Abstract:
The present invention couples shunting pads to the conductor leads of a suspension assembly for supporting a slider in a magnetic storage system, which can be use to temporarily shunt the leads to prevent against damage to the heads by electrostatic discharge. In one embodiment, the suspension assembly includes shunting pads that are sized and positioned to allow shunting using a probe. In another embodiment, a suspension assembly includes a built-in shunting tab that when applied, temporarily shunts the MR read head and prevents any transient voltage from developing across the head. In a further embodiment a tool having multiple probes is integrated into a jig, which is used for holding and shunting one or more suspension assemblies during processing. In one embodiment, the present invention is applied to an integrated lead suspension assembly.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    This invention relates in general to protection against damage to magnetic head assemblies caused by electrostatic discharge (ESD) during handling and assembly thereof on a suspension assembly for a magnetic storage device, and more particularly to a method of protecting a magneto-resistive (MR) head attached to a suspension assembly against damage caused by ESD.  
           [0003]    2. Description of Related Art  
           [0004]    MR sensors are well known and are particularly useful as read elements in thin film heads (“MR heads”) for sensing recorded signals on magnetic disks in magnetic disk drive systems used in the computer industry. A typical MR head includes a thin strip of magnetoresisitive material that is positioned between a pair of thin film gap layers, which are in turn sandwiched between a pair of thin film shield layers. The MR head along with a write transducer, which is used for recording information to the magnetic disk, are manufactured using thin film and photolithography process, as part of a slider. The slider is attached to the tip of a flexible member that is cantilevered from an actuator arm for positioning the head relative to the magnetic disk surface to perform read and write operations. This head and suspension assemblage is often referred to in the industry as a head-gimbal assembly or HGA.  
           [0005]    As the storage density of disk drives increase, the size of the MR heads are reduced, making it increasingly vulnerable to damage caused by ESD. A major problem that is encountered during manufacture, handling and use of MR heads is the buildup of electrostatic charge on various objects, such as assembly tools and fixtures which come into electrical contact with the heads. The discharge of electrostatic voltages of only a few volts through the MR heads is sufficient to produce electrical current capable of severely damaging or completely destroying the MR heads. Manufacturing yields can therefore be negatively affected because ESD damage may be introduced at any stage during the assembly of the disk drive, and the damaged MR head can only be practically tested and discovered towards the end of the manufacturing process. For those MR heads which were degraded as a result of damage during processing but which passed initial acceptance tests by the manufacturer, the performance, reliability, and service life of the assembled magnetic disk drive having the damaged heads are put into question.  
           [0006]    There have been a number of ESD protection schemes adopted in the past. U.S. Pat. No. 5,710,682 assigned to International Business Machines Corporation disclosed an ESD protection scheme for an integrated suspension assembly of the type that uses twisted leads for the read head, which deploys a shorting bar that automatically shorts the read head prior to final assembly. A shorting bar attached to the actuator arm automatically shunts the lead wires of the read head upon absence of support for the record head. This provides an electrostatic discharge path around the read head, rather than through it.  
           [0007]    In an integrated lead suspension (ILS) assembly, integrated conductor leads or traces are formed in a layer on the surface of the flexure, instead of twisted wire as described above in U.S. Pat. No. 5,710,682. ILS assemblies are significantly smaller in dimensions compared to integrated suspension assemblies, with leads/traces that are formed in close tolerance and clearance. The leads terminate on contact pads at the end face of the slider; one pair of leads is in electrical connection with the MR head and the other pair of leads is in electrical connection with a write transducer. The other ends of the leads terminate in a multiconnector that extends from the load bearing support structure (e.g., the load beam) of the ILS assembly. For ESD protection, a removable short-shunting strip is provided at the multiconnector to provide an effective means of temporarily protecting the read and write heads from ESD. In the ILS assembly process, the short-shunting strip is maintained, but it must be removed when the ILS assembly is ready to be tested for its functionality or to be installed in a disk drive.  
