Grinding Wheel

Abstract

To provide a grinding wheel capable of improving efficiency and quality of grinding.SOLUTION: A grinding wheel 34 for grinding a workpiece by creep feed grinding, is equipped with a disc-shaped wheel base 40, a plurality of first grinding wheels 42A including first abrasive grains and provided on one end surface side of the wheel base, and a plurality of second grinding wheels 42B including second abrasive grains and provided on the one end surface side of the wheel base. The wheel base is divided into a first region 50A and a second region 50B by a straight line 48 dividing the one end surface of the wheel base into two. The first grinding wheels are aligned in an arc-shape in the first region, and the second grinding wheels are aligned in an arc-shape in the second region. Distances from a center of the wheel base to the second grinding wheels are shorter than distances of the center of the wheel to the first grinding wheels. Hardness of the first grinding wheels is lower than the hardness of the second grinding wheels. An average grain size of the first abrasive grains is less than three times an average grain size of the second abrasive grains.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a grinding wheel for creep feed grinding of a workpiece. [Background technology]

[0002] In the device chip manufacturing process, a wafer is used in which devices are formed in multiple areas defined by multiple intersecting streets (planned division lines). This wafer is divided along the streets to obtain multiple device chips, each equipped with a device. The device chips are incorporated into various electronic devices such as mobile phones and personal computers.

[0003] In recent years, with the miniaturization of electronic devices, device chips are required to be made thinner. Therefore, a process of grinding the wafer before division using a grinding device to make it thinner is sometimes performed. The grinding device includes a chuck table having a holding surface for holding the workpiece, and a grinding unit for grinding the workpiece, and a grinding wheel including a grinding stone is attached to the grinding unit. The grinding device rotates the grinding wheel to bring the grinding stone into contact with the workpiece, thereby grinding the workpiece.

[0004] When grinding a workpiece such as a wafer using a grinding device, the positional relationship between the chuck table and the grinding unit is adjusted so that the center of the workpiece held by the chuck table overlaps with the trajectory of the grinding wheel. Then, when the grinding wheel is lowered along the processing feed direction (vertical direction) perpendicular to the holding surface while rotating the chuck table and the grinding wheel, the lower surface of the grinding wheel comes into contact with the upper surface of the workpiece, and the workpiece is ground. This type of grinding method is called in-feed grinding.

[0005] On the other hand, a grinding method called creep feed grinding is sometimes used to grind the workpiece. In creep feed grinding, the positional relationship between the chuck table and the grinding unit is adjusted so that the grinding wheel is positioned outside the workpiece and the lower surface of the grinding wheel is positioned lower than the upper surface of the workpiece. Then, the chuck table is moved along the processing feed direction (horizontal direction) parallel to the holding surface while rotating the grinding wheel. As a result, the upper surface of the workpiece is ground by the grinding wheel, cutting off the side of the workpiece in an arc shape (see Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2017-56522 A [Patent Document 2] JP 2020-93318 A Summary of the Invention [Problem to be solved by the invention]

[0007] The grinding conditions when grinding a workpiece with a grinding device are selected so that the workpiece is efficiently ground by a grinding wheel with high grinding power and the surface of the ground workpiece (ground surface) has high flatness. For example, the grain size of the abrasive grains contained in the grinding wheel is determined according to the material of the workpiece.

[0008] Here, a grinding wheel containing abrasive grains with a large grain size has the advantage of having a high grinding ability and being able to grind the workpiece efficiently in a short time, but has the disadvantage of being prone to leaving roughness on the ground surface of the workpiece. On the other hand, a grinding wheel containing abrasive grains with a small grain size has the advantage of being able to reduce the surface roughness of the ground surface of the workpiece, but has the disadvantage that the chips (grinding chips) generated by grinding the workpiece tend to adhere to the grinding wheel, causing the abrasive grains to protrude insufficiently (clogging), and the grinding ability tends to decrease. Therefore, it is difficult to achieve both the efficiency of the grinding process and the quality of the workpiece after grinding.

[0009] The present invention has been made in consideration of such problems, and has an object to provide a grinding wheel that can improve the efficiency and quality of grinding processing. [Means for solving the problem]

[0010] According to one aspect of the present invention, a grinding wheel for grinding a workpiece by creep feed grinding is provided, the grinding wheel comprising a disk-shaped wheel base, a plurality of first grinding wheels containing first abrasive grains and provided on one end surface side of the wheel base, and a plurality of second grinding wheels containing second abrasive grains and provided on one end surface side of the wheel base, the wheel base being partitioned into a first region and a second region by a straight line that bisects one end surface of the wheel base, the first grinding wheels being arranged in an arc shape in the first region, and the second grinding wheels being arranged in an arc shape in the second region, the first grinding wheels and the second grinding wheels are arranged along a circumference of a circle whose center position is different from that of the wheel base; A grinding wheel is provided in which the distance from the center of the wheel base to the second grinding wheel is shorter than the distance from the center of the wheel base to the first grinding wheel, the hardness of the first grinding wheel is lower than the hardness of the second grinding wheel, and the average grain size of the first abrasive grains is less than three times the average grain size of the second abrasive grains.

