Grinding method for workpieces

Abstract

To provide a grinding method of workpiece which can easily reduce thickness variation in non-circular workpiece.SOLUTION: A grinding method of workpiece for grinding non-circular workpiece by a grinding wheel having a grinding stone includes: a holding step of holding workpiece on a holding surface of a chuck table; an outer peripheral part grinding step of rotating a chuck table and a grinding wheel positioned so that a rotation locus of a grinding stone does not overlap a rotation axis of the holding surface, bringing the grinding stone into contact with workpiece, and thereby grinding the outer peripheral part of the workpiece, after the holding step; and a central part grinding step of rotating the chuck table and the grinding wheel positioned so that the rotation locus of the grinding stone overlaps the rotation axis of the holding surface, bringing the grinding stone into contact with the workpiece, and thereby grinding the central part of the workpiece, after the outer peripheral part grinding step.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a method for grinding a workpiece, in which a non-circular workpiece is ground with a grinding wheel.

Background Art

[0002] Device chips including devices are manufactured by dividing a wafer on which a plurality of devices are formed into individual pieces. Also, a package substrate is formed by mounting a plurality of device chips on a predetermined substrate and coating and sealing the mounted device chips with a resin layer (mold resin). By dividing this package substrate into individual pieces, a package device including a plurality of packaged device chips is manufactured. 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 has been a demand for thinning of device chips and package devices. Therefore, a process of grinding and thinning a wafer or a package substrate before division using a grinding device may be performed. The grinding device includes a chuck table for holding a workpiece and a grinding unit for performing grinding on the workpiece. The grinding unit incorporates a spindle, and an annular grinding wheel having a plurality of grinding wheels is mounted at the tip of the spindle. By holding the workpiece with the chuck table, rotating the chuck table and the grinding wheel, and bringing the grinding wheel into contact with the workpiece, the workpiece is ground and thinned.

[0004] Grinding equipment is 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 grinding non-circular workpieces in the same way as circular workpieces, variations in the thickness of the workpiece are likely to occur. For example, when grinding a rectangular workpiece with grinding equipment, grinding progresses less smoothly in areas close to the diagonals of the workpiece, and these areas tend to be thicker than other areas. Variations in the thickness of the workpiece after grinding can cause problems in subsequent processing (transportation, processing, etc.) of the workpiece, and may result in errors in the dimensions of chips obtained by dividing the workpiece.

[0005] Therefore, control methods for grinding devices to uniformly grind non-circular workpieces are being investigated. For example, Patent Document 1 discloses a grinding device in which, when grinding a square wafer, the rotation speed of the chuck table is adjusted by 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. In this way, by sequentially controlling the rotation speed of the chuck table according to the contact area between the wafer and the grinding wheel, the load on the wafer and the grinding wheel is made uniform, and variations in the thickness of the wafer after grinding are reduced. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2015-205358 [Overview of the project] [Problems that the invention aims to solve]

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

[0008] This invention has been made in view of the above problems, and aims to provide a method for grinding a workpiece that can easily reduce thickness variations in non-circular workpieces. [Means for solving the problem]

[0009] According to one aspect of the present invention, a method for grinding a non-circular workpiece with a grinding wheel equipped with a grinding wheel, comprising: a holding step of holding the workpiece on the holding surface of a chuck table; an outer periphery grinding step of grinding the outer periphery of the workpiece by rotating the chuck table and the grinding wheel, positioned such that the rotational trajectory of the grinding wheel does not coincide with the rotation axis of the holding surface, thereby bringing the grinding wheel into contact with the workpiece; and a central grinding step of grinding the central part of the workpiece by rotating the chuck table and the grinding wheel, positioned such that the rotational trajectory of the grinding wheel coincides with the rotation axis of the holding surface, thereby bringing the grinding wheel into contact with the workpiece. Following the central grinding step, a full-surface grinding step is performed in which the entire workpiece is ground by rotating the chuck table and the grinding wheel, which are positioned so that the rotational trajectory of the grinding wheel coincides with the rotation axis of the holding surface, thereby bringing the grinding wheel into contact with the workpiece. A method for grinding a workpiece including the following is provided. Furthermore, according to another aspect of the present invention, a method for grinding a workpiece with a grinding wheel equipped with a grinding wheel is provided, comprising: a holding step of holding the workpiece with the holding surface of a chuck table; an outer periphery grinding step of grinding the outer periphery of the workpiece by rotating the chuck table and the grinding wheel, positioned such that the rotational trajectory of the grinding wheel does not coincide with the rotation axis of the holding surface, to bring the grinding wheel into contact with the workpiece; and a central grinding step of grinding the central part of the workpiece by rotating the chuck table and the grinding wheel, positioned such that the rotational trajectory of the grinding wheel coincides with the rotation axis of the holding surface, to bring the grinding wheel into contact with the workpiece, wherein the number of rotations of the chuck table in the outer periphery grinding step is smaller than the number of rotations of the chuck table in the central grinding step.

[0010] According to yet another aspect of the present invention, a method for grinding a non-circular workpiece with a grinding wheel equipped with a grinding wheel includes: a holding step of holding the workpiece on the holding surface of a chuck table; an outer periphery grinding step of grinding the outer periphery of the workpiece by rotating the chuck table and the grinding wheel, positioned such that the rotational trajectory of the grinding wheel does not coincide with the rotation axis of the holding surface, thereby bringing the grinding wheel into contact with the workpiece; and a central grinding step of grinding the central part of the workpiece by rotating the chuck table and the grinding wheel, positioned such that the rotational trajectory of the grinding wheel coincides with the rotation axis of the holding surface, thereby bringing the grinding wheel into contact with the workpiece. In the outer periphery grinding step, the outer periphery of the workpiece is ground by rotating the chuck table while the grinding wheel is in contact with the side surface of the workpiece. A method for grinding a workpiece is provided.Preferably, the method for grinding the workpiece further includes a detection step, after the holding step and before the outer peripheral grinding step, in which the chuck table and the grinding wheel are brought closer together from a state in which the grinding wheel is separated from the side surface of the workpiece and the lower surface of the grinding wheel is positioned below the upper surface of the workpiece, and a detection step is made to detect that the grinding wheel has come into contact with the side surface of the workpiece.

