Abstract:
A suspension system for disk drives is formed out of a multi-layer metal laminate. An etch-retardant layer is received between two outer metal layers at a pre-determined depth from the outer surfaces of the metal layers. Utilizing conventional photo-chemical etching process techniques, the etch retardant layer stops or retards the chemical etching at this pre-determined depth. In this manner, the inherent variably in etch rate is controlled, permitting the formation of finer geometries in the head suspension than would be otherwise possible.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a head suspension assembly for a data storage system, and, more particularly, to such an assembly wherein the head suspension is manufactured using a laminate or clad composite sheet metal having one or more etch-stop layers formed therein. 
     2. Description of the Prior Art 
     Direct access storage devices of the type known as “Winchester” disk drives, or merely “disk drives”, are well known in the computer industry. Disk drives store information on concentric, recorded tracks written on one or more rotatable magnetic recording disks. A magnetic head or transducer element is provided for each such disk, and moves from track to track, to either read previously stored information or to record information on the magnetic tracks (“read”-“write”, respectively). The electromagnetic transducer typically is carried in a slider body mechanism that is supported over the surface of a rotating disk by a self-acting, hydrodynamic air bearing. 
     The slider body/transducer combination is referred to collectively as a “head”, and it is attached to a suspension assembly that suspends and loads the head toward the disk surface. The suspension assembly is in turn connected to a rotary or linear actuator that controllably moves the head from track to track on the disk, in response to electrical signals generated by controlling circuitry. To aid in accurate tracking, the head is attached to the suspension assembly in a manner that permits the head to gimbal. In this manner, variations in head orientation necessitated by the radial repositioning of the head, relative to the magnetic disk surface, can be easily accommodated. 
     The trend towards increasing density of memory storage devices has not escaped disk drives, which have decreased in size while their data storage capacity has increased. Continuing improvements in the magnetic recording media, the head designs, and the control circuitry have permitted the data tracks to become smaller and closer together. The large suspensions used in older disk drives are too stiff to support the required high precision positional adjustment of the smaller, lighter-weight heads and sliders. Lighter and more selectively flexible suspension systems are required. Such suspensions must be increasingly flexible in the vertical direction to accurately track with the lighter heads, while remaining rigid in the horizontal or lateral direction to prevent unwanted side-to-side movement and the resultant mistracking. 
     During the initial period of disk size reductions, this problem was addressed by utilizing suspension members of ever decreasing thickness, with proportionally increasing ratios of width to thickness. However, as improvements in head and control circuit technology continued to permit further downsizing, stainless steel, the material of choice for manufacturing suspension members, reached its lower milling thickness. Below about 0.025 mm. in thickness, irregularities in stainless steel grain structure result in thickness variations that make steel of such dimensions unsuitable for use in suspensions. 
     With mechanical methods for shaping the extremely thin metal stock ruled out, the manufacturers of suspension assemblies have turned to photo-chemical etching techniques. This well-known technology for creating printed circuit boards of unfathomable complexity appeared to offer great promise for use in creating the small geometries required to achieve the desired bending characteristics in suspension assemblies. After the initial milling and stamping operations, a photo-etch resist pattern is applied to a suspension member blank. A chemical solvent is applied to remove metal from the exposed areas, thereby achieving the fine geometries necessary to the operation of the suspension member. The removal of metal from selected locations of the suspension member, and the resultant variations in suspension metal thickness, both reduce the weight of the suspension member and change its dynamic characteristics. 
     The unremitting advance towards ever lighter and more flexible suspension assemblies has resulted in suspensions of increasingly elaborate geometries. The tolerances required to achieve such geometries are rapidly approaching the process limits for photo-resist etching. While the depth of material removal is substantially a linear function related to the amount of time the metal surface is exposed to the chemical solvent, there are a number of variables that affect the ability to precisely control the amount of metal removed. Where, as here, extremely small tolerances are required, it becomes difficult to consistently achieve the required etch depth due to unavoidable variations in both temperature, etching time, and chemical contamination. In addition to variances in the concentration of the solvent, as well as the flow velocity of the solvent (or agitation), impurities in both the solvent and the metal being etched, and variances in the metal thickness, can all create process control problems that affect the end result of the fabrication process. As a result, there are practical limitations to the degree of control exercisable over the depth and shape of certain fine or small geometries formed in the suspension metal blank. 
