U.S. patent application number 12/792497 was filed with the patent office on 2010-12-16 for abrasive article with uniform height abrasive particles.
Invention is credited to Zine-Eddine Boutaghou.
Application Number | 20100317262 12/792497 |
Document ID | / |
Family ID | 43306824 |
Filed Date | 2010-12-16 |
United States Patent
Application |
20100317262 |
Kind Code |
A1 |
Boutaghou; Zine-Eddine |
December 16, 2010 |
ABRASIVE ARTICLE WITH UNIFORM HEIGHT ABRASIVE PARTICLES
Abstract
A method of making an abrasive article including the step of
preparing a master plate with a surface having a shape. Depositing
a spacer layer on the surface of the master plate. A slurry
containing an adhesive and abrasive particles is deposited on a
surface of the spacer layer. A substrate embedded with abrasive
particles having a surface generally complementary to the surface
of the master plate is fabricated. A spacer layer is formed by
various method controlled the height of the protruded abrasive
particles. The master plate and the spacer layer are separated from
the substrate to expose abrasive particle protruding a
substantially uniform height. An abrasive article made according to
this method is also disclosed.
Inventors: |
Boutaghou; Zine-Eddine;
(North Oaks, MN) |
Correspondence
Address: |
Clise, Billion & Cyr, P.A.
605 U.S. Highway 169, Suite 300
Plymouth
MN
55441
US
|
Family ID: |
43306824 |
Appl. No.: |
12/792497 |
Filed: |
June 2, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61187658 |
Jun 16, 2009 |
|
|
|
Current U.S.
Class: |
451/41 ; 428/143;
51/295; 51/297 |
Current CPC
Class: |
Y10T 428/24372 20150115;
Y10T 428/24355 20150115; B24D 18/0009 20130101 |
Class at
Publication: |
451/41 ; 51/297;
428/143; 51/295 |
International
Class: |
B24B 1/00 20060101
B24B001/00; B24D 3/00 20060101 B24D003/00 |
Claims
1. A method of making an abrasive article comprising: preparing a
master plate with a surface having a shape; depositing a spacer
layer on the surface of the master plate; distributing a slurry
containing an adhesive and abrasive particles on a surface of the
spacer layer, wherein the abrasive particle comprise a primary
diameter greater than a thickness of the spacer layer; pressing a
substrate having a surface generally complementary to the surface
of the master plate against the slurry with sufficient force to
embed the abrasive particles into the substrate, and to penetrate
the spacer and contact the reference plane defined by the master
plate; at least partially curing the adhesive to form a reference
surface between the abrasive particles with a shape generally
complementary to the surface of the spacer layer; and separating
the master plate and the spacer layer from the substrate to expose
abrasive particle protruding a substantially uniform height above
the reference surface formed by the cured adhesive.
2. The method of claim 1 further comprising preparing the master
plate and the substrate with one of flat, concave, convex,
curvilinear, spherical, or grooved surfaces.
3. The method of claim 1 wherein the step of depositing the spacer
layer comprises one of spraying, coating, or printing the spacer
layer on the surface of the master plate.
4. The method of claim 1 further comprising applying a hard coat to
the surface of the master plate before depositing the spacer
layer.
5. The method of claim 1 wherein the substrate is selected from one
of metals, polymeric materials, ceramics, and composites
thereof.
6. A method of making an abrasive article comprising: preparing a
master plate with a surface having a shape; depositing a spacer
layer on the surface of the master plate; distributing a slurry
containing abrasive particles on a surface of the spacer layer,
wherein the abrasive particle comprise a primary diameter greater
than a thickness of the spacer layer; pressing a substrate having a
surface generally complementary to the surface of the master plate
against the slurry with sufficient force to embed the abrasive
particles into the substrate, and to penetrate the spacer and
contact the reference plane defined by the master plate; separating
the master plate and the spacer layer from the substrate to expose
abrasive particle protruding a substantially uniform height above
the reference surface formed by the master plate.
7. The method of claim 6 further comprising applying a hard coat to
the surface of the master plate before depositing the spacer
layer.
8. A method of making an abrasive article comprising: preparing a
master plate with a surface having a shape; forming a surface
barrier on the master plate; distributing a slurry containing a
carrier fluid and abrasive particles on; evaporating carrier fluid
from the slurry; depositing a substrate layer on to the seed layer
containing a bottom surface charged with abrasive particles and a
top surface containing the substrate material; releasing the
substrate containing the abrasive particles from the master plate;
and etching the bottom surface of the substrate layer to reveal the
abrasive particles.
9. The method of claim 8 further comprising depositing a seed layer
onto the master plate containing the abrasive particles prior to
the deposition of the substrate layer.
10. The method of claim 8 further comprising preparing the master
plate and the substrate with one of flat, concave, convex,
curvilinear, spherical, or grooved surfaces.
11. The method of claim 8 further comprising machining features
into the surface of the master plate.
12. The method of claim 8 wherein depositing the spacer layer
comprises one of spraying, coating, or printing the spacer layer on
the surface of the master plate.
13. The method of claim 8 wherein the evaporating spacer layer is
alcohol or water.
14. The method of claim 8 wherein the substrate is metallic
selected from low stress electrodeposited metals and its
corresponding alloys.
15. A substrate article of claim 8 further comprising a plurality
of abrasive particles protruding a substantially uniform height
above the etched surface.
16. A method of making an abrasive article comprising: preparing a
master plate with a surface having a shape; distributing a slurry
containing an a carrier fluid and abrasive particles on a surface
of the spacer layer; hardening the carrier fluid from the slurry;
depositing a substrate layer on to the seed layer containing a
bottom surface charged with abrasive particles and a top surface
containing the substrate material; releasing the substrate
containing the abrasive particles from the master plate; and
etching the bottom surface of the substrate layer to reveal the
abrasive particles.
