U.S. patent application number 12/723044 was filed with the patent office on 2011-09-15 for electrodeposition baths and systems.
This patent application is currently assigned to Xtalic Corporation. Invention is credited to John Cahalen, Nazila Dadvand, Alan C. Lund, Christopher A. Schuh, Jonathan C. Trenkle.
Application Number | 20110220511 12/723044 |
Document ID | / |
Family ID | 44558922 |
Filed Date | 2011-09-15 |
United States Patent
Application |
20110220511 |
Kind Code |
A1 |
Dadvand; Nazila ; et
al. |
September 15, 2011 |
ELECTRODEPOSITION BATHS AND SYSTEMS
Abstract
Electrodeposition baths and systems. The baths and systems are
useful for forming coated articles. The articles may include a base
material and a coating comprising silver formed thereon. In some
embodiments, the coating comprises a silver-based alloy, such as a
silver-tungsten alloy. The coating may, in some instances, include
at least two layers. For example, the coating may include a first
layer comprising a silver-based alloy and a second layer comprising
a precious metal. The coating can exhibit desirable properties and
characteristics such as durability (e.g., wear), hardness,
corrosion resistance, and high conductivity, which may be
beneficial, for example, in electrical and/or electronic
applications. In some cases, the coating may be applied using an
electrodeposition process.
Inventors: |
Dadvand; Nazila; (Gatineau,
CA) ; Schuh; Christopher A.; (Ashland, MA) ;
Lund; Alan C.; (Ashland, MA) ; Trenkle; Jonathan
C.; (Cambridge, MA) ; Cahalen; John;
(Somerville, MA) |
Assignee: |
Xtalic Corporation
Marlborough
MA
|
Family ID: |
44558922 |
Appl. No.: |
12/723044 |
Filed: |
March 12, 2010 |
Current U.S.
Class: |
205/238 ;
204/242 |
Current CPC
Class: |
C25D 5/18 20130101; C25D
5/10 20130101; C25D 3/64 20130101 |
Class at
Publication: |
205/238 ;
204/242 |
International
Class: |
C25D 3/56 20060101
C25D003/56; C25D 17/00 20060101 C25D017/00 |
Claims
1. A bath, comprising: silver ionic species; tungsten and/or
molybdenum ionic species; and at least one complexing agent,
wherein the bath is suitable for electrodeposition processes.
2. The electrodeposition bath of claim 1, wherein the at least one
complexing agent permits codeposition of silver and tungsten.
3. The bath of claim 1, wherein the at least one complexing agent
comprises an alkyl hydroxyl carboxylic acid.
4. The bath of claim 1, wherein the at least one complexing agent
comprises a substituted pyridine compound.
5. The bath of claim 1, wherein the at least one complexing agent
comprises a compound comprising an imide functional group.
6. The bath of claim 1, wherein the bath has a pH from about 7.0 to
9.0.
7. The bath of claim 1, wherein the bath is an aqueous
solution.
8. The bath of claim 1, further comprising a wetting agent.
9. The bath of claim 1, wherein the at least one complexing agent
comprises cyanide.
10. The bath of claim 1, wherein the electrodeposition bath is
substantially free of cyanide.
11. An electrodeposition system, comprising: a bath; at least one
electrode; and a power supply, wherein the bath comprises silver
ionic species, tungsten and/or molybdenum ionic species, and at
least one complexing agent, wherein the bath is associated with the
at least one electrode, wherein the power supply is connected to
the at least one electrode.
12. The electrodeposition system of claim 11, wherein the at least
one complexing agent comprises an alkyl hydroxyl carboxylic
acid.
13. The electrodeposition system of claim 11, wherein the at least
one complexing agent comprises a substituted pyridine compound.
14. The electrodeposition system of claim 11, wherein the at least
one complexing agent comprises a compound comprising an imide
functional group.
15. The electrodeposition system of claim 11, wherein the bath has
a pH from about 7.0 to 9.0.
16. The electrodeposition system of claim 11, wherein the bath is
an aqueous solution.
17. The electrodeposition system of claim 11, further comprising a
wetting agent.
18. The electrodeposition system of claim 11, wherein the power
supply is capable of generating a waveform having a reverse pulse
sequence.
Description
FIELD OF INVENTION
[0001] The present invention generally relates to electrodeposition
baths and systems.
BACKGROUND OF INVENTION
[0002] Many types of coatings may be applied on a base material.
Electrodeposition is a common technique for depositing such
coatings. Electrodeposition generally involves applying a voltage
to a base material placed in an electrodeposition bath to reduce
metal ionic species within the bath which deposit on the base
material in the form of a metal, or metal alloy, coating. The
voltage may be applied between an anode and a cathode using a power
supply. At least one of the anode or cathode may serve as the base
material to be coated. In some electrodeposition processes, the
voltage may be applied as a complex waveform such as in pulse
deposition, alternating current deposition, or reverse-pulse
deposition.
