JP7009572B1 - Manufacturing method of substrate for magnetic disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a substrate for a magnetic disk, a magnetic disk and a substrate for a magnetic disk having a small plate thickness and few read / write errors. A magnetic disk substrate 100 is a thin magnetic disk substrate, and when the distance from the center is r1> r2, r1 = radius R-0.5 mm and r2 = radius R-4.0 mm. In the measurement region surrounded by concentric circles, the arithmetic average swell Wa of a wavelength of 1 mm or more and 5 mm or less is 4.0 nm or less. [Selection diagram] Fig. 3

Description

The present invention relates to a method for manufacturing a substrate for a magnetic disk.

Magnetic disks are used in HDDs (Hard Disk Drives) used in data centers, computers, and the like. With the spread of smartphones and smart home appliances, the amount of data used by individuals and businesses is increasing. These huge amounts of data are read and written to the HDD in the data center via the Internet. In order to record a huge amount of data, it is required to increase the capacity of the HDD.

A disk made of aluminum, an aluminum alloy, or glass is used for the HDD. For example, Cited Document 1 discloses a glass substrate for a magnetic disk. As the large-capacity HDD in the data center, a disk having a diameter of 95 to 97 mm, which is 3.5 inches in size, is preferably used.

There are the following technological trends in order to increase the capacity of HDDs. That is, by reducing the thickness of the magnetic disk to increase the number of sheets mounted on the HDD, and increasing the diameter of the magnetic disk to make the data area on the disk surface as close as possible to the outer diameter end, the magnetic disk It is to expand the data area per sheet.

Japanese Unexamined Patent Publication No. 2013-225372

If the error rate during reading and writing exceeds the permissible range, it cannot be used as a magnetic disk, so evaluation is performed in advance before incorporating the magnetic disk into the HDD. As a quality evaluation method for a magnetic disk, media evaluation is known in which a head is levitated on a rotating magnetic disk and a signal from the magnetic disk is detected by the head. The magnetic disk that has passed this media evaluation is put into the next HDD manufacturing process. The media evaluation evaluates a magnetic disk having a magnetic film formed on the magnetic disk substrate, and cannot evaluate a magnetic disk substrate on which the magnetic film is not formed. Therefore, there is a problem that the manufacturing cost of the magnetic disk is wasted if the result is rejected by the media evaluation after the magnetic disk is manufactured. Therefore, it is being evaluated for a magnetic disk substrate on which a magnetic film is not formed. If the plate thickness is reduced, there is a problem that undulations are likely to occur on the surface. In the conventional undulation inspection method for magnetic disk substrates, is the error rate of the magnetic disk due to undulation within the allowable range before forming the magnetic film? There is also the problem that it cannot be clearly determined whether or not it is.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide a method for manufacturing a substrate for a magnetic disk, which has a small plate thickness and few read / write errors.

In order to achieve the above object, the method for manufacturing a substrate for a magnetic disk according to a third aspect of the present invention is
Grinding process for grinding magnetic disk substrates, and
For the magnetic disk substrate ground in the grinding step, when the distance from the center is r1> r2, the measurement is surrounded by concentric circles with r1 = radius R-0.5 mm and r2 = radius R-4.0 mm. In the region, the swell evaluation step for measuring the arithmetic average swell Wa with a wavelength of 1 mm or more and 5 mm or less, and
A determination step of determining whether or not the arithmetic mean undulation Wa measured in the undulation evaluation step is 4.0 nm or less, and extracting the magnetic disk substrate having an arithmetic average undulation Wa of 4.0 nm or less.
It is characterized by having.

According to the present invention, it is possible to provide a method for manufacturing a substrate for a magnetic disk having a small plate thickness and few read / write errors.

It is a figure which shows the substrate for a magnetic disk which concerns on embodiment. It is an enlarged sectional view which shows the substrate for a magnetic disk which concerns on embodiment. It is a figure which shows the surface waviness of the disk outer peripheral side of the magnetic disk substrate which concerns on embodiment. It is a flowchart which shows the manufacturing method 1 of the substrate for a magnetic disk which concerns on embodiment. It is a figure which shows the grind process of the substrate for a magnetic disk which concerns on embodiment. It is sectional drawing which shows the grind process of the substrate for magnetic disk which concerns on embodiment. It is an enlarged sectional view which shows the grind process of the substrate for a magnetic disk which concerns on embodiment. The outer peripheral portion of the ground board for a magnetic disk which concerns on embodiment is shown. It is a flowchart which shows the manufacturing method 2 of the substrate for a magnetic disk which concerns on embodiment. It is sectional drawing which shows the magnetic disk which concerns on embodiment. (A) is a figure which shows the measurement result of the substrate for a magnetic disk which concerns on Example, (B) is an enlarged view in the thickness direction of FIG. 11A, and FIG. 11C is FIG. 11 (A). ) Is a radial enlarged view. It is a figure which shows the arithmetic mean swell for each measurement area of the substrate for magnetic disk which concerns on Example.

Hereinafter, the magnetic disk substrate and the magnetic disk according to the embodiment of the present invention will be described with reference to the drawings.

