WO2025098869A1

WO2025098869A1 - An aqueous basic deposition composition for the electroless deposition of a metal on a surface of a substrate

Info

Publication number: WO2025098869A1
Application number: PCT/EP2024/080814
Authority: WO
Inventors: Lars Kohlmann; Heiko Brunner
Original assignee: Atotech Deutschland GmbH and Co KG
Current assignee: Atotech Deutschland GmbH and Co KG
Priority date: 2023-11-09
Filing date: 2024-10-31
Publication date: 2025-05-15
Anticipated expiration: 2026-05-09

Abstract

The present invention is directed to an aqueous basic deposition composition for the electroless deposition of a metal on a surface of a substrate, the composition comprising: (a) functionalized imidazole compounds selected from the group consisting of compounds having formula I: wherein R¹, R², R³ and R are identical or different; R¹, R², and R³ are independently selected from the group consisting of hydrogen, lower alkyl, preferably methyl, ethyl, propyl, isopropyl, n-butyl, 1-isobutyl or 2- isobutyl, and linear or branched alkyl amines; R is selected from the group consisting of a) hydrogen b) lower alkyl, preferably methyl, ethyl, propyl, isopropyl, n-butyl, 1- isobutyl or 2-isobutyl, c) allyl, preferably ethenyl, propenyl, or butenyl, d) alkaryl, preferably alkyl-substituted phenyl,, wherein n is selected as 2, 3, 4 or 5 and R⁴ and R⁵ f) CH₃-(CH₂)_n-CN; with the proviso that at least one of R¹, R², and R³ is selected as lower alkyl if R is hydrogen, and with the proviso that if R is not hydrogen then R¹, R², and R³ can be independently from each other be selected as lower alkyl or hydrogen; and wherein the compounds having formula I are present in the composition at a total concentration from 2 wt.-% to 15 wt.-% based on the total weight of the composition; and (b) at least one metal to provide metal ions to be deposited as metal onto the surface of the substrate wherein the deposited metal is different from the metal of the substrate; wherein the aqueous basic deposition composition comprises a pH from 8.5 to 12.5.

Description

AN AQUEOUS BASIC DEPOSITION COMPOSITION FOR THE ELECTROLESS DEPOSITION OF A METAL ON A SURFACE OF A SUBSTRATE

Field of the Invention

The present invention according to a first aspect relates to an aqueous basic deposition composition for the electroless deposition of a metal on a surface of a substrate.

According to a second aspect the present invention is further directed to a method for the electroless deposition of a metal on a surface of a substrate, preferably on a surface of an aluminum, zinc, or copper substrate, with an aqueous basic deposition composition according to the first aspect.

According to a third aspect the present invention is further directed to a substrate with a deposited metal layer on the surface of the substrate, wherein the deposited metal layer has been obtained by a method for the electroless deposition of a metal on a surface of a substrate according to the second aspect.

According to a fourth aspect the present invention is further directed to a use of an aqueous basic deposition composition according to the first aspect for the electroless deposition of a metal on a surface of a substrate.

According to a fifth aspect the present invention is further directed to an aqueous basic etching composition for the treatment of surfaces of metal substrates.

According to a sixth aspect the present invention is further directed to a method for treating a surface of a metal substrate with an aqueous basic etching composition according to the fifth aspect.

According to a seventh aspect the present invention is further directed to a metal substrate with an etched surface, wherein the etched surface has been obtained by a treating a surface of a metal substrate according to the sixth aspect. Background of the Invention

Substrates, such as metal-base substrates, can be coated by various metals or metal alloys to provide a metal coating layer on the surface of the respective substrate. Depending on the type of metal and the material of the surface of the substrate, various applications are possible.

EP 1 260 607 A2 refers to a method of improving the adhesion of a layer of silver deposited from an immersion plating bath comprising the step of: contacting a metal that is less electropositive than silver with an azole compound prior to contacting the metal with an immersion silver plating bath.

For example, US 3,472,742 refers to plating nickel on aluminum castings. Disclosed is a process comprising a step of treating aluminum with a relatively hot electroless nickel plating solution to apply a flash plate of nickel thereto.

US 3,666,529 refers to a method of conditioning aluminous surfaces for the reception of electroless nickel plating.

CN 115 110 072 A discloses an aqueous electroless copper deposition solution comprising beside others copper ions derived from a copper sulfate in a concentration of 5- 20 g/L complexing agent in a concentration of 5-20 g/L, stabilizing agent in a concentration of 0.01-0.1 g/L, and a reducing agent 8-12 g/L, wherein the pH of the composition is comprised between 8.5 and 12.5. The aqueous electroless copper deposition solution can be used on a substrate having active metallic palladium particles on its surface.

EP 3 360 988 A1 refers to a pyridinium compound comprising a building block -[A-D)- having a part (A) an imidazole or biuret structure which has at least at one pyridinium residue and a nitrogen-containing residue X1 and X2 and wherein the imidazole or biuret structure is bounded to a part (D) an ether or thioether group. The pyridinium compound is suitable as plating additive for copper deposition.

First, said metal coatings can serve as functional layers on the surface of the respective substrate to allow for an effective protection of the substrate, e.g. against aggres- sive gases or liquids by means of corrosion resistant metal coatings, the type of which is determined essentially by the intended use of the article.

Second, said metal coatings can serve as decorative layers on the surface of the respective substrate to allow for the desired optical surface characteristic.

Third, said metal coatings can provide electrically conductive structures on the surface of the respective substrate to allow for example for the preparation of electric circuit boards.

Exemplified metal coatings according to the present application comprise silver, nickel, copper, or cobalt coatings, which can be applied to a variety of substrates, for example metal substrates.

To apply said metal coatings to the respective substrates, the corresponding metals have to be stabilized in the respective deposition composition to avoid aggregation of metal deposits in said deposition compositions.

Objectives of the present invention

It was therefore the first objective of the present invention to provide a deposition composition and method for the electroless deposition of a metal on a surface of a substrate, which allow for an efficient metal deposition, in particular a metal deposition resulting in a homogenous and closed metal coating layer on the surface of a substrate. This preferably includes providing a simplified method such that for example less pretreatment steps or even no common pre-treatment steps are necessary anymore, generally resulting is a method sequence with a reduced number of steps.

It was therefore the second objective of the present invention to provide a deposition composition and method for the electroless deposition of a metal on a surface of a substrate, which can be applied using a wide variety of metals, for example silver, nickel, cobalt, or copper.

It was therefore the third objective of the present invention to provide a deposition composition and method for the electroless deposition of a metal on a surface of a substrate, which can be employed for the electroless deposition on a plurality of differ- ent surfaces, for example copper, brass, aluminum, zinc, and/or steel surfaces preferably zinc-coated steel.

It was therefore the fourth objective of the present invention to provide a deposition composition and method for the electroless deposition of a metal on a surface of a substrate, which can be used for the electroless deposition on a plurality of different metal substrates, for example large-area surfaces in the technical field of general manufacturing on the one side and also fine structures on printed circuit boards in the technical field of electronics on the other side.

It was therefore the fifth objective of the present invention to provide a deposition composition and method for the electroless deposition of a metal on a surface of a substrate, wherein the metal ions are effectively stabilized in the deposition composition to prevent precipitation.

It was therefore the sixth objective of the present invention to provide a deposition composition and method for the electroless deposition of a metal on a surface of a substrate, wherein additional layers, which are subsequently deposited on the deposited metal coating have superior functional and/or decorative qualities.

It was therefore the seventh objective of the present invention to provide a deposition composition and method for the electroless deposition of a metal on a surface of a substrate, which contains chemical compounds with a reduced toxicity.

