CN114729455A

CN114729455A - Electroless nickel alloy plating baths, methods of depositing nickel alloys, nickel alloy deposits, and uses of such formed nickel alloy deposits

Info

Publication number: CN114729455A
Application number: CN202080080727.9A
Authority: CN
Inventors: 塞巴斯蒂安·兰格
Original assignee: Germany Aituoteke Co ltd
Current assignee: Germany Aituoteke Co ltd
Priority date: 2019-11-20
Filing date: 2020-11-19
Publication date: 2022-07-08
Also published as: JP7244709B2; CA3158576A1; EP4061981A1; US20220389588A1; MX2022006118A; JP2022548419A; WO2021099475A1; KR20220103131A

Abstract

The present invention relates to an electroless nickel alloy plating bath comprising nickel ions; an additional reducible metal ion selected from the group consisting of: molybdenum ions, rhenium ions, tungsten ions, copper ions, oxygen-containing ions thereof, and mixtures thereof; at least one reducing agent adapted to reduce the nickel ions and the additional reducible metal ions to their respective metallic states; complexing agents CA1, CA2, CA3, and CA4, wherein CA1, CA2, CA3, and CA4 are all different from each other, wherein each of CA1 and CA2 is independently selected from the group consisting of: compounds having at least two carboxylic acid moieties, their corresponding salts, and mixtures thereof; wherein CA3 is selected from the group consisting of: aliphatic compounds having exactly one carboxylic acid moiety, their corresponding salts, and mixtures of the foregoing; and wherein CA4 is selected from the group consisting of: aromatic compounds having at least one carboxylic acid moiety, their corresponding salts, and mixtures thereof.

Description

Electroless nickel alloy plating baths, methods of depositing nickel alloys, nickel alloy deposits, and uses of such formed nickel alloy deposits

Technical Field

The present invention relates to electroless nickel alloy plating baths, methods of depositing nickel alloys, nickel alloy deposits and uses of such nickel alloy deposits. The nickel coatings obtained by the present invention show high uniformity and hardness, good wear resistance and improved corrosion resistance. Such coatings are suitable as functional coatings in the aerospace, automotive, electrical and chemical industries. Metal layers deposited from such plating baths may also be used as barrier and capping layers in semiconductor devices, printed circuit boards, IC substrates, and the like.

Background

Electroless nickel coatings are functional coatings applied to provide corrosion resistance, wear resistance, hardness, lubricity, solderability and bondability, deposition uniformity and non-magnetic properties (in the case of high phosphorus nickel alloys) to provide a non-porous barrier or to enhance the performance or service life of a particular component. The hardness and corrosion resistance of electroless nickel are key factors for many successful applications. Electroless nickel coatings are used in a variety of applications including electrical connectors, microwave housings, valve and pump bodies, printer shafts, computer components, and the like. Electroless nickel may be used to coat components made from a variety of materials including, but not limited to, steel, stainless steel, aluminum, copper, brass, magnesium, and any of several non-conductive materials.

Electroless nickel plating deposits a nickel alloy onto a substrate capable of catalyzing the deposition of the alloy from a processing solution containing nickel ions and a suitable chemical reducing agent capable of reducing the nickel ions in solution to metallic nickel. Various additives are also used in electroless nickel plating baths to stabilize the bath and further control the rate of nickel deposition on the substrate being plated. Reducing agents include, for example, borohydride (which produces a nickel boron alloy) and hypophosphite ions (which produces a nickel phosphorus alloy). Electroless nickel, in contrast to electroplating, does not require a rectifier, current or anode. The deposition process is autocatalytic, meaning that once a primary layer of nickel is formed on the substrate, that layer and each subsequent layer become catalysts that cause the plating reaction to continue.

In an electroless nickel plating bath using hypophosphite ions as a reducing agent, the nickel deposit comprises an alloy of nickel and phosphorus with a phosphorus content of from about 2% to greater than 12%. These alloys have unique characteristics in terms of corrosion resistance and (after heat treatment) hardness and wear resistance.

Compositions for electroless nickel plating solutions are known in the art. For example, U.S. Pat. No. 2,658,841 teaches the use of soluble organic acid salts as buffers for electroless nickel plating solutions. Us patent 2,658,842 teaches the use of short chain dicarboxylic acids as accelerators for EN baths. U.S. Pat. No. 2,762,723 teaches the use of sulfide and sulfur containing additives in electroless nickel plating baths to improve bath stability.

U.S. Pat. No. 2,847,327 describes other methods of stabilizing electroless nickel plating solutions. These include the use of higher purity starting materials; more effective stabilizers from heavy metals such as Pb, Sb, Bi, Cu and Se; inorganic compounds such as iodates and thio compounds; organic compounds such as unsaturated alkenes and alkynes, and others.

WO 2015/187402 discloses electroless nickel alloy plating baths comprising one or more dicarboxylic acids and one or more alpha hydroxycarboxylic acids.

WO2018/220220 discloses electroless nickel alloy plating baths for making data storage devices wherein all complexing agents comprise at least two carboxylic acid moieties.

CN 109112509A discloses an electroless nickel plating solution with high corrosion resistance and a preparation method thereof. The electroless nickel plating solution comprises nickel sulfate, sodium hypophosphite, sodium citrate, lactic acid, propionic acid and acetic acid, as well as specific wetting agents and stabilizers.

Objects of the invention

It is therefore an object of the present invention to provide an electroless nickel alloy plating bath that improves corrosion protection of metal substrates treated by said plating bath.

It is another object of the present invention to provide an electroless nickel alloy plating bath that is stable and does not exhibit any fouling.

It is yet another object of the present invention to provide an electroless nickel alloy plating bath with a sufficient plating rate.

It is a further object of the present invention to provide an electroless nickel alloy plating bath that, when plated on a metal surface such as aluminum or an aluminum alloy, for example, produces a nickel alloy deposit that adheres well to the underlying substrate surface.

Disclosure of Invention

The above object is solved by an electroless nickel alloy plating bath according to the invention, its use, a method for depositing a nickel alloy onto at least one surface of a substrate and a nickel alloy deposit obtained from an electroless nickel alloy plating bath according to the invention and its use.

