GRINDSTONE

Abstract

A grindstone includes abrasive grains and a binder for fixing the abrasive grains, and the binder contains a spherical filler for reinforcing the bonding material.

Description

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a grindstone used for processing a workpiece.

Description of the Related Art

Device chips including devices are manufactured by dividing and individualizing a wafer formed with a plurality of devices. In addition, a package substrate is formed by mounting a plurality of device chips on a predetermined substrate and covering the device chips with a resin layer (molding resin) to seal the device chips. By dividing and individualizing the package substrate, package devices including a plurality of packaged device chips are manufactured. The device chips and the package devices are incorporated into various electronic apparatuses such as mobile phones and personal computers.

In recent years, in association with miniaturization of the electronic apparatuses, thinning of the device chips and the package devices has been demanded. In view of this, a process of grinding the wafer or the package substrate prior to division by a grinding apparatus may be conducted. The grinding apparatus includes a chuck table for holding a workpiece and a grinding unit for grinding the workpiece. The grinding unit includes a spindle, and an annular grinding wheel including a plurality of grindstones is mounted to a tip end part of the spindle. The workpiece is held by the chuck table, and, while the chuck table and the grinding wheel are rotated, grinding surfaces of the grindstones are brought into contact with the workpiece to grind the workpiece (see Japanese Patent Laid-open No. 2000-288881).

The grindstones used for grinding the workpiece are formed by fixing abrasive grains with a binder (bond material). For example, a mixture containing diamond abrasive grains and a vitrified bond material is kneaded and granulated, followed by compression molding and firing, whereby a vitrified bond grindstone is obtained (see Japanese Patent Laid-open No. 2006-1007).

SUMMARY OF THE INVENTION

The binder of the grindstone contains a filler (aggregate) for reinforcing the binder. As the filler, typically, ceramic particles having an angular random shape (angular shape) are used. Addition of the filler to the binder enhances mechanical strength of the binder and prolongs the useful life of the binder. As a result, the cost of the grindstone is lowered, and lowering in processing efficiency attendant on replacing work of the grindstone is restrained. In addition, it has been confirmed that use of a filler of a larger size further enhances the strength of the binder.

However, even when a filler of an angular shape is contained in the binder of the grindstone, there is a limit in enhancing the strength of the grindstone. In addition, if the size of the filler of the angular shape is enlarged for enhancing the strength of the grindstone, sharp angular parts of the filler would largely project from the binder, and would be liable to collide against the workpiece during processing. As a result, although the contact between the abrasive grains and the workpiece should dominantly contribute to processing of the workpiece in a normal situation, the projecting angular parts of the filler would interfere with the workpiece, and may cause defective processing.

The present invention has been made in consideration of such a problem, and it is an object of the invention to provide a grindstone which is high in strength and is capable of restraining occurrence of defective processing.

In accordance with an aspect of the present invention, there is provided a grindstone including abrasive grains and a binder for fixing the abrasive grains, in which the binder contains a spherical filler for reinforcing the binder.

Note that, preferably, the average particle diameter of the filler is greater than the average particle diameter of the abrasive grains. In addition, preferably, the filler is ceramic particles, and the ratio of a short axis to a long axis of the ceramic particles is not less than 0.7. Besides, preferably, the content of the filler in the binder is 5 to 90 wt %. In addition, preferably, the binder is a vitrified bond or a resin bond.

In the grindstone according to one mode of the present invention, the binder for fixing the abrasive grains contains the spherical filler. As a result, it is possible to restrain occurrence of defective processing at the time of processing a workpiece by the grindstone, while enhancing the strength of the grindstone.

