developed in view of the above prior art. The problems of the present invention are to provide an electroless gold plating solution that is less likely to cause elution of copper from a copper raw material when forming a gold plating film on a substrate such as a nickel film. In addition, the problems of the present invention are to provide a method for manufacturing an electroless gold plating film using the electroless gold plating solution or a method for manufacturing an electronic component. Means for Solving the Problems

[0011] The present inventors conducted intensive studies to solve the above problems, and as a result, found that by adding a condensed ring compound having a nitrogen atom in the ring to the electroless gold plating solution, it becomes extremely difficult to elute copper from the copper raw material, and thus completed the present invention.

[0012] That is, the present invention provides an electroless gold plating solution containing: a water-soluble gold salt, and a condensed ring compound having a nitrogen atom in the ring.

[0013] In addition, the present invention provides a composition for preparing an electroless gold plating solution, which is used for preparing an electroless gold plating solution by adding water and a water-soluble gold salt, and the composition for preparing an electroless gold plating solution contains the above-mentioned condensed ring compound.

[0014] In addition, the present invention provides a method for manufacturing an electroless gold plating film, which uses the above-mentioned electroless gold plating solution to manufacture an electroless gold plating film.

[0015] In addition, the present invention provides a method for manufacturing an electronic component, which has an electroless gold plating film manufactured by the method for manufacturing an electroless gold plating film described above.

[0016] In addition, the present invention provides a method for manufacturing an electronic component, which includes the step of: using the above-mentioned electroless gold plating solution to form an electroless gold plating film. Advantages of the Invention

[0017] According to the present invention, an electroless gold plating solution can be provided that is less likely to cause elution of copper from a copper raw material when forming a gold plating film on a substrate such as a nickel film.

[0018] The electroless gold plating solution of this invention does not easily cause copper leaching from the copper raw material, and copper does not easily accumulate in the plating solution. Therefore, the aforementioned problems caused by copper accumulation will not occur, and the number of times the plating solution needs to be replaced can be reduced (extending the life of the plating solution). In mass production, by using the electroless gold plating solution of the present invention, the cost of expensive gold plating solutions can be suppressed, and productivity can be improved. Implementation

[0019] The present invention is described below, but the present invention is not limited to the following embodiments and can be implemented in any modified form.

[0020] Electroless gold plating solution The electroless gold plating solution of the present invention contains: a water-soluble gold salt, and a condensed ring compound having a nitrogen atom in the ring.

[0021] Water-soluble gold salts are used as the gold source for the electroless gold plating solution of this invention. There are no particular limitations as long as they are sufficiently stable in the plating solution, easily soluble in water, and suitable as the gold source for the plating solution. Specifically, examples include gold cyanide salts, gold chloride salts, gold sulfite salts, and gold thiosulfate salts. Gold cyanide salts (gold (I) cyanide salts and gold (III) cyanide salts) are preferred, and gold (I) cyanide salts are particularly preferred. There are no particular limitations on the relative cations that form the above salts; examples include alkali metal ions and ammonium ions. Examples of alkali metal ions include potassium ions, sodium ions, and lithium ions. Among water-soluble gold salts, potassium gold cyanide (I) is the best in terms of plating speed and stability.

[0022] Water-soluble gold salts can be used alone or in combination with two or more.

[0023] The concentration of water-soluble gold salts in the electroless gold plating solution (the total concentration when two or more water-soluble gold salts are used together) is not particularly limited, but in gold conversion, it is preferably 0.1 g / L or more, more preferably 0.3 g / L or more, and particularly preferably 0.5 g / L or more. Furthermore, it is preferably 5 g / L or less, more preferably 4 g / L or less, and particularly preferably 3 g / L or less. When the concentration of water-soluble gold salt is above the lower limit mentioned above, the plating speed can be significantly increased. When the concentration of water-soluble gold salt is below the upper limit mentioned above, the stability of the plating solution is easily maintained.

[0024] A condensed ring compound having a nitrogen atom in its ring is not specifically limited to any condensed ring compound (a compound in which two or more rings share two or more atoms and are bonded together) that has a nitrogen atom in its ring (i.e., any one or more of the atoms constituting the ring is a nitrogen atom). Hereinafter, "a condensed ring compound having a nitrogen atom in its ring" will sometimes be referred to as a "specific condensed ring compound".

