CHUCK TABLE, GRINDING APPARATUS, AND WORKPIECE GRINDING METHOD

Description

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a chuck table used as the time of grinding a flat plate-shaped workpiece having four or more corners in plan view, a grinding apparatus including this chuck table, and a workpiece grinding method that grinds a workpiece in this grinding apparatus.

Description of the Related Art

Device chips exemplified by integrated circuits (ICs) are indispensable components for various kinds of electronic equipment including mobile phones and personal computers. These chips are, for example, manufactured by grinding a reverse side of a package substrate that has on a face side thereof a plurality of devices arranged in a matrix and then dividing the package substrate along the boundaries of the plurality of devices.

A grinding apparatus used for grinding the reverse side of the package substrate typically includes a chuck table that is rotatable about a straight line passing through the center of a surface (holding surface) on which the package substrate is held, as a rotational axis, and a spindle having a distal end portion to which a grinding wheel including a plurality of grindstones disposed annularly at predetermined intervals is mounted.

Note that the package substrate typically has a square shape or a rectangular shape in plan view. Hence, the holding surface of the chuck table that holds this package substrate also typically has a square shape or a rectangular shape in plan view. Further, an outside diameter of the trajectory of the plurality of grindstones that is followed when the spindle is rotated is larger than the distance between the center of the holding surface of the chuck table and each of the corners.

The reverse side of the package substrate is ground in the grinding apparatus in the following order, for example. First, the face side of the package substrate is held on the holding surface of the chuck table. Next, the chuck table and the spindle are moved relative to each other such that the center of the reverse side of the package substrate and the abovementioned trajectory overlap in a predetermined direction (for example, the vertical direction).

Subsequently, while both being rotated, the chuck table and the spindle are caused to approach each other along the predetermined direction such that the reverse side of the package substrate and the plurality of grindstones come into contact with each other. As a result, a portion of the reverse side of the package substrate with which the plurality of grindstones have come into contact is ground.

Note that this grinding is performed with the area of contact (area to be ground) between the reverse side of the package substrate and the plurality of grindstones being increased or decreased. For example, the area to be ground when portions between the center of the reverse side of the package substrate and the corners are to be ground is larger than the area to be ground when other portions (for example, a portion between the center and the intermediate part between a pair of adjacent corners) are to be ground.

When the area to be ground is thus increased or decreased, the load (grinding load) caused to act on each of the chuck table and the spindle also increases or decreases in association with grinding. In this case, dispersion and concentration of force (grinding force) that is applied to the workpiece when the reverse side of the package substrate is ground are alternately repeated.

Specifically, when the portions between the center of the reverse side of the package substrate and the corners are ground, the grinding force is dispersed, and when the portions between the center and the intermediate part between each of the pairs of adjacent corners are ground, the grinding force is concentrated. Hence, when the reverse side of the package substrate is ground, the portions near the corners are not removed to a sufficient extent, and hence tend to have a finishing thickness greater than those of other portions.

In light of the abovementioned circumstances, in order to reduce the thickness variations caused in association with grinding of the package substrate, there has been proposed a method of grinding the holding surface of the chuck table (see, for example, Japanese Patent Laid-open No. 2020-55080). Specifically, this method proposes to grind the holding surface of the chuck table such that a curvature similar to the curvature formed on the reverse side of the package substrate due to the increase or decrease of the grinding area that occurs when the package substrate is ground is formed on the holding surface.

SUMMARY OF THE INVENTION

The factors that affect thickness variations caused in association with the grinding of the package substrate described above are not limited to the increase or decrease of the grinding area. Another example of these factors is a difference in the number of contact with any of the plurality of grindstones (grinding frequency) for each portion on the reverse side of the package substrate.

Specifically, when the package substrate is to be ground as described above, while the trajectory of the plurality of grindstones that is followed when the spindle is rotated always overlaps with the portions near the center of the reverse side of the package substrate, the trajectory intermittently overlaps with the portions near the outer periphery of the package substrate (for example, the portions near the corners or the portions near the intermediate part between the pair of adjacent corners).

In this case, the portions near the center of the reverse side of the package substrate are ground at a higher frequency than the portions near the outer periphery. Hence, in this case, the portions near the outer periphery are not removed to a sufficient extent, and hence tend to have a finishing thickness greater than those of the portions near the center.

In view of the abovementioned point, an object of the present invention is to reduce not only the thickness variations caused by the increase or decrease of the grinding area but also the thickness variations caused by the difference in grinding frequency, when a flat plate-shaped workpiece having four or more corners in plan view as exemplified by a package substrate is to be ground.

In accordance with an aspect of the present invention, there is provided a chuck table used at a time of grinding a flat plate-shaped workpiece having four or more corners in plan view, the chuck table including a holding surface partitioned into a circular first region and a polygonal second region that surrounds the first region and that has an outer periphery having four or more corners, in plan view, in which the holding surface has such a shape that a center of the first region is a lowest point and a height increases as a distance from the center increases, and an angle formed between a reference tangent plane of the holding surface at the center of the first region and a first tangent plane of the holding surface at points other than the center that are included in the first region is smaller than an angle formed between the reference tangent plane and a second tangent plane of the holding surface at points included in the second region.

In accordance with another aspect of the present invention, there is provided a grinding apparatus for grinding a flat plate-shaped workpiece having four or more corners in plan view, the grinding apparatus including a chuck table that includes a holding surface partitioned into a circular first region and a polygonal second region surrounding the first region and having an outer periphery having four or more corners, in plan view, and that is rotatable about a straight line passing through a center of the first region, as a rotational axis, and a spindle having a distal end portion to which a grinding wheel including a plurality of grindstones disposed annularly at predetermined intervals is mounted, in which an outer diameter of a trajectory of the plurality of grindstones that is followed when the spindle is rotated is larger than a distance between the center of the first region of the holding surface and each of the four or more corners, the holding surface has such a shape that the center of the first region is a lowest point and a height increases as a distance from the center increases, and an angle formed between a reference tangent plane of the holding surface at the center of the first region and a first tangent plane of the holding surface at points other than the center that are included in the first region is smaller than an angle formed between the reference tangent plane and a second tangent plane of the holding surface at points included in the second region.

