Abstract:
A magnetic head suspension assembly includes a load beam, a flexible member or flexure, and an air bearing slider. Disposed on the flexible member is a plurality of bonding pads. Bonding pads are also formed on the edge surfaces of the slider. The bonding pads of the slider and the corresponding bonding pads on the flexible member are attached to each other via bonding joints. One of the bonding pads is electrically linked to an electrostatic discharge (ESD) path and the other bonding pads are connected to electrical signal traces which convey electrical signals to and from magnetic transducers. The undesirable steps of epoxy application for adhering a slider to a flexure can be eliminated, thus resulting in a more reliable and accurately oriented slider in a magnetic head suspension assembly.

Description:
FIELD OF THE INVENTION 
     This invention relates to magnetic head suspensions and in particular to the attachment of an air bearing slider to a magnetic head suspension. 
     BACKGROUND OF THE INVENTION 
     Typically, a disk drive contains a number of magnetic disks attached to a common spindle for rotation. The surfaces of the magnetic disks have an associated head arm assembly which includes a head gimbal assembly (HGA). The head arm assemblies are generally attached to an actuator for positioning magnetic transducers formed with the HGAs with reference to data tracks on the magnetic disks. An HGA typically comprises a load beam, a flexible element or a flexure, and a slider. The flexure has one end attached to the load beam while the slider is joined to the other end of the flexure. The slider carries one or more transducers at it trailing edge, as is well known in the art. Transducer wires are connected to the transducers to conduct signals between the transducers and head circuitry. 
     To achieve shorter data seeking time, disk drives are designed not only with fast spinning disks, but also with rapidly moving head suspensions for accessing the data tracks registered on the storage disks. For these reasons, the slider must be securely attached to the flexure. Moreover, the constant motion of the slider and the frictional action of the slider results in an accumulation of electrostatic charge of sufficient magnitude which can be detrimental to the magnetic head. Accordingly, a well designed magnetic head suspension should incorporate an efficient electrostatic discharge (ESD) path for the slider in the gimbal assembly. 
     The HGA serves to dynamically adjust the orientation of the slider to conform to the disk surface while the disk is spinning. The topology of the disk surface, though highly polished, is not uniform if viewed at a microscopic scale. Moreover, the disk surfaces are not rotating about the common shaft at a perfectly perpendicular angle. A minute angular deviation would translate into varying disk-to-slider distances while the disk is spinning. For reliable data writing and reading, the slider thus has to faithfully follow the topology of the spinning disk. 
     Sliders are commonly attached to the flexure with adhesives that are resilient and are capable of buffering the thermal mismatches between the slider and the flexure. However, the use of adhesive to secure the slider to the flexure is undesirable because the manufacturing process is time-consuming and tedious. Applying an adhesive involves dispensing more than one adhesive component, for example, the epoxy base and the hardening agent. During production, the adhesive components are thoroughly mixed prior to application. After the adhesive is dispensed in a predetermined pattern on either the slider or the flexure, the slider is carefully aligned with the flexure for attachment. The amount of adhesive and the pattern need to be carefully controlled. Excessive adhesive may result in spillover causing undesirable problems. Deficiency in adhesive may compromise the overall adhesive effect. The adhesive is thereafter cured by exposing the epoxy pattern to ultraviolet (UV) light. As a further safeguard, the attached slider normally undergoes another elevated temperature curing process within the temperature range of between 100° C.-200° C. 
     The selected pattern on the flexure for UV light exposure has to be carefully designed. Normally, several openings are formed on the flexure as shown in FIG.  9 . UV light is illuminated from the back side of the flexure through the openings. The gap between the slider and the flexure allows the UV light to disperse and permeate the adhesive. If the openings are too large, the adhesive force per areal unit is reduced. On the other hand, if the openings are too small, there may be insufficient UV light to pass through which may result in spotty areas of uncured adhesives. Thus, the slider may separate from the flexure during operation of the disk drive. Furthermore, outgassing from uncured adhesives are sources of contamination in the disk drive. 
     The number of manufacturing steps can be reduced with the use of single-component adhesives. In such cases, the processes of premixing the constituent components are avoided. However, the subsequent steps of UV curing light and high-heat annealing are still required. The elevated temperatures in the curing and annealing processes may be damaging to the read/write transducers disposed on the air bearing slider. Consequently, production yield may be undesirably reduced. 
