U.S. patent application number 12/495323 was filed with the patent office on 2010-02-25 for copper residual stress relaxation reduction means for hard disk drive slider gimbals.
This patent application is currently assigned to NITTO DENKO CORPORATION. Invention is credited to Alex Enriquez CAYABAN, Jason Aquinde GOMEZ, Martin John MCCASLIN, Visit THAVEEPRUNGSRIPORN.
Application Number | 20100046351 12/495323 |
Document ID | / |
Family ID | 41696277 |
Filed Date | 2010-02-25 |
United States Patent
Application |
20100046351 |
Kind Code |
A1 |
MCCASLIN; Martin John ; et
al. |
February 25, 2010 |
COPPER RESIDUAL STRESS RELAXATION REDUCTION MEANS FOR HARD DISK
DRIVE SLIDER GIMBALS
Abstract
Disclosed are various techniques for reduction of the magnitude
of the residual stress in the HDD gimbal circuits, or more
specifically, the residual plastic strain. Various trace structures
of the gimbal circuits as well as stress suppressors are utilized
to achieve the reduction of the residual stress in the circuit.
Inventors: |
MCCASLIN; Martin John;
(Pleasanton, CA) ; THAVEEPRUNGSRIPORN; Visit;
(Bangkok, TH) ; CAYABAN; Alex Enriquez; (Fremont,
CA) ; GOMEZ; Jason Aquinde; (Santa Clara,
CA) |
Correspondence
Address: |
SUGHRUE MION, PLLC
2100 PENNSYLVANIA AVENUE, N.W., SUITE 800
WASHINGTON
DC
20037
US
|
Assignee: |
NITTO DENKO CORPORATION
Osaka
JP
|
Family ID: |
41696277 |
Appl. No.: |
12/495323 |
Filed: |
June 30, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61091323 |
Aug 22, 2008 |
|
|
|
Current U.S.
Class: |
369/247.1 ;
G9B/17 |
Current CPC
Class: |
G11B 5/4853 20130101;
G11B 5/4833 20130101; G11B 5/4826 20130101 |
Class at
Publication: |
369/247.1 ;
G9B/17 |
International
Class: |
G11B 17/00 20060101
G11B017/00 |
Claims
1. A hard drive (HDD) gimbal trace circuit characterized in reduced
magnitude of the residual stress or residual plastic strain, the
trace circuit comprising: a plurality of traces, the plurality of
traces forming a trace structure; and a strut configured to support
a transducer, wherein the trace structure has, in a proximity of a
high strain region, a characteristic shape selected from a group
consisting of an outward circle shape, a double outward circle
shape, a waving and narrowing shape, an outward jog, a partial
outward jog with a slot, a dual jog, and an inner trace
overlap.
2. The hard drive (HDD) gimbal trace circuit of claim 1, further
comprising at least one stress suppressor, the at least one stress
suppressor comprising at least one island structure disposed under
the plurality of traces in the proximity of the high strain region,
the at least one stress suppressor comprising stainless steel.
3. The hard drive (HDD) gimbal trace circuit of claim 2, wherein
the at least one stress suppressor has a circular shape.
4. The hard drive (HDD) gimbal trace circuit of claim 2, wherein
the at least one stress suppressor has a rectangular shape.
5. The hard drive (HDD) gimbal trace circuit of claim 2, wherein
the stress suppressor comprises at least two island structures.
6. The hard drive (HDD) gimbal trace circuit of claim 2, wherein
the stress suppressor comprises at least five island
structures.
7. The hard drive (HDD) gimbal trace circuit of claim 1, further
comprising a coverlayer window.
8. The hard drive (HDD) gimbal trace circuit of claim 1, further
comprising at least one stress suppressor, the at least one stress
suppressor comprising at least one protrusion of the strut disposed
under the plurality of traces in the proximity of the high strain
region.
9. A hard drive (HDD) gimbal trace circuit characterized in reduced
magnitude of the residual stress or residual plastic strain, the
trace circuit comprising: a plurality of traces, the plurality of
traces forming a trace structure; and a strut configured to support
a transducer; wherein the traces in the trace structure are either
narrowed or widened in a proximity of a high strain region.
