TWI750891B - Acidic aqueous binary silver-bismuth alloy electroplating compositions and methods - Google Patents

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.

Description

Acid aqueous binary silver-bismuth alloy electroplating composition and method

The present invention relates to an acidic aqueous binary silver-bismuth alloy electroplating composition and method. More specifically, the present invention relates to an acidic aqueous binary silver-bismuth alloy electroplating composition and method, wherein the acidic aqueous binary silver-bismuth alloy electroplating composition includes a 5-membered aromatic heterocyclic nitrogen compound with mercapto functionality, the The compounds enable the electrodeposition of silver-rich binary silver-bismuth alloys with low electrical contact resistance and good wear resistance.

In applications related to electronic component and jewelry manufacturing, silver and silver alloy plating baths are highly desirable for depositing silver and silver alloy systems on substrates. Due to its excellent electrical properties, especially low electrical contact resistance, substantially pure silver is used as a contact finish. However, its use as a contact terminal such as an electrical connector is limited (due to the electrical connector's poor resistance to mechanical wear and high silver-silver friction coefficient). Poor resistance to mechanical wear results in the connector being 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 the connector has a high coefficient of friction, the force required to plug the connector is very high and this can damage the connector or limit connector design choices. Silver alloy deposits such as silver-antimony and silver-tin result in improved wear characteristics but have unacceptably poor contact resistance, especially after exposure to elevated temperatures for extended periods of time.

Because many silver salts are essentially water-insoluble and water-soluble silver salts often form insoluble salts with various compounds commonly present in plating baths, the plating industry faces many challenges in formulating silver or silver alloy plating baths. The bath is stable long enough for practical plating applications and solves at least the aforementioned problems. Many silver and silver alloy plating baths contain cyanide compounds to enable practical use. However, cyanide compounds are highly toxic. Therefore, special wastewater treatment is required. This leads to increased processing costs. Furthermore, because these baths can only be used in the alkaline range, the type of alloying metal is limited since most metals are insoluble in alkaline environments. In addition, exposing the substrate to an alkaline bath can cause passivation of the substrate surface, making the surface difficult to plate.

Therefore, there is a need for a stable, acidic silver alloy plating bath that produces deposits with low electrical contact resistance and low coefficient of friction to provide improved wear resistance.

(I) 其中Q₁ -Q₄ 可以是取代或未取代的氮或取代或未取代的碳，其前提係Q₁ -Q₄ 中的至少兩個係氮，其中取代基包括，但不限於，氫、(C₁ -C₄ )烷基、胺基、胺基烷基、羧基、羧基(C₁ -C₄ )烷基或烷基磺酸酯，並且pH小於7。The present invention relates to a binary silver-bismuth alloy electroplating composition comprising a silver ion source, a bismuth ion source, and a 5-membered aromatic heterocyclic nitrogen compound having the following general formula:

(I) wherein Q ₁ -Q ₄ can be substituted or unsubstituted nitrogen or substituted or unsubstituted carbon, provided that _{at least two of Q 1} -Q ₄ are nitrogen, wherein the substituents include, but are not limited to, Hydrogen, (C ₁ -C ₄ )alkyl, amino, aminoalkyl, carboxyl, carboxyl (C ₁ -C ₄ )alkyl or alkyl sulfonate, and pH less than 7.

(I) 其中Q₁ -Q₄ 可以是取代或未取代的氮或取代或未取代的碳，其前提係Q₁ -Q₄ 中的至少兩個係氮，其中取代基包括，但不限於，氫、(C₁ -C₄ )烷基、胺基、胺基烷基、羧基、羧基(C₁ -C₄ )烷基或烷基磺酸酯，並且pH小於7；以及 c)  向該二元銀-鉍合金電鍍組成物和該基材施加電流以在該基材上電鍍銀-鉍合金沈積物。The present invention also relates to a method for electroplating a binary silver-bismuth alloy on a substrate, the method comprising: a) providing the substrate; b) contacting the substrate with a binary silver-bismuth alloy electroplating composition, the two The silver-bismuth alloy electroplating composition comprises a silver ion source, a bismuth ion source, and a 5-membered aromatic heterocyclic nitrogen compound having the following general formula:

(I) wherein Q ₁ -Q ₄ can be substituted or unsubstituted nitrogen or substituted or unsubstituted carbon, provided that _{at least two of Q 1} -Q ₄ are nitrogen, wherein the substituents include, but are not limited to, hydrogen, (C ₁ -C ₄ )alkyl, amino, aminoalkyl, carboxyl, carboxyl (C ₁ -C ₄ )alkyl, or alkyl sulfonate, and the pH is less than 7; and c) to the two The silver-bismuth alloy electroplating composition and the substrate apply a current to electroplate a silver-bismuth alloy deposit on the substrate.

The present invention further relates to an article comprising a binary silver-bismuth alloy layer adjacent to a surface of a substrate, wherein the binary silver-bismuth alloy layer comprises 90% to 99% silver and 1% to 10% bismuth and has 1 or less friction coefficient.

Inclusion of a 5-membered aromatic heterocyclic nitrogen compound of formula (I) above in an aqueous binary silver-bismuth alloy electroplating composition in an acidic environment enables deposition of a silver-rich binary silver-bismuth alloy on a substrate such that The silver-rich binary silver-bismuth alloy has essentially the good electrical properties of silver deposits, especially low electrical contact resistance. In addition, the silver-rich binary silver-bismuth alloy deposits have good resistance to mechanical wear. The silver-rich binary silver-bismuth deposits are uniform in appearance and matt to semi-gloss. The binary silver-bismuth alloy electroplating composition of the present invention is stable.

As used throughout the specification, unless the context clearly dictates otherwise, abbreviations have the following meanings: °C = Celsius; ppm = parts per million; 1 ppm = 1 mg/L; g = grams; mg = milligrams; L = liter; mL = milliliter; mm = millimeter; cm = centimeter; μm = micrometer; DI = deionized; A = ampere; ASD = ampere/dm ² = plating rate; DC = direct current; SI units; mΩ = milliohms = contact resistance; cN = hundredths of a newton = units 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 ⁺ molecular weight = 107.868 g/mol; and 3,6-dithia-1,8-octanediol molecular weight = 182.3 g/mol Ear.

