U.S. patent application number 11/464488 was filed with the patent office on 2007-01-11 for method of manufacturing head gimbal assemblies, actuators and disk drives by removing thermal pole-tip protrusion at the spin stand level.
Invention is credited to Keung Youn Cho, Hae Jung Lee, Sang Lee, Geng Wang.
Application Number | 20070006446 11/464488 |
Document ID | / |
Family ID | 32029299 |
Filed Date | 2007-01-11 |
United States Patent
Application |
20070006446 |
Kind Code |
A1 |
Wang; Geng ; et al. |
January 11, 2007 |
METHOD OF MANUFACTURING HEAD GIMBAL ASSEMBLIES, ACTUATORS AND DISK
DRIVES BY REMOVING THERMAL POLE-TIP PROTRUSION AT THE SPIN STAND
LEVEL
Abstract
Thermal pole tip protrusion is caused by the materials in and
around the head slider expanding during write operations till part
of those materials protrude, leading to contact with the rotating
disk surface, altering the flying height and often wearing down
part of the disk surface. While it is well known that read-write
heads expand during writing, the inventors are unaware of anyone
else who recognized this situation's significance, particularly as
the flying height decreases and the data rates increase, both of
which are required for high areal density disk drives. The
inventors realized that they could detect the problem at the spin
stand level by testing head gimbal assemblies to reliably, and
inexpensively, predict the tendency for thermal pole tip
protrusion. This leads to selection of head gimbal assemblies,
which do not have the thermal pole tip protrusion tendency. The
selected head gimbal assemblies have better reliability, as do
actuators and disk drives made with the selected head gimbal
assemblies.
Inventors: |
Wang; Geng; (San Jose,
CA) ; Lee; Hae Jung; (Santa Clara, CA) ; Cho;
Keung Youn; (San Jose, CA) ; Lee; Sang;
(Pleasonton, CA) |
Correspondence
Address: |
GREGORY SMITH & ASSOCIATES
3900 NEWPARK MALL ROAD, 3RD FLOOR
NEWARK
CA
94560
US
|
Family ID: |
32029299 |
Appl. No.: |
11/464488 |
Filed: |
August 14, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10256553 |
Sep 26, 2002 |
7089649 |
|
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11464488 |
Aug 14, 2006 |
|
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Current U.S.
Class: |
29/603.03 ;
G9B/5.145; G9B/5.148; G9B/5.153; G9B/5.155 |
Current CPC
Class: |
G11B 5/012 20130101;
Y10T 29/49027 20150115; G11B 5/4806 20130101; G11B 5/484 20130101;
Y10T 29/49025 20150115; Y10T 29/49036 20150115; G11B 5/3136
20130101; Y10T 29/49032 20150115; G11B 5/4833 20130101; G11B 5/455
20130101; Y10T 29/49028 20150115 |
Class at
Publication: |
029/603.03 |
International
Class: |
H04R 31/00 20060101
H04R031/00 |
Claims
1. A head gimbal assembly as a product of the process comprising
the steps: estimating a thermal pole tip protrusion tendency for
said head gimbal assembly containing a read-write head; and
selecting said head gimbal assembly whenever said head gimbal
assembly does not have said thermal pole tip protrusion tendency;
said method comprising, for each member of a track collection, the
step of: determining said thermal pole tip protrusion tendency for
said head gimbal assembly on said track collection member; and said
method, further comprising the step of: predicting said thermal
pole tip protrusion for said head gimbal assembly based upon, for
each of said track collection members, said thermal pole tip
protrusion tendency on said track collection member; wherein said
track collection is comprised of an inside diameter track of a disk
surface and an outside diameter track of said disk surface; wherein
said read-write head provides a magneto-resistance from a disk
surface while performing a write operation to said track collection
member on said disk surface and provides a voltage while reading
said track collection member at a bias current, for each of said
track collection members; wherein said disk surface rotates at a
rotational frequency; wherein the step determining said thermal
pole tip protrusion tendency is comprised of at least one member of
the collection comprising the steps of: monitoring a change of said
magneto-resistance while said read-write head performs said write
operation of said track collection member to determine said thermal
pole tip protrusion tendency; wherein the step monitoring said
change is further comprised of: observing said magneto-resistance
while said read-write head performs said write operation on said
track collection member to create a sudden MRR change event
collection and to create a MRR value; determining a number of said
sudden MRR change event collection members; determining a change
characteristic based upon an amount MRR change divided by said MRR
value, for each of said sudden MRR change event collection members;
and determining said thermal pole tip protrusion tendency based
upon said number of said sudden MRR change event collection members
and based upon said change characteristic for said sudden MRR
change event collection members.