[0003] Precious metal and precious metal alloy coatings may be
deposited using a process such as electrodeposition. In some
applications, a coating may at least partially wear off as a result
of repeated rubbing against a surface. Such an effect may be
undesirable, especially when the coating is applied at least in
part to improve electrical conductivity, since this effect can
increase the resistance of the coating.
SUMMARY OF INVENTION
[0004] Electrodeposition baths and systems, as well as coated
articles and related methods are provided.
[0005] In one aspect, a method of depositing a coating is provided.
The method comprises providing an anode, a cathode, an
electrodeposition bath associated with the anode and the cathode,
and a power supply connected to the anode and the cathode. The
method further comprises driving the power supply to electrodeposit
a coating on a base material. The coating comprises a silver-based
alloy. The silver-based alloy further comprises tungsten and/or
molybdenum. The silver-based alloy has an average grain size of
less than 1 micron.
[0006] In another aspect, a method of depositing a coating is
provided. The method comprises providing an anode, a cathode, an
electrodeposition bath associated with the anode and the cathode,
and a power supply connected to the anode and the cathode. The
method further comprises driving the power supply to electrodeposit
a coating on a base material. The coating comprises a silver-based
alloy. The silver-based alloy further comprises tungsten and/or
molybdenum, wherein the concentration of tungsten and/or molybdenum
in the silver-based alloy is between 0.1 atomic percent and 50
atomic percent.
[0007] In yet another aspect, a method of forming an electrical
connector is provided. The method comprises providing an anode, a
cathode, an electrodeposition bath associated with the anode and
the cathode, and a power supply connected to the anode and the
cathode. The method further comprises driving the power supply to
electrodeposit a coating on a conductive base material. The coating
comprising a silver-based alloy. The silver-based alloy further
comprising tungsten and/or molybdenum. The method further comprises
forming an electrical connector from the coated conductive base
material.
[0008] In still another aspect, a method of depositing a coating is
provided. The method comprises providing an anode, a cathode, an
electrodeposition bath associated with the anode and the cathode,
and a power supply connected to the anode and the cathode. The
method further comprises driving the power supply to electrodeposit
a coating on a base material. The coating comprises a silver-based
alloy. The silver-based alloy further comprises tungsten and/or
molybdenum, wherein the coating is deposited from an aqueous
solution.
[0009] In yet another aspect, an article is provided. The article
comprises a base material and a coating formed on the base
material, the coating comprising a silver-based alloy. The
silver-based alloy further comprising tungsten and/or molybdenum,
wherein the concentration of tungsten and/or molybdenum in the
silver-based alloy is at least 1.5 atomic percent and the
silver-based alloy has an average grain size of less than 1
micron.
[0010] In still another aspect, an article is provided. The article
comprises a base material and a coating formed on the base
material. The coating comprises a silver-based alloy. The
silver-based alloy further comprises tungsten and/or molybdenum,
wherein the silver-based alloy has an average grain size less than
50% of a thickness of the coating.
[0011] In yet another aspect, an electrical component is provided.
The electrical component comprises a conductive base material and a
coating formed on the base material, the coating comprising a
silver-based alloy, the silver-based alloy further comprising
tungsten and/or molybdenum.
[0012] In still another aspect, a bath is provided. The bath
comprises silver ionic species, tungsten and/or molybdenum ionic
species, and at least one complexing agent. The bath is suitable
for electrodeposition processes.
[0013] In yet another aspect, an electrodeposition system is
provided. The electrodeposition system comprises a bath, at least
one electrode, and a power supply. The bath comprises silver ionic
species, tungsten and/or molybdenum ionic species, and at least one
complexing agent. The bath is associated with the at least one
electrode, wherein the power supply is connected to the at least
one electrode.
[0014] Other aspects, embodiments and features of the invention
will become apparent from the following detailed description when
considered in conjunction with the accompanying drawings. The
accompanying figures are schematic and are not intended to be drawn
to scale. For purposes of clarity, not every component is labeled
in every figure, nor is every component of each embodiment of the
invention shown where illustration is not necessary to allow those
of ordinary skill in the art to understand the invention. All
patent applications and patents incorporated herein by reference
are incorporated by reference in their entirety. In case of
conflict, the present specification, including definitions, will
control.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 shows an electrodeposition system according to an
embodiment.
[0016] FIG. 2 shows an article according to an embodiment.
DETAILED DESCRIPTION
[0017] Coated articles and methods for applying coatings are
described. The article may include a base material and a coating
comprising silver formed thereon. In some embodiments, the coating
comprises a silver-based alloy, such as a silver-tungsten alloy.
The coating may, in some instances, include at least two layers.
For example, the coating may include a first layer comprising a
silver-based alloy and a second layer comprising a precious metal.
The coating can exhibit desirable properties and characteristics
such as durability (e.g., wear), hardness, corrosion resistance,
and high conductivity, which may be beneficial, for example, in
electrical and/or electronic applications. In some cases, the
coating may be applied using an electrodeposition process.
