Patent Publication Number: US-6905394-B2

Title: Apparatus and method for polishing row bars

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to the production of a magnetic head sliders used in magnetic disk apparatuses. More specifically, the present invention relates to an apparatus for polishing a row bar including magnetic head sliders and to a polishing method. 
   2. Description of the Related Art 
   Magnetic head sliders used in the magnetic disk apparatuses are, first, prepared in a large number in the form of a wafer by a film forming technology. The wafer is then cut into row bars including a plurality of magnetic head sliders. The row bars are then polished so that the floating surfaces of the magnetic head sliders become smooth, and are then cut into individual magnetic head sliders. 
   The row bar is polished through two steps, i.e., an initial polishing (ELG polishing) and a finish polishing (touch lap polishing or crown polishing). The polishing of a row bar is disclosed in, for example, Japanese Unexamined Patent Publication (Kokai) No. 2002-157723, and U.S. Pat. No. 6,375,539. The finish polishing is conducted to release the bending stress in the row bar after the initial polishing, to further improve the smoothness of the surface and to form a crown on the surface. 
   In the finish polishing, for example, a lapping surface plate having a spherical surface is used, the row bar is adhered to a jig made of an elastic member, and the polishing is carry out by pressing the row bar adhered to the elastic member against the rotating lapping surface plate. 
   The row bar is adhered to the elastic member and the positioning of the elastic member is difficult, so laborious work is required for precisely positioning the row bar and, besides, polishing the row bar is apt to be affected by a change in the surface state of the elastic member. Besides, as the row bar is held by the elastic member, the terminals of resistance elements of the row bar cannot be bonded to the terminals of a measuring device with bonding wires, so the resistance cannot be measured in the inprocess condition and is apt to be affected by the lapping rate, giving rise to the occurrence of defects such as over-cutting. 
   SUMMARY OF THE INVENTION 
   It is, therefore, an object of the present invention to provide an apparatus and a method for polishing a row bar of magnetic head sliders, capable of controlling the pushing pressure for the individual magnetic head sliders provided in the row bar to precisely polish the row bar. 
   Another object of the present invention is to provide an apparatus and a method for polishing a row bar of magnetic head sliders, capable of measuring the resistance during the inprocess operation. 
   An apparatus for polishing a row bar including magnetic head sliders, according to the present invention, comprises: a rotatable lapping surface plate; a movable housing above the lapping surface plate; a jig secured to the housing and comprising a rigid member having a plurality of holes and an elastic member fixed to the rigid member for holding a row bar; first pressing means for applying a pressure to the whole row bar; and second pressing means for the individually pressing portions of the elastic member corresponding to a plurality of magnetic head sliders of the row bar through the holes in the rigid member. 
   In this constitution, the jig comprising the rigid member and the elastic member can be easily and reliably secured to the housing so that it can easily and reliably hold the row bar at a predetermined position. The row bar can be held by the elastic member, by bringing the row bar into intimate contact with the elastic member, even if the row bar is not adhered to the elastic member. The pressing force applied to the elastic member through the holes in the rigid member is transmitted to the row bar to correct the shape of the row bar. 
   A method of polishing a row bar including magnetic head sliders, according to the present invention, comprises the steps of: securing a jig to a movable housing, the jig including a rigid member having a plurality of holes and an elastic member fixed to the rigid member; holding a row bar by said jig; moving the housing above a lapping surface plate; turning the lapping surface plate to polish the row bar while pressing the row bar onto the lapping surface plate; measuring a changes in the resistance of resistance elements provided in the row bar; and individually pressing portions of the elastic member corresponding to a plurality of magnetic head sliders of the row bar through the holes of the rigid member in response to a change in the resistance of resistance elements provided in the row bar. 
   In this constitution, the jig comprising the rigid member, and the elastic member, can be easily and reliably secured to the housing and the resistance of resistance elements provided in the row bar can be measured in the inprocess condition, whereby the portions of the elastic member corresponding to the magnetic head sliders of the row bar can be individually pressed with variable forces in response to the measured value. The polishing is finished when the target resistance is reached to accomplish more precise polishing. 