An electroless nickel alloy plating bath according to the invention comprises:

a) nickel ions;

b) an additional reducible metal ion selected from the group consisting of: molybdenum ions, rhenium ions, tungsten ions, copper ions, oxygen-containing ions thereof, and mixtures thereof;

c) at least one reducing agent adapted to reduce nickel ions and further reducible metal ions to their respective metallic states; preferably selected from the group consisting of: hypophosphorous acid, hypophosphites, and mixtures of the foregoing; and

d) complexing agents CA1, CA2, CA3 and optionally (preferably not optionally, but compulsorily, necessarily; i.e., without the option) CA4,

wherein CA1, CA2, CA3, and CA4 are all different from one another;

wherein each of CA1 and CA2 is independently selected from the group consisting of: compounds having at least two carboxylic acid moieties, their corresponding salts, and mixtures thereof;

wherein CA3 is selected from the group consisting of: aliphatic compounds having exactly one carboxylic acid moiety, their corresponding salts, and mixtures thereof; and

wherein CA4 is selected from the group consisting of: aromatic compounds having at least one carboxylic acid moiety, their corresponding salts, and mixtures thereof.

The two complexing agents CA1 and CA2 are different compounds having at least two carboxylic acid moieties, their corresponding salts and mixtures of the above.

The electroless nickel alloy plating bath according to the invention is used for depositing a nickel alloy onto at least one surface of at least one substrate.

A method of depositing a nickel alloy onto at least one surface of a substrate, the method comprising the following method steps in sequence:

A) providing a substrate comprising at least one surface;

B) at least one surface of the substrate is contacted with an electroless nickel alloy plating bath according to the invention, preferably a plating bath as preferably described throughout this document, thereby depositing a nickel alloy onto at least one surface of the substrate.

A nickel alloy deposit may be obtained by deposition from an electroless nickel alloy plating bath according to the invention, preferably a plating bath as preferably described herein throughout.

The electroless nickel alloy plating bath according to the invention and the method of the invention are suitable for providing nickel alloy deposits having an attractive bright or semi-bright appearance. In addition, the nickel alloy deposits adhere well to the underlying substrate surface.

The electroless nickel alloy plating bath according to the invention is stable and economical to use without showing fouling for a sufficient time during plating.

Detailed Description

The percentages in this specification are weight percentages (wt. -%), unless otherwise indicated. Unless otherwise stated, concentrations given in this specification refer to the volume or mass (preferably volume) of the entire solution. The terms "deposition" and "plating" are used interchangeably herein. Furthermore, "layer" and "deposit" are also used synonymously in this description. Fouling refers to the undesired decomposition of the plating bath. It should be understood that the preferred embodiments of the invention described in this specification may be combined unless this is not technically feasible or specifically excluded.

In the context of the present invention, the carboxylic acid moiety is a-C (═ O) OH group. It preferably includes salts thereof, if not explicitly stated. The term "CX-CY-compound" according to the present invention refers to compounds having X to Y carbon atoms (including the carbon atoms of any carboxylic acid moiety); wherein X and Y refer to natural numbers, and X may be less than Y.

The nickel alloys of the present invention comprise the elements nickel and one or more of molybdenum, tungsten, copper and rhenium, preferably in combination with phosphorus and/or boron, more preferably in combination with phosphorus. Even more preferred alloys comprise nickel, molybdenum and phosphorus. The most preferred alloys comprise nickel, molybdenum, copper and phosphorus as they provide improved corrosion protection of the metal substrate.

Electroless nickel alloy plating bath according to the invention

The electroless nickel alloy plating bath of the present invention contains nickel ions. The nickel ions may be provided by any water soluble salt or any water soluble nickel complex. Preferably, the nickel ions are provided by any one of nickel sulfate, nickel chloride, nickel acetate, nickel methane sulfonate, nickel sulfamate, and mixtures thereof.

The concentration of nickel ions in the electroless nickel alloy plating bath may vary widely and preferably ranges from 0.01 to 1.0mol/L, more preferably from 0.03 to 0.8mol/L, even more preferably from 0.04 to 0.5mol/L, yet even more preferably from 0.05 to 0.3mol/L, most preferably from 0.05 to 0.1 mol/L.

The electroless nickel alloy plating bath of the invention contains additional reducible metal ions (in addition to nickel ions). The additional reducible metal ion is selected from the group consisting of: molybdenum ions, rhenium ions, tungsten ions, copper ions, and mixtures thereof. The additional reducible metal ions may be provided by any water soluble salt or any water soluble complex of such additional reducible metals. Preferably, the molybdenum ions are formed from molybdic acid, alkaline molybdate (e.g., Na)₂MoO₄) Ammonium molybdate and mixtures thereof. Preferably, the tungsten ions are made of tungstic acid, alkaline tungstate (e.g. Na)₂WO₄) Ammonium tungstate and mixtures thereof. Preferably, the rhenium ion is formed from perrhenic acid, a basic perrhenate (e.g., NaReO)₄) Ammonium perrhenate and mixtures thereof. Preferably, the copper ions are provided by any of copper iodide, copper iodate, copper chloride and/or copper sulfate. Preference is given to molybdenum ions as ecologically unimportant stabilizers and complexesAnd (3) a gold component. Copper ions are preferred because they improve the leveling and brightness of the deposit and enhance process stability and corrosion resistance. In one embodiment of the present invention, the electroless nickel alloy plating bath of the present invention preferably contains only molybdenum ions as the additional reducible metal ions. In another preferred embodiment of the present invention, the electroless nickel alloy plating bath of the present invention preferably comprises a mixture of molybdenum ions and copper ions as the additional reducible metal ions. More preferably, the electroless nickel alloy plating bath of the invention does not contain any tungsten ions nor any rhenium ions, most preferably, if copper ions and/or molybdenum ions are present.

Therefore, preferred is the electroless nickel alloy plating bath of the invention wherein the further reducible metal ions are molybdenum ions, copper ions or mixtures thereof; preferably, the additional reducible metal ion is a molybdenum ion or a mixture of a molybdenum ion and a copper ion.

