US20030182982A1

US20030182982A1 - Ion milled punch and die for coining disc drive motor bearing surfaces

Info

Publication number: US20030182982A1
Application number: US10/400,986
Authority: US
Inventors: Edward Simpson; The Nguyen; Wesley Clark
Original assignee: Seagate Technology LLC
Current assignee: Seagate Technology LLC
Priority date: 1997-03-25
Filing date: 2003-03-27
Publication date: 2003-10-02

Abstract

Punches or dies are manufactured using a photolithographic process and an ion milling or ion beam etch process. The punches or dies are used for coining bearing surfaces in hydrodynamic bearing arrangements in computer disc drive spindle motor assemblies.

Description

RELATED APPLICATION DATA

This application claims the benefit of U.S. Provisional Application No. 60/041,539, filed on Mar. 25, 1997.[0001]

TECHNICAL FIELD

The present invention relates to, but is not limited to, a punch or die for use in coining disc drive bearing surfaces, and a method of manufacturing punch and dies for coining disc drive bearing surfaces. The invention also provides a hydrodynamic bearing arrangement, a method of making a hydrodynamic bearing surface, and a disc drive incorporating a hydrodynamic bearing arrangement

BACKGROUND OF THE INVENTION

Computer hard disc drives generally comprise an array of magnetic discs mounted to a spindle motor assembly. Data is written to, and read from, each magnetic disc by means of a read/write head located at the end of an arm which extends between the discs. Positioning of the arm is accomplished by means of a voice coil motor under the control of disc drive control electronics.

The array of magnetic discs is mounted to a hub of the spindle motor assembly. The hub is mounted for rotation with respect to a base of the spindle motor assembly by means of a bearing arrangement. In use, the hub is rotated by means of an electromagnetic motor.

Bearing arrangements for computer disc drives are normally chosen to be hydrodynamic bearing arrangements, due to their lower nonrepeatable runout (their vibration is not synchronized with the rotation of the motor), improved shock performance (the lubricant film in a hydrodynamic bearing acts as a shock absorber), reduced noise (as there is no metal to metal contact), and improved fatigue life (again as there is no metal to metal contact). Hydrodynamic bearings can also be designed to have high bearing and rocking stiffnesses.

Due to the small size of computer disc drive motors, the features of the various bearing surfaces are required to be within very small dimensional tolerances. Also, the method used to form the bearing surfaces is required to be fast, precise reliable and cost effective.

SUMMARY OF THE INVENTION

According to the invention there is provided a method of forming a coining tool, i.e. a punch or a die, from a slug, comprising the steps of:

applying a barrier material to a surface of the slug in a pattern which defines exposed and covered areas corresponding to desired coining tool features, and

bombarding at least part of the surface of the slug with ions, thereby to remove material from the surface of the slug.

More particularly, according to the invention the method comprises the steps of:

locating the slug in a fixturing means;

applying a layer of photoresist to a surface of the slug;

locating a photomask over the layer of photoresist;

exposing the photoresist through the photomask, to define portions of exposed and unexposed photoresist, in a pattern selected for the formation of coining tool features;

developing a selected one of the exposed and unexposed photoresist to leave a pattern of photoresist on the coining surface suitable for the formation of coining tool features;

ion milling the slug for the duration required to achieve a required feature depth; and removing any remaining photoresist from the slug.

The invention also includes a coining tool for coining bearing surfaces, comprising:

a body including at least one surface; and

coining features ion beam etched into the surface.

Also according to the invention there is provided a method of making a hydrodynamic bearing surface comprising the steps of:

providing a coining tool comprising a body including at least one surface having coining features ion beam etched therein; and

stamping bearing features into the hydrodynamic bearing surface with the coining tool.

Further according to the invention there is provided a disc drive comprising a disc, a base, and connected to the disc and the base a spindle motor assembly comprising:

a journal defining a journal bore;

a shaft mounted in the journal bore;

a thrust plate extending transversely from the shaft and being located adjacent to journal;

a counter plate being mounted to the journal and being located adjacent to the thrust plate,

the thrust plate having an arrangement of grooves and lands formed therein by stamping with an ion beam etched coining tool.

Other features of the present invention are disclosed or apparent in the section entitled: “BEST MODE FOR CARRYING OUT THE INVENTION.”

