JP5830795B1 - Nickel-free plating solution, plating film forming method, and electronic component manufacturing method - Google Patents

Abstract

The present invention provides a nickel-free plating technique that can be processed at a high current density by binary alloy plating of tin and iron. The nickel-free plating solution of the present invention comprises 0.150 to 0.700 mol / L of hydroxy acid or a salt thereof, 0.035 to 0.060 mol / L of nitrilotriacetic acid or a salt thereof; It contains 077 to 0.120 mol / L of iron and 0.040 to 0.070 mol / L of tin. [Selection figure] None

Description

  The present invention relates to a nickel-free plating solution, a method for forming a plating film, and a method for manufacturing an electronic component.

  Nickel plating has excellent corrosion resistance and a beautiful appearance. Nickel plating may be used as an underlayer for tin plating. Nickel plating may also be used for decorative purposes.

  However, in recent years, the problem of nickel allergy has been regarded as important, and the use of nickel is being regulated mainly in Europe. Therefore, the development of nickel-free plating technology that does not contain nickel is desired.

  In nickel-free plating technology, binary alloy plating of tin and iron has attracted attention as an alternative to nickel plating. Binary alloy plating of tin and iron has an appearance comparable to bright nickel plating. Various studies have been conducted on the binary alloy plating of tin and iron, and there are known techniques.

  For example, Patent Document 1 describes a technique for forming a plating film made of a binary alloy of tin and iron. This plating film has a glossy appearance despite being nickel-free, and also has excellent corrosion resistance.

JP 2006-274346 A

  In electroplating methods, particularly continuous plating, high productivity is required. For this purpose, it is necessary to perform plating at a high current density and to realize a target film thickness in a short time.

When the current density is increased to 6 A / dm ² or more within the scope of the technique described in Patent Document 1 described above, the present inventors generate a defect in appearance (burnt) in the plating film, and the quality of the plating film is significantly deteriorated. I found out. Therefore, when performing binary alloy plating of tin and iron at a high current density, a new technology that can suppress such abnormal precipitation is required.

  An object of the present invention is to provide a nickel-free plating technique by a binary alloy plating of tin and iron that can be processed at a high current density.

According to a first aspect of the present invention, there is provided a nickel-free plating solution for forming a binary alloy plating film of tin and iron, comprising 0.150 to 0.700 mol / L of a hydroxy acid or a salt thereof; A nickel-free plating solution containing 0.035 to 0.060 mol / L of nitrilotriacetic acid or a salt thereof, 0.077 to 0.120 mol / L of iron, and 0.040 to 0.070 mol / L of tin. Provided.

According to the second aspect of the present invention, the plating includes forming a nickel-free plating film by performing electroplating under a current density of 6.0 to 30 A / dm ² using the plating solution according to the first aspect. A method of forming a film is provided.

  According to a third aspect of the present invention, there is provided a method for forming a plating film according to the second aspect, further comprising forming a tin plating film on the plating film.

  According to the 4th side surface of this invention, the manufacturing method of the electronic component including forming a plating film with the formation method of the plating film which concerns on a 2nd side surface or a 3rd side surface is provided.

  According to the present invention, a nickel-free plating technique based on binary alloy plating of tin and iron that can be processed at a high current density is provided.

  Hereinafter, embodiments of the present invention will be described.

  The plating solution which concerns on 1 aspect of this invention is aqueous solution containing hydroxy acid or its salt, nitrilotriacetic acid or its salt, iron, and tin. This plating solution does not contain nickel, and typically does not contain poisons such as cyan.

  This plating solution contains iron, for example, as iron ions, polyatomic ions, complex ions, or a combination of two or more thereof. Iron combines with tin to form a plating film on the substrate.

  The iron concentration of this plating solution is in the range of 0.077 to 0.120 mol / L, more preferably in the range of 0.080 to 0.115 mol / L, and still more preferably 0.085 to 0.1. It exists in the range of 100 mol / L. When the iron concentration is lowered, the iron content in the plating film is lowered. When the iron concentration is increased, the iron content in the plating film increases. If the iron concentration is excessively lowered, the plating film becomes dull. If the iron concentration is excessively high, cracks are likely to occur in the plating film.

