GRINDING WHEEL AND GRINDING METHOD

Abstract

A grinding wheel includes an annular base, a plurality of pipe grindstones annularly arranged on the annular base, and a grinding water supply unit that supplies grinding water to the pipe grindstones. The grinding water supply unit includes a ring-shaped grinding water retaining part formed between a mount surface and an opposite surface of the annular base, a plurality of water supply holes opening in the mount surface, and a plurality of water feeding holes formed to allow communication between the grinding water retaining part and an inside of each of the pipe grindstones.

Claims

1. A grinding wheel comprising: an annular base having a mount surface mounted to a spindle mount of a grinding apparatus; a plurality of pipe grindstones annularly arranged on an opposite surface of the annular base opposite to the mount surface; and a grinding water supply unit that supplies grinding water to the pipe grindstones, wherein the grinding water supply unit includes a ring-shaped grinding water retaining part formed between the mount surface and the opposite surface of the annular base, a plurality of water supply holes opening in a plurality of water feeding holes formed to allow communication between the grinding water retaining part and an inside of each of the pipe grindstones.

2. The grinding wheel according to claim 1, wherein the grinding water retaining part has at an inner circumferential surface thereof a ring-shaped annular opening that opens to atmosphere.

3. A grinding method for grinding a workpiece by use of a grinding wheel including an annular base having a mount surface mounted to a spindle mount of a grinding apparatus, a plurality of pipe grindstones annularly arranged on an opposite surface of the annular base opposite to the mount surface, and a grinding water supply unit that supplies grinding water to the pipe grindstones, the grinding water supply unit including a ring-shaped grinding water retaining part formed between the mount surface and the opposite surface of the annular base, a plurality of water supply holes opening in the mount surface, and a plurality of water feeding holes formed to allow communication between the grinding water retaining part and an inside of each of the pipe grindstones, the grinding method comprising: supplying grinding water into each of the plurality of pipe grindstones; temporarily retaining the grinding water in the grinding water retaining part by centrifugal force generated by rotation of the grinding wheel; and grinding the workpiece by lower ends of the pipe grindstones while supplying the grinding water retained in the grinding water retaining part into each of the pipe grindstones from upper ends of the pipe grindstones.

4. The grinding method according to claim 3, wherein the grinding water is supplied from the grinding water retaining part into each of the pipe grindstones, and grinding water overflowing from the grinding water retaining part is supplied to an outer circumferential surface of each of the pipe grindstones.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] FIG. 1 is a perspective view of a grinding apparatus including a grinding wheel according to an embodiment of the present invention;

[0010] FIG. 2 is a side cross-sectional view depicting principal parts of the grinding apparatus illustrated in FIG. 1;

[0011] FIG. 3 is an enlarged cross-sectional view of part A of FIG. 2;

[0012] FIG. 4 is a perspective view of the grinding wheel according to the present embodiment, as seen from an obliquely upper side;

[0013] FIG. 5 is a perspective view of the grinding wheel according to the present embodiment, as seen from an obliquely lower side;

[0014] FIG. 6 is an enlarged cross-sectional view taken along line B-B of FIG. 4; FIG. 7 is a cross-sectional view equivalent to FIG.

[0015] 6, depicting a grinding wheel according to a first modification of the present embodiment;

[0016] FIG. 8 is a cross-sectional view equivalent to FIG. 6, depicting a grinding wheel according to a second modification of the present embodiment; and

[0017] FIG. 9 is a cross-sectional view equivalent to FIG. 6, depicting a grinding wheel according to a third modification of the present embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0018] An embodiment of the present invention is hereinafter described with reference to accompanying drawings. Described first is a configuration of a grinding apparatus including a grinding wheel according to the present embodiment with reference to FIG. 1 to FIG. 3. It is to be noted that, in the description below, arrow directions indicated in FIG. 1 are defined as X-axis directions (left-right directions), Y-axis directions (front-rear directions), and Z-axis directions (up-down directions).