BRIEF DESCRIPTION OF THE DRAWINGS

For fuller understanding of the present invention, reference is made to the accompanying drawings in the following detailed description of the Best Mode of Carrying Out the Invention. In the drawings: [0030]
FIG. 1 is a cross section through a spindle motor assembly incorporating a hydrodynamic bearing arrangement according to the invention; [0031]
FIG. 2 is a plan view of the striking surface of a punch or die according to the invention, and formed in accordance with a method of the invention; [0032]
FIG. 3 is a perspective schematic view of a fixture for use in a method of the invention; [0033]
FIG. 4 is a side view of the fixture of FIG. 3 without the alignment pins but with the shims in place; [0034]
FIG. 5 is a plan view of the fixture of FIG. 4; [0035]
FIG. 6 is a schematic representation of process steps in a method of the invention; and [0036]
FIG. 7 is a perspective view of an alignment pin and a tool used for inserting the alignment pin into the fixture.[0037]

BEST MODE FOR CARRYING OUT THE INVENTION

As spindle motors, hydrodynamic bearings and manufacturing techniques are well-known in the art, in order to avoid confusion while enabling those skilled in the art to practice the claimed invention, this specification omits many details with respect to known items. [0038]
FIG. 1 illustrates a cross section through a spindle motor assembly according to the invention, incorporating a hydrodynamic thrust bearing. The spindle motor assembly, generally indicated by the [0039] numeral 10, comprises a base 12 and a hub assembly 13. The spindle motor assembly is part of a disc drive, and serves to provide a means whereby the discs of the disc drive are rotated relative to the base 12 and hence relative to the remaining parts of the disc drive.
A [0040] shaft 14 is mounted to the base 12 by means of a nut 16.
The outer surface of the [0041] shaft 14 and the adjacent bore of a journal 18 together form a hydrodynamic journal bearing 20. The hydrodynamic journal bearing 20 includes a grooved surface provided on the shaft 14 or on the bore of the journal 18. The journal bearing 20 supports the journal 18 for rotation relative to the shaft 14 about axis 22, and is filled with a bearing fluid.
A [0042] thrust plate 24 is press-fitted to one end of the shaft 14 and extends transversely to the shaft 14. The thrust plate 24 defines a first thrust surface which, together with an adjacent thrust surface on the journal 18, defines a first hydrodynamic thrust bearing 26.
A [0043] counter plate 28 is press-fitted to the journal 18 adjacent to the thrust plate 24. The counter plate 28 defines a counter plate thrust surface which, together with a second thrust surface defined by the thrust plate 24, forms a second hydrodynamic thrust bearing 30. The counter plate 28 is sealed to the journal 18 by means of an O-ring 32.
The first and second [0044] hydrodynamic thrust bearings 26, 30, which are filled with bearing fluid, each include a grooved bearing surface which is formed by stamping or coining using a punch or die. The punch or die, and the method of manufacture thereof, will be described in more detail below. In the illustrated embodiment of the hydrodynamic bearing arrangement, the grooved surfaces are provided on the thrust plate 26. They could however alternatively be provided on the counter plate 30 and/or the adjacent surface of the journal 18.
A [0045] hub 34 is fitted around the journal 26. The hub 34 supports an array of magnetic discs (not shown).
The [0046] hub assembly 13 is rotated with respect to the base 12 in use by means of an electromagnetic motor. The electromagnetic motor comprises a stator assembly 36 mounted to the base 12, and a magnet 38 mounted to the journal 18. The hydrodynamic thrust bearings 26 and 30 prevent any substantial linear movement of journal 18 relative to shaft 14 along axis 22.
The configuration of the grooved surfaces on the [0047] thrust plate 24 can be appreciated by referring to FIG. 2, which illustrates the striking surface of a die or punch used to form the grooved surfaces on the thrust plate 24.
The striking surface, generally illustrated by the numeral [0048] 50, comprises a number of alternating lands 52 and grooves 54 in a curved herringbone pattern. When a thrust plate 24 is coined/stamped, the lands 52 on the striking surface will form grooves in the thrust plate 24, while the grooves 54 will define lands on the thrust plate.
It should be noted that the particular pattern and configuration of the [0049] lands 52 and the grooves 54 on the striking surface, and hence on the thrust plate 24, are illustrated and described to provide a clear understanding of the invention only, and do not form a part of the invention per se. The particular pattern and configuration of the lands 52 and grooves 54 is chosen to provide a desired bearing performance, and is determined by known hydrodynamic bearing design practice. It should however be noted that the actual structure of coined lands and grooves on a thrust plate differs identifiably from the structure resulting from lands and grooves made using a different manufacturing process, for the same basic design configuration.
