JP4513655B2 - Method for inspecting magnetic medium protrusions - Google Patents

Description

  The present invention relates to a method of inspecting a magnetic medium protrusion characterized by improvement of a surface protrusion inspection (glide height test) using a head in a magnetic disk (particularly a hard disk) which is a magnetic medium mounted on a magnetic disk device.

  For the magnetic media, a glide height test (hereinafter referred to as GHT), which is a surface protrusion test, is performed as a test before shipment. This GHT is a test for inspecting surface protrusions of a magnetic medium that may cause a phenomenon called head crash after being mounted on a magnetic disk device. When reading and writing data in a magnetic disk device, if the protrusion on the surface of the magnetic disk and the magnetic head repeatedly contact, the damage to the protrusion diffuses to the periphery of the magnetic disk, and the damaged dust is attracted to the magnetic head. The stable flying of the magnetic head is impaired and a read / write error occurs. This phenomenon is a head crash. In the GHT using the head (hereinafter referred to as the head GHT), one GH head is levitated on the rotating magnetic medium, the entire surface of the magnetic medium is scanned in a spiral, and the impact is detected when it touches the projection on the medium surface. Detect with sensor. The flying height of the GH head at this time is lowered to about half of the flying height of the read / write head of the magnetic disk in order to reliably detect surface protrusions in consideration of variations in the GH head. The output voltage is thresholded to select GHT defects. As shown in FIG. 1, the surface protrusions of the magnetic medium in the GHT are (1) protrusions (referred to as Type-A) whose output voltage of the vibration detection sensor is above the threshold when the GH head comes into contact ( 2) Protrusion where the output voltage of the vibration sensor is below the threshold when the GH head comes into contact (this protrusion is called Type-B), (3) Protrusion where the GH head does not contact (this protrusion is called Type-C) ), And magnetic media with at least one Type-A protrusion with a GHT defect are considered defective with GHT. In addition, the number of Type-B is several tens of times greater than Type-A on the medium surface. The knowledge about this number is that L number of GHT defects (= Type-A number) at the predetermined threshold of the output voltage of the vibration detection sensor, M pieces of GHT defects when the threshold of the output voltage of the vibration detection sensor is 0 (= From (Type-A number + Type-B number), it is known as (ML) / L. For this reason, regardless of whether the GHT is good or bad, the GH head is in contact with the Type-B protrusion on the surface of the magnetic medium, and damage to the GH head due to the accumulation of these contacts or adhesion of the protective film of the magnetic medium or lubricant to the GH head As a result, the GH head's low levitation occurred, and with this low levitation, Type-C, which had no contact with the GH head, changed to Type-B. Falls into a state where the GH head does not float on the magnetic medium (this is the life of the GH head). As the GH head progresses in a low-flying state, the GHT detects surface protrusions more excessively, so the magnetic media that became defective with the GHT are collected once and GHT (re-GHT) is performed again. Recovering the original non-defective product that has been rejected by over-detection with GHT. However, even in the re-GHT, the progress of the low flying height of the head is unavoidable, so that a magnetic medium that is originally good may be discarded as a defective in the re-GHT.

  Furthermore, as described in Patent Document 1, paying attention to the difference in the flying height of the upper and lower heads, when a defect is detected, the peripheral speed of the disk is reduced and a retry inspection is performed with the same head. A method for shortening the retry inspection time is known. Further, as described in Patent Document 2, there is also known a method of shortening a defect inspection time by dividing an inspection area of a disk in a radial direction and scanning each divided area with a separate head.

Japanese Patent Laid-Open No. 7-6365 Japanese Patent Laid-Open No. 9-63051

  First, as described above, the GH head has a problem to be solved that, when the GH head is in a low flying state due to contact with the Type-B protrusion on the surface of the magnetic medium, the suitability of the magnetic medium is impaired. Yes, the issue is the same for re-GHT. This problem cannot be solved even in Patent Documents 1 and 2 in which no consideration is given to accumulation of contact between the head and the Type-B protrusion.

