Abstract:
The grinding machine and the method of grinding are capable of grinding a bar member for a magnetic head with higher grinding accuracy. In the grinding machine, a holding frame holds a bar member and heads a first face of the bar member, which is to be ground, downward. A grinding plate grinds the first face of the bar member. An actuator presses a second face of the bar member held by the holding frame so as to press the first face onto the grinding plate. A resistance monitor monitors a resistance value of a sensing part of an ELG element section of the bar member so as to adjust a strip height of a magnetic head section of the bar member.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a grinding machine for a bar member for magnetic heads and a method of grinding the bar member. 
     Magnetic head elements, which are used in magnetic disk drive units, etc., are manufactured by forming magnetizable layers and non-magnetizable layers on a ceramic substrate (a ceramic wafer). A lot of magnetic head elements are formed on the ceramic substrate. Each of the magnetic head elements includes: a magnetic head element section, which has a magnetoresistance effect head (a regenerating head) including an MR element, etc. and an electromagnetic induction head (a recording head); an monitor ELG element section, which is arranged adjacent to the magnetic head element section; and terminals (pads) connected to the magnetic head element section and the ELG element section. 
     The magnetic head elements are manufactured by the steps of: forming the magnetic head element sections, the ELG element sections, the terminals, etc. on the wafer; cutting the wafer so as to form a plurality of thin bar member; and grinding a side face of each bar member. Tens of the magnetic head element sections are linearly arranged in each bar member. 
     The side face of the bar member is ground so as to adjust a height of a sensing part including the MR element, which is called a strip height or an MR height, to a prescribed height. The lower sensing part has higher sensitivity. These days, in the magnetic head elements, required accuracy of the strip height is 0.8 μm±0.2 μm. But, in the near future, it must be higher: 0.3 μm±0.03 μm. 
     Since the strip height must be highly precisely adjusted, the ELG element section, whose structure is equal to that of the magnetic head element section, is provided for each magnetic head section. The ELG element section is simultaneously ground, and its resistance value is measured so as to monitor the sprit height of the corresponded magnetic head element section. With this action, the magnetic head elements can be ground with high accuracy. 
     A jig for grinding the bar member is shown in FIG.  21 . The jig is disclosed in the U.S. Pat. No. 5,607,430. 
     The jig  10  is made of a metal or a ceramic. The bar member  12  is adhered onto the jig  10  with an adhesive, e.g., wax. A face of the bar member  10  to be ground is pressed onto a grinding plate, e.g., a lapping plate (not shown), with the jig  10  so as to grind the face to be ground. 
     The jig  10  includes a plurality of slits  14  having proper patterns and a plurality of actuator holes  16 . Actuators, e.g., air cylinder units (not shown), are respectively provided in the actuator holes  16 . 
     When the bar member  12  is ground, the actuators are driven to apply force to the jig  10 . Since the jig  10  has the slits  14 , the jig  10  can be bent by changing output force of the actuators. By bending the jig  10 , pressure applying to each part of the bar member  10 , from a bottom face, can be precisely controlled. Namely, the pressure applying to each magnetic head element section can be precisely controlled, so that grinding rate for each magnetic head element section can be controlled. 
     However, the conventional grinding machine and the conventional grinding method have following disadvantages. 
     As described above, the jig  10  is made of a metal or a ceramic having high strength, so the output force of the actuators must be great so as to bend the jig  10 . In spite of forming the slits  14 , it is difficult to bend the tough jig  10 . Namely, it is difficult to precisely partially control the pressure applying to the parts of the bar member  12 . Especially, it is very difficult to grind the bar member  12  with higher grinding accuracy. Further, a cost for manufacturing the jig  10  having the slits  14  must be increased. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a grinding machine and a method of grinding, which are capable of grinding a bar member for a magnetic head with higher grinding accuracy. 
     To achieve the object, the grinding machine of the present invention comprises: means for holding a bar member, the holding means heading a first face of the bar member, which is to be ground, downward; a grinding plate for grinding the first face of the bar member; an actuator for pressing a second face, which is an opposite face with respect to the first face, of the bar member held by the holding means so as to press the first face onto the grinding plate; and means for monitoring a resistance value of a sensing part of an ELG element section of the bar member so as to adjust a strip height of a magnetic head section of the bar member. 
     The grinding method of the present invention comprises the steps of: 
     holding a bar member and heading a first face of the bar member, which is to be ground, downward; pressing a second face, which is an opposite face with respect to the first face, of the bar member, by an actuator, so as to press the first face onto a grinding plate and grind the same; and 
     monitoring a resistance value of a sensing part of an ELG element section of the bar member so as to adjust a strip height of a magnetic head section of the bar member. 