Insoluble components of molybdenum, rhenium, and tungsten, such as molybdenum disulfide, are detrimental to nickel alloy deposit characteristics and, therefore, are preferably not used in electroless nickel alloy plating baths according to the present invention.

The total concentration of additional reducible metal ions in the electroless nickel alloy plating bath may vary and is preferably between 5 x 10 based on the total volume of the electroless nickel alloy plating bath^-5To 1 x 10^-2In the range of mol/L, more preferably 1 x 10^-4To 5 x 10^- ³mol/L, and even more preferably 2.5 x 10^-4To 2.5 x 10^-3mol/L. If more than one type of additional reducible metal ions are included in the electroless nickel alloy plating bath, the total concentration of all of the additional reducible metal ions used is preferably within the above-defined range (i.e., its total concentration).

In those cases where the electroless nickel alloy plating bath of the invention comprises a mixture of molybdenum ions and copper ions as additional reducible metal ions, the total concentration of molybdenum ions and copper ions in the electroless nickel alloy plating bath may vary and is preferably in the range of 1 x 10, based on the total volume of the electroless nickel alloy plating bath^-5(preferably from 5 x 10)^-5) To 1 x 10^-2In the range of mol/L, more preferably 1 x 10^-5(preferably from 5 x 10)^-5) To 5 x 10^-3mol/L, and even more preferably 1 x 10^-5(preferably from 5 x 10)^-5) To 5 x 10^-4mol/L. Preferably, the electroless nickel alloy plating bath of the invention comprises more molybdenum ions than copper ions on a molar basis. More preferably, the total concentration of molybdenum ions and copper ions in the electroless nickel alloy plating bath may vary and is preferably between 1 x 10 based on the total volume of the electroless nickel alloy plating bath^-5(preferably from 5 x 10)^-5) To 1 x 10^-2In the range of mol/L, more preferably 1 x 10^-5(preferably from 5 x 10)^-5) To 5 x 10^-3mol/L, and even more preferably 1 x 10^-5(preferably from 5 x 10)^-5) To 5 x 10^-4mol/L, and the molar ratio of the molybdenum ions to the copper ions is in the range of 1:1 to 30:1, preferably 5:1 to 20:1, more preferably 10:1 to 15: 1.

Concentrations outside the above ranges may be suitable in some cases, depending on the additional metal content desired in the nickel alloy deposit to be formed.

The electroless nickel alloy plating bath of the invention further comprises at least one reducing agent. The at least one reducing agent is preferably a chemical reducing agent. The at least one reducing agent is adapted to reduce nickel ions and additional reducible metal ions to their respective metallic states. Preferably, the at least one reducing agent is selected from the group consisting of:

hypophosphite compounds, such as hypophosphorous acid and hypophosphites, such as alkaline hypophosphites (e.g. sodium or potassium hypophosphite), ammonium hypophosphite, nickel hypophosphite, etc.;

boron-based reducing agents, such as aminoboranes, such as Dimethylaminoborane (DMAB) and morpholine borane, and borohydrides, such as sodium borohydride;

-hydrazine; and

hydrazine derivatives (such as hydrazine sulfate, hydrazine hydrochloride, hydrazine hydrate and other such components that may be used as reducing agents in the context of the present invention).

In the case of using a hypophosphite compound as a reducing agent, a nickel alloy deposit containing phosphorus is obtained. Such reducing agents provide a source of phosphorus in the deposited nickel alloy.

The borane-based reducing agent produces a nickel alloy deposit comprising boron and a hypophosphite compound, and the borane-based reducing agent produces a nickel alloy deposit comprising phosphorus and boron.

Nitrogen-based reducing agents such as hydrazine and hydrazine derivatives provide neither phosphorus nor boron to be incorporated into the nickel alloy.

The at least one reducing agent is more preferably selected from the group consisting of: hypophosphorous acid, hypophosphites, and mixtures of the foregoing. These reducing agents are preferred because the phosphorus built into the nickel alloys of the present invention significantly improves the magnetic properties of such nickel alloy deposits and produces (heat resistant) paramagnetic nickel alloys, among other things. The introduction of high amounts of phosphorus (e.g. 10wt. -% or more) also improves the protection against corrosion. Even more preferably, the at least one reducing agent is chosen to be a hypophosphite salt, as such salts are cost effective and easy to use. The molar concentration of the at least one reducing agent is generally in excess of an amount sufficient to reduce the nickel ions and additional reducible metal ions in the electroless nickel alloy plating bath. The concentration of the reducing agent is preferably in the range of 0.01 to 3.0mol/L, more preferably 0.1 to 1 mol/L.

The electroless nickel alloy plating bath comprises (different) complexing agents CA1 and CA2, wherein each of CA1 and CA2 is independently selected from the group consisting of: compounds having at least two carboxylic acid moieties, their corresponding salts (e.g., carboxylates), and mixtures thereof. Preferably, the compound having at least two carboxylic acid moieties is an aliphatic compound, preferably a C2-C12-aliphatic compound, more preferably a C2-C8-aliphatic compound. Aliphatic compounds include acyclic or cyclic, saturated or unsaturated carbon compounds, excluding aromatic compounds; the aliphatic compound is preferably acyclic.

Functionalization can theoretically be obtained by replacing at least one hydrogen with a functional group. Such optional (but in some cases preferred) functional groups are preferably selected from hydroxyl (-OH), amino (-NH)₂) A halide, an olefinic double bond (-C ═ C-), andtriple bonds (-C.ident.C-). The latter two naturally require that two hydrogen atoms of adjacent carbon atoms be theoretically replaced. More preferably, the optional functional group is selected from the group consisting of: hydroxyl groups and double bonds. Even more preferably, the optional functional group is a hydroxyl group.

