Patent Publication Number: US-2023158639-A1

Title: Grinding apparatus

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a grinding apparatus including a grinding wheel that has a plurality of grindstones arranged in an annular array. 
     Description of the Related Art 
     A grinding apparatus for grinding various plate-shaped workpieces such as semiconductor wafers includes a mount disk disposed on the distal end of a spindle and a grinding wheel mounted on the mount disk. A plurality of grindstones are arranged in an annular array on the lower surface of an annular base of the grinding wheel. When the spindle is rotated about its central axis, the grindstones are rotated to grind a workpiece that is held in abrasive contact with the grindstones. When the grindstones are worn beyond a certain limit, the grinding wheel needs to be replaced with a fresh one. There has been proposed in the art a mechanism for facilitating the replacement of unduly worn grinding wheels. 
     For example, JP 2019-202399A discloses a grinding apparatus including a base disposed on a spindle and having a plurality of first chuck claws and a second chuck claw for supporting a grinding wheel on a wheel mount. The grinding wheel is supported on the wheel mount by wedge engagement with the first and second chuck claws. Therefore, a complex fastening process such as screw tightening is not required to support the grinding wheel on the wheel mount. JP 2021-112781A reveals a grinding apparatus including a grinding unit that has a wheel engaging member mounted on the lower end of a spindle. When the wheel engaging member is moved toward a grinding wheel that is placed on a chuck table until the wheel engaging member engages the grinding wheel, the grinding wheel is mounted on the spindle by the wheel engaging member. 
     SUMMARY OF THE INVENTION 
     In order for a grinding apparatus to incorporate the mechanism disclosed in JP 2019-202399A or JP 2021-112781A, however, the grinding apparatus need to have a modified mount disk on the distal end of the spindle. In addition, a motor controller that controls an electric motor for rotating the spindle is required to change its settings based on the mount disk that has become heavier due to its modification. It is time-consuming to modify the mount disk and change the settings of the motor controller. Moreover, the spindle on which the mount disk is mounted may need to be replaced in some cases. 
     It is therefore an object of the present invention to provide a grinding apparatus including a grinding wheel mounted on the distal end of a spindle by a mount disk that has been modified in a short period of time from an existing structure for allowing the grinding wheel to be replaced easily. 
     In accordance with an aspect of the present invention, there is provided a grinding apparatus for grinding a workpiece, including a chuck table for holding the workpiece thereon, a spindle rotatable about a central axis thereof, a mount disk connected to a distal end of the spindle and having a mount surface, and a grinding wheel having an annular base having a mating surface for mating with the mount surface of the mount disk and a plurality of grindstones fixed in an annular array to the annular base, the grinding wheel being fastened to the mount disk by a plurality of bolts, in which the mount disk has at least three internally threaded holes defined therein at equal spaced intervals circumferentially thereon and extending therethrough between upper and lower surfaces thereof, and a plurality of protrusions protruding from the mount surface, each of the bolts includes an externally threaded shank, a neck coupled to a distal end of the externally threaded shank, and an engaging flange coupled to a distal end of the neck and extending radially outwardly from the neck, the grinding wheel includes an annular open hole defined in the mating surface, an annular slot defined in the annular base that is wider than the annular open hole and vertically fluidly connected to the annular open hole, at least three insertion holes defined in the annular open hole for allowing the engaging flange to be inserted therethrough into the annular slot, and a plurality of protrusion insertion holes defined in the annular open hole for receiving the engaging flanges of the bolts therein, and, for mounting the grinding wheel on the mount disk, the externally threaded shanks of the bolts are threaded into the internally threaded holes in the mount disk, with the engaging flanges projecting from the mount surface, after the engaging flanges are inserted from the insertion holes into the annular slot, the mount disk and the grinding wheel are rotated relatively to each other, and when the protrusion insertion holes and the protrusions are positionally aligned with each other, the bolts are rotated to insert the protrusions into the protrusion insertion holes and to fasten the mount disk and the grinding wheel to each other with the bolts. 
