JP2023003965A - grinding wheel - Google Patents

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

The present invention relates to a grinding wheel for grinding a workpiece by creep feed grinding.

In the process of manufacturing device chips, a wafer is used in which devices are formed in a plurality of areas partitioned by a plurality of streets (division lines) that intersect with each other. A plurality of device chips each having a device is obtained by dividing the wafer along the streets. Device chips are incorporated into various electronic devices such as mobile phones and personal computers.

In recent years, along with the miniaturization of electronic devices, there is a demand for thinner device chips. Therefore, a process of thinning the wafer by grinding it with a grinding machine may be carried out before splitting. The grinding apparatus includes a chuck table having a holding surface that holds a workpiece, and a grinding unit that grinds the workpiece. A grinding wheel including a grinding wheel is attached to the grinding unit. A grinding device grinds a workpiece by rotating a grinding wheel and bringing a grinding wheel into contact with the workpiece.

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 the trajectory of the grinding wheel. be done. When the chuck table and the grinding wheel are rotated and the grinding wheel is lowered along the processing feed direction (vertical direction) perpendicular to the holding surface, the lower surface of the grinding wheel comes into contact with the upper surface of the workpiece. A workpiece is ground. Such a grinding method is called infeed grinding.

On the other hand, a grinding method called creep feed grinding is sometimes used for grinding 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 below the upper surface of the workpiece. be. Then, while rotating the grinding wheel, the chuck table is moved along the processing feed direction (horizontal direction) parallel to the holding surface. As a result, the upper surface side of the workpiece is scraped off from the side surface of the workpiece in an arc shape by the grinding wheel, and the workpiece is ground (see Patent Literatures 1 and 2).

JP 2017-56522 A Japanese Patent Application Laid-Open No. 2020-93318

Grinding conditions for grinding a workpiece with a grinding apparatus are such that the workpiece is efficiently ground by a grinding wheel with high grinding ability and the surface of the ground workpiece (surface to be ground) is flat. selected to be high. For example, the grain size of the abrasive grains contained in the grinding wheel is determined according to the material of the workpiece.

Here, a grinding wheel containing abrasive grains with a large grain size has the advantage that it has a high grinding ability and can efficiently grind a workpiece in a short time, but it leaves a roughness on the ground surface of the workpiece. It has the disadvantage of being easy. 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 surface to be ground of the workpiece. There is a drawback that a phenomenon (clogging) in which the abrasive grains stick to the grindstone and the protrusion of the abrasive grains becomes insufficient tends to occur, and the grinding performance tends to decrease. Therefore, it is difficult to achieve both the efficiency of grinding and the quality of the workpiece after grinding.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a grinding wheel capable of improving the efficiency and quality of grinding.

According to one aspect of the present invention, there is provided a grinding wheel for grinding a workpiece by creep feed grinding, comprising a disk-shaped wheel base and first abrasive grains, one end face side of the wheel base A plurality of first grinding wheels provided in 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 comprising the wheel A straight line that bisects one end face of the base is divided into a first region and a second region, the first grinding wheel is arranged in an arc in the first region, and the second grinding wheel is arranged in the second region. 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, and the hardness of the first grinding wheel is , the hardness of the second grinding wheel is less than the average grain size of the first abrasive grains is less than three times the average grain size of the second abrasive grains.

Preferably, the plurality of first grinding wheels and the plurality of second grinding wheels are arranged along the circumference of a circle whose center position is different from the center position of the wheel base. Moreover, preferably, the bending strength of the first grinding wheel is 30% or more and 60% or less of the bending strength of the second grinding wheel. Also preferably, the concentration of the first abrasive grains on the first grinding wheel is less than 60% of the concentration of the second abrasive grains on the second grinding wheel. Also preferably, the number of said first grinding wheels is less than the number of said second grinding wheels. Also 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.

