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

Abstract

The present invention relates to electroless nickel alloy plating baths, methods of depositing nickel alloys, nickel alloy deposits and uses of such formed nickel alloy deposits. The invention relates to an electroless nickel alloy plating bath comprising nickel ions; additional reducible metal ions 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 metal states; complexing agents CA1, CA2, CA3 and CA4, wherein CA1, CA2, CA3 and CA4 are all different from one another.

Description

[0001] This application is a divisional application of an invention patent application with an application date of November 19, 2020, application number 202080080727.9, and invention name "Electroless nickel alloy plating bath, method for depositing nickel alloy, nickel alloy deposit, and uses of the nickel alloy deposits formed in this way." Technical Field

[0002] The present invention relates to electroless nickel alloy plating baths, methods for 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 high hardness, good wear resistance and improved corrosion resistance. Such coatings are suitable as functional coatings in the aerospace, automotive, electrical and chemical industries. The metal layers deposited from these plating baths can also be used as barrier layers and capping layers in semiconductor devices, printed circuit boards, IC substrates, etc. Background Art

[0003] Electroless nickel coatings are functional coatings applied to provide corrosion resistance, wear resistance, hardness, lubricity, solderability and bonding, deposition uniformity, and non-magnetism (in the case of high phosphorus nickel alloys), thereby providing a non-porous barrier or enhancing the performance or service life of a particular component. The hardness and corrosion resistance of electroless nickel are key factors in 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 more. Electroless nickel can be used to coat components made of a variety of materials including, but not limited to, steel, stainless steel, aluminum, copper, brass, magnesium, and any of several non-conductive materials.

[0004] Electroless nickel plating deposits nickel alloy onto a substrate that can catalyze the alloy deposition from a treatment solution containing nickel ions and a suitable chemical reducing agent that can reduce the nickel ions in the solution to metallic nickel. Various additives are also used in the electroless nickel plating bath to stabilize the bath and further control the nickel deposition rate on the plated substrate. Reducing agents include, for example, borohydrides (which produce nickel-boron alloys) and hypophosphite ions (which produce nickel-phosphorus alloys). In contrast to electroplating, electroless nickel does not require rectifiers, electric currents or anodes. The deposition process is autocatalytic, meaning that once a primary layer of nickel is formed on a substrate, this layer and each subsequent layer become catalysts that cause the plating reaction to continue.

[0005] In electroless nickel plating baths using hypophosphite ions as a reducing agent, the nickel deposit comprises an alloy of nickel and phosphorus, with phosphorus content ranging from about 2% to greater than 12%. These alloys have unique properties in terms of corrosion resistance and (after heat treatment) hardness and wear resistance.

[0006] 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. U.S. Pat. No. 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.

[0007] U.S. Patent 2,847,327 describes other methods for stabilizing electroless nickel plating solutions. These include using 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 olefins and alkynes and other substances.

[0008] WO 2015 / 187402 discloses an electroless nickel alloy plating bath comprising one or more dicarboxylic acids and one or more alpha hydroxycarboxylic acids.

[0009] WO2018 / 220220 discloses an electroless nickel alloy plating bath for preparing a data storage device, wherein all complexing agents contain at least two carboxylic acid moieties.

[0010] CN1 09112509A discloses a highly corrosion-resistant chemical nickel plating solution and a preparation method thereof, wherein the chemical nickel plating solution comprises nickel sulfate, sodium hypophosphite, sodium citrate, lactic acid, propionic acid and acetic acid as well as a specific wetting agent and stabilizer.

[0011] Purpose of the invention

[0012] It is therefore an object of the present invention to provide an electroless nickel alloy plating bath which improves the corrosion protection of metal substrates treated by said plating bath.

[0013] Another object of the present invention is to provide an electroless nickel alloy plating bath which is stable and does not show any fouling.

[0014] Yet another object of the present invention is to provide an electroless nickel alloy plating bath having a sufficient plating rate.

[0015] It is a further object of the present invention to provide an electroless nickel alloy plating bath which produces a nickel alloy deposit that adheres well to the underlying substrate surface, for example when plated on a metal surface such as aluminum or an aluminum alloy. Summary of the invention

[0016] The above objects are 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 the electroless nickel alloy plating bath according to the invention and its use.

[0017] The electroless nickel alloy plating bath according to the present invention comprises:

[0018] a) nickel ions;

[0019] b) another reducible metal ion selected from the group consisting of molybdenum ions, rhenium ions, tungsten ions, copper ions, oxygen-containing ions thereof, and mixtures thereof;

[0020] c) at least one reducing agent suitable for reducing nickel ions and further reducible metal ions to their corresponding metallic states; preferably selected from the group consisting of hypophosphorous acid, hypophosphite salts and mixtures thereof; and

[0021] d) complexing agents CA1, CA2, CA3 and optionally (preferably not optionally, but compulsorily, forcibly, necessarily; i.e. not optional) CA4,

[0022] Among them, CA1, CA2, CA3, and CA4 are all different from each other;

[0023] wherein each of CA1 and CA2 is independently selected from the group consisting of: a compound having at least two carboxylic acid moieties, a corresponding salt thereof, and a mixture thereof;

[0024] wherein CA3 is selected from the group consisting of: an aliphatic compound having exactly one carboxylic acid moiety, its corresponding salt, and a mixture thereof; and

[0025] Wherein CA4 is selected from the group consisting of: an aromatic compound having at least one carboxylic acid moiety, its corresponding salt and a mixture thereof.

