Abstract:
In an Integrated Lead Suspension system, it is desired that the stainless steel suspension is grounded to a controlled ground potential. This requires creating a grounding path between the stainless steel suspension and a copper trace layer through a layer of dielectric material that separates the stainless steel suspension and the copper layer. The copper trace layer and subsequently the stainless steel suspension can then be grounded to a controlled ground potential. 
     This invention proposes several methods of creating a ground path between the stainless steel suspension and the copper trace layer.

Description:
FIELD OF THE INVENTION 
     The present invention relates to electrical grounding circuitry for magnetic disk drives and more particularly to grounding schemes designed to protect against electrostatic discharge (ESD) and electrical overstress (EOS), and to reduce background noises in read/write transducers utilizing magnetoresistive read sensors. 
     DESCRIPTION OF THE RELATED ART 
     Magnetic head disk drive systems have been widely accepted in the computer industry as a cost-effective form of data storage. In a magnetic disk drive system, a magnetic recording medium in the form of a disk rotates at high speed while a magnetic read/write transducer, referred to as a magnetic head, “flies” slightly above the surface of the rotating disk. The magnetic disk is rotated by means of a spindle drive motor. The magnetic head is attached to or formed integrally with a “slider” which is suspended over the disk on a spring-loaded support arm known as the actuator arm. As the magnetic disk rotates at operating speed, the moving air generated by the rotating disk in conjunction with the physical design of the slider lifts the magnetic head, allowing it to glide or “fly” slightly above and over the disk surface on a cushion of air, referred to as an air bearing. The flying height of the magnetic head over the disk surface is typically only a few tens of nanometers or less and is primarily a function of disk rotation, the aerodynamic properties of the slider assembly and the force exerted by the spring-loaded actuator arm. 
     A major problem that is encountered during manufacture, handling and use of magnetic recording transducers, referred to as heads, is the buildup of electrostatic charges on the various elements of a head or other objects which come into contact with the heads, particular heads of the thin film type, and the accompanying spurious discharge of the static electricity thus generated. Static charges may be produced for example by the presence of certain materials, such as plastics, during manufacture and subsequent handling of the heads. These static charges arc across the edge of the insulating layer between the magnetic pole tips and adjacent conductive layers which are exposed and positioned adjacent to the transducing gap at the air bearing surface facing the recording medium thus causing erosion of the pole tips and degradation of the transducer in reading and writing of data. 
     As described above, when an MR sensor is exposed to ESD, or even a voltage or current input larger than that intended under normal operating conditions, referred to as electrical overstress or EOS, the MR sensor and other parts of the head may be damaged. This sensitivity to electrical damage is particularly severe for MR read sensors because of their relatively small physical size. For example, an MR sensor used for extremely high recording densities will have a cross-section of 100 Angstroms (.ANG.) by 1.0 micrometers (um) or smaller. Discharge of voltages of only a few volts through such a physically small sensor, behaving like a resistor, is sufficient to produce currents capable of severely damaging or completely destroying the MR sensor. The nature of the damage which may be experienced by an MR sensor varies significantly, including complete destruction of the sensor via melting and evaporation, contamination of the air bearing surface, generation of shorts via electrical breakdown, and milder forms of damage in which the head performance may be degraded. 
     Magnetoresistive sensors, also referred to as “MR heads,” are particularly useful as read elements in magnetic transducers, especially at high data recording densities. The MR sensor provides a higher output signal than an inductive read head. This higher output signal results in a higher signal-to-noise ratio for the recording channel and allows higher areal density of recorded data on a magnetic disk surface. 
     Another method to increase the signal-to-noise ratio and therefore the areal density of recorded data on a magnetic disk surface is to decrease the noise. Noise is introduced into the MR head readings by the MR head and slider picking up undesirable external voltage/EMF fluctuations during operation of the disk drive. The noise can be reduced if the MR head and slider is properly grounded. 
     Kudo et al. U.S. Pat. No. 5,657,186 discloses a method of electrically connecting a slider to a grounding pad via a conductive resin. 
     A need therefore exists for providing a layer assembly that can be grounded to a desired potential. 
