Title: Method of controlling pitch static attitude of sliders on integrated lead suspensions by improved plastic deformation processing
Abstract: A method is provided for controlling the pitch static attitude of a slider in an integrated lead suspension head gimbal assembly. The integrated lead suspension includes a load beam, a mount plate, a hinge and a flexure made out of a multi-layer material. The flexure legs and the outrigger leads are simultaneously plastically deformed to define the pitch static attitude. The flexure legs and the outrigger leads are deformed at approximately the same longitudinal location.
Patent Number: 6,993,824 Issued on 02/07/2006 to Childers, et al.
| Inventors:
|
Childers; William W. (Morgan Hill, CA);
Lawson; Drew B. (Los Gatos, CA);
Pan; Tzong-Shii (San Jose, CA);
Pattanaik; Surya (San Jose, CA)
|
| Assignee:
|
Hitachi Global Storage Technologies Netherlands B.V. (Amsterdam, NL)
|
| Appl. No.:
|
651262 |
| Filed:
|
August 28, 2003 |
| Current U.S. Class: |
29/603.03; 29/603.04; 29/603.06; 29/603.07; 360/245.3; 360/245.8; 360/245.9; 360/244.2; 360/244.8 |
| Current Intern'l Class: |
G11B 5/12.7 (20060101); H04R 31/00 (20060101) |
| Field of Search: |
29/60303,603.04,603.06,603.07
360/244.8,244.2,244,240,2944-2947,245.3,245.8,245.9
|
References Cited [Referenced By]
U.S. Patent Documents
| 4151014 | Apr., 1979 | Charschan et al.
| |
| 5405804 | Apr., 1995 | Yabe.
| |
| 5539596 | Jul., 1996 | Fontana et al.
| |
| 5739982 | Apr., 1998 | Arya et al.
| |
| 5818662 | Oct., 1998 | Shum.
| |
| 5828031 | Oct., 1998 | Pattanaik.
| |
| 5883758 | Mar., 1999 | Bennin et al.
| |
| 5896247 | Apr., 1999 | Pan et al.
| |
| 5922503 | Jul., 1999 | Spak et al.
| |
| 5956209 | Sep., 1999 | Shum.
| |
| 5956212 | Sep., 1999 | Zhu.
| |
| 5982584 | Nov., 1999 | Bennin et al.
| |
| 6021022 | Feb., 2000 | Himes et al.
| |
| 6055132 | Apr., 2000 | Arya et al.
| |
| 6125015 | Sep., 2000 | Carlson et al.
| |
| 6181526 | Jan., 2001 | Summers.
| |
| 6201664 | Mar., 2001 | Le et al.
| |
| 6249404 | Jun., 2001 | Doundakov et al.
| |
| 6282064 | Aug., 2001 | Palmer et al.
| |
| 6515832 | Feb., 2003 | Girard.
| |
| 6757137 | Jun., 2004 | Mei.
| |
| Foreign Patent Documents |
| 0 834 865 | Aug., 1998 | EP.
| |
| 2001007266 | Jan., 2001 | JP.
| |
Other References
"Design of large deflection electrostatic actuators"; Grade, J.D.; Jerman, H.;
Kenny, T.W.; Microelectromechanical Systems, Journal of vol. 12, Issue 3, Jun.
2003 Page(s): 335-343.
|
Primary Examiner: Tugbang; A. Dexter
Assistant Examiner: Kim; Paul D.
Attorney, Agent or Firm: Bracewell & Giuliani LLP
Claims
What is claimed is:
1. A method of processing an integrated lead suspension, comprising:
(a) providing an integrated lead suspension having a longitudinal axis, a lateral
axis transverse to the longitudinal axis, a flexure having flexure legs, and outrigger leads;
(b) configuring the integrated lead suspension such that at least a portion of
each of the outrigger leads is laterally spaced apart from the longitudinal axis
at an outrigger distance that is greater than a flexure leg distance between the
longitudinal axis and the flexure legs, thereby defining said at least a portion
of each of the outrigger leads as being outboard of the flexure legs; and then
(c) simultaneously plastically deforming both the flexure legs and the outrigger
leads to define a pitch static attitude.
2. The method of claim 1, wherein step (b) comprises locating at least one outrigger
lead on each lateral side of the flexure such that there is at least one outrigger
lead located outboard of each of the flexure legs.
3. The method of claim 1, further comprising the step of solder ball bonding
a slider to the outrigger leads.
4. The method of claim 3, wherein step (c) occurs before the solder ball bonding.
5. The method of claim 1, further comprising step-forming both the flexure legs
and the outrigger leads.
6. The method of claim 1, further comprising creasing both the flexure legs and
the outrigger leads.
