JP2024074420A - Method for grinding a workpiece - Google Patents

Abstract

[Problem] To provide a method for grinding a non-circular workpiece that can easily reduce thickness variation of the non-circular workpiece. [Solution] A method for grinding a non-circular workpiece with a grinding wheel equipped with a grinding wheel, comprising: a holding step for holding the workpiece on the holding surface of a chuck table; an outer periphery grinding step for grinding the outer periphery of the workpiece by rotating the chuck table and grinding wheel positioned so that the rotational locus of the grinding wheel does not overlap with the rotation axis of the holding surface and bringing the grinding wheel into contact with the workpiece after the holding step; and a center grinding step for grinding the center of the workpiece by rotating the chuck table and grinding wheel positioned so that the rotational locus of the grinding wheel overlaps with the rotation axis of the holding surface and bringing the grinding wheel into contact with the workpiece after the outer periphery grinding step. [Selected Figure] Figure 3

Description

The present invention relates to a method for grinding a non-circular workpiece using a grinding wheel.

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

In recent years, with the miniaturization of electronic devices, there is a demand for thinner device chips and package devices. Therefore, a grinding device is sometimes used to grind and thin undivided wafers and package substrates. The grinding device includes a chuck table that holds the workpiece and a grinding unit that performs grinding on the workpiece. The grinding unit has a built-in 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 the chuck table and grinding wheel are rotated, thereby grinding and thinning the workpiece.

Grinding machines are highly versatile and can be used not only to grind circular workpieces such as silicon wafers, but also to grind non-circular workpieces such as package substrates. However, when a grinding machine is used to grind a non-circular workpiece in the same way as a circular workpiece, the thickness of the workpiece is likely to vary. For example, when a rectangular workpiece is ground with a grinding machine, the areas closer to the diagonal of the workpiece tend to be harder to grind and 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 there may be errors in the dimensions of the chips obtained by dividing the workpiece.

Therefore, methods of controlling a grinding device for uniformly grinding a non-circular workpiece have been studied. For example, Patent Document 1 discloses a grinding device that uses a servo motor to adjust the rotation speed of the chuck table when grinding a square wafer 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 uniformized, and the variation in thickness of the wafer after grinding is reduced.

JP 2015-205358 A

As described above, by adjusting the rotation 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 thickness variations in the workpieces 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 more complex and increases costs.

The present invention was made in consideration of such problems, and aims to provide a method for grinding a workpiece that can easily reduce the thickness variation of a non-circular workpiece.

According to one aspect of the present invention, there is provided a method for grinding a non-circular workpiece with a grinding wheel having a grinding wheel, the method including: a holding step for holding the workpiece on the holding surface of a chuck table; a peripheral grinding step for grinding the peripheral portion of the workpiece by rotating the chuck table and the grinding wheel positioned so that the rotational path of the grinding wheel does not overlap with the rotational axis of the holding surface and bringing the grinding wheel into contact with the workpiece after the holding step; and a center grinding step for grinding the center of the workpiece by rotating the chuck table and the grinding wheel positioned so that the rotational path of the grinding wheel overlaps with the rotational axis of the holding surface and bringing the grinding wheel into contact with the workpiece after the peripheral grinding step.

Preferably, in the outer peripheral grinding step, the grinding wheel is brought into contact with the side surface of the workpiece, and the chuck table is rotated to grind the outer peripheral portion of the workpiece. Preferably, the grinding method for the workpiece further includes, after the holding step and before the outer peripheral grinding step, a detection step of bringing the chuck table and the grinding wheel 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 lower than the upper surface of the workpiece, and detecting that the grinding wheel has come into contact with the side surface of the workpiece.

Also, preferably, in the outer peripheral grinding step, the grinding wheel is moved away from the side of the workpiece and the chuck table is rotated to grind the outer peripheral portion of the workpiece.

