U.S. patent application number 17/556037 was filed with the patent office on 2022-04-14 for acidic aqueous binary silver-bismuth alloy electroplating compositions and methods.
The applicant listed for this patent is Rohm and Haas Electronic Materials LLC. Invention is credited to Jamie Y.C. Chen, Michael Lipschutz, Miguel A. Rodriguez, Youngmin Yoon.
Application Number | 20220112619 17/556037 |
Document ID | / |
Family ID | |
Filed Date | 2022-04-14 |
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United States Patent
Application |
20220112619 |
Kind Code |
A1 |
Rodriguez; Miguel A. ; et
al. |
April 14, 2022 |
ACIDIC AQUEOUS BINARY SILVER-BISMUTH ALLOY ELECTROPLATING
COMPOSITIONS AND METHODS
Abstract
Aqueous acid binary silver-bismuth alloy electroplating
compositions and methods enable electroplating silver rich binary
silver-bismuth deposits. The aqueous acid binary silver-bismuth
alloy electroplating compositions include 5-membered heterocyclic
nitrogen compounds with a thiol functionality which enable
deposition of the silver rich binary silver-bismuth alloys. The
silver rich silver-bismuth deposits are matte to semi-bright,
uniform and have a low coefficient of friction.
Inventors: |
Rodriguez; Miguel A.;
(Roxbury, MA) ; Lipschutz; Michael; (Natick,
MA) ; Chen; Jamie Y.C.; (Worcester, MA) ;
Yoon; Youngmin; (Boston, MA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Rohm and Haas Electronic Materials LLC |
Marlborough |
MA |
US |
|
|
Appl. No.: |
17/556037 |
Filed: |
December 20, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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16708783 |
Dec 10, 2019 |
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17556037 |
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International
Class: |
C25D 3/46 20060101
C25D003/46; C22C 5/06 20060101 C22C005/06; C25D 3/52 20060101
C25D003/52 |
Claims
1-6. (canceled)
7. A method of electroplating a binary silver-bismuth alloy on a
substrate comprising: a) providing the substrate; b) contacting the
substrate with a binary silver-bismuth alloy electroplating
composition comprising a source of silver ions, a source of bismuth
ions, wherein the binary silver-bismuth alloy electroplating
composition is free of additional alloying metals and a 5-membered
aromatic heterocyclic nitrogen compounds having general formula:
##STR00008## wherein Q.sub.1-Q.sub.4 can be a substituted or
unsubstituted nitrogen or a substituted or unsubstituted carbon
with the proviso that at least two of Q.sub.1-Q.sub.4 are nitrogen,
wherein substituent groups include, but are not limited to,
(C.sub.1-C.sub.4)alkyl, amino group, aminoalkyl group, carboxyl,
carboxy(C.sub.1-C.sub.4)alkyl or alkylsulfonate, an aliphatic thiol
terminal compound selected from the group consisting of
thioglycolic acid, 2-mercaptopropionic acid, 3-mercaptopropionic
acid, cysteine, mercaptosuccinic acid, 3-mercapto-l-propanesulfonic
acid, 2-mercaptoethanesulfonic acid, salts of the thiol terminal
compounds, and mixtures thereof, and a pH of less than 7; and c)
applying an electric current to the binary silver-bismuth alloy
electroplating composition and substrate to electroplate a binary
silver-bismuth deposit on the substrate.
8. The method of claim 7, wherein the 5-membered aromatic
heterocyclic nitrogen compound is selected from the group
consisting of 3-mercapto-1,2,4-triazole,
3-amino-1,2,4-triazole-5-thiol, 3-amino-5-mercapto-1,2,4-triazole,
3-mercapto-4-methyl-4H-1,2,4-triazole, 1H-imidazole-2-thiol, salts
of the 5-membered aromatic heterocyclic nitrogen compounds, and
mixtures thereof.
9. The method of claim 7, wherein the binary silver-bismuth alloy
electroplating composition further comprises a thioether or
mixtures thereof.
10. (canceled)
11. An article comprising a binary silver-bismuth alloy layer
adjacent a surface of a substrate made according to the method of
claim 7, wherein the binary silver-bismuth alloy layer comprises
90% to 99.8% silver and 0.2% to 10% bismuth, and has a coefficient
of friction of 1 or less.
Description
FIELD OF THE INVENTION
[0001] The present invention is directed to acidic aqueous binary
silver-bismuth alloy electroplating compositions and methods. More
specifically, the present invention is directed to acidic aqueous
binary silver-bismuth alloy electroplating compositions and
methods, wherein the acidic aqueous binary silver-bismuth alloy
electroplating compositions include 5-membered aromatic
heterocyclic nitrogen compounds having a thiol functionality which
enable electrodeposition of silver rich binary silver-bismuth
alloys having low electrical contact resistance and good wear
resistance.
BACKGROUND OF THE INVENTION
[0002] Silver and silver alloy plating baths are highly desirable
for depositing silver and silver alloys on substrates in
applications directed to the manufacture of electronic components
and jewelry. Substantially pure silver is used as a contact finish
because of its excellent electrical properties, specifically, low
electrical contact resistance. However, its use as a contact finish
for, example, electrical connectors are limited because of their
poor resistance to mechanical wear and high silver-on-silver
coefficient of friction. The poor resistance to mechanical wear
results in the connector becoming physically damaged after a
relatively low number of insertion-deinsertion cycles of the
connector. A high coefficient of friction contributes to this wear
problem. When connectors have a high coefficient of friction, the
force required to insert and deinsert the connector is very high
and this can damage the connector or limit the connector design
options. Silver alloy deposits, such as silver-antimony and
silver-tin, result in improved wear properties but have
unacceptably poor contact resistance, especially after exposure to
high temperatures for prolonged periods of time.
[0003] Since many silver salts are substantially water-insoluble
and silver salts which are water-soluble often form insoluble salts
with various compounds commonly present in plating baths, the
plating industry is faced with numerous challenges to formulate a
silver or silver alloy plating bath which is stable long enough for
practical plating applications and addresses at least the foregoing
problems. Many silver and silver alloy plating baths include
cyanide compounds to enable practical applications. However,
cyanide compounds are extremely poisonous. Therefore, special waste
water treatment is required. This results in a rise in treatment
costs. Further, since these baths can only be used in the alkaline
range, the types of alloying metals are limited because most metals
are not soluble in alkaline environments. Further, exposure of
substrates to alkaline baths can cause passivation of the surfaces
of the substrates, thus making the surfaces difficult to plate.
[0004] Therefore, there is a need for a silver alloy plating bath
which is stable, acidic, produces a deposit that has low electrical
contact resistance and low coefficient of friction to provide
improved wear resistance.
SUMMARY OF THE INVENTION
[0005] The present invention is directed to binary silver-bismuth
alloy electroplating compositions comprising a source of silver
ions, a source of bismuth ions, and a 5-membered aromatic
heterocyclic nitrogen compound having the general formula:
##STR00001##
[0006] wherein Q.sub.1-Q.sub.4 can be a substituted or
unsubstituted nitrogen or a substituted or unsubstituted carbon
with the proviso that at least two of Q.sub.1-Q.sub.4 are nitrogen,
wherein substituent groups include, but are not limited to,
hydrogen, (C.sub.1-C.sub.4)alkyl, amino group, aminoalkyl group,
carboxyl, carboxy(C.sub.1-C.sub.4)alkyl, or alkylsulfonate, and a
pH of less than 7.