     Accordingly, there is a need, in producing light, flexible, small suspension assemblies, for a process control technique that, when used with photo-resist etching, will permit a greater degree of control with respect to the etch depths achieved in the metal suspension assemblies. 
     SUMMARY OF THE INVENTION 
     The present invention provides a head suspension assembly (HSA) that is manufactured from a laminate or clad composite sheet metal having one or more layers formed therein that may be selectively used to stop or retard a chemical etching process. In limiting the amount of metal removed by a chemical solvent used in the photo-etch process, better control over the etching process can be obtained, thus enabling the chemical etching process to provide fine geometries in the head suspension that would otherwise not be possible given the variability inherent in the photo-etch process. 
     In accordance with the present invention, the etch-resistant material is embedded within conventionally-used sheet metal stock during its fabrication. This composite stock material may then undergo conventional, mechanical manufacturing processes that are used to create the disk drive suspensions. After the stock material has been subjected to the stamping, forming, and cutting operations, a photoresist material may be selectively applied to the surface of the shaped metal. An image will be photographically formed in the photo-resist layer, and the surface may then subjected to a chemical etching solution. 
     During the etching process the solvent will chemically react with and remove those areas of the metal surface not protected by the photoresist material, eventually reaching the etch-resistant layer. A material in this layer has been chosen on the basis of its having a lower reactivity in the presence of the etch solvent than the overlying stock material. This layer thus effectively “stops” the chemical etching process from proceeding further. In this manner, precise control over the depth to which the etching process proceeds may be achieved. This additional control will permit the formation of more precise geometric features within the stock material on a production basis than would otherwise be possible. 
     Additional features and advantages of the present invention are described in, and will be apparent from, the detailed description of the presently preferred embodiments and from the drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a top, plan view of a suspension assembly for a hard disk drive in accordance with the present invention; 
     FIG. 2 is a cross-sectional view taken along Line  2 — 2  of FIG. 1, with portions in phantom, showing a suspension known to the prior art; 
     FIG. 3A is a cross-sectional view taken along Line  3 — 3  of FIG. 1, showing a suspension of the present invention prior to chemical etching; 
     FIG. 3B is a cross-sectional view similar to FIG. 3A, showing a suspension of the present invention after chemical etching; 
     FIG. 3C is a cross-sectional view similar to FIGS. 3A and 3B, showing a suspension of the present invention after removal of a photoetch resist pattern from a surface of the suspension; 
     FIG. 4 is a top, plan view of an alternative embodiment of a suspension assembly of the present invention; 
     FIG. 5 is a cross-sectional view taken along Line  5 — 5  of FIG. 4; and 
     FIGS. 6,  7 , and  8  illustrate a magnetic disk drive which includes a head suspension assembly constructed according to the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Disk drive systems utilize one or more heads that electromagnetically act with one or more recording disks mounted on a rotatable spindle. Head suspension assemblies are provided to support and position the heads over desired radial positions on the magnetic disks. Head suspension assemblies include several independent members, terminating at a point of attachment for a slider that carries a transducer head. In the art, three separate thin metal members are attached together to support the slider as they radially move over the magnetic medium. An actuator motor is provided to rotate the head suspension assembly over its range of radial positions, with the head suspension assembly attached to the motor by a “support” or “mount” plate member. This support plate member is fabricated out of a rigid material, such as stainless steel, to provide a solid support surface to which the other head suspension assembly members are attached. 
     The head suspension assembly members become progressively thinner and more flexible, with the next member, the “load beam,” made of a thin piece of (typically) stainless steel of thickness between 0.03 to 0.08 mm. The load beam must be substantially inflexible horizontally—yet it cannot be as rigid as the support plate. The load beam must also be able to provide a vertical spring force reactive to the air-bearing force that supports the slider. The final support assembly member, known as the flexure, mechanically links the load beam to the slider. A flexure includes conventional means for maintaining a slider. Utilizing a metal sheet of minimal thickness, typically 0.02 mm. to 0.03 mm stainless steel, great performance demands are placed upon the flexure. The flexure must be extremely flexible in the vertical direction, permitting the slider to easily gimbal. At the same time, to enable the accurate radial positioning of the slider on the magnetic disk surface requires virtual absolute rigidity in the horizontal direction. 