     Preferably, the insertion holes double as the protrusion insertion holes. 
     Preferably, the protrusions, the engaging flanges, the insertion holes, and the protrusion insertion holes are cylindrical in shape. 
     According to the present invention, inasmuch as the grinding wheel can easily be replaced with a fresh one without the need for a complex mechanism on the mount disk, the mount disk is prevented from becoming heavier. Consequently, it is not necessary to change the settings of a motor controller for controlling the electric motor for rotating the spindle. In addition, as there is no need for the mount disk to hold the grinding wheel under suction forces, the mount disk does not need to be fluidly connected to a suction source, and hence the spindle does not need to be replaced. 
     The above and other objects, features and advantages of the present invention and the manner of realizing them will become more apparent, and the invention itself will best be understood from a study of the following description and appended claims with reference to the attached drawings showing a preferred embodiment of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a perspective view of a grinding apparatus according to an embodiment of the present invention; 
         FIG.  2    is a bottom view of a mount disk of the grinding apparatus; 
         FIG.  3    is an enlarged fragmentary cross-sectional view of the mount disk, a bolt, and a grinding wheel; 
         FIG.  4    is a plan view of an annular base of the grinding wheel; 
         FIG.  5    is a cross-sectional view illustrating the manner in which a bolt is to be inserted into an internally threaded hole in the mount disk; 
         FIG.  6    is a cross-sectional view illustrating the manner in which the bolt has been inserted into the internally threaded hole in the mount disk; 
         FIG.  7    is a cross-sectional view illustrating the manner in which an engaging flange of the bolt has engaged in an annular slot defined in the annular base and the mount disk and the grinding wheel are rotated relatively to each other; and 
         FIG.  8    is a cross-sectional view illustrating the manner in which a protrusion on the mount disk is inserted in a protrusion insertion hole in the annular base and the mount disk and the grinding wheel are fastened together by the bolt. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG.  1    illustrates in perspective a grinding apparatus  1  according to an embodiment of the present invention. In  FIG.  1   , the grinding apparatus  1  is illustrated in reference to a three-dimensional coordinate system having X-, Y-, and Z-axes indicated respectively by the arrows +X and −X, +Y and −Y, and +Z and −Z. The X-axis and the Y-axis lie on a horizontal plane, whereas the Z-axis extends vertically perpendicularly to the horizontal plane. 
     The grinding apparatus  1  is an apparatus for grinding a workpiece, not illustrated, typically a semiconductor wafer, held on a chuck table  2  with a grinding mechanism  3 . The chuck table  2  is horizontally movable along the Y-axis by a moving mechanism  4 , and the grinding mechanism  3  is vertically movable along the Z-axis by a grinding feed mechanism  5 . 
     The chuck table  2  includes a suction member  21  made of a porous material and a frame  22  supporting the suction member  21  thereon. The suction member  21  has an upper surface acting as a holding surface  210  for holding the workpiece under suction thereon. The holding surface  210  and an upper surface  220  of the frame  22  that surrounds the suction member  21  lie flush with each other. 
     The grinding apparatus  1  includes a table base  23  disposed below the chuck table  2  and supporting the chuck table  2  thereon. The table base  23  has at least three lower surface areas supported by respective three chuck support legs  24  (only two of them are illustrated in  FIG.  1   ) disposed therebelow. The chuck support legs  24  are combined respectively with load measuring units  25  for measuring vertical loads that are applied when the grinding mechanism  3  presses the workpiece held on the holding surface  210 . At least two of the chuck support legs  24  have a function to adjust the tilt of the holding surface  210  by adjusting the height of the chuck table  2 . 