When the grinding wheel according to the aspect of the present invention is used, the first grinding wheel efficiently grinds the workpiece, and then the second grinding wheel grinds the workpiece flat. This improves the efficiency and quality of grinding of the workpiece.

It is a perspective view which shows a grinding apparatus. FIG. 2(A) is a perspective view showing a chuck table and a grinding unit, and FIG. 2(B) is an enlarged cross-sectional view showing a part of a grinding wheel. FIG. 10 is a bottom view of the grinding wheel; FIG. 4A is a side view showing the chuck table and grinding unit in the preparation step, and FIG. 4B is a side view showing the chuck table and grinding unit in the grinding step. FIG. 5A is a cross-sectional view showing the workpiece in contact with the first grinding wheel, FIG. 5B is a cross-sectional view showing the workpiece in contact with the second grinding wheel, and FIG. ) is a cross-sectional view showing a workpiece to be ground by a second grinding wheel.

An embodiment according to one aspect of the present invention will be described below with reference to the accompanying drawings. First, a configuration example of a grinding apparatus capable of grinding a workpiece using the grinding wheel according to the present embodiment will be described. FIG. 1 is a perspective view showing a grinding device 2. FIG. 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, vertical direction, height direction) is a direction perpendicular to the X-axis direction and the Y-axis direction.

The grinding device 2 includes a base 4 that supports and accommodates each component constituting the grinding device 2 . A rectangular opening 4a whose longitudinal direction is along the X-axis direction is formed on the upper surface side of the base 4 . At the rear end of the base 4, a rectangular parallelepiped support structure 6 protruding upward from the upper surface of the base 4 is provided along the Z-axis direction.

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 plate-like member slidably attached to the pair of guide rails. and a moving table (not shown). A nut portion is provided on the rear (lower) side of the moving table, and a ball screw (not shown) arranged along the X-axis direction between a pair of guide rails is screwed into this nut portion. ing. 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.

A chuck table (holding table) 10 for holding a workpiece 11 is provided on the surface (upper surface) side of the moving table of the first moving mechanism 8 . The first moving mechanism 8 also includes a table cover 8a that surrounds the chuck table 10 . Furthermore, bellows-shaped dust and splash proof covers 12 that are extendable along the X-axis direction are provided in front and rear of the table cover 8a. The table cover 8a and the dust/splash proof cover 12 cover the constituent elements (guide rail, moving table, ball screw, pulse motor, etc.) of the first moving mechanism 8 arranged inside the opening 4a.

The upper surface of the chuck table 10 is a flat surface substantially parallel to the horizontal plane (XY plane), and constitutes a holding surface 10a for holding the workpiece 11 . The holding surface 10a is made of, for example, a porous material such as porous ceramics. (not shown). Note that FIG. 1 shows an example in which the holding surface 10a is formed in a circular shape assuming that a disk-shaped workpiece 11 is held, but the shape of the holding surface 10a can be appropriately changed according to the shape of the workpiece 11. can.

The chuck table 10 is moved along the X-axis direction by the first moving mechanism 8 together with the table cover 8a. 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 rotary shaft substantially parallel to the Z-axis direction. That is, the rotation axis of the chuck table 10 is set along the direction perpendicular to the holding surface 10a.

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 plate-like moving table 18 is attached to the pair of guide rails 16 so as to be slidable along the pair of guide rails 16 .

A nut portion (not shown) is provided on the rear surface side (rear surface side) of the moving table 18 . A ball screw 20 arranged along the Z-axis direction between the pair of guide rails 16 is screwed into the 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 along the pair of guide rails 16 in the Z-axis direction.

A support member 24 projecting forward from the front surface of the moving table 18 is fixed to the front side (surface side) 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 (up and down) of the grinding unit 26 in the Z-axis direction.

Grinding unit 26 comprises a hollow cylindrical housing 28 supported by support members 24 . The housing 28 accommodates a cylindrical spindle 30 arranged along the Z-axis direction. A tip (lower end) of the spindle 30 protrudes downward from the lower surface of the housing 28 . A rotational drive source (not shown) such as a motor is connected to the base end (upper end) of the spindle.