[0007] The present invention is also directed to a method of
electroplating binary silver-bismuth alloys on a substrate
including: [0008] a) providing the substrate; [0009] b) contacting
the substrate with a binary silver-bismuth alloy electroplating
composition comprising a source of silver ions, a source of bismuth
ions, and a 5-membered aromatic heterocyclic nitrogen compound
having the general formula:
[0009] ##STR00002## [0010] wherein Q.sub.1-Q.sub.4 can be a
substituted or unsubstituted nitrogen or a substituted or
unsubstituted carbon with the proviso that at least two of
Q.sub.1-Q.sub.4 are nitrogen, wherein substituent groups include,
but are not limited to, hydrogen, (C.sub.1-C.sub.4)alkyl, amino
group, aminoalkyl group, carboxyl, carboxy(C.sub.1-C.sub.4)alkyl,
or alkylsulfonate, and a pH of less than 7; and [0011] c) applying
an electric current to the binary silver-bismuth alloy
electroplating composition and the substrate to electroplate a
silver-bismuth alloy deposit on the substrate.
[0012] The present invention is further directed to an article
comprising a binary silver-bismuth alloy layer adjacent a surface
of a substrate, wherein the binary silver-bismuth alloy layer
comprises 90% to 99% silver and 1% to 10% bismuth, and has a
coefficient of friction of 1 or less.
[0013] Including 5-membered aromatic heterocyclic nitrogen
compounds having formula (I) above in aqueous binary silver-bismuth
electroplating compositions in an acidic environment enables
deposition of silver rich binary silver-bismuth alloys on a
substrate such that the silver rich binary silver-bismuth alloys
have substantially the good electrical properties of a silver
deposit, specifically, low electrical contact resistance. In
addition, the silver rich binary silver-bismuth alloy deposits good
mechanical wear resistance. The silver rich binary silver-bismuth
deposits are uniform and matte to semi-bright in appearance. The
binary silver-bismuth alloy electroplating compositions of the
present invention are stable.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a scanning electron microscope image at 10,000X of
a binary silver-bismuth alloy showing discrete sectors of bismuth
in a silver matrix.
[0015] FIG. 2 is a 2D profilometry graphic of a surface of a silver
metal deposit wherein the x-axis and y-axis are calibrated in
microns (.mu.m).
[0016] FIG. 3 is a 3D profilometry graphic of a surface of a silver
metal deposit wherein the x-axis, y-axis and z-axis are calibrated
in microns (.mu.m).
[0017] FIG. 4 is a 2D profilometry graphic of a surface of a
silver-bismuth alloy deposit of the invention wherein the alloy is
composed of 95% silver and 5% bismuth, and the x-axis, y-axis and
z-axis are calibrated in microns (.mu.m).
[0018] FIG. 5 is a 3D profilometry graphic of a surface of a
silver-bismuth alloy deposit of the invention wherein the alloy is
composed of 95% silver and 5% bismuth, and the x-axis, y-axis and
z-axis are calibrated in microns (.mu.m).
[0019] FIG. 6 is a 2D profilometry graphic of a surface of a
silver-bismuth alloy deposit of the invention wherein the alloy is
composed of 97% silver and 3% bismuth, and the x-axis, y-axis and
z-axis are calibrated in microns (.mu.m).
[0020] FIG. 7 is a 3D profilometry graphic of a surface of a
silver-bismuth alloy deposit of the invention wherein the alloy is
composed of 97% silver and 3% bismuth, and the x-axis, y-axis and
z-axis are calibrated in microns (.mu.m).
[0021] FIG. 8 is a 2D profilometry graphic of a surface of a
silver-bismuth alloy deposit of the invention wherein the alloy is
composed of 97% silver and 3% bismuth, and the x-axis, y-axis and
z-axis are calibrated in microns (.mu.m).
[0022] FIG. 9 is a 3D profilometry graphic of a surface of a
silver-bismuth alloy deposit of the invention wherein the alloy is
composed of 97% silver and 3% bismuth, and the x-axis, y-axis and
z-axis are calibrated in microns (.mu.m).
DETAILED DESCRIPTION OF THE INVENTION
[0023] As used throughout the specification the abbreviations have
the following meanings, unless the context clearly indicates
otherwise: .degree. C.=degrees Centigrade; ppm=parts per million;
one ppm=one mg/L; g=gram; mg=milligram; L=liter; mL=milliliter;
mm=millimeters; cm=centimeter; .mu.m=microns; DI=deionized;
A=amperes; ASD=amperes/dm.sup.2=plating speed; DC=direct current;
v=volts, which is the SI unit of electromotive force;
m.OMEGA.=milliohms=contact resistance; cN=centiNewtons=a unit of
force; N=newtons; COF=coefficient of friction; rpm=revolutions per
minute; s=seconds; 2D=two-dimensional; 3D=three-dimensional;
Ag=silver; Bi=bismuth; Au=gold; Cu=copper; Ag.sup.+ molecular
weight=107.868 g/mole; and 3,6-dithia-1,8-octanediol molecular
weight=182.3 g/mole.
[0024] The term "alky" means an organic functional group having the
general formula C.sub.nH.sub.2n+1 where C is carbon, H is hydrogen
and n is an integer. The term "aliphatic" means relating to or
denoting organic compounds in which carbon atoms form open chains
(as in alkanes), not aromatic rings. The term "binary" in reference
of an alloy means a metallic solid composed of a homogenous mixture
of two metals. The "----" dashed line in chemical structures means
an optional covalent bond. The term "adjacent" means directly in
contact with such that two metal layers have a common interface.
The term "contact resistance" means electrical resistance as a
function of applied force. The term "newtons" is the SI unit of
force and it is equal to the force that would give a mass of one
kilogram an acceleration of one meter per second per second, and is
equivalent to 100,000 dynes. The term "coefficient of friction" is
a value that shows the relationship between the force of friction
between two objects and the normal reaction between the objects
that are involved; and is shown by F.sub.f=.mu..mu.F.sub.n, wherein
Ff is the frictional force, .mu. is the coefficient of friction and
F.sub.n is the normal force. The term "normal force" means a force
applied perpendicular to the plane of contact between two objects.
The term "discrete" means individually separate and distinct. The
term "sector" means an area or portion that is distinct from other
areas. The term "matrix" means a surrounding metal or majority
metal, i.e., greater than 50%, of a metal alloy. The term "proviso"
means a condition or restriction. The term "tribology" means the
science and engineering of interacting surfaces in relative motion
and includes the study and application of the principles of
lubrication, friction and wear. The term "cold welding" means a
solid-state welding process in which joining takes place without
fusion or heating at the interface of the two parts to be welded
and no molten liquid or molten phase is present in the joint. The
term "aqueous" means water or water-based. The terms "composition"
and "bath" are used interchangeably throughout the specification.
The terms "deposit" and "layer" are used interchangeably throughout
the specification. The terms "electroplating", "plating" and
"depositing" are used interchangeably throughout the specification.
The term "matte" means dull or without luster. The terms "a" and
"an" can refer to both the singular and the plural throughout the
specification. All percent (%) values and ranges indicate weight
percent unless otherwise specified. All numerical ranges are
inclusive and combinable in any order, except where it is logical
that such numerical ranges are constrained to add up to 100%.
