Classifications

• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
  • C23C18/16—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by reduction or substitution, e.g. electroless plating
  • C23C18/1601—Process or apparatus
  • C23C18/1633—Process of electroless plating
  • C23C18/1646—Characteristics of the product obtained
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
  • C23C18/16—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by reduction or substitution, e.g. electroless plating
  • C23C18/31—Coating with metals
  • C23C18/32—Coating with nickel, cobalt or mixtures thereof with phosphorus or boron
  • C23C18/34—Coating with nickel, cobalt or mixtures thereof with phosphorus or boron using reducing agents
  • C23C18/36—Coating with nickel, cobalt or mixtures thereof with phosphorus or boron using reducing agents using hypophosphites
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
  • C23C18/16—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by reduction or substitution, e.g. electroless plating
  • C23C18/48—Coating with alloys
  • C23C18/50—Coating with alloys with alloys based on iron, cobalt or nickel

Definitions

• the present invention relates to aqueous plating bath compositions for electroless deposition of nickel and nickel alloys.
• the present invention relates further to a method utilizing the aqueous plating bath compositions for electrolessly depositing nickel and nickel alloys.
• the aqueous plating bath compositions have high stability against undesired decomposition.
• the nickel and nickel alloy coatings obtained by the invention show high corrosion resistance and adhesion to the subjacent substrate.
• Such coatings are suitable as a functional coating in aerospace, automotive, electronics and chemical industries.
• the metal layers deposited from such aqueous plating bath compositions are also useful as barrier and cap layers in semiconducting devices, printed circuit boards, IC substrates and the like.
• the metal layers deposited are also suitable as overcoat for hard disks or rigid memory disks (RMD).
• Barrier layers are used in electronic devices such as semiconducting devices, printed circuit boards, IC substrates and the like to separate layers of different composition, e.g.substrate layers and further layers, and thereby prevent undesired diffusion between such layers of different composition.
• barrier layer materials in electronic devices is as a cap layer which is e.g. deposited onto copper to prevent corrosion of copper.
• Rigid memory disks are used as magnetic data storage media in hard disk drives.
• the disks are basically composed of a substrate, made of aluminum, glass or ceramics.
• An overcoat is deposited onto the substrate by a vacuum deposition process or an electroless metal plating process.
• the overcoat may consist of various metallic, mostly non-magnetic, alloys one of which may be a nickel phosphorus alloy layer.
• the overcoat provides e.g. a smooth surface onto which the magnetic recording layers are deposited. Further protective layers are coated onto the recording layers.
• compositions for electroless nickel plating solutions are known in the art.
• US Patent 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 exaltants to electroless nickel baths.
• US Patent 2,762,723 teaches the use of sulfide and sulfur bearing additives to an electroless nickel plating bath for improved bath stability.
• Patent application JP 2005-194562 discloses an electroless nickel plating bath containing indium compounds as bath stabilizers.
• US Patent 4,189,324 describes an electroless nickel plating solution including of a source of gallium that improves stability of the solution. None of the prior art documents teaches a specific mixture of stabilizing agents having a particular good stabilizing effect in electroless nickel plating compositions.
• the invention further relates to a method for deposition of nickel and nickel alloys by contacting the substrate to be plated with above described composition.
• aqueous plating bath composition for electroless deposition of nickel and nickel alloys is also abbreviated as “composition” herein.
• the invention relates to a method for stabilizing any electroless plating bath for deposition of nickel and nickel alloys by adding a mixture of stabilizing agents to the electroless plating bath.
• Electroless nickel plating compositions for applying nickel coatings are well known in the art and plating processes and compositions are described in numerous publications such as U.S. Patents Nos. 2,935,425 ; 3,338,726 ; 3,597,266 ; 3,915,716 and 4,780,342 .
• Electroless plating generally describes methods without using external current sources for reduction of metal ions. Plating processes using external current sources are commonly described as electrolytic or galvanic plating methods.
• chemical reducing agents like hypophosphite, boranes or formaldehyde are used to reduce the metal ions to their metallic form and thereby forming a deposit on the substrate.