           [0008]    While these earlier schemes were satisfactory in reducing ESD damage to the MR heads in an ILS assembly, they are not without limitation. If the shunting strip remains on the ILS, it is impossible to conduct functionality tests on either MR read sensor, write transducer, or a combination of the two. The shunting strip shunts the ESD transient, but also shunts the signal from the sensors. As a consequence, the shunting strip becomes an issue in the quality control of disk drives. It should be removed at some point in time in the ILS assembly process.  
           [0009]    In the past, during the removal of the short-shunting strip, an ESD event may result from static buildup on a tool used to separate the strip, which for example can be an electrically conductive scissor. If the electrical current is large enough, damage can occur to part or all of the recording head. What is needed is a more reliable method for protecting the MR head of an ILS assembly from an ESD event. ESD protection schemes designed for integrated suspension assemblies with twisted wire can be difficult to implement or are not suitable for ILS assemblies, due to the significant size differences between the two types of assemblies. Further, once the short-shunting strip is removed, there is no shunting of ESD available when the ILS assembly is subsequently being handled. It is therefore desirable to provide a means for shunting that remains available on the ILS.  
         SUMMARY OF THE INVENTION  
         [0010]    The present invention overcomes the drawbacks of the prior art and allows functional tests to be conducted while MR heads remain ESD protected during the suspension manufacturing process. One aspect of the present invention provides at least two levels of ESD protection, shunting and grounding of a suspension assembly. Shunting is typically done by shorting the sensors to shunt the transient current to prevent the full amplitude of the current to pass through and damage the sensors. Grounding eliminates the transient current from reflecting back and forth in the circuit that consists of the sensors. Grounding provides a means of leveling off any electrical voltage offset between the suspended heads and objects such as tools, human bodies, or anything else that makes contact with the sensors. Shunting and grounding may be alternatively implemented to provide ESD protection. However, grounding coupled with shunting provides the most effective ESD protection.  
           [0011]    For purpose of illustrating the principles of the present invention and not limitation, the present invention is described by reference to an Integrated Lead Suspension (ILS) assembly. However, it is understood that the present invention can be implemented generally to other types of suspension assemblies without departing from the scope or spirit of the present invention.  
           [0012]    In the described embodiment, the present invention couples shunting (shorting) pads to the conductor leads of a suspension assembly, which can be used to temporarily shunt (short) the leads to prevent damage to the heads by ESD. In one embodiment, the suspension assembly includes shunting pads that are sized and positioned to allow shunting and/or grounding using a probe. In another embodiment, a suspension assembly includes a built-in shunting tab that when applied, temporarily shunts the MR read head and prevents any transient voltage from developing across the head. In a further embodiment, a tool having multiple probes is integrated into a jig, which is used for holding and shunting and/or grounding one or more suspension assemblies during processing. The present invention thus provides for functional tests to be conducted while MR heads remain ESD protected during the suspension manufacturing process.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    For a fuller understanding of the nature and advantages of the invention, as well as the preferred mode of use, reference should be made to the following detailed description read in conjunction with the accompanying drawings. In the following drawings, like reference numerals designate like or similar parts throughout the drawings.  
         [0014]    [0014]FIG. 1 is a perspective view of an ILS assembly embodying ESD protection in accordance with one embodiment of the present invention;  
         [0015]    [0015]FIG. 2 is an enlarged top view of the shunting (shorting) pad region, in accordance with one embodiment of the present invention;  
         [0016]    [0016]FIG. 3 is a top view of an ILS assembly with an integrated shunting tab in accordance with one embodiment of the present invention;  
         [0017]    [0017]FIG. 4 is a sectional view of a shunting tab taken along line  4 - 4  in FIG. 3.  
         [0018]    [0018]FIG. 5 is a top view of the ILS assembly attached to a jig having an integrated shorted probe tool (preferably grounded) in accordance with one embodiment of the present invention; and  
         [0019]    [0019]FIG. 6 is a simplified block diagram of a magnetic disk storage system embodying the present invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0020]    This invention is described in a preferred embodiment in the following description with references to the following figures. While this invention is described in terms of the best mode of achieving this invention&#39;s objectives, it will be appreciated by those skilled in the art that variation may be accomplished in view of these teachings without deviating from the spirit or scope of the invention. It is noted that the present invention is described, by way of example and not limitation, in reference to ILS. It is understood that the ESD protection concept of the present invention can be generally applied to suspension assemblies of other types.  
