Abstract:
A head suspension for supporting a head slider over a storage media in a dynamic storage device is provided with a head suspension component having a spring metal layer, an electrically conductive layer and a dielectric layer interposed between the metal layer and the electrically conductive layer. A plurality of electrically conductive traces with bond pads are formed in the electrically conductive layer. A feature datum is also formed in the electrically conductive layer on a detachable carrier strip. The feature datum defines a first edge in the electrically conductive layer parallel to an edge of the bond pads.

Description:
REFERENCE TO RELATED APPLICATION 
     This application is a division of U.S. patent application Ser. No. 11/037,281, filed Jan. 18, 2005 now U.S. Pat. No. 7,441,323, and entitled BOND PAD REGISTRATION FOR DISK DRIVE HEAD SUSPENSIONS, which is hereby incorporated by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to methods and structures for aligning head suspension structures in a disk drive head suspension assembly. 
     BACKGROUND OF THE INVENTION 
     Head suspensions for disk storage devices typically include a load beam, a flexure, and a base plate. The load beam typically includes a mounting region at a proximal end of the load beam for mounting the head suspension to an actuator of a disk drive, a rigid region at a distal end of the load beam, and a spring region between the mounting region and the rigid region. The base plate is mounted to the mounting region of the load beam to facilitate the attachment of the head suspension to the actuator. The flexure is positioned at the distal end of the load beam, and typically includes a gimbal region having a slider mounting surface to which a slider having a magnetic read/write head is mounted. The head slider is thereby supported in read/write orientation with respect to a rotating disk. The gimbal region is resiliently moveable with respect to the remainder of the flexure in response to aerodynamic forces acting on the head slider in the presence of an air bearing generated by the rotating disk. The spring force provided by the spring region counteracts the aerodynamic lift force generated by the head slider in the presence of the air bearing and causes the head slider to “fly” over the surface of the disk at a pre-determined height known as the fly height. 
     In one type of head suspension, the flexure is formed as a separate component and includes a mounting region that is rigidly mounted at the distal end of the load beam using conventional approaches, such as spot welds. In such a flexure, the gimbal region is located distally from the load beam mounting region of the flexure and generally includes a cantilever beam having the slider mounting surface to which the head slider is mounted. A dimple or other load point extends between the load beam and the slider mounting surface of the flexure and is formed in either the load beam or the slider mounting surface of the flexure. The dimple transfers the spring force generated by the spring region of the load beam to the flexure and the head slider to counteract the aerodynamic force generated by the air bearing between the head slider and the rotating disk. In this manner, the dimple acts as a “load point” between the flexure/head slider and the load beam. The dimple also provides clearance between the cantilever beam of the flexure and the load beam, and serves as a point about which the head slider can gimbal in pitch and roll directions in response to fluctuations in the aerodynamic forces generated by the air bearing. 
     As the number and density of magnetic domains on the rotating disk increase, it becomes increasingly important that the head slider be precisely aligned over the disk to ensure the proper writing and reading of data to and from the magnetic domains. The angular position of the head suspension and the head slider, also known as the static attitude, is calibrated so that when the disk drive is in operation the head slider assumes an optimal orientation at the fly height. It is therefore important that the static attitude of the head suspension and head slider be properly established. Toward this end, the head slider must be properly positioned on the flexure with respect to the dimple. Misalignments between the dimple and the head slider may cause a torque to be exerted on the head slider, and thus affect the fly height of the head slider and the orientation of the head slider at the fly height. Moreover, improper fly height and angular positioning of the head slider over the disk could result in the head slider “crashing” into the disk surface as the head slider gimbals due to the close proximity of the head slider to the rotating disk at the fly height. 
     Electrical interconnection between the read/write heads on the head slider and circuitry in the disk storage device is provided along the length of the head suspension. Conventionally, one or more conductive copper traces are bonded to the stainless steel load beam with a dielectric adhesive or are otherwise formed on the load beam, to provide electrical interconnection. Such an integrated lead or wireless head suspension may include one or more bond pads at the distal end of the traces to which terminals on the head slider are electrically connected. Misalignment between the head slider (and therefore the terminals on the head slider) and the bond pads of the traces may compromise the integrity of the electrical interconnection between the head slider and the electrical circuitry in the disk storage device. Therefore, in addition to being properly positioned on the flexure to promote desirable properties such as fly height and static attitudes, the head slider must also be aligned on the flexure relative to the bond pads to ensure a high quality interconnection between the bond pads and the terminals of the head slider. 
     The traces and bond pads may also be configured to provide desired mechanical connection and support to the gimbal region of the load beam. In one approach, described in U.S. Pat. No. 5,491,597 (Bennin, et al.) the traces include one or more symmetrical torsional arms extending from the load beam. Adjacent arms are shaped as back to back “P”s, with a semicircular indentation approximately at the middle of each back. The indentation defines a round clearance hole that fits around and receives the gimbal pivot (e.g., dimple). This allows the head assembly to swivel on the gimbal pivot. 