[0026] The two complexing agents CA1 and CA2 are different compounds having at least two carboxylic acid moieties, their corresponding salts and mixtures thereof.

[0027] The electroless nickel alloy plating bath according to the present invention is used to deposit a nickel alloy onto at least one surface of at least one substrate.

[0028] A method for depositing a nickel alloy onto at least one surface of a substrate, the method comprising the following method steps in sequence:

[0029] A) providing a substrate comprising at least one surface;

[0030] B) contacting at least one surface of the substrate with an electroless nickel alloy plating bath according to the present invention (preferably a plating bath as preferably described herein throughout) thereby depositing a nickel alloy onto at least one surface of the substrate.

[0031] The nickel alloy deposit may be obtained by deposition from an electroless nickel alloy plating bath according to the present invention, preferably a plating bath as preferably described herein throughout.

[0032] The electroless nickel alloy plating bath according to the invention and the method according to the invention are suitable for providing a nickel alloy deposit having an attractive bright or semi-bright appearance. In addition, the nickel alloy deposit adheres well to the underlying substrate surface.

[0033] The electroless nickel alloy plating bath according to the present invention is stable and does not show fouling during plating for a sufficient time to be economically used. DETAILED DESCRIPTION

[0034] The percentages in this specification are weight percentages (wt.-%), unless otherwise stated. Unless otherwise stated, the 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 in this document. In addition, "layer" and "deposit" are also used synonymously in this specification. Scaling refers to the undesirable decomposition of the plating bath. It should be understood that the preferred embodiments of the invention described in this specification can be combined, unless this is technically infeasible or specifically excluded.

[0035] In the context of the present invention, the carboxylic acid moiety is a -C(=O)OH group. If not explicitly stated, this preferably includes its salts. The term "CX-CY-compound" according to the present invention refers to a compound having X to Y carbon atoms (including any carbon atoms of the carboxylic acid moiety); wherein X and Y refer to natural numbers, and X may be less than Y.

[0036] The nickel alloy of the present invention comprises elemental 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.

[0037] Electroless nickel alloy plating bath according to the present invention

[0038] The electroless nickel alloy plating bath of the present invention contains nickel ions. The nickel ions can 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 methanesulfonate, nickel sulfamate and mixtures thereof.

[0039] The concentration of nickel ions in the electroless nickel alloy plating bath can vary widely and preferably ranges from 0.01 mol / L to 1.0 mol / L, more preferably from 0.03 mol / L to 0.8 mol / L, even more preferably from 0.04 mol / L to 0.5 mol / L, yet even more preferably from 0.05 mol / L to 0.3 mol / L, most preferably from 0.05 mol / L to 0.1 mol / L.

[0040] The electroless nickel alloy plating bath of the present invention comprises additional reducible metal ions (in addition to nickel ions). Additional reducible metal ions are selected from the group consisting of: platinum ions, rhenium ions, tungsten ions, copper ions and mixtures thereof. Additional reducible metal ions can be provided by any water-soluble salt or any water-soluble complex of these additional reducible metals. Preferably, platinum ions are provided by any one of molybdic acid, alkaline molybdates (e.g., Na2MoO4), ammonium molybdate and mixtures thereof. Preferably, tungsten ions are provided by any one of tungstic acid, alkaline tungstates (e.g., Na2WO4), ammonium tungstate and mixtures thereof. Preferably, rhenium ions are provided by any one of perrhenic acid, alkaline perrhenate (e.g., NaReO4), ammonium perrhenate and mixtures thereof. Preferably, copper ions are provided by any one of copper iodide, copper iodate, copper chloride and / or copper sulfate. Platinum ions are preferably used as ecologically unimportant stabilizers and alloy components. 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 platinum ions as additional reducible metal ions. In another preferred embodiment of the present invention, the electroless nickel alloy plating bath of the present invention preferably contains a mixture of platinum ions and copper ions as additional reducible metal ions. More preferably, the electroless nickel alloy plating bath of the present invention contains neither any tungsten ions nor any rhenium ions, most preferably, if copper ions and / or platinum ions are present.

[0041] Therefore, preferred is the electroless nickel alloy plating bath of the present invention, wherein the additional reducible metal ions are platinum ions, copper ions or a mixture thereof; preferably, the additional reducible metal ions are platinum ions or a mixture of platinum ions and copper ions.

