Cutting apparatus

A cutting apparatus includes a chuck table configured to hold the workpiece, and a cutting unit fitted with a cutting blade including an annular base and a cutting edge that includes abrasive grains and a binder configured to fix the abrasive grains, and is formed along an outer circumferential edge of the base. The cutting unit includes a spindle, a blade mount fitted to a distal end portion of the spindle, and a fixing nut configured to fix the cutting blade to the blade mount, and the blade mount or the fixing nut is provided with a corrosion layer formed of a material having a higher ionization tendency than a material constituting the binder.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a cutting apparatus that cuts a workpiece.

Description of the Related Art

A device chip manufacturing process uses a wafer having a device formed in each of a plurality of regions demarcated by a plurality of streets (planned dividing lines) arranged in a lattice manner. A plurality of device chips including respective devices are obtained by dividing the wafer along the streets. The device chips are incorporated into various electronic apparatuses such as mobile telephones, or personal computers.

A cutting apparatus is used to divide the wafer. The cutting apparatus includes a chuck table that holds a workpiece, and a cutting unit that performs cutting processing on the workpiece. The cutting unit includes a spindle. A distal end portion of the spindle is fitted with an annular cutting blade that cuts the workpiece (see Japanese Patent Laid-Open No. 2000-87282). The wafer is cut and divided by rotating the cutting blade, and making the cutting blade cut into the wafer held by the chuck table.

When the cutting apparatus cuts the workpiece, a liquid (cutting liquid) such as pure water is supplied to the workpiece and the cutting blade. The supply of the cutting liquid cools the workpiece and the cutting blade, and washes away a waste (cutting waste) produced by the cutting. However, because pure water has a high resistivity, static electricity tends to occur in a region of contact between the cutting blade rotated at a high speed and the workpiece when pure water is supplied as the cutting liquid to the workpiece and the cutting blade during the cutting processing. This may cause an electrostatic breakdown of the devices formed on the workpiece, and consequently decrease the yield of the device chips. Accordingly, a method of using pure water mixed with carbon dioxide (carbonated water) as the cutting liquid has been proposed (see Japanese Patent Laid-Open No. Hei 08-130201 and Japanese Patent Laid-Open No. Hei 11-300184). Carbonated water has a low resistivity as compared with pure water, and therefore does not readily cause static electricity even when supplied to the workpiece and the cutting blade during the cutting processing. The electrostatic breakdown of the devices is thereby suppressed.

SUMMARY OF THE INVENTION

When the workpiece is cut by using the cutting apparatus, and the supply of the cutting liquid to the cutting blade is continued, the cutting blade corrodes and wears due to the cutting liquid. In particular, when pure water mixed with carbon dioxide (carbonated water) is used as the cutting liquid, the corrosion of the cutting blade progresses easily. As a result, the strength of the cutting blade is decreased, and damage to the cutting blade and a processing defect in the workpiece tend to occur.

The present invention has been made in view of such problems. It is an object of the present invention to provide a cutting apparatus that can suppress the corrosion of a cutting blade.

In accordance with an aspect of the present invention, there is provided a cutting apparatus for cutting a workpiece. The cutting apparatus includes a chuck table configured to hold the workpiece, and a cutting unit fitted with a cutting blade including an annular base and a cutting edge that includes abrasive grains and a binder configured to fix the abrasive grains, and is formed along an outer circumferential edge of the base. The cutting unit includes a spindle, a blade mount fitted to a distal end portion of the spindle, and a fixing nut configured to fix the cutting blade to the blade mount, and the blade mount or the fixing nut is provided with a corrosion layer formed of a material having a higher ionization tendency than a material constituting the binder.

