U.S. patent application number 10/654584 was filed with the patent office on 2004-07-01 for high temperature, high strength, colorable materials for use with electronics processing applications.
This patent application is currently assigned to Entegris, Inc.. Invention is credited to Extrand, Charles W..
Application Number | 20040126521 10/654584 |
Document ID | / |
Family ID | 32176438 |
Filed Date | 2004-07-01 |
United States Patent
Application |
20040126521 |
Kind Code |
A1 |
Extrand, Charles W. |
July 1, 2004 |
High temperature, high strength, colorable materials for use with
electronics processing applications
Abstract
Certain embodiments include an electrostatic-discharge safe tray
for receiving and/or storing electronic components, e.g.,
read/write heads. Such trays may be made from a mixture of at least
one high temperature, high strength polymer, at least one metal
oxide, and at least one pigment. The use of the metal oxides as
conductive materials advantageously allows for light-colored
electrostatic-discharge safe materials to be made, so that such
materials may be colored with pigments without compromise of
material performance specifications.
Inventors: |
Extrand, Charles W.;
(Minneapolis, MN) |
Correspondence
Address: |
PATTERSON, THUENTE, SKAAR & CHRISTENSEN, P.A.
4800 IDS CENTER
80 SOUTH 8TH STREET
MINNEAPOLIS
MN
55402-2100
US
|
Assignee: |
Entegris, Inc.
|
Family ID: |
32176438 |
Appl. No.: |
10/654584 |
Filed: |
September 3, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60407749 |
Sep 3, 2002 |
|
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Current U.S.
Class: |
428/35.7 |
Current CPC
Class: |
Y10T 428/1352 20150115;
H05K 9/0067 20130101; B65D 1/36 20130101 |
Class at
Publication: |
428/035.7 |
International
Class: |
B65D 001/00 |
Claims
1. A colored article for receiving electronic components, the
article comprising: a colored tray having a plurality of pockets
that each have an electrostatic discharge-safe surface that
comprises a mixture of at least one high temperature, high strength
polymer, at least one metal oxide, and at least one pigment.
2. The article of claim 1 wherein the high temperature, high
strength polymer comprises a member of the group consisting of
polyphenylene sulfide, polyetherimide, polyarylketones,
polyetherketone, polyetheretherketone, polyetherketoneketone,
polyethersulfone.
3. The article of claim 1 wherein the metal oxide is present at a
concentration of about 40% to about 75% by weight.
4. The article of claim 3 wherein the surface has a L value of at
least about 55.
5. The article of claim 1 wherein the metal oxide is present at a
concentration of about 50% to about 60% by weight.
6. The article of claim 1 wherein the surface has a L value of at
least about 55.
7. The article of claim 1 wherein the surface has a L value of at
least about 65.
8. The article of claim 1 wherein at least a portion of the surface
comprises a bottom of the pocket, with the bottom being flatter
than an average of about 0.1 inches per inch.
9. The article of claim 1 wherein at least a portion of the surface
comprises a bottom of the pocket, with the bottom being flatter
than an average of about 0.015 inches per inch.
10. The article of claim 1 wherein the high temperature, high
strength polymer comprises a member of the group consisting of
polyphenylene oxide, ionomer resin, nylon 6 resin, nylon 6,6 resin,
aromatic polyamide resin, polycarbonate, polyacetal,
trimethylpentene resin, polysulfone,
tetrafluoroethylene/perfluoroalkoxyethylene copolymer,
high-temperature amorphous resin, polyallylsulfone, liquid crystal
polymer, polyvinylidene fluoride, ethylene/tetrafluoroethylene
copolymer, tetrafluoroethylene/hex- afluoropropylene copolymer, and
tetrafluoroethylene/hexafluoropropylene/pe- rfluoroalkoxyethylene
terpolymer.
11. The article of claim 1 wherein the at least one metal oxide
comprises a member of the group consisting of aluminum borate, zinc
oxide, basic magnesium sulfate, magnesium oxide, graphite,
potassium titanate, magnesium borate, titanium diboride, tin oxide,
and calcium sulfate.
12. The article of claim 1 wherein the at least one metal oxide
comprises antimony doped tin oxide.
13. The article of claim 1 wherein the at least one metal oxide
comprises a metal oxide doped ceramic.
14. The article of claim 1 wherein the at least one metal oxide is
disposed in particles.
15. The article of claim 14 wherein the particles are present in
the mixture at a concentration of at least 40 percent by
weight.
16. The article of claim 15 wherein the surface has an L value of
at least about 55.
17. The article of claim 14 wherein the metal oxide is present at a
concentration between about 50 and about 70 percent by weight.
18. The article of claim 14 wherein the particles comprise a
ceramic.
19. The article of claim 1 wherein at least a portion of the metal
oxide comprises a whisker.
20. The article of claim 19 wherein the whisker comprises a
material in the group consisting of titanate, potassium titanate,
and aluminum borate.
21. The article of claim 14 wherein the wherein the particles
comprise an isotropic flow shape.
22. The article of claim 1 wherein the pigment comprises a member
of the group consisting of titanium dioxide, iron oxide, chromium
oxide greens, iron blue, chrome green, aluminum sulfosilicate,
cobalt aluminate, barium manganate, lead chromates, cadmium
sulfides and selenides.
23. The article of claim 1 wherein the at least one metal oxide is
the at least one pigment.