[0025] By including a specific condensation ring compound in the electroless gold plating solution, the dissolution of copper in the electroless gold plating solution can be suppressed even when there is an exposed part of the copper raw material during electroless gold plating. This can be presumed to be due to the strong hydrophobicity of a specific condensation ring compound, which forms a protective layer on the copper surface to prevent copper leaching.

[0026] Examples of specific condensed ring compounds include condensed ring compounds formed by the condensation of a benzene ring or a pyridine ring with a heterocyclic five-membered ring having a nitrogen atom.

[0027] A particular condensed ring compound is preferably one having two or more non-carbon atoms in the ring. Since a particular condensed ring compound is one having at least one nitrogen atom in the ring, in other words, a particular condensed ring compound is preferably one having two or more nitrogen atoms in the ring, or having a nitrogen atom and non-carbon and non-nitrogen atoms. Examples of non-carbon and non-nitrogen atoms include: sulfur atoms, oxygen atoms, phosphorus atoms, etc.

[0028] A certain condensed ring compound has a hetero five-membered ring with a nitrogen atom, preferably having two or more non-carbon atoms in the hetero five-membered ring. Specifically, examples include: cases with 2 nitrogen atoms, cases with 3 nitrogen atoms, cases with 1 nitrogen atom and 1 sulfur atom, cases with 1 nitrogen atom and 1 oxygen atom, cases with 2 nitrogen atoms and 1 sulfur atom, and cases with 2 nitrogen atoms and 1 oxygen atom.

[0029] A specific condensed ring compound has at least one nitrogen atom in its molecule, but may have two nitrogen atoms, three nitrogen atoms, four nitrogen atoms, or even more than five nitrogen atoms.

[0030] Certain condensed ring compounds may also have nitrogen-containing substituents such as amino, alkylamine, and nitro groups. In this case, the term "nitrogen atom present in the molecule" is not limited to nitrogen atoms in the ring; the nitrogen atoms contained in these substituents are also equivalent to "nitrogen atoms present in the molecule".

[0031] Examples of specific structures of certain condensed ring compounds include compounds having the following skeletons (basic skeletons): indole skeleton, isoindole skeleton, benzimidazole skeleton, indazole skeleton, purine skeleton, benzothiazole skeleton, benzothiazole skeleton, benzotriazole skeleton, quinoline skeleton, isoquinoline skeleton, quinoxaline skeleton, quinazoline skeleton, cinnoline skeleton, phthalazine skeleton, pyrazolopyridine skeleton, and triazolopyridine skeleton.

[0032] A specific condensed ring compound having the above structure (basic skeleton) may or may not have substituents.

[0033] When substituents are present, specific examples of substituents include: alkyl, mercapto, hydroxyl, carboxyl, nitro, halogen, etc., having 1 to 6 carbon atoms. Specific examples of alkyl groups include: methyl, ethyl, propyl, isopropyl, n-butyl, dibutyl, isobutyl, terbutyl, etc. Specific examples of the halogen group include fluorine group, chlorine group, bromine group, iodine group, etc. When the above-mentioned substituents are present, the hydrophobicity of the specific condensation ring compound becomes stronger, so a protective layer for copper leaching protection can be formed more effectively, making the inhibition effect of copper leaching more significant.

[0034] When a specific condensed ring compound is a condensed ring compound formed by the condensation of a benzene ring or a pyridine ring with a hetero five-membered ring having a nitrogen atom, the substituents can be bonded to the benzene ring or the pyridine ring, or to a hetero five-membered ring having a nitrogen atom. Multiple substituents can each be bonded to the benzene ring or the pyridine ring, or to a hetero five-membered ring having a nitrogen atom.

[0035] The number of the aforementioned substituents in a particular condensed ring compound may be one, two, three, or four or more. When there are multiple substituents, the same substituent can be present at multiple locations, or different types of substituents can be present.

