JP2007220243A - Esd (electrostatic discharge) current occurrence prevention method in magnetic disk apparatus and magnetic disk apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ESD current occurrence prevention method by which a steep ESD current does not flow in a base made of metal from an insulation sheet constituted of an insulating sheet and a magnetic shield plate or constituted of the insulating sheet, the magnetic shield plate, a sound absorption member and the like and a leakage magnetic flux is effectively attenuated at a low cost and to provide a magnetic disk apparatus. <P>SOLUTION: An antistatic member is interposed between the magnetic shield plate and the base made of metal. The antistatic member is e.g. an antistatic film having 1×10<SP>5</SP>to 1×10<SP>12</SP>Ω/square surface resistivity. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to prevention of generation of an ESD current by a magnetic shield member for preventing leakage magnetic flux from a magnet member of a magnetic disk device from reaching a circuit board as much as possible.

  Conventionally, as shown in a schematic sectional view of a magnetic disk device in FIG. 3, in the magnetic disk device, a disk-shaped recording medium 1, a spindle motor 2 that rotates the recording medium 1, and data for the recording medium 1 are recorded. A magnetic head 3 for writing / reading, a head arm 4 for supporting the magnetic head 3, a positioner 5 for positioning the magnetic head 3 on the recording medium, and the like are incorporated in a base 6 of an aluminum die casting, for example. The circuit board 7 is fixed to the base 6 by a plurality of columns 7-1 in a region opposite to the positioner 5.

  The positioner 5 includes, for example, a magnetic circuit 5-1 including a permanent magnet 5-1-1 and a yoke 5-1-2, a rotation shaft 5-2 that supports the rotation operation of the head arm 4, and a magnetic force of the head arm 4. When a current flows through the coil 5-3 in the magnetic field generated by the magnetic circuit 5-1, the coil 5-3 attached to the end opposite to the end to which the head 3 is attached causes the head arm 4 to Is configured to generate a rotational force around the rotation shaft 5-2.

  The base 6 and the circuit board 7 are electrically connected to a ground wire of the magnetic disk device, and the ground wire is further electrically connected to a ground wire of a device such as a PC in which the magnetic disk device is incorporated.

  On the other hand, a sheet called an insulation sheet 8 is interposed between the circuit board 7 and the base 6. The insulation sheet 8 is mainly composed of an insulating sheet (hereinafter referred to as a PET film) 8-1 made of polyethylene terephthalate to prevent an electrical short circuit between the circuit board 7 and the base 6, for example. A circuit for leakage magnetic flux from the permanent magnet 5-1-1 and the coil 5-3 used in the magnetic circuit 5-1 of the positioner 5 and the sound absorbing member 8-2 for absorbing noise generated by the positioner operation. A magnetic shield plate 8-3 or the like for shielding the influence on the substrate 7 is attached so as to have an effective function at a low cost in a narrow space as much as possible.

  Therefore, as an example, for example, as shown in the cross-sectional view of the insulation sheet shown in the conventional example of FIG. 2, the insulating sheet 8-1 has a thickness as a sound absorbing member 8-2 on the surface of a PET film having a thickness of 1 mm or less. Place a plate-like polyurethane foam material of 2 mm or less, separate it so as not to overlap with the sound absorbing member 8-2, and attach an electromagnetic stainless steel plate with a thickness of 2 mm or less as a magnetic shield plate 8-3 with an adhesive tape, The other side was mounted in contact with the aluminum base of the device.

  In the insulation sheet as described above, the insulating sheet and the sound absorbing member are non-metallic materials and are easily charged with static electricity. Therefore, in order to prevent charging of the insulating sheet and the sound absorbing member, a PET film coated with an antistatic agent or a sound absorbing member made of a material having an antistatic effect has been used. When static electricity was made difficult, but it was still charged, it was thought that the static electricity would flow from the magnetic shield plate made of electromagnetic stainless steel through the aluminum base of the equipment to the equipment ground line.

  On the other hand, regarding the prevention of destruction of the MR head due to static electricity, the cause of the steep ESD current generated from the outside or the inside of the magnetic disk device is investigated, and the generation is suppressed or the ESD current does not flow to the MR head. Efforts have been made.

  However, it has been experimentally confirmed that a steep ESD current sometimes flows through the MR head even when the above-described insulation sheet is subjected to static electricity countermeasures.