2. The head gimbal assembly of claim 1, wherein said track
collection is further comprised of a middle diameter track of said
disk surface.
3. A method of making an actuator, comprising the step of:
assembling said actuator using at least one of said head gimbal
assemblies of claim 1.
4. Said actuator as a product of the process of claim 3.
5. A method of making a disk drive, comprising the step of
assembling said disk drive using said actuator of claim 4.
6. Said disk drive as a product of the process of claim 5.
7. A head gimbal assembly as a product of the process, comprising
the steps: estimating a thermal pole tip protrusion tendency for
said head gimbal assembly; and selecting said head gimbal assembly
whenever said head gimbal assembly does not have said thermal pole
tip protrusion tendency; wherein the step estimated said thermal
pole tip protrusion tendency, comprises: for each member of a track
collection, the step of: determining said thermal pole tip
protrusion tendency for said head gimbal assembly on said track
collection member; and predicting said thermal pole tip protrusion
tendency for said head gimbal assembly based upon, for each of said
track collection members, said thermal pole tip protrusion tendency
on said track collection member; wherein said track collection is
comprised of an inside diameter track of a disk surface and an
outside diameter track of said disk surface.
8. The head gimbal assembly of claim 7, wherein said read-write
head provides a magneto-resistance from a disk surface while
performing a write operation to said track collection member on
said disk surface and provides a voltage while reading said track
collection member at a bias current, for each of said track
collection members; wherein said disk surface rotates at a
rotational frequency; wherein the step determining said thermal
pole tip protrusion tendency is comprised of at least one member of
the collection comprising the steps of: monitoring a change of said
magneto-resistance while said read-write head performs said write
operation on said track collection member to determine said thermal
pole tip protrusion tendency; and detecting an amplitude modulation
envelope for said voltage at essentially said rotational frequency
for said track collection member written to determine said thermal
pole tip protrusion tendency.
9. The head gimbal assembly of claim 8, wherein the step monitoring
said change is further comprised of: observing said
magneto-resistance while said read-write head performs said write
operation on said track collection member to create a sudden MRR
change event collection and to create a MRR value; determining a
number of said sudden MRR change event collection members;
determining a change characteristic based upon an amount MRR change
divided by said MRR value, for each of said sudden MRR change event
collection members; and determining said thermal pole tip
protrusion tendency based upon said number of said sudden MRR
change event collection members and based upon said change
characteristic for said sudden MRR change event collection
members.
10. The head gimbal assembly of claim 8, wherein the step detecting
said amplitude modulation envelope is further comprised of the
steps of: said read-write head reading said track collection member
at a current bias to create a track voltage table; processing said
track voltage table at essentially said rotational frequency to
generate an amplitude modulation envelope for said voltage at
essentially said rotational frequency; calculating a maximum
voltage swing for said amplitude modulation envelope; calculating a
deviation from said maximum voltage swing for said amplitude
modulation envelope; and determining said thermal pole tip
protrusion tendency for said track collection member based upon
said deviation and based upon said maximum voltage swing.
11. The head gimbal assembly of claim 7, wherein said track
collection is further comprised of a middle diameter track of said
disk surface.
12. A method of making an actuator, comprising the step of:
assembling said actuator using at least one of said head gimbal
assemblies of claim 7.
13. Said actuator as a product of the process of claim 12.
14. A method of making a disk drive, comprising the step of
assembling said disk drive using said actuator of claim 13.