     SUMMARY OF THE INVENTION 
     A principle objective of the present invention is to provide a method to ground the stainless steel layer of an Integrated Lead Suspension (ILS) to a controlled ground potential. 
     In view of the foregoing objects, the present invention provides several methods to bring the stainless steel layer into contact with the copper layer through a layer of dielectric material. The first of these methods consist of creating a via from the copper layer, through the dielectric layer and onto the stainless steel layer exposing the surface of the stainless steel layer through the via. Conductive adhesive is then used to fill the via, creating a ground path between the stainless steel layer and the copper layer. The same can be done from the stainless steel to the copper layer. Instead of opening the via from copper layer to stainless steel layer, the via is opened from the stainless steel layer to the surface of the copper layer through the dielectric layer. 
     Instead of using conductive adhesive glue, solder can be used to create a grounding path between the copper layer and the stainless steel layer. 
     An alternative method calls for the recess of the copper layer layer and the dielectric layer, exposing the stainless steel layer. Solder is applied to the edge of this recess that overhangs the stainless steel and makes contact between the copper layer and the stainless steel layer. 
     A rivet can also be used to make contact between the copper layer and the stainless steel layer. A through hole is created through all three layers and a rivet attached that clamps down on the copper layer and the stainless steel layer. 
     A copper finger can also be used to make contact between the copper layer and the stainless steel layer. This method entails etching a copper finger which is connected to the copper layer. This copper finger is then pressed into contact with the stainless steel layer and welded in place. 
     The copper finger can also be sandwiched between the mount plate and the arm at the swage or between the mount plate and load beam at the layer weld process. 
     An alternative embodiment would be to create a via through the stainless steel layer and the dielectric layer to the surface of the copper layer. A dimple is then created on the load beam and during the assembly process, the load beam is pressed on top of the stainless steel layer and the dimple on the load beam is placed in the via. The dimple will make contact with the copper layer creating a ground path from the copper layer to the stainless steel layer. 
     Another embodiment is to punch a through hole through all three layers. By punching a through hole, the stainless steel will smear through the dielectric layer and make contact with the copper layer. Alternatively, the through hole can be punched through the copper layer to the stainless steel layer and in this case, the copper will smear through the dielectric layer and make contact with the stainless steel layer. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing and other objects, features and advantages of the present invention will be apparent from the following detailed description of the preferred embodiments of the invention, reference being made to the accompanying drawing, in which like reference numerals indicate like parts and in which: 
     FIG. 1 a  is an illustration showing elements of a first embodiment of the present invention; 
     FIG. 1 b  is an illustration showing the elements of FIG. 1 a  assembled on a slider arm; 
     FIG. 2 is an illustration showing the second embodiment of the present invention; 
     FIG. 3 is an illustration showing the third embodiment of the present invention; 
     FIG. 4 is an illustration showing the fourth embodiment of the present invention; 
     FIG. 5 is an illustration showing the fifth embodiment of the present invention; 
     FIG. 6 is an illustration showing a close up view of the fifth embodiment of the present invention; 
     FIG. 7 is an illustration showing the sixth embodiment of the present invention; 
     FIG. 8 is an illustration showing the seventh embodiment of the present invention. 
     FIG. 9 schematically depicts a hard disk drive. 
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Although the invention is described as embodied in a magnetic disk storage system, the invention also applies to other magnetic recording systems and applications using a sensor to detect a magnetic field, such as magnetic tape recording systems for example. 
     FIG. 1 illustrates an ILS with an embodiment of the present invention. A via is created in the ILS through the stainless steel layer  212  at  204 , the polymide layer  210  at  202 , and the copper layer  208  at  200  that exposes the arm surface. A drop of conductive adhesive is placed in the via to connect the stainless steel layer through the polymide layer to the copper layer and the arm surface. 
     FIG. 2 illustrates a second embodiment of the present invention. A via  300  is opened in the ILS from the copper layer  306  through the polymide layer  304  to the stainless steel layer  302  or alternatively from the stainless steel layer  302  through the polymide layer  304  to the copper layer  306 . This via  300  can be a round shape via  316  or a cross shaped via  314  which provides a larger contact surface for better grounding. Instead of using a drop of conductive adhesive, plated solder  310  or screen solder  312  can be used to connect the stainless steel layer to the copper layer. With either method, the solder is reflowed  318  for increased adhesion to the underlying material. 