   In lapping the magnetic head sliders, according to the present invention as described above, it is allowed to control the pressing force for each of the magnetic head sliders in the row bar, and a row bar of any shape can be corrected to be as straight as possible, making it possible to provide magnetic head sliders with good precision. In the apparatus of the static pressure type, in particular, no complex or fine mechanism is employed. Therefore, the unit is assembled through a very decreased number of steps accompanied by very decreased defects. Besides, as compressed air is directly used, dispersion is decreased in the thrust produced through the individual holes, and a highly precise control is accomplished. Besides, the resistance elements in the row bar are connected, by bonding wires, to the terminals of a relay board, to measure the resistance in the inprocess condition, which makes it possible to effect the lapping with high precision. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will become more apparent from the following description of the preferred embodiments, with reference to the accompanying drawings, in which: 
       FIG. 1  is a view illustrating a wafer in which many magnetic head sliders are fabricated; 
       FIG. 2  is a view illustrating a row bar cut from the wafer of  FIG. 1 ; 
       FIG. 3  is a schematic plan view illustrating a lapping surface plate, and a housing supporting the row bar, which are parts of the apparatus for polishing the row bar; 
       FIG. 4  is a schematic side view illustrating the polishing apparatus; 
       FIG. 5  is a sectional view illustrating the lapping surface plate, the housing and the jig of the polishing apparatus on an enlarged scale; 
       FIG. 6  is a view illustrating a drive mechanism for applying a force to a pin to move the pin; 
       FIG. 7  is a perspective view illustrating the jig comprising a rigid member and an elastic member; 
       FIG. 8  is a sectional view illustrating the lapping surface plate, the housing and the jig of the polishing apparatus according to another embodiment; 
       FIG. 9  is a view illustrating the holder, the jig and the air tube of  FIG. 8 ; 
       FIGS. 10A to 10C  are views illustrating air feed holes of  FIGS. 8 and 9 ; 
       FIG. 11  is a perspective view illustrating a jig comprising a rigid member and an elastic member; 
       FIG. 12  is a view illustrating an embodiment for measuring the resistance in the inprocess condition; and 
       FIG. 13  is a view illustrating an example of effecting the wire bonding regarding the embodiment of  FIG. 12 . 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The preferred embodiments of the present invention will now be described with reference to the drawings. 
     FIG. 1  is a view illustrating a wafer in which a number of magnetic head sliders are fabricated. The wafer  10  includes many magnetic head sliders  12  fabricated therein by known technology.  FIG. 2  is a view illustrating a row bar  14  cut from the wafer  10  of  FIG. 1 . The row bar  14  includes a plurality of magnetic head sliders (MR heads)  12 . An ELG resistance element  16  is provided in a boundary between the two magnetic head sliders  12 . 
   The surface of the row bar  14  which serves as a floating surface is polished. The row bar  14  is polished through two steps, i.e., an initial polishing (ELG polishing) and a finish polishing (touch lap polishing or crown polishing). The present invention is related to the finish polishing of the row bar  14  after the initial polishing is carried out. 
     FIG. 3  is a schematic plan view illustrating a lapping surface plate  22 , and a housing  24  supporting the row bar  14 , which are parts of the apparatus for polishing the row bar  14  including a plurality of magnetic head sliders  12 . The operation for polishing the row bar  14  is carried out by rotating the lapping surface plate  22  as indicated by the arrow A, reciprocally moving the row bar  14  in the radial direction of the lapping surface plate  22  as indicated by the arrow B, and pressing the row bar  14  onto the lapping surface plate  22 . For example, the lapping surface plate  22  has a spherical surface and rotates at a speed not higher than 10 rpm and, desirably, at 1 rpm. Fine diamond abrasive particles are buried in the surface of, or in the whole of, the lapping surface plate  22 . 
     FIG. 4  is a schematic side view illustrating the polishing apparatus  20 . A jig  26  is secured to the housing  24 , and the row bar  14  is held by the jig  26 . Referring to  FIG. 7 , the jig  26  comprises an elongated and straight plate-like rigid member  28  and an elongated and straight plate-like elastic member (anti-static rubber)  30  having a contour substantially the same as that of the rigid member  28  and fixed to the rigid member  28 . The elastic member  30  is produced by a rubber lining manufacturing method and is joined to the rigid member  28 . Typically, the elastic member  30  is joined to the rigid member  28  with an adhesive. It is desired that the rigid member  28  is made of a stainless steel and hardened so that it has a Rockwell hardness H RC  of not smaller than 55. It is further desired that the elastic member  30  is made of an anti-static rubber (surface resistivity of 10 6  to 10 9  Ω·cm). 