[0019] A grinding apparatus 1 illustrated in FIG. 1 is an apparatus that grinds, as a workpiece, resin R (refer to FIG. 2) coating an upper surface of a disk-shaped wafer W, and includes the following components. Specifically, the grinding apparatus 1 includes as its principal components a chuck table 10 that holds the wafer W thereon and rotates about its central axis, a grinding unit 20 that grinds the resin R coating the wafer W held under suction on the chuck table 10, a thickness measuring instrument 30 for measuring a thickness of the wafer W including the resin R during the grinding, an elevating mechanism 40 that raises and lowers the grinding unit 20 in directions (Z-axis directions) perpendicular to a holding surface 10a of the chuck table 10, a horizontal movement mechanism 50 that moves the chuck table 10 in directions (Y-axis directions) parallel to the holding surface 10a, and a grinding water supply unit 60 that supplies grinding water to a portion at which the resin R is being ground.

[0020] Here, the wafer W is a thin, disk-shaped member made of single-crystal silicon as a base material, and as illustrated in FIG. 2, a plurality of devices D are mounted on the upper surface of the wafer W. These devices D are coated with and protected by the resin R. Further, a tape T is affixed to a lower surface of the wafer W. The lower surface of the wafer W is held under suction by the holding surface 10a of the chuck table 10 with the tape T interposed therebetween, and the resin R on the upper surface of the wafer W is to be ground by the grinding unit 20.

[0021] Described next are configurations of the chuck table 10, the grinding unit 20, the thickness measuring instrument 30, the elevating mechanism 40, the horizontal movement mechanism 50, and the grinding water supply unit 60, which are the principal components of the grinding apparatus 1.

[0022] The chuck table 10 is a disk-shaped member and has a disk-shaped porous member 10A incorporated at an upper central part thereof as illustrated in FIG. 2. The porous member 10A here is made of porous ceramic or the like and has an upper surface constituting the holding surface 10a that holds the disk-shaped wafer W under suction. It is to be noted that the porous member 10A of the chuck table 10 is selectively connected to a suction source 13 such as a vacuum pump through suction paths 2 and 3 formed at respective axial centers of the chuck table 10 and a rotational axis 11 rotatably supporting the chuck table 10 and through piping 12 connected to the suction path 3. It is to be noted that the piping 12 is provided with an opening and closing valve V1 for selectively connecting the porous member 10A to the suction source 13.

[0023] The chuck table 10 is driven by an unillustrated rotational mechanism to rotate about its central axis at a predetermined speed. That is, in the chuck table 10, the rotational axis 11 is driven by the unillustrated rotational mechanism to rotate at a predetermined speed.

[0024] The grinding apparatus 1 further includes a base 100 in the form of a rectangular box elongated in the Y-axis directions (front-rear directions) as illustrated in FIG. 1, and the base 100 has a rectangular opening 100a that is elongated in the Y-axis directions and through which the chuck table 10 is exposed. The chuck table 10 is covered at its periphery in the opening 100a by a cover 14 in the form of a rectangular plate, and portions in the opening 100a in front of and behind the cover 14 (portions located in the-Y direction and the +Y direction with respect to the cover 14) are covered respectively by bellows-like covers 15 and 16 that are extensible and movable together with the cover 14.

[0025] As illustrated in FIG. 1, the grinding unit 20 includes a spindle motor 22 housed in a holder 21, a spindle 23 disposed vertically and driven by the spindle motor 22 to rotate about its central axis, a disk-shaped spindle mount 24 fixed to a lower end of the spindle 23, and a grinding wheel 25 a mount surface (upper surface) of which is detachably attached to a lower surface of the spindle mount 24 by a plurality of bolts 26 (refer to FIG. 2 and FIG. 3).

[0026] Here, as illustrated in FIG. 2, the spindle 23 and the spindle mount 24 have supply paths 4 and 5 formed vertically at respective axial centers thereof, and the spindle mount 24 has a plurality of supply paths 6 extending radially outward and horizontally from the supply path 5 and supply paths 7 extending vertically downward from the respective supply paths 6. It is to be noted that another supply path is formed vertically at an axial center of a rotor of the spindle motor 22, though not illustrated.