• NiP deposition solutions comprise at least three ingredients dissolved in a solvent, typically water. They are (1) a source of the nickel ions, (2) a reducing agent and (3) a complexing agent for metal ions sufficient to prevent their precipitation in solution. A large number of suitable complexing agents for NiP solutions are described in the above noted publications. If hypophosphite is used as the reducing agent, the deposit will contain nickel and phosphorus. Similarly, if an aminoborane is employed, the deposit will contain nickel and boron as shown in U.S. Pat. No. 3,953,654 .
• the aqueous plating bath composition for electroless deposition of nickel and nickel alloys of the present invention comprises a source of nickel ions.
• the source of nickel ions may be provided by the use of any soluble salt such as nickel sulfate, nickel chloride, nickel acetate, nickel methyl sulfonate, nickel sulfamate and mixtures thereof.
• the concentration of the nickel ions in the composition may vary widely and preferably ranges from 0.01 mol/l to 1 mol/l, more preferably from 0.03 mol/l to 0.8 mol/l, even more preferably from 0.06 mol/l to 0.3 mol/l.
• the aqueous plating bath composition for electroless deposition of nickel and nickel alloys of the present invention further comprises at least one reducing agent.
• the at least one reducing agent is preferably a chemical reducing agent. Reducing agents provide the electrons needed to reduce metal ions to their metallic form and thereby form a metal deposit on a substrate.
• the at least one reducing agent is preferably a hypophosphite salt or hypophosphorous acid, more preferably a hypophosphite salt.
• the hypophosphite salt is supplied to the composition by any suitable source such as sodium, potassium, ammonium and nickel hypophosphite.
• Other reducing agents such as aminoboranes, borohydrides, hydrazine and derivatives thereof and formaldehyde may also suitably be employed.
• Two or more reducing agents may be employed as a mixture in the composition.
• the concentration of the at least one reducing agent is generally in molar excess of the amount sufficient to reduce the nickel ions in the composition.
• the concentration of the reducing agent preferably ranges from 0.01 mol/l to 3.0 mol/l, more preferably from 0.1 mol/l to 1 mol/l.
• a hypophosphite compound is used as the reducing agent
• a Ni-P alloy deposit is obtained.
• Such reducing agents provide the source of phosphorus in the deposited alloy.
• a borane-based compound as reducing agent leads to a NiB alloy deposit and a mixture of hypophosphite and borane-based compounds as the reducing agents leads to a ternary Ni-B-P alloy deposit.
• a nitrogen-based reducing agent such as hydrazine and derivatives thereof as well as formaldehyde as reducing agent lead to nickel deposits.
• the aqueous plating bath composition for electroless deposition of nickel and nickel alloys of the present invention may be acidic, neutral or alkaline.
• An acidic or an alkaline pH adjustor may be selected from a wide range of materials such as ammonium hydroxide, sodium hydroxide, hydrochloric acid, sulfuric acid and the like.
• the pH of the composition may range from about 2 to 12.
• the compositions are preferably acidic. More preferably, the pH of the acidic compositions ranges from 3.5 to 7, even more preferably from 3.5 to 6.5, most preferably from 3.5 to 5.5.
• the compositions are preferably alkaline. More preferably the pH of the alkaline compositions ranges from 7.5 to 12, even more preferably from 8 to 10, most preferably from 8 to 9.
• the aqueous plating bath composition for electroless deposition of nickel and nickel alloys of the present invention further comprises at least one complexing agent.
• a complexing agent (sometimes also referred to as chelating agent) or mixture of complexing agents is included in the composition for nickel and nickel alloy plating.
• a complexing agent keeps metal ions dissolved and prevents their undesired precipitation in solution.
• the at least one complexing agent is preferably selected from complexing agents for nickel ions and complexing agents for alloying metal ions, more preferably from complexing agents for nickel ions.
• the at least one complexing agent is preferably selected from the group comprising alkyl amines, ammonia, carboxylic acids, hydroxyl carboxylic acids, aminocarboxylic acids, salts of the aforementioned and mixtures thereof.
• carboxylic acids, hydroxylcarboxylic acids, aminocarboxylic acids and salts of the aforementioned or mixtures thereof may be employed as the at least one complexing agent.
• Useful carboxylic acids include the mono-, di-, tri- and tetra-carboxylic acids.