     Turning now to FIG. 1, a load beam  10  has one or more etched areas of reduced thickness located at a first end  17  thereof. One such etched area of reduced thickness is indicated by reference numeral  15 . An attachment aperture  19  is formed in the load beam  10  adjacent a second end  23 . When operating, the load beam  10  is attached to an actuator arm (not shown) by either a swage or rivet connector (not shown) received by and within the attachment aperture  19 . An intermediate opening  27  may also be formed in the load beam  10 , the placement and geometric shape of which is determined according to the desired changes in the bending moment of the load beam  10 . 
     The geometric shape and location of the etched area  15  of reduced thickness, is likewise dictated by bending moment requirements. The prior art photo-etch process used to form the etched area  15  may be understood with reference to FIG.  2 . As mentioned previously, the load beam is typically fabricated out of stainless steel, full or ¾ hard, Type 302 or 304, of a thickness between 0.02054 and 0.0762 mm. Since mechanical methods of shaping this or other types of stainless steel become impractical as thickness values approach 0.025 mm, it is well known to use photo-chemical etching to form delicate features on the load beam  10   a.    
     In the prior art, a photo-etch resist pattern  33  (shown in phantom) is first applied to the load beam  10   a,  with the areas from which metal is to be removed remaining uncovered. Chemical etchants, such as ferric chloride, are then applied to the surface of the load beam  10   a,  forming an etched layer  37 . The amount of metal removal (depicted reference letter “d” in FIG. 2) is dependent upon such factors as the etchant concentration, the processing temperature, and the exposure time of the chemical etchant to the metal. Each of these criteria can vary according to the skill and knowledge of the practitioner. Nevertheless, practical limitations are reached with respect to precision control of the depth and shape of the etching process. The non-linear depiction of the etched surface  37  reflects the surface variability in the amount of metal removed. At the conclusion of the etching process, the photo-etch resist layer  33  is chemically removed from the load beam  10   a.    
     THE INVENTION 
     To address the inherent variability in thickness of the etched layer, the load beam  10  in FIG. 3A is shown having an etch-stop layer  43  sandwiched between a pair of metallic layers  47 . Together with the metallic layers  47 , the etch-stop layer  43  forms a metal laminate blank  49 . Although not shown in the Figures, the metal laminate blank  49  may be subjected to the conventional mechanical manufacturing steps involved in fabricating load beams for hard disk suspensions, including: stamping, forming, and cutting. The metal laminate blank  49  is of most benefit when photo-chemical etching processes are used to shape the metal laminate into the delicate geometries desired for the load beam. 
     In a known manner, the photo-etch resist layer  33  is applied to one or more surfaces of the metal laminate blank  49 . When the metallic layers  47  are stainless steel of the type described above, a dry or liquid photo-resist material may form a suitable photo-resist layer. After application, an overlying pattern may be placed upon the layer and the masked photo-etch resist may then be exposed to a light source to create a desired pattern image on the photo-resist layer  33 . A solvent, such as one comprising ferric chloride may then be applied to the surface to remove the unexposed portions. With the desired pattern formed in the photo-resist layer  33 , the chemical etching solution may then be applied to the metal laminate blank  49 . 
     Turning now to FIG. 3B, the metal laminate blank  49  has been subjected to an etching operation, chemically dissolving those portions of the upper metallic layer  47   a  not covered by the photo-etch resist layer  33 . While the etching process itself is known to the prior art, the use of the etch-stop layer  43  is not. The etch-stop layer  43  permits significantly greater precision and control over the desired dimensions and geometries in the load beam  10 . Having been selected from a material that is resistant to the chemical etching solvent, the non-reactive surface of the etch-stop layer  43  slows, if not terminates, the etching process. Thus, by the careful placement of the etch-stop layer  43 , control over the desired depths, features, and shapes required to form the load beam  10  is less susceptible to variations in chemical exposure time, etching solution impurities, temperature fluctuations, gelatinousness, and other variables that affect the chemical etching process. 