     The grinding mechanism  3  includes a vertical spindle  30  rotatable about a rotational axis extending along the Z-axis, an electric motor  31  for rotating the spindle  30 , a spindle housing  32  in which the spindle  30  is rotatably supported, a mount disk  6  coupled to the lower end of the spindle  30 , and a grinding wheel  34  mounted on the lower surface of the mount disk  6 . The spindle  30  has a grinding fluid inlet port  301  defined in the upper end thereof for introducing a grinding fluid into the spindle  30 . When the electric motor  31  is energized, it rotates the spindle  30  about its rotational axis, thereby rotating the grinding wheel  34  about its vertical central axis. The grinding wheel  34  includes an annular base  7  fixed to the lower surface of the mount disk  6  and a plurality of grindstones  8  fixed in an annular array to the lower surface of the annular base  7 . 
     The moving mechanism  4  includes a horizontal ball screw  40  rotatable about a rotational axis extending along the Y-axis, an electric motor  41  for rotating the ball screw  40 , a pair of guide rails  42  disposed one on each side of the ball screw  40  and extending parallel to the ball screw  40 , and a slide plate  43  having bottom surfaces held in slidable contact with the respective guide rails  42  and having a nut, not illustrated, on its lower surface that is operatively threaded over the ball screw  40 . The slide plate  43  has an upper surface supporting thereon the chuck support legs  24  and the load measuring units  25 . When the electric motor  41  is energized, it rotates the ball screw  40 , causing the nut to move the slide plate  43  along the Y-axis along the guide rails  42 . When the slide plate  43  is moved along the Y-axis, the chuck table  2  supported on the slide plate  43  is also moved in unison therewith along the Y-axis. 
     The grinding feed mechanism  5  includes a vertical ball screw  50  rotatable about a rotational axis extending along the Z-axis, an electric motor  51  for rotating the ball screw  50 , a pair of guide rails  52  disposed one on each side of the ball screw  50  and extending parallel to the ball screw  50 , a vertically movable plate  53  having side surfaces held in slidable contact with respective the guide rails  52  and having a nut, not illustrated, on its rear surface that is operatively threaded over the ball screw  50 , and a holder  54  coupled to the vertically movable plate  53  and supporting the spindle housing  32  on its front surface. When the electric motor  51  is energized, it rotates the ball screw  50 , causing the nut to move the vertically movable plate  53  along the Z-axis along the guide rails  52  perpendicularly to the holding surface  210 . When the vertically movable plate  53  is moved along the Z-axis, the grinding mechanism  3  is also moved in unison therewith along the Z-axis, moving the grindstones  8  toward or away from the holding surface  210  along the Z-axis. The position of the grinding mechanism  3  along the Z-axis is recognized by an encoder  55  that is combined with the electric motor  51 . 
     A thickness measuring unit  9  for measuring the thickness of the workpiece held on the chuck table  2  is disposed on one side of the track in which the chuck table  2  is movable along the Y-axis. The thickness measuring unit  9  includes a first measuring unit  91  for measuring the height of the upper surface of the workpiece on the holding surface  210  of the suction member  21  and a second measuring unit  92  for measuring the height of the upper surface  220  of the frame  22 . The thickness measuring unit  9  measures the difference between a measured value from the first measuring unit  91  and a measured value of the second measuring unit  92  as the thickness of the workpiece. 
     As illustrated in  FIG.  2   , the mount disk  6  is of an annular shape. The mount disk  6  has a lower surface as a mount surface  60  on which the grinding wheel  34  is mounted. The mount surface  60  has two cylindrical protrusions  61  protruding downwardly. The two protrusions  61  are disposed circumferentially on a common circle on the mount disk  6  in diametrically opposite relation to each other, i.e., angularly spaced from each other by 180 degrees around the center O of the mount disk  6 . 
     The protrusions  61  may be integral with the mount disk  6  or may be separate from and detachably mounted on the mount disk  6 . If the protrusions  61  are separate from and detachably mounted on the mount disk  6 , then they may have externally threaded distal ends threaded in respective internally threaded recesses defined in the mount surface  60  of the mount disk  6 . The protrusions  61  may be located in different positions on the mount disk  6  depending on the type of the grinding wheel  34  or may be of a polygonal shape depending on the type of the grinding wheel  34 . 