17. The method of claim 16 further comprising depositing a seed
layer onto the master plate containing the abrasive particles prior
to the deposition of the substrate layer.
18. The method of claim 16 further comprising preparing the master
plate and the substrate with one of flat, concave, convex,
curvilinear, spherical, or grooved surfaces.
19. The method of claim 16 further comprising the step of machining
features into the surface of the master plate.
20. The method of claim 16 wherein depositing the spacer layer
comprises one of spraying, coating, dip coating, spin coating, or
printing the spacer layer on the surface of the master plate.
21. The method of claim 16 wherein the deposited material is
Cupper, Nickel, Chrome, or Tin and their corresponding alloys.
22. An abrasive article of claim 16 comprising a plurality of
abrasive particles protruding a substantially uniform height above
the deposited seed layer.
23. A method of lapping a surface of a work piece comprising:
positioning an abrasive article opposite the surface of the work
piece; applying a lubricant to the abrasive article; and engaging
the surface of the work piece with the abrasive particles and
moving the work piece relative to the abrasive article to form a
substantial bearing ratio between the surface of the work piece and
the reference surface on the abrasive article.
24. The method of claim 23 wherein the work piece comprises one of
machined metal parts, silicon wafers, slider bars for hard disk
drives.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefits of the filing date of
U.S. Provisional Patent Application Ser. No. 61/187,658 filed Jun.
16, 2009, which is entitled "Abrasive Article with Uniform Height
Abrasive Particles" which is hereby incorporated herein in its
entirety by reference.
FIELD OF THE INVENTION
[0002] The present application is directed to an abrasive article
with abrasive particles that protruded a substantially uniform
height above a reference surface, and a method of making and using
the same. The present method permits the manufacture of abrasive
articles with micron and nano-scale diamond particles.
BACKGROUND OF THE INVENTION
[0003] Read-write heads for disk drives are formed at the wafer
level using a variety of deposition and photolithographic
techniques. Multiple sliders, up to as many as 40,000, may be
formed on one wafer. The wafer is then sliced into slider bars,
each having up to 60-70 sliders. The slider bars are lapped to
polish the surface that will eventually become the air bearing
surface. A carbon overcoat is then applied to the slider bars.
Finally, individual sliders are sliced from the bar and mounted on
gimbal assemblies for use in disk drives.
[0004] Slider bars are currently lapped using a tin plate charged
with small diamonds having an average diameter of about 250 nm. The
tin lapping plate is prepared in several steps. The first step is
to machine a flat tin plate. The second step is to machine grooves
or geometrical features that promote lubricant circulation and
control of the thickness of the hydrodynamic film between the oil
lubricant and the slider bars.
[0005] The third step is to charge the tin plate with diamonds,
such as illustrated in U.S. Pat. No. 6,953,385 (Singh, Jr.). Singh
teaches applying a ceramic impregnator downward on the lapping
plate surface with a controlled force while the diamond slurry is
supplied. The diamonds are impregnated into the relatively soft tin
layer of the lapping plate. Fourth, the impregnated lapping plate
is dressed with a dressing bar. The dressing bar reduces the height
variation by pressing the larger diamonds further into the tin,
producing a more uniform height of the diamonds. Several runs of
the dressing bar help improve height uniformity of the abrasive
diamonds impregnated into the tin. Current processes are
economically wasteful since over 90 percent of the diamonds are
lost and unrecoverable in the process.
[0006] During use, the lapping plate is flooded with a lubricant
(oil or water based). The viscosity of oil based lubricants is
about 4 orders of magnitude greater than the viscosity of air. The
lubricant causes a hydrodynamic film to be generated between the
slider bar and the lapping plate. The hydrodynamic film is critical
in establishing a stable interface during the lapping process and
to reduce vibrations and chatter. To overcome the hydrodynamic film
a relatively large force is exerted onto the slider bar to cause
interference with the diamonds necessary to promote polishing. A
preload of about 1 kg is not uncommon to engage a single slider bar
with the lapping media. Large preloads exacerbate scratches on the
slider bars caused by peaks on the lapping plate.
[0007] The above described challenges are not unique to disk drive
manufacturers, optical component manufacturers and semiconductor
manufacturer face similar challenges for fine finishing.
[0008] FIG. 1 illustrates a conventional tin lapping plate 50
charged with diamonds 52. Top surface 54 of the tin plate typically
has a certain level of waviness. The height 56 of the diamonds 52
tends to follow the contour of the top surface 54, even after the
lapping plate 50 is dressed. The waviness of the top surface 54
also creates a non-uniform hydrostatic film 58, creating
instability at the interface with the slider bar.
[0009] The preload is typically determined by the density of the
diamonds and the diamond height variation. As the industry moves to
nano-diamonds smaller than 250 nm, the preload will need to be
increased to reduce the fluid dynamic film a sufficient amount so
the diamonds contact the slider bars. Nano-diamonds are difficult
to embed in the tin plate. The risk of free diamonds damaging the
slider bar increases. Precisely grooved plates or lubricant
reformulation will be required to overcome the fluid dynamic
film.
[0010] Variables such as lapping media speed, preload on the slider
bar load, nominal diamond size, and lubricant type must be balanced
to yield a desirable material removal rate and finish. A balance is
also required between the hydrodynamic film and the height of the
embedded diamonds to achieve an interference level between the
slider bar and the diamonds.
[0011] FIG. 2 is a schematic side sectional view of a conventional
slider bar including a plurality of individual sliders before
lapping. Each slider in the slider bar typically includes
read-write transducers. As used herein, "read-write transducer"
refers to one or more of the return pole, the write pole, the read
sensor, magnetic shields, and any other components that are spacing
sensitive. Various methods and systems for finish lapping
read-write transducers are disclosed in U.S. Pat. No. 5,386,666
(Cole); U.S. Pat. No. 5,632,669 (Azarian et al.); U.S. Pat. No.