[0018] FIG. 1 shows an electrodeposition system 10 according to an
embodiment. System 10 includes a electrodeposition bath 12. As
described further below, the bath includes the metal sources used
to form the coating and one or more additives. An anode 14 and
cathode 16 are provided in the bath. A power supply 18 is connected
to the anode and the cathode. During use, the power supply
generates a waveform which creates a voltage difference between the
anode and cathode. The voltage difference leads to reduction of
metal ionic species in the bath which deposit in the form of a
coating on the cathode, in this embodiment, which also functions as
the substrate.
[0019] It should be understood that the illustrated system is not
intended to be limiting and may include a variety of modifications
as known to those of skill in the art.
[0020] The electrodeposition baths comprise a fluid carrier for the
metal source(s) and additive(s). In some embodiments, the fluid
carrier is water (i.e., the bath is an aqueous solution). However,
it should be understood that other fluid carriers may also be used
such as molten salts, cryogenic solvents, alcohol baths, amongst
others. In some embodiments, the fluid carrier is a mixture of
water and at least one organic solvent (i.e., an aqueous bath may
contain at least some organic solvent). Those of ordinary skill in
the art are able to select suitable fluid carriers.
[0021] The baths include suitable metal sources for depositing a
coating with the desired composition. When depositing a metal
alloy, it should be understood that all of the metal constituents
in the alloy have sources in the bath. The metal sources are
generally ionic species that are dissolved in the fluid carrier. As
described further below, during the electrodeposition process, the
ionic species are deposited in the form of a metal, or metal alloy,
to form the coating. In general, any suitable ionic species can be
used. The ionic species may be provided from metal salts. For
example, silver nitrate, silver sulfate, silver sulfamate may be
used to provide the silver ionic species when depositing a coating
comprising silver; sodium tungstate, ammonium tungstate, tungstic
acid, etc. may be used to provide the tungsten ionic species when
depositing a coating comprising tungsten. In some cases, the ionic
species may comprise molybdenum. Sodium molybdate, ammonium
molybdate, molybdenum oxide, etc. may be used to provide the
molybdenum ionic species when depositing a coating comprising
molybdenum. It should be understood that these ionic species are
provided as examples and that many other sources are possible. Any
suitable concentration of a metal species may be used, and one of
ordinary skill in the art will be able to select a suitable
concentration by routine experimentation. In some embodiments, the
ionic species in the bath may have a concentration between 0.1 g/L
and 100 g/L, between 5 g/L and 50 g/L, or between 1 and 20 g/L.
[0022] In some embodiments, the bath includes a substituted
pyridine compound. A substituted pyridine compound comprises a
pyridine ring, where at least one hydrogen of the pyridine ring is
replaced with substituent comprising a functional group. The
substituent may comprise any suitable functional group.
Non-limiting examples of a functional group include an amide, an
ester, an ether, a carbonyl, an amine, an alcohol, or combinations
thereof. Those of ordinary skill in the art will be able to
identify other functional groups. A substituted pyridine may
comprise at least one substituent, at least two substituents, at
least three substituents, at least four substituents, or at least
five substituents. One example of a substituted pyridine compound
is nicotinamide. As one of ordinary skill in the art will
recognize, nicotinamide has one substituent, the substituent being
an amide functional group.
[0023] As described herein, the electrodeposition baths may include
one or more additives that may improve the electrodeposition
process and/or quality of coatings. For example, the
electrodeposition bath may comprise at least one complexing agent
(i.e., a complexing agent or mixture of complexing agents). A
complexing agent refers to any species which can coordinate with
the ions contained in the solution. In some embodiments, a
complexing agent or mixture of complexing agents may permit
codeposition of at least two elements. For example, a complexing
agent or mixture of complexing agents may permit codeposition of
silver and tungsten.
[0024] The complexing agent may be an organic species, such as a
citrate ion, a compound comprising an imide functional group, or a
substituted pyridine compound. The complexing agent may be an
inorganic species, such as an ammonium ion. In some cases, the
complexing agent is a neutral species. In some cases, the
complexing agent is a charged species (e.g., negatively charged
ion, positively charged ion). Examples of complexing agents include
citrates, gluconates, tartrates, and other alkyl hydroxyl
carboxylic acids; cyanide; hydantoins (e.g.,
5,5-dimethylhydantoin), succinimides (e.g., succinimide), and other
compounds comprising an imide functional group; and substituted
pyridine compounds (e.g., nicotinamide).
[0025] Generally, a complexing agent, or mixture of complexing
agents, may be included in the electrodeposition bath within a
concentration range of 0.1-200 g/L, and, in some cases, within the
range of 40-80 g/L. In one embodiment, the mixture of complexing
agents comprises 5,5-dimethylhydantoin, citric acid, and
nicotinamide. When the complexing agent is a compound comprising an
imide functional group, the concentration of the complexing agent
may be within the range 30-70 g/L or 40-60 g/L. When the complexing
agent is an alkyl hydroxyl carboxylic acid, the concentration of
the complexing agent may, in some instances, be within the range
1-20 g/L or 5-15 g/L. When the complexing agent is a substituted
pyridine compound, the concentration of the complexing agent may be
within the range 0.5-20 g/L or 0.5-5 g/L. Concentrations outside
these ranges may be used, and those of ordinary skill in the art
will readily be able to determine suitable concentrations by
routine experimentation.
