Grinding wheel

Abstract

A grinding wheel which includes a plurality of vitrified bonded grindstone chips arranged on an outer periphery of an annular base metal thereof, and is configured to grind a workpiece with use of the grindstone chips while rotating the annular base metal, wherein each of the vitrified bonded grindstone chips is configured in such a manner that, in a rectangular parallelepiped including a rectangular grinding surface which is placed on an opposite side of the annular base metal and grinds the workpiece and four side surfaces adjacent to grinding surface, four ridge portions each of which is provided between the side surfaces are C-chamfered, each long side of the grinding surface is arranged along the outer periphery of the annular base metal, and each of the four ridge portions is C-chamfered in a range which is or more of a length of each short side of the grinding surface.

Claims

1. A grinding wheel comprising a plurality of vitrified bonded grindstone chips arranged on an outer periphery of an annular base metal thereof, the grinding wheel being configured to grind a workpiece with the use of the grindstone chips while rotating the annular base metal, wherein each of the vitrified bonded grindstone chips is configured in such a manner that: in a rectangular parallelepiped comprising: a rectangular grinding surface that is placed on an opposite side of the annular base metal and grinds the workpiece; and four side surfaces adjacent to the grinding surface, four ridge portions, each of which is provided between the side surfaces, are C-chamfered; the rectangular grinding surface comprises a plurality of long sides and a plurality of short sides; each long side is longer than each short side; each long side of the grinding surface is arranged along the outer periphery of the annular base metal; and each of the four ridge portions is C-chamfered in a range that is or more of a length of each short side of the grinding surface.

2. The grinding wheel according to claim 1, wherein a length of each long side of the grinding surface is or more of a length of each of the C-chamfered ridge portions.

3. The grinding wheel according to claim 2, wherein the grinding wheel is configured for double-disc grinding.

4. The grinding wheel according to claim 1, wherein the grinding wheel is configured for double-disc grinding.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a front view showing an example of a grinding wheel according to the present invention;

(2) FIG. 2 is a side view showing an example of the grinding wheel according to the present invention;

(3) FIG. 3 is an explanatory drawing showing an example of chamfered ridge portions (Example 1);

(4) FIG. 4 is an explanatory drawing showing another example of the chamfered ridge portions (Example 2);

(5) FIG. 5 is an explanatory drawing showing an example of a double-disc grinding apparatus;

(6) FIG. 6 is an explanatory drawing showing ridge portions in a grindstone chip used in Comparative Example 1;

(7) FIG. 7 is an explanatory drawing showing ridge portions in a grindstone chip used in Comparative Example 2;

(8) FIG. 8 is a graph showing a measurement result of a warp shape in Example 1;

(9) FIG. 9 is a graph showing a measurement result of a warp shape in Example 2;

(10) FIG. 10 is a graph showing a measurement result of a warp shape in Comparative Example 1;

(11) FIG. 11 is a graph showing a measurement result of a warp shape in Comparative Example 2; and

(12) FIG. 12 is a graph showing average variations of Bow before and after grinding in Examples 1 and 2 and Comparative Examples 1 and 2.

BEST MODE(S) FOR CARRYING OUT THE INVENTION

(13) Although an embodiment of the present invention will now be described hereinafter, the present invention is not restricted thereto.

(14) As described above, as a method for extending a life span of a grinding wheel, increasing a height dimension of a grindstone chip can be considered, but problems that a grindstone is broken when the grindstone chip is simply heightened, a central portion of a workpiece as a grinding target is intensively damaged when the grindstone chip is formed into a rectangular parallelepiped shape, and the like are observed. Thus, the present inventor has paid attention to a shape of the grindstone chip for grinding and arrangement on a annular base metal, and conducted various kinds of experiments.

(15) Consequently, as described above, when a grindstone chip having a rectangular parallelepiped shape is arranged in such a manner that long sides of its rectangular grinding surface are arranged along an outer periphery of an annular base metal (namely, in such a manner that they become substantially parallel to a rotating direction of a grinding wheel), breakage of the grindstone chip at the time of grinding can be avoided.

(16) Additionally, in case of the grindstone chip having the parallelepiped shape, since ridge portions each having an inner angle 90 as seen from a height direction (i.e., in the grindstone chip having the rectangular parallelepiped shape, four ridge portions between four side surfaces adjacent to a rectangular grinding surface) vertically cut into a workpiece center and a moving load to the rotating direction becomes large, the central portion of the workpiece is apt to be intensively damaged. However, the present inventor repeatedly conducted experiments and found out that performing C-chamfering to the four ridge portions in a range of or more of short sides of the rectangular grinding surface enables suppressing the intensive damage to the central portion of the workpiece, thereby bringing the present invention to completion.

(17) Although the present invention will be described hereinafter in detail as an embodiment with reference to the drawings, the present invention is not restricted thereto.

(18) FIG. 1 shows an example of a grinding wheel according to the present invention. It is a front view seen from a side which comes into contact with a workpiece as a grinding target. Further, FIG. 2 is a side view. A grinding wheel 1 according to the present invention includes an annular base metal (which will be also simply referred to as a base metal hereinafter) 2 and a plurality of vitrified bonded grindstone chips 3.