5,885,131 (Azarian et al.); U.S. Pat. No. 6,568,992 (Angelo et
al.); and U.S. Pat. No. 6,857,937 Bajorek), which are hereby
incorporated by reference.
[0012] Slider bars with trailing edges composed of metallic layers
and ceramic layers present very severe challenges during lapping.
Composite structures of hard and soft layers present differential
lapping rates when lapped using conventional abrasive lapping
plates. The variable polishing rates of the metallic and ceramic
materials lead to severe recessions, sensor damage, and other
problems.
[0013] FIG. 3 illustrates the bar of FIG. 2 after lapping with a
diamond-charged lapping plate. The diamond-charged plates cause
large transducer protrusion and recession variations, contact
detection area variation, substrate recession, microscopic
substrate fractures leading to particle release during operation of
the disk drive, scratches from free diamonds, and transducer
damage.
[0014] U.S. Pat. Nos. 7,198,533 and 6,123,612 disclose an abrasive
article including a plurality of abrasive particles securely
affixed to a substrate with a corrosion resistant matrix material.
The matrix material includes a sintered corrosion resistant powder
and a brazing alloy. The brazing alloy includes an element which
reacts with and forms a chemical bond with the abrasive particles,
thereby securely holding the abrasive particles in place. A method
of forming the abrasive article includes arranging the abrasive
particles in the matrix material, and applying sufficient heat and
pressure to the mixture of abrasive particles and matrix material
to cause the corrosion resistant powder to sinter, the brazing
alloy to flow around, react with, and form chemical bonds with the
abrasive particles, and allow the brazing alloy to flow through the
interstices of the sintered corrosion resistant powder and form an
inter-metallic compound therewith.
[0015] U.S. Pat. Publication No. 2009/0038234 (Yin) discloses a
method for making a conditioning pad using a plastic substrate 11
having a plurality of recesses 12. The abrasive grains 4 are
secured in the recesses 12 by adhesive 31. The second substrate 6
is formed around the exposed portions of the abrasive grains 4.
After the second substrate 6 hardens, the first substrate 11 is
removed, exposing the cutting surfaces of the abrasive grains
4.
[0016] Example 1 of Yin teaches recesses 12 are about 225
micrometers deep and about 450 micrometers wide, with a maximum
height difference between the highest and lowest peak of about 25
micrometers. Example 3 of Yin discloses a maximum height difference
between the highest and lowest peak of about 15 micrometers. Yin
discloses diamond abrasive grains with particle diameters ranging
from 10 mesh to 140 mesh. Applicants believe these mesh sizes
correspond generally to diamond particles with a major diameter of
about 2 millimeters to about 0.1 millimeters. The large size of the
diamonds of Yin allow for insertion into the recesses 12. Forming
the first substrate 11 with sub-micron sized recesses 12 and then
inserting sub-micron size abrasive grains, however, is not
currently commercially viable. Sorting sub-micron sized abrasive
grains is also problematic.
[0017] Other method for orienting and positioning discrete abrasive
particles are disclosed in U.S. Pat. No. 6,669,745 (Prichard et
al.) and U.S. Pat. No. 6,769,975 (Sagawa), and U.S. Pat.
Publication No. 2008/0053000 (Palmgren), which are hereby
incorporated by reference.
BRIEF SUMMARY OF THE INVENTION
[0018] The present application is directed to an abrasive article
with abrasive particles that protruded a substantially uniform
height above a reference surface. The present method permits the
height the abrasive particles extend above the substrate to be
precisely controlled, thereby allowing the hydrodynamic film of the
lubricant to also be controlled. The present method is also suited
for use with nano-scale abrasive particles.
[0019] The present uniform height fixed abrasive article provides a
substantially uniform height of the diamonds (dh) with respect to a
reference surface. A substantially uniform lubricating hydrodynamic
film (hf) forms with respect to the reference surface. The lapping
interference (I=dh-hf) defined as the difference between the
diamond height and the hydrodynamic film is positive to promote
material removal. The cutting forces and hydrodynamic pressure do
not excessively deform the substrate as to interfere with the
lapping process.
[0020] One embodiment is directed to a method of making an abrasive
article including the step of preparing a master plate with a
surface having a shape. A spacer layer is deposited on the surface
of the master plate. A slurry containing an adhesive and abrasive
particles is deposited on a surface of the spacer layer. The
abrasive particles have a primary diameter greater than a thickness
of the spacer layer. A substrate having a surface generally
complementary to the surface of the master plate is pressed against
the slurry with sufficient force to embed the abrasive particles
into the substrate and to penetrate the spacer to the surface of
the master plate. The adhesive is at least partially cured to form
a reference surface between the abrasive particles with a shape
generally complementary to the surface of the spacer layer. The
master plate and the spacer layer are separated from the substrate
to expose abrasive particle protruding a substantially uniform
height above the reference surface formed by the cured
adhesive.
[0021] The master plate and the substrate can be flat, concave,
convex, curvilinear, spherical, or grooved. In one embodiment,
features are machined into the surface of the master plate. In
another embodiment grooves are machined in the surface of the
master plate and complementary grooves are machined in the surface
of the substrate. The grooves include peaks and valleys. The peaks
in the surface of the substrate include a peak height greater than
a peak height of peaks on the surface of the master plate. The
abrasive particles are embedded primarily in the peaks of the
substrate.
[0022] The spacer layer can be deposited by spraying, coating, or
printing. In one embodiment, a discrete spacer layer is positioned
on the surface of the master plate. By varying the thickness of the
spacer layer, it is possible to vary the height the abrasive
particles protrude above the reference surface. In one embodiment
the spacer layer is a low surface tension material. In another
embodiment the thickness of the spacer layer is greater than the
height the abrasive particles protrude above the reference surface
in order to compensate for deformation during the impregnating
step.
