JP2001043528A - Method for reforming surface of aluminum substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To remove an alkaline residual liquid contained in the defective part of an Ni-P aluminum substrate and to prevent the corrosion of a work-affected layer by polishing by immersing the Ni-P aluminum substrate passing through a final polishing step in a functional water having a positive or negative oxidation-reduction potential(ORP) for a prescribed period, then washing the resultant substrate with pure water and drying it. SOLUTION: First an Ni-P aluminum substrate having a prescribed surface roughness through a final polishing process is, in a struck substance removing step, immersed in a functional water having a negative ORP and pH >=8, and washed with ultrasonic wave, if necessary to remove stuck substances such as abrasive grains or organic materials. Then the Ni-P aluminum substrate free from stuck substances is, in a surface reforming process, immersed in the functional water having a positive ORP and acidity for a prescribed period, is washed with pure water and then dried. Therefore, surface hardness of the Ni-P substrate can be improved and corrosion resistance of the substrate can be enhanced, thereby obtaing a desired smoothness small in the number of projections.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is mainly used for a hard disk or the like which is a storage medium of a computer.
A method for modifying the surface of an aluminum substrate (including an aluminum alloy substrate, which is the same in the present specification) plated with Ni-P (nickel-phosphorus), more specifically, improving the corrosion resistance of the substrate and reducing the surface roughness of a GMR head or the like. The present invention relates to a method for modifying a surface so as to be suitable for flying.

[0002]

2. Description of the Related Art Conventionally, as a magnetic disk substrate, an aluminum substrate (hereinafter, referred to as a Ni-P plated surface) has been used.
It is called a Ni-P aluminum substrate. ) Has been widely used, but with the recent demand for higher density HDDs, as the magnetic head has been required to have a lower flying height and a lower noise in the medium, the substrate surface has been smoothed and the substrate has been polished. There has been a growing demand for improved surface alteration layers.

[0003] In the HDD drive, a conventional MR head has been used in a flying height range of 400 to 600 angstroms (hereinafter referred to as "A").
Heads have come to be used at a flying height of 300 A or less for high-density recording. In magnetic recording, the spacing between the head and the medium has a great effect on the recording / reproducing characteristics. Fluctuations of 10% or more in spacing increase the possibility of causing an error during recording and reproduction.
For this reason, in a HDD having a flying height of 300 “A”, it has become necessary to keep the maximum projection height of the medium surface at 50 “A” or less.

In order to cope with high density HDD, the average roughness of the substrate surface and the maximum height of the protrusions are Ra10 to Ra5.
“A”, Rt100 “A” to Ra5 “A”, Rt50
Super finish substrates of “A” or less have been widely used.

[0005]

An aluminum substrate for a magnetic recording medium is usually used with its surface coated with Ni-P plating of about 10 μm in order to increase its surface hardness. As a manufacturing process, plating is 12μ by electroless method.
m, polished to 2 μm in order to obtain the required surface accuracy, subjected to a cleaning process such as a surfactant, ultrasonic cleaning or the like to remove abrasive grains and the like, and all the aluminum substrates are inspected and shipped. Therefore, if the performance at the time of inspection is maintained until the time of sputtering the magnetic film, there is no problem in the production yield as a magnetic recording medium.

[0006] Ni-P plating on an aluminum substrate
Usually, this is performed through the following process. That is, Ni-
Since P cannot be plated directly on an aluminum substrate, the aluminum substrate is processed into a predetermined shape, subjected to strain removal, annealing, and cleaning such as degreasing, and then subjected to a zincate treatment as a core of electroless plating. This is to deposit Zn on an aluminum substrate. Zn is discretely attached to the aluminum substrate in an island shape, and Ni-P is deposited on the aluminum substrate by the action of a local battery. Therefore, Ni-P
In the initial stage of growth, the film is not formed, but becomes a dense film only after growth of 1 to 5 μm. This suggests that the electroless plating solution may be taken into the growth defect at the beginning of growth.
As the electroless plating solution, a salt containing sodium such as sodium hypophosphite is used as a reducing agent and sodium citrate is used as a buffering agent. If these solutions remain in the plating film, they cause corrosion. For industrial products, 100
Since completeness is not possible, corrosion occurs. For this reason, Ni-P aluminum substrates have been provided with expiration dates after manufacture. In the case of the GMR low flying head, the maximum protrusion length is limited to about 50 “A” due to the S / N ratio of the medium and the running stability of the medium, and a new measure has been required. The present invention addresses this.