As a result of researching surface waviness, which is one of the defective items in order to reduce errors when reading and writing with a magnetic head in a thin magnetic disk, the inventors of the present application have found that the cause is surface waviness generated on the outer periphery of the disk. I found. A magnetic disk having a surface undulation on the outer periphery of the disk cannot be used because the error rate during reading and writing exceeds the allowable range. In addition, the conventional method for inspecting the waviness of a magnetic disk has also revealed a new problem that it is not possible to clearly determine whether or not the magnetic disk is within the allowable range of the error rate.

As shown in FIGS. 1 and 2, the magnetic disk substrate 100 of the present embodiment is a thin magnetic disk substrate, and when the distance from the center is r1> r2, r1 = radius R-0. In the measurement region MA surrounded by concentric circles of 5.5 mm and r2 = radius R-4.0 mm, the arithmetic mean swell Wa of the wavelength λ of 1 mm or more and 5 mm or less shown in FIG. 3 is 4.0 nm or less. More preferably, the arithmetic mean swell Wa is 3.0 nm or less. The plate thickness t1 is preferably 0.635 mm or less, more preferably 0.5 mm or less. The diameter is preferably 95 mm or more. When the arithmetic mean undulation Wa of the wavelength λ of 1 mm or more and 5 mm or less is 4.0 nm or less, when the magnetic disk substrate 100 is used as the magnetic disk substrate, the error rate of the magnetic disk is within the permissible range.

As the magnetic disk substrate 100, an aluminum substrate, an aluminum alloy substrate, a glass substrate, or the like can be used. Hereinafter, a case where an aluminum alloy substrate and a glass substrate are used will be described.

(Aluminum alloy substrate)
As the aluminum alloy substrate used as the substrate 100 for the magnetic disk, an Al—Mg alloy substrate such as JIS 5086 alloy or an Al—Fe alloy substrate is used. The Al—Mg-based alloy substrate has high strength and is preferably used. A substrate made of an Al—Fe-based alloy has high rigidity and is preferably used.

The Al—Mg alloy substrate contains Mg: 1.0 to 6.5% by mass, Cu: 0.070% by mass or less, Zn: 0.60% by mass or less, Fe: 0.50% by mass or less. , Si: 0.50% by mass or less, Cr: 0.20% by mass or less, Mn: 0.50% by mass or less, Zr: 0.20% by mass or less. It is an aluminum alloy consisting of aluminum and unavoidable impurities and other trace elements.

The Al—Fe alloy substrate contains Fe, which is an essential element, and one or two of Mn and Ni, which are selective elements, and the total content of these Fe, Mn, and Ni is 1.00 or more. It has a relationship of 7.00% by mass, and further, Si: 14.0% by mass or less, Zn: 0.7% by mass or less, Cu: 1.0% by mass or less, Mg: 3.5% by mass or less, Cr. : 0.30% by mass or less, Zr: 0.20% by mass or less, one or more, and the balance is an aluminum alloy composed of aluminum, unavoidable impurities and other trace elements. In this embodiment, the composition of the aluminum alloy substrate is not limited to the above composition.

Next, a method 1 for manufacturing a magnetic disk substrate 100 made of an aluminum alloy will be described.

As shown in FIG. 4, the manufacturing method 1 of the magnetic disk substrate 100 includes a casting / rolling process (step S101), a blanking process (step S102), a cutting process (step S103), and a grinding process (grinding process). (Step S104), a plating step (step S105), a polishing step (step S106), a waviness evaluation step (step S107), and a determination step (step S108).

First, in the casting / rolling step (step S101), an ingot is produced by a semi-continuous casting method, and the ingot is hot-rolled and cold-rolled to produce a plate material having a desired thickness. Alternatively, a plate material may be produced by continuous casting and then cold-rolled to produce a plate material having a desired thickness. The ingot may be heat treated for the purpose of homogenizing the structure. For the purpose of improving workability, heat treatment may be applied to the plate material before cold rolling, during cold rolling, and after cold rolling.

Next, in the blanking step (step S102), the plate material produced in the casting / rolling step (step S101) is punched by a press machine, and a disk having a desired inner diameter and outer diameter (hereinafter referred to as a blank) is punched. To make. After that, for the purpose of reducing the flatness of the blanks, the blanks may be laminated, a load may be applied to the laminated blanks, and a heat treatment may be performed.

Next, in the cutting step (step S103), the inner diameter portion and the outer diameter portion of the blank are machined by a lathe machine, and a disc having a desired inner diameter dimension, outer diameter dimension, and chamfered portion having a desired length (hereinafter referred to as a disc). , T-sub). Further, the surfaces of both sides of the blank may be machined to form a T-sub having a plate thickness of a desired thickness. Further, the T-sub may be heat-treated for the purpose of removing the machining strain generated inside the material by cutting.

Next, in the grind step (step S104), the T-sub is ground to produce a disc having a desired thickness (hereinafter referred to as G-sub). Further, for the purpose of removing the processing strain generated inside the material by the grinding process, the G sub during or after the grinding process may be heat-treated. The details of the grind step (step S104) will be described later.