10. The hard drive (HDD) gimbal trace circuit of claim 9, wherein
the trace structure has, in the proximity of the high strain
region, a characteristic shape selected from a group consisting of
an outward circle shape, a double outward circle shape, a waving
and narrowing shape, an outward jog, a partial outward jog with a
slot, a dual jog, and an inner trace overlap.
11. A hard drive (HDD) gimbal trace circuit characterized in
reduced magnitude of the residual stress or residual plastic
strain, the trace circuit comprising: a plurality of traces, the
plurality of traces forming a trace structure; a strut configured
to support a transducer; and at least one stress suppressor,
wherein the at least one stress suppressor is either a protrusion
of the strut or an island structure, the stress suppressor being
disposed under the plurality of traces in a proximity of a high
strain region.
12. The hard drive (HDD) gimbal trace circuit of claim 11, further
comprising a second stress suppressor, wherein the second stress
suppressor is a protrusion of the strut and wherein the second
stress suppressor being disposed under the plurality of traces.
13. The hard drive (HDD) gimbal trace circuit of claim 11, wherein
the at least one stress suppressor is the island structure having a
circular shape.
14. The hard drive (HDD) gimbal trace circuit of claim 11, wherein
the at least one stress suppressor is the island structure having a
rectangular shape.
15. The hard drive (HDD) gimbal trace circuit of claim 11, wherein
if the stress suppressor is the island structure disposed under the
plurality of traces, the stress suppressor further comprising at
least a second island structure.
16. The hard drive (HDD) gimbal trace circuit of claim 11, wherein
if the stress suppressor is an island structure disposed under the
plurality of traces, the stress suppressor further comprising at
least four additional island structures.
17. The hard drive (HDD) gimbal trace circuit of claim 11, further
comprising a coverlayer window.
18. The hard drive (HDD) gimbal trace circuit of claim 11, wherein
the trace structure in the proximity of the high strain region has
a characteristic shape selected from a group consisting of an
outward circle shape, a double outward circle shape, a waving and
narrowing shape, an outward jog, a partial outward jog with a slot,
a dual jog, and an inner trace overlap.
19. The hard drive (HDD) gimbal trace circuit of claim 11, wherein
the traces in the trace structure are either narrowed or widened in
the proximity of the high strain region.
20. The hard drive (HDD) gimbal trace circuit of claim 11, wherein
the at least one stress suppressor is the island structure
comprising stainless steel.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of priority to U.S.
Provisional Patent Application No. 61/091,323 filed on Aug. 22,
2008, which is incorporated by reference in its entirety for all
purposes as if fully set forth herein.
DESCRIPTION OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This invention generally relates to Hard Disk Drive design
engineering and process optimization and more specifically to
copper residual stress relaxation reduction for Hard Disk Drive
slider gimbals.
[0004] 2. Description of the Related Art
[0005] Hard Disk Drives (HDD) are normally utilized as data storage
units in various computer and consumer electronics applications.
Generally, HDDs operate by reading and writing digitized
information onto multiple stacked rotating magnetic disks. This
reading and writing is accomplished by a magnetic transducer "head"
embedded on a "slider", made typically of Aluminum-Titanium Carbon,
(ALTIC), which is mounted on a "suspension".
[0006] The read/write head assembly typically incorporates an
electromagnetic transducer flown by an air bearing slider. This
slider operates in a cooperative hydrodynamic relationship with a
thin layer of air dragged along by the spinning discs to fly the
head assembly in a closely spaced relationship to the disc surface.
In order to maintain the proper flying relationship between the
head assemblies and the discs, the head assemblies are attached to
and supported by head suspensions. The entire structure of the
slider and suspension is usually called the head gimbal assembly
(HGA). In a typical design, the gimbal may include stainless steel
gimbal struts with an attached flexible gimbal circuit board,
composed of a polyimide layer and a copper layer, for carrying the
electrical signals to and from the electromagnetic transducer.
