TWI887452B - Electroless Palladium Bath - Google Patents

Abstract

The present invention aims to provide an electroless palladium plating bath, which can suppress the reduction of the precipitation of palladium on the nickel-plated film and improve the stability of the plating bath. The plating bath contains at least a palladium compound, a reducing agent, a complexing agent and a stabilizer. The stabilizer is an organic compound formed by bonding a divalent sulfur compound and a compound having a heterocyclic structure, and the organic compound does not have a thiol group and a disulfide bond.

Description

Electroless Palladium Bath

The present invention relates to an electroless palladium plating bath.

In the electronics industry, the surface treatment method for printed circuit boards, IC package mounting parts, and terminal parts, for example, uses the electroless nickel (Ni)/electroless palladium (Pd)/substitution gold (Au) method (Electroless Nickel Electroless Palladium Immersion Gold: ENEPIG). By using the ENEPIG process, a coating film can be obtained by gradually forming an electroless nickel film, an electroless palladium film, and a substitution gold film.

The palladium film shows good electrical conductivity and excellent corrosion resistance. It also has the function of preventing the matrix nickel from diffusing to the gold surface due to thermal history. Therefore, the palladium film plays an important role in the above-mentioned ENEPIG process.

Therefore, the stability of the plating bath is generally required to be excellent. The known electroless palladium plating bath uses ethylenediaminetetraacetic acid or its salt as a stabilizer, but because the plating bath is prone to spontaneous decomposition, there is a problem of insufficient stability.

In view of this, a proposal has been made to add an organic compound to an electroless palladium plating bath, the organic compound containing divalent sulfur, and it is stated that the stability of the plating bath will be improved by using the organic compound containing divalent sulfur (for example, refer to Patent Document 1).

[Prior Art Literature] [Patent Literature]

[Patent Document 1] Japanese Patent No. 3972158.

Therefore, by adding an organic compound containing divalent sulfur to the above-mentioned conventional plating bath, the stability of the plating bath will be improved, but there is a problem that the precipitation of palladium on the nickel-plated film is reduced.

In recent years, the guaranteed operating temperature of the coated device has increased due to the nickel-plated film containing phosphorus (P) (nickel-plated film with a phosphorus concentration of 4% to 8% in the film), and the demand for nickel-plated films with low phosphorus content (nickel-plated films with a phosphorus concentration of less than 4% in the film) that can be formed in devices with high guaranteed operating temperatures is increasing. However, the above-mentioned known plating bath has the following problems: in particular, the precipitation of palladium on the nickel-plated film with a low phosphorus content is significantly reduced. Therefore, it is urgently desired to develop an electroless palladium plating bath that can form a nickel-plated film with a low phosphorus content.

Therefore, the present invention is completed to solve the above-mentioned problems, and its purpose is to provide an electroless palladium plating bath that can inhibit the reduction of the precipitation of palladium on the nickel-plated film and at the same time improve the stability of the plating bath.

In order to achieve the above-mentioned purpose, the electroless palladium plating bath of the present invention is a plating bath containing at least a palladium compound, a reducing agent, a complexing agent and a stabilizer. The stabilizer is an organic compound formed by bonding a divalent sulfur compound and a compound having a heterocyclic structure, and the organic compound does not have a thiol group and a disulfide bond.

According to the present invention, the reduction of the precipitation of palladium on the nickel-plated film can be suppressed, and the stability of the plating bath can be improved.

The electroless palladium plating bath of the present invention is described below.

[Electroless Palladium Bath]

The electroless palladium plating bath of the present invention is a plating bath containing a palladium compound, a reducing agent, a complexing agent, and a stabilizer.

(Palladium compounds)

Palladium compounds are palladium ion supply sources used to obtain palladium plating baths. The palladium compounds can be any water-soluble, for example: inorganic water-soluble palladium salts such as palladium chloride, palladium sulfate, and palladium acetate; organic water-soluble palladium salts such as tetraammine palladium hydrochloride, tetraammine palladium sulfate, tetraammine palladium acetate, tetraammine palladium nitrate, and ethylenediamine palladium chloride. It should be noted that the palladium compounds can be used alone or in combination of two or more.

