Workpiece grinding method

Abstract

To provide a grinding method for a workpiece that is able to reduce variations in a non-circular workpiece thickness.SOLUTION: A workpiece grinding method for grinding a non-circular workpiece by means of a grinding wheel including a plurality of grinding stones, comprises: a holding step of holding the workpiece on a holding surface of a chuck table; and a grinding step of, after the holding step, grinding the workpiece by bringing a plurality of grinding stones into contact with the workpiece while rotating the chuck table and the grinding, with rotational orbits of the plurality of grinding stones being kept positioned so as to overlap a rotational axis of the chuck table. The plurality of grinding grindstones is arranged such that a width of each of the rotational orbits is wider than that in a case distances from a rotational axis of the grinding wheel to the plurality of grinding grindstones are equal to each other and distances from the rotational axis of the grinding wheel to both ends of each of the grinding grindstones in a length direction thereof are equal to each other.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for grinding a non-circular workpiece with a grinding wheel. [Background technology]

[0002] A wafer on which a plurality of devices are formed is divided and diced to produce device chips each including a device. A package substrate is formed by mounting a plurality of device chips on a predetermined substrate and covering and sealing the mounted device chips with a resin layer (mold resin). A package device including a plurality of packaged device chips is manufactured by dividing and dicing the package substrate. The device chips and package devices are incorporated into various electronic devices such as mobile phones and personal computers.

[0003] In recent years, with the miniaturization of electronic devices, there is a demand for thinner device chips and package devices. Therefore, a grinding device may be used to grind and thin wafers and package substrates before division. The grinding device includes a chuck table for holding the workpiece and a grinding unit for grinding the workpiece. The grinding unit includes a spindle, and an annular grinding wheel equipped with multiple grinding stones is attached to the tip of the spindle. The workpiece is held by the chuck table, and the grinding stones are brought into contact with the workpiece while rotating the chuck table and the grinding wheel, thereby grinding and thinning the workpiece.

[0004] Grinding machines are highly versatile and can be used not only for grinding circular workpieces such as silicon wafers, but also for grinding non-circular workpieces such as package substrates. However, when a non-circular workpiece is ground in the same way as a circular workpiece using a grinding machine, the thickness of the workpiece is likely to vary. For example, when a rectangular workpiece is ground using a grinding machine, the grinding progresses more slowly in areas closer to the diagonal of the workpiece, and the area tends to be thicker than other areas. If there is variation in the thickness of the workpiece after grinding, it may cause problems in the subsequent processing (transportation, processing, etc.) of the workpiece, or errors may occur in the dimensions of the chips obtained by dividing the workpiece.

[0005] Therefore, a method for controlling a grinding device for uniformly grinding a non-circular workpiece has been studied. For example, Patent Document 1 discloses a grinding device that adjusts the rotation speed of the chuck table with a servo motor so that the rotation speed of the chuck table decreases as the contact area between the wafer and the grinding wheel increases when grinding a square wafer. In this way, the load on the wafer and the grinding wheel is uniformized by sequentially controlling the rotation speed of the chuck table according to the contact area between the wafer and the grinding wheel, and the thickness variation of the wafer after grinding is reduced. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2015-205358 A Summary of the Invention [Problem to be solved by the invention]

[0007] As described above, by adjusting the rotation speed of the chuck table according to the contact area between the workpiece and the grinding wheel, the non-circular workpiece can be ground uniformly and the thickness variation of the workpiece can be reduced. However, when using this method, it is necessary to drive the servo motor at high speed and high precision so that the chuck table rotates at the desired rotation speed at the desired timing. This makes the control of the grinding device complicated and increases the cost.

[0008] The present invention has been made in consideration of such problems, and has an object to provide a method for grinding a workpiece that can easily reduce thickness variations in a non-circular workpiece. [Means for solving the problem]

[0009] According to one aspect of the present invention, there is provided a method for grinding a workpiece in which a non-circular workpiece is ground with a grinding wheel having a plurality of grinding wheels, the method including: a holding step of holding the workpiece on a holding surface of a chuck table; and a grinding step of, after the holding step, grinding the workpiece by contacting the plurality of grinding wheels with the workpiece while rotating the chuck table and the grinding wheel with the rotational orbits of the plurality of grinding wheels positioned so as to overlap with the rotational axis of the chuck table, wherein the plurality of grinding wheels are positioned so that the distances from the rotational axis of the grinding wheel to the plurality of grinding wheels are equal and that the width of the rotational orbit is wider than when the distances from the rotational axis of the grinding wheel to both ends of the grinding wheels in the longitudinal direction are equal.

