COPPER RESIDUAL STRESS RELAXATION REDUCTION MEANS FOR HARD DISK DRIVE SLIDER GIMBALS
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.
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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 INVENTION1. Field of the Invention
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.
2. Description of the Related Art
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”.
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.
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.
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 INVENTIONThe 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.
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.
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.
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.
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.
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.
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:
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.
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.
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.
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.
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.
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.
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.
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.
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.
Type: Application
Filed: Jun 30, 2009
Publication Date: Feb 25, 2010
Applicant: NITTO DENKO CORPORATION (Osaka)
Inventors: Martin John MCCASLIN (Pleasanton, CA), Visit THAVEEPRUNGSRIPORN (Bangkok), Alex Enriquez CAYABAN (Fremont, CA), Jason Aquinde GOMEZ (Santa Clara, CA)
Application Number: 12/495,323
International Classification: G11B 17/00 (20060101);