[0011] According to yet another aspect of the present invention, a method for grinding a non-circular workpiece with a grinding wheel equipped with a grinding wheel includes: a holding step of holding the workpiece on the holding surface of a chuck table; an outer periphery grinding step of grinding the outer periphery of the workpiece by rotating the chuck table and the grinding wheel, positioned such that the rotational trajectory of the grinding wheel does not coincide with the rotation axis of the holding surface, thereby bringing the grinding wheel into contact with the workpiece; and a central grinding step of grinding the central part of the workpiece by rotating the chuck table and the grinding wheel, positioned such that the rotational trajectory of the grinding wheel coincides with the rotation axis of the holding surface, thereby bringing the grinding wheel into contact with the workpiece. In the outer circumference grinding step, the grinding wheel is moved from the side of the workpiece. To the side By rotating the chuck table from a separated position, the outer circumference of the workpiece is ground. A method for grinding a workpiece is provided. . [Effects of the Invention]

[0012] In a workpiece grinding method according to one aspect of the present invention, when grinding a non-circular workpiece, the outer periphery of the workpiece is ground first, followed by grinding the central part of the workpiece. This makes it possible to easily reduce variations in the thickness of the workpiece after grinding, which are caused by variations in the length from the center to the outer edge of the workpiece, without requiring complex control such as sequentially changing the rotation speed of the chuck table according to the contact area between the workpiece and the grinding wheel. [Brief explanation of the drawing]

[0013] [Figure 1] This is a partial cross-sectional side view showing a grinding device. [Figure 2] This is a cross-sectional view showing a chuck table. [Figure 3] This flowchart shows the grinding method for a workpiece. [Figure 4] This is a perspective view showing the grinding device during the holding step. [Figure 5] Figure 5(A) is a perspective view showing the grinding apparatus in the detection step, and Figure 5(B) is a plan view showing the workpiece and grinding wheel in the detection step. [Figure 6]FIG. 6(A) is a perspective view showing a grinding apparatus in the outer peripheral grinding step, and FIG. 6(B) is a plan view showing a workpiece and a grinding wheel in the outer peripheral grinding step. [Figure 7] FIG. 7(A) is a perspective view showing a grinding apparatus in the central grinding step, and FIG. 7(B) is a plan view showing a workpiece and a grinding wheel in the central grinding step. [Figure 8] It is a plan view showing a workpiece and a grinding wheel in the outer peripheral grinding step according to a modified example. [Figure 9] It is a plan view showing a rectangular workpiece and a grinding wheel.

MODE FOR CARRYING OUT THE INVENTION

[0014] Hereinafter, an embodiment according to an aspect of the present invention will be described with reference to the accompanying drawings. First, a configuration example of a grinding apparatus that can be used for implementing a method for grinding a workpiece according to the present embodiment will be described. FIG. 1 is a partial cross-sectional side view showing a grinding apparatus 2. In FIG. 1, the X-axis direction (first horizontal direction, front-rear direction) and the Y-axis direction (second horizontal direction, left-right direction) are perpendicular to each other. The Z-axis direction (height direction, up-down direction, vertical direction) is perpendicular to the X-axis direction and the Y-axis direction.

[0015] The grinding apparatus 2 includes a base 4 that supports or houses each component constituting the grinding apparatus 2. On the upper surface side of the base 4, a rectangular parallelepiped-shaped opening 4a is provided. Inside the opening 4a, a chuck table (holding table) 6 for holding a workpiece, which is an object of grinding by the grinding apparatus 2, is provided. The upper surface of the chuck table 6 constitutes a holding surface 6a for holding the workpiece.

[0016] FIG. 2 is a cross-sectional view showing the chuck table 6. The chuck table 6 includes a columnar frame body (main body portion) 8 made of a metal such as SUS (stainless steel), glass, ceramics, resin, or the like. A columnar concave portion 8b is provided concentrically with the upper surface 8a at the central portion on the upper surface 8a side of the frame body 8. Further, a disk-shaped holding member 10 made of a porous material such as porous ceramics is fitted into the concave portion 8b. The holding member 10 includes a large number of pores communicating from the upper surface to the lower surface of the holding member 10. The upper surface of the holding member 10 constitutes a circular suction surface 10a for sucking the workpiece when holding the workpiece by the chuck table 6.

[0017] The holding surface 6a of the chuck table 6 is constituted by the upper surface 8a of the frame body 8 and the suction surface 10a of the holding member 10. The holding surface 6a is connected to a suction source (not shown) such as an ejector through pores included in the holding member 10, a flow path 8c provided inside the frame body 8, a valve (not shown), and the like.

[0018] The holding surface 6a of the chuck table 6 is formed in a conical 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. Then, the chuck table 6 is arranged in a slightly inclined state such that a holding region 6b corresponding to a part of the holding surface 6a and extending from the center to the outer peripheral edge of the holding surface 6a is substantially parallel to the horizontal plane (XY plane). The region of the workpiece held by the holding region 6b or its vicinity is ground by a grinding unit 44 described later.