Coining of the hydrodynamic bearing pattern provides advantages over other methods such as chemical etching, as the coining process is a fast, reliable, repeatable, non-polluting technique which can be automated. [0050]
In the best mode method of the invention, the striking surface of the die or punch is formed using a combination of a photolithographic process and an ion milling process. [0051]
To describe the best mode method of making a coining tool according to the invention, reference will now be made to FIGS. [0052] 3 to 5, which illustrate a fixture used in the method, and FIG. 6, which illustrates the photolithographic and ion milling method steps schematically.
As shown in FIGS. 3 and 4, the fixture comprises a [0053] holder 62, a shield 64, and two mask alignment pins 61.
The [0054] holder 62 has a cylindrical hole 63 formed in the center thereof, which is sized to receive a slug 60 in an interference fit. The hole 63 extends through to the underside of the holder 62, such that a pin can be inserted into the hole 63 from the underside to push the slug 60 out of the holder 62 after completion of the process.
Similarly, two [0055] cylindrical holes 65 are formed in the fixture for receiving the mask alignment pins 61 in an interference fit. The holes 63 again extend through to the underside of the holder 62, such that a pin can be inserted into each hole 65 to push the alignment pins 61 out of the holder 62 after completion of the process.
In the method of the invention, the [0056] slug 60, from which the die or punch is to be made, is firstly mounted in the holder 62. This is done using an arbor press. The holder 62 is placed on a clean room tissue on the platen of the arbor press. The plunger of the arbor press is also covered with a clean room tissue to prevent the slug from being damaged. The slug 60 is aligned with the hole 63, and the shield 64 is placed around the slug 60. The fit between the slug 60 and the shield 63 is just enough of a clearance fit such that the slug will slide easily in the shield.
The slug is then positioned directly under the plunger of the arbor, and the [0057] slug 60 is pressed into the hole 63 such that the upper surface 66 of the slug 60 protrudes above the shield 64 by approximately 2 mm.
If the [0058] slug 60 is pressed too deeply into the hole 63, the holder 62 is inverted onto a cylindrical tube placed on the arbor press, with the slug 60 located inside the cylindrical tube. The slug 60 can then be pressed out of the holder to the desired height, using a pin that has a slightly smaller diameter than the slug 60. Again, clean room tissues are used between the holder 62 and the cylindrical tube, and the pin and the slug 60, to protect the surfaces of the slug 60 and the holder 62.
Referring now to FIG. 4, when the [0059] slug 60 has been inserted to the desired depth in the hole 63 (i.e., such that the upper surface 66 is approximately 2 mm above the upper surface of the shield 64), the shield 64 is shimmed up with two 0.009 in. shims 67. Each shim 67 has a sharp edge, and the shims 67 are placed in diametrically opposed positions under the shield 46, with the sharp edges facing in towards the slug 60. The reason for using the shims 67 is to provide a uniform gap between the shield 64 and the holder 62 for the glue to wick into.
The [0060] holder 62 is then placed on the platen of the arbor press, and a TEFLON™ disc is placed over the slug 60. The slug 60 is then pressed in the arbor press with the TEFLON™ disc between the slug 60 and the plunger of the arbor press, until the upper surface 66 of the slug 60 is flush with the upper surface of the shield 64. The alignment of the upper surface 66 of the slug 60 with the upper surface of the holder 62 can be verified using a 30× microscope. If both the upper surface 66 of the slug and the upper surface of the shield 64 are in focus at the same time, then the surfaces are at the same height.
To prevent the [0061] slug 60 and the shield 64 from moving relative to each other or to the holder 62, the slug 60 and the shield 64 are then glued in place as shown in FIG. 5. Firstly, two drops 68 of LOCTITE™ 498 cyanoacrylate glue are placed where the shield 64 and the holder 62 meet. Then, four drops 69 of LOCTITE™ 420 cyanoacrylate glue are placed where the shield 62 and the slug 60 meet. Then three short bursts of LOCTITE™ 712 accelerator are applied to the fixture 62, 64 from a distance of four inches, to begin the cure of the glue drops 68, 69.
