Grinding wheels

Abstract

To provide a grinding wheel capable of improving efficiency and quality of grinding.SOLUTION: A grinding wheel for grinding a workpiece by creep feed grinding, is equipped with a disc-shaped wheel base, a plurality of first grinding wheels including first abrasive grains and annularly aligned on one end surface side of the wheel base, and a plurality of second grinding wheels including second abrasive grains and annularly aligned on the one end surface side of the wheel base. The second grinding wheel is provided on a center side of the wheel base than the first grinding wheel. Hardness of the first grinding wheels is lower than hardness of the second grinding wheels. An average grain size of the first abrasive grains is less than three times a 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] The device chip manufacturing process uses a wafer in which devices are formed in multiple areas defined by multiple intersecting streets (planned division lines). By dividing this wafer along the streets, multiple device chips, each equipped with a device, are obtained. The device chips are incorporated into various electronic devices, such as mobile phones and personal computers.

[0003] In recent years, the miniaturization of electronic devices has led to a demand for thinner device chips. To address this demand, a process of thinning wafers by grinding them using a grinding device is sometimes performed. The grinding device includes a chuck table with a holding surface for holding the workpiece and a grinding unit for grinding the workpiece. The grinding unit is equipped with a grinding wheel containing a grinding stone. The grinding device grinds the workpiece by rotating the grinding wheel and bringing the grinding stone into contact with the workpiece.

[0004] When using a grinding machine to grind a workpiece such as a wafer, the relative positions of the chuck table and grinding unit are adjusted so that the center of the workpiece held by the chuck table coincides with the trajectory of the grinding wheel. Then, while the chuck table and grinding wheel are both rotated, the grinding wheel is lowered in a processing feed direction (vertical direction) perpendicular to the holding surface. The bottom surface of the grinding wheel comes into contact with the top surface of the workpiece, grinding it. This type of grinding method is called in-feed grinding.

[0005] Meanwhile, a grinding method called creep feed grinding is sometimes used to grind workpieces. In creep feed grinding, the grinding wheel is positioned outside the workpiece, and the relative positions of the chuck table and grinding unit are adjusted so that the bottom surface of the grinding wheel is positioned below the top surface of the workpiece. Then, while rotating the grinding wheel, the chuck table is moved along a processing feed direction (horizontal direction) parallel to the holding surface. As a result, the top surface of the workpiece is ground by the grinding wheel, cutting away an arc from the side surface of the workpiece (see Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2017-56522 [Patent Document 2] Japanese Patent Publication No. 2020-93318 Summary of the Invention [Problem to be solved by the invention]

[0007] When grinding a workpiece with a grinding device, the grinding conditions are selected so that the workpiece is ground efficiently with a grinding wheel having high grinding ability and the surface of the ground workpiece (ground surface) has high flatness. For example, the particle size of the abrasive grains contained in the grinding wheel is determined depending on the material of the workpiece, etc.

[0008] Grinding wheels containing large-grain abrasive grains have the advantage of high grinding power and the ability to efficiently grind workpieces in a short time, but the disadvantage of leaving roughness on the ground surface of the workpiece. On the other hand, grinding wheels containing small-grain abrasive grains have the advantage of reducing the surface roughness of the ground surface of the workpiece, but the disadvantage is that the debris (grinding debris) generated by grinding the workpiece tends to adhere to the grinding wheel, causing the abrasive grains to protrude insufficiently (clogging), which reduces the grinding power. Therefore, it is difficult to achieve both grinding efficiency and the quality of the workpiece after grinding.

[0009] The present invention has been made in view of the above 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 comprises a disk-shaped wheel base, a plurality of first grinding stones containing first abrasive grains and arranged in an annular pattern on one end surface side of the wheel base, and a plurality of second grinding stones containing second abrasive grains and arranged in an annular pattern on one end surface side of the wheel base, the second grinding stones being provided closer to the center of the wheel base than the first grinding stones, and the second grinding stones being arranged so as not to overlap with two adjacent first grinding stones in the radial direction of the wheel base, the hardness of the first grinding stones being lower than the hardness of the second grinding stones, and the average grain size of the first abrasive grains being less than three times the average grain size of the second abrasive grains. The flexural strength of the first grinding wheel is 30% to 60% of the flexural strength of the second grinding wheel. A grinding wheel is provided.

