BACKGROUND OF THE INVENTION

[0001] The present invention relates to an electrode tool for electrochemical machining and a manufacturing method thereof, and more particularly, to an electrode tool for electrochemical machining and a manufacturing method in which a thin insulating film applied to the electrode tool is a physical vapor deposition resin.

[0002] In a typical fluid dynamic pressure bearing (not illustrated) , which may be used, for example, in a hard disk storage device, a rotation shaft, which includes a flange, is fitted in a hollow sleeve 1 in which a radial dynamic pressure groove Ia and a thrust dynamic pressure groove Ib are formed. The radial dynamic pressure groove Ia is formed on a surface that faces a radial direction, and the thrust dynamic pressure groove Ib is formed on a surface that faces an axial direction, such as a step formed in the sleeve 1. Lubricant oil fills the minute spaces between the external circumference of the rotation shaft and inner circumference of the sleeve 1.

[0003] Fig. 1 shows a conventional electrochemical machining process for simultaneously forming the radial and thrust dynamic pressure grooves Ia, Ib on the sleeve of such a fluid dynamic bearing. An electrode tool 2 for electrochemical machining is inserted into the sleeve 1 to perform the process. The electrode tool 2 has a small

diameter portion 2c and large diameter portion 2d, and the electrode tool 2 is raised and lowered together with a stopper 3, which is made of urethane resin.

[0004] A conductive pattern 2a that corresponds to the radial dynamic pressure grooves Ia is formed on the external surface of the small diameter portion 2c. A conductive pattern 2b that corresponds to the thrust dynamic pressure groove is formed on the shoulder between the small diameter portion 2c and the large diameter portion 2d.

[0005] The lower end of the stopper 3 is tightly pressed against the upper end of the sleeve 1 when the stopper is axially aligned with the sleeve 1. A flow path 5 of electrolyte 4 is formed by a space between the external surface of the electrode tool 2, the inner surface of the stopper 3 and the inner surface of the sleeve 1. The electrolyte 4, which is supplied from a port at the top of the stopper 3 as shown, is conducted through the flow path 5 and is discharged from the bottom of the sleeve 1.

[0006] While the electrolyte 4 is present between the sleeve 1 and the electrode tool 2, pulsed direct current is applied through the electrolyte 4 between the inner surface of the sleeve 1 and the surface of the conductive patterns 2a, 2b of the electrode tool 2 for a predetermined period of time. Surface locations of the inner surface of the sleeve 1 that directly face the conductive patterns are electrochemically dissolved, thus forming the radial dynamic pressure groove Ia and the thrust dynamic pressure groove Ib on the inner

surface of the sleeve 1. In general, the minimum groove width of the dynamic pressure grooves is 40μm to 50μm.

[0007] Similarly, as shown in Fig. 2, electrochemical machining that forms a thrust dynamic pressure groove 10a on a thrust plate 10 of a fluid dynamic pressure bearing is performed by pressing a stopper 12 against the thrust plate 10. An electrode tool 11, which includes a conductive pattern 11a, is axially aligned with the thrust plate 10 such that the conductive pattern 11a corresponds to the thrust dynamic pressure groove 10a.

[0008] In the case of Fig. 1 or Fig. 2, surfaces of the electrode tool 2, 11 that do not include the conductive patterns 2a, 2b, 11a should be completely insulated by a non-conductive resin, or the like. If insulation is missing from a given location, then stray current will leak from that location. If the insulation is not sufficient, or too thin, current will leak over a wide area, and surfaces other than the locations of the grooves will be electrochemically dissolved, and the pattern of the electrochemical machined dynamic pressure grooves will be distorted.

[0009] A conventional electrode tool for forming dynamic pressure grooves in electrochemical machining is manufactured by the steps shown in Figs. 3-6. First, an electrode substrate 30 is cut with a micro-end mill with a flute diameter of 0.1mm to 1..0mm, leaving a conductive pattern surface 31. Projections 32, which have a width of approximately 40μm to 200μm and a height of 0.1mm to 0.5mm are formed. Then, the electrode substrate 30 is placed in a disposable

insulation material mold 33, which is filled with insulation material 34 (thermosetting epoxy resin) . Then vacuum is applied to remove the air bubbles in the insulation material 34. Then, the insulation material is hardened by thermosetting. The disposable mold 33 is removed, and the excessive insulation material 34 is removed by rough processing. Next, finish grinding process is performed so that the conductive pattern surface 31 and the surface of the insulation material 35 are flush.

[0010] The conventional manufacturing method requires at least nine steps including disposal of the mold 33, resulting in relatively high manufacturing costs . The nine steps are essentially as follows : initial blank processing; annealing; pattern forming; insulation filling and vacuum application; insulation hardening; removal of mold; rough processing of insulating material; finishing process of insulation material; and a finishing process.