In accordance with another aspect of the present invention, there is provided a cutting apparatus for cutting a workpiece. The cutting apparatus includes a chuck table configured to hold the workpiece, and a cutting unit fitted with a cutting blade including an annular base and a cutting edge that includes abrasive grains and a binder configured to fix the abrasive grains, and is formed along an outer circumferential edge of the base. The cutting unit includes a spindle, a blade mount fitted to a distal end portion of the spindle, and a fixing nut configured to fix the cutting blade to the blade mount, and the blade mount or the fixing nut is formed of a material having a higher ionization tendency than a material constituting the binder.

Incidentally, preferably, the binder and the corrosion layer are formed by a nickel plating layer containing sulfur, and a content rate of sulfur in the corrosion layer is higher than a content rate of sulfur in the binder. In addition, preferably, the content rate of sulfur in the corrosion layer is equal to or more than 1.2 times the content rate of sulfur in the binder.

In the cutting apparatus according to one aspect of the present invention, one or both the blade mount and the fixing nut are provided with a corrosion layer formed of a material having a higher ionization tendency than the material constituting the binder of the cutting edge of the cutting blade. Thus, when a cutting liquid is supplied to the cutting blade, the corrosion layer preferentially corrodes in a sacrificial manner, and suppresses the corrosion of the cutting edge of the cutting blade.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present embodiment will hereinafter be described with reference to the accompanying drawings. An example of a configuration of a cutting apparatus according to the present embodiment will first be described.FIG.1is a perspective view depicting a cutting apparatus2. Incidentally, inFIG.1, an X-axis direction (a processing feed direction, a left-right direction, or a first horizontal direction) and a Y-axis direction (an indexing feed direction, a forward-rearward direction, or a second horizontal direction) are directions perpendicular to each other. In addition, a Z-axis direction (a vertical direction, an upward-downward direction, or a height direction) is a direction perpendicular to the X-axis direction and the Y-axis direction.

The cutting apparatus2includes a base4that supports and houses each constituent element constituting the cutting apparatus2. A cover6that covers an upper surface side of the base4is provided to the upper side of the base4. A space (processing chamber) in which a workpiece11is processed is formed within the cover6. A cutting unit8that performs cutting processing on the workpiece11is provided within the processing chamber. The cutting unit8is fitted with an annular cutting blade (electroformed grindstone)20, which is a tool for cutting the workpiece11. In addition, ball screw type moving mechanisms (not depicted) that move the cutting unit8along the Y-axis direction and the Z-axis direction are coupled to the cutting unit8.

A chuck table (holding table)10that holds the workpiece11is provided below the cutting unit8. The upper surface of the chuck table10is a flat surface substantially parallel with a horizontal direction (XY plane direction), and constitutes a holding surface10athat holds the workpiece11. The holding surface10ais connected to a suction source (not depicted) such as an ejector via a flow passage (not depicted) formed within the chuck table10, and a valve. A ball screw type moving mechanism (not depicted) that moves the chuck table10along the X-axis direction is coupled to the chuck table10. In addition, a rotational driving source (not depicted) such as a motor that rotates the chuck table10about a rotational axis substantially parallel with the Z-axis direction is coupled to the chuck table10.

A cassette mounting base12is installed on a corner portion on the front side of the base4. A cassette14that can house a plurality of workpieces11is mounted on the upper surface of the cassette mounting base12. In addition, a raising and lowering mechanism (not depicted) that moves (raises and lowers) the cassette mounting base12along the Z-axis direction is coupled to the cassette mounting base12. A height (position in the Z-axis direction) of the cassette14is adjusted by the raising and lowering mechanism such that unloading of the workpiece11from the cassette14and loading of the workpiece11into the cassette14are performed properly.

