KR20050028712A - Method for detecting weak write head - Google Patents

Abstract

A method for detecting a weak write head is provided to measure a normal BER(Bit Error Rate) and a low BER to downsize a potential weak write head, and to re-measure the normal BER and the low BER to screen a head which is at less than a reference level, thereby improving a weak write defective proportion. A system performs an on-track write process on a target track, and obtains a normal BER and a low WC(Write Current)/OSC(Over Shoot Control) BER(S100). The system decides whether a difference between the normal BER and the low BER is bigger than a predetermined value and/or the low BER is smaller than a predetermined value(S200). If so, the system downsizes a capacity(S300). The system repeats the step 'S100' after downsizing(S400), and repeats the process of deciding whether the difference between the normal BER and the low BER is bigger than the predetermined value and/or the low BER is smaller than the predetermined value(S500). If so, the system fails the process(S530), and if not, the system proceeds to a burn-in test process(S510).

Description

Method for detecting weak 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 on the spindle motor, and 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 surface of the disk. 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 generally called low temperature wet write.

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 occurs 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 the temperature sensor built into the preamplifier. Temperature) by estimating the temperature of the environment through measurement, and increasing the write current (WC) and overshoot control (hereinafter referred to as OSC) values during low temperature sensing to increase the recordability at low temperature I'm using.

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 dc component of the write current is called WC and the standing component is called OSC. The WC serves to induce the strength of the magnetic field near the coercive force, and the OSC serves as a trigger to raise the strength of the magnetic field beyond the coercive force at the recording position.

Currently, most hard disk drives measure the preamp's die temperature to measure the ambient temperature of the hard disk drive's surroundings, and based on this, OSC or OSC By increasing the WC by a certain amount, it adopts a technology that has a writing characteristic suitable for low temperature environment.

However, in the case of the conventional method of increasing the WC and OSC values in a low temperature environment to increase the recordability at low temperatures, however, the magnetic head has a large die temperature measurement tolerance, and no matter how the magnetic head has a sharp drop in overwrite characteristics at a low temperature to a low temperature. Even with high WC and OSC, there is a problem that it cannot overcome low temperature wet write. Therefore, if the head representing the low temperature wet write is not screened in advance, the weak write failure may occur.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and the BER (Bit Error Rate) measured by low WC and OSC to secure the wet write characteristics and reliability of the hard disk drive. The purpose of the present invention is to provide a method for detecting a head representing a weak write using a.

Weak Write head detection method according to the present invention for achieving the above object, (A) On-Track Write to the target track and the normal BER using the normal WC and OSC on the target track and Obtaining a low BER using low WC and OSC; (B) determining whether a difference value between the normal BER and the low BER is greater than a predetermined value A and / or whether the low BER 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 BER in the target track for the plurality of zones; Measuring a low BER in a target track for the plurality of zones; Calculating a mean of normal BER and a mean of low BER for all measured zones.

Hereinafter, a method for detecting a weak write head 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 conveying apparatus includes a magnetic head assembly 30 on which the magnetic head 50 is mounted and rotatably installed around the pivot shaft 34 provided on the base 11, and the magnetic head assembly 30 by electromagnetic force. The actuator 40 for rotating by the 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 wet write head detection process according to the present invention is performed during a hard disk drive test process, in particular, a burn-in test process.

The present invention takes advantage of the characteristics that the degradation of the recording characteristics due to the increase in the coercive force of the media at low temperatures is equal to the performance of the head when writing with reduced WC and OSC at room temperature. In other words, the present invention takes advantage of the fact that, in the state of reducing the WC and OSC in the normal temperature state, the degradation of the recording characteristics due to the increase in the coercive force of the media at the low temperature can be most similarly reproduced.

4 is a flowchart illustrating a process of detecting a write write head according to the present invention.

Referring to FIG. 4, the present invention performs an on-track write to a target track and normal BER (bit error rate) and low WC / on the target track. Obtaining an OSC BER (hereinafter, low BER) value (S100), and determining whether the difference between the normal BER and the low BER is greater than a predetermined value (A) and / or whether the low BER is smaller than a predetermined value (B). Including the S200, a 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 BER and a low BER of S400 and determining whether the difference between the normal BER and the low BER is greater than a predetermined value A and / or whether the low BER is smaller than a predetermined value B. The method may further include repeating the process (S500) to determine whether the write head is a head. 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 turn-in task step (S510). ).

In step S100 of obtaining the normal BER and low BER values, on-track writing is performed on a target track (S101), the normal BER is measured on the target track (S103), and the low BER is measured on the target track ( S105). Then, the average of the normal BER and the average of the low BER is calculated (S107).

Low BER refers to the BER measured for this target track by reducing the WC and OSC at room temperature, reducing the WC and OSC at room temperature, in order to reduce the writeability characteristics with increasing coercivity of the media at low temperatures. At this time, the WC and OSC values used to obtain the low BER are properly optimized for hard disk drive characteristics and frequency bands in order to reproduce a 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 BER measurement value, in order to obtain a normal BER measurement using normal WC and OSC at room temperature, and to obtain a low BER measurement value, In this state, the WC and OSC are reduced to write to the target track so as to reduce the writeability characteristics due to the increase in the coercivity of the media at low temperatures.