[0011] In addition, electrode tools manufactured according to this method have inadequate adhesion between the electrode substrate and the insulation material. Therefore, the boundary between the electrode substrate and the insulation material is corroded by the electrolyte and damaged, and the insulation material peels from the electrode material. Consequently, high precision cannot be maintained for an extended period. In addition, to secure adequate adhesion area between the electrode substrate and the insulation material, the depth of the groove between the projections cannot be

reduced, and a minimum depth of approximately 0.1mm to 0.5mm is required.

[0012] Furthermore, during the pattern machining process that forms the projections, in general, a micro-end mill with a flute diameter of approximately 0.1mm to 1.0mm is used. Since the groove width between the projections and the inner arc portion of the contour of the conductive pattern are required to be greater than the flute diameter of the micro-end mill, miniaturization of the conductive pattern is limited.

[0013] Along with the miniaturization of fluid bearings, the conductive pattern of the electrode tool that forms the dynamic pressure grooves is becoming more miniaturized, and there is a need to reduce the width of the projections. The ratio of projection height to width can be as high as 25. The projection can become so thin that bending can occur very easily during machining, which results in defects .

[0014] Furthermore, during the pattern machining process, micro-end mills with minute flute diameters are easily broken and have a short life due to milling resistance. Consequently, the feed rate of micro-end mill should be reduced. Therefore, the process is time consuming and requires great care.

[0015] To have sufficient tool rigidity required for the machining process, a commercial micro-end mill has a flute length equal to the flute diameter, and the tool shank diameter is greater than the flute diameter. Consequently, the end mill tool cannot cut deeper than the

flute diameter. Therefore, with the conventional manufacturing method of Fig. 3, the smaller the flute diameter of the micro-end mill, the smaller the allowable cutting depth. Thus, the projections cannot have a great projection length when the pattern is miniaturized, which reduces the adhesion area between the electrode substrate and the insulation material .

[0016] During thermal curing of the insulation, air bubbles and pin holes can occur. Consequently, there is a risk of defects in the finished products made by the electrode tool from stray current that leaks during the electrochemical machining.

[0017] In addition, Japanese unexamined patent application publication 2002-79425 discloses an electrode tool for electrochemical machining in which the insulation area is formed by a coating of insulation resin, and micro-particles of the resin are adhered and baked on the electrode substrate .

[0018] In addition^ it is known to place a resin sheet having holes for the conductive pattern on a substrate to form a conductive pattern. The sheet is fastened to the surface of the electrode substrate .

[0019] It is also known that by using a resin layer made by adhering micro-particles of resin and baking them on the surface of the substrate to form insulating material or by using a resin sheet with the designated pattern, the adhesion to the substrate can be significantly improved compared to the conventional resist film formation and resin filling. Also it is known to employ polyimide resin, which has good insulation properties, as the material for the

micro-particle resin. (See Japanese unexamined patent application 2002-79425) .

[0020] However, the adhesion of the insulation resin to the substrate is easily undermined, and the insulation coating peels from the substrate due to the effect of electrolyte that flows during the electrochemical machining process. Conventionally, the non-conductive resin material used for this type of insulation coating is often cured by ultraviolet light or heat, and, in general, it has a low adhesion to the conductive substrate of the electrode tool.

[0021] In addition, such electrochemical machining is performed with a small gap between the electrode tool and the surface being processed. Therefore, a large shear force due to the flow of the electrolyte is applied to the insulation coating. When peeling of the insulation coating occurs, an accurate processing pattern cannot be transferred to the surface being processed. In addition, the peeled insulation coating clogs the gap between the electrode tool and the surface being processed. Such clogging inhibits the flow of the electrolyte and causes defects in the shape of the part. Consequently, the yield of the final products is affected. In addition, in the worst case, the clogging may cause an electric short circuit, which damages both the electrode tool and the surface being processed.

[0022] To solve some of these problems, Japanese unexamined patent application publication 2003-340648 discloses an electrode tool for electrochemical machining in which a workpiece being processed and

an electrode with a conductive pattern on its surface are immersed in electrolyte while facing each other. The workpiece and the electrode tool are respectively connected to positive and negative electrodes of a power supply, and an electric current is applied. As a result, a concave area having a shape that corresponds to the conductive pattern on the electrode is formed on the surface of the workpiece, and an electro-deposited insulation coating is formed on areas other than the conductive pattern. By taking into account the withstand voltage during the electrochemical machining and the corrosion resistance against the electrolyte, an epoxy resin, a urethane resin or a polyimide resin are suitably used as the electro-deposited resin. By using an electro-deposition coating as the insulation coating to coat the areas other than the conductive portion on the surface of the electrode tool, the adhesion between the substrate and the insulation coating was improved. Further, it is difficult for the electrolyte to penetrate between the adhered surfaces, and damage such as peeling is limited. Consequently, the conductive pattern on the electrode tool surface can be maintained for an extended period.

