JP3533880B2 - Electroless nickel plating solution and electroless nickel plating method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electroless nickel plating solution which is particularly suitable for manufacturing a hard disk and an electroless nickel plating method using the same.

[0002]

2. Description of the Related Art Conventionally, the problems to be solved by the invention
In manufacturing a hard disk, an electroless nickel plating film (hereinafter referred to as an electroless Ni-P film or simply Ni film) using hypophosphorous acid or its salt as a reducing agent is used as a base plating on an aluminum or aluminum alloy substrate (Al or Al alloy substrate). -P film) is formed.
As the step of forming the Ni-P film, Al or Al
After machining the alloy substrate, zinc substitution treatment is performed, and then electroless nickel plating is performed.

After the Ni-P film is formed in this manner, the surface thereof is mirror-polished to form a magnetic film, then an appropriate protective film, and if necessary, a lubricating layer, A hard disk (magnetic disk) is obtained.

Here, in order to increase the density of the hard disk device, it is effective to reduce the flying height of the recording / reproducing head, and the flying height of 0.03 μm is currently in practical use. In order to reduce the head flying height, polishing for smoothing the surface of the base plating film, that is, the Ni-P film (maximum roughness Rmax 100 to 200Å,
The center line average roughness Ra10 to 20Å) is required. However, in this case, if the polishing surface is so smooth, the head will stick to the substrate when the hard disk drive is stopped, and it will be difficult to re-float. As a countermeasure against this, after the above-mentioned smooth polishing, a process called a texture process for imparting a fine roughness (Ra50 to 100Å) controlled in a certain direction of the polished surface is performed.

However, in the manufacturing process of the above-mentioned hard disk, conventionally, much labor has been required mainly for smooth polishing of the Ni-P coating.

[0006] This is because when an electroless Ni-P film is formed on an Al or Al alloy substrate (hereinafter referred to as an Al substrate) to have a thickness of 10 to 20 µm, it has a bump shape or a hemispherical convex shape. This is because many nodules having a height of 0.1 to 0.7 μm and a diameter of 5 to 40 μm are generated.

Such a nodule is naturally not preferable for forming a magnetic film in the next step in the manufacture of a hard disk, and therefore, it is necessary to remove the nodule at the same time when performing surface smooth polishing after forming a Ni-P film. Therefore, it takes a considerably long time to remove the nodules and perform polishing work.

From this point of view, the applicant of the present invention has proposed an electroless nickel plating method which can reduce the generation of nodules as much as possible, particularly a pretreatment method for electroless nickel plating (Japanese Patent Laid-Open No. Hei. No. 230664).

However, it is desired that the electroless nickel plating solution itself be capable of forming a smooth electroless nickel plating film with a small amount of nodules. In particular, the surface roughness after plating of a Ni-P / Al-based substrate using a conventional electroless nickel plating solution is Ra100 Å or more, and there are still many nodules, and in order to support MR heads, Ra10 Å or less is required. Two-stage or three-stage polishing must be performed, which results in poor yield and high cost. Therefore, from such a point, there is a demand for an electroless nickel plating solution that provides a smooth plating film.

The present invention has been made in order to meet the above-mentioned demands, and an object of the present invention is to provide an electroless nickel plating solution which gives a smooth Ni-P coating and an electroless nickel plating method using the same.

[0011]

MEANS FOR SOLVING THE PROBLEMS AND BEST MODE FOR CARRYING OUT THE INVENTION As a result of intensive studies to achieve the above-mentioned object, the present inventor has found that nickel ions, their complexing agents, and hypophosphite ions One or two or more selected from thiosulfates, thiocyanates, thioureas and thioacetates, and one of water-soluble molybdates and tungstates for the electroless nickel plating solution as the main component. Or, by adding together with two or more kinds, smoothness and less nodules can be achieved.
When an i-P / Al-based substrate is manufactured, it satisfies all the characteristics required for the current Ni-P / Al-based substrate, such as a saturation magnetic flux density of 4 Gauss or less after heat treatment at 290 ° C for 2 hours, and has a surface Roughness Ra is usually 150-
The inventors have found that a surface having a smoothness of 100 Å or less, and 60 Å or less under the preferable conditions, while having 250 Å, and a nodule number of about 1/10 are obtained, and thus the present invention has been accomplished.

Accordingly, the present invention provides an electroless nickel plating solution containing nickel ions, a complexing agent therefor, and hypophosphite ions.
An electroless nickel plating solution containing one or more selected from thiourea and thioacetate in combination with a water-soluble molybdate and / or tungstate, and this plating. Immerse the object to be plated in the liquid,
Provided is an electroless nickel plating method, which comprises forming an electroless nickel plating film on the surface of an object to be plated.

The present invention will be described in more detail below.
The electroless nickel plating solution according to the present invention contains nickel ions, its complexing agent, and hypophosphite ions as main components.

Here, as the source of nickel ions, a water-soluble nickel salt such as nickel sulfate can be mentioned, and the nickel ion concentration in the plating solution is 2 to 10 g /
It is preferably 1 and particularly preferably 4 to 8 g / l.

As the complexing agent for nickel ions, conventionally known ones can be used, and examples thereof include monocarboxylic acids such as glycolic acid, lactic acid, gluconic acid and propionic acid, tartaric acid, malic acid and succinic acid. Tricarboxylic acids such as dicarboxylic acid and citric acid and carboxylic acids such as sodium salts, potassium salts and ammonium salts thereof are used alone or in combination of two or more. The concentration is 1 to 7 mol, especially 2 to 1 mol, of the water-soluble nickel salt.
It is preferably 6 mol.