[0025] The present invention is directed to an aqueous acidic
binary silver-bismuth electroplating composition, wherein the
aqueous acidic binary silver-bismuth electroplating composition
includes a source of silver ions, a source of bismuth ions and a
5-membered aromatic heterocyclic nitrogen compound having the
general formula:
##STR00003##
wherein Q.sub.1-Q.sub.4 can be a substituted or unsubstituted
nitrogen or a substituted or unsubstituted carbon with the proviso
that at least three of Q.sub.1-Q.sub.4 are nitrogen, wherein
substituent groups include, but are not limited to, hydrogen,
(C.sub.1-C.sub.4)alkyl, an amino group, an aminoalkyl group,
carboxyl group, carboxy(C.sub.1-C.sub.4)alkyl, or alkylsulfonate,
and a pH of less than 7. Preferably, the substituent groups are
hydrogen, (C.sub.1-C.sub.2)alkyl, a primary amino group such as
NH.sub.2, a secondary amino group such as NH--NH.sub.2, or an
amino(C.sub.1-C.sub.4)alkyl, further preferably, the substituent
groups are hydrogen, methyl or NH.sub.2, more preferably, a
nitrogen of the ring is substituted with hydrogen or methyl group
or a nitrogen of the ring is substituted with the NH.sub.2, or a
carbon of the ring is substituted with the NH.sub.2, most
preferably, a nitrogen of the ring is substituted with hydrogen or
methyl.
[0026] The matte to semi-bright and uniform silver rich binary
silver-bismuth alloy deposits have substantially good electrical
properties, such as low electrical contact resistance. The silver
rich binary silver-bismuth alloy deposit has a low coefficient of
friction such that the silver rich binary silver-bismuth alloy
layers have good mechanical wear resistance. The acidic aqueous
binary silver-bismuth alloy electroplating compositions of the
present invention are stable. The aqueous binary silver-bismuth
alloy electroplating compositions are free of any additional
alloying metals, such as, but not limited to, antimony, tin,
copper, nickel, cobalt, cadmium, gold, lead, indium, iron,
palladium, platinum, rhodium, ruthenium, tellurium, thallium,
selenium and zinc. Preferably, the acidic aqueous silver-bismuth
electroplating compositions are cyanide-free.
[0027] Examples of preferred 5-membered aromatic heterocyclic
nitrogen compounds of the present invention are the following:
##STR00004##
and salts of the 5-membered aromatic heterocyclic nitrogen
compounds having a thiol functionality. More preferably, the
5-membered aromatic heterocyclic nitrogen compounds having a thiol
functionality of the present invention are chosen from one or more
of 3-mercapto-1,2,4-triazole, 3-amino-1,2,4-triazole-5-thiol,
3-amino-5-mercapto-1,2,4-triazole,
3-mercapoto-4-methyl-4H-1,2,4-triazole, and salts of the 5-membered
aromatic heterocyclic nitrogen compounds having a thiol
functionality; even more preferably, the 5-membered aromatic
heterocyclic nitrogen compounds having a thiol functionality of the
present invention are chosen from one or more of
3-mercapto-1,2,4-triazole, 3-amino-1,2,4-triazole-5-thiol,
3-amino-5-mercapto-1,2,4-triazole,
3-mercapoto-4-methyl-4H-1,2,4-triazole, and salts of the 5-membered
aromatic heterocyclic nitrogen compounds having a thiol
functionality of the present invention; further preferably, the
5-membered aromatic heterocyclic nitrogen compounds having a thiol
functionality of the present invention are chosen from one or more
of 3-mercapto-1,2,4-triazole,
3-mercapoto-4-methyl-4H-1,2,4-triazole, and salts of the 5-membered
aromatic heterocyclic nitrogen compounds having a thiol
functionality of the present invention. Salts of the 5-membered
aromatic heterocyclic nitrogen compounds having a thiol
functionality of the present invention of the present invention
include, but are not limited to, alkali metal salts, such as
sodium, potassium and lithium salts, ammonium salts, tetraalkyl
ammonium salts, magnesium salts, silver salts and bismuth
salts.
[0028] The 5-membered aromatic heterocyclic nitrogen compounds
having a thiol functionality and salts thereof of the present
invention are included in sufficient amounts to enable
electroplating of a silver rich binary silver-bismuth alloy in an
aqueous acid environment. Preferably, the 5-membered aromatic
heterocyclic nitrogen compounds having a thiol functionality of the
present invention are included in amounts of 50 ppm or greater,
more preferably, in amounts of 100 ppm to 100 g/L, further
preferably, from 100 ppm to 20 g/L, even more preferably, from 100
ppm to 10 g/L, most preferably, from 100 ppm to 5 g/L.
[0029] The aqueous acid silver-bismuth alloy electroplating
compositions of the present invention include a source of silver
ions. Sources of silver ions can be provided by silver salts such
as, but not limited to, silver halides, silver gluconate, silver
citrate, silver lactate, silver nitrate, silver sulfates, silver
alkane sulfonates, silver alkanol sulfonates or mixtures thereof.
When a silver halide is used, preferably the halide is chloride.
Preferably, the silver salts are silver sulfate, a silver alkane
sulfonate, silver nitrate, or mixtures thereof, more preferably,
the silver salt is silver sulfate, silver methanesulfonate, or
mixtures thereof. Mixtures of silver salts can also be included in
the compositions. The silver salts are generally commercially
available or can be prepared by methods described in the
literature. Preferably, the silver salts are readily
water-soluble.
[0030] The amount of silver salts included in the aqueous acid
binary silver-bismuth electroplating compositions are in amounts
sufficient to provide a desired matte to semi-bright and uniform
silver rich binary silver-bismuth alloy deposit, preferably, where
the silver content of the silver rich binary silver-bismuth alloy
deposit contains 90% to 99.8% silver, further preferably, from 90%
to 99.7% silver, most preferably, from 95% to 99.7%, with bismuth
the remainder of the alloying metal, excluding unavoidable
impurities. Preferably, silver salts are included in the
compositions to provide silver ions at a concentration of at least
10 g/L, more preferably, silver salts are included in the
compositions in amounts to provide silver ion concentrations in
amounts of 10 g/L to 100 g/L, further preferably, silver salts are
included in amounts to provide silver ion concentrations of 20 g/L
to 80 g/L, most preferably, silver salts are included in amounts to
provide silver ions at concentrations of 20 g/L to 60 g/L.
[0031] The aqueous acid silver-bismuth alloy electroplating
compositions include a source of bismuth ions which provide the
electroplating bath with Bi ions in solution. Sources of bismuth
ions include, but are not limited to, bismuth salts of alkane
sulfonic acids such as bismuth methanesulfonate, bismuth
ethanesulfonate, bismuth propanesulfonate, 2-bismuth propane
sulfonate and bismuth p-phenolsulfonate, bismuth salts of
alkanolsulfonic acids such as bismuth hydroxymethanesulfonate,
bismuth 2-hydoxyethane-l-sulfonate and bismuth
2-hydroxybutane-1-sulfonate, and bismuth salts such as bismuth
nitrate, bismuth sulfate and bismuth chloride. Mixtures of bismuth
salts can also be included in the compositions. Preferably, the
bismuth salts are water soluble.