[0011] Preferably, , applicable The flexural strength of the first grinding wheel is 30% to 60% of the flexural strength of the second grinding wheel. Preferably, the concentration of the first abrasive grains in the first grinding wheel is less than 60% of the concentration of the second abrasive grains in the second grinding wheel. Preferably, the number of the first grinding wheels is less than the number of the second grinding wheels. Preferably, the width of the first grinding wheel in the radial direction of the wheel base is smaller than the width of the second grinding wheel in the radial direction of the wheel base. Effect of the Invention

[0012] When using the grinding wheel according to one aspect of the present invention, the workpiece is ground efficiently by the first grinding wheel, and then the workpiece is ground flat by the second grinding wheel, thereby improving the efficiency and quality of grinding the workpiece. [Brief description of the drawings]

[0013] [Figure 1] FIG. [Diagram 2] FIG. 2A is a perspective view showing the chuck table and the grinding unit, and FIG. 2B is an enlarged cross-sectional view showing a part of the grinding wheel. [Diagram 3] FIG. [Figure 4] FIG. 4(A) is a side view showing the chuck table and the grinding unit in a preparation step, and FIG. 4(B) is a side view showing the chuck table and the grinding unit in a grinding step. [Diagram 5] Figure 5(A) is a cross-sectional view showing a workpiece in contact with a first grinding wheel, Figure 5(B) is a cross-sectional view showing a workpiece in contact with a second grinding wheel, and Figure 5(C) is a cross-sectional view showing a workpiece being ground by the second grinding wheel. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, an embodiment according to one aspect of the present invention will be described with reference to the accompanying drawings. First, a configuration example of a grinding device capable of grinding a workpiece using a grinding wheel according to this embodiment will be described. FIG. 1 is a perspective view showing a grinding device 2. In FIG. 1, the X-axis direction (processing feed direction, front-rear direction, first horizontal direction) and the Y-axis direction (left-right direction, second horizontal direction) are perpendicular to each other. Also, the Z-axis direction (vertical direction, up-down direction, height direction) is perpendicular to the X-axis direction and the Y-axis direction.

[0015] The grinding device 2 includes a base 4 that supports and houses each of the components that make up the grinding device 2. A rectangular opening 4a with its longitudinal direction aligned with the X-axis direction is formed on the upper surface side of the base 4. In addition, a rectangular parallelepiped support structure 6 that protrudes upward from the upper surface of the base 4 is provided on the rear end of the base 4 along the Z-axis direction.

[0016] A first moving mechanism (first moving unit) 8 is provided inside the opening 4a. For example, the first moving mechanism 8 is a ball screw type moving mechanism, and includes a pair of guide rails (not shown) arranged along the X-axis direction, and a flat moving table (not shown) slidably mounted on the pair of guide rails. A nut portion is provided on the back surface (lower surface) side of the moving table, and a ball screw (not shown) arranged between the pair of guide rails along the X-axis direction is screwed into this nut portion. In addition, a pulse motor (not shown) is connected to an end of the ball screw. When the ball screw is rotated by the pulse motor, the moving table moves in the X-axis direction along the pair of guide rails.

[0017] A chuck table (holding table) 10 that holds a workpiece 11 is provided on the front (upper) surface side of the moving table of the first moving mechanism 8. The first moving mechanism 8 also has a table cover 8a provided so as to surround the chuck table 10. Furthermore, a bellows-shaped dust-proof and drip-proof cover 12 that is expandable and contractible along the X-axis direction is provided in front and behind the table cover 8a. The table cover 8a and the dust-proof and drip-proof cover 12 cover the components of the first moving mechanism 8 (guide rail, moving table, ball screw, pulse motor, etc.) that are arranged inside the opening 4a.

[0018] The upper surface of the chuck table 10 is a flat surface roughly parallel to the horizontal plane (XY plane) and constitutes a holding surface 10a that holds the workpiece 11. The holding surface 10a is made of a porous material such as porous ceramics, and is connected to a suction source (not shown) such as an ejector via a flow path (not shown) and a valve (not shown) formed inside the chuck table 10. Note that, while FIG. 1 shows an example in which the holding surface 10a is formed in a circular shape assuming that the disc-shaped workpiece 11 is held, the shape of the holding surface 10a can be changed as appropriate according to the shape of the workpiece 11.

[0019] The chuck table 10 is moved along the X-axis direction together with the table cover 8a by the first moving mechanism 8. A rotation drive source (not shown) such as a motor is connected to the chuck table 10, and this rotation drive source rotates the chuck table 10 around a rotation axis that is roughly parallel to the Z-axis direction. In other words, the rotation axis of the chuck table 10 is set along a direction perpendicular to the holding surface 10a.

