WO1997031369A1

WO1997031369A1 - Method of attaching and electrically interconnecting a read/write head to a flexure

Info

Publication number: WO1997031369A1
Application number: PCT/US1997/001412
Authority: WO
Inventors: Laurence V. Turner; David R. Keller
Original assignee: Quantum Corporation
Priority date: 1996-02-26
Filing date: 1997-02-07
Publication date: 1997-08-28
Also published as: AU2249697A

Abstract

An improved method for electrically interconnecting a read/write head (36) to a flexure (14) having integral conductors (30). The flexure includes patterned electrical conductors which are exposed at an end of the flexure. A tooling fixture holds the head in alignment with a mounting region of the flexure such that a portion of each conductor extends beyond an end surface of the head. An ultrasonic probe tip (40) is used to bend each extending conductor portion and to press it into contact with a corresponding electrical bonding pad fabricated on an end surface of the head. The ultrasonic probe tip is energized to complete the electrical interconnection of each of the flexure's conductors to the read/write head.

Description

METHOD OF ATTACHING

AND ELECTRICALLY

INTERCONNECTING A READ/WRITE HEAD

TO A FLEXURE

Field ofthe Invention

This invention relates generally to a head and flexure assembly for supporting the head adjacent to a relatively moving recording medium in a disk drive. More particularly, it relates to a method of assembling a read/write head to a flexure having integral conductors for use in supporting a high performance, low-mass head at the end of a load beam in the disk drive.

Background

Contemporary disk drives typically include a rotating rigid storage disk and a head positioner for positioning a data transducer at different radial locations relative to the axis of rotation ofthe disk, thereby defining numerous concentric data storage tracks on each recording surface ofthe disk. The head positioner is typically referred to as an actuator. Although numerous actuator structures are known in the art, in-line rotary voice coil actuators are now most frequently employed due to their simplicity, high performance, and their ability to be mass balanced about their axis of rotation, the latter being important for making the actuator less sensitive to perturbations. A closed-loop servo system is employed to operate the actuator and thereby position the heads with respect to the disk surface. The read/write transducer, which may be of a single or dual element design, is typically deposited upon a ceramic slider structure having an air bearing surface for supporting the transducer at a small distance away from the surface ofthe moving medium. Single element designs typically require two wire connections while dual element designs require four.

Magnetoresistive (MR) heads, in particular, generally require four wires. The combination of an air bearing slider and a read/write transducer is also known as a read/write head or a recording head.

Sliders are generally mounted to a gimbaled flexure structure attached to the distal end of a suspension's load beam structure. A spring biases the load beam, and therethrough the head, towards the disk, while the air pressure beneath the head pushes the head away from the disk. The equilibrium distance then determines the "flying height" ofthe head. By utilizing such an "air bearing" to support the head away from the disk surface, the head operates in a hydrodynamically lubricated regime at the head/disk interface rather than in a boundary lubricated regime. The air bearing maintains spacing between the transducer and the medium which reduces transducer efficiency, however, the avoidance of direct contact vastly improves the reliability and useful life ofthe head and disk components. Demand for increased areal densities may nonetheless require that heads be operated in pseudo contact or even boundary lubricated contact regimes, however.

The disk drive industry has been progressively decreasing the size and mass of the slider structures in order to reduce the moving mass ofthe actuator assembly and to permit closer operation ofthe transducer to the disk surface, the former giving rise to improved seek performance and the latter giving rise to improved transducer efficiency that can then be traded for higher areal density. The size (and therefore mass) of a slider is usually characterized with reference to a so-called standard 100% slider (minislider). The terms 70%, 50%, and 30% slider (microslider, nanoslider, and picoslider, respectively) therefore refer to more recent low mass sliders that have linear dimensions that are scaled by the applicable percentage relative to the linear dimensions of a standard minislider.

