TWI690618B - Electroless nickel plating bath - Google Patents

Abstract

An object of the present invention is to provide an electroless nickel plating bath that can obtain good bendability, is less prone to cracking even in a portion to which stress is applied, and has no concerns about plating.

The solution of the present invention is that the electroless nickel plating bath of the present invention contains a sulfur-containing benzothiazole-based compound represented by the following formula (1).

式中，X係碳數為2以上之烷基，或其鹽，X係可具有取代基。

In the formula, X is an alkyl group having 2 or more carbon atoms, or a salt thereof, and X may have a substituent.

Description

Electroless nickel plating bath

The present invention relates to an electroless nickel plating bath for obtaining electroless nickel plating films. Specifically, it relates to an electroless nickel plating bath for obtaining an electroless nickel plating film formed on a circuit board such as a flexible substrate used in electronic components such as printed wiring boards. Although the following description will focus on the flexible substrate, the present invention is not limited to this.

Flexible substrates are circuit boards that have flexibility and are thin, light, flexible, and durable. They are widely used in electronic equipment, etc. where miniaturization, high density, and bending resistance are necessary. In general, when connecting a circuit board such as a flexible substrate to an electronic component, electroless nickel plating is applied as a barrier metal on a pattern such as a copper pattern, and the reliability of the connection is improved as The purpose is to perform the ENIG (Electroless Nickel Immersion Gold) process for gold plating.

The electroless nickel plating film has the advantages of obtaining excellent film characteristics or good uniform precipitation of nickel. On the contrary, it also has the property that the film is very hard. Therefore, in the case of ENIG plating on a flexible substrate having flexibility, there is a nickel plating due to the bending of the substrate The coating film cracked and eventually caused problems such as circuit disconnection.

In order to solve such a problem, for example, Patent Document 1 discloses an electroless nickel plating bath that contains a predetermined alkylene diamine compound such as ethylene diamine, propylene diamine, and the like. It is described that if the above plating bath is used, the bending resistance of the nickel plating film is improved compared to copper forming the pattern portion of the substrate, and it is possible to form a highly reliable nickel plating film that is less prone to cracking.

[Prior Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Application Publication No. 2013-28866

According to the method of the above-mentioned Patent Document 1, the bending resistance can be obtained even when the thickness of the nickel plating film is about 3 μm, which is very useful. However, according to the results of the investigation by the present inventors, it was found that the nickel film was cracked at the portion where the stress was applied.

The present invention was completed in view of the above circumstances, and its object is to provide a novel electroless nickel plating bath, which can obtain good bending not only when the thickness of the nickel plating film is about 3 to 7 μm thick It is not easy to crack nickel plating film even in the part where stress is applied, and there is no doubt that there is no plating (non-plating).

The electroless nickel plating bath of the present invention that can solve the above-mentioned problems has the following gist: it contains a sulfur-containing benzothiazole-based compound represented by the following formula (1).

式中，X係碳數為2以上之烷基，或其鹽，X係可具有取代基。

In the formula, X is an alkyl group having 2 or more carbon atoms, or a salt thereof, and X may have a substituent.

According to the present invention, a novel electroless nickel plating bath can be provided, which can obtain good bendability not only in the case where the thickness of the nickel plating film is as thick as 3 to 7 μm, and even the portion where stress is applied is not easy Nickel plating film with cracks, and there is no doubt about no plating.

[Fig. 1] Fig. 1 is a photograph for investigating the presence or absence of micro-cracks by FE-SEM in Comparative Example 3 and Inventive Example 6.

The inventors have made repeated efforts to solve the above problems Force research. As a result, it was found that if a sulfur-containing benzothiazole-based compound represented by the above formula (1) is added to an electroless nickel plating bath, the desired object can be achieved, and the present invention is completed.

First, the sulfur-containing benzothiazole-based compound of the above formula (1) which is the most characteristic of the present invention will be described.

The above-mentioned compound has a basic S-X group in which a predetermined S-X group containing sulfur is bonded to a benzothiazole ring formed by condensing benzene and thiazole. The reason for achieving the above basic skeleton is as follows.