[0032] The amount of bismuth salts included in the aqueous acid
binary silver-bismuth electroplating compositions are in amounts
sufficient to provide a desired matte to semi-bright and uniform
silver rich binary silver-bismuth alloy deposit, preferably, where
the bismuth content of the silver rich binary silver-bismuth alloy
deposit contains 0.2% to 10% bismuth, further preferably, from 0.3%
to 10% bismuth, most preferably, from 0.3% to 5% bismuth.
Preferably, bismuth salts are included in the silver-bismuth
compositions to provide bismuth (III) ions in amounts of 50 ppm to
10 g/L, further preferably, from 100 ppm to 5 g/L, most preferably,
from 200 ppm to 5 g/L. Such bismuth salts are commercially
available or can be made according to disclosures in the chemical
literature. They are generally commercially available from a
variety of sources, such as Aldrich Chemical Company, Milwaukee,
Wis.
[0033] Preferably, in the aqueous acid silver-bismuth alloy
electroplating compositions of the present invention, the water
included as a solvent is at least one of deionized and distilled to
limit incidental impurities.
[0034] Optionally, an acid can be included in the binary
silver-bismuth alloy electroplating compositions to assist in
providing conductivity to the compositions. Acids include, but are
not limited to, organic acids such as acetic acid, citric acid,
arylsulfonic acids, alkanesulfonic acids, such as methanesulfonic
acid, ethanesulfonic acid or propanesulfonic acid, aryl sulfonic
acids such as phenylsulfonic acid or tolylsulfonic acid, and
inorganic acids such as sulfuric acid, sulfamic acid, hydrochloric
acid, hydrobromic acid or fluoroboric acid. Water-soluble salts of
the foregoing acids also can be included in the binary
silver-bismuth alloy electroplating compositions of the present
invention. Preferably, the acids are acetic acid, citric acid,
alkane sulfonic acids, aryl sulfonic acids, or salts thereof, more
preferably the acids are acetic acid, citric acid, methanesulfonic
acid, or salts thereof. Such salts include, but are not limited to,
sodium, potassium, silver, bismuth, magnesium, tetraalkylammonium
and ammonium salts. Although a mixture of acids can be used,
preferably, when used, a single acid is used. The acids are
generally commercially available or can be prepared by methods
known in the literature. Such acids can be included in amounts to
provide a desired conductivity. Preferably, the acids or salts
thereof are included in amounts of at least 5 g/L, more preferably,
from 10 g/L to 250 g/L, even more preferably, from 30 g/L to 150
g/L, most preferably from 30 g/1 to 125 g/L.
[0035] The pH of the aqueous acidic binary silver-bismuth alloy
electroplating composition is less than 7. Preferably, the pH is 0
to 6, more preferably, the pH is from 0 to 5, further preferably,
the pH is from 0 to 3, even more preferably, the pH is from 0 to
2.5, most preferably, the pH is from 0 to 2.
[0036] Optionally, a pH adjusting agent can be included in the
aqueous acid binary silver-bismuth alloy compositions of the
present invention. Such pH adjusting agents include inorganic
acids, organic acids, inorganic bases or organic bases and salts
thereof. Such acids include, but are not limited to, inorganic
acids such as sulfuric acid, hydrochloric acid, sulfamic acid,
boric acid, phosphoric acid or salts thereof. Organic acids
include, but are not limited to, acetic acid, citric acid, amino
acetic acid and ascorbic acid or salts thereof. Such salts include,
but are not limited to, trisodium citrate. Inorganic bases such as
sodium hydroxide and potassium hydroxide and organic bases such as
various types of amines can be used. Preferably, the pH adjusting
agents are chosen from acetic acid, citric acid, amino acetic acid
or salts thereof, most preferably, acetic acid, citric acid or
salts thereof. The pH adjusting agents can be added in amounts as
needed to maintain a desired pH range.
[0037] Optionally, but preferably, a thioether is included in the
aqueous acid binary silver-bismuth alloy electroplating
compositions of the present invention. Such thioethers include, but
are not limited to, 2,2'-thiodiethanol, 4,4'-thiodiphenol and
4,4'-thiobis(2-methyl-6-tert-butylphenol), dihydroxy bis-sulfide
compounds or mixtures thereof. Such dihydroxy bis-sulfide compounds
include, but are not limited to, 2,4-dithia-1,5-pentanediol,
2,5-dithia-1,6-hexanediol, 2,6-dithia-1,7-heptanediol,
2,7-dithia-1,8-octanediol, 2,8-dithia-1,9-nonanediol,
2,9-dithia-1,10-decanediol, 2,11-dithia-1,12-dodecanediol,
5,8-dithia-1,12-dodecanediol, 2,15-dithia-1,16-hexadecanediol,
2,21-dithia-1,22-doeicasanediol, 3,5-dithia-1,7-heptanediol,
3,6-dithia-1,8-octanediol, 3,8-dithia-1,10-decanediol,
3,10-dithia-1,8-dodecanediol, 3,13-dithia-1,15-pentadecanediol,
3,18-dithia-1,20-eicosanediol, 4,6-dithia-1,9-nonanediol,
4,7-dithia-1,10-decanediol, 4,11-dithia-1,14-tetradecanediol,
4,15-dithia-1,18-octadecanediol, 4,19-dithia-1,22-dodeicosanediol,
5,7-dithia-1,11-undecanediol, 5,9-dithia-1,13-tridecanediol,
5,13-dithia-1,17-heptadecanediol, 5,17-dithia-1,21-uneicosanediol
and 1,8-dimethyl-3,6-dithia-1,8-octanediol. Preferably, the
dihydroxy bis-sulfide compounds are chosen from
3,6-dithia-1,8-octanediol, 3,8-dithia-1,10-decanediol,
2,4-dithia-1,5-pentanediol, 2,5-dithia-1,6-hexanediol,
2,6-dithia-1,7-heptanediol, 2,7-dithia-1,8-octanediol, more
preferably, 3,6-dithia-1,8-octanediol, 2,4-dithia-1,5-pentanediol,
2,5-dithia-1,6-hexanediol, 2,6-dithia-1,7-heptanediol, or
2,7-dithia-1,8-octanediol, even more preferably,
3,6-dithia-1,8-octanediol, 2,6-dithia-1,7-heptanediol, or
2,7-dithia-1,8-octanediol, most preferably,
3,6-dithia-1,8-octanediol.
[0038] Preferably, thioether compounds can be included in the
aqueous acid binary silver-bismuth alloy electroplating
compositions in a molar ratio with silver of at least 1 mole of
thioether to 1 mole of silver, more preferably, from 1 to 5 moles
of thioether to 1 mole of silver, even more preferably, from 2 to 4
moles of thioether to 1 mole of silver, and most preferably, from
2.5 to 4 moles of thioether to 1 mole of silver.
[0039] Optionally, but preferably, the aqueous acid binary
silver-bismuth electroplating compositions of the present can
include an aliphatic thiol terminal compound. Such aliphatic thiol
terminal compounds include, but are not limited to, thioglycolic
acid, 2-mercaptopropionic acid, 3-mercaptopropionic acid, cysteine,
mercaptosuccinic acid, 3-mercapto-l-propanesulfonic acid,
2-mercaptoethanesulfonic acid, and salts thereof. Salts of the
thiol terminal compounds of the present invention include, but are
not limited to, alkali metal salts such as sodium and potassium
salts, or ammonium salts.
