U.S. patent application number 13/784009 was filed with the patent office on 2013-09-05 for composites of carbon black and metal.
The applicant listed for this patent is Rohm and Haas Electronic Materials LLC. Invention is credited to Jan FRANSAER, Linda STAPPERS, Michael P. TOBEN, Wan ZHANG-BEGLINGER.
Application Number | 20130228465 13/784009 |
Document ID | / |
Family ID | 47779943 |
Filed Date | 2013-09-05 |
United States Patent
Application |
20130228465 |
Kind Code |
A1 |
ZHANG-BEGLINGER; Wan ; et
al. |
September 5, 2013 |
COMPOSITES OF CARBON BLACK AND METAL
Abstract
Nano-sized particles of carbon black and various metal ions are
mixed to form substantially homogenous solutions or dispersions.
The nano-sized particles of carbon black and metal ions are
electroplated on various types of substrates as composites of one
or more metals and substantially uniformly dispersed nano-sized
particles of carbon black within the metals.
Inventors: |
ZHANG-BEGLINGER; Wan;
(Adligenswil, CH) ; STAPPERS; Linda; (Tienen,
BE) ; FRANSAER; Jan; (Leefdaal, BE) ; TOBEN;
Michael P.; (Smithtown, NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Electronic Materials LLC; Rohm and Haas |
|
|
US |
|
|
Family ID: |
47779943 |
Appl. No.: |
13/784009 |
Filed: |
March 4, 2013 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
61606170 |
Mar 2, 2012 |
|
|
|
Current U.S.
Class: |
205/50 ;
205/109 |
Current CPC
Class: |
C25D 3/12 20130101; C25D
3/46 20130101; C25D 5/04 20130101; C25D 3/02 20130101; C25D 3/30
20130101; H01B 1/02 20130101; C25D 3/50 20130101; C25D 5/20
20130101; C25D 15/00 20130101; C25D 3/54 20130101; C25D 3/38
20130101; C25D 21/10 20130101; C25D 3/48 20130101 |
Class at
Publication: |
205/50 ;
205/109 |
International
Class: |
C25D 3/02 20060101
C25D003/02; C25D 15/00 20060101 C25D015/00 |
Claims
1. A composition comprising one or more sources of metal ions and
carbon black nano-particles.
2. The composition of claim 1, wherein the carbon black
nano-particles range in size from 5 nm to 500 nm.
3. The composition of claim 1, wherein metal ions are chosen from
silver, gold, palladium, nickel, copper, tin and indium ions.
4. The composition of claim 1, wherein a concentration of the
carbon black nano-particles in the composition is at least 1
g/L.
5. The composition of claim 1, further comprising one or more
surfactants.
6. The composition of claim 5, wherein the surfactants are chosen
from alcohol phosphate esters.
7. A method comprising: a) providing a composition comprising one
or more sources of metal ions and carbon black nano-particles; b)
contacting a substrate with the composition; and c) electroplating
a composite of one or more metals and carbon black nano-particles
onto the substrate.
8. The method of claim 7, wherein the carbon black nano-particles
range in size from 5 nm to 500 nm.
9. The method of claim 7, wherein metal ions are chosen from
silver, gold, palladium, nickel, copper, tin and indium ions.
10. An article comprising a composite comprising one or more metals
and carbon black nano-particles dispersed within the one or more
metals.
11. The article of claim 10, wherein a thickness of the composite
is at least 0.1 .mu.m.
Description
[0001] This application claims the benefit of priority under 35
U.S.C. .sctn.119(e) to U.S. Provisional Application No. 61/606,170,
filed Mar. 2, 2012, the entire contents of which application are
incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The present invention is directed to composites of carbon
black particles and metal. More specifically, the present invention
is directed to composites of carbon black particles and metal where
the carbon black particles are in the nanometer range.
BACKGROUND OF THE INVENTION
[0003] Composite plating is a technology well documented and widely
practiced in both electrolytic and electroless plating. Composite
plating refers to the inclusion of particulate matter within a
metal plated layer. The development and acceptance of composite
plating stems from the discovery that the inclusion of particles
within a metal plated layer can enhance various properties of the
metal plated layer and in many situations actually provide entirely
new properties to the metal layer. Particles of various materials
can provide characteristics to the metal layer including wear
resistance, lubricity, corrosion resistance, phosphorescence,
friction altered appearances and other properties.