[0023] Any size or composition of abrasive particles can be used
with the method of the present invention. In one embodiment, the
abrasive particles are diamonds with a primary diameter of less
than about 10 micrometers. In another embodiment, the diamonds have
a primary diameter of less than about 1 micrometer.
[0024] A hard coat layer is optionally applied to the surface of
the master plate before depositing the spacer layer. The cured
adhesive occupies gaps between the surface of the substrate and the
surface of the spacer layer.
[0025] The substrate is selected from one of metals, polymeric
materials, ceramics, and composites thereof. The substrate can be a
flexible or a rigid material.
[0026] The present invention is also directed to a method of
lapping a surface of a work piece. An abrasive article according to
the present invention is positioned opposite the surface of the
work piece. A lubricant is applied to the abrasive article. The
surface of the work piece is engaged with the abrasive particles
and moved relative to the abrasive article to form a substantially
uniform hydrostatic film of lubricant between the surface of the
work piece and the reference surface on the abrasive article. The
work piece can be machined metal parts, silicon wafers, slider bars
for hard disk drives, and the like.
[0027] The present invention is also directed to an abrasive
article including a plurality of nano-scale abrasive particles
embedded in a substrate and protruding a substantially uniform
height above a reference surface formed by a cured adhesive located
between the abrasive particles.
[0028] The present invention is directed to a method of making an
abrasive article including the step of preparing a master plat with
a substantially flat surface. A slurry containing abrasive
particles carried in a fluid. The slurry is dispersed on the master
plate to provide a uniformly dispersed particle density onto the
master plate. The fluid carrier is evaporated to leave abrasive
particles dispersed with a uniform density. A seed layer is
deposited on the master plate with distributed diamonds. The seed
layer can be sputtered or evaporated onto the master plate
containing the abrasive particles. The seed layer can be Chrome or
Nickel to promote the electroplating of an additional substrate
layer formed from Cupper or Tin or Nickel. The seed layer can be
few nanometers thick to provide a conductive path for the
electro-deposition of the substrate layer. The substrate layer is
deposited from an electro platting process for example. Cupper,
Nickel and Tin materials can be grown to many microns thick with
very low film stress. Various deposition processes are commercially
available such as dry such as sputtering or a wet deposition
processes such as plating can be utilized to form the substrate and
the seed layer. A combination of processes can also be utilized.
First a sputtering process is used to encapsulate the abrasive
particles followed by a wet deposition process. Once the thickness
of the substrate reaches a desired value of microns, the substrate
containing the abrasives is removed from the master plate. Further
etching on the surface containing the abrasive particles removes a
substantially uniform thickness of the substrate layer revealing
the particle abrasives with a uniform height. The height of the
particle abrasives matches the amount of material etched from the
substrate surface.
[0029] The present invention is directed to a method of making an
abrasive article including the step of preparing a master plat with
a substantially flat surface. A slurry containing abrasive
particles carried in a fluid. The slurry is dispersed on the master
plate to provide a uniformly dispersed particle density onto the
master plate. The thickness of the fluid carrier is controlled to
match the desired abrasive protrusion. The fluid carrier is cross
linked by thermal or irradiative process to form an immobile
polymer structure layer to accept a seed layer. A seed layer is
deposited on the polymer structure. The seed layer can be sputtered
or evaporated onto the polymer structure containing the abrasive
particles. The seed layer can be Chrome or Nickel to promote the
electroplating of an additional substrate layer formed from Cupper
or Tin or Nickel. The seed layer can be few nanometers thick to
provide a conductive path for the electro-deposition of the
substrate layer. The substrate layer is deposited from an electro
platting process for example. Cupper, Nickel and Tin materials can
be grown to many microns thick with very low film stress. Various
deposition processes are commercially available such as dry such as
sputtering or a wet deposition processes such as plating can be
utilized to form the substrate and the seed layer. A combination of
processes can also be utilized. First a sputtering process is used
to encapsulate the abrasive particles followed by a wet deposition
process. Once the thickness of the substrate reaches a desired
value, 20 microns for example, the substrate containing the polymer
spacer and the abrasives is removed from the master plate. Further
etching on the surface containing the abrasive particles removes
the soft polymer layer revealing the particle abrasives with a
uniform height. The height of the particle abrasives matches the
thickness of the polymeric spacer.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
[0030] FIG. 1 is a schematic sectional view of a prior art
diamond-charged lapping plate.
[0031] FIG. 2 is a schematic side sectional view of a conventional
slider bar before lapping.
[0032] FIG. 3 illustrates the bar of FIG. 1 after lapping with a
conventional diamond-charged lapping plate.
[0033] FIG. 4 is a side sectional view of a prior art abrasive
article with macro-scale abrasive particles.
[0034] FIG. 5 is a schematic side sectional view of a fixture for
making an abrasive article in accordance with an embodiment of the
present invention.
[0035] FIG. 6 illustrates an abrasive slurry deposited on the
fixture of FIG. 5 in accordance with an embodiment of the present
invention.
[0036] FIG. 7 illustrates a substrate engaged with the abrasive
slurry FIG. 6 in accordance with an embodiment of the present
invention.
[0037] FIG. 8 illustrates the abrasive particles embedded in the
substrate and the spacer layer of FIG. 7 in accordance with an
embodiment of the present invention.
[0038] FIG. 9 is a schematic sectional view of an abrasive article
in accordance with an embodiment of the present invention.
[0039] FIG. 10 is a schematic side sectional view of an alternate
fixture with a structured surface for making an abrasive article in
accordance with an embodiment of the present invention.
