JP6025899B2 - Electroless nickel plating bath and electroless plating method using the same - Google Patents

Description

  The technology disclosed herein relates to electroless nickel plating.

  Electroless nickel plating is used for various applications such as electronic parts and automobile parts. For example, when bumps are provided on electrodes on a semiconductor wafer and bonded to other semiconductor chips or the like, an under barrier metal (UBM) made of nickel (Ni) or the like is formed by electroless plating before forming the bumps. Is provided.

  In the UBM formation technique, when forming an electroless nickel plating film, it is required to form a plating film having a stable and uniform film thickness. In addition, the appearance of the plating film is also required to be good.

  However, in the electroless nickel plating method, the appearance of the plating film is likely to deteriorate due to the aging of the plating bath due to the influence of the underlying electrode and the penetration of the metal.

  On the other hand, in patent document 1, the improvement of the external appearance of a plating film is aimed at by using an acetylene compound as a brightener.

JP 2008-274444 A

  However, since the electrodes on the wafer are small in size and may be subjected to special pretreatment, it may be difficult to obtain a plating film having good throwing power and sufficient gloss. In particular, when the unevenness of the plating film forming surface is severe, or when the film thickness of the plating film is small, it is generally difficult to obtain a shiny plating film.

  An object of the present invention is to form an electroless nickel plating film that is uniform and glossy even when unevenness or the like is present on the base.

  The electroless nickel plating bath disclosed in the present specification contains a water-soluble nickel salt, a brightener made of a polymer containing a urea group as a side chain, a monosulfide-based additive, and lead ions.

  According to the electroless nickel plating bath and the plating method using the same disclosed in this specification, it is possible to form an electroless nickel plating film having a uniform and glossy surface even when unevenness or the like is present on the base.

FIG. 1 is a flowchart showing an example of a UBM formation method using an electroless nickel plating bath. FIG. 2 is a diagram showing S-based additives used in plating baths according to examples and comparative examples. FIG. 3 is a diagram showing the criteria for evaluating the appearance of the nickel plating film.

  Hereinafter, embodiments of the electroless nickel plating bath and plating method disclosed in this specification will be described. Below, although the example which uses the plating bath which concerns on this embodiment for formation of UBM is shown, the use of the said electroless nickel plating bath is not limited to this.

-Plating bath composition-
The electroless nickel plating bath of this embodiment includes a water-soluble nickel (Ni) salt, a reducing agent, a complexing agent, a brightener made of a polymer containing a urea-based structure, a monosulfide-based additive, lead (Pb) ions. The water-soluble nickel salt can be used without particular limitation as long as it is soluble in the plating bath and an aqueous solution having a predetermined concentration can be obtained. For example, 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 can be used. These water-soluble nickel salts can be used alone or in combination of two or more.

  The concentration of nickel ions in the plating bath may be, for example, about 0.03 mol / L or more and 0.18 mol / L or less as metallic nickel, and more preferably about 0.06 mol / L or more and 0.12 mol / L or less. is there. If the nickel concentration is too low, the plating rate may be slow. If the nickel concentration is too high, the plating bath may become cloudy or the viscosity of the plating bath may increase, resulting in poor uniform precipitation and pits in the formed plating film.

  Further, as the reducing agent, various reducing agents used in known electroless nickel plating baths can be used.

  Examples of the reducing agent include hypophosphites and boron compounds. Examples of hypophosphites include sodium hypophosphite (sodium hypophosphite) and potassium hypophosphite. Examples of the boron compound include borohydride compounds such as sodium borohydride and potassium borohydride, and amine borane compounds such as dimethylamine borane, trimethylamine borane, and triethylamine borane.

  The concentration of the reducing agent varies depending on the type of complexing agent used, but may be, for example, about 0.01 mol / L to 1 mol / L, and more preferably 0.05 mol / L to 0.5 mol / L. Degree. If the reducing agent concentration is too low, the plating rate may be slow, and if the reducing agent concentration is too high, the bath stability may deteriorate and the plating solution may decompose.

  As the complexing agent, various complexing agents used in known electroless nickel plating baths can be used.