In accordance with a further aspect of the present invention, there is provided a workpiece grinding method of grinding a flat plate-shaped workpiece having four or more corners in plan view, in a grinding apparatus including a chuck table that has a holding surface partitioned into a circular first region and a polygonal second region surrounding the first region and having an outer periphery having four or more corners, in plan view, and that is capable of rotating about a straight line passing through a center of the first region, as a rotational axis, and a spindle having a distal end portion to which a grinding wheel including a plurality of grindstones disposed annularly at predetermined intervals is mounted, an outer diameter of a trajectory of the plurality of grindstones that is followed when the spindle is rotated being larger than a distance between the center of the first region of the holding surface and each of the four or more corners, the workpiece grinding method including holding a face side of the workpiece on the holding surface of the chuck table in a state in which each of the four or more corners included in the workpiece is positioned in a same direction as any of the four or more corners included in the second region as viewed from the center of the first region, after the holding, moving the chuck table and the spindle relative to each other such that the center of the first region and the trajectory overlap with each other in a predetermined direction, and, after the moving, causing the chuck table and the spindle to approach each other along the predetermined direction such that a reverse side of the workpiece and the plurality of grindstones come into contact with each other, while rotating both the chuck table and the spindle, in which the holding surface has such a shape that the center of the first region is a lowest point and a height increases as a distance from the center increases, and an angle formed between a reference tangent plane of the holding surface at the center of the first region and a first tangent plane of the holding surface at points other than the center that are included in the first region is smaller than an angle formed between the reference tangent plane and a second tangent plane of the holding surface at points included in the second region.

The chuck table according to the present invention has a holding surface having such a shape that the center of the circular first region is the lowest point and the height increases as the distance from the center increases. When a workpiece is to be ground with use of this chuck table, portions near the outer periphery are more likely to be removed than the portions near the center of the workpiece that overlaps with the center of the first region. Hence, in this case, thickness variations caused by the difference in grinding frequency can be reduced.

Further, in the chuck table according to the present invention, the angle formed between the reference tangent plane and the first tangent plane is smaller than the angle formed between the reference tangent plane and the second tangent plane. When a workpiece is to be ground with use of this chuck table, portions of near the corners of the workpiece that overlap with the second region are more likely to be removed than other portions. Hence, in this case, thickness variations caused by increase or decrease of the grinding area can be reduced.

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. 1A is a plan view schematically illustrating an example of a chuck table;

FIG. 1B is a longitudinal sectional view of the chuck table illustrated in FIG. 1A;

FIG. 2 is a sectional side view schematically illustrating part of a grinding apparatus that is capable of grinding a workpiece in a state in which the workpiece is held on a holding surface of the chuck table;

FIG. 3 is a flowchart schematically illustrating an example of a workpiece grinding method of grinding a workpiece in the grinding apparatus;

FIG. 4 is a plan view schematically illustrating an example of a chuck table suitable for use in grinding a workpiece having a rectangular shape in plan view;

FIG. 5 is a plan view schematically illustrating an example of a chuck table suitable for use in grinding a workpiece having a regular pentagon shape in plan view;

FIG. 6 is a plan view schematically illustrating an example of a chuck table suitable for use in grinding a workpiece having an isosceles trapezoid shape in plan view;

FIG. 7A is a plan view schematically illustrating an example of a chuck table including components that are separable from one another;

FIG. 7B is a longitudinal sectional view of the chuck table illustrated in FIG. 7A;

FIG. 8A is a plan view schematically illustrating a first member included in the chuck table illustrated in FIGS. 7A and 7B;

FIG. 8B is a longitudinal sectional view of the first member illustrated in FIG. 8A;

FIG. 9A is a plan view schematically illustrating an example of a chuck table including no porous plate; and

FIG. 9B is a longitudinal sectional view of the chuck table illustrated in FIG. 9A.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

With reference to the attached drawings, an embodiment of the present invention will be described. Note that the attached drawings are offered for easy understanding of the present invention and hence do not necessarily accurately reflect the products and/or methods implementing the present invention. FIG. 1A is a plan view schematically illustrating an example of a chuck table, and FIG. 1B is a longitudinal sectional view of the chuck table illustrated in FIG. 1A.

The chuck table illustrated in FIGS. 1A and 1B and denoted by 2 includes a frame 4 made of, for example, stainless steel (SUS). The frame 4 includes an upper surface 4a whose outer periphery has a square shape in plan view, and has a circular recessed portion formed on the upper surface 4a side. In other words, the frame 4 has the upper surface 4a having such a shape that a circular portion located at the center of a square in plan view is cut out.

Further, to the recessed portion, a circular plate-shaped porous plate 6 made of, for example, ceramic is fixed. Hence, in plan view, the chuck table 2 is partitioned into an upper surface 6a (first region) of the circular porous plate 6 and the upper surface 4a (second region) of the frame 4 which surrounds the upper surface 6a of the porous plate 6 and the outer periphery of which has a square shape.

An upper surface (the upper surface 4a of the frame 4 and the upper surface 6a of the porous plate 6) of the chuck table 2 has such a shape that a center C of the upper surface 6a of the porous plate 6 is the lowest point and the height increases as the distance from the center C increases. Specifically, the upper surface 6a of the porous plate 6 has a shape corresponding to the lateral surface of an inverted cone having the vertex at the center C. The upper surface 4a of the frame 4 has such a shape that the regions near the corners are higher than the regions located in the intermediate part between each of the pairs of adjacent corners.

Further, the upper surface 6a of the porous plate 6 is less inclined than the upper surface 4a of the frame 4. In other words, an angle formed between a tangent plane (reference tangent plane) of the upper surface 6a of the porous plate 6 at the center C of the upper surface 6a and the tangent plane (first tangent plane) of the upper surface 6a at points other than the center C that are included in the upper surface 6a is smaller than the angle between the reference tangent plane and the tangent plane (second tangent plane) of the upper surface 4a of the frame 4 at points included in the upper surface 4a.