[0036] Specific compound names for certain condensed ring compounds include: benzimidazole, 1-methylbenzimidazole, 2-methylbenzimidazole, 2-mercaptobenzimidazole, 2-glucopyranobenzimidazole, 1,2,3-benzotriazole, 5-methyl-1H-benzotriazole, 1-methyl-1H-benzotriazole, carboxybenzotriazole, hydroxybenzotriazole, carboxyhydroxybenzotriazole, nitrobenzotriazole, 1-aminobenzotriazole, 2-aminobenzothiazole, 1H-1,2,3-triazolidine, 3-aminoquinoline, 5-aminoindole, etc.

[0037] A specific condensation ring compound may be used alone or in combination with two or more compounds.

[0038] The concentration of the specific condensation ring compound in the electroless gold plating solution (the total concentration when two or more specific condensation ring compounds are used together) is not particularly limited, but is preferably 0.1 ppm or more, more preferably 0.5 ppm or more, and especially preferably 2 ppm or more. Furthermore, it is preferably 1000 ppm or less, more preferably 500 ppm or less, and especially preferably 100 ppm or less. When the concentration of a specific condensed ring compound is above the lower limit mentioned above, the effect of inhibiting copper dissolution is easily and fully realized. When the concentration of a specific condensed ring compound is below the upper limit mentioned above, costs can be suppressed, and in addition, precipitation of components exceeding the solubility can be prevented.

[0039] The electroless gold plating solution of this invention may further contain chelating agents. The function of the chelating agent is to prevent the precipitation of metals such as nickel, copper, palladium, iron, chromium, lead, and cobalt accumulated in the plating tank and to dissolve them stably during the operation of the electroless gold plating solution.

[0040] There are no particular limitations as long as the chelating agent is formulated with metals such as nickel, copper, palladium, iron, chromium, lead, and cobalt and is stably soluble in water. It is preferable to have chelating properties that are better than those of nickel, copper, palladium, etc.

[0041] Excellent chelating agents include: chelating agents with an intramolecular imine diacetic acid structure and chelating agents with a methylene phosphonic acid structure. These chelating agents exhibit good chelating properties relative to nickel, copper, palladium, etc.

[0042] Examples of chelating agents having an intramolecular imine diacetic acid structure include: ethylenediaminetetraacetic acid, aziridine triacetic acid, hydroxyethyl ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, triethylenetetraaminehexaacetic acid, dicarboxymethyl glutamic acid, propanediaminetetraacetic acid, 1,3-diamino-2-hydroxypropanetetraacetic acid, and other carboxylic acids or their salts.

[0043] Examples of chelating agents having a methylene phosphonic acid structure include aminotrimethylene phosphonic acid, hydroxyethylidene diphosphonic acid, ethylenediaminetetramethylene phosphonic acid, diethylenetriaminepentamethylene phosphonic acid, hexamethylenediaminetetramethylene phosphonic acid, and other phosphonic acids or their salts.

[0044] Among the chelating agents mentioned above, ethylenediaminetetraacetic acid, azirmonotriacetic acid, aminotrimethylenephosphonic acid, and ethylenediaminetetramethylenephosphonic acid are particularly preferred from the viewpoint of chelating characteristics or cost.

[0045] Chelating agents can be used alone or in combination of two or more.

[0046] The concentration of the chelating agent in the electroless gold plating solution (the total concentration when two or more chelating agents are used together) is not particularly limited, but it is preferably 0.5 g / L or more, more preferably 1 g / L or more, and particularly preferably 2 g / L or more. Furthermore, it is preferably 30 g / L or less, more preferably 20 g / L or less, and particularly preferably 10 g / L or less. When the concentration of the chelating agent is above the lower limit mentioned above, it achieves a sufficient chelating effect and easily prevents abnormal precipitation of metal accumulated in the plating bath. When the concentration of the chelating agent is below the upper limit mentioned above, it is cost-effective and can also prevent the precipitation of components exceeding the solubility.

[0047] The electroless gold plating solution of this invention may further contain a buffer. The buffer has the function of stabilizing the pH of the electroless gold plating solution. As long as it has this function, the type of buffer is not particularly limited, whether it is an organic compound or an inorganic compound, and it can be appropriately adjusted with acid, alkali or salt for use.

