Machining tools

Abstract

To provide a machining tool that can promote the self-sharpening of the cutting edge while maintaining machining performance. [Solution] The processing tool 1 comprises abrasive grains 10 and a binder 20 for fixing the abrasive grains 10. The abrasive grains 10 include first abrasive grains 11 and second abrasive grains 12 that are smaller in size (average particle size) than the first abrasive grains 11. Furthermore, the abrasive grains 10 are characterized in that the content (content ratio) of the second abrasive grains 12 is greater than the content (content ratio) of the first abrasive grains 11.

Description

Technical Field

[0001] The present invention relates to a processing tool.

Background Art

[0002] In recent years, as a semiconductor device capable of controlling high voltage and large current compared to an IC (Integrated Circuit), a power device has attracted attention and is used for power supplies such as electric vehicles, hybrid vehicles, and air conditioners, and inverter control.

[0003] A power device is formed by depositing a SiC single crystal film (also called an epi film) on the surface of a single crystal substrate made of SiC (hereinafter simply referred to as a SiC substrate) having better electrical characteristics than a silicon wafer by epitaxial growth. This SiC substrate is divided into individual devices by cutting, for example, by attaching a cutting blade (hereinafter referred to as a processing tool) to a known cutting device.

[0004] Here, the processing tool is appropriately selected and used according to the characteristics of the workpiece (such as a SiC substrate) from various blades in which diamond abrasive grains or the like are hardened with an electroformed bond such as nickel plating, or diamond abrasive grains or the like are hardened with a resin bond, a metal bond, or a vitrified bond (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, when machining difficult-to-cut materials such as SiC substrates, if the bonding agent (bond, especially electroformed bonds or metal bonds with high bonding strength) of the machining tool (cutting blade) has high abrasive grain retention, it becomes difficult for the abrasive grains to detach (hereinafter referred to as "self-sharpening"), leading to problems such as crushing and clogging of the abrasive grains. When crushing or clogging of the abrasive grains occurs, the machining load increases, resulting in a decrease in machining quality. Furthermore, in order to alleviate the increase in machining load and the decrease in machining quality, the grinding wheel must be dressed periodically, which also leads to a decrease in productivity.

[0007] This invention has been made in view of the above problems, and its purpose is to provide a machining tool that can promote the self-sharpening of the cutting edge of the machining tool while maintaining machining performance. [Means for solving the problem]

[0008] To solve the above-mentioned problems and achieve the objective, the present invention provides a machining tool comprising abrasive grains and a binder for fixing the abrasive grains, wherein the abrasive grains comprise first abrasive grains and second abrasive grains smaller in size than the first abrasive grains, and the content of the second abrasive grains is greater than the content of the first abrasive grains.

[0009] The average particle size of the first abrasive grains may be 4 μm or more and 20 μm or less, and the average particle size of the second abrasive grains may be 1 μm or more and 3 μm or less.

[0010] The content of the first abrasive grains may be 7.5% by volume or more and 11.25% by volume or less relative to the entire processing tool, and the content of the second abrasive grains may be 11.25% by volume or more and 26.25% by volume or less relative to the entire processing tool, and the sum of the content of the first abrasive grains and the content of the second abrasive grains may be 18.75% by volume or more and 37.5% by volume or less. [Effects of the Invention]

[0011] The present invention enables self-sharpening of the cutting tool while maintaining machining performance, as the second abrasive grains with a smaller average particle size preferentially detach during machining of the workpiece. As a result, the present invention can promote the self-sharpening of the cutting tool while maintaining machining performance. [Brief explanation of the drawing]

[0012] [Figure 1] Figure 1 is a perspective view showing an example of the configuration of a machining tool according to Embodiment 1. [Figure 2] Figure 2 is a cross-sectional view showing details of the machining tool in Figure 1. [Figure 3] Figure 3 is a perspective view showing an example of the configuration of a machining tool according to Embodiment 2. [Figure 4] Figure 4 is a diagram illustrating the operation and effects of the machining tool according to Embodiment 1. [Figure 5] Figure 5 is a diagram illustrating the operation and effects of the machining tool according to Embodiment 1. [Figure 6] Figure 6 is a diagram illustrating the operation and effects of the machining tool according to Embodiment 1. [Modes for carrying out the invention]