[0019] In FIG. 2, for convenience of explanation, the inclination of the holding surface 6a is exaggeratedly shown, 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 height difference (corresponding to the height of the cone) between the center and the outer peripheral edge of the holding surface 6a is set to about 20 μm or more and 40 μm or less.

[0020] A rotational drive source (not shown), such as a motor, is connected to the chuck table 6. The rotational drive source rotates the holding surface 6a of the chuck table 6 around the rotation axis 12. The rotation axis 12 of the chuck table 6 is set along the direction perpendicular to the radial direction of the holding surface 6a and is slightly inclined with respect to the Z-axis direction. The rotation axis 12 also intersects the holding surface 6a so as to pass through the center of the holding surface 6a.

[0021] As shown in Figure 1, the chuck table 6 is connected to a tilt adjustment mechanism 14 that adjusts the tilt of the chuck table 6. For example, the tilt adjustment mechanism 14 includes a disc-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 only one of the movable support members 18B is shown in Figure 1, and the other movable support member 18B is not shown.

[0022] One fixed support member 18A and two movable support members 18B are arranged 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 upper ends of the movable support members 18B are fixed to the lower surface of the outer periphery of the table base 16, respectively.

[0023] The fixed support member 18A is configured so that its upper end is fixed at a predetermined height. On the other hand, the movable support member 18B is configured so that its upper end can move (raise and lower) along the Z-axis direction. By inputting a control signal from the controller 62 (described later) to the movable support member 18B, the position (height position) of the upper ends of the two movable support members 18B in the Z-axis direction can be changed. This adjusts the tilt of the chuck table 6 and the rotation axis 12.

[0024] 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.

[0025] Specifically, the moving mechanism 20 includes a ball screw 22 positioned along the X-axis. A pulse motor 24 is connected to the end of the ball screw 22 to rotate it. The chuck table 6 and the tilt adjustment mechanism 14 are supported by a support base 26, to which a nut portion 28 is connected. The ball screw 22 is screwed into the nut portion 28, and when the pulse motor 24 rotates the ball screw 22, the chuck table 6 moves along the X-axis.

[0026] A rectangular parallelepiped support structure (column) 30 is provided behind the chuck table 6 and the moving mechanism 20 (on the right side in Figure 1). A moving mechanism (moving unit) 32 is provided on the front side (front side) of the support structure 30. The moving mechanism 32 includes a pair of guide rails 34 fixed to the front side of the support structure 30. The pair of guide rails 34 are arranged along the Z-axis direction and spaced apart from each other in the Y-axis direction.

[0027] A pair of hollow, cylindrical retaining members 36 are mounted on the guide rails 34 so as to be slidable along the guide rails 34. A nut portion 38 is connected to the back side of the retaining member 36, and a ball screw 40, which is positioned between the pair of guide rails 34 along the Z-axis direction, is screwed into the nut portion 38. A pulse motor 42 for rotating the ball screw 40 is also connected to the end of the ball screw 40. When the ball screw 40 is rotated by the pulse motor 42, the retaining member 36 moves (up and down) along the guide rails 34 in the Z-axis direction.

[0028] The holding member 36 holds a grinding unit 44 that performs grinding on a workpiece. The grinding unit 44 comprises a cylindrical housing 46 housed in the holding member 36. The lower surface of the housing 46 is supported by the bottom surface of the holding member 36 via a cushioning member 48 made of an elastic material such as rubber.

[0029] The housing 46 houses a cylindrical spindle 50 arranged along the Z-axis. The tip (lower end) of the spindle 50 is exposed from the housing 46 and protrudes downward from the lower surface of the retaining member 36 through an opening provided at the bottom of the retaining member 36. A rotational drive source (not shown), such as a motor, for rotating the spindle 50 is connected to the base (upper end) of the spindle 50.

[0030] A disc-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 the workpiece is detachably mounted on the underside of the wheel mount 52. For example, the grinding wheel 54 is fixed to the wheel mount 52 by fasteners such as bolts.

[0031] The grinding wheel 54 is made of a metal such as aluminum or stainless steel and includes an annular wheel base 56 formed to be approximately the same diameter as the wheel mount 52. The upper surface of the wheel base 56 is fixed to the lower surface of the wheel mount 52. Multiple grinding wheels 58 are fixed to the lower surface of the wheel base 56. For example, the grinding wheels 58 are formed in a rectangular parallelepiped shape and are arranged in an annular pattern at approximately equal intervals along the circumferential direction of the wheel base 56.

[0032] The grinding wheel 58 includes abrasive grains made of diamond, cBN (cubic boron nitride), etc., and a binder (bonding material) such as a metal bond, resin bond, or vitrified bond to fix the abrasive grains. However, there are no restrictions on the material, shape, structure, size, etc., of the grinding wheel 58. The number of grinding wheels 58 can also be set arbitrarily.

[0033] The grinding wheel 54 rotates around a rotation axis 60 set along the Z-axis direction by power transmitted from a rotation drive source (not shown) via the spindle 50 and wheel mount 52. That is, the rotation axis 60 corresponds to the rotation axis of the spindle 50, wheel mount 52, and grinding wheel 54. When the grinding wheel 54 is rotated, each of the multiple grinding wheels 58 revolves around the rotation axis 60 along an annular rotation trajectory (rotation path, rotation route) that is roughly parallel to the horizontal plane (XY plane).

[0034] A grinding fluid supply passage (not shown) for supplying a liquid (grinding fluid) such as pure water is provided inside or near the grinding unit 44. For example, the grinding fluid supply passage consists of a flow path formed inside the wheel mount 52 and the grinding wheel 54, or a nozzle provided near the grinding unit. When grinding a workpiece 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 the debris (grinding shavings) generated by the grinding process.

