TWI807443B - Electroless nickel plating bath - Google Patents

Abstract

The object of the present invention is to provide an electroless nickel plating bath for producing an electroless nickel plating film that can suppress nickel dropout and out-of-pattern precipitation, and has excellent corrosion resistance and appearance. The solution is that the electroless nickel plating bath of the present invention is characterized by containing a reducing agent and a nitro-containing aromatic compound containing more than one nitro group.

Description

Electroless nickel plating bath

The present invention relates to an electroless nickel plating bath for producing an electroless nickel plating film. In detail, it relates to an electroless nickel plating bath for producing an electroless nickel plating film formed on a circuit board such as a flexible substrate used in electronic components such as a printed wiring board.

When connecting circuit boards and electronic components such as flexible boards in the past, it was set on the copper pattern of the circuit board, and then electroless nickel plating for barrier metal was performed, followed by gold plating ENIG (Electroless Nickel Immersion Gold) for improving connection reliability, or ENIG (Electroless Nickel Immersion Gold) plating for improving connection reliability, or electroless nickel plating for barrier metal was performed on the pattern, electroless palladium film was formed on the nickel plating, and then gold plating was performed on top of it for the purpose of improving connection reliability. EPIG (Electroless Nickel Electroless Palladium Immersion Gold: ENEPIG) and other methods.

In recent years, electronic devices such as smartphones require further miniaturization of semiconductor components mounted on them. In order to facilitate the miniaturization of semiconductor components, it is necessary to miniaturize the circuit pattern and increase the density of the circuit pattern. However, when promoting the miniaturization of circuit patterns and the high integration of circuit patterns and implementing electroless nickel plating on the pattern, not only on the pattern, but also nickel will be deposited in the space between the pattern and the pattern (hereinafter referred to as precipitation outside the pattern), which may cause the current to flow and short circuit. In addition, reducing the reactivity of the electroless nickel plating bath can suppress the precipitation outside the pattern, but it may not be possible to laminate the electroless nickel plating film (hereinafter referred to as nickel omission) on the pattern.

Regarding an electroless nickel plating bath (electroless nickel plating solution) that can suppress nickel omission and out-of-pattern precipitation, the applicant proposed in Patent Document 1 an electroless nickel plating solution that added a compound having an S-S sulfur bond. Also, regarding an electroless nickel plating solution capable of suppressing nickel omission and out-of-pattern precipitation, as shown in Patent Document 2, an electroless nickel plating solution containing aluminum compounds such as copper, iron, and cobalt for metal components is added, and as shown in Patent Document 3, an electroless nickel plating solution is added with a soluble salt of a metal selected from silver, copper, zinc, etc.

However, when the electroless nickel plating solution of Patent Document 1 is used, the corrosion resistance of the circuit board is still insufficient. In addition, when using the electroless nickel plating solution of Patent Document 2 or Patent Document 3, metal components other than nickel such as copper added to the electroless nickel plating solution will be precipitated in the electroless nickel plating coating, which may change the film properties such as discoloration. prior art literature patent documents

[Patent Document 1] JP-A-8-269726 [Patent Document 2] JP-A-2005-82883 [Patent Document 3] Patent No. 5622678

The problem to be solved by the invention

The present invention provides an electroless nickel plating bath for manufacturing an electroless nickel plating quilt that can suppress nickel omission and out-of-pattern precipitation, and has excellent corrosion resistance and appearance. solution to the problem

The electroless nickel plating bath of the present invention is characterized by containing a reducing agent and a nitro-containing aromatic compound containing one or more nitro groups.

The above-mentioned nitro-containing aromatic compound is at least one selected from the group consisting of benzene which may have substituents other than nitro, naphthalene which may have substituents other than nitro, and alkali metal salts thereof. The substituent is preferably at least one selected from the group consisting of carboxyl, hydroxyl, halogen, sulfonic acid, ester, alkoxy, and amine.