[0013] Embodiments for carrying out the present invention will be described in detail with reference to the drawings. The present invention is not limited to the contents described in the following embodiments. Furthermore, the components described below include those that can be easily imagined by those skilled in the art, and those that are substantially the same. In addition, the components described below can be combined as appropriate. Furthermore, various omissions, substitutions, or modifications of the components can be made without departing from the spirit of the present invention.

[0014] [Embodiment 1] A machining tool 1 according to Embodiment 1 of the present invention will be described based on the drawings. Figure 1 is a perspective view showing an example of the configuration of the machining tool 1 according to Embodiment 1. Figure 2 is a cross-sectional view showing details of the machining tool 1 in Figure 1. Figure 2 is an enlarged cross-sectional view of an arbitrary part of the cross-section of the machining tool 1 in Figure 1. As shown in Figure 1, the machining tool 1 according to Embodiment 1 is a cutting blade that is plate-shaped with a predetermined thickness and has an annular cutting edge in plan view.

[0015] The machining tool 1 according to Embodiment 1 is, for example, mounted on the tip of a spindle and rotated by the spindle, which acts as the axis of rotation, to cut a workpiece held on a holding table or the like with the tip of the cutting edge. In the example shown in Figure 1, the machining tool 1 according to Embodiment 1 is used as a so-called hubless blade consisting substantially only of an annular cutting edge.

[0016] The machining tool 1 according to Embodiment 1 is not limited to this in the present invention, and may be fixed to the outer circumference of an annular base to form a so-called hub blade for use. The machining tool 1 according to Embodiment 1 is a preferred form because, from the viewpoint of including the particle size of the abrasive grains 10 described later, and the thickness of the cutting edge portion, a hubless blade is more preferably realized than a hub blade.

[0017] The workpiece to be processed by the processing tool 1 is, for example, a disc-shaped semiconductor device wafer or optical device wafer made of silicon, silicon carbide (SiC), sapphire, gallium arsenide, etc., as shown in Figure 1. The workpiece may also be a substrate made of gallium nitride, etc.

[0018] The workpiece to be processed by the processing tool 1 needs to be dressed frequently in the case of difficult-to-machine materials with conventional processing tools to maintain processing performance. Therefore, as described later, the processing tool 1 according to Embodiment 1 of the present invention that can promote self-generated cutting edges is effective. Here, the difficult-to-machine material in the workpiece to be processed by the processing tool 1 refers to a material (workpiece) that is likely to be clogged or blocked by chips with a conventional processing tool (cutting blade) compared to the case of processing a material having silicon as a base material (for example, a silicon wafer or the like) in Embodiment 1.

[0019] Specifically, the difficult-to-machine materials are, for example, disk-shaped wafers having silicon carbide (SiC), sapphire, gallium arsenide, etc. as base materials. Further, these difficult-to-machine materials are also materials for which processing is difficult to proceed with a conventional processing tool (cutting blade) compared to the case of processing a material having silicon as a base material.

[0020] In addition, the processing performance of cutting with a cutting blade such as the processing tool 1 refers to the quality of the cutting groove formed by the cutting process and the cutting marks on the outer periphery of the device chip divided by the cutting process. This processing performance is inspected by an inspection process such as a so-called kerf check that automatically checks whether the cutting process during cutting is executed within a normal range.

[0021] In Embodiment 1, this processing performance can be specifically evaluated by backside chipping inspected by a kerf check. Backside chipping refers to minute chips or cracks that may occur at the outer peripheral edge of the device chip divided from the workpiece on the back side (rear surface) opposite to the side (front surface) where the cutting process is performed when the cutting process is carried out. The size of the backside chipping is represented by the length from both ends of the cutting groove to the portion farthest in the width direction of the cutting groove in the backside chipping (chip or crack). In Embodiment 1, it can be determined that the processing performance is better as the size of this backside chipping is smaller and worse as it is larger.