7. The method of claim 1, further comprising simultaneously plastically deforming
the flexure legs and the outrigger leads at approximately a same longitudinal location
along the longitudinal axis.
8. A method of setting a pitch static attitude for a slider on an integrated
lead suspension, comprising:
(a) providing an integrated lead suspension having a longitudinal axis, a lateral
axis transverse to the longitudinal axis, a load beam, a mount plate, a flexure
having flexure legs and a tongue for providing a mechanical support structure,
and outrigger leads for carrying electrical signals;
(b) configuring the integrated lead suspension such that each of the outrigger
leads is laterally spaced apart from the longitudinal axis at an outrigger distance
that is greater than a flexure leg distance between the longitudinal axis and the
flexure legs, thereby defining said each of the outrigger leads as being completely
laterally outboard of the flexure legs;
(c) locating the outrigger leads on each lateral side of the flexure such that
there are outrigger leads located outboard of each of the flexure legs; and then
(d) simultaneously plastically deforming both the flexure legs and the outrigger
leads to correct the pitch static attitude of the slider.
9. The method of claim 8, further comprising the step of solder ball bonding
the slider to the outrigger leads.
10. The method of claim 9, wherein step (d) occurs before the solder ball bonding.
11. The method of claim 8, wherein step (d) comprises simultaneously creasing
both the flexure legs and the outrigger leads with a roller.
12. The method of claim 8, wherein step (d) comprises simultaneously step-forming
both the flexure legs and the outrigger leads.
13. The method of claim 8, wherein step (d) further comprises protecting the
outrigger leads from mechanical damage during the plastic deformation.
14. The method of claim 8, wherein step (d) comprises simultaneously plastically
deforming the flexure legs and the outrigger leads at approximately a same longitudinal
location along the longitudinal axis.
Description
This patent application is related to U.S. patent application Ser. No. 10/650,557,
entitled, Method of Localized Thermal Processing of Integrated Lead Suspensions
for Controlling the Pitch Static Attitude of Sliders, which was filed concurrently
with the present patent application.
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates in general to head gimbal assemblies for data recording
disk drives and, in particular, to an improved method for controlling pitch static
attitude of sliders on integrated lead suspensions in head gimbal assemblies by
improved processing during manufacturing thereof.
2. Description of the Related Art
Generally, a data access and storage system consists of one or more storage
devices that store data on magnetic or optical storage media. For example, a magnetic
storage device is known as a direct access storage device (DASD) or a hard disk
drive (HDD) and includes one or more disks and a disk controller to manage local
operations concerning the disks. The hard disks themselves are usually made of
aluminum alloy or a mixture of glass and ceramic, and are covered with a magnetic
coating. Typically, one to six disks are stacked vertically on a common spindle
that is turned by a disk drive motor at several thousand revolutions per minute (rpm).
A typical HDD also utilizes an actuator assembly. The actuator moves magnetic
read/write
heads to the desired location on the rotating disk so as to write information to
or read data from that location having an air bearing surface (ABS) that enables
the slider to fly at a constant height close to the disk during operation of the
disk drive, by a cushion of air generated by the rotating disk. Within most HDDs,
the magnetic read/write head transducer is mounted on a slider. A slider generally
serves to mechanically support the head and any electrical connections between
the head and the rest of the disk drive system. The slider is aerodynamically shaped
to glide over moving air in order to maintain a uniform distance from the surface
of the rotating disk, thereby preventing the head from undesirably contacting the
disk. Each slider is attached to the free end of a suspension that in turn is cantilevered
from the rigid arm of an actuator. Several semi-rigid arms may be combined to form
a single movable unit having either a linear bearing or a rotary pivotal bearing system.
The head and arm assembly is linearly or pivotally moved utilizing a magnet/coil
structure that is often called a voice coil motor (VCM). The stator of a VCM is
mounted to a base plate or casting on which the spindle is also mounted. The base
casting with its spindle, actuator VCM, and internal filtration system is then
enclosed with a cover and seal assembly to ensure that no contaminants can enter
and adversely affect the reliability of the slider flying over the disk. When current
is fed to the motor, the VCM develops force or torque that is substantially proportional
to the applied current. The arm acceleration is therefore substantially proportional
to the magnitude of the current. As the read/write head approaches a desired track,
a reverse polarity signal is applied to the actuator, causing the signal to act
as a brake, and ideally causing the read/write head to stop and settle directly
over the desired track.
The suspension of a conventional disk drive typically includes a relatively stiff
load beam with a mount plate at the base end, which subsequently attaches to the
actuator arm, and whose free end mounts a flexure that carries the slider and its
read/write head transducer. Disposed between the mount plate and the functional
end of the load beam is a 'hinge' that is compliant in the vertical bending direction
(normal to the disk surface). The hinge enables the load beam to suspend and load
the slider and the read/write head toward the spinning disk surface. It is then
the job of the flexure to provide gimbaled support for the slider so that the read/write
head can pitch and roll in order to adjust its orientation for unavoidable disk
surface run out or flatness variations.