Next, in the plating step (step S105), a disk (hereinafter referred to as M sub) in which plating having a desired thickness is formed on all surfaces including the surface, side surface, and chamfered surface of the G sub is produced. First, it is advisable to perform a zincate treatment as a pretreatment on the G sub for the purpose of improving the plating adhesion. Next, a plating process is performed. Ni-P electroless plating is preferably used for plating. Further, the M sub may be heat-treated for the purpose of removing the internal stress of Ni-P electroless plating. As a result, a base layer is formed on the M sub.

Next, in the polishing step (step S106), the surfaces of both sides of the M sub are polished with a polishing machine to obtain a disk having a desired thickness, that is, a substrate 100 for a magnetic disk.

Next, in the waviness evaluation step (step S107), when the distance from the center of the magnetic disk substrate 100 is r1> r2, r1 = radius R-0.5 mm and r2 = radius R-4.0 mm concentric circles. In the measurement region MA surrounded by, the arithmetic average swell Wa having a wavelength λ of 1 mm or more and 5 mm or less is measured. As a method for evaluating the waviness of the surface of the magnetic disk substrate 100, it can be evaluated by an optical inspection device. As the inspection device, PHASE SHIFT TECHNOLOGY's multi-function disc interferometer "OPTIFLAT", ZYGO's laser interferometer "Verifire", KLA-Tencor's optical interferometer MicroXAM, etc. are preferably used.

Next, in the determination step (step S108), it is determined whether or not the arithmetic average swell Wa measured in the swell evaluation step (step S107) is 4.0 nm or less, and the arithmetic average swell Wa is 4.0 nm or less. A certain magnetic disk substrate 100 is extracted. As a result, the substrate 100 for a magnetic disk that does not satisfy the condition that the arithmetic mean waviness Wa having a wavelength λ of 1 mm or more and 5 mm or less is 4.0 nm or less is removed. More preferably, it is determined whether or not the arithmetic mean undulation Wa is 3.0 nm or less, and the magnetic disk substrate 100 having the arithmetic average undulation Wa of 3.0 nm or less is extracted. In the waviness evaluation step (step S107) and the determination step (step S108), the magnetic disk substrate 100 may be evaluated and determined for all, and a part of the magnetic disk substrate 100 may be extracted and evaluated and determined. May be good.

It is considered that the cause of the undulation of the wavelength λ of 1 mm or more and 5 mm or less on the surface on the outer peripheral side of the disk described above is due to the grind step (step S104). Here, the details of the grind step (step S104) and the mechanism by which the waviness having a wavelength λ of 1 mm or more and 5 mm or less increases on the surface on the outer peripheral side of the disk will be described.

In the grind step (step S104), as shown in FIG. 5, the G-sub 110, which is a workpiece, is held by a support called a carrier 210 and revolves while rotating. The surfaces of both sides of the G sub 110 are ground by pressing the fixed abrasive grains 220 called a grindstone while rotating them from the upper and lower surfaces. During the grinding process, the coolant is poured on the G sub 110, the carrier 210, and the fixed abrasive grains 220.

As the carrier 210, one made of a resin containing an aramid resin, an epoxy resin or the like is preferably used. A fibrous reinforcing material such as carbon fiber or glass fiber may be contained for the purpose of improving the strength. The thickness of the carrier 210 can be arbitrarily selected depending on the thickness of the G sub 110 which is the workpiece. However, if the carrier is too thin, its strength will be insufficient and it may be damaged during grinding. From the viewpoint of carrier strength, the carrier thickness is preferably 0.3 mm or more, more preferably 0.4 mm or more. Therefore, in this processing method, it is difficult to process a G-sub 110 having a thickness of 0.3 mm or less.

The fixed abrasive grains 220 are made of a binder that binds the abrasive grains to the abrasive grains, and the abrasive grains are preferably Si—C particles, and the binder is preferably a porous sponge-like elastic body such as PVA. A cutting groove 221 may be dug in the fixed abrasive grains 220 for the purpose of improving the discharge of grinding debris generated in the grinding process.

The coolant is used for the purpose of cooling the heat generated by grinding, improving lubricity, and improving the discharge of grinding debris.

Ideally, the grinding debris generated in the grinding step (step S104) is discharged to the outside of the system by a coolant, but in reality, a part of the grinding debris is sent to the G sub 110, the carrier 210 or the fixed abrasive grains 220. Adhere to. Grinding debris directly adhering to the fixed abrasive grains 220 or grinding debris adhering to the fixed abrasive grains 220 via the G-sub 110 or the carrier 210 is deposited on the surface of the fixed abrasive grains 220, particularly in the porous holes. This phenomenon is called clogging of the fixed abrasive grains 220. It is considered that the portion where the fixed abrasive grains 220 are clogged is stagnant without being discharged from the porous holes, and further repeats a vicious cycle in which grinding debris is accumulated, which hinders the grindability of the G sub 110. The clogging of the fixed abrasive grains 220 depends on the flow of the coolant on the surface of the fixed abrasive grains 220 or the locus of the G sub 110 and the carrier 210, and occurs unevenly on the surface of the fixed abrasive grains 220. As shown in FIG. 6, as the discharge path of the grinding debris generated in the grinding process, the path DR1 from the surface of the G sub 110 to the cutting groove 221 of the fixed abrasive grain 220, and the G sub 110 from the surface of the G sub 110. There is a path DR2 that exits to the inner peripheral side and a path DR3 that exits from the surface of the G sub 110 to the outer peripheral side of the G sub 110.