After waiting for at least four minutes after the [0062] fixture 62, 64 has been sprayed with the accelerator, the shims 67 are removed, and the remaining gap between the shield 64 and the holder 62 is filled with LOCTITE™ 498 glue. The glue should extend from the base of the shield by about 3 mm. The glue is then allowed to cure partially at room temperature for at least one hour, or preferably overnight. This slow partial cure prevents the glue from cracking, and prevents bubbles or voids from forming in the glue.
After the partial cure, the holder is inverted, and the remaining recess above the bottom of the slug is overfilled with LOCTITE™ 498 glue, so that the glue bulges slightly from the underside of the [0063] holder 62. This overfill is done to take account of the fact that the glue will settle during baking of the fixture.
The [0064] fixture 62, 64 and the slug 60 are then baked at 100° C. for 30 minutes, after which more glue is added to the recess until the glue surface is flush with the underside of the holder. The fixture 62, 64 and the slug 60 are then baked again at 100° C. for 30 minutes.
After baking, excess glue is then removed from the [0065] slug 60/shield 64 interface, and from the underside of the holder 62, using a razor blade and acetone. After removing excess glue, the upper surfaces of the slug 60 and the shield 64 are wiped lightly with acetone to remove any glue residue.
The [0066] slug 60 is now secure in the fixture 62,64, and is ready for the photolithographic process, which takes place in a class 100 cleanroom.
The [0067] slug 60 is shown schematically in FIG. 6(a) at the beginning of the photolithographic process.
As illustrated in FIG. 6([0068] b), a layer of photoresist 70 is applied to the upper surface 66 of the slug 60. This is done using a Western Magnum XRL 120 laminator, and the photoresist is SF220 2 mil. thick Aquamer dry film photoresist with MYLAR™ backing.
The [0069] fixture 62,64 is loaded into a TEFLON™ lamination pallet, which has a number of recesses shaped and sized to receive holders 62. If necessary, metal shims are used under the holder 62, to bring the upper surface 66 of the slug 60 and the upper surface of the shield 64 to approximately 1 mm above the upper surface of the pallet. The pallet, with one or more fixtures 62, 64 is preheated at 120° C.±3° C. for at least 10 minutes but not more than 20 minutes.
The laminator is preheated for 20 minutes at a temperature of 105° C.±5° C., and set to a 48 psi. roller pressure, and a feed rate of 2 f.p.m. [0070]
The pallet with the [0071] fixtures 62,64 therein is then processed through the laminator in a known manner, to apply a layer 70 of the Aquamer photoresist to the upper surface 66 of the slug 60. After the pallet has passed through the laminator, the excess photoresist is trimmed from the shield 64 using a razor blade.
Preferably, a number of slugs are fixtured and have a layer of photoresist applied thereto in a single batch as described above. This allows a number of replacements to be available at this stage of preparation, should the layer of photoresist on a single slug be over or underexposed in the exposure step, or should there be any flaws in the photoresist or the slug. [0072]
The next step in the method is illustrated in FIG. 6([0073] c). In this step, the photoresist layer 70 is selectively exposed to define the required pattern in the photoresist for the subsequent creation of the desired punch or die features.
The [0074] photoresist 70 may be a positively acting or a negatively acting photoresist. In a negatively acting photoresist, exposure of the photoresist to light changes the structure of the photoresist from a more soluble condition to a less soluble condition. The application of developing liquid will therefor remove unexposed photoresist from a layer of selectively exposed photoresist, while leaving exposed photoresist behind.
In a positively acting photoresist, exposure of the photoresist to light changes the structure of the photoresist from a relatively insoluble condition to a much more soluble condition. The application of developing liquid will therefor remove exposed photoresist from a layer of selectively exposed photoresist, while leaving unexposed photoresist behind. [0075]
For purposes of conciseness, the photolithographic technique is described with reference to the Aquamer photoresist which is an ultraviolet light sensitive, negatively acting photoresist. If a positively acting photoresist is used, the mask will be a negative image of the mask used with a negatively acting photoresist. [0076]
Before selectively exposing the [0077] photoresist layer 70, the mask alignment pins 61 are inserted into the holes 65 in the holder 62. This is done in the arbor press using a special insertion tool 100 illustrated in FIG. 7.
