WO2006107382A2

WO2006107382A2 - Electrode tool and method of manufacturing same

Info

Publication number: WO2006107382A2
Application number: PCT/US2006/003488
Authority: WO
Inventors: Akio Okamiya; Motonori Usui; Masanori Nedate
Original assignee: Minebea Co., Ltd.
Priority date: 2005-03-31
Filing date: 2006-02-02
Publication date: 2006-10-12
Also published as: JP2006281333A; CN102017236A

Abstract

A method of manufacturing an electrode too increase the precision and quality of the tool's conductive pattern, consequently improves the quality of processed grove pattern, improves the tool life, and reduces the number of manufacturing processes compared to conventional electrode tool manufacturing methods. More specifically, an electrode blank is provided (28), and a thin film insulating resin coating (32) is applied to a processing surface of the electrode blank (28) by vapor deposition or vapor deposition polymerization. The thin film insulating resin coating is then easily removed from portions (36) of the processing surface of the electrode blank by a process such as etching to thereby form a predetermined conductive pattern surface portion without the need for time consuming and expensive deep carving machining and additional processing.

Description

ELECTRODE TOOL AND METHOD OF MANUFACTURING SAME

BACKGROUND OF THE INVENTION

[0001] The present invention relates to electrochemical machining (ECM) , and more specifically to an ECM electrode tool that is formed by coating an electrode blank with a thin film insulating layer and then removing only portions of the thin film insulating layer corresponding to a predetermined tool conductive pattern to thereby form the predetermined tool conductive pattern.

[0002] A conventional electrochemical machining (ECM) tool typically includes machining electrodes that are used to form a specific groove pattern on a workpiece, such as a pattern of dynamic pressure grooves on a hydrodynamic bearing for use in a hard disk storage device. More specifically, in such a bearing, a rotation shaft, which includes a flange, is fitted in a hollow sleeve in which radial and thrust dynamic pressure grooves are formed. The radial dynamic pressure groove is formed on a surface that is oriented in a radial sleeve direction, and the thrust dynamic pressure groove is formed on a surface, such as that of a step formed in the sleeve, that is oriented in an axial sleeve direction. Lubricant oil fills the minute spaces between the external circumference of the rotation shaft and inner circumference of the sleeve.

[0003] Referring to FIG.1, a conventional ECM process is known for simultaneously forming radial and thrust dynamic pressure grooves, such as the radial and thrust dynamic pressure grooves Ia, Ib, on the sleeve of such a fluid dynamic bearing. An ECM electrode tool (electrode tool) 2 is inserted from the large diameter side into the inner diameter of the sleeve 1. The electrode tool 2 has small and large diameter portions 2c, 2d and is raised and lowered together with a urethane resin stopper 3.

[0004] On the external surface of the small diameter portion

.2c, a tool conductive pattern 2a that corresponds to and forms the radial dynamic pressure groove Ia is formed. On the shoulder

•between the small diameter portion 2c and the large diameter portion

,2d, a tool conductive pattern 2b that corresponds to and forms the thrust dynamic pressure groove Ib is formed.

[0005] The lower end of the stopper 3 is tightly pressed against the upper end of the sleeve 1 when the stopper 3 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 is supplied from the top of the stopper 3 , flows 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 surfaces of the tool conductive patterns 2a, 2b of the electrode tool 2 for a designated period of time. Only the surface locations of the inner surface of the sleeve 1 that face the exposed tool conductive patterns 2a, 2b are electrochemically dissolved to form the radial dynamic pressure groove Ia and the thrust dynamic pressure groove Ib on the inner surface of the sleeve 1. Generally, the minimum width of the dynamic pressure grooves is 40μm to 50μm.

[0007] As shown in PIG. 2, ECM formation of a thrust dynamic pressure groove 10a on a thrust plate 10 of a fluid dynamic pressure bearing can be similarly performed by pressing a stopper 12 against the thrust plate 10. An electrode tool 11, which includes a tool conductive pattern 11a, is axially aligned with the thrust plate 10 such that the tool conductive pattern lla corresponds to a location on the thrust plate 10 at which the thrust dynamic pressure groove 10a is formed.