[0010] Preferably, the grinding wheel includes a grinding wheel group including a plurality of the grinding wheels, the plurality of grinding wheels being arranged at different distances from the rotation axis of the grinding wheel, and the plurality of grinding wheels are preferably arranged at different distances from the rotation axis of the grinding wheel to both ends in the longitudinal direction of the grinding wheels. Effect of the Invention

[0011] In a method for grinding a workpiece according to one aspect of the present invention, a non-circular workpiece is ground with a grinding wheel in which multiple grinding wheels are arranged so that the width of the rotational orbit is wider than that of a normal grinding wheel (in which the distances from the rotation axis of the grinding wheel to the multiple grinding wheels are equal, and the distances from the rotation axis of the grinding wheel to both ends in the longitudinal direction of the grinding wheels are equal). This makes it easier to grind the grinding surface of the workpiece uniformly, and easily reduces the variation in thickness of the workpiece. [Brief description of the drawings]

[0012] [Figure 1] FIG. 2 is a partial cross-sectional side view showing the grinding device. [Diagram 2] FIG. 4 is a cross-sectional view showing a chuck table. [Diagram 3] 4 is a flowchart showing a method for grinding a workpiece. [Figure 4] FIG. 4 is a perspective view showing the grinding device in a holding step. [Diagram 5] FIG. 5(A) is a perspective view showing the grinding device in the grinding step, and FIG. 5(B) is a partially sectional side view showing the grinding device in the grinding step. [Figure 6] FIG. [Figure 7] FIG. 13 is a bottom view showing a modified example of the grinding wheel. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, an embodiment according to one aspect of the present invention will be described with reference to the accompanying drawings. First, a configuration example of a grinding device that can be used to implement the grinding method of a workpiece according to this embodiment will be described. FIG. 1 is a partially cross-sectional side view showing a grinding device 2. In FIG. 1, the X-axis direction (first horizontal direction, front-back direction) and the Y-axis direction (second horizontal direction, left-right direction) are perpendicular to each other. Also, the Z-axis direction (height direction, up-down direction, vertical direction) is perpendicular to the X-axis direction and the Y-axis direction.

[0014] The grinding device 2 includes a base 4 that supports or houses each of the components that make up the grinding device 2. A rectangular parallelepiped opening 4a is provided on the upper surface side of the base 4. A chuck table (holding table) 6 that holds a workpiece that is an object to be ground by the grinding device 2 is provided inside the opening 4a. The upper surface of the chuck table 6 forms a holding surface 6a that holds the workpiece.

[0015] FIG. 2 is a cross-sectional view showing the chuck table 6. The chuck table 6 includes a cylindrical frame (main body) 8 made of metal such as SUS (stainless steel), glass, ceramics, resin, or the like. A cylindrical recess 8b is provided concentrically with the upper surface 8a in the center of the upper surface 8a of the frame 8. A disk-shaped holding member 10 made of a porous material such as porous ceramics is fitted into the recess 8b. The holding member 10 includes a large number of pores that communicate from the upper surface to the lower surface of the holding member 10. The upper surface of the holding member 10 forms a circular suction surface 10a that sucks in the workpiece when the workpiece is held by the chuck table 6.

[0016] The holding surface 6a of the chuck table 6 is configured by an upper surface 8a of the frame 8 and a suction surface 10a of the holding member 10. The holding surface 6a is connected to a suction source (not shown) such as an ejector via pores contained in the holding member 10, a flow path 8c provided inside the frame 8, a valve (not shown), and the like.

[0017] The holding surface 6a of the chuck table 6 is formed in a cone shape with the center of the holding surface 6a as the apex, and is slightly inclined with respect to the radial direction of the holding surface 6a. The chuck table 6 is arranged in a slightly inclined state so that a holding area 6b, which corresponds to a part of the holding surface 6a and extends from the center to the outer periphery of the holding surface 6a, is approximately parallel to the horizontal plane (XY plane). The area of ​​the workpiece held in the holding area 6b or in the vicinity thereof is ground by a grinding unit 44 described later.

[0018] In Fig. 2, the inclination of the holding surface 6a is exaggerated for convenience of explanation, but the actual inclination of the holding surface 6a is small. For example, when the diameter of the holding surface 6a is about 290 mm or more and 310 mm or less, the difference in height between the center and the outer periphery of the holding surface 6a (corresponding to the height of the cone) is set to about 20 µm or more and 40 µm or less.

[0019] A rotation drive source (not shown), such as a motor, is connected to the chuck table 6 to rotate the chuck table 6. The rotation drive source rotates the chuck table 6 around a rotation axis (center of rotation) 12. The rotation axis 12 of the chuck table 6 is set along a direction perpendicular to the radial direction of the holding surface 6a, and is slightly inclined with respect to the Z-axis direction. In addition, the rotation axis 12 intersects with the holding surface 6a so as to pass through the center of the holding surface 6a.