[0004] For some time the most common composites used for increasing
durability of articles were those deposited from electroless nickel
plating baths which included particles of diamond and
polytetrafluoroethylene (PTFE). Over the years the variety of
metals and fine particles has increased to produce a wide range of
different composites. JP09-007445 discloses a sliding contact
electric component which has an electroplated coating film of
graphite particles dispersed in a silver metal matrix. In addition
to graphite, particles of SiC, WC, ZrB, Al.sub.2O.sub.3, ZrO.sub.2
and Cr.sub.2O.sub.3 may also be incorporated into the composite.
Also, particles of TiO.sub.2, ThO.sub.2, MoO.sub.3, W.sub.2C, TiC,
B.sub.4C and CrB.sub.2 may be included to increase the hardness of
the deposited coating.
[0005] U.S. Pat. No. 6,635,166 discloses an electrolytic composite
plating method. In addition to fine particles of diamond and PTFE,
the patent discloses particles of SiC, glass, kaolin, corundum,
Si.sub.3N.sub.4, various metal oxides, graphite, graphite fluoride,
various colorants and other metal compounds such as compounds of W,
Mo and Ti. Metals which may be electroplated with such particles
include, for example, silver, gold, nickel, copper, zinc, tin,
lead, chromium and alloys thereof. To achieve the desired
properties mentioned above, azo-surfactants are included in the
composite plating formulations to enable an increase in the content
of the particles in the electroplating bath.
[0006] U.S. Pat. No. 7,514,022 discloses a composite of silver and
graphite particles used to electroplate a coating on switches and
connectors. The graphite particles range in size from 0.1 .mu.m to
1.0 .mu.m. Additives such as dispersing agents are excluded from
the formulation. Although including dispersing agents or
surfactants in composite plating baths may increase the content of
fine particles to some extent, the dispersing agent effect is known
to be limited. It is believed that the dispersing agent or
surfactant remains as it is on the fine particles which have been
deposited by electroplating in the adsorbed state. This is believed
to inhibit other fine particles from being deposited. Instead the
graphite particles are oxidized to achieve the desired dispersion
of particles in the silver electroplating baths. Such oxidizing
agents include nitric acid, hydrogen peroxide, potassium
permanganate, potassium persulfate, sodium persulfate and sodium
perchlorate.
[0007] In addition to achieving as high a concentration of fine
particles as possible in the electroplating bath, it is also
desirable to use particles with sufficient electrical conductivity
and as small a diameter as possible. This is important to ensure
electrical continuity between the plated mating surfaces of an
electronic connector. However, the smaller the particle the more
readily it is to agglomerate with other particles in the plating
bath causing the particles to rapidly settle to the bottom of the
plating vessel thus making them unavailable for codeposition.
Therefore codepositing all particles in a metal plating bath which
have diameters in the nanometer range has been challenging.
Accordingly, there is a need for a composite of nano-particles and
metal where the nano-particles have sufficient electrical
conductivity and at the same time do not readily agglomerate in the
metal electroplating bath.
SUMMARY OF THE INVENTION
[0008] In one aspect compositions include one or more sources of
metal ions and carbon black nano-particles.
[0009] In another aspect methods include providing a composition
including one or more sources of metal ions and carbon black
nano-particles; contacting a substrate with the composition; and
electroplating a composite of one or more metals and carbon black
nano-particles onto the substrate.
[0010] In an additional aspect articles include a composite
including one or more metals and carbon black nano-particles
dispersed within the one or more metals.
[0011] The compositions are substantially stable dispersions of
carbon black nano-particles and metal ions which can be
electroplated on various substrates to form coatings of composites
of metal or metal alloy having substantially uniform dispersions of
the carbon black nano-particles throughout a metal or metal alloy
matrix. The composites are electrically conductive and provide good
wear resistance with improved durability in comparison to many
conventional metal and metal alloy coatings. The composite coatings
may be used to replace hard gold coatings of gold/cobalt and
gold/nickel which are often used to coat articles which are exposed
to rigorous wear cycles or are prone to oxidation due to heat in
sliding processes, such as is typical in switches and
connectors.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a SEM at 3500.times. of a cross-section of a
composite of silver and graphite particles.