[0022] Furthermore, whether or not a cutting blade such as the processing tool 1 can promote self-sharpening can be evaluated, for example, by measuring the current value (hereinafter referred to as the spindle current value) of the current flowing to the motor that rotates the spindle on which the cutting blade of the processing tool 1 is mounted.

[0023] When the cutting blade of the machining tool 1 can promote self-sharpening, the degrading and clogging of the abrasive grains are suppressed, so no significant resistance (spindle resistance) is generated to the rotation of the spindle. For this reason, when the cutting blade of the machining tool 1 can promote self-sharpening, even when a predetermined amount of cutting is performed, the spindle current value does not increase and is maintained below a predetermined threshold.

[0024] On the other hand, if the cutting blade cannot promote self-sharpening, spindle resistance occurs due to the degrading or clogging of the abrasive grains. Consequently, if the cutting blade cannot promote self-sharpening, the spindle current value rises significantly and exceeds a predetermined threshold when a predetermined amount of cutting is performed.

[0025] Based on the above, whether or not a cutting blade such as machining tool 1 can promote self-sharpening can be evaluated based on whether or not the spindle current value when a predetermined amount of cutting is performed exceeds a predetermined threshold. Here, the predetermined amount is appropriately defined by the depth and length of the cutting groove formed by cutting, the number of lines that form cutting grooves, etc. The predetermined threshold is appropriately set according to the spindle specifications, the workpiece, the predetermined amount, etc.

[0026] As shown in Figure 2, the machining tool 1 is composed of abrasive grains 10 and a binder 20 for fixing the abrasive grains 10. As shown in Figure 2, the abrasive grains 10 include a first abrasive grain 11 and a second abrasive grain 12 which is smaller in size than the first abrasive grain 11. In the example of Embodiment 1 shown in Figure 2, the abrasive grains 10 do not include a third abrasive grain or the like other than the first abrasive grain 11 and the second abrasive grain 12, but the present invention is not limited to this and may include a third abrasive grain or the like. Here, in Embodiment 1, the size of the first abrasive grain 11 and the size of the second abrasive grain 12 are evaluated and expressed by the (average) particle size of the first abrasive grain 11 and the (average) particle size of the second abrasive grain 12, respectively.

[0027] Here, known methods exist for expressing the (average) particle size of the first abrasive grain 11 and the (average) particle size of the second abrasive grain 12, such as geometric diameter and equivalent diameter. Geometric diameters include the Ferret diameter, the maximum diameter in a given direction (i.e., the Krummbein diameter), the Martin diameter, the sieve diameter, etc., while equivalent diameters include the projected area circle equivalent diameter (i.e., the Heywood diameter), the equivalent diameter of an equisurface area sphere, the equivalent diameter of an equivolute sphere, the Stokes diameter, the light scattering diameter, etc.

[0028] In Embodiment 1, the overall particle size distribution curve of the abrasive grains 10 mixed with first abrasive grains 11 and second abrasive grains 12 shows at least two distribution peaks. These two distribution peaks include a first distribution peak having a first peak in the range of 4 μm to 20 μm, and a second distribution peak having a second peak in the range of 1 μm to 3 μm. The first peak represents the group of first abrasive grains 11 whose (average) particle size is in the range of 4 μm to 20 μm, and the second peak represents the group of second abrasive grains 12 whose (average) particle size is in the range of 1 μm to 3 μm. Thus, the average particle size of the first abrasive grains 11 is in the range of 4 μm to 20 μm, and the average particle size of the second abrasive grains 12 is in the range of 1 μm to 3 μm. Furthermore, the average particle size of the first abrasive grains 11 is larger than the average particle size of the second abrasive grains 12, and the particle size of any first abrasive grain 11 is larger than the particle size of any second abrasive grain 12.