[0011] Preferably, , applicable 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 smaller 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. [Effects of the Invention]

[0012] When using a 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 explanation of the drawings]

[0013] [Figure 1] FIG. [Figure 2]FIG. 2(A) is a perspective view showing the chuck table and the grinding unit, and FIG. 2(B) is an enlarged cross-sectional view showing a part of the grinding wheel. [Figure 3] FIG. 2 is a bottom view showing the grinding wheel. [Figure 4] FIG. 4(A) is a side view showing the chuck table and the grinding unit in the preparation step, and FIG. 4(B) is a side view showing the chuck table and the grinding unit in the grinding step. [Figure 5] Figure 5(A) is a cross-sectional view showing a workpiece contacting a first grinding wheel, Figure 5(B) is a cross-sectional view showing a workpiece contacting 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 INVENTION

[0014] An embodiment according to one aspect of the present invention will be described below with reference to the accompanying drawings. First, an example of the configuration 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. Furthermore, 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 top surface of the base 4. A rectangular parallelepiped support structure 6 that protrudes upward from the top 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 that 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 rear surface (lower surface) 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. A pulse motor (not shown) is connected to the 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 that is provided to surround the chuck table 10. Furthermore, accordion-shaped dust-proof and drip-proof covers 12 that are extendable and contractible along the X-axis direction are provided in front and behind the table cover 8a. The table cover 8a and the dust-proof and drip-proof covers 12 cover the components of the first moving mechanism 8 (guide rails, 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), a valve (not shown), and the like 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 to hold a disk-shaped workpiece 11, the shape of the holding surface 10a can be changed as appropriate depending on 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 rotary drive source (not shown), such as a motor, is connected to the chuck table 10, and this rotary 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 movement mechanism (second movement unit) 14 is provided on the front side of the support structure 6. The second movement mechanism 14 includes a pair of guide rails 16 arranged along the Z-axis direction. A flat plate-shaped movement 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 side (back side) of the moving table 18. A ball screw 20, which is disposed along the Z-axis direction between a pair of guide rails 16, is threadedly engaged with this nut portion. A pulse motor 22 is connected to the 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. The housing 28 accommodates a cylindrical spindle 30 arranged along the Z-axis direction. The tip end (lower end) of the spindle 30 protrudes downward from the bottom 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 that is roughly parallel to the Z-axis direction by power transmitted from a rotation drive source via the spindle 30 and the wheel mount 32. In other words, 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 path (not shown), such as a nozzle, is provided inside or near the grinding unit 26 to supply 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 section (control unit, control device) 36 that controls the grinding device 2 is provided inside or outside the grinding device 2. The control section 36 is connected to each component of the grinding device 2 (first moving mechanism 8, chuck table 10, second moving mechanism 14, grinding unit 26, etc.), and generates control signals for controlling the operation of each component.

[0027] For example, the control unit 36 ​​is configured by a computer and includes an arithmetic 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 arithmetic 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 divided into a plurality of rectangular regions by a plurality of streets (planned division lines) arranged in a grid pattern so as to intersect with one another. Furthermore, devices (not shown), such as ICs (Integrated Circuits), LSIs (Large Scale Integration), and LEDs (Light Emitting Diodes), are formed on the front surface 11a side of each of the regions divided 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 the grinding device 2 to thin the workpiece 11 before dividing it, 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. Furthermore, there are 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 workpiece 11 is placed on the chuck table 10 and a suction force (negative pressure) from a suction source is applied to the holding surface 10a, the workpiece 11 is sucked and held by the chuck table 10. Note that a protective tape made of resin or the like may be attached to the front surface 11a of the workpiece 11 to protect the front surface 11a side (device side) of the workpiece 11. In this case, the workpiece 11 is held on 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 also includes a plurality of grinding stones 42. The grinding stones 42 are fixed to one end face side (the second surface 40b side) of the wheel base 40 via an adhesive or the like. For example, the grinding stones 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 portion of the grinding wheel 42. The grinding wheel 42 includes abrasive grains 44 and a binder (bond material) 46 that secures the abrasive grains 44. Diamond, cBN (Cubic Boron Nitride), or the like is used as the abrasive grains 44. Furthermore, a metal bond, a resin bond, a vitrified bond, or the like is used as the binder 46.

[0035] 3 is a bottom view showing the grinding wheel 34. A circular opening 40d is provided in the center of a wheel base 40 provided on the grinding wheel 34, penetrating the wheel base 40 in the thickness direction. 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 (a first grinding wheel 42A and a second grinding wheel 42B) are fixed to one end face side (the second surface 40b side) of the wheel base 40. The first grinding wheel 42A is arranged in an annular shape so as to overlap the circumference of a first circle 48A that is concentric with the wheel base 40. The second grinding wheel 42B is arranged in an annular shape so as to overlap the circumference of a second circle 48B that is concentric with the wheel base 40 and has a smaller diameter than the first circle 48A. For example, the first grinding wheel 42A is arranged so that its length direction (longitudinal direction) follows the circumference of the first circle 48A. Similarly, for example, the second grinding wheel 42B is arranged so that its length direction (longitudinal direction) follows the circumference of the second circle 48B.