[0007] In a typical HDD, the consistent fly height of the
electromagnetic transducer over the surface of the magnetic disk
drive is very important for long-term reliability of the data read
and write operations of the HDD. On the other hand, residual stress
in the copper layer of the suspension gimbal circuit board of an
HDD can lead to long term drift in the pitch static attitude of the
gimbal, adversely effecting the electromagnetic transducer fly
height over the surface of the magnetic disk. This, in turn,
adversely affects the reliability of the read/write operations
performed by the HDD.
[0008] Thus, new ways for reducing the magnitude of the residual
stress or residual plastic strain in HDD gimbal circuit boards are
needed.
SUMMARY OF THE INVENTION
[0009] The inventive concept is directed to methods and systems
that substantially obviate one or more of the above and other
problems associated with conventional technology associated with
instability in pitch attitude of the gimbal over time, temperature
and handling processes, including ultrasonic cleaning.
[0010] One or more embodiments of the invention can provide
reduction means for the magnitude of the residual stress in the HDD
gimbal circuits, or more specifically, the residual plastic
strain.
[0011] In accordance with an aspect of the inventive concept, there
is provided a hard drive (HDD) gimbal trace circuit characterized
in reduced magnitude of the residual stress or residual plastic
strain. The inventive trace circuit including a plurality of
traces, the plurality of traces forming a trace structure and a
strut configured to support a transducer. In the inventive circuit,
the trace structure has, in a proximity of a high strain region, a
characteristic shape selected from a group consisting of an outward
circle shape, a double outward circle shape, a waving and narrowing
shape, an outward jog, a partial outward jog with a slot, a dual
jog, and an inner trace overlap. In accordance with another aspect
of the inventive concept, there is provided a hard drive (HDD)
gimbal trace circuit characterized in reduced magnitude of the
residual stress or residual plastic strain. The inventive trace
circuit including a plurality of traces, the plurality of traces
forming a trace structure; and a strut configured to support a
transducer. In the inventive circuit, the traces in the trace
structure are either narrowed or widened in a proximity of a high
strain region.
[0012] In accordance with yet another aspect of the inventive
concept, there is provided a hard drive (HDD) having a gimbal trace
circuit characterized in reduced magnitude of the residual stress
or residual plastic strain. The inventive trace circuit includes a
plurality of traces, the plurality of traces forming a trace
structure; a strut configured to support a transducer; and at least
one stress suppressor. In the inventive circuit, the at least one
stress suppressor is either a protrusion of the strut or an island
structure, the stress suppressor being disposed under the plurality
of traces in a proximity of a high strain region.
[0013] Additional aspects related to the invention will be set
forth in part in the description which follows, and in part will be
obvious from the description, or may be learned by practice of the
invention. Aspects of the invention may be realized and attained by
means of the elements and combinations of various elements and
aspects particularly pointed out in the following detailed
description and the appended claims.
[0014] It is to be understood that both the foregoing and the
following descriptions are exemplary and explanatory only and are
not intended to limit the claimed invention or application thereof
in any manner whatsoever.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] The accompanying drawings, which are incorporated in and
constitute a part of this specification exemplify the embodiments
of the present invention and, together with the description, serve
to explain and illustrate principles of the inventive technique.
Specifically:
[0016] FIG. 1 illustrates exemplary components of a disk drive
suspension viewed from above of the actuator arm.
[0017] FIG. 2 illustrates the components of a disk drive suspension
viewed from the surface of the magnetic disk drive.
[0018] FIG. 3 illustrates a half symmetry model locally of the
flexure tongue, copper trace circuit and SST struts, which provide
the major portion of the gimbal stiffness.
[0019] FIG. 4 illustrates the same structure as FIG. 3, except the
protective coverlayer is hidden.
[0020] FIG. 5 illustrates the related necessary process steps for
the suspension assembly, at least one of which, can result in
copper trace plastic deformation.