24. The article of claim 1 wherein the surface comprises a
resistivity in the range of 10.sup.3 to 10.sup.14 ohms per
square.
25. The article of claim 1 wherein the surface comprises a
resistivity in the range of 10.sup.4 to about 10.sup.7 ohms per
square.
26. A set of colored trays for electronic component processing, the
set comprising: at least two subsets of colored trays wherein each
colored tray has a plurality of pockets that each comprises an
electrostatic discharge-safe surface, with each subset comprising a
subset color distinct from the other subset colors, wherein the
surfaces comprise a high temperature, high strength polymer, a
metal oxide, and a pigment.
27. The set of trays of claim 25 wherein each subset of trays
corresponds to a different model of tray.
28. The set of trays of claim 26 wherein each subset of trays
corresponds to a type of component in the pockets of the trays.
29. The set of claim 26 wherein the pockets are flatter than an
average of about 0.1 inches per inch.
30. The set of claim 26 wherein the pockets are flatter than an
average of about 0.015 inches per inch.
31. The set of claim 26 wherein the surface has an L value of at
least about 55.
32. The set of claim 26 wherein the at least one metal oxide is
chosen from the group consisting of aluminum borate, zinc oxide,
basic magnesium sulfate, magnesium oxide, graphite, potassium
titanate, magnesium borate, titanium diboride, tin oxide, calcium
sulfate, and antimony doped tin oxide.
33. The set of claim 26 wherein the at least one metal oxide is
present at a concentration between 50 and 70 percent by weight.
34. An article for receiving electronic components, the article
comprising: a structure for contacting and supporting an electronic
component, the structure comprising at least one electrostatic
discharge-safe surface that comprises a mixture of at least one
high temperature, high strength polymer and at least one metal
oxide, wherein the surface has an L value of more than about
55.
35. The article of claim 34 wherein the surface comprises a bottom
of a pocket.
36. The article of claim 34 wherein the surface is flatter than an
average of about 0.1 inches per inch.
37. The article of claim 34 wherein the polymer has a stiffness of
at least about 1 GPa and a glass transition temperature or melting
point higher than about 150.degree. C.
38. The article of claim 34 wherein the metal oxide is present at a
concentration of about 40% to about 75% by weight.
39. The article of claim 34 wherein the at least one metal oxide
comprises a member of the group consisting of aluminum borate, zinc
oxide, basic magnesium sulfate, magnesium oxide, graphite,
potassium titanate, magnesium borate, titanium diboride, tin oxide,
calcium sulfate, and antimony doped tin oxide.
40. The article of claim 34 wherein the surface further comprises a
pigment.
41. A colored article for receiving electronic components, the
article comprising: a colored tray comprising a plurality of
pockets, each pocket comprising at least one electrostatic
discharge-safe surface that comprises a mixture of at least one
high temperature, high strength polymer, at least one metal oxide,
and at least one pigment, wherein the surface has an L value of
more than about 55.
42. The article of claim 41 wherein the surface is flatter than an
average of about 0.1 inches per inch.
43. The article of claim 41 wherein the polymer has a stiffness of
at least about 1 GPa and a glass transition temperature or melting
point higher than about 150.degree. C.
44. The article of claim 41 wherein the at least one metal oxide is
present at a concentration of about 40% to about 75% by weight.
45. The article of claim 41 wherein the at least one metal oxide is
present at a concentration of about 40% to about 75% by weight.
46. The article of claim 34 wherein the at least one metal oxide
comprises a member of the group consisting of aluminum borate, zinc
oxide, basic magnesium sulfate, magnesium oxide, graphite,
potassium titanate, magnesium borate, titanium diboride, tin oxide,
calcium sulfate, and antimony doped tin oxide.
47. The article of claim 41 wherein the pigment is the metal
oxide.
48. A method for processing electronic components, the method
comprising placing an electronic component on an electrostatic
discharge-safe surface of a colored tray that comprises a plurality
of pockets, with the surface being a bottom of a pocket and
comprising a mixture of at least one high temperature, high
strength polymer, at least one metal oxide, and at least one
pigment.
49. The method of claim 48 wherein the at least one the high
temperature, high strength polymer comprises a member of the group
consisting of polyphenylene sulfide, polyetherimide,
polyarylketones, polyetherketone, polyetheretherketone,
polyetherketoneketone, polyethersulfone.
50. The method of claim 48 wherein the at least one metal oxide is
present at a concentration is about 40% to about 75% by weight.
51. The method of claim 48 wherein the surface has a L value of at
least about 55.
52. The method of claim 48 wherein at least a portion of the
surface is flatter than an average of about 0.1 inches per
inch.
53. The method of claim 48 wherein the at least one metal oxides
comprises particles are present in the mixture at a concentration
of at least 40 percent by weight.
54. The method of claim 48 wherein at least a portion of the at
least one metal oxide comprises a whisker.
55. The method of claim 48 wherein the at least one metal oxide
comprises particles that comprise an isotropic flow shape.
56. The method of claim 48 wherein the at least one pigment is the
at least one metal oxide.
57. The method of claim 48 wherein the surface comprises a
resistivity in the range of 10.sup.3 to 10.sup.14 ohms per
square.
58. The method of claim 48 wherein the colored tray is a read/write
head tray.
59. The method of claim 48 wherein the at least one pigment
comprises a member of the group consisting of titanium dioxide,
iron oxide, chromium oxide greens, iron blue, chrome green,
aluminum sulfosilicate, cobalt aluminate, barium manganate, lead
chromates, cadmium sulfides and selenides.