[0037] Each of the second grinding wheels 42B is provided closer to the center O of the wheel base 40 than all of the first grinding wheels 42A. Specifically, the distance d from the center O of the wheel base 40 to the end of the first grinding wheel 42A located on the outer peripheral edge 40c side of the wheel base 40 is A is the distance d from the center O of the wheel base 40 to the end of the second grinding wheel 42B located on the outer peripheral edge 40c side of the wheel base 40. B 3, the second grinding wheels 42B are arranged so as not to overlap with the two adjacent first grinding wheels 42A in the radial direction of the wheel base 40.

[0038] There are no limitations on the dimensions (length, width, height), number, arrangement, etc. of the first grinding wheel 42A and the second grinding wheel 42B. 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.

[0039] 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 generally parallel to a horizontal plane. At this time, the outer diameter of the locus (movement path) of the first grinding wheel 42A becomes larger than the outer diameter of the locus (movement path) of the second grinding wheel 42B.

[0040] 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 likely to wear than the second grinding wheel 42B.

[0041] There are no limitations on the method for adjusting the hardness of the first grinding wheel 42A and the second grinding wheel 42B. For example, by using binders 46 (see FIG. 2(B)) that are made of different materials or have different densities (porosities) for 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.

[0042] 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 set appropriately depending on the material of the workpiece 11. However, the first abrasive grains and the second abrasive grains are selected so that the average grain size of the first abrasive grains is less than three times the average grain size of the second abrasive grains.

[0043] The grinding wheel 34 is mounted on the grinding unit 26 (see FIGS. 1 and 2A), 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 in 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.

[0044] First, as shown in Fig. 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 of the workpiece 11.

[0045] 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 spaced apart 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.

[0046] 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 (on the 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 height (position 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 the target value of the grinding amount of the workpiece 11 (the difference in thickness of the workpiece 11 before and after grinding) in the grinding step described below.

[0047] Next, the chuck table 10 and the grinding unit 26 are moved relatively in 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 stone 42 (grinding step). Fig. 4(B) is a side view showing the chuck table 10 and the grinding unit 26 in the grinding step.

[0048] 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.

[0049] Then, with the grinding wheel 34 rotating and the chuck table 10 not rotating, the chuck table 10 is moved at a predetermined speed along the X-axis direction by the first moving mechanism 8 (see FIG. 1). As a result, the chuck table 10 and the grinding wheel 34 move relatively toward each other along the processing feed direction at a predetermined processing feed speed. The movement speed of the chuck table 10 (processing feed speed) is set, for example, to 1 mm / s or more and 20 mm / s or less.

[0050] As the chuck table 10 moves, one end of the workpiece 11 (the front end in the direction of movement of the workpiece 11, the right end on the paper in FIG. 4(B)) reaches the trajectory of the grinding wheel 42, and the one end of the workpiece 11 is ground away by the grinding wheel 42. The chuck table 10 then moves along the X-axis direction until the other end of the workpiece 11 (the rear end in the direction of movement of the workpiece 11, the left end on the paper in FIG. 4(B)) is positioned so as to overlap with the trajectory 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.

[0051] 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 (a phenomenon known as self-sharpening). This prevents the grinding wheel 42 from losing its sharpness due to wear of the abrasive grains 44. It also prevents the grinding wheel 42 from clogging, maintaining the abrasive grains 44 in a protruding state.

[0052] Furthermore, 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 also washes away chips (grinding chips) generated by the grinding process.

[0053] Next, details of grinding the workpiece 11 by the grinding wheel 34 in the grinding step will be described with reference to Figures 5(A) to 5(C). Figure 5(A) is a cross-sectional view showing the workpiece 11 in contact with 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 finished thickness T, which is the target value for the thickness of the workpiece 11 after grinding.

[0054] When processing feed begins, 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 down by contact with the workpiece 11. Therefore, the first grinding wheel 42A is likely to self-sharpen while grinding the workpiece 11. As a result, the first grinding wheel 42A can grind the workpiece 11 while maintaining high grinding ability, and the back surface 11b side of the workpiece 11 is reliably ground away by the first grinding wheel 42A.

[0055] Fig. 5(B) is a cross-sectional view showing the workpiece 11 in contact with the second grinding wheel 42B. Note that Fig. 5(B) shows an exaggerated view of the wear of the first grinding wheel 42A.