     To assist in the alignment of the head suspension components and in the formation of head suspension features, the head suspension typically includes reference apertures or tooling holes that are engaged by an alignment tool. The apertures are typically longitudinally spaced apart and are formed in the rigid region of the load beam. In head suspensions that include a separate flexure mounted to the load beam, the flexure can include corresponding apertures formed in the load beam mounting region of the flexure. The reference apertures in the load beam and the flexure are typically circular, and are sized and positioned so as to be substantially concentric when the flexure is mounted to the load beam. 
     Rigid cylindrical pins on an alignment tool are typically used to align the individual head suspension components. The rigid pins are spaced apart an amount equal to the longitudinal spacing between the reference apertures in the components. The pins are inserted into and engage the apertures in the load beam and flexure, and in this manner concentrically align the apertures, and thus the load beam and the flexure, to one another. A similar method may be used to install the head slider to the slider mounting surface of the gimbal region of the flexure. 
     According to one approach described in U.S. Pat. No. 6,657,821 (Jenneke), a reference aperture is provided with a compliant feature configured to receive a tapered cylindrical pin for precisely locating a head suspension component relative to a desired reference. A spring beam tab of the compliant feature is engaged by the tapered pin to reliably locate the pin within the reference aperture. In an approach illustrated in U.S. Pat. No. 5,570,249 (Aoyagi et al.), rather than being circular, a distal aperture in the load beam is elongated and generally elliptical. The aperture includes a “v” shaped portion at one end. According to another approach described in U.S. Pat. No. 6,625,870 (Heeren et al.), an elongated alignment aperture is formed in a rigid region of a load beam, and a proximal alignment aperture and a distal alignment aperture are formed in the flexure. The elongated aperture overlaps at least a portion of the proximal and distal alignment apertures. Once aligned, the components can then be fastened together, as by welding or other known processes. 
       FIG. 1  is an illustration of a portion of a prior art head suspension assembly  10 . Head suspension  10  was used to support and properly orient a head slider over a rotating disk (not shown) in a magnetic disk storage device. Head suspension  10  was comprised of a load beam  12  coupled at a proximal end to an actuator arm (not shown). A stainless steel flexure  14  was mounted to a distal end of the load beam  12 . The flexure  14  was attached to a carrier portion or strip  16  detachable from the remainder of the flexure  14  at line  18 . Flexure  14  was formed with a gimbal region  20  having a slider mounting surface  22  for receiving a head slider  24  (shown partially cut away) having electrical terminals  26 . Integrated leads  28  were formed on flexure  14  to provide electrical interconnection between the electrical terminals  26  of the head slider  24  and circuitry in the magnetic disk storage device to which the head suspension  10  was mounted. Integrated leads  28  included one or more conductive traces  30  that provided such electrical interconnection. The traces  30  terminated in a plurality of bond pads  32  on the slider mounting surface  22  at the gimbal region  20  of the flexure  14 . The bond pads  32  were formed in a layer of copper separated from the stainless steel of the flexure  14  by a layer of dielectric material interposed therebetween. 
     The head suspension  10  included a circular aperture  34  extending through the flexure  14  at the carrier strip  16 . The aperture  34  was formed in a copper layer. That is, the aperture  34  included an opening in the stainless steel of the flexure  14  and an opening in a copper region formed on the stainless steel. The opening through the stainless steel was larger than the opening in the copper so that the edges of the aperture  34  were defined by copper. The aperture  34  was engageable by a tooling pin as described previously for assisting alignment of the bond pads  32  of the traces  30  to the load beam  12  and dimple  183 , thus assisting in the accuracy of the placement of the slider  24  in subsequent procedures. 
     There are various deficiencies and shortcomings associated with prior art head suspensions and tooling. Conventional reference apertures such as those described above include manufacturing tolerances that affect the interface between the alignment tool and the head suspension component. The pins on the alignment tools also include manufacturing and positioning tolerances. These tolerances are cumulative so as to affect the alignment of individual head suspension components, and affect the forming of head suspension features, such as the load point dimple, and mounting of the head slider to the flexure. In addition, when aligning individual head suspension components, the manufacturing tolerances in the apertures of the load beam and the flexure are “stacked” together because the head suspension components are engaged by common alignment pins, thus creating additional alignment problems. 
     A drawback to these prior art approaches is that the tooling pin is typically aligned to a reference feature (i.e. the reference or alignment aperture) formed in a stainless steel region of the load beam or flexure. When aligning a component such as the head slider to the bond pads, one must assume that the registration of the stainless steel layer of the reference aperture is perfect with respect to the copper layer of the bond pads. However, perfect alignment between the stainless steel layer and the copper layer is not typical. 