[0042] Insoluble components of molybdenum, rhenium and tungsten, such as molybdenum disulfide, are detrimental to the nickel alloy deposit characteristics and are therefore preferably not used in the electroless nickel alloy plating baths according to the present invention.

[0043] The total concentration of the additional reducible metal ions in the electroless nickel alloy plating bath may vary and is preferably within the range of 5 to 10 % based on the total volume of the electroless nickel alloy plating bath. -5 Up to 1*10 -2 mol / L, more preferably 1*10-4 Up to 5*10 - 3 mol / L, and even more preferably 2.5*10 -4 Up to 2.5*10 -3 mol / L. If more than one type of additional reducible metal ions is included in the electroless nickel alloy plating bath, the total concentration of all additional reducible metal ions used is preferably within the range defined above (ie the total concentration thereof).

[0044] In those cases where the electroless nickel alloy plating bath of the present invention contains a mixture of platinum ions and copper ions as the additional reducible metal ions, the total concentration of platinum ions and copper ions in the electroless nickel alloy plating bath may vary and is preferably in the range of 1 to 10 based on the total volume of the electroless nickel alloy plating bath. -5 (Preferably from 5*10 -5 ) to 1*10 -2 mol / L, more preferably 1*10 -5 (Preferably from 5*10 -5 ) to 5*10 -3 mol / L, and even more preferably 1*10 -5 (Preferably from 5*10 -5 ) to 5*10 -4 mol / L. Preferably, the electroless nickel alloy plating bath of the present invention comprises more platinum ions than copper ions based on molar concentration. More preferably, the total concentration of platinum ions and copper ions in the electroless nickel alloy plating bath may vary and is preferably in the range of 1*10 mol / L based on the total volume of the electroless nickel alloy plating bath. -5 (Preferably from 5*10 -5 ) to 1*10 -2 mol / L, more preferably 1*10 -5 (Preferably from 5*10 -5 ) to 5*10 -3 mol / L, and even more preferably 1*10 -5 (Preferably from 5*10 -5 ) to 5*10 -4 mol / L, and the molar ratio of platinum ions to copper ions is in the range of 1:1 to 30:1, preferably 5:1 to 20:1, and more preferably 10:1 to 15:1.

[0045] Concentrations outside of the above ranges may be useful in some cases, depending on the desired additional metal content in the nickel alloy deposit to be formed.

[0046] The electroless nickel alloy plating bath of the present 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 suitable for reducing nickel ions and other reducible metal ions to their corresponding metallic states. Preferably, the at least one reducing agent is selected from the group consisting of:

[0047] - hypophosphite compounds, such as hypophosphorous acid and hypophosphites, such as alkaline hypophosphites (e.g. sodium hypophosphite or potassium hypophosphite), ammonium hypophosphite, nickel hypophosphite, etc.;

[0048] - boron-based reducing agents, such as aminoboranes, e.g. dimethylaminoborane (DMAB) and morpholineborane, and borohydrides, e.g. sodium borohydride;

[0049] - hydrazine; and

[0050] - hydrazine derivatives (such as hydrazine sulfate, hydrazine hydrochloride, hydrazine hydrate and other such components which can be used as reducing agents in the context of the present invention).

[0051] In the case of using hypophosphite compounds as reducing agents, a nickel alloy deposit comprising phosphorus is obtained. Such reducing agents provide a source of phosphorus in the deposited nickel alloy.

[0052] Borane-based reducing agents produce a nickel alloy deposit comprising boron as well as a hypophosphite compound, and borane-based reducing agents produce a nickel alloy deposit comprising phosphorus and boron.

[0053] Nitrogen-based reducing agents such as hydrazine and hydrazine derivatives provide neither phosphorus nor boron to be incorporated into the nickel alloy.

[0054] The at least one reducing agent is more preferably selected from the group consisting of: hypophosphorous acid, hypophosphite and a mixture of the above substances. These reducing agents are preferred because the phosphorus built into the nickel alloy of the present invention particularly significantly improves the magnetic properties of these nickel alloy deposits and produces (heat-resistant) paramagnetic nickel alloys. The introduction of high phosphorus amounts (e.g., 10wt.-% or more) also improves corrosion protection. Even more preferably, at least one reducing agent is selected as a hypophosphite because these salts are cost-effective and easy to use. The molar concentration of at least one reducing agent is generally in excess of the amount sufficient to reduce the nickel ions and other reducible metal ions in the electroless nickel alloy plating bath. The concentration of the reducing agent preferably ranges from 0.01mol / L to 3.0mol / L, more preferably from 0.1mol / L to 1mol / L.

[0055] 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; aliphatic compounds are preferably non-cyclic.

[0056] 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 (-NH2), halides, olefin double bonds (-C=C-) and triple bonds (-C≡C-). The latter two naturally require that two hydrogen atoms of adjacent carbon atoms be replaced in theory. More preferably, the optional functional group is selected from the group consisting of: hydroxyl and double bonds. Even more preferably, the optional functional group is a hydroxyl.