The workpiece11is, for example, a disk-shaped wafer formed of a semiconductor material such as silicon. The workpiece11has a top surface and an undersurface substantially parallel with each other. The workpiece11is demarcated into a plurality of rectangular regions by a plurality of streets (planned dividing lines) arranged in a lattice manner so as to intersect each other. In addition, a device such as an integrated circuit (IC), large scale integration (LSI), a light emitting diode (LED), or a microelectromechanical systems (MEMS) device is formed in each of the top surface sides of the regions demarcated by the streets. When the workpiece11is cut and divided along the streets by the cutting apparatus2, a plurality of device chips each including the device are manufactured. However, a material, a shape, a structure, a size, and the like of the workpiece11are not limited. For example, the workpiece11may be a wafer (substrate) formed of a semiconductor other than silicon (GaAs, InP, GaN, SiC, or the like), sapphire, a glass (quartz glass, borosilicate glass, or the like), a resin, a ceramic, a metal, or the like. In addition, a kind, a quantity, a shape, a structure, a size, an arrangement, and the like of the devices are not limited either. No devices may be formed on the workpiece11. Further, the workpiece11may be a package substrate such as a chip size package (CSP) substrate, or a quad flat non-leaded package (QFN) substrate.

When the cutting apparatus2processes the workpiece11, the workpiece11is supported by an annular frame13for the convenience of handling (transporting, holding, or the like) of the workpiece11. The frame13is formed of a metal such as a stainless steel (SUS). A circular opening that penetrates the frame13in a thickness direction is provided in a central portion of the frame13. The diameter of the opening of the frame13is larger than the diameter of the workpiece11. The workpiece11is disposed on the inside of the opening of the frame13. A tape15is affixed to the workpiece11and the frame13. The tape15includes a film-shaped base material formed in a circular shape and an adhesive layer (glue layer) provided on the base material. The base material is, for example, formed of a resin such as polyolefin, polyvinyl chloride, or polyethylene terephthalate. In addition, the adhesive layer is formed of an epoxy-based, an acryl-based, or a rubber-based adhesive. Incidentally, the adhesive layer may be an ultraviolet curable resin cured by irradiation with ultraviolet rays. When a central portion of the tape15is affixed to the undersurface (lower surface) side of the workpiece11, and an outer circumferential portion of the tape15is affixed to the frame13, the workpiece11is supported by the frame13via the tape15. Then, the workpiece11is housed in the cassette14in a state in which the workpiece11is supported by the frame13.

A transporting mechanism (not depicted) that transports the workpiece11is provided in the vicinity of the cassette mounting base12. The transporting mechanism, for example, has a plurality of suction pads that suck and hold the upper surface side of the frame13. The transporting mechanism transports the workpiece11in an unprocessed state from the cassette14to the chuck table10, and transports the workpiece11in an already processed state from the chuck table10to the cassette14.

A display part (display unit)16is provided on a front surface6aside of the cover6. The display part16is constituted by various kinds of displays. The display part16displays various kinds of information related to the cutting apparatus2. The display part16can, for example, display an operating screen, a processing state, processing conditions, an image of the workpiece11, and the like. Incidentally, the display part16may be a touch panel type display. In this case, the display part16functions as a user interface, and an operator can input information to the cutting apparatus2by touch operation of the display part16. That is, the display part16functions also as an input part (an input unit or an input apparatus) for inputting information to the cutting apparatus2. However, the input part may be provided separately from and independently of the display part16. In this case, a keyboard, a mouse, or the like can be used as the input part.

Each constituent element (the cutting unit8, the chuck table10, the cassette mounting base12, the display part16, and the like) constituting the cutting apparatus2is connected to a control part (a control unit or a control apparatus)18. The control part18generates a control signal that controls operation of each constituent element of the cutting apparatus2. The control part18thereby controls operation of the cutting apparatus2. The control part18is, for example, constituted by a computer. Specifically, the control part18includes an arithmetic unit that performs operation necessary for the operation of the cutting apparatus2and a storage unit that stores various kinds of information (data, a program, or the like) used for the operation of the cutting apparatus2. The arithmetic unit includes a processor such as a central processing unit (CPU). In addition, the storage unit includes a memory such as a read only memory (ROM), and a random access memory (RAM).