[0026] In some embodiments, ammonium ions may be incorporated into
the electrolyte bath as complexing agents and to adjust solution
pH. For example, the electrodeposition bath may comprise ammonium
ions in the range of 1-50 g/L, and within the range of 10-30 g/L.
Other concentration ranges may also be suitable.
[0027] In some cases, the baths may include at least one wetting
agent. A wetting agent refers to any species capable of reducing
the surface tension of the electrodeposition bath and/or increasing
the ability of gas bubbles to detach from surfaces in the bath. For
example, the substrate may comprise a hydrophilic surface, and the
wetting agent may enhance the compatibility (e.g., wettability) of
the bath relative to the substrate. In some cases, the wetting
agent may also reduce the number of defects within the metal
coating that is produced. The wetting agent may comprise an organic
species, an inorganic species, an organometallic species, or
combinations thereof. In some embodiments, the wetting agent may be
selected to exhibit compatibility (e.g., solubility) with the
eletrodeposition bath and components thereof. For example, the
wetting agent may be selected to include one or more hydrophilic
species, including amines, thiols, alcohols, carboxylic acids and
carboxylates, sulfates, phosphates, polyethylene glycols (PEGs), or
derivatives of polyethylene glycol, to enhance the water solubility
of the wetting agent. In some embodiments, the wetting agent may
comprise a fluorosurfactant. In some embodiments, the wetting agent
may include Zonyl.RTM. FSJ (Dupont) or Captsone.TM. (Dupont).
[0028] Any suitable concentration of wetting agent may be used. For
example, the concentration of wetting agent may be between 10
microliters/L and 2000 microliters/L, between 20 microliters/L and
1000 microliters/L, or between 50 microliters/L and 500
microliters/L. Other concentration ranges may also be suitable.
[0029] Those of ordinary skill in the art would be able to select
the appropriate combination of ionic species, wetting agent,
complexing agent and/or other additives suitable for use in a
particular application. Generally, the additives in a bath are
compatible with electrodeposition processes, i.e., a bath may be
suitable for electrodeposition processes. One of ordinary skill in
the art would be able to recognize a bath that is suitable for
electrodeposition processes Likewise, one of ordinary skill in the
art would be able to recognize additives that, when added to a
bath, would make the bath not suitable for electrodeposition
processes.
[0030] In some aspects, various techniques can be used to monitor
the contents of the electrodeposition baths. For example, the
techniques may determine the concentration of one or more of the
additives in the bath such as the brightening agent(s), wetting
agent(s), complexing agent(s), etc. If the concentration of the
additive(s) is below or above a desired concentration, the bath
composition may be adjusted so that the concentration lies within
the desired range.
[0031] The pH of the electrodeposition bath can be from about 2.0
to 12.0. In some cases, the electrodeposition bath may have a pH
from about 7.0 to 9.0, or, in some cases, from about 7.6 to 8.4,
or, in some cases, from about 7.9 to 8.1. However, it should be
understood that the pH may be outside the above-noted ranges. The
pH of the bath may be adjusted using any suitable agent known to
those of ordinary skill in the art. In some embodiments, the pH of
the bath is adjusted using a base, such as a hydroxide salt (e.g.,
potassium hydroxide). In some embodiments, the pH of the bath is
adjusted using an acid (e.g., nitric acid).
[0032] In some cases, the operating range for the electrodeposition
baths described herein is 5-100.degree. C., 10-70.degree. C.,
10-30.degree. C., or, in some cases, 40-70.degree. C. However, it
should be understood that other temperature ranges may also be
suitable.
[0033] In general, the electrodeposition baths can be used in
connection with any electrodeposition process. Electrodeposition
generally involves the deposition of a coating on a substrate by
contacting the substrate with an electrodeposition bath and flowing
electrical current between two electrodes through the
electrodeposition bath, i.e., due to a difference in electrical
potential between the two electrodes. For example, methods
described herein may involve providing an anode, a cathode, an
electrodeposition bath associated with (e.g., in contact with) the
anode and cathode, and a power supply connected to the anode and
cathode. In some cases, the power supply may be driven to generate
a waveform for producing a coating, as described more fully below.
In some embodiments, at least one electrode may serve as the
substrate to be coated.
[0034] In general, during an electrodeposition process an
electrical potential may exist on the substrate to be coated, and
changes in applied voltage, current, or current density may result
in changes to the electrical potential on the substrate. In some
cases, the electrodeposition process may include the use of
waveforms comprising one or more segments, wherein each segment
involves a particular set of electrodeposition conditions (e.g.,
current density, current duration, electrodeposition bath
temperature, etc.). The waveform may have any shape, including
square waveforms, non-square waveforms of arbitrary shape, and the
like. In some methods, such as when forming coatings having
different portions, the waveform may have different segments used
to form the different portions. However, it should be understood
that not all methods use waveforms having different segments.
