Slurry delivery system for a metal polisher

A slurry delivery system for use with a polishing machine wherein the slurry delivery system is designed to reduce the incidence of oxidized metals or rust from flowing into a slurry compound used to polish substrates used in the manufacture of disk drives. The slurry delivery system comprises an extended drive shaft made from type 416 stainless steel having a longitudinally extending inner channel Inside of this inner channel is a type 316 slurry feed tube that is used to shield the type 416 stainless steel from a slurry containing corrosive de-ionized water. The drive shaft has a first end connected to a drive motor and a second distal end. Connected to the second distal end is a type 316 stainless steel hub. The hub is surrounded by a urethane slurry distribution plate that has channels cut for allowing slurry to flow. This slurry flows onto a urethane slurry isolation pad and through slurry distribution tubes mounted in holes in the platen and onto the surface of nickel plated substrates used to manufacture hard disk drives.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The invention relates to an improved polishing slurry delivery system for
 polishing electroless nickel plating used to manufacture hard disk drives.
 This slurry delivery system is for use with Wittig style machines
 2. Description of the Prior Art
 Polishing machines for polishing disk drives are known in the art. For
 example, U.S. Pat. No. 4,930,259 to Kobylenski et al. discloses a Magnetic
 Disk Substrate Polishing Assembly. In this case, the polishing assembly
 comprises a polish roller having a continuously fed polish cloth or polish
 tape. In addition, U.S. Pat. No. 4,845,816 to Nanis discloses a burnishing
 head for burnishing memory surfaces of computer memory disks.
 With regard to the field of the present invention, Seagate Recording Media
 in Anaheim, California manufactures computer hard drives using a Wittig
 Polisher. Hans Wittig, of Seagate developed a polisher that is used to
 planorize or make flat, and polish electroless nickel plating which has
 been deposited on aluminum substrates This polishing process can be
 accomplished in two steps. Step one uses a very aggressive polishing
 process to planorize the nickel plating. Step two involves a less
 aggressive polishing technique that polishes the nickel to a mirror
 finish. The resultant substrate has a surface that is flat to within a few
 millionths of an inch, and has virtually no scratches when viewed with a
 laser inspection machines. The polishing media is a slurry of very fine
 aluminum oxide, each particle being less than 0.1 micron in size, and
 de-ionized water. De-ionized water is corrosive to ferric metals, and will
 thus cause rapid oxidation to most iron carrying metals.
 The Wittig design has one problem in that the slurry and the de-ionized
 water must travel through more than a total of 20 feet of iron carrying
 metals per machine to reach the substrate surface. This results in iron
 oxide (rust) being mixed with the fine slurry and de-ionized water. Since
 the particles of rust can be several orders of magnitude larger than the
 very fine particles of the aluminum oxide polishing compound, the rust
 causes unacceptable scratches in the surface of the substrates.
 SUMMARY OF THE INVENTION
 It is therefore, an object of the invention to provide a slurry delivery
 system for a Wittig type polishing machine that can be assembled into a
 Wittig machine with little adjustment.
 It is another an object of the invention to provide a slurry delivery
 system for a Wittig type polishing machine that reduces the exposure of
 de-ionized water and slurry to ferrous metals.
 It is a further object of the invention to provide a slurry delivery system
 for a Wittig type polishing machine that reduces the amount of oxide
 impurities in an applied slurry.
 It is still a further object of the invention to provide a slurry delivery
 system for a Wittig type polishing machine that improves the polishing
 surface of disk drives and thus reduces the failure rate of disk drives to
 below 10%.
 These and other objects are achieved by providing a slurry delivery system
 for a Wittig machine comprising an extended length drive shaft made from
 type 416 stainless steel having a longitudinally extended inner channel.
 The heat treated type 416 stainless steel drive shaft provides the rugged
 high strength bearing journals required for this Wittig machine element.