The term "alkyl" is meant having the formula C _n H _{2n + 1} organic functional group, wherein the C-based carbon, H-based system hydrogen and n an integer. The term "aliphatic" is meant to refer to or denote organic compounds in which the carbon atoms form open chains (as in alkanes) rather than aromatic rings. The term "binary" when referring to an alloy means a metallic solid consisting of a homogeneous mixture of two metals. The "----" dotted line in the chemical structure means the optional covalent bond. The term "adjacent" means direct contact such that the two metal layers have a common interface. The term "contact resistance" means resistance as a function of applied force. The term "Newton" refers to the SI unit of force, and it is equal to the force that gives 1 kilogram of mass an acceleration of 1 meter/second/second, and is equal to 100,000 dynes. The term "coefficient of friction" is a value showing the relationship between the frictional force between two bodies and the normal reaction force between the bodies involved; and is _{shown by F f} = µF _n , where F _f is friction Force, µ is the coefficient of friction, and F _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 "section" means a region or portion that is distinct from other regions. The term "matrix" means the surrounding metal or most of the metal, ie greater than 50% of the metal alloy. The term "precondition" means a condition or limitation. The term "tribology" means the science and engineering of surfaces interacting 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 the joining occurs without melting or heating at the interface of the two parts to be welded, and where there is no molten liquid or molten phase at the joint. The term "aqueous" means water or water-based. Throughout the specification, 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. The term "matte" means dull or lacklustre. Throughout this specification, the term "a/an" may refer to both the singular and the plural. All percent (%) values and ranges indicate weight percent unless otherwise indicated. All numerical ranges are inclusive and combinable in any order, except where it is logical that such numerical ranges should be constrained to add up to 100%.

(I)The present invention relates to a hydrous acidic binary silver-bismuth alloy electroplating composition, wherein the hydrous acidic binary silver-bismuth alloy electroplating composition comprises a silver ion source, a bismuth ion source, and a 5-membered aromatic heterocycle having the following general formula Nitrogen compounds:

(I)

Wherein Q ₁ -Q ₄ can be substituted or unsubstituted nitrogen or substituted or unsubstituted carbon, the premise of _{which is that at least three of Q 1} -Q ₄ are nitrogen, wherein substituents include, but are not limited to, hydrogen, ( C ₁ -C ₄ )alkyl, amino, aminoalkyl, carboxy, carboxy(C ₁ -C ₄ )alkyl or alkyl sulfonate and pH less than 7. Preferably, the substituents are hydrogen, (C ₁ -C ₂ )alkyl, primary amine groups such as NH ₂ , secondary amine groups such as NH-NH ₂ , or amino (C ₁ -C ₄ )alkyl groups, Further preferably, the substituent is hydrogen, methyl or NH ₂ , more preferably, the nitrogen of the ring is substituted by hydrogen or methyl or the nitrogen of the ring is _{substituted by NH 2} , or the carbon of the ring is substituted _{by NH 2 ,} Most preferably, ring nitrogens are substituted with hydrogen or methyl.

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 low coefficient of friction of the silver-rich binary silver-bismuth alloy deposit allows the silver-rich binary silver-bismuth alloy layer to have good mechanical wear resistance. The acidic aqueous binary silver-bismuth alloy electroplating composition of the present invention is stable. The aqueous binary silver-bismuth alloy electroplating composition does not contain 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 alloy electroplating composition is free of cyanide.

(II) 3-巰基-1,2,4-三唑；

(III) 3-胺基-1,2,4-三唑-5-硫醇；

(IV) 4-胺基-3-肼基-5-巰基-1,2,4-三唑；

(V) 3-巰基-4-甲基-4H-1,2,4-三唑；

(VI) 1H -咪唑-2-硫醇；以及Examples of preferred 5-membered aromatic heterocyclic nitrogen compounds of the present invention are as follows:

(II) 3-mercapto-1,2,4-triazole;

(III) 3-amino-1,2,4-triazole-5-thiol;

(IV) 4-amino-3-hydrazino-5-mercapto-1,2,4-triazole;

(V) 3-mercapto-4-methyl-4H-1,2,4-triazole;

(VI) 1 H -imidazole-2-thiol; and

Salts of 5-membered aromatic heterocyclic nitrogen compounds with mercapto functionality. More preferably, the 5-membered aromatic heterocyclic nitrogen compound with mercapto functionality of the present invention is selected from one or more of the following: 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 , and salts of 5-membered aromatic heterocyclic nitrogen compounds with mercapto functionality; even more preferably, the 5-membered aromatic heterocyclic nitrogen compounds with mercapto functionality of the present invention are selected from one or more of the following: 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 and the salt of the 5-membered aromatic heterocyclic nitrogen compound with mercapto functionality of the present invention; further preferably, the present invention has The 5-membered aromatic heterocyclic nitrogen compound with mercapto functionality is selected from one or more of the following: 3-mercapto-1,2,4-triazole, 3-mercapto-4-methyl-4H-1,2,4 -Triazoles, and salts of 5-membered aromatic heterocyclic nitrogen compounds having mercapto functionality of the present invention. The salts of 5-membered aromatic heterocyclic nitrogen compounds with mercapto functionality of the present invention include, but are not limited to, alkali metal salts, such as sodium, potassium and lithium salts, ammonium salts, tetraalkylammonium salts, magnesium salts, Silver and bismuth salts.

The 5-membered aromatic heterocyclic nitrogen compounds with mercapto functionality of the present invention and salts thereof are included in an amount sufficient to enable electroplating of the silver-rich binary silver-bismuth alloy in an aqueous acidic environment. Preferably, in an amount of 50 ppm or more, more preferably in an amount of 100 ppm to 100 g/L, further preferably in an amount of 100 ppm to 20 g/L, even more preferably It is an amount of 100 ppm to 10 g/L, preferably an amount of 100 ppm to 5 g/L, which contains the 5-membered aromatic heterocyclic nitrogen compound having mercapto functionality of the present invention.