[0020] As shown in Fig. 1, a tilt adjustment mechanism 14 that adjusts the tilt of the chuck table 6 is connected to the chuck table 6. For example, the tilt adjustment mechanism 14 includes a disk-shaped table base 16 that supports the chuck table 6 via bearings (not shown), and one fixed support member 18A and two movable support members 18B that support the table base 16. Note that Fig. 1 shows only one movable support member 18B, and does not show the other movable support member 18B.

[0021] One fixed support member 18A and two movable support members 18B are disposed at approximately equal intervals (120° intervals) along the circumferential direction of the table base 16. The upper ends of the fixed support member 18A and the movable support members 18B are fixed to the lower surface side of the outer periphery of the table base 16, respectively.

[0022] The fixed support member 18A is configured so that its upper end is fixed at a predetermined height position. Meanwhile, the movable support member 18B is configured so that its upper end can be moved (raised and lowered) along the Z-axis direction. By inputting a control signal from a controller 62 (described later) to the movable support members 18B, the positions (height positions) of the upper ends of the two movable support members 18B in the Z-axis direction can be changed. This adjusts the tilt direction and tilt angle of the chuck table 6 and the rotating shaft 12.

[0023] A moving mechanism (moving unit) 20 is provided inside the base 4. The moving mechanism 20 is connected to the chuck table 6 and moves the chuck table 6 along the X-axis direction. Specifically, the moving mechanism 20 includes a ball screw 22 arranged along the X-axis direction. A pulse motor 24 that rotates the ball screw 22 is connected to an end of the ball screw 22. The chuck table 6 and the inclination adjustment mechanism 14 are supported by a support base 26, and a nut portion 28 is connected to the support base 26. The ball screw 22 is screwed into the nut portion 28, and when the ball screw 22 is rotated by the pulse motor 24, the chuck table 6 moves along the X-axis direction.

[0024] A rectangular parallelepiped support structure (column) 30 is provided behind the chuck table 6 and the moving mechanism 20 (to the right in FIG. 1). A moving mechanism (moving unit) 32 is provided on the front surface side (front side) of the support structure 30. The moving mechanism 32 includes a pair of guide rails 34 fixed to the front surface side of the support structure 30. The pair of guide rails 34 are disposed along the Z-axis direction and are spaced apart from each other in the Y-axis direction.

[0025] A holding member 36 formed in a hollow cylindrical shape is attached to the pair of guide rails 34 so as to be slidable along the guide rails 34. A nut portion 38 is connected to the rear side of the holding member 36, and a ball screw 40 arranged along the Z-axis direction between the pair of guide rails 34 is screwed into the nut portion 38. A pulse motor 42 that rotates the ball screw 40 is connected to an end of the ball screw 40. When the ball screw 40 is rotated by the pulse motor 42, the holding member 36 moves (rises and falls) along the guide rails 34 in the Z-axis direction.

[0026] The holding member 36 holds a grinding unit 44 that performs grinding on a workpiece. The grinding unit 44 includes a cylindrical housing 46 housed in the holding member 36. The lower surface side of the housing 46 is supported by the bottom surface of the holding member 36 via a buffer member 48 made of an elastic material such as rubber.

[0027] A cylindrical spindle 50 arranged along the Z-axis direction is accommodated in the housing 46. The tip end (lower end) of the spindle 50 is exposed from the housing 46, and protrudes downward from the lower surface of the holding member 36 through an opening provided in the bottom of the holding member 36. A rotation drive source (not shown), such as a motor, that rotates the spindle 50 is connected to the base end (upper end) of the spindle 50.

[0028] A disk-shaped wheel mount 52 made of metal or the like is fixed to the tip of the spindle 50. An annular grinding wheel 54 for grinding a workpiece is removably attached to the underside of the wheel mount 52. For example, the grinding wheel 54 is fixed to the wheel mount 52 by a fastener such as a bolt.

[0029] The grinding wheel 54 is equipped with an annular wheel base 56 made of a metal such as aluminum or stainless steel and formed to have approximately the same diameter as the wheel mount 52. The upper surface side of the wheel base 56 is fixed to the lower surface side of the wheel mount 52. In addition, a plurality of grinding wheels 58 are fixed to the lower surface side of the wheel base 56.

[0030] The grinding wheel 58 includes abrasive grains made of diamond, cBN (cubic boron nitride), etc., and a bonding material (bond material) such as metal bond, resin bond, vitrified bond, etc., that fixes the abrasive grains. However, there are no limitations on the material, shape, structure, size, etc., of the grinding wheel 58. The arrangement of the grinding wheel 58 will be described in detail later (see Figs. 6 and 7).