In one embodiment of the present invention, a method for grinding a workpiece involves grinding the outer periphery of a non-circular workpiece, followed by grinding the center of the workpiece. This makes it possible to easily reduce thickness variations in the workpiece after grinding, which are caused by variations in the length from the center to the outer periphery of the workpiece, without the need for complex control such as successively varying the rotation speed of the chuck table according to the contact area between the workpiece and the grinding wheel.

FIG. 2 is a partial cross-sectional side view showing the grinding device. FIG. 4 is a cross-sectional view showing a chuck table. 4 is a flowchart showing a method for grinding a workpiece. FIG. 4 is a perspective view showing the grinding device in a holding step. FIG. 5A is a perspective view showing the grinding device in the detection step, and FIG. 5B is a plan view showing the workpiece and the grinding wheel in the detection step. FIG. 6A is a perspective view showing the grinding device in the outer periphery grinding step, and FIG. 6B is a plan view showing the workpiece and the grinding wheel in the outer periphery grinding step. FIG. 7A is a perspective view showing the grinding device in the center grinding step, and FIG. 7B is a plan view showing the workpiece and the grinding wheel in the center grinding step. 13 is a plan view showing the workpiece and the grinding wheel in the outer periphery grinding step according to the modified example. FIG. FIG. 2 is a plan view showing a rectangular workpiece and a grinding wheel.

An embodiment according to one aspect of the present invention will be described below with reference to the attached drawings. First, an example of the configuration 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.

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. Inside the opening 4a, a chuck table (holding table) 6 is provided that holds the workpiece that is the object of grinding processing by the grinding device 2. The upper surface of the chuck table 6 forms a holding surface 6a that holds the workpiece.

Figure 2 is a cross-sectional view of the chuck table 6. The chuck table 6 has a cylindrical frame (main body) 8 made of metal such as SUS (stainless steel), glass, ceramics, resin, etc. 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 contains 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.

The upper surface 8a of the frame 8 and the suction surface 10a of the holding member 10 form the holding surface 6a of the chuck table 6. 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), etc.

The holding surface 6a of the chuck table 6 is formed in a cone shape with the apex at the center of the holding surface 6a, 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 roughly parallel to the horizontal plane (XY plane). The area of the workpiece held by the holding area 6b or its vicinity is ground by the grinding unit 44 described below.

For ease of explanation, the inclination of the holding surface 6a is exaggerated in FIG. 2, but the actual inclination of the holding surface 6a is small. For example, if the diameter of the holding surface 6a is approximately 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 approximately 20 μm or more and 40 μm or less.

A rotational drive source (not shown), such as a motor, is connected to the chuck table 6 to rotate the chuck table 6. The rotational drive source rotates the holding surface 6a of the chuck table 6 around a rotation axis 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.

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 a bearing (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 of the movable support members 18B, and does not show the other movable support member 18B.

The one fixed support member 18A and the 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 movable support members 18B are each fixed to the underside of the outer periphery of the table base 16.

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 the controller 62 (described below) to the movable support member 18B, the positions (height positions) of the upper ends of the two movable support members 18B in the Z-axis direction can each be changed. This adjusts the inclination of the chuck table 6 and the rotation axis 12.

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 movement 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 the end of the ball screw 22. 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 ball screw 22 is rotated by the pulse motor 24, the chuck table 6 moves along the X-axis direction.

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 surface side (front side) of the support structure 30. The moving mechanism 32 has a pair of guide rails 34 fixed to the surface side of the support structure 30. The pair of guide rails 34 are arranged along the Z-axis direction and are spaced apart from each other in the Y-axis direction.

A hollow cylindrical holding member 36 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 is screwed into the nut portion 38, which is disposed along the Z-axis direction between the pair of guide rails 34. A pulse motor 42 that rotates the ball screw 40 is connected to the 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.

The holding member 36 holds a grinding unit 44 that performs grinding on the workpiece. The grinding unit 44 has a cylindrical housing 46 housed in the holding member 36. The lower 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.