A groove 8 is formed in the upper surface 4a of the frame 4. The groove 8 includes a circular ring portion 8a whose inner periphery and outer periphery extend concentrically with the outer periphery of the upper surface 6a of the porous plate 6 and a square ring portion 8b in which the inner periphery of the circular ring portion 8a touches internally the center of each side included in a square shaped inner periphery and the outer periphery of the circular ring portion 8a touches internally the center of each side included in a square shaped outer periphery.

Further, the groove 8 includes two circular arc portions 8c and 8d disposed in each of the four regions defined by the circular ring portion 8a and the square ring portion 8b in plan view. The circular arc portions 8c and 8d each have both ends connected to the square ring portion 8b and extend in such a manner that the inner periphery and the outer periphery thereof overlap with part of a concentric circle of the outer periphery of the upper surface 6a of the porous plate 6.

A communication passage 10 is formed inside the frame 4. The communication passage 10 incudes a main path 10a that is open at the bottom face of the recessed portion formed on the upper surface 4a side of the frame 4 and that penetrates the frame 4 in the thickness direction and a plurality of intermediate paths 10b and 10c each having one end connected to the main path 10a and extending in such a manner as to intersect the main path 10a at right angles.

Further, the communication passage 10 includes a plurality of sub-paths 10d, 10e, 10f, and 10g each having one end connected to one of the plurality of intermediate paths, i.e., the intermediate path 10b or the intermediate path 10c, and each extending in parallel with the main path 10a. The other end of the sub-path 10d, the other end of the sub-path 10e, the other end of the sub-path 10f, and the other end of the sub-path 10g are connected respectively to the circular ring portion 8a, the square ring portion 8b, the circular arc portion 8c, and the circular art portion 8d of the groove 8.

Further, the communication passage 10 (specifically, the main path 10a) can, for example, communicate with a suction source such as an ejector provided in the grinding apparatus. When the suction source is operated in a state in which the communication passage 10 is in communication with the suction source, suction force acts in a space near the upper surface of the chuck table 2.

Specifically, in this case, suction force acts in the space near the upper surface 6a via the main path 10a and the porous plate 6, and suction force acts also in a space near the upper surface 4a of the frame 4 via the main path 10a, the plurality of intermediate paths 10b and 10c, the plurality of sub-paths 10d, 10e, 10f, and 10g, and the groove 8.

Hence, the chuck table 2, using its upper surface (the upper surface 4a of the frame 4 and the upper surface 6a of the porous plate 6) as a holding surface, can hold under suction a workpiece having such a shape that, in plan view, the outer periphery thereof is positioned on the inner side of the outer periphery of the frame 4 but on the outer side of the square ring portion 8b of the groove 8, for example.

FIG. 2 is a sectional side view schematically illustrating part of the grinding apparatus that is capable of grinding the workpiece in a state in which the workpiece is held on the holding surface of the chuck table 2. Note that the direction indicated by an arrow X (X direction) and the direction indicated by an arrow Y (Y direction) that are illustrated in FIG. 2 are directions orthogonal to each other in the horizontal plane and the direction (vertical direction) indicated by an arrow Z (Z direction) is a direction orthogonal to the X direction and Y direction.

Further, in FIG. 2, the holding surface (upper surface) of the chuck table 2 is illustrated as being substantially flat for the purpose of more accurately reflecting the actual scale such as the thickness and the width of the chuck table 2. That is, in FIG. 1B, the difference in thickness for each portion included in the chuck table 2 and the difference in inclination for each region included in the holding surface are illustrated in an exaggerated manner in order to allow easy understanding of the shape of the holding surface of the chuck table 2.

The grinding apparatus illustrated in FIG. 2 and denoted by 12 includes a base 14 that supports the components. On an upper surface of the base 14, an X direction moving mechanism 16 is provided. The X direction moving mechanism 16 includes a pair of guiderails 18 each extending along the X direction. Further, on the pair of guiderails 18, a rectangular parallelepiped X direction moving plate 20 is attached in such a manner as to be slidable along the X direction.

Between the pair of guiderails 18, a screw shaft 22 extending along the X direction is disposed. To one end of the screw shaft 22, a stepping motor 24 for rotating the screw shaft 22 is connected. Further, on the outer peripheral surface on which a screw thread of the screw shaft 22 is formed, a nut 26 accommodating a number of balls that circulate in association with the rotation of the screw shaft 22 is provided, constituting a ball screw.

Further, the nut 26 is fixed to a lower surface side of the X direction moving plate 20. Hence, when the screw shaft 22 is rotated by the stepping motor 24, the X direction moving plate 20 moves along the X direction together with the nut 26. Further, to the upper side of the X direction moving plate 20, the chuck table 2 is connected in such a manner as to be movable along the X direction together with the X direction moving plate 20.

Specifically, when the stepping motor 24 of the X direction moving mechanism 16 is actuated, the chuck table 2 moves between a loading/unloading position and a grinding position. The loading/unloading position is a position suitable for loading a workpiece to the chuck table 2 and unloading the workpiece from the chuck table 2, and is, for example, a position that does not overlap with a grinding wheel 56, which is to be described later, in the Z direction.

Further, the grinding position is a position suitable for grinding the workpiece held on the holding surface of the chuck table 2, and is, for example, a position where the trajectory of a plurality of grindstones 56c included in the grinding wheel 56 that is followed when the spindle 54, which is to be described later, is rotated and the center of the holding surface of the chuck table 2 (the center C of the upper surface 6a of the porous plate 6) overlap with each other in the Z direction.

Further, on the lower side of the chuck table 2, a rotational mechanism (not illustrated) for rotating the suction source described above and the chuck table 2 is provided. This rotational mechanism includes, for example, a pulley and a servomotor, etc. When this rotational mechanism is actuated, the chuck table 2 rotates about a straight line passing through the center of the holding surface, as the rotational axis.

Further, on the lower side of the chuck table 2, a cylindrical bearing 28 and a cylindrical table base 30 that support the chuck table 2 in a manner allowing rotation of the chuck table 2 are provided. The chuck table 2 is supported by an inclination adjustment mechanism 32 via the bearing 28 and the table base 30.