The hypophosphite ion is supplied by sodium hypophosphite or the like and its concentration is 10 to 50 g / l,
It is particularly preferably 20 to 40 g / l.

A water-soluble sulfur-based additive and a water-soluble molybdate and / or tungstate are used in combination with the electroless nickel plating solution of the present invention.

Here, examples of the sulfur-based additive include thiosulfates such as sodium thiosulfate, potassium thiosulfate and ammonium thiosulfate, thiocyanates such as sodium thiocyanate, potassium thiocyanate and ammonium thiocyanate, thiourea and thiol. Acetate or the like can be used,
These can be used alone or in combination of two or more.

The amount of the above-mentioned sulfur-based additive added is 0.000.
The amount is preferably 1 to 1 mg / l, and particularly preferably 0.005 to 0.5 mg / l. If the amount is too small, the plating film has no smoothing effect, and if the amount is too large, the heat-resistant non-magnetic properties may be adversely affected.

On the other hand, examples of the molybdate include sodium molybdate, potassium molybdate, ammonium molybdate, and the like, examples of tungstate include sodium tungstate, potassium tungstate, ammonium tungstate, and the like. Can be used alone or in combination of two or more.
The addition amount is 0.01 to 5 g / l, particularly 0.05 to 1 g
/ L is preferable, and if it is too small, there is no effect on the smoothness of the plating film and the heat-resistant non-magnetic properties, and if it is too large, the precipitation rate decreases significantly.

The plating solution of the present invention may further contain a stabilizer, a pH adjusting agent and the like, if necessary.

The pH of the plating solution of the present invention can be adjusted to 3 to 10. Therefore, the plating solution of the present invention can be prepared in any of an acidic bath, a neutral bath and an alkaline bath, but in the production of a hard disk. Prepared as an acidic electroless nickel plating solution having a pH of 3 to 7, particularly 4 to 6, and a phosphorus content of 9 to 13%
It is preferable to form a Ni-P film (% by weight, the same applies hereinafter).

When electroless nickel plating is performed using the electroless nickel plating solution of the present invention, a conventional method of immersing an object to be plated in this plating solution may be adopted.

In this case, the object to be plated may be any as long as it is capable of electroless nickel plating, but the present invention is particularly preferably used for an Al-based substrate for a hard disk. This Al-based substrate for a hard disk can be immersed in the plating solution of the present invention after being subjected to zinc substitution treatment according to a conventional method.
After the zinc substitution treatment by the method described in JP-A No. 64, electroless nickel plating can be performed.

When electroless nickel plating is performed using the plating solution of the present invention, the plating temperature is 75 to 95 ° C.
In particular, it is preferably set to 80 to 90 ° C.

Further, the Ni-P / for the above hard disk
When an Al-based substrate is obtained by using the plating solution of the present invention, the thickness of the plating film is preferably 1 to 30 μm, particularly 5 to 15 μm. In this case, the surface roughness of the obtained plating film is usually 100 Å or less, especially 60 Å or less, and the number of nodules is also very small. Therefore, the subsequent polishing step is changed from the current 2 or 3 steps to 1 step. It becomes possible.

[0027]

EXAMPLES The present invention will be specifically described below by showing Examples and Comparative Examples, but the present invention is not limited to the following Examples.

[Examples, Comparative Examples] An aluminum alloy plate (A5086) was subjected to electroless nickel plating having the following composition in the following steps. Plating process Degreasing → Etching → First pickling → First zinc substitution → Second pickling → Second zinc substitution → Electroless nickel plating (water washing is included in each step) Electroless nickel plating composition and plating conditions Sulfuric acid Nickel 6 g / l (as Ni ²⁺ ) Malic acid 18 g / l Succinic acid 16 g / l Sodium hypophosphite 30 g / l Sodium thiosulfate Amount shown in Table 1 Sodium thiocyanate 〃 Sodium molybdate 〃 Sodium tungstate 〃 Stabilizer Trace amount pH 4.4 Plating temperature 88 ° C Plating time 120 minutes Plating film thickness 14 μm Phosphorus content in plating film 11.5%

Next, the surface roughness R of the obtained plating film
a, Nodule number, and saturation magnetic flux density Bs after heat treatment at 290 ° C. for 2 hours were measured. The results are shown in Table 1.

[0030]

[Table 1]

[0031]

According to the present invention, an electroless nickel plating film having a smooth surface and less nodules can be obtained.

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP 5-230664 (JP, A) JP 8-232073 (JP, A) JP 8-269726 (JP, A) JP 5- 331654 (JP, A) JP 62-246145 (JP, A) JP 5-266457 (JP, A) JP 63-62882 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C23C 18/36

Claims (4)

(57) [Claims] 1. An electroless nickel plating solution containing nickel ions, a complexing agent therefor, and hypophosphite ions, which is selected from thiosulfates, thiocyanates, thioureas and thioacetates. Alternatively, an electroless nickel plating solution comprising a combination of two or more kinds and a water-soluble molybdate and / or tungstate. 2. The plating solution according to claim 1, which is for plating an aluminum alloy-based substrate of a hard disk. 3. An electroless nickel plating method, which comprises immersing an object to be plated in the electroless nickel plating solution according to claim 1 to form an electroless nickel plating film on the surface of the object to be plated. 4. The plating method according to claim 3, wherein the object to be plated is an aluminum substrate for a hard disk to which zinc substitution has been applied.