[0040] Preferably, the aliphatic thiol terminal aliphatic compounds
of the present invention are included in amounts of 1 g/L or
greater, more preferably, the aliphatic thiol terminal compounds
are included in amounts of 1 g/L to 100 g/L, most preferably, from
1 g/L to 60 g/L.
[0041] Optionally, one or more surfactants can be included in the
aqueous acid silver-bismuth alloy electroplating compositions of
the present invention. Such surfactants include, but are not
limited to, ionic surfactants such as cationic and anionic
surfactants, non-ionic surfactants and amphoteric surfactants.
Surfactants can be included in conventional amounts such as 0.05
g/L to 30 g/L.
[0042] Examples of anionic surfactants are sodium
di(1,3-dimethylbutyl) sulfosuccinate, sodium-2-ethylhexylsulfate,
sodium diamyl sulfosuccinate, sodium lauryl sulfate, sodium lauryl
ether-sulfate, sodium di-alkylsulfosuccinates and sodium
dodecylbenzene sulfonate. Examples of cationic surfactants are
quaternary ammonium salts such as perfluorinated quaternary
amines.
[0043] Further optional additives can be included in the
silver-bismuth electroplating compositions of the present
invention, such as biocides. Conventional biocides well known in
the art can be included in the silver-bismuth electroplating
compositions of the present invention. Biocides are included in
conventional amounts well known to those of ordinary skill in the
art.
[0044] Preferably, compounds which function as levelers are
excluded from the silver-bismuth electroplating compositions of the
present invention.
[0045] Preferably, the acidic aqueous binary silver-bismuth alloy
electroplating compositions of the present invention are composed
of water, silver ions and counter anions, bismuth (III) ions and
counter anions, a 5-membered aromatic heterocyclic nitrogen
compound having the general formula:
##STR00005##
wherein Q.sub.1-Q.sub.4 can be a substituted or unsubstituted
nitrogen or a substituted or unsubstituted carbon with the proviso
that at least two of Q.sub.1-Q.sub.4 are nitrogen, wherein
substituent groups include, but are not limited to, hydrogen,
(C.sub.1-C.sub.4)alkyl, an amino group, an aminoalkyl group,
carboxyl, carboxy(C.sub.1-C.sub.4)alkyl or alkylsulfonate,
optionally a thioether, optionally an aliphatic thiol terminal
compound or salt thereof, optionally an acid or salt thereof,
optionally a pH adjusting agent, optionally a biocide, and
optionally a surfactant, wherein a pH is less than 7.
[0046] Further preferably, the acidic aqueous binary silver-bismuth
alloy electroplating compositions of the present invention are
composed of water, silver ions and counter anions, bismuth (III)
ions and counter anions, a 5-membered aromatic heterocyclic
nitrogen compound having the general formula:
##STR00006##
wherein Q.sub.1-Q.sub.4 can be a substituted or unsubstituted
nitrogen or a substituted or unsubstituted carbon with the proviso
that at least two of Q.sub.1-Q.sub.4 are nitrogen, wherein
substituent groups include, but are not limited to, hydrogen,
(C.sub.1-C.sub.4)alkyl, an amino group, an aminoalkyl group,
carboxyl, carboxy(C.sub.1-C.sub.4)alkyl or an alkylsulfonate, a
thioether, optionally an aliphatic thiol terminal compound or salt
thereof, optionally an acid or salt thereof, optionally a pH
adjusting agent, optionally a biocide, and optionally a surfactant,
wherein a pH is 0-6.
[0047] More preferably, the acidic aqueous binary silver-bismuth
alloy electroplating compositions of the present invention are
composed of water, silver ions and counter anions, bismuth (III)
ions and counter anions, 5-membered aromatic heterocyclic nitrogen
compound having the general formula:
##STR00007##
wherein Q.sub.1-Q.sub.4 can be a substituted or unsubstituted
nitrogen or a substituted or unsubstituted carbon with the proviso
that at least two of Q.sub.1-Q.sub.4 are nitrogen, wherein
substituent groups include, but are not limited to, hydrogen,
(C.sub.1-C.sub.4)alkyl, an amino group, an aminoalkyl group,
carboxyl, carboxy(C.sub.1-C.sub.4)alkyl or an alkylsulfonate, a
dihydroxy bis-sulfide compound, an aliphatic thiol terminal
compound or salt thereof, an acid or salt thereof, optionally a pH
adjusting agent, optionally a biocide, and optionally a surfactant,
wherein a pH is 0-6.
[0048] Even more preferably, the acidic aqueous binary
silver-bismuth alloy electroplating compositions of the present
invention are composed of water, silver ions and counter anions,
bismuth (III) ions and counter anions, a compound selected from the
group consisting of 3-mercapto-1,2,4-triazole,
3-amino-1,2,4-triazole-5-thiol, 3-amino-5-mercapto-1,2,4-triazole,
3-mercapto-4-methyl-4H-1,2,4-triazole, 1H-imidazole-2-thiol, salts
of the 5-membered aromatic heterocyclic nitrogen compounds having a
thiol functionality, and mixtures thereof, a dihydroxy bis-sulfide
compound, an aliphatic thiol terminal compound selected from the
group consisting of thioglycolic acid, 2-mercaptopropionic acid,
3-mercaptopropionic acid, cysteine, mercaptosuccinic acid,
3-mercapto-l-propanesulfonic acid, 2-mercaptoethanesulfonic acid,
and salts thereof, an acid or salt thereof, optionally a pH
adjusting agent, optionally a biocide and optionally a surfactant,
wherein a pH is 0-3.
[0049] The acidic aqueous binary silver-bismuth alloy
electroplating compositions of the present invention can be used to
deposit binary silver-bismuth alloy layers on various substrates,
both conductive and semiconductor substrates. Preferably, the
substrates on which silver-bismuth alloy layers are deposited are
nickel, nickel alloys, copper and copper alloy substrates. Such
nickel alloy substrates include, but are not limited to, nickel
phosphorus and nickel boron. Such copper alloy substrates include,
but are not limited to, brass and bronze.
[0050] The electroplating composition temperatures during plating
can range from room temperature to 70.degree. C., preferably, from
30.degree. C. to 60.degree. C., more preferably, from 40.degree. C.
to 60.degree. C. The binary silver-bismuth alloy electroplating
compositions are preferably under continuous agitation during
electroplating.
[0051] The acidic aqueous binary silver-bismuth alloy
electroplating method of the present invention includes providing a
substrate, providing the acidic aqueous binary silver-bismuth alloy
electroplating composition of the present invention and contacting
the substrate with the acidic aqueous binary silver-bismuth alloy
electroplating composition such as by immersing the substrate in
the composition or spraying the substrate with the composition.
Applying a current with a conventional rectifier where the
substrate functions as a cathode and there is present a counter
electrode or anode. The anode can be any conventional soluble or
insoluble anode used for electroplating binary silver-bismuth
alloys. The binary silver-bismuth alloys are deposited adjacent a
surface of the substrate, wherein the surface of the substrate is
nickel, nickel alloy, copper or copper alloy.