The concentration of palladium ions in the electroless palladium plating bath is not particularly limited, but if the palladium ion concentration is too low, the deposition rate of the plating film may be significantly reduced. Therefore, the palladium ion concentration is preferably 0.1 g/L or more, more preferably 0.3 g/L or more, and more preferably 0.5 g/L or more. If the palladium ion concentration is too high, the physical properties of the film may be reduced due to abnormal deposition, etc. Therefore, the palladium ion concentration is preferably 10 g/L or less, more preferably 5 g/L or less, and more preferably 3 g/L or less.

It should be noted that the palladium ion concentration can be measured by atomic absorption spectrometry (AAS) using an atomic absorption spectrophotometer.

(Reducing agent)

The reducing agent has the function of precipitating palladium in the electroless palladium plating bath. Various known reducing agents can be used as the reducing agent, for example: formic acid or its salts, hydrazines, hypophosphorous acid or its salts, phosphorous acid or its salts, amine borane compounds, hydrogen borate compounds, formalin, ascorbic acid or its salts, etc.

Examples of the above-mentioned salts include: alkaline metal salts such as potassium and sodium; alkaline earth metal salts such as magnesium and calcium; ammonium salts; quaternary ammonium salts; amine salts containing primary to tertiary amines, etc.

In addition, examples of amine borane compounds include dimethylamine borane (DMAB) and trimethylamine borane (TMAB); examples of hydrogen boron compounds include alkali metal borohydrides such as sodium borohydride (SBH) and potassium borohydride (KBH).

It should be noted that from the perspective of taking into account both the stability of the plating bath and the precipitation of the coating film, it is better to use formic acid or its salt (such as sodium formate) among these reducing agents. These reducing agents can be used alone or in combination of two or more.

Considering the precipitation rate during the plating treatment and the stability of the plating bath, the content of the reducing agent in the electroless palladium plating bath can be appropriately adjusted (the amount of the reducing agent when used alone, and the total amount when two or more are mixed). The lower limit of the reducing agent content is preferably 1 g/L or more, more preferably 3 g/L or more, more preferably 5 g/L or more, and particularly preferably 10 g/L or more. The upper limit of the reducing agent content is preferably 100 g/L or less, more preferably 80 g/L or less, and more preferably 50 g/L or less.

(Complexing agent)

The complexing agent mainly has the function of stabilizing the solubility of palladium in the electroless palladium plating bath. As the complexing agent, various known complexing agents can be used, for example, at least one selected from ammonia and amine compounds, and preferably an amine compound. As amine compounds, methylamine, dimethylamine, trimethylamine, benzylamine, methylenediamine, ethylenediamine, ethylenediamine derivatives, butanediamine, diethylenetriamine, ethylenediaminetetraacetic acid (EDTA) or its alkali metal salt, EDTA derivative, glycine, etc. It should be noted that the complexing agents can be used alone or in combination of two or more.

Considering the stabilization of the above-mentioned palladium solubility, the content of the complexing agent in the electroless palladium plating bath can be appropriately adjusted (the amount of the complexing agent when used alone, and the total amount when two or more are used in combination). The lower limit of the content of the complexing agent is preferably 0.1g/L or more, more preferably 1g/L or more, and more preferably 3g/L or more. The upper limit of the content of the complexing agent is preferably 15g/L or less, and more preferably 10g/L or less.

(Stabilizer)

The stabilizer is added for the purpose of improving the stability of the plating bath, improving the appearance after plating, and adjusting the formation rate of the plating film. In the electroless palladium plating bath of the present invention, an organic compound formed by bonding a divalent sulfur compound (a compound containing divalent sulfur) and a compound having a heterocyclic structure as shown in the following formula (1) can be used.

[Chemical formula 1] R ₁ -R ₂ (1)

(In the formula, _R1 is a compound having a heterocyclic structure, _R2 is a divalent sulfur compound, and _R1 - _R2 represents an organic compound without a thiol group and a disulfide bond.)