Although smaller, low mass heads can provide both performance and economic advantages, the reductions in physical slider dimensions give rise to numerous problems that do not necessarily scale linearly with the dimensional changes. If, for example, the size and load force on the slider are simply halved, the air bearing stiffness in the pitch direction will be reduced on the order of 1/8. A flexure must have sufficient compliance to allow the slider adequate freedom to pitch and roll in order to maintain the trailing edge ofthe slider at the desired distance from the moving media surface because the failure to maintain adequate spacing can lead to signal modulation, data loss, or even catastrophic failure ofthe head or disk components. Accordingly, flexures designed for use with picosliders must have highly compliant gimbals, which are typically implemented by the flexure structure. Even assuming a highly compliant gimbal structure, however, a significant additional problem arises in that the wiring that interconnects the disk drive electronics to the transducers) on the slider contributes a nontrivial degree of bias to the gimbal structure, particularly when using dual element heads, which generally require 4 discrete wires.

To reduce the effects ofthe intrinsic wire stiffness or bias, integrated flexure/conductor structures have been proposed which effectively integrate the wires with the flexure such that the conductors are exposed at bonding pads positioned at the distal end ofthe flexure in the proximity ofthe head. U.S. Patent No. 5,006,946 to Matsuaki discloses an example of such a configuration. Due to the relatively lengthy run of exposed wire extending from the bonding pad to the head and the relatively circuitous routing ofthe wire, the disclosed flexure appears to present difficult manufacturing, handling, and assembly problems, especially in view ofthe extremely fragile nature ofthe fine gauge wire that must be employed to prevent undue increases in gimbal stiffness arising from the wire itself.

An alternative head-to-flexure interconnection scheme is disclosed in U.S. Patent No. 4,789,914 to Ainslie et al. which also provides bonding pads that are exposed at the head mounting region ofthe flexure. Since the bonding pads are positioned on the gimbaled portion ofthe flexure and are effectively fixed with respect to the head, the resultant electrical interconnection between the head and the bonding pad does not tend to separately contribute to the stiffness ofthe gimbal. Moreover, the disclosed interconnection scheme provides both electrical interconnection and mechanical support in a single operation. Although it may be desireable to mechanically and electrically interconnect the slider in a single step, such methods typically require that the slider be fabricated with electrical bonding pads on the top surface. Since the transducer(s) on the slider are conventionally fabricated at an end surface ofthe slider, such a bonding scheme unnecessarily complicates the slider fabrication process due to the additional steps that would be required to fabricate bonding pads on the top surface of a slider, which may not result in a net cost or yield improvement. Thus a need arises for a reliable and economical method of electrically interconnecting an electrical lead from the flexure/conductor structure to a conventionally configured bonding pad lying in a plane generally perpendicular to the nominal plane ofthe flexure/conductor structure.

The invention to be described provides a method for assembling a read/write head (i.e., slider) to a flexure with integral conductor structure to achieve an improved head/flexure assembly for attaching to a load beam in an actuator structure for use in a high performance rigid disk drive.

Summary ofthe Invention

A head/flexure assembly fabricated in accordance with the invention includes a flexure having integral conductive wiring and exposed conductor leads. The conductor leads ofthe flexure replace discrete prior art insulated conductor wires that would normally be bonded directly to the slider bonding pads. Exposed conductor leads are ultrasonically bonded to bonding pads on an end surface of a read/write head structure. The invention shows substantial performance, reliability, and manufacturing advantages relative to prior art HGA configurations.

A general object of the present invention is to provide a low-profile, robust, reliable, highly compliant head and flexure/conductor assembly and method for mechanically attaching a low mass read/write head to a load beam mounted to an actuator assembly in a disk drive and to provide a method of electrically interconnecting the read/write head to the flexure/conductor structure which overcomes limitations and drawbacks of the prior art. A more specific object of the present invention is to reduce the manufacturing time and complexity of connecting conductor leads to their respective bonding pads on sliders.

Yet another object of the present invention is to provide an improved method for manufacturing and assembling low mass head/gimbal assemblies (HGA's) which results in improved HGA yields.

