JP5526440B2 - Printed wiring board formed using reduced deposition type electroless gold plating solution for palladium film - Google Patents

Description

  The present invention relates to a reduction deposition type electroless gold plating solution capable of depositing a gold plating film directly on a palladium film.

  When bonding or soldering gold wires, aluminum wires, etc. on electronic parts, especially printed wiring boards, after forming an electroless nickel plating film as a surface treatment for the conductor part of the joint, form a gold plating film There are things to do. The purpose of this treatment is to protect the surface of the nickel plating film with a gold plating film to exhibit high solder joint strength and to ensure good solder wettability.

  In this case, usually, after forming an electroless nickel plating film of about 1 to 10 μm, a gold plating film of about 0.03 to 0.1 μm is formed using a displacement deposition type gold plating solution, For the purpose of imparting excellent heat resistance in gold wire bonding, a thick gold plating film having a thickness of about 0.2 to 1 μm may be formed by a displacement plating method or a reduction plating method.

  However, the above-described method has a problem in that when the gold plating film is formed by the displacement plating method, the surface of the nickel plating film is eroded because gold plating is deposited due to a potential difference from the underlying nickel plating film. is there. Such erosion of the nickel plating film causes deterioration of solderability and bonding property, and further causes contamination of the liquid.

  For this reason, a method of forming an electroless palladium plating film as an intermediate layer between the electroless nickel plating film and the displacement gold plating film has been proposed for the purpose of protecting the nickel plating film (Patent Document 1 below). reference). This method intends to suppress erosion of the nickel plating film by the displacement gold plating solution by forming a palladium plating film as an intermediate layer. However, when the electroless palladium plating film is thin, or there are defects in the object to be plated or the shape is complicated, the deposition of the palladium plating film becomes insufficient, and the exposed part of the nickel plating film May occur. In such a case, since nickel is a base metal than palladium, if even a part of the nickel plating film is exposed, the nickel in this part will be preferentially dissolved and the nickel surface will be eroded, reducing solderability. Cause.

Moreover, in order to improve the heat resistance at the time of wire bonding, a thick gold plating film of about 0.2 to 1 μm may be formed. However, when a displacement precipitation type gold plating solution is used, the film thickness is increased. Have difficulty. In addition, when performing the reduction deposition type gold plating, it is not usually deposited directly on the nickel film or the palladium film. It is necessary to increase the film thickness using a plating solution. For example, Patent Document 2 below describes a method of sequentially forming electroless nickel, substituted palladium or electroless palladium, substituted gold plating and electroless gold plating on the copper foil portion of the terminal. Since two steps are required to form the gold plating film, the processing work becomes complicated.
Japanese Patent Laid-Open No. 10-168578 Japanese Patent Laid-Open No. 9-8438

  The present invention has been made in view of the current state of the prior art described above, and its main purpose is that it can be directly deposited on a palladium film, and is particularly useful for surface treatment of a conductor circuit of a printed wiring board. It is to provide a deposition type electroless gold plating solution.

  The present inventor has intensively studied to achieve the above-described object. As a result, according to the reduction deposition type electroless gold plating solution containing a specific compound such as formaldehyde bisulfite, Rongalite or hydrazine as a reducing agent, the gold is deposited on the palladium film without performing substitution deposition type gold plating. It has been found that a plating film can be formed directly. And after forming an electroless nickel plating film in the conductor part of a printed wiring board and forming an electroless palladium plating film, a gold plating film is formed using the above-mentioned electroless gold plating solution containing a specific reducing agent. According to the method, even when the palladium plating film is thin, it is possible to form a gold plating film without eroding the underlying nickel plating film, and to perform substitution deposition type gold plating. It has been found that a thick gold plating film can be formed by a simplified processing step without performing the present invention, and the present invention has been completed here.

That is, the present invention provides the following reduced deposition type electroless gold plating solution for a palladium film and a printed wiring board.
1. An electroless gold plating solution comprising an aqueous solution containing a water-soluble gold compound, a reducing agent and a complexing agent, wherein the reducing agent is at least one compound selected from the group consisting of formaldehyde bisulfite, Rongalite and hydrazine A reduction deposition type electroless gold plating solution used for forming a gold plating film directly on a palladium film, characterized in that
2. Item 2. A printed wiring board in which an electroless nickel plating film, an electroless palladium plating film, and an electroless gold plating film are sequentially formed on a conductor portion of the printed wiring board, and the electroless gold plating film is the item 1 described above. A printed wiring board which is formed using the reduced deposition type electroless gold plating solution.
3. The electroless palladium plating film is made of an aqueous solution containing a palladium compound, a reducing agent, and a complexing agent, and the reducing agent is formed from an electroless palladium plating solution that is at least one selected from the group consisting of formic acid and salts thereof. Item 3. The printed wiring board according to Item 2 above.