Here, attention is paid to the outer peripheral side of the G sub 110. Of the above-mentioned discharge paths for grinding debris, the path DR3 passing from the surface of the G-sub 110 to the outer peripheral side depends on the gap between the G-sub 110 and the carrier 210, that is, the difference in plate thickness between the G-sub 110 and the carrier 210. The smaller the gap between the two and the difference in plate thickness, the smaller the discharge path, and the lower the discharge performance. When the dischargeability of grinding debris is reduced, the fixed abrasive grains 220 are likely to be clogged.

For example, the thickness of the carrier when polishing a conventional disc having a plate thickness of 1.27 mm (50 mil) is 1.0 mm, and the thickness of the carrier when polishing a disc having a plate thickness of 0.635 mm (25 mil) is 0. The one having a thickness of 5 mm is preferably used. When polishing a disc having a plate thickness of 0.5 mm (20 mil), a carrier having a thickness of about 0.4 mm is used. The smaller the plate thickness of the disc, the smaller the thickness of the carrier, and the smaller the difference in plate thickness between the disc and the carrier.

As the thickness of the carrier 210 decreases, the rigidity of the carrier 210 decreases, so that the carrier 210 tends to bend during the grinding process. For example, as shown in FIG. 7, when the carrier 210 is bent toward the upper surface side of the fixed abrasive grains 220, the discharge path DR31 on the upper surface side of the fixed abrasive grains 220 is small and the discharge path DR32 on the lower surface side is large. That is, as the thickness of the carrier 210 becomes smaller, the grinding debris discharge property of the path passing from the surface of the G sub 110 to the outer peripheral side partially fluctuates. It is considered that the easiness of clogging of the fixed abrasive grains 220 also partially varies, resulting in more non-uniform clogging of the fixed abrasive grains 220.

Further, as shown in FIG. 8, the outer peripheral sagging PS is generated on the outer peripheral side surface of the G sub 110 by the grind step (step S104). The outer peripheral sagging means that the thickness of the G-sub 110 plate gradually decreases from the center of the G-sub 110 to the outer circumference. It is considered that this is because the fixed abrasive grains 220 are elastically deformed during the grinding process, so that the plate thickness step portion at the boundary between the G sub 110 and the carrier 210 is smoothly scraped off. Here, if the fixed abrasive grains 220 have non-uniform clogging, the height D of the outer peripheral sagging PS becomes non-uniform in the G sub 110. This is because if the plate thickness step portion at the boundary between the G sub 110 and the carrier 210 is hit by a portion where the fixed abrasive grains 220 are not clogged, a relatively large amount is scraped off, and if the fixed abrasive grain 220 clogged portion is hit, grinding is performed. This is because the sex is hindered and the amount of scraping is relatively reduced. When the surface of the outer peripheral portion of the G sub 110 is observed along the circumferential direction of the G sub 110 having a non-uniform outer peripheral sagging PS, peaks and valleys, that is, uneven shapes can be seen. Of these, the component having a wavelength λ of 1 mm or more and 5 mm or less shown in FIG. 3 is the undulation shown in the present embodiment. Since the waviness of the component having a wavelength λ of 1 mm or more and 5 mm or less causes an error when reading and writing the magnetic disk, it is important to suppress this waviness.

To summarize the explanation so far, when the thickness of the G-sub 110 is small, the plate thickness of the carrier 210 used for grinding becomes small, and the difference in plate thickness between the G-sub 110 and the carrier 210 becomes small. Non-uniform grindstone clogging is likely to occur during machining, and non-uniform grindstone clogging causes uneven outer peripheral sagging PS on the surface on the outer peripheral side of the disk, which contributes to read / write errors of the magnetic disk. It is considered that the waviness of the wavelength λ of 1 mm or more and 5 mm or less increases.

If the height D of the outer peripheral sagging PS is too large, the polishing pad does not hit the portion in the subsequent polishing step of polishing the M sub (step S106), resulting in a defect region that is not sufficiently polished. Therefore, the height D of the outer peripheral sagging PS is preferably 10 μm or less. The height D is obtained by measuring the distance in the thickness direction between the straight line extending in the radial direction extending from the surface where the outer peripheral sagging PS does not occur and the chamfering start portion C.

Further, the outer peripheral edge of the G sub 110 is chamfered. Chamfering is performed to prevent the generation of foreign matter such as burrs at the end of the disk, but it is better to make it as small as possible in order to expand the data area. Specifically, the length L of the chamfered portion of the outer peripheral portion is preferably 0.15 mm or less, more preferably 0.10 mm or less. The length L of the chamfered portion is obtained by measuring the distance between the chamfering start portion C and the outer diameter end portion (chamfering end portion) E in the radial direction.

Next, details of a method for suppressing the occurrence of swell having a wavelength λ on the outer peripheral side of the G sub 110 of 1 mm or more and 5 mm or less will be described. As described above, the cause of the increase in waviness is non-uniform clogging of the fixed abrasive grains 220. If the clogging of the fixed abrasive grains 220 is suppressed, the waviness can also be suppressed. As a method for suppressing clogging of the fixed abrasive grains 220, for example, a surfactant or a lubricant may be appropriately added to the coolant in order to improve the discharge of grinding debris, or an appropriate cutting groove 221 may be dug in the fixed abrasive grains 220. Alternatively, a method such as periodically scraping off the surface of the fixed abrasive grains 220 (hereinafter referred to as dressing) before the fixed abrasive grains 220 are clogged can be mentioned.