The flexure in an integrated lead suspension is generally made out of a laminated
multi-layer material. Typically, it consists of a conductor layer (like copper),
a di-electric layer (like polyimide), and a support layer (like stainless steel).
The electrical lead lines are etched into the conductor layer, while the polyimide
layer serves as the insulator from the underlying steel support layer. The steel
support layer is also patterned to provide strength and gimbaling characteristics
to the flexure. The conducting leads, called traces, which electrically connect
the head transducer to the read/write electronics, are often routed on both sides
of the suspension, especially in the gimbal region. Normally the traces consist
of copper conductor with polyimide dielectric layer but no support stainless steel
layer and only provide the electrical function. The mechanical function is provided
by the flexure legs (stainless steel only), which normally run adjacent to the traces.
The static attitude of the slider is defined by the angular position of the slider
ABS with respect to the mounting platform and is specified by design in conjunction
with a specific ABS, so that the slider can maintain an optimal flying height for
the transducer thereon to read and/or write data on to the recording surface of
the disk. To counter the airlift pressure exerted on the slider during disk drive
operation, a pre-determined load is applied through a load point on the suspension
to a precise load point on the slider. The slider flies above the disk at a height
established by the equilibrium of the load on the load point and the lift force
of the air bearing. The load of the suspension together with static attitude, control
and maintain the optimal flying height of the slider.
The pitch static attitude in a suspension is produced to a desired value by forming
the flexure legs, and then adjusting by mechanical/thermal methods. Since, the
traces are an integral part of the flexure in an integrated lead suspension, joined
to the flexure legs near the transducer bonding area in the front and near the
back (leading edge) of the slider in the back, the traces provide resistance to
the deformation of flexure leg and deflection of flexure tongue by an opposing
force. Hence a significantly higher force is needed to plastically deform the flexure
legs to obtain a desired pitch angle that also includes the overcoming the opposite
forces produced by the traces. This process leaves residual stresses in the traces
and the traces do not remain in the same plane as that of the rest of the flexure.
One way to confirm the existence of stress in the traces is to cut the traces or
subject the suspension to thermal processes. The stress is relieved by either process
and as a result the pitch angle is increased.
This is an inherent problem of the integrated lead suspension. Once the suspension
is manufactured by the supplier with formed flexure legs and adjustment to achieve
desired pitch angle, it comes with variable amount of stress in the conductive
traces. A part or all of the stress is likely to be relieved if and when the said
suspension is subjected to a thermal process, thereby changing the pitch static
attitude of the suspension or head gimbal assembly.
To successfully achieve file performance, the read/write head must fly steadily
at a given fly height over the disk with minimal variations. Since the variations
in fly height are dependent on the various sensitivities of the fly height to the
process parameters as well as the variability of the parameters, a state-of-the-art
air bearing surface (ABS) design and tight process control are mandatory to minimize
such variations. Pitch static attitude and variations significantly affect the
fly height. Moreover, a very low or negative pitch static attitude can cause disk
damage and a very high pitch angle can promote a bi-stable behavior in fly height.
Thus, an improved method and system for controlling process parameters, such
as pitch static attitude, of sliders on integrated lead suspensions in head gimbal
assemblies for disk drives during the manufacturing thereof is needed.
SUMMARY OF THE INVENTION
The present invention is directed to an improvement in the manufacturing of integrated
lead suspension, which overcomes the disadvantages and limitations in the prior
art described above.
The integrated lead suspension is a multi-layer assembly having a load beam,
a mount plate, a hinge and a flexure. The flexure is made out of a multi layer
structure consisting of a support layer, a dielectric layer, and an electrically
conductive layer. The flexure has a gimbal area with a flexure tongue to which
a slider is attached. The electrically conductive layer is etched to form conductive
leads or traces interconnecting the head transducer to the read/write electronics.
The traces run parallel to the flexure legs made out of the support layer stainless
steel in the gimbal area.
In one embodiment of the present invention, the flexure legs and traces are simultaneously
plastically deformed to eliminate residual stresses in the traces during the manufacturing
of the integrated lead suspension. The flexure legs and the outrigger leads are
deformed at approximately the same longitudinal location. The deforming step may
comprise, for example, simultaneously creasing both the flexure legs and the outrigger
leads with a roller, or simultaneously step-forming both the flexure legs and the
outrigger leads. In addition, the method may further comprise protecting the outrigger
leads from mechanical damage, such as scratching, during the plastic deformation.