[0031] The grinding wheel 54 rotates around a rotation axis (center of rotation) 60 set along the Z-axis direction by power transmitted from a rotation drive source (not shown) via the spindle 50 and the wheel mount 52. In other words, the rotation axis 60 corresponds to the rotation axis (center of rotation) of the spindle 50, the wheel mount 52, and the grinding wheel 54. When the grinding wheel 54 is rotated, the multiple grinding stones 58 revolve along a circular rotational orbit (rotational path) centered on the rotation axis 60 and generally parallel to a horizontal plane (XY plane).

[0032] A grinding fluid supply path (not shown) for supplying liquid (grinding fluid) such as pure water is provided inside or near the grinding unit 44. For example, the grinding fluid supply path is composed of a flow path formed inside the wheel mount 52 and the grinding wheel 54, and a nozzle provided near the grinding unit. When the workpiece is ground with the grinding wheel 54, the grinding fluid is supplied to the workpiece and the grinding wheel 58. This cools the workpiece and the grinding wheel 58, and washes away debris (grinding debris) generated by the grinding process.

[0033] The grinding apparatus 2 also includes a controller (control unit, control section, control device) 62 that controls the grinding apparatus 2. The controller 62 is connected to the components of the grinding apparatus 2 (the chuck table 6, the tilt adjustment mechanism 14, the moving mechanism 20, the moving mechanism 32, the grinding unit 44, etc.), and generates control signals that control the operation of each component.

[0034] For example, the controller 62 is configured by a computer and includes a processing unit that performs processing such as calculations necessary for the operation of the grinding device 2, and a storage unit that stores various information (data, programs, etc.) used for the operation of the grinding device 2. The processing unit includes a processor such as a CPU (Central Processing Unit). The storage unit includes memories such as a ROM (Read Only Memory) and a RAM (Random Access Memory).

[0035] Next, a specific example of the grinding method of the workpiece according to this embodiment will be described. Fig. 3 is a flowchart showing the grinding method of the workpiece according to this embodiment. The grinding method of the workpiece according to this embodiment includes a holding step S1 and a grinding step S2. In particular, in this embodiment, a non-circular workpiece is ground by the grinding device 2.

[0036] Specifically, first, the workpiece is held by the holding surface 6a of the chuck table 6 (holding step S1). Fig. 4 is a perspective view showing the grinding device 2 in the holding step S1. In the holding step S1, the workpiece 11, which is an object to be ground by the grinding device 2, is held by the chuck table 6.

[0037] For example, the workpiece 11 is a plate-like member made of a semiconductor (Si, GaAs, InP, GaN, SiC, etc.), glass (quartz glass, borosilicate glass, etc.), ceramics, resin, metal, etc., and includes a front surface (first surface) 11a and a back surface (second surface) 11b that are generally parallel to each other. The workpiece 11 is a non-circular member in which the distance from the center to the outer periphery (side surface) is not constant. In the following, as an example, a case where the workpiece 11 is rectangular will be described. FIG. 4 illustrates the workpiece 11 having a square-shaped front surface 11a and back surface 11b.

[0038] For example, the workpiece 11 is a package substrate such as a CSP (Chip Size Package) substrate or a QFN (Quad Flat Non-leaded package) substrate. The package substrate is formed by covering and sealing a plurality of device chips mounted on a predetermined substrate with a resin layer (molding resin). For example, the package substrate is formed in a rectangular shape with a side length of 50 mm to 550 mm. The package substrate is divided into individual pieces to manufacture a package device including a plurality of packaged device chips. Also, a thin package device can be manufactured by grinding and thinning the resin layer with a grinding device 2 before dividing the package substrate.

[0039] However, so long as the shape of the workpiece 11 is non-circular, there are no limitations on the material, shape, structure, size, etc. of the workpiece 11. For example, the workpiece 11 may be a polygonal member having three or five or more corners and sides, or may be an elliptical or oblong member.

[0040] When the workpiece 11 is held by the chuck table 6, the workpiece 11 is supported by a support member 13. For example, the support member 13 is a highly rigid substrate formed in a disk shape. Specific examples of the material of the support member 13 are the same as those of the workpiece 11. The diameter of the support member 13 is set to be equal to or larger than the diameter of the suction surface 10a of the chuck table 6.

[0041] The support member 13 is fixed to the workpiece 11 via an adhesive or the like so as to cover the surface of the workpiece 11 opposite to the surface (grinding surface) to be ground by the grinding wheel 54. For example, when the front surface 11a of the workpiece 11 is the grinding surface, the support member 13 is fixed to the back surface 11b side of the workpiece 11 as shown in FIG.