         [0021]    Referring now to the drawings, FIG. 1 shows a perspective view of an ILS  50  and FIG. 2 shows a magnified view of the shunting pad region  46  of the ILS  50 . The ILS  50  is coupled to an actuator arm  52  (also shown in FIG. 6) that pivotally supports the ILS  50 . The ILS  50  comprises a load beam  58  and a flexure  60  including a section  62 . One end of the load beam  58  is attached to the actuator arm  52 , and the other end supports on its surface the flexure  60 . Bonded to the distal end of the flexure  60  is a slider  48 , comprising an integrated MR read head  65  and an inductive write transducer  66 . The flexure  60  includes an integrated assembly of a layer of flexible material  61 , such as stainless steel, and electrical conductive leads, such as conductive traces in the case of an ILS (e.g. MR read head conductor leads  20  and inductive write transducer conductor leads  22 ; which in combination will be referred to as integrated conductor leads). MR read head conductor leads  20  and inductive write transducer conductor leads  22  supported on the flexible material  61  and separated by an insulating layer. One end of the MR read head conductor leads  20  terminates at the slider  48 , where it is attached to and forms an electrical connection with the MR read head  65 . The other end of the leads terminates in a wire ribbon and multiconnector  30  that extends from the load bearing support structure (i.e., the multiconnector  30  is not supported against the surface of the actuator arm  52  or the load beam  58 ). The multiconnector  30  is used to electrically connect the slider  48  to the electronics of the control unit  56  (as shown in FIG. 6). A short-shunting strip  63  is connected to the multiconnector  30  for electrically shunting the inductive write transducer  66  and integrated MR read head  65  to prevent ESD during general manufacture and assembly processes.  
         [0022]    Along the MR read head conductor leads  20  are two integrated ESD shunting pads  32 , one for each of the separate conductor leads  20 . The two shunting pads  32  are formed as part of the layering and etching process along with the integrated conductor leads during flexure fabrication. The shape of the shunting pads  32  may be circular, square, or other shape, of a size that is relatively large to provide optimum surface area for a probe tab (as shown in FIG. 5) or other similar device to make contact with it. For example, for a suspension having a length on the order of 25 mm, the leads  20  may be on the order of 60 μm wide, and the pads may be on the order of about 125×125 μm square. The shunting pads  32  are located on any region of the suspension  50  that provides sufficient clearance for contact to be made by the shunting devices mentioned above. As shown in the figures, the shunting pads  32  may be located on the section  62  that supports the integrated conductor leads. Other locations on the suspension  50  may also be suitable for the shunting pads  32 . Preferably, the shunting pads will be located away from the slider  48 , somewhere between the mid-section and the actuator end of the suspension  50 , where larger structural surface area and clearance are available for supporting the pads.  
         [0023]    Additional shunting pads  33  or similar structure can be incorporated into the inductive write transducer conductor leads  22  for providing ESD protection to the inductive write transducer  66  in a manner similar to the shunting pads  32  for the integrated MR read head  65 . One end of the inductive write transducer conductor leads  22  is attached to and forms an electrical connection with the inductive write transducer  66  and the other lead terminates at the multiconnector  30 .  