[0035] In some embodiments, a coating, or portion thereof, may be
electrodeposited using direct current (DC) deposition. For example,
a constant, steady electrical current may be passed through the
electrodeposition bath to produce a coating, or portion thereof, on
the substrate. In some embodiments, the potential that is applied
between the electrodes (e.g., potential control or voltage control)
and/or the current or current density that is allowed to flow
(e.g., current or current density control) may be varied. For
example, pulses, oscillations, and/or other variations in voltage,
potential, current, and/or current density, may be incorporated
during the electrodeposition process. In some embodiments, pulses
of controlled voltage may be alternated with pulses of controlled
current or current density. In some embodiments, the coating may be
formed (e.g., electrodeposited) using pulsed current
electrodeposition, reverse pulse current electrodeposition, or
combinations thereof.
[0036] In some cases, a bipolar waveform may be used, comprising at
least one forward pulse and at least one reverse pulse, i.e., a
"reverse pulse sequence." As noted above, the electrodeposition
baths described herein are particularly well suited for depositing
coatings using complex waveforms such as reverse pulse sequences.
In some embodiments, the at least one reverse pulse immediately
follows the at least one forward pulse. In some embodiments, the at
least one forward pulse immediately follows the at least one
reverse pulse. In some cases, the bipolar waveform includes
multiple forward pulses and reverse pulses. Some embodiments may
include a bipolar waveform comprising multiple forward pulses and
reverse pulses, each pulse having a specific current density and
duration. In some cases, the use of a reverse pulse sequence may
allow for modulation of composition and/or grain size of the
coating that is produced.
[0037] The methods of the invention may utilize certain aspects of
methods described in U.S. Patent Publication No. 2006/02722949,
entitled "Method for Producing Alloy Deposits and Controlling the
Nanostructure Thereof using Negative Current Pulsing
Electro-deposition, and Articles Incorporating Such Deposits,"
which is incorporated herein by reference in its entirety. Aspects
of other electrodeposition methods may also be suitable including
those described in U.S. Patent Publication No. 2006/0154084 and
U.S. application Ser. No. 11/985,569, entitled "Methods for
Tailoring the Surface Topography of a Nanocrystalline or Amorphous
Metal or Alloy and Articles Formed by Such Methods", filed Nov. 15,
2007, and U.S. patent application Ser. No. 12/120,564, filed May
14, 2008 which are incorporated herein by reference in their
entireties.
[0038] A coating may be applied using an electrodeposition process
at a current density of at least 0.001 A/cm.sup.2, at least 0.01
A/cm.sup.2, or at least 0.02 A/cm.sup.2. Current densities outside
these ranges may be used as well.
[0039] The deposition rate of the coating may be controlled. In
some instances, the deposition rate may be at least 0.1
microns/minute, at least 0.3 microns/minute, at least 1
micron/minute, or at least 3 microns/minute. Deposition rates
outside these ranges may be used as well.
[0040] Those of ordinary skill in the art would recognize that the
electrodeposition processes described herein are distinguishable
from electroless processes which primarily, or entirely, use
chemical reducing agents to deposit the coating, rather than an
applied voltage. The electrodeposition baths described herein may
be substantially free of chemical reducing agents that would
deposit coatings, for example, in the absence of an applied
voltage.
[0041] FIG. 2 shows an article 20 according to an embodiment. The
article has a coating 22 formed on a base material 24. In some
embodiments, the coating comprises a plurality of layers. In some
embodiments, the coating may comprise a first layer 26 formed on
the base material and a second layer 28 formed on the first layer.
Each layer may be applied using a suitable process, as described in
more detail below. It should be understood that the coating may
include more than two layers. It should also be understood that the
coating may include only one layer. However, in some embodiments,
the coating may only include two layers, as shown. In some cases,
the coating may be formed on at least a portion of the substrate
surface. In other cases, the coating covers the entire substrate
surface.
[0042] In some embodiments, the coating comprises one or more
metals. For example, the coating may comprise a metal alloy. In
some cases, alloys that comprise silver (i.e., silver-based alloys)
are preferred. Such alloys may also comprise tungsten and/or
molybdenum. Silver-tungsten alloys may be preferred in some cases.
In some cases, the atomic percent of tungsten and/or molybdenum in
the alloy may be between 0.1 atomic percent and 50 atomic percent;
and, in some cases, between 0.1 atomic percent and 20 atomic
percent. In some embodiments, the atomic percent of tungsten and/or
molybdenum in the alloy may be at least 0.1 atomic percent, at
least 1 atomic percent, at least 1.5 atomic percent, at least 5
atomic percent, at least 10 atomic percent, or at least 20 atomic
percent. Other atomic percentages outside of this range may be used
as well.