[0042] However, as long as the support member 13 can support the workpiece 11, there are no limitations on the material, structure, dimensions, etc. of the support member 13. For example, a circular sheet can be used as the support member 13. The sheet includes a film-like base material and an adhesive layer (glue) provided on the base material. Also, a thermocompression sheet that does not include an adhesive layer (glue) and can be thermocompressed to the workpiece 11 can be used as the sheet.

[0043] The workpiece 11 is placed on the chuck table 6 so that the front surface 11a (the surface to be ground) is exposed upward and the back surface 11b (the support member 13 side) faces the holding surface 6a. At this time, the workpiece 11 is positioned so that the rotation axis 12 of the chuck table 6 passes through the center of the workpiece 11. In addition, the support member 13 is placed so as to cover the entire suction surface 10a. In this state, when the suction force (negative pressure) of the suction source is applied to the suction surface 10a, the workpiece 11 is sucked and held by the holding surface 6a of the chuck table 6 via the support member 13.

[0044] As described above, the holding surface 6a of the chuck table 6 is formed in a cone shape to be precise (see FIG. 2). When the suction surface 10a sucks the support member 13, the workpiece 11 and the support member 13 are held in a slightly deformed state along the holding surface 6a. As a result, the surface 11a of the workpiece 11 in the holding area 6b (see FIG. 2) or in the area held in the vicinity thereof is disposed approximately parallel to the horizontal plane (XY plane).

[0045] As described above, by placing the workpiece 11 on the chuck table 6 via the support member 13, even if the suction surface 10a is formed in a circular shape assuming the suction of a circular workpiece, a non-circular workpiece 11 can be held by the chuck table 6. However, the suction surface 10a may be appropriately changed according to the shape of the workpiece 11. For example, the suction surface 10a may be formed in a rectangular shape to accommodate a rectangular workpiece 11. In this case, the support member 13 can be omitted and the workpiece 11 can be directly suction-held by the suction surface 10a.

[0046] Next, the workpiece 11 is ground by bringing the grinding stone 58 of the grinding wheel 54 into contact with the workpiece 11 (grinding step S2). Fig. 5(A) is a perspective view showing the grinding device 2 in the grinding step S2, and Fig. 5(B) is a partially sectional side view showing the grinding device 2 in the grinding step S2.

[0047] In the grinding step S2, the grinding stones 58 of the grinding wheel 54 are brought into contact with the workpiece 11 while rotating the chuck table 6 and the grinding wheel 54, with the rotational orbits of the grinding stones 58 being positioned so as to overlap with the rotation axis 12 of the chuck table 6. As a result, the workpiece 11 is ground and thinned.

[0048] Specifically, first, with the grinding unit 44 disposed above the chuck table 6, the chuck table 6 is moved along the X-axis direction by the moving mechanism 20 (see FIG. 1), and the positional relationship between the chuck table 6 and the grinding wheel 54 is adjusted so that the rotational orbit of the grinding wheel 58 overlaps with the rotation axis 12 of the chuck table 6 in the Z-axis direction. As a result, the rotational orbit of the grinding wheel 58 is positioned so as to overlap with the center of the workpiece 11 (intersection of the diagonals) and the center of the holding surface 6a.

[0049] The diameter of the rotation orbit of the grinding wheels 58 is set to be, for example, equal to or greater than the length of the diagonal of the workpiece 11. Therefore, the multiple grinding wheels 58 are arranged so as to overlap with a substantially arc-shaped region extending from the center of the workpiece 11 to the outer periphery (side surface).

[0050] Next, while rotating the chuck table 6 and the grinding wheel 54, the chuck table 6 and the grinding wheel 54 are moved relatively close to each other along a direction (Z-axis direction) parallel to the rotation axis 60. As a result, the multiple grinding stones 58 come into contact with the workpiece 11, and the workpiece 11 is ground and thinned.

[0051] Specifically, first, the chuck table 6 is rotated around the rotation axis 12, and the grinding wheel 54 is rotated around the rotation axis 60. For example, the rotation speed of the chuck table 6 is set to 100 rpm or more and 900 rpm or less, and the rotation speed of the grinding wheel 54 (the rotation speed of the spindle 50) is set to 1000 rpm or more and 6000 rpm or less.