The [0078] insertion tool 100 is cylindrical in shape, and has a stepped bore 102 defined therein. The stepped bore 102 has a wider portion 104 for receiving the body of the alignment pin 61, and a narrower portion 106 for receiving the tip 75 of the alignment pin 61. The insertion tool 100 protects the tip 75 of the alignment pin 61 during insertion of the alignment pin 61. This is important, since the tips 75 of the alignment pins 61 are used to position a photomask over the slug 60, as will be described in more detail below. The insertion tool 100 also ensures that the alignment pin 61 is inserted straight into the hole 65, and not at an angle.
To insert each [0079] alignment pin 61, the holder 62 is placed in an arbor press, and the alignment pin 61 is positioned over the relevant hole 65. The insertion tool 100 is then placed on the alignment pin 61 with the tip 75 located in the narrower portion 106 of the stepped bore 102, as shown by the arrows in FIG. 7. The plunger of the arbor press is then lowered onto the insertion tool 100, and the insertion pin 61 is pressed into the hole 65, until the stepped surface 71 of each mask alignment pin is approximately 1 mm below the upper surfaces of the slug 60 and the shield 64.
A photomask, illustrated schematically in FIG. 6([0080] c) and identified by the reference numeral 72, has regions 74 which are opaque to UV light, and regions 76 which are transparent to UV light. The opaque regions 74 are in the pattern of the lands 52 on the striking surface 50 illustrated in FIG. 2, and serve to shield corresponding portions of the photoresist layer 70 from exposure to the UV light.
The [0081] photomask 72 also has alignment holes (not shown) defined therein, which correspond to the tips 75 of the alignment pins 61. The alignment holes and the alignment pins 61 serve to align the photomask accurately over the upper surface 66 of the slug 60 during exposure of the photoresist layer 70.
The [0082] photomask 72, which is made from emulsion coated plastic, is first inspected under a microscope to determine which side of the photomask 72 is the emulsion side. The photomask 72 is then placed on the alignment pins 61 and on the upper surface 66 of the slug, with the emulsion side of the mask 72 facing down. A 1.5 in. by 1.5 in. glass plate is then placed on top of the photomask 72 to hold the photomask 72 flat against the layer of photoresist 70.
For purposes of illustration and ease of understanding of the method, the [0083] photomask 72 is shown in FIG. 6(c) to be spaced apart from the layer of photoresist 70 during the exposure step. In practice, the photomask 72 is in contact with the layer of photoresist 70, to reduce the effects of UV ray diffraction at the edges of the mask opaque regions 74. The contact between the photomask 72 and the photoresist layer 70 should be as close to perfect as possible. Unsatisfactory contact between the photomask 72 and the photoresist layer 70 can be identified by the presence of interference fringes in the photoresist/photomask/glass slide combination.
After positioning of the [0084] photomask 72 over the upper surface 66 of the slug 60, and on the photoresist layer 70, UV light 78 is shone onto the photoresist layer 70 through the photomask 72, thereby to selectively expose the photoresist layer 70. Using a Cole Parmer Series 9815 15 W UV lamp, the exposure time will be approximately 5 minutes. After exposure, the photoresist layer 70 will comprise exposed portions 80 and unexposed portions 82.
After exposure, but before development of the [0085] photoresist layer 70, care must be taken to ensure that the photoresist layer 70 is not exposed to excessive white light, as this will cause the photoresist layer 70 to develop further. Preferably, the holder is placed under an opaque cover immediately after exposure.
After removing the [0086] photomask 72 and waiting for 20 minutes after the completion of the exposure step, the MYLAR™ backing is peeled off the layer of photoresist 70, and the layer of photoresist 70 is developed using a developing liquid.
Application of the developing liquid to the [0087] photoresist layer 70 will remove the unexposed portions 82, while leaving the exposed portions 80 substantially intact. This which will result in the structure illustrated in FIG. 6(d), where the area 84 of the upper surface 66 where the grooves 54 arc to be formed are not covered with photoresist, while the area 86 of the upper surface where the lands 52 will be, are covered with photoresist 80.
The photoresist layer is developed using a Silicon Valley Group developer. [0088]
The [0089] holder 62 is mounted in a vacuum chuck in the developer, and developed as follows:
Spray develop for 130 seconds at 1000 r.p.m [0090]
De-ionized water rinse for 30 seconds at 1000 r.p.m; and [0091]
Spin dry for 40 seconds at 3000 r.p.m. [0092]
The pattern of [0093] photoresist 80 is now inspected to cheek for alignment, over or underexposure, over or underdevelopment, or contamination. In the event that the inspection locates flaws in the developed photoresist layer 70, it can be stripped off using isopropyl alcohol, to return the slug 60 to the condition described with reference to FIG. 6(a).