[0020] A second moving mechanism (second moving unit) 14 is provided on the front side of the support structure 6. The second moving mechanism 14 includes a pair of guide rails 16 arranged along the Z-axis direction. A flat moving table 18 is mounted on the pair of guide rails 16 so as to be slidable along the pair of guide rails 16.

[0021] A nut portion (not shown) is provided on the rear surface side (back surface side) of the moving table 18. A ball screw 20 disposed along the Z-axis direction between the pair of guide rails 16 is screwed into this nut portion. In addition, a pulse motor 22 is connected to an end of the ball screw 20. When the ball screw 20 is rotated by the pulse motor 22, the moving table 18 moves in the Z-axis direction along the pair of guide rails 16.

[0022] A support member 24 is fixed to the front side (surface side) of the moving table 18, protruding forward from the front surface of the moving table 18. The support member 24 supports a grinding unit 26 that grinds the workpiece 11. The second moving mechanism 14 controls the movement (lifting and lowering) of the grinding unit 26 in the Z-axis direction.

[0023] The grinding unit 26 includes a hollow cylindrical housing 28 supported by the support member 24. A cylindrical spindle 30 arranged along the Z-axis direction is accommodated in the housing 28. The tip end (lower end) of the spindle 30 protrudes downward from the lower surface of the housing 28. A rotation drive source (not shown), such as a motor, is connected to the base end (upper end) of the spindle.

[0024] A disk-shaped wheel mount 32 made of metal or the like is fixed to the tip of the spindle 30. A grinding wheel 34 for grinding the workpiece 11 is attached to the underside of the wheel mount 32. For example, the grinding wheel 34 is fixed to the wheel mount 32 by a fastener such as a bolt.

[0025] The grinding wheel 34 rotates around a rotation axis roughly parallel to the Z-axis direction by power transmitted from a rotation drive source via the spindle 30 and the wheel mount 32. That is, the rotation axis of the grinding wheel 34 is set along a direction perpendicular to the holding surface 10a of the chuck table 10. In addition, a grinding fluid supply passage (not shown), such as a nozzle, is provided inside or near the grinding unit 26 for supplying a liquid (grinding fluid), such as pure water, to the workpiece 11 held by the chuck table 10 and the grinding wheel 34.

[0026] A control unit (control unit, control device) 36 that controls the grinding device 2 is provided inside or outside the grinding device 2. The control unit 36 ​​is connected to each component of the grinding device 2 (the first moving mechanism 8, the chuck table 10, the second moving mechanism 14, the grinding unit 26, etc.), and generates a control signal for controlling the operation of each component.

[0027] For example, the control unit 36 ​​is configured by a computer and includes a calculation unit that performs calculations necessary for controlling the grinding device 2, and a storage unit that stores various information (data, programs, etc.) used for controlling 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).

[0028] The grinding device 2 grinds the workpiece 11. For example, the workpiece 11 is a disk-shaped wafer made of a semiconductor material such as silicon, and has a front surface 11a and a back surface 11b. The workpiece 11 is partitioned into a plurality of rectangular regions by a plurality of streets (planned division lines) arranged in a lattice shape so as to intersect with each other. In addition, devices (not shown) such as ICs (Integrated Circuits), LSIs (Large Scale Integrations), and LEDs (Light Emitting Diodes) are formed on the front surface 11a side of each of the plurality of regions partitioned by the streets.

[0029] A plurality of device chips each equipped with a device are manufactured by dividing the workpiece 11 along the streets by cutting, laser processing, etc. Furthermore, if the back surface 11b side of the workpiece 11 is ground using a grinding device 2 to thin the workpiece 11 before dividing the workpiece 11, a thinned device chip can be obtained.

[0030] There are no limitations on the material, shape, structure, size, etc. of the workpiece 11. For example, the workpiece 11 may be a substrate made of a semiconductor other than silicon (GaAs, InP, GaN, SiC, etc.), sapphire, glass, ceramics, resin, metal, etc. There are also no limitations on the type, number, shape, structure, size, arrangement, etc. of devices formed on the workpiece 11, and the workpiece 11 does not necessarily have to have any devices formed thereon.

[0031] 2(A) is a perspective view showing the chuck table 10 and the grinding unit 26. When the suction force (negative pressure) of a suction source is applied to the holding surface 10a with the workpiece 11 placed on the chuck table 10, the workpiece 11 is sucked and held by the chuck table 10. Note that a protective tape made of resin or the like for protecting the surface 11a side (device side) of the workpiece 11 may be attached to the surface 11a side of the workpiece 11. In this case, the workpiece 11 is held by the holding surface 10a of the chuck table 10 via the protective tape.