The workpiece11housed in the cassette14is transported onto the chuck table10by the transporting mechanism and is held by the chuck table10. The workpiece11is, for example, disposed on the holding surface10aof the chuck table10via the tape15. When a suction force (negative pressure) of the suction source is made to act on the holding surface10ain this state, the workpiece11is sucked and held by the chuck table10via the tape15.

The workpiece11held by the chuck table10is processed by the cutting unit8. Specifically, the cutting unit8cuts the workpiece11by rotating a cutting blade20and making the cutting blade20cut into the workpiece11. Incidentally, during cutting processing, a liquid (cutting liquid) is supplied to the workpiece11and the cutting blade20. The cutting liquid cools the workpiece11and the cutting blade20, and washes away a waste (processing waste) produced by the cutting processing. Then, the workpiece11after being processed is transported by the transporting mechanism and is housed in the cassette14.

FIG.2Ais a perspective view depicting the cutting unit8. The cutting unit8is fitted with the annular cutting blade20that cuts the workpiece11. The cutting blade20includes an annular base22, and an annular cutting edge24formed on the base22.

The base22is formed of an electrically conductive metal (aluminum alloy or the like). The base22includes a front surface (first surface)22aand a back surface (second surface)22b, and an outer circumferential edge (side surface)22cconnected to the front surface22aand the back surface22b. A cylindrical opening portion22dthat penetrates the base22in the thickness direction is provided in a central portion of the base22. In addition, the front surface22aside of the base22is provided with an annular protruding portion22ethat protrudes from the front surface22ain the thickness direction of the base22. The annular cutting edge24is formed on the back surface22bside of the base22along the outer circumferential edge22c. The cutting edge24is formed so as to project outward in a radial direction of the base22from the outer circumferential edge22cof the base22. The cutting edge24includes abrasive grains formed of diamond, cubic Boron Nitride (cBN), or the like and a binder that is formed of a metal or the like and fixes the abrasive grains. The cutting edge24is, for example, formed by fixing the abrasive grains by nickel electrodeposited on an outer circumferential portion of the base22. In this case, the binder of the cutting edge24is formed by a nickel plating layer. However, the material of the abrasive grains, the grain diameter of the abrasive grains, the material of the binder, and the like are not limited, but are selected as appropriate according to the material of the workpiece11and processing conditions.

The cutting unit8includes a housing30formed in a hollow cylindrical shape. The housing30houses a cylindrical spindle32disposed along the Y-axis direction. A distal end portion (one end side) of the spindle32is exposed from the housing30. In addition, a rotational driving source (not depicted) such as a motor that rotates the spindle32is coupled to a proximal end portion (another end side) of the spindle32.

The distal end portion of the spindle32is fitted with a blade mount34that supports the cutting blade20. The blade mount34is formed of an electrically conductive metal (aluminum alloy or the like). The blade mount34includes a disk-shaped flange portion36and a cylindrical supporting shaft (boss portion)38. The blade mount34is, for example, fixed to the distal end portion of the spindle32by a fixture such as a bolt.

The flange portion36includes a front surface (first surface)36aand a back surface (second surface)36band an outer circumferential edge (side surface)36cconnected to the front surface36aand the back surface36b. In addition, an outer circumferential portion of the flange portion36is provided with an annular protruding portion36dalong the outer circumferential edge36c, the annular protruding portion36dprotruding from the front surface36ain the thickness direction of the flange portion36. The distal end surface of the protruding portion36dis a flat surface substantially parallel with the front surface36a, and constitutes a supporting surface36ethat supports the cutting blade20. The supporting shaft38is provided so as to project from a central portion of the front surface36aof the flange portion36. The central position of the flange portion36and the central position of the supporting shaft38substantially coincide with each other. In addition, a thread groove38ais formed in the outer circumferential surface of the supporting shaft38.