  Specific examples of complexing agents include amino acids such as glycine, alanine, arginine, aspartic acid, glutamic acid, monocarboxylic acids such as lactic acid, propionic acid, glycolic acid, gluconic acid, tartaric acid, oxalic acid, succinic acid, malic acid, etc. And tricarboxylic acids such as dicarboxylic acid and citric acid, and salts thereof such as sodium salt and potassium salt can also be used as complexing agents. These complexing agents can be used alone or in combination of two or more.

  The concentration of the complexing agent varies depending on the type of the complexing agent used, but may be, for example, about 0.01 mol / L to 2 mol / L, and more preferably about 0.05 mol / L to 1 mol / L. It is. If the complexing agent concentration is too low, precipitation of nickel hydroxide tends to occur, which is not preferable. On the other hand, when the complexing agent concentration is too high, the uniform precipitation may be lowered due to an increase in the viscosity of the plating solution.

  The monosulfide-based additive has an effect of improving the throwing power of plating, improving the uniformity of the plating film by refining the crystal of the plating film, and imparting gloss. In addition, a polymer containing a urea structure (particularly a polymer containing a urea group as a side chain) partially suppresses nickel deposition and fills a plating film with small scratches on the surface of the object to be plated, that is, leveling. It works to give effects. Furthermore, Pb suppresses metal deposition in the plating bath and covers the corners of the projections of the object to be plated having irregularities, so that the plating film is easily formed on the recesses where the plating film is not normally formed. This prevents the film thickness of the plating film from being different from that on the convex portion.

  In the electroless nickel plating bath of the present embodiment, a brightener composed of a polymer containing urea-based structures having different mechanisms of action (for example, a polymer containing urea groups as side chains) and a monosulfide-based additive are combined. Therefore, the variation in the plating film thickness can be reduced even on an uneven base. Since the electroless nickel plating bath of this embodiment further contains Pb ions, not only the long-term stability of the plating bath is improved, but also a nickel plating film having sufficient gloss can be formed. Yes. Moreover, in the electroless plating bath of this embodiment, it is possible to effectively reduce the occurrence of galling and skipping of the plating film. Here, the term “galling” means that the plating film has a jagged appearance on the edge portion of the object to be plated.

  In the electroless plating bath, the effect of smoothing the plating film and imparting the gloss to the plating film can be exhibited to some extent even by combining the brightening agent comprising a polymer containing a urea structure and the monosulfide additive. However, by adding Pb ions to the plating bath, not only can the long-term stability of the plating bath be improved, but it is also possible to form a plating film with a smooth surface even when the surface area is small and the surface is uneven. . Furthermore, by adding Pb ions, it is possible to suppress the occurrence of white cloudiness (nodules) in the plating film and to impart more excellent gloss.

  Moreover, when forming UBM on the electrode containing aluminum (Al) using the nickel plating bath of this embodiment, in order to perform the process (zincate process) which substitutes Al and zinc (Zn) as pre-processing, it is nickel. Zn is dissolved into the nickel plating bath during the formation of the plating film. When the Zn concentration in the nickel plating bath becomes high, white cloudiness tends to occur in the nickel plating film.

  In the nickel plating bath of the present embodiment, since the brightener, the monosulfide-based additive, and the Pb ions are included in combination, even if Zn is dissolved into the nickel plating bath by this synergistic effect. It is possible to effectively suppress the occurrence of white clouding in the nickel plating film and to impart excellent gloss. For this reason, if the nickel plating bath of this embodiment is used, the external appearance of the nickel plating film formed on a metal electrode can be improved, and the yield of a product can be raised. In addition, since the nickel plating bath of this embodiment is not easily affected by metals such as Zn, if the nickel plating bath is used, the replacement frequency of the plating bath can be reduced, and the amount of waste liquid can be reduced.

  In addition, while improving the film thickness uniformity of the plating film, the effect itself of flattening the surface of the plating film is possessed even by sulfur (S) additives other than monosulfide additives. For example, in the plating bath of this embodiment, even when a thiocyanate additive, a disulfide additive, a thiol additive, or a benzoisothiazole additive is used instead of the monosulfide additive, the fine electrode pad is used. A nickel plating film having a uniform film thickness can be formed.