[0035] Furthermore, the grinding device 2 includes a controller (control unit, control unit, control device) 62 that controls the grinding device 2. The controller 62 is connected to the components of the grinding device 2 (chuck table 6, tilt adjustment mechanism 14, moving mechanism 20, moving mechanism 32, grinding unit 44, etc.) and generates control signals to control the operation of each component.

[0036] For example, the controller 62 is composed of a computer and includes a calculation unit that performs calculations necessary for the operation of the grinding machine 2, and a storage unit that stores various information (data, programs, etc.) used for the operation of the grinding machine 2. The calculation unit includes a processor such as a CPU (Central Processing Unit). The storage unit includes memory such as ROM (Read Only Memory) and RAM (Random Access Memory).

[0037] Next, a specific example of the workpiece grinding method according to this embodiment will be described. Figure 3 is a flowchart of the workpiece grinding method. In this embodiment, a non-circular workpiece is ground using the grinding device 2.

[0038] Specifically, first, the workpiece is held by the holding surface 6a of the chuck table 6 (holding step S1). Figure 4 is a perspective view showing the grinding device 2 in holding step S1. In holding step S1, the workpiece 11, which is the object to be ground by the grinding device 2, is held by the chuck table 6.

[0039] For example, the workpiece 11 is a plate-shaped member made of semiconductors (Si, GaAs, InP, GaN, SiC, etc.), glass (quartz glass, borosilicate glass, etc.), ceramics, resin, metal, etc., and includes a surface (first surface) 11a and a back surface (second surface) 11b that are generally parallel to each other. Note that the workpiece 11 is a non-circular member in which the distance from the center to the outer edge (side surface) is not constant. Below, as an example, the case in which the workpiece 11 is rectangular will be described. Figure 4 shows a workpiece 11 having a square surface 11a and a back surface 11b.

[0040] 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 multiple 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 or more and 550 mm or less.

[0041] By dividing the package substrate into individual pieces, a package device containing multiple packaged device chips can be manufactured. Furthermore, by grinding and thinning the resin layer using the grinding device 2 before dividing the package substrate, a thin package device can be manufactured.

[0042] However, as long as the shape of the workpiece 11 is not circular, there are no restrictions on the material, shape, structure, size, etc. of the workpiece 11. For example, the workpiece 11 may be a polygonal member having 3 or 5 or more corners and sides, or it may be an elliptical or oblong member.

[0043] When the workpiece 11 is held by the chuck table 6, the workpiece 11 is supported by a support member 21. For example, the support member 21 is a highly rigid substrate formed in the shape of a disc. The specific material of the support member 21 is the same as that of the workpiece 11. The diameter of the support member 21 is set to be greater than or equal to the diameter of the suction surface 10a of the chuck table 6.

[0044] The support member 21 is fixed to the workpiece 11 via adhesive or the like so as to cover the surface of the workpiece 11 opposite to the surface being ground by the grinding wheel 54 (the surface to be ground). For example, if the surface 11a of the workpiece 11 is the surface to be ground, the support member 21 is fixed to the back surface 11b of the workpiece 11 as shown in Figure 4.

[0045] However, there are no restrictions on the material, structure, dimensions, etc. of the support member 21, as long as it can support the workpiece 11. For example, a circular sheet can be used as the support member 21. The sheet includes a film-like base material and an adhesive layer (sticking agent) provided on the base material. The base material is made of a resin such as polyolefin, polyvinyl chloride, or polyethylene terephthalate, and the adhesive layer is made of an epoxy-based, acrylic-based, or rubber-based adhesive. The adhesive layer may also be an ultraviolet-curing resin that hardens when exposed to ultraviolet light.

[0046] The workpiece 11 is positioned on the chuck table 6 such that its front surface 11a (the side to be ground) is exposed upwards and its back surface 11b (the side to the support member 21) 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. The support member 21 is also positioned 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 held by suction at the holding surface 6a of the chuck table 6 via the support member 21.

[0047] As mentioned above, the holding surface 6a of the chuck table 6 is formed in a conical shape (see Figure 2). When the support member 21 is sucked by the suction surface 10a, the workpiece 11 and the support member 21 are held in a state where they are slightly bent and deformed along the holding surface 6a. As a result, the surface 11a of the workpiece 11 held in the holding area 6b (see Figure 2) or its vicinity is positioned approximately parallel to the horizontal plane (XY plane).

[0048] As described above, by placing the workpiece 11 on the chuck table 6 via the support member 21, even if the suction surface 10a is formed in a circular shape to accommodate 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 correspond to a rectangular workpiece 11. In this case, the support member 21 can be omitted, and the workpiece 11 can be directly held by suction on the suction surface 10a.

[0049] Next, it is detected that the grinding wheel 58 of the grinding wheel 54 has come into contact with the side surface of the workpiece 11 (detection step S2). Figure 5(A) is a perspective view showing the grinding apparatus 2 in detection step S2, and Figure 5(B) is a plan view showing the workpiece 11 and the grinding wheel 54 in detection step S2.

[0050] In detection step S2, first, the positional relationship between the chuck table 6 and the grinding wheel 54 is adjusted so that the grinding wheel 58 is separated from the side surface of the workpiece 11, and the lower surface of the grinding wheel 58 is positioned below the upper surface of the workpiece 11.

[0051] Specifically, the chuck table 6 rotates, adjusting the orientation (angle) of the workpiece 11 so that one side of the workpiece 11 is aligned with the Y-axis direction. In addition, the position of the chuck table 6 in the X-axis direction is adjusted by the movement mechanism 20 (see Figure 1) so that the workpiece 11 does not overlap with the grinding wheel 54 and is positioned in front of the grinding wheel 54 (lower left side in Figure 5(A), left side in Figure 5(B)).