More preferably, the electroless nickel alloy plating bath comprises complexing agents CA1 and CA2, complexing agents CA1 and CA2 being independently selected from the group consisting of: unfunctionalized and functionalized aliphatic dicarboxylic acids, unfunctionalized and functionalized aliphatic tricarboxylic acids, unfunctionalized and functionalized aliphatic tetracarboxylic acids, unfunctionalized and functionalized aliphatic pentacarboxylic acids, unfunctionalized and functionalized aliphatic hexacarboxylic acids, their corresponding salts, and mixtures thereof.

Even more preferably, complexing agents CA1 and CA2 are independently selected from the group consisting of: unfunctionalized and functionalized aliphatic dicarboxylic acids, unfunctionalized and functionalized aliphatic tricarboxylic acids, unfunctionalized and functionalized aliphatic tetracarboxylic acids, their corresponding salts, and mixtures thereof.

Preferably, the complexing agent CA1 is an unfunctionalized aliphatic C2-C12-dicarboxylic acid and/or a salt thereof. Even more preferably, it is an unfunctionalized aliphatic C3-C6-dicarboxylic acid and/or salt thereof. Still even more preferably, complexing agent CA1 is selected from the group consisting of: malonic acid, succinic acid, glutaric acid, adipic acid, maleic acid, fumaric acid, glutaconic acid, itaconic acid, salts thereof, and mixtures thereof. Most preferably, complexing agent CA1 is malonic acid and/or a salt thereof.

Preferably, complexing agent CA2 is a functionalized or unfunctionalized (preferably functionalized) aliphatic C3-C12-dicarboxylic acid and/or salt thereof, preferably a functionalized or unfunctionalized (preferably functionalized) aliphatic C4-C6-dicarboxylic acid and/or salt thereof. More preferably, complexing agent CA2 contains at least one hydroxyl group (and is therefore hydroxyl-functionalized). Even more preferably, complexing agent CA2 is a hydroxyl-functionalized aliphatic C4-C6-dicarboxylic acid and/or a salt thereof. Still even more preferably, complexing agent CA2 is selected from the group consisting of: malic acid, tartaric acid, 1-hydroxyglutaric acid, 2-hydroxyglutaric acid, 1-hydroxyadipic acid, 2-hydroxyadipic acid, 3-hydroxyadipic acid, salts thereof, and mixtures thereof. Most preferably, complexing agent CA2 is malic acid and/or a salt thereof.

Preferably, the complexing agent CA3 is a functionalized or unfunctionalized aliphatic C1-C5-monocarboxylic acid and/or salt thereof, preferably a functionalized or unfunctionalized aliphatic C2-C4-monocarboxylic acid and/or salt thereof. More preferably, complexing agent CA3 is propionic acid and/or a salt thereof. Most preferably, complexing agent CA3 is propionic acid. It should be clearly noted that in the context of the present invention, two or more of the above described preferred embodiments for CA1, CA2 and CA3 may be combined.

Preferably, complexing agent CA4 is an aromatic carboxylic acid and/or salt thereof, either functionalized (in some cases preferred) or unfunctionalized (in some cases preferred). The preferred functionalization is hydroxyl functionalization. An "aromatic carboxylic acid" is a compound comprising at least one COOH group (and related salts thereof) and at least one aromatic ring. The aromatic ring may contain heteroatoms, preferably the aromatic ring is free of heteroatoms. Preferably, at least one COOH group is directly bonded to an aromatic ring, such as in, for example, benzoic acid, salicylic acid. More preferably, CA4 is benzoic acid and/or a salt thereof. Even more preferably CA4 is sodium benzoate.

In a very preferred embodiment of the present invention, complexing agents CA1, CA2, CA3 and C4 are each selected from each other, representing a respective different complexing agent according to the preferred embodiments described above for CA1, CA2 and CA 3.

Particularly preferred is an electroless nickel alloy plating bath according to the invention, wherein complexing agent CA1 is selected from the group consisting of: malonic acid, succinic acid, glutaric acid, adipic acid, maleic acid, fumaric acid, glutaconic acid, itaconic acid, salts thereof, and mixtures thereof (in particular, complexing agent CA1 is malonic acid and/or a salt thereof); complexing agent CA2 was selected from the group consisting of: malic acid, tartaric acid, 1-hydroxyglutaric acid, 2-hydroxyglutaric acid, 1-hydroxyadipic acid, 2-hydroxyadipic acid, 3-hydroxyadipic acid, salts thereof, and mixtures of the foregoing (in particular, complexing agent CA2 is malic acid and/or a salt thereof); and complexing agent CA3 is selected from the group consisting of: aliphatic monocarboxylic acids, salts thereof, and mixtures thereof. Most preferably, the above-mentioned substance is combined with complexing agent CA4 and is benzoic acid and/or a salt thereof.

Preferably, the concentration of complexing agent CA1 ranges from 50 to 300mmol/L, more preferably from 50 to 250mmol/L, and even more preferably from 50 to 200 mmol/L. Preferably, the concentration of complexing agent CA2 ranges from 50 to 200mmol/L, more preferably from 60 to 180mmol/L, and even more preferably from 70 to 150 mmol/L. Preferably, the concentration of complexing agent CA3 ranges from 40 to 1000mmol/L, more preferably from 40 to 800mmol/L, and even more preferably from 40 to 300 mmol/L. Preferably, the concentration of complexing agent CA4 ranges from 0 (preferably greater than 0) to 200mmol/L, more preferably from 7 to 150mmol/L, even more preferably from 15 to 75mmol/L, and yet even more preferably from 30 to 75 mmol/L. Preferably, the total concentration of complexing agents CA1, CA2, CA3 and CA4 is at least 0.15mol/L, more preferably at least 0.20mol/L, even more preferably at least 0.22 mol/L.

Preferably, the ratio of the total molar concentration of complexing agents CA1, CA2, CA3, and optionally CA4 (most preferably CA1, CA2, CA3, and CA4 together) to the molar concentration of nickel ions ranges from 4/1 to 8/1.