  However, according to the original study by the inventors of the present application, when an S-based additive other than the monosulfide-based additive is used, the unevenness is severe both immediately after preparation and after aging (that is, after using only a predetermined turnover). It has been clarified that the appearance of the nickel plating film formed on the ground becomes poor.

  Sulfur atoms contained in disulfide, thiocyan, thiol, benzoisothiazole and the like are more reactive than sulfur atoms contained in monosulfide. For this reason, when using a monosulfide type additive with the polymer and urea containing a urea type structure, it becomes possible to suppress nickel precipitation moderately, and it can be considered that the gloss of a plating film can be made favorable.

  The concentration of the monosulfide-based additive in the plating bath is not particularly limited. For example, if the concentration is 0.01 ppm or more and 100 ppm or less, a plating film is formed on a fine electrode having irregularities without inhibiting the nickel precipitation reaction. It can be formed uniformly. The concentration of the monosulfide-based additive in the plating bath is preferably from 0.1 ppm to 10 ppm, more preferably from 0.3 ppm to 3 ppm. If the concentration of the monosulfide-based additive is too low, the throwing power of the plating deteriorates and the gloss tends to be insufficient. If the concentration of the monosulfide-based additive is too high, the corrosion resistance of the film may be reduced, and nickel may be difficult to precipitate.

  Examples of the monosulfide-based additive include 2,2′-thiodiglycolic acid (hereinafter referred to as “TDA”), 3,3′-thiodipropionic acid (hereinafter referred to as “TDPA”), 3-[(amino Iminomethyl) thio] -1-propanesulfonic acid (hereinafter referred to as “UPS”), methionine, ethionine, thiodiglycol, 2,2′thiobis (ethylamine), thiodibutyric acid, thiodipropanesulfonic acid, and the like. It may be a mixture of drugs selected from these groups.

  Moreover, the polymer containing a urea structure may be a polymer containing a urea group as a side chain, for example. In this case, since the urea group of the side chain covers a portion where nickel is liable to precipitate, such as the convex portion of the object to be plated, and this portion suppresses nickel precipitation, this polymer should be combined with a monosulfide additive. Can exert a sufficient leveling effect. The polymer constituting the brightener may be, for example, a polymer represented by the following formula (I) or (II).

[Wherein, at least one of R ₁ and R ₂ and R ₃ are groups represented by the formula (—CH ₂ —NH—CONH ₂ ) or the formula (—CH ₂ —NH—CONH—CH ₃ ), l and m are each an integer of 1 to 5, and n is an integer of 1 to 200.

  The weight average molecular weight of the polymer constituting the brightener is not particularly limited as long as the viscosity of the plating bath can be in an appropriate range and precipitation is not caused. The weight average molecular weight of the polymer constituting the brightener is preferably 5000 or more and 20000 or less, for example. If the weight average molecular weight of the polymer is too high, galling or the like may occur, and if it is too low, the gloss may be insufficient. The concentration of the brightener in the plating bath is not particularly limited, but is preferably about 0.01 ppm to 100 ppm, more preferably about 0.1 ppm to 10 ppm. This is because if the concentration of the brightening agent is too high, it is difficult for nickel to be deposited on the entire object to be plated, and if the concentration of the brightening agent is too low, it is difficult to obtain a sufficient gloss depending on the conditions.

  The concentration of Pb ions in the plating bath is not particularly limited, but the Pb concentration is preferably about 0.01 ppm to 10 ppm, more preferably about 0.1 ppm to 3 ppm. If the Pb concentration is too high, Ni may be difficult to precipitate. If it is too low, the gloss will be insufficient, the bath stability will deteriorate, and the plating bath may decompose. A water-soluble lead salt such as lead nitrate or lead acetate may be used as a supply source of Pb ions, but is not limited thereto.