In another embodiment of an integrated lead suspension includes a slider that
is electrically interconnected with outrigger leads on the suspension by solder
ball bonding. Solder ball bonding requires significantly high temperatures to reflow
the solder balls. When such temperatures are applied to the suspension during the
head gimbal assembly process, the pitch static attitude of the slider can go out
of control as the excess heat from solder ball bonding flows through the conductors
of outrigger leads. Solder ball bonding thereby thermally affects the residual
stress level in the outrigger leads and, thus, affects the pitch static attitude
of the slider. A similar situation can also arise if the integrated lead suspension
or the head gimbal assembly made of an integrated lead suspension is subjected
to other thermal processes.
To overcome this problem, both the flexure legs and the outrigger leads are simultaneously
plastically deformed during the manufacturing of the integrated lead suspension,
to permanently define a stable pitch static attitude before solder ball bonding.
The flexure legs and the outrigger leads are deformed at approximately the same
longitudinal location. The deforming step may comprise, for example, simultaneously
creasing both the flexure legs and the outrigger leads with a roller, or simultaneously
step-forming both the flexure legs and the outrigger leads. In addition, the method
may further comprise protecting the outrigger leads from mechanical damage, such
as scratching, during the plastic deformation.
The foregoing and other objects and advantages of the present invention will
be apparent to those skilled in the art, in view of the following detailed description
of the preferred embodiment of the present invention, taken in conjunction with
the appended claims and the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
So that the manner in which the features and advantages of the invention, as
well
as others which will become apparent, are attained and can be understood in more
detail, more particular description of the invention briefly summarized above may
be had by reference to the embodiment thereof which is illustrated in the appended
drawings, which drawings form a part of this specification. It is to be noted,
however, that the drawings illustrate only an embodiment of the invention and therefore
are not to be considered limiting of its scope as the invention may admit to other
equally effective embodiments.
FIG. 1 is a schematic top plan view of one embodiment of a hard disk drive.
FIG. 2
a is a top plan view of an integrated lead suspension utilized
by the disk drive of FIG. 1.
FIG. 2
b is a perspective view of the head gimbal assembly using the integrated
lead suspension of FIG. 2
a.
FIGS. 3
a and 3
b are top plan and side views, respectively,
of the head gimbal assembly of FIG. 2
b.
FIG. 4 is a top plan view of a distal portion of an integrated lead suspension.
FIG. 5 is an enlarged side elevational view of a distal portion of the head
gimbal assembly of FIG. 4.
FIG. 6 is a top plan view of the distal portion of the integrated lead suspension
of FIG. 5.
FIG. 7 is a side view of the integrated lead suspension during the deformation process.
DETAILED DESCRIPTION OF THE INVENTION
Referring to FIG. 1, a schematic drawing of one embodiment of an information
storage system comprising a magnetic hard disk file or drive
111 for a computer
system is shown. Drive
111 has an outer housing or base
113 containing
a plurality of stacked, parallel magnetic disks
115 (one shown) which are
closely spaced apart. Disks
115 are rotated by a spindle motor assembly
having a central drive hub
117. An actuator
121 comprises a plurality
of parallel actuator arms
125 (one shown) in the form of a comb that is
pivotally mounted to base
113 about a pivot assembly
123. A controller
119 is also mounted to base
113 for selectively moving the comb of
arms
125 relative to disks
115.
In the embodiment shown, each arm
125 has extending from it at least one
cantilevered integrated lead suspension
127. A magnetic read/write transducer
or head is mounted on a slider
129 and the slider is attached to the end
of the integrated lead suspension
127. The read/write heads magnetically
read data from and/or magnetically write data to disks
115. The level of
integration called the head gimbal assembly
130 is the head and the slider
129, which are mounted on integrated lead suspension
127. The slider
129 is usually bonded to the end of integrated lead suspension
127.
In the embodiment shown, the head may be pico size (approximately 1250×1000×300
microns) and formed from ceramic or intermetallic materials. The head also may
be nano size (approximately 2050×1600×450 microns), or femto size (approximately
850×700×230 microns). The slider
129 is pre-loaded against the
surface of disk
115 (preferably in the range one to four grams) by integrated
lead suspension
127.
Integrated lead suspensions
127 have a spring-like quality, which
biases or urges the air bearing surface of slider
129 against the disk
115
to enable the creation of the air bearing film between the slider
129 and
the surface of disk
115. A voice coil
133 housed within a conventional
voice coil motor magnet assembly
134 (top pole not shown) is also mounted
to arms
125 opposite the head gimbal assemblies. Movement of the actuator
121 (indicated by arrow
135) by controller
119 moves the sliders
129 of the head gimbal assemblies radially across tracks on the disks
115
until the heads settle on the target tracks. The head gimbal assemblies operate
in a conventional manner and always move in unison with one another, unless drive
111 uses multiple independent actuators (not shown) wherein the arms
125
can move independently of one another.