Here, the flatness of the substrate will be described. When the waviness of a substrate surface with a large flatness is measured by an optical inspection device, the measurement light emitted from the inspection device is reflected by the substrate surface and returns to the sensor of the inspection device. The measurement light reflected by a part of the surface, especially on the outer peripheral side of the substrate, does not return to the sensor of the inspection device, and the swell evaluation of the desired region cannot be performed. Therefore, the flatness of the substrate should be as small as possible. Specifically, it is preferably 20 μm or less.

(Glass substrate)
As the glass substrate used as the substrate 100 for a magnetic disk, aluminosilicate glass is preferably used because it has a high hardness.

Specifically, the aluminosilicate glass contains SiO ₂ : 55 to 70% by mass as a main component, Al ₂ O ₃ : 25% by mass or less, Li ₂ O: 12% by mass or less, and Na ₂ O: 12% by mass or less. , K2O: ₈ % by mass or less, MgO: 7% by mass or less, CaO: 10% by mass or less, ZrO2: 10% by mass or less, TiO ₂ : ₁ % by mass or less, one or more. The balance consists of unavoidable impurities and other trace elements. The composition of the glass substrate in this embodiment is not limited to these compositions.

Next, a method 2 for manufacturing the magnetic disk substrate 100 using the glass substrate will be described.

As shown in FIG. 9, the manufacturing method 2 of the magnetic disk substrate 100 includes a melting / glass base plate step (step S201), a coring step (step S202), and a wrapping step (grinding step) (step S203). , A polishing step (step S204), a waviness evaluation step (step S205), and a determination step (step S206).

First, in the melting / glass base plate step (step S201), the glass material prepared to a predetermined chemical composition is melted, and the molten mass is press-molded from both sides by a direct press method to obtain a glass having a desired thickness. Make the original plate. The production of the glass base plate is not limited to the direct press method, and may be a float method, a fusion method, a redraw method, or the like.

Next, in the coring step (step S202), the glass base plate is coraled in an annular shape, and the inner diameter portion and the outer diameter portion are further polished to have a desired inner diameter dimension, outer diameter dimension, and chamfer length. It shall be an annular glass plate.

Next, in the wrapping step (step S203), the surfaces of both surfaces of the annular glass plate are wrapped (ground) with a grinding machine to obtain an annular glass substrate having a desired plate thickness and flatness. The wrapping step (step S203) corresponds to the grind step (step S104) described in the magnetic disk substrate 100 made of an aluminum alloy substrate.

Further, in the polishing step (step S204), the surfaces of both surfaces of the annular glass substrate are polished with a polishing machine to produce a disk having a desired thickness, that is, a glass substrate. During the polishing process, a chemical strengthening treatment with a sodium nitrate solution, a potassium nitrate solution, or the like may be performed.

Next, the swell evaluation step (step S205) and the determination step (step S206) are carried out. The waviness evaluation step (step S205) and the determination step (step S206) in the manufacturing method 2 of the magnetic disk substrate 100 using the glass substrate are the waviness evaluation steps in the manufacturing method 2 of the magnetic disk substrate 100 using the aluminum alloy substrate. (Step S107) and the determination step (step S108) are the same.

The problem of increasing the waviness of the wavelength λ of 1 mm or more and 5 mm or less on the surface on the outer peripheral side of the disk, which is a problem of the present embodiment, is caused by the wrapping step (step S203). In the wrapping step (step S203), the annular glass plate, which is the workpiece, is held by the carrier and rotates and revolves in the same manner as in the grind step (step S104) described above. By pressing the fixed abrasive grains (grinding stones) while rotating them from the upper and lower surfaces, the surfaces of both the upper and lower surfaces of the annular glass plate are ground. During the grinding process, coolant is poured over the annular glass plate, carrier, and grindstone.

As the carrier, one made of a resin such as an aramid resin or an epoxy resin is preferably used. A fibrous reinforcing material such as carbon fiber or glass fiber may be contained for the purpose of improving the strength. The thickness of the carrier can be arbitrarily selected depending on the thickness of the disk to be processed, but if it is too small, the strength will be insufficient and it will be damaged during grinding. From the viewpoint of carrier strength, the carrier thickness is preferably 0.3 mm or more, more preferably 0.4 mm or more. Therefore, in this processing method, it is difficult to process a disc having a disc thickness of 3.0 mm or less.

The grindstone is composed of a binder that binds the grindstone to the grindstone, and diamond particles are preferably used as the grindstone.

The coolant is used for the purpose of cooling the heat generated by grinding, improving lubricity, and improving the discharge of grinding debris.

The mechanism by which the waviness having a wavelength λ of 1 mm or more and 5 mm or less increases on the surface on the outer peripheral side of the disk is considered to be due to non-uniform clogging of the grindstone, as in the case of the above-mentioned aluminum alloy substrate for magnetic disk 100.