[0048] Specific examples of buffers include: adipic acid, benzyl acid, citric acid, malic acid, succinic acid, formic acid, acetic acid, lactic acid, malonic acid, phthalic acid, oxalic acid, tartaric acid, glycine, glutamic acid, glutaric acid, iminodiacetic acid, dehydroacetic acid, maleic acid, fumaric acid, and other carboxylic acids or their salts; amine compounds such as ethylenediamine, hydroxylamine, ethanolamine, diethanolamine, and triethanolamine or their salts; and inorganic acids such as boric acid, phosphoric acid, pyrophosphoric acid, phosphorous acid, thiosulfate, sulfurous acid, nitric acid, sulfuric acid, hydrochloric acid, and thiocyanate or their salts.

[0049] Preferred buffers include acids containing atoms with intermediate oxidation states, or salts of such acids. Additionally, compounds with potentials intermediate between oxidizing and reducing agents can be listed.

[0050] Excellent buffers include: phosphorous acid or its salts, sulfurous acid or its salts, etc. Examples of salts of phosphorous acid or sulfurous acid include: lithium salts, sodium salts, potassium salts, magnesium salts, calcium salts, barium salts, ammonium salts, etc.

[0051] Based on the fact that insoluble salts are not easily formed in the plating solution, the best buffers can be listed as: sodium sulfite, potassium sulfite, sodium phosphite, etc.

[0052] Buffers can be used alone or in combination with two or more.

[0053] The concentration of the buffer in the electroless gold plating solution (the total concentration when two or more buffers are used together) is not particularly limited, but it is preferably 1 g / L or more, more preferably 2 g / L or more, and especially preferably 3 g / L or more. Furthermore, it is preferably 300 g / L or less, more preferably 200 g / L or less, and especially preferably 100 g / L or less. When the concentration of the buffer is above the lower limit mentioned above, it is easy to achieve a sufficient buffering effect. When the concentration of the buffer is below the upper limit mentioned above, it is cost-effective and can prevent the precipitation of components exceeding the solubility.

[0054] The electroless gold plating solution of this invention mainly maintains pH stability by means of the aforementioned buffer. The ideal pH range is preferably 4 or higher, more preferably 4.5 or higher, and especially preferably 5 or higher. Furthermore, it is preferably 8 or lower, more preferably 7.5 or lower, and especially preferably 7 or lower. When the pH is above the lower limit mentioned above, water-soluble gold salts can exist stably in the liquid. When the pH is below the upper limit mentioned above, the resist on the substrate is not easily etched.

[0055] The electroless gold plating solution of the present invention can be a displacement-type electroless gold plating solution, a reduction-type electroless gold plating solution, or a displacement-reduction-type electroless gold plating solution.

[0056] When using a reduced-type electroless gold plating solution or a replacement reduced-type electroless gold plating solution, the reducing agents contained in the electroless gold plating solution of the present invention can be listed as follows: ascorbic acid, isoascorbic acid, glyoxylic acid, formic acid, thioglycolic acid, formamidinesulfinic acid, and aspartic acid. Organic acids such as tartaric acid and their salts; inorganic acids such as hypophosphoric acid and their salts; thioureas such as 1-allyl-2-thiourea, 1-allyl-3-(2-hydroxyethyl)-2-thiourea, 1,3-diethyl-2-thiourea, trimethylthiourea, 1,3-dimethylthiourea, 1-acetylatedhiurea, N-allylthiourea, ethylene thiourea, and N-methylthiourea; hydrazine derivatives such as thiosemicarbazide, hydrazine, p-hydrazinebenzenesulfonic acid, isonicotinic acetylhydrazine, and hydrazine sulfate; boron compounds such as dimethylaminoborane, trimethylaminoborane, sodium borohydride, potassium borohydride, diethylaminoborane, and triethylaminoborane; aldehydes such as formaldehyde and acetaldehyde; hydroxylamine; and hydroquinone.

[0057] From the viewpoint of the stability of the plating solution, ascorbic acid or its salts and thiourea are particularly preferred among the reducing agents mentioned above.

[0058] Reducing agents can be used alone or in combination with two or more.