Further, it was an eight objective to provide an improved electroless deposition composition and method for the electroless deposition of a metal on a surface of a substrate, such that use of an electrical current for deposition can be avoided.

Summary of the Invention

The aforementioned objectives are solved according to the present invention and in particular according to the first aspect to fourth aspect.

According to the first aspect the objectives are solved by an aqueous basic deposition composition for the electroless deposition of a metal on a surface of a substrate, the composition comprising: (a) functionalized imidazole compounds selected from the group consisting of compounds having formula I:

wherein

R¹, R², R³ and R are identical or different;

R¹, R², and R³ are independently selected from the group consisting of hydrogen, lower alkyl, preferably methyl, ethyl, propyl, isopropyl, n-butyl, 1-isobutyl or 2- isobutyl, and linear or branched alkyl amines; R is selected from the group consisting of a) hydrogen b) lower alkyl, preferably methyl, ethyl, propyl, isopropyl, n-butyl, 1- isobutyl or 2-isobutyl, c) allyl, preferably ethenyl, propenyl, or butenyl, d) alkaryl, preferably alkyl-substituted phenyl,

wherein n is selected as 2, 3, 4 or 5 and R4 and R5 are independently selected from the group consisting of hydrogen, lower alkyl, lower alkaryl, lower allyl and aryl, and f) CH₃-(CH₂)n-CN with the proviso that at least one of R¹, R², and R³ is selected as lower alkyl if R is hydrogen, and with the proviso that if R is not hydrogen then R¹, R², and R³ can be independently from each other be selected as lower alkyl or hydrogen; and wherein the compounds having formula I are present in the composition at a total concentration from 2 wt.-% to 15 wt.-% based on the total weight of the composition; and

(b) at least one metal to provide metal ions to be deposited as metal onto the surface of the substrate wherein the deposited metal is different from the metal of the substrate; wherein the aqueous basic deposition composition comprises a pH from 8.5 to 12.5.

The used aqueous basic deposition composition for the electroless deposition of a metal on a surface of a substrate allows for an efficient deposition of a wide variety of metals on a wide variety of substrate surfaces (see examples below). “Surface of a substrate” in the context of the present invention comprises a substrate made of metal or metal layers having a metal surface (wherein the metal or metal layer provides the surface to be treated). The substrate can also comprise any other (non-metallic) material as resin, glass, or composites thereof comprising a metal surface to be treated onto the non-metallic substrate. Both substrates will be used therein interchangeable, if not mentioned otherwise.

If “functionalized imidazole compounds” is mentioned in the following it always excludes the meaning of “and/or salts thereof”, except it is stated otherwise. This is due to the fact, that is has been found that salts of the functionalized imidazole compounds according to formula I impair the deposition of metal onto the surface of the substrate.

Therefore, the “functionalized imidazole compounds” according to formula I according to the present disclosure do not comprise any salts thereof. It was surprisingly found that the functionalized imidazole compound as defined under (a) provides outstanding capabilities in dissolving, complexing, and depositing this wide variety of metals on said wide variety of substrate surfaces.

Thereby, the metal to be deposited onto the surface of the substrate as defined under b) is oxidized under the alkaline conditions of the composition resulting in a positively charged metal ion, which is in-situ complexed by the functionalized imidazole compound, thereby form a metal-imidazole complex within the deposition composition. Metal-imidazole complex in this context is understood as metal ion - imidazole complex. For example, when using copper, nickel, cobalt, or silver as a metal defined under b) copper-imidazole complexes, cobalt-imidazole complexes, nickel-imidazole complexes or silver-imidazole complexes are formed.

This in particular relevant, since said metal-imidazole complexes solely form within the deposition composition simply by the addition of the functionalized imidazole compound and the metal into a basic, i.e. basic composition without the necessity to add any additional oxidizing agents suitable to oxidize the at least one metal to be deposited also named therein as etchant. In particular the composition does not comprise an oxidizing agent as persulfate compounds, perchlorate compounds or hydrogen peroxide suitable to oxidize the at least one metal to be deposited.

However, it is emphasized that due to the oxidation process no metal salts can be used as a metal source for forming the metal-imidazole complex, but exclusively elemental metal, which is for example provided as a solid elemental metal piece, or as an elemental metal granules, or as an elemental metal powder. Therefore the aqueous basic deposition composition does not comprise or contain any metal salt to provide metal ions to be deposited with the composition, preferably does not comprise copper salt, nickel salt or cobalt salt. In particular, the deposition composition does not comprise any anions as counter ions to the metal ions to be deposited. Preferably, the aqueous basic deposition composition does not comprise or contain sulfate, carbonate, chloride, or anions basing on said anions as e.g. copper sulfate, nickel sulfate or cobalt sulfate.

In one embodiment, the aqueous basic deposition composition does not comprise any sulfate anions, carbonate anions, chloride anions, or anions basing on said anions. For example, after filtration, a clean, clear, sometimes colored, aqueous basis solution with a pH between 8.5 and 12.5 is obtained, which comprises said metal-imidazole complexes and which can be used in the electroless deposition of a metal on a surface of a substrate.

During the electroless deposition the metal ion of the metal-imidazole complexes receive electrons for the metallic surface of the substrate, resulting in the disruption of the metal-imidazole complexes and the deposition of the metal ion onto said metallic surface of the substrate, thereby forming a deposition layer. Therefore no reducing agent is needed.

These generated metal ions are directly deposited onto the surface of the substrate or freshly prepared surface of the substrate. Also surprisingly, the deposition onto the surface does neither require an electrical current nor a reducing agent for reducing said metal ions, since the electrons are provided by the metallic substrate itself. This means that pure metal layers can be deposited onto the surface. In this context “pure” means that no alloying elements as boron or nitrogen were co-deposited which normally occurs by using boron or nitrogen containing reducing agents, “pure” in this context means a metal content of the deposited metal layer of at least 98 wt.-%, more preferred 99 wt.-% and most preferred 99.9 wt.-%.

As a consequence of the aforementioned, the aqueous basic deposition composition is used according to the invention for the electroless deposition of a metal, wherein the electroless deposition is a so-called immersion deposition wherein the aqueous basic deposition composition does not comprise any intentionally added reducing agent (further details see in the text below). In consequence it means, the metals or the metal ions, respectively, to be deposited from the deposition composition are different from the metal of the substrate.

The aqueous basic deposition composition allows for an efficient deposition of silver, nickel, copper, or cobalt. From the definition of “at least one metal to be deposited” above, it becomes clear, that e.g. copper cannot be deposited if copper is also the metal of the surface to be treated.

Moreover, the aqueous basic deposition composition allows for a homogenous deposition of the metal on the surface of the substrate during the deposition process, which in turn minimizes surface defects of the resulting metal coating. Such an efficient deposition process is in particular characterized by a constant deposition rate, which allows for an evenly distributed deposition of metal on the substrate surface during the deposition process, which in turn results in an even and closed surface, which can be obtained after the deposition process, “closed” in this context means that the obtained surface does not show depositing errors as holes.

Moreover, without to be bound by theory, the aqueous basic deposition composition seems to provide an effective roughness of the surface to be treated onto which the metal layer is deposited. This in turn improves the adhesion of the deposited layer and also of any additional layers, which are subsequently deposited on the deposited metal coatings. Such effective roughness of the treated surface can obviously be transmitted to the additionally deposited layer, which consequently also comprise an increased roughness, resulting in optimal functional and/or decorative properties of the resulting surfaces.

Further, the deposited surface shows good anti-tarnishing characteristics. It could be found by own experiments, that the obtained surface did not tarnish over time and also fingerprints did not remain on the surface or could be wiped away easily. Without to be bound by theory, it seems that the used compound (a) in the aqueous basic deposition composition remains at the resulting surface as a film and mitigates the improved antitarnishing effect. Own experiments show anti-tarnishing protection e.g. of a deposited silver surface of several months up to one year. The deposited thin film of compound (a) also shows a positive effect on corrosion resistance.