     The traces and bond pads are often formed on the load beam through etching (subtractive) or deposition (additive) processes. Conventional etching processes make use of a laminate including a dielectric layer between stainless steel and copper layers. Using known photolithography and etching processes, regions of the copper layer are subjected to etching or corrosive chemicals, which etch or remove the copper to form specific features, for example, traces and bond pads. The mass of these formed copper components is inversely related to the length of time the copper is subjected to etching chemicals. Thus, as the copper components are subject to the etching process, areas of copper mass become smaller and openings or apertures in areas of copper become larger. Small variations in processing, including etching time, can sometimes lead to variations in the size and location of the copper components, including the traces and bond pads. Such variations can result in misalignment of the electrical terminals of the head slider to the bond pads. 
     For example, it is possible for the head slider to be positioned on the flexure so as to promote certain properties, such as fly height and static attitude, yet be mis-aligned relative to the bond pads due to bond pad positional variation so as to form none or a low quality electrical interconnection. Conversely, the terminals of the head slider may be adequately aligned to the bond pads to form a high quality interconnection, yet because of positional variation of the bond pads, the position of the head slider on the flexure adversely effects such characteristics as fly height of the head slider and static attitude of the head suspension assembly. 
     There is, therefore, a continuing need for an improved method and structure for aligning individual head suspension components, for aligning the head slider to the bond pads on the flexure and for establishing the proper static attitude of the head suspension assembly. 
     SUMMARY OF THE INVENTION 
     According to one embodiment, the present invention is a head suspension for supporting a head slider over a storage media in a dynamic storage device. The head suspension comprises a head suspension component having a spring metal layer, an electrically conductive layer and a dielectric layer interposed between the metal layer and the electrically conductive layer. A plurality of electrically conductive traces with bond pads and a datum feature are formed in the electrically conductive layer. The datum feature is a circular aperture in the electrically conductive layer. According to another embodiment, the datum feature is a v-shaped aperture in the electrically conductive layer. According to yet another embodiment, the datum feature is an aperture defining a first edge in the electrically conductive layer. The bond pads define a second edge in the electrically conductive layer. The first edge is parallel to the second edge. 
     According to another embodiment, the present invention is a head suspension for supporting a head slider over a storage media in a dynamic storage device. The head suspension comprises a head suspension component having a spring metal layer, an electrically conductive layer and a dielectric layer interposed between the metal layer and the electrically conductive layer. A plurality of electrically conductive traces with bond pads are formed in the electrically conductive layer, and a datum feature is formed in the electrically conductive layer and defined by the bond pads. 
     According to another embodiment, the present invention is a method of aligning components for installation on a head suspension assembly for supporting a head slider over a storage media in a dynamic storage device. The head suspension assembly having a spring metal layer, an electrically conductive layer, and a dielectric layer interposed between the metal layer and the electrically conductive layer. A plurality of electrically conductive traces terminate in bond pads in the electrically conductive layer. The method includes the step of forming a datum feature in the electrically conductive layer. The datum feature has a first edge parallel to an edge of the bond pads. The electrically conductive layer is subjected to etching chemicals so that the bond pad edge migrates towards the datum feature first edge and the datum feature first edge migrates away from the bond pad edge at an equal rate. A head slider is aligned to the datum feature so that the head slider is aligned to the bond pad edge. The head slider is installed to the head suspension assembly in electrical interconnection with the bond pads. 
     According to another embodiment, the present invention is a method of manufacturing a head suspension assembly for supporting a head slider over a storage media in a dynamic storage device. The head suspension assembly is of the type having a spring metal layer, an electrically conductive layer, and a dielectric layer interposed between the metal layer and the electrically conductive layer, and a plurality of traces formed in the electrically conductive layer and terminating in bond pads adjacent a slider mounting surface. The method includes the steps of forming a datum feature in the electrically conductive layer adjacent to the bond pads and spaced apart from the slider mounting surface. A head slider is installed at the slider mounting surface. The coordinates of the head slider relative to the datum feature is determined. The head suspension assembly is discarded if the coordinates of the head slider are not within preset ranges. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a portion of a prior art head suspension assembly. 
         FIG. 2  is a perspective view of a portion of a head suspension assembly including a flexure and load beam according to one embodiment of the present invention. 
         FIG. 3  is a detailed top view of a portion of the flexure of  FIG. 2  at first and second stages in the copper layer formation process. 
         FIG. 4  is a perspective view of a portion of a flexure and load beam according to another embodiment of the present invention at first and second stages in the copper layer formation process. 
         FIG. 5A  is a detailed top view of a portion of a flexure and load beam showing a feature datum according to yet another embodiment of the present invention. 
         FIG. 5B  is a detailed top view of a portion of a flexure and load beam showing the feature datum of  FIG. 5A  in a reverse configuration according to yet another embodiment of the present invention. 
         FIG. 5C  is a detailed top view of a portion of a flexure and load beam showing a feature datum according to yet another embodiment of the present invention. 
         FIG. 6A  is a detailed top view of a portion of a flexure and load beam showing a feature datum according to another embodiment of the present invention. 