[0029] In Embodiment 1, the abrasive grains 10, which include the first abrasive grains 11 and the second abrasive grains 12, specifically use abrasive grains such as diamond or CBN (Cubic Boron Nitride). In Embodiment 1, both the first abrasive grains 11 and the second abrasive grains 12 are diamond abrasive grains, but the present invention is not limited to this, and abrasive grains of other same material such as CBN may be used for both, or abrasive grains of different materials may be used for each.

[0030] As shown in Figure 2, the binder 20 is provided to fill the gaps between each abrasive grain 10, and it bonds and fixes the abrasive grains 10 together. The binder 20 bonds and fixes the gaps between the first abrasive grains 11 and the first abrasive grains 11, between the first abrasive grains 11 and the second abrasive grains 12, and between the second abrasive grains 12 and the second abrasive grains 12. Specifically, in Embodiment 1, the binder 20 used is a metal plating such as nickel plating (electroformed bond), a resin bond, a metal bond, a vitrified bond, etc.

[0031] In Embodiment 1, the content (ratio) of the first abrasive grains 11 relative to the entire machining tool 1 is 7.5% by volume or more and 11.25% by volume or less, and the content (ratio) of the second abrasive grains 12 relative to the entire machining tool 1 is 11.25% by volume or more and 26.25% by volume or less. Furthermore, in Embodiment 1, the content (ratio) of the second abrasive grains 12 relative to the entire machining tool 1 is greater than the content (ratio) of the first abrasive grains 11 relative to the entire machining tool 1. In addition, the sum (total) of the content (ratio) of the first abrasive grains 11 relative to the entire machining tool 1 and the content (ratio) of the second abrasive grains 12 relative to the entire machining tool 1 is 18.75% by volume or more and 37.5% by volume or less.

[0032] Depending on the content (content ratio) of the first abrasive grains 11 and the second abrasive grains 12 in the entire machining tool 1, the content (content ratio) of the binder 20 and the third abrasive grains, etc., in the entire machining tool 1 other than the first abrasive grains 11 and the second abrasive grains 12 is 62.5% by volume or more and 81.25% by volume or less. In the example of Embodiment 1 in which the abrasive grains 10 do not contain the third abrasive grains, etc., the content (content ratio) of the binder 20 in the entire machining tool 1 is 62.5% by volume or more and 81.25% by volume or less.

[0033] When the binder 20 is an electroformed bond, the processing tool 1 can be manufactured, for example, as follows. First, the electrodeposited substrate and the electrolytic metal formed from the material constituting the binder 20 (such as nickel) are immersed in an electrolyte containing the first abrasive grains 11 and the second abrasive grains 12 so that the amounts of the first abrasive grains 11 and the second abrasive grains 12 are as described above. Next, a predetermined current-conducting means is provided between the electrodeposited substrate and the electrolytic metal to enable current to flow between them. Then, a voltage and current are applied using a voltage-applying means provided between the electrodeposited substrate and the electrolytic metal to ensure that the amounts of the first abrasive grains 11 and the second abrasive grains 12 are as described above. By continuing to apply this voltage and current for a certain period of time, an electrodeposited layer is grown on the electrodeposited substrate, consisting of the first abrasive grains 11 and the second abrasive grains 12 and the electrolytic metal (binder 20), with the amounts of the first abrasive grains 11 and the second abrasive grains 12 being as described above. Subsequently, the grown electrodeposited layer is removed, molded into a desired shape (annular), and subjected to appropriate adjustment processes to manufacture a machining tool 1 in which the first abrasive grains 11 and the second abrasive grains 12 have the above-mentioned content (content ratio).

[0034] In the machining tool 1, the binder 20 is preferably an electroformed bond, and the first abrasive grains 11 and the second abrasive grains 12 are uniformly distributed within the binder 20 by the method described above. Therefore, when the binder 20 is an electroformed bond, the machining tool 1 can more preferably achieve the effect of promoting the self-sharpening of the machining tool 1 while maintaining machining performance.