Furthermore, the aqueous basic deposition composition can be applied for the electroless deposition on a variety of different substrates, in particular metal substrates with a surface, as foils, sheets, screws, bolts and the like or a substrate comprising a surface, such as larger surface areas onto plastic parts in the technical field of general metal finishing; or smaller surface areas as panels, foils, printed circuit boards (PCBs) or metallic structures e.g. conductive lines and vias, in the technical field of electronics. The substrates which can be used with the present invention are e.g. substrates selected from the group consisting of copper-coated laminate or resin; copper-plated FR4- or HMP-panels; PCBs or ABS resin having a copper surface; glass panels or silicon wafer having at least one copper surface to be treated; sheets or foils made of copper, brass, zinc-coated steel parts; copper or copper-plated panels; connector or socket substrates as aluminum or copper sockets/connectors; and hinges and rims made of aluminum.

Moreover, the functionalized imidazole compounds selected from the group consisting of compounds having formula I of the aqueous basic deposition composition allow for an efficient stabilization of the metal ions present in the deposition composition, in particular by complexing, so that the precipitation tendency of said metal ions is almost zero, means precipitation is avoided.

In particular the aqueous basic deposition composition does not need the addition of further stabilizing agents, preferably the aqueous basic deposition composition does explicitly not contain stabilizing agents for stabilizing the metal ions in the deposition composition, because the functionalized imidazole compounds according to the present invention are able to form chelates of the obtained metal ions and thereby stabilizing the metal ions.

Moreover, the compounds of formula I are less toxic compared to other deposition compounds previously used in the prior art.

The objectives mentioned above are solved according to the invention. A use is preferred wherein the aqueous basic deposition composition uses preferably at least one metal to be deposited as metal onto the surface of the substrate, wherein the at least one metal is selected from a group consisting of

(i) a metal anode material which is in contact with the aqueous basic deposition composition, wherein said metal anode material is oxidized by applying an electric current to said anode, to enable an anodic oxidation process, resulting in a release of metal ions into the aqueous basic deposition composition; and

(ii) a solid metal piece or solid metal pieces which is or are in contact with the aqueous basic deposition composition, wherein said solid metal piece or solid metal pieces is or are oxidized by an oxidizing agent dissolved the aqueous basic deposition composition, to enable an oxidation process, resulting in a release of metal ions into the aqueous basic deposition composition.

The alternative (ii) is preferably provided in a separate tank to directly provide a solution of a complex of (a) and (b) wherein the oxidizing agent is preferably completely consumed. This solution is then added to the aqueous basic deposition composition to be used. This avoids the presence of oxidizing agent in the aqueous basic deposition composition. Preferably oxygen only, which is solved within the deposition composition, added to the deposition composition (e.g. by mixing and agitation of the deposition composition) thereby only allows for an effective oxidization of the solid metal piece or solid metal pieces in the deposition composition, thereby providing metal ions to be plated in the deposition composition. More preferred solved oxygen is the only oxidizing agent, wherein no other oxidizing agent is added.

Preferably the at least one metal a metal anode material which is in contact with the aqueous basic deposition composition, wherein said metal anode material is oxidized by applying an electric current to said anode, to enable an anodic oxidation process, resulting in a release of metal ions into the aqueous basic deposition composition, wherein preferably the composition does not comprise any additionally added oxidation agents.

The objectives mentioned above are solved according to a second aspect by a method for the electroless deposition of a metal on a surface of a substrate, preferably on a surface of an aluminum, zinc, or copper substrate, the method comprising the steps:

(A) providing an aqueous basic deposition composition for the electroless deposition of a metal on a surface of a substrate according to the first aspect, and

(B) contacting the substrate with said aqueous basic deposition composition such that the metal is deposited on the surface of the substrate in an electroless way wherein the deposited metal is different from the metal of the substrate.

Said method for electroless deposition according to the second aspect allows for a superior metal deposition on the substrate to be treated.

The objectives mentioned above are solved according to a third aspect by a substrate with a deposited metal layer on the surface of the substrate, wherein the deposited metal layer has been obtained by a method for the electroless deposition of a metal on a surface of a substrate according to the second aspect. Said substrate, in particular metal substrate, comprises an effective metal deposit. The objectives mentioned above are solved according to a fourth aspect by a use of an aqueous basic deposition composition according to the first aspect for the electroless deposition of a metal on a surface of a substrate.

Surprisingly, it could be observed, that during and after the deposition of the metal derived from the metal ions to be deposited, the functionalized imidazole compounds are partly coated as a thin film onto the deposited surface. This film functions on the one hand as corrosion protection layer and anti-tarnishing layer e.g. for silver deposits. On the other hand, the coated functionalized imidazole compounds lose its complexing activity and the re-resolution of the deposited metal.

Detailed Description of the Invention

In the context of the present invention, the term "at least one" or “one or more” denotes (and is exchangeable with) "one, two, three or more then three".

The term C_x-C_y according to the present invention refers to a substance comprising a total number from X carbon atoms to Y carbon atoms. For example, the term Ci-Ce alkyl refers to alkyl compounds comprising a total number from 1 carbon atom to 6 carbon atoms.

“lower alkyl” in the context of the present invention is selected from the group consisting of linear or branched alkyl groups and linear or branched alkylamine groups containing 1 to 6 carbon atoms, preferably selected from the group consisting of methyl, ethyl, propyl, isopropyl, n-butyl, 1-isobutyl, 2-isobutyl, and aminepropyl.

“lower allyl” in the context of the present invention is selected from the group consisting of linear or branched allyl groups containing 1 to 6 carbon atoms.

“lower alkaryl” in the context of the present invention is selected from the group consisting of alkyl-substituted phenyl containing alkyl groups containing 1 to 6 carbon atoms. The present invention according to the first aspect provides an aqueous basic deposition composition for the electroless deposition of a metal on a surface of a substrate, the composition comprising:

(a) functionalized imidazole compounds selected from the group consisting of com- pounds having formula I:

I wherein

R¹, R², R³ and R are identical or different; R¹, R², and R³ are independently selected from the group consisting of hydrogen, lower alkyl, preferably methyl, ethyl, propyl, isopropyl, n-butyl, 1-isobutyl or 2- isobutyl, and linear or branched alkyl amines;

R is selected from the group consisting of a) hydrogen b) lower alkyl, preferably methyl, ethyl, propyl, isopropyl, n-butyl, 1- isobutyl or 2-isobutyl, c) allyl, preferably ethenyl, propenyl, or butenyl, d) alkaryl, preferably alkyl-substituted phenyl,

wherein n is selected as 2, 3, 4 or 5 and R4 and R5 are independently selected from the group consisting of hydrogen, lower alkyl, lower alkaryl, lower allyl and aryl, and f) CH₃-(CH₂)n-CN; with the proviso that at least one of R¹, R², and R³ is selected as lower alkyl if R is hydrogen, and with the proviso that if R is not hydrogen then R¹, R², and R³ can be independently from each other be selected as lower alkyl or hydrogen; and wherein the compounds having formula I are present in the composition at a total concentration from 2 wt.-% to 15 wt.-% based on the total weight of the composition; and

The pH normally is self-adjusted without addition of any pH adjuster. If needed the pH can be adjusted by using hydroxide ions, preferably using sodium or kalium hydroxide.

In one embodiment R is selected from the group consisting of a), b), c), d), and e).

One advantage, which is achieved by the use of the aqueous basic deposition composition according to the first aspect of the present invention, results in an efficient deposition, for a variety of metals, in particular silver, nickel, cobalt, or copper, preferably silver, nickel or copper, in particular resulting in a homogenous metal deposit.