         FIG. 6B  is a detailed top view of the flexure and load beam of  FIG. 6A  in which the feature datum has an angular orientation. 
         FIG. 7  is a detailed top view of a portion of a flexure and load beam showing a feature datum according to still another embodiment of the present invention. 
         FIG. 8  is a detailed top view of a portion of a flexure and load beam showing a feature datum according to another embodiment of the present invention. 
         FIG. 9  is a detailed top view of a portion of a flexure and load beam showing a feature datum according to another embodiment of the present invention. 
         FIG. 10  is a detailed top view of a portion of a flexure and load beam showing a feature datum according to another embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 2  is an illustration of a portion of a head suspension assembly  100  according to one embodiment of the present invention. Head suspension  100  includes a load beam  102  and a flexure  104  mounted to the load beam  102 . The flexure  104  includes a detachable carrier portion or strip  110  separable from the remainder of the flexure  104  at line  112 . Flexure  104  is formed with a gimbal region  109  having a slider mounting surface  111  for receiving a head slider  130  (shown partially cut away) having electrical terminals  132 . Integrated leads  120  are formed in a copper layer of the flexure  104  and are separated from a stainless steel layer of the flexure  104  by a layer of dielectric material interposed therebetween. Integrated leads  120  include one or more conductive traces  122  terminating in bond pads  124  on the slider mounting surface  111  at the gimbal region  109  of the flexure  104 . The bond pads  124  are provided with a bond pad edge  126  in the copper layer towards the proximal end of the flexure  104 . The edge  126  of the bond pad  124  is generally perpendicular to a longitudinal axis L of the flexure  104 . 
     Head suspension assembly  100  further includes an alignment structure  140  formed in the copper layer of the flexure  104 . Alignment structure  140  forms a tooling datum to facilitate alignment of the flexure  104 , or components of the flexure  104 , to other components of the head suspension assembly  100  during construction of the head suspension assembly  100 . The alignment structure  140  includes an aperture  144  extending through a copper region  142  of the carrier strip  110  of the flexure  104 . Aperture  144  extends through both the stainless steel layer and the copper layer of the flexure  104 . However, the opening in the stainless steel layer is larger than the opening in the copper layer such that the edges of the aperture  144  are defined by the copper layer. The aperture  144  has a curved segment or edge  146  towards the proximal end of the flexure  104  and a straight segment or edge  148  towards the distal end of the flexure  104  forming a half-moon shape. Aperture  144  is positioned on the flexure  104  so that edge  148  is parallel to the edges  126  of the bond pads  124 . 
       FIG. 3  illustrates a portion of the flexure  104  and load beam  102 , including the bond pads  124  and the alignment structure  140 , at two different stages in the aforementioned etching process. The solid lines represent the copper edges of the alignment structure  140  and bond pads  124  at a first stage in the etching process. The dashed lines represent the copper edges of the alignment structure  140  and bond pads  124  at a second stage in the etching process, after a period of further exposure to etching chemicals. As described previously, throughout the etching process, masses of copper, such as bond pads  124 , decrease in size as the copper edges of such masses are etched away. Bond pad  124  is configured such that edge  126  etches or migrates through out the etching process towards the distal end of the flexure  104 . Edge  126  is generally perpendicular to the longitudinal axis L of the flexure  104 , such that edge  126  migrates or retracts substantially entirely along the longitudinal axis L without any lateral migration. As also described previously, throughout the etching process, voids in the copper layer, such as aperture  144 , increase in size as the copper edges of such voids etch away. In the present example, aperture  144  is configured such that edge  148  etches distally, away from the edges  126  of the bond pads  124 . Edge  148  is parallel to edge  126  of the bond pads  124 , such that edge  148  also retracts substantially entirely along the longitudinal axis L. 
     The rate of etching is generally the same for both the bond pads  124  and aperture  144 , such that migration along the axis L is substantially the same for the bond pad edge  126  and the aperture edge  148 . A distance d between the edges  126  of the bond pads  124  and the edge  148  of the aperture  144  at the first stage of the etching process is the same as a distance d′ between the edges  126  of the bond pads  124  and the edge  148  of the aperture  144  at a second stage in the etching process. Generally, the distance d remains the same throughout the etching process. The position of the alignment feature  140  tracks the location of the bond pad edges  126  throughout the etching process. Any variations in the location of the bond pad edge  126  due to variations in the etching process (i.e. over or under etching) are tracked by the alignment feature  140 . The alignment feature  140  is more accurately positioned on the flexure  104  relative to the bond pads  124 . If, as described previously, the aperture  144  is engaged by a tooling pin to facilitate installation of the head slider  130  to the flexure  104 , the tooling pin and thus the head slider  130  will be more accurately positioned on the flexure  104  relative to the bond pads  124 . This increases the likelihood of forming a high quality electrical interconnection between the terminals  132  of the head slider  130  and the bond pads  124  of the traces  122  despite etching related positional variations of the bond pads  124 . 