[0023] In addition, it is known from Japanese unexamined patent application publication 2003-340648 to provide a coating made of a different non-conductive resin material on top of the electro-deposited insulation coating. The non-conductive resin material used in this case is not specifically limited; however, it is desirable to select the resin by taking into account the adherence

(affinity) with the electro-deposition coating formed. A polishing process or the like is applied to the substrate where the non-conductive resin material is formed to remove the non-conductive resin material and the electro-deposition coating from the conductive portion of the surface, to expose the conductive pattern. The result is an electrode tool with an even surface that includes a conductive portion and an area coated with insulation.

[0024] When the insulation is applied by electro-deposition, the thickness of the coating film is affected by the distribution of the concentration of the electro-deposition coating and the current density in the electro-deposition bath. Therefore, control of the thickness of the coating film is difficult. In addition, it is difficult to form a coating film with an even thickness at corners and with a minute conductive pattern. Consequently, parts of the insulation coating of the electrode tool may become thin, and the insulation performance may be inadequate. In addition, to reduce the impact on the environment, a large-scale waste water treatment facility is required.

[0025] There is additional representative prior art regarding electrode tools for electrochemical machining prepared in which a concave portion is formed on an area not corresponding to the dynamic pressure groove on a portion of the electrode tool that faces the workpiece. A non-conductive material is coated on the entire area that faces the workpiece. Then, the surface of the electrode portion

is exposed and is made flush with the surface of the non-conductive material (See Japanese Patent 3339792) .

[0026] In a method for the electrochemical machining of a dynamic pressure groove using such an electrode tool, the electrochemical machining is carried out while the surface of the exposed electrode portion is even with the surface of the non-conductive material. Therefore, even if the gap between the workpiece and the electrode tool is narrowed to improve precision, there is no accumulation of the electrochemical product generated due to the process or heated electrolyte, and desirable electrolysis conditions are maintained. At the same time, there is no clogging by peelings of the non-conductive material generated by the collision of the electrochemical products against the non-conductive material . Thus, a reduction of the electrolyte flow speed is prevented, which prevents a reduction of the electric current density. Consequently, the smoothness of the processed surface of the workpiece is improved and the electrochemical machining speed is increased.

[0027] In addition, in the method of Japanese Patent 3339792, the concave portions are formed by etching or cutting, and the entire surface that faces the workpiece is coated by a non-conductive material such as an epoxy, using printing or the like. Then the electrode portion is exposed by polishing, so that the exposed electrode exposure portion and the surface of the non-conductive material coated on the concave portion become flush, or even.

[0028] However, when applying epoxy resin or the like by printing, the adhesion between the electrode substrate and the epoxy resin is not adequate. Therefore, the boundary between the electrode substrate and the non-conductive material is corroded by the electrolyte and damaged, and the insulation material peels from the electrode material. Consequently, high precision cannot be maintained for an extended period.

[0029] With a conventional coating method in which a polyamide acid solution is coated on the electrode substrate and converted to polyimide by heating, the resulting insulation film is not uniform in thickness, as shown in Fig. 7. As shown in Fig. 7, the insulation film 76 tends to be relatively thin at the outer corners 74 of the projections 70 and relatively thick at the inner corners 75 of the projections 70.

[0030] In addition, with the conventional electro-deposition coating method, the amount of material electro-deposited as a coating on the electrode substrate surface depends on the distribution of the concentration of the solution (aqueous electro-deposition coating) and the electric current density. Therefore, defects similar to those shown in Fig. 7 may occur. Furthermore, as shown in Fig. 8, in the case of a minute conductive pattern where the distance between the projections is narrowed to a few tens of micrometers (μm) , it may not be possible to make the electro-deposition coating 79 normal on the lateral surface of the projections 77 or the bottom surface 78, between the projections 77.

[0031] When the film is thin in some locations or abnormally formed, insulation defects will occur during a subsequent finishing process, and current may leak during the electrochemical processing due to non-uniform insulation, and areas of the workpiece other than the desired area may be dissolved. Consequently, the dynamic pressure groove will be distorted, or abnormal.

BRIEF SUMMARY OF THE INVENTION

[0032] It is an object of the invention to provide an electrode tool for electrochemical machining and a manufacturing method for the same in which a very high adhesion exists between the insulation material and the electrode substrate such that electrolyte is limited from penetrating between the insulation material and the electrode substrate even after an extended period. This maintains high precision for an extended period. Such a method is relatively simple and does not require an insulation mold.