Furthermore, the present invention also includes an electroless nickel plating method, which is characterized in that the object to be plated is immersed in an electroless nickel plating bath, and an electroless nickel plating film is formed on the surface of the object to be plated. The effect of the invention

By using the electroless nickel plating bath of the present invention, it is possible to obtain an electroless nickel plating film that can suppress nickel omission and out-of-pattern precipitation, and has excellent corrosion resistance and appearance.

The electroless nickel plating bath of the present invention is used to form an electroless nickel plating film (hereinafter simply referred to as film) on the surface of the object to be plated. For example, the object to be plated is immersed in the electroless nickel plating bath to form a film on the surface of the above-mentioned object to be plated.

The inventors of the present invention found that by including a reducing agent and a nitro-containing aromatic compound in an electroless nickel plating bath, a film that not only suppresses nickel drop-out and out-of-pattern precipitation (hereinafter referred to as good patternability) but also has excellent corrosion resistance and appearance can be obtained, and completed the present invention.

The details of the mechanism by which the above-mentioned action is exerted by using the above-mentioned nitro-containing aromatic compound are not known, but are presumed as follows. In the electroless nickel plating bath, electrons can be released from the reducing agent by the oxidation reaction of the reducing agent contained in the electroless nickel plating bath. When the electroless nickel plating bath does not contain nitro-aromatic compounds, the release of electrons from the reducing agent will reduce the nickel ions and excessively precipitate nickel, which may cause out-of-pattern precipitation in highly integrated circuit patterns. However, when the electroless nickel plating bath contains nitro-containing aromatic compounds, the electrons released by the reducing agent will be used in the reduction reaction of nitro groups prior to the reduction reaction of nickel ions, so nickel will not be excessively precipitated, and precipitation outside the pattern can be suppressed. In addition, the electroless nickel plating bath of the present invention is a general term for a mixture containing these, and the electroless nickel plating bath can also be positioned.

In the electroless nickel plating bath of the present invention, the types of compounds other than the nitro-containing aromatic compound and the reducing agent are not particularly limited, and the present invention can also use those commonly used in electroless nickel plating baths.

＜Nitro-containing aromatic compounds＞ The above-mentioned nitro-containing aromatic compound may contain one or more nitro groups. That is, the nitro group contained in an aromatic compound may be one or plural. The above-mentioned nitro-containing aromatic compound preferably contains 1 to 3 nitro groups, more preferably 1 to 2 nitro groups, more preferably 1 nitro group from the viewpoint of handleability.

In addition, the nitro-containing aromatic compound is at least one selected from the group consisting of benzene which may have substituents other than nitro, naphthalene which may have substituents other than nitro, and alkali metal salts thereof. The substituent is preferably at least one selected from the group consisting of carboxyl, hydroxyl, halogen, sulfonic acid, ester, alkoxy, and amine.

The aforementioned substituent is more preferably at least one selected from the group consisting of carboxyl group, hydroxyl group, halogen atom, sulfonic acid group, and amino group.

When the above-mentioned nitro-containing aromatic compound is an alkali metal salt, the above-mentioned nitro-containing aromatic compound is preferably at least one selected from the group consisting of sodium salt and potassium salt.

The aforementioned halogen group is preferably at least one selected from the group consisting of chloro, bromo, and iodo.

The content (concentration) of nitro-containing aromatic compounds in the electroless nickel plating bath is preferably more than 0.001mmol/L and less than 20mol/L, preferably more than 0.1mol/L and less than 10mol/L, more preferably more than 0.5mol/L and less than 5mol/L. When the lower limit of the above-mentioned content is lower than 0.001 mmol/L, it may not be possible to improve patternability. Moreover, when the upper limit of the said content exceeds 20 mol/L, nickel skipping may occur. When using multiple nitro-containing aromatic compounds, the content of nitro-containing aromatic compounds refers to the total content of all nitro-containing aromatic compounds.