The aqueous acidic silver-bismuth alloy electroplating composition of the present invention includes a source of silver ions. The source of silver ions may be provided by a silver salt such as, but not limited to, silver halide, silver gluconate, silver citrate, silver lactate, silver nitrate, silver sulfate, silver alkanesulfonate, silver alkanolsulfonate, or mixtures thereof. When silver halide is used, a halide-based chloride is preferred. Preferably, the silver salt is silver sulfate, silver alkanesulfonate, silver nitrate, or a mixture thereof, more preferably, the silver salt is silver sulfate, silver methanesulfonate, or a mixture thereof. Mixtures of silver salts may also be included in the composition. Silver salts are generally commercially available or can be prepared by methods described in the literature. Preferably, the silver salt is readily soluble in water.

The silver salt is included in the aqueous acidic binary silver-bismuth alloy electroplating composition in an amount sufficient to provide the desired matt to semi-bright and uniform silver-rich binary silver-bismuth alloy deposit, preferably Yes, wherein the silver content of the silver-rich binary silver-bismuth alloy deposit contains 90% to 99.8% silver, more preferably 90% to 99.7% silver, most preferably 95% to 99.7% silver Silver, the remainder of the alloying metal is bismuth, excluding inevitable impurities. Preferably, the silver salt is included in the composition to provide a concentration of silver ions of at least 10 g/L, and more preferably, the silver salt is included in the composition to provide a concentration of silver ions in an amount ranging from 10 g/L to 100 g/L. The amount is included in the composition, further preferably, the silver salt is included in the composition in an amount to provide a silver ion concentration of 20 g/L to 80 g/L, most preferably, the silver salt is included in the composition to provide An amount of silver ion concentration of 20 g/L to 60 g/L is included in the composition.

The aqueous acidic silver-bismuth alloy electroplating composition includes a source of bismuth ions that provides an electroplating bath ^{with Bi 3+ ions in solution.} Sources of bismuth ions include, but are not limited to, bismuth salts of alkanesulfonic acids such as bismuth methanesulfonate, bismuth ethanesulfonate, bismuth propanesulfonate, bismuth 2-propanesulfonate, and bismuth p-phenolsulfonate, bismuth alkanolsulfonates Salts such as bismuth hydroxymethanesulfonate, bismuth 2-hydroxyethane-1-sulfonate and bismuth 2-hydroxybutane-1-sulfonate, and bismuth salts such as bismuth nitrate, bismuth sulfate and bismuth chloride. Mixtures of bismuth salts may also be included in the composition. Preferably, the bismuth salt is water-soluble.

The bismuth salt is included in the aqueous acidic binary silver-bismuth alloy electroplating composition in an amount sufficient to provide the desired matt to semi-bright and uniform silver-rich binary silver-bismuth alloy deposit, preferably Yes, wherein the bismuth content of the silver-rich binary silver-bismuth alloy deposit contains 0.2% to 10% bismuth, further preferably 0.3% to 10% bismuth, and most preferably 0.3% to 5% bismuth bismuth. Preferably, the bismuth salt is included in the silver-bismuth composition to provide 50 ppm to 10 g/L, further preferably 100 ppm to 5 g/L, most preferably 200 ppm to 5 g/L L amount of bismuth(III) ions. Such bismuth salts are commercially available or can be prepared according to disclosures in the chemical literature. They are generally commercially available from various sources such as Aldrich Chemical Company, Milwaukee, Wisconsin.

Preferably, in the aqueous acidic silver-bismuth alloy electroplating composition of the present invention, at least one of aqueous deionized water and distilled water is included as a solvent to limit incidental impurities.

Optionally, an acid may be included in the binary silver-bismuth alloy electroplating composition to provide conductivity to the composition. 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), arylsulfonic acids (such as benzenesulfonic acid or toluenesulfonic acid) ); and inorganic acids such as sulfuric acid, sulfamic acid, hydrochloric acid, hydrobromic acid or fluoroboric acid. Water-soluble salts of the aforementioned acids may also be included in the binary silver-bismuth alloy electroplating composition of the present invention. Preferably, the acid is acetic acid, citric acid, alkanesulfonic acid, arylsulfonic acid, or a salt thereof, more preferably, the acid is acetic acid, citric acid, methanesulfonic acid, or a salt thereof. Such salts include, but are not limited to, sodium, potassium, silver, bismuth, magnesium, tetraalkylammonium, and ammonium salts. Although mixtures of acids can be used, it is preferred to use individual acids when used. Acids are generally commercially available or can be prepared by methods known in the literature. Such acids can be included in amounts that provide the desired conductivity. Preferably, the acid or its salt is at least 5 g/L, more preferably 10 g/L to 250 g/L, even more preferably 30 g/L to 150 g/L, most preferably The amount of 30 g/l to 125 g/L is included.

The pH of the aqueous acidic binary silver-bismuth alloy electroplating composition is less than 7. Preferably pH is 0 to 6, more preferably pH is 0 to 5, further preferably pH is 0 to 3, even more preferably pH is 0 to 2.5, most preferably pH 0 to 2.

Optionally, a pH adjuster may be included in the aqueous acidic binary silver-bismuth alloy electroplating composition 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, mineral 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, aminoacetic 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 can be used, as well as organic bases such as various types of amines. Preferably, the pH adjusting agent is selected from acetic acid, citric acid, aminoacetic acid or a salt thereof, most preferably, acetic acid, citric acid or a salt thereof. The pH adjuster can be added in the amount required to maintain the desired pH range.

Optionally, but preferably, sulfide is included in the aqueous acidic binary silver-bismuth alloy electroplating composition of the present invention. Such thioethers include, but are not limited to, 2,2'-thiodiethanol , 4,4'-thiobiphenol, and 4,4'-thiobis(2-methyl-6-tertiarybutyl) phenol), dihydroxydisulfide compounds or mixtures thereof. Such dihydroxy disulfide compounds include, but are not limited to, 2,4-dithia-1,5-pentanediol, 2,5-dithia-1,6-hexanediol, 2,6-dithia-1,6-hexanediol, Thia-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-di Thia-1,16-hexadecanediol, 2,21-dithia-1,22-docosanediol, 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-octadecanedi Alcohol, 4,19-dithia-1,22-docosanediol, 5,7-dithia-1,11-undecanediol, 5,9-dithia-1,13 -tridecanediol, 5,13-dithia-1,17-heptadecanediol, 5,17-dithia-1,21-hecosanediol, and 1,8-dimethyldiol base-3,6-dithia-1,8-octanediol. Preferably, the dihydroxy disulfide compound is selected from 3,6-dithia-1,8-octanediol, 3,8-dithia-1,10-decanediol, 2,4-dithia Thia-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 Preferred is 3,6-dithia-1,8-octanediol.