[0033] The invention includes an electrode tool for electrochemical machining. The electrode tool includes a work surface, which faces a workpiece during a electrochemical machining process. The electrode tool further includes the following: a conductive pattern formed on the work surface by an exposed conductive substrate, wherein the conductive pattern corresponds to a desired groove pattern that is to be electrochemically machined on a workpiece with the electrode tool; a thin insulating film that is a vapor deposition polymerization resin or vapor deposition resin, wherein the thin insulating film is applied on the work surface of the electrode substrate other than the location of the conductive pattern.

[0034] In another aspect of the invention, the surface of the conductive pattern and the surface of the thin insulating film are flush.

[0035] In another aspect of the invention, the conductive pattern is formed by at least one projection, which is formed in the substrate.

[0036] In another aspect of the invention, the height of the projection is 5μm to 50μm.

[0037] In another aspect of the invention, the thickness of the thin insulating film is 5μm to 50μm.

[0038] In another aspect of the invention, the thin insulating film is selected from the group consisting of a vapor deposition polymerized polyimide resin, a vapor deposited perfluoroalkoxy-tetrafluoroethylene copolymer (PFA) , and a vapor deposited tetrafluoroethylene-hexafluoropropylene copolymer (FEP) .

[0039] In another aspect of the invention, the electrode substrate of the electrode tool is selected from the group consisting of copper, brass, phosphor bronze, an iron-copper alloy, stainless steel, tungsten, titanium alloy, copper tungsten alloy and a cobalt alloy.

[0040] The invention further includes a method of manufacturing an electrode tool. The method includes the following: removing a portion of the surface of an electrode substrate to create a proj ection in a work surface of the electrode substrate, wherein the work surface faces a workpiece during an electrochemical machining process; forming a uniform, insulating film with a thickness of 5μm to 50μm by vapor deposition or vapor deposition polymerization, which are physical vapor deposition methods, so that the work surface, including the projection, is coated with the insulating film; and removing the

insulating film from an outer end of the projection to form a conductive pattern that is surrounded by the insulation film. [0041] In another aspect of the invention, the removing of the insulation film is performed by grinding or etching. [0042] In another aspect of the invention, during the grinding or etching, the surface of the conductive pattern and the surface of the insulating film are made flush with one another. [0043] In another aspect of the invention, the projection is formed by etching.

[0044] In another aspect of the invention, the projection is formed by a method selected from the group consisting of a cutting removal process, a laser removal process, and a precision blast removal process .

BRIEF DESCRIPTION OF THE DRAWINGS

[0045] The accompanying figures, in which like reference numerals refer to identical or functionally similar elements throughout the separate views and which, together with the detailed description below, are incorporated in and form part of the specification, serve to further illustrate various embodiments and to explain various principles and advantages all in accordance with the present invention.

[0046] FIG. 1 is a diagrammatic partial cross sectional view of a conventional method of electrochemical machining dynamic pressure grooves on a bearing sleeve;

[0047] FIG. 2 is a diagrammatic partial cross sectional view of a conventional method of electrochemical machining dynamic pressure grooves on a thrust plate;

[0048] FIG. 3 is a diagrammatic view of a first stage in a conventional method of making an electrode tool;

[0049] FIG. 4 is a diagrammatic cross sectional view of a second stage in a conventional method of making an electrode tool ;

[0050] FIG. 5 is a diagrammatic cross sectional view of a third stage in a conventional method of making an electrode tool;

[0051] FIG. 6 is a diagrammatic cross sectional view of a fourth stage in a conventional method of making an electrode tool;

[0052] FIG. 7 is a cross sectional diagram of a conventionally formed insulation layer, which was formed by electro-deposition;

[0053] FIG. 8 is a cross sectional diagram of a conventionally formed insulation layer, which was formed by electro-deposition,-

[0054] FIG. 9 is a diagrammatic cross sectional view of a vapor deposition polymerization chamber, or reaction chamber;

[0055] FIG. 10 is a cross sectional diagram of an insulation layer formed by the method of the present invention;

[0056] FIG. 11 is a diagram of the chemical structure of a polyimide coating of the present invention;

[0057] FIG. 12 is a diagram of the chemical structure of a PFA

(perfluoroalkoxy-tetrafluoroethylene copolymer) coating of the present invention;

[0058] FIG. 13 is a diagram of the chemical structure of a FEP

(tetrafluoroethylene-hexafluoropropylene copolymer) coating of the present invention;

[0059] FIG. 14 is a table showing characteristics of various coating materials;

[0060] FIG. 15 is a table showing examples of carboxylic acid monomers that can be used in a vapor deposition polymerization process to produce a polyimide insulation layer;

[0061] FIG. 16 is a table of examples of diamine monomers that can be used in a vapor deposition polymerization process to produce a polyimide insulation layer;

[0062] FIG. 17 is a diagrammatic perspective view of an electrode tool for forming both radial and thrust groove patterns;