＜Reducing agent＞ The type of reducing agent is not particularly limited, and various reducing agents generally used in known electroless nickel plating baths can be used. Such reducing agents include hypophosphite, boron compounds, and the like. Examples of the above-mentioned hypophosphite include sodium hypophosphite (base hypophosphite), potassium hypophosphite, and the like. Further, the boron compound mentioned above includes boron hydride compounds such as sodium borohydride and potassium borohydride; amine borane compounds such as dimethylamine borane (DMAB), trimethylamine borane, and triethylamine borane, and the like.

The preferred concentration of the above-mentioned reducing agent will vary depending on the type of reducing agent used. For example, when sodium hypophosphite is used as the reducing agent, it is preferably 0.1-0.5 mol/L. By controlling such concentration, it is possible to prevent unfavorable situations such as prolonging the molding time due to the slow reduction of nickel ions in the plating solution, and the decomposition of the plating bath. The concentration of sodium hypophosphite is more preferably 0.15-0.35 mol/L. Thereby, the above-mentioned problems can be more effectively prevented.

Also, when the reducing agent is DMAB which is a boron compound, the concentration of DMAB is preferably 0.01-0.2 mol/L. In this way, it can prevent the unsuitable situation of prolonging the molding time, and prevent the plating bath from disintegrating, etc. The concentration of DMAB is more preferably 0.05-0.09 mol/L. Thereby, the above-mentioned problems can be more effectively prevented.

The electroless nickel plating bath is not specifically limited to the elements other than nitroaromatic compounds and reducing agents, but it is better to properly adjust the desired characteristics. In addition, the electroless nickel plating bath may contain water-soluble nickel salts, complexing agents, stabilizers, and sulfur-containing compounds in addition to nitroaromatic compounds and reducing agents. It is preferable to contain water-soluble nickel salts and complexing agents. The water-bath nickel salt, complexing agent, stabilizer, and sulfur-containing compound will be specifically described below.

＜Water-soluble nickel salt＞ The water-soluble nickel salt can be dissolved in the plating solution to obtain an aqueous solution with a certain concentration, and is not particularly limited. Such water-soluble nickel salts include inorganic water-soluble nickel salts such as nickel sulfate, nickel chloride, and nickel hypophosphite; organic water-soluble nickel salts such as nickel acetate and nickel malate, and the like. These water-soluble nickel salts can be used alone or in combination of two or more.

The concentration of the water-soluble nickel salt is preferably 0.05-0.17 mol/L. By controlling it to the above range, it is possible to effectively prevent the unfavorable situation that the deposition rate of the film is very slow and the film formation time is prolonged, the unfavorable situation that the viscosity of the plating solution is increased and the fluidity of the liquid is reduced, which has a negative impact on the uniform precipitation of nickel plating, and the unfavorable situation that the formed coating is formed. Cavities, etc.

＜Complexing agent＞ The complexing agent can effectively prevent the precipitation of nickel compounds such as water-soluble nickel salts, and make the precipitation reaction of nickel have an appropriate speed. Various complexing agents commonly used in known electroless nickel plating baths can be used in the present invention. Specific examples of such complexing agents include monocarboxylic acids such as glycolic acid, lactic acid, gluconic acid, and propionic acid; dicarboxylic acids such as malic acid, succinic acid, tartaric acid, malonic acid, oxalic acid, and adipic acid; aminocarboxylic acids such as glycine, glutamic acid, aspartic acid, and alanine acid; , N’,N’-tetrahydroxyethylethylenediamine) and other ethylenediamine derivatives; 1-hydroxyethane-1,1-diphosphonic acid, ethylenediaminetetrakiscene phosphonic acid and other phosphonic acids; and their soluble salts, etc. These complexing agents can be used alone or in combination of two or more.