The housing 46 contains a cylindrical spindle 50 arranged along the Z-axis direction. The tip (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. In addition, a rotational 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.

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 the 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.

The grinding wheel 54 is made of a metal such as aluminum or stainless steel and has an annular wheel base 56 formed with 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. In addition, a plurality of grinding stones 58 are fixed to the lower surface of 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 grinding wheel 58 includes abrasive grains made of diamond, cBN (cubic boron nitride), etc., and a bonding material (bond material) such as a metal bond, a resin bond, or a vitrified bond that secures 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 as desired.

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 the wheel mount 52. In other words, the rotation axis 60 corresponds to the rotation axis of the spindle 50, the wheel mount 52, and the grinding wheel 54. When the grinding wheel 54 is rotated, each of the multiple grinding stones 58 revolves around the rotation axis 60 along a circular rotation trajectory (rotational orbit, rotational path) that is roughly parallel to the horizontal plane (XY plane).

A grinding fluid supply passage (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 passage 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 any debris (grinding debris) generated by the grinding process.

The grinding device 2 also 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 that control the operation of each component.

For example, the controller 62 is configured by a computer and includes a calculation unit that performs calculations necessary for the operation of the grinding device 2, and a storage unit that stores various information (data, programs, etc.) used in the operation of the grinding device 2. The calculation 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).

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

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 the object to be ground by the grinding device 2, is held by the chuck table 6.

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. Figure 4 illustrates a workpiece 11 with a square-shaped front surface 11a and back surface 11b.

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 specific substrate with a resin layer (molding resin). For example, the package substrate is formed into a rectangle with a side length of 50 mm to 550 mm.

By dividing the package substrate into individual pieces, a package device having multiple packaged device chips is manufactured. In addition, by grinding and thinning the resin layer with a grinding device 2 before dividing the package substrate, a thin package device can be manufactured.

However, as long as the shape of the workpiece 11 is non-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 three or five or more corners and sides, or an elliptical or oblong member.

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 into a disk shape. Specific examples of the material of the support member 21 are the same as those of the workpiece 11. The diameter of the support member 21 is set to be equal to or larger than the diameter of the suction surface 10a of the chuck table 6.

The support member 21 is fixed to the workpiece 11 via an adhesive or the like so as to cover the surface of the workpiece 11 opposite the surface to be ground by the grinding wheel 54 (the surface to be ground). For example, when the front 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 FIG. 4.

However, as long as the support member 21 can support the workpiece 11, there are no limitations on the material, structure, dimensions, etc. of the support member 21. For example, a circular sheet can be used as the support member 21. The sheet includes a film-like substrate and an adhesive layer (glue) provided on the substrate. The substrate is made of a resin such as polyolefin, polyvinyl chloride, or polyethylene terephthalate, and the adhesive layer is made of an epoxy-, acrylic-, or rubber-based adhesive. The adhesive layer may be an ultraviolet-curing resin that is cured by exposure to ultraviolet light.

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 21 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. 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 suction-held by the holding surface 6a of the chuck table 6 via the support member 21.

As mentioned above, the holding surface 6a of the chuck table 6 is formed in a cone shape (see FIG. 2). When the suction surface 10a sucks the support member 21, the workpiece 11 and the support member 21 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 nearby is positioned roughly parallel to the horizontal plane (XY plane).

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 modified as appropriate depending on 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 21 can be omitted and the workpiece 11 can be directly suction-held by the suction surface 10a.

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

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 of the workpiece 11 and the bottom surface of the grinding wheel 58 is positioned lower than the top surface of the workpiece 11.

Specifically, the chuck table 6 rotates, and the orientation (angle) of the workpiece 11 is adjusted so that one side of the workpiece 11 is aligned along 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 FIG. 1) so that the workpiece 11 does not overlap the grinding wheel 54 and is positioned in front of the grinding wheel 54 (lower left side in FIG. 5(A), left side in FIG. 5(B)).