[0027] Described next are details of a configuration of the grinding wheel 25 according to the present embodiment with reference to FIG. 2 to FIG. 6. The grinding wheel 25 includes an annular base 25A and a plurality of pipe grindstones 25B attached perpendicularly as a processing tool to a lower surface (an opposite surface opposite to the upper surface serving as the mount surface) of the annular base 25A as illustrated in FIG. 4 and FIG. 5. In the present embodiment, as illustrated in FIG. 5, 24 pipe grindstones 25B are annularly arranged at an equal angular pitch of 15 in a circumferential direction on the opposite surface (oriented upward in FIG. 5) of the annular base 25A.

[0028] Meanwhile, as illustrated in FIG. 3 and FIG. 6, there is defined a tapered circular space S between the mount surface (upper surface) and the opposite surface (lower surface) of the annular base 25A of the grinding wheel 25, and at an outer circumferential portion in the space S, there is formed a ring-shaped grinding water retaining part S1 where grinding water made to flow radially outward by centrifugal force generated by the rotation of the grinding wheel 25 is temporarily retained. The grinding water retaining part S1 is formed into an annular shape by a tapered surface 25a defining the space S in the annular base 25A and by a vertical surface 25b continuous from the tapered surface 25a and a bottom surface 25c, and an inner circumferential surface of the grinding water retaining part S1 forms a ring-shaped annular opening S11 that opens to the atmosphere. Further, in the present embodiment, the vertical surface 25b of the annular base 25A defining the grinding water retaining part S1 is flush with part of an inner circumferential surface of each pipe grindstone 25B as illustrated in FIG. 6.

[0029] The annular base 25A further has a plurality of water supply holes 8 extending vertically therethrough continuously from the respective supply paths 7 formed in the spindle mount 24 as illustrated in FIG. 3, and each of the water supply holes 8 opens to the mount surface (upper surface) of the annular base 25A and to the grinding water retaining part S1. In the present embodiment, as illustrated in FIG. 4, 24 water supply holes 8 are formed on the mount surface (upper surface) of the annular base 25A at an equal angular pitch of 15 in the circumferential direction.

[0030] As illustrated in FIG. 3 and FIG. 6, the annular base 25A has at its bottom part a plurality of water feeding holes 9 formed to allow communication between the grinding water retaining part S1 and an inside of each of the pipe grindstones 25B. The grinding water retaining part S1 formed inside the annular base 25A of the grinding wheel 25 and the plurality of water supply holes 8 and the plurality of water feeding holes 9 formed in the annular base 25A constitute a grinding water supply unit for supplying grinding water into each of the pipe grindstones 25B. It is to be noted that, as illustrated in FIG. 4, the annular base 25A has formed therein a plurality of (in the example illustrated, eight) screw holes 27 into which the bolts 26 (refer to FIG. 2 and FIG. 3) for fastening the annular base 25A to the spindle mount 24 are screwed, at an equal angular pitch of 45 in the circumferential direction.

[0031] The thickness measuring instrument 30 is a measuring instrument for measuring the thickness of the wafer W including the resin R being ground, the wafer W being held on the chuck table 10, and includes a first probe 31 that makes contact with an upper surface of the resin R and a second probe 32 that makes contact with an upper surface of the chuck table 10. In the thickness measuring instrument 30, the first probe 31 measures the height of the upper surface of the resin R being ground, and the thickness of the wafer W including the resin R and the tape T is obtained from a difference between the height of the upper surface of the resin R measured by the first probe 31 and the height of the upper surface of the chuck table 10 measured by the second probe 32.

[0032] The elevating mechanism 40 is a mechanism that raises and lowers the grinding unit 20 along directions (Z-axis directions) perpendicular to the holding surface 10a of the chuck table 10, and is disposed on a Y-axis direction end surface (front surface) of a rectangular box shaped column 110 disposed to stand perpendicularly at a +Y-axis direction end portion (rear end portion) on an upper surface of the base 100 as illustrated in FIG. 1. The elevating mechanism 40 raises and lowers a rectangular elevating plate 41 attached to a rear surface of the holder 21 of the grinding unit 20, along a pair of left and right guide rails 42 in the Z-axis directions together with the holder 21 and the spindle 23 and the grinding wheel 25 held by the holder 21. The pair of left and right guide rails 42 are disposed on the front surface of the column 110 to extend along the Z-axis directions and in parallel with each other.