[0057] More preferably, the electroless nickel alloy plating bath comprises complexing agents CA1 and CA2, which 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, their corresponding salts and mixtures of the above substances.

[0058] Even more 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.

[0059] Preferably, the complexing agent CA1 is an unfunctionalized aliphatic C2-C12-dicarboxylic acid and / or its salt. Even more preferably, it is an unfunctionalized aliphatic C3-C6-dicarboxylic acid and / or its salt. Even more preferably, 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, its salt and a mixture of the above substances. Most preferably, the complexing agent CA1 is malonic acid and / or its salt.

[0060] Preferably, complexing agent CA2 is a functionalized or unfunctionalized (preferably functionalized) aliphatic C3-C12-dicarboxylic acid and / or its salt, preferably a functionalized or unfunctionalized (preferably functionalized) aliphatic C4-C6-dicarboxylic acid and / or its salt. More preferably, complexing agent CA2 comprises at least one hydroxyl group (and is therefore hydroxy-functionalized). Even more preferably, complexing agent CA2 is a hydroxy-functionalized aliphatic C4-C6-dicarboxylic acid and / or its salt. Even more preferably, complexing agent CA2 is selected from the group consisting of: malic acid, tartaric acid, 1-hydroxyglutaric acid, 2-hydroxyglutaric acid, 1-hydroxyhexanedioic acid, 2-hydroxyhexanedioic acid, 3-hydroxyhexanedioic acid, a mixture of its salt and the above-mentioned substances. Most preferably, complexing agent CA2 is malic acid and / or its salt.

[0061] Preferably, complexing agent CA3 is a functionalized or unfunctionalized aliphatic C1-C5-monocarboxylic acid and / or its salt, preferably a functionalized or unfunctionalized aliphatic C2-C4-monocarboxylic acid and / or its salt. More preferably, complexing agent CA3 is propionic acid and / or its salt. 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 preferred embodiments of CA1, CA2 and CA3 can be combined.

[0062] Preferably, complexing agent CA4 is a functionalized (preferred in some cases) or unfunctionalized (preferred in some cases) aromatic carboxylic acid and / or its salt. Preferred functionalization is hydroxyl functionalization. "Aromatic carboxylic acid" is a compound comprising at least one COOH group (and its related salt) and at least one aromatic ring. The aromatic ring may contain heteroatoms, preferably the aromatic ring does not contain heteroatoms. Preferably, at least one COOH group is directly bonded to the aromatic ring, such as in, for example, benzoic acid, salicylic acid. More preferably, CA4 is benzoic acid and / or its salt. Even more preferably, CA4 is sodium benzoate.

[0063] In a very preferred embodiment of the present invention, complexing agents CA1, CA2, CA3 and C4 are selected from each other to represent respective different complexing agents according to the preferred embodiments described above with respect to CA1, CA2 and CA3.

[0064] Particularly preferred is an electroless nickel alloy plating bath according to the present invention, wherein 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 (particularly, the complexing agent CA1 is malonic acid and / or its salts); 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 thereof (particularly, the complexing agent CA2 is malic acid and / or its salts); and the complexing agent CA3 is selected from the group consisting of aliphatic monocarboxylic acids, salts thereof and mixtures thereof. Most preferably, the above substances combined with the complexing agent CA4 are benzoic acid and / or its salts.

[0065] 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 200mmol / 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 150mmol / 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 300mmol / 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 even more preferably from 30 to 75mmol / L. Preferably, the total concentration of complexing agents CA1, CA2, CA3 and CA4 is at least 0.15 mol / L, more preferably at least 0.20 mol / L, even more preferably at least 0.22 mol / L.

[0066] 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.

[0067] The electroless nickel alloy plating bath according to the present invention is preferably an aqueous solution. The term "aqueous solution" means that the main liquid medium as solvent in the solution is water. Further liquids miscible with water may be added, such as alcohols and other polar organic liquids miscible with water. Preferably at least 95 wt.-%, more preferably 99 wt.-% of all solvents used are water because of their ecologically benign characteristics. The electroless nickel alloy plating bath according to the present invention is preferably prepared by dissolving all components in an aqueous liquid medium, preferably in water.

[0068] The electroless nickel alloy plating bath according to the present invention may be acidic, neutral or alkaline. Acidic or alkaline pH regulators such as (mineral) acids or bases may be selected from a wide range of substances, such as ammonia, ammonium hydroxide, sodium hydroxide, hydrochloric acid, sulfuric acid, etc. The pH of the electroless nickel alloy plating bath according to the present invention is preferably about 2 to 12. In one embodiment, the electroless nickel alloy plating bath according to the present invention preferably has a neutral or acidic pH value (hereinafter referred to as "acidic electroless nickel alloy plating bath"). This is particularly useful if platinum ions and / or rhenium ions are selected as additional reducible metal ions; in particular, if platinum is selected as the only additional reducible metal ion. More preferably, the acidic electroless nickel alloy plating bath according to the present invention has a pH value in the range of 3.5 to 7, even more preferably 3.5 to 5.0, and even more preferably 4.0 to 4.8, most preferably 4.2 to 4.7. This allows for the best results in terms of high stability of the bath and the paramagnetic properties of the nickel alloy deposit formed from this bath (including its retention at high temperatures). If tungsten ions are chosen as the only additional reducible metal ions, a pH range of 8 to 10 is preferred.