When the surface of a material is machined, the surface of the material is subjected to some action by the action of the working force, the generated heat, the action of the polishing liquid, etc., and the surface layer of the finished surface has a certain depth from the outermost surface By the way, a deteriorated layer having a different property from that of the lower fabric is generated (Nikkei Technical Book S59 “Surface polishing finishing technology”). In the case of a Ni-P aluminum substrate, as shown in FIG. 1, the thickness of the affected layer is approximately 1 μm. The affected layer is gelled by the action of fine cracks and polishing liquid, and is very soft. Note that FIG.
FIG. 4 is a characteristic diagram showing a relationship between the surface depth and the hardness when an i-P aluminum substrate is not treated with the functional water of the method of the present invention and when it is performed.

[0008] Due to the residual plating solution on the defective portion of the coating and the deteriorated layer during polishing, the Ni-P aluminum substrate has corrosion projections on the surface thereof with the lapse of time after production in a normal cleaning process. Come. After the magnetic film is sputtered, residual liquid is removed by heating vacuum during sputtering, and the sputtered magnetic film covers the surface, so it does not react with moisture gas in the air, etc. It is not necessary to consider the occurrence of corrosion.

For this reason, substrate manufacturers have responded by limiting the period of use of the substrate. However, in order to satisfy the demands for lowering the flying height and improving the S / N ratio, the period of use has been further shortened, and Measures have been required.

The present invention has been made in view of the above circumstances, and an object thereof is to control the occurrence of corrosion based on an alkali residual liquid and a work-affected layer contained in a defective portion of a Ni-P aluminum substrate. Another object of the present invention is to provide a method for modifying the surface of a Ni-P aluminum substrate, which enables stable production of an aluminum substrate for a magnetic recording medium corresponding to a low flying GMR head.

[0011]

Conventionally, functional water such as ionized water, oxygen gas or hydrogen gas introduced water has been used for cleaning semiconductors, cleaning liquid crystal glass, and the like. However, most of them are intended for cleaning to remove adhered fine particles on the alkali side where the oxidation-reduction potential (ORP) is negative, and there are few examples in which functional water is used for surface modification. The present invention is characterized in that ORP uses positive or negative functional water. It has been confirmed that by using such functional water, the effects of extending the effective period (expiration date) and improving the production yield by improving the work-affected layer, which have been problems with the conventional Ni-P aluminum substrate, can be obtained. did.

[0012] ORP is a positive functional water, ORP
200-1300 mV, preferably 300-700 m
V. Use acidic functional water having a pH of 2 to 7, preferably 4 to 7. The Ni-P aluminum substrate that has undergone the final polishing step is immersed in this functional water for a predetermined period of time, washed with pure water, and dried to modify the surface of the Ni-P aluminum substrate. That is, the alkaline residual liquid contained in the defective portion of the Ni-P aluminum substrate is removed, and corrosion of the altered layer due to polishing is prevented.

[0013] If the Ni-P aluminum substrate to be treated has an attached substance such as abrasive grains or other dust, the conventional washing with functional water, that is, the attached substance is removed with an ORP-negative alkaline functional water. ORP of the present invention
May be treated with positive acidic functional water. The processing conditions are appropriately selected depending on the processing conditions such as the composition of the electroless plating solution used, the type and particle size of the abrasive grains, and the type of the polishing solution.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The surface modification of a Ni-P aluminum substrate according to the present invention includes the following steps when a final cleaning step is performed on a substrate having a predetermined surface roughness after a final polishing step. Achieved by passing through. The following is an example of a case where ORP uses functional water with a positive value. (1) Adhered matter removal step ORP is negative, and N
The i-P aluminum substrate is immersed, ultrasonic waves are applied if necessary, and the substrate is washed to remove extraneous matter such as abrasive grains and other organic substances adhered to the Ni-P aluminum substrate. (2) Surface modification step The Ni-P aluminum substrate from which deposits have been removed in the step (1) is immersed in ORP-plus acidic functional water for a predetermined time,
After washing with pure water, it is dried. The functional water makes the substrate and the attached matter have the same potential, and exerts a cleaning ability by electric repulsion. Since the same operation is performed on both the anode side and the cathode side, the step (1) is not necessary depending on the type of the contaminants.