[0052] Next, the grinding unit 44 is lowered along the Z-axis direction by the moving mechanism 32 (see FIG. 1). As a result, the chuck table 6 and the grinding wheel 54 move relatively along a direction parallel to the rotation axis 60 (Z-axis direction), and the workpiece 11 and the multiple grinding stones 58 approach each other. At this time, the relative movement speed (processing feed speed) between the chuck table 6 and the grinding wheel 54 in the Z-axis direction is set to, for example, 1 μm / s or more and 6 μm / s or less.

[0053] When the grinding wheels 58 come into contact with the surface 11a of the workpiece 11, the grinding wheels 58 each rotate to pass through the rotation axis 12 of the chuck table 6 or its vicinity, while grinding the surface 11a of the workpiece 11. This causes the workpiece 11 to be thinned. Then, when the workpiece 11 is thinned to a predetermined thickness (finishing thickness), the grinding unit 44 rises, the grinding wheels 58 move away from the workpiece 11, and grinding of the workpiece 11 is stopped.

[0054] Here, when a non-circular workpiece 11 is ground with a normal grinding wheel, the thickness of the workpiece 11 is generally likely to vary. More specifically, in the region of the workpiece 11 that overlaps with the diagonal of the surface 11a (diagonal region), the distance from the center of the workpiece 11 to the outer periphery is longer than in other regions of the workpiece 11. When the diagonal region of the workpiece 11 is ground, the contact area between the workpiece 11 and the grinding wheel 58 is larger than when other regions of the workpiece 11 are ground. This increases the load on the grinding wheel 58, and the grinding progresses more slowly in the region closer to the diagonal region of the workpiece 11. As a result, the amount of grinding of the workpiece 11 varies, and the workpiece 11 after grinding is likely to have a curved shape on the surface 11a side.

[0055] Therefore, in the grinding wheel 54 of this embodiment, the multiple grinding stones 58 are arranged so that the width of the rotational orbit of the multiple grinding stones 58 is wider than that of a normal grinding wheel. This makes it easier to grind the surface of the workpiece 11 uniformly, and reduces variations in the thickness of the workpiece 11.

[0056] 6 is a bottom view showing the grinding wheel 54. As described above, the grinding wheel 54 includes a plurality of grinding stones 58 fixed to the wheel base 56. For example, the grinding stones 58 are formed in a rectangular parallelepiped shape and are arranged in a ring shape at approximately equal intervals along the circumferential direction of the wheel base 56. The tip surface (bottom surface) of the grinding stone 58 constitutes a grinding surface that comes into contact with the workpiece 11 to grind the workpiece 11.

[0057] 6, L indicates the length of the grinding wheel 58, and W indicates the width of the grinding wheel 58. The length L of the grinding wheel 58 corresponds to the length in the longitudinal direction (length of the long side) of the grinding surface of the grinding wheel 58, and the width W of the grinding wheel 58 corresponds to the length in the lateral direction (length of the short side) of the grinding surface of the grinding wheel 58. The rotational direction, radial direction, and circumferential direction of the wheel base 56 correspond to the rotational direction, radial direction, and circumferential direction of the grinding wheel 54, respectively.

[0058] In a typical grinding wheel, multiple grinding wheels are arranged in a ring shape so that the distances from the rotation axis of the grinding wheel to the multiple grinding wheels are equal. Also, each grinding wheel is arranged so that its length is parallel to the rotation direction (tangential direction) of the grinding wheel and its width is parallel to the radial direction of the grinding wheel. In other words, the orientation (angle) of the grinding wheel is adjusted so that the distances from the rotation axis of the grinding wheel to both ends of the grinding wheels in the length direction are equal. Therefore, the width of the rotational track of the multiple grinding wheels is approximately equal to the width of the grinding wheels.

[0059] On the other hand, in the grinding wheel 54 according to this embodiment, the grinding wheels 58 are arranged so that the width of the rotational orbit of the grinding wheels 58 is wider than that of the normal grinding wheel. For example, the grinding wheel 54 includes a grinding wheel group 70 including a plurality of grinding wheels 58. FIG. 6 shows, as an example, a case in which the grinding wheel 54 includes four grinding wheel groups 70, and each grinding wheel group 70 includes four grinding wheels 58 (grinding wheels 58A, 58B, 58C, 58D). However, the number of grinding wheel groups 70 and grinding wheels 58 can be changed as appropriate.

[0060] Each grinding wheel 58 is disposed so that its length L direction (longitudinal direction) is parallel to the rotation direction (tangential direction) of the grinding wheel 54, and its width W direction (short-side direction) is parallel to the radial direction of the grinding wheel 54. Therefore, a distance d1 from the rotation axis 60 of the grinding wheel 54 to one end of the grinding wheel 58 in the length L direction is equal to a distance d2 to the other end. That is, the orientation (angle) of the grinding wheel 58 is set in the same way as a normal grinding wheel.