• the carboxylic acids may be substituted with various substituent moieties such as hydroxy or amino groups and the acids may be introduced into the composition as their sodium, potassium or ammonium salts.
• Some complexing agents such as acetic acid, for example, may also act as a pH buffering agent, and the appropriate concentration of such additive components can be optimised for any composition in consideration of their dual functionality.
• monocarboxylic acids such as acetic acid, hydroxyacetic acid (glycolic acid), aminoacetic acid
• Preferred carboxylic acids are acetic acid, aminoacetic acid, propanoic acid, 2-hydroxy propanoic acid, succinic acid, hydroxy succinic acid, adipic acid or 2-hydroxy-1,2,3-propane-tricarboxylic acid.
• mixtures of two or more of the above complexing/chelating agents are utilised in the composition according to the present invention.
• Alkyl amines may also be used as the at least one complexing agent, for example mono-, di- and trialkylamines.
• C 1 - C 3 alkyl amines, for example triethanolamine are preferred.
• Ammonia may also be used as the at least one complexing agent.
• the concentration of the at least one complexing agent or, in case more than one complexing agent is used, the concentration of all complexing agents in total preferably ranges from 0.01 mol/l to 3.0 mol/l, more preferably from 0.1 mol/l to 1.0 mol/l and even more preferably from 0.2 mol/l - 0.6 mol/l.
• the aqueous plating bath composition for electroless deposition of nickel and nickel alloys comprises a mixture of stabilizing agents according to (ii) comprising
• Stabilizing agents are compounds that stabilize an electroless metal plating solution against undesired plate out in the bulk solution and spontaneous decomposition.
• plate out means undesired and/or uncontrolled deposition of the metal on surfaces other than substrate surfaces.
• the indium ion may be selected from any indium ions, preferably from the group comprising indium(III) ions and indium(I) ions and mixtures thereof. More preferably, the indium ion is an indium(III) ion.
• the gallium ion may be selected from any gallium ions, preferably from the group comprising gallium(III) ions, gallium(I) ions and mixtures thereof. More preferably, the gallium ion is a gallium(III) ion.
• the indium ion or the gallium ion may be in the form of their salts.
• the salts of indium ions or gallium ions are preferably selected from the group comprising indium(III) sulfate (In 2 (SO 4 ) 3 ), indium(III) hydroxide (In(OH) 3 ), indium(III) oxide (In 2 O 3 ), indium(III) methane sulfonate (In(CH 3 -SO 3 ) 3 ), indium(III) nitrate (In(NO 3 ) 3 ), indium(III) chloride (InCl 3 ), indium(III) bromide (InBr 3 ), indium(III) fluoride (InF 3 ), indium(III) acetate (In(CH 3 -COO) 3 ), indium(I) chloride (InCI), indium(I) bromide (InBr), gallium(III) sulfate (Ga 2 (SO 4 ) 3 ), gallium(III) hydroxide (Ga(OH) 3 ), gallium(III) methane
• the concentration of the at least one metal ion according to (ii)a) preferably ranges from 0.01 mmol/l to 0.5 mmol/l, more preferably from 0.01 mmol/l to 0.1 mmol/l, even more preferably from 0.02 mmol/l to 0.08 mmol/l.
• Higher concentrations of the at least one metal ion according to (ii)a) result in deposition of nickel or nickel alloy layers of dull appearance and skip plating.
• Skip plating is a plating defect in which the coating undesirably does not cover all areas of the plated substrate.
• the mixture i.e.
• the combination, of metal ions according to (ii)a) with stabilzing agents according to (ii)b) allows to shift the lower concentration limit of metal ions according to (ii)a) to the lower values as described above, without impairing stability of the composition.
• concentration range of metal ions according to (ii)a) suitable for stabilizing the composition and any electroless plating bath for deposition of nickel and nickel alloys, and suitable for depositing nickel or nickel alloy layers of good quality is widened.
• the wider process window improves process control for plating.
• the at least one stabilizing agent according to (ii)b) is preferably selected from the group comprising iodide ion containing compounds and iodate ion containing compounds; more preferably iodide ion containing compounds.