[0040] FIG. 11 illustrates a substrate engaged with the abrasive
slurry of FIG. 10 in accordance with an embodiment of the present
invention.
[0041] FIG. 12 is a schematic sectional view of an abrasive article
with a structure surface in accordance with an embodiment of the
present invention.
[0042] FIG. 13 is a schematic sectional view of an abrasive article
with a concave surface in accordance with an embodiment of the
present invention.
[0043] FIG. 14 is a schematic sectional view of an abrasive article
with abrasive particles sintered to a substrate in accordance with
an embodiment of the present invention.
[0044] FIG. 15A-D is a schematic sectional view of an abrasive
article with abrasive particles dispersed on a master plate in
accordance with an embodiment of the present invention.
[0045] FIG. 16A-C is a schematic sectional view of an abrasive
article with abrasive particles dispersed on a master plate in
accordance with an embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0046] FIG. 5 illustrates fixture 100 for making a substantially
uniform height diamond charged abrasive article in accordance with
a method of the present invention. Master plate 102 is machined and
polished to a substantially flat surface 104.
[0047] Roughness of a surface can be measured in a number of
different ways, including peak-to-valley roughness, average
roughness, and RMS roughness. Peak-to-valley roughness (Rt) is a
measure of the difference in height between the highest point and
lowest point of a surface. Average roughness (Ra) is a measure of
the relative degree of coarse, ragged, pointed, or bristle-like
projections on a surface, and is defined as the average of the
absolute values of the differences between the peaks and their mean
line.
[0048] The master plate 102 is preferably silicon, since wafer
planarization infrastructure is capable of achieving a very smooth
surface with small waviness values in the order of 1 nm and 100 nm,
respectively. The fine finish requirements for the surface 104
include short length waviness, long waviness, and surface finish
quality. Planarization of silicon is disclosed in U.S. Pat. No.
6,135,856 (Tjaden et al.) and U.S. Pat. No. 6,194,317 (Kaisaki et
al.), which are hereby incorporated by reference.
[0049] Once the master plate 102 is machined, a hard coat 106 is
preferably applied to protect the surface 104. Surface 107 of the
hard coat 106 generally tracks the surface 104 of the master plate
102. The desired thickness 108 of the hard coat 106 can be in the
range of about 50 nanometers or greater. In one embodiment, the
hard coat 106 is diamond-like carbon ("DLC") with a thickness 108
of about 50 nanometers to about 200 nanometers. DLC hardness is
preferably more than about 5 GPa to adequately protect the surface
104. It is highly desirable to generate DLC hardness in the range
of 70-100 GPa.
[0050] In one embodiment the DLC is applied by chemical vapor
deposition. As used herein, the term "chemically vapor deposited"
or "CVD" refers to materials deposited by vacuum deposition
processes, including, but not limited to, thermally activated
deposition from reactive gaseous precursor materials, as well as
plasma, microwave, DC, or RF plasma arc jet deposition from gaseous
precursor materials. Various methods of applying a hard coat to a
substrate are disclosed in U.S. Pat. No. 6,821,189 (Coad et al.);
U.S. Pat. No. 6,872,127 (Lin et al.); U.S. Pat. No. 7,367,875
(Slutz et al.); and U.S. Pat. no. 7,189,333 (Henderson), which are
hereby incorporated by reference.
[0051] The next step is to apply a spacer layer 110. The spacer
layer 110 is preferably a low surface energy coating, such as for
example Teflon. The spacer layer 110 acts as a spacer to set height
112 abrasive particles 114 protrude above reference surface 116 on
the abrasive article 118 (see FIG. 9). Consequently, by varying the
thickness 112' of the spacer layer 110, the height 112 of the
abrasive particles 114 can be controlled. In some embodiments, the
thickness 112' may be different than the height 112 of the abrasive
particles 114 to compensate for deformation of the spacer layer 110
during impregnation of the substrate (see FIG. 8). As a result, the
thickness 112' of the spacer layer 110 corresponds to the desired
height the abrasive particles 114 protrude above the reference
surface 116, but there is not necessarily a one-to-one
correlation.
[0052] In one embodiment the spacer layer 110 is a preformed sheet
bonded or adhered to the surface 107 of the hard coat 106. In
another embodiment, the spacer layer 110 is sprayed or printed onto
the surface 107, such as disclosed in U.S. Pat. No. 7,485,345 (Renn
et al.) and U.S. Pat. Publication No. 2008/0008822 (Kowalski et
al.), which are hereby incorporated by reference.
[0053] As illustrated in FIG. 6, adhesive slurry 120 of adhesive
122 containing abrasive particles 114 is distributed evenly over
surface 124 of the spacer layer 110. Using a spacer layer 110 made
from a low surface tension material aids in wetting the adhesive
122. Methods of uniformly dispersing nanometer size abrasive grains
are disclosed in U.S. Pat. Pub. No. 2007/0107317 (Takahagi et al.),
which is hereby incorporated by reference.
[0054] Abrasive particles of any composition and size can be used
with the method and apparatus of the present invention. The
preferred abrasive particles 114 are diamonds with primary
diameters less than about 1 micrometer, also referred to as
nano-scale.
[0055] Substrate 126 illustrated in FIG. 7 is then pressed against
the adhesive slurry 120. In the illustrated embodiment, the
substrate 126 is a tin plate. Note that surface 128 of the
substrate 126 has some waviness, which will be irrelevant in the
finished abrasive article 118 according to the present invention.
The substrate 126 can be manufactured from a variety of metals,
polymeric materials, ceramics, or composites thereof. The substrate
126 can also be flexible, rigid, or semi-rigid.