The invention provides an economical and reliable method for electrically interconnecting a transducer mounted on a slider to an integrated flexure/conductor structure which implements a gimbal and includes exposed conductor leads positioned near the slider mounting region at the distal end of the flexure. The exposed conductors generally lie in the plane of the overall flexure conductor structure and extend beyond an edge of the slider mounting portion of the flexure/conductor structure. The flexure is positioned in alignment with and in contact with the slider whereupon an ultrasonic probe tip is used to bend the extending conductors out-of-plane and in contact with the respective slider bonding pad at the end surface of the slider. The aforesaid probe tip is then energized to ultrasonically bond the conductor to the slider bonding pad, resulting in a reliable and robust electrical interconnection. After the heads are connected to the flexures, electrical testing of the head/flexure assemblies is facilitated prior to loadbeam attachment, which makes it possible to avoid assembling defective head/flexure assemblies with loadbeams. This results in cost savings via cost avoidance, because the assembly and material costs associated with the assembly of defective head/flexure assemblies to loadbeams is substantially eliminated. Accordingly, HGA assembly yields are significantly improved while the net manufacturing costs of the final, yielded HGA assemblies is substantially reduced.

These and other objects, advantages, aspects, and features of the present invention will be more fully appreciated and understood upon consideration of the following detailed descriptions of a preferred embodiment presented in conjunction with the accompanying drawings.

Brief Description ofthe Drawings

In the Drawings:

Fig. 1 is a plan view of a fully assembled head-gimbal-assembly (HGA) in accordance with the present invention.

Fig. 2 is a plan view of an integrated flexure/conductor structure prior to assembly with a recording head.

Fig. 3 A is a diagrammatic, not-to-scale side elevation of a flexure/conductor structure bonded to a recording head prior to electrical interconnect by an ultrasonic probe tip.

Fig. 3B is a diagrammatic, not-to-scale side elevation of the flexure/conductor structure and recording head combination of Fig. 3A showing the position of the ultrasonic probe tip during an ultrasonic bonding operation. Fig. 4 is an enlarged dimetric view of the distal end of the flexure/conductor structure and recording head of Fig. 3B showing a completed electrical interconnection.

Fig. 5 is an oblique view of a slider having eight bonding pads for electrical interconnection to a pair of dual element transducers.

Detailed Description of a Preferred Embodiment

Referring to the drawings, where like characters designate like or corresponding parts throughout the views, Fig. 1 shows a plan view of a fully assembled head-gimbal-assembly (HGA) 10 in accordance with a preferred embodiment of the present invention. HGA 10 includes a slider 12 mounted to a flexure 14 which is in turn mounted to a suspension 16. Suspension 16 typically includes a rigid baseplate 20 for mounting HGA 10 to an actuator arm or E-block (not shown) in a disk drive, a spring section 22 extending from the baseplate region, and a generally rigid, cantilevered loadbeam 24 extending from the spring section for both supporting and preloading slider 12. Loadbeam 24 includes a load protuberance 25 (or pivot) positioned in contact with slider 12 through which the preload force from spring section 22 is applied to head 12. Loadbeam 24 further includes one or more stiffening flanges or rails 26 for improved mechanical performance.

In the preferred embodiment illustrated in Fig. 1, flexure 14 is a generally planar polyamide or Kapton flex-circuit type structure having integrated, but electrically isolated copper conductors 28. Bond line 29 is a boundary demarcating the proximal region of flexure 14, which is bonded to loadbeam 24, from the distal region of flexure 14, which is not bonded to loadbeam 24 and which is therefore capable of limited relative movement, hence slider 12, which is attached to flexure 14, is effectively gimbaled about the protuberance 25. Turning now to Fig. 2, at the distal end of the flexure 14, conductors 28 extend from the main body to form exposed conductor leads 30 (see Fig. 2) that are ultimately bent at an approximately 90-degree angle to mate with corresponding electrical bonding pads fabricated at an end surface of slider 12. Flexure 14 has one or more tooling holes, such as tooling holes 32 and 34, respectively, to ensure that the components of HGA 10 are properly aligned during assembly. An ultrasonic bonder is used to mechanically and electrically bond conductor leads 30 to their respective bonding pads on slider 12. Conductor leads 30 are gold plated, as are the corresponding bonding pads.