[0032] A grinding wheel 34 is attached to the grinding unit 26. The grinding wheel 34 includes a disk-shaped (annular) wheel base 40 made of metal or the like and formed to have approximately the same diameter as the wheel mount 32. The wheel base 40 includes a first surface (upper surface) 40a and a second surface (lower surface) 40b that are approximately parallel to each other, and an outer circumferential edge (side surface) 40c connected to the first surface 40a and the second surface 40b.

[0033] The grinding wheel 34 further includes a plurality of grinding wheels 42. The grinding wheels 42 are fixed to one end surface side (the second surface 40b side) of the wheel base 40 via an adhesive or the like. For example, the grinding wheels 42 are formed in a rectangular parallelepiped shape and arranged along the outer periphery of the wheel base 40.

[0034] 2(B) is an enlarged cross-sectional view showing a part of the grinding wheel 42. The grinding wheel 42 includes abrasive grains 44 and a binder (bond material) 46 that fixes the abrasive grains 44. Diamond, cBN (Cubic Boron Nitride), etc. are used as the abrasive grains 44. Furthermore, a metal bond, a resin bond, a vitrified bond, etc. are used as the binder 46.

[0035] 3 is a bottom view showing the grinding wheel 34. A circular opening 40d penetrating the wheel base 40 in the thickness direction is provided at the center of the wheel base 40. The center position of the opening 40d roughly coincides with the position of the center O of the wheel base 40. In other words, the wheel base 40 and the opening 40d are arranged concentrically.

[0036] Two types of grinding wheels 42 (first grinding wheel 42A and second grinding wheel 42B) are fixed to one end face side (second surface 40b side) of the wheel base 40. Specifically, the wheel base 40 is divided into a first region 50A and a second region 50B by a straight line 48 that bisects one end face (second surface 40b) of the wheel base 40. The first grinding wheels 42A are arranged in an arc shape in the first region 50A. The second grinding wheels 42B are arranged in an arc shape in the second region 50B.

[0037] 3 shows an example in which the first grinding wheel 42A and the second grinding wheel 42B are arranged along the circumference of a circle 52. The circle 52 is arranged so as to overlap with the wheel base 40, and the circumference of the circle 52 corresponds to an annular imaginary line set at a position overlapping with the wheel base 40.

[0038] The diameter of the circle 52 is smaller than the outer diameter of the wheel base 40 (the diameter of the outer peripheral edge 40c) and is larger than the inner diameter of the wheel base 40 (the diameter of the opening 40d). In addition, the position of the center O of the wheel base 40 and the position of the center O' of the circle 52 are different. In other words, the wheel base 40 and the circle 52 are arranged non-concentrically, and the circle 52 is eccentric with respect to the wheel base 40.

[0039] For example, the straight line 48 is set so as to pass through the center O' of the circle 52 and bisect the circle 52. In this case, the second surface 40b of the wheel base 40 is divided by the straight line 48 into a first region 50A and a second region 50B having different areas. Fig. 3 shows an example in which the area of ​​the first region 50A is smaller than the area of ​​the second region 50B.

[0040] The first grinding wheel 42A is arranged so as to overlap a portion of the circumference of the circle 52 that belongs to the first region 50A. The second grinding wheel 42B is arranged so as to overlap a portion of the circumference of the circle 52 that belongs to the second region 50B. For example, the first grinding wheel 42A and the second grinding wheel 42B are arranged so that their length directions (longitudinal directions) are along the circumference of the circle 52. As a result, the first grinding wheel 42A and the second grinding wheel 42B are arranged so that their distances from the center O of the wheel base 40 gradually change.

[0041] The first grinding wheel 42A is disposed so that the closer it is to the straight line 48, the closer it is to the center O of the wheel base 40. For example, the distance d from the end of the first grinding wheel 42A disposed at the farthest position from the straight line 48 (the end on the outer peripheral edge 40c side of the wheel base 40) to the center O of the wheel base 40 is A1is the distance d from the end of the first grinding wheel 42A (the end on the outer circumferential edge 40c side of the wheel base 40) located closest to the straight line 48 to the center O of the wheel base 40. A2 Longer than.

[0042] The second grinding wheel 42B is disposed so that the farther it is from the straight line 48, the closer it is to the center O of the wheel base 40. For example, the distance d from the end of the second grinding wheel 42B disposed closest to the straight line 48 (the end on the outer peripheral edge 40c side of the wheel base 40) to the center O of the wheel base 40 is B1 is the distance d from the end of the second grinding wheel 42B located at the farthest position from the straight line 48 (the end on the outer circumferential edge 40c side of the wheel base 40) to the center O of the wheel base 40. B2 Longer than.

[0043] The second grinding wheels 42B are provided closer to the center O of the wheel base 40 than all of the first grinding wheels 42A. That is, the distance from the center O of the wheel base 40 to the second grinding wheels 42B is shorter than the distance from the center O of the wheel base 40 to the first grinding wheels 42A. Therefore, the distance d A2 is the distance d B1 Longer than.