[0035] Furthermore, if the binder 20 is a resin bond, metal bond, vitrified bond, etc., the machining tool 1 can be manufactured, for example, as follows. First, a mixture is formed by homogeneously mixing the first abrasive grains 11, the second abrasive grains 12, and the materials constituting the binder 20 so that the first abrasive grains 11 and the second abrasive grains 12 have the above-mentioned content (content ratio). Next, this mixture is molded into a desired shape (annular). Then, the mixture molded into the desired shape (annular) is fired at a predetermined temperature (for example, 100°C to 1000°C, etc.), and appropriate adjustment processing is performed to manufacture a machining tool 1 in which the first abrasive grains 11 and the second abrasive grains 12 have the above-mentioned content (content ratio).

[0036] The machining tool 1 according to Embodiment 1, having the configuration described above, comprises abrasive grains 10 and a binder 20 for fixing the abrasive grains 10. The abrasive grains 10 include first abrasive grains 11 and second abrasive grains 12 that are smaller in size than the first abrasive grains 11, with a higher content of second abrasive grains 12 than of first abrasive grains 11. Therefore, the machining tool 1 according to Embodiment 1 can self-sharpen while maintaining machining performance, as the second abrasive grains 12, which have a smaller (average) particle size, preferentially fall off when machining a workpiece. As a result, the machining tool 1 according to Embodiment 1 has the effect of promoting self-sharpening of the machining tool 1 while maintaining machining performance.

[0037] The machining tool 1 according to Embodiment 1 allows for self-sharpening of the cutting edge, particularly when the workpiece is a difficult-to-machine material that is prone to clogging or defacement with conventional machining tools (cutting blades), as the second abrasive grains 12 preferentially fall off in this manner. As a result, the machining tool 1 according to Embodiment 1 can promote self-sharpening of the cutting edge while maintaining machining performance, particularly when the workpiece is a difficult-to-machine material that is prone to clogging or defacement with conventional machining tools (cutting blades).

[0038] Furthermore, in the machining tool 1 according to Embodiment 1, the average particle size of the first abrasive grains 11 is 4 μm or more and 20 μm or less, and the average particle size of the second abrasive grains 12 is 1 μm or more and 3 μm or less. Therefore, the machining tool 1 according to Embodiment 1 can more preferably preferentially detach the second abrasive grains 12 when machining a workpiece while maintaining machining performance, thereby promoting the self-sharpening of the machining tool 1.

[0039] Furthermore, in the machining tool 1 according to Embodiment 1, the content of the first abrasive grains 11 is 7.5% to 11.25% by volume relative to the entire machining tool 1, and the content of the second abrasive grains 12 is 11.25% to 26.25% by volume relative to the entire machining tool 1, and the sum of the content of the first abrasive grains 11 and the second abrasive grains 12 is 18.75% to 37.5% by volume. Therefore, the machining tool 1 according to Embodiment 1 can, while maintaining machining performance, more preferably preferentially shed the second abrasive grains 12 when machining a workpiece, thereby promoting the spontaneous sharpening of the machining tool 1.

[0040] [Embodiment 2] A machining tool 1-2 according to Embodiment 2 of the present invention will be described based on the drawings. Figure 3 is a perspective view showing an example of the configuration of the machining tool 1-2 according to Embodiment 2. As shown in Figure 3, the machining tool 1-2 according to Embodiment 2 is a grinding wheel formed in an arc shape having a constant width in plan view.

[0041] In the example shown in Figure 3, the machining tool 1-2 according to Embodiment 2 is arranged in multiples at equal intervals along the circumferential direction on one end face side of an annular wheel base 30, and is used as a grinding wheel 40. The machining tool 1-2 has such a grinding wheel 40 mounted on the tip of a spindle, and is rotated by the spindle which is the axis of rotation, thereby grinding a workpiece similar to that in Embodiment 1, which is held on a holding table or the like, with the end face portion facing the tip side of the machining tool 1-2.

