KR100546380B1 - Method for detecting weak write head - Google Patents

Abstract

A method of detecting a weak write head during a hard disk drive process is disclosed.

The disclosed weak write head detection method includes (a) performing an on-track write to a target track and using a normal write current (WC) and overshoot control on the target track and a low write current. Obtaining a low bit error rate using (WC) and overshoot control; and (b) whether the difference between the normal bit error rate and the low bit error rate is greater than a predetermined value (A) and / or the low bit error rate is greater than a predetermined value (B). Determining whether the size is small, and performing capacity downsizing on the head whose determination result in step (c) (b) is yes; (D) repeating steps (a) and (b) again after downsizing.

Description

Method for detecting weak write head

1 is a waveform diagram of a write current;

2 is a view schematically showing a main part of a hard disk drive;

3 is a perspective view schematically showing the magnetic head of FIG.

4 is a flow chart illustrating weak write head detection in accordance with one preferred embodiment of the present invention.

<Description of the symbols for the main parts of the drawings>

20.Hard Disk

70 ... magnetic head (read / write head)

The present invention relates to the field of hard disk drives, and more particularly, to a method for detecting a weak write head during a hard disk drive process.

A hard disk drive (HDD) is a device that reads information written to a disk by a magnetic head or writes data to a disk. The disk is rotatably mounted to the spindle motor, and the information is accessed by a magnetic head (read / write head) mounted on an actuator arm that is rotated by a voice coil motor. The voice coil motor is excited by the current to rotate the actuator and move the head. The read / write head senses the change of magnetism coming out of the surface of the disk and reads the information recorded on the disk surface. To write information to the data track, current is supplied to the head. The electric current generates a magnetic field, which magnetizes the disk surface.

Media used in hard disk drives, for example, hard disks are made of a magnetic material based on CoCrPt material, and the magnetic layer of the media changes in accordance with changes in ambient temperature. In particular, in low temperature environments, the coercivity of the magnetic layer of the media is increased, which requires a stronger write field to overwrite the recorded information.

In general, at low temperatures, the coercivity of the magnetic layer of the media based on the CoCrPt material, for example, the magnetic layer of the hard disk, is increased, resulting in a decrease in the write characteristics compared to the room temperature. Degradation problem occurs.

If the characteristics of the magnetic head do not overcome the increase in the coercive force at low temperatures, a poor write such as bit cracking may occur due to inadequate writing. This phenomenon is commonly referred to as low temperature weak writing.

Writability is a very important characteristic in hard disk drives, and this write performance is affected by the environment.

The writeability of the magnetic head depends on the characteristics of the head writer design and the preamp.

In general, in the design of the head writer, overwrite and adjacent track erase (hereinafter referred to as ATE) are taken into consideration, and these characteristics are opposite to each other, so that trade off occurs.

Here, the phenomenon in which data written to a track adjacent to the target track (hereinafter, adjacent track) is erased by the write current provided to the magnetic head is called ATE.

In addition, even when the head writer design is optimized, the overwrite characteristic shows a normal distribution due to the tolerance of the wafer and the slider constituting the magnetic head. Weak write problem due to low temperature overwrite characteristics.

In order to solve this problem, a head, for example, a head gimbal assembly (HGA), exhibiting low overwrite characteristics is screened by measuring the overwrite characteristic of a single piece of Dynamic Electric Test (DET). However, due to the limitation of room temperature measurement, it is not possible to completely solve the deterioration of the recording characteristics caused by the increase in the coercivity of the media at low temperatures.

In addition, screens in this HGA state are measured using a single fixed preamplifier rather than the preamplifier used directly on the hard disk drive, and therefore include characteristic differences for each preamplifier that affects writeability. There is also a disadvantage that can not be evaluated.

On the hard disk drive side, preamp die temperature is the temperature detected by the preamplifier by a temperature sensor built into the preamplifier. Temperature) by measuring the temperature of the environment and increasing the write current (WC) and overshoot control (OSC) values during low temperature sensing to increase the recordability at low temperature. Doing.