• the iodide ion containing compounds are preferably selected from the group comprising potassium iodide, sodium iodide, ammonium iodide, calcium iodide, barium iodide, magnesium iodide, lithium iodide, zinc iodide, and hydrates of the aforementioned; more preferably potassium iodide, sodium iodide, ammonium iodide, and hydrates of the aforementioned; even more preferably potassium iodide and hydrates thereof.
• the iodate ion containing compounds are preferably selected from water soluble iodate salts.
• the water soluble iodate salts are preferably iodate salts of alkali metals or earth alkali metals.
• the iodate salt is preferably selected from the group comprising potassium iodate, sodium iodate, ammonium iodate, calcium iodate, barium iodate, magnesium iodate, lithium iodate and hydrates of the aforementioned; more preferably potassium iodate, sodium iodate, ammonium iodate, lithium iodate and hydrates of the aforementioned; even more preferably potassium iodate and hydrates thereof.
• the periodate ion containing compounds may be selected from the group comprising preferably metaperiodate ion containing compounds (IO 4 - ), and or-thoperiodate ion containing compounds (IO 6 5- ).
• the periodate ion containing compounds are preferably selected from the group comprising potassium metaperiodate (KIO 4 ), sodium metaperiodate (NaIO 4 ) and sodium ortho periodate (Na 3 H 2 IO 6 ).
• the concentration of the at least one stabilizing agent according to (ii)b) preferably ranges from 0.05 to 50.0 mmol/l, more preferably from 0.1 to 30.0 mmol/l, even more preferably from 0.5 to 10.0 mmol/l, and even more preferred from 1.0 mmol/l to 5.0 mmol/l.
• the stabilizing agents of the present invention are suitable to enhance the stability of the aqueous plating bath composition for electroless deposition of nickel and nickel alloys of the present invention against undesired, spontaneous decomposition.
• Undesired, spontaneous decomposition means undesired formation of a black precipitate, undesired plate out of nickel in the bulk solution or undesired and/or uncontrolled deposition of nickel, for example on the bottom of a plating tank or on other surfaces different from the substrate.
• the stabilizing effect is particularly pronounced when the stabilizing agents are used as a mixture, i.e. in combination.
• the combination of metal ions according to (ii)a) with stabilizing agents according to (ii)b) provides in particular a long life to the composition of the present invention.
• the bath stability imparted by the combination of stabilizing agents is much higher than the stabilizing effect of one of the stabilizing agents alone.
• the combination of stabilizing agents of the present invention has a synergistic effect on the bath stability.
• the combination of stabilizing agents of the present invention also imparts an improved resistance of the composition against contamination with catalytic metals.
• Contamination with catalytic metals may be caused by metal ions dissolving from the substrate material while in contact with the composition, or metal ions are dragged into the composition from pre-treatment or activation steps.
• Catalytic metals may be palladium, platinum, rhodium, ruthenium or mixtures thereof, preferably palladium.
• composition of the present invention containing a combination of stabilizing agents, namely metal ions according to (ii)a) and stabilizing agents according to (ii)b), are suitable for plating on electrically non-conductive substrates, on electrically conductive substrates, and on electrically semi-conductive substrates.
• the combination of stabilizing agents according to the invention has a synergistic effect on the bath stability and the composition containing the combination of stabilizing agents is much less prone to contamination with catalytic metals. Simultaneously, the combination of stabilizing agents according to the invention has only a low effect on the deposition rate, i.e. increasing the concentration of the stabilizing agents does not alter the deposition rate and the combination of stabilizing agents does not decrease the deposition rate of the composition of the present invention.
• the deposited nickel or nickel alloy layers are of good quality, i.e. the quality of the nickel or nickel alloy layers are not influenced disadvantageously by the combination of stabilizing agents according to the invention. The deposited nickel or nickel alloy layers completely cover the substrate surface; no skip plating is obtained.
• the deposited nickel or nickel alloy layers are of uniform thickness, adhere well to the substrate surface and have a good appearance. Good appearance means herein, that the nickel or nickel alloy layers have no pitting, no blistering, no increased nodular structure and no unusual color.
• the combination of stabilizing agents according to the present invention has no negative effect on the plating bath performance and no negative effect on the coating quality.
• the aqueous plating bath composition for electroless deposition of nickel and nickel alloys of the present invention further shows a high stability during idle periods.