In the event that the [0094] photoresist layer 70 is over or underexposed, the UV exposure time for a subsequent slug 66 will be increased to correct underexposure, or decreased to correct overexposure. Corrections to the exposure time will usually be done in one minute increments.
The next step in the process is the ion milling of the [0095] slug 60 to form the die or punch striking surface 50. Ion milling is also commonly referred to as ion beam etching.
Ion milling involves the bombardment of a surface with high energy ions to remove surface material by dislodging surface atoms or molecules. The most common ion milling utilizes argon ions. In argon ion milling, argon atoms enter a vacuum chamber and are subjected to a stream of high energy electrons. The high energy electrons strip electrons from the argon atoms, thereby to form positively charged argon ions. The argon ions are formed into a beam using electrically biased grids. The argon ion beam is directed towards the part which is to be ion milled, and impact it. The resulting momentum transfer from the argon ions to the impacted surface causes material removal. The removal process is known as sputtering. [0096]
Accordingly, a number of [0097] slugs 60, in their respective holders 62 and shields 64, are mounted in the ion milling machine. The requisite vacuum is drawn, the argon is introduced into the vacuum chamber and the requisite electrical potentials are generated to commence the ion milling.
As illustrated in FIG. 6([0098] e), a high energy beam of argon ions 88 reaching a slug 60 impacts the exposed area 84 and the photoresist 80. The exposed area 84 is milled by the high energy argon ions, while the photoresist 80 acts as a barrier to prevent the covered area 86 from being ion milled. The photoresist layer 80 is not completely immune to the sputtering action of the ion beam 88, and there is thus some photoresist material which is lost during the ion milling step. The photoresist layer is however of a thickness which is selected to be thick enough to protect the covered area 86 completely during the ion milling step.
The ion milling proceeds for a sufficient time to mill the exposed area down to the desired depth of the punch or die [0099] groove 54. This will take place in a number of steps as follows:
Firstly, the [0100] upper surface 66 of the slug 60 is ion milled for the duration required to reach one half of the target groove depth, based on the nominal etch rate from previous recent punch and die ion mill runs. A holder 60 which has a in-process monitor slug mounted therein is then removed from the ion mill, and a small piece of photoresist (approximately 1 mm²) is chipped off the monitor slug. The depth of the groove 54 is measured using a surface stylus profilometer. A new etch rate is then calculated using the measured depth of the groove and the duration of the ion milling (rate=depth/duration).
The [0101] holder 60 with the monitor slug is then replaced in the ion mill. Using the calculated etch rate, the milling time required to ion mill to 85% of the target groove depth is calculated. The slugs 60 are then ion milled for this duration. The monitor slug is removed, a small piece of photoresist is chipped off, and the groove depth is again measured using the surface stylus profilometer. A new etch rate is calculated from the measured groove depth and the total milling duration to reach that depth.
The monitor slug is replaced in the ion mill, and using the new calculated etch rate, the slugs are ion milled for the duration required to reach the target groove depth. Once again, the monitor slug is removed, a piece of photoresist is chipped off, and the actual groove depth measured. If the measured groove depth is more than 2% shallower than the target groove depth, the slugs are ion milled for the duration required to bring the groove depth to the target value. [0102]
Ion milling is highly directional process, resulting in good definition of the sides and edges of the [0103] grooves 54. The resulting sharp definition of the die or punch features increases punch or die life when compared to dies or punches made using other techniques.
After completion of the ion milling, each [0104] slug 60 is removed from the ion mill, and the photoresist 80 is stripped from the top of the slug 60 (which is now a punch or die) using the appropriate solvents. The resulting structure is illustrated in plan view in FIG. 2, and a cross section of one of the grooves 54 is shown in FIG. 6(f).
The slug/holder/shield combination is soaked in acetone for approximately four hours to dissolve the glue between the various parts. The [0105] slug 60 is then pressed out of the holder 62 by inverting the holder 62 onto a cylindrical tube placed on the platen of the arbor press, with the upper surface of the shield 64 resting on the cylindrical tube. The slug 60 can then be pressed out of the holder 62 and shield 64, using a pin that has a slightly smaller diameter than the slug 60.