The effective range of the ORP of the functional water used in the present invention is 200-1300 mV, and the preferred range is 400-7.
00mV, the effective range of pH is 2 to 7, and the preferable range is 4 to 7.
It is. When the ORP is less than 200 mV, the surface modification ability is weak, and the treatment takes a long time. When the ORP exceeds 1300 mV, the surface is oxidized. When the pH is lower than 2, the substrate is etched, and when the pH is higher than 7, the effect of the modification is weakened.

[0016]

EXAMPLE Ni-P was plated to 12 μm on an aluminum 6063 alloy using an electroless polishing solution under the following conditions, and polished to 2 μm with colloidal silica abrasive grains.
The substrate “A” was prepared, washed with an ultrasonic cleaner containing a surfactant, and spin-dried. As a result of the inspection including the AFM, no protrusion due to corrosion was found on the surface. Plating solution: Electroless polishing solution (acid bath) pH: 5 Solution temperature: 40 degrees Liquid composition: (unit: g / 1 liter water) Nickel sulfate 30 Sodium hypophosphite 20 Sodium acetate 14 Sodium citrate 24 Ammonium chloride 5 Lactic acid 0.5 abrasive: (unit: g / 1 liter water) silicon dioxide 30 sodium oxide 0.6 pH 10 particle size 0.01 μm or less

This material was used as a reference sample, and no sample, that is, a sample not subjected to a cleaning treatment with functional water, was used as a sample. 19 was set. Of the above samples, the untreated sample (Sample No. 19) was left as it was, and the remaining samples were washed with functional water under the following conditions. Table 1 shows the processing conditions.

[Table 1]

PH and ORP of functional water (wash water) in Table 1
Is as follows. Cathode water not added pH 7.8 ORP -580 mV ＮＨ NH3 added pH 10 ORP -800 mV Ozone water 1 ppm pH 6.7 ORP 1200 mV 〃 10 ppm pH 6.7 ORP 1200 mV Anode water added pH 6 ORP 550 mV 〃 HCL added pH 2 ORP 1150mV

The Ni-P aluminum substrate was treated under the conditions of pH, ORP and immersion time set forth in Table 1, rinsed in pure water for 3 minutes, and then spin-dried. Sample No. obtained by the above test After leaving 1 to 18 samples in a clean room for 20 days, the area of 20 × 20 μm was observed by AFM, and the number of protrusions and the maximum height of the protrusions were measured. The measurement results are as shown in Table 2.

[Table 2]

FIGS. 2 to 8 show the metal surface structures of a typical aluminum substrate in the case where the Ni—P aluminum substrate is not treated and when it is treated with anode water, cathode water and ozone water, respectively. This is shown by a substitute AFM photograph.
FIG. 3 to 8 show the sample Nos. 3, 6, 9, 12, 15, and 18, respectively.

As is clear from Table 2, the sample No.
10, 13, 14 and 15 have 0 projections and a maximum projection height of 50 "A" or less, showing extremely good results. Sample No. Nos. 1 to 6 are much more excellent in smoothness than the conventional method. From the above examples, it can be understood that the ORP of 400 to 700 mV and the pH of 4 to 7 are preferable ranges in the method of the present invention.

The above embodiment is performed under a certain condition. If the electroless plating condition and the polishing condition change, the optimum treatment condition of the functional water changes. If the electroless plating is performed in an alkaline bath and the polishing is performed in an acidic bath, the optimum functional water treatment conditions are opposite to the ORP and pH. When the ORP uses negative functional water, the ORP is -500 to -80.
0 mV and a pH of 7 to 10 are effective ranges.