     Another method of the present invention comprises the steps of: adhering flexible film onto a second face of a bar member, which is an opposite face with respect a first face thereof to be ground; holding the bar member with the flexible film and heading the first face of the bar member downward; pressing the second face of the bar member and the flexible film, by an actuator, so as to press the first face onto a grinding plate and grind the same; and monitoring a resistance value of a sensing part of an ELG element section of the bar member so as to adjust a strip height of a magnetic head section of the bar member. 
     In the present invention, the second face of the bar member is pressed, directly or with the flexible film, by the actuator, so that pressure can be differently and precisely applied to each element and the grinding accuracy can be improved. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Embodiments of the present invention will now be described by way of examples and with reference to the accompanying drawings, in which: 
     FIG. 1 is an explanation view of a state in which a bar member is held by a holding frame and the bar member is pressed onto a lapping plate by actuators; 
     FIG. 2 is a plan view of the state shown in FIG. 1; 
     FIG. 3 is a front view of the state shown in FIG. 1; 
     FIG. 4 is an explanation view of a state in which the bar member is pressed by the actuator; 
     FIG. 5 is an explanation view of another state in which the bar member is pressed by the actuator; 
     FIG. 6 is an explanation view of an actuator having a roller; 
     FIG. 7 is an explanation view showing load distribution when the actuator having the roller is used; 
     FIG. 8 is an explanation view of a movable actuator; 
     FIG. 9 is a plan view of a state in which the bar member is held by a holding frame having partitions; 
     FIG. 10 is a sectional view taken along a line A—A′ shown in FIG. 9; 
     FIG. 11 is a plan view of a state in which the bar member is adhered on flexible film; 
     FIG. 12 is a front view of a state in which the bar member is held by the holding frame together with the flexible film; 
     FIG. 13 is a sectional view taken along a line B—B′ shown in FIG. 12; 
     FIG. 14 is a longitudinal sectional view of the state shown in FIG. 12; 
     FIG. 15 is a sectional view of the state in which the bar member is held by the holding frame together with the flexible film; 
     FIG. 16 is a plan view of a state in which the bar member is adhered, by an adhesive, on the flexible film; 
     FIG. 17 is a plan view of a state in which the bar member is cut to from a plurality of headpieces; 
     FIG. 18 is a sectional view of a state in which the head pieces are held by the holding frame together with the flexible film; 
     FIG. 19 is a sectional view of a state in which the head pieces are held by the holding frame, which has the partitions, together with the flexible film; 
     FIG. 20 is an explanation view of a state in which cable patterns are removed from the flexible film; and 
     FIG. 21 is a front view of the conventional jig for grinding the bar member. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings. 
     First Embodiment 
     First Embodiment will be explained with reference to FIGS. 1-3. 
     In FIG. 1, a holding frame  20 , which is an example of holding means, is a mere frame which has a vertical through-hole. Namely, an upper face and a bottom face of the holding frame  20  are opened. The holding frame  20  may be made of a metal, a ceramic, etc. 
     A bar member  22  is adhered, by an adhesive, e.g., wax, on the bottom face of the holding frame  20 . A first face of the bar member  22 , which will be ground, is headed downward. Therefore, a second face of the bar member  22 , which is an opposite face with respect to the first face, is exposed in the through-hole of the holding frame  20 . 
     Tens of magnetic head elements are linearly arranged in the bar member  22 . Each of the magnetic head elements includes: a magnetic head element section, which has a magnetoresistance effect head (a regenerating head) including an MR element, etc. and an electromagnetic induction head (a recording head); an monitor ELG element section, which is arranged adjacent to the magnetic head element section; and terminals (pads) connected to the magnetic head element section and the ELG element section. The structure of the bar member  22  is well known, so it is not shown in the drawings. 
     FIG. 2 is a plan view of a state in which the bar member  22  is fixed to the holding frame  20 ; FIG. 3 is a front view thereof. 
     As shown in FIG. 3, a printed circuit board  26 , on which cable patterns  24  are formed, is fixed to a side face of the holding frame  20 . The cable patterns  24  of the circuit board  26  are respectively electrically connected to the terminals (not shown) of the ELG element sections by wires  28 . By touching the cable pattern  24  of the selected ELG element section with a prove pin of a resistance monitor so as to measure the resistance value of the selected ELG element section. 
     In FIG. 1, a plurality of actuators  30  are provided in the through-hole of the holding frame  20 . Each actuator  30  includes an air cylinder unit, a voice coil motor, a piezo element, etc. Each actuator  30  directly contacts a pair of the magnetic head element section and the ELG element section, from the second face side, so as to press the first face onto a lapping plate  32 , which is an example of a grinding plate. 
     Namely, the first face of the bar member  22  can be ground by the steps of: 
     holding the bar member  22  and heading the first face downward by the holding frame  20 ; and directly pressing the second face of the bar member  22 , which has been held by the holding frame  20 , by the actuators  30 , onto the lapping plate  32 . 