An annular fixing nut40that fixes the cutting blade20to the blade mount34is fastened to the thread groove38aof the supporting shaft38. The fixing nut40is formed of an electrically conductive metal (aluminum alloy or the like). The fixing nut40includes a front surface (first surface)40aand a back surface (second surface)40b, and an outer circumferential edge (side surface)40cconnected to the front surface40aand the back surface40b. A cylindrical opening portion40dthat penetrates the fixing nut40in the thickness direction is provided in a central portion of the fixing nut40. In addition, a thread groove corresponding to the thread groove38aof the supporting shaft38is formed in the inner circumferential surface of the fixing nut40which inner circumferential surface is exposed within the opening portion40d.

The cutting blade20is fitted to the blade mount34such that the supporting shaft38is inserted into the opening portion22d. When the fixing nut40is screwed and fastened to the thread groove38aof the supporting shaft38in this state, the cutting blade20comes into contact with the supporting surface36eof the flange portion36and the back surface40bof the fixing nut40, and is sandwiched by the blade mount34and the fixing nut40. The cutting blade20is thereby fitted and fixed to the blade mount34. Then, power transmitted from the rotational driving source via the spindle32and the blade mount34rotates the cutting blade20about a rotational axis substantially parallel with the Y-axis direction.

FIG.2Bis a perspective view depicting the cutting unit8fitted with a blade cover42. The cutting blade20fitted to the cutting unit8is covered by the blade cover42in a box shape which blade cover is fixed to the housing30. The blade cover42includes a pair of connecting portions44supplied with the cutting liquid and a pair of nozzles46connected to the connecting portions44and disposed so as to sandwich a lower end portion of the cutting blade20. Supply ports (not depicted) opening toward the cutting blade20are formed in each of the pair of nozzles46. Piping such as tubes, or pipes as flow passages of the cutting liquid is connected to the connecting portions44. During the cutting of the workpiece11, the cutting liquid supplied to the connecting portion44flows into the nozzles46and is supplied from the supply ports of the nozzles46to the front surface and the back surface of the cutting blade20. Pure water, for example, is used as the cutting liquid. In addition, a liquid having a lower resistivity than pure water may be used in order to suppress the generation of static electricity during the cutting processing. For example, pure water mixed with carbon dioxide (carbonated water) can also be used as the cutting liquid.

Incidentally, when the supply of the cutting liquid to the cutting blade20is continued during the cutting of the workpiece11, the cutting edge24of the cutting blade20corrodes and wears due to the cutting liquid. In particular, when pure water mixed with carbon dioxide (carbonated water) is used, the corrosion of the cutting edge24progresses easily. When the corrosion of the cutting edge24occurs, the strength of the cutting edge24is decreased, and damage to the cutting blade20and a processing defect in the workpiece11tend to occur. Accordingly, in the present embodiment, a corrosion layer (sacrificial layer) that produces sacrificial corrosion protection is provided to one or both the blade mount34and the fixing nut40. Thus, while the cutting liquid is supplied to the cutting blade20, the corrosion layer preferentially corrodes in a sacrificial manner, and suppresses the corrosion of the binder of the cutting edge24. As a result, a decrease in the strength of the cutting edge24is suppressed.

FIG.3is a perspective view depicting the blade mount34. A cylindrical opening portion34athat opens in the back surface36bof the flange portion36is provided to a central portion of the blade mount34. When the blade mount34is fitted to the spindle32(seeFIG.2A), the distal end portion of the spindle32is inserted into the opening portion34a. In addition, the blade mount34is provided with a corrosion layer (sacrificial layer)50that produces sacrificial corrosion protection. For example, the corrosion layer50in an annular shape having a predetermined width is formed on the back surface36bside of the flange portion36so as to surround the opening portion34a. However, the number, a size, a shape, a position, and the like of the corrosion layer50are not limited as long as the corrosion layer50is electrically connected to the blade mount34. For example, a plurality of corrosion layers50may be arranged on the back surface36bside of the flange portion36at substantially equal intervals along the circumferential direction of the flange portion36. In addition, the corrosion layer50may be formed on the front surface36a(seeFIG.2A) of the flange portion36, the outer circumferential edge36c, or the supporting shaft38.