[0008] The aforementioned tool conductive patterns on the conventional ECM tool are defined by machining electrodes. These electrodes are typically formed by providing an electrode blank and then deep carving the electrode blank using a micro end mill to form the electrodes as protruding portions in the desired groove patterns. The resulting carved electrode blank is then placed in a jig, and the jig is filled with an insulating resin. Once the j ig is filled with the resin and the carved electrode blank is covered by the resin, a vacuum is created to remove bubbles from the insulating resin. A thermosetting procedure is then performed to cure the resin. After the resin is cured, the jig is removed, and excess insulating resin is removed through rough processing. Subsequently, the groove pattern surface is exposed by grinding processing to complete the manufacturing process.

[0009] However, the aforementioned manufacturing process used to form the machining electrodes has certain associated limitations . Specifically, the micro end mill required for the deep carving of the electrode blank to form the electrodes must have a flute diameter of 1.0 mm or less. Therefore, the requisite processing time is great due to the small size of the flute diameter. In addition, the micro end mill is prone to fracturing due to its small diameter and therefore has an extremely short associated tool life. Such limitations result in high costs for both electrode tool manufacturing and for ECM processes using such tools. Also, although current applications require smaller and more precise groove patterns, there are limitations as to the extent that the flute diameter can be decreased.

[0010] Further, manufacturing cost and time are increased due to the need to remove the excess insulating resin subsequent to the resin mold being removed. In addition, as the ratio of the electrode blank machining depth to the protruding portion width may be as high as 25:1, the protruding portions become too thin. As a result, the protruding portions have a tendency to collapse, and/or machining burrs are formed, thereby resulting in poor conductive pattern quality.

[0011] Also, the thermosetting of the insulating resin may result in the formation of bubbles and pinholes in the resin, thereby resulting in workpiece defects due to stray current during the electrochemical machining of the dynamic pressure grooves in the workpiece. Finally, due to the number of steps required in the manufacture of the electrode tool, prompt implementation of conductive pattern design changes becomes problematic. SUMMARY OF THE INVENTION

[0012] To overcome the above limitations, the present invention provides a method of manufacturing an electrode tool that increases the precision and quality of the tool conductive pattern and that reduces the number of manufacturing processes by- eliminating time consuming processes such as deep carving, resin filling and thermosetting, and removing excess resin.

[0013] More specifically, according to the electrode tool manufacturing method of the present invention, an electrode blank is provided, and a thin film insulating coating formed from an insulating resin is applied to a processing surface of the electrode blank by vapor deposition or vapor deposition polymerization. The thin film insulating coating is then removed from portions of the processing surface of the electrode blank by a process such as etching to thereby form a predetermined conductive pattern surface portion without the need for time consuming and expensive deep carving machining prior to application of the insulating resin.

[0014] According to various other more specific aspects of the present invention, the thin film insulating coating may be removed from portions of the process surface of the electrode blank so as to form a conductive pattern to process a dynamic pressure groove pattern of a hydrodynamic bearing. Also, a top metal coating capable of imparting better mechanical, electrical and/or chemical characteristics such as, for example, better electrical conductivity, better standard electrical potential, resistance to corrosion due to electrolyte exposure, and improved hardness and wear resistance, to the electrode blank may then be applied to the conductive pattern after the thin film insulating coating has been removed from portions of the process surface of the electrode blank. Further, one or more layers of metal coating similarly capable of - imparting better mechanical, electrical and/or chemical characteristics to the electrode blank, and/or to improve the adherence of top metal coating to the electrode blank, may be applied to the conductive pattern prior to the application of the top metal coating to the conductive pattern.

[0015] The thin film insulating coating preferably has a thickness in a range of approximately 5μm - 50μm, and the top metal coating has a thickness less than or equal to that of the thin film insulating coating. If more than one metal coating is applied, the total thickness of the metal coatings is then less than or equal to that of the thin film insulating coating.

[0016] According to another aspect of the present invention, an electrode tool includes an electrode blank formed from a conductive material and including a process surface. A vapor deposition or vapor deposition polymerization thin film insulating resin coating covers the process surface except for portions of the process surface that define a conductive pattern. The conductive pattern is recessed relative to the thin film insulating coating. A top metal coating capable of imparting better mechanical, electrical and/or chemical characteristics to the electrode blank may be included to cover the conductive pattern. One or more metal coatings also similarly capable of imparting better mechanical, electrical and/or chemical characteristics to the electrode blank, and/or of improving the adherence of top metal coating to the electrode blank, may be located between the conductive pattern and the top metal coating. The combined thickness of the top metal coating and all other metal coatings is less than or equal to that of the thin film insulating coating.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] 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.