   The rigid member  28  has a series of pin insertion holes (through holes)  32  corresponding to the plurality of magnetic head sliders  12  provided in the row bar  14 , while the elastic member  30  does not have such holes. The rigid member  28  has jig securing threaded holes  34  on the outer sides of a series of pin insertion holes  32 . Therefore, the jig  26  can be easily and reliably secured to the housing  24  by driving screws into the jig securing threaded holes  34  through corresponding holes provided in the housing  24 . 
   In  FIG. 4 , the polishing apparatus  20  has a slide member  38  that can move along a horizontal guide  36 , and an elevator  40  mounted on the slide member  38  so as to move in a vertical direction. The housing  24  is mounted on the elevator  40 . An air cylinder  42  is arranged in the elevator  40  to press the row bar  14 , held by the jig  26  secured to the housing  24 , toward the lapping surface plate  22 . As shown in  FIG. 3 , therefore, the lapping surface plate  22  rotates as indicated by the arrow A, the row bar  14  reciprocally moves in the radial direction of the lapping surface plate  22  as indicated by the arrow B, and the row bar  14  as a whole is pressed to the lapping surface plate  22 . 
     FIG. 5  is a sectional view illustrating the lapping surface plate  22 , the housing  24  and the jig  26  of the polishing apparatus  20 , on an enlarged scale. The row bar  14  is held by the jig  26  and is pressed to the lapping surface plate  22  by the action of the air cylinder  42 . 
   The housing  24  has a plurality of pin insertion holes  44  in alignment with the plurality of pin insertion holes  32  of the rigid member  28 , the pin insertion holes  44  of the housing  24  being communicated with the pin holes  32  of the rigid member  28 , respectively. 
   A plurality of pins  46  are arranged corresponded to a plurality of aligned pin insertion holes  32  and  44 . Each pin  46  is inserted in a set of aligned pin insertion holes  32  and  44 . The pins  46  individually receive the pressing force, as indicated by the arrows C, and individually press the portions of the elastic member  30  corresponding to the magnetic head sliders  12  of the row bar  14  through the pin insertion holes  44  in the housing  24  and the pin insertion holes  32  in the rigid member  28 . Therefore, each pin  46  applies a pressing force to each point of the elastic member  30  corresponding to each magnetic head slider  12  of the row bar  14 . In general, the polishing rate varies in proportion to the lapping pressure and, hence, a point of the row bar  14  that is pressed is locally polished with an increased rate. The pins  46  selectively and separately press the portions of the elastic member  30  corresponding to the magnetic head sliders  12  of the row bar  14  through the pin insertion holes  32  in the rigid member  28 . 
     FIG. 6  is a view illustrating a drive mechanism for moving the pin  46 . A plurality of drive mechanisms are provided in parallel in the number same as the number of the pins  46  in  FIG. 5 . For example, there are provided 28 pins  46 , and related drive mechanisms, in parallel, the drive mechanisms being capable of controlling the pressing force for the related pins  46  independently from each other. 
   The drive mechanism comprises an air cylinder  48 , a rack  50 , pinions  52  and  54 , and a lever  56  provided integrally with the pinion  54 . As the piston pin of the air cylinder  48  extends, the rack  50  advances, whereby the pinion  54  and the lever  56  rotate, and the lever  56  pushes the pin  46  down. The pinion  52  turns to support the rack  50 . The pin  46  is pushed down to press the elastic member  30  of the jig  26 . 
   Therefore, the pin  46  presses the portion of the elastic member  30  corresponding to the magnetic head slider  12  of the row bar  14 . By utilizing this principle, even a slight bending of the row bar  14  can be corrected. The air cylinder  48  may be of the single-acting type working in the pushing direction only. A plurality of air cylinders  48 , the racks  50 , and pinions  52  and  54  are arranged in a unit casing  58  that support and guide them. The housing  24  is disposed neighboring the unit casing  58 . The air cylinder  42  for pressing the row bar  14  as a whole and the air cylinders  48  for pressing respective magnetic head sliders  12  of the row bar  14 , are connected to a source of compressed air through tubes or pipes. An electric-pneumatic pressure conversion regulator is arranged in the tube or the pipe, and is controlled by a control unit. 