  The electroless gold plating solution of the present invention is a reduction precipitation type gold plating solution comprising an aqueous solution containing a water-soluble gold compound, a reducing agent and a complexing agent as essential components, and may be either a non-cyan bath or a cyan bath. . The electroless gold plating solution of the present invention is characterized in that it contains at least one compound selected from the group consisting of formaldehyde bisulfite, Rongalite and hydrazine as a reducing agent, and a gold film is formed on the palladium film. It is used for directly forming a plating film. Hereinafter, the reduction precipitation type electroless gold plating solution of the present invention will be specifically described.

Reduced deposition type electroless gold plating solution In the reduced deposition type electroless gold plating solution of the present invention, the water-soluble gold compound is particularly limited as long as it is soluble in the plating solution and can obtain an aqueous solution of a predetermined concentration. Can be used without For example, potassium gold sulfite, sodium gold sulfite, gold ammonium sulfite, potassium gold cyanide, sodium gold cyanide, ammonium gold cyanide and the like can be used. The water-soluble gold salt can be used alone or in combination of two or more. The content of the water-soluble gold salt is preferably about 0.1 to 20 g / L, and more preferably about 0.3 to 5 g / L.

  A known complexing agent can be used as the complexing agent. For example, amines such as ethylenediamine and diethylenetriamine; aminopolycarboxylic acids such as ethylenediaminediacetic acid, ethylenediaminetetraacetic acid and diethylenetriaminepentaacetic acid, sodium salts, potassium salts and ammonium salts thereof; glycine, alanine, iminodiacetic acid, nitrilotriacetic acid, L Amino acids such as glutamic acid, L-glutamic acid diacetic acid, L-aspartic acid, taurine, ammonium salts, potassium salts, sodium salts thereof; aminotrimethylenephosphonic acid, 1-hydroxyethylidene-1,1-diphosphonic acid, Ethylenediaminetetramethylene phosphonic acid, ammonium salts, potassium salts, sodium salts thereof and the like can be used. Complexing agents can be used alone or in combination of two or more. As the complexing agent, ethylenediamine is particularly preferable. The complexing agent content is preferably about 0.5 to 100 g / L, more preferably about 5 to 50 g / L.

  The reduction deposition type electroless gold plating solution of the present invention is characterized in that it contains at least one compound selected from the group consisting of formaldehyde bisulfite, longalite and hydrazine as a reducing agent. According to the electroless gold plating solution using such a specific compound as a reducing agent, the gold is deposited on the various palladium films such as the electroless palladium plated film and the electrolytic palladium plated film without performing substitution deposition type gold plating. A plating film can be directly formed. When such a specific reducing agent is used, the ability to directly form a reduced deposition type electroless gold plating film on the palladium film is a novel discovery that has not been known at all.

  Among the reducing agents, as formaldehyde bisulfite, in addition to formaldehyde bisulfite, soluble salts such as ammonium salt, potassium salt and sodium salt of formaldehyde bisulfite can be used.

  Examples of hydrazines that can be used include hydrazine; hydrazine salts such as hydrazine sulfate and hydrazine hydrochloride; hydrazine derivatives such as pyrazoles, triazoles, and hydrazides. Among these, as pyrazoles, pyrazole derivatives such as 3,5-dimethylpyrazole and 3-methyl-5-pyrazolone can be used in addition to pyrazole. As triazoles, 4-amino-1,2,4-triazole, 1,2,3-triazole and the like can be used. As the hydrazides, adipic acid hydrazide, maleic acid hydrazide, carbohydrazide and the like can be used. As the hydrazines, hydrazine sulfate, hydrazine hydrochloride, adipic hydrazide, maleic hydrazide, carbohydrazide and the like are particularly preferable.

  The above reducing agents can be used singly or in combination of two or more.

  As the reducing agent, in particular, sodium formaldehyde bisulfite, Rongalite, etc. are preferable in that the bath stability of the gold plating bath is good.

  The content of the reducing agent described above is preferably about 0.5 to 100 g / L, and more preferably about 1 to 30 g / L.