[0056] As illustrated in FIG. 8, the substrate 126 is applied with
a sufficient force F to cause the abrasive particles 114 to
substantially penetrate the spacer layer 110, without substantial
penetration or indentations in the hard coat 106. The abrasive
particles 114 are simultaneously embedded in surface 128 of the
substrate 126. The adhesive 122 fills gaps 130 between the surface
128 of the substrate 126 and the surface 124 of the spacer layer
110. The adhesive 122 also follows the contour of the surface 124
of the spacer layer 110, as will be discussed below.
[0057] The spacer layer 110 permits the abrasive particles 114 to
contact the surface 107 of the hard coat 106 and limits the amount
of penetration into the substrate 126. Depending on the material
selected, the thickness of the spacer layer 110 may be increased to
compensate for deformation during the impregnating step of FIG.
8.
[0058] The surface 128 of the substrate 126 preferably has a
flatness that is less than about the height of the abrasives
particles 114, so the abrasive particles 114 are sufficiently
embedded in the surface 128. If the abrasive particles 114 are not
sufficiently embedded into the substrate 126, the adhesive 122 may
be the primary mode of attachment, leading to release during
lapping.
[0059] FIG. 9 illustrates the abrasive article 118, with the
sacrificial spacer layer 110 removed in accordance with an
embodiment of the present invention. Using a spacer layer 110 made
from a low surface tension material facilitates removal of the
master plate 102. The at least partially cured adhesive 122 forms a
substantially flat reference surface 116 from which height 112 of
the abrasive particles 114 can be measured.
[0060] The waviness of the surface 128 on the carrier is not
reflected in the uniform height 112 of the abrasive particles 114
or the reference surface 116. The uniform distance 112 between the
peaks 115 of the abrasive particles 114 and the reference surface
116 permits formation of a substantially uniform hydrodynamic film
relative to the height 112 of the abrasive particles 114. As used
herein, "substantially uniformly" and "substantially flat" refers
to both an entire surface of a substrate or an abrasive article and
to selected portions of the substrate or abrasive article. For
example, localized uniformity or flatness may be sufficient for
some applications.
[0061] Various processes can be used to activate and/or cure the
adhesive 122 to bond the diamonds 114 to the substrate 126 and
create the reference surface 116, such as for example ultraviolet
or infrared RF energy, chemical reactions, heat, and the like. As
used herein, "cure" or "activate" refers to any chemical
transformation (e.g., reacting or cross-linking), physical
transformation (e.g., hardening or setting), and/or mechanical
transformation (e.g., drying or evaporating) that allows an
adhesive to change or progress from a first physical state
(generally liquid or flowable) into a more permanent second
physical state or form (generally solid).
[0062] The present method provides a number of benefits over prior
art diamond charged lapping plates. The present abrasive article
118 provides a uniform height 112 of the diamonds 114 ("dh") with
respect to a substantially flat reference surface 116. There is no
need to condition the present abrasive article 118. Knowledge of
the lapping conditions, lubricant type, and the lapped bar can be
used to calculate the hydrodynamic film thickness ("hf") relative
to the reference surface 116 formed by the cured adhesive 122. Once
the hydrodynamic film thickness is known, the interference ("I")
can be calculated from the uniform height 112 of the diamonds 114
from the hydrodynamic film (I=dh-hf). The substantially flat
reference surface 116 provides a generally uniform hydrodynamic
film, which translates into uniform forces at the slider
bar/abrasive article interface. Constant interference (I) of the
abrasive diamonds 114 during the lapping process leads to a notable
reduction in occurring of scratches, a substantial improvement in
pole tip recession critical to the performance of magnetic
recording heads, and a substantial improvement in surface
roughness.
[0063] Note that the substrate 126 has historically been a tin
plate because of ease of charging the diamonds 114 and dressing the
plate. Since the height 112 of the protruding diamonds 114 is
controlled by the thickness of the spacer layer 110, however, other
relatively harder materials are also good candidates for this
application, such as for example soft steels, copper, aluminum, and
the like.
[0064] While the application discussed above is lapping slider bars
for disk drives, for the present abrasive article 118 has a wide
range of other industrial applications, such as for example lapping
semiconductor wafers and polishing metals.
[0065] FIG. 10 illustrates a fixture 150 for manufacturing an
abrasive article 152 with a structured substrate 154 (see FIG. 12)
in accordance with an embodiment of the present invention. The
desired structures 156 are machined in the master plate 158. The
structures 156 can be linear, curvilinear, regular, irregular,
continuous, discontinuous, or a variety of other configurations.
Various structured substrates and adhesives suitable for use in the
present invention are disclosed in U.S. Pat. No. 6,194,317 (Kaisaki
et al); U.S. Pat. No. 6,612,917 (Bruxvoort); U.S. Pat. No.
7,160,178 (Gagliardi et al.); U.S. Pat. No. 7,404,756 (Ouderkirk et
al.); and U.S. Publication No. 2008/0053000 (Palmgren et al.),
which are hereby incorporated by reference.
[0066] In the illustrated embodiment, the structures 156 are a
series of grooves. The surfaces 160 of the grooves 156 can be
machined with a continuous curvilinear shape, a series of discrete
curvilinear or flat shapes with transition locations, or a
combination thereof. In the illustrated embodiment, the grooves 156
include valleys 160A, peaks 160B, and side surfaces 160C
(collectively "160"). The peaks 160B have substantially uniform
peak height 168.
[0067] In the illustrated embodiment, the master plate 158 is
machined with a hard ceramic material such as TiC or TiN. The hard
coat is optional and is not shown in the embodiment of FIG. 10.
Spacer layer 162 is then deposited on the surface 160 of the
grooved master plate 158 with a thickness 164 corresponding* the
desired protruding height of abrasive particles 166. An adhesive
slurry 170 including adhesive 172 and abrasive particles 166 is
distributed evenly over the grooved surface 174 of the spacer layer
162.