• Idle periods are defined as time periods in which the operating parameters, like temperature or pH value, of a plating bath are adjusted to its desired value for plating operation, but no substrate is immersed in the plating bath.
• the combination of stabilizing agents according to the invention also keeps the composition stable against undesired, spontaneous decomposition during prolonged periods at high temperature while not plating. This effect is better than with stabilizing agents known in the art, e.g. tin ions, bismuth ions or antimony ions.
• compositions according to the present invention may include pH buffers, wetting agents, accelerators, brighteners, additional stabilizing agents etc.
• the composition may contain further organic stabilizing agents and/or further inorganic stabilizing agents. These materials are known in the art.
• the composition may contain further metal stabilizing agents such as Cu-, Se-, Sn-, Bi- or Sb-ions.
• concentration of the metal ions can vary and e.g. range between 0.1 - 100 mg/l, preferably between 0.1 - 50 mg/l, more preferably between 0.1 - 10 mg/l.
• the composition does not contain toxic heavy metals.
• the composition does preferably not contain lead, cadmium, antimony, bismuth, arsenic or mercury.
• the aqueous plating bath composition for electroless deposition of nickel and nickel alloys of the present invention may further comprise at least one alloying element.
• nickel alloy layers containing the alloying element are deposited from the composition.
• the at least one alloying element may be selected from phosphorus, boron, and a metal which is not nickel.
• the alloying elements phosphorus or boron may be comprised in the composition in the form of a hypophosphite salt, hypophosphorous acid or a borane-based compound, such as aminoboranes or borohydrides, as mentioned above as reducing agents.
• the metal which is not nickel may be comprised in the composition in the form of a water-soluble metal salt containing the ions of the alloying metal M.
• the optional alloying metal M is preferably selected from the group consisting of titanium, vanadium, chromium, manganese, zirconium, niobium, molybdenum, hafnium, tantalum, tungsten, copper, silver, gold, aluminum, iron, cobalt, palladium, ruthenium, rhodium, osmium, iridium, platinum, zinc, cadmium, gallium, indium, tin, antimony, thallium, lead, and bismuth. More preferably, the optional alloying metal M is selected from the group consisting of molybdenum, tungsten, copper, silver, gold, aluminum, zinc and tin.
• the concentration of the optional alloying metal M preferably ranges from 10 -5 to 0.2 mol/l, more preferably from 10 -4 to 0.2 mol/l, even more preferably from 10 -2 to 0.1 mol/l.
• Ni-M-P, Ni-M-B, and Ni-M-B-P are deposited.
• a water-soluble salt of an alloying metal M and a water-soluble salt of a second alloying metal M * are added to the composition.
• nickel alloy deposits comprising alloying metals M and M* are obtained.
• a suitable composition may be formed by dissolving the ingredients in water and adjusting the pH to the desired range.
• the indium or gallium salts may be dissolved in an acid prior to adding them to the composition.
• the present invention further relates to a method for electroless deposition of nickel and nickel alloys by contacting the substrate to be plated with the above described aqueous plating bath composition for electroless deposition of nickel and nickel alloys.
• the deposition method comprises the steps of
• the substrate to be nickel or nickel alloy plated may be plated to the desired thickness and deposit quantity by contacting the substrate with the composition.
• the inventive composition may be maintained over a temperature range of 20 °C to 100 °C, preferably 70 °C to 95 °C, more preferably 85 °C to 95 °C during deposition.
• a deposit thickness of up to 100 ⁇ m, or higher may be employed.
• the thickness of the nickel or nickel phosphorus (NiP) deposits varies between 1 - 60 ⁇ m. The thickness depends on the technical application and can be higher or lower for some applications. For example, if the nickel or NiP layer is deposited to provide a corrosion resistant coating, a thickness of between 30 - 60 ⁇ m is desired, while for electronics applications a thickness of between 1 - 15 ⁇ m is applied.
• the thickness of the nickel or nickel-phosphorus deposits preferably ranges from 9 to 13 ⁇ m.
• the thickness of the nickel or nickel-phosphorus deposits preferably ranges from 1 to 5 ⁇ m. Thicknesses of nickel or nickel alloy layers may be measured with x-ray fluorescence (XRF) which is known in the art.