[0033] Between the pair of left and right guide rails 42, a rotatable ball screw 43 is disposed to stand along the Z-axis directions (up-down directions), and an upper end of the ball screw 43 is coupled to a servo motor 44 that is a driving source and can rotate normally and reversely. The servo motor 44 is attached to the column 110 in the state of being vertically oriented, through a rectangular plated shaped bracket 45 attached to an upper surface of the column 110. The ball screw 43 has its lower end rotatably supported by the column 110, and is screwed into an unillustrated nut member disposed to protrude horizontally rearward (in the +Y-axis direction) from a rear surface of the elevating plate 41.

[0034] With the configuration described above, when the servo motor 44 is activated to cause the ball screw 43 to rotate normally or reversely, the elevating plate 41 to which the unillustrated nut member in screw engagement with the ball screw 43 is attached moves up or down along the pair of guide rails 42 together with the grinding unit 20, and accordingly, the grinding unit 20 is raised or lowered to set a grinding amount (grinding allowance) of the resin R by the pipe grindstones 25B.

[0035] The horizontal movement mechanism 50 is a mechanism that moves the chuck table 10 in directions (in the Y-axis directions) parallel to the holding surface 10a, and is disposed on a rectangular block shaped internal base 120 housed in the base 100 as illustrated in FIG. 1. The horizontal movement mechanism 50 has a block shaped slider 51 that is slidably movable in the Y-axis directions (front-rear directions) along a pair of left and right guide rails 52 disposed in parallel with each other along the Y-axis directions. The chuck table 10 supported on the slider 51 is thus movable in the Y-axis directions together with the slider 51.

[0036] Between the pair of left and right guide rails 52 on the internal base 120, a rotatable ball screw 53 is disposed to extend along the Y-axis directions (front-rear directions), and one end (in FIG. 1, a left end) of the ball screw 53 in the Y-axis directions is coupled to a servo motor 54 that is a driving source and can rotate normally and reversely. The other end (in FIG. 1, a right end) of the ball screw 53 in the Y-axis directions is rotatably supported to the internal base 120 by a bearing 55 standing on the internal base 120, and the ball screw 53 is screwed into an unillustrated nut member disposed to protrude downward from the slider 51.

[0037] With the configuration described above, when the servo motor 54 is activated to cause the ball screw 53 to rotate normally or reversely, the unillustrated nut member in screw engagement with the ball screw 53 slidably moves along the ball screw 53 in the Y-axis directions (front-rear directions) together with the slider 51, and accordingly, the chuck table 10 moves in the Y-axis directions together with the slider 51. Thus, the wafer W held under suction on the holding surface 10a of the chuck table 10 moves in the Y-axis directions as well.

[0038] The grinding water supply unit 60 supplies grinding water to the plurality of pipe grindstones 25B of the grinding wheel 25, more specifically, to contact portions (grinding portions) between the pipe grindstones 25B and the resin R being ground. As illustrated in FIG. 1, the grinding water supply unit 60 includes a grinding water supply source 61 and piping 62 that extends from the grinding water supply source 61 to be connected to the axial center of the spindle motor 22 of the grinding unit 20, and the piping 62 is provided with an opening and closing valve V2. It is to be noted that pure water is preferably used as the grinding water.

[0039] Desecribed next is an action of the grinding apparatus 1 configured as described above, that is, a grinding method for grinding the resin R coating the upper surface of the wafer W.

[0040] In the grinding of the resin R by the grinding apparatus 1 illustrated in FIG. 1, the wafer W is placed on the holding surface 10a of the chuck table 10 with the tape T oriented downward as illustrated in FIG. 2. When the opening and closing valve V1 provided in the piping 12 illustrated in FIG. 2 is opened, an evacuation force is applied from the suction source 13 to the porous member 10A of the chuck table 10 to generate a negative pressure on the porous member 10A, so that the wafer W placed on the holding surface 10a of the porous member 10A through the tape T is held under suction on the holding surface 10a by the negative pressure.