[0013] FIG. 2 is a SEM at 5000.times. of a cross-section of a
composite of silver and carbon black nano-particles.
[0014] FIG. 3 is a graph of contact resistance in mOhm versus
contact forces in cN of a silver and silver and carbon black
nanoparticles.
[0015] FIG. 4 is a SEM at 10,000.times. of a cross section of a
composite of silver and carbon black nano-particles.
DETAILED DESCRIPTION OF THE INVENTION
[0016] As used throughout this specification, the terms
"depositing", "plating" and "electroplating" are used
interchangeably, and the terms "composition" and "bath" are used
interchangeably. The indefinite articles "a" and "an" are intended
to include both the singular and the plural.
[0017] The following abbreviations have the following meanings
unless the context clearly indicates otherwise: .degree. C.=degrees
Celsius; g=grams; ml=milliliter; L=liter; cm=centimeters;
A=amperes; dm=decimeter; ASD=A/dm.sup.2; .mu.m=microns;
nm=nanometers; mmol=millimoles; mOhm=milliohms; cN=centiNewtons;
SEM=scanning electron micrograph; and EO/PO=thylene oxide/propylene
oxide. All percentages and ratios are by weight unless otherwise
indicated. All ranges are inclusive and combinable in any order
except where it is logical that such numerical ranges are
constrained to add up to 100%.
[0018] Compositions are aqueous dispersions of carbon black
nano-particles and one or more sources of metal ions. Carbon black
is an amorphous form of carbon with a high surface area to volume
ratio and is electrically conductive. In contrast to carbon black,
diamond and graphite are crystalline in structure. Diamond has a
tetrahedral configuration. Graphite has a layered, planar crystal
structure where each carbon atom is bonded to three other carbons
forming a hexagonal structure. Graphite is much softer than diamond
and the layered, planar type structure facilitates easy cleavage
along the planes which makes it desirable as a solid lubricant but
is not very durable in coatings which are exposed to rigorous wear
cycles. In general, it has a relatively low coefficient of
friction.
[0019] Carbon black nano-particles have an average diameter range
from 5 nm to 500 nm, preferably from 10 nm to 250 nm, more
preferably from 15 nm to 100 nm and most preferably from 15 nm to
30 nm The carbon black nano-particles are spherical or elliptical
in shape, not fibers or nano-tubes. Carbon black may be obtained
from various commercial sources or prepared by one or more
conventional methods known in the art. Carbon black may be produced
industrially, for example, by the incomplete combustion of heavy
petroleum products such as coal tar and ethylene cracking tar. A
commercially available source of carbon black is Degussa.RTM.
Carbon Black (available from Orion Engineered Carbons, Germany).
Typically, the commercially available carbon black is agglomerated
and is not within the desired particle size range. Accordingly, to
achieve the desired particle size range the agglomerated carbon
black particles may be de-agglomerated using ultrasonic methods and
apparatus well known in the art.
[0020] The carbon black nano-particles may be added to an aqueous
solution of one or more water-soluble metal salts which may include
one or more surfactants and conventional additives found in metal
plating baths. In general, the surfactants are added to the water
first then the carbon black nano-particles are added and this
mixture is added to the plating bath. The carbon black
nano-particles may also be mixed in commercially available metal
electroplating baths. The components of the bath are typically
mixed using high power ultrasonic laboratory mixing apparatus to
achieve a substantially uniform dispersion of carbon black
nano-particles and plating bath components. Carbon black
nano-particles are included in the metal electroplating baths in
amounts of at least 1 g/L, preferably at least 10 g/L, more
preferably from 20 g/1 to 200 g/l, most preferably from 50 g/L to
150 g/L.