  This plating solution contains tin as, for example, tin ions, polyatomic ions, complex ions, or a combination of two or more thereof.

  The tin concentration of the plating solution is in the range of 0.040 to 0.070 mol / L, more preferably in the range of 0.045 to 0.063 mol / L, and still more preferably 0.050 to 0.0. It is in the range of 060 mol / L. When the tin concentration is lowered, the iron content in the plating film increases. When the tin concentration is increased, the iron content in the plating film decreases. If the tin concentration is excessively low or high, the plating appearance deteriorates.

  The molar ratio of iron to tin in the plating solution is, for example, in the range of 1.54 to 2.40, more preferably in the range of 1.60 to 2.30, and still more preferably 1.70 to 2.30. It is in the range of 2.00.

  When preparing this plating solution, as a metal element source of iron and tin, for example, nitrate, sulfate, chloride, or a combination of two or more thereof can be used.

  This plating solution contains a hydroxy acid or a salt thereof. Hydroxy acids serve as complexing agents for iron and tin.

  Hydroxy acids are, for example, gluconic acid, citric acid or tartaric acid. As the hydroxy acid, one kind of compound may be used, or more compounds may be used in combination. As the salt of hydroxy acid, for example, potassium salt, sodium salt, or a combination thereof can be used.

  The concentration of the hydroxy acid in this plating solution is in the range of 0.150 to 0.700 mol / L, preferably in the range of 0.170 to 0.650 mol / L, and more preferably 0.200 to 0.000. It exists in the range of 500 mol / L. When the hydroxy acid concentration is lowered, the iron content in the plating film increases. When the hydroxy acid concentration is increased, the iron content in the plating film decreases. If the hydroxy acid concentration is excessively low or high, the plating appearance deteriorates.

  This plating solution contains nitrilotriacetic acid or a salt thereof. When the salt of nitrilotriacetic acid is used, for example, potassium salt, sodium salt, or a combination thereof can be used. Nitrilotriacetic acid acts as a complexing agent of iron and has an effect of suppressing abnormal precipitation of iron. Therefore, nitrilotriacetic acid can suppress the generation of kogation due to excessive current in the plating process of this aspect.

  The concentration of nitrilotriacetic acid in this plating solution is in the range of 0.035 to 0.060 mol / L, preferably in the range of 0.040 to 0.055 mol / L, and more preferably 0.045 to 0. Within the range of .053 mol / L. When the nitrilotriacetic acid concentration is lowered, the iron content in the plating film increases. When the nitrilotriacetic acid concentration is increased, the iron content in the plating film decreases. If the nitrilotriacetic acid concentration is too low or high, the plating appearance will deteriorate.

  The plating solution can further contain other components. For example, it may further contain a pH buffer, a conductive salt, a brightener or a surfactant.

  The pH buffer has an effect of suppressing a rapid change in pH. The pH buffer is, for example, urea, boric acid, sodium borate, or a combination of two or more thereof. The pH buffer of the plating solution is preferably added so as to have a concentration of about 0.1 mol / L.

  Conductive salts allow processing at relatively low voltages. The conductive salt is, for example, ammonium chloride, ammonium sulfate, potassium sulfate, potassium chloride, sodium sulfate, sodium chloride, or a combination of two or more thereof. The concentration of the conductive salt in the plating solution is preferably in the range of 10 to 80 g / L.

  The brightener is used to increase the glossiness of the plating film. The brightener is, for example, a water-soluble polymer compound. The water-soluble polymer compound is, for example, polyethyleneimine, polyethylene glycol, polyethylene glycol nonylphenyl ether, polyvinyl alcohol, polyvinyl pyrrolidone, polyallylamine, polydiallylamine, or a combination of two or more thereof.

  The average molecular weight of the water-soluble polymer compound is, for example, in the range of 600 to 200000, and preferably in the range of 10,000 to 70000. Here, the “average molecular weight” is the number average molecular weight.

  The brightener concentration of the plating solution is, for example, in the range of 1.60 to 11.2 g / L, preferably in the range of 4.00 to 10.8 g / L, and more preferably 4.80 to It is in the range of 10.40 g / L.