  Moreover, although the pH of the electroless nickel plating bath of this embodiment is not specifically limited, For example, about 3.0 or more and 12.0 or less may be sufficient. The pH of the plating bath is preferably 4.0 or more and 9.0 or less. If the pH is too low, the plating reaction may not occur, and if the pH is too high, the stability of the plating bath may be deteriorated. During the formation of the plating film, the temperature of the plating bath may be, for example, about 40 ° C. or more and 100 ° C. or less. The temperature of the plating bath is preferably 60 ° C. or higher and 90 ° C. or lower. If the plating bath temperature is too low, the plating reaction may not occur, and if it is too high, the stability of the plating bath may be deteriorated.

  The composition of the electroless nickel plating bath described above is an example of the embodiment, and can be appropriately changed without departing from the gist of the present invention.

-Method of forming UBM using electroless nickel plating bath-
FIG. 1 is a flowchart showing an example of a UBM formation method using the electroless nickel plating bath of the present embodiment. Here, a method of forming a UBM using a double zincate method will be described.

  As shown in FIG. 1, first, electrode pads and wirings made of a metal containing Al are formed on a wafer made of silicon or the like by a known method. Next, after forming a passivation film having an opening in the region where the electrode pad is formed, a protective film is formed to cover a region of the wafer surface where the UBM is not formed. The size of the opening of the passivation film is, for example, about 100 μm × 100 μm. Subsequently, the wafer surface including the electrode pad is cleaned using a chemical solution such as Epitus (registered trademark) MCL-16 (manufactured by Uemura Kogyo Co., Ltd.) (step S1).

  Next, if necessary, the natural oxide film formed on the electrode pad is removed by wet etching using a known chemical solution (step S2). In this step, for example, a chemical solution such as Epitus (registered trademark) LEC-18 (manufactured by Uemura Kogyo Co., Ltd.) is used.

Subsequently, the surface of the electrode pad is oxidized using nitric acid (HNO ₃ ) or the like to form a thin oxide film on the electrode pad (step S3).

  Next, a primary zincate process is performed (step S4). Specifically, a part of Al contained in the Al oxide film was replaced with Zn while removing the oxide film using a chemical solution containing Zn such as Epitus (registered trademark) MCT-22 (manufactured by Uemura Kogyo Co., Ltd.). Then, a Zn substitution film is formed on the electrode pad.

Next, the Zn-substituted film is removed using a chemical solution such as HNO ₃ and a thin oxide film is formed again on the electrode pad (step S5).

  Subsequently, a secondary zincate process is performed (step S6). Specifically, a uniform Zn-substituted film with good adhesion is formed using a chemical solution containing Zn such as Epitus (registered trademark) MCT-22 (manufactured by Uemura Kogyo Co., Ltd.). By the above pretreatment, the oxide film formed on the electrode pad is removed, and a nickel plating film having good adhesion can be formed on the electrode pad.

  Next, a UBM made of nickel is formed in a predetermined region including on the electrode pad using the electroless nickel plating bath of the present embodiment (step S7). This step is performed, for example, at about 70 to 90 ° C. for about 10 to 60 minutes. In this step, Zn in the Zn substitution film elutes into the plating bath and substitutes for nickel. Thereafter, nickel is reduced and deposited on the substituted and deposited nickel. Thereby, for example, a nickel plating film having a film thickness of about 2 μm to 12 μm and good adhesion to the electrode pad is formed.

  The area of the exposed portion of each electrode pad is very small, and a step is formed by the electrode pad and the passivation film, but if the electroless nickel plating bath of this embodiment is used, not only the passivation film but also the recesses are formed. A nickel plating film having a uniform film thickness and a good appearance can also be formed on the electrode pad.

  Thereafter, the protective film is removed from the wafer, and the plating film is evaluated. Next, solder or metal bumps are formed on the electrode pads with the nickel plating film interposed therebetween. In addition, before removing a protective film, you may perform electroless gold plating as needed.

  By the above method, a substrate for mounting a semiconductor element including a plurality of electrodes can be manufactured.

  The conditions of electroless nickel plating for forming the UBM, such as temperature and processing time, can be appropriately changed according to the target film thickness of the plating film, the size of the electrode pad, and the like. Moreover, the nickel plating bath of this embodiment can be preferably used also for uses other than formation of UBM.