The concentration of the complexing agent will vary depending on the type of complexing agent used, and is not particularly limited, generally in the range of 0.001-2 mol/L. By controlling the concentration of the complexing agent within this range, it is possible to prevent the deposition of nickel hydroxide and the decomposition of the plating bath due to excessive redox reactions. In addition, it can prevent the problem of slowing down the deposition rate of the film, and the problem of reducing the uniformity of deposition due to the increase of the viscosity of the plating solution. A more preferable concentration of the complexing agent is 0.002-1 mol/L. This can more effectively prevent nickel hydroxide precipitation, plating bath decomposition, and the like.

＜Stabilizer＞ The electroless nickel plating bath of the present invention may further contain a known stabilizer if necessary. In the electroless nickel plating bath of the present invention, out-of-pattern precipitation can be suppressed even if no stabilizer is added, but nickel omission and out-of-pattern precipitation can also be suppressed when a stabilizer is added. The above-mentioned stabilizer can use the known stabilizers described in Patent Document 1 or Patent Document 2, such as inorganic compounds such as P6 compounds such as lead acetate, Bi compounds such as bismuth acetate, etc.; organic compound stabilizers such as butynediol. These stabilizers can be used alone or in combination of two or more.

＜Sulfur-containing compounds＞ The electroless nickel plating bath of the present invention may further contain known sulfur-containing compounds if necessary. The above-mentioned sulfur-containing compounds include thiodiglycolic acid, thioglycolic acid, thiosulfate base, sulfite base and the like. These sulfur-containing compounds may be used alone or in combination of two or more.

<Phosphorus concentration in coating> According to the concentration of phosphorus in the coating, it can be divided into four types: low phosphorus (concentration of phosphorus in the coating: 1.5-3.0%), medium phosphorus (concentration of phosphorus in the coating: 6.0-7.5%), medium-high phosphorus (concentration of phosphorus in the coating: 8.0-9.5%), and high phosphorus (concentration of phosphorus in the coating: 10.5-12.0%). Therefore, the plating bath for forming a high-phosphorus film will not contain sulfur, but the plating bath for forming a low-phosphorus, medium-phosphorus, and medium-high-phosphorus film will contain a large amount of sulfur. Regardless of the presence or absence of sulfur-containing compounds in the electroless nickel plating bath of the present invention, nickel omission and out-of-pattern precipitation can be suppressed. That is, regardless of the concentration of phosphorus in the film, nickel drop-out and out-of-pattern precipitation can be suppressed.

＜pH of electroless nickel plating bath＞ The pH of the electroless nickel plating bath of the present invention is preferably around 4.0 to 9.0, more preferably 4.0 to 6.5. When the pH is in the above-mentioned range, the reduction reaction can be efficiently caused by the reducing agent, and the decomposition of the reducing agent can be prevented, and the reduction of electroplating precipitation and the decomposition of the plating solution can be prevented. In addition, when the pH is within the above range, it is possible to prevent the stability of the plating bath from being lowered due to an excessively high reduction potential of the reducing agent. As a pH adjuster for adjusting the above pH, alkalis such as ammonia water and sodium hydroxide, acids such as sulfuric acid, hydrochloric acid, nitric acid, and phosphoric acid, and the like can be used.

＜Other＞ The electroless nickel plating bath of the present invention may further contain various known additives added to the electroless nickel plating bath if necessary. Additives such as reaction accelerators, gloss agents, surfactants, function-imparting agents, etc. The types of these are not particularly limited, and generally used ones can be used.

When the electroless nickel plating bath contains metal components other than nickel, the metal components other than nickel may be precipitated in the coating, and the metal components other than nickel will change the properties of the coating, so it is not suitable. The concentration of metal components other than nickel in the electroless nickel plating bath is preferably less than 1 mg/L, more preferably less than 0.1 mg/L.