Preferably, a sulfide compound may be included in the aqueous acidic binary silver-bismuth alloy electroplating composition, and its molar ratio to silver is at least 1 molar sulfide to 1 molar silver, more preferably, 1 to 5 moles of sulfide to 1 mole of silver, even more preferably 2 to 4 moles of sulfide to 1 mole of silver, and most preferably 2.5 to 4 moles of sulfide to 1 mole of silver Ear silver.

Optionally, but preferably, the aqueous acidic binary silver-bismuth alloy electroplating composition of the present invention may contain aliphatic mercapto-terminated compounds. Such aliphatic sulfhydryl terminal compounds include, but are not limited to, mercaptoacetic acid, 2-mercaptopropionic acid, 3-mercaptopropionic acid, cysteine, mercaptosuccinic acid, 3-mercapto-1-propanesulfonic acid, 2-mercaptopropionic acid Ethanesulfonic acid, and its salts. Salts of the aliphatic thiol-terminated compounds of the present invention include, but are not limited to, alkali metal salts such as sodium and potassium salts, or ammonium salts.

Preferably, the aliphatic thiol-terminated aliphatic compound of the present invention is contained in an amount of 1 g/L or more, and more preferably, the aliphatic thiol-terminated compound is contained in an amount of 1 g/L to 100 g/L. , Most preferably, an amount of 1 g/L to 60 g/L is included.

Optionally, one or more surfactants may be included in the aqueous acidic silver-bismuth alloy electroplating composition of the present invention. Such surfactants include, but are not limited to, ionic surfactants, such as cationic and anionic surfactants, nonionic surfactants, and amphoteric surfactants. Surfactants can be included in conventional amounts such as 0.05 g/L to 30 g/L.

Examples of anionic surfactants are sodium bis(1,3-dimethylbutyl)sulfosuccinate, sodium 2-ethylhexyl sulfate, sodium dipentylsulfosuccinate, sodium lauryl sulfate, lauryl ether Sodium sulfate, sodium dialkylsulfosuccinate, and sodium dodecylbenzenesulfonate. Examples of cationic surfactants are quaternary ammonium salts, such as perfluorinated quaternary amines.

Additional optional additives may be included in the silver-bismuth alloy electroplating compositions of the present invention, such as biocides. Conventional biocides well known in the art can be included in the silver-bismuth alloy electroplating compositions of the present invention. Biocides are included in conventional amounts well known to those skilled in the art. Preferably, the silver-bismuth alloy electroplating composition of the present invention does not include a compound acting as a leveling agent.

(I)Preferably, the acidic aqueous binary silver-bismuth alloy electroplating composition of the present invention is composed of water, silver ions and counter anions, bismuth (III) ions and counter anions, and a 5-membered aromatic heterocyclic nitrogen compound having the following general formula: , Optionally thioether, optional aliphatic thiol-terminated compound or salt thereof, optional acid or salt thereof, optional pH adjuster, optional biocide and optional surfactant consisting of:

(I)

Wherein Q ₁ -Q ₄ can be substituted or unsubstituted nitrogen or substituted or unsubstituted carbon, the premise of _{which is that at least two of Q 1} -Q ₄ are nitrogen, wherein substituents include, but are not limited to, hydrogen, ( C ₁ -C ₄ )alkyl, amino, aminoalkyl, carboxy, carboxy(C ₁ -C ₄ )alkyl or alkyl sulfonate, wherein the pH is less than 7.

(I)Further preferably, the acidic aqueous binary silver-bismuth alloy electroplating composition of the present invention is composed of water, silver ions and counter anions, bismuth (III) ions and counter anions, and a 5-membered aromatic heterocyclic nitrogen having the following general formula: Compounds, thioethers, optionally aliphatic thiol-terminated compounds or salts thereof, optionally acids or salts thereof, optionally pH adjusters, optionally biocides, and optionally surfactants consisting of:

(I)

Wherein Q ₁ -Q ₄ can be substituted or unsubstituted nitrogen or substituted or unsubstituted carbon, the premise of _{which is that at least two of Q 1} -Q ₄ are nitrogen, wherein substituents include, but are not limited to, hydrogen, ( C ₁ -C ₄ )alkyl, amino, aminoalkyl, carboxy, carboxy(C ₁ -C ₄ )alkyl or alkyl sulfonate, wherein the pH is 0-6.

(I)More preferably, the acidic aqueous binary silver-bismuth alloy electroplating composition of the present invention is composed of water, silver ions and counter anions, bismuth (III) ions and counter anions, and a 5-membered aromatic heterocyclic nitrogen having the following general formula: Compounds, dihydroxydisulfide compounds, aliphatic thiol-terminated compounds or salts thereof, acids or salts thereof, pH adjusters as needed, biocides as needed, and surfactants as needed consist of:

(I)

Wherein Q ₁ -Q ₄ can be substituted or unsubstituted nitrogen or substituted or unsubstituted carbon, the premise of _{which is that at least two of Q 1} -Q ₄ are nitrogen, wherein substituents include, but are not limited to, hydrogen, ( C ₁ -C ₄ )alkyl, amino, aminoalkyl, carboxy, carboxy(C ₁ -C ₄ )alkyl or alkyl sulfonate, wherein the pH is 0-6.

Even more preferably, the acidic aqueous binary silver-bismuth alloy electroplating composition of the present invention consists of water, silver ions and counter anions, bismuth(III) ions and counter anions, compounds 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 mercapto functionality, and mixtures thereof, di Hydroxy disulfide compound, aliphatic thiol-terminated compound selected from the group consisting of: mercaptoacetic acid, 2-mercaptopropionic acid, 3-mercaptopropionic acid, cysteine, mercaptosuccinic acid, 3-mercapto-1- Propanesulfonic acid, 2-mercaptoethanesulfonic acid, and salts thereof, acids or salts thereof, pH adjusters as needed, biocides as needed, and surfactants as needed, wherein the pH is 0-3.