         [0024]    [0024]FIG. 3 and FIG. 4 show another embodiment of the present invention comprising an ILS  50  having a shunting tab  102 , located near the integrated MR read head shunting pads  32 . The shunting tab  102  is generally rectangular shaped and preferably made with a spring material such as stainless steel, copper, Kovar, etc. In one embodiment, the shunting tab  102  can also be made with a non-conductive material, such as ESD dissipative plastics. Additionally, the shunting tab  102  can have a line of perforation  103 , preferably as low as possible towards the base of the ground tab  102  to help facilitate the mechanical removal of the shunting tab  102  when desired. Attached to the underside of the shunting tab  102  (the side facing the shunting pads  32 ) are two contact pads  53  that are connected to a pair of conductor leads  104 . The contact pads  53  can be made with a conductive material or an ESD dissipative material such as zirconia ceramic (on the order of 10 9  ohms) and the conductor leads  104  typically consist of a wire or printed wire on Mylar material. The conductor leads  104  run along the section  62  and terminate into two access pads  105  (as shown schematically in FIG. 3) that can either be attached to an area of the ILS  50  or extends beyond the ILS  50 . The access pads  105 , which are larger in planar area than the shunting pads  32 , facilitate probing using probes  106 . The probes  106  may be applied for conducting continuity checks, testing the MR head and write transducer, grounding and/or shorting the conductor leads  20  and  22  to the slider  48 .  
         [0025]    It can be appreciated that the larger access pads  105  are easier to work with using the probes  106 , compared to the smaller shunting pads  32 . The contact pad  53  on the shunting tab  102  is aligned with the shunting pads  32  such that when the shunting tab  102  is depressed towards the flexure, the contact pad  53  and shunting pad  32  contact each other. Probes  106  may be shorted and/or grounded. During the time that the shunting pads  32  are in contact with the contact pads  53 , the integrated MR head  65  is shorted (e.g., via leads  104  and access pads  105 ), thereby protecting it from ESD damage. When pressure is removed from the shunting tab  102 , the contact pads  53  and shunting pads  32  are separated.  
         [0026]    In another embodiment, the shunting tab  102  can be made with a conductive material such as stainless steel, to which the contact pads  53  are attached. When the shunting tab  102  is depressed towards the flexure, the contact pads  53  contact the shunting pads  32  and short the integrated MR head  65 , protecting it from ESD damage. In addition, the entire shunting tab  102  may be grounded via a conductor lead to a grounding point (not shown), in a similar fashion as the leads  104  in FIG. 4.  
         [0027]    During assembly, in order to test the integrated MR read head  65  are installed on the ILS  50 , the short-shunting strip  63  needs to be removed from the multiconnector  30  (as shown in FIG. 1). A cutting tool such as a pair of scissors is used to remove the short-shunting strip  63 . If the scissor is not designed for ESD protection then it is possible for the scissor to hold a static charge, which can be released upon contact through the integrated conductor leads, and into the integrated MR read head  65  and or inductive write transducer  66 . Static buildup on the scissor is possible if, for example, the scissor contains metal blades and a plastic handle. To prevent the described ESD damage from occurring, the shunting tab  102  is depressed prior to the removing the short-shunting strip  63  from the multiconnector  30 . By providing a shunting tab  102 , additional shunting may be undertaken when needed during subsequent manufacturing steps and handling of the ILS. At the point of final assembly, the shunting tab  102  may be physically and permanently removed if desired, for example by snapping off the tab  102  from the ILS  50 .  
         [0028]    [0028]FIG. 5 is a schematic view of a jig  130  and tool  120  used to hold and protect the ILS  50  from ESD damage during its assembly. The tool  120  comprises of a pair of probes  121  which make contact with the shunting pads  32  when activated. The tool  120  is applied to the jig  130  by means of a robotic structure, for example, a hinge or track (not shown). The jig  130  provides automated accurate positioning of the tool  120  for probing the shunting pads  32  (if shunting tab  102  has been removed or not been utilized) and/or access pad  105  (using probes  106 ; if shunting tab  102  is still in place). The tool  120  may also be shorted to provide a shunt and/or electrically grounded to dissipate any transient current that may otherwise reach and damage the MR head.  
         [0029]    The probes are made with an electrically conducting material or contain grounded tips made of such material. The diameter of each probe tip is typically less than the diameter of the shunting pads  32  to reduce the chances of it contacting surrounding parts.  