The inclination adjustment mechanism 32 includes two movable shafts 32a and 32b and one fixed shaft 32c that are disposed at substantially equal angular intervals along the circumferential direction of the chuck table 2 and that each have the lower end fixed to the upper surface side of the X direction moving plate 20. When at least one of the two movable shafts, i.e., the movable shaft 32a or the movable shaft 32b, partially lifts or lowers the chuck table 2, the inclination of the rotational axis of the chuck table 2 is adjusted.

On the end portion of the base 14, a support structure 34 extending along the Z direction is provided. On a surface of the support structure 34 on the chuck table 2 side, a Z direction moving mechanism 36 is provided. The Z direction moving mechanism 36 includes a pair of guiderails 38 each extending along the Z direction. To a front surface of the pair of guiderails 38, a rectangular parallelepiped Z direction moving plate 40 is attached in such a manner as to be slidable along the Z direction.

Between the pair of guiderails 38, a screw shaft 42 extending along the Z direction is disposed. To one end portion (upper end portion) of the screw shaft 42, a stepping motor 44 for rotating the screw shaft 42 is connected. Further, on the outer peripheral surface on which a screw thread of the screw shaft 42 is formed, a nut 46 accommodating a number of balls that circulate in association with the rotation of the screw shaft 42 is provided, constituting a ball screw.

The nut 46 is fixed to the rear surface side of the Z direction moving plate 40. Hence, when the screw shaft 42 is rotated by the stepping motor 44, the Z direction moving plate 40 moves along the Z direction together with the nut 46. Further, on the front surface side of the Z direction moving plate 40, a bottomed cylindrical cover 48 is fixed. At the center of the bottom portion of the cover 48, a through hole 48a is formed.

Further, a housing 50 is provided inside the cover 48. The housing 50 is supported on the bottom portion of the cover 48 via two spacers 52a and 52b and houses part of the spindle 54 extending along the Z direction in such a manner that the spindle 54 can be rotated.

Further, the housing 50 also houses a servomotor (not illustrated) that is connected to the proximal end portion (upper end portion) of the spindle 54. The spindle 54 is protruding downward through the through hole 48a formed in the bottom portion of the cover 48. A distal end portion (lower end portion) 54a of the spindle 54 has a circular plate shape and functions as a wheel mount.

In the distal end portion 54a of the spindle 54, a plurality of through holes are formed at substantially equal angular intervals along the circumferential direction. Further, to the distal end portion 54a of the spindle 54, the grinding wheel 56 is mounted with use of fixtures (not illustrated) such as bolts that are inserted into the respective through holes.

The grinding wheel 56 includes an annular wheel base 56a that is made of a metal material such as SUS. Further, on the lower surface of the wheel base 56a, a plurality of grindstones 56b are disposed annularly at predetermined intervals. Note that each of the plurality of grindstones 56b includes a binder such as a vitrified binder or a resinoid binder and abrasive grains such as diamond dispersed in the binder.

When the servomotor connected to the proximal end portion of the spindle 54 is actuated, the grinding wheel 56 rotates together with the spindle 54. Note that the outer diameter of the trajectory of the plurality of grindstones 56b that is followed when the spindle 54 is rotated is larger than the distance between the center of the holding surface of the chuck table 2 (the center C of the upper surface 6a of the porous plate 6) and each of the four corners.

FIG. 3 is a flowchart schematically illustrating an example of a workpiece grinding method that grinds a workpiece in the grinding apparatus 12. Note that one example of the workpiece is a package substrate that has a plurality of devices formed on the face side and that has such a shape that the outer periphery thereof is located on the inner side of the outer periphery of the frame 4 but on the outer side of the square ring portion 8b of the groove 8 in plan view.

In this method, first, the face side of the workpiece is held on the holding surface of the chuck table 2 (holding step S1). Specifically, in the holding step S1, after the workpiece is placed on the holding surface of the chuck table 2 that is positioned to the loading/unloading position, such that the reverse side of the workpiece faces upward and the porous plate 6 and the grooves 8 are covered, the suction source communicating with the communication passage 10 is operated.

After the holding step S1, the chuck table 2 is moved such that the center of the holding surface of the chuck table 2 is positioned immediately below the trajectory of the plurality of grindstones 56b that is followed when the spindle 54 is rotated (disposing step S2). Specifically, in the disposing step S2, the stepping motor 24 of the X direction moving mechanism 16 is operated in such a manner as to position the chuck table 2 to the grinding position.

After the disposing step S2, while both the chuck table 2 and the spindle 54 are rotated, the spindle 54 is lowered to cause the reverse side of the workpiece and the plurality of grindstones 56b to come into contact with each other (grinding step S3). Specifically, in the grinding step S3, while both the servomotor included in the rotational mechanism provided on the lower side of the chuck table 2 and the servomotor housed in the housing 50 are operated, the stepping motor 44 of the Z direction moving mechanism 36 is operated. When the reverse side of the workpiece and the plurality of grindstones 56b come into contact with each other, the reverse side of the workpiece is ground.

The holding surface of the chuck table 2 has such a shape that the center C of the upper surface 6a (first region) of the circular porous plate 6 is the lowest point and the height increases as the distance from the center C increases. When a workpiece is to be ground with use of the chuck table 2, portions near the outer periphery are more likely to be removed than the portions near the center of the workpiece that overlaps with the center C of the first region. Hence, in this case, thickness variations caused by the difference in grinding frequency can be reduced.

Further, in the chuck table 2, the angle formed between the tangent plane (reference tangent plane) of the upper surface 6a of the porous plate 6 at the center C of the upper surface 6a and the tangent plane (first tangent plane) of the upper surface 6a at points other than the center C that are included in the upper surface 6a is smaller than the angle formed between the reference tangent plane and the tangent plane (second tangent plane) of the upper surface 4a of the frame 4 at points included in the upper surface 4a. When a workpiece is to be ground with use of the chuck table 2, portions near the corners in the workpiece that overlap with the upper surface 4a (second region) of the frame 4 that surrounds the upper surface 6a of the porous plate 6 and the outer periphery of which is of a square shape are more likely to be removed than other portions. Hence, in this case, thickness variations caused by increase or decrease of the grinding area can be reduced.