• XRF x-ray fluorescence
• the present invention further relates to a method for stabilizing any electroless plating bath for deposition of nickel and nickel alloys, the method comprises the steps of
• the mixture of stabilizing agents comprises
• the electroless plating bath may be any electroless plating bath for deposition of nickel and nickel alloys.
• the electroless plating bath is the aqueous plating bath composition for electroless deposition of nickel and nickel alloys according to the present invention.
• the electroless plating bath may be a freshly prepared electroless plating bath.
• the electroless plating bath may be already used for some time for plating.
• the electroless plating bath may be stored for some time without plating. During storage the electroless plating bath may be kept at a temperature ranging from 15 to 100 °C.
• the concentrations of the stabilizing agents of the inventive mixture may be determined during plating or storage and replenished if below a threshold value. Replenishment is performed by adding the stabilizing agents of the inventive mixture or combination to the electroless plating baths.
• the mixture of stabilizing agents of the present invention keeps the electroless plating bath stable against undesired, spontaneous decomposition during prolonged periods of plating, during prolonged storage times and during prolonged periods at high temperature while not plating, e.g. idle periods.
• the overall consumption of metal ions according to (ii)a) as stabilizing agents is lower during plating if the inventive mixture of stabilizing agents is used. Therefore, the amount of metal ions according to (ii)a) which has to be replenished per metal turnover (MTO) is decreased in comparison to electroless plating baths that include only metal ions according to (ii)a) as stabilizing agents.
• MTO metal turnover
• a further advantage is that the metal ions according to (ii)a) can be employed in lower concentration ranges, thus preventing dull appearance of nickel or nickel alloy layers and skip plating while still ensuring stability of the composition.
• the stabilizing agents of the inventive mixture may be added as a solid or a powder or may be dissolved in a solvent prior to adding to the electroless plating baths.
• the indium or gallium salts may be dissolved in an acid prior to adding them to the electroless plating bath.
• the aqueous plating bath composition for electroless deposition of nickel and nickel alloys and the methods of the present invention are suitable to provide nickel and nickel alloy coatings having an attractive bright or semi-bright appearance.
• the compressive stress of the deposited nickel or nickel alloy layers is maintained.
• the mixture of stabilizing agents of the present invention does not shift the internal stress to neutral or tensile stress.
• the advantages of nickel or nickel alloy layers having compressive stress are high corrosion resistance and good adhesion to the substrate surface.
• a high phosphorus NiP alloy is herein defined as a metallic coating containing less than 91 wt.% Ni and more than 9 wt.% P, e.g. 10.5 wt.%. Generally, high phosphorus alloys contain up to 15 wt.% P.
• a nickel-phosphorus (NiP) alloy containing more than about 10.5% phosphorus is known as a high phosphorus NiP coating and is paramagnetic (non-magnetic) as plated.
• a mid phosphorus NiP alloy is herein defined as a metallic coating containing between 5 - 9 wt.% P.
• a low-phosphorus NiP alloy is herein defined as a metallic coating containing between 1 - 5 wt.% P.
• the aqueous plating bath composition for electroless deposition of nickel and nickel alloys and the methods of the present invention are suitable to provide nickel phosphorus alloy coatings with a wide range of P content of between 1-15 wt.% P.
• the composition and the methods of the present invention are particularly suitable for depositing nickel phosphorus alloys, e.g. high NiP alloys as defined above.
• the combination of stabilizing agents according to the present invention does not change the phosphorus content of the deposited nickel alloy layers compared to electroless nickel-phosphorus baths containing no stabilizer or single stabilizing agents according to (ii)a) or (ii)b).
• the combination of stabilizing agents according to the present invention has no negative effect on the bath performance and no negative effect on the coating quality.
• the phosphorus content of nickel alloy layers and the thickness of nickel or nickel alloy layers were measured by x-ray fluorescence (XRF) which is well known to persons skilled in the art.
• XRF x-ray fluorescence
• the XRF measurements make use of the characteristic fluorescence radiation emitted from a sample (substrate, deposit) being excited with x-rays.
• phosphorus content and layer thicknesses can be calculated.