60. A method of producing an article for electronic processing, the
method comprising: molding a tray having a plurality of pockets
that each comprise an electrostatic discharge-safe surface that
comprises a high temperature, high strength polymer and a
conductive filler, an L value of at least about 55, and a
resistivity in the range of 10.sup.3 to 10.sup.14 ohms per square,
wherein the surface is flatter than an average of about 0.1 inches
per inch.
61. The method of claim 60 wherein the polymer has a glass
transition temperature or melting point higher than about
150.degree. C. and a stiffness of at least about 1 GPa.
62. The method of claim 60 wherein the conductive filler is a metal
oxide present in a concentration of about 40% to about 75% by
weight.
63. The method of claim 60 wherein the article is a read/write head
tray.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to U.S. Provisional Patent
Application Serial No. 60/407,749, filed Sep. 3, 2002, which is
hereby incorporated by reference herein.
BACKGROUND
[0002] Read/Write heads are electronic components that read
information on magnetic media and/or write information onto
magnetic media. Read/Write heads are used in many electronic
devices and are commonly used in computers to read and write
information to and from a computer's memory.
[0003] Complicated assembly lines are typically used to make the
Read/Write heads and to install them into electronic components.
The Read/Write heads are stored and transported in special
Read/Write head trays that facilitate shipping the heads and
processing them at the assembly line. Most Read/Write head trays
must prevent any electrostatic discharge (ESD). A tray is made
ESD-safe by making the surface that the Read/Write head rests upon
into a conductive surface. A conductive surface allows static
electricity to dissipate so that a static charge can not build up
on the surface.
[0004] The Read/Write heads are dark-colored and small; in
appearance, they resemble black peppercorns. The Read/Write heads
are therefore difficult to see if the tray has a dark color. A dark
color makes it difficult to verify that the read/write heads are
present in the tray and to remove them from the tray, especially
when machine vision is used.
[0005] Read/Write head trays are conventionally from a material
made by mixing a polymer with stainless steel. The stainless steel
is sometimes referred to as a filler because it supplements the
polymer's electrical properties by making the polymer into a
conductive ESD safe material. The stainless steel is conductive and
performs well at high temperatures, but, without pigment, creates a
dark color. Stainless steel, however, is difficult to mix with a
polymer to achieve a uniform distribution of stainless steel.
Without a uniform distribution, the material is more prone to have
small insulated spots that compromise the ESD-safe properties of
the material. Further, the stainless steel has magnetic properties
that could potentially damage the Read/Write heads. Moreover,
materials made with stainless steel require high concentrations of
pigments to color them, so that other properties of the material
are compromised.
SUMMARY OF THE INVENTION
[0006] These problems are solved by making Read/Write head trays
that avoid the use of stainless steel. Instead of stainless steel,
metal oxide fillers are used; consequently, the materials are
colorable. The materials are colorable because they are
light-colored and do not require high concentrations of pigments to
color them. The materials for making the trays are preferably made
with a high temperature, high strength polymer and a metal
oxide.
[0007] A preferred embodiment of the invention is a Read/Write head
tray, at least a portion of the tray comprising an electrostatic
discharge-safe surface for receiving a Read/Write head, with the
surface being made of a mixture of at least one high temperature,
high strength polymer and at least one metal oxide. The lightness
of the color of the materials may be measured and assigned an L
value in the CIE L*a*b* index (see discussion, below), e.g., more
than about 55.
[0008] Certain embodiments relate to a colored article for
receiving electronic components that is a tray having a plurality
of pockets that each have an electrostatic discharge-safe surface
that comprises a mixture of at least one high temperature, high
strength polymer, at least one metal oxide, and at least one
pigment. Certain embodiments relate to a set of trays for
electronic component processing, the set having at least two
subsets of trays wherein each tray has a plurality of pockets that
each comprises an electrostatic discharge-safe surface, with each
subset comprising a subset color distinct from the other subset
colors. Certain embodiments relate to an article for receiving
electronic components, the article having a structure for
contacting and supporting an electronic component, and with the
structure comprising at least one electrostatic discharge-safe
surface that comprises a mixture of at least one high temperature,
high strength polymer and at least one metal oxide, wherein the
surface has an L value of more than about 55 or 65.
[0009] Certain embodiments relate to an article for receiving
electronic components, the article comprising a tray having a
plurality of pockets, each pocket comprising at least one
electrostatic discharge-safe surface that comprises a mixture of at
least one high temperature, high strength polymer at least one
metal oxide, and at least one pigment, wherein the surface has an L
value of more than about 55 or 65. Certain embodiments relate to a
method of producing an article for electronic processing, the
method comprising: molding a tray having a pocket that comprises an
electrostatic discharge-safe surface that comprises a high
temperature, high strength polymer and a conductive filler, wherein
the surface comprises, an L value of at least about 55 or 65, and a
resistivity in the range of 10.sup.3 to 10.sup.14 ohms per square,
wherein the surface is flatter than an average of about 0.1 or
0.015 inches per inch. Certain embodiments relate to a method of
producing an article for electronic processing, the method
comprising molding a tray having a pocket that comprises an
electrostatic discharge-safe surface that comprises a high
temperature, high strength polymer and a conductive filler, wherein
the surface comprises, an L value of at least about 55 or 65, and a
resistivity in the range of 10.sup.3 to 10.sup.14 ohms per square,
wherein the surface is flatter than an average of about 0.1 or
0.015 inches per inch.