  In general, an electroless nickel plating film is considered to be inferior in gloss to an electric nickel plating film, but the electric nickel is not suitable for plating an article having a complicated shape. The electroless nickel plating film formed by the method of the present embodiment is also formed on an article having a complicated shape or an article having fine irregularities, and has a gloss comparable to that of an electric nickel plating film. Applicable to a wide range of uses other than UBM.

  In the present embodiment, Al is used as an object to be plated, but the object to be plated is not particularly limited. For example, a metal other than Al, such as copper (Cu) or iron (Fe), is suitable. By performing the treatment, it can be used as an object to be plated.

  Below, the Example of the electroless nickel plating bath of this embodiment is described.

-Preparation of plating bath-
Electroless nickel plating baths according to Examples 1 to 21 and plating baths according to Comparative Examples 1 to 36 were prepared. The plating baths according to these examples and comparative examples are all 5 g / L nickel, 25 g / L sodium hypophosphite, 5 g / L citric acid, 10 g / L malic acid, 5 g / L gluconic acid. Is a plating bath in which any one of a brightener, an S-based additive, and a bath stabilizer is changed as shown in Tables 2 to 12 below. The pH of the plating bath was adjusted to 4.8 for all.

  In the plating baths according to Examples and Comparative Examples, as the brightener, any of the chemicals represented by the following formula (I) or formula (II) was used at a concentration of 5 ppm.

  In the plating baths according to Examples 1 to 21 and Comparative Examples 1 to 31, the concentration of Pb ions (divalent) was 0.5 ppm.

  Moreover, in FIG. 2, the S type additive used by the Example and the comparative example was shown.

<Example 1>
A plating bath was prepared by adding the brightener represented by the formula (I) having a weight average molecular weight of about 8000, the S-based additive TDA, and Pb to the basic composition described above. It was set to 1. R ₁ in the formula (I) was -CONH ₂ and R ₂ was -CH ₂ -NH-CONH ₂ (see Table 2).

<Example 2>
A plating bath was prepared by adding the brightener represented by the formula (I) having a weight average molecular weight of about 15000, the S-based additive TDA, and Pb to the above basic composition. 2. R ₁ in formula (I) was —CONCH ₃ and R ₂ was —CH ₂ —NH—CONH ₂ (see Table 2).

<Example 3>
A plating bath was prepared by adding the brightener represented by the formula (I) having a weight average molecular weight of about 20,000 to the above basic composition, the S-based additive TDA, and Pb, and this was used as an example. It was set to 3. R ₁ in the formula (I) was —CH ₂ —NHCOCH ₃ and R ₂ was —CH ₂ —NH—CONH ₂ (see Table 2).

<Example 4>
A plating bath was prepared by adding the brightener represented by the formula (I) having a weight average molecular weight of about 15000, the S-based additive TDA, and Pb to the above basic composition. It was set to 4. R ₁ in formula (I) was —CH ₂ —NH ₂ and R ₂ was —CH ₂ —NH—CONH ₂ (see Table 2).

<Example 5>
A plating bath in which the brightener represented by the formula (II) having a weight average molecular weight of about 5000, the S-based additive TDA, and Pb was added to the above basic composition was prepared. It was set to 5. R ₃ in the formula (II) was —CH ₂ —NH—CONH ₂ (see Table 2).

<Examples 6 to 11>
Except having changed the composition of the brightener, the plating bath of the same composition as the plating bath which concerns on Examples 1-5 was prepared, and this was made into Examples 6-11.

Specifically, a plating bath using a brightener represented by the formula (I) having a weight average molecular weight of about 12000 was prepared. In the formula (I), R ₁ was -CONH ₂ and R ₂ was -CH ₂ -NH-CONH-CH ₃ (see Table 3).

A plating bath using a brightener represented by the formula (I) having a weight average molecular weight of about 18,000 was prepared. R ₁ in formula (I) was —CONCH ₃ and R ₂ was —CH ₂ —NH—CONH—CH ₃ (see Table 3).

A plating bath using a brightener represented by the formula (I) having a weight average molecular weight of about 20,000 was prepared, and this was designated as Example 8. R ₁ in the formula (I) was —CH ₂ —NHCOCH _3, and R ₂ was —CH ₂ —NH—CONH—CH ₃ (see Table 3).