Examples of the compound _R1 having a heterocyclic structure include compounds having a nitrogen-containing heterocyclic structure or a sulfur-containing heterocyclic structure such as imidazole, tetrahydroimidazole, imidazoline, oxadiazole, oxazine, thiadiazole, thiazole, tetrahydrothiazole, tetrazole, triazine, triazole, piperazine, piperidine, pyrazine, pyrazole, pyrazolidine, pyridine, oxazine, pyrrole, pyrrolidine, benzothiazole, benzimidazole, isoquinoline, thiophene, tetrahydrothiophene, pentamethylene sulfide, and derivatives of the foregoing compounds.

Examples of the divalent sulfur compound _R2 include thiadiazole, thiazole, tetrahydrothiazole, benzothiazole, thiophene, tetrahydrothiophene, methyl mercaptan, benzenethiol, pentamethylene sulfide, dimethyl sulfide, methyl mercaptan, The invention also includes the following: mercaptan), ethanethiol, allyl mercaptan, thiopropionic acid, thioacetic acid, methyl ethyl sulfide, 1-propanethiol, 2-propanethiol, 2-aminoethanethiol, 2-butylethanol, 4-butylpyridine, dimethyl sulfoxide, tetrahydrothiazole, methyl mercaptan acetate, ethyl sulfide, methyl propyl sulfide, 1-butanethiol, thioglycolic acid, 2-(methylthio)ethanol, 3-butyl-1-propanol, 2-methylthiazoline, cyclopentanethiol, 2-methyltetrahydrothiophene, pentamethylene sulfide, thiomorpholine, S-methylthiopropionic acid, 3-butylpropionic acid and derivatives of the foregoing compounds.

Examples of the stabilizer represented by the above formula (1) include 2-(4-thiazolyl)benzimidazole, 2-(methylthio)benzimidazole, 2-(methylthio)benzothiazole, (2-benzothiazolylthio)acetic acid, 3-(2-benzothiazolylthio)propionic acid, 2-(methylthio)pyridine, (4-pyridylthio)acetic acid, 4,4'-dipyridyl sulfide, 2-methylthio-4-hydroxypyrimidine, S-methylthiobarbituric acid, 4-amino-6-chloro-2-(methylthio)pyrimidine, 5-(methylthio)-1H-tetrazole, 5-(ethylthio)-1H-tetrazole, N-(phenylthio)phthalimide, and 5-(methylthio)thiophene-2-carboxaldehyde. It should be noted that these stabilizers can be used alone or in combination of two or more. The chemical formulas of these stabilizers are shown below.

It should be noted that the organic compound (R ₁ -R ₂ ) used as a stabilizer in the electroless palladium plating bath of the present invention includes an organic compound in which the divalent sulfur compound R ₂ bonded to the compound R ₁ having a heterocyclic structure is derived from a compound containing a thiol group (-SH).

More specifically, for example, the above-mentioned 2-(methylthio)benzimidazole is an organic compound (R ₁ -R ₂ ) in which R ₁ , i.e., benzimidazole, and R ₂ , i.e., methylthiol, are bonded. As shown in the above chemical formula, R _{1 -R 2} does not have a thiol group (-SH), but R ₂ (methylthiol) before bonding to R ₁ has a thiol group (-SH), so R ₂ bonded to R 1 is derived from a compound (methylthiol) containing a thiol group (-SH). The same is true for 2-(methylthio)benzothiazole (R ₁ : benzothiazole, R ₂ : methylthiol) and 2-(methylthio)pyridine (R ₁ : pyridine, R ₂ : methylthiol).

For example, (2-benzothiazolylthio)acetic acid does not have a thiol group (-SH) in the R ₁ -R ₂ state (R ₁ : benzothiazole, R ₂ : thioacetic acid) as shown in the above chemical formula, but R ₂ (thioacetic acid) before bonding to R ₁ has a thiol group (-SH), so R ₂ bonded to R ₁ is derived from a compound (thioacetic acid) containing a thiol group (-SH). It should be noted that the same is true for (4-pyridylthio)acetic acid (R ₁ : pyridine, R ₂ : thioacetic acid).