The above and other objects, features and advantages of the present invention and the manner of realizing them will become more apparent, and the invention itself will best be understood from a study of the following description and appended claims with reference to the attached drawings showing a preferred embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view depicting a grinding apparatus;

FIG. 2 is a perspective view depicting a grinding wheel;

FIG. 3 is a sectional view depicting a part of a grindstone; and

FIG. 4 is a graph depicting the results of measurement of strengths of grindstones.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

An embodiment according to one mode of the present invention will be described with reference to the attached drawings. First, a configuration example of a grinding apparatus that can grind a workpiece by use of a grinding wheel according to the present embodiment will be described. FIG. 1 is a perspective view depicting a grinding apparatus 2 for grinding a workpiece 11. Note that, in FIG. 1, an X-axis direction (a first horizontal direction, a front-rear direction) and a Y-axis direction (a second horizontal direction, a left-right direction) are mutually perpendicular directions. In addition, a Z-axis direction (a height direction, a vertical direction, an up-down direction) is a direction perpendicular to both the X-axis direction and the Y-axis direction.

For example, the workpiece 11 is a disk-shaped wafer formed of a semiconductor material such as single crystal silicon, and has a front surface (a first surface) 11a and a back surface (a second surface) 11b which are substantially parallel to each other. The workpiece 11 is partitioned into a plurality of rectangular regions by a plurality of streets (scheduled division lines) arranged in a grid pattern in such a manner as to mutually intersect. In addition, such devices (not illustrated) as integrated circuits (ICs), large scale integration (LSI) circuits, light emitting diodes (LEDs), and micro electro mechanical systems (MEMS) devices are formed respectively on the front surface 11a side of the plurality of regions partitioned by the streets. As a result of dividing the workpiece 11 along the streets, a plurality of device chips respectively provided with the devices are manufactured. For division of the workpiece 11, there can be used various processing apparatuses such as a cutting apparatus for cutting the workpiece 11 by an annular cutting blade and a laser processing apparatus for processing the workpiece 11 by applying a laser beam. In addition, when the back surface 11b side of the workpiece 11 is preliminarily ground by the grinding apparatus 2 to thin the workpiece 11 prior to the division of the workpiece 11, thinned device chips are obtained.

It is to be noted, however, that the kind, material, size, shape, structure, and the like of the workpiece 11 are not limited to any particular ones. For example, the workpiece 11 may be a wafer (substrate) formed of a semiconductor other than silicon (GaAs, InP, GaN, SiC, etc.), sapphire, glass, ceramic, resin, metal, or the like. In addition, the kinds, number, shapes, structures, sizes, layout, and the like of the devices are not limited to any particular ones, and the workpiece 11 may not be formed with the devices.

The grinding apparatus 2 includes a base 4 for supporting or accommodating each of constituent elements constituting the grinding apparatus 2. On the upper surface side of the base 4, a rectangular opening 4a is formed such that the longitudinal direction thereof extends along the X-axis direction. In addition, on the upper surface side of a rear end part of the base 4, a rectangular parallelepiped support structure 6 is provided along the Z-axis direction.

On the inside of the opening 4a, a chuck table (a holding table) 8 for holding the workpiece 11 is provided. An upper surface of the chuck table 8 is a flat surface substantially parallel to a horizontal plane (XY plane), and constitutes a holding surface 8a for holding the workpiece 11. The holding surface 8a is connected to a suction source (not illustrated) such as an ejector through a flow channel (not illustrated) formed inside the chuck table 8, a valve (not illustrated), and the like.

An X-axis moving unit 10 for moving the chuck table 8 along the X-axis direction is connected to the chuck table 8. The X-axis moving unit 10 is, for example, a ball screw type moving mechanism, and is provided inside the opening 4a. Specifically, the X-axis moving unit 10 includes an X-axis ball screw (not illustrated) disposed along the X-axis direction and an X-axis pulse motor (not illustrated) for rotating the X-axis ball screw. The X-axis moving unit 10 includes a flat plate-shaped table cover 12 provided in such a manner as to surround the chuck table 8. On the front side and the rear side of the table cover 12, bellows-like dustproof and droplet-proof covers 14 capable of contracting and extending in the X-axis direction are provided. The table cover 12 and the dustproof and droplet-proof covers 14 are provided in such a manner as to cover the constituent elements (the X-axis ball screw, the X-axis pulse motor, and the like) of the X-axis moving unit 10 accommodated inside the opening 4a. When the X-axis moving unit 10 is operated, the chuck table 8 is moved in the X-axis direction together with the table cover 12, and is positioned at a front end part (conveying position) or a rear end part (grinding position) of the opening 4a. In addition, a rotational drive source (not illustrated) such as a motor for rotating the chuck table 8 around a rotational axis substantially parallel to the Z-axis direction is connected to the chuck table 8.