  As a reducing agent, thiourea, ascorbic acid, dimethylamine borane, sodium tetrahydroborate, sodium hypophosphite, etc. can be used in combination, but when these reducing agents are used alone, palladium A uniform gold plating film cannot be formed directly on the film. When using a reducing agent other than the reducing agent comprising at least one compound selected from the group consisting of formaldehyde bisulfite, longalite and hydrazine, the content of these reducing agents is, for example, 0.1 It can be in the range of ˜50 g / L.

  Furthermore, the electroless gold plating solution may contain a stabilizer such as a nitrogen compound such as a cyanide compound or an ethylenediamine derivative, or a sulfur compound such as a thiourea derivative, alone or in combination. The blending amount of the stabilizer can be, for example, about 0.0001 g / L to 20 g / L.

  The pH of the reduced deposition type electroless gold plating solution of the present invention is preferably about 4 to 9. For pH adjustment, inorganic acids such as sulfuric acid and phosphoric acid, sodium hydroxide, aqueous ammonia and the like can be used. If the pH is too low or too high, the printed circuit board or the like is undesirably damaged particularly with respect to the solder resist.

  According to the reduction deposition type electroless gold plating solution of the present invention described above, substitution deposition is performed on various palladium films such as an electroless palladium plating film, an electrolytic palladium plating film, and a palladium film formed by a vapor phase method. A reduction precipitation type electroless gold plating film can be formed directly without performing electroless gold plating.

  For example, the gold plating film can be directly formed on the palladium film by immersing the object to be plated on which the palladium film is formed in the above-described reduction deposition type electroless gold plating solution.

  The treatment temperature of the electroless gold plating solution of the present invention is preferably about 35 ° C. to 95 ° C., more preferably about 45 ° C. to 90 ° C.

Method of plating on printed wiring board The reduced deposition type electroless gold plating solution of the present invention is particularly suitable for electroless nickel plating film with a conductive part such as a pad part, a circuit part, and a terminal part of the printed wiring board being plated. After forming, in the method of forming an electroless palladium plating film and then forming a gold plating film, the plating solution is particularly useful as an electroless gold plating solution for forming a gold plating film.

  By using the reduced deposition type electroless gold plating solution of the present invention in the above method, a gold plating film can be formed directly on the palladium plating film without performing substitution deposition type gold plating. For this reason, even if the nickel plating film is not completely covered with the palladium plating film and an exposed portion of the nickel plating film is generated, the nickel surface is not eroded during gold plating, and solderability is improved. There is no reduction. Further, since the thick gold plating can be performed only by the reduction precipitation type gold plating, the processing process can be simplified.

  As a printed wiring board, for example, a substrate in which a conductor portion made of copper or the like is formed using epoxy resin, polyimide resin or the like as a base material; a conductor portion made of copper, silver, tungsten, molybdenum or the like is made of glass or ceramics as a base material A formed substrate or the like can be used.

  The electroless nickel plating film can be formed according to a conventional method. Usually, the object to be plated may be immersed in an electroless nickel plating solution. When the object to be plated does not have catalytic activity for electroless nickel plating, electroless nickel plating may be performed after depositing a metal catalyst nucleus such as a palladium nucleus according to a conventional method. During electroless nickel plating, the plating solution can be agitated and the object to be plated can be swung as necessary.

  The electroless nickel plating solution is not particularly limited, and a known electroless nickel plating solution made of an aqueous solution containing a water-soluble nickel compound, a reducing agent, and a complexing agent as essential components can be used. An example of the electroless nickel plating solution is as follows.

  The water-soluble nickel compound can be used without particular limitation as long as it is soluble in the plating solution and can obtain an aqueous solution having a predetermined concentration. For example, nickel sulfate, nickel chloride, nickel sulfamate, nickel hypophosphite, or the like can be used. A water-soluble nickel compound can be used individually by 1 type or in mixture of 2 or more types. In particular, nickel sulfate is preferable in terms of good solubility.

  The content of the water-soluble nickel compound is preferably about 0.5 to 50 g / L, and more preferably about 2 to 10 g / L.

  As the reducing agent, hypophosphorous acid, hypophosphite (sodium salt, potassium salt, ammonium salt, etc.), dimethylamine borane, hydrazine and the like can be used. The content of the reducing agent is preferably about 0.01 to 100 g / L, and more preferably 0.1 to 50 g / L.