     Upon completion of the chemical etching, the photo-etch resist layer  33  is removed using known solvents appropriate for the particular resist layer material used. FIG. 3C illustrates the resulting load beam structure. In comparison with the prior art load beam  10   a  (FIG.  2 ), the etching depth d′ is considerably more uniform over the etched layer than is the case where no etch-stop layer  43  is utilized. Although exaggerated in the Figures for illustrative purposes, partial etching yields surface variations of up to ±10% of original thickness using prior art etching techniques without an etch-stop layer. The etch-stop layer  43  reduces such variations to ±4% of original thickness. 
     The present invention also contemplates the use of multiple stop layers imbedded within a metal laminate, permitting the creation of patterns having various metal layer thicknesses. A multiple metal-layered suspension  53  for use with hard disk drives is shown in FIGS. 4 and 5. A laminate stock  61  having a plurality of layers of an etch-retardant material  63 , each sandwiched between a corresponding pair of metal layers  67  is subjected to a multi-step photo-etching process with sequential metal removing processing steps to fabricate the desired pattern and thicknesses on the metal layered suspension  53 . After application of a first photo-etch resist pattern (not shown), the etching solution is applied until the first etch-stop layer is encountered. When the etch-stop layer is encountered, a second solvent can then be applied to chemically react with and remove the exposed etch-stop layer. For example, assume that the etch-stop layer comprises a thin tungsten sheet. In this case, potassium ferro-cyanide will remove the etch-stop layer. For a gold etch-stop layer, potassium iodide may be used. After removal of stop layer material, the chemical etching solution can be reapplied to dissolve the now-exposed metal layer. Alternatively, the photo-etch resist layer can be removed and replaced with a different resist pattern, which in turn is etched into the metal. Thus, the selective application of etching solutions and/or etch-retardant material permits fabrication of the metal-layered suspension  53  into various patterns and thicknesses. 
     In FIGS. 4 and 5, for example, this fabrication technique results in the utilization of the multi-layered laminate stock  61  to form an entire suspension assembly. That portion of the metal-layered suspension  53  that was least etched, i.e., the thickest portion, forms a mount plate  71 . This area of maximum thickness, having the most metal layers remaining after the chemical etching process is completed provides the structural strength needed at the point of attachment between the suspension system and the actuator arm (not shown). The remaining portion of the multi-layered suspension  53  consists of a flexure  75 . In FIGS. 4 and 5 the flexure  75  is shown as consisting primarily of a single metal layer. Additionally, the photo-etch resist process has been utilized to create a geometric aperture  76  formed in the flexure  75 , and to provide a geometric patter of increased thickness, forming a stiffener  77 . By the appropriate selection of both the pattern and the thickness value, the stiffener  77  may be used to fine tuning of the spring-like force required to balance the forces generated by an attached slider  81  when the slider  81  “flies” over a rotating magnetic disk. Thus, the precise shape of the stiffener  77  will vary in accordance with the overall design of the metal-layered suspension  53 , with the resulting design intended to permit the head/slider  81  to pitch and roll as required to best track the surface of the rotating magnetic medium (not shown in the Figures). It is further believed that by constructing the metal-layered suspension  53  out of the multiple-layered laminate stock  61 , the resulting sandwiched metal may also have desirable damping characteristics. 
     The laminate stock of the present invention can be fabricated by several different methods. In a preferred process, the etch-stop material, such as tungsten or gold, is sputtered on the surface of a clean metal sheet of full hard or ¾ hard type 302 or type 304 stainless steel. The sheet, with the deposited etch-stop layer, is then rolled against another stainless steel metal sheet in a cladding operation, thereby bonding the sheets together. In addition to tungsten and gold, other metals can also serve as the etch-stop material, including nickel. Also, other deposition processes besides sputtering can be used to apply the etch-stop layer, such as evaporation, plasma deposition, or plating. Ideally, the resulting etch-stop layer need only be a few atoms in thickness. 