On a front surface side of the support structure 6, a Z-axis moving unit 16 is provided. The Z-axis moving unit 16 includes a pair of Z-axis guide rails 18 disposed along the Z-axis direction. A flat plate-shaped Z-axis moving plate 20 is mounted to the pair of Z-axis guide rails 18 in such a manner as to be slidable along the Z-axis guide rails 18. On a back surface side (a rear surface side) of the Z-axis moving plate 20, a nut section (not illustrated) is provided. The nut section is in screw engagement with a Z-axis ball screw 22 disposed along the Z-axis direction between the pair of Z-axis guide rails 18. In addition, a Z-axis pulse motor 24 for rotating the Z-axis ball screw 22 is connected to an end part of the Z-axis ball screw 22. When the Z-axis ball screw 22 is rotated by the Z-axis pulse motor 24, the Z-axis moving plate 20 is moved (lifted or lowered) in the Z-axis direction along the Z-axis guide rails 18.

A support member 26 is fixed to a front surface side of the Z-axis moving plate 20. The support member 26 supports a grinding unit 28 for grinding the workpiece 11. The grinding unit 28 includes a cylindrical housing 30 supported by the support member 26. A cylindrical spindle 32 disposed along the Z-axis direction is accommodated in the housing 30. A tip end part (a lower end part) of the spindle 32 projects downward from a lower surface of the housing 30. In addition, a rotational drive source (not illustrated) such as a motor is connected to a base end part (an upper end part) of the spindle 32.

A disk-shaped wheel mount 34 made of metal or the like is fixed to the tip end part of the spindle 32. An annular grinding wheel 36 for grinding the workpiece 11 is detachably mounted to a lower surface side of the wheel mount 34. The grinding wheel 36 includes an annular wheel base 38 and a plurality of grindstones 40 fixed to the wheel base 38. The grinding wheel 36 is rotated around a rotational axis substantially parallel to the Z-axis direction by motive power transmitted from the rotational drive source through the spindle 32 and the wheel mount 34. Note that the configuration and functions of the grinding wheel 36 will be described later (see FIG. 2).

The grinding apparatus 2 includes a controller (control unit, control section, control device) 42 for controlling the grinding apparatus 2. The controller 42 is connected to each of constituent elements (the chuck table 8, the X-axis moving unit 10, the Z-axis moving unit 16, the grinding unit 28, etc.) of the grinding apparatus 2. The controller 42 sends control signals to the constituent elements of the grinding apparatus 2 to thereby control the operation of the grinding apparatus 2. For example, the controller 42 includes a computer. Specifically, the controller 42 includes a processing section for performing calculations and the like for the operation of the grinding apparatus 2 and a storage section for storing various kinds of information (data, a program, and the like) used for the operation of the grinding apparatus 2. The processing section includes a processor such as a central processing unit (CPU). In addition, the storage section includes a memory such as a read only memory (ROM) and a random access memory (RAM).

In grinding the workpiece 11 by the grinding apparatus 2, first, the workpiece 11 is held by the chuck table 8. For example, the workpiece 11 is disposed on the chuck table 8 such that the front surface 11a side faces the holding surface 8a and the back surface 11b side is exposed to the upper side. In this state, a suction force (negative pressure) of the suction source is made to act on the holding surface 8a, whereby the workpiece 11 is held under suction by the chuck table 8. Thereafter, the chuck table 8 is moved by the X-axis moving unit 10, and is positioned on the lower side of the grinding wheel 36 (grinding position). Then, while the chuck table 8 and the spindle 32 are rotated at predetermined rotating speeds in respective predetermined directions, the grinding wheel 36 is lowered at a predetermined speed by the Z-axis moving unit 16, to bring the grindstones 40 into contact with the workpiece 11. As a result, the back surface 11b side of the workpiece 11 is ground away, and the workpiece 11 is ground and thinned.