  A known complexing agent can be used as the complexing agent. For example, monocarboxylic acids such as acetic acid and formic acid, ammonium salts, potassium salts, sodium salts thereof; dicarboxylic acids such as malonic acid, succinic acid, adipic acid, maleic acid, fumaric acid, ammonium salts, potassium salts thereof, Sodium salts, etc .; hydroxycarboxylic acids such as malic acid, lactic acid, glycolic acid, gluconic acid, citric acid, ammonium salts, potassium salts, sodium salts, etc .; aminopolyamines such as ethylenediaminediacetic acid, ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid Carboxylic acids, ammonium salts thereof, potassium salts, sodium salts and the like; Glycine, alanine, iminodiacetic acid, nitrilotriacetic acid, L-glutamic acid, L-glutamic acid diacetic acid, L-aspartic acid, taurine and other amino acids, ammonium salts thereof , Mosquito Ammonium salt, sodium salt, etc .; aminotrimethylenephosphonic acid, 1-hydroxyethylidene-1,1-diphosphonic acid, ethylenediaminetetramethylenephosphonic acid, ammonium salts, potassium salts, sodium salts thereof; amine compounds such as ethylenediamine, diethylenetriamine Etc. can be blended. Complexing agents can be used alone or in combination of two or more. The compounding amount of the complexing agent is preferably about 0.5 to 100 g / L, and more preferably about 5 to 50 g / L.

  In addition to the electroless nickel plating solution, various commonly used additives can be blended as necessary. For example, as a stabilizer, lead salts such as lead nitrate and lead acetate; bismuth salts such as bismuth nitrate and bismuth acetate; sulfur compounds such as thiodiglycolic acid may be added singly or in combination of two or more. it can. Although the addition amount of a stabilizer is not specifically limited, For example, it can be set as about 0.01-100 mg / L.

  Furthermore, a surfactant can be blended for the permeability of the plating solution. As the surfactant, nonionic, cationic, anionic, and amphoteric surfactants can be added singly or in combination of two or more. The addition amount is preferably about 0.1 to 100 mg / L.

  The pH of the above electroless nickel plating solution is preferably about 2 to 9, and more preferably about 3 to 8. For pH adjustment, inorganic acids such as sulfuric acid and phosphoric acid, sodium hydroxide, aqueous ammonia and the like can be used.

  The treatment temperature with the electroless nickel plating solution is usually about 50 to 95 ° C, and preferably about 60 to 90 ° C.

  The film thickness of the electroless nickel plating film is not particularly limited, but is preferably about 0.1 to 15 μm, and more preferably about 0.2 μm to 10 μm. If the thickness of the nickel plating solution is too thin, it is difficult to obtain the effect of nickel plating, and if it is too thick, an effect of a certain level cannot be obtained, which is not economical.

  Subsequently, after forming an electroless nickel plating film by the above-described method, an electroless palladium plating film is formed. Usually, an electroless palladium plating film can be formed by immersing an object on which an electroless nickel plating film is formed in an electroless palladium plating solution.

  The electroless palladium plating solution is not particularly limited, and an electroless palladium plating solution comprising an aqueous solution containing a palladium compound, a reducing agent and a complexing agent as essential components can be used. An example of the electroless palladium plating solution is as follows.

  First, the palladium compound can be used without particular limitation as long as it is soluble in the plating solution and can obtain an aqueous solution having a predetermined concentration. For example, water-soluble palladium compounds such as palladium sulfate, palladium chloride, palladium acetate, dichlorodiethine rediamine palladium, and tetraammine palladium dichloride can be used. Further, as the palladium compound, a so-called palladium solution in which palladium is made into a solution can also be used. As the palladium solution, for example, a dichlorodiethylenediamine palladium solution or a tetraammine palladium dichloride solution can be used. A palladium compound can be used individually by 1 type or in mixture of 2 or more types.

  The content of the palladium compound is preferably about 0.1 to 30 g / L as palladium, and more preferably about 0.3 to 10 g / L.

  As a reducing agent for electroless palladium plating, formic acid, hypophosphorous acid, phosphorous acid, salts thereof (sodium salt, potassium salt, ammonium salt, etc.) and the like can be used. These reducing agents can be used singly or in combination of two or more.

  The content of the reducing agent is preferably about 0.1 to 100 g / L, more preferably 1 to 50 g / L.