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 lower surface of the wheel mount 32 . For example, grinding wheel 34 is secured to wheel mount 32 by fasteners such as bolts.

Grinding wheel 34 rotates about a rotation axis generally parallel to the Z-axis direction by power transmitted from a rotational drive source via spindle 30 and wheel mount 32 . That is, the rotation axis of the grinding wheel 34 is set along the direction perpendicular to the holding surface 10 a of the chuck table 10 . Further, inside or near the grinding unit 26, a grinding liquid supply path ( (not shown) are provided.

A control section (control unit, control device) 36 for controlling the grinding device 2 is provided inside or outside the grinding device 2 . The control unit 36 is connected to each component (the first moving mechanism 8, the chuck table 10, the second moving mechanism 14, the grinding unit 26, etc.) of the grinding device 2, and controls the operation of each component. Generate control signals.

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. Prepare. The calculation unit includes a processor such as a CPU (Central Processing Unit). Further, the storage unit includes memories such as ROM (Read Only Memory) and RAM (Random Access Memory).

A workpiece 11 is ground by the grinding device 2 described above. 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 rear 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 so as to intersect each other. Devices (not shown) such as ICs (Integrated Circuits), LSIs (Large Scale Integrations), and LEDs (Light Emitting Diodes) are formed on the surface 11a side of a plurality of regions partitioned by the streets.

A plurality of device chips each having a device are manufactured by dividing the workpiece 11 along the streets by cutting, laser processing, or the like. If the back surface 11b side of the workpiece 11 is ground using the grinding device 2 before the workpiece 11 is divided to thin the workpiece 11, a thinned device chip can be obtained.

The material, shape, structure, size, etc. of the workpiece 11 are not limited. 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, or the like. Moreover, there are no restrictions on the type, quantity, shape, structure, size, arrangement, etc. of the devices formed on the workpiece 11, and devices may not be formed on the workpiece 11. FIG.

FIG. 2A is a perspective view showing the chuck table 10 and the grinding unit 26. FIG. When the workpiece 11 is placed on the chuck table 10 and the suction force (negative pressure) of the suction source is applied to the holding surface 10a, the workpiece 11 is held by the chuck table 10 by suction. A protective tape made of resin or the like and 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.

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 generally parallel to each other, and an outer peripheral edge (side surface) 40c connected to the first surface 40a and the second surface 40b.

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

FIG. 2B is an enlarged cross-sectional view showing a portion of the grinding wheel 42. FIG. The grinding wheel 42 includes abrasive grains 44 and a binding material (bonding material) 46 that fixes the abrasive grains 44 . Diamond, cBN (Cubic Boron Nitride), or the like is used as the abrasive grains 44 . As the binding material 46, a metal bond, a resin bond, a vitrified bond, or the like is used.

3 is a bottom view of the grinding wheel 34. FIG. 40 d of circular openings which penetrate the wheel base 40 in the thickness direction are provided in the center part of the wheel base 40 with which the grinding wheel 34 is provided. The center position of the opening 40 d substantially coincides with the position of the center O of the wheel base 40 . That is, the wheel base 40 and the opening 40d are arranged concentrically.

Two types of grinding wheels 42 (a first grinding wheel 42A and a second grinding wheel 42B) are fixed to one end surface 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 surface (second surface 40b) of the wheel base 40 . The first grinding wheels 42A are arranged in an arc shape in the first region 50A. Also, the second grinding wheels 42B are arranged in an arc shape in the second region 50B.

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

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 larger than the inner diameter of the wheel base 40 (the diameter of the opening 40d). Further, the position of the center O of the wheel base 40 and the position of the center O' of the circle 52 are different. That is, 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 .

Then, for example, a 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.