[0052] Furthermore, the position of the grinding unit 44 in the Z-axis direction is adjusted by the moving mechanism 32 (see Figure 1) so that the lower surface of the grinding wheel 58 is positioned below the upper surface (surface 11a, the surface to be ground) of the workpiece 11. The difference in height between the upper surface of the workpiece 11 and the lower surface of the grinding wheel 58 at this time corresponds to the target value of the amount of grinding of the workpiece 11 (the difference in thickness of the workpiece 11 before and after grinding) in the outer peripheral grinding step S3 described later.

[0053] Next, with the workpiece 11 and grinding wheel 54 positioned as described above, the chuck table 6 and the grinding wheel 54 are brought closer together, and the grinding wheel 58 is brought into contact with the side surface of the workpiece 11. Specifically, while the grinding wheel 54 is rotated around the rotation axis 60, the chuck table 6 is moved along the X-axis direction by the moving mechanism 20 (see Figure 1) to bring it closer to the grinding wheel 54. As a result, the grinding wheel 58 comes into contact with the side surface of the workpiece 11.

[0054] The grinding device 2 then detects when the grinding wheel 58 comes into contact with the side surface of the workpiece 11. For example, the grinding device 2 includes a motor 64 and load measuring devices 66, 68 that function as detectors (sensors) to detect when the grinding wheel 58 comes into contact with the side surface of the workpiece 11.

[0055] Motor 64 is a rotational drive source connected to the spindle 50. When a control signal is input to motor 64 from controller 62 (see Figure 1), motor 64 is driven, causing the spindle 50, wheel mount 52, and grinding wheel 54 to rotate around the rotation axis 60. The current value of motor 64 is also input to controller 62 and monitored by controller 62.

[0056] The load measuring devices 66 and 68 are composed of load cells, for example. Load measuring device 66 is connected to the chuck table 6 and measures the load applied to the chuck table 6. Load measuring device 68 is connected to the spindle 50 and measures the load applied to the spindle 50, wheel mount 52, and grinding wheel 54. The loads measured by load measuring devices 66 and 68 are input to the controller 62 (see Figure 1).

[0057] When the grinding wheel 58 comes into contact with the side surface of the workpiece 11, a load is applied to the grinding wheel 58. As a result, the torque of the spindle 50 required to maintain the rotation of the grinding wheel 54 increases, and the current value of the motor 64 also increases. Therefore, the controller 62 can detect that the grinding wheel 58 has come into contact with the side surface of the workpiece 11 by comparing the current value of the motor 64 with a preset reference value (threshold).

[0058] Furthermore, when the grinding wheel 58 comes into contact with the side surface of the workpiece 11, a load is applied to the chuck table 6 and the spindle 50, and the load measured by the load measuring devices 66 and 68 increases. Therefore, the controller 62 can detect that the grinding wheel 58 has come into contact with the side surface of the workpiece 11 by comparing the load value measured by the load measuring device 66 or the load measuring device 68 with a preset reference value (threshold).

[0059] However, there are no restrictions on the method for detecting contact between the workpiece 11 and the grinding wheel 58. For example, an optical sensor or the like may be used to detect when the grinding wheel 58 has come into contact with the side surface of the workpiece 11. Alternatively, the operator may directly visually inspect the workpiece 11 and the grinding wheel 54 to confirm whether or not the grinding wheel 58 is in contact with the workpiece 11.

[0060] When it is detected that the grinding wheel 58 has come into contact with the workpiece 11, the movement of the chuck table 6 stops. This positions the chuck table 6 and the grinding wheel 54 so that the rotational trajectory of the grinding wheel 58 is in contact with the side surface of the workpiece 11.

[0061] Next, the outer periphery of the workpiece 11 is ground by bringing the grinding wheel 54's grinding wheel 58 into contact with the workpiece 11 (outer periphery grinding step S3). Figure 6(A) is a perspective view showing the grinding apparatus 2 in the outer periphery grinding step S3, and Figure 6(B) is a plan view showing the workpiece 11 and the grinding wheel 54 in the outer periphery grinding step S3.

[0062] In the outer circumference grinding step S3, the chuck table 6 and grinding wheel 54, positioned so that the rotational trajectory of the grinding wheel 58 does not overlap with the rotation axis 12 of the holding surface 6a, are rotated to bring the grinding wheel 58 into contact with the workpiece 11. This allows the outer circumference (corner portion) 13B of the workpiece 11 to be ground while leaving a circular unground area (an area not ground by the grinding wheel 58) in the central part 13A of the workpiece 11.

[0063] Specifically, once the aforementioned detection step S2 is completed, the grinding wheel 54 rotates and the grinding wheel 58 comes into contact with the side surface of the workpiece 11. At this time, the rotational trajectory of the grinding wheel 58 is positioned so as not to overlap with the rotation axis 12 of the chuck table 6 in the Z-axis direction (see Figure 6(B)). Then, when the chuck table 6 is rotated while maintaining the rotation of the grinding wheel 54, the grinding wheel 58 comes into contact with the outer periphery 13B (near the four corners) of the workpiece 11 without contacting the central part 13A. As a result, only the outer periphery 13B of the workpiece 11 is ground and thinned, leaving a circular ungrinded region in the central part 13A of the workpiece 11 where the thickness does not change before and after grinding. The radius of the ungrinded region corresponds to the distance from the rotation axis 12 of the chuck table 6 to the rotational trajectory of the grinding wheel 58.