15. Said disk drive as a product of the process of claim 14.
16. Said head gimbal assembly as a product of the process
comprising the steps: determining a thermal pole tip protrusion
tendency for said head gimbal assembly containing a read-write
head; and selecting said head gimbal assembly whenever said head
gimbal assembly does not have said thermal pole tip protrusion
tendency; wherein the step determining said thermal pole tip
protrusion tendency, further comprises: for each member of a track
collection, the step of: determining said thermal pole tip
protrusion tendency for said head gimbal assembly on said track
collection member; and predicting said thermal pole tip protrusion
for said head gimbal assembly based upon, for each of said track
collection members, said thermal pole tip protrusion tendency on
said track collection member; wherein said track collection is
comprised of an inside diameter track of a disk surface and an
outside diameter track of said disk surface wherein said read-write
head provides a magneto-resistance from a disk surface while
performing a write operation to said track collection member on
said disk surface and provides a voltage while reading said track
collection member at a bias current, for each of said track
collection members; wherein said disk surface rotates at a
rotational frequency; wherein the step determining said thermal
pole tip protrusion tendency is comprised of the step of: detecting
an amplitude modulation envelope for said voltage at essentially
said rotational frequency for said track written to determine said
thermal pole tip protrusion tendency; wherein the step detecting
said amplitude modulation envelope is further comprised of the
steps of: said read-write head reading said track collection member
at a current bias to create a track voltage table; processing said
track voltage table at essentially said rotational frequency to
generate an amplitude modulation envelope for said voltage at
essentially said rotational frequency; calculating a maximum
voltage swing for said amplitude modulation envelope; calculating a
deviation from said maximum voltage swing for said amplitude
modulation envelope; and determining said thermal pole tip
protrusion tendency for said track collection member based upon
said deviation and based upon said maximum voltage swing.
17. The method of claim 16, wherein said track collection is
further comprised of a middle diameter track of said disk
surface.
18. A method of making an actuator, comprising the step of:
assembling said actuator using at least one of said head gimbal
assemblies of claim 16.
19. Said actuator as a product of the process of claim 18.
20. A method of making a disk drive, comprising the step of
assembling said disk drive using said actuator of claim 19.
21. Said disk drive as a product of the process of claim 20.
Description
CROSS REFERENCE TO RELATED PATENT APPLICATIONS
[0001] This Application is a Divisional of pending U.S. patent
application Ser. No. 10/256,553 filed Sep. 26, 2003.
TECHNICAL FIELD
[0002] This invention relates to improving disk drive reliability
by removing head gimbal assemblies with thermal pole tip protrusion
tendencies early in the manufacturing process.
BACKGROUND ART
[0003] Disk drives are an important data storage technology.
Read-write heads are one of the crucial components of a disk drive,
directly communicating with a disk surface containing the data
storage medium. Read-write heads generate heat during write
operations due to the large currents required for that operation.
The inventors have discovered quality problems associated with
thermal expansion, causing tip protrusion. A review of the relevant
background will be made before discussing their discovery of the
problem and their solutions.
[0004] FIG. 1A illustrates a typical prior art high capacity disk
drive 10 including actuator arm 30 with voice coil 32, actuator
axis 40, head arms 50-58 with head suspension assembly 60 placed
among the disks.
[0005] FIG. 1B illustrates a typical prior art high capacity disk
drive 10 with actuator 20 including actuator arm 30 with voice coil
32, actuator axis 40, head arms 50-56 and head suspension
assemblies 60-66 with the disks removed.
[0006] FIG. 2A illustrates a head gimbal assembly including head
suspension assembly 60 with head slider 100 containing the
read-write head 200 of the prior art.
[0007] Since the 1980's, high capacity disk drives 10 have used
voice coil actuators 20-66 to position their read-write heads over
specific tracks. The heads are mounted on head sliders 100, which
float a small distance off the disk drive surface when in
operation. The flotation process is referred to as an air bearing.