[0068] As illustrated in FIG. 11, the substrate 154 with features
182 generally corresponding to grooves 156 is then pressed against
the adhesive slurry 170 with a sufficient force to cause the
abrasive particles 166 to substantially penetrate the spacer layer
162, without substantial penetration into the master plate 158. The
abrasive particles 166 also penetrate into the substrate 154,
primarily at peaks 184.
[0069] The grooves 182 in the substrate 154 are preferably
fabricated with a peak height 180 greater than peak height 168 of
the grooves 156 machined in the grooved master plate 158. The
greater peak height 180 on the substrate 154 permits the abrasive
particles 166 located along critical peaks 184 to be firmly
embedded in the substrate 154. Any inaccuracy in the machining of
the heights 168, 180 of the grooves 156, 182 is preferably located
in the non-critical valleys 190 on the abrasive article 152. Note
that portion of the abrasive particles 166' located in the valleys
190 are not embedded in the substrate 154, but are secured to the
substrate 154 by the adhesive 172.
[0070] The spacer layer 162 controls the depth of penetration of
the abrasive particles 166 into the substrate 154. The adhesive 172
fills any gaps 192 between the surface 186 of the substrate 154 and
the surface 174 of the spacer layer 162. The flatness requirement
of the substrate 154 is less than about the height of the abrasives
particles 166 so as to be embedded a sufficient amount in the
surface 186 of the substrate 154.
[0071] FIG. 12 illustrates the abrasive article 152, with the
sacrificial spacer layer 162 removed. The at least partially cured
adhesive 172 forms a substantially flat reference surface 194 from
which height 196 of the abrasive particles 166 can be measured. The
reference surface 194 also provides a substantially uniform
hydrodynamic film relative to the height 196 of the abrasive
particles 166.
[0072] The grooves 198 in the abrasive article 152 are designed to
promote lubricant transfer from inner diameter to outer diameter
under centrifugal forces to carry the wear by-products and reduce
the height of the hydrodynamic film to promote aggressive material
removal. Various geometrical features and arrangement of abrasive
particles on abrasive articles are disclosed in U.S. Pat. No.
4,821,461 (Holmstrand), U.S. Pat. No. 3,921,342 (Day), and U.S.
Pat. No. 3,683,562 (Day), and U.S. Pat. Pub. No. 2004/0072510
(Kinoshita et al), which are hereby incorporated by reference.
[0073] The present method of manufacturing uniform height fixed
abrasive articles includes preparing a master plate with a shape
that is generally a mirror image of the desired uniform height
fixed abrasive article. A hard coat is optionally applied protect
the surface of the master plate. A spacer layer is deposited on the
master plate or hard coat. An adhesive slurry containing an
adhesive and abrasive particles is distributed evenly over surface
of the spacer layer. A substrate with a surface that is generally a
mirror image of the master plate is then pressed against the
adhesive slurry to embed the abrasive particles into the substrate.
The spacer layer controls the penetration of the abrasive particles
into the substrate. The adhesive fills gaps between the surface of
the substrate and the surface of the spacer layer. The substrate
containing the embedded abrasive particles is separated from the
master plate and the sacrificial spacer layer is removed. The at
least partially cured adhesive forms a substantially flat reference
surface between the protruding abrasive particles.
[0074] It will be appreciated that the present method of
manufacturing uniform height fixed abrasive articles can be used
with a variety of shaped substrates, such as for example concave
surfaces, convex surfaces, cylindrical surfaces, spherical
surfaces, and the like. The present method is not dependent on the
size or composition of the abrasive particles.
[0075] FIG. 13 is a side sectional view of a uniform height fixed
abrasive article 250 with a convex surface 252 in accordance with
an embodiment of the present invention. The convex surface 252 can
be circular, curvilinear, and a variety of other regular and
irregular curved shapes. As with the embodiments discussed above,
adhesive 254 provides a uniform reference surface 256. The abrasive
particles 258 extend a substantially uniform amount above the
reference surface 256. The reference surface 256 is also smooth so
as to promote a substantially uniform hydrodynamic film. A concave
and cylindrical surface can be designed the same embodiments
discussed above. The curved abrasive articles (concave and convex
surfaces) are particularly suited for polishing machined metal
parts, such as for example components for engines and
transmissions, where a significant reduction in friction will
translate into greater fuel efficiency.
[0076] FIG. 14 illustrates a uniform height fixed abrasive article
300 that uses the two step adhesion process disclosed in U.S. Pat.
Nos. 7,198,553 and 6,123,612, which are hereby incorporated by
reference. Elevated heat and pressure are applied to a sintered
powder matrix material and a brazing alloy 302 to create a chemical
bond between the abrasive particles 304 and surface 314 of the
substrate 306. The sacrificial spacer 308 (shown in phantom) is
preferably a soft metal to avoid excessive deformation during
heating of the matrix 302.
[0077] The matrix 302 lacks the ability to fill the spaces 310
between the sintered material 302 and the spacer 308. A low
viscosity curable material 314, such as for example a thermo set
adhesive, is provided to fill the spaces 310 and to provide the
reference surface 312 between the abrasive particles 304. The
curable material 314 also acts as a corrosion barrier to protect
the sintered material 302 from corrosion and other interaction in
chemical mechanical polishing applications.