 The relatively high tensile strength of the type 416 stainless steel will
 allow for long drive shaft life and improved durability. Type 416
 stainless steel is a martensitic stainless steel containing 12-14%
 chromium as an alloying agent. Because stainless steels derive their
 resistance to corrosion from the presence of chromium, increasing the
 chromium content in steel progressively enhances the resistance to
 rusting. There is a slurry delivery tube made from type 316 stainless
 steel disposed within the drive shaft. Type 316 stainless steel has a
 chromium content of about 16-18% that is noticeably higher than type 416
 stainless steel. In addition, type 316 stainless steel contains between
 10-14% nickel which can be used to greatly improve the delivery tubels
 resistance to nonoxygenating media such as the abrasive slurry. Type 316
 stainless steel also contains a higher level of manganese, which does not
 alter the corrosion resistance of the chromium, and molybdenum that
 improves resistance to solutions of halogen salts and pitting in seawater.
 Thus, this slurry delivery tube is less prone to corrosion than the type
 416 stainless steel used for the drive shaft. In this way, the slurry
 delivery tube contained within the drive shaft eliminates the possibility
 that de-ionized water will contact and oxidize any iron based metal.
 The de-ionized water is fed through a type 316 stainless steel slurry
 delivery tube in the central core of the drive shaft, which attaches to a
 type 316 stainless steel cross tube, within the drive shaft, that connects
 to a suitable manifold assembly that is inert to de-ionized water. The
 slurry leaves the manifold and continues through a modified slurry bowl
 and U-Joint to the type 316 stainless steel hub. After the de-ionized
 water and slurry passes through the hub -t flows into a large urethane
 plate attached to the upper Meehanite Platen. The slurry and de-ionized
 water flows through this urethane plate and down into type 316 stainless
 steel delivery tubes inserted into the Meehanite Upper Platen. A thin
 urethane pad with adhesive backing isolates the slurry from the top
 surface of the Meehanite Upper Platen.
 This new design mimics the spring rate and stiffness of the current platen
 support so as not to introduce any unknown variables that could effect the
 polishing process.
 Thus, this type design provides a corrosion free path for the transition of
 slurry, de-ionized water, and air to the substrate surfaces. In this case,
 the entire tool upgrade can be delivered on site and installed reasonably
 quickly in a Wittig type polishing machine resulting in minimum tool
 downtime. This design provides a complete low cost, long term effective
 solution for Wittig serviceability for a long time.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
 Referring to the drawings, FIG. 1 shows a cross-sectional view of a prior
 art representation of a Wittig machine 1. Wittig machine 1 is used to
 polish nickel plated aluminum substrates in hard disk drives. Wittig
 machine 1 contains an upper platen 2, and a lower platen 4. When polishing
 nickel plated substrates for hard disk drives, both upper platen 2 and
 lower platen 4 are driven in a circular motion and are independent of each
 other. The upper platen often rotates in the opposite direction from that
 of the lower platen. Upper platen 2 includes a slurry delivery system that
 delivers slurry through the platen to polish these substrates. In FIG. 1
 the slurry passes through drive shaft 5 made from 8620 steel, through
 internal holes in the 8620 steel drive shaft 6, through tubing 7 and on
 into the upper platen support 8 and upper platen 2. Both the upper platen
 support 8 and upper platen 2 are made from Meehanite cast iron. Meehanite
 cast iron has a substantially uniform grain structure which gives top
 platen 2 uniform thermal expansion. This uniform thermal expansion is
 necessary to keep upper platen 2 from deforming when polishing substrates.
 However, since the 8620 drive shaft, the upper platen 2, the upper platen
 support 8, are made from materials containing huge amounts of iron, the
 slurry, and de-ionized water will rapidly oxidize the iron and create rust
 impurities within the system.
 The invention as shown in FIGS. 2 and 3 is an improvement on this slurry
 delivery system that eliminates the contact between ferrous metals and the
 slurry that contains de-ionized water. In FIG. 2, the new slurry delivery
 system, consisting of a type 416 stainless steel extended length drive
 shaft, type 316 stainless steel central core and cross feed, suitable
 manifold inert to the slurry, type 316 stainless steel hub, urethane
 slurry delivery plate, type 316 stainless steel slurry delivery tubes with
 laser welded head, and a urethane isolation pad, is used to replace the
 original assembly shown in FIG. 10. The slurry delivery system shown in
 FIG. 2 is an improvement over the prior art of FIG. 1 since the slurry
 consisting of a very fine aluminum oxide and de-ionized water flows
 through the system from its introduction to the input of the polishing
 machine through the entire path to the surface of the aluminum substrates
 while only contacting components made from type 316 stainless steel and
 urethane, both inert to the slurry mixture. This new corrosion free path
 absolutely prevents the possibility of the slurry coming into contact with
 any ferrous materials and eliminates the formation of rust that will cause
 unacceptable scratches on the surface of the nickel plated aluminum
 substrates.