For example, 3-(2-benzothiazolylthio)propionic acid does not have a thiol group (-SH) in the R ₁ -R ₂ state (R ₁ : benzothiazole, R ₂ : thiopropionic acid) as shown in the above chemical formula, but R ₂ (thiopropionic acid) before bonding to R ₁ has a thiol group (-SH), so R ₂ bonded to R ₁ is derived from a compound (thiopropionic acid) containing a thiol group (-SH).

For example, 4,4'-dipyridyl sulfide does not have a thiol group (-SH) in the R ₁ -R ₂ state (R ₁ : pyridine, R ₂ : 4-hydroxypyridine) as shown in the above chemical formula, but R ₂ (4-hydroxypyridine) before bonding with R ₁ has a thiol group (-SH), so R ₂ before bonding with R ₁ is derived from a compound (4-hydroxypyridine) containing a thiol group (-SH).

Therefore, as mentioned above, by adding an organic compound containing divalent sulfur, the stability of the plating bath is improved, but there is a problem that the precipitation of palladium on the nickel-plated film is reduced. In particular, there is a problem that the precipitation of palladium on the nickel-plated film with a low phosphorus content is significantly reduced.

In view of this, the inventors of the present application examined the above problems and found that the use of a stabilizer composed of an organic compound can suppress the reduction of the precipitation of palladium on the nickel-plated film and improve the stability of the plating bath; the organic compound is an organic compound formed by bonding a divalent sulfur compound and a compound having a heterocyclic structure (i.e., the above R ₁ -R ₂ ).

The inventors of this application have also found that if a compound having a thiol group or a disulfide bond is used in an organic compound formed by bonding a divalent sulfur compound and a compound having a heterocyclic structure, the thiol group or the disulfide bond will be deteriorated due to the oxidation-reduction reaction in the plating bath (i.e., the disulfide bond is generated by the oxidation reaction of the thiol group, and the thiol group is generated by the reduction reaction of the disulfide bond). Therefore, not only the precipitation of palladium will change, but also the stability of the plating bath will be reduced.

That is, an organic compound formed by bonding a divalent sulfur compound and a compound having a heterocyclic structure is used as a stabilizer. This organic compound does not have a thiol group and a disulfide bond, thereby being able to take into account both the precipitation of palladium and the stability of the plating bath.

It is also possible to precipitate palladium in a tiny portion of a nickel-plated film with a low phosphorus content.

Considering the precipitation of palladium during plating and the stability of the plating bath, the content of the stabilizer in the electroless palladium plating bath can be appropriately adjusted (the amount of the stabilizer when used alone, and the total amount when two or more are mixed). The lower limit of the stabilizer content is preferably 0.01 mg/L or more, more preferably 0.03 mg/L or more, and more preferably 0.05 mg/L or more. The upper limit of the stabilizer content is preferably 10 mg/L or less, more preferably 5 mg/L or less, and more preferably 1 mg/L or less.

(Other ingredients)

In addition to the above-mentioned components, various additives commonly used in the field of electrolytic palladium plating can be added to the electroless palladium plating bath of the present invention. Examples of such additives include pH adjusters, buffers, and surfactants.

pH adjusters are additives that have the function of adjusting the pH value of the plating bath, such as acids such as hydrochloric acid, sulfuric acid, nitric acid, citric acid, malonic acid, apple acid, tartaric acid, phosphoric acid, and bases such as sodium hydroxide, potassium hydroxide, and ammonia water. It should be noted that these pH adjusters can be used alone or in combination of two or more.

The following situations exist: if the pH value is too low, the precipitation rate of palladium is likely to decrease; if the pH value is too high, the stability of the electroless palladium plating bath decreases. Therefore, the pH value of the electroless palladium plating bath of the present invention is preferably 4 to 10, and more preferably 5 to 8.