[0044] However, there is no limitation on the position where the straight line 48 is set. For example, the straight line 48 may be set so as to pass through the center O of the wheel base 40 and bisect the second surface 40b of the wheel base 40. In this case, the area of ​​the first region 50A and the area of ​​the second region 50B are equal to each other.

[0045] As long as the second grinding wheel 42B is disposed closer to the center O of the wheel base 40 than the first grinding wheel 42A, there is no limitation on the arrangement, dimensions (length, width, height), number, etc. of the first grinding wheel 42A and the second grinding wheel 42B. For example, the first grinding wheel 42A and the second grinding wheel 42B may be arranged along an elliptical arc. Alternatively, one of the first grinding wheel 42A and the second grinding wheel 42B may be arranged along a circular arc, and the other of the first grinding wheel 42A and the second grinding wheel 42B may be arranged along an elliptical arc. Furthermore, the dimensions and number of the first grinding wheel 42A may be the same as or different from the dimensions and number of the second grinding wheel 42B.

[0046] When the grinding wheel 34 is rotated, the first grinding wheel 42A and the second grinding wheel 42B each move along a circular movement path (rotation path) that is substantially parallel to a horizontal plane. At this time, the outer diameter of the path (movement path) of the first grinding wheel 42A becomes larger than the outer diameter of the path (movement path) of the second grinding wheel 42B.

[0047] Here, the hardness of the first grinding wheel 42A is lower than the hardness of the second grinding wheel 42B. That is, the second grinding wheel 42B is harder than the first grinding wheel 42A. Therefore, when the workpiece 11 is ground with the grinding wheel 34 (see FIG. 2(A)), the first grinding wheel 42A is more easily worn than the second grinding wheel 42B.

[0048] There is no limitation on the method for adjusting the hardness of the first grinding wheel 42A and the second grinding wheel 42B. For example, by using a binder 46 (see FIG. 2(B)) having a different material or density (porosity) between the first grinding wheel 42A and the second grinding wheel 42B, the magnitude relationship between the hardness of the first grinding wheel 42A and the hardness of the second grinding wheel 42B can be adjusted.

[0049] The size of the abrasive grains 44 (first abrasive grains) contained in the first grinding wheel 42A and the size of the abrasive grains 44 (second abrasive grains) contained in the second grinding wheel 42B are appropriately set according to the material of the workpiece 11. However, the first abrasive grains and the second abrasive grains are selected such that the average grain size of the first abrasive grains is less than three times the average grain size of the second abrasive grains.

[0050] The grinding wheel 34 is attached to the grinding unit 26 (see Figs. 1 and 2(A)), and the workpiece 11 is ground by the grinding wheel 34. In this embodiment, the workpiece 11 is thinned by performing creep feed grinding, in which the chuck table 10 and the grinding wheel 34 are moved relatively along a direction parallel to the holding surface 10a to process the workpiece 11. A specific example of a method for grinding the workpiece 11 using the grinding device 2 will be described below.

[0051] 2(A), the workpiece 11 is held by the chuck table 10 (holding step). For example, the workpiece 11 is placed on the chuck table 10 so that the front surface 11a faces the holding surface 10a and the back surface 11b is exposed upward. In this state, when the suction force (negative pressure) of the suction source is applied to the holding surface 10a, the workpiece 11 is sucked and held by the chuck table 10. As described above, a protective tape may be attached to the front surface 11a side of the workpiece 11.

[0052] Next, the positional relationship between the chuck table 10 and the grinding unit 26 is adjusted (preparatory step). Fig. 4(A) is a side view showing the chuck table 10 and the grinding unit 26 in the preparatory step. In the preparatory step, the positional relationship between the chuck table 10 and the grinding unit 26 is adjusted so that the workpiece 11 and the grinding wheel 42 are separated from each other in the processing feed direction (X-axis direction) parallel to the holding surface 10a, and the lower surface of the grinding wheel 42 is positioned a predetermined distance below the upper surface (rear surface 11b) of the workpiece 11.

[0053] Specifically, first, the position of the chuck table 10 in the X-axis direction is adjusted by the first moving mechanism 8 (see FIG. 1) so that the workpiece 11 is positioned in front of the grinding wheel 34 (left side of the paper in FIG. 4(A)) without overlapping with the grinding wheel 34. In addition, the position of the grinding unit 26 in the Z-axis direction is adjusted by the second moving mechanism 14 (see FIG. 1) so that the lower surface of the grinding wheel 42 is positioned lower than the upper surface of the workpiece 11. The difference ΔH in the height positions (positions in the Z-axis direction) between the upper surface of the workpiece 11 and the lower surface of the grinding wheel 42 at this time corresponds to a target value for the grinding amount of the workpiece 11 in a grinding step described later (the difference in thickness of the workpiece 11 before and after grinding).