  The surfactant has an effect of suppressing the generation of pits in the plating film. As the surfactant, for example, sodium dodecyl sulfate (SDS) can be used. The concentration of the surfactant in this plating solution is preferably 0.02 g / L or less.

  This plating solution is typically an acidic solution. The pH of this plating solution is, for example, in the range of 2.5 to 5.0, and preferably in the range of 3.0 to 4.0.

  This plating solution is very stable. This plating solution does not decompose or precipitate the contained components even after one month or more after production.

  Formation of the plating film using this plating solution is performed, for example, by electroplating.

  The electroplating method is a surface treatment method in which a metal is electrochemically deposited on a metal or a non-metallic surface having conductivity. In the electroplating method, generally, the magnitude of current and the formation rate of the plating film are correlated. This plating solution can be plated at a high current density. Therefore, when this plating solution is used, the plating process can be performed at a high speed. That is, this plating solution can improve production efficiency.

In the electroplating process, the current density is set, for example, within a range of 6.0 to 30 A / dm ² , and preferably within a range of 13 to 25 A / dm ² . When the current density is excessively lowered, the plating film becomes dull. When the current density is excessively increased, cracks are likely to occur on the surface of the plating film.

  The temperature of the plating bath is set, for example, within a range of 30 to 60 ° C., and preferably within a range of 40 to 50 ° C.

  The nickel-free plating film thus obtained is composed of iron and tin. The iron content in the plating film is, for example, in the range of 15.0 to 30.0 mass percent concentration, preferably in the range of 15.4 to 25.9 mass percent concentration, more preferably 17 Within the range of .8 to 22.2 weight percent concentration. When the iron content in the plating film is less than 15.0 mass percent, the plating film tends to be dull. When the iron content in the plating film is larger than 30% by mass, the plating film is easily cracked.

  This plating film can be used, for example, as an underlayer between a copper or copper alloy substrate and tin plating in an electronic component. Generally, copper or a copper alloy is used for the conductive parts of electronic parts such as terminals and connectors. The surface of copper or copper alloy is easily oxidized in the atmosphere. This oxide layer increases the electrical resistance of the conductive part.

  Tin exhibits sacrificial corrosion resistance to copper and a sufficiently low electrical resistance value. Tin usually has a thin and stable natural oxide film on its surface. Although tin oxide has high corrosion resistance, its electrical resistance is large. However, the natural oxide film made of tin is destroyed with a little force. Therefore, tin plating shows the low electrical resistance value which tin itself has. Tin plating is excellent in solder wettability. For this reason, the conductive part of the electronic component is usually subjected to tin plating.

However, when tin plating is deposited directly on copper or a copper alloy, copper diffuses into the tin plating layer. Then, at the interface between the copper or copper alloy and tin plating, since the intermetallic compound of copper and tin represented by Cu ₆ Sn ₅ is generated, the generation of whiskers is prone. Further, when a component having such a plating film is heated, copper diffuses into the tin plating layer, causing discoloration and a decrease in solder wettability.

Conventionally, a plating layer made of nickel has been used as an underlayer for preventing the diffusion of copper. However, nickel diffuses into the tin plating layer at a high temperature to produce an intermetallic compound of nickel and tin represented by Ni ₃ Sn ₄ . Therefore, the nickel underlayer may not have sufficient effects of suppressing discoloration and solder wettability. Moreover, as described above, the use of nickel is being regulated due to allergy problems.

On the other hand, according to this embodiment, a nickel-free tin-iron alloy underlayer that functions as a copper diffusion prevention layer can be obtained. Since this tin-iron alloy underlayer does not contain Ni ₃ Sn ₄ , it can achieve sufficient performance in preventing discoloration and solder wettability deterioration at high temperatures. High performance can be achieved.

  As described above, a tin plating film may be further formed on this plating film. The surface of the tin plating film thus formed may be subjected to an antioxidant treatment in order to further suppress the decrease in solder wettability after heating. For example, a zinc oxide film can be formed on the surface of the tin plating film.

