JPS6021236B2 - Manufacturing method of high recording density magnetic disk - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION In manufacturing a high recording density magnetic disk, the present invention
The present invention relates to a plating method for forming a defect-free base plating film as a base for a magnetic plating film.

Magnetic disks used in external storage devices for computers are generally made of aluminum alloy material as a recording medium.
-A coated disk coated with magnetic iron oxide such as Fe203 is used.

However, with this type of disk, there is a limit to how thin the film thickness of the recording medium can be made without impairing the magnetic properties or its uniformity (at least about 0.5 m), so the recording density of the magnetic disk is also 10,000 bits/m. The limit is 1 inch, and it is difficult to increase it any higher. On the other hand, Ni-C
When a magnetic plating film such as O1P is used, it is possible to form a thinner recording medium (0.05 to 0.1 French m) with excellent magnetic properties and uniformity. Therefore, when a magnetic plated film is used as a recording medium, the recording density is 20,000~
In principle, a magnetic disk with an extremely high recording density of 2,500 sailboats/inch is possible. However, magnetic disks that use a nutritious plated film as a recording medium (hereinafter referred to as plated disks) have better thermal stability than coated disks, and have a flatter, smoother, and defect-free base surface. is necessary. In the magnetic disk after coating, the polished aluminum alloy substrate surface is used as a base and a recording medium is coated thereon as it is, but this is not suitable as a base for a plated disk. This is because magnetic plating cannot be directly applied to the surface of an aluminum alloy substrate. For this purpose, a treated film that can be electroplated is formed on the surface of the aluminum alloy substrate in advance, a relatively hard non-magnetic base plating film is formed thereon, and then this base plating film is polished.
It is necessary to create a base surface that satisfies the required characteristics. Conventionally, industrial nickel-phosphorus plating and electrolytic nickel-phosphorus plating have been used as the base plating film, but these plating films have problems with thermal stability and cannot be used for plating discs. This was a major obstacle to achieving higher recording densities. This is because plated disks with high green density require heat treatment at 300°C or higher in order to stabilize the magnetic properties of the medium and to form a thin oxide protective film on the surface of the magnetic plated film. This is because the above-mentioned nickel-phosphorous plated film changes into a ferromagnetic material by heat treatment. Therefore, the inventor discovered that an electrical steel-tin alloy plating film was suitable as an alternative non-magnetic base plating film with excellent thermal stability.
109978). However, when a base plating film is formed in a conventional copper-tin plating bath, it is not possible to prevent the formation of dents (hereinafter referred to as bits) with a diameter of 10 m◇ to 150 mJ on the plating surface. Ta. For this reason, there are many defects of 5rm0 or more on the polished surface after mechanical polishing, and since these affect the magnetic plating film, there is a so-called bit drop problem in which signals are not recorded in terms of recording characteristics. In other words, such defects on the underlying surface have been a serious hindrance to the production of high-density, warm-up disks. SUMMARY OF THE INVENTION An object of the present invention is to provide a method for forming a defect-free underplating film for producing a plated disk with high recording density, eliminating the drawbacks of the prior art.

Furthermore, specifically, it is an object of the present invention to provide a method for forming a copper-tin-plated film with a copper-tin-plated layer that is effective in preventing the occurrence of bits on the surface of the copper-tin-plated film. In order to achieve the above object, the inventor has developed a method for producing electrical steel with cuprous cyanide 2.
0-50 evening/final, potassium stannate (trihydrate) 30-55
Tano〆, Potassium cyanide 40-100 evenings/night, Potassium hydroxide 10-30 evenings/The general formula R○ (CQC day 20) nH (where R is CmH2+p, We found that adding a surfactant (m is an integer of 12 to 18, n is an integer of 20 to 50, and p is 1 or -1) is extremely effective for bit generation, and did. On the base surface of the plating disk obtained by mechanically polishing the copper-tin base plating film formed with the above plating grade, almost no defects of 5rm◇ or more were observed, and no defects of 5 mJ or more were observed. It has been found that it is possible to easily produce discs with no plating. The present invention will be explained in detail with reference to Examples below.

Example 1 FIG. 1 is a diagram showing the layer structure of a plated disk.

In FIG. 1, a magnetic disk base 1 is a disk having a flat surface, an outer diameter of 356 mm, an inner diameter of 168 mm, and a thickness of 2 legs, manufactured by machining a corrosion-resistant aluminum alloy material.
A treated film 2 having a thickness of 2 mm to 5 rm was formed on both surfaces of this disk substrate by zinc substitution treatment and cyanide steel plating. Next, a copper-tin alloy base plating film 3 having a thickness of 30 rm and a copper content of 90% was formed on the treated film 2 according to the bath composition and plating conditions shown in the table.

In the table, the A rating is the one conventionally used as a base plating rating, the B bath is the bath of the present invention, and the C rating is a polyoxyethylene alcohol ether-based surfactant as a bit generation prevention agent. is added to the B rating. Note that the copper-tin undercoat plating is performed using a plating method to obtain a uniform plating thickness table, which is characterized by using a perforated jammer plate and an auxiliary cathode as described in Samurai Koko Sho 45-9447. Inside,
This was done while rotating the disk base.

One side of the disc (area 7.7 dm
) The number of bits (size 101 m◇ or more) was about 50 on average in the secondary A bath, but on average 10 in the B bath of the present invention, and 3 on average in the C grade. decreased significantly.