FIGS. 2-4 show various views and details of the head gimbal assembly
130
and the integrated lead suspension
127 for a better understanding of the
problem and the present invention. Such an integrated lead suspension
127
comprises a load beam
155, to which is welded a flexure assembly
163.
The flexure assembly is generally an elongated structure that is aligned with the
load beam
155. The flexure assembly comprises a support layer
174
such as stainless steel, a dielectric layer
175 such as polyimide, and a
conductive layer such as copper from which a set of electrical traces
173
have been patterned by etching. The integrated lead suspension
127, also
has a hinge
159 and mount plate or base plate
157 welded to the back
end which is swaged to the actuator arm
125 during head stack assembly operation.
FIG. 3A is a top plan view and FIG. 3B shows a side cross-sectional view of
the head gimbal assembly
130, as shown in FIG. 2. The pitch static attitude
of a slider in a head gimbal assembly is defined as the angle between the plane
of the slider air bearing surface (ABS)
140 and the plane of the mounting
surface of the mount plate
157, when the center of the ABS is at the design
specific "offset" height (illustrated in FIG. 3B).
FIG. 4 is a top plan view of the gimbal area of the integrated lead suspension
127. As described earlier, the flexure is made out of a multilayer laminate
structure having a support layer
174, a dielectric layer
175 and
a conductive layer that has been patterned to provide traces
173 to interconnect
the head transducer to the read/write electronics. Two flexure legs
165
of support layer stainless steel connect the main body of the flexure to the flexure
tongue
169 to which a slider is attached to form a head gimbal assembly.
It can be seen from FIG. 4 that the conductive traces
173, on either side
of the flexure assembly, run reasonably parallel to the flexure legs
165,
except where they are connected to each other in areas
181,
182 towards
the back of the flexure tongue and areas
183,
184 towards the front
side of the flexure tongue. It is also clear that the conductive traces
173
do not have the support layer stainless steel between areas
181-
182
and
183-
184. The conductive traces
173 terminate at pads
185
to which the head pads in the slider are connected by various methods. In some
cases, the dielectric layer
175 is made by a 3-layer structure; a core layer
of Kapton with thin layers of thermo plastic polyimide on either side. The thermo
plastic polyimide (TPI) layer has a glass transition temperature (Tg) close to
200 deg C. and helps in bonding of the core Kapton layer to stainless steel base
layer
174 on one side and the conductive copper layer on the other side.
The pitch static attitude of an integrated lead suspension assembly is defined
similar to that of the head gimbal assembly (FIG. 3
b), as the angle between
the plane of the flexure tongue and the plane of mounting area of the mount plate,
with the center of the flexure tongue at a specified "offset" height, different
from that of head gimbal assembly by the thickness of the slider. In an integrated
lead suspension, the desired pitch static attitude is normally achieved by plastically
deforming the flexure legs
165 during the manufacturing of the integrated
lead suspension so that the flexure tongue is rotated. The degree of deformation
needed depends on the magnitude of pitch static attitude required by design.
Since the flexure legs and traces are connected as described earlier, the traces
adjacent to the flexure legs are in a state of stress when the flexure legs are
plastically deformed. The deformation of the flexure leg tries to rotate the flexure
tongue in a direction away from the dimple (positive pitch static attitude), whereas
the traces try to hold them back as they are not plastically deformed. As a result,
the final rotation of the flexure tongue which in turn provides the pitch static
attitude, is less than what would have been achieved if the traces were not present.
The traces also stay out of the plane of the flexure legs, and bowed as shown in
FIG. 5. The existence of stress in the traces, its release and effect on pitch
static attitude can easily be verified by cutting the traces. When the traces are
cut, the stress is released, the tongue moves to the appropriate position dictated
by the deformation of flexure legs without the hold back from traces. As a result
the pitch static attitude is increased.
The stress in the traces can also be partially or fully relieved when the integrated
lead suspension or head gimbal assembly built thereof is subjected to thermal exposures.
In such cases the pitch static attitude will increase to different degrees. One
such case is when the slider and integrated lead suspension are electrically connected
by a process called solder ball bonding (assignee's U.S. Pat. No. 5,828,031). The
pads
185 are connected to the slider bond pads, by placing and reflowing
discrete solder balls. The heat applied to melt the solder balls flows thru the
traces, and softens the thermo plastic polyimide layer under the traces. Such softening
in the areas
183,
184 relieves the stress on the traces from flexure
leg forming and increases the pitch static attitude. A similar effect can also
be observed if the integrated lead suspension, or the head gimbal assembly is subject
to any thermal exposures in the process.