The position of the grinding unit 44 in the Z-axis direction is adjusted by the movement mechanism 32 (see FIG. 1) so that the bottom surface of the grinding wheel 58 is positioned lower than the top surface (surface 11a, the surface to be ground) of the workpiece 11. The difference in height between the top surface of the workpiece 11 and the bottom surface of the grinding wheel 58 at this time corresponds to the target value for 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 below.

Next, with the workpiece 11 and grinding wheel 54 positioned as described above, the chuck table 6 and grinding wheel 54 are brought closer together, and the grinding wheel 58 is brought into contact with the side of the workpiece 11. Specifically, while rotating the grinding wheel 54 around the rotation axis 60, the chuck table 6 is moved along the X-axis direction by the movement mechanism 20 (see FIG. 1) to bring it closer to the grinding wheel 54. This brings the grinding wheel 58 into contact with the side of the workpiece 11.

The grinding device 2 then detects that the grinding wheel 58 has come into contact with the side of the workpiece 11. For example, the grinding device 2 includes a motor 64 and load measuring devices 66 and 68 that function as a detector (sensor) that detects that the grinding wheel 58 has come into contact with the side of the workpiece 11.

The motor 64 is a rotary drive source connected to the spindle 50. When a control signal is input from the controller 62 (see FIG. 1) to the motor 64, the motor 64 is driven to rotate the spindle 50, the wheel mount 52, and the grinding wheel 54 around the rotation axis 60. In addition, the current value of the motor 64 is input to the controller 62 and monitored by the controller 62.

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

When the grinding wheel 58 comes into contact with the side 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 of the workpiece 11 by comparing the current value of the motor 64 with a preset reference value (threshold value).

Furthermore, when the grinding wheel 58 comes into contact with the side of the workpiece 11, a load is applied to the chuck table 6 and 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 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 value).

However, there is no limit to the method of detecting contact between the workpiece 11 and the grinding wheel 58. For example, an optical sensor or the like may be used to detect that the grinding wheel 58 has come into contact with the side of the workpiece 11. Also, an operator may directly visually check the workpiece 11 and the grinding wheel 54 to confirm whether the grinding wheel 58 is in contact with the workpiece 11.

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 side of the workpiece 11 and the rotational trajectory of the grinding wheel 58 are in contact.

Next, the grinding stone 58 of the grinding wheel 54 is brought into contact with the workpiece 11 to grind the outer periphery of the workpiece 11 (outer periphery grinding step S3). FIG. 6(A) is a perspective view showing the grinding device 2 in the outer periphery grinding step S3, and FIG. 6(B) is a plan view showing the workpiece 11 and the grinding wheel 54 in the outer periphery grinding step S3.

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

Specifically, when the above-mentioned detection step S2 is completed, the grinding wheel 54 rotates and the grinding wheel 58 comes into contact with the side of the workpiece 11. At this time, the rotation path 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 FIG. 6B). Then, when the chuck table 6 is rotated while the grinding wheel 54 continues to rotate, the grinding wheel 58 comes into contact with the outer periphery 13B (near the four corners) of the workpiece 11 without coming into contact with the center 13A. As a result, only the outer periphery 13B of the workpiece 11 is ground and thinned, and a circular unground area whose thickness does not change before and after grinding remains in the center 13A of the workpiece 11. The radius of the unground area corresponds to the distance from the rotation axis 12 of the chuck table 6 to the rotation path of the grinding wheel 58.

In the outer peripheral grinding step S3, the rotational speed of the chuck table 6 is set to, for example, 10 rpm or more and 300 rpm or less. Also, the rotational speed of the grinding wheel 54 is set to, for example, 1000 rpm or more and 6000 rpm or less. However, it is preferable that the rotational speed _n1 of the chuck table 6 in the outer peripheral grinding step S3 is smaller than the rotational speed _n2 of the chuck table 6 in the center grinding step S4 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 peripheral portion 13B of the workpiece 11 to be ground uniformly by the grinding wheel 58, and makes it difficult for thickness variations to occur in the outer peripheral portion 13B of the workpiece 11.