Here, referring to FIG. 1 showing an example of the waveform of the write current, the write current shows a sharp standing shape at the turning point 3 of the data 2a and 2b written in the magnetic layer 1 of the media. The direct current (dc) component of the write current is called the write current (WC), and the standing component is called the overshoot control (OSC). The write current WC serves to induce the magnetic field strength near the coercive force, and the overshoot control serves as a trigger for raising the magnetic field strength above the coercive force at the recording position.

Currently, most hard disk drives measure the preamp's die temperature to measure the ambient temperature around the hard disk drive, and based on this, overshoot to cope with the high coercivity with increasing coercivity of the media to improve writeability at low temperatures. The technology increases the control and write current (WC) by a certain amount, and has a writing characteristic suitable for a low temperature environment.

However, in the conventional method of increasing the write current (WC) and the overshoot control value in a low temperature environment to increase the recordability at a low temperature, the die temperature measurement tolerance is large, and the overwrite characteristic at a low temperature to a low temperature is drastically decreased. In the case of the magnetic head, even if the high write current (WC) and the overshoot control are used, there is a problem that the low temperature weak write cannot be overcome. Thus, if the head indicating low temperature weak writing is not screened in advance, weak writing failure may occur.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and the bit error rate measured by the low write current (WC) and overshoot control to ensure the weak write characteristics and reliability of the hard disk drive It is an object of the present invention to provide a method for detecting a head indicating weak write using Bit Error Rate (BER).

In the weak write head detection method according to the present invention for achieving the above object, (a) performing an on-track write to a target track and the normal write current (WC) and overshoot on the target track; Obtaining a normal bit error rate using control and a low bit error rate using low write current (WC) and overshoot control; (B) determining whether a difference value between the normal bit error rate and the low bit error rate is larger than a predetermined value (A) and / or whether the low bit error rate is smaller than a predetermined value (B); (C) performing capacity downsizing on the head whose determination result in step (b) is yes; (D) repeating steps (a) and (b) again after downsizing.

Here, the step (a) includes: performing on-track writing to the target track; Measuring a normal bit error rate in the target track for the plurality of zones; Measuring a low bit error rate in the target track for the plurality of zones; Calculating an average of a normal bit error rate and an average of a low bit error rate for all measured zones.

Hereinafter, a weak write head detecting method according to the present invention will be described in detail with reference to the accompanying drawings.

The hard disk drive has a magnetic head mated to the read / write side of a rotating hard disk. In the hard disk drive, since several hard disks are usually installed on the same rotation axis, several magnetic heads are disposed correspondingly. The magnetic head writes or reads information by magnetizing or detecting the magnetic field of the disk surface.

Read / write in a hard disk drive is performed by a swing arm driving method that uses a rotation of a magnetic head assembly rotatably installed on a base to transfer a magnetic head installed at its end to an appropriate position on a rotating disk.

2 is a plan view schematically illustrating an example of a hard disk drive structure. Referring to FIG. 2, the hard disk drive 10 moves a hard disk 20 to which predetermined information is recorded, and moves the magnetic head 50 to a desired track position on the hard disk 20 for recording and reading information. And a magnetic head feeder. Here, the hard disk 20 may be divided into a recording area 22 in which information is recorded and a parking area 21 provided so that the magnetic head 50 is parked when the rotation of the hard disk 20 is stopped. .

The disk 20 is rotatably installed on the base 11 and is rotated by a spindle motor (not shown). In Figure 2 c corresponds to the axis of rotation of the spindle motor.

The magnetic head feeder includes a magnetic head assembly 30 and a magnetic head assembly 30 on which a magnetic head 50 is mounted and rotatably installed about a rotation shaft 34 provided on a base 11. An actuator 40 for rotating by electromagnetic force is provided.

The magnetic head assembly 30 includes a suspension 31 coupled to an end of the actuator arm 32 rotatably coupled to the rotational shaft 34, and records information on the hard disk 20, and the hard disk 20. It comprises a magnetic head slider 50 provided with a magnetic head (70 in Fig. 3) for reading the information recorded in the suspension 31.

The magnetic head slider 50 is biased toward the hard disk 20 by the suspension 31. When the hard disk 20 starts to rotate, the magnetic head slider 50 is hardened by the air dynamic pressure generated by the rotation of the hard disk 20. It is flying with respect to the disk 20. At this time, the flying height of the magnetic head slider 50 while floating is due to the gram load of the suspension 31 and the air flow due to the rotation of the hard disk 20. It is determined by lift and the like.