Next, a configuration example of the grinding wheel 36 mounted to the grinding unit 28 of the grinding apparatus 2 will be described. The grinding wheel 36 is fixed to the wheel mount 34 (see FIG. 1) by fixing means (not illustrated) such as fastening bolts, for example. As a result, the grinding wheel 36 is mounted to the tip end part of the spindle 32 through the wheel mount 34.

FIG. 2 is a perspective view depicting the grinding wheel 36 including the wheel base 38 and the plurality of grindstones 40. For example, the wheel base 38 is formed of such metal as an aluminum alloy, and is formed in an annular shape substantially equal in diameter to the wheel mount 34 (see FIG. 1). In addition, the wheel base 38 includes a first surface 38a and a second surface 38b which are substantially parallel to each other. The first surface 38a corresponds to a fixed end face fixed to the wheel mount 34 (see FIG. 1), whereas the second surface 38b corresponds to a free end face which is not fixed to the wheel mount 34. The wheel base 38 is provided in a central part thereof with an opening 38c penetrating the wheel base 38 in the thickness direction from the first surface 38a to the second surface 38b. For example, the opening 38c is formed in a frustoconical shape whose diameter increases from the first surface 38a toward the second surface 38b. On the second surface 38b side of the wheel base 38, an annular groove 38d is provided. The groove 38d is formed concentrically with the wheel base 38 on the outer circumferential side of the wheel base 38 than the opening 38c. On the inside of the groove 38d, the plurality of grindstones 40 for grinding the workpiece 11 are fixed.

The plurality of grindstones 40 are each formed, for example, in a rectangular parallelepiped shape, and are arranged in an annular pattern at substantially equal intervals along the groove 38d. Note that the width of the grindstones 40 and the width of the groove 38d are substantially equal, and the grindstones 40 are arranged such that the lengthwise direction (longitudinal direction) thereof is along the tangential direction (circumferential direction) of the groove 38d. In addition, the grindstone 40 includes a rectangular grinding surface 40a which is exposed to the side opposite to the wheel base 38. The grinding surface 40a is a surface that comes into contact with the workpiece 11 at the time of grinding, and the workpiece 11 is ground by the grinding surface 40a.

In addition, the wheel base 38 includes a plurality of grinding liquid supply passages 38e penetrating the wheel base 38 from the first surface 38a to the second surface 38b. One end side of the grinding liquid supply passage 38e is opened in the first surface 38a, whereas the other end side of the grinding liquid supply passage 38e is opened in that region of the second surface 38b which is located between the opening 38c and the groove 38d. The openings of the plurality of grinding liquid supply passages 38e exposed in the second surface 38b are arranged in an annular pattern at substantially equal intervals along the circumferential direction of the wheel base 38.

As depicted in FIG. 1, the grinding wheel 36 is mounted to the wheel mount 34 which is fixed to the tip end part of the spindle 32. When the spindle 32 is rotated in this state, the grinding wheel 36 is rotated around a rotational axis which is substantially parallel to the Z-axis direction. As a result, the plurality of grindstones 40 are each rotated (slewed) along an annular rotational route centered on a rotational axis of the grinding wheel 36. With the grinding surfaces 40a of the rotating grindstones 40 made to come into contact with the workpiece 11, the workpiece 11 is ground.

At the time of grinding the workpiece 11 by the grinding wheel 36, liquid (grinding liquid) such as pure water is supplied to one end side of the grinding liquid supply passage 38e (the first surface 38a side of the wheel base 38), and the grinding liquid is supplied from the other end side of the grinding liquid supply passage 38e to the workpiece 11 and the plurality of grindstones 40. As a result, the workpiece 11 and the grindstones 40 are cooled, and swarf (grinding swarf) generated by grinding of the workpiece 11 is washed away.