     In the present embodiment, Each actuator  30  directly contacts a pair of the magnetic head element section and the ELG element section, the pairs of the magnetic head element section and the ELG element section can be respectively pressed by the actuators  30 . Namely, each pair can be properly pressed, with proper pressure, by the actuator, so that grinding accuracy can be higher, e.g., three-sigma limit 3σ≦0.1 μm. 
     Basic pressing force “F” may be effectively applied to the holding frame  20  by an independent actuator (not shown). In this case, each actuator  30  may apply small pressing force ΔF, so that the pressing force of each actuator  30  can be precisely controlled. 
     Since the bar member  22  will be ground about 5-6 μm, the bar member  22  may be roughly ground at the beginning, but the last 1 μm must be precisely finished. While the bar member  22  is precisely finished, amount of grinding (lapping) is monitored so as to effectively precisely grind. 
     Low pressure, e.g., about 1 Kg/cm 2 , is applied to the bar member  22  so as to grind the bar member  22  with proper lapping rate. If the pressure of 1 Kg/cm  2  is applied to the bar member  22 , the bar member  22  is wholly pressed with the pressing force of 480-600 g. Namely, each magnetic head element receives the pressing force of about 16 g. 
     While precisely grinding the last 1 μm, amount of grinding the magnetic head elements are varied about 0.12 μm, and the variations respectively applied to the magnetic head elements so as to solve the variations of 0.12 μm (max. 0.3 μm). In the case that each magnetic head element receives the average pressing force of 16 g, the difference between the pressing forces is 1.92 g when the variation is 0.12 μm; maximum difference is 4.8 g (the variation: 0.3 μm). 
     The slight difference between the pressing forces cannot be realized by the conventional jig  10  shown in FIG.  21 . 
     On the other hand, in the present embodiment, the magnetic head elements in the bar member  22  are respectively independently pressed by the actuators  30 . Further, the actuators  30  directly contact the bar member  22 . Therefore, the slight difference between the pressing forces can be easily and correctly realized, and the grinding accuracy can be highly improved. 
     Preferably, each actuator  30  presses a pair of the magnetic head element section and the ELG head element section. But the actuators  30  may press as shown in FIGS. 4 and 5. 
     In FIG. 4, each actuator  30  directly presses the magnetic head element section  22   a ; in FIG. 5, each actuator  30  presses the magnetic head element section  22   a  and the adjacent ELG element section  22   b.    
     In the present invention, the state of “pressing the magnetic head element section and the ELG element section with the actuator” includes the states shown in FIGS. 4 and 5. 
     Second Embodiment 
     In the First Embodiment, a plurality of the actuators  30  press the bar member  22 ; in the Second Embodiment, one actuator  30  presses the bar member  22  as shown in FIG.  6 . 
     In the present embodiment, the actuator  30  is moved in the longitudinal direction of the bar member  22  by means  34  for moving the actuator  30 , e.g., a ball screw. The second face of the bar member  22  is pressed by a roller  31 , which is rotatably provided to a lower end of the actuator  30 . The roller  31  is capable of pressing the second face at any positions on its stroke. The roller  31  linearly contacts the second face, but the pressing force is transmitted downward within angle of about 45°, so that the pressing force works to one magnetic head element in the first face. Distribution of the pressing force is shown in FIG.  7 . 
     Third Embodiment 
     In Third Embodiment too, as shown in FIG. 8, one actuator  30  is moved in the longitudinal direction of the bar member  22  by the moving means  34 . In the present embodiment, the second face of the bar member  22  is pressed by a pressing member  33  of the actuator  30 . A bottom face of the pressing member  33  has prescribed area, which is equal to, for example, area of one magnetic head element. By releasing the pressing force working to the second face, the actuator  30  can be moved along the bar member  22 . 
     Fourth Embodiment 
     Fourth Embodiment will be explained with reference to FIG.  9  and FIG.  10 . 
     In the present embodiment, the holding frame  20  has a plurality of partitions  21 , each of which corresponds to each ELG element section of the bar member  22 . The holding frame  20  is capable of holding the bar member  22  and heading the first face of the bar member  22  downward. 
     The bar member  22  is adhered on the bottom face of the holding frame  20  by an adhesive, e.g., wax. The ELG element sections of the bar member  22  are electrically connected as well as the First Embodiment shown in FIG.  3 . 
     As shown in FIG. 10, a plurality of the actuators  30  are respectively inserted in through-holes of the holding frame  20 . And, the actuators  30  directly press the second face of the bar member  22 , which is held by the holding frame  20 , so as to press the first face thereof onto the lapping plate  32 . 