• High NiP alloys are obtained when the plating process is performed at a plating rate of preferably between 5 - 14 ⁇ m / hour, more preferred 6 - 12 ⁇ m / hour, even more preferred 6 - 10 ⁇ m / hour.
• Such plating rate can be obtained by adjusting the plating parameters, like pH or temperature.
• High NiP alloys obtained by the composition according to the present invention contribute to generating alloys having high compressive stress.
• the stress values for example range between 0 to -70 N/mm 2 , preferably between 0 to - 50 N/mm 2 , more preferably between -30 to -50 N/mm 2 .
• Such deposits show high corrosion resistance and excellent adhesion to the underlying substrate they are plated on.
• the combination of stabilizing agents according to the present invention does also not change the stress of the deposited nickel-phosphorus layer compared to electroless nickel-phosphorus baths containing no stabilizer or only a single stabilizing agent.
• the combination of stabilizing agents according to the present invention has also no negative effect on the coating quality in terms of stress.
• the combination of stabilizing agents imparts a significantly higher stability to nickel and nickel alloy baths at comparable bath performance and coating quality.
• substrates can be metal plated with an aqueous plating bath composition for electroless deposition of nickel and nickel alloys and the methods of the present invention.
• the substrates to be metal plated can be selected from the group comprised of electrical non-conductive substrates, electrical conductive substrates, and electrical semi-conductive substrates.
• the electrical non-conductive substrates to be metal plated can be selected from the group comprising glass, ceramics, and plastics.
• Plastics can be selected from the group comprising acrylnitrile-butadiene-styrol-copolymer (ABS copolymer); polyamide; a mixture of an ABS copolymer and at least one other polymer which is different to the ABS copolymer; polycarbonate (PC); ABS/PC blends; epoxy resin; bismaleimide-triazine resin (BT); cyanate ester resin; polyimide; polyethylene terephthalate (PET); polybutylene terephthalate (PBT); polylactic acid (PLA); polypropylene (PP); and polyester.
• ABS copolymer acrylnitrile-butadiene-styrol-copolymer
• PC polycarbonate
• ABS/PC blends ABS/PC blends
• epoxy resin bismaleimide-triazine resin
• BT bismaleimide-triazine resin
• PBT polycyanate ester resin
• polyimide polyethylene terephthalate
• PET polybutylene tere
• the electrical conductive substrates to be metal plated can be selected from the group comprised of metallic substrates, and conductive metal oxides.
• the metallic substrates to be metal plated can be selected from the group comprised of copper, zinc, silver, gold, platinum, palladium, iron, iridium, tin, aluminum and nickel.
• the conductive metal oxides to be metal plated can be selected from indium tin oxide (ITO), antimony tin oxide (ATO) and aluminum doped zinc oxide (AZO).
• ITO indium tin oxide
• ATO antimony tin oxide
• AZO aluminum doped zinc oxide
• the electrical semi-conductive substrates to be metal plated can be selected from the group comprised of silicon, germanium, gallium, arsenide and silicon carbide.
• a stock solution of an electroless nickel plating bath comprising: Nickel sulfate hexahydrate 22.4 g/l Sodium orthophosphite (pre-aging salt) 60.0 g/l Lactic acid (90%) (complexing agent/chelating agent) 14.4 g/l Malic acid (complexing agent/chelating agent) 19.8 g/l Succinic acid (complexing agent/chelating agent) 6.1 g/l Sodium hypophosphite monohydrate (reducing agent) 24.0 g/l
• composition of the stock solution corresponds to the composition of the electroless nickel bath disclosed in patent application WO 2010/045559 A1 (Example 4 therein) with the exception that the present stock solution does not contain lead nitrate as a stabilizer.
• Sodium orthophosphite was contained in the stock solution as a pre-aging salt.
• Orthophosphite salts are by-products of the chemical reduction process when hypophosphite is used as the reducing agent. The amount of this by-product in an electroless nickel plating bath depends on how long the bath has been used. This bath age is referred to in the plating industry as the number of metal turnovers or MTOs of the bath.
• nickel salt and a reducing agent When an electroless nickel plating bath is used, nickel salt and a reducing agent must be replenished as nickel is plated, so as to continue the effective use (or life) of the bath.