A buffering agent having a buffering effect may also be added. Examples of such buffering agents include citric acid such as trisodium citrate dihydrate, tartaric acid, apple acid, phthalic acid and other carboxylic acids, phosphoric acid such as orthophosphoric acid, phosphorous acid, hypophosphorous acid, pyrophosphoric acid and other phosphoric acids, or their potassium salts, sodium salts (such as trisodium phosphate dodecahydrate, etc.), ammonium salts and other phosphates, boric acid, tetraboric acid and the like. It should be noted that such buffering agents may be used alone or in combination of two or more.

In order to improve stability, prevent pits, and improve the appearance of coating, a surfactant is added as needed. There is no particular limitation on the surfactant, and non-ionic, cationic, anionic, and amphoteric surfactants can be used.

(Purpose)

The electroless palladium plating bath of the present invention can be used, for example, to form a multilayer coating having a palladium-plated film and a gold-plated film. The substrate for forming the palladium-plated film is not particularly limited, and examples thereof include various well-known substrates such as aluminum (Al) or aluminum-based alloys, copper (Cu) or copper-based alloys, iron (Fe), cobalt (Co), nickel (Ni), copper, zinc (Zn), silver (Ag), gold, platinum (Pt), or alloys thereof, etc., which are catalytic for the reduction and precipitation of the palladium-plated film and are coated with a substrate to form a coating. Even non-catalytic metals can be used as coated objects by various methods.

In addition, the electroless palladium plating bath of the present invention can be applied to the ENEPIG process. In the ENEPIG process, for example, a multilayer coating film (electroless nickel/palladium/gold coating film) having a nickel coating, the above-mentioned palladium coating, and a gold coating thereon can be obtained on aluminum or aluminum-based alloy, copper or copper-based alloy forming an electrode. It should be noted that the formation of each coating film can adopt a commonly used method.

Next, a method for manufacturing a multilayer coating having a palladium coating formed by the electroless palladium coating bath of the present invention using the above-mentioned ENEPIG process is described. It should be noted that the formation conditions of the palladium coating are not limited thereto and can be appropriately changed according to known techniques.

There are no special restrictions on the plating conditions and plating equipment when using an electroless nickel plating bath for electroless nickel plating, and various known methods can be appropriately selected. For example, the object to be plated can be in contact with an electroless nickel plating bath at a temperature of 50°C to 95°C for about 15 minutes to 60 minutes. The thickness of the nickel-plated film can be appropriately set according to the required characteristics, usually about 3μm to 7μm. In addition, the electroless nickel plating bath can use various known compositions such as nickel-phosphorus alloys and nickel-boron (B) alloys.

When using the electroless palladium plating bath of the present invention for electroless palladium plating, the plating conditions and plating equipment are not particularly limited, and various known methods can be appropriately selected. For example, the coated object with a nickel film formed thereon is brought into contact with an electroless palladium plating bath at a temperature of 50°C to 95°C for about 15 minutes to 60 minutes. The thickness of the palladium film can be appropriately set according to the required characteristics, and is usually about 0.001μm to 1.0μm.

There are no special restrictions on the plating conditions and plating equipment when using an electroless gold plating bath for electroless gold plating, and various known methods can be appropriately selected. For example, the object to be plated with a palladium-plated film can be brought into contact with an electroless gold plating bath at a temperature of 40°C to 90°C for about 3 minutes to 20 minutes. The thickness of the gold-plated film can be appropriately set according to the required characteristics, and is usually about 0.001μm to 2μm.

The electroless palladium plating bath of the present invention is also useful for components of electronic devices having a coating. Examples of such components of electronic devices include chip components, quartz oscillators, bump electrodes, connectors, lead frames, ring materials, semiconductor packages, printed circuit boards, and other components that constitute electronic devices.

[Palladium-plated film]

The palladium-plated film of the present invention can be obtained by using the electroless palladium plating bath of the present invention, and the palladium-plated film includes both a pure palladium film and a palladium-plated alloy film containing an alloy component. This is because the palladium-plated film may contain elements other than palladium depending on the type of reducing agent used. It should be noted that there are also cases where components from the above-mentioned various additives are contained. The residue of the palladium-plated film is palladium and inevitable impurities.