[0021] FIG. 6 illustrates a typical conventional construction of
outrigger trace circuit and SST strut, an embodiment of the present
invention with traces routed to circle outwards in order to reduce
the residual plastic strain component, an embodiment with traces
narrowed in order to reduce the residual plastic strain component,
and an embodiment of this invention with a SST support member
strategically located under the traces in order to reduce the
residual plastic strain component.
[0022] FIG. 7 illustrates a typical conventional construction of
outrigger trace circuit and SST strut, an embodiment of the present
invention with traces routed to circle outwards twice, in order to
reduce the residual plastic strain component, an embodiment of the
present invention with traces narrowed and with wave shapes in
order to reduce the residual plastic strain component, and an
embodiment of this invention with two SST support members
strategically located under the traces in order to reduce the
residual plastic strain component.
[0023] FIG. 8 illustrates a typical conventional construction of
outrigger trace circuit and SST strut, and an embodiment of this
invention with five SST support members strategically located under
the traces in order to reduce the residual plastic strain
component.
[0024] FIG. 9 illustrates various outrigger trace circuits with SST
struts.
[0025] FIG. 10 illustrates various FEM results for plastic strain
versus applied SST strut forming moment.
[0026] FIG. 11 illustrates various FEM results for residual plastic
strain after forming.
[0027] FIG. 12 illustrates various embodiments of the present
invention in regard to the SST support strut member and its
location, as compared to the conventional technology.
DETAILED DESCRIPTION
[0028] In the following detailed description, reference will be
made to the accompanying drawing(s), in which identical functional
elements are designated with like names. The aforementioned
accompanying drawings show by way of illustration, and not by way
of limitation, specific embodiments and implementations consistent
with principles of the present invention. These implementations are
described in sufficient detail to enable those skilled in the art
to practice the invention and it is to be understood that other
implementations may be utilized and that structural changes and/or
substitutions of various elements may be made without departing
from the scope and spirit of present invention. The following
detailed description is, therefore, not to be construed in a
limited sense.
[0029] One of the aspects of the present invention is directed
towards overcoming instability in pitch attitude of the HDD gimbal
over time, temperature and handling. The aforesaid instability in
the pitch attitude of the HDD gimbal results in the instability of
the electromagnetic transducer fly height over the surface of the
magnetic disk and, consequently, reduced reliability of the
read/write operations performed by the HDD. Accordingly, achieving
the aforesaid stability in the gimbal pitch attitude is crucial to
improving the performance reliability of the HDD.
[0030] In accordance with an embodiment of the inventive concept, a
simulation method for stress relaxation was developed, which has
been used to uncover the specific location of the plastic strain in
the structure of the gimbal circuit board. Subsequently, several
ways were conceived to circumvent the plastic strain by design of
the geometry locally, opening the design space to include changes
in any or all the polyimide, copper and stainless steel layers
forming the gimbal. Third, the aforesaid simulation tool was
exercised to discover which gimbal design solutions are most
effective for overcoming the residual stress problem. This resulted
in the gimbal designs most effective for overcoming the residual
stress condition. The results are described below with reference to
the specific exemplary embodiments of the improved gimbal
configuration and illustrated in the accompanying drawings.
[0031] Using one or more of the aspects of the invention, the
effects of the residual stress problem can be reduced and a more
consistent and stable fly height of the slider and Read/Write
transducer can be realized. Also, because pitch static attitude of
the gimbal is a frequently measured (inspected) parameter, the
manufacturing yields of the HDDs can be improved due to the
inherent improved stability of the gimbal assembly.
[0032] FIG. 1 illustrates the exemplary components of a hard disk
drive suspension viewed from above of the actuator arm. The
transducer (not shown) is facing downward and hidden in this view.
Typical constructions of the suspension include four components:
baseplate 101, hinge 102, loadbeam 103 and trace/gimbal (or flexure
circuit) 104. Some designs involve three component constructions,
as shown, combining the hinge and loadbeam into one component. Such
constructions can also include a load beam dimple with a dome
protrusion downward 105, and a lift tab 106.