 The prior art of FIG. 1 allows the slurry mixture to travel through more
 than 20 feet of passageways containing iron that will rapidly produce rust
 in the presence of the slurry.
 In FIG. 2, shows a cross-sectional view of the slurry delivery system that
 is designed to substitute for the prior art of the Wittig machine shown in
 FIG. 1. This slurry delivery system contains an extended length stainless
 steel drive shaft 12 made from type 416 stainless steel. Inside of this
 drive shaft is an elongated channel 13. At a top end of drive shaft 12 are
 two type 316 stainless steel socket screws 14 and a type 316 slurry feed
 tube 160 At an opposite end, a cross feed supply 20 made from type 316
 stainless steel is connected to tube 16 within drive shaft 12 via a
 bushing not shown. Slurry flows through tube 16 and feeds into channel 21
 on cross feed supply 20. Fittings, 22, are inserted into cross feed supply
 20 and are used to connect to slurry distribution tubes 30 to the modified
 slurry bowl 32 via joint 34. The slurry next flows through channel 36 in
 the U-Joint and on into hub 40. Hub 40 is manufactured from type 316
 stainless steel and extends around drive shaft 12 in a ring. Hub 40
 connects and secures to Meehanite Platen 60 via socket head cap screws 45.
 Disposed between hub 40 and Meehanite platen 60 is a urethane slurry
 distribution pad 55 that shields Meehanite platen 60 from slurry and
 de-ionized water.
 Urethane slurry distribution plate 50 surrounds hub 40 and is secured to
 Meehanite platen via screws 46 and 47. With this assembly, slurry flows
 through channel 36 down through drill hole 41 and out through channels 44.
 Next the slurry and de-ionized water flows into slot 52 contained between
 urethane plate 50 and urethane pad 55 disposed on Meehanite platen 60. In
 addition, a series of stainless steel slurry delivery tubes 65 are
 inserted into holes 5758 and 59 within urethane pad 55 and into holes 66,
 67, and 68 within Meehanite platen 60. These stainless steel delivery
 tubes 65 are used to deliver the slurry through holes within Meehanite
 platen 60 to a series of nickel plated aluminum substrates.
 FIG. 3 shows a cross-sectional view of a second embodiment of the
 invention. In this embodiment, fitting 22 is threaded to the ends of cross
 feed supply 20 and coupled to a second type plastic slurry distribution
 tube 310 The other end of tube 31 is connected to a second fitting 37,
 mounted on urethane distribution plate 50. This connection allows slurry
 to flow through plastic distribution tubes 31, through type 316 stainless
 steel fittings 37, directly into channels 52 in urethane plate 50, and
 down through stainless steel delivery tubes 65 disposed within Meehanite
 platen 60. The slurry next flows out of polishing pad 70 (as shown in FIG.
 11.) and on to the nickel plated aluminum substrates. With this second
 embodiment, the slurry follows an alternative shorter path outside of hub
 40, avoiding much of the internal components shown in FIG. 2.
 FIG. 4 shows a cross-sectional view of elongated type 416 stainless steel
 drive shaft 12. In this view, inner channel 13 is shown extending
 longitudinally through drive shaft 12. In addition, drive shaft 12 expands
 incrementally at expansion points 15 and 15' to define three stages of the
 shaft, namely 12', 12" and 12" with each stage having a successively
 larger diameter. At the bottom end is cross channel 17 that intersects
 inner channel 13 perpendicularly. Cross channel 17 houses cross feed 20.
 Finally, at the bottom end of shaft 12 is a threaded hole 19 designed to
 receive a high strength cap screw for attaching drive shaft 12 to the
 remainder of the lower platen.