  If the insulation sheet is charged with static electricity, the metal magnetic shield plate may be induction charged, but even if the metal magnetic shield plate is induction charged, one side of the metal magnetic shield plate is the device. It is in contact with the aluminum base surface. For this reason, it was thought that a steep ESD current did not occur first. However, in the structure described above, if the state of contact with the surface of the aluminum base, which is considered to be in contact with the induction-charged metal magnetic shield plate, is electrically unstable, for example, in FIG. When the plate receives an impact force and collides with the base 6 of the aluminum die casting, an ESD current flows from the magnetic shield plate 8-3 to the base 6, the head amplifier 10 and the magnetic head 3 in FIG. It has been observed that there is a potential difference between the terminals that can destroy the GMR head element. This is shown in the conventional example of the potential difference waveform between the GMR head terminals in FIG. A maximum potential difference of +104 mV and a minimum of −100 mV is observed between the GMR head terminals of channel 2.

  It was found that the conditions under which the ESD current flows were different depending on the degree of oxidation of the surface of the aluminum base and the surface of the magnetic shield plate, and the contact condition, and the state was unstable.

  Even if the insulation sheet and sound absorbing member are changed to those of antistatic material, the ground voltage is unstable unless the metal magnetic shield plate is electrically connected to the ground wire. When it comes into contact with the metal surface, a steep ESD current may flow. In other words, even if one surface of the magnetic shield plate is attached to an insulating sheet that has been subjected to antistatic treatment, the problem is that the opposite surface is in contact with the metal surface of the base while remaining the metal surface. .

  However, when the magnetic shield plate is wrapped with an insulating member, if the insulating member is in contact with the metal surface of the base, if the insulating member is charged, static electricity accumulated on the surface of the insulating member will cause a steep current to the base. May flow. Further, if the magnetic shield plate is placed at a position away from the base surface, the effect of preventing leakage magnetic field leaking through the base from leaking to the circuit board as much as possible is reduced. A solution to secure a sufficient thickness of the magnetic shield plate in a narrow space and to attenuate the leakage flux effectively and inexpensively was required.

As a known technique related to this, for example, Japanese Patent Application Laid-Open No. 2001-23102 describes a magnetic disk device in which the MR head is prevented from being destroyed by static electricity in the HSA manufacturing process of the magnetic disk device, and a coil holder for a coil of a positioner Is covered with a static shield film, and the connector pin of the MR head connection connector and the connection portion of the printed wiring circuit are covered with a high resistance member of 1 × 10 ⁵ Ω or more to prevent the MR head from being charged. A technique for preventing electric breakdown is described.

The technology described in Japanese Patent Laid-Open No. 2001-23102 describes the prevention of electrification between the MR head and the MR head after the MR head connection connector. The steep ESD current at the location before the MR head connection connector is described. The inflow is not mentioned.
Japanese Patent Laid-Open No. 2001-23102

  In order to solve the above problems, the present invention provides an insulating sheet and a magnetic shield plate, or an insulation sheet composed of an insulating sheet, a magnetic shield plate, a sound absorbing member, and the like, to a metal base. It is an object of the present invention to provide a method for preventing a steep ESD current from flowing and effectively attenuating a leakage magnetic flux at a low cost, and a magnetic disk device embodying this method.

According to a first aspect of the present invention, in the magnetic disk device, a positioner unit for positioning a magnetic head attached to a first surface of a metal base of the magnetic disk device, and the positioner unit relating to the base A circuit board disposed on the side of the second surface opposite to the surface on which is mounted, an insulating layer provided between the circuit board and the second surface, the insulating layer, and the second A magnetic shield layer that reduces magnetic field strength exerted on the circuit board by a magnetic flux leaked from the magnet of the positioner portion, and a surface of the magnetic shield layer facing the second surface. The magnetic disk apparatus is characterized in that an antistatic member having a surface resistivity of 1 × 10 ⁵ Ω / □ or more and 1 × 10 ¹² Ω / □ or less is interposed therebetween.