FIG. 3 is a sectional view depicting a part of the grindstone 40. The grindstone 40 includes abrasive grains 50 formed of diamond, cubic boron nitride (cBN), or the like and a binder (bonding material) 52 for fixing the abrasive grains 50. As the binder 52, there can be used a vitreous vitrified bond containing SiO₂ or the like as a main constituent, a resin bond containing resin as a main constituent, or the like. In addition, a number of pores (not illustrated) are formed inside the binder 52. It is to be noted, however, that the material and grain diameter of the abrasive grains 50 and the material of the binder 52 are not limited to any kind.

The binder 52 contains a filler (aggregate) 54 for reinforcing the binder 52. With the filler 54 contained in the binder 52, mechanical strength of the binder 52 is enhanced, and consumption of the grindstones 40 is suppressed. Particularly, in the present embodiment, a spherical filler 54 is contained in the binder 52. In other words, the filler 54 does not have an angular random shape (angular shape), and is particles (powder material) having a true spherical shape or a shape resembling a true sphere.

Specifically, the ratio of a short axis a to a long axis b (aspect ratio a/b) of the filler 54 is not less than 0.7, preferably not less than 0.8, and more preferably not less than 0.9. The short axis a of the filler 54 passes through the center (center of gravity) of the filler 54 and corresponds to the length of a shortest straight line connecting two points on the surface of the filler 54. Meanwhile, the long axis b of the filler 54 passes through the center (center of gravity) of the filler 54 and corresponds to the length of a longest straight line connecting two points on the surface of the filler 54. For example, in the case where the filler 54 is in the shape of a long sphere (a body of rotation obtained by rotating an ellipse around the long axis of the ellipse), the short axis a corresponds to a short diameter of the filler 54, and the long axis b corresponds to a long diameter of the filler 54. In addition, the circularity of the filler 54 is, for example, not less than 0.95, preferably not less than 0.96, and more preferably not less than 0.97. Further, the convexity of the filler 54 is, for example, not less than 0.97, preferably not less than 0.98, and more preferably not less than 0.99, and the solidity of the filler 54 is, for example, not less than 0.94, preferably not less than 0.95, and more preferably not less than 0.96. For example, spherical ceramic particles formed of aluminum oxide (alumina, Al₂O₃), silicon dioxide (silica, SiO₂), or the like are used as the filler 54. As a commercial product which can be used as the filler 54, there may be mentioned true spherical fine particles (trade name: ADMAFINE (registered trademark)) made by ADMATECHS COMPANY LIMITED.

The amount of the filler 54 contained in the binder 52 is adjusted according to the strength of the binder 52 required. Specifically, the content of the filler 54 in the binder 52 can be set to be 5 to 90 wt %, and preferably 60 to 80 wt %. This content corresponds to the ratio of the mass of the filler 54 based on the mass of the binder 52 in which the filler 54 is contained (the total of the mass of the binder 52 and the mass of the filler 54).

Note that it was confirmed, as described later, that, when the spherical filler 54 is used, the strength of the binder 52 is high as compared to the case where a filler of an angular shape is used (see FIG. 4). Hence, by the spherical filler 54 being contained in the binder 52, it is possible to more securely reinforce the binder 52, and to restrain consumption of the binder 52. In addition, as described later, it was also confirmed that the strength of the binder 52 is higher as the size of the filler 54 is greater (see FIG. 4). Hence, it is preferable that the average particle diameter of the filler 54 be greater than the average particle diameter of the abrasive grains 50. For example, the average particle diameter of the filler 54 is 1.1 to 20 times the average particle diameter of the abrasive grains 50. The particle diameters of the abrasive grains 50 and the filler 54 can be measured, for example, by a laser diffraction method.

Note that, in the case where the filler 54 has an angular shape, when the average particle diameter of the filler 54 is set larger than the average particle diameter of the abrasive grains 50, the sharp angular parts of the filler 54 largely project from the binder 52 to be liable to collide against the workpiece 11, and defective processing may occur. On the other hand, when the spherical filler 54 is used as in the present embodiment, even if the filler 54 projects from the binder 52, only a smooth surface (curved surface) of the filler 54 would make contact with the workpiece 11. Hence, even when the average particle diameter of the filler 54 is greater than the average particle diameter of the abrasive grains 50, damaging of the workpiece 11 by the filler 54 is not liable to occur, and defective processing is restrained.