  As the reducing agent, formic acid or a salt thereof is particularly preferable. The palladium plating film obtained by using this becomes a high-purity film of 99% or more, the adhesion with the gold plating film is particularly good, and the solder joint strength is also improved.

  A known complexing agent can be used as the complexing agent. For example, amines such as ethylenediamine and diethylenetriamine; aminopolycarboxylic acids such as ethylenediaminediacetic acid, ethylenediaminetetraacetic acid and diethylenetriaminepentaacetic acid, sodium salts, potassium salts and ammonium salts thereof; glycine, alanine, iminodiacetic acid, nitrilotriacetic acid, L -Amino acids such as glutamic acid, L-glutamic acid diacetic acid, L-aspartic acid, taurine, sodium salts, potassium salts, ammonium salts thereof; aminotrimethylenephosphonic acid, 1-hydroxyethylidene-1,1-diphosphonic acid, Ethylenediaminetetramethylene phosphonic acid, sodium salts, potassium salts, ammonium salts and the like thereof can be blended. Complexing agents can be used alone or in combination of two or more. The compounding amount of the complexing agent is preferably about 0.5 to 100 g / L, and more preferably about 5 to 50 g / L.

  The pH of the electroless palladium plating solution is preferably about 2 to 9, and more preferably about 3 to 8. For pH adjustment, inorganic acids such as sulfuric acid and phosphoric acid, sodium hydroxide, aqueous ammonia and the like can be used.

  The treatment temperature of the electroless palladium plating solution is preferably about 30 ° C to 90 ° C, particularly about 40 ° C to 80 ° C.

  The thickness of the electroless palladium plating film is preferably about 0.001 μm or more, more preferably about 0.005 μm or more, and further preferably about 0.05 μm or more. When the thickness of the palladium plating film is too thin, gold plating is not uniformly deposited, which is not preferable.

  The upper limit of the film thickness of the palladium plating film is not particularly limited, but is preferably about 2 μm or less, for example, considering the cost. In addition, when solder bonding is performed on the gold plating film, the film thickness of the palladium plating film is preferably about 1 μm or less, and about 0.5 μm or less in order to obtain sufficient solder bonding strength. It is more preferable. If the palladium film is too thick, the palladium plating film has poor diffusibility into the solder, and therefore remains on the surface of the electroless nickel plating film during soldering, causing a decrease in solder joint strength. This is not preferable. By using the reduced deposition type electroless gold plating solution of the present invention described above, even if the palladium plating film is very thin of 1 μm or less, the underlying electroless nickel plating film is not eroded, so that solder It is possible to form a plating film with high bonding strength.

  After forming a palladium plating film by the above-described method, a gold plating film is formed using the reduction deposition type electroless gold plating solution of the present invention. Usually, after forming an electroless palladium plating film, a gold plating film can be formed by immersing an object to be plated in the reduction deposition type electroless gold plating solution.

  The treatment temperature of the electroless gold plating solution is preferably about 35 ° C to 95 ° C, more preferably about 45 ° C to 90 ° C.

  The film thickness of the electroless gold plating film may be appropriately selected depending on the purpose. However, if it is too thin, the performance as a gold plating film is not sufficiently exhibited, and the soldering property, wire bonding property and the like are inferior. Usually, the film thickness may be about 0.001 μm or more. The upper limit of the film thickness of the gold plating film is not particularly limited, but if it is too thick, the cost becomes high, and this may be determined in consideration of this point. For example, in order to obtain sufficient solder joint strength, the thickness may be up to about 0.3 μm. Moreover, in order to improve the heat resistance in wire bonding, a thick gold plating film having a thickness of up to about 1 μm may be formed, but it is also possible to thicken the gold plating film.

  The electroless gold plating solution of the present invention is a reduction deposition type electroless gold plating solution capable of directly depositing a gold plating film on a palladium film.

  By using the reduced deposition type electroless gold plating solution of the present invention, when forming a multilayer plating film having a structure in which a nickel plating film, a palladium plating film and a gold plating film are laminated on a conductor circuit portion of a printed wiring board, A gold plating film can be formed without eroding the underlying nickel plating film. As a result, it is possible to obtain a plating film excellent in solderability, wire bonding property, and the like.

  Furthermore, when the gold plating film is thickened, it is possible to thicken only by the reduction precipitation type gold plating, and a plating film having excellent heat resistance in wire bonding can be formed by a simple processing step.

  Hereinafter, the present invention will be described in more detail with reference to examples.