Note that the details described above represent one mode of the present invention, the present invention is not limited to the details described above. For example, the chuck table according to the present invention may have a holding surface having such a shape that its longitudinal cross section is curved.

Specifically, the chuck table according to the present invention may have such an upper surface that the angle formed between the tangent plane (reference tangent plane) of the holding surface at the center and the tangent plane of the holding surface at a point other than the center becomes greater as the point gets farther away from the center.

Moreover, the chuck table according to the present invention may, for example, have a holding surface of a polygonal shape other than a triangle or a square in plan view. That is, the chuck table according to the present invention can appropriately be modified to have shapes suitable for use in grinding a flat plate-shaped workpiece having four or more corners.

FIG. 4 is a plan view schematically illustrating an example of a chuck table having a shape suitable for use in grinding a workpiece having a rectangular shape in plan view. The chuck table illustrated in FIG. 4 and denoted by 58 includes a frame 60 made of, for example, SUS. The frame 60 includes an upper surface 60a whose outer periphery has a rectangular shape in plan view, and has a circular recessed portion formed on the upper surface 60a side. In other words, the frame 60 includes the upper surface 60a having such a shape that a circular portion positioned at the center of a rectangle in plan view is cut out.

To this recessed portion, a circular plate-shaped porous plate 62 made of, for example, ceramic is fixed. Hence, the holding surface of the chuck table 58 is, in plan view, partitioned into an upper surface 62a (first region) of the circular porous plate 62 and the upper surface 60a (second region) of the frame 60 that surrounds the upper surface 62a of the porous plate 62 and the outer periphery of which has a rectangular shape.

A groove 64 is formed in the upper surface 60a of the frame 60. The groove 64 includes a circular ring portion 64a whose inner periphery and outer periphery extend concentrically with the outer periphery of the upper surface 62a of the porous plate 62 and a rectangular ring portion 64b in which the inner periphery of the circular ring portion 64a touches internally the center of each of the long sides included in the rectangular inner periphery and the outer periphery of the circular ring portion 64a touches internally the center of each of the long sides included in the rectangular outer periphery, in plan view.

The groove 64 further includes two circular arc portions 64c and 64d disposed in each of the two regions defined by the circular ring portion 64a and the rectangular ring portion 64b in plan view. The circular arc portions 64c and 64d each have both ends connected to the rectangular ring portion 64b and extend in such a manner that the inner periphery and the outer periphery thereof overlap with part of a concentric circle of the outer periphery of the upper surface 62a of the porous plate 62. Further, the circular arc portion 64d extends in such a manner that the inner periphery thereof touches internally the center of each of the short sides included in the inner periphery of the rectangular ring portion 64b and the outer periphery thereof touches internally the center of each of the short sides included in the outer periphery of the rectangular ring portion 64b.

The groove 64 further includes a circular arc portion 64e disposed in each of the four regions defined by the rectangular ring portion 64b and the circular arc portion 64d in plan view. The circular arc portion 64e has both ends connected to the rectangular ring portion 64b and extends in such a manner that the inner periphery and the outer periphery thereof overlap with part of a concentric circle of the outer periphery of the upper surface 62a of the porous plate 62.

The chuck table 58 is used, for example, to grind a workpiece having such a shape that the outer periphery thereof is located on the inner side of the outer periphery of the upper surface 60a of the frame 60 but on the outer side of the rectangular ring portion 64b of the groove 64 in plan view.

FIG. 5 is a plan view schematically illustrating an example of a chuck table having a shape suitable for use in grinding a workpiece having a regular pentagon shape in plan view. The chuck table illustrated in FIG. 5 and denoted by 66 includes a frame 68 made of, for example, SUS. The frame 68 includes an upper surface 68a whose outer periphery has a regular pentagon shape in plan view, and has a circular recessed portion formed on the upper surface 68a side. In other words, the frame 68 includes the upper surface 68a having such a shape that the circular portion located at the center of a regular pentagon in plan view is cut out.

To this recessed portion, a circular plate-shaped porous plate 70 made of, for example, ceramic is fixed. Hence, the holding surface of the chuck table 66 is, in plan view, partitioned into an upper surface 70a (first region) of the circular porous plate 70 and the upper surface 68a (second region) of the frame 68 that surrounds the upper surface 70a of the porous plate 70 and the outer periphery of which has a regular pentagon shape.

A groove 72 is formed in the upper surface 68a of the frame 68. The groove 72 includes a circular ring portion 72a whose inner periphery and outer periphery extend concentrically with the outer periphery of the upper surface 70a of the porous plate 70 and a regular pentagon-shaped ring portion 72b that extends in such a manner that the inner periphery of the circular ring portion 72a touches internally the center of each of the sides included in the regular pentagon inner periphery and the outer periphery of the circular ring portion 72a touches internally the center of each of the sides included in the regular pentagon outer periphery, in plan view.

The groove 72 further includes a circular arc portion 72c disposed in each of the five regions defined by the circular ring portion 72a and the regular pentagon-shaped ring portion 72b in plan view. The circular arc portion 72c has both ends connected to the regular pentagon-shaped ring portion 72b and extends in such a manner that the inner periphery and the outer periphery thereof overlap with part of a concentric circle of the outer periphery of the upper surface 70a of the porous plate 70.

The chuck table 66 is used, for example, for grinding a workpiece having such a shape that the outer periphery is located on the inner side of the outer periphery of the upper surface 68a of the frame 68 but on the outer side of the regular pentagon-shaped ring portion 72b of the groove 72 in plan view.

FIG. 6 is a plan view schematically illustrating an example of a chuck table having a shape suitable for use in grinding a workpiece having an isosceles trapezoid shape in plan view. The chuck table illustrated in FIG. 6 and denoted by 74 includes a frame 76 made of, for example, SUS. The frame 76 includes an upper surface 76a whose outer periphery has an isosceles trapezoid shape in plan view, and has a circular recessed portion formed on the upper surface 76a side. In other words, the frame 76 has the upper surface 76a having such a shape that a circular portion located at the center of an isosceles trapezoid in plan view is cut out.