In one embodiment of the current invention, the stresses in the traces are eliminated
at the source, that is during the flexure leg forming to attain the desired pitch
static attitude (PSA)
145. This can be achieved by simultaneous plastic
deformation (such as with rollers or other mechanical devices
199 in FIG.
7) of the flexure legs
165 as well as the outrigger lead traces
173
as shown in area
179a of FIG. 4.
There are several parameters that measure the performance of the slider
129.
Fly height
141 (FIG. 5) is the separation between a point on the ABS
140
of the slider
129 and the surface of disk
115, such as the center
of the trailing edge
143 of the ABS
140 and the surface of disk
115.
Pitch is the tilting of the flying slider
129 in the longitudinal direction
(see longitudinal axis
151 and lateral axis
153 in FIG. 6) with respect
to the plane of disk
115. Roll (not illustrated) is the tilting of the flying
slider
129 in the lateral or transverse direction with respect to the plane
of the disk
115. Fly height, pitch, and roll are all dependent on parameters
like ambient pressure, temperature, air viscosity, linear velocity (product of
radius from center of the disk and disk angular velocity or rpm), skew angle (angle
between the longitudinal axis of the slider and the tangent to the current radius
from the center of the disk), pre-load (the force applied by, for example, integrated
lead suspension
127), integrated lead suspension moments (moments applied
in the pitch and roll directions by integrated lead suspension
127), slider
flatness, and the design of the slider air bearing
140 itself. The design
of the slider
129 targets a low velocity and low skew dependent, fly height
profile that remains substantially flat across the radius of the disk
115.
The spacing between the head
142 and the disk
115 is described by
fly height, together with its pitch and roll.
The performance of a slider head also may be measured in terms of sensitivities.
The sensitivities of the slider
129 describe its change in fly height, pitch,
or roll when another parameter that affects the fly height changes by one unit.
For example, "sensitivity to pre-load" measures the decrease in fly height when
the pre-load force is increased by one gram. "Sensitivity to slider flatness" is
another parameter. The various surfaces of the slider air bearing are not perfectly
flat since the slider
129 exhibits a longitudinal curvature or crown, a
transverse curvature or camber, and a cross curvature or twist. Among these features,
crown has a significant effect on fly height.
In general, the parameters that affect fly height are associated with the integrated
lead suspension
127 (pre-load, location of the dimple
144 with respect
to the slider
129, static attitudes in the pitch and roll directions), slider
129 (flatness and size of ABS, etch depths, mask alignment, and rail width),
and operating conditions (ambient temperature, pressure, viscosity, and velocity).
It is desirable for slider
129 to have low sensitivities since that implies
that the departure of fly height from its desired target is small. Each parameter
affecting fly height is described statistically by its mean and standard deviation.
A tight distribution of values for a parameter around their mean implies that the
spread or standard deviation is small.
For example, "fly height sigma" is a statistical estimator of the fly height
variation of a group of sliders. This parameter is proportional to the standard
deviation of other parameters that affect fly height, and to the sensitivities
of the design of air bearing. Thus, by designing a slider to possess low sensitivities,
and by ensuring that the manufacturing process is very repeatable, a tight distribution
of fly heights is realized.
There are also a number of specific requirements for the head and slider that
should be met. Since disks are not perfectly flat and exhibits waviness or curvature
that affects fly height, it is desirable that sliders respond consistently to changes
in the curvature of the disks. There are at least two disk curvatures of interest.
One is in the tangential direction is related to the crown of the slider. Another
is in the radial direction and is related to the camber of the slider. Because
of the magnitude of the radial curvature near the rim of the disk (also called
roll-off or ski jump), it is important for sliders to feature a low transverse
curvature sensitivity. The flatness sensitivity of sliders is significant in this respect.
Another requirement for sliders is low fly height and roll sigmas. The variability
in fly height of sliders must be consistent. In particular, the roll standard deviation
must be small since it is the spacing between the trailing edge
143 (FIG.
5) of head
142 and disk
115 that controls the fly height. If the
trailing edge
143 is perfectly parallel to the disk
115, the clearance
is uniform. Any amount of roll creates an uneven clearance in the lateral direction
between the head
142 and the disk
115.
As a related requirement, sliders should have good load/unload performance. During
operation, a slider
129 is loaded onto a spinning disk
115 and must
establish its supportive air bearing to avoid contact with the disk
115.
Ideally, there will be no exposure to contact during the load/unload sequences.
However, physical contact with the disk
115 is almost inevitable and can
be a disturbing event on the fly height
141 as it causes the head
142
and slider
129 to lose support and cause damage to the disk
115.