[0063] FIG. 18 is a diagrammatic perspective view showing an electrode tool for forming thrust groove patterns; [0064] FIG. 19 is a diagrammatic view of a first stage in a method of making an electrode tool;

[0065] FIG. 20 is a diagrammatic cross sectional view of a second stage in a method of making an electrode tool;

[0066] FIG. 21 is a diagrammatic cross sectional view of a third stage in a method of making an electrode tool;

[0067] FIG. 22 is a diagrammatic view of a first stage in a method of making an electrode tool ;

[0068] FIG. 23 is a diagrammatic cross sectional view of a second stage in a method of making an electrode tool;

[0069] FIG. 24 is a diagrammatic cross sectional view of a third stage in a method of making an electrode tool ;

[0070] FIG. 25 is a flow chart of a method of forming an electrode tool according to the present invention;

[0071] FIG. 26 is a photograph of a cross section of an electrode tool made according to Example 1;

[0072] FIG. 27 is a photograph of an end surface of the electrode tool formed in accordance with Example 1 ;

[0073] FIG. 28 is a scanning electron microscopic photograph of the electrode tool of Fig. 28; and

[0074] FIG. 29 is a side view photograph of the electrode tool of Example 2.

DETAILED DESCRIPTION OF THE INVENTION

[0075] Fig. 9 shows an exemplary diagram of apparatus for performing vapor deposition polymerization of a polyimide resin in a vacuum reactor 63. Although not illustrated, a vacuum pump is connected to the interior of the vacuum reactor to apply a vacuum to the interior of the vacuum reactor so that the vapor deposition polymerization is performed under a pressure that is lower than atmospheric pressure.

[0076] Fig. 9 shows a method in which vaporized carboxylic acid anhydrate monomer 61 and vaporized diamine monomer 62 are introduced from a first inlet 66 and a second inlet 67, respectively. The vapor phase carboxylic acid anhydrate monomer 61 and diamine monomer 62 are separately introduced to the vacuum reactor 63 at a temperature of approximately 200 ⁰ C. An electrode substrate 60, which is a substrate of an electrode tool, is stationed within the vacuum reactor 63. Then, polymerization is performed under the vapor phase condition so that a thin film 64 of polyimide acid is evenly formed with a desired thickness on the surface of the electrode substrate 60. Un-reacted monomer 65 is exhausted from the outlet 68 to the outside of the reactor 63. The thickness of the film 64 is determined by the polymerization reaction time, allowing easy control of the film thickness.

[0077] The details of vapor deposition polymerization are known to skilled artisans and are thus not described in detail. Basically,

when the monomer gases enter the vacuum reactor 63 , they mix with each other by diffusion and form a uniform atmosphere. The gasses are supplied until the pressure inside the reactor 63 is equal to the vapor pressure of the monomers . The monomers react in a gaseous phase resulting in a dimer or a trimer, which are intermediate materials in the polymerization. The dimer or trimer has a lower vapor pressure than the monomers. Consequently, when the reaction occurs near the work piece, the dimer or trimer is deposited on the surface of the workpiece (the substrate, or tool) in a thin layer. The deposited dimer or trimer continues to react until it is transformed into a polymer (polyamide acid) . The conditions inside the reactor chamber, such as temperature and pressure, are controlled to produce the desired deposition polymerization.

[0078] There are many combinations of possible monomers and resulting polymers. For example, one monomer can be a carboxylic anhydride monomer such as pyromellitic dianhydride (PMDA) , and the other monomer can be a diamine monomer such as 4 , 4 ^■ -oxydianiline

(ODA) .

[0079] Next, the electrode substrate 60 and the thin film 64 are heated at approximately 300 ⁰ C to promote dehydration and to convert the polyamide acid to polyimide. The resulting polyimide film has superior insulation performance and very strongly adheres to the electrode substrate 60. The resulting polymer film is a nanostructure thin film. Therefore the thin polyimide film is strong and has no pinholes. The dehydration and conversion to polyimide can

be performed in the vacuum reactor chamber 63 or it can be performed in a separate location after the substrate 60 is removed from the chamber 63.

[0080] The thin insulating film 71 produced by the vapor deposition polymerization of the present invention, which is a physical vapor deposition, is, as shown in Fig. 10, formed uniformly with the desired thickness even at the outer corners 74 and the inner corners 75 of the miniaturized conductive pattern. Therefore, the electrode substrate 60 is properly insulated, which results in a precise electrode tool that forms highly precise dynamic pressure grooves.

[0081] Alternatively, the insulation resin such as PFA or FEP can be applied by, for example, vapor deposition assisted by an energetic beam, which is also a physical vapor deposition process. This type of vapor deposition is known and thus will not be described in detail . Basically, in such vapor deposition of PFA or FEP coating, a monomer such as an acrylate monomer is evaporated in a vacuum chamber in which the substrate is located, and the vapor phase is subjected to an irradiation of electron beam, plasma beam, ultraviolet ray or the like to facilitate the polymerization on the electrode substrate . Then, the polymer is deposited on the substrate in a thin, uniform layer.