     The mount disk  6  has eight internally threaded holes  62  defined therein at equal spaced intervals on the common circle on which the protrusions  61  are disposed. Though the mount disk  6  is illustrated as having eight internally threaded holes  62  in  FIG.  2   , the mount disk  6  may have at least three internally threaded holes  62 . As illustrated in  FIG.  3   , each of the internally threaded holes  62  extends axially through the mount disk  6  between its upper and lower surfaces. The mount disk  6  also has a grinding fluid channel  63  defined therein through which the grinding fluid introduced from the grinding fluid inlet port  301  into the spindle  30  and flowing through a fluid channel, not illustrated, defined in the spindle  30  flows into the mount disk  6 . 
     As illustrated in  FIG.  3   , a bolt  64  is threaded into each of the internally threaded holes  62 . The bolt  64  has an externally threaded shank  641 , a neck  642  coupled to a distal end of the externally threaded shank  641 , and a cylindrical engaging flange  643  coupled to a distal end of the neck  642  and extending radially outwardly from the neck  642 , the cylindrical engaging flange  643  being larger in diameter than the neck  642 . The bolt  64  includes a plunger  644  disposed in a cavity defined in the distal end of the neck  642  and normally biased to project axially in a direction out of the cavity by a spring  645  disposed in the cavity. The bolt  64  includes a hexagon head bolt having an engaging portion  646  disposed adjacent to the externally threaded shank  641  remotely from the neck  642  for engagement with a hexagonal wrench. 
     As illustrated in  FIG.  4   , the annular base  7  of the grinding wheel  34  has an upper surface as a mating surface  70  for mating with the mount surface  60  of the mount disk  6 . The mating surface  70  has an annular open hole  71  defined therein. As illustrated in  FIG.  5   , the annular base  7  has a bottomed annular slot  72  defined therein that is wider than the annular open hole  71  and vertically fluidly connected to the annular open hole  71 . The annular base  7  also has grinding fluid ejection passages  73  defined therein that have upwardly open upper ends fluidly connected to the grinding fluid channel  63  in the mount disk  6  and downwardly open lower ends. 
     As illustrated in  FIG.  4   , the annular open hole  71  includes a plurality of cylindrical insertion holes  74  angularly spaced at equal intervals. The cylindrical insertion holes  74  are capable of receiving the respective cylindrical engaging flanges  643  of the bolts  64 , i.e., are slightly larger in diameter than the cylindrical engaging flanges  643  of the bolts  64 . Though the annular open hole  71  is illustrated as including eight cylindrical insertion holes  74  in  FIG.  4   , the annular open hole  71  may include at least three cylindrical insertion holes  74 . 
     The annular open hole  71  also includes a plurality of protrusion insertion holes  75 , which are formed at equal intervals, for receiving therein the protrusions  61  of the mount disk  6 . The annular open hole  71  includes as many protrusion insertion holes  75  as the number of the protrusions  61 . Since the two protrusions  61  are angularly spaced from each other by 180 degrees in  FIG.  2   , there are also two protrusion insertion holes  75  angularly spaced from each other by 180 degrees. 
     A process of mounting the annular base  7  of the grinding wheel  34  on the mount disk  6  will be described below with reference to  FIGS.  5  through  8   . The mount disk  6  illustrated in cross section in  FIG.  5    is taken along line A-O-B of  FIG.  2   . The grinding wheel  34  illustrated in cross section in  FIGS.  5  and  6    is taken along line A-O-B of  FIG.  4   . 
     First, as illustrated in  FIG.  5   , the operator threads the externally threaded shanks  641  of the bolts  64  into the respective internally threaded holes  62  in the mount disk  6 , with the cylindrical engaging flanges  643  projecting downwardly from the mount surface  60 . Then, the operator inserts the cylindrical engaging flanges  643  into the respective cylindrical insertion holes  74  illustrated in  FIG.  4   , thereby inserting the cylindrical engaging flanges  643  into the bottomed annular slot  72  to the full depth thereof. With the cylindrical engaging flanges  643  inserted in the bottomed annular slot  72 , the operator rotates the mount disk  6  and the grinding wheel  34  relatively to each other. 
