JP3202072B2 - Electric aluminum plating method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for efficiently electroplating aluminum using a composition containing aluminum.

[0002]

2. Description of the Related Art Aluminum electroplating is difficult to perform in an aqueous plating bath because aluminum has a high affinity for oxygen and has a lower potential than hydrogen.
For this reason, electroplating of aluminum has conventionally been studied in a non-aqueous solution-based plating bath, particularly in an organic solvent-based plating bath.

[0003] As an organic solvent-based plating bath, Al is used.
Representative examples are those in which Cl ₃ and LiAlH ₄ or LiH are dissolved in ether, and those in which AlCl ₃ and LiAlH ₄ are dissolved in tetrahydrofuran (for example,
D. E. FIG. Couch et al. Electroche
m. , 99 (6), 234). However, since these plating baths all contain very active LiAlH ₄ or LiH in the bath, if oxygen or moisture is present, they react with them and decompose to lower the current efficiency, There is a disadvantage that the life is shortened. In addition, there is a problem that the boiling point of the organic solvent used is low and the risk of explosion and combustion is high.

Further, as another example, a plating bath in which triethylaluminum and NaF are dissolved in toluene has been proposed (R. Schuentrunk, Z. Wer.).
kstofftech. , Vol. 12, p. 190). However, also in this case, there is a very problem in handling highly dangerous triethylaluminum, and it is considered that practical use is difficult.

Recently, Japanese Patent Application Laid-Open No. Sho 62-70592 discloses
JP, JP-A 1-227788, JP-A 1-2
No. 72790 discloses an electroplating method using a low melting point composition comprising an onium halide and an aluminum halide as a plating bath. However, even when such a plating bath is used, the plating state changes greatly due to the incorporation of moisture, so that a good plating film cannot always be obtained even if other plating conditions are constant.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to obtain a good and uniform quality aluminum plating film by using a plating bath composed of an onium halide and an aluminum halide even when plating conditions are fixed. An object of the present invention is to provide an electric aluminum plating method which can be easily used as a practical application technique.

[0007]

According to the present invention, a low-melting composition obtained by mixing and melting an onium halide and an aluminum halide is used as a plating bath, and the amount of water in the bath is adjusted to 2%.
This is an electroaluminum plating method characterized in that aluminum is deposited on the cathode while maintaining the content at not more than wt%.

Hereinafter, the present invention will be described in detail. Examples of the onium halide used in the present invention include quaternary ammonium salts such as tetraethylammonium bromide and trimethylethylammonium chloride, pyridinium salts such as butylpyridinium chloride, imidazolium salts such as 1-ethyl-3-methylimidazolium chloride, and ethyl. Examples thereof include phosphonium salts such as tributylphosphonium bromide.

The aluminum halide used in the present invention is a compound represented by AlX ₃ (X represents a halogen atom), specifically, AlF ₃ , AlCl ₃ , AlBr
₃ and AlI ₃ .

The compounding ratio of the aluminum halide in the plating bath used in the present invention is preferably 20 to 80 mol%.
The compounding ratio of the onium halide is preferably from 80 to 20 mol%.

According to the present invention, the water content in the plating bath is set to 2 watts.
t% or less, preferably 0.1 wt% or more, 1.5 wt%
% Of aluminum is deposited on the cathode while maintaining the concentration at not more than 10%. When the water content exceeds 2 wt%, a good white plated film cannot be obtained. When the content exceeds 1.5 wt%, the range of the current density at which a good plating film can be obtained may be narrowed. Even when the content is less than 0.1 wt%, the effect corresponding to the improvement may not be recognized.

As a method of maintaining the water content in the bath at 2 wt% or less, a method of mixing a plating solution with a small water content while quantifying the water content in the bath can be used in addition to replacing with a new solution. . As a method of quantifying the amount of water, a quantification method of measuring the O—H stretching vibration wave frequency near 3360 cm ⁻¹ using an infrared spectrophotometer is desirable. In the Karl Fischer method, which is a general simple moisture determination method, it is difficult to detect the moisture mixed in the plating solution because it does not exist as water.

The measuring cell used for the infrared spectrophotometer is Ca
F ₂ , KRS-5 (TlI, TlBr mixture), As ₂
A liquid closed cell made of a material having low solubility in water such as Se ₃ and Ge is preferable.

The plating conditions are as follows: bath temperature 0 to 300 ° C., current density 0.01 to 50 A /
dm ² is preferable, and uniform plating can be performed with good current efficiency. If the bath temperature is too low, uniform plating is not obtained, and if the bath temperature is too high or the current density is too high, onium cations are decomposed, the plating layer becomes non-uniform, and the current efficiency is lowered, which is not preferable. .