[0054] Next, the chuck table 10 and the grinding unit 26 are moved relatively along the processing feed direction (X-axis direction) while rotating the grinding wheel 34, and the workpiece 11 is ground from one end side to the other end side by the grinding wheel 42 (grinding step). Fig. 4(B) is a side view showing the chuck table 10 and the grinding unit 26 in the grinding step.

[0055] In the grinding step, the workpiece 11 is ground by creep feed grinding. Specifically, first, the spindle 30 is rotated to rotate the grinding wheel 34 around a rotation axis that is approximately perpendicular to the holding surface 10a of the chuck table 10. The rotation speed of the grinding wheel 34 is set to, for example, 1000 rpm or more and 3000 rpm or less.

[0056] Then, while the grinding wheel 34 is rotating and the chuck table 10 is not rotating, the chuck table 10 is moved along the X-axis direction at a predetermined speed by the first moving mechanism 8 (see FIG. 1). As a result, the chuck table 10 and the grinding wheel 34 move relatively to each other along the processing feed direction at a predetermined processing feed speed and approach each other. The moving speed of the chuck table 10 (processing feed speed) is set to, for example, 1 mm / s or more and 20 mm / s or less.

[0057] When the chuck table 10 moves and one end of the workpiece 11 (the front end in the moving direction of the workpiece 11, the right end in FIG. 4(B)) reaches the track of the grinding wheel 42, the one end of the workpiece 11 is ground off by the grinding wheel 42. Then, the chuck table 10 moves along the X-axis direction until the other end of the workpiece 11 (the rear end in the moving direction of the workpiece 11, the left end in FIG. 4(B)) is positioned at a position overlapping with the track of the grinding wheel 42. As a result, the workpiece 11 is ground from one end to the other end by the grinding wheel 42, and the entire workpiece 11 is thinned.

[0058] When the workpiece 11 is ground with the grinding wheel 42, the binder 46 (see FIG. 2(B)) of the grinding wheel 42 gradually wears away, causing the exposed abrasive grains 44 (see FIG. 2(B)) to fall off and newly exposing the abrasive grains 44 embedded inside the binder 46 (self-sharpening edge). This prevents the deterioration of the sharpness of the grinding wheel 42 due to wear of the abrasive grains 44. Also, clogging of the grinding wheel 42 is prevented, and the abrasive grains 44 are maintained in a protruding state.

[0059] In addition, when the workpiece 11 is ground by the grinding wheel 42, a grinding fluid such as pure water is supplied to the workpiece 11 and the grinding wheel 42. This cools the workpiece 11 and the grinding wheel 42, and washes away debris (grinding debris) generated by the grinding process.

[0060] Next, details of grinding the workpiece 11 by the grinding wheel 34 in the grinding step will be described with reference to Fig. 5(A) to Fig. 5(C). Fig. 5(A) is a cross-sectional view showing the workpiece 11 contacting the first grinding wheel 42A. The difference in height between the lower surfaces of the first grinding wheel 42A and the second grinding wheel 42B and the lower surface (surface 11a) of the workpiece 11 corresponds to the finishing thickness T, which is the target value of the thickness of the workpiece 11 after grinding.

[0061] When the processing feed is started, first, one end of the workpiece 11 comes into contact with the rotating first grinding wheel 42A and is ground by the first grinding wheel 42A. Here, the first grinding wheel 42A has low hardness and is easily worn by contact with the workpiece 11. Therefore, the first grinding wheel 42A is likely to generate its own cutting edge while grinding the workpiece 11. As a result, the first grinding wheel 42A can grind the workpiece 11 while maintaining a high grinding ability, and the back surface 11b side of the workpiece 11 is reliably ground by the first grinding wheel 42A.

[0062] 3, the wheel base 40 has a plurality of first grinding wheels 42A arranged along the circumference of a circle 52 that is eccentric with respect to the wheel base 40. Therefore, as the processing feed progresses, the number of first grinding wheels 42A that come into contact with the workpiece 11 gradually increases.

[0063] Fig. 5(B) is a cross-sectional view showing the workpiece 11 in contact with the second grinding wheel 42B. Note that in Fig. 5(B), the wear of the first grinding wheel 42A is exaggerated.

[0064] During grinding of the workpiece 11 by the first grinding wheel 42A, the first grinding wheel 42A, which has a low hardness, wears and the height of the first grinding wheel 42A gradually decreases, causing the height position of the lower surface of the first grinding wheel 42A to fluctuate. As a result, the area of ​​the workpiece 11 ground by the first grinding wheel 42A becomes slightly thicker than the finishing thickness T. Then, the area that was not ground by the first grinding wheel 42A comes into contact with the second grinding wheel 42B rotating inside the first grinding wheel 42A.

[0065] 5(C) is a cross-sectional view showing the workpiece 11 being ground by the second grinding wheel 42B. After the workpiece 11 comes into contact with the second grinding wheel 42B, as the processing feed advances further, the area that was not ground by the first grinding wheel 42A is ground away by the second grinding wheel 42B.