BRIEF DESCRIPTION OF THE FIGURES
[0010] FIG. 1 depicts the coordinate system for 1976 CIE L*a*b*
Space and the L value for certain embodiments;
[0011] FIG. 2 depicts a multipocketed tray for receiving electrical
components;
[0012] FIG. 3 depicts a cross-section of FIG. 2 in a view as
indicated by line 3-3 in FIG. 2; and
[0013] FIG. 4 depicts a plurality of the trays of FIG. 2 in a
stacked configuration.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0014] A preferred embodiment of the invention is an ESD-safe
Read/Write head tray that is light in color, is made of a high
temperature, high strength polymer, and contains a metal oxide
filler. The metal oxide filler preferably includes ceramics.
[0015] The lightness of the color of a material is objectively
quantifiable using the Commission Internationale d'Eclairage L*a*b*
color system (CIELab, see K. McLaren The Development of the CIE
1976 (L*a*b*) Uniform Colour-Space and Colour-Difference Formula,
J. Society of Dyers and Colourists, 92:338-341 (1976) and G. A.
Agoston, Color Theory and Its Application in Art and Design,
Hedelberg, 1979). As shown in FIG. 1, the 1976 CIE L*a*b* system
assigns every color a position on a three-coordinate axis. L is the
measure of lightness, and has a value that ranges from 0 (black) to
100 (white). "L" is used herein for the 1976 CIE L*a*b* system:
elsewhere, L* may be used to refer to the same value described
herein as "L". The a* axis indicates the amount of red or green and
the b* axis indicates the amount of yellow or blue. Thus a value of
0 for both "a*" and "b*" indicates a balanced gray. Since the
CIELab system is device-independent, it is a popular choice for
computer imaging applications. The CIELab values are measurable
using standardized tests that are familiar to those skilled in
these arts, for example, by using a reflectance meter. For example,
reflectance meters are manufactured by Photovolt Instruments, Inc.,
Minneapolis, Minn., (Photovolt Model 577 and by Minolta
Corporation, Ramsey, N.J., (model Minolta CM 2002). Thus L is an
objective, quantifiable, and reproducible measure of the lightness
of any color.
[0016] Referring to FIG. 1, certain embodiments of materials are
set forth herein that provide for an L value that ranges from
essentially 0 to about 100. For example, a very dark, near black,
color may be achieved by mixing polymers with carbon black to
achieve an L value of close to 0. And white pigments, e.g.,
titanium oxides, can be added to achieve a near-white color close
to 100. An example of an electrostatic discharge-safe material
suitable for use as a support for electronic component processing
having a light color is a polyetheretherketone mixed with about 54%
by weight antimony-doped tin oxide conductive material, which has
an L value of 64.9, see "65" in FIG. 1, as measured using a
reflectance spectrophotometer with output programmed for the CIELab
system. The other samples described herein have been visually
determined to fall within the ranges as set forth, below.
[0017] In contrast to conventional processing methods in the
relevant field of art, certain embodiments set forth herein provide
for materials having a high L value while maintaining suitable
mechanical and electrostatic discharge-safe conductive properties.
Moreover, certain embodiments retain moldability characteristics
such as flatness. An aspect of certain of these embodiments is the
use of metal oxides or ceramics to achieve the electrostatic
discharge-safe and coloration properties. Another aspect of certain
of these embodiments is the use of high temperature, high strength
polymers. Another aspect of certain of these embodiments is the use
of isotropic flow particles. All ranges in the continuum from about
0 to about 100 are contemplated. Other embodiments achieve
colorations having an L value of at least about 33, about 45, about
55, about 66, or about 80. Some embodiments have colorations that
fall within an L value ranging from about 45 to about 100, from
about 55 to about 99, and from about 66 to about 90. For example, a
material with an L value of more than about 55 would mean that the
material in question was closer to white on the CIELab scale than a
material with an L value of about 55. As described herein, the
conductive, polymeric, and conductive material concentrations are
adjusted until a desired combination of mechanical, color, or
conductive properties are achieved for the contemplated
application. Such adjustment could readily be performed by a person
of ordinary skill in these arts after reading this disclosure.
[0018] A high temperature, high strength polymer is preferably one
having high resistance to heat and chemicals. The polymer is
preferably resistant to the chemical solvent N-methyl pyrilidone,
acetone, hexanone, and other aggressive polar solvents. A high
temperature, high strength polymer has a glass transition
temperature and/or melting point higher than about 150.degree. C.
Further, the high strength, high temperature polymer preferably has
a stiffness of at least 2 GPa.
[0019] Examples of high temperature, high strength polymers are
polyphenylene oxide, ionomer resin, nylon 6 resin, nylon 6,6 resin,
aromatic polyamide resin, polycarbonate, polyacetal, polyphenylene
sulfide (PPS), trimethylpentene resin, polyetheretherketone (PEEK),
polyetherketone (PEK), polysulfone (PSF),
tetrafluoroethylene/perfluoroal- koxyethylene copolymer (PFA),
polyethersulfone (PES), high-temperature amorphous resin (HTA),
polyallylsulfone (PASF), polyetherimide (PEI), liquid crystal
polymer (LCP), polyvinylidene fluoride (PVDF),
ethylene/tetrafluoroethylene copolymer (ETFE),
tetrafluoroethylene/hexafl- uoropropylene copolymer (FEP),
tetrafluoroethylene/hexafluoropropylene/per- fluoroalkoxyethylene
terpolymer (EPE), and the like. Mixtures, blends, and copolymers
that include the polymers described herein may also be used.