[0033] FIG. 2 illustrates the components of a hard disk drive
suspension as viewed from the surface of the magnetic disk. The
slider 201 will house the read/write transducers at the trailing
edge 202 of the Air Bearing Surface (ABS). Flexure welds 203
attached the circuit board to the loadbeam 103. The dotted line 204
and the gimbal struts 205 (preferably made of stainless steel)
signify the region of focus for the various embodiments of the
present invention.
[0034] FIG. 3 illustrates a half symmetry model locally of the
flexure tongue 301, copper trace circuit with supporting polyimide
struts 304 and SST struts 305, which provide the major contribution
to the overall stiffness of the gimbal. Exposed copper pads and
traces 303 accept solder connections to the slider/head (not
shown). A polyimide coverlayer 302 on top of the copper traces
exists for protection purposes.
[0035] FIG. 4 illustrates the same structure as FIG. 3 except the
coverlayer is hidden. Also depicted are forming jigs 401 that are
used for simulation of the mechanical adjust process and necessary
because of the finite dimple height. The gimbal flexure tongue is
spaced off the load beam, in an angular fashion, by an amount equal
to the dimple height, typically 50 to 70 microns. This defines the
natural pitch angle of the flexure tongue, to which the slider
bonds to. One of the forming jigs 401, is fixed, while the other
rotates in order to permanently bend the SST strut 305 in FIG.
3.
[0036] FIG. 5 illustrates the related necessary process steps for
the suspension assembly that result in copper trace plastic
deformation. First, a flat flexure is placed onto a load beam 501.
During this step, the flexure tongue will experience a natural
pitch angle. The flexure is then spot welded to the load beam 502.
The SST struts are then mechanically coarse-adjusted to nullify the
natural pitch angle 503, and the copper will exhibit some permanent
plastic behavior. Lasers fine-adjust the SST struts in order to set
the final, optimal pitch/roll angle 504, wherein the residual
copper stress/strain prevails. The pitch and roll static attitude
(PSA/RSA) from this step onward must be stable with regards to
handling, temperature and time. Subsequently, the flexure is
subject to ultrasonic washing 505.
[0037] Very local plastic strain behavior of the gimbal results
from the mechanical forming of the SST struts. The simulation
details for studying this behavior are beyond the scope of this
specification. The Finite Element Model (FEM) of the mechanical
gimbal forming process nullifies the natural pitch angle. The
object is to make the pitch angle relaxation less sensitive to the
geometry of the local region.
[0038] The basic idea to reduce CU contribution to PSA stability is
outlined by the process as follows. First, the location of copper
plastic deformation is learned thru simulation. The traces are then
thinned or widened locally, depending on the circumstances.
Subsequently, the traces may need alternate routing to either an
outer loop or into other shapes in order to reduce plastic behavior
in the copper.
[0039] When examined, the plastic component of the strain is
non-elastic, and results in a finite residual strain component
contributing to undesirable pitch angle relaxation versus handling,
ultrasonic cleaning, temperature and time.
[0040] FIG. 6 illustrates a typical conventional construction 601
of outrigger trace circuit and SST strut; an embodiment of the
present invention 602 with traces 605 routed to circle outwards 606
in order to reduce the copper residual plastic strain component; an
embodiment 603 with traces 605 narrowed 607 in order to reduce the
copper residual plastic strain component; and an embodiment of this
invention 604 with a SST support member strategically located under
608 the traces 605 in order to reduce the residual plastic strain
component. These constructions are shown as an example, but should
not limit the scope of materials that could be employed, or shapes
that are possible in the spirit of this invention. These
constructions may be implemented individually, or conjunction with
each other in many combinations.
[0041] FIG. 7 illustrates a typical conventional construction 701
of outrigger trace circuit and SST strut ; an embodiment of the
present invention 702 with traces routed to circle outwards twice;
in order to reduce the residual plastic strain component, an
embodiment of the present invention 703 with traces 705 narrowed
and with wave shapes 707 in order to reduce the copper residual
plastic strain component; and an embodiment of this invention 704
with two SST support members 708 strategically located under the
traces 705 in order to reduce the copper residual plastic strain
component.