[0018] FIG. 1 is a diagrammatic partial cross sectional view of a conventional method of electrochemical machining dynamic pressure grooves on a bearing sleeve;

[0019] FIG. 2 is a diagrammatic partial cross sectional view of a conventional method of electrochemical machining dynamic pressure grooves on a thrust plate,-

[0020] Figs. 3A-3D are successive cross-sectional views illustrating a method of manufacturing an electrode tool in accordance with a first preferred embodiment of the present invention;

[0021] FIG. 4 is a table listing the properties of a thin film insulation layer that is applied during the method of manufacturing described in FIGs. 3A-3D;

[0022] FIG. 5 is an enlarged photograph of a portion of an electrode tool conductive pattern formed by the method illustrated in FIGs. 3A-3D without an applied metal coating,- [0023] Fig. 6 is a perspective view of a sleeve electrode tool with a resulting conductive pattern formed by the method illustrated in FIGs. 3A-3D;

[0024] FIG.7A is a perspective view of a thrust plate electrode tool with a resulting conductive pattern formed by the method illustrated in FIGs. 3A-3D,-

[0025] FIG. 7B is an enlarged plan view of the resulting conductive pattern on the thrust plate electrode shown in FIG. 7A;

[0026] FIG. 8 is a graph showing changes in dynamic pressure groove processing widths over time for an electrode tool manufactured by a method according to the first preferred embodiment of the present invention and two electrode tools manufactured by a method according to a second preferred embodiment of the present invention;

[0027] FIG. 9 is a graph showing changes in dynamic pressure groove depth processing speed over time for an electrode tool manufactured by the method according to the first preferred embodiment of the present invention and two electrode tools manufactured by a method according to the second preferred embodiment of the present invention;

[0028] FIGs. 10A-10E are successive cross-sectional views illustrating a method of manufacturing an electrode tool according to a third preferred embodiment of the present invention;

[0029] FIG. 11 is a diagram of the chemical structure of a polyimide coating applied to an electrode tool manufactured by a method of the present invention; [0030] FIG. 12 is a diagram of the chemical structure of a PFA (perfluoroalkoxy-tetrafluoroethylene copolymer) coating applied to an electrode tool manufactured by a method of the present invention;

[0031] FIG. 13 is a diagram of the chemical structure of an FEP (tetrafluoroethylene-hexafluoropropylene copolymer) coating applied to an electrode tool manufactured by a method of the present invention;

[0032] FIG. 14 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; and

[0033] FIGs .15A-15C are tables of examples of diamine monomers that can be used in a vapor deposition polymerization process to produce a polyimide insulation layer on an electrode tool manufactured by a method of the present invention.

DETAILED DESCRIPTION OP THE PREFERRED EMBODIMENTS

[0034] The present invention will now be described in detail in accordance with the drawings. The illustration and description of some components are omitted where their inclusion would not be necessary for one skilled in the art to understand the present invention. In addition, like reference numbers reference like components throughout the drawings .

[0035] FIGs. 3A-3D illustrate a method of manufacturing an electrode tool for use in an electrochemical machining (ECM) process in which a conductive pattern is formed on an electrode blank and in accordance with a first preferred embodiment of the present invention. The electrode tool with such a conductive pattern may^¬ be used to process, for example, a pattern of dynamic pressure grooves on a hydrodynamic bearing for use in a hard disk storage device . Each of the processes in the method are shown and identified by reference numbers 20, 22, 24 and 26, respectively in FIGs.3A-3D. At 20, an electrode blank 28 is provided. The electrode blank 28, which includes a top process surface, or more generally a process surface, 30, may be any type of base material that has good conductivity characteristics. Exemplary base materials that may be used as the electrode blank include copper, tungsten, phosphor bronze, brass, stainless steel, titanium alloy, copper tungsten alloy and cobalt alloy.

[0036] At 22, a thin film insulating coating 32 formed from an insulating resin is applied to the process surface 30 of the electrode blank 28. The thin film insulating coating 32 is preferably a polyimide group coating, a tetrafluoroethylene-hexafluoropropylene copolymer (FEP) group coating, or a perfluoroalkoxy-tetrafluoroethylene copolymer (PFA) group coating that is deposited on the process surface 30 by a well known physical vapor deposition (PVD) process.