The static attitude of the slider maintains the angular position of the slider
with respect to the mounting platform and is specified by design in conjunction
with a specific ABS. In this way, the slider can maintain an optimal flying height
for the transducer thereon to read and/or write data on to the recording surface
of the disk. To counter the airlift pressure exerted on the slider during disk
drive operation, a pre-determined load is applied through a load point on the suspension
to a precise load point on the slider. The slider flies above the disk at a height
established by the equilibrium of the load on the load point and the lift force
of the air bearing. The load of the suspension, together with static attitude,
control and maintain the optimal flying height of the slider.
The pitch static attitude in a suspension is produced to a desired value by forming
the flexure legs, and then making adjustments by mechanical and/or thermal methods
during the manufacturing of the suspension. The traces are joined to the flexure
legs near the transducer bonding area in front of the slider, and also near the
back (i.e., the leading edge) of the slider. Since the traces are an integral part
of the flexure in an integrated lead suspension, the traces provide resistance
to the deformation of the flexure leg and the deflection of the flexure tongue
by an opposing force. Hence, a significantly higher force is needed to plastically
deform the flexure legs to obtain a desired pitch angle, which also includes the
overcoming the opposite forces produced by the traces. This process leaves residual
stresses in the traces, which cause the traces to move out-of-plane with the rest
of the flexure. One way to confirm the existence of stress in the traces is to
cut the traces or subject the suspension to thermal processes. The residual stresses
in the traces are relieved by either process and, as a result, the slider pitch
angle is increased.
The presence of residual stresses in the traces is an inherent problem of the
integrated lead suspension. Once the suspension is manufactured by the supplier
with formed flexure legs and adjustment to achieve a desired pitch angle, it comes
with a variable amount of stress in the conductive traces. A part or all of the
stress is likely to be relieved if and when the suspension is subjected to a thermal
process, thereby changing the pitch static attitude of the suspension or head gimbal assembly.
In one embodiment, the flexure
163 is formed from stainless steel. A set
of flexure legs
165 form a portion of the flexure
163 and define
an aperture
167 near the distal end of the flexure
163. A tongue
169 extends into the aperture
167 from the flexure legs
165
for providing a mechanical support structure to which the slider
129 is
bonded. The flexure legs
165 are spaced apart from the longitudinal axis
151 at a lateral, flexure leg distance
171 that is measured between
the longitudinal axis
151 and the flexure legs
165. The flexure leg
distance
171 need not be identical for each flexure leg
165.
Integrated lead suspension
127 also comprises a set of outrigger
leads
173 that are mounted to the flexure
163 for carrying electrical
signals. In one embodiment, the outrigger leads
173 are formed from copper
and are electrically insulated from flexure
163 by insulating layer
175.
Insulation
175 may comprise, for example, a dielectric (such as polyimide)
that itself is formed from, e.g., three layers of materials. Insulation
175
has as an inert core layer of Kapton® that is covered on each side by another
material, such as a thermoplastic polyimide, that bonds to the copper leads
173
and the steel of flexure
163. As shown in FIG. 6, the copper outrigger leads
173 "exit" from the end of stainless steel flexure
163 beyond slider
129 approximately at the areas
172, such that outrigger leads
173
are "outboard" of flexure
163, as will be described below.
In the embodiment shown, the outrigger leads
173 are located on each lateral
side
180 of the flexure
163 such that there are outrigger leads
173
located laterally outboard of each of the flexure legs
165. In this version,
there are two outrigger leads
173 on each side
180 of the integrated
lead suspension
127. Each of the outrigger leads
173 is laterally
spaced apart from the longitudinal axis
151 at an outrigger distance
177
that is greater than the flexure leg distance
171. The various individual
outrigger leads
173 typically have different outrigger distances
177,
but each of the outrigger legs
173 is completely laterally outboard of the
flexure legs
165.
The slider
129 mounted to the tongue
169 of the flexure
163
such that electrical contact is established between the slider
129 and the
outrigger leads
173. The slider
129 is electrically interconnected
with the outrigger leads
173 by solder ball bonding, which requires significantly
high temperatures (approximately 200+ degrees C.) to reflow the solder balls
170
(FIG. 5). Such relatively high temperatures during the head gimbal assembly process
causes the pitch static attitude
145 of the slider
129 to go out
of control in the prior art as the excess heat from solder ball bonding flows through
the conductors of outrigger leads
173. Solder ball bonding thermally affects
the residual stress level in the outrigger leads
173 and, thus, affects
the pitch static attitude
145 of the slider
129. The outrigger leads
173 have residual stress due to the techniques used to form them in the
prior art.
A similar effect can also be observed if the integrated lead suspension, or the
head gimbal assembly is subject to any elevated temperature thermal exposures.