FIG.4is a perspective view depicting the fixing nut40. The fixing nut40is provided with corrosion layers (sacrificial layers)52that produce sacrificial corrosion protection. For example, a plurality of arcuate corrosion layers52(four arcuate corrosion layers52inFIG.4) having a predetermined width are arranged on the front surface40aside of the fixing nut40at substantially equal intervals along the circumferential direction of the fixing nut40. However, the number, a size, a shape, a position, and the like of the corrosion layers52are not limited as long as the corrosion layers52are electrically connected to the fixing nut40. For example, an annular corrosion layer52may be formed continuously along the circumferential direction of the fixing nut40. In addition, the corrosion layer(s)52may be formed on the back surface40bor the outer circumferential edge40cof the fixing nut40.

When the cutting blade20is fitted to the blade mount34(seeFIG.2A), the cutting edge24comes into contact with the supporting surface36eof the flange portion36. Thus, the binder of the cutting edge24and the corrosion layer50(seeFIG.3) are electrically connected to each other via the flange portion36. In addition, the base22comes into contact with the back surface40bof the fixing nut40. Thus, the binder of the cutting edge24and the corrosion layers52(seeFIG.4) are electrically connected to each other via the base22and the fixing nut40.

Incidentally, the corrosion layer50(seeFIG.3) is preferably provided to a region other than a region that comes into contact with the cutting blade20(supporting surface36e, seeFIG.2A) when the cutting blade20is fitted to the blade mount34. Similarly, the corrosion layers52(seeFIG.4) are preferably provided to a region other than a region that comes into contact with the cutting blade20(the back surface40bof the fixing nut40, seeFIG.2A) when the cutting blade20is fitted to the blade mount34. In this case, wear and peeling of the corrosion layers50and52due to contact between the corrosion layers50and52and the cutting blade20do not occur easily.

During the cutting processing, the cutting liquid is continuously supplied to the cutting blade20at a predetermined flow rate, and the cutting blade20, the blade mount34, and the fixing nut40are exposed to the cutting liquid. Here, the corrosion layers50and52are formed of a material having a higher ionization tendency than a material constituting the binder of the cutting edge24of the cutting blade20. Therefore, while the cutting liquid is supplied to the cutting blade20, the corrosion layers50and52corrode preferentially in place of the binder of the cutting edge24. Specifically, when pure water mixed with carbon dioxide or the like is supplied as the cutting liquid to the cutting blade20, metal ions are preferentially eluted from the corrosion layers50and52rather than from the binder of the cutting edge24, and the corrosion of the corrosion layers50and52progresses. As a result, a sacrificial corrosion protecting effect of suppressing the corrosion of the binder of the cutting edge24is produced by the corrosion of the corrosion layers50and52.

A concrete material of the corrosion layers50and52can be selected as appropriate according to the material of the binder of the cutting edge24. For example, in a case where the binder of the cutting edge24is formed by a nickel plating layer, a metal such as aluminum, or zinc having a higher ionization tendency than nickel can be used as the corrosion layers50and52. However, the binder of the cutting edge24and the corrosion layers50and52can also be formed by using a same material. For example, both the binder of the cutting edge24and the corrosion layers50and52may be formed by a nickel plating layer containing sulfur. In this case, the magnitude of ionization tendencies of the binder of the cutting edge24and the corrosion layers50and52is controlled by sulfur content. Specifically, the ionization tendency of the corrosion layers50and52can be made higher than the binder of the cutting edge24by making the content rate of sulfur in the corrosion layers50and52higher than the content rate of sulfur in the binder of the cutting edge24. Incidentally, in order to effectively activate sacrificial corrosion protection by ensuring a sufficient difference between the ionization tendencies of the binder of the cutting edge24and the corrosion layers50and52, the content rate of sulfur in the corrosion layers50and52is preferably set to be equal to or more than 1.2 times the content rate of sulfur in the binder of the cutting edge24. For example, the content rate of sulfur in the corrosion layers50and52is set to be equal to or more than 0.27% by mass and equal to or less than 0.33% by mass, and the content rate of sulfur in the binder of the cutting edge24is set to be equal to or more than 0.17% by mass and equal to or less than 0.22% by mass.