[0037] In addition, the structures of polyimide, FEP and PFA group coatings are shown in FIGs. 11, 12 and 13, respectively. The symbols R and R¹ in FIG. 11 represent alkyl groups. Similarly, the symbol Rf in FIG. 12 represents a fluoroalkyl group.

[0038] The carboxylic acid monomers shown in the table in FIG. 14 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. 14 include tetracarboxylic acid anhydrate, polyisocyanate compounds and halogenated carboxylic acid. In particular, tetracarboxylic acid anhydrate can be suitably employed.

[0039] The diamine monomers shown in the tables of FIGs. 15A-15C are further examples of monomers that can be used in a vapor deposition polymerization process to form the polyimide resin in the present invention.

[0040] When a polyimide group coating is used as the thin film insulating coating 32, vapor deposition polymerization with a subsequent dehydration process is employed to deposit the coating on the process surface 30. More specifically, two monomers, a carboxylic acid anhydrate monomer and a diamine monomer, are evaporated and introduced in a vacuum chamber at approximately 200⁰C. Polymerization resulting in deposition of a thin film of polyamide acid on the electrode blank surface then occurs . The thin film of polyamide acid is then dehydrated at approximately 300⁰C and transformed to polyamide.

[0041] When an FEP group coating or PFA group coating is used as the thin film insulating coating 32, a vapor deposition process is employed to deposit the coating on the process surface 30 wherein, for example, an acrylate monomer is evaporated and the vapor phase thereof is irradiated by an electron beam, a plasma beam, an ultraviolet ray or the like to facilitate the polymerization on the process surface 30.

[0042] Conventional methods for forming a thin film insulating coating over an electrode blank process surface including, for example, electro-deposition, coating the blank with a resin solution followed by drying or formation of a resist film, are well known. However, the formation of the thin film insulating coating 32 over the process surface 30 of the electrode blank 28 by vapor deposition or vapor deposition polymerization as described above is more advantageous because it provides better control of film thickness, more uniform film thickness and stronger adherence of the film to the process surface 30, thereby resulting in longer tool life.

[0043] The thin film insulating coating 32 preferably has an associated thickness of approximately 5μm - 50μm when deposited on the process surface 30 and can withstand a continuous duty temperature of approximately 200⁰C. Its electrical insulation ability equates to a volume resistance of at least 10¹² Ω at 25°C. Exemplarypropertyvalues for the above thin film insulating coating materials are summarized in the table shown in FIG.4. The thin film insulating coating 32 should have a minimum thickness of approximately 5μm to ensure high quality ECM processing. The thin film insulating coating 32 need not exceed 50μm, as the formation of a film thicker than 50μm is difficult and time consuming.

[0044] Because the thin film insulating coating 32 is deposited in such a manner, the number of processes required to manufacture the electrode tool is reduced, as there is no need for disposable jigs for insulating resin filling purposes and therefore there is no need for subsequent excess resin removal. In addition, problems in prior art manufacturing methods relating to bubble and pinhole formation during thermosetting of the insulating resin are eliminated, as the thermosetting is no longer a necessary process.

[0045] Referring now to FIG.3C, at 24, the thin film insulating coating 32 is removed from the process surface 30 only at portions corresponding to a desired conductive pattern 34 which, as shown in FIG. 3C, includes exemplary conductive portions 36a-36d. In other words, the process surface 30 of the electrode blank 28 is exposed through the thin film insulating coating 32 in a manner that defines the conductive pattern 34. The thin film insulating coating 32 may be removed by one of any of a number of processes, including, for example, fine etching, laser processing, precision blasting or even by milling using a micro end mill. The resulting exposed portions of the process surface 30 therefore define the desired conductive pattern 34 as being a concave pattern located below remaining portions of the thin film insulating coating 32.

[0046] FIG. 5 is a photograph of an exemplary conductive pattern at 37 that is formed by the process 24 described above in connection with FIG. 3C. More specifically, this high resolution photograph, which shows grooves having widths of approximately 100 to 250μm and depths of approximately 15μm, is of a tool conductive pattern that is formed by etching a thin film insulating polyimide group coating on a process surface of an electrode blank such as discussed above in connection with FIG. 3C. The photograph illustrates that the method of the present invention is capable of forming a conductive pattern with high precision and minimal burring.