     Alternatively, a thin layer (1-7 microns&#39; thickness) of an adhesive material, such as a thermoplastic polyimide, can be used to form the etch-stop layer, as well as to bond the two metal layers together. In this case, it is immaterial as to whether the adhesive material is itself inert to the chemical etching solution, or whether the adhesive has the etch-stop material added/mixed therein. An example of such a bonding material that also functions as an etch-stop is the family of epoxy adhesives, sold as Hysol epoxy, manufactured by Mitsui Corporation. It is contemplated that other adhesive materials might also be useful in this regard. 
     It is also contemplated under the present invention that the etchstop layer need not be a continuous layer between the bonded metal layers. The etch-stop material can be applied in a manner that forms a pattern, resulting in the etching of the metal being stopped only in certain desired areas. For example, where the etch-stop layer is sputtered on one of the metal surfaces, the extreme thinness of the layer permits the photo-chemical etching process to create apertures in the metal laminate substrate. Where only one etch-stop layer is provided, the selective application of the chemical etching solution to both sides of the metal laminate at a co-located position will result in the formation of a hole in the metallic laminate. 
     Where the etch-stop material forms a layer having a different color or lustre from the surrounding metal layers, the task of measuring the thickness of the metal after etching is considerably simplified over the prior art. Previously, with the variations in the rate of etching inherent in the chemical etching process, the degree or depth to which the etching process had penetrated was not always apparent. However, under the present invention, by using an etch-stop material of a different color or lustre from the base metal layer, the point at which the etching process is complete may readily be visually determined. 
     Finally, by the selection of the particular etch-stop layer, it is also possible to provide either an electrically insulating layer or a conductive path for electricity. For example, by creating the etch-stop layer out of a poorer conductor of electricity, such as niobium or cobalt, a relatively non-conductive layer is formed in the suspension that provides a degree of electromagnetic shielding in the embedded etch-stop layer. 
     Referring now to FIGS. 6,  7 , and  8 , there is illustrated a magnetic disk drive  130  which employs a head/suspension assembly (HSA)  132  that includes a load beam embodying this invention. The disk drive has a disk stack assembly  134  and a head stack assembly  136 . The disk stack assembly  134  includes a plurality of vertically stacked disks  138  which are supported for rotation on a spindle  140 , the spindle  140  being rotated by a motor  142 . The head stack assembly  136  includes a plurality of vertically stacked suspensions  144 , each suspension being mounted to a respective actuator arm  146 . Each actuator arm  146  is mounted for rotation on an actuator hub  148  which is selectively rotated by a voice coil  150 . Each suspension  144  includes a respective HSA  132  and a load beam  152 , the HSA being mounted on the load beam as will be explained in more detail hereinafter. The load beam  152  of each HSA  132  has mounted to it a slider  154  which carries a magnetic head (not shown) for reading and writing magnetic signals on the disk  13 . Processing circuitry  156  is operatively connected to the motor  142 , the voice coil  150 , and the magnetic heads for rotating the disks  138 , selectively rotating the actuator arms  46 , and reading and writing on the disks, respectively. When the voice coil  150  is operated, the magnetic heads on the slider  154  are moved to selected circular tracks on the disks where information is magnetically read and magnetically written by the heads. Because of direct access to these circular tracks by simple rotation of the actuator arms  146 , this type of storage device is known as a direct access storage device (DASD). 
     Each HSA  132  includes a load beam  152  built according to this invention. Each load beam  152  preloads a respective slider  154  on a surface of a disk  138 . When the disks  138  are rotated, each disk creates a cushion of air (an “air bearing”) which counterbalances preloading of the load beam  152 , causing a slider to fly slightly off of the surface of a disk, in the order of 0.075 microns. The surface of the slider supported by this air bearing is known as an air bearing surface (ABS). In some applications, the surface of the disk  38  may be provided with a lubricant allowing the ABS of the slider to slightly contact the surface of the disk when the disks are rotated. The HSA  132  allows for slight movements in pitch and roll of the slider  154  during rotation of the magnetic disk  138 . 
     It should be understood that various changes and modifications to the presently preferred embodiment that are described herein will be apparent to those skilled in the art. Such changes and modifications can be made without departing from the spirit and scope of the present invention and without diminishing its attendant advantages. It is therefore intended that such changes and modifications be covered in the appended claims.