[0059] The concentration of the reducing agent in the electroless gold plating solution (the total concentration when two or more reducing agents are used together) is not particularly limited, but it is preferably 0.01 g / L or more, even more preferably 0.05 g / L or more, and particularly preferably 0.2 g / L or more. Furthermore, it is preferably 50 g / L or less, even more preferably 20 g / L or less, and particularly preferably 5 g / L or less. When the concentration of the reducing agent is above the lower limit mentioned above, stable plating precipitation is obtained. When the concentration of the reducing agent is below the upper limit mentioned above, it is cost-effective, and the plating solution exhibits excellent stability.

[0060] The electroless gold plating solution of this invention may further contain: chelating agent, surfactant, crystallization modifier, etc. When impurity metals are mixed into the electroless gold plating solution, chelating agents can remove their influence. Surfactants play a role in controlling the wetting properties of electroless gold plating solutions. Crystallization modifiers have the function of controlling the crystal structure of the electroless gold plating film that is deposited.

[0061] [Composition for preparing electroless gold plating solution] The present invention also relates to a composition for preparing an electroless gold plating solution, which is used to prepare an electroless gold plating solution by adding water and water-soluble gold salt, the composition for preparing the electroless gold plating solution containing the aforementioned specific condensed ring compound.

[0062] Water-soluble gold salts, an essential component of the electroless gold plating solution of this invention, are extremely expensive and are usually traded at market price. Furthermore, storing water-soluble gold salts in an aqueous solution is not economical, and storing them in an aqueous solution can reduce the performance of the plating solution. Therefore, it is better to store water-soluble gold salts separately in an undissolved state, and add them to an aqueous solution containing other ingredients (which may be all or part of the ingredients contained in the electroless gold plating solution) when the electroless gold plating solution is to be used.

[0063] The composition for preparing the electroless gold plating solution of the present invention contains the aforementioned specific condensed ring compound, and may contain the aforementioned chelating agent, buffer, chelating agent, surfactant, crystallization modifier, and reducing agent as needed.

[0064] The form of the components used in the preparation of the electroless gold plating solution of the present invention is not limited, and can be in powder or aqueous solution form. In the case of an aqueous solution, the concentration of a specific condensed ring compound can be set to be higher than that of the specific condensed ring compound in the aforementioned electroless gold plating solution. When it is to be used as an electroless gold plating solution, water is added further (to dilute the concentration of the specific condensed ring compound).

[0065] The electroless gold plating solution of the present invention can be prepared by adding water-soluble gold salt, or water-soluble gold salt and water, to the composition for preparing the electroless gold plating solution of the present invention.

[0066] The composition for preparing the electroless gold plating solution of the present invention may be all or part of the components (chelating agents, buffers, chelating agents, surfactants, crystallization modifiers, reducing agents, etc.) of the electroless gold plating solution. In other words, these components, like water-soluble gold salts or water, may be added separately to the composition for preparing the electroless gold plating solution during the preparation of the electroless gold plating solution.

[0067] [Method for manufacturing electroless gold plating coating] The present invention also relates to a method for manufacturing an electroless gold plating film, which uses the aforementioned electroless gold plating solution to manufacture the electroless gold plating film.

[0068] The manufacturing process for the electroless gold plating film of the present invention is not particularly limited, and can be applied to processes such as the following: forming an electroless gold plating film on top of an electroless nickel film formed on a copper material (ENIG); forming an electroless palladium film on top of an electroless nickel film formed on a copper material, and further forming an electroless gold plating film on top of it (ENEPIG); forming a displacement gold plating film on top of an electroless nickel film formed on a copper material, and further forming a reduction gold plating film on top of it (ENEAG), etc.

[0069] According to the method for manufacturing an electroless gold plating film of the present invention, even if there are a few exposed copper portions due to undeposited nickel film or poor dry film formation, the dissolution of copper from these exposed portions can be suppressed. Therefore, in the method for manufacturing an electroless gold plating film of the present invention, problems caused by copper accumulation in the electroless gold plating solution are less likely to occur, reducing the frequency of electroless gold plating solution replacement and improving production efficiency.