When a strip or the like is to be plated continuously continuously, it is necessary to supply Al ions to the plating bath to maintain the Al ion concentration in the bath within a certain range. In this case, the anode is connected to a soluble aluminum electrode. Then, Al ions are automatically replenished in accordance with the amount of energization, and the Al ion concentration can be kept within a certain range regardless of the replenishment of the aluminum halide.

For efficient plating at a low temperature, it is effective to add an organic solvent to the plating bath in order to reduce the viscosity of the plating bath. As organic solvents, benzene,
Inert solvents such as toluene, xylene, and chlorobenzene are preferred, and the added amount is 5 to 95 vol%. It is also effective to add a halide of an alkali metal or an alkaline earth metal to increase the conductivity of the plating bath or to make the aluminum plating layer uniform. Examples of the alkali metal or alkaline earth metal halide include LiCl, NaCl, NaF, and Ca.
Cl _{2 and the} like can be mentioned, and the addition amount is 0.1 to 30 mol%.

[0017]

EXAMPLE A plating solution used in the following Example 1 and Comparative Example 1 was prepared as follows. A plating solution composed of 33 mol% of 1-ethyl-3-methylimidazolium chloride synthesized under a dry nitrogen atmosphere and 67 mol% of aluminum trichloride, and 1.5 g of water, 5.0 g of water,
8.0 g or 10.0 g was further added to prepare a 500 g plating solution.

Next, the amount of water in the plating solution was determined as As ₂
Infrared spectrophotometer using Se ₃ liquid sealed cell
It was determined by measuring the infrared absorption intensity appearing at 360 cm -1. Table 1 shows the results. In addition, it was confirmed that the relationship between the infrared absorption intensity and the water content showed good linearity.
The results are shown in FIG.

[0019]

[Table 1]

Example 1 Of the plating solutions prepared, the water content was 0.2 wt% (no water added), 0.5 wt% (1.5 g water added), 1.2 wt%
% (Addition of 5.0 g of water) and 1.8 wt% (addition of 8.0 g of water) were used to obtain electric aluminum plating. As a result, a good white plated film was obtained using any of the plating solutions. FIG. 2 shows a scanning electron micrograph of a cross section of the plating obtained using a plating solution having a water content of 0.5 wt%.

Further, using these plating solutions, a bath solution 60
Table 2 shows the results obtained by conducting a Hull cell test at 0 ° C. to determine a current density range in which a good white plated film can be obtained.

Comparative Example 1 The prepared plating solution had a water content of 2.2 wt% (water 1
A Hull cell test was performed using a plating solution (0.0 g added), but only black plating was obtained over the entire surface.

Example 2 A plating solution 20 having a water content of 2.2 wt% used in Comparative Example 1
The plating solution was prepared by mixing 200 g of the plating solution having a water content of 0.2 wt% (no water added) used in Example 1 with 0 g. When the amount of water in the plating solution was measured by an infrared spectrophotometer, it was 0.6 wt% (infrared absorption intensity: 0.38
7). A Hull cell test was performed to determine a current density range in which a good white plated film was obtained. Table 2 shows the results.

[0024]

[Table 2]

[0025]

According to the method of the present invention, it is possible to obtain an aluminum plating film having good productivity and always good plating state in a plating bath composed of an onium halide and an aluminum halide.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the amount of water in a plating bath and the infrared absorption intensity.

FIG. 2 is a scanning electron micrograph showing a plating cross section obtained by the method of the present invention.

──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Asato Kominato 8-3-1 Chuo, Ami-cho, Inashiki-gun, Ibaraki Pref. Mitsubishi Tsuka Corporation Tsukuba Research Laboratory (56) References JP-A-4-254600 (JP, A) JP-A-62-70592 (JP, A) JP-A-1-272788 (JP, A) JP-A-1-272790 (JP, A) "Applied spectros" copy "Vol. 32, No. 4 (1978), p. 362-366 (58) Field surveyed (Int. Cl. ⁷ , DB name) C25D 3/66 C25D 21/14

Claims (2)

(57) [Claims] 1. A low melting point composition obtained by mixing and melting an onium halide and an aluminum halide is used as a plating bath, and a composition having a viscosity of about 3360 cm ^-1 is measured using an infrared spectrophotometer .
Measure the OH stretching vibration wave number to determine the water content in the plating bath
, And depositing aluminum on the cathode while maintaining the water content at 2 wt% or less. 2. The composition according to claim 1, wherein the low melting point composition comprises 20 to 80 mol% of aluminum halide and onium halide 8
The electroaluminum plating method according to claim 1, comprising 0 to 20 mol%.