As in the experimental example of Table 1 described below, when the range of WC is approximately 20 to 50 mA and the range of OSC is 0 to 31, the WC and OSC used in the steady state to obtain a normal BER are, for example, 35 mA and 12, respectively. The WC and OSC used to obtain a low BER can be, for example, about 25 mA and about 3, respectively.

In FIG. 4, after performing on-track writing to the target track, the normal BER and the low BER are measured, which is written using the normal WC and OSC at room temperature, and the normal BER is measured. It should also be considered to include the case where the WC and OSC are reduced and written to the target track at room temperature, and then the low BER is measured.

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

Next, using the normal BER average value and the low BER average value obtained in the step S107, whether the difference (delta BER) between the normal BER and the low BER is greater than a predetermined value A and / or the low BER is a predetermined value ( It is determined whether it is smaller than 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 BER is less than or equal to the predetermined value A and / or low BER is greater than or equal to the predetermined value B), the process proceeds to the next test step (S210). In step S200, if the determination result is yes (delta BER is greater than the predetermined value (A) and / or low BER is smaller than the predetermined value (B)), the capacity down sizing proceeds, that is, , By lowering the BPI to secure the BER margin (S300).

Then, in the downsized state, the process of obtaining a normal BER and a low BER (S100) is repeated (S400), and the delta BER is larger than the predetermined value A and / or the low BER is smaller than the predetermined value B. If it is determined that the issue (S500), even after the BPI is reduced (issue), it is determined by the Weak Write head to fail in the process (S530). That is, even after the BPI is reduced, if the determination result is no, the process proceeds to the next burn-in test process step (S510). If the determination result is yes, the process is failed (process fail) (S530).

According to an embodiment of the method for detecting a write write head according to the present invention, only a delta BER may be used to determine a potential write head or to determine a write write head.

That is, the difference between the normal BER measured using the WC and OSC used at room temperature and the low BER measured using the low WC and OSC, that is, the delta BER (normal BER-low BER) is greater than or equal to the criteria. In the case of a head with a low low BER value, there is a high possibility of low temperature wet write. Therefore, a head detected as a potential wet write head is primarily downsized (BPI down). If the delta BER is still larger than the criteria after the BPI down, the delta BER can be judged as a Weak Write Head and failed in the process.

Alternatively, according to another embodiment of the method for detecting the wet write head according to the present invention, both conditions in which the delta BER is greater than or equal to a certain value and the low BER is less than the reference value may be used as a criterion for determining the weak write head. It may be.

That is, in the present invention, the criteria for downsizing the potential Weak Write head or screening the Weak Write head is determined based on the case where the delta BER is above a certain criterion or when the absolute value of the low BER itself is bad. Both of these criteria can be applied or the Weak Write head can be determined and screened using only the delta BER.

As an experimental example, Table 1 shows a low BER average, a normal BER average, and a delta BER measured on log scales of various hard disk drives. The results in Table 1 show that when the range of WC is approximately 20-50 mA and the range of OSC is 0-31, the WC and OSC used in steady state to obtain a normal BER are, for example, about 35 mA and 12, respectively, The WC and OSC used to obtain the BER are obtained when, for example, 25 mA and 3, respectively.

The shaded area in Table 1 shows the drive where the Weak Write occurred during the low temperature read / write operation of the hard disk drive. As shown in Table 1, when the delta BER is 0.7 or more on a logarithmic scale, a hard disk drive having a high probability of error can be detected.

drive # Low BER Average Normal BER Mean delta BER #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, after the capacity downsizing for the head determined to be a potential Weak Write head, it is again checked whether it is a Weak Write head. In addition, if the BER characteristic is good after the capacity downsizing of the potential Weak Write head, the burn-in test process is normally performed. If the BER characteristic is not good, the Weak Write head is judged to fail in the process.

Therefore, according to the present invention as described above, the normal BER and low BER measurement during the hard disk drive process, using the same to detect the potential Weak Write head downsized again after the normal BER and low BER measurement, using By screening the head below the standard, it is possible to improve the Weak Write defects (to secure the Weak Write characteristics and reliability of the hard disk drive), thereby reducing the defect rate in the market.

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.

Figure 4 is a flow chart showing detection of the Weak Write head in accordance with a 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)

Claims (2)

(A) performing an on-track write to the target track and obtaining a normal BER using normal WC and OSC and a low BER using low WC and OSC on the target track; (B) determining whether a difference value between the normal BER and the low BER is greater than a predetermined value A and / or whether the low BER 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 BER in the target track for the plurality of zones; Measuring a low BER in a target track for the plurality of zones; Calculating a mean of normal BERs and a mean of low BERs for all measured zones.