First of all, according to the results of the investigation by the present inventors, it was found that the following comparative example having a ring other than the benzothiazole ring cannot obtain good bendability, and the folding endurance test (in order to The number of MITs was evaluated).

Comparative Examples 5 and 8 with benzimidazole skeleton Benzo

Comparative example 6 of azole skeleton Comparative Example 7 with thiazole skeleton Comparative Example 9 with triazole skeleton

In addition, it is also known that among the above Comparative Examples 5 to 9, Comparative Examples 6 to 9 are the decrease in the precipitation rate of the plating reactivity test (evaluated by the precipitation rate of nickel) performed in the field of the example described later, and Is there any risk of plating.

In addition, although both Comparative Example 5 and Comparative Example 8 have a benzimidazole ring, the reason why the precipitation rate of Comparative Example 8 is about 1/2 lower than that of Comparative Example 5 is presumed that Comparative Example 8 is in the above formula (1) Contains the thiol group of X=H.

Furthermore, according to the results of the investigation by the present inventors, it is found that even those having a benzothiazole ring, in the above (1), those with X=H and X=CH ₃ cannot obtain the desired characteristics.

First, in the case of X=H (that is, in the case of having SH=mercapto group), as confirmed by Comparative Example 4 described later, it is understood that although it has good flexibility, no cracks are observed even in the portion where the stress is applied However, since the precipitation rate of nickel plating is slow, there is a possibility that there is no plating.

Similarly, in the case of X=CH ₃ (alkyl group with a carbon number of 1), as confirmed by Comparative Example 10 described later, it is known that the precipitation rate of nickel plating is slow, so that there is a possibility that some plating does not occur.

Therefore, in the present invention, those with X=H and X=CH ₃ in the above (1) are excluded from the scope of the present invention for the above reasons.

The alkyl group used for the above X may have a straight chain or a branched chain as long as the desired characteristics are obtained, and the number of carbon numbers is not particularly limited as long as it is 2 or more, but considering the practically usable range, The upper limit of the carbon number is preferably about 6, and the upper limit of the carbon number is more preferably about 4.

In addition, the aforementioned X series may have a substituent. The type of the substituent is not particularly limited as long as the desired characteristics can be obtained, but examples thereof include a sulfonic acid group (SO ₃ H), a carboxyl group (COOH), and a hydroxyl group (OH group).

The compound of the above (1) may exist as a salt, and examples thereof include alkali metal salts such as Na salt and K salt; and alkaline earth metal salts such as Ca salt and Mg salt.

In addition, for example, Japanese Unexamined Patent Publication No. 2006-316350 describes that a heterocyclic compound containing a sulfur atom in the molecule has an abnormal precipitation prevention effect of electroless nickel plating, but it has not been disclosed to have the same effect as the present invention. . However, the aforementioned gazette discloses that mercaptobenzothiazole that is not the subject of the present invention can also be used, and it is different from the present invention in terms of technical aspects that do not focus on the usefulness of the compound (1) specified in the present invention.

In addition to the above publications, Japanese Unexamined Patent Publication No. 2000-256886 discloses the use of 2-mercaptobenzothiazole as an organic inhibitor for electroless nickel plating baths, but does not disclose the above-mentioned compound (1) specified by the present invention Has the same effect as the present invention.

The characteristic part of the present invention is characterized in that the electroless nickel plating bath contains the sulfur-containing benzothiazole-based compound represented by (1) above, and other requirements are not particularly limited. It is recommended to make appropriate adjustments to achieve the desired characteristics Play effectively.

For example, the content (concentration) of the sulfur-containing benzothiazole-based compound of (1) in the electroless nickel plating bath is approximately 0.1 mg/L or more, 10 g/L or less, and more preferably 1 mg/L or more , Below 1g/L. If the lower limit of the above content is less than 0.1 mg/L, good film flexibility cannot be obtained. On the other hand, if the upper limit of the above content exceeds 10 g/L, although good film flexibility can be obtained, there is a possibility that no plating occurs.