Example 1
Hereinafter, the composition of the plating solution used in the examples and comparative examples of the present invention is shown.
(I) Electroless nickel plating solution (1) Nickel bath A:
Nickel sulfate hexahydrate 22.5g / L
Sodium hypophosphite 20 g / L
Malic acid 10 g / L
Succinic acid 10 g / L
Sodium thiosulfate 0.2mg / L
pH 4.6 (adjusted with sodium hydroxide)

(II) Electroless palladium plating solution (1) Palladium bath A
Dichlorodiethylenediamine palladium solution 2g / L (as palladium)
Ethylenediamine 10g / L
Sodium formate 10g / L
pH 6.0
(2) Palladium bath B
Dichlorodiethylenediamine palladium solution 2g / L (as palladium)
Ethylenediamine 10g / L
Sodium phosphite 10g / L
pH 6.0
(3) Palladium bath C:
Dichlorodiethylenediamine palladium solution 2g / L (as palladium)
Ethylenediamine 10g / L
Sodium hypophosphite 10g / L
pH 6.0

(III) Reduced deposition type electroless gold plating solution The following gold plating bath A (non-cyan bath) is used as a basic bath, and 5 g / L of the reducing agent shown in Table 1 below is added thereto, and sulfuric acid or sodium hydroxide is added. The plating bath adjusted to pH 7.0 by using was used.

(1) Gold plating bath A
Ethylenediaminetetraacetic acid disodium 20g / L
Potassium gold sulfite 2g / L (as gold)
S-methylisothiourea 0.5mg / L

  A printed circuit board in which a copper circuit and a resist were formed on a resin substrate was used as an object to be plated. The printed circuit board is obtained by forming various shapes of conductor circuits on a 4 cm × 6 cm resin substrate using a copper foil having a thickness of 18 μm.

  First, after the degreasing treatment was performed on the object to be plated, etching of about 0.5 μm was performed with a sodium persulfate solution, and a catalyst application solution (trade name: ICP Axela, manufactured by Okuno Pharmaceutical Co., Ltd.) in 200 ml / L And a catalyst for electroless plating was applied by immersion for 1 minute at room temperature.

  Thereafter, using the above nickel bath A as an electroless nickel plating solution, the object to be plated is immersed in a plating solution having a bath temperature of 80 ° C. for 20 minutes while stirring in the air, and a nickel plating film having a thickness of about 5 μm. Formed.

  Subsequently, it was immersed in each palladium plating bath shown in Table 1 at 60 ° C. for 10 minutes to form a 0.2 μm electroless palladium plating film.

  Then, using the electroless gold plating solution containing the reducing agent shown in the following Table 1, it was immersed in a gold plating bath having a bath temperature of 80 ° C. for 30 minutes or 120 minutes to form a gold plating film.

  About each sample which formed the gold plating film by the above-mentioned method, the deposition state of the gold plating film was judged visually, and also the film thickness of the gold plating film was measured with a fluorescent X-ray film thickness measuring device. In addition, in the object to be plated, an area of 1 × 4 cm where the gold plating film was formed was cut into the surface of the gold plating film using a cutter knife to form 100 squares of 1 mm square. The tape was applied and peeled off in the vertical direction. At this time, the adhesion of the gold plating film was evaluated by measuring the number of cells peeled off.

  The above results are shown in Table 1 below.

As is clear from the above results, according to the electroless gold plating solutions of Examples 1 to 8 and Reference Examples 1 to 16 containing formaldehyde bisulfite, Rongalite or hydrazine as a reducing agent, uniform on the palladium film. A gold plating film can be formed. In particular, when the underlying palladium film is a film formed from a palladium bath A using sodium formate as a reducing agent, a film having good adhesion is formed even when a thick gold plating film is formed. it can.

Claims (1)

A printed wiring board in which an electroless nickel plating film, an electroless palladium plating film, and an electroless gold plating film are sequentially formed on a conductor portion of the printed wiring board,
The electroless palladium plating film is made of an aqueous solution containing a palladium compound, a reducing agent and a complexing agent, and the reducing agent is at least one selected from the group consisting of formic acid and salts thereof. Formed,
The electroless gold plating film is composed of an aqueous solution containing a water-soluble gold compound, a reducing agent and a complexing agent, and the reducing agent is at least one selected from the group consisting of formaldehyde bisulfite, Rongalite and hydrazines. It is formed using a certain reduced precipitation type electroless gold plating solution.
Printed wiring board.