A method for electroless copper depositing onto a surface of a non-conductive or carbonfibres containing substrate

Abstract

The present invention relates to a method for electroless copper depositing onto a surface of a non-conductive or carbon-fibres containing substrate, the method comprising the steps: (I) activating the surface of a non-conductive or carbon-fibres containing substrate for electroless copper depositing, the activation method using an aqueous, palladium-free activation composition comprising (i) a first species of dissolved transition metal ions which are copper ions and additionally metal particles thereof which are copper particles, (ii) one or more than one complexing agent, and (iii) permanently or temporarily one or more than one reducing agent, and (II) an enhancer treatment of the activated surface of a non-conductive or carbon-fibres containing substrate, the enhancer treatment method using an alkaline aqueous enhancer composition comprising water and a formaldehyde compound; and (III) an electroless copper depositing of the enhanced surface of a non-conductive or carbon-fibres containing substrate, the electroless copper depositing method using an electroless copper metallizing solution and substrates, and method for subsequent metallization.

Description

[0001] A method for electroless copper depositing onto a surface of a non-conductive or carbon- fibres containing substrate

[0002] Field of the Invention

[0003] The present invention relates to a method for electroless copper depositing onto of surfaces of non-conductive or carbon-fibres containing substrates and method for subsequent metallization.

[0004] Background of the Invention

[0005] A metallization of substrates having non-conductive surfaces is commercially of high interest. In many aspects of daily life such substrates comprise at least partly conductive structures or layers of metal, either for decorative or functional applications. For example, typically non-conductive plastic substrates are used to manufacture sanitary articles with several electroless and electrolytical deposited metal layer layers having a shiny chromium layer as final outer layer. Furthermore, quite a number of chromium covered plastic substrates are used in the automotive industry.

[0006] Besides such decorative articles, a functional metallization is essential in for example manufacturing printed circuit boards. In such boards typically a non-conductive resin-containing laminate is used as a base material usually harboring a circuitry of copper lines.

[0007] Carbon-fibres containing substrates experience an increasing potential as catalytically active surfaces in e.g. power-to-gas, power-to-fuel, and power-to-chemicals applications, and batteries.

[0008] All these applications require a usually multi-step preparation of the non-conductive or carbon-fibres containing substrate to make it receptive for subsequent metallization.

[0009] In a first step usually a cleaning of the surface of the non-conductive or carbon-fibres containing substrate is carried out, e.g. to remove grease or impurities.

[0010] In a second step typically a conditioning (also called pre-treatment) of said surface is conducted in order to make the surface receptive to the following activation.

[0011] In a third step the important activation is carried out. In such an activation usually a very thin seed or activation layer is deposited / anchored on the surface of the non-conductive or carbon-fibres containing substrate, serving as starting point for a subsequent first metallization layer. As a result, an activated surface for metallization is obtained. The seed or activation layer usually serves as mediator between said surface of the non-conductive or carbon- fibres containing substrate and the one or more following metallization layers. Typically, the seed / activation layer is formed by depositing metal nanoparticles on said surface, for exampie from a colloidal activation composition.

[0012] In a fourth step typically said first metallization layer is deposited on the seed / activation layer, most commonly by electroless plating. In some cases, this electroless plating includes a deposition of a metal or metal alloy through autocatalytic deposition, which means a deposition facilitated by means of a reducing agent.

[0013] US 2021 / 246559 A1 relates to electro less copper plating bath for depositing a copper or copper alloy layer on an activated surface of a substrate, including copper ions; a reducing agent; a complexing agent for copper ions; wherein the bath further includes a by-pyridine compound. The compound acts mainly as bath stabilizer.

[0014] In a fifth step typically a second metallization layer is deposited on the first metallization layer by electrolytic deposition.

[0015] Basically, the skilled person is well familiar with such a sequence of steps. Typically, in a common colloidal activation composition, noble metal nanoparticles are utilized very often as palladium nanoparticles. However, noble metals are generally expensive and wastewater treatment is of high concern in order to recycle remaining noble metals. Alternatively, less expensive metal ions are more and more utilized in respective activation compositions.

[0016] For example, CN 107460459 A relates to simple nano-copper activation liquid utilizing stabilizers and reducing agents to prevent agglomeration and oxidation, respectively, of the nanoparticles.

[0017] US 4,323,594 discloses a process and compositions for preparing dielectric substrates for electroless coating or plating of a metallic surface thereon, and to provide an electroless coating process including such preparation. The composition is a colloidal composition comprising a copper colloid admixed with cuprous compound and wherein the admixing takes place subsequent to the production of the copper colloid. The copper colloid composition uses a stabilizer compound to stabilize the copper colloids in the composition.