Fabrication of the HGA proceeds as illustrated in Fig. 3 A, with slider

12 being placed in a rigid tooling fixture (omitted for clarity of illustration). An adhesive is applied to the surface of slider 12 opposite air bearing rail 36 and then flexure 14 is placed in position adjacent to the slider. Tooling holes 32 and 34 (see Fig. 2) are used to ensure accurate alignment of flexure 14 within the tooling fixture which ensures accurate alignment with slider

12. Heat and pressure are applied to the flexure/slider combination to mechanically bond flexure 14 to slider 12. The exposed, gold-plated conductor leads 30 of flexure 14 extend slightly beyond the transducer bearing end surface of slider 12. Ultrasonic probe tip 40 is brought into position adjacent one of the exposed conductor leads 30. The probe tip is translated laterally in the direction indicated by arrow 42 which deforms the exposed conductor lead 30. As shown in Fig. 3B, probe tip 40 is subsequently pressed downward in the direction indicated by arrow 44 of Fig. 3B to force the exposed conductor lead 30 into conductive contact with a corresponding gold bonding pad (illustrated in Fig. 4) fabricated at the end of slider 14 and then probe tip 40 is energized to ultrasonically bond the conductor lead 30 with the corresponding bonding pad of slider 12. The process is repeated for each of the remaining conductor leads to complete the electrical interconnection.

The described interconnection method results in a durable, conductive gold-to-gold interface which is relatively impervious to corrosion and the like, which avoids problems inherent with conductive interfaces consisting of different metals, such as would be the case with a solder reflow type connection, for example. Moreover, the aforesaid method requires only a single electrical termination interface at the distal end of the resultant HGA (for each conductor) which enhances reliability and results in a low resistance interconnection. Excessive resistance can adversely affect head and performance. Finally, the disclosed method is tolerant of minor offset and registrational errors of the bonding pads and the conductor leads which tends to improve assembly yields.

In an alternative preferred embodiment of the invention (also with reference to Figs. 3 A and 3B), flexure 14 may be loaded onto a tooling substrate (not shown) with exposed conductor leads extending beyond the edge ofthe substrate. An adhesive is applied to to slider 12 (or alternatively to flexure 14) and then slider 12 is positioned in contact with flexure 14 such that the transducer bearing end surface of slider 12 is aligned with the edge of the tooling substrate. The slider is clamped into position and pressure and heat are applied to the slider/flexure assembly to complete the mechanical bonding of slider 12 to flexure 14. Other mechanical bonding techniques may be employed in the alternative. Although performing the mechanical bonding at this stage is convenient, it is not essential.

The subsequent steps proceed in essentially the same manner as previously described. Ultrasonic probe tip 40 is positioned adjacent to exposed conductor lead 30, with tip 40 approaching but not contacting the end surface of the tooling substrate. Ultrasonic probe tip 40 is moved laterally in the direction indicated by arrow 42 to bend the conductor lead 30 approximately 90 degrees such that the conductor lead is registered with its associated bonding pad on the end surface ofthe slider. Probe tip 40 is then translated vertically to force conductor lead 30 into conductive contact with the bonding pad of slider 12. Probe tip 40 is energized to complete the bond and then the probe tip is retracted. This procedure is repeated until all ofthe bonds are completed. Alternatively, a ganged array of probe tips may be utilized in parallel to concurrently bend and bond each of the conductor leads 30 in a single operation. Either method may be performed with automated or robotic manufacturing techniques.