For example, when formic acid or its salts, hydrazine or its salts are used as reducing agents, a pure palladium film can be obtained. In contrast, when a phosphoric acid compound such as hypophosphite or phosphite is used as a reducing agent other than formic acid or its salts, a palladium-plated film containing phosphorus can be obtained. When a boron compound such as an amine borane compound or a hydrogen boron compound is used, a palladium-plated film containing boron can be obtained. When both the above-mentioned phosphoric acid compound and the boron compound are used, a palladium-plated film containing both phosphorus and boron can be obtained.

(Implementation example)

The invention of this application will be described in more detail below based on embodiments and comparative examples, but the invention is not limited to the following embodiments.

(Example 1 to Example 18, Comparative Example 1 to Comparative Example 8, Reference Example 1)

(Preparation of plating bath)

The palladium compound (palladium salt), ethylenediamine as a complexing agent, trisodium citrate dihydrate as a buffer, sodium formate as a reducing agent, and a stabilizer were mixed and stirred to achieve the concentrations shown in Tables 2 to 4, thereby preparing the plating baths of Examples 1 to 18, Comparative Examples 1 to 8, and Reference Example 1 (an example without a stabilizer). It should be noted that the temperature of the plating bath (the temperature of the plating treatment) was set to 60°C and the pH value was set to 6.0.

The chemical formulas of the stabilizers used in Comparative Examples 1 to 8 are shown below.

(Pre-treatment)

Before forming the electroless plating film, the substrate was subjected to pretreatment steps 1 to 5 shown in Table 1.

Step 1: Use MCL-16 (manufactured by Uemura Industries, trade name: EPITHAS (registered trademark) MCL-16) to perform degreasing and cleaning treatment on the substrate (Si, TEG wafer).

Step 2: Then, a 30% by mass nitric acid solution was used for pickling to form an oxide film on the surface of the substrate.

Step 3: Then, the substrate was zinced using MCT-51 (manufactured by Uemura Industries, trade name: EPITHAS (registered trademark) MCT-51).

Step 4: Then, the Zn replacement film is removed by pickling with a 30 mass% nitric acid solution, and an oxide film is formed on the substrate surface.

Step 5: Then, the substrate was subjected to secondary galvanizing using MCT-51 (manufactured by Uemura Industries, trade name: EPITHAS (registered trademark) MCT-51).

(Coating treatment)

Next, the substrate subjected to the above pretreatment was subjected to the plating treatment step 6 shown in Table 1, thereby forming an electroless nickel film on the substrate. More specifically, an electroless plating treatment was performed using a nickel plating bath (manufactured by Uemura Industries, trade name: NIMUDEN (registered trademark) NPR-18) to form an electroless nickel film containing phosphorus (a nickel film having a phosphorus concentration of 4% to 8%) on the substrate. In addition, electroless plating was performed using a nickel plating bath (manufactured by Uemura Industries, trade name: NIMUDEN (registered trademark) NLL-1) to form a nickel plating film with a low phosphorus content (a nickel plating film with a phosphorus concentration of less than 4%) on the substrate.

Next, the substrate on which the nickel film has been formed was subjected to the plating treatment step 7 shown in Table 1 (electroless plating treatment using the palladium plating bath of Examples 1 to 18, Comparative Examples 1 to 8, and Reference Example 1), and a palladium film was formed on the surface of the nickel film (100μm×100μm pad and 2mm×3mm pad) on the substrate.

(Measurement of film thickness of palladium plating film)

Next, the thickness of the palladium coating formed on each pad was measured using a fluorescent X-ray measuring instrument (manufactured by Fischer Instrumentation, trade name: XDV-μ). The above results are shown in Tables 2 to 4.

(Evaluation of bath stability)

The presence of palladium particles in the palladium plating bath after electroless palladium plating was visually observed and evaluated based on the following criteria. The above results are shown in Tables 2 to 4.

○: Even after one week after the plating treatment, no precipitation of palladium particles was confirmed.