According to the first aspect of the present invention, the antistatic member is interposed between the magnetic shield plate and the metal base. The antistatic member is, for example, an antistatic film having a surface specific resistance value in the range of 1 × 10 ⁵ Ω / □ to 1 × 10 ¹² Ω / □. The antistatic film may be in the form of an adhesive tape or a film that does not have an adhesive surface. In the case of an adhesive tape, it may be attached to the surface of a metal base, or may be a magnetic shield. It may be affixed to the surface of the plate. The antistatic member having the above-mentioned surface specific resistance value which is neither an insulator nor a good conductor has a surface specific resistance value range of 1 × 10 ⁵ Ω / □ which is defined by ANSI / EIA541 and is 1 × Up to 10 ¹² Ω / □.

  As described above, since there is an antistatic member having electrostatic diffusibility between the magnetic shield plate and the metal base, even if the magnetic shield plate is in contact with the static insulating member, or Even if the magnetic shield plate is inductively charged, static electricity can be prevented from flowing steeply to the metal base.

  Here, it is more preferable that the surface of the insulating sheet is subjected to an antistatic treatment because static electricity is prevented from being accumulated around the magnetic shield plate.

  According to a second aspect of the present invention, a sound absorbing member made of a material having an antistatic effect without overlapping with the magnetic shield layer is disposed on the surface of the insulating layer on the side where the magnetic shield layer is disposed. This is a magnetic disk device.

  According to the second aspect of the present invention, since the antistatic member is interposed between the magnetic shield plate and the metal base, the magnetic shield plate can be used regardless of the presence or absence of the antistatic treatment on the surface of the insulating sheet. Even when dielectric charging is performed, it is possible to suppress a steep ESD current from flowing from the magnetic shield plate toward the metal base. Therefore, even if a sound absorbing member made of a material having an antistatic effect is arranged, a steep ESD current does not flow from the sound absorbing member toward the metal base, and the insulating sheet, the sound absorbing member, and the magnetic shield It can be set as the stable insulation sheet which combined the board.

According to a third aspect of the present invention, a positioner portion for positioning a magnetic head attached to a first surface of a metal base of a magnetic disk device, and the positioner portion is attached to the base. A circuit board disposed on the side of the second surface opposite to the surface, an insulating layer provided between the circuit board and the second surface, and between the insulating layer and the second surface And a magnetic shield layer that reduces magnetic field strength exerted on the printed board by leakage magnetic flux from the magnet of the positioner unit, between the surface of the magnetic shield layer facing the second surface. Is an ESD current generation prevention method characterized by interposing an antistatic member having a surface resistivity of 1 × 10 ⁵ Ω / □ or more and 1 × 10 ¹² Ω / □ or less.

  According to the present invention, in a magnetic disk device, an insulating sheet and a magnetic shield plate are provided for effectively attenuating leakage magnetic flux and suppressing steep ESD current from flowing into a metal base. Alternatively, a low-cost and stable insulation sheet composed of an insulating sheet, a magnetic shield plate, and a sound absorbing member can be obtained.

  FIG. 3 is a schematic sectional view of the magnetic disk device. FIG. 3 has already been outlined, but will now be described in detail.

  In the magnetic disk apparatus, a disk-shaped recording medium 1, a spindle motor 2 that rotates the recording medium 1, a magnetic head 3 that writes / reads data to / from the recording medium 1, and a head arm 4 that supports the magnetic head 3. , And a positioner 5 for positioning the magnetic head 3 on the recording medium are incorporated in the base 6 of the aluminum die casting, and the circuit board 7 is provided with a plurality of columns 7-1 in a region opposite to the positioner 5 with respect to the base 6. It is being fixed to the base 6 by.

  The positioner 5 is a rotary type positioner, a magnetic circuit 5-1 composed of a permanent magnet 5-1-1 and a yoke 5-1-2, a rotating shaft 5-2 for supporting the rotating operation of the head arm 4, and a head arm. When a current flows through the coil 5-3 in the magnetic field created by the magnetic circuit 5-1, the coil 5-3 is attached to the end opposite to the end to which the magnetic head 3 is attached. The arm 4 is configured to generate a rotational force around the rotation shaft 5-2.

  The magnetic head 3 is, for example, a GMR head, and in the production line, great care is taken with respect to the GMR head so as not to cause breakdown due to a steep ESD current due to static electricity.

  Each lead wire of the R / W head of the magnetic head 3 is connected to an FPC 9 extending along the head arm 4 and connected to the head amplifier 10 through an intermediate head preamplifier (not shown). The head amplifier 10 and the circuit board 7 are further connected by another FPC 9.