     Typically, variations in bond pad positioning resulted in misalignment of other installed components such as the head slider  130  with respect to the bond pads  124 . A reference aperture placed in the same layer as the bond pads, as described with respect to prior art  FIG. 1 , does not compensate for bond pad positional variation. A head suspension assembly  100  according to the present embodiment, however, is configured to reduce misalignment of the alignment feature  140  to the bond pads  124  despite etching-induced variations in the position of the bond pads  124 . In particular, the edge  148  of the aperture  144  tracks the edges  126  of the bond pads  124 . The alignment feature  140  is advantageously effectively continuously self-aligned to the edges  126  of the bond pads  124  throughout the manufacturing process. A tooling pin or other alignment tools employing the alignment feature  140  will be more accurately aligned to the edges  126  of the bond pads  124 . Head suspension components, including the head slider  130 , can therefore be more consistently mounted to the gimbal region  109  in accurate alignment with the bond pads  124  despite variances in location of the bond pads  124  due to variances in the copper etching processes. 
     Alignment feature  140  is optionally further comprised of a second aperture  160  in the copper region  142  of the carrier strip  110 . In one embodiment, second aperture  160  has tapered edges  162 ,  164  and is generally V-shaped. A second tooling pin coupled to the reference pin engages the second aperture  160 . The second pin is used to push or pull the flexure  104  to bring the reference pin to a consistent location in the aperture  144 . According to one embodiment, a second pin engages the second aperture  160  and is used to push or pull the reference pin to engage the straight edge  148  of the aperture  144 . The addition of the second alignment aperture  160  allows the reference pin to be consistently located with respect to the alignment structure  140 . Optionally, second aperture  160  may be located in another layer of the flexure  104 , may take another shape, or may be used for installing other components onto the head suspension assembly  100 . 
     Returning to  FIG. 2 , the head slider  130  can be mounted to the flexure  104  so that bond pads  124  are electrically interconnected to terminals  132  on the head slider  130  using conventional techniques, such as ultrasonic welding or solder balls. During installation of the slider  130 , the terminals  132  must be precisely aligned with the bond pads  124  to provide a good electrical interconnection. In particular, the slider  130  must be installed on the head suspension assembly  100  so that the longitudinal distance dx along a longitudinal axis L of the head suspension assembly  100  between the terminals  132  and the edges  126  of the bond pads  124  are from about 5 μm to about 50 μm. Preferably, the longitudinal distance dx between the terminals  132  of the mounted head slider  130  and the edges  126  is less than about 20 μm. 
     As shown in  FIG. 3 , the bond pads  124  also etch along side edges  127 . A lateral misalignment of the terminals  132  with respect to a side edge  127  of the bond pads  124  may also reduce the quality of the electrical interconnection between the terminals  132  and the bond pads  124 . Therefore, it is contemplated that the alignment feature  140  may also include an edge angled or parallel to the side edges  127  of the bond pads  124 . In this manner, the alignment feature  140  may be configured to track lateral migration of the bond pads  124  as well as longitudinal migration. 
     It is also contemplated that the alignment feature  140  be positioned on the head suspension assembly  100  elsewhere than the carrier strip  110 . For example, the alignment feature  140  may be located on the load beam  102  or the flexure  104 . 
       FIG. 4  shows a portion of a head suspension assembly  200  according to another embodiment of the present invention at two stages in a copper etching process. The head suspension assembly  200  includes a load beam  202 , flexure  204  and bond pads  224  configured as generally described with reference to  FIG. 2 . The bond pads  224  are provided with an edge  226  in the copper layer of the flexure  204  extending generally perpendicular to a longitudinal axis L of the flexure  204  as previously described. Head suspension assembly  200  further includes an alignment structure  240  positioned on a carrier strip  210  separable from the flexure  204  at a line  212 . The alignment structure  240  includes a generally V-shaped aperture  244  extending through a copper region  242  of the carrier strip  210 . The aperture  244  is comprised of a curved edge or segment  246  interposed between first and second opposing angled edges or segments  248  and  250  opening towards the proximal end of the flexure  204 . Angled edges  248 ,  250  are preferably positioned at approximately 45° and 135° degrees, respectively, with respect to the edge  226  of the bond pads  224 . Such a configuration provides equal weight to both the longitudinal axis L and a perpendicular lateral axis. Aperture  244  extends through both the stainless steel layer and the copper layer of the flexure  204 . The opening in the stainless steel layer is larger than the opening in the copper layer such that the edges  246 ,  248  and  250  of the aperture  244  are defined by the copper layer. 