Especially preferable are PEK, PEEK, PES, PEI, PSF, PASF, PFA, FEP,
HTA, LCP and the like. Examples of high temperature, high strength
polymers are also given in, for example, U.S. Pat. Nos. 5,240,753;
4,757,126; 4,816,556; 5,767,198, and patent applications EP 1 178
082 and PCT/US99/24295 (WO 00/34381) which are hereby incorporated
herein by reference.
[0020] A metal oxide filler is a conductive material that includes
metal oxide and can be added to a high temperature, high strength
polymer to create an ESD safe material having a light color and
sufficient mechanical properties for use as a Read/Write head tray.
The metal oxides are preferably mixed with ceramics or coated upon
ceramics e.g., metal oxide doped ceramics. Such fillers typically
have a light color that allows them to be used to make a light
colored material. Since they have a light color, other coloring
agents may be added to impart a particular color to the material.
Further, ceramics are durable, and metal oxide/ceramic combination
materials typically have electroconductive properties that are
independent of humidity. A ceramic is a material consisting of
compounds of a metal combined with a non-metallic element. Ceramics
include metal oxides.
[0021] Examples of suitable metal oxides are exemplified by
aluminum borate, zinc oxide, basic magnesium sulfate, magnesium
oxide, potassium titanate, magnesium borate, titanium diboride, tin
oxide, and calcium sulfate. This list of oxides is exemplary and
not intended to limit the scope of the invention. Further examples
of fillers are provided in, for example, U.S. Pat. Nos. 6,413,489;
6,329,058; 5,525,556; 5,599,511; 5,447,708; 6,413,489; 5,338,334;
and 5,240,753, which are hereby incorporated herein by reference.
In general, the metal oxides may be doped or coated with another
metal as needed to impart or enhance conductivity.
[0022] A preferred filler is tin oxide, particularly antimony-doped
tin oxide, for example, the family of products provided under the
trade name Zelec.RTM. by Milliken Chemical Co. These products are
small, roughly spherical-shaped, and light blue-gray to light
green-gray in color. These colors allow for the creation of
materials with a wide range of light colors, including white.
Further, the antimony-doped tin oxide materials can be used to make
transparent films and have the advantages of most ceramics, such
as, non corrosiveness, resistance to acids, bases, oxidizers, high
temperatures, and many solvents.
[0023] Another preferred class of fillers is whiskers, especially
titanate whiskers, and more particularly potassium titanate and
aluminum borate whiskers, which are described in, for example, U.S.
Pat. Nos. 5,942,205 and 5,240,753, which are hereby incorporated
herein by reference. The term whisker refers to a single crystal
filament having a cross-sectional area of up to about
8.times.10.sup.-5 of a square inch and a length of about at least
10 times the average diameter. Whiskers are typically free of flaws
and are therefore much stronger than polycrystals that have a
similar composition. Thus certain whisker fillers can improve the
strength of a composite material as well as impart other properties
such as improved rigidity, abrasion resistance, and electrostatic
dissipation. A preferred class of whiskers are provided under the
trade name DENTALL by Otsuma Chemical Co., Japan; these are ceramic
whiskers coated with a thin layer of tin oxide.
[0024] The sizes and shapes of the fillers are not limited and may
be e.g., whiskers, spheres, particles, fibers, or other shapes. The
sizes of the fillers are not limited, but small particles such as
whiskers or comparably sized spheres, or very small sizes are
preferable. Technologies for making very small particles, e.g.,
using nanotechnology, may be employed.
[0025] Suitable metal oxide fillers may be disposed in a variety of
configurations. For example, an inert core particle may be coated
with a metal oxide. The metal oxide coating is thus extended by the
inert particle to result in a less expensive product.
Alternatively, a hollow core may be used instead of an inert
particle. Or, the size of the particles may be made smaller by
omitting the core. Or, a ceramic may be doped with a metal oxide.
Doped materials can be conductive while retaining the mechanical
and coloring properties of the ceramic.
[0026] The metal oxide conductors should be disbursed in the
material so that three-dimensional interconnecting networks of the
conductors are formed. The networks serve as a circuit to drain
static charges. The concentration of the metal oxide conductors is
related to the ESD properties of the material. Very low
concentrations of metal oxide conductors create a high surface
resistivity. The resistivity drops slowly as the concentration of
metal oxide conductors is increased until a "percolation threshold"
is reached when the metal oxide conductors begin touching each
other and further increases in the metal oxide conductor
concentration cause rapid drops in resistivity. Eventually, a
ceramic concentration is reached wherein further increases in the
metal oxide conductor concentration fails to create substantial
drops in resistivity because the metal oxide conductors have
already formed an optimal number of networks. Typically, the
addition of materials having less conductivity than the metal oxide
conductors will result in increased surface resistivity. Thus, the
addition of pigments can affect surface resistivity but
compositions that have a desired resistivity can be made by
adjusting the amounts of pigment and conductive filler.