A plating bath using a brightener represented by the formula (I) having a weight average molecular weight of about 15000 was prepared. R ₁ in formula (I) was —CH ₂ —NH ₂ and R ₂ was —CH ₂ —NH—CONH—CH ₃ (see Table 3).

A plating bath using a brightener represented by the formula (II) having a weight average molecular weight of about 8000 was prepared. R ₃ in the formula (II) was —CH ₂ —NH—CONH—CH ₃ (see Table 3).

A plating bath using a brightener represented by the formula (I) having a weight average molecular weight of about 13,000 was prepared. R ₁ in formula (I) was —CH ₂ —NH—CONH _2, and R ₂ was —CH ₂ —NH—CONH—CH ₃ (see Table 3).

<Examples 12 to 16>
In the plating baths according to Examples 1 to 5, plating baths in which the S-based additive was changed from TDA to TDPA were prepared, and these were designated as Examples 12 to 16 (see Table 5).

<Examples 17 to 21>
In the plating baths according to Examples 1 to 5, plating baths in which the S-based additive was changed from TDA to UPS were prepared, and these were designated as Examples 17 to 21 (see Table 6).

<Comparative Example 1>
Using TDA as the S-based additive and Pb as the bath stabilizer, a plating bath without the brightener was prepared, and this was designated as Comparative Example 1 (see Table 4).

<Comparative Examples 2-6>
A plating bath was prepared using TDA as an S-based additive, Pb as a bath stabilizer, and a chemical having no urea-based structure as a brightener, and these were designated as Comparative Examples 2 to 6 (see Table 4). .

In the plating bath according to Comparative Example 2, the brightener represented by the formula (II) having a weight average molecular weight of about 14,000 was used. R ₃ in the formula (II) was —CONH ₂ .

In the plating bath according to Comparative Example 3, the brightener represented by the formula (II) having a weight average molecular weight of about 12000 was used. R ₃ in the formula (II) was —CON— (CH ₃ ) ₂ .

In the plating bath according to Comparative Example 4, the brightener represented by the formula (II) having a weight average molecular weight of about 12000 was used. R ₃ in the formula (II) was —CH ₂ —NHCOCH ₃ .

In the plating bath according to Comparative Example 5, the brightener represented by the formula (II) having a weight average molecular weight of about 15000 was used. R ₃ in the formula (II) was —CH ₂ —NH ₂ .

In the plating bath according to Comparative Example 6, the brightener represented by the formula (I) having a weight average molecular weight of about 15000 was used. R ₁ in the formula (I) was —CH ₂ —NHCOCH _3, and R ₂ was —CH ₂ —NH ₂ .

<Comparative Examples 7-11>
In the plating baths according to Examples 1 to 5, plating baths in which the S-based additive was changed to sodium thiocyanate (indicated as “ST” in Table 7) were prepared, and these were designated as Comparative Examples 7 to 11 (Tables). 7).

<Comparative Examples 12-16>
In the plating baths according to Examples 1 to 5, plating baths in which the S-based additive was changed to 3,3′-dithiobis (1-sodium propanesulfonate) (indicated as “SPS” in Table 8) were prepared, and these Were Comparative Examples 12 to 16 (see Table 8).

<Comparative Examples 17-21>
In the plating baths according to Examples 1 to 5, plating baths were prepared in which the S-based additive was changed to 3-mercaptopropionic acid (indicated as “MPA” in Table 9), and these were designated as Comparative Examples 17 to 21, respectively. (See Table 9).

<Comparative Examples 22-26>
In the plating baths according to Examples 1 to 5, plating baths in which the S-based additive was changed to saccharin were prepared, and these were designated as Comparative Examples 22 to 26 (see Table 10).

<Comparative Examples 27-31>
A plating bath having a composition in which the S-based additive was removed from the plating baths according to Examples 1 to 5 was prepared, and these were designated as Comparative Examples 27 to 31 (see Table 11).

<Comparative Examples 32-36>
A plating bath having a composition obtained by removing the bath stabilizer from the plating baths according to Examples 1 to 5 was prepared, and these were designated as Comparative Examples 32-36, respectively (see Table 12).

