JPH06212440A - Method for electroless plating on nonconductive base - Google Patents

Abstract

PURPOSE:To significantly improve the surface appearance of an electroless plating film when a nonconductive base is subjected to sensitizing treatment and activating treatment for electroless plating by irradiating the surface with ultrasonic waves after the activating treatment. CONSTITUTION:A nonconductive base (such as glass) is subjected to sensitizing treatment with a tin (II) chloride soln. or the like, then to activating treatment with palladium salt soln., and then to electroless plating in a nickel salt bath. After the activating treatment, the base body is washed while applying irradiation with ultrasonic waves. The ultrasonic waves have 20-1600KHz frequency and 0.5-10W/cm<2> power density depending on the size of the tank, and the washing time is about 15sec. to 2min. Thereby, fine projections in the electroless plating film can be decreased and the obtd. film has a smooth surface with small surface roughness.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for electroless plating on a non-conductive substrate, which is free from abnormal grain growth.
The present invention relates to a method for obtaining a uniform and extremely smooth electroless plating film surface.

[0002]

2. Description of the Related Art Conventionally, when performing various electroless plating on a non-conductive substrate, it is known to adsorb a catalyst nucleus for advancing the electroless plating reaction on the surface of the non-conductive substrate. . Then, as a pretreatment for that purpose, a method of degreasing, pickling, sensitizing (sensitizing) the non-conductive substrate, and then activating (activating) it has been used.

However, in the method of forming such a catalyst nucleus, since the catalyst nucleus of palladium or the like reduced and deposited on the non-conductive matrix is microscopically nonuniform, coarse particles are formed on the non-conductive matrix. As a result, there is a problem that minute projections are generated in the formed electroless plating film and the surface roughness is increased.

[0004]

The electroless plating treatment on the non-conductive substrate can be applied to the case of forming the underlayer of the magnetic disk, for example. With the demand for higher density in magnetic disks, it is required to reduce the flying height of the head from the magnetic disk during recording and reproduction. Therefore, the surface of the magnetic disk should not have protrusions larger than the flying height of the head, and the surface roughness is required to be small.

However, in the method using the above-mentioned catalyst nucleus, fine projections are formed on the electroless plating film and the surface roughness becomes large, so that a good magnetic disk cannot be obtained. Therefore, for the purpose of removing such minute protrusions, a method of polishing and smoothing the surface is adopted.
However, the polishing process after the electroless plating requires a lot of labor, and a process capable of simplifying the polishing process, that is,
A method of forming an electroless plating film having a microscopically uniform surface state without microprojections on the non-conductive substrate has been desired.

[0006]

Means for Solving the Problems As a result of intensive studies to meet the above demands, the present inventors have found that when forming an electroless plating film on a non-conductive substrate, cleaning after completion of activation. It was found that the surface appearance of the obtained electroless plating film is remarkably improved and the number of microscopic protrusions is remarkably reduced by carrying out the process under ultrasonic irradiation, and the present invention has been completed.

That is, the gist of the present invention is, firstly, that in a method of performing electroless plating after activating a non-conductive substrate, cleaning after the activating treatment is performed while irradiating ultrasonic waves. In the electroless plating method on the non-conductive substrate, which is characterized by
In a magnetic disk substrate formed by coating a glass substrate with a metal thin film, the surface roughness Ra of the formed metal thin film is within 1.2 times the surface roughness Ra of the substrate before metal coating. The present invention resides in a substrate for a magnetic disk.

The present invention will be described in detail below. The electroless plating treatment on the non-conductive substrate of the present invention is performed in the order of sensitizing treatment, activating treatment, and then electroless plating. Then, usually, a degreasing step and a pickling step are provided before the sensitizing treatment. A washing step may be provided between the steps, and a drying step may be provided after the washing after the activating treatment.

Degreasing, pickling, sensitizing treatment, activating treatment and electroless plating may be carried out by usual methods, and washing after the activating treatment may be carried out by usual methods other than irradiating ultrasonic waves. I'm fine. The ultrasonic wave irradiation may be performed by arranging the ultrasonic wave vibrator anywhere in the tank. The wavelength of ultrasonic waves is 20 to 1600 KHz
The degree is preferable, and as the frequency becomes higher, it becomes possible to remove agglomerated particles having a small particle size. Further, the output size is preferably about 0.5 to 10 W / cm ^{2 with} respect to the size of the tank.

The cleaning while irradiating with ultrasonic waves may be performed at room temperature, but may be heated if necessary. The cleaning time is 15 seconds or more, more preferably 20 seconds or more,
Even if the cleaning time is extended, the effect of reducing the coarse particles on the non-conductive substrate, that is, the effect of reducing the fine projections of the electroless plating film is saturated, so that the cleaning may be performed for about 2 minutes at the longest.