     The relative rotation of the mount disk  6  and the grinding wheel  34  causes the necks  642  to enter the annular open hole  71  and also causes the cylindrical engaging flanges  643  to enter and engage in the bottomed annular slot  72 . The mount disk  6  and the grinding wheel  34  are continuously rotated relatively to each other until the protrusion insertion holes  75  defined in the annular base  7  and the cylindrical protrusions  61  of the mount disk  6  are positionally aligned with each other. The bottomed annular slot  72  should preferably include a plurality of recesses, not illustrated, defined in the bottom thereof for receiving respective distal ends of the plungers  644  at the time when the protrusion insertion holes  75  and the cylindrical protrusions  61  are positionally aligned with each other. During the relative rotation of the mount disk  6  and the grinding wheel  34 , the plungers  644  that are normally biased to project axially in the direction out of the cavities by the springs  645  have their distal ends pressed against the bottom of the annular slot  72 . Therefore, the mount disk  6  and the grinding wheel  34  are prevented from rotating freely relatively to each other. 
     When the protrusion insertion holes  75  and the cylindrical protrusions  61  are positionally aligned with each other, the operator brings the mount disk  6  and the grinding wheel  34  to a halt against relative rotation. Then, as illustrated in  FIG.  8   , the operator applies a hexagonal wrench successively to the engaging portions  646  of the bolts  64  and turns the hexagonal wrench to rotate the bolts  64  in the respective internally threaded holes  62 , bringing the mount disk  6  and the annular base  7  toward each other and into intimate contact with each other. The cylindrical protrusions  61  are now inserted into the respective protrusion insertion holes  75 . The bolts  64  are tightened to fasten the mount disk  6  and the annular base  7  of the grinding wheel  34  to each other. 
     The grinding wheel  34  is thus mounted on the mount disk  6  by causing the cylindrical engaging flanges  643  of the bolts  64  inserted in the respective internally threaded holes  62  in the mount disk  6  to engage in the bottomed annular slot  72  in the annular base  7 , rotating the annular base  7  and the mount disk  6  relatively to each other, and tightening the bolts  64  when the protrusion insertion holes  75  and the cylindrical protrusions  61  are positionally aligned with each other. The grinding wheel  34  can be removed from the mount disk  6  by loosening the bolts  64 , rotating the annular base  7  and the mount disk  6  relatively to each other, and pulling the cylindrical engaging flanges  643  from the corresponding cylindrical insertion holes  74 . 
     The bottomed annular slot  72  may include recesses for receiving the distal ends of the plungers  644 , defined in its bottom at the centers of the respective cylindrical insertion holes  74 . Since the spring-loaded plungers  644  snap into the recess at the centers of the respective cylindrical insertion holes  74  when the bolts  64  are aligned with the respective cylindrical insertion holes  74 , the operator knows when the grinding wheel  34  has reached the angular position with respect to the mount disk  6  where the grinding wheel  34  can be detached from the mount disk  6 . 
     According to the illustrated embodiment, inasmuch as the grinding wheel  34  can easily be replaced with a fresh one without the need for a complex mechanism on the mount disk  6 , the mount disk  6  is prevented from becoming heavier. Consequently, it is not necessary to change the settings of a motor controller for controlling the electric motor  31  for rotating the spindle  30 . In addition, as there is no need for the mount disk  6  to hold the grinding wheel  34  under suction forces, the mount disk  6  does not need to be fluidly connected to a suction source, and hence the spindle  30  does not need to be replaced. 
     The annular base  7  according to the present embodiment has the insertion holes  74  and the protrusion insertion holes  75  separately from each other. However, the insertion holes  74  may double as the protrusion insertion holes  75 . 
     The present invention is not limited to the details of the above described preferred embodiment. The scope of the invention is defined by the appended claims and all changes and modifications as fall within the equivalence of the scope of the claims are therefore to be embraced by the invention.