The air bearing is formed by the read-write heads 200, illustrated
in FIG. 2A, and head slider 100, as illustrated in FIGS. 1A-2A. The
flying height of the air bearing is very small, often about 100
Angstroms, or about 0.4 millionths of an inch, which is far smaller
than a human hair.
[0008] Often there is one head per head slider for a given disk
drive surface. There are usually multiple heads in a single disk
drive, but for economic reasons, usually only one voice coil
actuator.
[0009] Voice coil actuators are further composed of a fixed magnet
actuator 20 interacting with a time varying electromagnetic field
induced by voice coil 32 to provide a lever action via actuator
axis 40. The lever action acts to move head gimbal assemblies
50-56, positioning head suspension assemblies 60-66, and their
associated head sliders 100 containing read-write heads 200, over
specific tracks with speed and accuracy. Actuator arms 30 are often
considered to include voice coil 32, actuator axis 40, head gimbal
assemblies 50-56 and head suspensions 60-66. An actuator arm 30 may
have as few as a single head gimbal assembly 50. A single head
gimbal assembly 52 may connect with two head suspensions 62 and 64,
each with at least one head slider.
[0010] FIG. 2B illustrates the relationship between the principal
axis 110 of an actuator arm 50 containing suspension 60, which in
turn contains head slider 100, as found in the prior art.
[0011] FIG. 2C illustrates a simplified schematic of a disk drive
controller 1000 of the prior art, which may be used to control a
spin stand test unit.
[0012] Disk drive controller 1000 controls an analog read-write
interface 220 communicating resistivity found in the spin valve
within read-write head 200. Disk drive controller 1000 concurrently
controls servo-controller 240 driving voice coil 32, of the voice
coil actuator, to position read-write head 200 to access a rotating
magnetic disk surface 12 of the prior art.
[0013] Analog read-write interface 220 frequently includes a
channel interface 222 communicating with pre-amplifier 224. Channel
interface 222 receives commands, from embedded disk controller 100,
setting at least the read_bias and write_bias.
[0014] Various disk drive analog read-write interfaces 220 may
employ either a read current bias or a read voltage bias. By way of
example, the resistance of the read head is determined by measuring
the voltage drop (V_rd) across the read differential signal pair
(r+ and r-) based upon the read bias current setting read_bias,
using Ohm's Law.
[0015] FIG. 2D illustrates a detailed view head suspension 60 of
the prior art.
[0016] A prior art head suspension 60 includes suspension load beam
80 mechanically coupled via hinge 82 with extended base plate 84.
Head suspension 60 further includes flexure 86, providing
electrical interconnections of the read and write differential
signal pairs 210, between the disk drive analog interface 220 and
read-write head 200 (both in FIG. 2C).
[0017] The head gimbal assembly includes head slider 100 rigidly
mounted on head suspension 60, with read-write head 200
electrically connected to flexure 86. Head slider 100 is mounted
over the right portion of suspension load beam 80 so that
read-write head 200 makes contact with flexure 86.
[0018] The hinge 82 includes a spring mechanism. Suspension load
beam 80, hinge 82 and extended base plate 84 are all typically made
from stainless steel. Flexure 86 is a flex printed circuit
typically made using polyamide and copper traces.
[0019] What is needed are reliable head gimbal assemblies and
actuators, which will minimize read-write head crashes by reliably
maintaining the flying height, even as the flying height decreases
and the data rates increase, to insure the quality of the disk
drives in which they are used. The inventors know of no known
discussion of the relationship between thermal pole tip protrusion
to reliably maintaining the flying height.
SUMMARY OF THE INVENTION
[0020] Thermal pole tip protrusion is caused by the materials in
and around the head slider expanding during write operations till
part of those materials protrude, leading to contact with the
rotating disk surface. Contact can degrade the write performance by
altering the flying height. Contact can also wear down part of the
disk surface.
[0021] While it is well known that read-write heads expand during
writing, the inventors are unaware of anyone else who recognized
this situation's significance, particularly as the flying height
decreases and the data rates increase, both of which are required
for high areal density disk drives.