The acidic aqueous binary silver-bismuth alloy electroplating compositions of the present invention can be used to deposit binary silver-bismuth alloy layers on a variety of substrates, both conductive and semiconductor substrates. Preferably, the substrate on which the silver-bismuth alloy layer is deposited is nickel, nickel alloy, copper and copper alloy substrates, and 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.

During plating, the plating composition temperature may be room temperature to 70°C, preferably 30°C to 60°C, more preferably 40°C to 60°C. During electroplating, the binary silver-bismuth alloy electroplating composition is preferably under continuous stirring.

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 electroplating the substrate with the acidic aqueous binary silver-bismuth alloy The composition is contacted, such as by dipping the substrate into the composition or spraying the substrate with the composition. Current is applied with a conventional rectifier, where the substrate acts as the cathode and there is a counter or anode. The anode can be any conventional soluble or insoluble anode used for electroplating binary silver-bismuth alloys. A binary silver-bismuth alloy is deposited adjacent to the surface of the substrate, wherein the surface of the substrate is nickel, nickel alloy, copper or copper alloy.

The acidic aqueous binary silver-bismuth alloy electroplating compositions of the present invention enable the deposition of matte to semi-bright and uniform silver-rich silver-bismuth alloy layers over a wide range of current densities. The silver rich binary silver-bismuth alloy comprises 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 It is 95% to 99.7% silver and 0.3% to 5% bismuth, excluding the inevitable impurities in the alloy.

Current densities for electroplating the matte to semi-bright and uniform silver-rich silver-bismuth alloys of the present invention may be 0.1 ASD or higher. Preferably, the current density is 0.5 ASD to 70 ASD, more preferably 1 ASD to 40 ASD, more preferably 1 ASD to 30 ASD, and even more preferably 1 ASD to 15 ASD.

The thickness of the binary silver-bismuth alloy layer of the present invention can vary depending on the function of the silver-bismuth alloy layer and the type of substrate to which it is plated. Preferably, the binary silver-bismuth alloy layer is 1 µm or larger. Further preferably, the binary silver-bismuth alloy layer has 1 μm to 100 μm, more preferably 1 μm to 50 μm, even more preferably 1 μm to 10 μm, most preferably 1 μm thickness range up to 5 μm.

Although it is contemplated that the acidic aqueous binary silver-bismuth alloy electroplating compositions of the present invention may be used to coat various substrates that may include a silver-bismuth alloy layer, it is preferred that the acidic aqueous binary silver-bismuth alloy of the present invention- Bismuth alloy electroplating compositions are used for electroplating top layers or coatings on electrical connectors where substantial contact forces and wear are expected. Silver rich binary silver-bismuth alloy deposits are highly desirable alternatives to conventional silver coatings found on conventional connectors. Silver-bismuth alloy deposits have low electrical contact resistance. In addition, the silver-bismuth alloy deposit of the present invention has a low COF, preferably 1 or less, more preferably 0.6 or less COF. The COF of the silver-bismuth alloy deposit of the present invention preferably has a COF of 40% or less of the COF of the substantially pure silver deposit, therefore, the binary silver of the present invention has a COF relative to substantially pure silver -Bismuth alloys have a marked improvement in wear resistance. Surface wear of metal deposits can be determined from conventional tribological and profilometry measurements well known in the art.

The following examples are included to further illustrate the present invention, but are not intended to limit its scope. Binary Silver - Bismuth Alloy Electroplating Examples 1-22 : Electroplating Process

In all cases, the electroplated substrate was a 5 cm x 5 cm brass (70% copper, 30% zinc) coupon unless otherwise specified. Prior to electroplating, coupons were electrocleaned in RONACLEAN™ GP-300 LF Electrolytic Cleaner (Alkaline Degreaser) (available from DuPont) with DC at 5 ASD current density at 80°C for continuation 30 seconds. After electrocleaning, the coupons were rinsed with DI water, activated in 10% sulfuric acid for 30 seconds, rinsed again with DI water, and then placed in a plating bath. Plating was performed with DC at a current density of 1 ASD (actual current applied was 0.56 A) for 6 minutes. Electroplating was performed in square glass beakers using platinized titanium anodes. Agitation was provided by a 5 cm long TEFLON™ coated stir bar at 400 rpm. Electroplating is carried out at a temperature of 55°C. The binary silver-bismuth alloy deposit is about 6 µm thick. All binary silver-bismuth alloy electroplating baths are water based. Water was added to each bath to bring it to the desired volume. The pH of the electroplating bath was adjusted with potassium hydroxide or methanesulfonic acid.

The thickness and elemental composition of the plated binary silver-bismuth alloys were measured using a Bowman Series PX radiofluorometer (XRF) available from Bowman, Schaumburg, IL. XRF uses pure element thickness standards of silver and bismuth (from Hitachi (Chiyoda, Tokyo, Japan), Fischer GmbH (Sindelfingen, Germany)) Calibrated with Vecco (available in Plainview, NY, USA) and using the software package included with the Bowman Series PX Fluorometer by combining pure elemental standards with Fundamental Parameter (FP) calculations to calculate alloy composition and thickness. Contact resistance measurement

Contact resistance was evaluated using custom-designed equipment including a Starrett MTH-550 manual dynamometer stand (Athol, MA, USA) equipped with a Starrett DFC-20 digital dynamometer. , USA)). The digital dynamometer is equipped with a gold-plated copper probe with a 2.5 mm diameter hemispherical tip. A 4-wire resistance measurement was used to measure the contact resistance between a gold plated probe and a flat specimen plated with the silver alloy of interest as the contact force varied. The current source was a Keithley 6220 DC current source (operating at 10 mA) and the voltmeter was a Keithley 2182A nanovoltmeter (Cleveland, OH, USA). These instruments operate in thermoelectric compensation mode for maximum accuracy. Abrasion resistance measurement

Tribological measurements were performed using an Anton Paar TRB3 pin-on-disk tribometer (available from Anton Paar GmbH, Graz, Austria) equipped with a linear reciprocating stage. All tests were performed using a 1 N load, 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 specimen and spherical ball were each plated with the same silver (SILVER GLO™ 3K Bright Silver Bath, cyanide available from DuPont base product) or silver-bismuth alloy metal deposits. The balls used were made of C260 brass (70% copper, 30% zinc) and had a diameter of 5.55 mm and were plated with about 5 µm silver. Flat specimens were also made of C260 brass and plated with about 2 µm of silver or silver-bismuth alloy. During the test, the coefficient of friction was monitored using a tribometer. Wear mark depth was measured using laser profilometry. Measurements were made for 100 or 500 cycles as specified in each case.