[0042] FIG. 8 illustrates a typical conventional construction of
outrigger trace circuit and SST strut 800 and also illustrates an
embodiment of the present invention 801 with five SST support
members strategically located under the traces in order to reduce
the residual plastic strain component. Any number of SST islands
located under the copper high strain region, for example 4, 5, 6,
or more, would be consistent within the concepts and spirit of
various embodiments of the present invention.
[0043] FIG. 9 illustrates various outrigger trace circuit
configurations with SST struts. Configuration 901 shows a typical
conventional construction of outrigger trace circuit and SST strut.
Configuration 902 shows a typical conventional construction of
outrigger trace circuit and SST strut, but a more simplified view.
Configuration 903 illustrates an embodiment of the present
invention with a coverlayer opening window 908 in order to reduce
the residual plastic strain component. Configuration 904
illustrates an embodiment of the present invention with traces
routed in a jog outward 909 in order to reduce the copper residual
plastic strain component. Configuration 905 illustrates an
embodiment of the present invention with some traces routed in a
jog outward 910 to reduce the copper residual plastic strain
component. A polyimide layer 911 window acts to separate these
traces from the inner trace. Configuration 906 illustrates an
embodiment of the present invention with traces narrowed 912 in
order to reduce the copper residual plastic strain component. The
SST strut 913, as shown, can also be widened and tapered to a
narrower dimension. Configuration 907 illustrates an embodiment of
this invention with some traces routed in a jog outward, but
internal trace routes inward 914 onto the SST strut in order to
reduce the copper residual plastic strain component. A polyimide
layer window 915 acts to separate these traces from the inner
trace.
[0044] FIG. 10 illustrates various FEM results for plastic strain
versus applied SST strut forming moment. The right hand y-axis
depicts the magnitude of the applied moment in a 4 step time
sequence. Jigs 401 of FIG. 4 are the recipient of this moment
loading and the solid line depicted with triangles 1001 illustrates
that this moment is ramped from zero, up to a value, and back to
zero. The left hand y-axis 1002 represents the maximum plastic
component of strain in the copper traces 303 in FIG. 3, so the
figure of merit for any design will be the residual plastic strain
when the moment load is released, or brought to zero, or after load
step #4. Two examples are provided.
[0045] FIG. 11 summarizes the various FEM results for copper
residual plastic strain after forming. The y-axis 1101 is the same
as described in FIG. 10.
[0046] FIG. 12 illustrates various embodiments of the present
invention in regards to the SST support member and its location.
Configuration 1201 illustrates an embodiment of this invention with
one circular SST support member 1205 strategically located under
the traces high strain region in order to reduce the residual
plastic strain component. Configuration 1202 illustrates an
embodiment of this invention with one rectangular SST support
member 1206 strategically located under the copper traces of the
high strain region in order to reduce the residual plastic strain
component. Configuration 1203 illustrates an embodiment of this
invention with one rectangular SST support member 1207
strategically located under the traces high strain region in order
to reduce the residual plastic strain component. This rectangular
island connects to the inner SST strut rather than being an
isolated island as in 1202. Configuration 1204 illustrates an
embodiment of this invention with two rectangular SST support
members 1208 strategically located to straddle the traces high
strain region in order to reduce the residual plastic strain
component. These rectangular islands connect to the inner SST strut
rather than being isolated. An obvious variation of this
configuration is to have one island connect to strut and the other
not connect, and vice versa.
[0047] As it would be appreciated by those of skill in the art,
other implementations of the invention will be apparent from
consideration of the specification and practice of the invention
disclosed herein. Various aspects and/or components of the
described embodiments may be used singly or in any combination in
the structures for reducing residual stress in gimbal trace
circuits. It is intended that the specification and examples be
considered as exemplary only, with a true scope and spirit of the
invention being indicated by the following claims and their
equivalents.
* * * * *