Next, the center of the workpiece 11 is ground by bringing the grinding stone 58 of the grinding wheel 54 into contact with the workpiece 11 (center grinding step S4). FIG. 7(A) is a perspective view showing the grinding device 2 in center grinding step S4, and FIG. 7(B) is a plan view showing the workpiece 11 and the grinding wheel 54 in center grinding step S4.

In the center grinding step S4, the chuck table 6 and the grinding wheel 54 are rotated so that the rotational trajectory of the grinding wheel 58 overlaps with the rotation axis 12 of the holding surface 6a, and the grinding wheel 58 is brought into contact with the workpiece 11. This causes the center 13A of the workpiece 11 to be ground and removed.

Specifically, first, with the grinding unit 44 positioned 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 trajectory of the grinding wheel 58 overlaps with the rotation axis 12 of the chuck table 6 in the Z-axis direction (see FIG. 7(B)).

The diameter of the rotational path of the grinding wheel 58 is larger than the radius of the unground area of the workpiece 11. For example, the diameter of the rotational path of the grinding wheel 58 is set to be equal to or larger than the diameter of the unground area (length of one side of the workpiece 11). Therefore, the multiple grinding wheels 58 are positioned so as to overlap with an arc-shaped area extending from the center of the unground area to the outer periphery (side surface).

Next, while rotating the chuck table 6 and the grinding wheel 54, the chuck table 6 and the grinding wheel 54 are moved relative to each other along a direction parallel to the rotation axis 60 (Z-axis direction). This causes the grinding wheel 58 to come into contact with the central portion 13A (unground area) of the workpiece 11, grinding and thinning the central portion 13A.

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.

Next, the grinding unit 44 is lowered along the Z-axis direction by the moving mechanism 32 (see FIG. 1). This causes the chuck table 6 and the grinding wheel 54 to move relatively along a direction parallel to the rotation axis 60 (Z-axis direction), bringing the center 13A of the workpiece 11 closer to the grinding wheel 58. 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.

When the grinding wheel 58 comes into contact with the central portion 13A of the workpiece 11, the grinding wheel 58 rotates to pass through the rotating shaft 12 while grinding the surface 11a side of the central portion 13A of the workpiece 11. This thins the unground area of the workpiece 11.

As described above, in the center grinding step S4, the disk-shaped unground area remaining in the center 13A of the workpiece 11 due to the implementation of the outer periphery grinding step S3 is ground. This allows the center 13A of the workpiece 11 to be ground and thinned in the same way as a disk-shaped workpiece (such as a silicon wafer).

Here, if the entire rectangular workpiece 11 is ground without performing the outer peripheral grinding step S3, the thickness of the workpiece 11 is likely to vary. Specifically, in the area of the workpiece 11 that overlaps with the diagonal of the surface 11a (diagonal area), the distance from the center of the workpiece 11 to the outer peripheral edge is longer than in other areas of the workpiece 11. When the diagonal area of the workpiece 11 is ground, the contact area between the workpiece 11 and the grinding wheel 58 is larger than when other areas of the workpiece 11 are ground. This increases the load on the grinding wheel 58, and the grinding progresses more slowly in areas closer to the diagonal area 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.

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 disk-shaped unground area remaining in the center 13A of the workpiece 11 is ground in the center grinding step S4. In the outer periphery grinding step S3, since only the outer periphery 13B of the workpiece 11 is ground, the grinding area is small and thickness variation is unlikely to occur in the outer periphery 13B. Also, in the center grinding step S4, since the unground area with a constant length from the center to the outer periphery is ground, thickness variation is unlikely to occur in the center 13A either. As a result, the entire workpiece 11 is ground approximately uniformly.