Regarding the method of suppressing the generation of undulations having a wavelength λ on the outer peripheral side of the disk of 1 mm or more and 5 mm or less, it is sufficient to suppress the clogging of the grindstone in the same manner as the above-mentioned aluminum alloy substrate. Methods such as appropriately adding a surfactant or a lubricant to the coolant, digging a suitable groove 221 for the grindstone, or periodically scraping the surface of the grindstone before the grindstone is clogged can be mentioned. Further, similarly to the aluminum alloy substrate described above, by executing the waviness evaluation step (step S107) and the determination step (step S108), it is determined whether or not the arithmetic mean waviness Wa is 4.0 nm or less, and the arithmetic operation is performed. A glass substrate having an average waviness Wa of 4.0 nm or less is extracted. As a result, the glass substrate that does not satisfy the condition that the arithmetic mean waviness Wa of the wavelength λ of 1 mm or more and 5 mm or less is 4.0 nm or less is removed.

(Magnetic disk)
As shown in FIG. 10, the magnetic disk 10 has a magnetic disk substrate 100 and a magnetic film 11 arranged on the surface of the magnetic disk substrate 100.

As a large-capacity magnetic disk for a data center, a perpendicular magnetic recording system (PMR: Perpendicular Magnetic Recording) or a shingled magnetic recording system (SMR) is preferably used. In order to realize even larger capacity, technologies such as heat-assisted magnetic recording (HAMR) and Microwave Assisted Magnetic Recording (MAMR) have been developed, and these methods are used. You may.

The size of the magnetic disk 10 used for the 3.5-inch HDD is preferably 95 mm or more and 97 mm or less in diameter. In order to realize a large capacity, it is desired to use the data area up to the limit of the outer peripheral edge of the disk, but the outer peripheral side is particularly important because it greatly contributes to the expansion of the data area area.

(Evaluation method of magnetic disk)
The following method is known as a quality evaluation method for the magnetic disk 10. It is a method of floating a head on a rotating magnetic disk 10 and detecting a signal from the magnetic disk 10 with the head (hereinafter referred to as media evaluation). The magnetic disk that has passed this media evaluation is put into the next HDD manufacturing process. When the plate thickness of the magnetic disk 10 becomes small, the defect rate of media evaluation increases. As a result of investigating the cause by the inventor of the present application, it was found that the poor media evaluation is caused by the surface waviness of the wavelength λ on the outer peripheral side of the magnetic disk 10 of 1 mm or more and 5 mm or less. It was also found that the surface waviness did not differ significantly before and after forming the magnetic film 11. Therefore, it is more preferable to evaluate the surface waviness on an aluminum alloy substrate or a glass substrate before forming the magnetic film 11. Further, as described above, this surface waviness is caused by the grindstone in the grinding process in the case of an aluminum alloy substrate and the grindstone in the wrapping process in the case of a glass substrate. Therefore, it is more preferable to evaluate the waviness of the substrate after the grind step or the wrapping step is completed because the quality of the substrate for each processing batch can be confirmed immediately. The waviness evaluation step (step S107) and the determination step (step S108) described above are carried out after the polishing step (step S106), but more preferably after the grind step (step S104). Is good. Further, the waviness evaluation step (step S205) and the determination step (step S206) are carried out after the polishing step (step S204), but more preferably after the wrapping step (step S203). ..

The reason why the waviness measurement region MA is defined as a region surrounded by concentric circles with r1 = radius R-0.5 mm and r2 = radius R-4.0 mm will be described. The surface waviness generated on the outer peripheral side of the magnetic disk 10 tends to occur in a region surrounded by concentric circles having a distance from the center of R and R-4.0 mm, where R is the radius of the disk. However, if the area is set as the swell measurement area, the error of the swell measurement value becomes large. In the optical system where the measurement light emitted from the swell inspection device is reflected on the surface of the substrate and returned to the sensor of the inspection device, the measurement light is diffusely reflected at the chamfered portion at the outer peripheral edge of the disk, resulting in an error in the swell measurement value. It is thought to be born. Waviness can be measured stably by masking the outer peripheral edge of the disk with a width of 0.5 mm. The above is the reason why the waviness measurement region MA is defined as a region surrounded by concentric circles with r1 = radius R-0.5 mm and r2 = radius R-4.0 mm.

As described above, according to the method for manufacturing the magnetic disk substrate 100 and the magnetic disk substrate of the present embodiment, they are surrounded by concentric circles with r1 = radius R-0.5 mm and r2 = radius R-4.0 mm. In the measurement region MA, when the arithmetic mean undulation Wa of the wavelength λ of 1 mm or more and 5 mm or less is 4.0 nm or less, the thickness of the magnetic disk 10 can be reduced and the number of sheets mounted on the HDD can be increased. Further, by enlarging the recording area of the magnetic disk 10 and making the data area on the disk surface as close as possible to the outer diameter end, it is possible to expand the data area per magnetic disk, and the capacity of the HDD can be increased. Can contribute. Further, the poor media evaluation of the magnetic disk 10 is caused by the surface waviness of the wavelength λ on the outer peripheral side of the magnetic disk 10 of 1 mm or more and 5 mm or less, and the surface waviness has a large difference before and after forming the magnetic film 11. Therefore, it is possible to evaluate the magnetic disk substrate 100 on which the magnetic film 11 is not formed. Since the magnetic disk substrate 100 can be evaluated before the magnetic disk 10 is manufactured, it is possible to reduce the number of magnetic disk 10s that are rejected by the media evaluation. On the other hand, the conventional swell evaluation is not a method focusing on a specific region of the substrate. For example, the measurement region is an arithmetic mean swell in the entire surface of the substrate or an arbitrary region of the substrate surface. Is a way to evaluate. With that method, there is a problem that the swell on the outer peripheral side of the substrate cannot be accurately captured.

Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited thereto.

(Effect of the grind process on the swell of the outer circumference of the disc)
In order to confirm the effect of the grind process on the waviness of the outer peripheral portion of the disk, grind processing was performed under various conditions to prepare an aluminum alloy substrate for a magnetic disk.

The specific composition of the aluminum alloy is Fe: 0.7% by mass, Mn: 0.9% by mass, Ni: 1.7% by mass, Si: 0.06% by mass, Zn: 0.3% by mass, Cu. : 0.02% by mass, the balance consists of aluminum and other trace elements.

First, an ingot was produced by a semi-continuous casting method, and the ingot was hot-rolled and cold-rolled to produce a plate material having a thickness of 0.52 mm.

Next, this plate material was punched by a press machine to obtain a blank having an inner diameter of 24 mm and an outer diameter of 98 mm, and then the blanks were laminated with each other, and a load was applied to the laminated blank to perform heat treatment.

Next, the inner diameter portion and the outer diameter portion of this blank were cut and chamfered with a lathe processing machine to prepare a T-sub having an inner diameter dimension of 25 mm and an outer diameter dimension of 97 mm, and heat-treated.

Next, the surfaces of both sides of the T-sub were ground with a grinding machine to prepare a G-sub having a thickness of 0.48 mm. The grind processing conditions are as follows.

After dressing the grindstone, 10 sheets were made into one batch, and a total of 200 sheets were grinded from 1 to 20 batches. The coolant used was a Mechanoaqua Cut ECO # 408 stock solution manufactured by Daichi Chemical Industry, which contained a surfactant and a lubricant, diluted to 1% with water, and the flow rate was 3.5 L / min. This is called grind test 1.

Next, after dressing the grindstone again, 10 sheets were made into one batch, and a total of 100 sheets were grinded from 1 to 10 batches. The coolant used was Mechanoaqua Cut ECO # 408 undiluted solution manufactured by Daichi Chemical Industry diluted to 0.1% with water, and the flow rate was 3.5 L / min. This is called grind test 2.

Here, sample A-1 is sampled from the first batch of grind test 1, sample A-2 is sampled from the tenth batch, sample A-3 is sampled from the 20th batch, and sample A-4 is sampled from the first batch of grind test 2. One batch and one sample A-5 were sampled from the tenth batch.

Next, these G-subs were plated. First, a pretreatment was performed for the purpose of improving the plating adhesion, then an electroless Ni-P plating treatment having a thickness of 11 μm per side was performed, and then a heat treatment was performed.

Further, the surfaces of both sides of the M sub were polished with a polishing machine to prepare an aluminum alloy substrate having a thickness of 0.5 mm and an outer diameter of 97 mm.

Next, the performance of these samples was evaluated.

First, using the stylus type shape measuring machine Contracer C-3000, as shown in FIGS. 11A to 11C, the length L of the chamfered portion on the outer peripheral side of the substrate and the height D of the outer peripheral sagging PS are used. And the length L of the chamfered portion of the outer peripheral portion was measured. X1 and X2 are reference points, and the distance from the outer diameter end to X1 is 30 mm, and the distance to X2 is 15 mm. The height D was obtained by measuring the distance in the thickness direction between the straight line passing through X1 and X2 and the chamfering start portion C. The length L of the chamfered portion was obtained by measuring the distance between the chamfering start portion C and the outer diameter end portion (chamfering end portion) E in the radial direction. Next, the flatness of the substrate was measured using the optical inspection device ZYGO Mesa. Next, using the optical inspection device OPTIFLAT, the swell evaluation of the arithmetic mean swell Wa having a wavelength λ on the substrate surface in the measurement region 1 of 1 mm or more and 5 mm or less was performed. The undulation measurement region 1 is an evaluation method of the present embodiment focusing on the outer peripheral side of the substrate, and specifically, is a region surrounded by concentric circles with distances r1 = 48 mm and r2 = 44.5 mm from the center of the substrate. The measurement area 1 is the same area as the measurement area MA described above. As the acceptance criteria, those with an arithmetic mean swell Wa of 4.0 nm or less were marked with ◯, and those with an arithmetic mean swell Wa of more than 4.0 nm were marked with x. The above results are shown in Table 1.