     The solid lines represent the edges of the alignment structure  240  and bond pads  224  at a first stage in the etching process. The dashed lines represent the edges of the alignment structure  240  and bond pads  224  at a second stage in the etching process, after a period of further exposure to etching chemicals. As described previously, throughout the etching process the size of the aperture  244  continues to increase while the size of the bond pads  224  continues to decrease. This includes the edges  226  of the bond pads  224  retracting or migrating along the axis L. The edges  248  and  250  of the aperture  244  migrate or retract at opposing angles relative to the axis L. This angular migration includes some migration along the axis L in the same direction as the migration of the edges  226  of the bond pads  224 . The amount of migration along the axis L relative to the migration of the edges  226  of the bond pads  224  is in part dependent upon the angle of the edges  248  and  250  relative to the edges  226  of the bond pads  224 . 
     Throughout the etching process the position of the alignment structure  240  migrates partially in the same direction as the edges  226  of the bond pads  224 . Thus, the alignment feature  240  is more accurately aligned to the bond pads  224  for facilitating alignment of a head slider (not shown) to the bond pads  224 . 
     While the head slider  130  may be properly aligned with the bond pads  124  to provide a good electrical connection, the actual location of the head slider  130  on the gimbal region  109  should also be such as to promote proper static attitudes of the head suspension assembly  100 . Generally, the head slider  130  needs to be aligned in a given or specified location, i.e. in the X and Y axes, as well as a rotating axis, with respect to another component, typically the load beam  102 , and more specifically a dimple or load point  183  formed between the flexure  104  and the load beam  102 . This alignment is desirable to achieve optimum positioning and fly height of the head slider  130  during operation. 
     For this reason, it is often desirable to determine the position of the head slider  130  on the flexure  104  relative to a feature of interest on the flexure  104 , for example, the load point  183 . One method of doing so is to determine the location of the edges  126  of the bond pads  124  relative to the load point  183 . As the head slider  130  must be aligned to the edges  126  to form a good electrical interconnection, the location of the head slider  130  can be inferred from the location of the edges  126 . However, the installed head slider  130  typically obscures the edges  126  of the bond pads  124 . Furthermore, the installed head slider  130  typically obscures the load point  183 . 
     Returning to  FIG. 2 , the head suspension assembly  100  optionally includes a feature datum  180  for determining the location of the head slider  130  relative to the load point  183  in accordance with one embodiment of the present invention. The feature datum  180  is positioned at a predetermined location relative to the load point  183  and to the edges  126  of the bond pads  124 . Following installation of the head slider  130 , the position of head slider  130  relative to the feature datum  180  is measured and used to infer the position of the head slider  130  relative to the load point  183 . If the head slider  130  is positioned incorrectly relative to the load point  183 , even though properly aligned to the bond pads  124 , the part may be rejected. 
     The feature datum  180  includes a circular aperture  182  in a copper region  184  positioned equidistant between adjacent bond pads  124   a  and  124   b . The aperture  182  includes an opening through the stainless steel of the flexure  104  and an opening through the copper region  184  formed on the flexure  104 . The opening through the stainless steel is larger than the opening through the copper region  184  such that the edges of the aperture  182  are defined by copper. The feature datum  180  remains visible following installation of the head slider  130  to the slider mounting surface  111 . 
     Feature datum  180  provides a convenient reference point for taking measurements for determining the location of the head slider  130  relative to the load point  183 . The edges of the aperture  182  are optically readable by vision scanning devices to determine their coordinates. The positional relationship between the feature datum  180  and the load point  183  is pre-determined, such that the location of the head slider  130  on the flexure  104  relative to the load point  183  can easily be determined. 
     Feature datum  180  is preferably formed in the same copper layer as the bond pads  124  as described above. Doing so reduces tolerance stack ups in the same manner as described with respect to the alignment features or tooling datums previously described with respect to the embodiments shown generally in  FIGS. 2-4 . Feature datum  180  and bond pads  124 , and thus head slider  130 , will track in position together regardless of any differential in registration between the copper layer and the stainless steel layer. 
     According to another embodiment, the feature datum  180  serves as a reference point for determining the location of the head slider  130  on the flexure  104  independent of the load point  183 . For example, the feature datum  180  may be used to facilitate determining the coordinates of the installed head slider  130 . If the actual coordinates of the head slider  130  are not within pre-determined limits, the part may be rejected. 
       FIG. 5A  illustrates a portion of a head suspension assembly  300  according to another embodiment of the present invention. Head suspension assembly  300  is in many respects similar to the head suspension assembly  100  of  FIG. 2 , so that like parts are given like numbering, although numbered from  300  onward. The head suspension assembly  300  includes a load beam  302 , flexure  304 , integrated leads  320  and bond pads  324  configured as generally described with reference to  FIG. 2 . The head suspension  300  further includes a feature datum  380 . The feature datum  380  is a copper component formed on the flexure  304  and spaced apart from the bond pads  324 . The feature datum  380  is positioned on the flexure  304  such that it remains visible following installation of other components, for example, the head slider  130 . The feature datum  380  is generally U-shaped and is positioned on the flexure  304  such that an open side of the feature datum  380  faces the bond pads  324 . Feature datum  380  defines a pair of parallel inner side edges  381   a  and a perpendicularly-extending inner back edge  383   a . In one embodiment, the inner back edge  383   a  is generally parallel to an edge  326  of the bond pads  324 . 