[0043] In some embodiments, the silver-based alloy may form first
layer 26 of the coating. In some embodiments, second layer 28
comprising one or more precious metals may form a second layer of
the coating. In some cases, the first layer comprising a silver
alloy is formed on the base material, and the second layer
comprising one or more precious metals is formed on the first
layer. Examples of suitable precious metals include Ru, Os, Rh, Re,
Ir, Pd, Pt, Ag, Au, or any combination thereof. Gold may be
preferred in some embodiments. In some embodiments, a layer
consists essentially of one precious metal. In some embodiments, it
may be preferable that a layer (e.g., the second layer) is free of
tin. In other cases, a layer may comprise an alloy that includes at
least one precious metal and at least one other element. The
element may be selected from Ni, W, Fe, B, S, Co, Mo, Cu, Cr, Zn
and Sn, amongst others. For example, a layer may comprise a Ni--Pd
alloy, a Au--Co alloy, and/or a Au--Ni alloy.
[0044] In some embodiments, the coating may include a layer
comprising nickel (e.g., a nickel alloy such as nickel-tungsten).
In some cases, the layer comprising nickel may be disposed between
the base material and the silver-based alloy layer. In one
embodiment, the coating comprises a first layer comprising nickel,
a second layer comprising the silver-based alloy, and a third layer
comprising one or more precious metals, where the first layer is
formed on the base material, the second layer is formed on the
first layer, and the third layer is formed on the second layer.
[0045] A layer of the coating may have any suitable thickness. In
some embodiments, it may be advantageous for a layer to be thin,
for example, to save on material costs. For example, a layer
thickness may be less than 30 microinches (e.g., between about 1
microinch and about 30 microinches; in some cases, between about 5
microinches and about 30 microinches); in some cases the layer
thickness may be less than 20 microinches (e.g., between about 1
microinch and about 20 microinches; in some cases, between about 5
microinches and about 20 microinches); and, in some cases, the
layer thickness may be less than 10 microinches (e.g., between
about 1 microinch and about 10 microinches; in some cases, between
about 5 microinches and about 10 microinches). In some embodiments,
the thickness of a layer is chosen such that the layer is
essentially transparent on the surface. It should be understood
that other layer thicknesses may also be suitable.
[0046] The second layer may cover the entire first layer. However,
it should be understood that in other embodiments, the second layer
covers only part of the first layer. In some cases, a second layer
covers at least 50% of the surface area of a first layer; in other
cases, at least 75% of the surface area of a first layer. In some
cases, an element from a first layer may be incorporated within a
second layer and/or an element from a second layer may be
incorporated into a first layer.
[0047] In some embodiments, it may preferable for the first layer
to be formed directly on the base material. Such embodiments may be
preferred over certain prior art constructions that utilize a layer
between the first layer and the base material because the absence
of such an intervening layer can save on overall material costs.
Though, it should be understood that in other embodiments, one or
more layers may be formed between the first layer and the base
material. For example, in some embodiments, a barrier layer may be
formed between the base material and the first layer. The barrier
layer, in some embodiments, comprises nickel. In some cases, the
barrier layer comprises nickel-tungsten or sulfamate nickel.
[0048] In some embodiments, a lubricant layer may be formed as an
upper portion of the coating. The lubricant layer may comprise, for
example, an organic material, a self-assembled monolayer, carbon
nanotubes, and the like.
[0049] In some cases, the coating (e.g., the first layer and/or the
second layer) may have a particular microstructure. For example, at
least a portion of the coating may have a nanocrystalline
microstructure. As used herein, a "nanocrystalline" structure
refers to a structure in which the number-average size of
crystalline grains is less than one micron. The number-average size
of the crystalline grains provides equal statistical weight to each
grain and is calculated as the sum of all spherical equivalent
grain diameters divided by the total number of grains in a
representative volume of the body. The number-average size of
crystalline grains may, in some embodiments, be less than 100 nm.
In some cases, the silver-based alloy has a number-average grain
size less than 50% of a thickness of the silver-based alloy layer.
In some instances, the number-average grain size may be less than
10% of a thickness of the silver-based alloy layer. In some
embodiments, at least a portion of the coating may have an
amorphous structure. As known in the art, an amorphous structure is
a non-crystalline structure characterized by having no long range
symmetry in the atomic positions. Examples of amorphous structures
include glass, or glass-like structures. Some embodiments may
provide coatings having a nanocrystalline structure throughout
essentially the entire coating. Some embodiments may provide
coatings having an amorphous structure throughout essentially the
entire coating.
[0050] In some embodiments, the coating may be crystalline having a
face-centered cubic structure. In some embodiments, the coating may
be a solid solution where the metals comprising the coating are
essentially dispersed as individual atoms. Such a structure may be
produced using an electrodeposition process. A solid solution may
be distinguished from an alternative structure formed, for example,
using an electroless process where granules comprising a first
phase containing a first metal species (i.e., tungsten and/or
molybdenum) are dispersed within a coating comprising a second
phase containing a second metal species (i.e., silver), the second
phase having a different composition and/or crystal structure than
the first phase. In some cases, the solid solution may be
essentially free of oxygen.
[0051] In some embodiments, the coating may comprise various
portions having different microstructures. For example, the first
layer may have a different microstructure than the second layer.