The first grinding wheel 42A is arranged so as to overlap a portion of the circumference of the circle 52 belonging to the first region 50A. Also, the second grinding wheel 42B is arranged so as to overlap a portion of the circumference of the circle 52 belonging to the second region 50B. For example, the first grinding wheel 42A and the second grinding wheel 42B are arranged along the circumference of the circle 52 in the length direction (longitudinal direction). As a result, the first grinding wheel 42A and the second grinding wheel 42B are arranged so that the distance from the center O of the wheel base 40 gradually changes.

The first grinding wheel 42A is arranged so that the closer it is to the straight line 48, the closer the distance from the center O of the wheel base 40 is. For example, the distance d _A1 from the end of the first grinding wheel 42A arranged farthest 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 a straight line It is longer than the distance _dA2 from the end of the first grinding wheel 42A arranged closest to 48 (the end on the side of the outer peripheral edge 40c of the wheel base 40) to the center O of the wheel base 40.

The second grinding wheel 42B is arranged so that the farther it is from the straight line 48, the closer the distance from the center O of the wheel base 40 is. For example, the distance d _B1 from the end of the second grinding wheel 42B arranged 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 the straight line It is longer than the distance d _B2 from the end of the second grinding wheel 42</b>B located farthest from 48 (the end on the outer peripheral edge 40 c side of the wheel base 40 ) to the center O of the wheel base 40 .

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. That is, the distance from the center O of the wheel base 40 to the second grinding wheel 42B is shorter than the distance from the center O of the wheel base 40 to the first grinding wheel 42A. Therefore, the distance d _A2 is longer than the distance d _B1 .

However, the setting position of the straight line 48 is not limited. For example, the straight line 48 may be set 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.

Also, as long as the second grinding wheel 42B is arranged closer to the center O of the wheel base 40 than the first grinding wheel 42A, the arrangement and dimensions (length, width, height), number, etc. For example, the first grinding wheel 42A and the second grinding wheel 42B may each be arranged along an elliptical arc. Alternatively, one of the first grinding wheel 42A and the second grinding wheel 42B may be arranged along an 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 wheels 42A may be the same as or different from the dimensions and number of the second grinding wheels 42B.

When the grinding wheel 34 is rotated, the first grinding wheel 42A and the second grinding wheel 42B each move along an annular movement path (rotational path) generally parallel to the horizontal plane. At this time, the outer diameter of the trajectory (moving path) of the first grinding wheel 42A becomes larger than the outer diameter of the trajectory (moving path) of the second grinding wheel 42B.

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 by the grinding wheel 34 (see FIG. 2A), the first grinding wheel 42A wears more easily than the second grinding wheel 42B.

The method of adjusting the hardness of the first grinding wheel 42A and the second grinding wheel 42B is not limited. For example, the first grinding wheel 42A and the second grinding wheel 42B are made of different materials and have different densities (porosity) in the bonding material 46 (see FIG. 2B). The magnitude relationship with the hardness of the grinding wheel 42B can be adjusted.

Also, 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 depend on the material of the workpiece 11, etc. is set as appropriate. 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.

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

First, as shown in FIG. 2A, the workpiece 11 is held by the chuck table 10 (holding step). For example, the workpiece 11 is arranged on the chuck table 10 so that the front surface 11a side faces the holding surface 10a and the back surface 11b side is exposed upward. When the suction force (negative pressure) of the suction source is applied to the holding surface 10a in this state, the workpiece 11 is held by the chuck table 10 by suction. In addition, as described above, a protective tape may be attached to the surface 11a side of the workpiece 11 .

Next, the positional relationship between the chuck table 10 and the grinding unit 26 is adjusted (preparation step). FIG. 4A is a side view showing the chuck table 10 and grinding unit 26 in the preparation step. In the preparation step, 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 aligned with the upper surface (rear surface 11b) of the workpiece 11. ), the positional relationship between the chuck table 10 and the grinding unit 26 is adjusted.