As described above, in the grindstones 40 according to the present embodiment, the binder 52 for fixing the abrasive grains 50 contains the spherical filler 54. As a result, it is possible to restrain occurrence of defective processing at the time of processing the workpiece 11 by the grindstones 40, while enhancing the strength of the grindstones 40.

Note that the structures, methods, and the like concerning the above embodiment can appropriately be modified in carrying out the present invention insofar as the modifications do not depart from the scope of the object of the invention.

Next, the results of evaluation of the strength of the grindstones according to the present invention will be described. In this evaluation, a plurality of grindstones in which the material and size of the filler contained in the binder differ were formed, and the strength of each of the grindstones was measured.

In this evaluation, a plurality of rectangular parallelepiped grindstones (with the length of 20 mm, the width of 10 mm, and the thickness of 4 mm) containing no abrasive grains but fillers in the binder (vitrified bons) were used. Specifically, a grindstone A containing aluminum oxide of an angular shape as the filler, a grindstone B containing spherical aluminum oxide as the filler, and a grindstone C containing spherical silicon dioxide as the filler were formed. More specifically, two kinds of grindstones A, four kinds of grindstones B, and three kinds of grindstones C, which were different in particle diameter of the filler, were prepared. The particle diameters of the filler (aluminum oxide of angular shape) contained in the two kinds of grindstones A were 0.5 μm and 2 μm. The particle diameters of the filler (spherical aluminum oxide) contained in the four kinds of grindstones B were 0.7 μm, 4.2 μm, 5 μm, and 5.4 μm. The particle diameters of the filler (spherical silicon dioxide) contained in the three kinds of grindstones C were 1.6 μm, 3 μm, and 5.7 μm.

For the total of nine kinds of grindstones, measurement of strength (bending stress) by a three-point bending test was conducted. FIG. 4 is a graph depicting the measurement results of the strength of the grindstones.

As depicted in FIG. 4, it was confirmed that the strengths of the grindstones B and C using the spherical fillers are higher than the strength of the grindstone A using the filler of the angular shape having the equivalent size. It is conjectured that this difference comes from such facts that, on one hand, the filler of the angular shape is liable to generate cracks in the inside of the binder by sharp angular parts, and, on the other hand, the spherical fillers make contact with the binder by their smooth surfaces and, hence, are not liable to generate cracks in the inside of the binder.

In addition, comparison of the strengths of the grindstones B and C has verified that the grindstone B containing spherical aluminum oxide is higher in strength than the grindstone C containing silicon dioxide. It is conjectured that the aluminum oxide particles are higher in strength than the silicon dioxide particles, and the strengths of the fillers are reflected on the strengths of the grindstones B and C.

Further, in any one of the grindstones A, B, and C, the strength of the grindstone was higher as the particle diameter of the filler was greater. As a result, it was confirmed that enlargement of the filler is effective for enhancing the strength of the grindstone. Specifically, by use of spherical aluminum oxide as the filler, a grindstone B having a strength of not less than 10 MPa, not less than 30 MPa, or not less than 40 MPa was obtained. In addition, by use of spherical silicon dioxide as the filler, a grindstone C having a strength of not less than 5 MPa or not less than 10 MPa was obtained.

The present invention is not limited to the details of the above described preferred embodiment. The scope of the invention is defined by the appended claims and all changes and modifications as fall within the equivalence of the scope of the claims are therefore to be embraced by the invention.

Claims

1. A grindstone comprising:

abrasive grains; and

a binder for fixing the abrasive grains,

wherein the binder contains a spherical filler for reinforcing the binder.

2. The grindstone according to claim 1,

wherein an average particle diameter of the filler is greater than an average particle diameter of the abrasive grains.

3. The grindstone according to claim 1,

wherein the filler is ceramic particles, and

a ratio of a short axis to a long axis of the ceramic particles is not less than 0.7.

4. The grindstone according to claim 1,

wherein a content of the filler in the binder is 5 to 90 wt %.

5. The grindstone according to claim 1,

wherein the binder is a vitrified bond or a resin bond.