         [0030]    To verify that contact has been made between the tool  120  and the shunting pads  32 , the resistance of the integrated MR read head  65  can be measured through the tool  120  by using a resistance meter  140 . Typically, a functioning integrated MR read head  65  may have a resistance on the order of 40 ohms. If, for example, the measurement from the resistance meter  140  indicates a relatively large resistance, this can either indicate that the integrated MR read head  65  is defective or that the tool  120  is not securely contacting the shunting pads  32 . Reference may be made to U.S. Pat. No. 5,959,827, assigned to IBM Corporation, which discloses a grounding unit, which may be modified to facilitate probing (e.g., testing, shunting and/or grounding) the ILS  50  with shunting pads  32  in accordance with the present invention. While FIG. 5 shows the operation of the jig  130  and tool  120  for one ILS assembly, it is within the scope and spirit of the present invention to scale up the jig  130  and tool  120  to allow probing of more than one ILS assemblies, either simultaneously or in sequence.  
         [0031]    While the foregoing discussions were in reference to shunting pads  32  for the MR read head  65 , they are also applicable to the shunting pads  33  for the inductive write transducer  66 . The MR read head  65  and the inductive write transducer  66  can be probed simultaneously or in sequence if necessary. In the case of shunting the inductive write transducer  66 , while the inductive write transducer  66  is not as ESD sensitive as the MR read head  65 , an ESD transient through a inductive write transducer  66  can be introduced to the MR read head  65  by capacitance coupling, for example, of integrated leads (for both read and write). Ideally, both the MR read head  65  and the inductive write transducer  66  should be shunted for the best ESD protection on the MR read head  65 .  
         [0032]    [0032]FIG. 6 illustrates a simplified schematic block diagram of a magnetic disk storage system  100  embodying the ILS in accordance with the present invention. The magnetic disk storage system comprises at least one rotatable magnetic disk  82  which is supported on a spindle  26  and rotated by a disk drive motor  30 , and at least one slider  48  positioned in close proximity to the magnetic disk  82  at the disk surface  36 . Data is stored on each disk  82  in the form of an annular pattern of concentric data tracks (not shown). Each slider  48  contains one or more integrated MR read heads  65  and inductive write transducers  66  which are attached to an actuator arm  52  by means of a suspension assembly  50 . Each actuator arm  52  is attached to an actuator  42 . The actuator as shown in FIG. 1 may be a voice coil motor (VCM). As the disk  82  rotates, the slider  48  is controlled to move across the disk surface  36  by the actuator  42  so that the slider  48  may access different portions of the disk surface  36  where desired data is recorded or read. The slider  48  flies in close proximity over the rotating disk surface  36 , riding on an air bearing  70  formed between the magnetic head&#39;s MR read heads  65 , inductive write transducers  66  and the rotating disk surface  36 . The ILS  50  provides a slight spring force which biases the slider  48  against the disk surface  36  and controls flexibility in slight vertical as well as roll and pitch movements of the slider  48  relative to the rotating disk surface  36 . The various components of the magnetic disk storage system are controlled in operation by control signals generated by the control unit  56 , such as drive motor signals of line  38 , head position and seek control signals on line  44 . Read and write signals are communicated to and from MR read head  65  and inductive write transducer  66  by means of a recording channel  40 . All of the components of the magnetic disk storage system are enclosed in housing  45 .  
         [0033]    In summary, the present invention provides a method of protecting the integrated transducers of a suspension assembly from an ESD event by providing shunting pads that are directly attached to the integrated conductor leads and which can be shorted and/or grounded by various means as described in the different embodiments. The shunting pads can provide ESD protection during and after removal of the prior art short-shunting strip because the pads are permanently attached to the suspension. In addition, the shunting pads are supported on the load bearing structure of the suspension, thus providing a stable structure for applying the shunting tab or probe. The built-in shunting tab provides an additional advantage of being reusable at anytime the suspension is handled during assembly and does not require a shunting probe.  
         [0034]    While the present invention has been described with respect to the preferred embodiments in accordance therewith, it will be apparent to those in the skilled art that various modifications and improvements may be made without departing from the scope and spirit of the invention. Accordingly, the disclosed invention is to be considered merely as illustrative and limited in scope only as specified in the appended claims.