Fig. 4 shows a completed bond along an end surface of the flexure/slider assembly with one of the conductor leads 30 being bent and bonded to the corresponding electrical bonding pad 50. The bonding pads 50 are typically formed via thin-film deposition and patterning techniques in conjunction with thin-film transducers 52. Conventional deposited conductors (not shown) electrically interconnect transducers 52 to the bonding pads 50. Thus it is seen that the present method obviates the need to perform additional, relatively expensive thin-film deposition on the top surface of the slider during slider fabrication, and unlike conventional wire stitch or solder (or conductive epoxy) fillet type interconnection methods, there is only one electrical bond interface between the conductor structures 28 of flexure 14 and the transducers 52. Because the conductor leads 30 are initially coplanar with the flexure body, flexure handling is facilated and damage to the leads is less likely and less problematic. After the remaining bonds are completed, the flexure/slider assembly may be electrically tested for opens and shorts and to confirm that at least one of the transducers operates within acceptable parameters. Additionally, because the gimbal structure is substantially complete, it is possible to dynamically test each flexure/slider assembly by, e.g., employing a vacuum chuck to hold the flexure/slider assembly and to position it in an X-Y stage. Automated optical alignment methods may then be employed to accurately determine the pivot point location so that a force may be applied at the determined pivot location to preload the slider in the direction of a moving test disk, thereby facilitating the automated dynamic testing of the slider prior to final HGA assembly.

This provides a significant improvement over the prior art assembly and test methods, because in accordance with the prior art, the wire bonding operation is normally performed near the completion of an HGA assembly and therefore testing is only possible thereafter. In accordance with the present method, the transducers and the electrical bonds may be tested both statically and dynamically prior to assembly ofthe flexure/slider units to the suspensions, which signficantly improves the resultant HGA yield and can result in a significantly lower yielded HGA cost, relative to the prior art.

Turning now to Fig. 5, it can be seen that the instant bonding method is readily extensible to newer sliders having advanced dual-element transducers. Typically, the tranducers 52 are fabricated redundantly at the end of each slider rail 36 so that a working slider can be obtained even if one of the transducers is not functional. In a dual-element, four-wire transducer design, such as that now in use with magnetoresistive technology, the potential for yield losses due to poor bonding, wire misregistration, or wafer-level processing are significant. The present invention therefore provides a more robust interconnection and interconnection scheme which facilitates earlier electrical testing of the slider/flexure combination and which is tolerant of misregistration between the conductor leads and the bonding pads.

In summary, the instant invention discloses a flexure-to-head assembly method that reduces the overall cost of yielded HGA's while improving the robustness and reliability of the electrical interconnection, particular when used in advanced applications employing ultra low mass sliders with advance dual element heads which require numerous electrical interconnections. Thus the present invention facilitates the design and fabrication of more reliable and higher performance disk drives.

Although the present invention has been described in terms of the presently preferred embodiment, i.e., a flex circuit type flexure which implements a gimbal, it should be clear to those skilled in the art that the present invention may also be utilized in conjunction with other flexures having integral deposited or embedded conductors, e.g., stainless steel flexures with patterned conductors isolated by an insulating layer. Thus, it should be understood that the instant disclosure is not to be interpreted as limiting. Various alterations and modifications will no doubt become apparent to those skilled in the art after having read the above disclosure. Accordingly, it is intended that the appended claims be interpreted as covering all alterations and modifications as fall within the true spirit and scope ofthe invention.

Claims

In Re the ClaimsWhat is claimed is:

1. A method of electrically interconnecting a read write head having a bonding pad on an end surface to a generally planar integrated flexure/conductor structure for pivotably supporting the read/write head at a distal end of an actuator assembly in a disk drive, the flexure/conductor structure having an exposed conductive lead at an end thereof, the method comprising the steps of: holding the read/write head adjacent to the flexure/conductor structure in a tooling fixture, the exposed conductive lead extending beyond the end surface in a direction generally orthogonal to the end surface; positioning an ultrasonic bonder tip adjacent to the exposed conductive lead; translating the ultrasonic bonder tip in a direction generally parallel to the end surface to bend the exposed conductive lead out-of-plane with respect to the generally planar flexure/conductor structure and in registration with the bonding pad; pressing the ultrasonic bonder tip toward the end surface to force the exposed conductive lead into contact with the bonding pad; and energizing the ultrasonic bonder tip to bond the exposed conductive lead into conductive contact with the bonding pad.