[0041] With the wafer W thus held under suction on the chuck table 10, the horizontal movement mechanism 50 illustrated in FIG. 1 is driven to move the chuck table 10 in the +Y-axis direction (rearward), and thereby position the wafer W below the grinding wheel 25 of the grinding unit 20. More specifically, when the servo motor 54 is activated to cause the ball screw 53 to rotate, the slider 51 to which the unillustrated nut member in screw engagement with the ball screw 53 is attached moves slidably along the pair of left and right guide rails 52 in the +Y-axis direction together with the chuck table 10 and the like, and accordingly, the wafer W held on the holding surface 10a of the chuck table 10 is positioned below the grinding wheel 25 of the grinding unit 20. It is to be noted that, at this time, horizontal position adjustment between the wafer W and the grinding wheel 25 is carried out such that lower surfaces (processing surfaces) of the pipe grindstones 25B pass the center of the wafer W (resin R).

[0042] Thereafter, the unillustrated rotational mechanism is driven to rotate the chuck table 10 and thereby rotate the wafer W held on the holding surface 10a of the chuck table 10 together with the resin R at a predetermined speed, while at the same time the spindle motor 22 of the grinding unit 20 is driven to rotate the grinding wheel 25 at a predetermined speed.

[0043] With the wafer W and the grinding wheel 25 each being rotated as described above, the elevating mechanism 40 is driven to lower the grinding wheel 25 in the Z-axis direction. Then, the lower surfaces (grinding surfaces) of the pipe grindstones 25B of the grinding wheel 25 make contact with the resin R coating the upper surface of the wafer W. By the pipe grindstones 25B being lowered at a constant feed speed, the entire upper surface of the resin R coating the upper surface of the wafer W is ground. It is to be noted that the thickness of the wafer W including the resin R and the tape T during the grinding is measured by the thickness measuring instrument 30.

[0044] Further, while the entire upper surface of the resin R coating the upper surface of the wafer W is being ground by the lower surfaces (grinding surfaces) of the pipe grindstones 25B of the grinding wheel 25 being rotated as described above, the grinding water is supplied to the contact portions (grinding portions) between the resin R and the pipe grindstones 25B by the grinding water supply unit 60. More specifically, when the opening and closing valve V2 provided in the piping 62 of the grinding water supply unit 60 is opened, the grinding water is supplied from the grinding water supply source 61 through the piping 62 to the grinding unit 20. The grinding water supplied to the grinding unit 20 is supplied to the grinding wheel 25 through the unillustrated supply path formed in the axial center of the spindle motor 22 and the supply path 4 formed in the axial center of the spindle 23. The grinding water supplied to the grinding wheel 25 then flows from the supply path 5 through the plurality of supply paths 6 and 7 formed in the spindle mount 24, and is jetted from the plurality of water supply holes 8 formed in the annular base 25A toward the space S defined in the annular base 25A, as indicated by arrows in FIG. 2 and FIG. 3.

[0045] Since the grinding wheel 25 is being rotated at a predetermined speed, a radially outward centrifugal force acts on the grinding water jetted from the plurality of water supply holes 8 toward the space S in the annular base 25A. This centrifugal force causes the grinding water to impinge on the vertical surface 25b of the ring-shaped grinding water retaining part S1 at the outer circumferential portion in the space S in the annular base 25A, whereby the flow of the grinding water is temporarily stopped. The grinding water is thus temporarily retained in the grinding water retaining part S1. The grinding water temporarily retained in the grinding water retaining part S1 in the annular base 25A is thereafter supplied into each of the pipe grindstones 25B through the plurality of water feeding holes 9. That is, since the flow of the grinding water flowing radially outward of the grinding wheel 25 is blocked by the vertical surface 25b, the grinding water having flowed into the pipe grindstones 25B flows down in the pipe grindstones 25B in the state in which a slightly larger amount thereof is located at a rear portion in each pipe grindstone 25B in the direction of rotation of the grinding wheel 25 due to the rotation of the grinding wheel 25. Hence, grinding swarf is prevented from adhering to those portions on inner side surfaces of the pipe grindstones 25B which correspond to the rear portion in each pipe grindstone 25B in the direction of rotation of the grinding wheel 25.

[0046] In addition, when the amount of grinding water temporarily retained in the grinding water retaining part S1 of the annular base 25A exceeds a predetermined amount, part of the grinding water overflows to the atmosphere from the ring-shaped annular opening S11 formed as the inner circumferential surface of the grinding water retaining part S1. The grinding water thus overflowing is acted on by the centrifugal force generated by the rotation of the grinding wheel 25, scatters radially outward as indicated by arrows in FIG. 3 and FIG. 6, and is supplied to outer circumferential surfaces of the pipe grindstones 25B.