[0082] Unlike vapor deposition polymerization of polyimide, where two different monomers are evaporated, only one monomer is evaporated in physical vapor deposition of FEP or PFA. In the vapor deposition process of PFA or FEP, the monomer which will become the polymer to

be applied is vaporized by heating in a chamber in which the substrate is located. The conditions of temperature and energetic beam irradiation inside the chamber are controlled such that the vaporized monomer is deposited on the substrate at a desired rate. [0083] After the vapor deposition of PFA or FEP, no dehydration is required, in contrast to the vapor deposition polymerization process of polyimide as described above.

[0084] The insulation resin used in the present invention can be any insulation resin material as long as the material has a high chemical resistance against the electrolyte, which can be NaNO ₃ (sodium nitrate) , for example, a high volume resistivity, a superior adhesiveness to the electrode substrate and is depositable either by vapor deposition or vapor deposition polymerization. The material can be selected from polymerized polyimide resins, which are formed by vapor deposition polymerization. Alternatively, if vapor deposition is used, the material can be selected from perfluoroalkoxy-tetrafluoroethylene (PFA) and tetrafluoroethylene-hexafluoropropylene copolymer (FEP) copolymers .

[0085] It is preferable that the thin insulating film 71 is a material that tolerates continuous duty at a temperature of 200 ⁰ C, is not affected by the electrolyte, demonstrates a high volume resistivity, and fails to conduct current during the electrochemical machining process. Any resin material that satisfies these requirements is acceptable, and a polyimide resin, a PFA resin

(perfluoroalkoxy-tetrafluoroethylene copolymer) , or an FEP resin (tetrafluoroethylene-hexafluoropropylene copolymer) are suitable vapor deposition polymerization or physical vapor deposition resins for this purpose. The structures of these three materials are shown in Figs. 11, 12 and 13, respectively. The table of Fig. 14 shows some characteristics of these three materials. The symbols R and R ¹ in Fig. 11 represent alkyl groups. Similarly, the symbol Rf in Fig. 12 represents an fluoroalkyl group.

[0086] The carboxylic acid monomers shown in the table of Fig. 15 are examples of monomers that can be used in a vapor deposition polymerization process to form the polyimide resin in the present invention. The materials shown in Fig. 15 include tetracarboxylic acid anhydrate, polyisocyanate compounds and halogenated carboxylic acid. In particular, tetracarboxylic acid anhydrate can be suitably employed.

[0087] The diamine monomers shown in the table of Fig. 16 are further examples of monomers that can be used in a vapor deposition polymerization process to form the polyimide resin in the present invention.

[0088] Representative electrode tools of the present invention are an electrode tool for a sleeve with the shape shown in Fig. 17 and an electrode tool for a thrust plate with the shape shown in Fig. 18. A manufacturing method for these electrode tools is shown schematically in Figs. 19-21. Figs. 19-21 illustrate a series of stages in chronological order.

[0089] As shown in Fig. 19, projections 70, which have a predetermined height, are provided on the surface of an electrode substrate 60 made of, for example, blanked copper, brass, phosphor bronze, stainless steel, tungsten, titanium alloy, copper tungsten alloy, or cobalt alloy. Other suitable materials for the electrode substrate 60 are copper alloys or iron alloys. Suitable examples of copper alloys are brass and phosphor bronze. Suitable examples of iron alloys are iron-copper alloy or stainless steel. (SUS303, 304, or the like) .

[0090] A conductive pattern is formed by removing a portion of the surface of the electrode substrate 60 using a chemical removal method or a mechanical removal method. In other words, the projections are formed by chemical means or by mechanical means. [0091] An insulating thin film 71, which has a predetermined uniform thickness, is evenly formed by vapor deposition polymerization or physical vapor deposition on at least the surface of the electrode substrate 60 where a conductive pattern is formed. The insulating thin film 71 is polymerization resin or a vapor deposition resin. It is desirable that the thickness of the insulating thin film 71 is 5μm to 50μm. When the thickness of the insulating thin film 71 is less than 5μm, the insulation capability is insufficient, and the processing precision of the resulting tool is reduced due to current leakage. When the thickness of the insulating thin film 71 exceeds 50μm, the thin film formation by vapor deposition polymerization or vapor deposition is difficult, and the

formation time of the insulating thin film 71 is excessive. Therefore, the process is not cost-efficient.