  Next, issues related to GHT processing time are described. An outline of the head GHT device is shown in FIG. 2A is a plan view of the magnetic medium 1 and the GH head 2. The GH head 2 has a support arm 2b attached to a carriage 2a, and a vibration detection sensor 2d attached to a slider 2c at the tip of the support arm 2b. It has an attached configuration. FIGS. 2B to 2D show the positional relationship between the magnetic medium 1 loaded on the spindle 3 and the GH head 2 when the GHT is performed. 3a is a spindle motor. In GHT, (1) Magnetic medium loading-Magnetic medium unmounted state (Fig. 2- (b)) is changed to magnetic medium loaded state (Fig. 2- (c)). (2) GH head loading-GH The head is moved to the start position of the test and loaded by a loading mechanism (not shown). (3) Inspection of surface projection of magnetic medium by GH head-Spindle motor is rotated to float the GH head on the magnetic medium. The GH head is moved in the radial direction of the magnetic medium by the carriage mechanism, and the surface protrusions of the magnetic medium are scanned by the GH head in a spiral shape (FIG. 2- (d)), (4) GH head unloading-GH The head is retracted from the magnetic medium. (5) Unloading of the magnetic medium—The process includes removing the tested magnetic medium and putting the magnetic medium into the unmounted state. The time required for the surface protrusion inspection in (3) is as follows. , (1) , (2), (4), and (5) are overwhelmingly longer than the total time required, so the time required for GHT largely depends on the surface protrusion inspection of (3). On the other hand, since the head GHT is a test for each magnetic medium, the test time affects the cost of the magnetic medium, and shortening the test time can reduce the capital investment of the GHT equipment. Therefore, shortening the time required for the surface protrusion inspection is a constant problem to be solved in the head GHT. Another problem is that re-GHT also increases the total head GHT time.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a magnetic medium protrusion inspection method that solves the above-described problems.

  The present invention is a method for inspecting a protrusion of a magnetic medium for performing a glide height test using a head with respect to the magnetic medium. When a defect is detected by scanning the magnetic medium with a primary head, the secondary head is The magnetic medium is moved to the defect detection position, and the secondary head is used to perform a protrusion inspection only in the vicinity of the defect detection position.

  Here, the sensitivity of the primary head can be corrected with reference to the protrusion detection level of the secondary head.

  Further, the inspection area of the magnetic medium is divided, and each inspection area is scanned using each of two or more primary heads. If any of the primary heads detects a defect, the defect is detected. The protrusion inspection by the secondary head with respect to the detection position can be executed.

  According to the present invention, the surface protrusion scanning time can be shortened in a glide height test using a magnetic medium head. In addition, there is an effect that the quality determination of the magnetic medium becomes accurate.

(Example 1)
FIG. 3 shows a head GHT device having two GH heads facing each other in the diameter direction of the magnetic medium in the magnetic medium head GHT. The area where GHT is not performed on the inner and outer circumferences of the magnetic medium is an area which is not guaranteed to float when the magnetic medium is mounted on the magnetic disk device.

  FIG. 3A shows the relationship between the magnetic medium 1 and the two GH heads. In this embodiment, a GH head A as a primary head for performing GHT and a GH head B as a secondary head are arranged facing the loaded magnetic medium 1 in the diameter direction of the magnetic medium 1. is there. The GHT defect 5 is illustrated in the magnetic medium 1. The two GH heads A and B and the spindle motor 3a are connected to the controller 4 and are controlled by the controller 4 as follows.

  The controller 4 compares a detection output voltage from each vibration detection sensor 2d of the two GH heads A and B with a predetermined GHT threshold value to detect a Type-A protrusion, and two GH heads A, A carriage control circuit for controlling the driving of each carriage 2a of B, a motor control circuit for controlling the driving of the spindle motor 3a, and these circuits are connected, and the carriage control circuit and the motor are referenced with reference to the detection signal of the protrusion detection circuit. The CPU includes a CPU that supplies a control signal to the control circuit, a ROM that stores a control procedure executed by the CPU, and a RAM that provides a work area for the CPU. The CPU in the controller 4 executes GHT as described below according to the control procedure in the ROM (this configuration is the same in the second and third embodiments).

  Under the control of the controller 4, the GHT of the primary head executes loading of the magnetic medium → loading of the GH head A, scanning of the surface protrusion of the magnetic medium, unloading → unloading of the magnetic medium (FIG. 3B). . Up to this point, there is no difference from the conventional GHT with one GH head. In the prior art, magnetic media in which GHT defects are detected by this GHT are collected as defective media and re-circulated for GHT. However, in the present embodiment, when a GHT defect is detected, during the scanning of the GH head A, the CPU determines based on the detection signal from the protrusion detection circuit in the controller 4 and the control signal to the carriage control circuit. Since the GHT defect position in the radial direction of the magnetic medium 1 can be specified, the GH head B, which is the secondary head, is further moved to the position of the GHT defect 5 under the control of the controller 4, and this GH head B is used. GHT defect scanning is performed only on the ring region (indicated by 6 in FIG. 3C) near the position of the GHT defect 5. This GHT defect scan complements the conventional re-GHT, and magnetic media in which Type-A protrusions are not detected in this GHT defect scan are considered good products, and magnetic media in which Type-A protrusions are detected are discarded as defective media. The Therefore, in this embodiment, there is no re-GHT, and the size of the ring region of the GHT defect scanning depends on the defect length of the GHT defect, but the defect length of the GHT defect in recent years is almost several microns or less. The ring region is very small compared to the GHT region of the magnetic medium. Therefore, the processing time is greatly shortened. Furthermore, since the contact frequency of the GH head B with the Type-B protrusion is extremely lower than that of the GH head A, the flying height of the GH head B hardly occurs. In the conventional re-GHT, the flying height of the head is reduced even during the re-GHT, but this problem is also avoided in this embodiment.