The coating may include, for example, one or more portions having a
nanocrystalline structure and one or more portions having an
amorphous structure. In one set of embodiments, the coating
comprises nanocrystalline grains and other portions which exhibit
an amorphous structure. In some cases, the coating, or a portion
thereof (e.g., a portion of the first layer, a portion of the
second layer, or a portion of both the first layer and the second
layer), may comprise a portion having crystal grains, a majority of
which have a grain size greater than one micron in diameter. In
some embodiments, the coating may include other structures or
phases, alone or in combination with a nanocrystalline portion or
an amorphous portion. Those of ordinary skill in the art would be
able to select other structures or phases suitable for use in the
context of the invention.
[0052] Advantageously, the coating (i.e., the first layer, the
second layer, or both the first layer and the second layer) may be
substantially free of elements or compounds having a high toxicity
or other disadvantages. In some instances, it may also be
advantageous for the coating to be substantially free of elements
or compounds that are deposited using species that have a high
toxicity or other disadvantages. For example, in some cases, the
coating is free of chromium (e.g., chromium oxide), which is often
deposited using chromium ionic species that are toxic (e.g.,
Cr.sup.6+). In some cases, the coating may be deposited from an
electrodeposition bath that is substantially free of cyanide. Such
coating may provide various processing, health, and environmental
advantages over certain previous coatings.
[0053] In some embodiments, metal, non-metal, and/or metalloid
materials, salts, etc. (e.g., phosphate or a redox mediator such as
potassium ferricyanide, or fragment thereof) may be incorporated
into the coating.
[0054] The composition of the coatings, or portions or layers
thereof, may be characterized using suitable techniques known in
the art, such as Auger electron spectroscopy (AES), X-ray
photoelectron spectroscopy (XPS), etc. For example, AES and/or XPS
may be used to characterize the chemical composition of the surface
of the coating.
[0055] The coating may have any thickness suitable for a particular
application. For example, the coating thickness may be greater than
about 1 microinch (e.g., between about 1 microinch and about 100
microinches, between about 1 microinch and 50 microinches); in some
cases, greater than about 5 microinches (e.g., between about 5
microinches and about 100 microinches, between about 5 microinches
and 50 microinches); greater than about 25 microinches (e.g.,
between about 25 microinches and about 100 microinches, between
about 1 microinch and 50 microinches). It should be understood that
other thicknesses may also be suitable. In some embodiments, the
thickness of the coating is chosen such that the coating is
essentially transparent on the surface. Thickness may be measured
by techniques known to those of ordinary skill in the art.
[0056] Base material 30 may be coated to form coated articles, as
described above. In some cases, the base material may comprise an
electrically conductive material, such as a metal, metal alloy,
intermetallic material, or the like. Suitable base materials
include steel, copper, aluminum, brass, bronze, nickel, polymers
with conductive surfaces and/or surface treatments, transparent
conductive oxides, amongst others. In some embodiments, copper base
materials are preferred.
[0057] The articles can be used in a variety of applications
including electrical applications such as electrical connectors
(e.g., plug-type). In some embodiments, the coating on an
electrical connector includes a first layer comprising a silver
alloy, the first layer disposed on a base material, and a second
layer comprising a precious metal, the second layer disposed on the
first layer. The coating can impart desirable characteristics to an
article, such as durability, hardness, corrosion resistance, and
reduced electrical resistivity. These properties can be
particularly advantageous for articles in electrical applications
such as electrical connectors, which may experience rubbing or
abrasive stress upon connection to and/or disconnection from an
electrical circuit that can damage or otherwise reduce the
conductivity of a conductive layer on the article. Non-limiting
examples of electrical connectors include infrared connectors, USB
connectors, battery chargers, battery contacts, automotive
electrical connectors, etc. In some embodiments, the presence of
the first layer of a coating may provide at least some of the
durability and corrosion resistance properties to the coating. In
some embodiments, the coating may impart decorative qualities, for
example a blue tint and reduced tarnish. Additionally, the presence
of the first layer may allow the thickness of the second layer to
be reduced, thereby reducing the amount of precious metal on the
article significantly.
[0058] The coatings described herein may impart advantageous
properties to an article, such as an electrical connector. In some
embodiments, the coating, or layer of the coating, may have a low
electrical resistivity. For example, the electrical resistivity may
be less than 100 microohm-centimeters, less than 50
microohm-centimeters, less than 10 microohm-centimeters, or less
than 2 microohm-centimeters.
[0059] The coating or layer of the coating may have a hardness of
at least 1 GPa, at least 1.5 GPa, at least 2 GPa, at least 2.5 GPa,
or at least 3 GPa. Those of ordinary skill in the art would readily
be able to measure these properties.
[0060] As noted above, coating 20 may be formed using an
electrodeposition process. In some cases, each layer of the coating
may be applied using a separate electrodeposition bath. In some
cases, individual articles may be connected such that they can be
sequentially exposed to separate electrodeposition baths, for
example in a reel-to-reel process. For instance, articles may be
connected to a common conductive substrate (e.g., a strip). In some
embodiments, each of the electrodeposition baths may be associated
with separate anodes and the interconnected individual articles may
be commonly connected to a cathode.