[0069] The electroless nickel alloy plating bath according to the present invention may preferably include other additives such as pH buffers, wetting agents, accelerators, brighteners, other stabilizers known in the art, plating rate regulators such as those disclosed in European Patent Application EP 3 034 650 A1.

[0070] It is further preferred that the electroless nickel alloy plating bath of the present invention does not contain thiourea, which is commonly used as a stabilizer for electroless nickel plating baths due to its toxicity and ecological issues.

[0071] Method according to the invention

[0072] In step A) of the method according to the invention, a substrate comprising at least one surface is provided.

[0073] The electroless nickel alloy plating bath according to the present invention and the method according to the present invention can be used to plate nickel alloys on various substrates. Preferably, a metal substrate is used in the method according to the present invention. The metal substrate to be plated with nickel alloy is preferably selected from the group consisting of: copper, zinc, silver, palladium, iron, iridium, tin, aluminum, nickel, its alloys and mixtures of the above substances. Preferably, the substrate provided in step A) is completely made of metal (preferably at least one of the above-mentioned preferred metals), or it preferably comprises at least one surface, which is made of metal, preferably at least one of the above-mentioned preferred metals. This surface made of metal can also be one or more palladium activation layers, which are usually used to make non-conductive surfaces such as glass, plastics or ceramics accept nickel alloy plating.

[0074] Before step B), the substrate is subjected to optional pretreatment. Such pretreatments are known in the art. Typical pretreatments include etching, cleaning, zincating and activation steps. Useful pretreatments can improve the plating results by removing undesirable dirt or oxides from the substrate surface. Surface activation is generally understood to be the deposition of a thin and possibly discontinuous layer of, for example, palladium on an otherwise non-conductive surface, so that the surface is suitable for subsequent metal plating, preferably nickel alloy plating. Pretreatments can vary widely depending on the substrate provided. Some guidance can be found exemplarily in WO 2015 / 161959 A1 (page 13, line 11 to page 15, line 30).

[0075] In step B) of the method according to the invention, at least one surface of a substrate is brought into contact with an electroless nickel alloy plating bath according to the invention.

[0076] A substrate to be plated with nickel alloy may be plated to a desired thickness and deposition amount by contacting the substrate with the electroless nickel alloy plating bath of the present invention.

[0077] During deposition, i.e. most preferably during step B), the electroless nickel alloy plating of the present invention is preferably maintained in a temperature range of 20°C to 100°C, preferably 70°C to 95°C, more preferably 80°C to 90°C, even more preferably 83°C to 87°C.

[0078] The substrate may be contacted with the electroless nickel alloy plating bath of the present 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 desired use of the deposit or a product containing the deposit. As a non-limiting example, a range of 30 to 180 minutes, preferably 40 to 90 minutes, and more preferably a contact duration of 50 to 70 minutes is generally considered sufficient.

[0079] Nickel alloy deposits can be formed with a thickness 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 can 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 technical 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 known in the art.

[0080] Various ways of contacting the substrate with the electroless nickel alloy plating bath of the present invention are known in the art. For example, the substrate can be completely or partially immersed (which is preferred) in the electroless nickel alloy plating bath of the present invention, and the electroless nickel alloy plating bath of the present invention can be sprayed or wiped thereon.

[0081] Optionally, the electroless nickel alloy plating bath of the present invention is agitated before and / or during plating. Agitation can be achieved, for example, by mechanical movement of the electroless nickel alloy plating bath of the present invention such as shaking, stirring or continuous pumping of liquid or inherently by ultrasonic treatment, by high temperature or by gas feed (such as purging the aqueous plating bath with an inert gas or air).

[0082] Industrial standards require that the plating rate is preferably 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 also further improve the plating speed without sacrificing quality during plating.

[0083] The method 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 of the method of the invention only provide general guidance for practicing the invention.

[0084] The electroless nickel alloy plating bath of the present invention can be used to deposit a nickel alloy onto the surface of a substrate.

[0085] Nickel alloy deposit according to the invention and its use

[0086] The present invention further relates to a nickel alloy deposit obtainable by deposition from an electroless nickel alloy plating bath according to the invention. Surprisingly, although these deposits appear to be identical in elemental composition (i.e. the content of nickel, further reducible metal ions and optionally phosphorus and / or boron), the nickel alloy deposit formed from the electroless nickel alloy plating bath according to the invention exhibits excellent corrosion resistance.