A cycle is one round trip of the tribometer. Move the sample in one direction, then reverse the direction, and move the tribometer back to its original position, always under a load of 1 N and in contact with the spherical ball. This is a cycle.

Profilometry measurements were performed using a Keyence VK-X laser scanning confocal microscope (available from Keyence Corporation of America, Elmwood Park, NJ). Wear marks were measured at 200X magnification using laser profilometry. 3D and 2D profilometry maps were created from these measurements using the VK-X multi-analyzer software from Keyence. Example 1 (the present invention)

An aqueous acidic binary silver-bismuth alloy electroplating bath was prepared having the following composition: Silver methanesulfonate supplying 20 g/L of silver ions 3,6-Dithia-1,8-octanediol: 102 g/L Bismuth mesylate supplied with bismuth ions at 0.8 g/L Cysteine: 1.4 g/L 3-Mercapto-1,2,4-triazole: 1.5 g/L pH adjusted to 1.6

After plating, the electrodeposited coating appeared semi-bright with a composition of 98.9% silver and 1.1% bismuth. Example 2 (the present invention)

An aqueous acidic binary silver-bismuth alloy electroplating bath was prepared having the following composition: Silver methanesulfonate supplying 20 g/L of silver ions 3,6-Dithia-1,8-octanediol: 102 g/L Bismuth methanesulfonate supplied with bismuth ions at 5 g/L Cysteine: 9 g/L 2-Mercapto-1,2,4-triazole: 400 ppm pH adjusted to 2

After plating, the electrodeposited coating appeared metallic and semi-bright, with a composition of 95% silver and 5% bismuth. Figure 1 is a scanning electron microscope image of a binary silver-bismuth alloy at 10,000X magnification showing discrete regions of bismuth (indicated by bright spots) in the silver matrix. Example 3 (the present invention)

An aqueous acidic binary silver-bismuth alloy electroplating bath was prepared having the following composition: Silver methanesulfonate supplying 20 g/L of silver ions 3,6-Dithia-1,8-octanediol: 102 g/L Bismuth methanesulfonate supplied with bismuth ions at 5 g/L 3-Mercapto-1-propanesulfonic acid sodium salt: 13.2 g/L 3-Mercapto-1,2,4-triazole: 400 ppm pH adjusted to 2

After plating, the electrodeposited coating appeared metallic and semi-bright, with a composition of 96% silver and 4% bismuth. Example 4 (the present invention)

An aqueous acidic binary silver-bismuth alloy electroplating bath was prepared having the following composition: Silver methanesulfonate supplying 20 g/L of silver ions 3,6-Dithia-1,8-octanediol: 102 g/L Bismuth methanesulfonate supplied with bismuth ions at 5 g/L 3-Mercapto-1-ethanesulfonic acid sodium salt: 12.2 g/L 3-Mercapto-1,2,4-triazole: 400 ppm pH adjusted to 2

After the plating procedure, the electrodeposited coating appeared metallic and semi-bright, with a composition of 96% silver and 4% bismuth. Example 5 (the present invention)

An aqueous acidic binary silver-bismuth alloy electroplating bath was prepared having the following composition: Silver methanesulfonate supplying 20 g/L of silver ions 3,6-Dithia-1,8-octanediol: 102 g/L Bismuth methanesulfonate supplied with bismuth ions at 5 g/L Mercaptosuccinic acid: 11.1 g/L 3-Mercapto-1,2,4-triazole: 400 ppm pH adjusted to 2

After plating, the electrodeposited coating appeared metallic and matte, with a composition of 98% silver and 2% bismuth. Example 6 (the present invention)

An aqueous acidic binary silver-bismuth alloy electroplating bath was prepared having the following composition: Silver methanesulfonate supplying 20 g/L of silver ions 3,6-Dithia-1,8-octanediol: 102 g/L Bismuth methanesulfonate supplied with bismuth ions at 5 g/L Cysteine: 9 g/L 3-Mercapto-4-methyl-4H-1,2,4-triazole: 400 ppm pH adjusted to 2

After plating, the electrodeposited coating appeared metallic and semi-bright, with a composition of 95% silver and 5% bismuth. Example 7 (the present invention)

An aqueous acidic binary silver-bismuth alloy electroplating bath was prepared having the following composition: Silver methanesulfonate supplying 20 g/L of silver ions 3,6-Dithia-1,8-octanediol: 34 g/L Mercaptosuccinic acid: 35 g/L Bismuth methanesulfonate supplied with bismuth ions at 2 g/L 3-Mercapto-1,2,4-triazole: 400 ppm pH adjusted to 2

After plating, the electrodeposited coating appeared metallic and semi-bright, with a composition of 97% silver and 3% bismuth. Example 8 (the present invention)

An aqueous acidic binary silver-bismuth alloy electroplating bath was prepared having the following composition: Silver methanesulfonate supplying 20 g/L of silver ions 3,6-Dithia-1,8-octanediol: 34 g/L Mercaptosuccinic acid: 35 g/L Bismuth methanesulfonate supplied with bismuth ions at 2 g/L 3-Mercapto-4-methyl-4H-1,2,4-triazole: 400 ppm pH adjusted to 2

After plating, the electrodeposited coating appeared metallic and semi-bright, with a composition of 97% silver and 3% bismuth. Example 9 (the present invention)

An aqueous acidic binary silver-bismuth alloy electroplating bath was prepared having the following composition: Silver methanesulfonate supplying 20 g/L of silver ions 3,6-Dithia-1,8-octanediol: 34 g/L Mercaptosuccinic acid: 35 g/L Bismuth methanesulfonate supplied with bismuth ions at 2 g/L 1H-imidazole-2-thiol: 400 ppm pH adjusted to 2