The electroplating conditions and the electroplating apparatus when electroless plating is performed using the electroless nickel plating bath of the present invention are not particularly limited, and can be appropriately selected according to conventional methods. Specifically, the object to be plated may be brought into contact by immersing it in an electroless nickel plating solution or the like having the above-mentioned composition. The plating temperature at this time varies depending on the composition of the plating bath, but is preferably 50 to 95°C. At this temperature, it is possible to prevent non-deposition of the film and poor appearance due to the slowdown of the plating deposition reaction. In addition, the plating treatment time can be appropriately set in accordance with the film thickness of the film to be formed, etc., but it is generally about 15 to 60 minutes.

Also, the type of the object to be plated used in the present invention is not particularly limited, for example, metals such as iron, cobalt, nickel, palladium or their alloys generally have catalytic properties with respect to the reduction and precipitation of electroless nickel plating; non-catalytic metals such as copper, glass, ceramics, etc. When using the former metal with catalytic properties, the film can be formed directly after pretreatment according to the usual method. Also, when using the latter non-catalytic metal, electroless nickel plating can be performed after attaching a metal catalyst core such as a palladium core according to the usual method.

The film thickness of the film thus obtained is about 3 to 7 μm, preferably 4 to 5 μm. When such a film thickness is obtained, it is very useful from the viewpoint that cracks and the like do not occur even if the film thickness of the film is increased as described above in order to ensure corrosion resistance and the like.

Moreover, the object to be plated on which the electroless nickel plating film is formed is suitable for the production of printed circuit boards. Example

The following examples will be used to describe the present invention in more detail, but the present invention is not limited to the following examples, and can be implemented within the scope of the gist of the foregoing and the following, which are all included in the technical scope of the present invention.

(Method for forming electroless nickel plating film) First, a Uemura test pattern substrate manufactured by Uemura Kogyo Co., Ltd. was prepared by laminating a rolled copper foil with a thickness of 18 μm on a polyimide substrate and forming a pattern. The above-mentioned patterned substrates prepared were a substrate with a line and space pattern in which lines and spaces are alternately formed, and a line L of 20 μm and a space S of 20 μm (hereinafter referred to as substrate A), and a substrate with a line L of 40 μm and a space S of 20 μm (hereinafter referred to as substrate B). Also, the line system represents the pattern width (line width), and the space system represents the interval between adjacent patterns (gap width).

Using the above-mentioned substrate A or the above-mentioned substrate B as the object to be plated, the processes in Table 1 were performed sequentially with respect to the above-mentioned object to be plated. In detail, first, cleaning (degreasing) was performed with ACL-007 manufactured by Uemura Industrial Co., Ltd. Next, perform soft etching with 100g/L sodium persulfate solution (SPS). Then remove the etching residue (pickling) with 10% sulfuric acid (H ₂ SO ₄ ) solution, and then pre-dip with 3% sulfuric acid (H ₂ SO ₄ ) solution. Thereafter, Pd catalyst (activation treatment) was applied to MNK-4 produced by Kamimura Industrial Co., Ltd., and the above-mentioned to-be-plated object after the activation treatment was immersed in the electroless nickel plating bath described later to form an electroless nickel plating film with a thickness of 5 μm. Finally, electroless gold plating was performed using Goblite (registered trademark) TIG-10 manufactured by Uemura Industrial Co., Ltd. to form an electroless gold plating film with a thickness of 0.05 μm. The temperature and time of cleaning, soft etching, pickling, pre-dipping, activation, electroless nickel plating, and electroless gold plating are shown in Table 1.

(Electroless nickel plating bath) Prepare a mixed solution containing nickel sulfate as a water-soluble nickel salt, sodium hypophosphite as a reducing agent, and malonic acid, lactic acid, and caproic acid as a complexing agent, and add the additives listed in Table 2 or Table 3 to the mixed solution to be used as an electroless nickel plating bath. Specifically, the additives refer to the nitro-containing aromatic compounds listed in Table 2 in Examples 1-39, the monosubstituted benzene rings listed in Table 3 in Comparative Examples 1-8, the sulfur-containing compounds listed in Table 3 in Comparative Examples 9 and 10, and the metal components listed in Table 3 in Comparative Examples 11-13. In addition, among the nitro-containing aromatic compounds used in Examples 1-39, R ¹ , R ² , R ³ , R ⁴ and R ⁵ of the nitro-containing aromatic compound (following (I)) are hydrogen atoms unless otherwise specified in Table 2.