×: Within one week after the coating treatment, the precipitation of palladium particles was confirmed.

It can be seen from Tables 2 to 3 that in Examples 1 to 18, an organic compound formed by bonding a divalent sulfur compound and a compound having a heterocyclic structure is used as a stabilizer, and the organic compound does not have a thiol group and a disulfide bond, and the film thickness of the palladium-plated film on the nickel-plated film (100μm×100μm pad and 2mm×3mm pad) is maintained similar to the film thickness of the palladium-plated film in Reference Example 1 without a stabilizer, and even when a stabilizer is used, the reduction in the precipitation of palladium can be suppressed. In particular, it can be seen that even on a nickel-plated film with a low phosphorus content (a nickel-plated film with a phosphorus concentration of less than 4%), palladium is sufficiently precipitated to the same extent as on an electroless nickel-plated film containing phosphorus (a nickel-plated film with a phosphorus concentration of 4% to 8%).

Even after one week after the plating treatment, no palladium particles were found to be precipitated in the plating bath, indicating that the stability of the plating bath is excellent.

On the other hand, it can be seen from Table 4 that: in Comparative Examples 1 to 3, a divalent sulfur compound not bonded to a compound having a heterocyclic structure was used as a stabilizer; in Comparative Examples 4, 6, and 8, an organic compound formed by bonding a divalent sulfur compound to a compound having a heterocyclic structure was used as a stabilizer, and the organic compound had a thiol group; in Comparative Examples 5 and 7, an organic compound formed by bonding a divalent sulfur compound to a compound having a heterocyclic structure was used as a stabilizer, and the organic compound had a disulfide bond, and no palladium was precipitated on the nickel-plated film (100μm×100μm pad) with a low phosphorus content. Within one week after the electroplating treatment, palladium particles were confirmed to be precipitated in the plating bath, indicating that the stability of the plating bath was lacking.

[Industry Availability]

The present invention is particularly suitable for use in electroless palladium plating baths used in multilayer plating with palladium plating films and gold plating films, ENEPIG processes, etc.

Claims (2)

An electroless palladium plating bath is a plating bath containing at least a palladium compound, a reducing agent, a complexing agent and a stabilizer, wherein the stabilizer is an organic compound formed by bonding a divalent sulfur compound and a compound having a heterocyclic structure, and the organic compound does not have a thiol group and a disulfide bond; the compound having the heterocyclic structure is at least one selected from the group consisting of imidazole, tetrahydroimidazole, imidazoline, oxadiazole, oxazine, thiadiazole, thiazole, tetrahydrothiazole, tetrazole, triazine, triazole, piperazine, piperidine, pyrazine, pyrazole, pyrazolidine, pyridine, pyrazine, pyrrole, pyrrolidine, benzimidazole, isoquinoline, thiophene, tetrahydrothiophene, pentamethylene sulfide and derivatives thereof; the divalent sulfur compound is at least one selected from the group consisting of thiophene, At least one selected from the group consisting of triazole, thiazole, tetrahydrothiazole, benzothiazole, thiophene, tetrahydrothiophene, methyl mercaptan, benzenethiol, pentamethylene sulfide, dimethyl sulfide, ethanethiol, allyl mercaptan, thiopropionic acid, thioacetic acid, methyl ethyl sulfide, 1-propanethiol, 2-propanethiol, 2-aminoethanethiol, 2-butylethanol, dimethyl sulfoxide, tetrahydrothiazole, methyl mercaptan acetate, ethyl sulfide, methyl propyl sulfide, 1-butyl mercaptan, thioglycolic acid, 2-(methylthio)ethanol, 3-butyl-1-propanol, 2-methylthiazoline, cyclopentanethiol, 2-methyltetrahydrothiophene, pentamethylene sulfide, thiomorpholine, S-methylthiopropionic acid, 3-butylpropionic acid and derivatives thereof. The electroless palladium plating bath as recited in claim 1, wherein the concentration of the aforementioned stabilizer in the electroless palladium plating bath is 0.01 mg/L to 10 mg/L.