[0092] It is desirable that the finished electrode have a flat or approximately flat surface. This is accomplished by grinding or etching. The finished height of the projections is 5μm to 50μm. Therefore, the initial length of the projections can be slightly greater than the finished height to account for material that is removed in the finishing process. Examples of methods to remove a portion of the surface of the electrode substrate 60 include the following: grinding; micro-end milling; laser processing; etching; and precision blasting.

[0093] The insulating thin film 71 that coats the upper end surfaces of the projections 70 is removed by the finishing process. Thus, and the electrode substrate is exposed at the distal end surfaces of the projections 70, which results in a conductive pattern.

[0094] It is acceptable for the surface 72 of the conductive pattern where the electrode substrate is exposed, as shown in Fig. 21, to be higher than a surface 73 of the thin insulating film 71 that coats an area between parts of the conductive pattern.

[0095] Figs. 22-24 show an alternative method of forming a conductive pattern on an electrode tool in a series of chronological stages. Note that in Fig. 23, unlike Fig. 20, the thickness of the insulation film 71 is greater than the height of the projections 70. As shown in Fig. 24, the finishing can be performed such that the insulation on the surface of the conductive pattern has a planar outer

surface 73, which is flush, or even, with the surface 72 of the conductive pattern.

[0096] Slightly removing not only material at the top, or outer, surface of the projections 70 but also material at the outer surface 73 of the insulating thin film 71 results in a smooth, flush finished surface. Alternatively, a flush surface finish can be accomplished by removing only the insulation that covers the outer ends of the projections 70 in Fig. 22.

[0097] Fig. 25 illustrates the manufacturing processes of the electrode tool of the present invention. The method of the present invention requires only five processes. In comparison, the prior art method requires nine processes.

[0098] Some of the advantages of present invention are as follows: The entire substrate can be coated with an insulating thin film so that a filling process for the insulation resin is not required. Therefore, rough processing for removing the insulation resin can be omitted, and a filling tool is not required.

[0099] The manufacturing of the electrode tool is more efficient compared with the prior art. Therefore, manufacturing time and cost are reduced .

[0100] By evenly forming an insulating thin film on the electrode v

' I substrate surface using vapor deposition or vapor deposition polymerization, the generation of air bubbles or pin holes during the thermosetting of the insulation resin is avoided. Therefore, the flow of stray current (current leakage) during electrochemical

machining is prevented. Consequently, the quality of the dynamic pressure groove processed by the electrode tool is improved. [0101] The adhesion of the insulating thin film is improved. Therefore, the insulating thin film resists peeling even if the projections are relatively short. Consequently, the life of the electrode tool is longer compared to the prior art. [0102] The height of the projections 70 of the electrode tool is only 50μm or less. Therefore, a minute conductive pattern can be formed using a variety of processing methods.

[0103] The electrode tool is not limited to the shapes shown in Figs. 17 and 18. Any shape is acceptable, as long as the tool includes a conductive pattern formed by exposing the end surfaces of projections 70 and an insulating thin film 71 with a thickness of 5μm to 50μm, which is made of a vapor deposition polymerization resin or a vapor deposition resin. The insulation layer coats areas of the electrode substrate that do not form the conductive pattern. In addition, the electrode tool of present invention can be used for forming a dynamic pressure groove on any bearing member and not only the sleeve or thrust plate. For example, the tool can form a groove on the external circumference of a rotation shaft or the edge of a flange portion of a rotation shaft.

EXAMPLE 1

[0104] An electrode tool 40 for a thrust plate with the shape shown in Fig. 18 was manufactured in accordance with the procedure shown

in the series of stages of Figs. 19-21. Copper was used for the electrode substrate 60. The material was blank processed, and a multiplicity of projections 70 with a height of 30μm and a minimum width of 30μm were formed one end surface 41 of a substrate 60 of the tool 40 using a micro-end mill with a flute diameter of 0.04mm to 0.5mm. The projections 70 were formed in a herring bone-shaped pattern as shown in Fig. 18. The electrode substrate 60, where the conductive pattern was formed, was placed in the vacuum reactor 63 of Fig. 9. A combination of tetracarboxylic acid anhydrate and aromatic diamine were selected as the monomers, and the temperature inside the vacuum reactor 63 was set to be 200 ⁰ C. Vaporized monomers were supplied from the feeding inlets 67 and 66 into the reactor 63. The monomers were polymerized in the vapor phase to form polyamide acid polymer 64, which uniformly adhered to the surface of the electrode substrate 60. The un-reacted monomers were exhausted from the exhaust outlet 65. The reaction continued until the desired thickness of polyamide acid polymer 64 was applied. After the desired thickness of polyamide acid polymer 64 was formed on the surface of the electrode substrate 60, the electrode substrate 60 was removed from inside the vacuum reactor 63 and heated at approximately 300 ⁰ C. The polyamide acid polymer 64 was dehydrated so that it was converted to polyimide.