The electroless nickel alloy plating bath according to the invention is preferably an aqueous solution. The term "aqueous solution" means that the primary liquid medium that is the solvent in the solution is water. Further liquids miscible with water, such as water-miscible alcohols and other polar organic liquids, may be added. Preferably at least 95wt. -%, more preferably 99wt. -% of all solvents used are water because of its ecologically benign characteristics. The electroless nickel alloy plating bath according to the invention is preferably prepared by dissolving all components in an aqueous liquid medium, preferably in water.

Electroless nickel alloy plating baths according to the present invention may be acidic, neutral or alkaline. Acidic or basic pH adjusting agents such as (mineral) acids or bases can be selected from a wide range of substances such as ammonia, ammonium hydroxide, sodium hydroxide, hydrochloric acid, sulfuric acid, and the like. The pH of the electroless nickel alloy plating bath according to the invention is preferably about 2 to 12. In one embodiment, the electroless nickel alloy plating bath according to the invention preferably has a neutral or acidic pH (hereinafter referred to as "acidic electroless nickel alloy plating bath"). This is particularly useful if molybdenum ions and/or rhenium ions are selected as the further reducible metal ions; in particular if molybdenum is chosen as the only further reducible metal ion. More preferably, the acidic electroless nickel alloy plating bath according to the invention has a pH value in the range of 3.5 to 7, even more preferably 3.5 to 5.0, yet even more preferably 4.0 to 4.8, most preferably 4.2 to 4.7. This allows for optimum results in terms of high stability of the bath and paramagnetic properties of the nickel alloy deposit formed from the bath, including its retention at high temperatures. If tungsten ions are chosen as the only further reducible metal ions, a pH in the range of 8 to 10 is preferred.

The electroless nickel alloy plating bath according to the invention may preferably comprise other additives such as pH buffers, wetting agents, promoters, brighteners, other stabilizers known in the art, plating rate modifiers such as those disclosed in european patent application EP 3034650 a 1.

It is further preferred that the electroless nickel alloy plating bath of the present invention is free of thiourea, which is commonly used as a stabilizer for electroless nickel plating baths due to its toxicity and ecological issues.

Method according to the invention

In step a) of the method according to the invention, a substrate comprising at least one surface is provided.

Various substrates may be plated with a nickel alloy using the electroless nickel alloy plating bath according to the invention and the method according to the invention. Preferably, a metal substrate is used in the method according to the invention. The metal substrate to be plated with the nickel alloy is preferably selected from the group consisting of: copper, zinc, silver, palladium, iron, iridium, tin, aluminum, nickel, alloys thereof, and mixtures thereof. Preferably, the substrate provided in step a) is made entirely of metal (preferably at least one of the preferred metals mentioned above) or it preferably comprises at least one surface made of metal, preferably at least one of the preferred metals mentioned above. This surface, which may also be made of metal, may also be one or more palladium activated layers, typically used to render non-conductive surfaces such as glass, plastic or ceramic receptive to nickel alloy plating.

The substrate is optionally pretreated before step B). Such pretreatments are known in the art. Typical pre-treatments include etching, cleaning, zincating and activation steps. Useful pretreatments can improve plating results by removing undesirable scale or oxides from the substrate surface. Activation of a surface is generally understood to be the deposition of a thin and possibly discontinuous layer of, for example, palladium on an otherwise non-conductive surface to render the surface suitable for subsequent metal plating, preferably nickel alloy plating. The pretreatment may vary widely depending on the substrate provided. Some guidance can exemplarily be found in WO 2015/161959 a1 (page 13, line 11 to page 15, line 30).

In step B) of the method according to the invention, at least one surface of the substrate is brought into contact with the electroless nickel alloy plating bath according to the invention.

A substrate to be plated with a nickel alloy can be plated to a desired thickness and deposition amount by contacting the substrate with the electroless nickel alloy plating bath of the invention.

During deposition, i.e. most preferably during step B), the electroless nickel alloy plating of the invention is preferably maintained at a temperature in the range of 20 ℃ to 100 ℃, preferably 70 ℃ to 95 ℃, more preferably 80 ℃ to 90 ℃, even more preferably 83 ℃ to 87 ℃.

The substrate may be contacted with the electroless nickel alloy plating bath of the invention for any period of time sufficient to plate a nickel alloy deposit of a desired thickness. The thickness of the nickel alloy deposit depends inter alia on the intended use of the deposit or the product containing the deposit. By way of non-limiting example, a contact duration in the range of 30 to 180 minutes, preferably 40 to 90 minutes, and more preferably 50 to 70 minutes, is generally considered sufficient.

Nickel alloy deposits can be formed with thicknesses of up to 100 μm or more. Preferably, the thickness of the nickel alloy deposit varies, preferably in the range of 1 to 60 μm. The thickness depends on the technical application and may be higher or lower for some applications. For example, if the nickel alloy deposit is to provide a corrosion resistant coating, a thickness in the range of 30 to 60 μm is generally desired, while for electronic applications a thickness in the range of 1 to 15 μm is preferably applied. In the field of rigid storage disks, the thickness of the nickel alloy deposit is preferably in the range of 5 to 20 μm, more preferably 7 to 16 μm. In the field of semiconductor technology, the thickness of the nickel or nickel-phosphorus deposit is preferably in the range of 1 to 5 μm. The thickness of the nickel alloy deposit can be measured using X-ray fluorescence (XRF), as is known in the art.

Various ways of contacting a substrate with an electroless nickel alloy plating bath of the invention are known in the art. For example, the substrate may be fully or partially immersed in, and preferably sprayed or wiped onto, the electroless nickel alloy plating bath of the invention.

Optionally, the electroless nickel alloy plating bath of the invention is agitated prior to and/or during plating. Agitation may be achieved, for example, by mechanical movement of the electroless nickel alloy plating bath of the invention, such as shaking, stirring, or continuous pumping of the liquid or inherently by sonication, by elevated temperatures, or by gas feed (such as purging the aqueous plating bath with an inert gas or air).

Industry standards require that the plating rate preferably be at least 2.5 μm/h. This allows a sufficiently economical process. More preferably, the plating rate in combination with the present invention is in the range of 8.0 to 12.0 μm/h. Such plating rates not only allow a sufficiently economical process while improving the retention of the desired paramagnetic properties at high temperatures, but further improve the plating speed without sacrificing quality during plating.