[0061] In some embodiments, the invention provides coated articles
that are capable of resisting corrosion, and/or protecting an
underlying substrate material from corrosion, in one or more
potential corrosive environments. Examples of such corrosive
environments include, but are not limited to, aqueous solutions,
acid solutions, alkaline or basic solutions, or combinations
thereof. For example, coated articles described herein may be
resistant to corrosion upon exposure to (e.g., contact with,
immersion within, etc.) a corrosive environment, such as a
corrosive liquid, vapor, or humid environment.
[0062] The corrosion resistance may be assessed using tests such as
ASTM B845, entitled "Standard Guide for Mixed Flowing Gas (MFG)
Tests for Electrical Contacts" following the Class IIa protocol,
may also be used to assess the corrosion resistance of coated
articles. These tests outline procedures in which coated substrate
samples are exposed to a corrosive atmosphere (i.e., a mixture of
NO.sub.2, H.sub.2S, Cl.sub.2, and SO.sub.2). The mixture of flowing
gas can comprise 200+/-50 ppb of NO.sub.2, 10+/-5 ppb of H.sub.2S,
10+/-3 ppb of Cl.sub.2, and 100+/-20 ppb SO.sub.2. The temperature
and relative humidity may also be controlled. For example, the
temperature may be 30+/-1.degree. C., and the relative humidity may
be 70+/-2%.
[0063] The low-level contact resistance of a sample may be
determined before and/or after exposure to a corrosive environment
for a set period of time according to one of the tests described
above. In some embodiments, the low-level contact resistance may be
determined according to specification EIA 364, test procedure 23.
Generally, the contact resistivity of a sample may be measured by
contacting the sample under a specified load and current with a
measurement probe having a defined cross-sectional area of contact
with the sample. For example, the low-level contact resistance may
be measured under a load of 25 g, 50 g, 150 g, 200 g, etc.
Generally, the low-level contact resistance decreases as the load
increases.
[0064] In some embodiments, a coated article has reduced low-level
contact resistance. Reduced low-level contact resistance may be
useful for articles used in electrical applications such as
electrical connectors. In some cases, an article may have a
low-level contact resistance under a load of 25 g of less than
about 100 mOhm; in some cases, less than about 10 mOhm; in some
cases, less than about 5 mOhm; and, in some cases, less than about
1 mOhm. It should be understood that the article may have a
low-level contact resistance outside this range as well. It should
also be understood that the cross-sectional area of contact by the
measurement probe may affect the value of the measured low-level
contact resistance.
[0065] The following example should not be considered to be
limiting but illustrative of certain features of the invention.
EXAMPLE
[0066] This example demonstrates coating thickness, tungsten
content, grain size, coating hardness, and contact resistance
achieved with various samples.
[0067] Coatings were electrodeposited on base materials in aqueous
electrodeposition baths using an electrodeposition process. The
electrodeposition baths contained a silver ionic species, a
tungsten ionic species, and a complexing agent. The coatings were
formed directly on the base material substrate. Additionally, for
samples 28-35, a nickel layer was electrodeposited on the substrate
prior to electrodepositing the silver-based alloy.
[0068] Tables 1 and 2 show the results obtained for these
coatings.
TABLE-US-00001 TABLE 1 Thickness, tungsten content, grain size and
hardness for various samples. Thickness Tungsten Grain Hardness
Sample (microns) (atomic %) Size (nm) (GPa) 1 2.9 1.0 22 2.4 2 3.1
1.5 20 N.D. 3 3.4 1.4 15 N.D. 4 3.8 1.7 14 2.4 5 3.7 7.9 5 2.2 6
3.8 7.7 5 2.1 7 4.2 7.1 6 N.D. 8 4.1 6.4 7 1.6 9 N.D. 1.2 N.D. N.D.
10 3.1 1.2 96 2.1 11 4.5 1.6 N.D. N.D. 12 4.5 1.3 49 N.D. 13 9.8
1.4 55 2.6 14 7.5 1.4 49 N.D. 15 6.4 4.9 10 2.9 16 8.2 3.1 25 2.8
17 7.9 4.6 10 1.8 18 2.4 1.8 35 2.4 N.D. = not determined.
TABLE-US-00002 TABLE 2 Substrate, tungsten content, and contact
resistance for various samples. Tungsten Contact Resistance Sample
Substrate (atomic %) (milliohms) 19 brass 1.3 4.6 20 brass 1.5 4.2
21 brass 2.9 6.8 22 brass 6.9 8.8 23 brass 7.0 7.2 24 brass 1.6 5.9
25 brass 1.9 5.3 26 brass 7.3 10.4 27 brass 5.5 N.D. 28 Ni/brass
1.8 7.7 29 Ni/brass 2.3 6.6 30 Ni/brass 6.8 8.4 31 Ni/brass 5.5
10.4 32 Ni/brass 0.9 6.6 33 Ni/brass 1.5 5.9 34 Ni/brass 6.7 8.4 35
Ni/brass 7.4 8.0 N.D. = not determined.
* * * * *