2. The method of Claim 1, wherein the bonding pad and the conductive lead are gold plated.

3. A method of electrically interconnecting a read/write head having a plurality of bonding pads on an end surface to a generally planar integrated flexure/conductor structure for pivotably supporting the read/write head at a distal end of an actuator assembly in a disk drive, the flexure/conductor structure having a plurality of exposed conductive lead at an end thereof, the method comprising the steps of: holding the read/write head adjacent to the flexure/conductor structure in a tooling fixture, the exposed conductive leads extending beyond the end surface in a direction generally orthogonal to the end surface; positioning a plurality of ultrasonic bonder tips adjacent to the exposed conductive leads; translating the ultrasonic bonder tips in a direction generally parallel to the end surface to bend the exposed conductive leads out-of-plane with respect to the generally planar flexure/conductor structure and in registration with the bonding pads; pressing the ultrasonic bonder tips toward the end surface to force the exposed conductive leads into contact with the bonding pads; and energizing the ultrasonic bonder tips to bond the exposed conductive leads into conductive contact with the bonding pads.

4. The method of Claim 3, wherein the bonding pads and the conductive leads are gold plated.

5. The method of Claim 3, wherein the ultrasonic bonder tips are arranged in a ganged array.

6. A method of assembling a head/gimbal assembly including a read/write head having a bonding pad on an end surface and a generally planar integrated flexure/conductor structure attached to a load beam for pivotably supporting the read/write head at a distal end of an actuator assembly in a disk drive, the flexure/conductor structure having first and second ends including an exposed conductive lead at the first end electrically connected to a test pad at the second end, the method comprising the steps of: holding the read/write head adjacent to the flexure/conductor structure in a tooling fixture, the exposed conductive lead extending beyond the end surface in a direction generally orthogonal to the end surface; bonding the head to the flexure/conductor structure; positioning an ultrasonic bonder tip adjacent to the exposed conductive lead; translating the ultrasonic bonder tip in a direction generally parallel to the end surface to bend the exposed conductive lead out-of-plane with respect to the generally planar flexure/conductor structure and in registration with the bonding pad; pressing the ultrasonic bonder tip toward the end surface to force the exposed conductive lead into contact with the bonding pad; energizing the ultrasonic bonder tip to bond the exposed conductive lead into conductive contact with the bonding pad; and mounting the flexure/conductor structure to the load beam.

7. The method of Claim 6, comprising the further step of verifying head functionality by connecting a tester to the test pad after the energizing step.

8. An HGA for use in a disk drive, the HGA including a read write head having a bonding pad on an end surface and a generally planar integrated flexure/conductor structure attached to a load beam for pivotably supporting the read/write head at a distal end of an actuator assembly in the disk drive, the flexure/conductor structure having first and second ends including an exposed conductive lead at the first end electrically connected to a test pad at the second end, the HGA being assembled by a method comprising the steps of: holding the read/write head adjacent to the flexure/conductor structure in a tooling fixture, the exposed conductive lead extending beyond the end surface in a direction generally orthogonal to the end surface; bonding the head to the flexure/conductor structure; positioning an ultrasonic bonder tip adjacent to the exposed conductive lead; translating the ultrasonic bonder tip in a direction generally parallel to the end surface to bend the exposed conductive lead out-of-plane with respect to the generally planar flexure/conductor structure and in registration with the bonding pad; pressing the ultrasonic bonder tip toward the end surface to force the exposed conductive lead into contact with the bonding pad; energizing the ultrasonic bonder tip to bond the exposed conductive lead into conductive contact with the bonding pad; verifying head functionality by connecting a tester to the test pad; and mounting the flexure/conductor structure to the load beam.

9. The HGA of claim 8, wherein the exposed conductive lead and the bonding pad are gold plated.