The process according to the invention optionally comprises a rinsing step, preferably with water, and/or a drying step. The above parameters of the electroless nickel alloy plating bath according to the invention and the method of the invention provide only general guidance for practicing the invention.

The electroless nickel alloy plating bath of the invention may be used to deposit a nickel alloy onto a surface of a substrate.

Nickel alloy deposit according to the invention and use thereof

The invention further relates to a nickel alloy deposit obtainable by deposition from an electroless nickel alloy plating bath according to the invention. Surprisingly, nickel alloy deposits formed from electroless nickel alloy plating baths according to the present invention exhibit excellent corrosion resistance, although such deposits appear to be identical in terms of elemental composition (i.e., content of nickel, additional reducible metal ions, and optionally phosphorus and/or boron).

The content of the further reducible metal (preferably the total content) in the nickel alloy deposit is preferably in the range of 0.5 to 5.0wt. -%, more preferably 0.8 to 4.0wt. -%, even more preferably 1.0 to 3.0wt. -%, and yet even more preferably 1.2 to 2.5wt. -%.

Preferably, the content of phosphorus and/or boron (more preferably phosphorus alone) in the nickel alloy deposit is 10wt. -% or higher, more preferably in the range of 10.0 to 16.0wt. -%, preferably 10.5 to 15.0wt. -%, and more preferably 11.0 to 14.5wt. -%. Other preferred ranges are 10 to 15wt. -%, more preferably 10.5 to 13wt. -%, most preferably 10.8 to 12.5wt. -%.

The remainder of the nickel alloy deposit, which is neither a further reducible metal nor phosphorus and/or boron, is usually predominantly nickel (usually. gtoreq.98 wt. -%, preferably. gtoreq.99 wt. -%, more preferably. gtoreq.99.9 wt. -% of the remainder), irrespective of trace impurities usually present in technical raw materials and co-deposited other materials, such as those derived from e.g. organic impurities and stabilizers. Most preferably, the nickel alloy deposit according to the invention consists (essentially) of nickel, molybdenum and phosphorus, or consists (essentially) of nickel, molybdenum, copper and phosphorus (without taking into account trace impurities usually present in technical raw materials and other materials unintentionally co-deposited, such as those derived from, for example, organic impurities and optionally stabilizers).

The invention further relates to the use of a nickel alloy deposit obtainable by deposition from an electroless nickel alloy plating bath according to the invention and to a method of the invention. This nickel alloy deposit is preferably used to protect the workpiece from environmental acidic corrosive conditions. By "environment" is meant the environment of the workpiece such that the workpiece may be subjected to acidic corrosive conditions, most preferably under outdoor natural conditions.

The details and preferred embodiments described for one aspect of the invention are applicable to the other aspects mutatis mutandis. They are not described again to avoid unnecessary repetition.

The invention will now be illustrated by reference to the following non-limiting examples.

Examples of the invention

Unless otherwise stated hereinafter, commercial products were used as described in the technical data sheet available at the filing date of this specification.

155 (soaking in detergent) and

701 (electric cleaner) is a product of Atotech Deutschland GmbH (armett germany llc).

0.7dm was used in all plating experiments described below²Area steel plate (Q panel type QD). Prior to plating the nickel alloy, the panel is pretreated as described below.

Determination of the thickness and plating Rate of a Metal or Metal alloy deposit

The phosphorus content and the deposition thickness were measured at 5 points per substrate using an XRF instrument Fischer XDV-SDD (Helmut Fischer GmbH, germany). Layer thickness can be calculated from this XRF data by assuming a layered structure of the deposit. The plating rate was calculated by dividing the obtained layer thickness by the time required to obtain the layer thickness.

Measurement of pH value

Using a pH meter (WTW, Typ pH 3110, electrode:

41, gel electrode with temperature sensor, reference electrolyte: 3mol/L KCl) at 25 ℃. The measurement is continued until the pH value becomes constant, but in any case lasts at least 2 minutes. The pH meter was calibrated before use with Fluka and Certipur supplied standards of buffer solutions at pH values of 2, 4 and 7.

Composition of deposited nickel alloy

The composition of the deposited nickel alloy was measured using X-ray photoelectron spectroscopy (VersaProbe XPS, Physical Electronics GmbH).

Working examples

For comparative reasons, several nickel alloy plating baths of the invention were prepared (1L each) containing the following composition:

6g/L of nickel ions (102.2mmol/L, provided in the form of nickel sulphate),

33g/L sodium hypophosphite (0.375mol/L),

24mg/L (2.50X 10) of molybdenum ions^-4mol/L, provided in the form of sodium molybdate),

copper ions 2.0mg/L (3,15 x 10)^-5mol/L, provided as copper (II) sulfate pentahydrate,

complexing agents at different concentrations (in g/L) as given in table 1,

the pH was adjusted to 4.6 with ammonia solution (25wt. -% in water)

The temperature of the nickel alloy plating bath was set to 86 ℃ and the substrate was immersed in the bath for 60 minutes.

Table 1: examples 1 to 16

#		1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16
																		Malonic acid	[g/L]	5.3	5.3	5.3	5.3	5.3	0	2	10	20	5.3	5.3	5.3	5.3	5.3	5.3	5.3
Malic acid	[g/L]	17	17	17	17	17	17	17	17	17	10	25	17	17	17	17	17
																		Propionic acid	[g/L]	0	1	10	25	50	3.6	3.6	3.6	3.6	3.6	3.6	3.6	3.6	3.6	3.6	3.6
Sodium benzoate	[g/L]	3	3	3	3	3	3	3	3	3	3	3	0	1	3	10	20
																		Plating rate	[μm/h]	8.6	9.2	10.2	9.1	8.8	8.5	9.1	8.9	7.7	9.7	7.0	8.9	9.2	9.3	9.3	10.6
Phosphorus content	[wt.-％]	11.1	10.9	11.2	11.0	11.8	11.1	10.7	10.9	12.1	10.0	11.6	11.5	11.2	10.9	11.0	10.1
																		Stress	[N/mm²]	-17	-20	-14	-17	-18	-8	-19	-20	-20	Skip over	-20	-19	-18	-18	-15	-6

Even with the use of different amounts of CA1, CA2, CA3, and CA4, the first trials using the electroless nickel alloy plating baths of the invention (examples 2 to 5, 7 to 11, and 13 to 16) showed sufficient plating rates and phosphorus content.