  The base 6 and the circuit board 7 are electrically connected to a ground wire of the magnetic disk device, and the ground wire is further electrically connected to a ground wire of a device such as a PC in which the magnetic disk device is incorporated.

  FIG. 2 shows a conventional example of an insulation sheet.

  A sheet called an insulation sheet 8 is interposed between the circuit board 7 and the base 6. The insulation sheet 8 is formed by, for example, a positioner operation mainly on an insulating sheet (PET film) 8-1 made of polyethylene terephthalate to prevent an electrical short between the circuit board 7 and the base 6. The sound absorbing member 8-2 for absorbing generated noise and the leakage magnetic flux from the permanent magnet 5-1-1 and the coil 5-3 used in the magnetic circuit 5-1 of the positioner 5 to the circuit board 7 A magnetic shield plate 8-3 or the like for shielding the influence is affixed to provide an effective function at a low cost in a narrow space as much as possible.

  Therefore, as shown in the conventional example of the insulation sheet in FIG. 2, a plate-like polyurethane foam having a thickness of 2 mm or less as a sound absorbing member 8-2 on the surface of a PET film having a thickness of 1 mm or less as an insulating sheet 8-1. Place the material so that it does not overlap with the sound absorbing member 8-2, and attach an electromagnetic stainless steel plate with a thickness of 2 mm or less as the magnetic shield plate 8-3 with adhesive tape, etc. It was mounted in contact with the base. The insulating sheet 8-1 and the sound absorbing member 8-2 constituting the insulation sheet are non-metallic materials and are easily charged with static electricity. Therefore, in order to prevent the insulation sheet 8-1 and the sound absorbing member 8-2 from being charged, a PET film coated with an antistatic agent or a sound absorbing member having an antistatic effect has been used. It was hard to be charged with static electricity.

  FIG. 1 shows an embodiment according to the invention. FIG. 1 shows a schematic cross-sectional view of the magnetic disk device. FIG. 3 shows a positioner 5, a base 6, a circuit board 7, an insulating sheet 8-1, a sound absorbing member 8-2, a magnetic shield plate 8-3, and a magnetic shield plate 8-3. The part of is enlarged and related. The same reference numerals in FIG. 1 and FIG. 3 denote the same parts.

  In FIG. 1, a) shows an upper surface of a magnetic shield plate 8-3 having a thickness of about 2 mm or less made of an electromagnetic stainless steel plate or a high-permeability material made of rust-resistant nickel-plated iron plate, and aluminum. In this embodiment, an antistatic film 12 having a thickness of 1 mm or less is provided between the bases 6 of the manufactured apparatus. Compared with the conventional example of insulation shown in FIG. 2, in the conventional example, nothing is interposed between the upper surface of the magnetic shield plate 8-3 and the base 6 of the apparatus made of aluminum. Also in FIG. 2, as in FIG. 1, the same reference numerals in FIG. 3 denote the same parts.

  Here, the antistatic film 12 is wider than the magnetic shield plate 8-3 so that the edge portion of the magnetic shield plate 8-3 does not come close to the base 6 directly.

  FIG. 1b shows an embodiment in which the antistatic film 13 is provided so as to cover the magnetic shield plate 8-3.

Furthermore, c) in FIG. 1 is an embodiment in which a sound absorbing member 8-2 is provided. In this case, the sound absorbing member 8-2 is made of, for example, a urethane foam material in which carbon particles having an antistatic effect that is hard to be charged with static electricity are mixed, or an antistatic agent on the surface of the urethane foam material. It is made with a coating. Even in this case, a steep ESD current due to dielectric charging does not flow into the base 6 from the magnetic shield plate 8-3, and at the same time, static electricity does not suddenly flow into the base 6 from the sound absorbing member 8-2.

  FIG. 4 shows the potential difference waveform measured between the GMR head terminals mounted on the magnetic disk apparatus when the conventional magnetic shield plate 8-1 shown in FIG. 2 is directly brought into contact with the base 6. It is an example. An antistatic agent is applied to the surface of the sound absorbing member 8-2.