[0042] The workpiece to be machined by machining tools 1-2 is a difficult-to-machine material, and with conventional machining tools, frequent dressing is required to maintain machining performance. Therefore, machining tools 1-2 according to Embodiment 2 of the present invention, which can promote self-sharpening as described later, are effective.

[0043] The processing performance of grinding using grinding wheels such as processing tools 1-2 refers to the quality of the ground surface formed by the grinding process. This processing performance is inspected, for example, by an inspection process that automatically checks whether the grinding process used to form the ground surface was performed within a normal range. In Embodiment 2, this processing performance can be specifically evaluated by the intensity of the reflected light reflected from the ground surface after light irradiated onto the ground surface. In Embodiment 2, the processing performance can be determined to be good if the intensity of this reflected light is high, and poor if the intensity of this reflected light is low.

[0044] Furthermore, whether or not grinding wheels such as processing tools 1-2 can promote self-sharpening can be evaluated by measuring the spindle current value of the spindle to which the grinding wheel 40, which is formed by arranging multiple grinding wheels such as processing tools 1-2, is mounted, similar to Embodiment 1.

[0045] A detailed view of the machining tool 1-2 according to Embodiment 2, showing an enlarged cross-sectional view of an arbitrary part of the cross-section of the machining tool 1-2, is similar to that of the machining tool 1 according to Embodiment 1, as shown in Figure 2. That is, as shown in Figure 2, the machining tool 1-2 is composed of abrasive grains 10 similar to those in Embodiment 1 and a binder 20 similar to those in Embodiment 1 for fixing the abrasive grains 10. The (average) particle size, material, and content (content ratio) of the first abrasive grains 11 and second abrasive grains 12 contained in the abrasive grains 10 are the same as in Embodiment 1. The material and content (content ratio) of the binder 20 are the same as in Embodiment 1.

[0046] The processing tool 1-2 according to Embodiment 2 can be manufactured in the same manner as in Embodiment 1 by modifying the processing tool 1 according to Embodiment 1 so that instead of forming it into an annular shape, it is formed into an arc shape having a certain width in a plan view.

[0047] The machining tool 1-2 according to Embodiment 2, having the configuration described above, is composed of abrasive grains 10 and a binder 20 for fixing the abrasive grains 10, similar to the machining tool 1 according to Embodiment 1. The abrasive grains 10 include first abrasive grains 11 and second abrasive grains 12 that are smaller in size than the first abrasive grains 11, with a higher content of second abrasive grains 12 than of first abrasive grains 11. Furthermore, the average particle size and content of the first abrasive grains 11 and second abrasive grains 12 contained in the abrasive grains 10 of the machining tool 1-2 according to Embodiment 2 are the same as those of Embodiment 1. For this reason, the machining tool 1-2 according to Embodiment 2 will have the same effects and advantages as Embodiment 1.

[0048] [Examples] Next, the inventors of the present invention confirmed the effects of the machining tool 1 according to Embodiment 1. Figures 4, 5, and 6 illustrate the effects of the machining tool 1 according to Embodiment 1. Figure 4 is a table summarizing the average particle size and content conditions of the first abrasive grains 11 and the second abrasive grains 12 in the machining tool 1 of the embodiment when the effects were confirmed, and the average particle size and content conditions of the abrasive grains in the machining tool of the comparative example. Figure 5 is a graph summarizing the results of the changes in spindle current values ​​obtained when cutting was performed under each of the conditions shown in Figure 4. Figure 6 is a graph summarizing the results of backside chipping obtained when cutting was performed under each of the conditions shown in Figure 4.

[0049] "Comparative Example 1" is a machining tool (cutting blade) in which abrasive grains with an average particle size of 12 μm are contained in a quantity of 8.75% by volume relative to the entire machining tool, with the remainder being a binder.