[0064] In the outer circumference grinding step S3, the rotational speed of the chuck table 6 is set to, for example, 10 rpm to 300 rpm. The rotational speed of the grinding wheel 54 is set to, for example, 1000 rpm to 6000 rpm. However, it is preferable that the rotational speed n1 of the chuck table 6 in the outer circumference grinding step S3 is smaller than the rotational speed n2 of the chuck table 6 in the central part grinding step S4, which will be described later. For example, the rotational speed n1 is set to 90% or less of the rotational speed n2, preferably 80% or less, and more preferably 70% or less. This makes it easier for the outer circumference 13B of the workpiece 11 to be uniformly ground by the grinding wheel 58, and makes it less likely for variations in thickness to occur in the outer circumference 13B of the workpiece 11.

[0065] Next, the grinding wheel 54's grinding wheel 58 is brought into contact with the workpiece 11 to grind the central part of the workpiece 11 (central grinding step S4). Figure 7(A) is a perspective view showing the grinding apparatus 2 in the central grinding step S4, and Figure 7(B) is a plan view showing the workpiece 11 and the grinding wheel 54 in the central grinding step S4.

[0066] In the central grinding step S4, the chuck table 6 and grinding wheel 54 are rotated so that the rotational trajectory of the grinding wheel 58 coincides with the rotation axis 12 of the holding surface 6a, bringing the grinding wheel 58 into contact with the workpiece 11. As a result, the central part 13A of the workpiece 11 is ground and removed.

[0067] Specifically, first, with the grinding unit 44 positioned above the chuck table 6, the chuck table 6 is moved along the X-axis using the moving mechanism 20 (see Figure 1) to adjust the positional relationship between the chuck table 6 and the grinding wheel 54 so that the rotational trajectory of the grinding wheel 58 coincides with the rotation axis 12 of the chuck table 6 in the Z-axis direction (see Figure 7(B)).

[0068] Furthermore, the diameter of the rotational trajectory of the grinding wheel 58 is larger than the radius of the ungrinded area of ​​the workpiece 11. For example, the diameter of the rotational trajectory of the grinding wheel 58 is set to be greater than or equal to the diameter of the ungrinded area (greater than or equal to the length of one side of the workpiece 11). Therefore, multiple grinding wheels 58 are arranged so as to overlap with an arc-shaped region extending from the center of the ungrinded area to the outer edge (side).

[0069] Next, with the chuck table 6 and grinding wheel 54 rotating, the chuck table 6 and grinding wheel 54 are moved relative to each other along a direction parallel to the rotation axis 60 (Z-axis direction). As a result, the grinding wheel 58 comes into contact with the central part 13A (ungrinded area) of the workpiece 11, and the central part 13A is ground and thinned.

[0070] Specifically, the chuck table 6 is first rotated around the rotation axis 12, and the grinding wheel 54 is rotated around the rotation axis 60. For example, the rotational speed of the chuck table 6 is set to between 100 rpm and 900 rpm, and the rotational speed of the grinding wheel 54 (the rotational speed of the spindle 50) is set to between 1000 rpm and 6000 rpm.

[0071] Next, the grinding unit 44 is lowered along the Z-axis direction by the moving mechanism 32 (see Figure 1). As a result, the chuck table 6 and the grinding wheel 54 move relative to each other along the direction parallel to the rotation axis 60 (Z-axis direction), bringing the central part 13A of the workpiece 11 closer to the grinding wheel 58. The relative movement speed (machining feed rate) 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.

[0072] When the grinding wheel 58 comes into contact with the central part 13A of the workpiece 11, the grinding wheel 58 rotates so as to pass through the rotation axis 12, grinding the surface 11a side of the central part 13A of the workpiece 11. As a result, the ungrinded area of ​​the workpiece 11 is thinned.

[0073] As described above, in the central grinding step S4, the disc-shaped ungrinded area remaining in the central part 13A of the workpiece 11 after the outer peripheral grinding step S3 is ground. This makes it possible to grind and thin the central part 13A of the workpiece 11 in the same way as a disc-shaped workpiece (such as a silicon wafer).

[0074] If the entire rectangular workpiece 11 is ground without performing the outer peripheral grinding step S3, variations in thickness are likely to occur in the workpiece 11. Specifically, in the region of the workpiece 11 that overlaps with the diagonal of the surface 11a (the diagonal region), the distance from the center of the workpiece 11 to the outer peripheral edge is longer compared to 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 becomes larger than when other regions of the workpiece 11 are ground. As a result, the load on the grinding wheel 58 increases, and grinding becomes more difficult in areas closer to the diagonal region of the workpiece 11. Consequently, variations in the amount of grinding of the workpiece 11 occur, and the workpiece 11 after grinding is likely to have a curved shape on the surface 11a side.

[0075] On the other hand, in this embodiment, after grinding the outer periphery 13B of the workpiece 11 in the outer periphery grinding step S3, the remaining disc-shaped ungrinded area in the central part 13A of the workpiece 11 is ground in the central part grinding step S4. In the outer periphery grinding step S3, only the outer periphery 13B of the workpiece 11 is ground, so the grinding area is small and thickness variations in the outer periphery 13B are less likely to occur. Also, in the central part grinding step S4, since the ungrinded area with a constant length from the center to the outer edge is ground, thickness variations in the central part 13A are less likely to occur. As a result, the entire workpiece 11 is ground fairly uniformly.

[0076] Then, when the central portion 13A is ground down until its thickness is the same as that of the outer circumference 13B, the unground area is removed, and the overall thickness of the workpiece 11 becomes uniform. After that, the grinding unit 44 rises, the grinding wheel 58 separates from the workpiece 11, and grinding of the workpiece 11 by the grinding wheel 54 stops. As a result, a thinned workpiece 11 with uniform thickness is obtained.