[0021] Metals which may be co-deposited with the carbon black
nano-particles are provided by one or more sources of water-soluble
metal salts. Although silver is the most preferred metal for
forming the composite with the carbon black nano-particles, it is
envisioned that other metals and metal alloys may be used to form
the composites. Water-soluble metal salts which provide metal ions
for the deposition of metals include, but are not limited to,
silver, gold, palladium, tin, indium, copper and nickel. Such
water-soluble metal salts are generally commercially available from
a variety of suppliers or may be prepared by methods well known in
the art. It is envisioned that alloys of such metals may also be
co-deposited with the carbon black nano-particles. Such alloys may
include, but are not limited to, tin/silver, tin/copper,
palladium/nickel and tin/silver/copper. Preferably the metal
co-deposited with the carbon black nano-particles is silver, gold,
palladium, tin or palladium/nickel alloy. More preferably the metal
co-deposited with the carbon black nano-particles is silver or tin.
Most preferably the metal co-deposited with the carbon black
nano-particles is silver. In general, one or more sources of metal
ions are included in the electroplating baths in amounts of 0.1 g/L
to 200 g/L.
[0022] Sources of silver ions include, but are not limited to,
silver oxide, silver nitrate, silver sodium thiosulfate, silver
cyanide, silver gluconate; silver-amino acid complexes such as
silver-cysteine complexes; silver alkyl sulfonates, such as silver
methane sulfonate and silver hydantoin and silver succinimide
compound complexes. Although silver cyanide may be a source of
silver ions, preferably silver and silver alloy electroplating
baths are cyanide-free. The sources of silver ions are included in
the aqueous baths in amounts of 1 g/L to 150 g/L.
[0023] Sources of gold ions include, but are not limited to, gold
salts which provide gold (I) ions. Such sources of gold (I) ions
include, but are not limited to, alkali gold cyanide compounds such
as potassium gold cyanide, sodium gold cyanide, and ammonium gold
cyanide, alkali gold thiosulfate compounds such as trisodium gold
thiosulfate and tripotassium gold thiosulfate, alkali gold sulfite
compounds such as sodium gold sulfite and potassium gold sulfite,
ammonium gold sulfite, and gold (I) and gold (III) halides such as
gold (I) chloride and gold (III) trichloride. Typically, the alkali
gold cyanide compounds are used such as potassium gold cyanide. The
amount of gold salts ranges from 1 g/L to 50 g/L.
[0024] A wide variety of palladium compounds may be used as a
source of palladium ions. Such palladium compounds include, but are
not limited to, palladium complex ion compounds with ammonia as the
complexing agent. Such compounds include, but are not limited to,
dichlorodiammine palladium (II), dinitrodiammine palladium (II),
tetrammine palladium (II) chloride, tetrammine palladium (II)
sulfate, tetrammine palladium tetrachloropalladate, tetramine
palladium carbonate and tetramine palladium hydrogen carbonate.
Additional sources of palladium include, but are not limited to,
palladium dichloride, palladium dibromide, palladium sulfate,
palladium nitrate, palladium monoxide-hydrate, palladium acetates,
palladium propionates, palladium oxalates and palladium formates.
Palladium compounds are included in the plating compositions is
amounts of 10 g/L to 50 g/L.
[0025] Water-soluble nickel salts include, but are not limited to,
halides, sulfates, sulfites and phosphates. Typically, the nickel
halide and sulfate salts are used. Water-soluble nickel salts are
included in amounts of 0.1 g/L to 150 g/L.
[0026] Water-soluble tin compounds include, but are not limited to
salts, such as tin halides, tin sulfates, tin alkane sulfonates and
tin alkanol sulfonates. When tin halide is used, it is typical that
the halide is chloride. The tin compound is typically tin sulfate,
tin chloride or tin alkane sulfonate, and more typically tin
sulfate or tin methane sulfonate. Tin salts are included in the
compositions in amounts of 5 to 100 g/L.
[0027] Water-soluble copper salts include without limitation:
copper sulfate; copper halides such as copper chloride; copper
acetate; copper nitrate; copper fluoroborate; copper
alkylsulfonates; copper arylsulfonates; copper sulfamate; and
copper gluconate. Exemplary copper alkylsulfonates include copper
(C.sub.1-C.sub.6)alkylsulfonate and more typically copper
(C.sub.1-C.sub.3)alkylsulfonate. Typically, the copper salt is
included in amounts of 10 g/L to 180 g/L of plating
composition.