   In this embodiment, the drive mechanism is constituted by the air cylinder, the rack and the pinion mechanism and the lever. The drive mechanism, however, may be constituted by using any other actuator and any other link mechanism. The jig  26  and the housing  24  are each secured by using two screws. Instead of using the screws, however, they may be secured relying upon a mechanical locking system or a vacuum adsorption system. 
     FIG. 8  is a sectional view illustrating the lapping surface plate  22 , the housing  24  and the jig  26  of the polishing apparatus  20 , according to another embodiment.  FIG. 9  is a view illustrating the housing  24 , the jig  26  and the air tube of  FIG. 8 . The polishing apparatus  20  of the embodiment of  FIGS. 8 and 9  has the lapping surface plate  22 , the housing  24  and the jig  26  like the polishing apparatus  20  of  FIG. 5 . The jig  26  comprises an elongated and straight plate-like rigid member (stainless steel)  28  and an elongated and straight plate-like elastic member (anti-static rubber)  30  having a contour substantially the same as that of the rigid member  28  and is fixed to the rigid member  28  ( FIG. 11 ). The elastic member  30  is produced by a rubber lining manufacturing and joined to the rigid member  28 . The elastic member  30  is joined to the rigid member  28  with an adhesive. 
   The polishing apparatus  20  of the embodiment of  FIG. 5  uses the pins  46  and the drive mechanisms therefor, whereas the polishing apparatus  20  of the embodiment of  FIG. 8  is of a static pressure type which directly presses the elastic member  30  with the compressed air, without using the pins  46 . Namely, the rigid member  28  has a series of air feeding holes (through holes)  62  corresponding to a plurality of magnetic head sliders  12  provided in the row bar  14 , but the elastic member  30  does not have such holes. The rigid member  28  has jig securing threaded holes  34  on the outer sides of a series of the air feed holes  62  ( FIG. 11 ). By driving screws into the jig securing threaded holes  34  through corresponding hole provided in the housing  24 , therefore, the jig  26  can be easily and reliably secured to the housing  24 . The air feed holes  62  are formed corresponded to the slider pitch in the row bar  14 , and its width should be smaller than the slider pitch. 
   The housing  24  has a plurality of air feed holes  64  in alignment with the plurality of air feed holes  62  in the rigid member  28 , the air feed holes  64  in the housing  24  being communicated with the air feed holes  62  in the rigid member  28 , respectively. 
   Air tube  66  is connected to the air feed hole  64  in the housing  24  through a coupling  68 . The air tube  66  is connected to the source  70  of compressed air, and an electric-pneumatic pressure conversion regulator (control valve)  72  is arranged in the air tube  66 . The air tube  66  feeds the compressed air into the air feed hole  62  in the rigid member  28  through the air feed hole  64  in the housing  24 . The air tubes  66  are in a number same as the number of the magnetic head sliders  12  in the row bar  14 , and are connected to the air feed holes  62  in the rigid member  28 . 
   The compressed air fed into the air feed holes  62  in the rigid member  28  through the air tubes  66  and the air feed holes  64  in the housing  24 , works to individually press the portions of the elastic member  30  corresponding to the magnetic head sliders  12  of the row bar  14 . Therefore, the operation of the embodiment of  FIGS. 8 and 9  is the same as the operation of the embodiment of  FIG. 5 . 
   The air tubes  66  are very fine tubes having an outer diameter of, for example, 1.3 mm. The air feed holes  64  in the housing  24  and the air feed holes  62  in the rigid member  28  are round holes of a diameter of 1 mm. The air feed holes  62  may assume any other shape in cross section. 
     FIGS. 10A to 10C  are views illustrating air feed holes  62  in the rigid member  28  of the jig  26  of  FIGS. 8 and 9 .  FIG. 10A  illustrates a round air feed hole  62  of a diameter of 1 mm,  FIG. 10B  illustrates an air feed hole  62  of an elliptic shape measuring 1 mm×1.2 mm, and  FIG. 10C  illustrates a rectangular air feed hole  62  measuring 1 mm×1.2 mm. 