[0077] However, after the unground area is removed and the thickness of the central part 13A and the outer circumference 13B of the workpiece 11 are equal, the entire workpiece 11 (central part 13A and outer circumference 13B) may be further ground by a predetermined amount using the grinding wheel 54 (full surface grinding step). Specifically, even after the unground area of ​​the workpiece 11 is removed, the rotation of the chuck table 6 and the grinding wheel 54 is maintained while the machining feed continues. The rotation speed of the chuck table 6 and the grinding wheel 54 and the machining feed rate in the full surface grinding step can be set in the same way as in the central part grinding step S4.

[0078] When the full-surface grinding step is performed, the grinding marks (saw marks) formed on the outer periphery 13B of the workpiece 11 in the outer periphery grinding step S3 are removed. This prevents random grinding marks from remaining on the surface 11a side of the workpiece 11.

[0079] Furthermore, it is preferable that the amount of grinding of the workpiece 11 in the full-surface grinding step be set to a small value within the range in which the grinding marks formed on the outer periphery 13B of the workpiece 11 in the outer periphery grinding step S3 are removed. For example, the amount of grinding of the workpiece 11 in the full-surface grinding step is set to 10 μm or less, preferably 5 μm or less. This makes it possible to suppress thickness variations that occur when grinding the entire rectangular workpiece 11.

[0080] As described above, in the workpiece grinding method according to this embodiment, when grinding a non-circular workpiece 11, the outer periphery 13B of the workpiece 11 is ground first, and then the central part 13A of the workpiece 11 is ground. This makes it possible to easily reduce variations in the thickness of the workpiece 11 after grinding, which are caused by variations in the length from the center to the outer edge of the workpiece 11, without having to perform complex control such as sequentially changing the rotation speed of the chuck table 6 according to the contact area between the workpiece 11 and the grinding wheel 58.

[0081] In the above embodiment, an example was described in which the outer periphery 13B of the workpiece 11 is ground by rotating the chuck table 6 while the grinding wheel 58 of the grinding wheel 54 is in contact with the side surface of the workpiece 11 (detection step S2 and outer periphery grinding step S3). However, there are no restrictions on the method of grinding the outer periphery of the workpiece 11.

[0082] Figure 8 is a plan view showing the workpiece 11 and grinding wheel 54 during the outer circumference grinding step S3'. The outer circumference grinding step S3' is a modified example of the outer circumference grinding step S3 (see Figures 6(A) and 6(B)).

[0083] In the outer circumference grinding step S3', first, the positional relationship between the chuck table 6 and the grinding wheel 54 is adjusted using the same procedure as in the detection step S2 (see Figures 5(A) and 5(B)). However, the chuck table 6 and the grinding wheel 54 are positioned so that the grinding wheel 58 is separated from the side surface of the workpiece 11. That is, a gap of distance d is ensured between the side surface of the workpiece 11 and the rotational trajectory of the grinding wheel 58. In addition, the rotational trajectory of the grinding wheel 58 is positioned so as not to overlap with the rotation axis 12.

[0084] Then, with the grinding wheel 54 rotating, the chuck table 6 is rotated. As a result, the outer circumference 13B (near the four corners) of the workpiece 11 is ground, while an unground area remains in the central part 13A of the workpiece 11.

[0085] As described above, when the chuck table 6 is rotated with the grinding wheel 58 separated from the side surface of the workpiece 11, the area of ​​the outer circumference 13B that is ground by the grinding wheel 58 becomes smaller, and the thickness variation in the outer circumference 13B is further reduced. As shown in Figure 8, the unground area remaining in the central part 13A of the workpiece 11 is not a perfect circle, but the variation in the distance from the center of the unground area to the outer edge is small. Therefore, even if the unground area of ​​the workpiece 11 is ground and removed in the subsequent central grinding step S4, the thickness variation in the central part 13A of the workpiece 11 is kept small.

[0086] Furthermore, in the above embodiment, a method of grinding the outer periphery 13B of the workpiece 11 by impacting the grinding wheel 58 against the side surface of the workpiece 11 was described (see Figures 6(A), 6(B), and 8). However, there are no restrictions on the method of grinding the outer periphery 13B of the workpiece 11. For example, in the outer periphery grinding step S3, the outer periphery 13B of the workpiece 11 may be ground by pressing the grinding wheel 54 against the outer periphery 13B from the surface 11a side of the workpiece 11.

[0087] Specifically, first, similar to the central grinding step S4, the chuck table 6 holding the workpiece 11 is positioned below the grinding wheel 54 (see Figures 7(A) and 7(B)). However, the positional relationship between the chuck table 6 and the grinding wheel 54 is adjusted so that the rotational trajectory of the grinding wheel 58 does not overlap with the central part 13A of the workpiece 11 in the Z-axis direction, but overlaps with the outer circumference 13B in the Z-axis direction.

[0088] Next, by rotating the chuck table 6 and grinding wheel 54 while lowering the grinding unit 44 along the Z-axis, the rotating grinding wheel 58 is brought into contact with the surface 11a side of the workpiece 11. This makes it possible to grind and thin the outer periphery 13B while leaving an ungrinded area in the central part 13A of the workpiece 11.

[0089] Furthermore, the above embodiment described an example of grinding a square-shaped workpiece 11 with four sides of approximately the same length. However, the workpiece grinding method according to the present invention can also be used to grind workpieces of other shapes.

[0090] Figure 9 is a plan view showing a rectangular workpiece 15 and a grinding wheel 54. The workpiece 15 is a rectangular workpiece that includes a pair of long sides and a pair of short sides. When grinding the workpiece 15, in the outer peripheral grinding step S3, the chuck table 6 is rotated with the grinding wheel 58 in contact with the side corresponding to the long side of the workpiece 15. This makes it possible to grind and thin the outer peripheral 17B (near the four corners) of the workpiece 15 while leaving a circular ungrinded area in the central part 17A of the workpiece 15.