While the various parameters of the photolithographic and ion mill processes will vary depending on the particular materials and machinery used, these parameters will be readily determinable for each particular case by a person skilled in the photolithographic and ion milling arts. In summary, and by way of example only, the best mode process parameters and materials are as follows:



Slug material:	tungsten carbide
Photoresist type:	SF220 Aquamer dry film photoresist
Photoresist layer thickness:	2 mil
Photoresist exposure time:	5 minutes
Beam voltage:	700 V
Beam current:	700 mA
Argon gas pressure:	1.4 * 10⁻⁴Torr.
Magnet current:	0.45 A
Suppressor voltage:	300 V
Table angle:	−35°
Table rotation speed:	3 r.p.m
Typical ion milling rate:	368 angstroms/minute
Typical ion milling duration:	380 min.
Nominal groove depth:	14 μm

It will be appreciated that the invention is not limited to the embodiment of the invention described above, and many modifications are possible without departing from the spirit and the scope of the invention. [0107]

Claims

What is claimed is:

1. In a disc drive having a disc, a base, a journal defining a journal bore, a shaft mounted in the journal bore, the combination comprising:

means for providing a hydrodynamic bearing pattern on a thrust plate surface, and

a rotary member hydrodynamically coupled to the hydrodynamic bearing pattern on said thrust plate surface.

2. A method of making a coining tool from a slug, for coining bearing surfaces, comprising:

applying a barrier material to a surface of the slug in a pattern which defines exposed and covered areas on the surface of the slug corresponding to desired coining tool features, and

bombarding at least part of the surface of the slug with ions to thereby to remove material from the surface of the slug.

3. A method of making a coining tool according to claim 2 wherein the step of applying a barrier material comprises a photolithographic process.

4. A method of making a coining tool according to claim 2 wherein the step of applying a barrier material comprises the steps of:

coating the surface of the slug with a layer of photoresist;

selectively exposing the photoresist to define a pattern in the photoresist for creating the desired coining tool features; and

stripping unwanted photoresist from the surface to leave photoresist on the surface in the pattern defining exposed and covered areas on the surface of the slug corresponding to the desired coining tool features.

5. A method of making a coining tool according to claim 4 further comprising the step of:

locating the slug in a shield prior to the step of ion bombardment to protect the sides of the slug from the ion bombardment.

6. A method of making a coining tool according to claim 3 wherein the step of bombarding the surface is accomplished by argon ion milling.

7. A coining tool manufactured using the method of claim 6.

8. A method of making a coining tool from a slug, for coining bearing surfaces, comprising the steps of:

applying a layer of photoresist to a surface of the slug;

locating a photomask over the layer of photoresist;

developing a selected one of the exposed and unexposed photoresist to leave a pattern of photoresist on the surface suitable for the formation of coining tool features;

ion milling the slug for the duration required to achieve a required feature depth; and

removing any remaining photoresist from the slug.

9. A method of making a coining tool according to claim 8 wherein the step of ion milling comprises the step of:

argon ion milling the slug for the duration required to achieve a required feature depth.

10. A method of making a coining tool according to claim 9 further comprising the step of locating the slug with fixturing means.

11. A method of making a coining tool according to claim 10 wherein the step of locating the slug with fixturing means includes the step of:

locating the slug in a shield to protect the sides of the slug from the ion milling.

12. A coining tool manufactured using the method of claim 8.

13. A coining tool for coining bearing surfaces, comprising:

a body including at least one surface; and

coining features ion beam etched into the surface.

14. A hydrodynamic bearing arrangement comprising:

a journal defining a journal bore;

a shaft mounted in the journal bore;

15. A method of making a hydrodynamic bearing surface comprising the steps of:

16. A disc drive comprising a disc, a base, and connected to the disc and the base a means for fluidically coupling the disc to the base to achieve rotation of the disc relative to the base.

17. A disc drive according to claim 16 wherein the means for fluidically coupling the disc to the base comprises:

a journal defining a journal bore;

a shaft mounted in the journal bore;