[0105] As shown schematically in Figs. 19-21, a thin insulating film 71 made of polyimide was evenly formed with a film thickness of 7μm. Fig. 26 is a magnified cross-sectional photo that shows the

condition of the insulating thin film 71 that was formed on the surface of the electrode substrate 60. It was found that a thin insulating film 71 made of polyimide was formed with an even, or uniform, thickness, even at the inner and outer corners.

[0106] Next, at the end surfaces of the projections that were coated with the thin insulating film 71, 20μm of insulation material was removed by grinding, which resulted in and a conductive pattern being formed by exposing the end surfaces 72; that is, by exposing the electrode substrate 60. Thus, the resulting electrode tool 40 for a thrust plate had projections with a height of 17μm and an insulating film with a thickness of 7μm. Fig. 27 shows end surfaces of the projections of the electrode tool 40 of this example. [0107] Fig. 28 is a magnified scanning electron microscopic photo of a portion of the same end surface shown in Fig. 27. In Fig. 28, the surface of the insulating thin film is black and the metal surface of the conductive pattern is white. Fig.28 shows that the conductive pattern was clearly formed and the insulating film was evenly formed without pinholes .

EXAMPLE 2

[0108] In this example, an electrode tool for a sleeve 50 with the shape shown in Fig. 17 was manufactured. Copper was used as the material for the electrode substrate 60. The following method was employed: A small-diameter member 51 and a large-diameter member 52 of the electrode tool 50 in Fig. 17 were processed as separate members,

and projections were formed on each blank, or workpiece, using a micro-end mill. Then the small-diameter member 51 and the large-diameter member 52 were assembled to make a unit . Essentially, the procedures shown in Figs. 20-22 were performed to form the conductive pattern.

[0109] For the small diameter member 51, a cylindrical blank was processed, and a plurality of projections 53 with a height of 50μm and a minimum width of 50μm were formed on the outer surface 51a using a micro-end mill with a flute diameter of 0.2mm to 0.7mm. The projections 53 had a herring bone-shaped pattern that corresponds to a desired radial dynamic pressure groove for a bearing sleeve.

[0110] Similarly, for the large-diameter member, a cylindrical blank that had a center hole on the end surface 52b was processed, and a plurality of projections 54 with a height of 30μm, and a minimum width of 30μm were formed on an end surface, outward of the center hole, using a micro-end mill with a flute diameter of 0.04mm to 0.5mm. A herring bone-shaped pattern that corresponds to the desired thrust dynamic pressure groove of the sleeve was formed. Next, the small diameter member was press fitted in the center hole of the large diameter member to make an electrode substrate 60.

[0111] As shown in Fig. 10, an insulating thin film 71 made of polyimide was evenly formed with a film thickness of lOμm by applying the same vapor deposition polymerization process of Example 1. A grinding process, using a cylindrical grinder, was performed to remove 20μm of the top surface of the projections 53 of the small diameter

portion 51 and 10μm of the top surface of the projections 54 of the large diameter portion 52 , which were coated by the insulation coating 71. An electrode tool 50 resulted in which a conductive pattern was formed by exposing the electrode substrate 60. The small diameter portion 51 was finished so that it was concentric with the large diameter portion 52. Fig. 29 is a side view photograph of the electrode tool 50 of this example.

EXAMPLE 3

[0112] In the third example, the electrode tool of Fig. 17 was manufactured in the manner of Figs. 22-24.

[0113] Brass, which is a copper alloy, was used for the electrode substrate 60. As with Example 2, a plurality of projections 53 and 52, which had a height of 20μm were formed on the electrode substrate 60, which is a combination of a small diameter member 51 and large diameter member 52. As shown in Fig. 23, a thin insulating film 71 made of polyimide was evenly formed with a film thickness of 20μm applying the same vapor deposition polymerization process of Example 1.

[0114] Etching was performed to remove only the insulating thin film 71 that coated the distal end surfaces 72 of the projections in Fig. 24 to expose the electrode substrate 60. Thus a conductive pattern was formed so that the outer surface 73 of the insulating thin film 71 and the outer surface 72 of the conductive pattern were

flush; that is, the outer surface 73 of the insulation and the outer surface 72 of the conductive pattern were on the same surface. [0115] This disclosure is intended to explain how to fashion and use various embodiments in accordance with the invention rather than to limit the true, intended, and fair scope and spirit thereof. The invention is defined solely by the appended claims, as they may be amended during the pendency of this application for patent, and all equivalents thereof. The foregoing description is not intended to be exhaustive or to limit the invention to the precise form disclosed. Modifications or variations are possible in light of the above teachings. The embodiments were chosen and described to provide the best illustration of the principles of the invention and its practical application, and to enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims, as may be amended during the pendency of this application for patent, and all equivalents thereof, when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.