Specifically, first, the chuck table 10 is positioned in the X-axis direction so that the workpiece 11 is arranged in front of the grinding wheel 34 (on the left side of the drawing in FIG. 4A) without overlapping the grinding wheel 34 . is adjusted by the first moving mechanism 8 (see FIG. 1). Also, 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 below the upper surface of the workpiece 11 . The difference ΔH in the height position (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 is the amount of grinding of the workpiece 11 in the later-described grinding step (the workpiece before and after grinding). (difference in thickness of object 11).

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

In the grinding step, the workpiece 11 is ground by creep feed grinding. Specifically, first, by rotating the spindle 30 , the grinding wheel 34 is rotated around a rotation axis substantially perpendicular to the holding surface 10 a 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.

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

When the chuck table 10 moves and one end of the workpiece 11 (the front end in the movement direction of the workpiece 11, the right end of the paper surface in FIG. 4B) reaches the track of the grinding wheel 42, the one end of the workpiece 11 is scraped off by the grinding wheel 42 . Then, the chuck table 10 is placed at a position where the other end of the workpiece 11 (the rear end in the movement direction of the workpiece 11, the left edge of the paper surface in FIG. 4B) overlaps the trajectory of the grinding wheel 42. Move along the X-axis direction. 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.

When the workpiece 11 is ground by the grinding wheel 42, the bonding material 46 (see FIG. 2B) of the grinding wheel 42 is gradually worn away, and the exposed abrasive grains 44 (see FIG. 2B) As the abrasive particles 44 fall off, a phenomenon (self-sharpening) occurs in which the abrasive grains 44 embedded in the bonding material 46 are newly exposed. As a result, deterioration in sharpness of the grinding wheel 42 due to abrasion of the abrasive grains 44 is suppressed. In addition, clogging of the grinding wheel 42 is suppressed, and the protruding state of the abrasive grains 44 is maintained.

Also, when the workpiece 11 is ground by the grinding wheel 42 , a grinding liquid such as pure water is supplied to the workpiece 11 and the grinding wheel 42 . As a result, the workpiece 11 and the grinding wheel 42 are cooled, and scraps (grinding scraps) generated by the grinding process are washed away.

Next, the details of the grinding of the workpiece 11 by the grinding wheel 34 in the grinding step will be described with reference to FIGS. 5(A) to 5(C). FIG. 5A is a cross-sectional view showing the workpiece 11 in contact with the first grinding wheel 42A. The height difference 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 is the target value of the thickness of the workpiece 11 after grinding. It corresponds to a certain finished thickness T.

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 a low hardness and is easily worn by contact with the workpiece 11 . Therefore, during grinding of the workpiece 11, the first grinding wheel 42A tends to generate a self-sharpening. 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 scraped off by the first grinding wheel 42A.

As shown in FIG. 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. As shown in FIG. Therefore, the number of first grinding wheels 42A in contact with the workpiece 11 gradually increases as the processing feed progresses.

FIG. 5B is a cross-sectional view showing the workpiece 11 in contact with the second grinding wheel 42B. In addition, in FIG. 5B, the wear of the first grinding wheel 42A is exaggerated.

During the grinding of the workpiece 11 by the first grinding wheel 42A, the first grinding wheel 42A having a low hardness is worn, the height of the first grinding wheel 42A gradually decreases, and the height of the lower surface of the first grinding wheel 42A position changes. As a result, the area ground by the first grinding wheel 42A of the workpiece 11 becomes slightly thicker than the finished thickness T. Then, the area that has failed to be ground by the first grinding wheel 42A comes into contact with the second grinding wheel 42B that rotates inside the first grinding wheel 42A.

FIG. 5C is a cross-sectional view showing the workpiece 11 ground by the second grinding wheel 42B. After the workpiece 11 comes into contact with the second grinding wheel 42B, the second grinding wheel 42B scrapes off the area that has failed to be ground by the first grinding wheel 42A as the work progresses further.

As shown in FIG. 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. As shown in FIG. Therefore, the number of second grinding wheels 42B in contact with the workpiece 11 gradually increases as the processing feed progresses.