By using said aqueous basic deposition composition according to the first and/or second aspect of the present invention an effective roughness of the obtained metal deposits can be achieved, which allows for an efficient adhesion of any additional layer deposited on the metal deposit. Moreover, due to the nitrogen functionalities present in the functionalized imidazole compounds having formula I, a highly efficient stabilization of metal ions in the composition can be achieved by complexing of said metal ions, which results in a reduced or avoided precipitation of said metal ions.

Preferably, the deposition composition comprises atmospheric oxygen dissolved in the deposition composition as the only oxidizing agent for oxidizing the at least one metal in the deposition composition.

Preferably, the aqueous basic deposition composition according to the first aspect consist of the functionalized imidazole compounds selected from the group consisting of compounds having formula I according to selection a) and of the at least one metal to be deposited as metal onto the surface of the substrate wherein the deposited metal is different from the metal of the substrate according to selection b).

This means that in said preferred embodiment besides the functionalized imidazole compounds according to selection a) and the at least one metal to be deposited according to selection b) no additional compounds are present in the aqueous basic deposition composition according to the first aspect. In particular, this means that no additional oxidizing agents (except for atmospheric oxygen necessarily dissolved in the composition) are present in the compositions. In particular, this means also that no additional reducing agent are present in the aqueous basic deposition composition according to the first aspect is present, since during the deposition process, the electrons required are provided by the metal of the surface of the substrate itself.

In the following, advantageous embodiments of the deposition composition to be used according to the present invention will be explained in more detail.

According to the first aspect, the deposition composition is an aqueous basic deposition composition, which preferably comprises more than 50 vol.-% water, based on the total volume of the aqueous basic deposition composition, more preferably comprises 75 vol.-% or more water, even more preferably comprises 85 vol.-% or more water, even more preferably comprises 90 vol.-% or more water, even more preferably comprises 95 vol.-% or more water, and most preferably comprises 99 vol.-% or more water. Preferably, water is the only solvent in the aqueous basic deposition composition. An aqueous basic deposition composition is preferred, wherein R¹, R², and R³ are selected as hydrogen.

An aqueous basic deposition composition is preferred, wherein R is selected as lower alkyl, preferably methyl, propanamine, preferably, propan-1-amine, and wherein R is most preferably selected as methyl.

An aqueous basic deposition composition is preferred, wherein the at least one metal to be deposited is selected as a solid elemental metal piece, which is immersed in the aqueous basic deposition composition, wherein said solid elemental metal piece is oxidized in the aqueous basic deposition composition, resulting in a release of metal ions from the solid metal piece into the aqueous basic deposition composition, wherein preferably the at least one metal to be deposited is not selected as a metal salt.

According to the invention, the term “solid elemental metal piece” refers to elemental metal, and thereby excludes any metal salts. According to the invention, the term “solid elemental metal piece” comprises a single solid piece of elemental metal, but can also comprise a plurality of elemental metal pieces, such as granules of elemental metal and/or a powder of elemental metal.

An aqueous basic deposition composition is preferred, wherein the at least one metal to be deposited comprises copper, wherein preferably the composition comprises from 0.01 wt.-% to 0.25 wt.-% copper, more preferably 0.05 wt.-% copper; and/or wherein the at least one metal to be deposited comprises nickel, wherein preferably the composition comprises from 0.01 wt.-% to 0.25 wt.-% nickel, more preferably 0.05 wt.-% nickel; and/or wherein the at least one metal to be deposited comprises cobalt, wherein preferably the composition comprises from 0.01 wt.-% to 0.25 wt.-% cobalt, more preferably 0.05 wt.-% cobalt; and/or wherein the at least one metal to be deposited comprises silver, wherein preferably the composition comprises from 0.01 wt.-% to 0.25 wt.-% silver, more preferably 0.05 wt.-% silver. In embodiment the copper metal content for preparation of the aqueous basic deposition composition copper can be 50 - 2.500 mg/L, preferred 250 - 1.000 mg/L, most preferred 500 mg/L; cobalt can be 50 - 2.500 mg/L preferred 250 - 1.000 mg/L, most preferred 500 mg/L, nickel can be 50 - 2.500 mg/L preferred 250 - 1.000 mg/L, most preferred 500 mg/L, and/or silver can be 50 - 2.500 mg/L preferred 250 - 1.000 mg/L, most preferred 500 mg/L.

An aqueous basic deposition composition is preferred, wherein the compounds having formula I are present in the composition at a total concentration from preferably from 5 wt.-% to 15 wt.-%, more preferably from 7 wt.-% to 15 wt.-%, even more preferably from 8 wt.-% to 12 wt.-%, and most preferably 10 wt.-%.

By selecting the concentration of the compounds having formula I of compound (a) in the preferred concentration ranges an efficient deposition process can be ensured.

An aqueous basic deposition composition is preferred, wherein the compounds having formula I are exclusively selected as 1-Methyl-1 H-imidazole.

An etchant in the context of the present invention means an oxidizing agent which is suitable to oxidize the metal of the substrate, in particular the metal surface of the substrate. An aqueous basic deposition composition is preferred, wherein the composition does not comprise any etchants, wherein the composition preferably does not comprise persulfate compounds, perchlorate compounds and hydrogen peroxide.

An aqueous basic deposition composition is preferred, wherein the functionalized imidazole compounds according to formula I and the at least one metal to be deposited form metal-imidazole complexes, preferably copper-imidazole complexes, cobaltimidazole complexes, nickel-imidazole complexes and/or silver-imidazole complexes.

The aqueous deposition composition is an aqueous basic deposition composition. In the context of the present invention, the term “basic” denotes alkaline, i.e. having a pH above 7. The pH of the deposition composition according to the first aspect is ranging from 8.5 to 12.5. An aqueous basic deposition composition is preferred, wherein the aqueous basic deposition composition comprises a pH from 9 to 11, preferably from 9.2 to 10, more preferably 9.2 to 9.7. By selecting the pH in the preferred ranges an efficient deposition process can be ensured.

An aqueous basic deposition composition is preferred, wherein the aqueous basic deposition composition does not comprise any mineral acids and organic acids.

An aqueous basic deposition composition is preferred, wherein the at least one metal, which is to be deposited onto the surface, is selected from the group consisting of silver, copper, cobalt, and nickel, preferably silver, copper, and nickel. In case, the at least one metal is selected from the group consisting of copper, silver, cobalt, and nickel, the metal of the surface to be treated cannot be copper, cobalt, silver or nickel at the same time, because the metal of the surface must be less noble than the metal to be deposited.

An aqueous basic deposition composition is preferred, wherein the composition does not comprise an anionic agent. It could be found by own experiments that the addition of an acid, as hydrochloric acid, sulfuric acid, bromic acid, carboxylic acids as mono-, di- or tricarboxylic acid, e.g. acetic acid or citric acid, alkyl sulfonic acid as methane sulfonic acid, methane-disulfonic acid, methane-trisulfonic acid, aryl sulfonic acid as tosylate compounds, and metal salts thereof have a deteriorate effect of the deposition. It was observed that the addition of an anionic agent will prevent or defer the release of the metal ions to be deposited from functionalized imidazole compounds - metal ion complex.

According to a second aspect the present invention is further directed to a method for the electroless deposition of a metal on a surface of a substrate, preferably on a surface of an aluminum, zinc, or copper substrate, the method comprising the steps:

(B) contacting the substrate with said aqueous basic deposition composition such that the metal is deposited on the surface of the substrate in an electroless way wherein the deposited metal is different from the metal of the substrate. The method according to the second aspect ensures an efficient deposition process.