[0061] The grinding wheels 58 included in the grinding wheel group 70 are arranged so that they are different in distance from the rotation axis 60 of the grinding wheel 54. For example, the grinding wheels 58A, 58B, 58C, and 58D are arranged in order along the circumferential direction of the grinding wheel 54 so that the distance from the rotation axis 60 of the grinding wheel 54 to the grinding wheels 58A, 58B, 58C, and 58D is closer in this order. In other words, the distances from the rotation axis 60 of the grinding wheel 54 to the grinding wheels 58A, 58B, 58C, and 58D are respectively defined as d A ,d B ,d C ,d D Then, the positional relationship between the rotation axis 60 of the grinding wheel 54 and the grinding stones 58A, 58B, 58C, and 58D is d A >d B >d C >d D This is expressed as:

[0062] In other words, the grinding wheels 58A, 58B, 58C, and 58D are arranged on the circumference of concentric circles having different diameters. A , C B , C C , C D The diameter of each is φ A , φ B , φ C , φ D (φ A >φ B >φ C >φ D ), the grinding wheels 58A, 58B, 58C, and 58D are each arranged in a circle C A , C B , C C , C D are arranged so as to overlap the circumference of the circle.

[0063] When the grinding wheel 54 is rotated around the rotation axis 60, the grinding wheels 58 describe a circular rotational track 72. The rotational track 72 corresponds to an area where the rotational tracks of the individual grinding wheels 58 are joined together and integrated. The outer diameter of the rotational track 72 corresponds to the path of the outer end of the grinding wheel 58 (grinding wheel 58A) closest to the outer periphery of the wheel base 56. The inner diameter of the rotational track 72 corresponds to the path of the inner end of the grinding wheel 58 (grinding wheel 58D) closest to the center (rotation axis 60) of the wheel base 56. The width Wo of the rotational track 72 corresponds to 1 / 2 of the difference between the outer diameter and the inner diameter of the rotational track 72.

[0064] Each grinding wheel 58 is arranged so that its rotational orbit contacts or overlaps with the rotational orbit of another grinding wheel 58. For example, the difference in distance (d A -d B , d B -d C , d C -d D ) are set to be equal to or smaller than the width W of the grinding wheel 58. Therefore, no gaps are generated between the rotation paths of the individual grinding wheels 58 within the rotation track 72.

[0065] The width Wo of the rotational orbit 72 can be adjusted by the width W and position of the grinding wheel 58. For example, the width W, position, etc. of the grinding wheel 58 are set so that the width Wo of the rotational orbit 72 is at least twice, preferably at least three times, and more preferably at least five times, the width W of the grinding wheel 58. Also, for example, the width Wo of the rotational orbit 72 is set to at least 1 / 20, preferably at least 1 / 10, and more preferably at least 1 / 5 of the length of each side of the workpiece 11.

[0066] As described above, by providing a plurality of grinding wheels 58 at different distances from the rotation axis 60 of the grinding wheel 54, the width Wo of the rotation track 72 can be made wider than that of a normal grinding wheel without increasing the width W of the grinding wheel 58. When the width Wo of the rotation track 72 is increased, the contact area between the workpiece 11 and the grinding wheels 58 during one rotation of the grinding wheel 54 increases, and the proportion of the area that is ground uniformly on the grinding surface of the workpiece 11 increases. This reduces the variation in thickness of the workpiece 11 when grinding a non-circular workpiece 11.

[0067] In the above, an example has been described in which the length L direction of the grinding wheel 58 is aligned with the rotation direction (tangential direction) of the grinding wheel 54. However, the length L direction of the grinding wheel 58 may be inclined with respect to the rotation direction (tangential direction) of the grinding wheel 54, and the width W direction of the grinding wheel 58 may be inclined with respect to the radial direction of the grinding wheel 54. In this case, the distance d1 from the rotation axis 60 of the grinding wheel 54 to one end of the grinding wheel 58 in the length L direction and the distance d2 to the other end have different values.

[0068] As described above, in the method for grinding a workpiece according to this embodiment, the non-circular workpiece 11 is ground by the grinding wheel 54 in which the grinding wheels 58 are arranged so that the width Wo of the rotational orbit 72 is wider than that of a normal grinding wheel (in which the distances from the rotation axis 60 of the grinding wheel 54 to the grinding wheels 58 are equal and the distances from the rotation axis 60 of the grinding wheel 54 to both ends of the grinding wheels 58 in the length direction are equal). This makes it easier to grind the surface of the workpiece 11 uniformly, and the thickness variation of the workpiece 11 is easily reduced.

