JP4191756B2 - Magnetic disk unit - Google Patents

Description

  The present invention relates to a magnetic disk device having a head disk assembly (HDA).

The HDA used in the magnetic disk apparatus is made of metal as a housing for housing a magnetic head that records and reproduces magnetic information facing a magnetic disk that is a recording medium or a magnetic disk that rotates at high speed, a head drive mechanism, and the like. Due to an airtight structure having a base and a cover and sealing the contact portion between the base and the cover, dust can be prevented from entering the housing. In recent years, as a member for sealing between the base and cover members, a three-layer seal tape in which a metal layer is sandwiched between insulating resin layers is generally used as described in Patent Documents 1 and 2, for example. It has become the target. The metal layer of the seal tape exhibits an electromagnetic shielding effect, and the insulating resin layer imparts flexibility to the seal tape and improves hermeticity. This three-layer seal tape is adhered along the outer peripheral surface of the base and cover with an adhesive applied to one of the insulating resin layers, thereby sealing the contact portion between the base and the cover. .
JP 07-073658 A JP 10-055662 A

  Conventionally, the sealing with the sealing tape is performed manually one by one. In order to improve the degree of sealing, the sticking position of the seal is strictly defined. If the sticking position of the sticker deviates from the specified position, it is necessary to peel off the sticking tape and reapply a new sealing tape. . However, it has been found that when the seal tape peeling operation is performed, the element portion of the HDA is damaged.

  The present invention has been made in view of the above problems, and an object of the present invention is to obtain a magnetic disk device that prevents electrostatic discharge between the seal tape and the HDA and does not damage the HDA element portion.

  The present invention has been completed with the conclusion that the cause of damage to the HDA element due to the sealing tape peeling work is the electrostatic discharge generated between the sealing tape and the HDA. The mechanism by which electrostatic discharge occurs between the seal tape and the HDA due to the seal tape peeling operation is considered as follows. That is, since the sealing tape has a layer structure having a metal layer in the insulating resin layer, when the sealing tape is peeled off from the contact portion between the base and the cover, first, the adhesive-coated side (attached to the HDA) The high-voltage peeling charge is generated in the insulating resin layer (lower insulating resin layer) on the other side, and charge is induced in the metal layer by this peeling charging. As the amount of peeling of the sealing tape increases (the adhesive area between the sealing tape and HDA decreases), the amount of charge induced in the metal layer increases, and between the metal layer and the HDA facing each other across the lower insulating resin layer. The capacitance decreases, and the voltage between the metal layer and the HDA increases as the capacitance decreases. When the voltage between the metal layer and the HDA exceeds the withstand voltage of the lower insulating layer, electrostatic discharge (high voltage discharge) occurs between the metal layer and the HDA, and the element portion of the HDA is damaged by this electrostatic discharge. The potential for electrostatic discharge is greatest at the moment the seal tape is completely removed from the HDA. Therefore, the present invention has a four-layer structure of the seal tape of elastic layer / metal layer / elastic layer / conductive layer, and charges are accumulated between the metal layer and the conductive layer, so that the seal layer is peeled off between the metal layer and the HDA. We propose to suppress the voltage increase.

  That is, the present invention provides a magnetic disk having a head disk assembly including a metal base and cover for housing a magnetic head structure, and a seal tape attached to the outer peripheral surface of the base and cover to seal between the two members. In the disk device, the seal tape is formed by laminating a lower elastic insulating layer, a metal layer, an upper elastic insulating layer, and a conductive layer in order from the base and the cover side. By providing a conductive layer on the upper elastic insulating layer, the metal layer and the conductive layer facing each other across the upper elastic insulating layer function as a parallel plate capacitor, and charges are accumulated between the metal layer and the conductive layer. Even if the capacitance between the metal layer and the HDA is reduced due to the peeling, the voltage between the metal layer and the HDA is not excessively increased due to the capacitance between the metal layer and the conductive layer.

Upper elastic insulating layer is not thin than the lower elastic insulating layer. The thinner the upper elastic insulating layer interposed between the metal layer and the conductive layer, the larger the capacitance between the metal layer and the conductive layer, and the lower elastic insulating layer interposed between the metal layer and the base and cover. Since the withstand voltage of the lower elastic insulating layer increases as the thickness of the lower elastic insulating layer increases, it is possible to further suppress an increase in voltage between the metal layer and the HDA due to peeling of the seal tape. Since the thickness of the lower elastic insulating layer is actually determined according to the frequency of electromagnetic shielding, it is preferable that the upper elastic insulating layer is at least thinner than the lower elastic insulating layer.