 FIG. 5a shows a side view of type 316 stainless steel slurry feed tube 16
 having a tube body 16' attached to a connecting hub 18. Hub 18 has an
 inner channel 23 that is in communication with inner channel 13 in tube
 16'. In addition, as shown in FIG. 5b hub 18 is beveled with bevel points
 25 so that it can receive socket screws 14 (FIG. 2) which are used to stop
 hub 18 from turning once feed tube 16 is inserted into drive shaft 12.
 Slurry feed tube 16; having type 316 stainless steel, shields shaft 12,
 having type 416 stainless steel, from the corrosive effects of the slurry
 and de-ionized water. Tube 16 feeds into the center hole 23 of cross feed
 supply tube 20 shown in FIG. 6a. Tube 16 may include a threaded tip 16" to
 thread into hole 23 of tube 20.
 FIG. 6a shows a cross sectional view of cross feed supply tube 20 which is
 disposed within elongated stainless steel drive shaft 12 at opening 17.
 Cross feed supply tube 20 is disposed perpendicular to elongated channel
 13 and its ends 20' past the surface of stainless steel drive shaft 12.
 The bore at each tube end 20' is preferably threaded so as to engage a
 threaded nipple having multiple openings 22. Flexible tubes 30 can then be
 coupled to these nipples to conduct the fluid through the slurry bowl 32.
 Tube 20 contains a cross feed inner channel 21 that is connected at its
 center with channel 13 so that it receives a flow of slurry from inner
 channel 13FIG. 6b is an end view of the cross feed supply tube 20 which is
 designed to have an outer diameter that is slightly smaller than shaft
 opening 17 so that tube 20 fits snugly within shaft 12.
 FIG. 7a shows a top view of type 316 stainless steel hub 40 having an outer
 circumference 80, and an inner circumference 82. Spaced along hub 40
 adjacent to inner circumference 82 are a series of drill holes 41 designed
 to allow slurry and de-ionized water to flow from channel 36 through drill
 hole 41 and out through channel 44. In addition, drill holes 84, which are
 not associated with drill holes 41, are designed to receive a series of
 head cap screws 43. (FIG. 2). Furthermore, drill holes 86, disposed
 adjacent to outer circumference 80 are used to receive head cap screws 45,
 wherein screws 43 and 45 are designed to secure hub 40 to Meehanite platen
 60.
 FIGS. 7b and 7c show alternative views of hub 40 taken along its cross
 section. FIG. 7b is an end view of hub 40 showing drill holes 84 and 86
 via dashed dotted lines, and channels 44.
 FIG. 7c is a cross sectional view of hub 40 showing hole 41 and channel 44.
 Channel 44 connects with channel 52 of urethane plate 50 to allow slurry
 to flow into channel 52 of plate 50.
 FIG. 8a is a top view of a urethane slurry distribution plate 50 having an
 outer circumference 100 and an inner circumference 102. In addition;
 within distribution plate 50 are a series of bore holes 53 and 54 (FIG.
 8b) in concentric rings with bore holes 53 adjacent to inner diameter 102
 and bore holes 54 adjacent to outer diameter 100. As shown in FIGS. 2 and
 3, each bore hole 53 is designed to receive a screw 46 while each bore
 hole 54 is designed to receive a screw 47.
 FIG. 8c shows a bottom view of urethane slurry distribution plate 50 having
 a series of concentric tracks 104, 106 and 108 for conveying slurry around
 plate 50 received from six radially extending channels 52. Channels 52
 extend radially outwardly from inner diameter 102 so that the slurry will
 flow into a series of holes 66, 67 and 68 each forming a circumferential
 ring on Meehanite platen in FIG. 2. In this way, this series of drill
 holes or channels 41, 44, 52 and 66, 67 and 68 and 104, 106 and 108 allows
 for a uniform distribution of slurry while eliminating the contact of
 slurry with any ferrous materials.
 FIG. 9 shows a top view of urethane slurry isolation pad 55 having an inner
 diameter 110 and an outer diameter 112. Disposed within isolation pad 55
 are a series of bore holes 56, 57 and 58 designed to receive a slurry
 delivery tube 65. There are also a second series of bore holes 59 and 61
 each designed to receive screws 45 and 47. As shown in FIGS. 2 and 3
 urethane slurry isolation pad 55 is disposed between urethane slurry
 distribution plate 50 and Meehanite platen 60. In this case, urethane
 slurry isolation pad 55 attaches to Meehanite platen 60 with a sticky back
 adhesive.