[0052] The acidic aqueous binary silver-bismuth alloy
electroplating compositions of the present invention enable
deposition of matte to semi-bright and uniform silver rich
silver-bismuth alloy layers over broad current density ranges. The
silver rich binary silver-bismuth alloy includes 90% to 99.8%
silver and 0.2% to 10% bismuth, preferably, 90% to 99.7% silver and
0.3% to 10% bismuth, most preferably, from 95% to 99.7% silver and
from 0.3% to 5% bismuth, excluding unavoidable impurities in the
alloy.
[0053] Current densities for electroplating the matte to
semi-bright and uniform silver rich silver-bismuth alloy of the
present invention can range from 0.1 ASD or higher. Preferably, the
current densities range from 0.5 ASD to 70 ASD, further preferably,
from 1 ASD to 40 ASD, more preferably, from 1 ASD to 30 ASD, even
more preferably from 1 ASD to 15 ASD.
[0054] The thickness of the binary silver-bismuth alloy layers of
the present invention can vary depending on the function of the
silver-bismuth alloy layer and the type of substrate on which it is
plated. Preferably, the binary silver-bismuth alloy layer ranges
from 1 .mu.m or greater. Further preferably, the binary
silver-bismuth layers have thickness ranges of 1 .mu.m to 100
.mu.m, more preferably, from 1 .mu.m to 50 .mu.m, even more
preferably, from 1 .mu.m to 10 .mu.m, most preferably from 1 .mu.m
to 5 .mu.m.
[0055] While it is envisioned that the acidic aqueous binary
silver-bismuth alloy electroplating compositions of the present
invention can be used to plate various substrates which can include
silver-bismuth alloy layers, preferably, the acidic aqueous binary
silver-bismuth alloy electroplating compositions of the present
invention are used to electroplate top layers or coatings on
electrical connectors where substantial contact forces and wear are
expected to prevail. The silver rich binary silver-bismuth alloy
deposit is a highly desirable substitute for conventional silver
coatings found on conventional connectors. The silver-bismuth alloy
deposit has low electrical contact resistance. In addition, the
silver-bismuth alloy deposit of the present invention has a low
COF, preferably, a COF of 1 or less, more preferably, 0.6 or less.
The COF of the silver-bismuth alloy deposit of the present
invention has a COF of, preferably, 40% or less than the COF of
substantially pure silver deposits, thus the binary silver-bismuth
alloy of the present invention has substantial improvement in wear
resistance over substantially pure silver. Surface wear can be
determined for a metal deposit according to conventional
tribological and profilometry measurements well known in the
art.
[0056] The following examples are included to further illustrate
the invention but are not intended to limit its scope.
Binary Silver-Bismuth Alloy Electroplating Examples 1-22
Electroplating Process
[0057] Unless otherwise noted, in all cases, the electroplating
substrate was a 5cm x 5cm brass (70% copper, 30% zinc) coupon.
Prior to electroplating, the coupons were electrocleaned in
RONACLEANTM GP-300 LF Electrolytic Cleaner an alkaline degreaser
(available from DuPont) at 80.degree. C. for 30 seconds with DC at
a current density of 5 ASD. After electrocleaning, the coupons were
rinsed with DI water, activated in 10% sulfuric acid for 30
seconds, rinsed with DI water again, then placed in the
electroplating bath. Electroplating was performed with DC at a
current density of 1 ASD (actual current applied is 0.56 A) for 6
minutes. Electroplating was performed in a square, glass beaker
using a platinized titanium anode. Agitation was provided by a 5 cm
long, TEFLON.TM.-coated stir-bar at a rotation rate of 400 rpm.
Electroplating was performed at a temperature of 55.degree. C. The
binary silver-bismuth alloy deposits were about 6 .mu.m thick. All
the binary silver-bismuth electroplating baths were aqueous based.
Water was added to each bath to bring it to a desired volume. The
pH of the electroplating baths was adjusted with potassium
hydroxide or methanesulfonic acid.
[0058] The thickness and elemental composition of the electroplated
binary silver-bismuth alloy was measured using a Bowman Series P
X-Ray Fluorimeter (XRF) available from Bowman, Schaumburg, Ill. The
XRF was calibrated using pure element thickness standards for
silver and bismuth, available from Hitachi (Chiyoda, Tokyo, Japan),
Fischer GmbH (Sindelfingen, Germany) and Veeco (Plainview, New
York, USA), and calculated alloy composition and thickness by
combining the pure element standards with Fundamental Parameter
(FP) calculations using the software package accompanying the
Bowman Series P X-Ray Fluorimeter.
Contact Resistance Measurements
[0059] Contact resistance was evaluated using a custom designed
apparatus containing a Starrett MTH-550 manual force tester stand
equipped with a Starrett DFC-20 digital force gauge (Athol, Mass.,
USA). The digital force gauge was equipped with a gold-plated
copper probe with a hemispherical tip 2.5 mm in diameter. The
electrical resistance of the contact between the gold-plated probe
and the flat coupon plated with the silver alloy of interest was
measured using a 4-wire resistance measurement as the contact force
was varied. The current source was a Keithley 6220 DC Current
Source operating at 10 mA and the voltmeter was a Keithley 2182A
Nanovoltmeter (Cleveland, Ohio, USA). These instruments were
operated in thermoelectric compensation mode for maximum
accuracy.
Wear Resistance Measurements
[0060] Tribological measurements were performed using an Anton Paar
TRB3 Pin-on-Disk tribometer equipped with a linear reciprocating
stage (available from Anton Paar GmbH, Graz, Austria). All tests
were performed using 1 N loading, a stroke length of 10 mm, and a
sliding speed of 5 mm/s. All tests were performed "like-on-like",
meaning that the flat coupon and the spherical ball were each
plated with the same silver (SILVER GLOTM 3K Bright Silver plating
bath, a cyanide-based product available from DuPont) or
silver-bismuth alloy metal deposit. The ball used was made of C260
brass (70% copper, 30% zinc) and was 5.55 mm in diameter and was
electroplated with about 5.mu.m of silver. The flat coupon was also
made of C260 brass and electroplated with about 2.mu.m of silver or
silver-bismuth alloy. During the test, coefficient of friction was
monitored using the tribometer. Wear track depth was measured using
laser profilometry. The measurements were done for either 100 or
500 cycles, as specified in each case.
[0061] A cycle was one round trip of the tribometer. The sample was
moved in one direction, then the direction was reversed and the
tribometer was moved back to its original location, all the while
under the 1 N load and in contact with the spherical ball. This was
one cycle.
[0062] The profilometry measurements were performed using a Keyence
VK-X Laser Scanning Confocal Microscope (available from Keyence
Corporation of America, Elmwood Park, N.J.). The wear tracks were
measured using laser profilometry at a magnification of 200X. The
3D and 2D profilometry graphics were created from these
measurements using VK-X Multianalyzer software from Keyence.
EXAMPLE 1 (invention)
[0063] An aqueous acid binary silver-bismuth electroplating bath of
the following composition was prepared:
[0064] silver methanesulfonate to supply 20 g/L silver ions
[0065] 3,6-dithia-1,8-octanediol: 102 g/L
[0066] bismuth methanesulfonate to supply 0.8 g/L of bismuth
ions
[0067] cysteine: 1.4 g/L
[0068] 3-mercapto-1,2,4-triazole: 1.5 g/L
[0069] pH adjusted to 1.6
[0070] After plating, the electrodeposited coating appeared
semi-bright, with a composition of 98.9% silver and 1.1%
bismuth.