The type of the compound other than the above (1) in the electroless nickel plating bath of the present invention is not particularly limited, and the present invention can also be used by ordinary users in the electroless nickel plating bath. In addition, the electroless nickel plating bath of the present invention refers to a general term including such mixtures, and may also be defined as electroless nickel plating liquid.

Hereinafter, the details will be described.

(1) Water-soluble nickel salt

The water-soluble nickel salt system is not particularly limited as long as it is soluble in the plating solution and can obtain an aqueous solution of a predetermined concentration. Examples of such water-soluble nickel salts include inorganic water-soluble nickel salts such as nickel sulfate, nickel chloride, and nickel hypophosphite; and organic water-soluble nickel salts such as nickel acetate and nickel malate. These water-soluble nickel salts can be used alone or in combination of two or more.

The concentration of the above-mentioned water-soluble nickel salt is preferably 5-50 g/L, for example. By controlling within the above range, the following defects can be effectively prevented: the precipitation speed of the nickel plating film is very slow, and the defects that require a long time when the film is formed, the viscosity of the plating solution is increased, and the fluidity of the solution is reduced. Defects that are adversely affected by the uniform precipitation of nickel plating, defects such as dents in the formed nickel plating film, etc. The better concentration of water-soluble nickel salt is about 15~40g/L. This can effectively prevent defects such as a slow precipitation speed of the nickel plating film and dents on the nickel plating film.

(2) Reducing agent

The type of the above-mentioned reducing agent is not particularly limited, and can be used for various reducing agents commonly used in well-known electroless nickel plating solutions. Examples of such a reducing agent include hypophosphite and boron compounds. Examples of the hypophosphite system include sodium hypophosphite. ), potassium hypophosphite, etc. Examples of the boron compound system include borohydride compounds such as sodium borohydride and potassium borohydride; amine borane compounds such as dimethylamine borane (DMAB), trimethylamine borane, and triethylamine borane. .

Although the preferred concentration of the above reducing agent varies depending on the type of reducing agent used, for example, when sodium hypophosphite is used as the reducing agent, it is preferably about 20 to 50 g/L. By controlling to such a concentration, the reduction of nickel ions in the plating solution can be prevented from slowing down, and defects in the film formation for a long time, or decomposition of the plating bath, etc. can be prevented. More preferably, the concentration of sodium hypophosphite is 20~35g/L. With this, the above problems can be prevented more effectively.

In addition, when DMAB of a boron compound is used as the reducing agent, the preferred concentration of DMAB is 1 to 10 g/L. By this, it is possible to prevent the defects having a long time in the film formation, the decomposition of the plating bath, and the like. The better concentration of DMAB is 3~5g/L. With this, the above problems can be prevented more effectively.

(3) Complexing agent

The above-mentioned complexing agent is effective for preventing the precipitation of nickel compounds, and the precipitation reaction of nickel is set to an appropriate rate. In the present invention, various complexing agents commonly used in well-known electroless nickel plating solutions can be used. Specific examples of such complexing agents include monocarboxylic acids such as glycolic acid, lactic acid, gluconic acid, and propionic acid; malic acid, succinic acid, tartaric acid, malonic acid, oxalic acid, adipic acid, and the like. Carboxylic acids; amino carboxylic acids such as glycine, glutamic acid, aspartic acid, alanine, etc.; ethylenediaminetetraacetic acid, VERSENOL (N-hydroxyethylethylenediamine-N,N',N'- Triacetic acid), QUADROL (N,N,N',N'-tetrahydroxyethylethylenediamine) and other ethylenediamine derivatives; 1-hydroxyethane-1,1-diphosphonic acid, ethylenediaminetetramethylenephosphonic acid Such as phosphonic acid; and these soluble salts. These complexing agents can be used alone or in combination of two or more.