To this recessed portion, a circular plate-shaped porous plate 78 made of, for example, ceramic is fixed. Hence, the holding surface of the chuck table 74 is, in plan view, partitioned into an upper surface 78a (first region) of the circular porous plate 78 and the upper surface 76a (second region) of the frame 76 that surrounds the upper surface 78a of the porous plate 78 and the outer periphery of which has an isosceles trapezoid shape.

A groove 80 is formed in the upper surface 76a of the frame 76. The groove 80 includes, in plan view, a circular ring portion 80a whose inner periphery and outer periphery extend concentrically with the outer periphery of the upper surface 78a of the porous plate 78 and an isosceles trapezoid-shaped ring portion 80b that extends in such a manner that the inner periphery of the circular ring portion 80a touches internally the center of each of the shorter base and the longer base included in the isosceles trapezoid-shaped inner periphery and the outer periphery of the circular ring portion 80a touches internally the center of each of the shorter base and the longer base included in the isosceles trapezoid-shaped outer periphery.

The groove 80 further includes two circular arc portions 80c and 80d disposed in each of the two regions defined by the circular ring portion 80a and the isosceles trapezoid-shaped ring portion 80b in plan view. The circular arc portions 80c and 80d each have both ends connected to the isosceles trapezoid-shaped ring portion 80b and each extend in such a manner that the inner periphery and the outer periphery thereof overlap with part of a concentric circle of the outer periphery of the upper surface 78a of the porous plate 78. Further, the circular arc portion 80d extends in such a manner that the inner periphery thereof touches internally the sides other than the bases included in the inner periphery of the isosceles trapezoid-shaped ring portion 80b and the outer periphery thereof touches internally the sides other than the bases included in the outer periphery of the isosceles trapezoid-shaped ring portion 80b.

The groove 80 further includes a circular arc portion 80e disposed in each of the two regions defined by the shorter base side of the isosceles trapezoid-shaped ring portion 80b and the circular arc portion 80d in plan view. The circular arc portion 80e has both ends connected to the isosceles trapezoid-shaped ring portion 80b and extends in such a manner that the inner periphery and the outer periphery thereof overlap with part of a concentric circle of the outer periphery of the upper surface 78a of the porous plate 78.

Further, the groove 80 includes three circular arc portions 80f, 80g, and 80h disposed in each of the two regions defined by the longer base side of the isosceles trapezoid-shaped ring portion 80b and the circular arc portion 80d in plan view. The circular arc portions 80f, 80g, and 80h each have both ends connected to the isosceles trapezoid-shaped ring portion 80b and extend in such a manner that the inner periphery and the outer periphery thereof overlap with part of a concentric circle of the outer periphery of the upper surface 78a of the porous plate 78.

The chuck table 74 is used for grinding a workpiece having such a shape that the outer periphery thereof is located on the inner side of the outer periphery of the upper surface 76a of the frame 76 but on the outer side of the isosceles trapezoid-shaped ring portion 80b of the groove 80 in plan view.

The chuck table according to the present invention may include components separable from each other. FIG. 7A is a plan view schematically illustrating an example of such a chuck table, and FIG. 7B is a longitudinal sectional view of the chuck table illustrated in FIG. 7A.

The chuck table illustrated in FIGS. 7A and 7B and denoted by 82 includes a first member 84. The first member 84 includes a circular plate-shaped dense frame 86 made of, for example, ceramic. The frame 86 includes a protruding portion 88 the lateral surface of which has a circular cylindrical shape. On an upper stage surface 88a side of the protruding portion 88, a circular recessed portion in plan view is formed.

In other words, the protruding portion 88 of the frame 86 includes the upper stage surface 88a having such a shape that the circular portion located at the center of a circle in plan view is dented. To the recessed portion formed in the upper stage surface 88a of the protruding portion 88, a circular plate-shaped porous plate 90 made of, for example, ceramic is fixed.

A lower stage surface 88b that constitutes part of the protruding portion 88 and surrounds the upper stage surface 88a in plan view is provided with an annular dense second member 92 that is made of, for example, metal such as SUS or aluminum or ceramic. The second member 92 has a circular inner periphery and a square outer periphery in plan view. In other words, the second member 92 is a structure of such a plate shape that the circular portion located at the center of a square in plan view is cut out.

The inner diameter of the second member 92 in plan view is equal to or slightly larger than the diameter of the upper stage surface 88a of the protruding portion 88. Hence, in plan view, the upper surface (holding surface) of the chuck table 82 is partitioned into a circular region (the upper stage surface 88a of the protruding portion 88 and the upper surface 90a of the porous plate 90) (first region) and a region that surrounds the first region and the outer periphery of which has a square shape (the upper surface 92a of the second member 92) (second region).

The holding surface of the chuck table 82 (the upper stage surface 88a of the protruding portion 88, the upper surface 90a of the porous plate 90, and the upper surface 92a of the second member 92) has such a shape that the center of the upper surface 90a of the porous plate 90 is the lowest point and the height increases as the distance from the center increases. Specifically, the upper stage surface 88a of the protruding portion 88 and the upper surface 90a of the porous plate 90 have a shape corresponding to the lateral surface of an inverted cone having the vertex at the center of the upper surface 90a of the porous plate 90. Further, the upper surface 92a of the second member 92 has such a shape that the regions near the corners are higher than the regions located in the intermediate part between each of the pairs of adjacent corners.

Further, the upper stage surface 88a of the protruding portion 88 and the upper surface 90a of the porous plate 90 are less inclined than the upper surface 92a of the second member 92. In other words, the angle formed between the tangent plane (reference tangent plane) of the upper surface 90a of the porous plate 90 at the center of the upper surface 90a and the tangent plane (first tangent plane) of the upper stage surface 88a of the protruding portion 88 and the upper surface 90a of the porous plate 90 at points other than the center that are included in the upper stage surface 88a and the upper surface 90a is smaller than the angle formed between the reference tangent plane and the tangent plane (second tangent plane) of the upper surface 92a of the second member 92 at points included in the upper surface 92a.