  The conductive layer is preferably an antistatic layer formed of a polyoxyethylene surfactant or an anionic / cationic surfactant. Or it is preferable that it is the conductive resin layer formed of the conductive resin material. Of course, the conductive layer can be formed of a metal material, but it is necessary to consider durability due to corrosion or the like.

  It is practical that the lower elastic insulating layer is formed of an insulating adhesive layer that adheres to the base and the cover, and an insulating resin layer that is interposed between the adhesive layer and the metal layer.

  According to the present invention, the metal layer and the conductive layer facing each other across the upper elastic insulating layer function as a capacitor. Therefore, even if the capacitance between the metal layer and the HDA is reduced due to peeling of the seal tape, the metal layer -The increase in voltage between the metal layer and the HDA is suppressed by the capacitance between the conductive layers. As a result, a magnetic disk device that prevents electrostatic discharge between the seal tape and the HDA and does not damage the HDA element portion can be obtained.

  1 to 3 show a magnetic disk device having an HDA according to an embodiment of the present invention. FIG. 1 is an external view of the HDA. The HDA includes a magnetic head structure such as an element unit composed of a plurality of magnetic heads, a plurality of magnetic disks, a drive mechanism for driving the element unit, and a metal base 10 and a cover for housing the magnetic head structure. 20 and a seal tape 30 which is affixed along the outer peripheral surfaces of the base 10 and the cover 20 and seals between both members. The base 10 and the cover 20 have a substantially rectangular shape and are separated from each other in the HDA thickness direction, and are integrated by a screw member (not shown). A contact portion (contact surface, contact position) α between the base 10 and the cover 20 is indicated by a broken line in FIG.

  2A is a sectional view and FIG. 2B is a plan view showing the seal tape 30 as a single unit. The seal tape 30 includes a metal layer 32 that exhibits an electromagnetic shielding effect, and a lower elastic insulating layer 31 and an upper elastic insulating layer that are laminated above and below the metal layer 32 to give the seal tape 30 flexibility and increase hermeticity. 33 and a conductive layer 34 formed on the upper elastic insulating layer 33 to form a multilayer structure. In this specification, the elastic insulating layer on the side to be bonded to the base 10 and the cover 20 is defined as a lower elastic insulating layer 31.

  The metal layer 32 is formed with a thickness of about 10 μm from a metal material such as aluminum or nickel. The metal layer 32 exists over the entire length of the seal tape 30, and the width dimension (dimension in the short direction) W <b> 32 of the metal layer 32 is completely covered by the lower elastic insulating layer 31 and the upper elastic insulating layer 33. The lower elastic insulating layer 31 and the upper elastic insulating layer 33 are set to be narrower than the width dimensions (dimensions in the short direction) W31 and W33. When the seal tape 30 is affixed to the base 10 and the cover 20, the metal layer 32 functions as a parallel plate capacitor together with the base 10 and the cover 20 facing each other with the lower elastic insulating layer 31 interposed therebetween, while the upper elastic insulating layer 33. It functions as a parallel plate capacitor together with the conductive layer 34 facing each other.

  The lower elastic insulating layer 31 includes an insulating adhesive layer 31 a that adheres to the base 10 and the cover 20, and an insulating resin layer 31 b that is interposed between the insulating adhesive layer 31 a and the metal layer 32. The insulating adhesive layer 31a is made of, for example, an insulating resin adhesive tape (sheet) made of acrylic or the like, and the adhesive surface (the surface facing the base 10 and the cover 20) 31a1 is peeled off before the seal tape 30 is applied. Covered with paper. The insulating resin layer 31b is formed of an insulating resin material such as polyethylene terephthalate (PET) or polyvinyl chloride (PVC). As the thickness of the lower elastic insulating layer 31 is increased, the capacitance generated between the metal layer 32 and the base 10 and the cover 20 when the seal tape 30 is attached to the base 10 and the cover 20 is reduced. The breakdown voltage can be increased. The thickness of the lower elastic insulating layer 31 is specifically about 30 μm in the present embodiment, but it is practical that it is determined according to the frequency of the metal layer 32 that is electromagnetically shielded.

  The upper elastic insulating layer 33 is formed of an insulating resin material such as polyethylene terephthalate (PET) or polyvinyl chloride (PVC), similarly to the insulating resin layer 31b. Since the upper elastic insulating layer 33 is interposed between the metal layer 32 and the conductive layer 34, the capacitance between the metal layer 32 and the conductive layer 34 can be increased as the thickness is reduced. The thickness of the upper elastic insulating layer 33 is specifically about 10 μm, and is set thinner than the lower elastic insulating layer 31.