Although the concentration of the above-mentioned complexing agent varies depending on the type of complexing agent used and is not particularly limited, it is preferably in the range of 0.001 to 2 mol/L. By suppressing the concentration of the complexing agent in such a range, the decomposition of the plating bath due to the precipitation of nickel hydroxide and excessive oxidation-reduction reaction can be prevented. In addition, problems such as a slower precipitation rate of the nickel plating film and a decrease in uniform precipitation property due to a higher viscosity of the plating solution can also be prevented. The concentration of the better complexing agent is 0.002~1mol/L. With this, the precipitation of nickel hydroxide and the decomposition of the plating bath can be prevented more effectively.

(4) stabilizer

Examples of the stabilizer include inorganic compounds such as Pb compounds such as lead acetate and Bi compounds such as bismuth acetate; and organic compound stabilizers such as butynediol. These stabilizers can be used alone or in combination of two or more.

The basic composition of the electroless nickel plating bath of the present invention is as described above, and its pH is preferably about 4 to 5. The pH can be adjusted by alkalis such as ammonia, sodium hydroxide, etc.; acids such as sulfuric acid, hydrochloric acid, nitric acid, etc.

(5) Other

The electroless nickel plating bath of the present invention may further contain as needed Various well-known additives blended in electroless nickel plating baths. Examples of the additive system include reaction accelerators, gloss agents, surfactants, and function-imparting agents. These types are not particularly limited, and can be used by ordinary users.

When the electroless nickel plating bath of the present invention is used for electroless plating, the plating conditions and the plating apparatus are not particularly limited, and can be appropriately selected in accordance with ordinary methods. Specifically, it suffices to immerse the electroless nickel plating solution of the above composition into the object to be plated or the like and bring it into contact. The plating temperature at this time is preferably 70 to 90°C. In addition, although the plating treatment time can be appropriately set according to the thickness of the nickel plating film to be formed, etc., it is generally about 15 to 60 minutes.

In addition, the type of the object to be plated used in the present invention is not particularly limited, but examples thereof include reduction precipitation of electroless nickel plating such as metals such as iron, cobalt, nickel, palladium, or these alloys. Catalysts; non-catalyst metals such as copper, glass, ceramics, etc. In the case of using the former catalytic metal, etc., the electroless nickel plating film can be directly formed after the pretreatment according to the usual method. On the other hand, in the case of using the latter non-catalytic metal or the like, it is possible to perform electroless nickel plating after attaching a metal catalytic core such as a palladium core according to the usual method.

The thickness of the nickel plating film thus obtained is approximately 3 to 7 μm. According to the present invention, it is very useful in that even if the thickness of the nickel plating film is increased as described above in order to ensure corrosion resistance, cracks and the like do not occur.

This application is based on the application on July 28, 2015 Japanese Patent Application No. 2015-148881, claiming priority benefits. The entire contents of the specification of Japanese Patent Application No. 2015-148881 filed on July 28, 2015 are for reference and are incorporated in this application.

[Example]

Although the following examples illustrate the present invention in more detail, the present invention is not limited to the following examples, and can be implemented with changes within the scope applicable to the gist of the foregoing/later described. Both are included in the technical scope of the present invention.

In this example, as shown in Table 1, various types of electrolysis including Ni sulfate, Na hypophosphite as a reducing agent, lactic acid as a complexing agent, additives in Table 1, and Pb acetate as a stabilizer were used. In the nickel plating bath, the following experiment was conducted. The pH of each plating bath is shown in Table 1.

As the object to be plated, 40 copper patterns (copper thickness 18 μm) with a line width of 5 mm and a gap width of 75 μm are formed on a polyimide resin (thickness 25 μm) with a size of 2 cm×7 cm, and a copper lining with a size of 1 cm×4 cm is formed Pad.

After the above-mentioned object to be plated is cleaned, soft etched, pickled, pre-dipped, and activator as shown in Table 2, it is immersed in the electroless nickel plating bath of Table 1 above, and the plating described in Table 1 The bath temperature and the plating time were plated to form an electroless nickel plating film with a thickness of 5 μm.

Next, electroless gold plating was performed as shown in Table 2, An electroless gold plating film with a thickness of 0.05 μm is formed.