EXAMPLE 2 (invention)
[0071] An aqueous acid binary silver-bismuth alloy electroplating
bath of the following composition was prepared:
[0072] silver methanesulfonate to supply 20 g/L silver ions
[0073] 3,6-dithia-1,8-octanediol: 102 g/L
[0074] bismuth methanesulfonate to supply 5 g/L of bismuth ions
[0075] cysteine: 9 g/L
[0076] 2-mercapto-1,2,4-triazole: 400 ppm
[0077] pH adjusted to 2
[0078] After plating, the electrodeposited coating appeared
metallic and semi-bright, with a composition of 95% silver and 5%
bismuth. FIG. 1 is a scanning electron microscope image at
10,000.times. magnification of the binary silver-bismuth alloy
showing discrete zones of bismuth, indicated by the bright spots,
in a silver matrix.
EXAMPLE 3 (invention)
[0079] An aqueous acid binary silver-bismuth alloy electroplating
bath of the following composition was prepared:
[0080] silver methanesulfonate to supply 20 g/L silver ions
[0081] 3,6-dithia-1,8-octanediol: 102 g/L
[0082] bismuth methanesulfonate to supply 5 g/L of bismuth ions
[0083] 3-mercapto-l-propanesulfonate, sodium salt: 13.2 g/L
[0084] 3-mercapto-1,2,4-triazole: 400 ppm
[0085] pH adjusted to 2
[0086] After plating, the electrodeposited coating appeared
metallic and semi-bright, with a composition of 96% silver and 4%
bismuth.
EXAMPLE 4 (invention)
[0087] An aqueous acid binary silver-bismuth alloy electroplating
bath of the following composition was prepared:
[0088] silver methanesulfonate to supply 20 g/L silver ions
[0089] 3,6-dithia-1,8-octanediol: 102 g/L
[0090] bismuth methanesulfonate to supply 5 g/L of bismuth ions
[0091] 3-mercapto-l-ethanesulfonate, sodium salt: 12.2 g/L
[0092] 3-mercapto-1,2,4-triazole: 400 ppm
[0093] pH adjusted to 2
[0094] After the plating procedure, the electrodeposited coating
appeared metallic and semi-bright, with a composition of 96% silver
and 4% bismuth.
EXAMPLE 5 (invention)
[0095] An aqueous acid binary silver-bismuth alloy electroplating
bath of the following composition was prepared:
[0096] silver methanesulfonate to supply 20 g/L silver ions
[0097] 3,6-dithia-1,8-octanediol: 102 g/L
[0098] Bismuth methanesulfonate to supply 5 g/L of bismuth ions
[0099] mercaptosuccinic acid: 11.1 g/L
[0100] 3-mercapto-1,2,4-triazole: 400 ppm
[0101] pH adjusted to 2
[0102] After plating, the electrodeposited coating appeared
metallic and matte, with a composition of 98% silver and 2%
bismuth.
EXAMPLE 6 (invention)
[0103] An aqueous acid binary silver-bismuth electroplating bath of
the following composition was prepared:
[0104] silver methanesulfonate to supply 20 g/L silver ions
[0105] 3,6-dithia-1,8-octanediol: 102 g/L
[0106] bismuth methanesulfonate to supply 5 g/L of bismuth ions
[0107] cysteine: 9 g/L
[0108] 3-mercapto-4-methyl-4H-1,2,4-triazole: 400 ppm
[0109] pH adjusted to 2
[0110] After plating, the electrodeposited coating appeared
metallic and semi-bright, with a composition of 95% silver and 5%
bismuth.
EXAMPLE 7 (invention)
[0111] An aqueous acid binary silver-bismuth electroplating bath of
the following composition was prepared:
[0112] silver methanesulfonate to supply 20 g/L silver ions
[0113] 3,6-dithia-1,8-octanediol: 34 g/L
[0114] Mercaptosuccinic acid: 35 g/L
[0115] bismuth methanesulfonate to supply 2 g/L of bismuth ions
[0116] 3-mercapto-1,2,4-triazole: 400 ppm
[0117] pH adjusted to 2
[0118] After plating, the electrodeposited coating appeared
metallic and semi-bright, with a composition of 97% silver and 3%
bismuth.
EXAMPLE 8 (invention)
[0119] An aqueous acid binary silver-bismuth electroplating bath of
the following composition was prepared:
[0120] silver methanesulfonate to supply 20 g/L silver ions
[0121] 3,6-dithia-1,8-octanediol: 34 g/L
[0122] Mercaptosuccinic acid: 35 g/L
[0123] bismuth methanesulfonate to supply 2 g/L of bismuth ions
[0124] 3-mercapto-4-methyl-4H-1,2,4-triazole: 400 ppm
[0125] pH adjusted to 2
[0126] After plating, the electrodeposited coating appeared
metallic and semi-bright, with a composition of 97% silver and 3%
bismuth.
EXAMPLE 9 (invention)
[0127] An aqueous acid binary silver-bismuth electroplating bath of
the following composition was prepared:
[0128] silver methanesulfonate to supply 20 g/L silver ions
[0129] 3,6-dithia-1,8-octanediol: 34 g/L
[0130] Mercaptosuccinic acid: 35 g/L
[0131] bismuth methanesulfonate to supply 2 g/L of bismuth ions
[0132] 1H-imidazole-2-thiol: 400 ppm
[0133] pH adjusted to 2
[0134] After plating, the electrodeposited coating appeared
metallic and semi-bright, with a composition of 97% silver and 3%
bismuth.
EXAMPLE 10 (comparative)
[0135] An aqueous acid binary silver-bismuth electroplating bath of
the following composition was prepared:
[0136] silver methanesulfonate to supply 20 g/L silver ions
[0137] bismuth methanesulfonate to supply 10 g/L of bismuth
ions
[0138] methanesulfonic acid: 150 g/L
[0139] PLURONIC.TM. L-44 surfactant (purchased from BASF): 10
g/L
[0140] O-chlorobenzaldehyde: 100 ppm
[0141] 3,6-dithia-1,8-octanediol: 80 g/L
[0142] pH <1
[0143] After the plating procedure, the electrodeposited coating is
metallic and semi-bright, with a composition of 46% silver and 54%
bismuth.
EXAMPLE 11 (comparative)
[0144] An aqueous acid binary silver-bismuth electroplating bath of
the following composition was prepared:
[0145] silver methanesulfonate to supply 20 g/L silver ions
[0146] 3,6-dithia-1,8-octanediol: 102 g/L
[0147] bismuth methanesulfonate to supply 5 g/L of bismuth ions
[0148] cysteine: 9 g/L
[0149] 4-amino-1,2,4-triazole: 400 ppm
[0150] pH adjusted to 2
[0151] After plating, the electrodeposited coating appeared
metallic and matte, with a composition of 97% silver and 3%
bismuth.