[0069] In the above embodiment, the multiple grinding wheels 58 are arranged at different distances from the rotation axis 60 of the grinding wheel 54 (see FIG. 6). However, there is no restriction on the arrangement of the multiple grinding wheels 58 as long as the width Wo of the rotation track 72 is configured to be larger than that of a normal grinding wheel.

[0070] 7 is a bottom view showing a grinding wheel 54A which is a modified example of the grinding wheel 54. The configuration of the grinding wheel 54A is similar to that of the grinding wheel 54 (see FIG. 6) except for the arrangement of the multiple grinding stones 58.

[0071] The grinding wheel 54A is configured such that a plurality of grinding wheels 58 are arranged on the circumference of a circle centered on the rotation axis 60 of the grinding wheel 54, and the distances from the rotation axis 60 of the grinding wheel 54 to the plurality of grinding wheels 58 are equal. In other words, the positions of the plurality of grinding wheels 58 are set in the same manner as in a normal grinding wheel.

[0072] On the other hand, in the grinding wheel 54A, the orientations (angles) of the multiple grinding wheels 58 are set so that the length L direction of the grinding wheels 58 is inclined with respect to the rotation direction (tangential direction) of the grinding wheel 54A and the width W direction of the grinding wheels 58 is inclined with respect to the radial direction of the grinding wheel 54A. Therefore, the distance d1 from the rotation axis 60 of the grinding wheel 54A to one end of the grinding wheels 58 in the length L direction is different from the distance d2 to the other end.

[0073] When the grinding wheel 54A is rotated around the rotation axis 60, a circular rotational orbit 72A is described by the multiple grinding stones 58. The outer diameter of the rotational orbit 72A corresponds to the path of the end of the grinding stones 58 closest to the outer periphery of the wheel base 56. The inner diameter of the rotational orbit 72A corresponds to the path of the end of the grinding stones 58 closest to the center (rotation axis 60) of the wheel base 56.

[0074] As described above, when the grinding wheels 58 are arranged so as to be inclined with respect to the rotation direction of the grinding wheel 54A, the width Wo A is wider than that of a normal grinding wheel. This reduces the variation in thickness of the workpiece 11 when grinding a non-circular workpiece 11.

[0075] In addition, the structures, methods, etc. according to the above-described embodiments can be modified as appropriate without departing from the scope of the object of the present invention. [Explanation of symbols]

[0076] 11 Workpiece 11a Surface (first side) 11b Back side (2nd side) 13 Support member 2 Grinding equipment 4 Foundation 4a aperture 6 Chuck table (holding table) 6a Holding surface 6b Holding area 8 Frame (main body) 8a Top 8b Recess 8c Flow Path 10 Retaining member 10a Suction surface 12 Rotation axis (center of rotation) 14 Tilt adjustment mechanism 16 Table Base 18A Fixed support member 18B Movable support member 20 Mobile mechanism (mobile unit) 22 Ball screw 24 Pulse motor 26 Support stand 28 Nut 30 Support structure (column) 32 Mobile mechanism (mobile unit) 34 Guide rail 36 Retaining member 38 Nut 40 Ball screw 42 Pulse motor 44 Grinding Unit 46 Housing 48 Cushioning material 50 Spindle 52 Wheel mount 54,54A Grinding Wheel 56 Wheel base 58, 58A, 58B, 58C, 58D Grinding wheels 60 Rotation axis (center of rotation) 62 Controller (control unit, control section, control device) 70 Grindstone Group 72,72A Rotational Orbit

Claims

1. A method for grinding a non-circular workpiece with a grinding wheel having a plurality of grinding stones, comprising: a holding step of holding the workpiece on a holding surface of a chuck table; a grinding step of, after the holding step, grinding the workpiece by bringing the grinding wheels into contact with the workpiece while rotating the chuck table and the grinding wheel in a state where the rotational orbits of the grinding wheels are positioned so as to overlap with the rotational axis of the chuck table, A method for grinding a workpiece, characterized in that the multiple grinding wheels are arranged so that the distances from the rotation axis of the grinding wheel to the multiple grinding wheels are equal, and the width of the rotational orbit is wider than when the distances from the rotation axis of the grinding wheel to both ends of the grinding wheels in the longitudinal direction are equal.

2. The grinding wheel includes a wheel group including a plurality of the grinding wheels; 2. The method for grinding a workpiece according to claim 1, wherein the plurality of grinding wheels included in the grinding wheel group are arranged at different distances from the rotation axis of the grinding wheel.

3. 2. The method for grinding a workpiece according to claim 1, wherein the plurality of grinding wheels are arranged such that the distances from the rotation axis of the grinding wheel to both ends in the longitudinal direction of the grinding wheels are different.

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