A method of the present invention is preferred, wherein step (A) comprises a first substep (A-1), which comprises providing the functionalized imidazole compounds according to formula I in water comprising a pH from 8.5 to 12.5 without the at least one metal to be deposited, and wherein step (A) comprises a second substep (A-1), which comprises adding the at least one metal to be deposited to the aqueous composition obtained after the first substep (A-1) to obtain the aqueous basic deposition composition which comprises in-situ formed metal-imidazole complexes.

A method of the present invention is preferred, wherein between step (A) and step (B), preferably between the second substep (A-2) and step (B), and additional step (F) is performed, which comprises filtering said aqueous basic deposition composition to remove any precipitate.

A method of the present invention is preferred, wherein step (A) of the method, in particular step (A-2) of the method, is performed at a temperature from 20 °C to 60 °C, preferably from 20 °C to 50 °C.

By performing the step (A), i.e. step (A-2) of the method at the preferred temperature ranges, a highly efficient metal-imidazole complex formation can be achieved.

A method of the present invention is preferred, wherein step (B) of the method is performed at a temperature from 20 °C to 100 °C, preferably from 30 °C to 80 °C, more preferably from 40°C to 70 °C, or 40°C to 60 °C, most preferably at 50 °C to 60 °C, or at 50 °C.

By performing step (B) of the method at the preferred temperature ranges, a highly efficient deposition reaction can be ensured.

A method of the present invention is preferred, wherein the substrates to be treated comprise metal substrates, wherein preferably the metal substrates or substrates comprising surfaces comprise all metals and metal alloys used for immersion deposition (e.g. silicon, titanium, tantalum and zirconium therefore are excluded) which are less noble than gold and less noble than the metal to be deposited according to their electrochemical standard potential (measured against hydrogen by known methods), preferably with the exception of iron, chromium, and nickel-chromium steel alloys. A method of the present invention is preferred, wherein the substrates to be treated comprise metals or metal alloys selected from the group consisting of aluminum, copper, nickel, cobalt, manganese, zinc, lead, antimony, tin, rare earth metals, for example neodymium, copper-zinc alloy, copper-tin alloy, copper-nickel alloy, and aluminummagnesium alloy.

A method of the present invention is preferred, wherein the metal or surfaces of the substrates to be treated comprise copper, nickel, zinc, aluminum, zinc-coated steel and/or cobalt.

Thereby, the deposition efficiency of the method is adjusted to allow for an efficient deposition of a huge variety of metal substrates.

In some cases, a method of the present invention is particularly preferred, wherein the substrate and the surface thereof comprise, preferably are, aluminum or an aluminum alloy. This is most preferred if the metal for electroless deposition comprises, preferably is, nickel, silver, and/or copper.

A method of the present invention is preferred, wherein during method step (B) no voltage is applied to the substrate. This means that no electrical current is involved as electron donor for reducing metal ions to the metal upon electroless deposition.

Furthermore, a method of the present invention is preferred, wherein the aqueous basic deposition composition is substantially free of, preferably does not comprise, a reducing agent for the electroless deposition of the metal, respectively, most preferably if the metal is or comprises nickel and/or copper and/or silver. This preferably also applies generally to the aqueous basic deposition composition of the present invention. Thus, a conventional, e.g. chemical compound for reducing the metal is preferably not needed.

Instead, a method of the present invention is most preferred, wherein the electroless deposition is an immersion deposition. This means that said deposition comprises a redox reaction involving said metal (preferably the metals as defined throughout the present text, more preferably silver, copper and/or nickel) and the surface of the substrate (preferably aluminum, zinc, or copper). In other words, the immersion deposition includes an electron transfer between at least two metals, meaning an electron transfer from a less noble metal to a more noble metal, “more noble metal” means view of the electrochemical series in this context that the redox potential of the complex of metal ions to be deposited and the functionalized imidazole compounds is more noble than the metal of the surface, e.g. copper ions complexed by the inventive functionalized imidazole compounds are found to be more noble than the metallic aluminum substrate. In the context of the present invention, the substrate (including its surface) and its surface thereof, is not considered as a reducing agent, but is part of the redox reaction between metal of surface and metal ions to be plated. Typically, such type of metal deposition is called immersion deposition. Also typically, such a metal deposition is preferably self-limiting because the more metal is deposited and thereby covering the substrate surface, the less access is provided to the surface metal to drive the process forward.

Thus, according to the method of the present invention, the metal for deposition is different from the substrate, more specially from the metal or surface of the substrate.

During the deposition of metal on the surface, the concentration of the metal ions of the surface of the substrate rises in the deposition composition while the concentration of the metal ions derived from the source of metal ions declines. The accumulates metal ions derived from the surface of the substrate (or metal substrate) build precipitates and sink to the button of the depositing tank.

A method of the present invention is preferred, wherein the metal substrate provided during step (A) is formed as a flexible metal substrate, preferably as a flexible copper substrate, more preferably as a flexible copper-coated polymer.

In some other cases, a flexible foil is preferred, most preferably an aluminum foil. This is most preferred, if the metal, respectively, for electroless deposition is copper, silver, cobalt or nickel.

A method of the present invention is preferred, wherein the substrate provided during step (A) is formed as a copper-coated laminate or resin, or a uniform copper substrate.

By depositing metals on different kind of substrates with different chemical and physical properties the method can be applied in a wide scope of applications and is therefore generally usable. For example, for printed circuit boards (PCBs) a copper-coated resin, in particular polymer, can be used or a copper-coated glass can be used as substrates. Alternatively, for general manufacturing goods, copper-coated plastics or copper-coated sheet metal can be used as substrates.

A method of the present invention is preferred, wherein step (A) and/or (B) is performed under stirring, preferably at a stirring rate from 20 rpm to 1.000 rpm, more preferably from 50 rpm to 500 rpm. Most preferably, for step (A) a stirring rate of 500 rpm is used. Most preferably, for step (B) a stirring rate of 200 rpm is used.

A method of the present invention is preferred, wherein step (B) is performed for a duration less than 2 hours, preferably less than 1 hour, more preferably less than 45 min, even more preferably less than 30 min, and most preferably less than 15 min.

A method of the present invention is preferred, wherein step (B) is performed for a duration from 1 min to 2 hours, preferably from 5 min to 1.5 hours, more preferably from 15 min to 1 hour and most preferably from 50 min to 15 min.

Preferably, when silver is used as the at least one metal to be deposited, step (B) is performed for a duration from 5 min to 15 min.

Preferably, when nickel or copper is used as the at least one metal to be deposited, step (B) is performed for a duration from 5 min to 90 min, more preferably for 45 min.

The preferred stirring and time intervals of the method allow for an efficient deposition, which can be individually adjusted according to the used metal substrate.

A method of the present invention is preferred, wherein the method comprises a step (P), which is performed prior to step (B), wherein step (P) comprises:

(P1) pre-rinsing the substrate with an acidic solution, preferably comprising sulfuric acid to obtain a pre-rinsed substrate,

(P2) washing the pre-rinsed substrate with a wash solution, preferably comprising desalted water, to obtain a washed substrate, and wherein the washed substrate is contacted with said aqueous basic deposition composition during step (B). By pre-rinsing the substrate with the acidic solution and a subsequent washing step, an efficient cleaning of the surface on which the metal is deposited during step (B) can be ensured, thereby increasing the effectivity of the method. By pre-rinsing the substrate any potential corrosion of the substrate and/or surface contaminations of the substrate can be efficiently removed before transferring the substrate into the aqueous basic deposition composition.

However, method step (P) is an optional method step, and the method according to the second aspect the present invention can be also performed without method step (P).