     Even with the advent of automatic manufacturing processes in magnetic head suspension fabrication, the adhesives are still commonly dispensed manually with potential contamination. The harmful effect of constant UV light exposure to the operator is also of concern. 
     In addition to the tedious processes mentioned above, the use of adhesives is not very effective in regard to ESD dissipation. As mentioned before, electrostatic charge built up in the slider during constant movements needs to be effectively discharged. If the assembly is electrically isolated, the built-up electrostatic charge can affect data integrity and can even damage the magnetic head. With the conventional method, the discharge is realized via conducting charge through the adhesive with metallic particles. The high resistance value substantially impedes any efficient flow of electrostatic discharge. Therefore relying on the cured adhesives for ESD protection does not appear to be a viable solution. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide a magnetic head suspension assembly with a slider reliably and economically attached to the assembly. 
     It is another object of the invention to provide a magnetic head suspension assembly having an effective ESD path. 
     It is a further object of the invention to provide a magnetic head suspension having an air bearing slider attached to the suspension without annealing and curing processes, thereby realizing an improved production yield. 
     In accordance with this invention, a magnetic head suspension includes a load beam, a flexible member or flexure, and a slider, wherein a plurality of bonding pads are disposed on the flexure. Formed on the edge surfaces of the slider is another plurality of bonding pads. The bonding pads of the slider and the corresponding bonding pads on the flexure are attached to each other via bonding joints. In the preferred embodiment, the bonding joints are attached to the bonding pads through ultrasonic means. In the final head assembly, one of the bonding pads is electrically tied to the electrostatic discharge (ESD) path, and the other bonding pads are connected to electrical signal traces which are linked to the read and write transducers. Thus, the time-consuming steps of epoxy application can be avoided resulting in a more reliable and accurately oriented slider in the final magnetic head suspension assembly. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be described in greater detail with reference to the drawings in which: 
     FIG. 1 is a fragmentary view of an exemplary use of the magnetic head suspension of the invention; 
     FIG. 2 is an exploded view, partly broken away, of the gimbal assembly of the magnetic head suspension as shown in FIG. 1; 
     FIG. 3 is a cross-sectional side view taken along the line  3 — 3  of FIG. 1; 
     FIG. 4 is a cross-sectional side view of FIG. 3 with the slider displaced from the load beam illustrating the attachment relationship of the various components of the gimbal assembly; 
     FIG. 5 is an isometric view of an assembled gimbal assembly in accordance with the invention showing the slider&#39;s air bearing surface and trailing edge; 
     FIG. 6 is an isometric view of an assembled gimbal assembly in accordance with the invention showing the slider&#39;s air bearing surface and leading edge; 
     FIGS. 7A-7D are sequential views illustrating the ultrasonic bonding process in accordance with the invention; 
     FIG. 8 is a cross-sectional side view showing the effect on the slider&#39;s air bearing surface curvature by the attachment process of the invention; and 
     FIG. 9 is a cross-sectional side view showing the effect on the slider&#39;s air bearing surface curvature when using the prior art attachment process. 
    
    
     Like reference numerals refer to like parts. 
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 illustrates an actuator arm assembly  2  and a stack of spaced apart disks  4  rotatable about a common spindle  5 . The actuator arm assembly  2  is also rotatable about an actuator arm axis  6 . The arm assembly  2  includes actuator arms  8 A- 8 C which extend into the spacings between the disks  4 A and  4 B. Attached to each of the actuator arms  8 A- 8 C is a magnetic head suspension  10 , which comprises a resilient load beam  12 , a flexible member or flexure  14  and an air bearing slider  16 . 
     FIG. 2 illustrates the magnetic head suspension  10  in further detail. In FIG. 2, the air bearing surface (ABS)  18  of the slider  16  is exposed. As shown, the flexure  14  is disposed between the load beam  12  and the slider  16 . The slider  16  is fixedly attached to the tongue portion  20  of the flexure  14  via the bonding joints  22 . Disposed on the flexure  14  are electrical signal traces  34 A- 34 D which are dielectrically separated from the flexure  14  by a thin layer of insulating material  36 . In the preferred embodiment, the insulating material  36  is made of polyimide. Atop the insulating material  36  is also a plurality of signal bonding pads  42 A- 42 D connected to the respective electrical signal traces  34 A- 34 D. In this embodiment, after the slider  16  is attached to the flexure  14  (shown in FIGS.  5  and  6 ), signal traces  34 A and  34 B are electrically connected to a magnetic transducer  38  disposed on the slider  16 . 