  Also, when the GH head A falls into a state where it does not float on the magnetic medium (the GH head has a lifetime) and is replaced with a new head, the entire GHT is switched to the GH head B and GHT defect scanning is switched to the new GH head A. . As a result, it is possible to always perform GHT defect scanning with a GH head in which low flying height hardly occurs.

  Next, an example of correcting the sensitivity of the primary head (correcting the GHT threshold voltage) from the protrusion detection level of the secondary head will be described. The new GH head mounted on the GHT is shipped by the head manufacturer after confirming that the output voltage of the vibration sensor is within a certain range when it comes into contact with a reference protrusion (bump) whose height and shape are known. It is a thing. Therefore, the GHT threshold voltage Ve of the vibration sensor is constant regardless of the head. If the output voltage of the vibration detection sensor for the GHT defect by the primary head is V1, and the output voltage of the vibration detection sensor for the same GHT defect by the secondary head is V2, the sensitivity correction coefficient k is k = V1 / V2. In the subsequent GHT of the primary head, when the GHT threshold voltage of the primary head in the protrusion detection circuit is switched to k × Ve (correction of the sensitivity of the primary head), the quality of the magnetic medium is good even when the primary head is in a low flying state. Judgment can be made properly. If the secondary head does not detect the GHT defect detected by the primary head, considering the fact that V = 0 and k = ∞, the upper limit value k · max of the sensitivity correction coefficient is set, and the life of the GH head The head replacement can also be performed by outputting a replacement warning or the like from the controller 4 (or a warning display) at k> k · max before the process is completed.

(Example 2)
As shown in FIG. 4- (a), the GHT region of the magnetic medium 1 is divided into the GHT region I on the outer peripheral side and the GHT region II on the inner peripheral side, and the surface protrusion scanning of the GHT regions I and II is performed for each GH. Share heads A and B (Fig. 4- (b)). At this time, the lengths in the radial direction of the respective regions are equal (L1 = L2 in FIG. 4A). Naturally, the moving speeds of the GH heads A and B in the radial direction are also equal. The surface protrusion scanning time of the GHT regions I and II are both 1/2 hours of the conventional GHT. If this embodiment is applied, the surface protrusion scanning time of the GHT can be shortened to half that of the conventional GHT.

(Example 3)
FIG. 5 shows an example of a head GHT apparatus having three GH heads in the head GHT. First, using the GH heads A and B, Example 2 (GHT of two divided regions) is applied. Next, when the first embodiment is applied and a GHT defect is detected in the region-divided GHT, the GH head C performs GHT defect scanning. According to this example,
(1) Eliminate GHT again (2) Accurately judge the quality of magnetic media (3) Reduce the GHT surface protrusion scanning time to half that of the conventional GHT, and simultaneously achieve the effects of the first and second embodiments can get.

It is a figure which shows the relationship between description according to the type of protrusion, and the output voltage of a vibration detection sensor. (A) is a plan view of the magnetic medium 1 and the GH head 2, and (b), (c) and (d) show the positional relationship between the magnetic medium 1 loaded on the spindle 3 and the GH head 2 when performing GHT. FIG. (A) is a figure which shows the relationship between the magnetic medium 1 and two GH heads, (b), (c) is a figure which shows the relationship between the magnetic medium 1 and two GH heads. (A) is a figure which shows the other relationship between the magnetic medium 1 and two GH heads, (b), (c) is a figure which shows the other relationship between the magnetic medium 1 and two GH heads. It is a figure which shows the other relationship between the magnetic medium 1 and three GH heads.

Explanation of symbols

1 Magnetic medium 3 Spindle 4 Controller 5 GHT defect A, B GHT head

Claims (3)

A method for inspecting a protrusion of a magnetic medium for performing a glide height test using a head against the magnetic medium,
When a defect is detected by scanning the magnetic medium with a primary head, the secondary head is moved to the defect detection position of the magnetic medium, and a ring near the defect detection position is used by using the secondary head. to perform the projection examination region only, the size of the ring region is dependent on the defect length of the defect, the defect length projection inspection method of the magnetic medium characterized der Rukoto than several microns of the defect. In claim 1,
A method for inspecting a protrusion on a magnetic medium, wherein the sensitivity of the primary head is corrected with reference to the protrusion detection level of the secondary head. In claim 1 or 2,
When the inspection area of the magnetic medium is divided and scanning is performed using each of two or more primary heads for each inspection area, and any of the primary heads detects a defect, the defect detection position A method for inspecting a protrusion of a magnetic medium, wherein the protrusion inspection by the secondary head is executed.

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