Further, the non-conductive substrate in the present invention means
Glass, ceramics, plastics, etc. are used, and glass is preferably used for magnetic disk applications. Next, each step will be described. Sensitizing process,
The activating process is a process of providing the non-conductive substrate with a catalytic activity necessary for initiating electroless plating. That is, since the surface of the non-conductive substrate has no catalytic activity, in order to start the electroless plating, a catalytic nucleus of a noble metal such as Au, Pt, Pd, or Ag should be formed on the surface of the non-conductive substrate. is necessary.

In the sensitizing treatment, a metal ion is adsorbed on the surface of the base material by immersing the non-conductive base material in a sensitizer (sensitizing agent) solution.
As a sensitizer solution, S which has been conventionally known
Any solution containing a divalent metal ion composed of n, Ti, Pb, Hg, etc. may be used, and is not particularly limited.
"Metal surface technology" (16 volumes, No. 1, 1965, p.
As described in 26), a liquid containing stannous chloride or stannous sulfate as a main component can be used. Usually, a stannous chloride solution is preferably used, and a method in which an inorganic acid such as hydrochloric acid coexists in order to dissolve stannous chloride in water is also used.

In the present invention, a 1 g to 100 g / l stannous chloride solution is preferably used. The type of sensitizer does not change greatly depending on the type of non-conductive substrate and the type of electroless plating. Then, the immersion of the sensitizer solution of the non-conductive substrate is performed at room temperature to 50 ° C. for 1 to 5 minutes.

The activating treatment is a process of uniformly forming fine metal particles having a strong catalytic activity on the surface of the substrate by the reducing action of the metal ions adsorbed on the substrate by the sensitizing process. The activating process of the present invention is carried out by immersing the non-conductive substrate after the sensitizing process in the activating solution.

The activating solution generally comprises:
An aqueous solution of a noble metal salt such as Pd, Pt, Au, or Ag is used, and of these, an aqueous solution of a palladium salt is preferable. In the present invention, a 0.1 g to 1.0 g / l palladium chloride aqueous solution is preferably used. The cleaning step after the activating treatment is performed for the purpose of removing the activating agent adhering to the surface of the base material. As the cleaning method, running water cleaning, immersion cleaning, etc. are used.
Ion exchange water, ultrapure water, etc. are used.

The electroless plating is generally widely used to impart various functions to the non-conductive substrate, and when electroless nickel plating is performed, the plating solution is usually a water-soluble nickel salt or an organic solution. A known plating bath containing an acid salt (complexing agent) and a reducing agent such as hypophosphorous acid or hypophosphite (sodium hypophosphite) is used. The plating bath may be an acidic bath or an alkaline bath, for example p
The range of H4 to 10 is adopted. Incidentally, in the production of the underlayer of the magnetic disk, an acidic electroless nickel plating bath having a pH of 4 to 6 is usually used to form a Ni-P coating having a phosphorus content of 11 to 12% by weight to a film thickness of about 0.1 to 15 μm. Is being done.

The degreasing step for the non-conductive substrate is a step for cleaning the surface of the substrate, and the conditions are selected according to the material of the substrate by a known method. For example, when a glass substrate is used, an alkaline degreasing liquid is generally preferable, and a potassium hydroxide or sodium hydroxide aqueous solution of about 1 to 30% by weight is particularly preferably used. Further, in order to further enhance the effect of degreasing, it is preferable to carry out under ultrasonic irradiation.

The pickling is for promoting the adsorption of metal ions in the sensitizing treatment in the next step, and plays a role of neutralization when the alkaline degreasing solution in the previous step remains. A sulfuric acid aqueous solution or the like is used as the pickling solution, and a sulfuric acid aqueous solution having a pH of about 2 to 3 is preferably used.
The drying step before electroless plating has the effect of increasing the adhesion strength between the non-conductive base material and the metal fine particles that are the catalyst nuclei, and improving the adhesion between the base material and the plating film, and as a result, there is no microprotrusion. It becomes possible to form an electroless plating film having a uniform surface roughness. As a drying method, a method of washing the substrate with water, immersing it in pure water and gradually pulling it up to dry it is preferable, but a usual air drying process, a drying method with a heater or the like may be adopted.

The magnetic disk substrate according to the present invention is a non-conductive substrate, particularly a glass substrate coated with a metal, and has a surface state in which the surface shape of the substrate before metal coating is maintained almost as it is. is doing. The surface roughness (average roughness Ra) of the metal thin film is within 1.2 times the surface roughness (average roughness Ra) of the substrate before metal coating, preferably 0.7 to.
It is 1.2 times.

[0020]

EXAMPLES The present invention will be described in more detail with reference to examples below, but the present invention is not limited to the following examples as long as the gist thereof is not exceeded. In addition, in each of the following examples, each measurement was performed by the following method. (1) Appearance of Ni-P coating The degree of appearance unevenness was visually observed using an Olympus illumination device Model LSD. (2) Centerline average roughness (Ra) and protrusion height (obtained by subtracting base height from maximum protrusion height) Surface roughness meter (rank Taylor Hobson (Rank Taylor Hobson ( "Taristep" manufactured by)
Measurement length 1 mm, measurement magnification 200,000, measurement speed 0.
The measurement was performed under the conditions of 025 mm / sec and a filter of 0.33 Hz.