After plating, the electrodeposited coating appeared metallic and semi-bright, with a composition of 97% silver and 3% bismuth. Example 10 (comparison)

An aqueous acidic binary silver-bismuth alloy electroplating bath was prepared having the following composition: Silver methanesulfonate supplying 20 g/L of silver ions Bismuth methanesulfonate supplied with bismuth ions at 10 g/L Methanesulfonic acid: 150 g/L PLURONIC™ L-44 Surfactant (purchased from BASF): 10 g/L o-Chlorobenzaldehyde: 100 ppm 3,6-Dithia-1,8-octanediol: 80 g/L pH < 1

After the plating procedure, the electrodeposited coating was metallic and semi-bright with a composition of 46% silver and 54% bismuth. Example 11 (comparison)

An aqueous acidic binary silver-bismuth alloy electroplating bath was prepared having the following composition: Silver methanesulfonate supplying 20 g/L of silver ions 3,6-Dithia-1,8-octanediol: 102 g/L Bismuth methanesulfonate supplied with bismuth ions at 5 g/L Cysteine: 9 g/L 4-Amino-1,2,4-triazole: 400 ppm pH adjusted to 2

After plating, the electrodeposited coating appeared metallic and matte, with a composition of 97% silver and 3% bismuth. Example 12 (comparison)

An aqueous acidic binary silver-bismuth alloy electroplating bath was prepared having the following composition: Silver methanesulfonate supplying 20 g/L of silver ions 3,6-Dithia-1,8-octanediol: 102 g/L Bismuth methanesulfonate supplied with bismuth ions at 5 g/L Cysteine: 9 g/L 1,2,4-Triazole: 400 ppm pH adjusted to 2

After plating, the electrodeposited coating appeared metallic and matt, with a composition of 97% silver and 3% bismuth Example 13 (comparison)

An aqueous alkaline cyanide-based silver electroplating bath was prepared having the following composition: Potassium silver cyanide to supply 40 g/L of silver ions Potassium cyanide: 120 g/L Potassium carbonate: 15 g/L Potassium selenocyanate: 7 mg/L

After plating, the electrodeposited coating appeared metallic and bright, with a composition of 100% silver. Example 14 (comparison)

An aqueous alkaline cyanide-based binary silver-antimony electroplating bath was prepared having the following composition: Potassium silver cyanide to supply 40 g/L of silver ions Potassium cyanide: 120 g/L Potassium carbonate: 15 g/L Potassium selenocyanate: 6 mg/L Sodium Potassium Tartrate: 10 g/L Tripotassium citrate: 19 g/L Potassium antimony tartrate: 7.8 g/L

After plating, the electrodeposited coating appeared metallic and bright, with a composition of 98% silver and 2% antimony. Example 15 Contact Resistance Measurement

The flat nickel coupons from Comparative Example 13 plated with about 3 µm of silver, the silver-antimony alloy from Comparative Example 14 (98% silver, 2% antimony), and Examples 2, 8 and 9 from above ( The binary silver-bismuth alloy of the aqueous acidic binary silver-bismuth alloy electroplating bath disclosed in the present invention) was tested. The samples were heated in an oven at 150°C for 100 hours before measurement. The contact resistance of this sample is shown in Table 1 below. [Table 1] Force ( cN ) Example 2 (the present invention) ( mΩ ) Example 8 (the present invention) ( mΩ ) Example 9 (the present invention) ( mΩ ) Example 13 (Comparative) ( mΩ ) Example 14 (Comparative) ( mΩ ) 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 twenty four 70 0.8 0.7 0.9 0.6 twenty two 80 0.8 0.7 0.8 0.5 twenty one 90 0.7 0.7 0.8 0.5 20 100 0.6 0.6 0.8 0.5 18 Example 16 (comparison)

Abrasion resistance measurements were performed on silver metal deposits electroplated using the bath described in Example 13 (comparative). The test was performed for 100 cycles. Figure 2 is a series of 2D profilometry maps of silver deposits showing major surface wear of silver from 600 µm to 800 µm along the x-axis and from +2 µm to -5 µm along the y-axis. Figure 3 is a 3D profilometry map of the silver deposit further illustrating the significant surface wear of the silver deposit after 100 cycles. Inspection of the balls indicated material accumulation and significant prow formation was observed at the ends of the wear marks, indicating cold welding during the wear process. The coefficient of friction was determined to be about 1.6 throughout the experiment. The coefficient of friction is measured by a sensor on the tribometer, which measures the frictional force, and then divides the frictional force by the reported downward force to obtain the coefficient of friction. Example 17 (comparison)

Abrasion 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 about 0.3 throughout the experiment. However, the wear marks observed were substantially the same as those observed for Example 16 above, showing significant wear. Example 18 (comparison)

Abrasion 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 about 0.7 throughout the experiment. However, the wear marks observed were essentially the same as those observed for the silver metal in Example 16 above, showing significant wear. Example 19 (comparison)

Abrasion 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 about 0.7 throughout the experiment. However, the wear marks observed were substantially the same as those observed for Example 16 above, showing severe wear. Example 20 (Invention)

Abrasion 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. Figure 4 is a 2D profilometry image of a silver-bismuth alloy deposit showing no observable wear of the silver-bismuth alloy along the width of the sample. Figure 5 is a 3D profilometry image 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 balls did not show material accumulation and did not show the formation of protrudes observable at the ends of the wear marks, indicating that no cold welding occurred during the wear process. The coefficient of friction was determined to be about 0.6 throughout the experiment. These results represent a significant improvement over the comparative example. Example 21 (the present invention)

Abrasion 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. Figure 6 is a 2D profilometry map of a silver deposit showing less wear of the silver-bismuth alloy along the width of the sample, albeit significantly less than the comparative example. Figure 7 is a series of 3D profilometry images of the silver-bismuth alloy deposit further showing less wear of the silver-bismuth deposit after 500 cycles. Inspection of spherical balls showed no accumulation of material, and no protrusion formation was observed at the ends of the wear marks, indicating that no cold welding occurred during the wear process. The coefficient of friction was determined to be about 0.9 throughout the experiment. These results represent a significant improvement over the comparative example. Example 22 (the present invention)

Abrasion 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. Figure 8 is a 2D profilometry map of a silver deposit showing minimal wear of the silver-bismuth alloy along the width of the sample. Figure 9 is a 3D profilometry image of the silver-bismuth alloy deposit further showing minimal surface wear of the silver-bismuth deposit after 500 cycles. Inspection of spherical balls showed no accumulation of material, and no protrusion formation was observed at the ends of the wear marks, indicating that no cold welding occurred during the wear process. The coefficient of friction was determined to be about 0.5 throughout the experiment. These results represent a significant improvement over the comparative example.

none

[ FIG. 1 ] is a scanning electron microscope image of a binary silver-bismuth alloy at 10,000X showing discrete sectors of bismuth in a silver matrix.