[0087] The content (preferably total content) of further reducible metals in the nickel alloy deposit is preferably in the range of 0.5 to 5.0 wt.-%, more preferably 0.8 to 4.0 wt.-%, even more preferably 1.0 to 3.0 wt.-%, and yet even more preferably 1.2 to 2.5 wt.-%.

[0088] Preferably, the content of phosphorus and / or boron (more preferably phosphorus alone) in the nickel alloy deposit is 10 wt.-% or more, more preferably in the range of 10.0 to 16.0 wt.-%, preferably 10.5 to 15.0 wt.-%, and more preferably 11.0 to 14.5 wt.-%. Other preferred ranges are 10 wt.-% to 15 wt.-%, more preferably 10.5 wt.-% to 13 wt.-%, most preferably 10.8 wt.-% to 12.5 wt.-%.

[0089] The remainder of the nickel alloy deposit which is neither another reducible metal nor phosphorus and / or boron is typically predominantly nickel (typically ≥98 wt.-%, preferably ≥99 wt.-%, more preferably ≥99.9 wt.-% of said remainder), not taking into account trace impurities typically present in technical raw materials and other materials co-deposited (such as those derived from, for example, organic impurities and stabilizers). Most preferably, the nickel alloy deposit according to the invention consists (essentially) of nickel, molybdenum and phosphorus, or (essentially) of nickel, molybdenum, copper and phosphorus (not taking into account trace impurities typically present in technical raw materials and other materials unintentionally co-deposited (such as those derived from, for example, organic impurities and optional stabilizers).

[0090] The present invention further relates to the use of a nickel alloy deposit obtainable by deposition from an electroless nickel alloy plating bath according to the present invention and to the method of the present invention. This nickel alloy deposit is preferably used to protect a workpiece from environmental acidic corrosive conditions. "Environment" refers to the environment of the workpiece such that the workpiece is likely to experience acidic corrosive conditions, most preferably under outdoor natural conditions.

[0091] The details and preferred embodiments described for one aspect of the present invention are applicable to the other aspects by mutatis mutandis and are not described again in order to avoid unnecessary repetition.

[0092] The invention will now be illustrated by reference to the following non-limiting examples.

[0093] Examples

[0094] Unless otherwise stated in the following, commercial products were used as described in the technical data sheets available on the filing date of this specification. 155 (soaking cleaner) and 701 (Electric Cleaner) is a product of Atotech Deutschland GmbH.

[0095] In all plating experiments described below, a 0.7 dm 2The panels were pre-treated as described below before being plated with nickel alloy.

[0096]

[0097] Determination of thickness and deposition rate of metal or metal alloy deposits

[0098] Use XRF instrument Fischerscope XDV-SDD (Fischer GmbH, Germany) to measure phosphorus content and deposition thickness at 5 points of each substrate. By assuming the layered structure of the deposit, the layer thickness can be calculated from this XRF data. The coating rate is calculated by dividing the layer thickness obtained by the time required to obtain the layer thickness.

[0099] pH Measurement

[0100] Use a pH meter (WTW, Typ pH 3110, electrode: 41, gel electrode with temperature sensor, reference electrolyte: 3 mol / L KCl) at 25°C to measure pH. Continue measuring until the pH becomes constant, but in any case for at least 2 minutes. Calibrate the pH meter before use with buffer solution standards with pH values ​​of 2, 4 and 7 provided by Fluka and Certipur.

[0101] Composition of deposited nickel alloy

[0102] The composition of the deposited nickel alloy was measured using X-ray photoelectron spectroscopy (VersaProbe XPS, Physical Electronics GmbH).

[0103] Working Example

[0104] For comparison reasons, several nickel alloy plating baths of the present invention (1 L each) were prepared containing the following components:

[0105] - Nickel ions 6g / L (102.2mmol / L, provided in the form of nickel sulfate),

[0106] - Sodium hypophosphite 33g / L (0.375mol / L),

[0107] -Molybdenum ion 24mg / L (2.50*10 -4 mol / L, provided in the form of sodium molybdate),

[0108] -Copper ion 2.0mg / L (3,15*10 -5mol / L, provided as copper(II) sulfate pentahydrate),

[0109] - complexing agent at different concentrations (in g / L) as given in Table 1,

[0110] - pH was adjusted to 4.6 with ammonia solution (25 wt.-% in water)

[0111] The temperature of the nickel alloy plating bath was set to 86°C and the substrate was immersed in the bath for 60 minutes.

[0112] Table 1: Examples 1 to 16

[0113] # 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 <![CDATA[[N / mm 2 ]]]> -17 -20 -14 -17 -18 -8 -19 -20 -20 jump over -20 -19 -18 -18 -15 -6

[0114] The first tests using the electroless nickel alloy plating baths of the present invention (Examples 2 to 5, 7 to 11 and 13 to 16) showed sufficient plating rates and phosphorus contents even though different amounts of CA1, CA2, CA3 and CA4 were used.