     In addition to the signal pads  42 A- 42 D and the signal traces  34 A- 34 D, ESD bonding pads  44 A and  44 B are disposed on the tongue portion  20 . The ESD pads  44 A and  44 B are directly disposed on the flexure  14  without any insulating layer interposed therebetween. Formed on the tongue portion  20  are several ridges  46 A- 46 C which perform the duty of supporting the slider  18  after attachment. 
     Stamped on the tongue portion  20  is a dimple  24  which is convex in shape directed toward the load beam  12 . The slider  16  and the flexure  14  with the dimple constitute the head gimbal assembly of the magnetic head suspension  10 , as shown in FIGS. 3 and 4. It should be noted that, as an alternative, the dimple  24  can be stamped on the load beam  12  so that the dimple  24  on the load beam  12  would be urged against the tongue portion  20  of the flexure  14 . 
     With reference to FIG. 3, the flexure  14  has a proximal end  14 A which is affixed to the load beam  12 , and a distal end  14 B which is attached to the slider  16  via the tongue portion  20 . FIG. 4 shows the physical relationship of the load beam  12 , the flexure  14 , and the slider  16  in further detail. When the slider  16  is pulled in the direction of ther arrow  28 , one fixed area of attachment is between the proximal end  14 A of the flexure  14  and the load beam  12 , and the other area of attachment is between the slider  16  and the tongue portion  20  of the flexure  14 . The dimple  24  which is against the load beam  12  provides gimbaling action of the suspension assembly  10 . 
     With reference to FIG. 1, during disk drive operation, the disks  4  spin at high angular speed in the direction of the arrow  30  about the spindle  5 . The aerodynamics of the moving air between the slider  16  and the disk surface  28  provides sufficient air cushioning to float the slider  16  above the disk surface  32 . At the same time, the spring force of the resilient load beam  12  pushes the slider toward the disk surface  28 . An equilibrium point is reached at which the slider  16  flies over the disk surface  28  at a substantially constant spacing. 
     During data seeking, the actuator arm  8 A moves the slider across the disk surface  32  in directions  48  at a rapid rate. The large force associated with the swift acceleration and deceleration is exerted on the slider  16 . As a result, the slider  16  has to be firmly attached to the flexure  14 . In prior art devices, sliders are glued onto the flexures with epoxy. As mentioned before, the use of epoxy has disadvantages. In the magnetic head suspension of the invention, the slider  16  is attached to the flexure  14  through metallic joints. 
     FIG. 2 shows the metallic joints  22 . The slider  16  has an air bearing surface (ABS) 18  and an opposing surface  50 . The slider is formed with edge surfaces  52 A- 52 D. As shown in FIG. 2, the leading and trailing edge surfaces are labeled  52 A and  52 B, respectively and the side edge surfaces are designated by the reference numerals  52 C and  52 D. Disposed on the trailing edge surface  52 B are bonding pads  54 A- 54 D. Signal pads  54 A- 54 D are electrically connected to the read/write transducer  38  disposed on the slider  16 . A pair of bonding pads  56 A and  56 B are positioned on the leading edge surface  52 A in a similar fashion. 
     The bonding pads  54 A- 54 D,  56 A and  56 B on the slider  16  are attached to corresponding signal pads  42 A- 42 D and ESD pads  44 A and  44 B, respectively, through the bonding joints  22 , preferably made of gold or silver. 
     FIGS. 5 and 6 are isometric views partially illustrating a fully assembled magnetic head suspension  10 . FIG. 5 shows the rear attachment of the bonding pads  54 A- 54 D on the trailing edge surface  52 B of the slider  16  onto the corresponding bonding pads  42 A- 42 D on the flexure  14  via a plurality of bonding joints  22 . In like manner, FIG. 6 shows the front attachment of the bonding pads  56 A and  56 B on the leading edge surface  52 A of the slider  16  onto the corresponding bonding pads  44 A and  44 B on the flexure  14  via a plurality of other bonding joints  22 . 