[0066] 3, the wheel base 40 has a plurality of second grinding wheels 42B arranged along the circumference of a circle 52 that is eccentric with respect to the wheel base 40. Therefore, as the processing feed progresses, the number of second grinding wheels 42B that come into contact with the workpiece 11 gradually increases.

[0067] Here, the second grinding wheel 42B has high hardness and is not easily worn even when it comes into contact with the workpiece 11. Therefore, even when the workpiece 11 is ground with the second grinding wheel 42B, the height position of the lower surface of the second grinding wheel 42B is not easily changed. As a result, the thickness of the area of ​​the workpiece 11 ground by the second grinding wheel 42B becomes approximately equal to the finishing thickness T.

[0068] In addition, the hardness of the second grinding wheel 42B is higher than that of the first grinding wheel 42A, and the second grinding wheel 42B is less likely to develop self-sharpening edges than the first grinding wheel 42A. Therefore, the second grinding wheel 42B is less likely to have a state in which the abrasive grains 44 (see FIG. 2(B)) excessively protrude from the binder 46 (see FIG. 2(B)), and the surface roughness of the back surface 11b of the workpiece 11 after grinding is reduced.

[0069] The second grinding wheel 42B is less likely to develop self-sharpening than the first grinding wheel 42A, and is therefore more likely to become clogged. However, when the workpiece 11 reaches the second grinding wheel 42B, most of the area to be ground on the workpiece 11 has already been removed by the first grinding wheel 42A, and the amount of grinding allocated to the second grinding wheel 42B is small. Therefore, the amount of grinding waste generated when the workpiece 11 is ground by the second grinding wheel 42B is reduced, and in reality, the grinding ability of the second grinding wheel 42B is not significantly reduced due to clogging.

[0070] Here, if the average grain size of the abrasive grains 44 (first abrasive grains) contained in the first grinding wheel 42A is three times the average grain size of the abrasive grains 44 (second abrasive grains) contained in the second grinding wheel 42B, rough irregularities will be formed in the area of ​​the workpiece 11 ground by the first grinding wheel 42A, and the roughness will likely remain in the workpiece 11 even after subsequent grinding by the second grinding wheel 42B.

[0071] Furthermore, when the workpiece 11 is ground by the first grinding wheel 42A, the abrasive grains 44 that have fallen off from the first grinding wheel 42A may get in between the workpiece 11 and the second grinding wheel 42B when the workpiece 11 is ground by the second grinding wheel 42B. In this case, if the average grain size of the first abrasive grains is three times that of the second abrasive grains, the workpiece 11 may be scraped off by the large-sized first abrasive grains that have gotten in between the workpiece 11 and the second grinding wheel 42B, and unexpected roughness may remain on the workpiece 11 after grinding.

[0072] However, as described above, the average grain size of the first abrasive grains is set to be less than three times the average grain size of the second abrasive grains. Therefore, rough irregularities are unlikely to remain in the area of ​​the workpiece 11 ground by the first grinding wheel 42A. Even if the first abrasive grains get between the workpiece 11 and the second grinding wheel 42B, unexpected roughness is not left on the workpiece 11.

[0073] Grinding of the workpiece 11 by the grinding device 2 is realized by controlling the operation of each component of the grinding device 2 with the control unit 36 ​​(see FIG. 1). Specifically, a program describing a series of operations of each component of the grinding device 2 required to perform a holding step, a preparation step, and a grinding step in that order is stored in the memory of the control unit 36. Then, when grinding the workpiece 11, the control unit 36 ​​reads and executes the program, and sequentially outputs control signals to each component of the grinding device 2. This controls the operation of the grinding device 2, and the grinding method of the workpiece according to this embodiment is automatically performed.

[0074] In order to make the cutting ability of the first grinding wheel 42A higher than that of the second grinding wheel 42B, it is preferable that the size of the first abrasive grains contained in the first grinding wheel 42A is larger than the size of the second abrasive grains contained in the second grinding wheel 42B. Specifically, the average grain size of the first abrasive grains is larger than the average grain size of the second abrasive grains. Or, the grain size of the first abrasive grains is smaller than the grain size of the second abrasive grains. However, as described above, the average grain size of the first abrasive grains is suppressed to less than three times the average grain size of the second abrasive grains. For example, diamonds with a grain size of #3000 can be used as the first abrasive grains, and diamonds with a grain size of #5000 can be used as the second abrasive grains.