Example 14 was chosen as representative of the present invention for further testing and describing the advantages of the present invention.

Corrosion test 1 (time)

Corrosion test 1 was carried out according to the standard AASS-DIN EN ISO 9227.

Materials: q panel type QD RA <0.5 μm; the thickness of the deposit is approximately equal to 10 mu m

The defect area was determined as red rust and compared to the total area ("relative defect area") and rated according to the following scheme:

if no defect is detected, i.e. a relative defect area of 0%, a rating of 10 is assigned. Thus, the following scale (corresponding relative defect areas in parentheses) is specified: 9(> 0% to 0, 1%); 8(> 0.1% to 0.25%); 7(> 0.25% to 0.5%); 6(> 0.5% to 1.0%); 5(> 1.0% to 2.5%), 4(> 2.5% to 5.0%); 3(> 5.0% to 10%), 2(> 10% to 25%); 1(> 25% to 50%); 0(> 50%).

Table 2: rating in Corrosion test 1 after a certain amount of time

	0 hour	24 hours	48 hours	72 hours	96 hours
						Example 12 (comparison)	10	8	7	6	5
Example 14 (inventive)	10	10	10	9	8

As shown in table 2, example 14 (according to the invention) shows significantly improved corrosion resistance compared to example 12 (comparative). In example 12, no aromatic carboxylic acid was used. Thus, aromatic carboxylic acids clearly have a beneficial effect on corrosion resistance.

Corrosion test 2(MTO)

Based on commercially available products (

HP 1151, a product of amett), additional tests were performed with another comparative example; hereinafter referred to as example 17. This comparison allows for extensive corrosion performance studies.

Example 17 is based on the general formulation as listed above, but without the use of copper and molybdenum ions. Further, example 17 contained three carboxylic acids corresponding to CA1, CA2, and CA3, but no aromatic carboxylic acid (i.e., no CA 4).

Corrosion test 2 was also carried out according to the standard AASS-DIN EN ISO 9227.

Table 3: corrosion test 2-determination of time (in hours) until > 1% Red Rust on surface

MTO*	0	2	4	6
					Example 14 (inventive)	312 hours	312 hours	224 hours	36 hours
Example 17 (comparative)	204 hours	156 hours	100 hours	12 hours

Indicates the metal turnover

Table 3 shows that also for corrosion test 2, a significant improvement in corrosion resistance is observed. Further experiments showed that the improved effect was attributed to the presence of CA4 (data not shown).

Inherent stress test

Bending strip

The stress in the coating was measured by using a stress bar with two fingers, which were painted on one side. The test strip is made of a chemically etched beryllium copper alloy and has spring-like characteristics. Prior to the stress measurement, the plating rate of the bath was determined with an accuracy of ± 10% to determine the plating time for the stress measurement. After surface cleaning by appropriate pretreatment, the stress bar fingers were in electrical contact with the test panel and both were very carefully immersed in the treatment bath. Based on the known plating rate, the plating duration was calculated to yield a coating thickness of 10 μm. After plating, the test strips were rinsed with deionized water and carefully dried using a paper towel. Since stress bars are mechanically fragile and tend to deform very quickly, they need to be evaluated immediately. Oxide formation on the newly plated surface will change the beam deflection over time. The plated stress strip fingers will be mounted on a test bed that measures the distance the test strip fingers spread after plating. Distance U determines the incremental distance between the stress bar fingers and is included in the calculation at N/mm²The deposit stress of the meter.

Stress

T is the deposit thickness in μm (microns) and K is a bar calibration constant provided by the supplier. Each batch of test strips manufactured will have slight differences when used for deposit stress testing. The supplier will determine the degree of difference when calibrating each batch of test strips. The K value will be provided with each batch of test strips provided by professional Testing and Development Co. Stress is determined as a compressive or tensile property. If the test strip legs spread outwardly on the plated side, the deposit stress is tensile in nature. If the test strip legs spread inward on the plated side, the deposit stress is compressive in nature. The compressive stress is conventionally given in negative number, so that the result of the above equation is multiplied by-1 in the case of compressive stress.

Intrinsic stress tests were performed during the bath life by relating the stress value to the concentration of phosphite (hereinafter abbreviated as OP). OP is a suitable indicator of bath age, as phosphite is a reaction product of hypophosphite oxidation and accumulation over time.

Table 4: inherent stress

Table 4 shows that the initial (i.e., OP ═ 0) stress values are very similar/close to each other. In addition, the absolute value coincides with the stress value based on OP ═ 0 also shown in table 1.

However, after aging, table 4 shows that the presence of aromatic carboxylic acid improves the compressive stress profile in long-term bath utilization. This means that the presence of aromatic carboxylic acids leads to an improved tolerance with respect to increased OP concentration and thus to a closer to optimal level of internal stress (see example 14: "20" versus example 17: "92"). Thus, as shown in example 14, a more optimal compressive stress level is maintained until a higher bath age, especially if the OP reaches a concentration above 100 g/L.

Bath stability

Beaker stability testing was performed as follows:

the method is a plating test for determining the chemical stability of an electroless nickel treatment bath. It is suitable for the autocatalytic deposition of nickel-phosphorus coatings. First, a high-shaped 1 liter beaker was cleaned and used with 1:1HNO₃Stripping agentThe solution was stripped for 1 hour to avoid any residue on the bottom and walls of the beaker that could negatively impact the test. Then 1 liter of EN bath solution (test solution) was taken and treated therein as described below. A stirrer was used and set at 250 rpm. The test starts when the operating temperature is reached. The EN test solution was first left uncoated for 1 hour. The beaker was then examined for any nickel deposition on the bottom and walls. If not, the beaker test may be continued and a pre-treated 1dm was plated in the EN bath solution²A mild steel plate. The plates must be plated for 1 hour without any replenishment. When this is over, a loop is realized. Thus, one cycle corresponds to 1 hour of no plating +1 hour of plating. Replenishment was carried out after the plating period. If no precipitation or nickel deposition occurred on the bottom or walls of the beaker, the test could be continued with 1 hour of no plating and 1 hour of plating in the next cycle. The beaker test was ended when extensive plating or plate-out was visible on the bottom or wall of the beaker. The number of cycles achieved is recorded. With the number of cycles achieved, stability can be evaluated.