• the bath When the amount of the replenished nickel salt is equal to the initial amount of nickel contained in the original plating bath, the bath is said to have plated one metal turnover (MTO).
• MTO metal turnover
• the amount of orthophosphite used herein corresponds to 2.5 MTO level.
• the stock solution did not contain any stabilizers.
• Indium ions and iodide ions were added as stabilizers. Indium ions were added in the form of indium(III) hydroxide and iodide ions were added in the form of potassium iodide. Concentrations of the stabilizers in the electroless nickel plating bath were as outlined in Table 2. One batch of the electroless nickel plating bath was used without any stabilizer as comparison. The electroless nickel plating bath had a pH value of 4.4.
• Stability of the electroless nickel plating baths containing the respective concentrations of stabilizers was measured by determining the stability number and by visual inspection.
• the stability number achieved for the investigated plating bath corresponds to the number of palladium test solution additions (each 0.2 ml) within a one minute interval to the plating bath until formation of a gray precipitate.
• the stability test was done twice for each plating bath sample. The average stability number is given in Table 2.
• the entry "5" for an electroless plating bath solely containing iodide ions as stabilizers corresponds to an addition of 5 times 0.2 ml of a palladium chloride solution to the plating bath. After 1 ml (5 times 0.2 ml/l added in one minute intervals) and 5 minutes, a gray precipitate occurs.
• the test for determining the stability number does not only show improved stability of electroless nickel plating baths containing the combination of stabilizing agents, but also an improved resistance of such electroless nickel plating baths against contamination with catalytic metals, like Pd.
• Aluminum plates were used as substrates for deposition of nickel-phosphorus alloy layers.
• the substrates were pre-treated as summarized in Table 1 in order to clean and double zincate the substrate surface prior to nickel deposition.
• Table 1 Pre-treatment of substrates Pre-treatment step Atotech Product Concentration Temp.
• the substrates were immersed in electroless nickel plating baths of compositions as described in Example 1. Deposition was done in 2L-beakers. Each beaker was placed on a heater and temperature was maintained at 89.5 °C. Mechanical agitation with 175 RPM was applied by a magnetic stirrer. Bath loading was 1.4 dm 2 /l corresponding to two substrates per bath volume. Deposition time was 60 minutes.
• the phosphorus content and deposit thickness were measured at 5 points of each substrate by XRF using the XRF instrument Fischerscope XDV-SDD (Helmut Fischer GmbH, Germany).
• the deposition rate was calculated by using the deposition time and the measured deposit thickness. Results are summarized in Table 2.
• the deposited nickel-phosphorus alloy layers completely covered the substrate surface; no skip plating was obtained.
• the deposited nickel-phosphorus alloy layers were of uniform thickness, adhered well to the substrate surface and had a good appearance with technical brightness and a typical gray color.
• the combination of stabilizing agents according to the present invention did neither decrease the deposition rate nor changed the phosphorus content of the deposited nickel alloy layers compared to electroless nickel plating baths containing no stabilizer or a single stabilizing agent.
• the combination of stabilizing agents according to the present invention had no negative effect on the bath performance and no negative effect on the coating quality.
• U is the number of increments spread
• T is the deposit thickness
• K is the strip calibration constant.
• the deposit thickness T was determined by XRF as described in Example 2.
• Stress was also determined to be of compressive or tensile nature. If the test strip legs were spread outward on the side that has been plated, the deposit stress was tensile in nature. If the test strip legs were spread inward on the side that has been plated, the deposit stress was compressive in nature.
• the stress of the deposited nickel-phosphorus alloy layer was measured to be between -35 and -45 N/mm 2 and thus, was compressive. Results are summarized in Table 2.
• Table 2 also shows that the combination of stabilizing agents according to the present invention did not change the stress of the deposited nickel-phosphorus layer compared to electroless nickel plating baths containing no stabilizer or only a single stabilizing agent. Thus, the combination of stabilizing agents according to the present invention had also no negative effect on the coating quality in terms of stress. In summary, the combination of stabilizing agents imparted a significantly higher stability to electroless plating baths for deposition of nickel and nickel alloys at comparable bath performance and coating quality.

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• 2014
  • 2014-11-26 EP EP14194890.1A patent/EP3026143A1/fr not_active Withdrawn
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