[0047] The grinding water having been supplied into each of the pipe grindstones 25B and to the outer circumferential surface of each of the pipe grindstones 25B as described above is then supplied to the contact portions (grinding portions) between the pipe grindstones 25B and the resin R as the workpiece, so that the contact portions are cooled by the grinding water, and grinding swarf generated by the grinding is washed away and removed from the surface of the resin R by the grinding water.

[0048] Accordingly, with the grinding wheel 25 according to the present embodiment, unlike the related art in which grinding water is directly supplied to the pipe grindstones, the grinding water is temporarily retained in the grinding water retaining part S1 in the annular base 25A by the centrifugal force generated by the rotation of the grinding wheel 25, and then supplied from the grinding water retaining part S1 into each of the pipe grindstones 25B. Besides, the grinding water overflowing from the grinding water retaining part S1 is supplied to the outer circumferential surface of each of the pipe grindstones 25B. In this manner, the grinding water is supplied to the inside and outside of each of the pipe grindstones 25B, so that the adhesion of grinding swarf to the inner side surfaces and outer side surfaces of the pipe grindstones 25B is suppressed. Consequently, the grinding swarf is prevented from adhering to the inner circumferential surfaces of the pipe grindstones 25B, and it is thus possible to prevent the grinding swarf from causing significant damage to the resin R as the workpiece.

[0049] Described hereinafter are modifications of the grinding wheel 25 according to the present embodiment with reference to FIG. 7 to FIG. 9. It is to be noted that, in FIG. 7 to FIG. 9, constituent elements same as those illustrated in FIG. 6 are denoted by the same reference symbols, and redundant description thereof is omitted.

First Modification

[0050] In a grinding wheel 25X according to a first modification illustrated in FIG. 7, each of the pipe grindstones 25B is mounted obliquely with its central line CL inclined radially outward (rightward in FIG. 7) by an angle with respect to a vertical line N as illustrated, but the rest of the configuration of the grinding wheel 25X is the same as the configuration of the grinding wheel 25 illustrated in FIG. 6. It is to be noted that the lower end surfaces (grinding surface) of the pipe grindstones 25B are formed to be horizontal.

[0051] In the grinding wheel 25X according to the present modification as well, the grinding water jetted from the water supply holes 8 toward the space S in the annular base 25A is temporarily retained in the grinding water retaining part S1 by the centrifugal force generated by the rotation of the grinding wheel 25X, and then supplied from the grinding water retaining part S1 into each of the pipe grindstones 25B. Besides, the grinding water overflowing from the grinding water retaining part S1 is supplied to the outer circumferential surface of each of the pipe grindstones 25B. In this manner, the grinding water is supplied to the inside and outside of each of the pipe grindstones 25B, so that the adhesion of grinding swarf to the inner side surfaces and outer side surfaces of the pipe grindstones 25B is suppressed. Consequently, the grinding swarf is prevented from adhering to the inner circumferential surfaces of the pipe grindstones 25B, and it is thus possible to prevent the grinding swarf from causing significant damage to the upper surface of the resin R as the workpiece.

[0052] Moreover, in the grinding wheel 25X according to the present modification, each of the pipe grindstones 25B is mounted obliquely with its central line CL inclined radially outward (rightward in FIG. 7) by the angle with respect to the vertical line N as illustrated. Hence, particularly in the case where the workpiece is such soft resin as the resin R in the present embodiment, the inclined pipe grindstones 25B contribute to efficient grinding of the surface of the resin R.

[0053] Meanwhile, when each of the pipe grindstones 25B is mounted obliquely with its central line CL inclined radially outward by the angle with respect to the vertical line N as illustrated, a component force F.sub.1=F.Math.sin of centrifugal force F acting horizontally outward on the grinding water flowing obliquely downward along the inner circumferential surface of each of the pipe grindstones 25B is applied in a direction along the inner circumferential surface of the pipe grindstone 25B. However, since the vertical surface 25b causes the grinding water to flow down in the vertical direction, the grinding water is supplied also to an inner portion in the radial direction of the grinding wheel 25 on the inner side surface of each of the pipe grindstones 25B and to a rear portion in the direction of rotation of the grinding wheel 25 on the inner side surface of each of the pipe grindstones 25B. Accordingly, the grinding water is efficiently supplied to the contact portions (grinding portions) between the pipe grindstones 25B and the resin R, and it is possible to prevent the adhesion of grinding swarf to the inner side surfaces of the pipe grindstones 25B.