The concentration of each component in the electroless nickel plating bath is, nickel sulfate: 20g/L (0.129 mol/L), additive: 0.5 mol/L, sodium hypophosphite: 30g/L (0.283 mol/L), malonic acid: 10g/L (0.096 mol/L), lactic acid: 10g/L (0.111 mol/L), adipic acid: 10g/L (0.068 mol/L). The pH of each plating bath was 4.6.

The following physical properties and characteristic evaluations were performed using the electroless nickel plating bath.

(Phosphorus concentration in the film) Form a film with a film thickness of 5 μm or more on a 3cm×3cm copper-clad laminate. The phosphorus concentration in the film was measured using a fluorescent X-ray analyzer ZSX Primus IV manufactured by Rigaku Corporation.

(graphical) According to the above-mentioned film forming method, a film was formed on each of the above-mentioned substrate A and the above-mentioned substrate B, and then visually observed according to the following criteria. 1( a ) and ( b ) are photographs of the surface of the substrate A after the coating is formed. good: no nickel precipitation in the space (Fig. 1(a)) Poor: Nickel precipitates in the space (Figure 1(b))

(Corrosion resistance (nitric acid immersion test)) The BGA (Ball Grid Array) substrate was immersed in each of the above-mentioned electroless nickel plating baths, and a film with a film thickness of 5 μm was formed on the surface of the BGA substrate. After immersing the film in a solution of 60% nitric acid diluted twice with water at 25°C for 30 seconds, check visually for discoloration of the film. When the coating was discolored to black, it was evaluated as "discolored", and when no discoloration of the coating was observed, it was evaluated as "no discoloration" (excellent corrosion resistance).

(capsule analysis) SUS 304 was immersed in an electroless nickel plating bath to form a film with a thickness of 30 μm on the surface of SUS 304. After immersing the film in nitric acid at 50°C for 1 hour to completely dissolve it, the presence or absence of metals and species in the film was measured in the dissolved nitric acid containing the film using the Horiba Ultima 2 ICP emission analyzer.

These results are recorded in Table 2 and Table 3. In Examples 1 to 39 using the electroless nickel plating bath of the present invention, it is possible to obtain a high-phosphorus electroless nickel plating film that can suppress nickel omission and out-of-pattern precipitation, and has excellent corrosion resistance and appearance. In addition, Comparative Examples 1 to 8 in which the additive was an aromatic compound not containing a nitro group had poor patternability. Comparative Examples 9 and 10 in which the additive is a sulfur-containing compound have relatively poor corrosion resistance. In Comparative Examples 11 to 13 in which the additive is a metal, metals derived from additives other than nickel are contained in the electroless nickel plating film.

none.

Fig. 1 is a photograph of a state in which an electroless nickel plating film is formed on a pattern substrate.

Claims (2)

An electroless nickel plating bath is characterized in that it contains a reducing agent, a nitro-containing aromatic compound containing more than one nitro group, and a water-soluble nickel salt. The content (concentration) of the above-mentioned nitro-containing aromatic compound is more than 0.001mmol/L and less than 20mol/L. Benzene with substituents other than nitro, naphthalene which may have substituents other than nitro, and at least one selected from the group consisting of alkali metal salts of these, said substituent being at least one selected from the group consisting of halogen atoms, sulfonic acid groups, ester groups, alkoxy groups, and amine groups. An electroless nickel plating method, characterized in that the object to be plated is immersed in the electroless nickel plating bath as claimed in claim 1, and an electroless nickel plating film is formed on the surface of the above-mentioned object to be plated.