For the following test procedure, the 1 liter samples were taken from treatment baths of different ages at the respective treatment baths. Samples taken at 0MTO correspond to freshly prepared treatment baths, with higher MTOs corresponding to increased bath age.

Table 5: beaker stability test (cycle times)

Indicates the metal turnover

Table 5 shows that the samples taken from the treatment according to example 14 have a higher stability (5 cycles each) than the samples taken from the treatment according to example 17. Although example 17 shows a relatively constant number of cycles (3 to 4 cycles each), absolute stability is improved by at least one cycle in the presence of the aromatic carboxylic acid compound.

Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification or practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope of the invention being indicated by the following claims.

Claims

1. An electroless nickel alloy plating bath comprising:

a) nickel ions;

c) at least one reducing agent adapted to reduce the nickel ions and the additional reducible metal ions to their respective metallic states; preferably selected from the group consisting of: hypophosphorous acid, hypophosphites, and mixtures of the foregoing; and

d) complexing agents CA1, CA2, CA3, and CA4, wherein CA1, CA2, CA3, and CA4 are all different from each other;

2. The electroless nickel alloy plating bath according to claim 1, wherein the complexing agents CA1 and CA2 are independently selected from the group consisting of: unfunctionalized and functionalized aliphatic dicarboxylic acids, unfunctionalized and functionalized aliphatic tricarboxylic acids, unfunctionalized and functionalized aliphatic tetracarboxylic acids, unfunctionalized and functionalized aliphatic pentacarboxylic acids, unfunctionalized and functionalized aliphatic hexacarboxylic acids, the corresponding salts thereof and mixtures thereof; preferably, the complexing agents CA1 and CA2 are independently selected from the group consisting of: unfunctionalized and functionalized aliphatic dicarboxylic acids, unfunctionalized and functionalized aliphatic tricarboxylic acids, unfunctionalized and functionalized aliphatic tetracarboxylic acids, their corresponding salts, and mixtures thereof.

3. The electroless nickel alloy plating bath according to any of the foregoing claims, characterized in that the complexing agent CA1 is an unfunctionalized aliphatic C2-C12-dicarboxylic acid and/or salt thereof, preferably an unfunctionalized aliphatic C3-C6-dicarboxylic acid and/or salt thereof.

4. The electroless nickel alloy plating bath according to any of the foregoing claims, characterized in that the complexing agent CA1 is selected from the group consisting of: malonic acid, succinic acid, glutaric acid, adipic acid, maleic acid, fumaric acid, glutaconic acid, itaconic acid, salts thereof, and mixtures thereof.

5. The electroless nickel alloy plating bath according to any of the foregoing claims, characterized in that the complexing agent CA2 is a functionalized or unfunctionalized aliphatic C3-C12-dicarboxylic acid and/or salt thereof, preferably a hydroxyl-functionalized aliphatic C4-C6-dicarboxylic acid and/or salt thereof.

6. The electroless nickel alloy plating bath according to any of the foregoing claims, characterized in that the complexing agent CA2 is selected from the group consisting of: malic acid, tartaric acid, 1-hydroxyglutaric acid, 2-hydroxyglutaric acid, 1-hydroxyadipic acid, 2-hydroxyadipic acid, 3-hydroxyadipic acid, salts thereof, and mixtures of the foregoing.

7. The electroless nickel alloy plating bath according to any of the foregoing claims, characterized in that the complexing agent CA3 is a functionalized or unfunctionalized aliphatic C1-C5-monocarboxylic acid and/or salt thereof, preferably a functionalized or unfunctionalized aliphatic C2-C4-monocarboxylic acid and/or salt thereof; more preferably CA3 is propionic acid and/or a salt thereof.

8. The electroless nickel alloy plating bath according to any of the foregoing claims, characterized in that the complexing agent CA4 is a functionalized or unfunctionalized aromatic carboxylic acid and/or a salt thereof, preferably CA4 is benzoic acid and/or a salt thereof, more preferably CA4 is sodium benzoate.

9. The electroless nickel alloy plating bath according to any of the preceding claims, characterized in that it has a pH value in the range of 3.5 to 5.0, preferably 4.0 to 4.8, more preferably 4.2 to 4.7.

10. The electroless nickel alloy plating bath according to any of the foregoing claims, characterized in that the further reducible metal ions are molybdenum ions, copper ions or mixtures thereof; preferably, the additional reducible metal ion is a molybdenum ion or a mixture of a molybdenum ion and a copper ion.

11. The electroless nickel alloy plating bath according to any of the preceding claims, wherein the further reducible metal ions have a valence number between 1 x 10 based on the total volume of the electroless nickel alloy plating bath^-4To 5 x 10^-3Total concentration in the mol/L range.

12. Use of an electroless nickel alloy plating bath according to any of claims 1 to 11 for depositing a nickel alloy onto at least one surface of at least one substrate.

13. A method of depositing a nickel alloy onto at least one surface of a substrate, comprising the following method steps in sequence:

A) providing the substrate comprising the at least one surface;

B) contacting the at least one surface of the substrate with the electroless nickel alloy plating bath of any of claims 1 to 11, thereby depositing a nickel alloy onto the at least one surface of the substrate.

14. A nickel alloy deposit obtainable by deposition from the electroless nickel alloy plating bath of any of claims 1 to 11.

15. Use of a nickel alloy deposit according to claim 14 for protecting a workpiece from environmental acidic corrosive conditions.