Here, the flying height is provided on the tip side of the magnetic head slider 50 when the magnetic head slider 50 floats with respect to the hard disk 20 during the rotation of the hard disk 20. And a gap between the surface of the hard disk 20. The gram load refers to the force exerted by the suspension 31.

3 shows an example of a magnetic head 70 that may be used in the hard disk drive of FIG. 2. As shown, the magnetic head 70 includes a magnetoresistive head 74 for reading and an inductive recording head for writing. The magnetoresistive head 74 detects and reads a magnetic signal written to the hard disk 20. The induction recording head has a top pole 71 and a bottom pole 72 for forming a leakage magnet to the hard disk 20 and a recording coil 73 for generating a magnetic field as a current is supplied. And writes a desired magnetic signal to the hard disk 20.

The magnetic heads 70 as described above are arranged to correspond to the surfaces of the hard disks 20 one by one.

Referring again to FIG. 2, the actuator 40, as is well known, includes a magnet (not shown) and a voice coil 41. A current is applied to the voice coil 41 to move the magnetic head 70 to the desired track position on the hard disk 20.

The spindle motor, voice coil 41 and magnetic head 70 are electrically connected to the electronic circuit of the printed circuit board assembly 15. The electronic circuit includes a preamplifier, a read / write channel circuit, and a servo controller. The electronic circuit is electrically connected to the magnetic heads that detect the magnetic field of the hard disk.

The magnetic head 70 generates a read signal corresponding to the magnetic field of the hard disk. The read signal is amplified by the preamp and sent to the read / write channel circuit. The read / write channel circuit modulates the amplified analog signal read by the magnetic head 70 into a digital signal, and executes signal processing to convert user data into a write current so that it can be written to the hard disk 20. do. The servo controller collectively controls the hard disk drive.

After assembling the hard disk drive having the above configuration, a process for verifying and optimizing the hard disk drive is performed. The weak write head detection process according to the invention is performed during the hard disk drive test process, in particular the Burn-In test process.

The present invention takes advantage of the characteristic that the degradation of the recording characteristics due to the increase in the coercive force of the media at low temperature is equal to the performance of the head when writing with reduced write current (WC) and overshoot control at room temperature. In other words, the present invention takes advantage of the fact that the write current (WC) and the overshoot control are reduced in the normal temperature state, and can be most similarly reproduced in the recording property deterioration due to the increase in the coercive force of the medium at low temperature.

4 is a flowchart illustrating a weak write head detection process according to the present invention.

Referring to FIG. 4, the present invention performs an on-track write to a target track and normal bit error rate (BER) and low write current on the target track. Obtaining a (WC) / overshoot control bit error rate (hereinafter referred to as low bit error rate) value (S100), and whether the difference between the normal bit error rate and the low bit error rate is greater than a predetermined value (A) and / or the low bit error rate is Determining whether the value is less than the predetermined value B (S200), the potential weak write head is detected.

In addition, if the result of the determination process (S200) is yes, the present invention includes performing capacity downsizing (S300), and performing on-track writing to a target track after downsizing, Repeating step S100 of obtaining a normal bit error rate and a low bit error rate of (S400), whether the difference between the normal bit error rate and the low bit error rate is greater than a predetermined value (A) and / or the low bit error rate is a predetermined value (B). The method may further include repeating the process of determining whether the size is smaller (S500) to determine whether the write head is weak. If it is determined in step S500 that the determination result is yes (ie, a weak write head), the process fails in the process (S530). If the determination result is no, the process proceeds to the next check-in step (S510). ).

In step S100 of obtaining the normal bit error rate and the low bit error rate value, an on-track write is performed on a target track (S101), the normal bit error rate is measured on the target track (S103), and the low bit error rate on the target track. It is measured (S105). Then, the average of the normal bit error rate and the average of the low bit error rate are calculated (S107).

The low bit error rate is the bit error rate measured for this target track by reducing the write current (WC) and overshoot control at room temperature to reduce the writeability characteristics of the media at higher temperatures. . At this time, the write current (WC) and overshoot control values used to obtain the low bit error rate are properly optimized for the characteristics of the hard disk drive and the frequency band to reproduce the low temperature environment at room temperature.