When the central portion 13A is ground until the thickness of the central portion 13A and the thickness of the outer peripheral portion 13B become the same, the unground area is removed and the overall thickness of the workpiece 11 becomes uniform. After that, the grinding unit 44 rises and the grinding wheel 58 moves away from the workpiece 11, and grinding of the workpiece 11 by the grinding wheel 54 is stopped. This results in a thinned workpiece 11 with a uniform thickness.

However, after the unground area is removed and the thickness of the central portion 13A and the outer periphery 13B of the workpiece 11 is uniform, the entire workpiece 11 (central portion 13A and outer periphery 13B) may be ground by a predetermined amount with the grinding wheel 54 (full surface grinding step). Specifically, even after the unground area of the workpiece 11 is removed, the processing feed is continued while the chuck table 6 and grinding wheel 54 continue to rotate. Note that the rotation speed and processing feed rate of the chuck table 6 and grinding wheel 54 in the full surface grinding step can be set in the same way as in the central portion grinding step S4.

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 makes it possible to prevent random grinding marks from remaining on the surface 11a side of the workpiece 11.

The amount of workpiece 11 ground in the full surface grinding step is preferably set to a small value within a range in which the grinding marks formed on the outer periphery 13B of workpiece 11 in outer periphery grinding step S3 are removed. For example, the amount of workpiece 11 ground 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 caused by grinding the entire rectangular workpiece 11.

As described above, in the method for grinding a workpiece according to this embodiment, when grinding a non-circular workpiece 11, the outer peripheral portion 13B of the workpiece 11 is ground, and then the central portion 13A of the workpiece 11 is ground. This makes it possible to easily reduce the variation in thickness of the workpiece 11 after grinding, which is caused by the variation in the length from the center to the outer peripheral edge of the workpiece 11, without performing complex control such as successively varying the rotation speed of the chuck table 6 according to the contact area between the workpiece 11 and the grinding wheel 58.

In the above embodiment, an example has been described in which the outer periphery 13B of the workpiece 11 is ground by rotating the chuck table 6 while the grinding stone 58 of the grinding wheel 54 is in contact with the side of the workpiece 11 (detection step S2 and outer periphery grinding step S3). However, there is no limitation on the method for grinding the outer periphery of the workpiece 11.

Figure 8 is a plan view showing the workpiece 11 and grinding wheel 54 in the outer peripheral grinding step S3'. The outer peripheral grinding step S3' corresponds to a modified version of the outer peripheral grinding step S3 (see Figures 6(A) and 6(B)).

In the outer peripheral grinding step S3', first, the positional relationship between the chuck table 6 and the grinding wheel 54 is adjusted in 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 spaced apart from the side of the workpiece 11. In other words, a gap of distance d is secured between the side of the workpiece 11 and the rotation path of the grinding wheel 58. In addition, the rotation path of the grinding wheel 58 is positioned so that it does not overlap with the rotation axis 12.

Then, while rotating the grinding wheel 54, the chuck table 6 is rotated. As a result, the outer periphery 13B (near the four corners) of the workpiece 11 is ground, while an unground area remains in the center 13A of the workpiece 11.

As described above, when the chuck table 6 is rotated with the grinding wheel 58 spaced away from the side of the workpiece 11, the area of the outer periphery 13B ground by the grinding wheel 58 is reduced, further reducing the thickness variation in the outer periphery 13B. As shown in FIG. 8, the unground area remaining in the center 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 periphery is small. Therefore, even if the unground area of the workpiece 11 is ground and removed in the subsequent center grinding step S4, the thickness variation in the center 13A of the workpiece 11 is kept small.

In the above embodiment, the method of grinding the outer periphery 13B of the workpiece 11 by colliding the grinding wheel 58 with the side of the workpiece 11 has been described (see Figures 6(A), 6(B), and 8). However, there is no limitation 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.