Here, the second grinding wheel 42B has a high hardness and is hardly worn even when it comes into contact with the workpiece 11 . Therefore, even if the workpiece 11 is ground by the second grinding wheel 42B, the height position of the lower surface of the second grinding wheel 42B is less likely to fluctuate. As a result, the thickness of the region of the workpiece 11 ground by the second grinding wheel 42B becomes substantially equal to the finished thickness T.

Further, the hardness of the second grinding wheel 42B is higher than the hardness of the first grinding wheel 42A, so that the second grinding wheel 42B is less prone to self-sharpening than the first grinding wheel 42A. Therefore, the second grinding wheel 42B is less likely to cause the abrasive grains 44 (see FIG. 2(B)) to protrude excessively from the bonding material 46 (see FIG. 2(B)). The surface roughness of 11b is reduced.

In addition, since the second grinding wheel 42B is less prone to self-sharpening than the first grinding wheel 42A, the second grinding wheel 42B is prone to clogging. However, when the workpiece 11 reaches the second grinding wheel 42B, most of the area to be ground of the workpiece 11 has already been removed by the first grinding wheel 42A and is assigned to the second grinding wheel 42B. The amount of grinding is small. Therefore, the amount of grinding waste generated when the workpiece 11 is ground by the second grinding wheel 42B is suppressed, and in reality, the grinding ability of the second grinding wheel 42B is not greatly reduced due to clogging.

Here, it is assumed that 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 unevenness is formed in the area of the workpiece 11 ground by the first grinding wheel 42A, and the roughness remains on the workpiece 11 even after the subsequent grinding by the second grinding wheel 42B. easier.

In addition, the abrasive grains 44 dropped from the first grinding wheel 42A when the workpiece 11 is ground by the first grinding wheel 42A are removed from the workpiece 11 and the second grinding wheel when the workpiece 11 is ground by the second grinding wheel 42B. 42B. At this time, when the average grain size of the first abrasive grains reaches three times the average grain size of the second abrasive grains, the large-sized first abrasive grains that have entered between the workpiece 11 and the second grinding wheel 42B The workpiece 11 may be scraped off by the abrasive grains, leaving unexpected roughness on the workpiece 11 after grinding.

However, as described above, the average grain size of the first abrasive grains is set to less than three times the average grain size of the second abrasive grains. Therefore, rough unevenness is less likely to remain in the area of the workpiece 11 that has been ground by the first grinding wheel 42A. Moreover, even if the first abrasive grains enter between the workpiece 11 and the second grinding wheel 42B, the workpiece 11 does not have unexpected roughness.

Grinding of the workpiece 11 by the grinding device 2 is realized by controlling the operation of each component of the grinding device 2 by the controller 36 (see FIG. 1). Specifically, the memory of the control unit 36 stores a program that describes a series of operations of each component of the grinding apparatus 2 required to sequentially perform the holding step, the preparation step, and the grinding step. When grinding the workpiece 11 , the control unit 36 reads out and executes the program, and sequentially outputs control signals to each component of the grinding device 2 . As a result, the operation of the grinding device 2 is controlled, and the method for grinding a workpiece according to this embodiment is automatically performed.

In order to make the cutting power of the first grinding wheel 42A higher than that of the second grinding wheel 42B, the size of the first abrasive grains contained in the first grinding wheel 42A is the same as the size of the first abrasive grains contained in the second grinding wheel 42B. It is preferably larger than the size of the abrasive grains. 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 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, a #3000 grain size diamond can be used as the first abrasive grains, and a #5000 grain size diamond can be used as the second abrasive grains.