Second Modification

[0054] In a grinding wheel 25Y according to a second modification illustrated in FIG. 8, as with the grinding wheel 25 illustrated in FIG. 6, the pipe grindstones 25B are mounted perpendicularly to the opposite surface (lower surface) of the annular base 25A. Meanwhile, the grinding water retaining part S1 formed in the annular base 25A does not have a partial opening to the atmosphere (the annular opening S11 in the grinding wheel 25 illustrated in FIG. 6 is not provided). Hence, the grinding water supplied from the water supply holes 8 of the annular base 25A is temporarily retained in the grinding water retaining part S1 by the centrifugal force generated by the rotation of the grinding wheel 25Y, and then all of the grinding water is supplied through the water feeding holes 9 into each of the pipe grindstones 25B.

[0055] Accordingly, in the grinding wheel 25Y according to the present modification, the grinding water supplied through the water supply holes 8 of the annular base 25A is temporarily retained in the grinding water retaining part S1 by the centrifugal force generated by the rotation of the grinding wheel 25Y, and then supplied into each of the pipe grindstones 25B. Thus, the grinding water is supplied evenly to the respective pipe grindstones 25B, and the adhesion of grinding swarf contained in the grinding water to the inner side surfaces of the pipe grindstones 25B is suppressed. Consequently, the grinding swarf is prevented from adhering to the inner circumferential surfaces of the pipe grindstones 25B, and it is thus possible to prevent the grinding swarf from causing significant damage to the resin R as the workpiece.

Third Modification

[0056] A grinding wheel 25Z according to a third modification illustrated in FIG. 9 is characterized in that it is based on the configuration of the grinding wheel 25Y illustrated in FIG. 8, but each of the pipe grindstones 25B is mounted obliquely with its central line CL inclined radially outward (rightward in FIG. 9) by the angle with respect to the vertical line N as illustrated, as with the grinding wheel 25X illustrated in FIG. 7. The rest of the configuration of the grinding wheel 25Z is the same as the configuration of the grinding wheel 25Y illustrated in FIG. 8.

[0057] According to the grinding wheel 25Z according to the present modification, in addition to the effect obtained by the grinding wheel 25Y illustrated in FIG. 8, the following effect is also achievable. Specifically, although the component force F.sub.1=F.Math.sin of the centrifugal force F acting horizontally outward on the grinding water flowing obliquely downward along the inner circumferential surface of each of the pipe grindstones 25B is applied in the direction along the inner circumferential surface of the pipe grindstone 25B, since the vertical surface 25b causes the grinding water to flow down in the vertical direction, the grinding water is supplied also to the inner portion in the radial direction of the grinding wheel 25 on the inner side surface of each of the pipe grindstones 25B and to the rear portion in the direction of rotation of the grinding wheel 25 on the inner side surface of each of the pipe grindstones 25B. Accordingly, the grinding water is efficiently supplied to the contact portions (grinding portions) between the pipe grindstones 25B and the resin R, and it is possible to prevent the adhesion of grinding swarf to the inner side surfaces of the pipe grindstones 25B.

[0058] It is to be noted that, while the above embodiment has been described taking as an example the case where the resin coating the upper surface of the wafer is ground as the workpiece, the present invention is applicable also when a wafer or any other kind of workpiece is ground.

[0059] Furthermore, while adopted in the embodiment described above is infeed grinding in which the grinding wheel is disposed at such a position that the pipe grindstones thereof are to pass the center of the wafer and is lowered to grind the workpiece, the grinding method is not limited to this. Creep feed grinding in which the workpiece and the grinding wheel are moved horizontally relative to each other to grind the upper surface of the workpiece in such a manner as to slice off chips from the workpiece may alternatively be adopted.

[0060] 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.