Four grooves 94 are formed on the upper surface 92a side of the second member 92. Each of the grooves 94 includes, in plan view, an L-shaped bracket portion 94a and a circular arc portion 94b extending in such a manner that the inner periphery and the outer periphery thereof overlap with part of a concentric circle of the outer periphery of the upper surface 90a of the porous plate 90 and both ends thereof are connected to both ends of the L-shaped bracket portion 94a.

Further, each of the grooves 94 includes two circular arc portions 94c and 94d and a linear portion 94e that are located in each of the regions defined by the L-shaped bracket portion 94a and the circular arc portion 94b. The circular arc portions 94c and 94d each extend in such a manner that the inner periphery and the outer periphery thereof overlap with part of a concentric circle of the outer periphery of the upper surface 90a of the porous plate 90 and both ends thereof are connected to the L-shaped bracket portion 94a.

The linear portion 94e extends along the radial direction of the upper surface 90a of the porous plate 90 such that the outer end thereof is connected to the center of the L-shaped bracket portion 94a and that the inner end thereof is connected to the center of the circular arc portion 94b. That is, the linear portion 94e extends in such a manner as to penetrate the center of each of the two circular arc portions 94c and 94d.

Inside the second member 92, a plurality of through passages 96 each penetrating the second member 92 in the thickness direction are provided. Note that the plurality of through passages 96 are each open at the bottom face of the linear portion 94e of the groove 94. In other words, the plurality of through passages 96 are lined up along the radial direction of the upper surface 90a of the porous plate 90.

One of the plurality of through passages 96 that is located at the outermost side is open at the center of the L-shaped bracket portion 94a of the groove 94, that is, the spot where the L-shaped bracket portion 94a and the linear portion 94e connect with each other. One of the through passages 96 that is located at the innermost side is open at the spot where the circular arc portion 94c of the groove 94 and the linear portion 94e connect with each other.

Inside the frame 86 of the first member 84, a first communication passage 98 is formed. The first communication passage 98 includes a main path 98a that is open at the bottom face of the recessed portion formed on the upper stage surface 88a side of the protruding portion 88 and that penetrates the frame 86 in the thickness direction and a plurality of intermediate paths 98b and 98c each having one end connected to the main path 98a and extending in such a manner as to intersect the main path 98a at right angles.

The first communication passage 98 includes a plurality of sub-paths 98d each having one end connected to one of the plurality of intermediate paths, i.e., the intermediate path 98b or the intermediate path 98c, and each extending in parallel with the main path 98a. The plurality of sub-paths 98d are formed in such a manner that each are open at the lower stage surface 88b of the protruding portion 88 and each overlap, in the vertical direction, with the plurality of through passages 96 formed inside the second member 92.

In the chuck table 82, the first member 84 and the second member 92 are separable from each other. FIG. 8A is a plan view schematically illustrating the first member 84 in a state in which the second member 92 is separated therefrom, and FIG. 8B is a longitudinal sectional view of the first member 84 illustrated in FIG. 8A.

Inside the frame 86 of the first member 84, a second communication passage 100 is further formed. The second communication passage 100 includes a main path 100a that extends along the thickness direction of the frame 86 and an intermediate path 100b that is connected to the main path 100a and that extends in a circular ring shape in such a manner as to surround the recessed portion.

The second communication passage 100 further includes a plurality of sub-paths 100c each having one end connected to the intermediate path 100b and each extending in parallel with the main path 100a. Each of the sub-paths 100c is formed in such a manner as to be open at the lower stage surface 88b of the protruding portion 88 and to overlap with a region defined by the L-shaped bracket portion 94a, the two circular arc portions 94b and 94c, and the linear portion 94e of the second member 92 in plan view.

The first communication passage 98 (specifically, the main path 98a) and the second communication passage 100 (specifically, the main path 100a) can, for example, communicate with a suction source such as an ejector provided in the grinding apparatus. Specifically, the first communication passage 98 is connected to the suction source via a first valve, and the second communication passage 100 is connected to the suction source via a second valve different from the first valve.

When the suction source is operated with first valve closed and the second valve opened, suction force acts in the space near the lower stage surface 88b of the protruding portion 88 of the first member 84. Specifically, in this case, suction force acts in the space near the lower stage surface 88b of the protruding portion 88 via the main path 100a, the intermediate path 100b, and the plurality of sub-paths 100c of the second communication passage 100 formed in the first member 84.

Hence, when suction force is caused to act in the manner described above in a state in which the second member 92 is placed on the first member 84 as illustrated in FIGS. 7A and 7B, the second member 92 can be held under suction on the lower stage surface 88b of the protruding portion 88 of the first member 84. Further, when the first valve is opened and the second valve is closed while the suction source is kept being operated, suction force acts in the space near the upper surface 90a of the porous plate 90 and the upper surface 92a of the second member 92.

Specifically, in this case, suction force acts in the space near the upper surface 90a of the porous plate 90 via the main path 98a of the first communication passage 98 formed in the first member 84 and the porous plate 90, and suction force acts in the space near the upper surface 92a of the second member 92 via the main path 98a, the plurality of intermediate paths 98b and 98c, and the plurality of sub-paths 98d of the first communication passage 98 formed in the first member 84 and the plurality of through passages 96 and the four grooves 94 formed in the second member 92.

Hence, the chuck table 82, using the upper stage surface 88a of the protruding portion 88 and the upper surface 90a of the porous plate 90 of the first member 84 and the upper surface 92a of the second member 92 as the holding surface, is capable of holding under suction a workpiece having such a shape that, in plan view, for example, the outer periphery thereof is located on the inner side of the outer periphery of the second member 92 but on outer side of the L-shaped bracket portion 94a of each groove 94.

Further, the chuck table according to the present invention may be free of a porous plate. FIG. 9A is a plan view schematically illustrating an example of a chuck table of such a type, and FIG. 9B is a longitudinal sectional view of the chuck table illustrated in FIG. 9A.