Preferably, the aforementioned regarding the aqueous basic deposition composition according to the first aspect of the present invention and the method according to the second aspect of the present invention, preferably what is described as being preferred, applies likewise to the substrate according to the third aspect of the present invention.

Preferably, the aforementioned regarding the aqueous basic deposition composition according to the first aspect of the present invention and the method according to the second aspect of the present invention, preferably what is described as being preferred, applies likewise to the use according to the fourth aspect of the present invention.

In one embodiment an aqueous basic deposition composition and a method is preferred wherein an aqueous basic deposition composition for the electroless deposition of a metal on a surface of a substrate, the composition consist of:

(a) functionalized imidazole compounds selected from the group consisting of compounds having formula I:

wherein

(b) at least one metal to provide metal ions to be deposited as metal onto the surface of the substrate wherein the deposited metal is different from the metal of the substrate; wherein the aqueous basic deposition composition comprises a pH from 8.5 to 12.5 and the pH can be adjusted by using hydroxide ions.

The invention in the following is described by preferred examples. The examples will not limit the overall scope of the invention.

E X A M P L E S

1. Copper deposition on surfaces of substrates

1.1 Preparation of a first aqueous basic copper deposition composition

50.00 g (0.6089 mol) of 1-Methyl-1 H-imidazole and a magnetic stir bar were placed in a 500 mL Erlenmeyer flask. 445.00 mL deionized water was added. Stirring was performed at 500 rpm for 10 minutes at 22 °C until a clear solution was obtained. 5.00 g (0.0787 mol) of copper granules were added. Stirring was carried out for 48 hours at 22 °C at a speed of 500 rpm. At the end of the reaction time a black-brown suspension was obtained. Under reduced pressure of 400 mbar, the suspension was aspirated through a 3 glass frit. The residue in the frit was washed 3 times with a little deionized water and discarded. After replenishing the filtrate with deionized water, 500 g of deep blue electrolyte were obtained. pH was 9.5. The obtained yield is 500.00 g (100.00 %). An AAS analysis revealed a complexed copper content of 805.1 mg/ L. After prepara- tion, the first aqueous basic copper deposition composition was used for the electroless deposition of copper on surfaces of aluminum substrates.

Even if not described in further detail, the first aqueous basic copper deposition composition was also used for etching a variety of metallic substrates.

Electroless deposition of copper on a surface of an aluminum sheet

500 g of the first aqueous basic copper deposition composition as prepared above was heated to 50 °C in a 500 mL Erlenmeyer flask with a magnetic stir bar for 20 minutes at a stirring rate of 200 rpm. The aluminum sheet was immersed in 5% sulfuric acid for 10 seconds, then rinsed with plenty of deionized water and immediately coated by immersing the aluminum sheet in the first aqueous basic copper deposition composition at 50 °C for 90 minutes. The composition was stirred at about 200 rpm during coating. After coating, the copper-plated aluminum sheet was rinsed clear with deionized water and dried with compressed air. XRF analysis determined the copper layer thickness as 2.28 pm.

1.2 Preparation of a second aqueous basic copper deposition composition

50.00 g (0.6089 mol) of 1-Methyl-1 H-imidazole and a magnetic stir bar were placed in a 500 mL Erlenmeyer flask. 445.00 mL of deionized water was added. Stirring was performed at 500 rpm for 10 minutes at 22 °C until a clear solution was obtained. The solution was heated to 50 °C in 25 minutes at a stirring rate of 500 rpm. 5.00 g (0.0779 mol) of copper powder 99 % was added. Stirring was carried out for 20 hours at 50 °C at a speed of 500 rpm. At the end of the reaction time a black-brown suspension was obtained. Under reduced pressure of 400 mbar, the suspension was aspirated through a 3 glass frit. The residue in the frit was washed 3 times with a little deionized water and discarded. After replenishing the filtrate with deionized water, 500 g of blue electrolyte were obtained. pH was 9.5. The obtained yield is 500.00 g (100.00 %). An AAS analysis revealed a complexed copper content of 244.8 mg/ L. After preparation, the second aqueous basic copper deposition composition was used for the electroless deposition of copper on surfaces of aluminum substrates.

Even if not described in further detail, the second aqueous basic copper deposition composition was also used for etching a variety of metallic substrates. Electroless deposition of copper on a surface of an aluminum sheet

500 g of the second aqueous basic copper deposition composition as prepared above was heated to 50 °C in a 500 mL Erlenmeyer flask with a magnetic stir bar in 25 minutes at a stirring rate of 200 rpm. The aluminum sheet was immersed in 5% sulfuric acid for 10 seconds, then rinsed with plenty of deionized water and immediately coated by immersing the aluminum sheet in the second aqueous basic copper deposition composition at 50 °C for 90 minutes. The composition was stirred at about 200 rpm during coating. After coating, the copper-plated aluminum sheet was rinsed clear with deionized water and dried with compressed air. XRF analysis determined the copper layer thickness as 1.74 pm.

1.3 Preparation of a third aqueous basic copper deposition composition

20.00 g (0.1598 mol) of 3-(1 H-imidazol-1-yl)propan-1-amine and a magnetic stir bar were placed in a 500 mL Erlenmeyer flask. 180.00 mL of deionized water was added. Stirring was performed at 500 rpm for 10 minutes at 22 °C until a clear, colorless solution was obtained. 2.00 g (0.0312 mol) of copper granules were added. Stirring was carried out for 16 hours at 22 °C at a speed of 500 rpm. At the end of the reaction time a blue suspension was obtained. Under reduced pressure of 400 mbar, the suspension was aspirated through a 3 glass frit. The residue in the frit was washed 3 times with a little deionized water and discarded. After replenishing the filtrate with deionized water, 200 g of blue electrolyte were obtained. pH was 9.3. The obtained yield is 200.00 g (100.00 %). An AAS analysis revealed a complexed copper content of 505.9 mg/L. After preparation, the fourth aqueous basic copper deposition composition was used for the electroless deposition of copper on surfaces of substrates.

Even if not described in further detail, the fourth aqueous basic copper deposition composition was also used for etching a variety of metallic substrates.

Electroless deposition of copper on a surface of an aluminum sheet

200 g of the fourth aqueous basic copper deposition composition as prepared above was heated to 50 °C in a 500 mL Erlenmeyer flask with a magnetic stir bar in 20 minutes at a stirring rate of 200 rpm. The aluminum sheet was immersed in 5% sulfuric acid for 10 seconds, then rinsed with plenty of deionized water and immediately coated by immersing the aluminum sheet in the aqueous basic copper deposition composition at 50 °C for 15 minutes. The composition was stirred at about 200 rpm during coating. After coating, the copper-plated aluminum sheet was rinsed clear with deionized water and dried with compressed air. XRF analysis determined the copper layer thickness as 0.24 pm.

2. Nickel deposition on surfaces of aluminum substrates

Preparation of an aqueous basic nickel deposition composition

50.00 g (0.6089 mol) of 1-Methyl-1 H-imidazole and a magnetic stir bar were placed in a 500 mL Erlenmeyer flask. 445.00 mL of deionized water was added. Stirring was performed at 500 rpm for 10 minutes at 22 °C until a clear solution was obtained. 5.00 g (0.0843 mol) of nickel powder 99 % were added. Stirring was carried out for 48 hours at 22 °C at a speed of 500 rpm. At the end of the reaction time a grey suspension was obtained. Under reduced pressure of 400 mbar, the suspension was aspirated through a 3 glass frit. The residue in the frit was washed 3 times with a little deionized water and discarded. After replenishing the filtrate with deionized water, 500 g of colorless electrolyte were obtained. pH was 9.5. The obtained yield is 500.00 g (100.00 %). An AAS analysis revealed a complexed nickel content of 81.5 mg/ L. After preparation, the aqueous basic nickel deposition composition was used for the electroless deposition of nickel on surfaces of substrates.