  The conductive layer 34 is formed by dipping (a step of coating the surface of the seal tape 30 by immersing the seal tape 30 in a solution comprising a polyoxyethylene surfactant or an anionic / cationic surfactant). A conductive resin layer formed of a prevention layer or a resin material mixed with a conductive material such as carbon or metal fiber, and has a thickness of about 10 μm. The conductive layer 34 covers the upper surface of the upper elastic insulating layer 33 and is not in contact (non-conductive) with the metal layer 32.

  The sticking position of the seal tape 30 is strictly defined with respect to the base 10 and the cover 20 in order to ensure the airtightness of the HDA, and the seal sticking position with respect to the HDA whose position is deviated from a preset prescribed position. Needs to peel off the seal tape 30 from the base 10 and the cover 20 and reapply a new seal. The seal tape peeling operation is performed in a state where the base 10 and the cover 20 are connected to the ground potential, and the conductive layer 34 on the surface of the seal tape is connected to the ground potential. When the sealing tape 30 is peeled off, peeling electrification occurs in the lower elastic insulating layer 31, and induced charges due to the peeling charging are induced in the metal layer 32 and accumulated between the metal layer 32 and the conductive layer 34. As the peeling distance of the sealing tape increases, the amount of charge induced in the metal layer 32 increases. At this time, the capacitance between the metal layer 32 and the base 10 and the cover 20 facing each other across the lower elastic insulating layer 31 decreases, but the capacitance between the metal layer 32 and the conductive layer 34 increases. Due to the capacitance between the layer 32 and the conductive layer 34, an increase in voltage between the metal layer 32-base 10 and the cover 20 is suppressed.

  Below, with reference to FIG. 3, the voltage increase suppression effect between the metal layer 32-base 10 and the cover 20 by the electrostatic capacitance between the metal layer 32-conductive layer 34 is demonstrated in detail.

In the seal tape 30 attached along the outer peripheral surfaces of the base 10 and the cover 20, when the metal layer 32 and the base 10 and the cover 20 facing each other with the lower elastic insulating layer 31 interposed therebetween are considered as parallel plate capacitors, a dielectric constant ε, When the surface area S of the metal layer 32 and the distance from the metal layer 32 to the base 10 and the cover 20 (thickness of the lower elastic insulating layer 31) d1 are electrostatic charges generated between the metal layer 32-base 10 and the cover 20 The capacitance C1 is given by the following equation (1).
C1 = ε · S / d1 (1)

Next, let us consider the capacitance change and voltage change due to the seal tape peeling operation. When the sealing tape 30 is peeled off, it is presumed that peeling electrification occurs in the lower elastic insulating layer 31 of the sealing tape 30 and electric charges are induced in the metal layer 32 by this peeling charging. When the charge amount generated by the peeling charging is Q, the voltage V1 between the metal layer 32-base 10 and the cover 20 is given by the following equation (2).
V1 = Q / (C1 + Cf) (2)
Where Cf: stray capacitance.
At this time, assuming that the total length L of the seal tape 30 is the separation distance x, the capacitance C1 between the metal layer 32-base 10 and the cover 20 is expressed by the following equation (3).
C1 = (ε · S (1-x / L)) / d1 (3)
As is clear from the equation (3), when the peeling distance x is increased by the sealing tape peeling operation, the capacitance C1 between the metal layer 32-base 10 and the cover 20 is reduced.

Here, when the metal layer 32 and the conductive layer 34 facing each other with the upper elastic insulating layer 33 interposed therebetween are also considered as parallel plate capacitors, the distance from the metal layer 32 to the conductive layer 34 (thickness of the upper elastic insulating layer 33) d2. When the conductive layer 34 is grounded, the capacitance C2 generated between the metal layer 32 and the conductive layer 34 is given by the following equation (4).
C2 = ε · S / d2 (4)

Therefore, the voltage V between the metal layer 32-base 10 and the cover 20 is given by the following equation (5).
V = Q / (C1 + C2 + Cf) (5)

When the seal tape 30 is completely peeled off, the peel distance x becomes equal to the total length L of the seal tape 30, so that the capacitance C1 = 0 between the metal layer 32 and the base 10 and the cover 20, and the metal layer 32 and the base 10. The voltage V between the cover 20 and the cover 20 is expressed by the following equation (6).
V = Q / (C2 + Cf) (6)
Here, the capacitance C2 between the metal layer 32 and the conductive layer 34 is much larger than the stray capacitance Cf (C2 >> Cf), and the stray capacitance Cf is negligible in the equation (6). Therefore, as apparent from the equation (6), the voltage V between the metal layer 32 and the base 10 and the cover 20 depends on the capacitance C2 between the metal layer 32 and the conductive layer 34, and this capacitance C2 is It can be seen that the voltage V decreases as the value increases.