Examples 1 to 6 Two kinds of glass substrates (potassium reinforced soda lime glass) 2.5 inch in diameter and 0.889 mm in thickness A (center line average roughness average Ra8Å) and B (same Ra9Å) were used. On the other hand, the following electroless plating treatment was performed to form a nickel-phosphorus film on the surface of the glass substrate. Each step was performed while rotating the substrate using a rotating jig, and ultrapure water was used as cleaning water in each cleaning step. First, the glass substrate is immersed in a 5% aqueous solution of potassium hydroxide for 5 minutes,
After degreasing, wash with running water for 2 minutes, then pH
After pickling with an aqueous solution of 2-3 sulfuric acid for 1 minute, washing with running water for 2 minutes was performed.

After that, the glass substrate was placed on a 1 g / l first chloride solution.
It was immersed in an aqueous tin solution (adjusted to pH 3 with hydrochloric acid) for 1 minute, subjected to sensitizing treatment, and washed with running water for 1 minute. Then, it was immersed in a 0.2 g / l palladium chloride aqueous solution (pH adjusted to 3 with hydrochloric acid) for 1 minute to carry out an activating treatment. Next, the glass substrate was washed with running water at room temperature for 1 minute and then immersed in an ultrapure water bath at room temperature to generate an ultrasonic wave generator (ULTRASONIC CLE manufactured by Electronic Technology Co., Ltd.).
28 KHz, 60 by ANERUS-600CRS)
Ultrasonic waves of 0 W (1.6 W / cm ² ) were irradiated within the time period (15 to 60 seconds) shown in Table 1. Then, using an automatic 2-tank type warm pure water drying device manufactured by Speed Fam Clean System Co., Ltd., it was once immersed in a pure water tank at 40 ° C.
It was pulled up from the washing tank at a pulling rate of / min and dried.

Next, using a nickel plating solution for magnetic disks ("Niclad 719" manufactured by Okuno Chemical Industries Co., Ltd.), plating is performed for 120 seconds under the conditions of pH 4.5 and bath temperature 81 ° C, and 1500Å on a glass substrate. Ni-P coating of The appearance of the surface of each of the obtained Ni-P plated substrates was good. Further, the center line average roughness and the protrusion height were measured, and the results are shown in Table 1. From this result, Ni-
The surface roughness Ra of the P-plated substrate was about 1.1 times the average value for the glass substrate A and about 1.0 times the average value for the substrate B, as compared with the surface roughness Ra of the glass substrate.

Embodiments 7 and 8 In Embodiments 3 and 6, FINK manufactured by Pretec Co., Ltd. was used as an ultrasonic wave generator after washing with water after the activating treatment.
E-SONIC PT-08M (Frequency 800 KHz,
A Ni-P film was formed on a glass substrate in the same manner as in Examples 1 to 6 except that 650 W) was used. The appearance of the surface of each of the obtained Ni-P plated substrates was good. Further, the center line average roughness and the protrusion height were measured, and the results are shown in Table 1. From this result, the surface roughness Ra of the Ni-P plated substrate was
Was about 0.8 times the average value for the glass substrate A and about 0.9 times for the substrate B as compared with the surface roughness Ra of the glass substrate.

Comparative Examples 1-2 In the same manner as in Examples 1-6, except that in Examples 1-6, washing with water after the activating treatment was performed only by washing with running water without irradiation of ultrasonic waves. A Ni-P coating was formed on the substrate. The appearance of the surface of each of the obtained substrates was poor. Table 1 shows the measurement results of the center line average roughness and the protrusion height.
Shown in. As a result, the surface roughness Ra of the Ni-P plated substrate
Was about 1.9 times for the glass substrate A and about 1.3 times for the substrate B with respect to the surface roughness Ra of the glass substrate.

[0026]

[Table 1]

[0027]

According to the present invention described above, by performing ultrasonic cleaning, it is possible to reduce the fine projections of the electroless plating film and obtain a smooth surface with a small surface roughness. Therefore, in the case of manufacturing the base film for a magnetic disk, the polishing process of the Ni-P coating can be simplified, and a low floating substrate suitable for high density can be obtained.

Claims (2)

[Claims] 1. A method of performing a sensitizing treatment on a non-conductive substrate, an activating treatment, and then an electroless plating, wherein cleaning after the activating treatment is performed while irradiating ultrasonic waves. Method for electroless plating on non-conductive substrate 2. In a magnetic disk substrate comprising a glass substrate coated with a metal thin film, the surface roughness Ra of the formed metal thin film is 1.2 times or less than the surface roughness Ra of the glass substrate before metal coating. Magnetic disk substrate having a certain surface shape