[0028] Sources of indium ions include, but are not limited to,
indium salts of alkane sulfonic acids and aromatic sulfonic acids,
such as methanesulfonic acid, ethanesulfonic acid, butane sulfonic
acid, benzenesulfonic acid and toluenesulfonic acid, salts of
sulfamic acid, sulfate salts, chloride and bromide salts of indium,
nitrate salts, hydroxide salts, indium oxides, fluoroborate salts,
indium salts of carboxylic acids, such as citric acid, acetoacetic
acid, glyoxylic acid, pyruvic acid, glycolic acid, malonic acid,
hydroxamic acid, iminodiacetic acid, salicylic acid, glyceric acid,
succinic acid, malic acid, tartaric acid, hydroxybutyric acid,
indium salts of amino acids, such as arginine, aspartic acid,
asparagine, glutamic acid, glycine, glutamine, leucine, lysine,
threonine, isoleucine, and valine. Water-soluble indium salts are
included in the compositions in amounts of 5 g/L to 70 g/L.
[0029] In addition to the sources of metal ions, the electroplating
baths optionally include one or more conventional additives
typically included in metal electroplating baths. Such additives
may vary depending on the type of metal to be plated. Such
additives are well known in the art and the literature. In general,
such conventional additives include, but are not limited to,
complexing agents and chelating agents for metal ions, suppressors,
levelers, stabilizers, antioxidants, grain refiners, buffers to
maintain the pH of the electroplating bath, electrolytes, acids,
bases, salts of acids and bases, surfactants and dispersing agents.
Some minor experimentation may be required to determine the proper
amount of an additive to tailor a particular formulation to improve
electroplating performance in view of the addition of the carbon
black nono-particles to the bath.
[0030] In general, the pH of the electroplating baths may range
from less than 1 to 14, typically, the pH ranges from 1 to 12, more
typically from 3 to 10. The pH depends on the particular metal or
metal alloy to be co-deposited with the carbon black nano-particles
as well as the other bath components. Conventional inorganic and
organic acids and bases may be used to modify the pH.
[0031] In addition to conventional surfactants and dispersing
agents, the carbon black nano-particle and metal electroplating
baths may include one or more surfactants to assist in providing a
uniform dispersion of carbon black nano-particles. In general,
surfactants may be included in the baths in amounts of 1 g/L to 100
g/L, preferably from 1 g/L to 60 g/L. Such surfactants include, but
are not limited to, secondary alcohol ethoxylates, EO/PO
copolymers, beta-naphthol ethoxylates, alkyl ether phosphates, also
known as alcohol phosphate esters, and alkyldiphenyloxide
disulfonates, and surfactants such as cetyltrimethylammonium
hydrogensulfate and quaternary polyvinylimidazole. When tin is used
as the metal for the composite, fluorocarbon polymers, such as
tetrafluoroethylene fluorocarbon polymers, are included in the
plating bath. Examples of commercially available surfactants are
TERGITOL.TM. XD EO/PO copolymer, POLYMAX.TM. PA-31 ethoxylated
beta-naphthol, BASOTRONIC.TM. PVI quaternary polyvinylimidazole,
and TEFLON.TM. tetrafluoroethylene fluorocarbon polymers.
[0032] Exemplary alcohol phosphate esters have a general
formula:
##STR00001##
where R' is hydrogen, C.sub.4-C.sub.20 alkyl, phenyl or
C.sub.4-C.sub.20 alkyl phenyl, R'' is C.sub.2-C.sub.3 alkyl, m is
an integer from 0 to 20 and n is an integer from 1 to 3, preferably
n is an integer from 1 to 2. When silver is used as the metal for
the composite, the silver electroplating bath preferably includes
such alcohol phosphate esters.
[0033] The compositions of carbon black nano-particles and one or
more metal ions may be electroplated onto substrates using
conventional electroplating methods. In general, current densities
may range from 0.1 ASD and greater. Typically current densities
range from 0.1 ASD to 100 ASD. Preferably, current densities range
from 0.1 ASD to 10 ASD. When the compositions are electroplated by
jet plating, current densities may be from 10 ASD and greater, more
typically from 20 ASD to 100 ASD. Composition temperatures during
electroplating may range from room temperature to 90.degree. C.