[0047] Referring now to FIG. 3D, at 26, a top metal coating (metal coating) 38 of, for example, platinum, gold, silver, rhodium, palladium, ruthenium, chrome or nickel is applied over the conductive pattern 34 of the electrode blank 28 by, for example, electroplating, electroless plating or vapor deposition. As a result, the conductive surfaces, such as exemplary conductive surface 36a shown in FIG. 3D, are less concave than if the metal coating 38 was not applied. For example, if SUS304 stainless steel is used to form the electrode blank 28, and the thin film insulating coating 32 is formed from a polyimide thin film having a thickness of approximately 15μm through a vapor deposition polymerization process, the metal coating 38 may be formed on the electrode blank 28 from a layer of platinum plating having a thickness of, for example, approximately lOμm by an electroplating process.

[0048] More specifically, the above metal coating 38 may be formed when the electrode and thin film insulating coating combination are immersed in a high alkalinity platinum plating solution that contains an appropriate amount of hexahydroxo platonic acid, and a platinum coating with a thickness of lOμm is as a result formed on the exposed process surface 30 of the electrode blank 28 under the processing conditions of a bath temperature of 80⁰C and a current density of 1.5 A/dm2. If it is desired to make the level difference of the surface after plating and the surface of the thin film insulating coating 32 larger, it is possible to coat the process surface 30 with a platinum coating of a thickness of only approximately lμm by an electroless plating process.

[0049] In addition, when a titanium alloy is used instead of stainless steel as the material for the electrode blank 28 and platinum is used to form the metal coating 38, the resulting electrode tool has excellent corrosion resistance and can be used in combination with a wide range of electrolytes in ECM processes regardless of the alkalinity or acidity of the electrolytes.

[0050] Alternatively, a metal consisting of a single layer of an alloy into which a plurality of metals is mixed may be used to form the metal coating 38 in place of the above identified metals. For example, for gold plating, a gold alloy that contains approximately 0.1 to 0.5% silver, copper, nickel, cobalt or iridium may be used depending upon the required physical properties, such as the hardness and abrasion resistance of the plating coating. This type of hard alloy gold plating improves hardness by a factor of two and abrasion resistance by a factor of three relative to pure gold plating. In addition, this plating is lower in cost than platinum plating. Other metals can also be used depending upon the application. For example, chromium or nickel plating can be applied over the conductive pattern 34 to improve hardness and resistance to corrosion due to electrolyte exposure whereas rhodium plating shows a hardness in a range of approximately Hv800 to 1000, which is a hardness that is equivalent to that of chromium plating, and in addition exhibits good electrical and chemical properties similar to those exhibited by platinum.

[0051] At this point it is noted that application of a top metal coating over the concave conductive pattern on the exposed process surface of the electrode blank as described above is very easy to implement, as the metal used for the metal coating is chosen to exhibit better mechanical, electrical and/or chemical characteristics such as, for example, better electrical conductivity, better standard electrical potential, resistance to corrosion due to electrolyte exposure, and improved hardness and wear resistance, than the metal used to form the electrode blank. Depending upon its desired thickness, the metal coating effectively minimizes, or altogether eliminates, surface concavities resulting from removal of the thin film insulating coating so that debris and other material that would otherwise diminish the accuracy of the transferred groove pattern does not adhere to the conductive pattern surface due to the combined effect of improved chemical characteristics and appropriate concavity depth. In addition, as metal such as platinum has an associated high standard electrode potential, the metal coating facilitates improved groove pattern transfer accuracy, which in turn increases the transfer precision of the processing width with respect to the conductive pattern width of the electrode tool.

[0052] Exemplary electrode tools that may be formed from the above method of manufacturing are shown in FIGs . 6 and 7. More specifically, an exemplary sleeve electrode 40 shown in FIG. 6 includes the thin film insulating coating 32 and conductive patterns 34a, 34b including the metal coating 38 for forming a radial dynamic pressure groove pattern and a thrust dynamic pressure groove pattern, respectively on a workpiece (not shown) . An exemplary thrust plate electrode 42 shown in FIGs. 7A and 7B also includes the thin film insulating coating 32 and a conductive pattern 34c including the metal coating 38 for forming a thrust dynamic pressure groove pattern on a workpiece (not shown) . One skilled in the art will appreciate that the above described method may be used to manufacture electrodes of any type of configuration in a manner that reduces the number of processes required by as much as a factor of 2/3 compared to conventional ECM electrode tool manufacturing methods .