[0027] There are numerous advantages to having a light-colored
material for a Read/Write head tray. One advantage is that the
Read/Write heads may be visualized. Another advantage is that the
trays are colorable. Thus the color may be optimized to make the
heads more easily visible. Or different types of Read/Write head
trays may be made with different colors so that different models
and applications of trays maybe easily recognized by a user. Or
various types or sizes of heads may be stored in trays of different
colors so that shipping and use of the heads is efficient.
[0028] Certain embodiments further incorporate pigments to achieve
not only a desired L value, but also a particular color, e.g., red,
green, blue, yellow, or combinations thereof. The pigments are
added in a concentration suitable to achieve the desired color. The
desired coloration may be accomplished by adding pigments known to
those skilled in these arts, and mixing them with conductive
materials and polymers as described herein to achieve a desired
color, conductivity, and mechanical characteristics. Examples of
pigments include titanium dioxide, iron oxide, chromium oxide
greens, iron blue, chrome green, aluminum sulfosilicate, cobalt
aluminate, barium manganate, lead chromates, cadmium sulfides and
selenides. Carbon black may be used if a black color is desired or
if the carbon black is used in concentrations that do not create an
overly dark or black color. Colors that may be achieved with the
use of pigments spans the spectrum of visible light, including
white.
[0029] The filler(s) are preferably present in amounts sufficient
to make the Read/Write head tray have a surface resistivity in the
range of about 10.sup.3 to about 10.sup.14 ohms per square, a range
that embues the surface with ESD-safe properties; more preferably
the surface resistivity is in the range between about 10.sup.4 to
less than about 10.sup.7 ohms per square. Further, the filler is
preferably evenly distributed through the material so as to avoid
small insulated spots that compromise its ESD-safe properties.
Further, the filler is preferably present in the concentration that
avoids creating a black color in the material, and more preferably
avoids creating a dark color in the material. The concentration of
carbon black that is required to make an ESD safe material causes
the material to be dark, and essentially black. Microchip trays are
conventionally made with carbon black.
[0030] A material made of a polymer and a carbon filler is commonly
used to make microchip trays for holding microchips. Prior art
microchip trays, however, are not suitable for use as Read/Write
head trays because the microchip trays are very dark colored due to
the presence of the carbon filler. In a microchip tray, the
Read/Write heads would be difficult to see because the Read/Write
heads are small and dark and the microchip tray is dark. As a
result, it would be difficult to use such prior art trays in
conjunction with Read/Write heads. Further, an acceptable chip tray
surface resistivity is usually in the range of at least about
10.sup.7 to 10.sup.8 per square. In contrast, an acceptable
read/write head tray surface resistivity is usually in the range of
about 10.sup.4 to less than about 10.sup.7 ohms per square. Since a
conductive material must be added to a polymer to create an ESD
safe material, and material with a resistivity of, e.g., 10.sup.8
ohms per square has more filler than a material with a resistivity
of, e.g., 10.sup.4 ohms per square. Because of the uncertainties
associated with increasing the amount of filler to high levels,
approaches for making the ESD safe materials for computer chip
trays can not be assumed to be transferable to read/right head
trays. Moreover, materials used for use with computer chip
processing, for example wafer carriers, must have very low levels
of extractable metal ions, but this is not a major concern for
Read/Write head tray materials. Therefore technologies and
approaches for making microchip trays are not applicable to making
Read/Write head trays.
[0031] For these reasons, scientists making Read/Write head trays
have developed technologies that are different from technologies
for making computer chip trays. Instead of using a carbon filler,
Read/Write head trays are conventionally made with a metallic
filler such as stainless steel. The stainless steel is conductive,
performs well at high temperatures, and does not create a dark
color in the material. Since the material is not dark, the
read/write heads may be readily visualized.
[0032] The inventors have unexpectedly found the surprising result
that high temperature, high-strength polymers may be mixed with
more than about 40% ceramics by weight to achieve an ESD safe
material without losing desirable processing properties such as
moldability and flowability and without losing desirable mechanical
properties such as compressive and tensile strength and appropriate
rigidity. This result is surprising because, although polymers may
be mixed with moderate amounts of non polymeric materials without
losing the desirable properties of the polymer in the final
product, the addition of a large amount of non polymeric materials,
i.e. more than about 40% by weight, would be expected to result in
a final product with properties that did not resemble those of the
polymer. Ceramics treated with, or doped with, metal oxides are
preferable for creating ESD safe materials. Large amounts of such
ceramics, however, are typically required to achieve the desired
conductivity in the materials. The preferred concentration range of
ceramics is between about 40% and about 75%, a more preferred
concentration range is between about 45% percent and about 70%, and
a yet more preferable range is between about 50% and about 60%.
[0033] Moreover, it is surprising that the addition of more than
about 40% by weight metal oxides and/or ceramics to a high
strength, high temperature polymer can result in materials having
surfaces that are flat, and even more surprisingly, flatter than
surfaces achieved with stainless steel. In fact, however, the use
of metal oxides with a high strength, high temperature polymer
results in a Read/Write head tray that is more flat than trays made
with stainless steel. The term smooth may sometimes used to refer
to a lack of warp, as was the case in the priority document of this
application, but, for the sake of clarity, the term flat is adopted
herein to denote a lack of warp. Warp is curvature that is
sometimes undesirably introduced into a surface in a molding or
other processing step. The term flat is thus not to be confounded
with measures of roughness. Flatness is a desirable feature of
Read/Write head trays. One possible reason for the unexpected
flatness is that the metal oxides used in the flat surfaces had
isotropic flow shapes. An isotropic flow shape is a shape that
resists becoming oriented in any particular direction as a result
of forces created by a flowing fluid; in other words the flow
characteristics of the particle are approximately the same in all
directions. Thus a spherical particle has an isotropic flow shape
because the particle does not become oriented in any particular
direction when the particle is mixed in a flowing fluid. In
contrast, a rod-shaped particle does not have an isotropic flow
shape because it tends to align its longest axis in the direction
parallel to the direction of flow.