[0075] In addition, in order to promote the wear of the first grinding wheel 42A, the first grinding wheel 42A and the second grinding wheel 42B may be different in factors other than hardness. For example, the flexural strength (bending strength) of the first grinding wheel 42A may be lower than the flexural strength of the second grinding wheel 42B within a range in which the grinding of the workpiece 11 by the first grinding wheel 42A is not hindered. Specifically, the flexural strength of the first grinding wheel 42A is preferably 30% to 60% of the flexural strength of the second grinding wheel 42B. This makes the first grinding wheel 42A more susceptible to wear than the second grinding wheel 42B, and promotes the self-sharpening of the first grinding wheel 42A. The flexural strengths of the first grinding wheel 42A and the second grinding wheel 42B can be measured by a three-point bending test.

[0076] Also, the concentration of the first abrasive grains in the first grinding wheel 42A may be smaller than the concentration of the second abrasive grains in the second grinding wheel 42B. Specifically, the concentration of the first abrasive grains in the first grinding wheel 42A is preferably less than 60% of the concentration of the second abrasive grains in the second grinding wheel 42B. This makes the first grinding wheel 42A more susceptible to wear than the second grinding wheel 42B, promoting the self-sharpening of the first grinding wheel 42A.

[0077] The number of the first grinding wheels 42A may be less than the number of the second grinding wheels 42B. A (see FIG. 3) is the width W of the second grinding wheel 42B in the radial direction of the wheel base 40.B (See FIG. 3) This makes the first grinding wheel 42A more susceptible to wear than the second grinding wheel 42B, promoting self-sharpening of the first grinding wheel 42A.

[0078] As described above, when the grinding wheel 34 according to this embodiment is used, the workpiece 11 is ground efficiently by the first grinding wheel 42A, and then the workpiece 11 is ground flat by the second grinding wheel 42B. This improves the efficiency and quality of grinding the workpiece 11.

[0079] Furthermore, since the average particle size of the first abrasive grains contained in the first grinding wheel 42A is kept to less than three times the average particle size of the second abrasive grains contained in the second grinding wheel 42B, the first abrasive grains that fall off from the first grinding wheel 42A are less likely to adversely affect the grinding of the workpiece 11 by the second grinding wheel 42B, and deterioration in the quality of the workpiece 11 after grinding is prevented.

[0080] The number of times the creep feed grinding is performed (the number of times the preparation step and the grinding step are performed) can be set appropriately depending on the material of the workpiece 11, the amount of grinding, etc. In other words, the workpiece 11 may be thinned down to the finishing thickness by performing the preparation step and the grinding step two or more times.

[0081] In addition, the structures, methods, etc. according to the above-described embodiments can be modified as appropriate without departing from the scope of the object of the present invention. [Explanation of symbols]

[0082] 11 Workpiece 11a surface 11b Back side 2 Grinding equipment 4 Foundation 4a aperture 6 Support structure 8 First moving mechanism (first moving unit) 8a Table cover 10 Chuck table (holding table) 10a Holding surface 12 Dust-proof / water-proof cover 14 Second moving mechanism (second moving unit) 16 Guide rail 18 Mobile Table 20 Ball screw 22 Pulse motor 24 Support member 26 Grinding unit 28 Housing 30 Spindle 32 Wheel mount 34 Grinding Wheel 36 Control section (control unit, control device) 40 Wheel base 40a 1st side (top side) 40b 2nd side (bottom side) 40c Outer edge (side) 40d aperture 42 Grinding Wheel 42A No. 1 Grinding Wheel 42B No. 2 Grinding Wheel 44 Abrasive grain 46 Bonding material 48 straight line 50A 1st area 50B 2nd area 52 yen

Claims

1. 1. A grinding wheel for creep feed grinding of a workpiece, comprising: A disk-shaped wheel base, a plurality of first grinding wheels including first abrasive grains and provided on one end surface side of the wheel base; a plurality of second grinding wheels including second abrasive grains and provided on one end surface side of the wheel base; the wheel base is divided into a first region and a second region by a straight line that bisects one end surface of the wheel base, The first grinding wheels are arranged in an arc in the first region; The second grinding wheels are arranged in an arc in the second region; the first grinding wheels and the second grinding wheels are arranged along a circumference of a circle whose center position is different from the center position of the wheel base; a distance from the center of the wheel base to the second grinding wheel is shorter than a distance from the center of the wheel base to the first grinding wheel; The hardness of the first grinding wheel is lower than the hardness of the second grinding wheel; A grinding wheel, wherein the average grain size of the first abrasive grains is less than three times the average grain size of the second abrasive grains.

2. 2. The grinding wheel according to claim 1, wherein the flexural strength of the first grinding wheel is 30% to 60% of the flexural strength of the second grinding wheel.

3. 3. The grinding wheel of claim 1, wherein the concentration of the first abrasive grains in the first grinding wheel is less than 60% of the concentration of the second abrasive grains in the second grinding wheel.

4. 4. The grinding wheel of claim 1, wherein the number of the first grinding stones is less than the number of the second grinding stones.

5. 5. The grinding wheel according to claim 1, wherein the width of the first grinding wheel in the radial direction of the wheel base is smaller than the width of the second grinding wheel in the radial direction of the wheel base.

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