In the step S101 of performing on-track writing to the target track, in order to obtain a normal bit error rate measurement value, the write to the target track is performed using normal write current (WC) and overshoot control at room temperature, and a low bit is performed. In order to obtain an error rate measurement value, the write current WC and the overshoot control are reduced to write to the target track so as to reduce the writeability characteristic according to the increase in the coercivity of the media at low temperature at room temperature.

As in the experimental example of Table 1 described below, when the range of the write current (WC) is approximately 20 to 50 mA and the range of the overshoot control is 0 to 31, the write current used in the normal state to obtain a normal bit error rate ( WC) and overshoot control may be, for example, about 35 mA and 12, respectively, and the write current (WC) and overshoot control used to obtain a low bit error rate may be, for example, about 25 mA and 3, respectively.

In FIG. 4, after performing an on-track write to the target track, the normal bit error rate and the low bit error rate are measured. This is performed by using the normal write current (WC) and overshoot control at room temperature on the target track. It should be considered to include writing and measuring the normal bit error rate, then again writing to the target track by reducing the write current (WC) and overshoot control at room temperature and then measuring the low bit error rate.

The normal bit error rate measurement S103 and the low bit error rate measurement S105 are performed for a plurality of desired predetermined zones. The average value of the normal bit error rate and the average value of the low bit error rate are average values for all the measured zones. Normal bit error rate and low bit error rate measurements may be performed for all zones in the media, or only for some of the worst zones. Here, the normal bit error rate measurement and the low bit error rate measurement are preferably performed for a plurality of zones in the media. Accordingly, a process of calculating the normal bit error rate average and the low bit error rate average is required.

Next, the difference between the normal bit error rate and the low bit error rate (delta bit error rate) is greater than a predetermined value A by using the average value of the normal bit error rate and the average value of the low bit error rate obtained in the step S107. It is determined whether the low bit error rate is smaller than the predetermined value B (S200). Here, as in the case of the experimental example of Table 1 to be described later, the predetermined value (A) may be about 0.7 on a log scale, for example. The predetermined value B may be, for example, about −7.2 on a logarithmic scale. Table 1 is illustrated for ease of understanding, and the predetermined value A and the predetermined value B may be changed in actual application.

In step S200, if the determination result is no (delta bit error rate is less than the predetermined value (A) and / or low bit error rate is more than the predetermined value (B)), proceed to the next burn-in test process step It becomes (S210). In step S200, if the determination result is yes (delta bit error rate is greater than the predetermined value (A) and / or low bit error rate is less than the predetermined value (B), capacity down sizing (Capacity Down) In other words, the bit error rate margin is secured by lowering the bit per unit inch (BPI) (S300).

Then, in the downsized state, the process of obtaining the normal bit error rate and the low bit error rate (S100) is repeated (S400), and if the delta bit error rate is larger than the predetermined value A and / or the low bit error rate is If it is less than the predetermined value (B) (S500), and if the issue (issue) even after the bit per unit (BPI) is reduced, it is determined as a weak write head to fail in the process (S530). That is, if the determination result is no even after the bit per unit inch (BPI) is reduced, the process proceeds to the next burn-in test process step (S510). If the determination result is YES, the process fails (S530). ).

According to one embodiment of the weak write head detection method according to the present invention, only a delta bit error rate may be used to determine a potential weak write head or a weak write head.

That is, the difference between the normal bit error rate measured using the write current (WC) and the overshoot control used at room temperature, and the low bit error rate measured using the low write current (WC) and the overshoot control, that is, delta (delta) ) If the bit error rate (normal bit error rate-low bit error rate) is higher than the criterion and the low bit error rate value itself is bad, there is a high possibility of low-temperature weak writes, and thus it is detected as a potential weak write head. Heads are downsized primarily (bits per inch (BPI) down), and the delta bit error rate is measured again in the downsized state so that deltas are still present after bits per inch (BPI) down. delta) If the bit error rate is greater than the criterion, it may be determined as a weak write head and may fail in the process.

Alternatively, according to another embodiment of the weak write head detection method according to the present invention, a criterion for determining the weak write head is based on both conditions when the delta bit error rate is above a certain value and the low bit error rate is below a reference value. It can also be used as a criteria.