-Appearance evaluation of plating film-
Using the plating baths according to the above-described Examples and Comparative Examples, a nickel plating film was formed on a 5 cm × 5 cm pure Al plate (A1050P) in a 1 L beaker by the following method, and the appearance of the plating film was evaluated. .

  First, pretreatment by the double zincate method shown in steps S1 to S6 of FIG. 1 was performed. Table 1 shows the chemicals and treatment conditions used in the pretreatment.

  As shown in Table 1, the surface of the Al plate was cleaned using Epitus (registered trademark) MCL-16 under the conditions of 50 ° C. and 180 seconds. The natural oxide film removal step (step S2) shown in FIG. 1 was not performed.

Next, an oxide film was formed on the surface of the Al plate using 60% by weight of HNO ₃ under the conditions of 21 ° C. and 30 seconds. Subsequently, primary zincate treatment was performed using Epitas (registered trademark) MCT-22 at 25 ° C. for 30 seconds. Here, MCT-22-M was used at a concentration of 200 mL / L, and MCT-22-A was used at a concentration of 100 mL / L. Subsequently, the Zn-substituted film was peeled off using 60% by weight of HNO ₃ under the conditions of 21 ° C. and 60 seconds, and an oxide film was formed on the surface of the Al plate. Next, secondary zincate treatment was performed using Epitas (registered trademark) MCT-22 under the conditions of 25 ° C. and 20 seconds. In addition, between each process, the Al substrate was washed with water.

  Subsequently, electroless plating treatment was performed at 80 ° C. for 30 minutes using the plating baths according to Examples and Comparative Examples containing the chemicals shown in Tables 2 to 12, and a nickel plating film was formed on the surface of the Al plate. It was. The target film thickness of the nickel plating film was 4-5 μm.

  FIG. 3 is a diagram showing the criteria for evaluating the appearance of the nickel plating film. The nickel plating film formed by the above-described method was evaluated according to the criteria shown in FIG. Specifically, when it is close to the sample that looks the blackest, it is judged as ◯ (good) because the gloss of the plating film is most excellent, and as the color of the plating film becomes whitish, △ (insufficient), x (bad), XX (remarkably poor) was determined. The result evaluated by the above-mentioned method was used as the determination result for the new bath. In addition, a plating film was formed using a pseudo-aging bath prepared by adding 20 ppm of Zn to each of the plating baths according to Examples and Comparative Examples, and the appearance of the formed plating film was also evaluated.

-Evaluation of bath stability-
After performing the pretreatment process by the same method as the above-mentioned appearance evaluation, electroless plating treatment is performed using the plating baths according to the examples and comparative examples, and the surface of a pure AL plate (A1050P) having a size of 5 cm × 10 cm is formed. A nickel plating film was formed. The amount of the plating bath per unit area was 1 dm ² / L, and the plating film was formed at 80 ° C. for 60 minutes. This electroless plating treatment was performed using a 1 L beaker.

  The state of the plating bath after the electroless plating treatment was visually observed, and a case where no nickel was precipitated in the plating bath and no nickel was deposited on the inner surface of the beaker was determined as “good”. On the other hand, when the plating bath was decomposed to cause nickel precipitation or nickel precipitation on the inner surface of the beaker, it was determined that the bath stability was insufficient ("decomposition" in Tables 2 to 11).

−Evaluation of precipitation on fine pads−
After performing the pretreatment process by the same method as the above-described appearance evaluation, electroless plating treatment was performed using the plating baths according to Examples and Comparative Examples. A TEG wafer having a size of 1 cm × 1 cm provided with an electrode pad made of an Al—Cu alloy was used as an object to be plated. Next, a nickel plating film was formed on the surface of an electrode pad having a size of 100 μm × 100 μm at 80 ° C. for 30 minutes. The target film thickness of the plating film was 4 μm to 5 μm.

  Subsequently, the deposition property of the plating film was evaluated using a confocal microscope (“OPTELICS C130”, manufactured by Lasertec Corporation). When no galling or the like was found on the plating film, it was judged as “good”, and when galling or the like was found on the plating film, it was judged as “bad” (“galling” in Table 11).