[0078] FIG. 15A shows a slurry containing abrasive particles
dispersed on master plate. The master plate may be coated with a
non stick substance such as Teflon or other low energy surface
material to prevent strong adhesion forces. The film thickness can
be a monolayer of material applied or thicker. The description
herein omits showing the low surface tension film on the master
plate. The slurry is formed of a carrier fluid 404 and abrasive
particles 402. The slurry is dispersed on the master plate 400 to
provide a uniformly particle dispersion with a uniform particle
distribution density on the master plate. FIG. 15B shows the
carrier fluid evaporated from the master plate surface leaving
abrasive particles distributed uniformly. The carrier fluid can be
a low volatility fluid such as alcohol or water. FIG. 15C shows a
process containing two steps. The first deposition step deposits a
seed layer 412 to provide a conductive path required for an
electro-deposition process. The seed layer can be sputtered or
evaporated onto the master plate 400 containing the abrasive
particles 402. An additional substrate layer formed from Cupper or
Tin or Nickel 410 is then deposited on top of the conductive seed
layer 412. The metal formed a matrix encapsulating the abrasive
particles. The seed layer 412 can be few nanometers thick to
provide a conductive path for the electro-deposition of the
substrate layer. The seed layer is usually Chrome but other
candidates are readily available. The substrate layer is deposited
from an electro platting process for example. Cupper and Tin
materials can be grown to many microns thick with very low film
stress. A dry process such as MOCVD to deposit the substrate
material is preferred as an initial deposition process to lock the
abrasive particles in place. Once the abrasive particles are
secured a wet process can be applied. Wet deposition processes such
as electroplating are economical. Once the thickness of the
substrate reaches a desired value, 20 microns for example, the
substrate containing the abrasives is removed from the master plate
as shown in FIG. 15D. Further etching on the surface containing the
abrasive particles removes a substantially uniform thickness of the
substrate layer exposes the abrasive particles 402 with a uniform
height 420 as shown in FIG. 15E. The height of the protruding
abrasive particles 420 matches the amount of material etched from
the substrate surface.
[0079] FIG. 16A shows a slurry containing a carrier fluid 504 and
abrasive particles 502 dispersed on a master plate 500. The slurry
is dispersed on the master plate 500 to provide a uniformly
dispersed particle distribution onto the master plate. The
thickness of the fluid carrier 508 is controlled to match the
desired abrasive protrusion. The fluid carrier is cross linked by
thermal or irradiative processes such as UV process to form a cured
polymer structure layer to accept a seed layer. FIG. 16B gives a
depiction of a seed layer 510 deposited on the polymeric structure
512 and the abrasive particles 502. The seed layer 510 can be
sputtered or evaporated onto the polymer structure 512 containing
the abrasive particles 502. The seed layer can be Chrome or Nickel
to promote the electroplating of an additional substrate layer
formed from Cupper, Tin or Nickel. The seed layer can be few
nanometers thick to provide a conductive path for the
electro-deposition of the substrate layer. The substrate layer is
deposited from an electro platting process for example. Cupper and
Tin materials can be grown to many microns thick with very low
residual film stress. Once the thickness of the substrate reaches a
desired value, 20 microns for example, the substrate containing the
polymer spacer and the abrasives is removed from the master plate
as shown in FIG. 16C. Further etching on the surface containing the
abrasive particles removes the soft polymer layer revealing the
particle abrasives with a uniform height 520 matching the thickness
of the polymeric film. The height of the particle abrasives matches
the thickness of the polymeric spacer.
[0080] Where a range of values is provided, it is understood that
each intervening value, to the tenth of the unit of the lower limit
unless the context clearly dictates otherwise, between the upper
and lower limit of that range and any other stated or intervening
value in that stated range is encompassed within the inventions.
The upper and lower limits of these smaller ranges which may
independently be included in the smaller ranges is also encompassed
within the inventions, subject to any specifically excluded limit
in the stated range. Where the stated range includes one or both of
the limits, ranges excluding either both of those included limits
are also included in the inventions.
[0081] Unless defined otherwise, all technical and scientific terms
used herein have the same meaning as commonly understood by one of
ordinary skill in the art to which these inventions belong.
Although any methods and materials similar or equivalent to those
described herein can also be used in the practice or testing of the
present inventions, the preferred methods and materials are now
described. All patents and publications mentioned herein, including
those cited in the Background of the application, are hereby
incorporated by reference to disclose and described the methods
and/or materials in connection with which the publications are
cited.
[0082] The publications discussed herein are provided solely for
their disclosure prior to the filing date of the present
application. Nothing herein is to be construed as an admission that
the present inventions are not entitled to antedate such
publication by virtue of prior invention. Further, the dates of
publication provided may be different from the actual publication
dates which may need to be independently confirmed.
[0083] Other embodiments of the invention are possible. Although
the description above contains much specificity, these should not
be construed as limiting the scope of the invention, but as merely
providing illustrations of some of the presently preferred
embodiments of this invention. It is also contemplated that various
combinations or sub-combinations of the specific features and
aspects of the embodiments may be made and still fall within the
scope of the inventions. It should be understood that various
features and aspects of the disclosed embodiments can be combined
with or substituted for one another in order to form varying modes
of the disclosed inventions. Thus, it is intended that the scope of
at least some of the present inventions herein disclosed should not
be limited by the particular disclosed embodiments described
above.
[0084] Thus the scope of this invention should be determined by the
appended claims and their legal equivalents. Therefore, it will be
appreciated that the scope of the present invention fully
encompasses other embodiments which may become obvious to those
skilled in the art, and that the scope of the present invention is
accordingly to be limited by nothing other than the appended
claims, in which reference to an element in the singular is not
intended to mean "one and only one" unless explicitly so stated,
but rather "one or more." All structural, chemical, and functional
equivalents to the elements of the above-described preferred
embodiment that are known to those of ordinary skill in the art are
expressly incorporated herein by reference and are intended to be
encompassed by the present claims. Moreover, it is not necessary
for a device or method to address each and every problem sought to
be solved by the present invention, for it to be encompassed by the
present claims. Furthermore, no element, component, or method step
in the present disclosure is intended to be dedicated to the public
regardless of whether the element, component, or method step is
explicitly recited in the claims.
* * * * *