A method of forming the corrosion layers50and52can be selected as appropriate according to the material of the corrosion layers50and52. For example, in a case where a nickel plating layer containing sulfur is to be formed as the corrosion layers50and52, a plating tank retaining a plating solution is first prepared. An electrolytic solution including nickel (nickel sulfate, nickel chloride, nickel sulfamate, or the like) is used as the plating solution. In addition, an additive liquid that contains sulfur at a predetermined concentration is added to the plating solution. An added amount of the additive liquid is adjusted according to a target value of sulfur content of the corrosion layers50and52. Next, the blade mount34and the fixing nut40are immersed in the plating solution. At this time, masks covering regions other than regions on which to form the corrosion layers50and52are formed on the blade mount34and the fixing nut40. Then, a direct current is fed to the plating solution while the plating solution is stirred. Consequently, nickel is electrodeposited on the blade mount34and the fixing nut40, so that nickel plating layers (corrosion layers50and52) including a predetermined content of sulfur are formed.

Incidentally, only one of the blade mount34and the fixing nut40may be provided with a corrosion layer(s). Specifically, in a case where the corrosion layer50is provided to the blade mount34, the corrosion layers52can be omitted. Similarly, in a case where the corrosion layers52are provided to the fixing nut40, the corrosion layer50can be omitted.

As described above, in the cutting apparatus according to the present embodiment, one or both the blade mount34and the fixing nut40are provided with a corrosion layer(s) formed of a material having a higher ionization tendency than the material constituting the binder of the cutting edge24of the cutting blade20. Thus, when the cutting liquid is supplied to the cutting blade20, the corrosion layer(s) preferentially corrode(s) in a sacrificial manner, and suppress(es) corrosion of the cutting edge24of the cutting blade20.

Incidentally, the corrosion layers50and52may be provided so as to be embedded in the blade mount34and the fixing nut40. For example, an annular groove is formed on the back surface36bside of the flange portion36of the blade mount34so as to surround the opening portion34a. Then, the corrosion layer50is formed so as to fill the groove. Similarly, a plurality of arcuate grooves are formed on the front surface40aside of the fixing nut40so as to surround the opening portion40d. Then, the corrosion layers52are formed so as to fill the grooves. Thus, the peeling of the corrosion layers50and52does not occur easily.

In addition, instead of forming the corrosion layers50and52, the blade mount34and the fixing nut40themselves may be made to function as a sacrificial corrosion protecting member. Specifically, the blade mount34and the fixing nut40may be formed by a material having a higher ionization tendency than the material constituting the binder of the cutting edge24of the cutting blade20. It is thereby possible to omit a process of forming the corrosion layers50and52on the blade mount34and the fixing nut40. For example, the blade mount34is formed of a simple substance of a metal selected from iron, chromium, zinc, manganese, aluminum, and zirconium or an alloy including at least one of these metals. In addition, for example, the fixing nut40is formed of a simple substance of a metal selected from iron, chromium, zinc, manganese, titanium, and zirconium or an alloy including at least one of these metals.

Incidentally, only one of the blade mount34and the fixing nut40may be formed by a material having a higher ionization tendency than the material constituting the binder of the cutting edge24. In addition, the whole of each of the blade mount34and the fixing nut40may be formed by a material having a higher ionization tendency than the material constituting the binder of the cutting edge24, or only a partial region of each of the blade mount34and the fixing nut40may be formed by a material having a higher ionization tendency than the material constituting the binder of the cutting edge24.

Besides, structures, methods, and the like according to the foregoing embodiment can be modified and implemented as appropriate without departing from the objective scope of the present invention.