Even if not described in further detail, the first aqueous basic nickel deposition composition was also used for etching a variety of metallic substrates.

Electroless deposition of nickel on a surface of an aluminum sheet

500 g of the aqueous basic nickel deposition composition as prepared above was heated to 50 °C in a 500 mL Erlenmeyer flask with a magnetic stir bar in 20 minutes at a stirring rate of 200 rpm. The aluminum sheet was immersed in 5% sulfuric acid for 10 seconds, then rinsed with plenty of deionized water and immediately coated by immersing the aluminum sheet in the aqueous basic nickel deposition composition at 50 °C for 90 minutes. The composition was stirred at about 200 rpm during coating. After coating, the nickel-plated aluminum sheet was rinsed clear with deionized water and dried with compressed air. XRF analysis determined the nickel layer thickness as 0.007 pm.

3. Silver deposition on surfaces of substrates

Preparation of a first aqueous basic silver deposition composition

50.00 g (0.6089 mol) of 1-Methyl-1 H-imidazole and a magnetic stir bar were placed in a 500 mL Erlenmeyer flask. 445.00 mL of deionized water was added. Stirring was performed at 500 rpm for 10 minutes at 22 °C until a clear solution was obtained. 5.00 g (0.0464 mol) of silver pellets were added. Stirring was carried out for 48 hours at 22 °C at a speed of 500 rpm. At the end of the reaction time a colorless solution was obtained. A small amount of undissolved silver pellets lay at the bottom of the Erlenmeyer flask. The supernatant solution was decanted, the undissolved silver pellets were washed 3 times with a little deionized water. After replenishing the solution with deionized water, 500 g of colorless electrolyte were obtained. pH was 9.5. The obtained yield is 500.00 g (100.00 %). An AAS analysis revealed a complexed silver content of 18.4 mg/ L. After preparation, the first aqueous basic silver deposition composition having a pH of 9.5 was used for the electroless deposition of silver on surfaces of substrates.

Even if not described in further detail, the first aqueous basic silver deposition composition was also used for etching a variety of metallic substrates.

Electroless deposition of silver on a surface of an aluminum sheet

500 g of the first aqueous basic silver deposition composition as prepared above was heated to 50 °C in a 500 mL Erlenmeyer flask with a magnetic stir bar in 20 minutes at a stirring rate of 200 rpm. The aluminum sheet was immersed in 5% sulfuric acid for 10 seconds, then rinsed with plenty of deionized water and immediately coated by immersing the aluminum sheet in the first aqueous basic silver deposition composition at 50 °C for 30 minutes. The composition was stirred at about 200 rpm during coating. After coating, the silver-plated aluminum sheet was rinsed clear with deionized water and dried with compressed air. XRF analysis determined the silver layer thickness as 0.010 pm.

Electroless deposition of silver on a surface of a copper sheet 500 g of the first aqueous basic silver deposition composition as prepared above was heated to 50 °C in a 500 mL Erlenmeyer flask with a magnetic stir bar in 20 minutes at a stirring rate of 200 rpm. The copper sheet was immersed in 5% sulfuric acid for 10 seconds, then rinsed with plenty of deionized water and immediately coated by immersing the copper sheet in the first aqueous basic silver deposition composition at 50 °C for 30 minutes. The composition was stirred at about 200 rpm during coating. After coating, the silver-plated copper sheet was rinsed clear with deionized water and dried with compressed air. XRF analysis determined the silver layer thickness as 0.126 pm.

Preparation of a second aqueous basic silver deposition composition

50.00 g (0.6089 mol) of 1-Methyl-1 H-imidazole and a magnetic stir bar were placed in a 500 mL Erlenmeyer flask. 444.49 mL of deionized water was added. Stirring was performed at 500 rpm for 10 minutes at 22 °C until a clear solution was obtained. The solution was heated to 50 °C in 25 minutes at a stirring rate of 500 rpm. 5.00 g (0.0464 mol) of silver pellets were added. Stirring was carried out for 20 hours at 50 °C at a speed of 500 rpm. At the end of the reaction time a colorless solution was obtained. A small amount of undissolved silver pellets lay at the bottom of the Erlenmeyer flask. The supernatant solution was decanted, the undissolved silver pellets were washed 3 times with a little deionized water. After replenishing the solution with deionized water, 500 g of colorless electrolyte was obtained. pH was 9.6. The obtained yield is 500.00 g (100.00 %). An AAS analysis revealed a complexed silver content of 12.4 mg/ L. After preparation, the aqueous basic silver deposition composition was used for the electroless deposition of silver on surfaces of substrates.

Even if not described in further detail, the second aqueous basic silver deposition composition was also used for etching a variety of metallic substrates.

Electroless deposition of silver on a surface of an aluminum sheet

500 g of the second aqueous basic silver deposition composition as prepared above was heated to 50 °C in a 500 mL Erlenmeyer flask with a magnetic stir bar in 20 minutes at a stirring rate of 200 rpm. The aluminum sheet was immersed in 5% sulfuric acid for 10 seconds, then rinsed with plenty of deionized water and immediately coated by immersing the aluminum sheet in the aqueous basic silver deposition composition at 50 °C for 30 minutes. The composition was stirred at about 200 rpm during coating. After coating, the silver-plated aluminum sheet was rinsed clear with deionized water and dried with compressed air. XRF analysis determined the silver layer thickness as 0.013 pm.

Electroless deposition of silver on a surface of a copper sheet

500 g of the second aqueous basic silver deposition composition as prepared above was heated to 50 °C in a 500 mL Erlenmeyer flask with a magnetic stir bar in 20 minutes at a stirring rate of 200 rpm. The copper sheet was immersed in 5% sulfuric acid for 10 seconds, then rinsed with plenty of deionized water and immediately coated by immersing the copper sheet in the second aqueous basic silver deposition composition at 50 °C for 30 minutes. The composition was stirred at about 200 rpm during coating. After coating, the silver-plated copper sheet was rinsed clear with deionized water and dried with compressed air. XRF analysis determined the silver layer thickness as 0.065 pm.

4. Comparative examples

4.1 Preparation of a first comparative aqueous basic copper deposition composition 50.51 g (0.7345 mol) of 1H-imidazole 99 % and a magnetic stir bar were placed in a 500 mL Erlenmeyer flask. 444.49 ml deionized water was added. Stirring was performed at 500 rpm for 10 minutes at 22 °C until a clear, yellowish solution was obtained. The solution was heated to 50 °C in 20 minutes at a stirring rate of 500 rpm. 5.00 g (0.0779 mol) of copper powder 99 % was added. Stirring was carried out for 20 hours at 50 °C at a speed of 500 rpm. At the end of the reaction time a black-blue suspension was obtained. Under reduced pressure of 400 mbar, the suspension was aspirated through a 3 glass frit. The residue in the frit was washed 3 times with a little deionized water and discarded. After replenishing the filtrate with deionized water, 500 g of blue electrolyte were obtained. The pH was 9.5. The obtained yield is 500.00 g (100.00 %). An AAS analysis revealed a complexed copper content of 615.0 mg/ L. After preparation, the fifth aqueous basic copper deposition composition was used for the electroless deposition of copper on surfaces of substrates similar to the process above, but no deposition was observed.

4.2 Preparation of a second comparative aqueous basic copper deposition composition 449.51 mL deionized water and a magnetic stir bar were placed in a 500 mL erlen- meyer flask. 0.486 g (0.0019 mol) copper sulfate pentahydrate 99 %ww were added. Stirring was performed at 500 rpm for 4 minutes at 22 °C until a clear blue solution was obtained. 50.00 g (0.6089 mol) of 1 -Methyl-1 H-imidazole were added over a period of 1 minute at a stirring rate of 500 rpm. At the end 500 g of the blue electrolyte were obtained. pH was 9.5. The obtained yield is 500.00 g (100.00 %). The calculated copper content of the blue electrolyte is 244.8 mg/ L. After preparation, the aqueous alkaline copper deposition composition is ready for the electroless deposition of copper on surfaces of substrates.