[0034] Many embodiments herein have been described in terms of
Read/Write head trays because that is a preferred embodiment.
However, these descriptions should also be understood as applying
more generally to all types of trays that used in electronic
processing. Trays are used, for example, for microchips, computer
components, and audio component processes, see also U.S. Pat. No.
6,079,565 and U.S. patent Ser. No. 10/241,815, filed Sep. 11, 2002,
which are hereby incorporated herein by reference. Electronic
processing includes those manufacturing processes that involve
assembling components for the electronics industry. Trays are
useful for such processes because the components must be moved
and/or stored in a fashion that is convenient and protects the
components from contaminations and static discharges. A tray
includes an electrostatic discharge-safe surface that receives and
contacts an electronic component to thereby support it. Trays have
a plurality of pockets, for example, as in FIGS. 2 and 3. The
component is contained by the tray pocket, which may be, for
example, an indentation, a space surrounded by walls, posts, or
protrusions, a groove, or other structure that limits the
component's mobility while on the tray so that the tray can
successfully be moved without dislodging the component from the
tray. Trays are preferably stackable (FIG. 4) and the stacks are
preferably also stackable, e.g., on pallets, so as to facilitate
processing.
[0035] A surface may comprise a material by molding the surface
from the material. Thus the materials in the surface are known if
the material from which the surface is molded are known. Thus a
surface may be assumed to resemble a material's bulk composition,
even though it is appreciated that the very uppermost portions of a
surface can have a composition that is distinct form the bulk of
the material. Further, a surface may be determined to have an
average flatness that is measurable in inches per inch.
Conventional flatness measurements or L value calorimetric
measurements may be used that provide an average for a significant
portion of the surface. Such measurements can thus be distinguished
from measurements that provide an average for a very small portion
of the surface, e.g., atomic force microscopy.
[0036] Referring to FIGS. 2-4, which depict a tray 100 having a
plurality of pockets 180. The pockets 180 have bottom surfaces 120
that form sides 102 that contain objects on the bottom surfaces
120. The top surface 132 of tray 100 is continuous and defines
separations between pockets 180. Outer edge 116 of top surface 132
is continuous with and perpendicular to upper tray side 122. Tray
side 122 is perpendicular to lip 112. Lip 112 is perpendicular to
lower tray side 114. Referring to FIG. 4, trays 100 may be placed
in a stacked configuration 101 without bottom tray surface 126
impinging on an electrical component, e.g., depicted by 208. Lip
112 acts as a stop for bottom tray surface 126.
EXAMPLE 1
[0037] Prototype Read/Write head trays were prepared by molding
them from a mixture of metal oxide ceramics with PEEK, as indicated
in Table 1. The molding process was essentially the same as the
process used for PEEK loaded with stainless steel, although the
molding temperature was adjusted slightly downwards. The results of
these experiments showed that Zelec.RTM. ECP 1410T was a preferable
metal oxide ceramic for use in making light colored Read/Write head
trays. Moreover, the high temperature, high-strength polymer could
be loaded with more than 40 percent of the filler without
compromising the mechanical properties needed for the Read/Write
head trays. Furthermore, the surfaces for holding the Read/Write
heads were surprisingly found to be flat, with a flatness that
exceeded the flatness obtained with stainless steel fillers.
1TABLE 1 Mixtures of metal oxide particles with high temperature,
high-strength polymer. Surface Resistivity Metal Oxide Filler
Loading (wt. %) Color (ohms/square) Zelec .RTM. ECP 1410T 40 Light
Gray 10.sup.13 Zelec .RTM. ECP 1410T 60 Light Gray 10.sup.5 Zelec
.RTM. ECP 1410M 40 Dark Gray 10.sup.5 Zelec .RTM. ECP 1410M 60 Did
not work -- Zelec .RTM. ECP 1410XC 40 Did not work -- Zelec .RTM.
ECP 1410XC 60 Did not work --
EXAMPLE 2
[0038] Prototype Read/Write head trays were prepared by molding
them from a mixture PEEK and a metal oxide ceramic, as indicated in
Table 2. The molding process was essentially the same as the
process used for PEEK loaded with stainless steel, although the
molding temperature was adjusted slightly downwards. The results of
these experiments showed that metal oxide ceramics could be used to
make light colored Read/Write head trays that are ESD safe.
Moreover, the high temperature, high-strength polymer could be
loaded with more than 40 percent of the filler without compromising
the mechanical properties needed for the Read/Write head trays.