[0034] The substrates may be immersed in the electroplating bath,
such as in vertical electroplating or by horizontal plating where
the substrate is placed on a conveyor and the bath is sprayed onto
the substrate. Typically the electroplating bath is agitated during
plating usually through pumping the plating solution within the
tank or in the case of reel-to-reel plating pumping the solution
from the sump tank to the plating cell. Reel-to-reel plating allows
for select plating of metal. Various reel-to-reel apparatus are
known by those of skill in the art. The method can plate strips of
manufactured products or reels of raw material before they are
stamped into parts. The electroplating bath may also be agitated
using ultrasound with conventional ultrasound apparatus.
[0035] Electroplating times vary depending on the type of metal or
metal alloy to be co-deposited with the carbon black
nano-particles. The deposited composites are a matrix of metal or
metal alloy with carbon black nano-particles substantially
uniformly dispersed throughout the metal or metal alloy matrix.
Preferably the composites have a matrix of silver, gold, palladium,
tin or palladium/nickel alloy. More preferably the composites have
a matrix of silver or tin. Most preferably the composites have a
silver matrix. Composite thicknesses may vary depending on the
metal or metal alloy and the function of the substrate plated. In
general, composite thicknesses are at least 0.1 .mu.m, typically
from 1 .mu.m to 1000 .mu.m. Preferably, the composite has a
thickness of 0.5 .mu.m to 100 .mu.m, more preferably from 1 .mu.m
to 50 .mu.m.
[0036] The composites may be electroplated adjacent conductive
surfaces of various types of substrates. Such conductive surfaces
include, but are not limited to, copper, copper alloys, nickel,
nickel alloys, tin and tin alloys. The composites are electrically
conductive and provide a wear resistant deposit with improved
durability in comparison to many conventional metal and metal alloy
coatings. The composite coatings may be used to replace hard gold
coatings of gold/cobalt and gold/nickel which are often used to
coat articles which are exposed to rigorous wear cycles or are
prone to oxidation due to heat in sliding processes, such as is
typical in switches and connectors.
[0037] The following examples are included to illustrate the
invention but are not intended to limit the scope of the
invention.
Example 1 (Comparative)
[0038] An aqueous silver electroplating solution was prepared as
shown in the table below.
TABLE-US-00001 TABLE 1 COMPONENT AMOUNT Silver ions as silver
5,5-dimethyl hydantoin 40 g/L 5,5-dimethyl hydantoin 70 g/L
Sulfamic acid 35 g/L Potassium hydroxide 50 g/L Graphite (400 nm)
20 g/1 pH 9.5
[0039] Graphite nano-particles supplied by Nanostructured &
Amorphous Materials Inc having an average diameter of 400 nm at a
concentration of 20 g/L were mixed with the silver electroplating
bath. A clean copper rotating disk cathode was immersed into the
solution and was connected to a rectifier. The counter electrode
was a silver anode. The temperature of the silver electroplating
bath was maintained at 60.degree. C. during silver composite
electroplating. The current density was 1 ASD. Electroplating was
done until a layer of silver 25 .mu.m thick was deposited on the
copper rotating disk. The silver plated disk was removed from the
electroplating bath and rinsed with deionized water at room
temperature. To ensure that the graphite particles were well
dispersed in the plating solution and to facilitate the graphite
particle incorporation, a UP400S 400 Watt full amplitude ultrasonic
probe, supplied by Hielscher Ultrasonics, Germany, was inserted in
the vicinity of the cathode prior to and during the electroplating,
at 60% amplitude and 0.5 duty cycle.
[0040] Nano-particle incorporation was investigated by a SEM using
a Philips SEM XL-30 microscope on cross sections of the deposits.
FIG. 1 is a SEM image (secondary electrons) of a cross-section of
the composite layer on the copper substrate at 3500.times.,
obtained using secondary electrons. The dark sections or bands
indicate where graphite nano-particles were incorporated into the
silver metal matrix. As is evidenced by the SEM the nano-particle
incorporation was both sparse and not homogeneous. The
nano-particles of graphite agglomerated in the composite.