[0053] Referring back to FIGs. 3A-3C, a method of manufacturing an ECM electrode tool in accordance with a second preferred embodiment of the present invention will now be described. Specifically, in the method according to the second embodiment, an electrode tool is manufactured by implementation of only the processes 20, 22 and 24. The process of adding the metal coating 38 as shown at 26 in FIG. 3D is eliminated. A resulting electrode tool , while not including the metal coating 38 , and therefore lacking some of the precision of the electrode tool manufactured in accordance with the first preferred embodiment, may be acceptable for certain manufacturing processes when it is desired to minimize manufacturing costs. The differences in the resulting electrode tools manufactured according to both the above discussed first and second embodiments of the present invention will now be discussed. [0054] FIGs. 8 and 9 are graphs showing changes in dynamic pressure groove processing widths over time and changes in dynamic pressure groove depth processing speed over time, respectively, for an electrode tool manufactured by a method according to the first preferred embodiment of the present invention and two electrode tools manufactured by a method according to a second preferred embodiment of the present invention. In FIGs .8 and 9, the three electrodes have the same conductive pattern as shown in FIG. 5 and the same polyimide insulating coating applied by vacuum deposition polymerization with a thickness of 15μm. Data curves 48 and 52 correspond to an SUS304 electrode tool manufactured in accordance with the method of the second embodiment that does not include a metal coating (electrode tool A) . Data curves 44 and 50 correspond to a brass electrode tool manufactured in accordance with the method of the second embodiment that does not include a metal coating (electrode tool B) . Data curves 46 and 54 correspond to an SUS304 electrode tool with platinum plating that is approximately lOμm in thickness and that is manufactured in accordance with the method of the first embodiment (electrode tool C) .

[0055] The^' ECM tests using each of the electrode tools A, B and C were performed with an electrolyte containing 15% by weight of NaNO₃, an electrolyte flow rate of 8 to 12 m/s and a process gap of 0.05 mm between the electrode surface and a phosphor bronze workpiece. For each electrode tool, twenty workpieces were processed consecutively and dynamic pressure grooves were formed. As the width of the conductive pattern is not constant, the width and the depth of a processed dynamic pressure groove on each processed workpiece were measured at the location where the corresponding conductive pattern width was 200μm. This location was selected because ease of measurement corresponds directly to the width of the processed dynamic pressure groove.

[0056] Regarding FIG. 8, the graphical data was collected by operating the three electrode tools A, B and C to form groove patterns on phosphor bronze workpiece material . The phosphor bronze material used as workpiece material tends to exhibit a high degree of sagging, thereby increasing production width during normal ECM processing.

[0057] As shown at 44 and 48 in FIG.8, workpiece groove patterns formed by an electrode tool manufactured by the method of the second preferred embodiment described above and including a brass electrode blank and a SUS304 stainless steel electrode blank, respectively, exhibited minimal changes in processing width over 20 samples.

[0058] As shown at 46, workpiece groove patterns formed by an electrode tool manufactured by the method of the first preferred embodiment described above and including an SUS304 stainless steel electrode blank with a platinum metal coating applied to the conductive pattern exhibited even smaller changes in processing width over 20 samples compared to either of the electrode tools manufactured according to the method of the second preferred embodiment. As shown, although the increase in processing width over the samples at 44-48 were all minimal, the processing width achieved by the electrode tool manufactured by the method of the first preferred embodiment was about one-half that achieved by either of the electrode tools manufactured by the method of the second preferred embodiment .

[0059] Specifically, the average processed width for the electrode tool C was approximately 440μm compared to approximately 840μm for electrode tools A and B. This means that the increase in processed width for electrode tool C was almost one-half that of electrode tools A and B. Therefore, electrode tool C exhibited higher precision with respect to conductive pattern transfer. Such higher precision is of great significance in manufacturing very fine dynamic pressure grooves such as dynamic pressure grooves with minimum widths of 20μm or less. For example, to form a groove that is 20μm in width, an electrode tool such as electrode tool C must have a conductive pattern with a width of lOμm, whereas an electrode tool such as electrode tools A and B requires a conductive pattern with a width of 5μm, which is much more difficult to manufacture.