Samples A-1 and A-2 passed when the arithmetic mean waviness Wa on the outer peripheral portion of the substrate was 4.0 nm or less. Samples A-3, A-4, and A-5 were rejected because the arithmetic mean waviness Wa on the outer peripheral portion of the substrate exceeded 4.0 nm. Comparing the samples A-1, A-2, and A-3, the arithmetic mean swell Wa on the outer peripheral portion of the substrate showed a tendency of A-1 <A-2 <A-3. The less the clogging of the grindstone during the grinding process, the smaller the waviness on the outer peripheral side of the substrate. Comparing the samples A-1 and A-4, the arithmetic mean swell Wa of the outer peripheral portion of the substrate was A-1 <A-4. All of them are grinded immediately after dressing the grindstone to remove the clogging, but the coolant concentration is different. Since the coolant concentration of A-4 was low, it is probable that the effect of the coolant that discharges the grinding debris generated during grinding to the outside of the system was not fully exhibited, and the grindstone was immediately clogged during grinding. .. In this case, in the grind step (step S104) described above, the Mechano Aqua Cut ECO # 408 undiluted solution manufactured by Daichi Chemical Industry Co., Ltd., which is the condition for grinding the samples A-1 and A-2, diluted to 1% with water. , The flow rate is 3.5 L / min, and the grinding conditions may be set based on the condition that the grindstone is dressed and then ground from the first batch to the tenth batch.

(Effectiveness of swell evaluation method)
In order to confirm the effectiveness of the swell evaluation method, swell evaluation was performed under various conditions.

Samples A-1 to A-3 are the aluminum alloy substrates of Examples 1 and 2, and Sample B-1 is a magnetic disk made of an aluminosilicate glass substrate having a thickness of 0.635 mm and an outer diameter of 95 mm that has passed the media evaluation. The disk and sample B-2 are magnetic disks made of an aluminosilicate glass substrate having a thickness of 0.5 mm and an outer diameter of 97 mm that have passed the media evaluation.

An optical inspection device OPTIFLAT was used to evaluate the waviness, and the arithmetic mean waviness Wa of the substrate surface having a wavelength λ of 1 mm or more and 5 mm or less was evaluated in each measurement region shown below. The measurement region 1 is a region surrounded by concentric circles of r1 = R-0.5 (mm) and r2 = R-4.0 (mm), and is the same as the measurement region MA according to the present embodiment. The measurement area 2 is surrounded by concentric circles of r1 = R-0.5 (mm) and r3 = R-30.5 (mm) (r3 = R-29.5 (mm) for sample B-1). Area. The measurement area 3 is surrounded by concentric circles of r2 = R-4.0 (mm) and r3 = R-30.5 (mm) (for sample B-1, r3 = R-29.5 (mm)). Area. The measurement area 2 and the measurement area 3 are measurement areas different from those of the present embodiment. The measurement area 1 and the measurement area 3 are not in a comprehensive relationship (measurement area 1 ≠ measurement area 3), and the measurement area 2 is composed of the measurement area 1 and the measurement area 3 (measurement area 2 = measurement area 1 + measurement area 3). The results are shown in Table 2 and FIG.

In the measurement region 1, samples A-1 and A-2 were judged to pass when the arithmetic mean swell Wa was 4.0 nm or less, and sample A-3 was judged to be rejected when the arithmetic mean swell Wa exceeded 4.0 nm. In addition, the samples B-1 and B-2 that passed the media evaluation were also judged to pass when the arithmetic mean swell Wa was 4.0 nm or less.

When the swell evaluation was performed under the conditions of the measurement area 2 and the measurement area 3, the swell Wa was measured to be 4.0 nm or less in all the samples including the sample A-3 which was judged to be unacceptable in the measurement of the measurement area 1. rice field. In the method of measuring the measurement area 2 or the measurement area 3, it is not possible to accurately capture the area with high swell on the outer peripheral side of the substrate, and it is impossible to determine the read / write error when the substrate is made into a magnetic disk. I understand.

The present invention allows for various embodiments and modifications without departing from the broad spirit and scope of the invention. Further, the above-described embodiments are for explaining the present invention, and do not limit the scope of the present invention. That is, the scope of the present invention is shown not by the embodiment but by the scope of claims. And, various modifications made within the scope of the claims and the equivalent meaning of the invention are considered to be within the scope of the present invention.

10 Magnetic disk 11 Magnetic disk film 100 Magnetic disk substrate 110 G sub 210 Carrier 220 Fixed abrasive grain 221 Cutting groove MA Measurement area R Radius PS Outer circumference sagging D Height L Length

Claims (3)

Grinding process for grinding magnetic disk substrates, and
For the magnetic disk substrate ground in the grinding step, when the distance from the center is r1> r2, the measurement is surrounded by concentric circles with r1 = radius R-0.5 mm and r2 = radius R-4.0 mm. In the region, the swell evaluation step for measuring the arithmetic average swell Wa with a wavelength of 1 mm or more and 5 mm or less, and
A determination step of determining whether or not the arithmetic mean undulation Wa measured in the undulation evaluation step is 4.0 nm or less, and extracting the substrate for the magnetic disk having an arithmetic average undulation Wa of 4.0 nm or less.
A method for manufacturing a substrate for a magnetic disk, which comprises. The plate thickness of the magnetic disk substrate is 0.5 mm or less.
The method for manufacturing a substrate for a magnetic disk according to claim 1 . The diameter of the magnetic disk substrate is 95 mm or more and 97 mm or less.
The method for manufacturing a substrate for a magnetic disk according to claim 1 or 2 , wherein the substrate is manufactured.

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