  As described above, this plating solution can be used to form a base layer for preventing metal diffusion, for example, in the manufacture of electronic components involving surface mounting. Moreover, this plating solution can be used, for example, for decorative purposes and anticorrosion purposes in addition to the method for manufacturing electronic components.

  The tests conducted in connection with the present invention are described below.

<Example 1>
In this example, the influence of the hydroxy acid concentration in the plating solution on the appearance of the plating film and the iron content in the plating film was examined.

  First, samples 1A to 1L were prepared as plating solutions having different hydroxy acid concentrations. Tin sulfate was used as the tin source, and ferrous sulfate heptahydrate was used as the iron source. As the hydroxy acid, potassium gluconate, which is a salt thereof, was used. Further, urea was used as a pH buffer, ammonium chloride as a conductive salt, sodium dodecyl sulfate as a surfactant, and polyethyleneimine as a brightener. The average molecular weight of polyethyleneimine was 15000. Table 1 below summarizes the compositions of Samples 1A to 1L. The iron / tin molar ratio indicates the ratio of the molar concentration of iron to the molar concentration of tin.

  Next, using the samples 1A to 1L, a plating film was formed on the surface of the cathode by electroplating. These electrodepositions were performed under the same conditions as shown in Table 1.

  About the plating film formed as mentioned above, the plating appearance was confirmed and the iron content in the plating film was confirmed by fluorescent X-ray analysis. The permissible range of the iron content in the plating film was 15.0 to 30.0 mass percent concentration.

  The plating appearance was evaluated according to the criteria described in the lower left column of Table 1. The overall evaluation of the plating appearance and the iron content in the plating film was evaluated according to the criteria described in the lower right column of Table 1.

  The evaluation results are summarized in Table 1. As shown in Table 1, when the hydroxy acid concentration is in the range of 0.150 to 0.700 mol / L, the iron content in the plating film is in the range of 15.0 to 30.0 mass percent concentration. A plating film could be obtained. When the hydroxy acid concentration is in the range of 0.170 to 0.650 mol / L, a shiny plating film can be obtained. Furthermore, when the hydroxy acid concentration is in the range of 0.200 to 0.500 mol / L, a plating film having gloss and no color unevenness could be obtained.

<Example 2>
In this example, the influence of the nitrilotriacetic acid concentration in the plating solution on the appearance of the plating film and the iron content in the plating film was examined.

  First, samples 2A to 2L were prepared as plating solutions having different concentrations of nitrilotriacetic acid. Here, the same compound as that used in Example 1 was used as the compound used for the preparation of the plating solution. Next, a film was formed by the same method as described in Example 1, and the plating appearance and the iron content in the plated film were examined by the same method as in Example 1. The results are shown in Table 2.

  As shown in Table 2, when the nitrilotriacetic acid concentration is in the range of 0.035 to 0.060 mol / L, the iron content in the plating film is in the range of 15.0 to 30.0 mass percent concentration. A certain plating film could be obtained. When the nitrilotriacetic acid concentration is in the range of 0.040 to 0.055 mol / L, a bright plating film can be obtained. Furthermore, when the nitrilotriacetic acid concentration is in the range of 0.045 to 0.053 mol / L, a plating film having gloss and no color unevenness could be obtained.

<Example 3>
In this example, the influence of the iron concentration in the plating solution on the appearance of the plating film and the iron content in the plating film was examined.

  First, samples 3A to 3M were prepared as plating solutions having different iron concentrations. Here, the same compound as that used in Example 1 was used as the compound used for the preparation of the plating solution. Next, a film was formed by the same method as described in Example 1, and the plating appearance and the iron content in the plated film were examined by the same method as in Example 1. The results are shown in Table 3.

  As shown in Table 3, when the iron concentration is in the range of 0.077 to 0.120 mol / L, the iron content in the plating film is in the range of 15.0 to 30.0 mass percent concentration. A film could be obtained. When the iron concentration is in the range of 0.080 to 0.115 mol / L, a glossy plating film can be obtained. Furthermore, when the iron concentration was in the range of 0.085 to 0.100 mol / L, a plating film having gloss and no color unevenness could be obtained.

<Example 4>
In this example, the influence of the tin concentration in the plating solution on the appearance of the plating film and the iron content in the plating film was examined.