[0060] By implementing the manufacturing methods of the first and second preferred embodiments, it is possible to minimize expansion of the processing width of the resulting electrode tools to a large extent and in a cost-effective manner. Minimization of the processing width is important in formation of fine dynamic pressure grooves and in improving groove pattern transfer accuracy.

[0061] Regarding FIG. 9, experimental data was measured regarding processing depth on phosphor bronze workpieces per unit time, which corresponds to the electrode depth processing speed. Data shown at 50 and 52 is for the above discussed electrode tools A and B manufactured according to the method of the second preferred embodiment of the present invention, and data shown at 54 is for the above discussed electrode tool C manufactured according to the method of the first preferred embodiment of the present invention. As shown at 50 and 52, workpiece groove patterns formed by electrode tools A and B and respectively including an electrode blank formed from SUS304 stainless steel and from a brass electrode blank exhibited minimal change in processing depth over 20 samples. Therefore, an electrode tool manufactured by the method of the second preferred embodiment represents a more cost effective means of achieving consistent results regarding processing depth compared to conventionally manufactured electrode tools.

[0062] The average depth processing speed for electrode tool C over 20 samples was approximately 50μm compared to approximately 25μm for electrode tools A and B. Electrode tool C also exhibited a higher processing productivity because the depth processing speed was twice that compared to electrode tools A and B. Therefore, by- implementing electrode tool Amanufactured by the method of the first preferred embodiment, it is possible to improve ECM productivity due to the increase in the groove depth processing speed.

[0063] Referring to FIGs. 10A-10E, a method of manufacturing an electrode tool for use in an ECM process for forming a specific groove pattern on a workpiece in accordance with a third preferred embodiment of the present invention will now be described. Specifically, in the method according to the third embodiment, an electrode tool is manufactured by implementation of not only the processes 20, 22 and 24 shown and described in connection with FIGs. 3A-3C, but also through additional processes, shown at 56 and 57, in which an additional, or second, metal coating 58 is applied to the tool conductive pattern 34 prior to application of the (first) metal coating 38.

[0064] The second metal coating 58 may be applied so that the first metal coating 38 when applied is flush, or nearly flush, with the surface of the remaining thin film insulating coating 32. In accordance with this method, the second metal coating 58 may be a layer of, for example, gold, which is not as hard as platinum and has a lower associated conductivity and cost. The second metal coating 58 is deposited as shown at 56 prior deposition of the first metal coating 38. As gold is less expensive than platinum, implementation of the method shown in FIGs. 10A-10E reduces overall manufacturing costs while still maintaining the overall improved operating parameters associated with the electrode tool manufactured in accordance with the method of the second preferred embodiment described above in connection with FIGs. 3A-3D.

[0065] Alternatively, it should be noted that silver may be used as the second metal coating 58, and a layer of rhodium having a thickness of approximately lμm or less may be applied as the first metal coating 38 to prevent discoloration (blackening) of the silver which may cause decrease of electrical conductivity. Further, the number of different metal coatings is not limited to two. A plurality of different metal coatings, consisting of a single metal or alloy, can be applied over the conductive pattern.

[0066] In view of the above, one skilled in the art will appreciate that the method of the present invention eliminates the need for a micro end mill for pattern carving of protruding electrodes by requiring only that portions of a thin film insulating material that covers an electrode blank be removed to define a conductive pattern surface portion. As the need for a micro end mill is eliminated, increased costs due to mill breakage and toppling of the milled protruding electrode portions are also eliminated. As pattern shapes may be formed through processes such as etching, finer and more miniaturized pattern shapes that could not be formed using a conventional micro end mill are now possible.

[0067] Further, the manufacturing method of the present invention eliminates processes such as pattern carving, insulating resin filling, and extra insulating resin rough removal required in conventional electrode tool manufacturing methods, so cost is reduced and tool delivery time is improved. As the pattern forming process of the method of the present invention is the final process, pattern changes can be quickly implemented merely by varying the final process without the need to alter any of the preceding processes, thereby enabling prompt handling of design changes. Along this same line, it is therefore possible to process electrode blanks in common lots up to application of the thin film insulating material regardless the pattern design, thereby increasing manufacturing productivity and flexibility for ECM electrode tools . [0068] The disclosure is intended to explain how to fashion and use various embodiments in accordance with the invention and 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 modifications as are suited to the particular use contemplated, and which fall within the scope of the invention as determined by the appended claims, and all equivalents thereof, when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.