[0050] "Example 1" is a cutting tool (cutting blade) in which, as shown in the "Example 1" column of Figure 4, the content of first abrasive grains with an average particle size of 12 μm is 8.75 volume% of the total cutting tool, and the content of second abrasive grains with an average particle size of 2 μm is 11.25 volume% of the total cutting tool, with the remainder being a binder.

[0051] "Example 2" is a cutting tool (cutting blade) in which the first abrasive grains with an average particle size of 4 μm are present in an amount of 7.5 volume% of the total cutting tool, the second abrasive grains with an average particle size of 1 μm are present in an amount of 11.25 volume%, and the remainder is made up of a binder. "Example 3" is a cutting tool (cutting blade) in which the first abrasive grains with an average particle size of 4 μm are present in an amount of 11.25 volume%, the second abrasive grains with an average particle size of 1 μm are present in an amount of 26.25 volume%, and the remainder is made up of a binder.

[0052] "Example 4" is a cutting tool (cutting blade) in which the first abrasive grains with an average particle size of 20 μm are present in an amount of 7.5 volume% of the total cutting tool, the second abrasive grains with an average particle size of 3 μm are present in an amount of 11.25 volume%, and the remainder is made up of a binder. "Example 5" is a cutting tool (cutting blade) in which the first abrasive grains with an average particle size of 20 μm are present in an amount of 11.25 volume%, the second abrasive grains with an average particle size of 3 μm are present in an amount of 26.25 volume%, and the remainder is made up of a binder.

[0053] All of the cutting tools (cutting blades) in the examples and comparative examples were formed under the same conditions, except for the average particle size and content of the abrasive grains as described above. All of the cutting tools (cutting blades) in the examples and comparative examples were formed using diamond abrasive grains (first abrasive grains and second abrasive grains) and nickel plating (electroformed bond) as the binder. All of the cutting tools (cutting blades) in the examples and comparative examples were formed in the same shape as hubless blades, in the form of a plate of a predetermined thickness and annular in shape when viewed from above, with the same outer diameter (e.g., 52.5 mm), the same thickness (e.g., 0.05 mm), and the same inner diameter (e.g., 40 mm).

[0054] First, all the cutting tools (cutting blades) of the examples and comparative examples were dressed using the same dresser board under the same conditions to achieve perfect roundness and abrasive grain protrusion (sharpening). The dresser board used for dressing was formed by bonding white alundum (WA) abrasive grains with an average particle size of 7.1 μm to 8.9 μm (grit size #2000). The dressing conditions involved cutting the dresser board to the same length with the same depth of cut (e.g., 0.20 mm) and the same feed rate (e.g., 5 mm / sec, 15 mm / sec, 30 mm / sec, etc.). In all cases, the cutting process during dressing was performed using a so-called down-cut method, where the cutting tool (cutting blade) was rotated in front of the workpiece in the direction of movement, from the top surface to the bottom surface, while cutting into the workpiece.

[0055] Then, using the cutting tools (cutting blades) of all the examples and comparative examples dressed as described above, similar SiC substrates, which are difficult to cut, were cut, and the spindle current values ​​were measured during the cutting process. Here, the cut SiC substrate is a wafer made of silicon carbide (SiC) as the base material, formed in a disc shape, with an outer diameter of 150 mm (Φ150) and a thickness of 0.36 mm. Furthermore, on the surface of this cut SiC substrate, multiple division lines are formed along a first direction and a second direction intersecting (orthogonal to) the first direction. These division lines consist of 19 lines along the first direction at a constant pitch (e.g., approximately 3.7 mm) and at equal intervals from each other, and 19 lines along the second direction at a constant pitch (e.g., approximately 3.7 mm) and at equal intervals from each other, for a total of 38 lines.