That is, in the present invention, the criteria of downsizing the potential weak write head or screening the weak write head is based on the case where the delta bit error rate is above a certain criterion or the absolute value of the low bit error rate itself is bad. Both of these criteria can be applied or the weak write head can be determined and screened using only the delta bit error rate.

As an experimental example, Table 1 shows a low bit error rate average value, a normal bit error rate average value, and a delta bit error rate measured on various hard disk drives in log scale. The results in Table 1 show that the write current (WC) and the over-current used in the steady state to obtain a normal bit error rate when the write current (WC) is approximately 20 to 50 mA and the overshoot control is 0 to 31. The shoot control is, for example, about 35 mA and 12, respectively, and the write current (WC) and overshoot control used to obtain the low bit error rate are obtained when, for example, 25 mA and 3, respectively.

The shaded areas in Table 1 indicate that the hard disk drive has a weak write during low temperature read / write operation. As can be seen from Table 1, when the delta bit error rate is 0.7 or more on a logarithmic scale, a hard disk drive having a high probability of error can be detected.

drive # Low Bit Error Rate Average Normal Bit Error Rate Average Delta bit error rate #One -7.01 -8.16 1.148 #2 -6.57 -7.62 1.050 # 3 -7.26 -8.26 1.002 #4 -7.44 -8.38 0.938 # 5 -7.28 -8.19 0.910 # 6 -7.52 -8.43 0.902 # 7 -7.52 -8.38 0.855 #8 -7.64 -8.49 0.843 # 9 -7.38 -8.21 0.830 # 10 -7.46 -8.19 0.734 # 11 -7.56 -8.29 0.729 # 12 -7.74 -8.46 0.723 # 13 -7.70 -8.42 0.718 # 14 -7.55 -8.23 0.682 # 15 -7.67 -8.35 0.678 # 16 -7.64 -8.31 0.669 # 17 -7.78 -8.44 0.663 # 18 -7.67 -8.34 0.661 # 19 -7.68 -8.33 0.644 # 20 -7.12 -7.76 0.638 # 21 -7.63 -8.26 0.634 # 22 -7.80 -8.41 0.608 # 23 -6.76 -7.33 0.578 # 24 -7.51 -8.06 0.546 # 25 -7.76 -8.31 0.546 # 26 -7.74 -8.27 0.536 # 27 -7.84 -8.36 0.528 # 28 -7.17 -7.69 0.522 # 29 -7.72 -8.23 0.509 # 30 -8.02 -8.53 0.501 # 31 -7.55 -8.04 0.498 # 32 -7.80 -8.29 0.496 # 33 -7.07 -7.55 0.484 # 34 -7.59 -8.06 0.475

According to the present invention as described above, the head determined to be a potential weak write head is again checked for weak write head after capacity downsizing. Further, if the bit error rate characteristic is good after capacity downsizing for the potential weak write head, the burn-in test process is normally performed. If the bit error rate characteristic is not good, the weak write head is judged to be failed in the process.

Therefore, according to the present invention as described above, the normal bit error rate and the low bit error rate is measured during the hard disk drive process, and the normal bit error rate and the low bit error rate are measured again after downsizing the potential weak write head detected using the same. By using the screen to screen the sub-standard head, it is possible to improve the weak write failure (to secure the weak write characteristics and reliability of the hard disk drive), thereby reducing the failure rate in the market.

Claims (2)

(A) Perform on-track writes to the target track and use the normal write current (WC) and overshoot controls on this target track to control the normal bit error rate, low write current (WC), and overshoot control. Obtaining a low bit error rate using; (B) determining whether a difference value between the normal bit error rate and the low bit error rate is larger than a predetermined value (A) and / or whether the low bit error rate is smaller than a predetermined value (B); (C) performing capacity downsizing on the head whose determination result in step (b) is yes; (D) repeating steps (a) and (b) again after downsizing; detecting a weak write head comprising: a. The method of claim 1, wherein (a) comprises Performing an on-track write to the target track; Measuring a normal bit error rate in the target track for the plurality of zones; Measuring a low bit error rate in the target track for the plurality of zones; Calculating an average of the normal bit error rate and the average of the low bit error rate for all measured zones.

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