[0091] Furthermore, the structures, methods, etc., according to the above embodiments can be modified as appropriate without departing from the scope of the objectives of the present invention. [Explanation of Symbols]

[0092] 11 Workpiece 11a Surface (first side) 11b Back side (2nd side) 13A Central part 13B Outer periphery (corner) 15 Workpiece 17A Central part 17B Outer periphery 21 Support member 2. Grinding device 4 base 4a aperture 6. Chuck table (holding table) 6a Holding surface 6b Holding area 8. Frame (main body) 8a Top 8b recess 8c channel 10 Retaining member 10a Suction surface 12 Rotation axes 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 section 30. Support Structure (Column) 32. Mobile Mechanism (Mobile Unit) 34 Guide rails 36 Retaining member 38 Nut section 40 Ball screw 42 pulse motor 44 Grinding Unit 46 Housing 48. Cushioning material 50 spindles 52 Wheel Mount 54 Grinding Wheels 56 Wheel base 58 Grinding Wheel 60 Rotation axis 62 Controllers (control units, control units, control devices) 64 motors 66,68 Load measuring instrument

Claims

1. A method for grinding a workpiece, comprising grinding a non-circular workpiece with a grinding wheel equipped with a grinding wheel, A holding step in which the workpiece is held on the holding surface of the chuck table, Following the holding step, the chuck table and grinding wheel are rotated so that the rotational trajectory of the grinding wheel does not overlap with the rotation axis of the holding surface, thereby bringing the grinding wheel into contact with the workpiece and grinding the outer periphery of the workpiece in an outer periphery grinding step. Following the outer periphery grinding step, a central grinding step is performed in which the central part of the workpiece is ground by rotating the chuck table and the grinding wheel, which are positioned so that the rotational trajectory of the grinding wheel coincides with the rotation axis of the holding surface, thereby bringing the grinding wheel into contact with the workpiece. A method for grinding a workpiece, characterized by comprising, after the central grinding step, a full-surface grinding step in which the chuck table and the grinding wheel are rotated so that the rotational trajectory of the grinding wheel coincides with the rotation axis of the holding surface, thereby bringing the grinding wheel into contact with the workpiece and grinding the entire workpiece.

2. A method for grinding a workpiece, comprising grinding a non-circular workpiece with a grinding wheel equipped with a grinding wheel, A holding step in which the workpiece is held on the holding surface of the chuck table, Following the holding step, the chuck table and grinding wheel are rotated so that the rotational trajectory of the grinding wheel does not overlap with the rotation axis of the holding surface, thereby bringing the grinding wheel into contact with the workpiece and grinding the outer periphery of the workpiece in an outer periphery grinding step. The process includes, after the outer periphery grinding step, a central grinding step in which the central part of the workpiece is ground by rotating the chuck table and the grinding wheel, which are positioned so that the rotational trajectory of the grinding wheel coincides with the rotation axis of the holding surface, thereby bringing the grinding wheel into contact with the workpiece, A method for grinding a workpiece, characterized in that the rotational speed of the chuck table in the outer circumference grinding step is smaller than the rotational speed of the chuck table in the central circumference grinding step.

3. A method for grinding a workpiece, comprising grinding a non-circular workpiece with a grinding wheel equipped with a grinding wheel, A holding step in which the workpiece is held on the holding surface of the chuck table, Following the holding step, the chuck table and grinding wheel are rotated so that the rotational trajectory of the grinding wheel does not overlap with the rotation axis of the holding surface, thereby bringing the grinding wheel into contact with the workpiece and grinding the outer periphery of the workpiece in an outer periphery grinding step. The process includes, after the outer periphery grinding step, a central grinding step in which the central part of the workpiece is ground by rotating the chuck table and the grinding wheel, which are positioned so that the rotational trajectory of the grinding wheel coincides with the rotation axis of the holding surface, thereby bringing the grinding wheel into contact with the workpiece, A method for grinding a workpiece, characterized in that, in the outer circumference grinding step, the outer circumference of the workpiece is ground by rotating the chuck table while the grinding wheel is in contact with the side surface of the workpiece.

4. The method for grinding a workpiece according to claim 3, further comprising a detection step of bringing the chuck table and the grinding wheel closer together after the holding step and before the outer peripheral grinding step, from a state in which the grinding wheel is separated from the side surface of the workpiece and the lower surface of the grinding wheel is positioned below the upper surface of the workpiece, and detecting that the grinding wheel has come into contact with the side surface of the workpiece.

5. A method for grinding a workpiece, comprising grinding a non-circular workpiece with a grinding wheel equipped with a grinding wheel, A holding step in which the workpiece is held on the holding surface of the chuck table, Following the holding step, the chuck table and grinding wheel are rotated so that the rotational trajectory of the grinding wheel does not overlap with the rotation axis of the holding surface, thereby bringing the grinding wheel into contact with the workpiece and grinding the outer periphery of the workpiece in an outer periphery grinding step. The process includes, after the outer periphery grinding step, a central grinding step in which the central part of the workpiece is ground by rotating the chuck table and the grinding wheel, which are positioned so that the rotational trajectory of the grinding wheel coincides with the rotation axis of the holding surface, thereby bringing the grinding wheel into contact with the workpiece, A method for grinding a workpiece, characterized in that, in the outer periphery grinding step, the outer periphery of the workpiece is ground by rotating the chuck table while the grinding wheel is positioned laterally away from the side surface of the workpiece.

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