[0115] In order to further test and describe the advantages of the present invention, Example 14 was selected as a representative of the present invention.

[0116] Corrosion test 1 (time)

[0117] Corrosion tests were carried out according to standard AASS–DIN EN ISO 92271.

[0118] Material: Q panel type QD RA < 0.5 μm; deposit thickness ≈ 10 μm

[0119] The defect area as red rust is determined and compared to the total area ("Relative Defect Area") and rated according to the following scheme:

[0120] If no defects are detected, i.e. the relative defect area is 0%, a grade of 10 is assigned. Therefore, the following grades are assigned (with the corresponding relative defect areas in brackets): 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%).

[0121] Table 2: Ratings in corrosion test 1 after a certain amount of time

[0122] 0 hours 24 hours 48 hours 72 hours 96 hours Example 12 (Comparison) 10 8 7 6 5 Example 14 (present invention) 10 10 10 9 8

[0123] As shown in Table 2, Example 14 (according to the present invention) shows significantly improved corrosion resistance compared to Example 12 (comparative). In Example 12, no aromatic carboxylic acid was used. Therefore, the aromatic carboxylic acid clearly has a beneficial effect on corrosion resistance.

[0124] Corrosion Test 2 (MTO)

[0125] Based on commercially available products ( HP 1151, a product of Atotech), additional tests were performed with another comparative example; referred to hereinafter as Example 17. This comparison allowed an in-depth study of the corrosion performance.

[0126] Example 17 is based on the general formula listed above, but without the use of copper ions and molybdenum ions. In addition, Example 17 contains three carboxylic acids corresponding to CA1, CA2 and CA3, but does not contain an aromatic carboxylic acid (ie, does not contain CA4).

[0127] Corrosion test 2 was also carried out according to standard AASS–DIN EN ISO 9227.

[0128] Table 3: Corrosion Test 2 - Determination of time until >1% red rust on surface (in hours)

[0129] MTO* 0 2 4 6 Example 14 (present invention) 312 hours 312 hours 224 hours 36 hours Example 17 (Comparison) 204 hours 156 hours 100 hours 12 hours

[0130] *Indicates metal flip

[0131] Table 3 shows that also for corrosion test 2, a significant improvement in corrosion resistance was observed. Further experiments showed that the improved effect was due to the presence of CA4 (data not shown).

[0132] Intrinsic stress test

[0133] Curved bar

[0134] The stress in the coating is measured by using a stress bar with two fingers, which are painted on one side. The test bar is made of chemically etched beryllium copper alloy and has spring-like properties. Before the stress measurement, the plating rate of the bath is determined with an accuracy of ±10% to determine the plating time for stress measurement. After surface cleaning by appropriate pretreatment, the stress bar fingers are electrically contacted with the test panel and both are immersed in the treatment bath very carefully. Based on the known plating rate, the plating duration is calculated to produce a coating thickness of 10μm. After plating, the test bar is rinsed with deionized water and carefully dried using a paper towel. Since the stress bar fingers 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 bar fingers will be mounted on a test bench, which measures the distance the test bar fingers are spread out after plating. The distance U determines the incremental distance between the stress bar fingers and is included in the calculation of the N / mm 2 The formula for calculating sediment stress is given in Figure 2.

[0135]

[0136] T is the deposit thickness in μm (micrometers), and K is the bar calibration constant provided by the supplier. Each batch of test bars 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 bars. The K value will be provided with each batch of test bars provided by Specialty Testing & Development Co. Stress is determined to be compressive or tensile in nature. If the test bar legs are spread outward on the plated side, the deposit stress is essentially tensile. If the test bar legs are spread inward on the plated side, the deposit stress is essentially compressive. Compressive stress is given as a negative number by convention, so that the result of the above equation is multiplied by -1 in the case of compressive stress.

[0137] The intrinsic stress test is performed during the bath life by relating the stress value to the concentration of phosphite (abbreviated OP in the following). OP is a suitable indicator of the bath age, since phosphite is a reaction product of the oxidation of hypophosphite and accumulates over time.

[0138] Table 4: Intrinsic stress

[0139]

[0140] Table 4 shows that the initial (ie, OP=0) stress values ​​are very similar / close to each other. Furthermore, the absolute values ​​are consistent with the stress values ​​based on OP=0 also shown in Table 1.

[0141] However, after aging, Table 4 shows that the presence of aromatic carboxylic acids improves the compressive stress profile in long-term bath utilization. This means that the presence of aromatic carboxylic acids produces improved resistance to increasing OP concentrations and thereby maintains internal stress closer to the optimal level (see Example 14: "20" vs. Example 17: "92"). Thus, as shown in Example 14, more optimized compressive stress levels are maintained until higher bath ages, especially if OP concentrations above 100 g / L are reached.