[0056] Furthermore, the cutting process involves first attaching adhesive tape to one side of a SiC substrate (wafer), and then, starting from the side opposite to the side with the adhesive tape, performing a so-called full cut along all predetermined division lines in a fixed order, at the same feed rate (e.g., 6 mm / sec, 15 mm / sec, 30 mm / sec, etc.) to a depth that penetrates through the thickness direction and completely divides the substrate into multiple device chips. Specifically, 19 division lines along the first direction were cut one by one in the same direction, sequentially from one side to the other, and 19 division lines along the second direction were similarly cut one by one in the same direction, sequentially from one side to the other, to divide the substrate into multiple device chips.

[0057] Figure 5 is a graph showing the correlation (trend) between the measured spindle current value during cutting of the planned division line and the number of lines cut after dressing and the start of cutting (hereinafter referred to as "line count"), for each condition shown in Figure 4. In the graph of Figure 5, the horizontal axis is the line count and the vertical axis is the spindle current value. As shown in Figure 5, in Comparative Example 1, the spindle current value increased as the line count increased and exceeded a predetermined threshold of 51 (0.4A in this example and comparative example), while in Examples 1 to 5, the increase in the spindle current value was suppressed even as the line count increased and remained below the predetermined threshold of 51.Therefore, it was found that in Comparative Example 1, abrasive grain crushing and clogging occurred, while in Examples 1 to 5, abrasive grain crushing and clogging were suppressed, that is, spontaneous cutting could be promoted.

[0058] Furthermore, backside chipping was measured on device chips obtained by cutting and dividing similar SiC substrates, which are difficult to machine, using the cutting tools (cutting blades) of all the examples and comparative examples dressed as described above. Figure 6 is a graph showing the measurement results of backside chipping under each condition shown in Figure 4. As shown in Figure 6, in all of Comparative Example 1 and Examples 1 to 5, the size of backside chipping was kept below a predetermined threshold of 52 (20 μm in these examples and comparative examples). Therefore, it was found that all the cutting tools (cutting blades) of all the examples and comparative examples dressed as described above provided sufficiently good machining performance.

[0059] As shown above, the examples and comparative examples in Figures 4, 5, and 6 demonstrate that by setting the content of first abrasive grains with an average particle size of 4 μm to 20 μm to 7.5 volume% to 11.25 volume% of the total machining tool, and the content of second abrasive grains with an average particle size of 1 μm to 3 μm to 11.25 volume% to 26.25 volume% of the total machining tool, and setting the sum of the content of the first and second abrasive grains to 18.75 volume% to 37.5 volume%, it is possible to promote the self-sharpening of the machining tool while maintaining machining performance.

[0060] Furthermore, while Figures 4, 5, and 6 show examples and comparative examples where the processing tool is a hubless cutting blade, the same trends and results were obtained even when the processing tool was a hub cutting blade, as shown in Figures 4, 5, and 6. Similarly, the same trends and results were obtained even when the processing tool was a grinding wheel, as shown in Figures 4, 5, and 6.

[0061] It should be noted that the present invention is not limited to the embodiments described above. That is, it can be implemented with various modifications without departing from the core principles of the present invention. [Explanation of Symbols]

[0062] 1,1-2 Processing tools 10 abrasive grains 11 First abrasive grain 12. Second abrasive grain 20 Binding material

Claims

1. A machining tool, It comprises abrasive grains and a binder for fixing the abrasive grains, The abrasive grains include a first abrasive grain and a second abrasive grain that is smaller in size than the first abrasive grain. The content of the second abrasive grain is greater than the content of the first abrasive grain. A machining tool characterized by the following features.

2. The average particle size of the first abrasive grain is 4 μm or more and 20 μm or less. The average particle size of the second abrasive grain is 1 μm or more and 3 μm or less. The machining tool according to claim 1.

3. The content of the first abrasive grain is 7.5% by volume or more and 11.25% by volume or less relative to the entire machining tool. The content of the second abrasive grain is 11.25% by volume or more and 26.25% by volume or less relative to the entire machining tool. The sum of the content of the first abrasive grains and the content of the second abrasive grains is 18.75% by volume or more and 37.5% by volume or less. The machining tool according to claim 1 or 2.

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