(19) As the base metal 2, it is possible to adopt a base metal on which the grindstone chips 3 can be arranged and which can be rotated by a motor or the like at the time of grinding. It is to be noted that a rotating direction is denoted by R.

(20) Furthermore, as a shape of each grindstone chip 3, a part of a rectangular parallelepiped is chamfered. FIGS. 1 and 2 show a simplified state where chamfering is omitted.

(21) The shape of the grindstone chip 3 will now be more specifically described. First, it has a rectangular grinding surface 4 at a position opposite to a side fixed on the base metal 2, and also has four rectangular side surfaces 5 adjacent to the grinding surface 4. Each ridge portion, which is between side surfaces adjacent to each other, of the four side surfaces 5 is C-chamfered.

(22) It is to be noted that the rectangular parallelepiped of the grindstone chip 3 and the rectangular grinding surface 4 described herein mean a shape of the grindstone chip 3 before the chamfering and a shape of the grinding surface 4 before the chamfering, respectively. Moreover, the long side and the short side of the rectangular grinding surface 4 described herein mean a long side and a short side in a rectangular state before the chamfering.

(23) Here, FIGS. 3 and 4 show examples of the C-chamfered ridge portions. FIGS. 3 and 4 show the grindstone chip 3 seen from the grinding-surface-4 side. In both the drawings, four ridge portions 6 are C-chamfered.

(24) In regard to a chamfering amount, in the present invention, C-chamfering each ridge portion in a range of or more of a length of each short side 7 (see an arrow of a solid line in FIG. 3) of the rectangular grinding surface 4 can suffice, and the chamfering amount is not restricted in particular. FIG. 3 shows an example where each ridge portion is C-chamfered by an amount corresponding to of a length of a short side 7, and the grinding surface 4 has an octagonal shape. On the other hand, FIG. 4 shows an example where each ridge portion is C-chamfered by an amount corresponding to a length of a short length 7 and the grinding surface 4 has a hexagonal shape.

(25) Since the C-chamfering is performed as described above, a central portion of a workpiece is not excessively cut at the time of grinding the workpiece, and the central portion of the workpiece can be prevented from being intensively damaged. Additionally, just performing the chamfering can suffice, and hence shape forming is easy.

(26) On the other hand, when the chamfering amount is less than of the length of the short side 7, the excessive cutting cannot be effectively avoided, and the workpiece gets damaged.

(27) Further, in the present invention, the arrangement of the rectangular parallelepiped grindstone chips 3 is elaborated. The plurality of the grindstone chips 3 are arranged along an outer periphery of the base metal 2. The number of the chips to be arranged is not restricted in particular, and it can be appropriately determined. At this time, the chips are arranged in such a manner that the long sides 8 of the grinding surface 4 are arranged along the outer periphery of the base metal 2. That is, since the grindstone chips 3 are arranged in such a manner that the long sides 8 become substantially parallel to a rotating direction of the grinding wheel 1, it is possible to withstand bending stress at the time of grinding the workpiece and effectively avoid breakage of the grindstone chips 3.

(28) In conventional products, when a height of each grindstone chip is increased to extend a life span of the grinding wheel, the grindstone chips get broken due to the bending stress. However, in the present invention, since the arrangement is elaborated and therefore resistance properties to the bending stress are provided, the height of each grindstone chip 3 can be increased while avoiding the damage, and the life span of the grinding wheel 1 can be extended. It is to be noted that the height 9 of the grindstone chip 3 means a length of each C-chamfered ridge portion as shown in FIG. 2.

(29) Furthermore, to avoid such damage as described above, when a length of each long side 8 of the grinding surface 4 (see an arrow of a dotted line in FIG. 3) is or more of the height 9 of the grindstone chip 3, the effect is enhanced. The longer the length of each long side 8 of the grinding surface 4 is to the height of the grindstone chip 3, the higher the resistance properties to the bending stress is, which is preferable.

(30) A grinding apparatus including the grinding wheel 1 according to the present invention will now be described. Although a double-disc grinding apparatus will be described here, the grinding wheel 1 according to the present invention is not restricted to one for the double-disc grinding apparatus. It is possible to adopt the grinding wheel 1 which can grind a workpiece with the grindstone chips 3 while rotating the grinding wheel 1 itself, and the grinding wheel 1 can be used in any grinding apparatus.

(31) FIG. 5 shows an example of a double-disc grinding apparatus 10. The double-disc grinding apparatus 10 mainly includes a pair of grinding wheels 1, a rotatable carrier 12 which holds a workpiece 11 from an outer peripheral side along a radial direction of the workpiece 11, and a holder portion 13 having the carrier 12 disposed thereto.

(32) When the pair of grinding wheels 1 are rotated while rotating the carrier 12 and the holder portion 13 to rotate the workpiece 11, both surfaces of the workpiece 11 can be ground at the same time. When the grinding wheels 1 of the present invention are used, the grindstone chips 3 are not broken, a central portion of the workpiece 11 is not intensively damaged, and high-quality grinding can be carried out.