[0022] The inventors realized that they could detect the problem at
the spin stand level by testing head gimbal assemblies to reliably,
and inexpensively, predict the tendency for thermal pole tip
protrusion. This leads to selection of head gimbal assemblies,
which do not have the thermal pole tip protrusion tendency. The
selected head gimbal assemblies have better reliability, as do
actuators and disk drives made with the selected head gimbal
assemblies.
[0023] These and other advantages of the present invention will
become apparent upon reading the following detailed descriptions
and studying the various figures of the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] FIG. 1A illustrates a typical prior art high capacity disk
drive 10 including actuator arm 30 with voice coil 32, actuator
axis 40, suspension or head arms 50-58 with slider/head unit 60
placed among the disks;
[0025] FIG. 1B illustrates a typical prior art high capacity disk
drive 10 with actuator 20 including actuator arm 30 with voice coil
32, actuator axis 40, head arms 50-56 and slider/head units 60-66
with the disks removed;
[0026] FIG. 2A illustrates a suspended head slider 60 containing
the read-write head 200 of the prior art;
[0027] FIG. 2B illustrates the relationship between the principal
axis 110 of an actuator arm 50 containing suspension 60, which in
turn contains head slider 100, as found in the prior art;
[0028] FIG. 2C illustrates a simplified schematic of a disk drive
controller 1000 of the prior art, which may be used to control a
spin stand test unit;
[0029] FIG. 2D illustrates a detailed view head suspension 60 of
the prior art;
[0030] FIG. 3A illustrates an extension of program system 2000 of
FIG. 2C estimating a thermal pole tip protrusion tendency for a
head gimbal assembly containing a read-write head;
[0031] FIG. 3B illustrates a detail flowchart of operation 2010 of
FIG. 3A further determining the thermal pole tip protrusion
tendency for a track collection member, as at least one, and often
preferably both, of the operations in this flowchart;
[0032] FIG. 4A illustrates a sudden MRR change event with an amount
MRR change (.DELTA.MRR) and a MRR value;
[0033] FIG. 4B illustrates an amplitude modulation envelope at
essentially the rotational frequency showing a maximum voltage
swing V and a deviation .DELTA.V from the maximum voltage swing
V;
[0034] FIG. 5 illustrates a detail flowchart of operation 2052 of
FIG. 3B further monitoring the change in magneto-resistance;
and
[0035] FIG. 6 illustrates a detail flowchart of operation 2062 of
FIG. 3B further detecting the amplitude modulation envelope.
DETAILED DESCRIPTION OF THE INVENTION
[0036] Thermal pole tip protrusion is caused by the materials in
and around the head slider expanding during write operations until
part of those materials protrude, leading to contact with the
rotating disk surface. Contact can degrade the write performance by
altering the flying height. Contact can also wear down part of the
disk surface.
[0037] While it is well known that read-write heads expand during
writing, the inventors are unaware of anyone else who recognized
this situation's significance, particularly as the flying height
decrease and the data rates increase, which is required for high
areal density disk drives.
[0038] The inventors realized that they could detect the problem at
the spin stand level by testing head gimbal assemblies to reliably,
and inexpensively, estimate the tendency for thermal pole tip
protrusion. This leads to selection of head gimbal assemblies,
which do not have the thermal pole tip protrusion tendency. The
selected head gimbal assemblies have better reliability, as do
actuators and disk drives made with the selected head gimbal
assemblies.
[0039] In the following figures will be found flowcharts of at
least one method of the invention possessing arrows with reference
numbers. These arrows will signify flow of control and sometimes
data supporting implementations, including at least one program
step, or program thread, executing upon a computer, inferential
links in an inferential engine, state transitions in a finite state
machine, and dominant learned responses within a neural
network.
[0040] The operation of starting a flowchart refers to at least one
of the following. Entering a subroutine in a macro instruction
sequence in a computer. Entering into a deeper node of an
inferential graph. Directing a state transition in a finite state
machine, possibly while pushing a return state. And triggering a
collection of neurons in a neural network.