Specifically, first, as in the central grinding step S4, the chuck table 6 holding the workpiece 11 is positioned below the grinding wheel 54 (see Figs. 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 the central portion 13A of the workpiece 11 in the Z-axis direction, but overlaps the outer peripheral portion 13B in the Z-axis direction.

Next, while rotating the chuck table 6 and the grinding wheel 54, the grinding unit 44 is lowered along the Z-axis direction, bringing the rotating grinding wheel 58 into contact with the surface 11a of the workpiece 11. This allows the outer periphery 13B of the workpiece 11 to be ground and thinned while leaving an unground area in the center 13A of the workpiece 11.

In the above embodiment, an example of grinding a square workpiece 11 with four sides of approximately the same length has been described. However, the grinding method of the workpiece according to the present invention can also be used to grind workpieces of other shapes.

Figure 9 is a plan view showing a rectangular workpiece 15 and a grinding wheel 54. The workpiece 15 is a rectangular workpiece including a pair of long sides and a pair of short sides. When grinding the workpiece 15, in the outer periphery grinding step S3, the chuck table 6 is rotated with the grinding wheel 58 in contact with the side surface corresponding to the long side of the workpiece 15. This allows the outer periphery 17B (near the four corners) of the workpiece 15 to be ground and thinned while leaving a circular unground area in the center 17A of the workpiece 15.

In addition, the structures, methods, etc. relating to the above embodiments can be modified as appropriate without departing from the scope of the purpose of the present invention.

11 Workpiece 11a Surface (first surface)
11b Back side (second surface)
13A: central portion; 13B: outer periphery (corner portion)
15 Workpiece 17A Central portion 17B Outer periphery 21 Support member 2 Grinding device 4 Base 4a Opening 6 Chuck table (holding table)
6a Holding surface 6b Holding area 8 Frame (main body)
8a Upper surface 8b Recess 8c Flow path 10 Holding member 10a Suction surface 12 Rotation shaft 14 Tilt adjustment mechanism 16 Table base 18A Fixed support member 18B Movable support member 20 Moving mechanism (moving unit)
22 ball screw 24 pulse motor 26 support base 28 nut portion 30 support structure (column)
32 Moving mechanism (moving unit)
34 Guide rail 36 Holding member 38 Nut portion 40 Ball screw 42 Pulse motor 44 Grinding unit 46 Housing 48 Cushioning member 50 Spindle 52 Wheel mount 54 Grinding wheel 56 Wheel base 58 Grinding stone 60 Rotating shaft 62 Controller (control unit, control section, control device)
64 Motor 66, 68 Load measuring device

Claims (4)

A method for grinding a non-circular workpiece with a grinding wheel having a grinding stone, comprising:
a holding step of holding the workpiece on a holding surface of a chuck table;
an outer periphery grinding step in which, after the holding step, the chuck table and the grinding wheel are rotated so that the rotational path 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, thereby grinding the outer periphery of the workpiece;
and a center grinding step of grinding the center of the workpiece by rotating the chuck table and the grinding wheel, which are positioned so that the rotational trajectory of the grinding wheel overlaps with the rotational axis of the holding surface, to bring the grinding wheel into contact with the workpiece. The method for grinding a workpiece according to claim 1, characterized in that in the outer peripheral grinding step, the grinding wheel is brought into contact with the side surface of the workpiece and the chuck table is rotated to grind the outer peripheral portion of the workpiece. The method for grinding a workpiece according to claim 2, further comprising a detection step of bringing the chuck table and the grinding wheel 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 lower than the upper surface of the workpiece after the holding step and before the outer peripheral grinding step, and detecting that the grinding wheel has come into contact with the side surface of the workpiece. 2. The method for grinding a workpiece according to claim 1, wherein in the outer peripheral grinding step, the outer peripheral portion of the workpiece is ground by rotating the chuck table while the grinding wheel is spaced from the side of the workpiece.

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