As described above for FIG. 7, all of both the flexure legs
165 and the
outrigger leads
173 are simultaneously plastically deformed during the manufacturing
of the integrated lead suspension to permanently define a pitch static attitude
angle
145 of the slider
129. In one embodiment, the flexure legs
165 and the outrigger leads
173 are plastically deformed at approximately
a same longitudinal location
179 along the longitudinal axis
151.
In operation, the present invention also comprises a method of setting the pitch
static attitude
145 for the slider
129 on the integrated lead suspension
127. The method comprises providing an integrated lead suspension
127
having a longitudinal axis
151, a lateral axis
153 transverse to
the longitudinal axis
151, a load beam
161, a mount plate
162,
a flexure
163 having flexure legs
165 and a tongue
169 for
providing a mechanical support structure, and outrigger leads
173 for carrying
electrical signals. The method further comprises configuring the integrated lead
suspension
127 such that each of the outrigger leads
173 is laterally
spaced apart from the longitudinal axis
151 at an outrigger distance
177
that is greater than a flexure leg distance
171 between the longitudinal
axis
151 and the flexure legs
165, thereby defining said each of
the outrigger legs
173 as being completely laterally outboard of the flexure
legs
165. Again, the individual distances
171,
177 are not
necessarily required to be identical for each flexure leg
165 and outrigger
lead
173, respectively. The method may comprise locating the outrigger leads
173 on each lateral side of the flexure
163 such that there are outrigger
leads
173 located outboard of each of the flexure legs
165.
The slider
129 is mounted to the tongue
169 of the flexure
163,
and electrical contact is established between the slider
129 and the outrigger
leads
173 through a heating process that incidentally alters the residual
stresses in the outrigger leads
173 and changes the pitch static attitude
145 of the slider
129. This method is ideally designed for integrated
lead suspensions (ILS) rather than circuit integrated suspensions (CIS), and preferably
includes solder ball bonding the slider
129 to the outrigger leads
173.
Prior art ILS joining techniques used gold ball bonding (GBB) to electrically interconnect
the leads and slider. Gold ball bonding occurs at relatively low temperatures,
such as room temperature, which do not thermally affect the residual stress level
in the leads and, thus, do not affect the pitch static attitude of the slider.
The next step of the method of the present invention includes simultaneously
plastically deforming both the flexure legs
165 and the outrigger leads
173 during the manufacturing of the integrated lead suspension to produce
a stable pitch static attitude
145 of the slider
129. As shown in
FIG. 7, the deforming step may comprise, for example, simultaneously creasing both
the flexure legs
165 and the outrigger leads
173 with a roller, or
simultaneously step-forming both the flexure legs
165 and the outrigger
leads
173. Moreover, this step may comprise simultaneously plastically deforming
all of both the flexure legs
165 and the outrigger leads
173 at approximately
the same longitudinal location
179 (FIG. 6) along the longitudinal axis
151. In addition, the method may further comprise protecting the outrigger
leads
173 from mechanical damage, such as scratching, during the plastic
deformation. The prior art cannot satisfy the present invention's step of deforming
(incidentally or otherwise) the outrigger leads
173 by relieving stress
in the outrigger leads
173 with heat from the heating process.
The present invention has several advantages and is ideally suited for providing
an improved method, system, and apparatus for controlling process parameters, such
as pitch static attitude, of sliders on integrated lead suspensions in head gimbal
assemblies for disk drives. The slider of the integrated lead suspension is electrically
interconnected with the outrigger leads on the suspension by solder ball bonding.
Solder ball bonding requires significantly high temperatures to reflow the solder
balls. When such temperatures are applied to the suspension during the manufacturing
process, the pitch static attitude of the slider can go out of control as the excess
heat from solder ball bonding flows through the conductors of outrigger leads.
Solder ball bonding thereby thermally affects the residual stress level in the
outrigger leads and, thus, affects the pitch static attitude of the slider.
This problem is overcome by simultaneously plastically deforming both the flexure
legs and the outrigger leads during the manufacturing of the integrated lead suspension.
The process eliminates any stress on the traces and produces a stable pitch static
attitude that is not affected by subsequent thermal processes. The flexure legs
and the outrigger leads are deformed at approximately the same longitudinal location.
The deforming step may comprise, for example, simultaneously creasing both the
flexure legs and the outrigger leads with a roller, or simultaneously step-forming
both the flexure legs and the outrigger leads. In addition, the method may further
comprise protecting the outrigger leads from mechanical damage, such as scratching,
during the plastic deformation.
While the invention has been shown or described in only some of its forms,
it should be apparent to those skilled in the art that it is not so limited, but
is susceptible to various changes without departing from the scope of the invention.
*