Example 2
[0041] The method of Example 1 was repeated except that 5 g/L of
carbon black nano-particles with an average diameter of 25 nm
(available from Orion Engineered Carbons) were mixed with the
silver electroplating bath in Table 2. The plating parameters were
the same as described above.
TABLE-US-00002 TABLE 2 COMPONENT AMOUNT Silver ions as silver
5,5-dimethyl hydantoin 40 g/L 5,5-dimethyl hydantoin 70 g/L
Sulfamic acid 35 g/L Potassium hydroxide 50 g/L Carbon Black (25
nm) 5 g/1 pH 9.5
[0042] After plating a 25 um thick composite of silver and carbon
black nano-particles on the copper substrate, the substrate was
cross-sectioned and examined for nano-particle incorporation in the
silver matrix using SEM. FIG. 2 is a 5000.times. SEM cross-section
(back scattered electrons) of the composite. The dark sections
indicate areas where the nano-particles of carbon black were
incorporated into the silver matrix. As is evident from the SEM in
FIG. 2 substantial amounts of nano-particles were incorporated into
the silver matrix. The incorporation was homogeneous in contrast to
the graphite incorporation of Example 1.
[0043] Contact resistance of the composite of silver and carbon
black nano-particles was determined and compared to a silver
deposit without carbon black nano-particles. Each bath was prepared
under the same conditions. The silver and carbon black
nano-particle plating bath was the same as in Table 2 above. The
silver plating bath was the same as in Table 2 above except that
the carbon black nano-particles were excluded from the formulation.
A clean copper rotating disk cathode was immersed into each bath
and was connected to a rectifier. The counter electrode was a
silver anode. The temperature of the baths was maintained at
60.degree. C. during electroplating. The current density was 1 ASD.
To ensure that the carbon black particles were well dispersed in
the plating solution and to facilitate the carbon black particle
incorporation, an ultrasonic probe UP400S was inserted in the
vicinity of the cathode prior to and during the electroplating at
60% amplitude and 0.5 duty cycle. Electroplating was done until a
layer of silver or silver composite of 25 um thick was deposited on
the copper rotating disks. The plated disks were removed from the
electroplating baths and rinsed with deionized water at room
temperature.
[0044] Contact resistance measurements were done using a KOWI 3000
Contact Resistance Tester manufactured by WSK Mess- und
Datentechnik GmbH, Germany. FIG. 3 shows the contact resistance in
mOhms of both the composite of silver and carbon black
nano-particles (AgCB) and the silver (Ag), under varied contact
forces in centiNewtons. The results indicated that the contact
resistance of the silver and carbon black nano-particles composite
remained substantially the same as the silver deposit over the
various forces applied.
Example 3
[0045] The method of Example 2 was repeated with 50 g/L of carbon
black nano-particles. Instead of using ultrasonic disintegration, a
surfactant was added into the plating solution to facilitate the
particle dispersion. The bath formulation was as disclosed in Table
3. The plating parameters were the same as described above in
Example 2.
TABLE-US-00003 TABLE 3 COMPONENT AMOUNT Silver ions as silver
5,5-dimethyl hydantoin 40 g/L 5,5-dimethyl hydantoin 70 g/L
Sulfamic acid 35 g/L Potassium hydroxide 50 g/L PHOSPHOLAN .TM. PS
331 50 g/1 (an alcohol phosphate ester) Carbon Black (25 nm) 50 g/1
pH 9.5
[0046] The addition of an alcohol phosphate surfactant to the bath
stabilized the carbon black nano-particle dispersion and assisted
particle incorporation into the composite. FIG. 4 is a
10,000.times. SEM cross-section of the composite. The dark sections
indicate areas where the nano-particles of carbon black were
incorporated into the silver matrix. As is evident from the SEM in
FIG. 4 substantial amounts of nano-particles were incorporated into
the silver matrix. The incorporation was homogeneous in contrast to
the graphite incorporation of Example 1.
* * * * *