EXAMPLE 12 (comparative)
[0152] An aqueous acid binary silver-bismuth electroplating bath of
the following composition was prepared:
[0153] silver methanesulfonate to supply 20 g/L silver ions
[0154] 3,6-dithia-1,8-octanediol: 102 g/L
[0155] bismuth methanesulfonate to supply 5 g/L of bismuth ions
[0156] cysteine: 9 g/L
[0157] 1,2,4-triazole: 400 ppm
[0158] pH adjusted to 2
[0159] After plating, the electrodeposited coating appeared
metallic and matte, with a composition of 97% silver and 3%
bismuth
EXAMPLE 13 (comparative)
[0160] An aqueous, alkaline, cyanide-based, silver electroplating
bath of the following composition was prepared:
[0161] potassium silver cyanide to supply 40 g/L silver ions
[0162] potassium cyanide: 120 g/L
[0163] potassium carbonate: 15 g/L
[0164] potassium selenocyanate: 7 mg/L
[0165] After plating, the electrodeposited coating appeared
metallic and bright, with a composition of 100% silver.
EXAMPLE 14 (comparative)
[0166] An aqueous, alkaline, cyanide-based, binary silver-antimony
electroplating bath of the following composition was prepared:
[0167] potassium silver cyanide to supply 40 g/L silver ions
[0168] potassium cyanide: 120 g/L
[0169] potassium carbonate: 15 g/L
[0170] potassium selenocyanate: 6 mg/L
[0171] potassium sodium tartrate: 10 g/L
[0172] tripotassium citrate: 19 g/L
[0173] potassium antimony tartrate: 7.8 g/L
[0174] After plating, the electrodeposited coating appeared
metallic and bright, with a composition of 98% silver and 2%
antimony.
EXAMPLE 15
Contact Resistance Measurements
[0175] Tests were performed using flat, nickel coupons
electroplated with about 3 .mu.m of silver from comparative Example
13, silver-antimony alloy (98% silver, 2% antimony) from
comparative example 14, and with binary silver-bismuth alloys from
the aqueous acid binary silver-bismuth alloy electroplating baths
disclosed in Examples 2, 8, and 9 (invention) above. Prior to
measurement, the coupons were heated in an oven at 150.degree. C.
for 100 hours. The contact resistance for the coupons is in Table 1
below.
TABLE-US-00001 TABLE 1 Example 2 Example 8 Example 9 Example 13
Example 14 Force (invention) (invention) (invention) (comparative)
(comparative) (cN) (m.OMEGA.) (m.OMEGA.) (m.OMEGA.) (m.OMEGA.)
(m.OMEGA.) 1 18.4 10.4 16.1 8.1 >1000 5 7.6 7.4 8.9 4.5 560 10
4.4 3.6 4.6 2.2 164 20 2.4 2.1 2.7 1.7 118 30 1.6 1.4 2.0 1.4 89 40
1.2 1.2 1.6 1.3 58 50 1.1 1.0 1.2 1.1 28 60 0.9 0.8 1.0 0.8 24 70
0.8 0.7 0.9 0.6 22 80 0.8 0.7 0.8 0.5 21 90 0.7 0.7 0.8 0.5 20 100
0.6 0.6 0.8 0.5 18
EXAMPLE 16 (comparative)
[0176] Wear resistance measurements were performed on silver metal
deposits electroplated using the bath described in Example 13
(comparative). The test was performed for 100 cycles. FIG. 2 is the
2D profilometry graph of the silver deposit which shows major
surface wear of the silver from 600 .mu.m to 800 .mu.m along the
x-axis and from +2 .mu.m to +5 um along the y-axis. FIG. 3 is the
3D profilometry graph of the silver deposit which further
exemplifies the significant surface wear of the silver deposit
after 100 cycles. Examination of the ball indicated accumulation of
material and significant prow formation was observed at the ends of
the wear track indicating cold welding during the wear process. The
coefficient of friction was determined to be approximately 1.6
throughout the experiment. The coefficient of friction was measured
by a sensor on the tribometer which measured the frictional force
and then divides the frictional force by the reported downward
force to give the coefficient of friction.
EXAMPLE 17 (comparative)
[0177] Wear resistance measurements were performed on
silver-bismuth alloy deposits electroplated using the bath
described in Example 10 (comparative). The test was performed for
500 cycles. The coefficient of friction was determined to be
approximately 0.3 throughout the experiment. However, the wear
track observed was substantially the same as that observed for
Example 16 above showing significant wear.
EXAMPLE 18 (comparative)
[0178] Wear resistance measurements were performed on
silver-bismuth alloy deposits electroplated using the bath
described in Example 11 (comparative). The test was performed for
500 cycles. The coefficient of friction was determined to be
approximately 0.7 throughout the experiment. However, the wear
track observed was substantially the same as that observed for
Example 16 above for silver metal showing significant wear.
EXAMPLE 19 (comparative)
[0179] Wear resistance measurements were performed on
silver-bismuth alloy deposits electroplated using the bath
described in Example 12 (comparative). The test was performed for
500 cycles. The coefficient of friction was determined to be
approximately 0.7 throughout the experiment. However, the wear
track observed was substantially the same as that observed for
Example 16 above showing serious wear.
EXAMPLE 20 (invention)
[0180] Wear resistance measurements were performed on
silver-bismuth alloy deposits electroplated using the bath
described in Example 2 (invention). The test was performed for 500
cycles. FIG. 4 is the 2D profilometry graph of the silver-bismuth
alloy deposit which shows no observable wear of the silver-bismuth
alloy along the width of the sample. FIG. 5 is the 3D profilometry
graph of the silver-bismuth alloy deposit which further shows no
observable surface wear of the silver-bismuth alloy deposit after
500 cycles. Examination of the spherical ball showed no
accumulation of material and no observable prow formation at the
ends of the wear track indicating no cold welding took place during
the wear process. The coefficient of friction was determined to be
approximately 0.6 throughout the experiment. These results
represented a significant improvement over the comparative
examples.
EXAMPLE 21 (invention)
[0181] Wear resistance measurements were performed on
silver-bismuth alloy deposits electroplated using the bath
described in Example 8 (invention). The test was performed for 500
cycles. FIG. 6 is the 2D profilometry graph of the silver deposit
which shows minor wear of the silver-bismuth alloy along the width
of the sample, though significantly less than the comparative
examples. FIG. 7 is the 3D profilometry graph of the silver-bismuth
alloy deposit which further shows minor wear of the silver-bismuth
deposit after 500 cycles. Examination of the spherical ball
indicated no accumulation of material and no prow formation was
observed at the ends of the wear track indicating no cold welding
took place during the wear process. The coefficient of friction was
determined to be approximately 0.9 throughout the experiment. These
results represented a significant improvement over the comparative
examples.
EXAMPLE 22 (invention)
[0182] Wear resistance measurements were performed on
silver-bismuth alloy deposits electroplated using the bath
described in Example 10 (invention). The test was performed for 500
cycles. FIG. 8 is the 2D profilometry graph of the silver deposit
which shows minimal wear of the silver-bismuth alloy along the
width of the sample. FIG. 9 is the 3D profilometry graph of the
silver-bismuth alloy deposit which further shows the minimal
surface wear of the silver-bismuth deposit after 500 cycles.
Examination of the spherical ball indicated no accumulation of
material and no prow formation was observed at the ends of the wear
track indicating no cold welding took place during the wear
process. The coefficient of friction was determined to be
approximately 0.5 throughout the experiment. These results
represented a significant improvement over the comparative
examples.
* * * * *