Electroless deposition of copper on a surface of an aluminum sheet, 5 minutes

500 g of the aqueous alkaline copper deposition composition as prepared above was heated to 50 °C in a 500 mL erlenmeyer flask with magnetic stir bar in 20 minutes at a stirring rate of 200 rpm. The aluminum sheet was immersed in 5% sulfuric acid for 10 seconds, then rinsed with plenty of deionized water and immediately coated by immersing the aluminum sheet in the aqueous alkaline copper deposition composition at 50 °C for 5 minutes. The composition was stirred at about 200 rpm during coating. After coating, the aluminum sheet was rinsed clear with deionized water and dried with compressed air. There was no copper deposition.

Electroless deposition of copper on a surface of an aluminum sheet, 15 minutes

500 g of the aqueous alkaline copper deposition composition as prepared above was heated to 50 °C in a 500 mL erlenmeyer flask with magnetic stir bar in 20 minutes at a stirring rate of 200 rpm. The aluminum sheet was immersed in 5% sulfuric acid for 10 seconds, then rinsed with plenty of deionized water and immediately coated by immersing the aluminum sheet in the aqueous alkaline copper deposition composition at 50 °C for 15 minutes. The composition was stirred at about 200 rpm during coating. After coating, the aluminum sheet was rinsed clear with deionized water and dried with compressed air. There was no copper deposition. 4.3 Preparation of a third comparative aqueous basic copper deposition composition

Preparation of the aqueous alkaline copper deposition composition

449.00 mL deionized water and a magnetic stir bar were placed in a 500 mL erlen- meyer flask. 1.004 g (0.0040 mol) copper sulfate pentahydrate 99 %ww were added. Stirring was performed at 500 rpm for 4 minutes at 22 °C until a clear blue solution was obtained. 50.00 g (0.3994 mol) of 3-(1 H-imidazol-1 -yl)propan- 1 -amine were added over a period of 1 minute at a stirring rate of 500 rpm. At the end 500 g of the blue electrolyte were obtained. pH was 9.5. The obtained yield is 500.00 g (100.00 %). The calculated copper content of the blue electrolyte LK3295 is 505.9 mg/ L. After preparation, the aqueous alkaline copper deposition composition is ready for the electroless deposition of copper on surfaces of substrates.

Electroless deposition of copper on a surface of an aluminum sheet, 5 minutes 500 g of the aqueous alkaline copper deposition composition as prepared above was heated to 50 °C in a 500 mL erlenmeyer flask with magnetic stir bar in 20 minutes at a stirring rate of 200 rpm. The aluminum sheet was immersed in 5% sulfuric acid for 10 seconds, then rinsed with plenty of deionized water and immediately coated by immersing the aluminum sheet in the aqueous alkaline copper deposition composition at 50 °C for 5 minutes. The composition was stirred at about 200 rpm during coating. After coating, the aluminum sheet was rinsed clear with deionized water and dried with compressed air. There was no copper deposition.

Claims

1. An aqueous basic deposition composition for the electroless deposition of a metal on a surface of a substrate, the composition comprising:

I wherein

2. The aqueous basic deposition composition according to claim 1, wherein R¹, R², and R³ are selected as hydrogen.

3. The aqueous basic deposition composition according to claim 1 or 2, wherein R is selected as lower alkyl, preferably methyl, propanamine, preferably, propan-1-amine, and wherein R is most preferably selected as methyl.

4. The aqueous basic deposition composition according to any of the preceding claims, wherein the at least one metal to be deposited is selected as a solid elemental metal piece, which is immersed in the aqueous basic deposition composition, wherein said solid elemental metal piece is oxidized in the aqueous basic deposition composition, resulting in a release of metal ions from the solid metal piece into the aqueous basic deposition composition, wherein the at least one metal to be deposited is not selected as a metal salt.

5. The aqueous basic deposition composition according to any of the preceding claims, wherein the at least one metal to be deposited comprises copper, wherein preferably the composition comprises from 0.01 wt.-% to 0.25 wt.-% copper, more preferably 0.05 wt.-% copper; and/or wherein the at least one metal to be deposited comprises nickel, wherein preferably the composition comprises from 0.01 wt.-% to 0.25 wt.-% nickel, more preferably 0.05 wt.-% nickel; and/or wherein the at least one metal to be deposited comprises cobalt, wherein preferably the composition comprises from 0.01 wt.-% to 0.25 wt.-% cobalt, more preferably 0.05 wt.-% cobalt; and/or wherein the at least one metal to be deposited comprises silver, wherein preferably the composition comprises from 0.01 wt.-% to 0.25 wt.-% silver, more preferably 0.05 wt.-% silver.

6. The aqueous basic deposition composition according to any of the preceding claims, wherein the compounds having formula I are present in the composition at a total concentration from 5 wt.-% to 15 wt.-%, preferably from 7 wt.-% to 15 wt.-%, more preferably from 8 wt.-% to 12 wt.-%, and even more preferably 10 wt.-%.

7. The aqueous basic deposition composition according to any of the preceding claims, wherein the compounds having formula I are exclusively selected as 1-Methyl- 1H-imidazole.

8. The aqueous basic deposition composition according to any of the preceding claims, wherein the composition does not comprise any added oxidizing agent suitable to oxidize the at least one metal to be deposited, wherein the composition preferably does not comprise persulfate compounds, perchlorate compounds and hydrogen peroxide.

9. The aqueous basic deposition composition according to any of the preceding claims, wherein the functionalized imidazole compounds according to formula I and the at least one metal to be deposited form metal-imidazole complexes, preferably copper- imidazole complexes, cobalt-imidazole complexes, nickel-imidazole complexes and/or silver-imidazole complexes.

10. The aqueous basic deposition composition according to any of the preceding claims, wherein the aqueous basic deposition composition comprises a pH from 9 to

11, preferably from 9.2 to 9.7.

11. The aqueous basic deposition composition according to any of the preceding claims, wherein the aqueous basic deposition composition does not comprise any mineral acids and organic acids.

12. The aqueous basic deposition composition according to any of the preceding claims does not comprise metal salt to provide metal ions to be deposited, preferably does not comprise any anions as counter ions to the metal ions to be deposited; preferably does not comprise or contain sulfate, carbonate, chloride, or anions basing on said anions.

13. A method for the electroless deposition of a metal on a surface of a substrate, preferably on a surface of an aluminum, zinc, or copper substrate, the method comprising the steps:

(A) providing an aqueous basic deposition composition for the electroless deposition of a metal on a surface of a substrate according to any one of claims 1 to 11 , and

14. The method according to claim 13, wherein step (A) comprises a first substep (A-1), which comprises providing the functionalized imidazole compounds according to formula I in water comprising a pH from 8.5 to 12.5 without the at least one metal to be deposited, and wherein step (A) comprises a second substep (A-1), which comprises adding the at least one metal to be deposited to the aqueous composition obtained after the first substep (A-1) to obtain the aqueous basic deposition composition which comprises in-situ formed metal ion - imidazole complexes.

15. A substrate with a deposited metal layer on the surface of the substrate, wherein the deposited metal layer has been obtained by a method for the electroless deposition of a metal on a surface of a substrate according to claim 13 or 14.

16. Use of an aqueous basic deposition composition according to any one of claims 1 to 12 for the electroless deposition of a metal on a surface of a substrate.