 FIG. 10a shows a cross sectional view of a cylindrically shaped slurry
 delivery tube 65 that has an elongated channel. Slurry delivery tube 65 is
 made from type 316 stainless steel. At one end of tube 65 is a flange 120
 that is laser welded onto one end of slurry delivery tube 65 as shown in
 FIG. 10b.
 FIG. 11 shows a exploded side view of the lower platen assembly 2. During
 assembly, a urethane polishing pad 70 is attached to the bottom surface of
 Meehanite plate 60 via a sticky back adhesive so that holes 71, 72, and 73
 are aligned with holes 66, 67, and 68 on Meehanite plate 60. Urethane pad
 55 is then placed on a top surface of Meehanite plate 60 so that
 circumferential holes 56, 57 and 58 are aligned with holes 66, 67 and 68
 on Meehanite plate 60. Then, slurry delivery tubes 65 are pushed through
 holes 56, 57, and 58 on pad 55 and fit snugly within circumferential holes
 66, 67 and 68 on plate 60. In this way, these tubes 65 shield Meehanite
 plate from contact with the slurry and de-ionized water. In a preferred
 embodiment, there are 122 holes and delivery tubes disposed within platen
 50. Flange 120 of each delivery tube 65 is seated on the surface of pad
 55. Urethane plate 50 is then sealed to the top of pad 55 by screws 46 and
 47 (FIG. 2) so that channels 52 become aligned with holes 5758 and 59 on
 pad 55. Finally, hub 40 is placed inside of plate 50 so that channel 44
 aligns with channel 52 in urethane plate 50.
 FIG. 12 shows a detailed cross-sectional view of the taken through the
 platen 60 and one of the slurry distribution tubes 65. Flange 120, which
 has a thickness of about 0.013 inches, is pressed into pad 55, which has a
 thickness of about 0.060 inches, so that a top surface of flange 120 is
 flush against a top surface of pad 55. In addition, to keep this seal
 between flange 120 and pad 55 consistent, pad 55 is pressed onto Meehanite
 platen 60 with an adhesive backing 130 so that pad 55 remains sealed and
 fixed in position when the system is in use. Slurry distribution tubes 65
 has a polished interior surface designed to allow slurry to travel through
 these tubes without catching or clogging the tubes. In addition, slurry
 distribution tubes 65 have a diameter of 0.12 inches and fit tightly
 inside platen holes 66, 67, and 68 which have a diameter of 0.125 inches.
 Any small gap 122 which is formed around tube 65 will fill up with slurry
 124 that hardens and forms a a tight seal between tubes 65 and Meehanite
 platen 60.
 After the components of the invention are assembled into the Wittig type
 polishing machines the combination of the slurry and de-ionized water is
 pumped under pressure through a rotary joint connected to the top of shaft
 12 as shown in FIG. 2. The fluid is conducted down through tube 13 in
 shaft 12 to cross feed tube 20, through holes 41 and channels 44 of hub 40
 and then is injected into radial channels 52 of plate 50. The pressurized
 slurry then travels circumferentially along circular channels 104, 106,
 and 108 over pad 55 and passes through delivery tubes 65 where it is fed
 onto the substrates to be polished.
 With this design, it is possible to deliver slurry and deionized water in a
 uniform manner to the surface of the substrates being polished. In
 addition, since the corrosive slurry and de-ionized water flows through a
 series of passages made only from type 316 stainless steel and urethane,
 both inert to the slurry mixture, no oxides of iron (rust) will form
 within the polishing slurry media, which will produce unacceptable
 scratches on the nickel plated substrate surface. This design has produced
 yields of more than 97%, during the polishing operation, an increase of 10
 to 15% above the prior art shown in FIG. 1.
 Accordingly, while several embodiments of the present invention have been
 shown and described, it is to be understood that many changes and
 modifications may be made thereunto without departing from the spirit and
 scope of the invention as defined in the appended claims.