Using each sample obtained in this way, the following characteristics were evaluated.

(Evaluation of bendability by MIT test)

In this example, in order to investigate the bendability of the electroless nickel plating film obtained in the above manner, the folding resistance by the MIT test was performed. The MIT test is a test method used to evaluate the strength of the test piece with respect to bendability. In this example, the MIT testing machine "MIT FOLDING ENDURANCE" of Yasuda Precision Machinery was used, and the test was conducted in accordance with JIS P8115. The details of the test conditions are as follows.

Test piece size: width 15mm, length about 110mm, thickness 43μm

Test speed: 175cpm

Bending angle: 135°

Load: 0.25~2.0kgf (0.25kgf step)

R of bending fixture: 0.38mm

Bending fixture gap: 0.25mm

When the MIT test is performed, the greater the number of bendings (the number of MITs) until the test piece breaks, the better the bendability (folding resistance) of the electroless nickel plating film can be evaluated.

(Confirmation of micro-cracks by FE-SEM)

For the sample obtained in the above manner, the sample subjected to the bending test of the above MIT test was used in order to investigate whether it will occur when stress is applied Cracked, and the above sample was wound on a rod with a diameter of 8 mm and held for 10 seconds. Next, an electric field emission-type scanning electron microscope (Field Emission-Scanning Electron Microscope, FE-SEM) was used to observe the wound portion and confirm the presence or absence of micro-cracks.

In detail, in this example, FE-SEM observation was performed at a magnification of 50,000 times and an observation field of 2 μm×1.5 μm, and the presence or absence of microcracks was observed along the grain boundaries. Even if only one micro-crack occurred in the observation field of view, it was evaluated as “yes”, and the case where no micro-cracks occurred at all was evaluated as “none”.

(Measurement of precipitation speed)

In this example, in order to investigate the coverage of the nickel plating film, a fluorescent X-ray film thickness meter (XRF, SFT-9550 made by SII) was used to measure the Ni film thickness of the above test piece, and the per unit time was calculated Ni precipitation rate (μm/hr).

These results are recorded in Table 1.

From the results of Table 1, it can be examined as follows.

First of all, the examples of the present invention in Table 1A are all examples in which an electroless nickel plating bath containing additives specified in the present invention is used. The number of MITs exceeds 100 times and has good flexibility, and no micro-cracks are observed. The precipitation rate of Ni is also large, so there is no doubt about no plating.

In contrast, the comparative example in Table 1B is an example in which an electroless nickel plating bath containing no additives specified in the present invention is used, and there are any problems.

First of all, Comparative Example 1 is an example that does not contain additives. The number of MITs is as small as 10, and the bendability is significantly reduced.

Comparative Examples 2 and 3 are examples in which the additives described in Patent Document 1 were used, and microcracks occurred.

Comparative Examples 4 and 10 are examples of using the compound of the above formula (1) defined by the present invention, and the additives of X=H and X=CH ₃ reduce the precipitation rate of Ni in either case.

Comparative Examples 5 to 9 are examples in which a compound having a ring other than the benzothiazole ring specified in the above formula (1) is used as an additive. In any case, the number of MITs is as little as 40 to 88, and the flexibility is reduced. In addition, in Comparative Examples 6 to 9 other than Comparative Example 5, the precipitation rate of Ni also decreased.

For reference, FIG. 1 shows the above-mentioned FE-SEM photographs of Comparative Example 3 and Inventive Example 6. As is clear from comparison of these photographs, it is understood that the comparative example 3 system has micro-cracks along the grain boundaries, whereas in the invention example 6, no micro-cracks occurred.

Claims (1)

An electroless nickel plating bath, characterized in that it contains a sulfur-containing benzothiazole-based compound represented by the following formula (1), and the sulfur-containing benzo-containing compound of the above formula (1) in the electroless nickel plating bath The content of the thiazole-based compound is 0.1 mg/L or more and 10 g/L or less,

In the formula, X is an alkyl group having 2 or more carbon atoms, or a salt thereof, and X may have a substituent.

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