  In addition, although the used insulating sheet 8-1 used the PET material, the withstand voltage of this PET material was about 2,000V. In addition, when the magnetic shield plate 8-1 insulating sheet was charged, the magnetic shield plate 8-1 was connected to the factory ground (ground wire installed in the factory and connected to the electrode rod embedded in the ground. FIG. 5 shows the waveform of the ESD voltage discharged. A maximum voltage of + 12.4V and a minimum voltage of -9.2V were observed.

  Similarly, the potential difference waveform between the GMR head terminals was observed. The result is as shown in the conventional example of the potential difference waveform between the GMR head terminals in FIG. An ESD current flows from the magnetic shield plate 8-3 to the base 6, the head amplifier 10 and the magnetic head 3 in FIG. 3 via the FPC 9, and there is a potential difference that may destroy the GMR head element between the head terminals. It was observed to occur. This is shown in the conventional example of the potential difference waveform between the GMR head terminals in FIG. A maximum potential difference of +104 mV and a minimum of −100 mV is observed between the GMR head terminals of channel 2. If the allowable value in this case is, for example, 100 mV in absolute value, a voltage exceeding the allowable value is generated.

Next, an adhesive tape having a surface resistance of about 1 × 10 ⁶ Ω / □ was used as the antistatic file 8-3 in the configuration of FIG. 1B), and the other conditions were the same as the waveform measurement in FIG. However, it was almost 0 mV. The observed value at this time is shown in the potential difference waveform between the GMR head terminals in the magnetic disk apparatus of the present invention in FIG.

  The ESD current does not flow greatly from the magnetic shield plate 8-3 to the base 6, and the potential difference waveform between the GMR head terminals is close to 0 mV.

  As described above, in the insulation sheet having the structure shown in FIG. 2, when the contact state between the induction-charged metal magnetic shield plate and the surface of the aluminum base is electrically unstable, for example, the magnetic shield plate When 8-3 vibrates and collides with aluminum die-cast base 6, ESD current flows from magnetic shield plate 8-3 to base 6, head amplifier 10 and magnetic head 3 in FIG. 3 via FPC 9, and between the head terminals. In this case, a potential difference with a risk of destroying the GMR head element is generated, but the problem is solved by taking the countermeasure shown in FIG.

Is an embodiment according to the present invention. Is a conventional example of an insulation sheet Is a schematic sectional view of a magnetic disk drive Is a conventional example of a potential difference waveform between GMR head terminals ESD voltage waveform discharged to factory ground Potential difference waveform between GMR head terminals in magnetic disk apparatus of the present invention

Explanation of symbols

1 Recording medium 2 Spindle motor
3 Magnetic Head 4 Head Arm 5 Positioner 6 Base 7 Circuit Board 8 Insulation Sheet 9 FPC
10 Head amplifier 11 Cover

Claims (3)

In the magnetic disk unit,
A positioner unit for positioning the magnetic head attached to the first surface of the metal base of the magnetic disk device;
A circuit board disposed on the second surface side opposite to the surface to which the positioner portion is attached with respect to the base;
An insulating layer provided between the circuit board and the second surface;
A magnetic shield layer that reduces magnetic field strength exerted on the circuit board by leakage magnetic flux from the magnet of the positioner portion between the insulating layer and the second surface;
An antistatic member having a surface resistivity of 1 × 10 ⁵ Ω / □ or more and 1 × 10 ¹² Ω / □ or less is interposed between the second surface and the surface of the magnetic shield layer facing the second surface. A magnetic disk device characterized in that:   A magnetic disk drive comprising: a sound absorbing member made of a material having an antistatic effect without overlapping the magnetic shield layer on the surface of the insulating layer on the side where the magnetic shield layer is disposed. A positioner unit for positioning the magnetic head attached to the first surface of the metal base of the magnetic disk device;
A circuit board disposed on the second surface side opposite to the surface to which the positioner portion is attached with respect to the base;
An insulating layer provided between the circuit board and the second surface;
In the magnetic disk drive having a magnetic shield layer between the insulating layer and the second surface for reducing magnetic field strength exerted on the printed board by magnetic flux leaked from the magnet of the positioner unit,
An antistatic member having a surface resistivity of 1 × 10 ⁵ Ω / □ or more and 1 × 10 ¹² Ω / □ or less is interposed between the second surface and the surface of the magnetic shield layer facing the second surface. An ESD current generation prevention method characterized by:

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