On the other hand, when the conductive layer 34 is not present on the upper elastic insulating layer 33 or when the conductive layer 34 is not grounded, the peeling distance x is equal to the sealing tape 30 when the sealing tape 30 is completely peeled off. Therefore, the capacitance C1 = 0 between the metal layer 32-base 10 and the cover 20 is obtained, and the voltage V ′ between the metal layer 32-base 10 and the cover 20 is given by the following equation (7). It is done.
V ′ = Q / (Cf) (7)
As described above, since the stray capacitance Cf is very small, the voltage V ′ between the metal layer 32 and the base 10 and the cover 20 becomes very large as is apparent from the equation (7). When the voltage V ′ between the metal layer 32 and the base 10 and the cover 20 increases as described above, breakdown of the lower elastic insulating layer 31 may occur, and electrostatic discharge may occur between the metal layer 32 and the base 10 and the cover 20. Will become bigger.

As described above, the conductive layer 34 exists on the upper elastic insulating layer 33 and the conductive layer 34 is grounded when the seal tape is peeled off, and the conductive layer 34 exists on the upper elastic insulating layer 33. When the voltage V, V ′ between the metal layer 32 and the base 10 and the cover 20 is compared when the sealing tape 30 is completely peeled off when the conductive layer 34 is not grounded or when the conductive layer 34 is not grounded, The ratio V: V ′ is given by equation (8).
V: V ′ = (Q / (C2 + Cf)): (Q / Cf)
= 1: (C2 / Cf + 1) (8)

  As is clear from the above equation (8), when the conductive layer 34 exists on the upper elastic insulating layer 33 and the conductive layer 34 is grounded during the peeling operation of the seal tape, the upper elastic insulating layer The voltage between the metal layer 32 and the base 10 and the cover 20 is very small as compared with the case where the conductive layer 34 is not present on 33 or the case where the conductive layer 34 is present but not grounded. An increase in voltage between the metal layer 32-base 10 and the cover 20 due to tape peeling can be suppressed. If an increase in voltage between the metal layer 32-base 10 and the cover 20 due to peeling of the sealing tape is suppressed, electrostatic discharge does not occur between the metal layer 32-base 10 and the cover 20, and the element of the HDA during the sealing tape peeling operation You can avoid the damage.

  In the above embodiment, the antistatic layer formed of a polyoxyethylene surfactant or an anionic / cationic surfactant, or a resin material mixed with a conductive material such as carbon or metal fiber is used. Although the conductive resin layer is used as the conductive layer 34, the conductive layer 34 can of course be formed of a metal material. However, when the conductive layer 34 is formed of a metal material, it is necessary to consider durability due to corrosion or the like.

  In this embodiment, the thickness of the upper elastic insulating layer 33 is set to be thinner than the thickness of the lower elastic insulating layer 31, but the thicknesses of the upper elastic insulating layer 33 and the lower elastic insulating layer 31 are appropriately set. Also good. If the thickness of the upper elastic insulating layer 33 is reduced as in the present embodiment, the capacitance C2 between the metal layer 32 and the conductive layer 34 is increased, and if the thickness of the lower elastic insulating layer 31 is increased, the capacitance C2 is increased. Since the withstand voltage of the lower elastic insulating layer 31 is increased, an increase in voltage between the metal layer 32-base 10 and the cover 20 due to peeling of the seal tape can be further suppressed.

1 is an external view showing an HDA of a magnetic disk device to which the present invention is applied. (A) It is sectional drawing which shows the structure of a seal tape. (B) It is a top view of a seal tape. It is sectional drawing explaining a seal tape peeling operation | work.

Explanation of symbols

10 Base 20 Cover 30 Sealing Tape 31 Lower Elastic Insulating Layer 31a Insulating Adhesive Layer 31b Insulating Resin Layer 32 Metal Layer 33 Upper Elastic Insulating Layer 34 Conductive Layer

Claims (4)

In a magnetic disk device having a head disk assembly comprising a metal base and cover for housing a magnetic head structure, and a seal tape affixed to the outer peripheral surface of the base and cover and sealing between the two members.
The sealing tape is formed by laminating a lower elastic insulating layer, a metal layer, an upper elastic insulating layer and a conductive layer in order from the base and cover side ,
The magnetic disk drive according to claim 1, wherein the upper elastic insulating layer is thinner than the lower elastic insulating layer . 2. The magnetic disk drive according to claim 1 , wherein the conductive layer is an antistatic layer formed of a polyoxyethylene surfactant or an anionic / cationic surfactant. 2. The magnetic disk drive according to claim 1 , wherein the conductive layer is a conductive resin layer formed of a conductive resin material. The magnetic disk drive according to any one of claims 1 to 3, wherein the lower elastic insulating layer includes an insulating adhesive layer adhering to the base and the cover, is interposed between the adhesive layer and the metal layer A magnetic disk device formed of an insulating resin layer.