     Instead of a via, stepped-back edges  320  can be used. With stepped-back edges, the copper layer  306  or the stainless steel layer  302  and the polymide layer  304  are intentionally stepped back to expose the lower layer. For example, when the copper layer  306  is stepped back, the stainless steel layer  302  is exposed. Solder  308  or conductive adhesive can be applied to over hang the stepped back edge to connect the upper layer with the lower layer. 
     FIG. 3 illustrates another embodiment of the present invention. A through hole  408  is made through the copper layer  402 , the polymide layer  404 , and the stainless steel layer  406 . A rivet  400  is then used to connect the copper layer  402  to the stainless steel layer  406 . 
     FIG. 4 illustrates another embodiment of the present invention which incorporates other components of the suspension, namely the load beam  508 . Connected to the copper layer  500  is a copper finger  506  that overhangs the polymide layer  502 , the stainless steel  504  and the load beam  508 . This copper finger  506  can be etched from the copper layer  500 . The copper finger  506  is pressed and welded into place in contact with the load beam  508 . Alternatively, the stainless steel layer  504  is extended so that the copper finger  506  may be pressed onto the stainless steel layer  504  and welded in place. 
     FIG. 5 illustrates another embodiment of the present invention. A copper finger is etched from the copper layer as illustrated in the previous embodiment of the present invention. This copper finger is then sandwiched between the mounting plate  604  and the arm during the assembly process. In this illustration, a swage process for a higher level assembly to the arm is shown. This illustration depicts a suspension design that has its load beam integrally manufactured from the ILS steel layer  602 . More traditionally and well known in the art is to weld a separate load beam onto the ILS and mount plate  604 . In this type of welding process for suspension assembly the copper finger can be sandwiched between the mount plate  604  and the separately fabricated load beam. 
     FIG. 6 illustrates a close up view of the copper finger  700  in the previous embodiment of the present invention being sandwiched between the mounting plate  702  and the arm during the swage process for higher level of assembly to the arm. 
     FIG. 7 illustrates another embodiment of the present invention. A dimple  808  is created on the load beam steel  810 . In the ILS, a via  812  is created through the stainless steel layer  802  and the polymide layer  804  exposing the copper layer  806 . During assembly, when the load beam and the ILS are assembled, the load beam will be in surface contact with the stainless steel layer of the ILS and the dimple is placed in the via  812  and pressed into contact with the copper layer  806 . This will create a grounding path between the stainless steel layer  802  of the ILS and the copper layer  806 . 
     FIG. 8 illustrates another embodiment of the present invention. A punch  900  is used to punch a hole through all three layers of the ILS. The copper layer  906  and the stainless steel layer  902  are harder that the polymide layer  904  material and will smear through the polymide layer as illustrated by  908 . This will create a grounding path  908  between the copper layer  906  and the stainless steel layer  902 . 
     The above methods illustrates how to create a grounding path between the stainless steel layer and the copper layer of the ILS. The copper layer and in turn the stainless steel layer can be grounded to a controlled ground via a dedicated grounding path etched in the copper layer to a grounding terminal. 
     The above methods can also be altered to provide methods of creating grounding paths between multiple layers of copper and stainless steel. The top-most conductive layer that is to be connected to the grounding path in a two or more layer structure is herein referred to as the top grounded layer. There may be one or more conductive layers that reside on top of the top grounded layer which is not connected to the grounding path and therefore is not the top grounded layer. Conductive layers below the top grounded layer are referred to as underlying conductive layers. 
     An integrated lead suspension (ILS) can utilize any of these methods to create a ground path from the stainless steel layer to the copper layer, which can then be ground to a controlled ground potential. 
     A hard drive shown in FIG. 9 which contains a magnetic disk  1004 , a read/write head  1002 , can also contain an integrated lead suspension  1000  with a grounding path between the stainless steel layer and the copper layer manufactured using any of these methods. 
     It will be clear to one skilled in the art that the above embodiment may be altered in many ways without departing from the scope of the invention. Accordingly, the scope of the invention should be determined by the following claims and their legal equivalents.