EXAMPLES

(33) Although the present invention will now be described hereinafter in detail with reference to examples and comparative examples, the present invention is not restricted thereto.

Examples 1 and 2 and Comparative Examples 1 and 2

(34) Such a double-disc grinding apparatus 10 for workpieces as shown in FIG. 5 was used to perform double-disc grinding to a silicon wafer having a diameter of 300 mm. This silicon wafer was sliced off from an ingot manufactured by a CZ method (a Czochralski method).

(35) First, grinding wheels each having a plurality of vitrified bonded grindstone chips shown in FIG. 3, each of which is formed into a shape that a C-chamfered region is of a short side of a grinding surface, arranged thereon were provided in such a double-disc grinding apparatus 10 as shown in FIG. 5, and five silicon wafers were ground (Example 1).

(36) Then, grinding wheels each having a plurality of vitrified bonded grindstone chips shown in FIG. 4, each of which is formed into a shape that a C-chamfered region is of a short side of a grinding surface, arranged thereon were provided in such a double-disc grinding apparatus 10 as shown in FIG. 5, and five silicon wafers were ground (Example 2).

(37) Subsequently, grinding wheels each having a plurality of unchamfered vitrified bonded grindstone chips which are shown in FIG. 6 arranged thereon were provided in a double-disc grinding apparatus which is the same as that shown in FIG. 5, and five silicon wafers were ground (Comparative Example 1).

(38) At last, grinding wheels each having a plurality of vitrified bonded grindstone chips shown in FIG. 7, each of which is formed into a shape that a C-chamfered region is of a short side of a grinding surface, arranged thereon were provided in a double-disc grinding apparatus which is the same as that shown in FIG. 5, and five silicon wafers were ground (Comparative Example 2).

(39) The grindstone chips in Examples 1 and 2 and Comparative Examples 1 and 2 described above are all formed into a shape in which a height is 10 mm, a length of each long side substantially parallel to a rotating direction is 5 mm, and a length of each short side is 3 mm.

(40) At the time of grinding, no grindstone chip was broken in all of Examples 1 and 2 and Comparative Examples 1 and 2.

(41) It is to be noted that, aside from Examples 1 and 2 and Comparative Examples 1 and 2, square-pillar-shaped grindstone chips each having a height of 10 mm and a side length of 3 mm (i.e., chips formed into a shape that respective sides of a grinding surface have the same length and side lengths have no difference) were also evaluated (Comparative Example 3).

(42) However, in this Comparative Example 3, all the grindstone chips were broken, and no silicon wafer was ground.

(43) As evaluation of the ground silicon wafers, a warp shape of each ground silicon wafer or a variation (Bow) of Bow (a magnitude and a direction of a warp) before and after grinding can be used as an index.

(44) When a warp shape of a central portion (a range with a radius of approximately 50 mm) after grinding has a precipitous convex or concave shape, it can be understood that either a front or back surface got intensively damaged, and an imbalance of associated residual stress was caused on the front and back surfaces.

(45) Moreover, with Bow, the damage to the front and back surfaces due to grinding or a balance of the associated residual stress can be evaluated as a numerical value. When the front and back surfaces have the similar damage or the similar associated residual stress, Bow approximates zero.

(46) In measurement of the warp shape or Bow, SBW-330 (manufactured by Kobelco Research Institute, Inc.) was used.

(47) It is to be noted that Bow is preferably 5 m or more and 5 m or less.

(48) FIGS. 8 to 11 show warp shapes after grinding the respective silicon wafers with the shapes of the grindstone chips according to Examples 1 and 2 and Comparative Examples 1 and 2.

(49) A precipitous change in warp shape of the central portion is not observed in Examples 1 and 2. However, formation of a radical convex part was observed in the central portion in Comparative Examples 1 and 2, and it can be understood that that either a front or back surface got intensively damaged, and an imbalance of associated residual stress was caused on the front and back surfaces.

(50) FIG. 12 shows average variations of Bow before and after grinding when five silicon wafers were ground with the shapes of the grindstone chips according to Examples 1 and 2 and Comparative Examples 1 and 2.

(51) An error bar represents a deviation. Example 1 has Bow=0.17 m, Example 2 has Bow=0.57 m, and both are excellent. On the other hand, Comparative Example 1 has Bow=5.39 m, Comparative Example 2 has Bow=5.10 m, and it can be understood that the residual stress is off-balance on the front and back surfaces.

(52) It can be understood from the above results that the intensive damage to the central portion of each wafer surface can be suppressed by setting the C-chamfered region to or more of each short side of the rectangular grinding surface like Examples 1 and 2 which embody the present invention. On the other hand, in Comparative Examples 1 and 2 which do not embody the present invention, the central portion of each wafer surface got intensively damaged, and the warp shape or Bow was adversely affected.

(53) It is to be noted that the present invention is not restricted to the foregoing embodiment. The foregoing embodiment is an illustrative example, and any example which has substantially the same structure and exerts the same functions and effects as the technical concept described in claims of the present invention is included in the technical scope of the present invention.