     In the present embodiment too, the magnetic head elements are respectively pressed by the actuator  30 , so that the grinding accuracy can be higher, e.g., three-sigma limit 3σ≦0.12 μm. 
     Fifth Embodiment 
     Fifth Embodiment will be explained with reference to FIGS. 11-14. 
     In the present embodiment, flexible film  36  is adhered on the second face of the bar member  22 . The holding frame  20  is capable of holding the bar member  22 , together with the flexible film  36 , and heading the first face of the bar member  22  downward. The bar member  22  is adhered on the bottom face of the holding frame  20 , with the flexible film  36 , by the adhesive. The holding frame  20  is equal to the holding frame shown in FIG.  1 . 
     Monitor cable patterns  38 , each of which will be electrically connected to each ELG element section of the bar member  22 , are formed on the flexible film  36 . The cable patterns  38  are respectively electrically connected to terminals of the ELG element sections by gold balls  39 . They may be connected by electric-conductive paste, wires, etc. instead of the gold balls. 
     As shown in FIGS. 12 and 13, the flexible film  36  is bent, so that the cable patterns  38  faces to a front face of the holding frame  20 . By touching the capable pattern  38  of the selected ELG element section with the prove pin of the resistance monitor (not shown) so as to measure the resistance value of the selected ELG element section to be ground. 
     The actuators  30  press the second face of the bar member  22 , which is held by the holding frame  20 , together with the flexible film  36  (see FIG.  14 ), so as to press the first face thereof onto the lapping plate  32 . 
     As shown in FIG. 14, each actuators  30  presses a pair of the magnetic head element section and the ELG element section. Note that, one movable actuator, which is shown in FIG. 6 or  8 , may be employed. 
     In the present embodiment too, the bar member  22  is pressed, together with the flexible film  36 , by the actuators  30 . Unlike the conventional method in which the tough jig  10  shown in FIG. 21 is used, the bar member  22  can be bent by small pressing force because of the flexible film  36 . Further, the magnetic head elements can be respectively pressed by the actuators  30 , so that the grinding accuracy can be higher, e.g., three-sigma limit 3σ≦0.12 μm. 
     The holding frame  20  has a plurality of the partitions  21 , each of which corresponds to each ELG element section of the bar member  22 . The holding frame  20  is capable of holding the bar member  22  and heading the first face of the bar member  22  downward. 
     Sixth Embodiment 
     Sixth Embodiment will be explained with reference to FIGS. 16-20. 
     In the present embodiment, as shown in FIG. 16, the flexible film  36  is adhered, on the second face of the bar member  22 , by an adhesive, e.g., a both-sided adhesive tape. The monitor cable patterns  38  are formed on the flexible film  36 . 
     Next, as shown in FIG. 17, the bar member  22 , to which the flexible film  36  is adhered, is cut to form a plurality of head pieces, each of which includes the magnetic head element section and the ELG element section. 
     The cable patterns  38  and the ELG element sections are mutually connected before or after cutting the bar member  22 . 
     Next, as shown in FIG. 18, the bar member  22 , to which the flexible film  36  is adhered, is adhered to the holding frame  20 , which has no partitions as well as the holding frame of the First Embodiment, by the adhesive. Then, the actuators  30  press the second face of the bar member  22 , which has been divided into a plurality of the headpieces. By pressing the bar member  22 , the first face of the bar member  22  is pressed onto the lapping plate  32 , so that the first face can be ground. 
     Unlike the example shown in FIG. 18, the bar member  22 , to which the flexible film  36  is adhered, may be adhered to the holding frame  20 , which has the partitions (see FIG.  19 ), then the actuators  30  may press the second face of the bar member  22  so as to grind the first face thereof. 
     Preferably, the bar member  22  is ground after cutting the bar member  22  because amount of grinding can be monitored for each head piece. However, the head pieces are very small pieces, whose sizes are about 1 mm, so it is impossible to grind the small head pieces. 
     In the present embodiment, the small head pieces are adhered on the flexible film  36 , so that they will never separate and they can be ground as one body. Since the bar member  22  is cut and formed into the head pieces, each actuator  30  can securely press the corresponding head piece only, so that the grinding accuracy can highly improved. 
     In the following steps, e.g., crown lapping, forming an air bearing surface (ABS), the head pieces are integrated by the flexible film  36 . In this case, as shown in FIG. 20, a useless part of the flexible film  36 , in which the cable patterns  38  are formed, may be removed for the following steps. 
     In the above described embodiments, in which the bar member  22  is adhered on the flexible film  36  then the bar member  22  is ground, the holding means need not be formed into the frame shape. For example, the holding means may be constituted by a pair of chucking units (not shown), which are capable of holding both ends of the bar member  22 . By employing the chucking units too, the bar member  22  can be ground. 
     The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.