  First, samples 4A to 4L were prepared as plating solutions having different tin concentrations. Here, the same compound as that used in Example 1 was used as the compound used for the preparation of the plating solution. Next, a film was formed by the same method as described in Example 1, and the plating appearance and the iron content in the plated film were examined by the same method as in Example 1. The results are shown in Table 4.

  As shown in Table 4, when the tin concentration is in the range of 0.040 to 0.070 mol / L, the iron content in the plating film is in the range of 15.0 to 30.0 mass percent concentration. A film could be obtained. When the tin concentration is in the range of 0.045 to 0.063 mol / L, a shiny plating film can be obtained. Furthermore, when the tin concentration is in the range of 0.050 to 0.060 mol / L, a plating film having gloss and no color unevenness could be obtained.

<Example 5>
In this example, the nickel-free plating solution of the prior art was used for plating treatment at a high current density, and the appearance of the plating film was examined.

  Samples 5A to 5D were prepared as conventional binary alloy plating solutions of tin and iron. Tin sulfate was used as the tin source, and ferrous sulfate heptahydrate was used as the iron source. As the organic acid or a salt thereof, sodium gluconate or a combination of sodium gluconate and ethylenediaminetetraacetic acid (EDTA) was used. Further, polyethylene glycol was used as a brightener. The average molecular weight of polyethylene glycol was 1000. Table 5 below summarizes the compositions of Samples 5A to 5D.

Next, using each of samples 5A to 5D, to form a plated film on the surface of the cathode by ^{13A / dm 2, 18A / dm} 2 , and electroplating at a current density of 25A / dm ^2. These electrodepositions were performed under the conditions shown in Table 5.

  With respect to the plating film formed as described above, the appearance of plating was examined in the same manner as in Example 1.

  As shown in Table 5, when Samples 5A to 5D were used, no matter which value the current density was set, the plating film was rough and blackened, and gloss plating could not be obtained.

  The invention described in the original claims is appended below.
[1]
  0.150 to 0.700 mol / L of a hydroxy acid or a salt thereof,
  0.035 to 0.060 mol / L of nitrilotriacetic acid or a salt thereof,
  0.077 to 0.120 mol / L of iron;
  0.040 to 0.070 mol / L of tin
Nickel-free plating solution containing
[2]
  0.170 to 0.650 mol / L hydroxy acid or a salt thereof;
  0.040 to 0.055 mol / L nitrilotriacetic acid or a salt thereof;
  0.080 to 0.115 mol / L of iron;
  0.045 to 0.063 mol / L tin and
Nickel-free plating solution containing
[3]
  Using the plating solution according to [1] or [2], 6.0 to 30 A / dm ² A plating film forming method including electroplating under a current density of 2 to form a binary alloy plating film of tin and iron.
[4]
  The method for forming a plating film according to [3], further comprising forming a tin plating film on the plating film.
[5]
  The manufacturing method of the electronic component including forming a plating film by the formation method of the plating film as described in [3] or [4].

Claims (5)

A nickel-free plating solution for forming a binary alloy plating film of tin and iron,
0.150 to 0.700 mol / L of a hydroxy acid or a salt thereof,
0.035 to 0.060 mol / L of nitrilotriacetic acid or a salt thereof,
0.077 to 0.120 mol / L of iron;
A nickel-free plating solution containing 0.040 to 0.070 mol / L of tin. A nickel-free plating solution for forming a binary alloy plating film of tin and iron,
0.170 to 0.650 mol / L hydroxy acid or a salt thereof;
0.040 to 0.055 mol / L nitrilotriacetic acid or a salt thereof;
0.080 to 0.115 mol / L of iron;
A nickel-free plating solution containing 0.045 to 0.063 mol / L of tin. Plating including forming a binary alloy plating film of tin and iron by performing electroplating using the plating solution according to claim 1 or 2 under a current density of 6.0 to 30 A / dm ² . Method for forming a film.   The method for forming a plating film according to claim 3, further comprising forming a tin plating film on the plating film.   The manufacturing method of the electronic component including forming a plating film by the formation method of the plating film of Claim 3 or 4.