[0041] The operation of termination in a flowchart refers to at
least one or more of the following. The completion of those
operations, which may result in a subroutine return, traversal of a
higher node in an inferential graph, popping of a previously stored
state in a finite state machine, return to dormancy of the firing
neurons of the neural network.
[0042] A computer as used herein will include, but is not limited
to an instruction processor. The instruction processor includes at
least one instruction processing element and at least one data
processing element, each data processing element controlled by at
least one instruction processing element.
[0043] FIG. 3A illustrates an extension of program system 2000 of
FIG. 2C estimating a thermal pole tip protrusion tendency for a
head gimbal assembly containing a read-write head.
[0044] Operation 2012 performs determining the thermal pole tip
protrusion tendency for the head gimbal assembly on the track
collection member, for each track collection member. Operation 2022
performs predicting the thermal pole tip protrusion tendency for
the head gimbal assembly based upon, for each of the track
collection members, the thermal pole tip protrusion tendency on the
track collection member.
[0045] The track collection includes at least an inside diameter
track of a disk surface and an outside diameter track of the disk
surface. The track collection may further preferably include a
middle diameter track of the disk surface.
[0046] The invention utilizes the following, for each of the track
collection members. The read-write head can provide a
magneto-resistance from a disk surface while performing a write
operation to the track collection member on the disk surface, as
well as provide a voltage while reading the track collection member
at a bias current. The disk surface rotates at a rotational
frequency during these operations. Typical rotational frequencies
include the following: 120 Hz for a 7200 RPM disk and 240 Hz for a
14400 RPM disk.
[0047] FIG. 3B illustrates a detail flowchart of operation 2010 of
FIG. 3A further determining the thermal pole tip protrusion
tendency for a track collection member, as at least one, and often
preferably both, of the operations in this flowchart.
[0048] Operation 2052 performs monitoring a change of the
magneto-resistance while the read-write head performs the write
operation on the track collection member to determine the thermal
pole tip protrusion tendency. Operation 2062 performs detecting an
amplitude modulation envelope for the voltage at essentially the
rotational frequency for the track collection member written to
determine the thermal pole tip protrusion tendency.
[0049] FIG. 4A illustrates a sudden MRR change event with an amount
MRR change (.DELTA.MRR) and a MRR value.
[0050] FIG. 4B illustrates an amplitude modulation envelope at
essentially the rotational frequency showing a maximum voltage
swing V and a deviation .DELTA.V from the maximum voltage swing
V.
[0051] FIG. 5 illustrates a detail flowchart of operation 2052 of
FIG. 3B further monitoring the change in magneto-resistance.
[0052] Operation 2072 performs observing the magneto-resistance
while the read-write head performs the write operation on the track
collection member to create a sudden MRR change event collection
and to create a MRR value. Operation 2082 performs determining a
number of the sudden MRR change event collection members. Operation
2092 performs determining a change characteristic based upon an
amount MRR change divided by the MRR value, for each of the sudden
MRR change event collection members. Operation 2102 performs
determining the thermal pole tip protrusion tendency based upon the
number of the sudden MRR change event collection members and based
upon the change characteristic for the sudden MRR change event
collection members.
[0053] FIG. 6 illustrates a detail flowchart of operation 2062 of
FIG. 3B further detecting the amplitude modulation envelope.
[0054] Operation 2132 performs the read-write head reading the
track collection member at a current bias to create a track voltage
table. Operation 2142 performs processing the track voltage table
at essentially the rotational frequency to generate an amplitude
modulation envelope for the voltage at essentially the rotational
frequency. Operation 2152 performs calculating a maximum voltage
swing for the amplitude modulation envelope. Operation 2162
performs calculating a deviation from the maximum voltage swing for
the amplitude modulation envelope. Operation 2172 performs
determining the thermal pole tip protrusion tendency for the track
collection member based upon the deviation and based upon the
maximum voltage swing.
[0055] The preceding embodiments have been provided by way of
example and are not meant to constrain the scope of the following
claims.
* * * * *