   When the compressed air is fed through the air tube  66 , pressure is applied to the air feed hole  62  in the rigid member  28 . Where the thrust exerted on the elastic member  30  is denoted by F, the sectional area of the air feed hole  62  by S, and the pressure of the compressed air by P, there is a relationship F=S×P. Here, the pressure P of the compressed air is presumed to be 0.5 MPa. When the air feed hole  62  in the rigid member  28  is a round hole having a diameter of 1 mm, the thrust F is 39.25 gf. In the case of an elliptic hole of 1 mm×1.2 mm, the thrust F becomes 49.25 gf. In the case of a rectangular hole C measuring 1 mm×1.2 mm, a thrust F of 60.25 gf is obtained. 
   On the other hand, the machining pressure during the practical lapping operation is not larger than 1 Kgf per a row bar  14 , from past experience. If each row bar  14  contains 30 magnetic head slides  12 , the force applied to each magnetic head slider  12  can be simply calculated to be 1 Kgf/30=33 gf, which is smaller than the thrust F=39.25 gf produced by the round hole. Therefore, the bending of the magnetic head slider  14  can be corrected by the compressed air to a sufficient degree. 
   The coupling  68  is of a special shape having a portion onto which the air tube  66  of an outer diameter of 1.3 is fitted, a portion of an expanded diameter that comes in contact with the surface of the housing  24 , and a portion which is fitted into the air feed hole  64  of a diameter of 1 mm of the housing  24 . By using such a coupling  68 , it is possible to adapt for the size of the air feed holes  62  and  64  and to prevent the leakage of air between the air tube  66  and the housing  24 . The lower surface of the housing  24  and the upper surface of the rigid member  28  are flattened; i.e., the lower surface of the housing  24  is intimately contacted to the upper surface of the rigid member  28  to constitute a mechanical sealing preventing the leakage of air between the housing  24  and the rigid member  28 . As the air feed holes  62  in the rigid member  28  are straight holes, the air feed holes  62  are not clogged when the rigid member  28  is to be lined with the elastic member  30 , by providing a masking in the air feed hole  62 , and by removing the masking after the lining. 
     FIG. 12  is a view illustrating an embodiment of measuring the resistance in the inprocess condition. A support plate  74  is attached to the housing  24  of the polishing apparatus  20 , and a relay board (printed board)  76  is attached to the support plate  74 . As described earlier, the row bar  14  has two terminals of the ELG resistance element  16  at the boundary between the two magnetic head sliders  12 . The ELG resistance element  16  is connected to the terminals  80  of the relay board  76  through bonding wires  78 . Many ELG resistance elements  16  are provided, and it is desired that the bonding wires  78  of the same number as the number of the terminals of the ELG resistance elements  16  are connected. 
   The relay board  76  has probing terminals  82 . A probe (not shown) of the resistance measuring means is brought into contact with the probing terminals  82  to measure the resistance in the inprocess condition. 
     FIG. 13  is a view illustrating how to bond the wires in the embodiment of  FIG. 12 . The jig  26 , the housing  24  and the relay board  76  are assembled together and the assembly is set onto a base  82  for wire bonding. This is effected by a vacuum attraction method. Then, a holding plate  84  is brought into contact with the row bar  14  and is secured by screws  86  while the row bar  14  is pressed against the elastic member  30 . Then, the wire bonding is carried out by a wire bonding machine. 
   As the row bar  14  is held by the jig  26  relying simply upon the sticking force of the rubber constituting the elastic member  30 , and it is probable that the row bar  14  may be peeled off the elastic member  30  at the time of bonding the wires, it is recommended that the row bar  14  is pressed against the elastic member  30  in this manner. Besides, as the row bar  14  is in contact with the rubber that constitutes the elastic member  30 , and ultrasonic oscillation for effecting the wire bonding is absorbed by the rubber, so it is difficult to properly execute the wire bonding. Upon employing the constitution illustrated in  FIG. 13 , however, the ultrasonic wave oscillation absorption action of the rubber is decreased, and the wire bonding can be properly effected. Therefore, the operation for polishing the row bar  14  is conducted while measuring the resistance as illustrated in  FIG. 12  in the inprocess condition.