In brief, except that the first member 84 is replaced with a first member 104, the chuck table illustrated in FIGS. 9A and 9B and denoted by 102 has the same structure as the chuck table 82 illustrated in FIGS. 7A and 7B. The first member 104 is a circular plate-shaped dense structure made of, for example, metal such as aluminum or ceramic, and includes a protruding portion 106 the lateral surface of which has a cylindrical shape.

The protruding portion 106 includes an upper stage surface 106a that has a circular shape in plan view. On a lower stage surface 106b that is part of the protruding portion 106 and that surrounds the upper stage surface 106a in plan view, for example, the abovementioned second member 92 is provided. The diameter of the protruding portion 106 in plan view is equal to or slightly smaller than the inner diameter of the second member 92 in plan view.

Hence, the upper surface (holding surface) of the chuck table 102 is, in plan view, partitioned into a circular region (the upper stage surface 106a of the protruding portion 106) (first region) and a region that surrounds the first region and that has a square-shaped outer periphery (the upper surface 92a of the second member 92) (second region).

The holding surface of the chuck table 102 (the upper stage surface 106a of the protruding portion 106 and the upper surface 92a of the second member 92) has such a shape that the center of the upper stage surface 106a of the protruding portion 106 is the lowest point and the height increases as the distance from the center increases. Specifically, the upper stage surface 106a of the protruding portion 106 has a shape corresponding to the lateral surface of an inverted cone having the vertex at the center. The upper surface 92a of the second member 92 has such a shape that the regions near the corners are higher than the regions located in the intermediate part between each of the pairs of adjacent corners.

The upper stage surface 106a of the protruding portion 106 is less inclined than the upper surface 92a of the second member 92. In other words, the angle formed between the tangent plane (reference tangent plane) of the upper stage surface 106a of the protruding portion 106 at the center of the upper stage surface 106a and the tangent plane (first tangent plane) of the upper stage surface 106a of the protruding portion 106 at points other than the center that are included in the upper stage surface 106a is smaller than the angle formed between the reference tangent plane and the tangent plane (second tangent plane) of the upper surface 92a of the second member 92 at points included in the upper surface 92a.

A groove 108 is formed in the upper stage surface 106a side of the protruding portion 106 of the first member 104. The groove 108 includes a plurality of circular ring portions 108a each having an inner periphery and an outer periphery extending concentrically with the outer periphery of the upper stage surface 106a and two main linear portions 108b each having both ends connected to the circular ring portion 108a and extending in such a manner as to pass through the center of the upper stage surface 106a and to intersect each other at right angles.

The groove 108 further includes a sub-linear portion 108c in each of the four regions defined by one of the plurality of circular ring portions 108a that is located on the outermost side and the two main linear portions 108b. The sub-linear portion 108c extends in such a manner that its outer end is connected to one of the plurality of circular ring portions 108 that is located on the outermost side and its inner end is connected to one of the plurality of circular ring portions 108a that is located on the innermost side. Further, the sub-linear portion 108c extends along the directions with which the directions in which the two main linear portions 108b extend form an angle of 45°.

Inside the first member 104, a first communication passage 110 and a second communication passage (not illustrated) that is similar to the second communication passage 100 illustrated in FIGS. 8A and 8B are formed. The first communication passage 110 includes a main path 110a that extends along the thickness direction of the first member 104 and a plurality of intermediate paths 110b and 110c each having one end connected to the main path 110a and extending in such a manner as to intersect the main path 110a at right angles.

The first communication passage 110 further includes a plurality of inner sub-paths 110d and a plurality of outer sub-paths 110e each having one end connected to one of the plurality of intermediate paths, i.e., the intermediate path 110b or the intermediate path 110c, and each extending in parallel with the main path 110a.

The plurality of inner sub-paths 110d are each open at the bottom face of the groove 108 formed in the upper stage surface 106a of the protruding portion 106. Further, a plurality of outer sub-paths 110e are formed in such a manner that each are open at the lower stage surface 106b of the protruding portion 106 and overlap with the plurality of through passages 96 formed inside the second member 92, in the vertical direction.

The first communication passage 110 (specifically, the main path 110a) and the second communication passage can, for example, communicate with a suction source such as an ejector provided in the grinding apparatus. Specifically, the first communication passage 110 is connected to the suction source via a first valve, and the second communication passage is connected to the suction source via a second valve different from the first valve.

When the suction source is actuated with the first valve closed and the second valve opened, suction force acts in the space near the lower stage surface 106b of the protruding portion 106 of the first member 104. Specifically, in this case, suction force acts in the space near the lower stage surface 106b of the protruding portion 106 via the second communication passage formed in the first member 104.

Hence, when suction force is caused to act in the manner described above in a state in which the second member 92 is placed on the first member 104 as illustrated in FIGS. 9A and 9B, the second member 92 can be held under suction on the lower stage surface 106b of the protruding portion 106 of the first member 104. When the first valve is opened and the second valve is closed while the suction source is kept being operated, suction force acts in the space near the upper stage surface 106a of the protruding portion 106 and the space near the upper surface 92a of the second member 92.

Specifically, in this case, suction force acts in the space near the upper stage surface 106a of the protruding portion 106 via the main path 110a, the plurality of intermediate paths 110b and 110c, and the plurality of inner sub-paths 110d of the first communication passage 110 formed in the first member 104, and suction force acts in the space near the upper surface 92a of the second member 92 via the main path 110a, the plurality of intermediate paths 110b and 110c, and the plurality of the outer sub-paths 110e of the first communication passage 110 formed in the first member 104 and via the plurality of through passages 96 and the four grooves 94 formed in the second member 92.

Hence, the chuck table 102, using the upper stage surface 106a of the protruding portion 106 of the first member 104 and the upper surface 92a of the second member 92 as the holding surface, is capable of holding under suction a workpiece having such a shape that the outer periphery thereof is located on the inner side of the outer periphery of the second member 92 but on the outer side of the L-shaped bracket portion 94a of the grooves 94 in plan view, for example.

Other structures, methods, and the like according to the embodiment described above may be implemented with appropriate changes within the scope not departing from the object of the present invention.

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.