Claims

1. A method of manufacturing an electrode tool, comprising: providing an electrode blank formed from a conductive material; applying a thin film insulating resin coating to a process surface of the electrode blank by one of vapor deposition and vapor deposition polymerization; and removing the thin film insulating resin coating from portions of the process surface of the electrode blank so as to form a conductive pattern.

2. The method of claim 1, wherein the removing of the thin film insulating coating from portions of the process surface of the electrode blank so as to form a conductive pattern comprises removing the thin film insulating coating from portions of the process surface of the electrode blank so as to form a conductive pattern for processing a hydrodynamic pressure groove pattern in a hydrodynamic bearing.

3. The method of claim 1, further comprising applying a top metal coating over the conductive pattern after the removing of the thin film insulating resin coating from portions of the process surface of the electrode blank.

4. The method of claim 3, wherein the applying of a top metal coating over the conductive pattern comprises applying a metal coating including at least one metal selected from a group consisting of platinum, gold, silver, rhodium, palladium, ruthenium, chrome and nickel over the conductive pattern.

5. The method of claim 3, further comprising applying at least one additional different metal coating over the conductive pattern prior to the applying of a top metal coating over the conductive pattern.

6. The method of claim 5, wherein the applying of at least one additional different metal coating over the conductive pattern comprises applying one of gold and silver over the conductive pattern.

7. The method of claim 1, wherein the applying of a thin film insulating resin coating to a process surface of the electrode blank comprises applying one of a thin film polyimide group coating, a tetrafluoroethylene-hexafluoropropylene copolymer (FEP) group coating, and a perfluoroalkoxy-tetrafluoroethylene copolymer (PFA) group coating.

8. The method of claim 1, wherein the providing of an electrode blank formed from a conductive material comprises providing an electrode blank formed from a conductive material selected from a group consisting of copper, tungsten, phosphor bronze, brass, stainless steel, iron copper alloy, titanium alloy, copper tungsten alloy and cobalt alloy.

9. The method of claim 1 , wherein the removing of the thin film insulating resin coating from portions of the process surface of the electrode blank so as to form a conductive pattern comprises removing the thin film insulating coating by one of a fine etching, laser, precision blasting and milling.

10. The method of claim 1, wherein the applying of a thin film insulating resin coating to a process surface of the electrode blank comprises applying a thin film insulating resin coating having a thickness in a range of approximately 5μm - 50μm to a process surface of the electrode blank.

11. The method of claim 3, wherein the applying of a top metal coating over the conductive pattern comprises applying a metal coating having a thickness less than or equal to that of the thin film insulating coating to the conductive pattern.

12. The method of claim 5, wherein the applying of at least one additional different metal coating over the conductive pattern comprises applying a plurality of metal coatings to the conductive pattern so that a sum of thicknesses of all metal coatings including the top metal coating is less than or equal to that of the thin film insulating coating.

13. The method of claim 3 , wherein the applying of a top metal coating over the conductive pattern comprises applying a metal coating to the conductive pattern having a thickness that is approximately equal to that of the thin film insulating coating.

14. A method of forming an electrode tool for use in electrochemical machining, the method comprising: providing an electrode blank formed from a conductive material; applying a thin film insulating resin coating to a process surface of the electrode blank by one of vapor deposition and vapor deposition polymerization; removing the thin film insulating coating from portions of the process surface of the electrode blank so as to form a conductive pattern for processing a hydrodynamic bearing dynamic pressure groove pattern,- and applying a top metal coating over the conductive pattern.

15. The method of claim 14, further comprising applying at least one additional different metal coating on the conductive pattern prior to applying a top metal coating over the conductive pattern.

16. An electrode tool, comprising: an electrode blank formed from a conductive material and including a process surface; and a vapor deposition or vapor deposition polymerization thin film insulating resin coating for covering the process surface except for removed portions thereof that expose the process surface in a manner that defines a conductive pattern.

17. The electrode tool of claim 16, wherein the conductive pattern is recessed relative to the thin film insulating coating.

18. The electrode tool of claim 16, further comprising a top metal coating covering the conductive pattern.

19. The electrode tool of claim 18, further comprising at least one additional different metal coating located between the conductive pattern and the top metal coating.

20. The electrode tool of claim 19 , wherein the top metal coating and the at least one additional different metal coating have a combined thickness approximately equal to that of the thin film insulating resin coating.