[0142] Bath stability

[0143] The beaker stability test was performed as follows:

[0144] This 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. A high-shaped 1-liter beaker is first cleaned and stripped with a 1:1 HNO3 stripper solution for 1 hour to avoid any residue on the bottom and walls of the beaker that may negatively affect the test. Then take 1 liter of the EN bath solution (test solution) and treat it as described below. Use a stirrer and set it to 250 rpm. When the operating temperature is reached, the test begins. The EN test solution is first kept free of plating for 1 hour. The bottom and walls of the beaker are then checked for any nickel deposits. If none are seen, the beaker test can continue and a pre-treated 1dm 2 Mild steel plate. The plate must be plated for 1 hour without any replenishment. When this is over, one cycle is achieved. Therefore, one cycle corresponds to 1 hour without plating + 1 hour of plating. Replenishment is carried out after the plating period. If no precipitation or nickel deposition occurs on the bottom or walls of the beaker, the test can be continued with 1 hour without plating and 1 hour of plating in the next cycle. The beaker test ends when extensive plating or plating out is visible on the bottom or walls of the beaker. The number of cycles achieved is recorded. With the number of cycles achieved, the stability can be evaluated.

[0145] For the following test procedures, the 1 liter samples were taken from treatment baths at different ages of the respective treatment baths. The samples taken at 0 MTO corresponded to newly prepared treatment baths, with higher MTOs corresponding to increasing bath ages.

[0146] Table 5: Beaker stability test (number of cycles)

[0147] MTO* 0 2 4 6 Example 14 (present invention) 5 5 5 5 Example 17 (Comparison) 3 4 4 3.5

[0148] *Indicates metal flip

[0149] Table 5 shows that the samples taken from the treatment according to Example 14 had higher stability (5 cycles each) compared to the samples taken from the treatment according to Example 17. Although Example 17 showed a relatively constant number of cycles (3 to 4 cycles each), the absolute stability was improved by at least one cycle in the presence of the aromatic carboxylic acid compound.

[0150] 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.The specification and examples are intended to be exemplary only, with the true scope of the invention being limited only by the following claims.

Claims

1. An electroless nickel alloy plating bath comprising: a) nickel ions; b) another reducible metal ion which is a mixture of platinum ions and copper ions; c) at least one reducing agent suitable for reducing the nickel ions and the additional reducible metal ions to their respective metallic states; preferably selected from the group consisting of hypophosphorous acid, hypophosphite salts and mixtures thereof; and d) complexing agents CA1, CA2, CA3 and CA4, wherein CA1, CA2, CA3 and CA4 are different from each other; wherein each of CA1 and CA2 is independently selected from the group consisting of: a compound having at least two carboxylic acid moieties, a corresponding salt thereof, and a mixture thereof; wherein CA3 is selected from the group consisting of: an aliphatic compound having exactly one carboxylic acid moiety, its corresponding salt, and a mixture 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 concentration of the complexing agent CA1 ranges from 50 to 300 mmol / L; The concentration of the complexing agent CA2 ranges from 50 to 200 mmol / L; The concentration of the complexing agent CA3 ranges from 40 to 1000 mmol / L; and The concentration of the complexing agent CA4 ranges from 7 to 150 mmol / L.

2. The electroless nickel alloy plating bath according to claim 1, characterized in that 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, their corresponding salts 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. An electroless nickel alloy plating bath according to any one of the preceding claims, characterised in that The complexing agent CA1 is an unfunctionalized aliphatic C2-C12-dicarboxylic acid and / or a salt thereof, preferably an unfunctionalized aliphatic C3-C6-dicarboxylic acid and / or a salt thereof.

4. The electroless nickel alloy plating bath according to claim 1 or 2, 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 claim 1 or 2, characterized in that The complexing agent CA2 is a functionalized or unfunctionalized aliphatic C3-C12-dicarboxylic acid and / or a salt thereof, preferably a hydroxy-functionalized aliphatic C4-C6-dicarboxylic acid and / or a salt thereof.

6. The electroless nickel alloy plating bath according to claim 1 or 2, 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 thereof.

7. The electroless nickel alloy plating bath according to claim 1 or 2, characterized in that The complexing agent CA3 is a functionalized or unfunctionalized aliphatic C1-C5-monocarboxylic acid and / or its salt, preferably a functionalized or unfunctionalized aliphatic C2-C4-monocarboxylic acid and / or its salt; more preferably CA3 is propionic acid and / or its salt.

8. The electroless nickel alloy plating bath according to claim 1 or 2, 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 claim 1 or 2, characterized in that It has a pH value ranging from 3.5 to 5.0, preferably from 4.0 to 4.8, more preferably from 4.2 to 4.

7.

10. The electroless nickel alloy plating bath according to claim 1 or 2, characterized in that Based on the total volume of the electroless nickel alloy plating bath, the additional reducible metal ion has a volume of 1*10 -4 Up to 5*10 -3 Total concentration in the mol / L range.

Images