Since the anode and cathode functional water generally has a small molecular size, it easily penetrates into fine cracks in the Ni—P aluminum substrate, and removes alkali components and other harmful ions in the cracks by a substitution effect. After the surface modification with the anode, cathode electrolyzed water, etc., no special chemicals are used, so that a special wastewater treatment required when a normal surfactant is used is not required, which is economical.

[0024]

As described above, according to the surface modification method of the present invention, the hardness of the surface of the Ni-P aluminum substrate is improved,
In addition to the improved corrosion resistance, the number of projections on the surface is very small, and the smoothness with a maximum projection height of 50 "A" or less is obtained, and stable production of a fluorinium substrate suitable for a low-flying GMR head can be achieved. It is possible.

[Brief description of the drawings]

FIG. 1 is a characteristic diagram showing a relationship between a depth from a surface and a hardness when a functional water treatment is not performed on a Ni—P aluminum substrate and when a functional water treatment is performed.

FIG. 2 is an AFM photograph showing a surface metal structure of an untreated state of a Ni—P aluminum substrate.

FIG. 3 is an AFM photograph showing the surface metal structure of a Ni—P aluminum substrate after a cathode water / no addition treatment.

FIG. 4 is an AFM photograph showing a surface metal structure of a Ni—P aluminum substrate after a cathode water / NH 3 addition treatment.

FIG. 5 is an AFM photograph showing the surface metallographic structure of a Ni—P aluminum substrate after 1 ppm ozone water treatment.

FIG. 6 is an AFM photograph showing a surface metal structure of a Ni—P aluminum substrate after a 10 ppm ozone water treatment.

FIG. 7 is an AFM photograph showing a surface metal structure of a Ni—P aluminum substrate after an anode water / no addition treatment.

FIG. 8 is an AFM photograph showing a surface metal structure of a Ni—P aluminum substrate after an anode water / HCL addition treatment.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Mitsuru Maekawa 2-19-4 Nishi-Shimbashi, Minato-ku, Tokyo Inside Media Research Laboratories (72) Inventor Yuichi Hyakuzuka 2-19-4 Nishi-Shimbashi, Minato-ku, Tokyo (72) Inventor Tadao Tokushima 2021-3 Taocho, Kohoku-ku, Yokohama-shi, Kanagawa Prefecture (72) Inventor Masaaki Kato 1-79-8 Futamagawa, Asahi-ku, Yokohama-shi, Kanagawa MA Heights 201 F term (reference) 4K053 PA07 PA10 QA06 QA07 RA07 SA06 SA18 YA01 5D112 AA02 AA24 BA06 GA08 GA09 GA28 GA30

Claims (8)

[Claims] In a washing step after a polishing step of an Ni-P-plated aluminum substrate, the surface of the aluminum substrate is treated with functional water having a redox potential of plus or minus for a required time. Quality way. 2. The method for modifying the surface of an aluminum substrate according to claim 1, wherein anode water or ozone water having an acidic pH is used as the functional water. 3. The functional water is a functional water generated by direct electrolysis of water or a functional water generated by diffusing oxygen gas generated by electrolysis into water by an oxygen permeable membrane. A method for modifying the surface of an aluminum substrate according to claim 1. 4. An oxidation-reduction potential of 200 to 1300 mV,
The method for modifying the surface of an aluminum substrate according to claim 1, 2, or 3, wherein functional water of preferably 300 to 700 mV is used. 5. The method for modifying the surface of an aluminum substrate according to claim 1, wherein functional water having a pH of 2 to 7, preferably 4 to 7 is used. 6. The method for modifying the surface of an aluminum substrate according to claim 1, wherein cathodic electrolyzed water having an alkaline pH is used as the functional water. 7. The method for modifying the surface of an aluminum substrate according to claim 6, wherein functional water having an oxidation-reduction potential of -500 to -800 mV is used. 8. The surface modification of an aluminum substrate according to claim 1, wherein the immersion time in the functional water is 1 to 20 minutes, preferably 1 to 5 minutes. Method.