[0070] When forming the electroless gold plating film according to the manufacturing method of the present invention, the thickness of the electroless gold plating film (the thickness measured by the method described in the following embodiments) is not particularly limited, but is preferably 0.005 μm or more, more preferably 0.01 μm or more, and particularly preferably 0.02 μm or more. Furthermore, it is preferably 1 μm or less, more preferably 0.7 μm or less, and particularly preferably 0.5 μm or less. Above the aforementioned lower limit, the performance as a coating can be fully utilized. Furthermore, below the aforementioned upper limit, it is cost-effective.

[0071] As a side note, the term "coating" is not limited to a uniformly flat membrane; membranes with pores or granular portions are also called "coatings." The term "coating" is synonymous with "layer."

[0072] The temperature of the electroless gold plating solution used in the process of forming the electroless gold plating film using the method of manufacturing an electroless gold plating film is preferably 10°C or higher, more preferably 15°C or higher, and especially preferably 20°C or higher. Furthermore, it is preferably 100°C or lower, more preferably 95°C or lower, and especially preferably 90°C or lower. Furthermore, the time (plating time) for forming the electroless gold plating film using the manufacturing method of electroless gold plating film is preferably 0.5 minutes or more, more preferably 1 minute or more, and particularly preferably 2 minutes or more. Furthermore, it is preferably 240 minutes or less, more preferably 120 minutes or less, and particularly preferably 60 minutes or less. When the temperature or plating time of the electroless gold plating solution is within the above-mentioned range, it is easy to form a film thickness within the aforementioned range.

[0073] Manufacturing methods for electronic components The present invention also relates to a method for manufacturing an electronic component having an electroless gold plating film manufactured by the aforementioned method for manufacturing an electroless gold plating film. Furthermore, the present invention also relates to a method for manufacturing an electronic component, comprising the following steps: forming an electroless gold plating film using the aforementioned electroless gold plating solution. [Example]

[0074] The following series of examples and comparative examples illustrate the present invention in more detail, but the present invention is not limited to these examples without departing from its spirit. As a side note, "ppm" means "mass ppm" unless otherwise specified.

[0075] [Preparation of Electroless Gold Plating Solution] Examples 1 to 18, Comparative Examples 1 to 6 In a base solution A prepared by dissolving each component in ion-exchanged water at the concentrations shown below, the nitrogen-containing condensed ring compounds or comparative compounds shown in Table 1 were dissolved at a concentration of 10 ppm relative to the overall electroless plating solution, and the pH was adjusted to 6.5 to prepare the electroless gold plating solutions of Examples 1 to 18 and Comparative Examples 1 to 6. Note that when adjusting the pH, an aqueous solution of sodium hydroxide was used to increase the pH, and sulfuric acid was used to decrease the pH.

[0076] <Base Fluid A>

[0077] Examples 19 to 20 In a base solution B prepared by dissolving each component in ion-exchanged water at the concentrations shown below, the nitrogen-containing condensed ring compounds shown in Table 1 were dissolved at a concentration of 10 ppm relative to the overall electroless plating solution, and the pH was adjusted to 6.5 to prepare the electroless gold plating solutions of Examples 19 and 20. Note that when adjusting the pH, an aqueous solution of sodium hydroxide was used to increase the pH, and sulfuric acid was used to decrease the pH.

[0078] <Base Fluid B>

[0079] Examples 21 to 22 In a base solution C prepared by dissolving each component in ion-exchanged water at the concentrations shown below, the nitrogen-containing condensed ring compounds shown in Table 1 were dissolved at a concentration of 10 ppm relative to the overall electroless plating solution, and the pH was adjusted to 6.5 to prepare the electroless gold plating solutions of Examples 21 and 22. Note that when adjusting the pH, an aqueous solution of sodium hydroxide was used to increase the pH, and sulfuric acid was used to decrease the pH. The electroless gold plating solution using base solution C is a reduced electroless plating solution.

[0080] <Base Fluid C> Sodium ascorbate 2g / L

[0081] [Table 1]

[0082] [Assessment of Copper Leaching] The electroless gold plating solutions prepared in each embodiment and comparative example were heated to 85°C. After immersing three 2.0cm×2.5cm copper plates in 100mL of the electroless gold plating solution, the electroless gold plating solution was cooled to room temperature. Note that the copper plate used should be treated as shown in Table 2 before immersing it in the electroless gold plating solution.