2TABLE 2 ESD properties of mixtures of metal oxide particles with
high temperature, high-strength polymer. Loading Surface
Resistivity Static Dissipation (percent %) (ohms/square) (seconds)
40 10.sup.13 100 47 10.sup.13 120 52 10.sup.7 0.03 54 10.sup.5 0.03
60 10.sup.5 0.03 60 10.sup.5 0.03
EXAMPLE 3
[0039] The properties of various compositions of PEEK mixed with
metal oxide ceramics were compared, as indicated in Table 3, with a
carbon fiber composition (18% wt.) and neat mixture of PEEK used as
controls. Zelec.RTM. ECP 1410T (52%) was used as the metal oxide
ceramic. The molding process was essentially the same as the
process used for PEEK loaded with stainless steel, although the
molding temperature was adjusted slightly downwards for most
compositions. Shrinkage in the prototype head trays ranged from
0.008 to 0.013 in/in, an acceptable amount. Further, the prototypes
were remarkably flat. The first prototype head tray model had a
surface for receiving a Read/Write head having an average flatness
of 0.004.+-.0.001 in/in with a maximum of 0.007 in/in. a second
prototype head tray model had a surface for receiving a Read/Write
head that had an average flatness of 0.013.+-.0.010 in/in with a
maximum of 0.017 in/in.
[0040] The results of these experiments showed that metal oxides
could be used to make light colored ESD safe Read/Write head trays
with more than 40 percent by weight of metal oxide filler without
compromising the mechanical properties needed for the head trays.
Further, these experiments showed that unexpectedly flat surfaces
could be obtained using a high temperature, high strength polymer
in combination with a metal oxide, such as a metal oxide
ceramic.
3TABLE 3 Properties of various compounds of metal oxides and PEEK.
Metal Oxide Carbon Fiber Ceramic Neat (18%) (52%) Specific gravity
1.3 1.4 2.1 Melt temperature 349 344 344 (.degree. C.) Modulus
(GPa) 3.9 11 6.5 Break stress (MPa) 80 110 90 Break strain (%) 50
1.8 1.8
EXAMPLE 4
[0041] The resin purity properties of various compositions of PEEK
mixed with metal oxide ceramics were compared, as indicated in
Table 4, with a carbon fiber composition (18% wt.) and neat mixture
of PEEK used as controls. Zelec.RTM. ECP 1410T (52% wt) was used as
the metal oxide ceramic. The outgassing was measured by maintaining
a sample for 30 minutes and a 10 Tenax tube at 100.degree. C. and
analyzing the released gasses using an automated thermal desorption
unit-gas chromatograph/mass spectrograph. Metals were analyzed by
placing plaques of the material in dilute nitric acid at 85.degree.
C. for one-hour and analyzing the extracted metals by ICP/MS
inductively coupled plasma/mass spectrometer. Anions were analyzed
by exposing the material to dilute water at 85 degrees C. for
one-hour, followed by analyzing the water by ion chromatography.
Table 5 shows the metals recovered. Table 6 shows the anions
recovered.
[0042] The results of these experiments showed that the metal oxide
ceramics had significantly more extractable metals than comparable
materials formed using carbon fiber. The amount of extracted
metals, however, was adequate for use in a Read/Write head
tray.
4TABLE 4 Resin purity for various high temperature, high-strength
compounds containing metal oxides. Metal Oxide Carbon Fiber Ceramic
Neat PEEK (18%) (52%) Outgassing 0.60 0.62 0.50 (.mu.g/gram) Metals
6658 1057 2278 (ng/g) Anions 464 1104 419 (ng/g)
[0043]
5TABLE 5 Metal levels of the compositions of Table 4. Metals
present Neat Al, Ca, Co, Fe, K, Na, Ni, Pb, Sn, Ti Carbon fiber
(18%) B, Ca, Co, Fe, K, Mg, Na, Ni, Zn Metal Oxide Ceramic (52%)
Al, B, Ba, Ca, Co, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, Pb, Sb, Sn, Ti,
Zn
[0044]
6TABLE 6 Anions of the various PEEK compounds of Table 4. Anion
Carbon fiber Metal oxide (ng/g) Neat (18%) (52%) Fluoride 410 34 56
Chloride BDL 400 280 Nitrate BDL 130 14 Sulfate 10 For 70 60
Phosphate 44 BDL 900 BDL indicates below detection limits
[0045] The embodiments described herein are provided as examples of
the invention and are not intended to limit the scope and spirit of
the invention. All patents and publications set forth in this
application are hereby incorporated herein by reference.
[0046] An embodiment of the invention is a read/write head tray, at
least a portion of the tray comprising an electrostatic
discharge-safe surface for receiving a read/write head, with the
surface being made of a mixture of at least one high temperature,
high strength polymer and at least one metal oxide. Another
embodiment of the invention is a tray made with a high temperature,
high strength polymer chosen from the group consisting of
polyphenylene sulfide, polyetherimide, polyarylketones,
polyetherketone, polyetheretherketone, polyetherketoneketone, and
polyethersulfone. Another embodiment of the invention is a tray
wherein the at least one metal oxide is chosen from the group
consisting of aluminum borate, zinc oxide, basic magnesium sulfate,
magnesium oxide, graphite, potassium titanate, magnesium borate,
titanium diboride, tin oxide, calcium sulfate, and antimony doped
tin oxide. Another embodiment of the invention is a tray wherein
the metal oxide is disposed in particles, and the particles are
present in the mixture at a concentration of at least 40 percent by
weight, or at a concentration of between 50 and 70 percent. The
particles may also further comprise a ceramic. Further the metal
oxide may be disposed in a whisker. Moreover, the whiskers may be
chosen from the group consisting of whiskers made of potassium
titanate and aluminum borate. Another embodiment of the invention
is a filler comprising metal oxide disposed in a particle, wherein
the particle has an isotropic flow shape.
* * * * *