     Feature datum  380  may be used to generate a convenient reference point for determining the location of head suspension components, for example, the head slider  130 . According to one embodiment, vision scanning devices are used to identify the side edges  381   a  and back edge  383   a . A representative reference point is generated at a location equidistant from the inner side edges  381   a  and the inner back edge  383   a , as shown by the numeral X. Alternately, a mid-line is generated between the inner side edges  381   a  (shown in dashed line) and a reference point is generated at the intersection of the mid-line and the inner back edge  383   a  (shown as numeral X 2 ). According to other embodiments, reference may be taken from outer side edges  381   b  and outer back edge  383   b  rather than the inner edges, although in a similar manner. Alternately, as shown in  FIG. 5B , the feature datum  380  may be positioned to face away from the bond pads  324 . Again, either the inner or outer edges of the feature datum  380  may be used to generate a reference point. 
     Rather than generating a representative reference point based upon the location of the feature datum  380 , an edge of the feature datum  380  can be compared to, for example, an edge of the bond pads  324 . Along the axis L, the position of the bond pads  324  can be determined as the distance between the edge  326  of the bond pads  324  and the edge  383   a  of the feature datum  380 . With respect to a lateral or perpendicular axis of the head suspension assembly  300 , the lateral distance the edge  381   a  of the feature datum  380  and a longitudinally extending edge  327  of the bond pad  324  can be determined. As described previously, because both the bond pads  324  and the feature datum  380  are formed in the copper layer, the position of the feature datum  380  with respect to the bond pads  324  is independent of any mis-registration of the stainless steel and copper layers, and positional variances of the bond pads  324  due to under- or over-etching of the copper layer are likewise repeated in the feature datum  380 . 
       FIG. 5C  shows a head suspension assembly  300 ′ in accordance with another embodiment of the present invention. Head suspension assembly  300 ′ is in many respects similar to the head suspension assembly  300  of  FIGS. 5A and 5B , so that like parts are given like numbering, with the addition of a prime indicator. The feature datum  380 ′ of head suspension assembly  300 ′ is U-shaped as described with respect to the feature datum of  FIGS. 5A and 5B , but has curved or circular edges. An inner edge  385 ′ of the feature datum  380 ′ has a circular profile and forms a portion of a circle, shown in dashed lines. Optical scanners as are known in the art may be employed to read the edge  385 ′ of the feature datum  380 ′ and calculate the center of the circle, which then serves as a reference point. 
       FIG. 6A  illustrates a portion of a head suspension assembly  400  according to another embodiment of the present invention. Head suspension assembly  400  is in many respects similar to the head suspension assembly  100  of  FIG. 2 , so that like parts are given like numbering, although numbered from  400  onward. The head suspension assembly  400  includes a load beam  402 , flexure  404 , integrated leads  420  and bond pads  424  configured as generally described with reference to  FIG. 2 . The head suspension  400  includes a datum feature  480  formed by the edges of the bond pads  424 . In the present example, first and second bond pads  425  and  428  are adjacent and spaced apart. First bond pad  425  has a first edge  425   a  facing second bond pad  428  and formed with a concave curved profile. Second bond pad  428  is provided with a second edge  428   a  facing bond pad  425  and is also formed with a concave curved profile. Curved edges  425   a  and  428   a  partially define a circle  429 . The circle  429 , however, is undefined at a pair of gaps  431  between the bond pad edges  425   a ,  428   a.    
     Following installation of a head slider  130  to a slider mounting surface  411  on the flexure  404  (shown in dotted lines), the edges  425   a  and  428   a  of the bond pads  424  remain visible. Optical scanners as are known in the art may be employed to read the edges  425   a  and  428   a  and calculate the center of the circle  429 , as described previously. The calculated center of the circle  429  then serves as a reference point. The gaps  431  introduce uncertainty into the reading of the circle  429  and the calculation of a center point. While the size of the gaps  431  may be reduced to more fully form the circle  429 , the gaps  431  should not be eliminated, as doing so would electrically couple adjacent bond pads  425  and  428 . As shown in the present example, gaps  431  are aligned along a longitudinal axis L of the head suspension  400 . Any uncertainty in the reading of the circle  429  is therefore primarily along the L axis. 
       FIG. 6B  shows a head suspension assembly  400 ′ according to another embodiment of the present invention. Head suspension assembly  400 ′ is generally similar to the head suspension assembly  400  shown in  FIG. 6A , such that like parts are given like numbering with the addition of the prime numeral. The head suspension assembly  400 ′ includes a feature datum  480 ′ in which edges of the bond pads  425 ′,  428 ′ are formed such that the gaps  431 ′ are aligned at an angle with respect to the axis L. Any uncertainty in the reading of the circle  429 ′ due to the gaps  431 ′ is more evenly distributed along the L axis and a perpendicular or lateral axis, rather than solely along the L axis. While the embodiments illustrated in  FIGS. 6A and 6B  show the geometric shape formed by the adjacent bond pad edges  425   a ,  428   a  as circular, it is contemplated that additional shapes, such as ellipsoids and rectangles, would suffice as well. 