[0083] [Table 2]

[0084] The electroless gold plating solution, prepared at room temperature, was accurately measured to 100 mL in a volumetric flask and homogenized by stirring. The copper concentration was then quantified and the amount of copper leaching was assessed using an ICPS-7510 plasmaluminescence spectrophotometer (manufactured by Shimadzu Corporation). The results are presented in Table 1.

[0085] [Fabrication of the Coated Layer] Copper foil was attached to the glass cloth epoxy material (FR-4), and a diameter was set using solder resist. A 0.5mm opening is used to form a substrate (40mm × 40mm × 1mm) as the substrate to be plated, and the plating layer is fabricated according to the steps in Table 3. In the electroless gold plating, the electroless gold plating solution prepared in each embodiment is used.

[0086] [Table 3]

[0087] [Determination of gold plating film thickness] The thickness of the gold plating in the fabricated deposit was determined using a fluorescence X-ray spectrophotometer (FT-150, manufactured by Hitachi High-Tech Science Co., Ltd.). The results are presented in Table 1.

[0088] [Evaluation of the appearance of gold plating] The plating openings of the fabricated deposit were observed using an optical microscope at 10x magnification. A uniform, golden color was considered "normal," while an orange or brown color, or an uneven color, was considered "defective." The results are presented in Table 1.

[0089] The electroless gold plating solution of the present invention, containing a specific condensation ring compound, exhibits almost no copper leaching and can form a high-quality gold plating layer. [Industry applicability]

[0090] Because the electroless gold plating solution of the present invention contains a specific condensation ring compound, it is not easy to produce copper leaching from copper raw materials when forming gold plating films on substrates such as nickel films. Therefore, it can be widely used to form gold plating films for connecting terminals of electronic components.

Claims

1. A method for manufacturing an electroless gold plating film, wherein an electroless gold plating solution containing a water-soluble gold salt and a condensed ring compound having a nitrogen atom in the ring is used to manufacture the electroless gold plating film when forming a gold plating film on a substrate.

2. The method for manufacturing an electroless gold plating film as described in claim 1, wherein, The aforementioned condensed ring compounds are condensed ring compounds formed by the condensation of a benzene ring or a pyridine ring with a heterocyclic five-membered ring containing a nitrogen atom.

3. The method for manufacturing an electroless gold plating film as described in claim 1, wherein, The aforementioned condensed ring compound is a condensed ring compound having two or more non-carbon atoms in the ring.

4. The method for manufacturing an electroless gold plating film as described in claim 1, wherein, The aforementioned condensed ring compound is a condensed ring compound having one or more substituents selected from the group consisting of alkyl, mercapto, hydroxyl, carboxyl, nitro and halogen groups having 1 to 6 carbon atoms.

5. The method for manufacturing an electroless gold plating film as described in claim 1, wherein, The aforementioned electroless gold plating solution also contains chelating agents.

6. The method for manufacturing an electroless gold plating film as described in claim 5, wherein, The aforementioned chelating agent contains one or more chelating agents selected from the group consisting of chelating agents having an imine diacetic acid structure within the molecule and chelating agents having a methylene phosphonic acid structure.

7. The method for manufacturing an electroless gold plating film as described in claim 1, wherein, The aforementioned electroless gold plating solution also contains a buffer.

8. The method for manufacturing an electroless gold plating film as described in claim 7, wherein, The aforementioned buffer contains one or more compounds selected from the group consisting of sulfurous acid, phosphorous acid, and their salts.

9. The manufacturing method as described in claim 1, wherein, The aforementioned substrate is a nickel coating.

10. The manufacturing method as described in claim 1 can be applied to the following processes: forming an electroless gold plating film on top of an electroless nickel film formed on a copper raw material (ENIG); forming an electroless palladium film on top of an electroless nickel film formed on a copper raw material, and further forming an electroless gold plating film on top of it (ENEPIG); forming a displacement gold plating film on top of an electroless nickel film formed on a copper raw material, and further forming a reduction gold plating film on top of it (ENEAG).

11. A method for manufacturing an electronic component, wherein, The electronic component has an electroless gold plating film manufactured by the manufacturing method of any one of claims 1 to 10.