Further, in order to accelerate the wear of the first grinding wheel 42A, the first grinding wheel 42A and the second grinding wheel 42B may differ in factors other than hardness. For example, the bending strength (bending strength) of the first grinding wheel 42A is lower than the bending strength of the second grinding wheel 42B within a range that does not hinder the grinding of the workpiece 11 by the first grinding wheel 42A. good too. Specifically, the bending strength of the first grinding wheel 42A is preferably 30% or more and 60% or less of the bending strength of the second grinding wheel 42B. As a result, the first grinding wheel 42A wears more easily than the second grinding wheel 42B, and the self-sharpening of the first grinding wheel 42A is promoted. The bending strength of the first grinding wheel 42A and the second grinding wheel 42B can be measured by a three-point bending test.

Also, the degree of concentration of the first abrasive grains on the first grinding wheel 42A may be smaller than the degree of concentration of the second abrasive grains on the second grinding wheel 42B. Specifically, the degree of concentration of the first abrasive grains on the first grinding wheel 42A is preferably less than 60% of the degree of concentration of the second abrasive grains on the second grinding wheel 42B. As a result, the first grinding wheel 42A wears more easily than the second grinding wheel 42B, and the self-sharpening of the first grinding wheel 42A is promoted.

Also, the number of first grinding wheels 42A may be less than the number of second grinding wheels 42B. Furthermore, the width W _A (see FIG. 3) of the first grinding wheel 42A in the radial direction of the wheel base 40 is smaller than the width W _B (see FIG. 3) of the second grinding wheel 42B in the radial direction of the wheel base 40. may As a result, the first grinding wheel 42A wears more easily than the second grinding wheel 42B, and the self-sharpening of the first grinding wheel 42A is promoted.

As described above, when the grinding wheel 34 according to the present embodiment is used, the workpiece 11 is efficiently ground 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 of the workpiece 11 .

In addition, since the average particle size of the first abrasive grains contained in the first grinding wheel 42A is suppressed to less than three times the average particle diameter of the second abrasive grains contained in the second grinding wheel 42B, the first grinding wheel The first abrasive grains falling off from 42A are less likely to adversely affect the grinding of the workpiece 11 by the second grinding wheel 42B, thus preventing deterioration in the quality of the workpiece 11 after grinding.

The number of creep-feed grinding operations (the number of preparatory steps and grinding steps) can be appropriately set according to the material of the workpiece 11, the amount of grinding, and the like. That is, the workpiece 11 may be thinned to the finished thickness by performing the preparation step and the grinding step two or more times.

In addition, the structures, methods, and the like according to the above-described embodiments can be modified as appropriate without departing from the scope of the present invention.

REFERENCE SIGNS LIST 11 workpiece 11a front surface 11b back surface 2 grinding device 4 base 4a opening 6 support structure 8 first moving mechanism (first moving unit)
8a table cover 10 chuck table (holding table)
10a holding surface 12 dust and splash proof cover 14 second moving mechanism (second moving unit)
16 guide rail 18 moving 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 first surface (upper surface)
40b Second surface (lower surface)
40c Outer edge (side surface)
40d opening 42 grinding wheel 42A first grinding wheel 42B second grinding wheel 44 abrasive grain 46 binding material (bond material)
48 straight line 50A first area 50B second area 52 circle

Claims (6)

A grinding wheel for grinding a workpiece by creep feed grinding,
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;
A plurality of second grinding wheels containing 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 wheel is arranged in an arc in the first region,
The second grinding wheel is arranged in an arc in the second region,
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,
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. The plurality of first grinding wheels and the plurality of second grinding wheels are arranged along the circumference of a circle whose center position is different from the center position of the wheel base. Grinding wheel as described. 3. The grinding wheel according to claim 1, wherein the bending strength of the first grinding wheel is 30% or more and 60% or less of the bending strength of the second grinding wheel. 4. The concentration of the first abrasive grains on the first grinding wheel is less than 60% of the concentration of the second abrasive grains on the second grinding wheel. A grinding wheel as described in . 5. A grinding wheel according to any preceding claim, wherein the number of first grinding wheels is less than the number of second grinding wheels. 6. 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. Grinding wheel as described.

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