-Evaluation results-
The evaluation result about an Example and a comparative example is put together in Tables 2-11, and is shown.

  From the results shown in Table 2, Table 5 and Table 6, the plating baths according to Examples 1 to 21 containing a brightener made of a polymer having a urea structure, a monosulfide additive, and Pb ions were used. In each case, a nickel plating film having a good appearance was obtained, and it was confirmed that the bath stability and the deposition on a fine pad were also good. Moreover, in the plating bath which concerns on Examples 1-21, it was confirmed that the nickel plating film which has a favorable external appearance can be formed not only in the state of a new bath but in the aging state.

  Further, from the results of Examples 1 to 11 in which the brightener was changed, not only a polymer obtained by polymerizing only a monomer having a urea structure, but also a copolymer of two kinds of monomers having at least one of the urea structures. Then, it was confirmed that generation of white cloudiness can be effectively suppressed as a brightener.

  On the other hand, from the comparison between the results of Examples 1 to 10 and the results of Comparative Examples 1 to 6, when the brightener does not contain a urea structure, even if it contains a monosulfide additive and Pb ions. It was confirmed that whitish cloudiness was generated in the plating film and precipitation on a fine pad was likely to be poor. In these comparative examples, when using an aging bath, the appearance was worse than when using a new bath.

  In addition, all the evaluation items were good in the plating baths according to Examples 1 to 21 containing the monosulfide additive, whereas the thiocyan additive (ST) and the disulfide additive (SPS). In the plating baths according to Comparative Examples 7 to 26 containing a thiol-based additive (MPA) or a benzoisothiazole-based additive (saccharin), the precipitation of fine pads was good, but the occurrence of white haze was suppressed. It was confirmed that it was not possible. From the result that galling occurs in the plating film in the plating baths according to Comparative Examples 27 to 31 that do not contain the S-based additive, it can be seen that the S-based additive has the effect of improving the precipitation on a fine pad. From the comparison with the results of the examples, it is possible to suppress the occurrence of white haze more effectively due to the synergistic effect, particularly by using the monosulfide-based additive together with the brightener containing urea-based structure and Pb ions. I understood.

  Further, from the comparison between the results using the plating baths according to Examples 1 to 5 and the results using the plating baths according to Comparative Examples 32 to 36 that do not contain Pb, the brightener containing the urea structure and the addition of the monosulfide system It was confirmed that not only the bath stability but also the appearance of the plating film can be improved by including Pb ions in the plating bath together with the agent. This result suggests that Pb contributes not only to the stabilization of the bath but also to the smoothing of the plating film together with the brightener and the monosulfide-based additive.

  As described above, the electroless nickel plating bath according to an example of the present disclosure can be applied to plating of various articles including electronic components.

Claims (5)

A water-soluble nickel salt,
A brightener comprising a polymer containing a urea group as a side chain;
A monosulfide additive,
Electroless nickel plating bath containing lead ions. The electroless nickel plating bath according to claim 1,
The brightener is an electroless nickel plating bath characterized by comprising a polymer represented by the following formula (I) or (II).
[Wherein, at least one of R ₁ and R ₂ and R ₃ are groups represented by the formula (—CH ₂ —NH—CONH ₂ ) or the formula (—CH ₂ —NH—CONH—CH ₃ ), l and m are each an integer of 1 to 5, and n is an integer of 1 to 200] In the electroless nickel plating bath according to claim 1 or 2,
The monosulfide additives include 2,2′-thiodiglycolic acid, 3,3′-thiodipropionic acid, 3-[(aminoiminomethyl) thio] -1-propanesulfonic acid, methionine, ethionine, thio An electroless nickel plating bath, which is at least one selected from the group consisting of diglycol, 2,2′thiobis (ethylamine), thiodibutyric acid and thiodipropanesulfonic acid. In the electroless nickel plating bath according to any one of claims 1 to 3,
The electroless nickel plating bath, wherein the polymer constituting the brightener has a weight average molecular weight of 5000 or more and 20000 or less. A method of forming an electroless nickel plating film on an electrode provided on a wafer,
The method to form a nickel membrane | film | coat using the electroless nickel plating bath as described in any one of Claims 1-4.