       FIG. 7  illustrates a portion of a head suspension assembly  500  according to another embodiment of the present invention. Head suspension assembly  500  is in many respects similar to the head suspension assembly  100  of  FIG. 2 , so that like parts are given like numbering, although numbered from  500  onward. The head suspension assembly  500  includes a load beam  502 , flexure  504  and bond pads  524  configured as generally described with reference to  FIG. 2 . The head suspension  500  includes a datum feature  580  formed integrally with the bond pads  524 . In the present example, adjacent bond pads  525  and  528  are provided with protrusions  596  and  586 . Protrusions  596  and  586  are provided with circular apertures  587 ,  588  therethrough, respectively. 
     Following installation of a head slider  130  to a slider mounting surface  511  (shown in dotted lines), the apertures  587 ,  588  therethrough remain visible. Optical scanners may be employed to determine a middle point between the adjacent apertures  587 ,  588 . The location of the middle point may then serves as a reference point for determining the location of components of the head suspension assembly  500 , for example, of head slider  130  relative to a load point  183  (See  FIG. 2 ). 
       FIG. 8  illustrates a portion of a head suspension assembly  600  according to another embodiment of the present invention. Head suspension assembly  600  is in many respects similar to the head suspension assembly  100  of  FIG. 2 , so that like parts are given like numbering, although numbered from  600  onward. The head suspension assembly  600  includes a load beam  602 , flexure  604  and bond pads  624  configured as generally described with reference to  FIG. 2 . The head suspension  600  is also shown with an additional center trace line  624   a  which may be a ground line, as is know in the art. The head suspension assembly  600  includes a feature datum  680  provided in a copper region bussed to or formed from the center trace  624   a . Feature datum  680  is rectangle-shaped and has side edges  681  and opposing end edges  683 . Vision scanning devices may be used to identify the edges  681  and  683  to generate reference points. For example, the intersection of representative diagonal lines extending from the corners of the feature datum  680  (shown in dashed lines) may serve as a reference point. Alternately, the intersection of a representative mid-line between opposing edges  681  and end edge  683  may serve as a reference point, similar to that described with respect to  FIGS. 5A and 5B . 
       FIG. 9  illustrates a portion of a head suspension assembly  700  according to another embodiment of the present invention. Head suspension assembly  700  is in many respects similar to the head suspension assembly  100  of  FIG. 2 , so that like parts are given like numbering, although numbered from  700  onward. The head suspension assembly  700  includes a load beam  702 , flexure  704  and bond pads  724  configured as shown generally in  FIG. 2 . The head suspension  700  includes a feature datum  780  provided in a copper region adjacent the bond pads  724 . The feature datum  780  is bussed to or formed integrally with a trace line  720 . The feature datum  780  includes a copper protrusion  789  extending from the trace line  720 . 
       FIG. 10  shows another embodiment of a head suspension assembly including a feature datum in accordance with the present invention. Head suspension assembly  800  is in many respects similar to the head suspension assembly  100  of  FIG. 2 , so that like parts are given like numbering, although numbered from  800  onward. The feature datum  880  includes an aperture  882  extending through the flexure  804  at a copper region  884 . As described previously with respect to the alignment structure  140  of  FIG. 2 , the aperture  882  includes an opening through the stainless steel of the flexure  804  and an opening through a layer of copper formed on the flexure  804 . The opening through the stainless steel is larger than the opening through the copper such that the edges of the aperture  882  are defined by copper. The feature datum  880  is preferably positioned approximately equidistant between adjacent bond pads  824   a  and  824   b . The copper region  884  is electrically connected to or bussed to bond pad  824  via a bus  884   a.    
     Feature datum  880  is generally similar to that the feature datum  180  shown generally in  FIG. 2 , and remains visible following installation of a head slider  130  to a slider mounting surface  811  on the flexure  304  (shown in dotted lines). However, feature datum  880  is electrically coupled to bond pad  824  via the bus  884   a . This electrical interconnection facilitates an electro-plating process that may be used to deposit gold onto the copper region as is known in the art. According to the present example, an electrical current applied to the integrated leads  820  and bond pads  824  for the purpose of electro-plating will also be applied to the datum feature  880 . It is not necessary to apply a separate electrical current to the feature datum  880 , as would be necessary were the feature datum  880  electrically isolated from the remaining copper features as is the feature datum  180  shown generally in  FIG. 2 . 
     Although the present invention has been described with reference to preferred embodiments, those skilled in the art will recognize that changes can be made in form and detail without departing from the spirit and scope of the invention.