[ Figure 2 ] is a 2D profilometry plot of the surface of a silver metal deposit, where the x- and y-axes are calibrated in micrometers (µm).

[ Figure 3 ] is a 3D profilometry map of the surface of a silver metal deposit, with the x-, y-, and z-axes calibrated in micrometers (µm).

[ FIG. 4 ] is a 2D profilometry map of the surface of the silver-bismuth alloy deposit of the present invention, wherein the alloy is composed of 95% silver and 5% bismuth, and the x-axis, y-axis and z-axis are in micrometers (µm ) meter to calibrate.

[ FIG. 5 ] is a 3D profilometry view of the surface of the silver-bismuth alloy deposit of the present invention, wherein the alloy is composed of 95% silver and 5% bismuth, and the x-axis, y-axis and z-axis are in micrometers (µm ) meter to calibrate.

[ FIG. 6 ] is a 2D profilometry map of the surface of the silver-bismuth alloy deposit of the present invention, wherein the alloy is composed of 97% silver and 3% bismuth, and the x-axis, y-axis and z-axis are in micrometers (µm ) meter to calibrate.

[ FIG. 7 ] is a 3D profilometry view of the surface of the silver-bismuth alloy deposit of the present invention, wherein the alloy is composed of 97% silver and 3% bismuth, and the x-axis, y-axis and z-axis are in micrometers (µm ) meter to calibrate.

[ FIG. 8 ] is a 2D profilometry view of the surface of the silver-bismuth alloy deposit of the present invention, wherein the alloy is composed of 97% silver and 3% bismuth, and the x-axis, y-axis and z-axis are in micrometers (µm ) meter to calibrate.

[ FIG. 9 ] is a 3D profilometry view of the surface of the silver-bismuth alloy deposit of the present invention, wherein the alloy is composed of 97% silver and 3% bismuth, and the x-axis, y-axis and z-axis are in micrometers (µm ) meter to calibrate.

none

Claims (11)

A binary silver-bismuth alloy electroplating composition, comprising a silver ion source, a bismuth ion source, and a 5-membered aromatic heterocyclic nitrogen compound having the following general formula:

wherein Q ₁ -Q ₄ can be substituted or unsubstituted nitrogen or substituted or unsubstituted carbon, provided that _{at least two of Q 1} -Q ₄ are nitrogen, wherein the substituents include, but are not limited to, (C ₁ -C ₄ ) alkyl group, amino group, amino alkyl group, carboxyl group, carboxyl group (C ₁ -C ₄ ) alkyl group or alkyl sulfonate, and the pH is less than 7, wherein the binary silver-bismuth alloy electroplating composition Free of tin. The binary silver-bismuth alloy electroplating composition according to claim 1, wherein the 5-membered aromatic heterocyclic nitrogen compound is selected from the group consisting of: 3-mercapto-1,2,4-triazole, 3-mercapto-1,2,4-triazole, -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. The binary silver-bismuth alloy electroplating composition according to claim 1, further comprising a sulfide or a mixture thereof. The binary silver-bismuth alloy electroplating composition according to claim 3, wherein the sulfide is a hydroxybissulfide compound. The binary silver-bismuth alloy electroplating composition according to claim 1, further comprising an aliphatic mercapto terminal compound or a mixture thereof. The binary silver-bismuth alloy electroplating composition according to claim 5, wherein the aliphatic thiol end compound is selected from the group consisting of: mercaptoacetic acid, 2-mercaptopropionic acid, 3-mercaptopropionic acid, cysteine Amino acid, mercaptosuccinic acid, 3-mercapto-1-propanesulfonic acid, 2-mercaptoethanesulfonic acid, salts of the aliphatic sulfhydryl terminal compounds, and mixtures thereof. A method for electroplating a binary silver-bismuth alloy on a substrate, the method comprising: a) providing the substrate; b) contacting the substrate with a binary silver-bismuth alloy electroplating composition, the binary silver-bismuth The alloy electroplating composition includes a source of silver ions, a source of bismuth ions, and a 5-membered aromatic heterocyclic nitrogen compound having the following general formula:

wherein Q ₁ -Q ₄ can be substituted or unsubstituted nitrogen or substituted or unsubstituted carbon, provided that _{at least two of Q 1} -Q ₄ are nitrogen, wherein the substituents include, but are not limited to, (C ₁ -C ₄ ) alkyl group, amino group, amino alkyl group, carboxyl group, carboxyl group (C ₁ -C ₄ ) alkyl group or alkyl sulfonate, and the pH is less than 7, wherein the binary silver-bismuth alloy electroplating composition free of tin; and c) applying a current to the binary silver-bismuth alloy electroplating composition and a substrate to electroplate a binary silver-bismuth deposit on the substrate. 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-thiols, salts of the 5-membered aromatic heterocyclic nitrogen compounds, and mixtures thereof. The method of claim 7, wherein the binary silver-bismuth alloy electroplating composition further comprises sulfide or a mixture thereof. The method of claim 7, wherein the binary silver-bismuth alloy electroplating composition further comprises an aliphatic thiol-terminated compound or a mixture thereof. An article comprising a binary silver-bismuth alloy layer adjoining a surface of a substrate, wherein the binary silver-bismuth alloy layer comprises 90% to 99.8% silver and 0.2% to 10% bismuth by weight, and has 1 or less, wherein the binary silver-bismuth alloy layer is formed by the method according to claim 7.

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