     The bonding joints  22  can be affixed to the bonding pads by different methods of bonding, such as thermocompression or ultrasonic. In the preferred embodiment, the ultrasonic method is used. FIGS. 7A-7D are sequential drawings schematically illustrating an attachment of a bonding joint  22  onto the two bonding pads  56 B and  44 B. First, after proper alignment of the slider  16  onto the tongue portion  20  of the flexure  14 , a compression force in the direction of arrow  58  is mildly but snugly applied onto the ABS  18  of the slider  16  as shown in FIG. 7A. A stylus  60  carrying a wire  62  made of the same material as the bonding joints  22  is positioned as shown in FIG.  7 B. After the stylus  60  is correctly positioned, a burst of ultrasonic vibrations  64  (represented by the bidirectional arrow) is applied to the stylus  60  as shown in FIG.  7 C. Thereafter, the wire  62  is severed through an internal cutter (not shown) inside the stylus  60 . The combination of pressure and vibration accomplishes the joining of the bonds  22  onto the pads  56 B and  56 D as shown in FIG.  7 D. 
     In the preferred embodiment, the material for the pads  54 A- 54 D,  42 A- 42 D,  56 A,  56 B,  44 A,  44 B and the bonding joints  22  can be of any of the inert metals such as gold (Au) or silver (Ag). As an alternative, other metals such as copper (Cu), aluminum (Al), or tin/lead (Sn/Pb) alloy can also be used. With metal as a conductor, instead of metal-doped adhesives, the resistance of the ESD path as realized by the bonding on the leading edge surface  52 A, as shown in FIG. 6, can be within the milli-ohm range. 
     By virtue of this invention, a reduction in manufacturing steps is realized and the slider  16  is also more precisely bonded onto the flexure  14 . FIG. 8 is an enlarged cross-sectional view of the slider  16  of the invention which includes a slightly curved ABS  18  characterized by a convex height h with reference to an otherwise planar surface. The curved ABS of the slider  16  is physically ground to facilitate the slider&#39;s take off or landing during normal usage. The convex height h is typically less than a micron. With the slider  16  attached in accordance with the invention, the orientation of the slider  16  can be mounted with reasonable predictability, thereby correctly positioning the slider with respect to the disk surface  32 , in contrast to a corresponding prior art method of slider mounting. FIG. 9 shows a prior art slider  66  attached to the flexure  68  by use of epoxy  70 . In accordance with the prior art method, the glue pattern for the epoxy  70  is of critical importance in the final orientation of the ABS  72  with respect to the disk surface  32 . The shape and volume of the cured epoxy controls the eventual positioning of the slider  66  relative to the disk surface  32 . For example, if the epoxy  70  is initially applied in a skewed attitude, a tilted slider  66  would result which would adversely affect the aerodynamics of the flying slider  66 . 
     During the epoxy attachment of the prior art slider  66  onto the flexure  68  during the curing process, the dosage of UV light exposure has to be carefully controlled. Typically, several openings  74  have to be formed on the flexure  68  as shown in FIG.  9 . UV light is then illuminated from the back side of the flexure  68  through the openings  74 . The clearance gap  76  between the slider  72  and the flexure  66  allows the UV light to disperse and permeate the epoxy  70 . If the openings  74  are too large, the remaining area on the flexure  66  for retaining the epoxy is decreased resulting in reduction in attachment force. On the other hand, if the openings  74  are too small, there may be insufficient UV light to pass through, thereby yielding a spotty pattern of uncured adhesives which seriously affects reliability. The magnetic head suspension assembly of this invention does not use epoxy and thus is capable of avoiding all the aforementioned problems. 
     It should be understood that modifications and variations of the magnetic head structure described above are possible within the scope of the invention. For example, the areas of attachment of the slider  16  to the flexure  14  need not be confined to the trailing and leading edge surfaces  52 A and  52 B. It is possible to have the attachment on a combination of other edge surfaces, including the side edge surfaces  52 C and  52 D, as long as the slider  16  can be securely attached to the flexure  14 . Other materials for the bonding pads  54 A- 54 D,  42 A- 42 D,  56 A,  56 B,  44 A,  44 B and the bonding joints  22  than those described may be used effectively. The invention need not be limited to a hard drive configuration, but may be implemented with other types of storage systems. The invention can be used in a multi-head structure as well as a single head structure.