Next, the copper-tin alloy base plating film obtained by these three types of plating methods was mechanically polished to obtain a 5R
The relationship between the number of defects larger than m0 and the amount of polishing is shown in FIG. Incidentally, FIG. 2 shows representative examples of disks obtained with each plating method. The base plated film of the disk obtained by plating with the A rating of the secondary has a large number of defects even after polishing, as shown in Figure 2 6, and in order to obtain a defect-free base surface, it is necessary to polish more than 20 peaks. The yield for producing plated disks with defect-free substrates was less than 5%. On the other hand, the base plated film of the disk obtained by plating with the B method of the present invention has extremely few defects as shown in FIG. It has been found that the yield of manufacturing disks with a ground surface can be improved to about 70%. In addition, the base plating film of the disc obtained by plating with the C rating of the present invention has even fewer defects as shown in FIG. It has been found that the yield of disk manufacturing can be improved to about 80%.

As described above, by forming the base plating edge of a plated disk using the electrolytic copper-tin plating plate of the present invention,
It has been found that a defect-free surface can be obtained with a much smaller amount of polishing than with the secondary method. For this purpose, a predetermined magnetic plating film 4 is formed on the copper-tin alloy base plating film 3,
Furthermore, by forming the protective film 5 thereon, it has become possible to manufacture a magnetic disk with high recording density and no bit loss. Example 2 In place of B general shown in Table 1, cuprous cyanide 20 to 50 minutes/so, potassium stannate (trihydrate)
30-55 evenings/evening, potassium cyanide 40-100 evenings/
Potassium hydroxide for 10 to 30 min/Various electrical steels having the same composition -Various steels obtained by plating in a tin plating bath-
The composition of the tin alloy base plating film 3 is 80 to 95% copper, but the properties of the copper-tin alloy base plating film are almost the same as those obtained in B bath, and the number of defects is also the same as in B bath. It was found that it can be used to manufacture plated disks with a high recording density.

In addition, the general formula R
0(CQCH20)nH (where R is CmH2h10p,
m is an integer from 12 to 18, n is an integer from 20 to 50, p is 1
Or a steel-tin alloy obtained by plating in a matting bath to which a polyoxyethylene alcohol ether surfactant represented by -1) is added in a range of 0.05 m/s to 5 m/m. It was found that the number of bits on the underplated surface was smaller than that obtained without the addition of the surfactant, and that a plated disk with a high recording density could be produced at a higher rate. The reason why the defects of the steel-tin alloy base-plated waist surface obtained by plating with the copper-tin plating method of the present invention is much less than that of the conventional one is that the cathode current efficiency of plating is lower than that of the conventional one. This is considered to be because hydrogen bubbles, which adhere to the cathode surface and interfere with precipitation and cause bit generation, are hardly generated because the hydrogen content is extremely high at 99% or more, compared to 90% or less.

As described above, the amount of polishing can be reduced compared to the conventional electric steel-tin plating bath by forming the base plating film on the plating disk using the electric steel-tin plating bath of the present invention. The polishing cost has been significantly reduced from 20 mm or more to 8 French m or less, and the manufacturing yield of plated discs with a defect-free base surface of 51 mm or more has been increased from the conventional 5% or less to 70 mm. % or more. This has made it possible to manufacture plated disks with high recording density, which was previously impossible.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the layer structure of a plating disk using a nutritious plating film as a recording medium, and FIG. 2 is a diagram showing the effect of the plating bath of the present invention on reducing defects. 1... Magnetic disk substrate, 2... Treated film, 3
......Copper-tin alloy base plating film, 4...Nutritious plating film, 5...Protective film, 6...Steel obtained by plating with conventional grade. Lines 7 and 8 represent the relationship between the number of defects on the base surface after polishing the tin base plating film and the amount of polishing.
A line showing the relationship between the number of defects on the base surface after polishing of the steel-tin base plating film obtained by plating with the grade of the present invention and the amount of polishing. Ochozu soup Z diagram

Claims (1)

[Claims] 1. After forming a film capable of electroplating on the surface of a magnetic disk substrate, this surface is coated with 20 to 50% cuprous cyanide.
g/l, potassium stannate (trihydrate) 30-55 g/l,
A copper-tin alloy plating film is formed by electroplating using an electrolytic copper-tin alloy plating bath having a composition of 40 to 100 g/l of potassium cyanide and 10 to 30 g/l of potassium hydroxide. - High recording performance characterized by polishing the tin alloy plated film to make a flat and smooth surface, forming a magnetic film on this surface by plating, and forming a protective film on this magnetic film. Method for manufacturing density magnetic disks. 2 After forming a film that can be electroplated on the surface of the magnetic disk substrate, apply 20 to 50% cuprous cyanide to this surface.
g/l, potassium stannate (trihydrate) 30-50 g/l,
Potassium cyanide 40-100g/l, potassium hydroxide 10-30g/l, general formula RO(CH_2CH_2O)
nH (where R is CmH2m+p, n is 12-1
8 integer, n is an integer from 20 to 50, p is 1 or -1)
A copper-tin alloy plating film is formed by electroplating using an electrolytic copper-tin alloy plating bath to which a surfactant represented by is added, and this copper-tin alloy plating film is polished. 1. A method of manufacturing a high recording density magnetic disk, which comprises forming a flat and smooth surface, forming a magnetic film on this surface by plating, and forming a protective film on the magnetic film.