[0056] During grinding of the workpiece 11 by the first grinding wheel 42A, the first grinding wheel 42A, which has a low hardness, wears down, gradually reducing the height of the first grinding wheel 42A and 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 finish thickness T. Then, the area that was not ground by the first grinding wheel 42A comes into contact with the second grinding wheel 42B, which rotates inside the first grinding wheel 42A.

[0057] 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 progresses further, the area that was not ground by the first grinding wheel 42A is ground away by the second grinding wheel 42B.

[0058] 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.

[0059] Furthermore, 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 abrasive grains 44 (see FIG. 2(B)) excessively protruding 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.

[0060] The second grinding wheel 42B is less likely to self-sharpen than the first grinding wheel 42A, and is therefore more susceptible to clogging. However, by the time 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 that can be allocated to the second grinding wheel 42B is small. This reduces the amount of grinding waste generated when the workpiece 11 is ground by the second grinding wheel 42B, and in reality, the grinding ability of the second grinding wheel 42B does not decrease significantly due to clogging.

[0061] Here, if the average particle size of the abrasive grains 44 (first abrasive grains) contained in the first grinding wheel 42A is three times the average particle 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.

[0062] Furthermore, when the workpiece 11 is ground by the first grinding wheel 42A, abrasive grains 44 that have fallen off from the first grinding wheel 42A may get caught 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 the average grain size of the second abrasive grains, the large-sized first abrasive grains that have gotten between the workpiece 11 and the second grinding wheel 42B may scrape off the workpiece 11, and unexpected roughness may remain on the workpiece 11 after grinding.

[0063] However, as described above, the average particle size of the first abrasive grains is set to be less than three times the average particle 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. Furthermore, even if the first abrasive grains get between the workpiece 11 and the second grinding wheel 42B, unexpected roughness will not remain in the workpiece 11.

[0064] Grinding of the workpiece 11 by the grinding apparatus 2 is achieved by the control unit 36 ​​(see FIG. 1) controlling the operation of each component of the grinding apparatus 2. Specifically, a program describing the series of operations of each component of the grinding apparatus 2 required to sequentially perform a holding step, a preparation step, and a grinding step is stored in the memory of the control unit 36. 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 apparatus 2. This controls the operation of the grinding apparatus 2, and the workpiece grinding method according to this embodiment is automatically performed.

[0065] In order to increase the cutting ability of the first grinding wheel 42A compared to the second grinding wheel 42B, it is preferable that the size of the first abrasive grains contained in the first grinding wheel 42A be 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. Alternatively, the grain size of the first abrasive grains is smaller than the grain size of the second abrasive grains. However, as mentioned above, the average grain size of the first abrasive grains is limited 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.

[0066] Furthermore, to promote 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 that of the second grinding wheel 42B, as long as 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, promoting 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 using a three-point bending test.

[0067] Furthermore, 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 self-sharpening of the first grinding wheel 42A.

[0068] 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, and promotes self-sharpening of the first grinding wheel 42A.

[0069] 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.

[0070] Furthermore, because 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, rough irregularities are unlikely to remain in the area of ​​the workpiece 11 ground by the first grinding wheel 42A, and the first abrasive grains that fall off the first grinding wheel 42A are unlikely to adversely affect the grinding of the workpiece 11 by the second grinding wheel 42B. As a result, deterioration in the quality of the workpiece 11 after grinding is prevented.

[0071] The number of times creep feed grinding is performed (the number of times the preparation step and 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 preparation step and grinding step may be performed two or more times to thin the workpiece 11 to the finishing thickness.

[0072] 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]

[0073] 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 Dustproof / waterproof 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 spindles 32 Wheel mount 34 Grinding Wheel 36 Control unit (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 grains 46 Bonding material 48A 1st Circle 48B 2nd Yen

Claims

1. A grinding wheel for grinding a workpiece by creep feed grinding, comprising: A disc-shaped wheel base, a plurality of first grinding wheels including first abrasive grains and arranged in an annular shape on one end surface side of the wheel base; a plurality of second grinding wheels including second abrasive grains and arranged in an annular shape on one end surface side of the wheel base; the second grinding wheel is provided closer to the center of the wheel base than the first grinding wheel, the second grinding wheels are arranged so as not to overlap with two adjacent first grinding wheels in the radial direction of the wheel base; The hardness of the first grinding wheel is lower than the hardness of the second grinding wheel; the average particle size of the first abrasive grains is less than three times the average particle size of the second abrasive grains; A grinding wheel characterized in that the flexural strength of the first grinding wheel is 30% or more and 60% or less of the flexural strength of the second grinding wheel.

2. 2. 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.

3. 3. The grinding wheel according to claim 1, wherein the number of the first grinding wheels is less than the number of the second grinding wheels.

4. 4. 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.

Images