[0018] US 4,278,712 discloses a method for the activation of a weakly active colloidal dispersion useful in the preparation of non-conductors prior to electroless plating. The method is based upon controlled oxidation of otherwise weakly active colloids by treatment with suitable gases and / or chemical agents, which render said controlled oxidation. However, the presence of at least one colloid stabilizer is mandatory. In this way a reversible equilibrium is not maintained. A common disadvantage is that such activation compositions naturally experience a form of decay or decomposition. Typically, the nanoparticles agglomerate and form insoluble, precipitating agglomerates, rendering the composition mostly inoperable. It is therefore typically desired to stabilize the nanoparticles after they have been formed through reducing respective metal ions. For this purpose, usually stabilizer compounds are used, altering the charge distribution of the particles, limiting the particle size, and / or preventing oxidation of the particles. In many cases polymers and / or anti-oxidation agents and / or metal ions (such as tin ions) are used for these purposes.

[0019] Such approaches as described in the art typically have the disadvantage that they are sooner or later sensitive to agglomeration and precipitation, mostly because the stabilizer compounds do not sufficiently stabilize the particles over time. As a result, product lifetime very strongly depends on the date of production, delivery time, and the quality of stabilization.

[0020] Furthermore, it appears that such stabilizer compounds often reduce the ability of the nanoparticles to effectively activate the respective surface. It seems that the additives on the one hand - at least to a certain degree - avoid agglomeration but on the other hand hinder these particles to adsorb on the surface quickly and strongly.

[0021] WO 2020 / 201387 A1 discloses method for activating a surface of a non-conductive or carbon-fibres containing substrate for metallization and a respective activation composition, which is on the one hand simple and highly effective, and on the other hand is in particular insensitive to agglomeration and precipitation to ensure a long service life.

[0022] WO 2022 / 043417 A1 discloses a method for activation of surfaces of non-conductive or carbon-fibres containing substrates for subsequent metallization wherein after a conditioning step a selector treatment step is conducted followed by an activating step. The selector step improves the solder shock test results.

[0023] It was found that metallized substrates prepared according to such processes above exhibit still a non-optimal performance in the solder shock test or the performance in the solder shock test was not stable.

[0024] Objective of the present Invention

[0025] It was therefore an objective of the present invention to provide an improved method for electroless copper depositing of a copper layer onto a surface of a non-conductive or carbon- fibres containing substrate which overcomes the problems of the prior art above, in particular providing and improving a method which uses a palladium-free activation of non-conductive or carbon-fibres containing substrate for subsequent metallization. It was another objective of the present invention to provide a respective method with reduced environmental burden, e.g. with less sophisticated waste-water treatment and reduced effective concentrations of chemicals.

[0026] It was another objective of the present invention to provide a respective method that exhibits a good and stable performance in the standard solder shock test at 288°C.

[0027] Further it is an object of the present invention to pass also solder shock test at 326°C at lower defect rates, which is more often demanded by customers to secure higher reliability of the formed interconnects even in a high thermal stress situation.

[0028] It was still another objective of the present invention to provide an improved electrical reliability of copper-to-copper (Cu-Cu) interconnections in e.g. electronic articles as printed circuit boards.

[0029] Summary of the Invention

[0030] The objectives mentioned above are solved by a method for electroless copper depositing a first copper layer onto a surface of a non-conductive or carbon-fibres containing substrate, preferably used for subsequent metallization, the method comprising the steps:

[0031] (I) activating the surface of a non-conductive or carbon-fibres containing substrate for metallization, the activation method comprising the steps of

[0032] (a) providing the substrate;

[0033] (b) providing an aqueous, palladium-free activation composition comprising

[0034] (i) a first species of dissolved transition metal ions, wherein the first species are copper ions, and additionally metal particles thereof, wherein the metal particles are copper particles,

[0035] (ii) one or more than one complexing agent, and

[0036] (iii) permanently or temporarily one or more than one reducing agent, wherein

[0037] - the first species of the dissolved transition metal ions and the metal particles thereof are present in a reversible equilibrium, with the proviso that the metal particles are formed from the dissolved transition metal ions through a continuous or semi-continuous reduction through the one or more than one reducing agent, - the dissolved transition metal ions are formed from the metal particles through continuous or semi-continuous oxidation of said particles, and

[0038] - the dissolved transition metal ions and the metal particles thereof, respectively, are repeatedly involved in said reduction and said oxidation such that no precipitating agglomerates of said metal particles are formed; and

[0039] (c) contacting the substrate with said activation composition such that a transition metal is deposited on the surface of said substrate and an activated surface for metallization is obtained;

[0040] (II) an enhancer treatment of the activated surface of a non-conductive or carbon-fibres containing substrate, the enhancer treatment method comprising the steps of

[0041] (a) providing said substrate;

[0042] (b) providing an alkaline aqueous enhancer composition comprising or consisting of water and a formaldehyde or a water-soluble formaldehyde precursor, wherein the alkaline aqueous enhancer composition has a pH from 7.1 to 13; and

[0043] (c) contacting the substrate with the alkaline aqueous enhancer composition such that an enhanced surface is obtained; and

[0044] (III) an electroless copper depositing of the enhanced surface of a non-conductive or carbon-fibres containing substrate, the electroless copper depositing method comprising the steps of

[0045] (a) providing said substrate;

[0046] (b) providing an electroless copper metallizing solution; and

[0047] (c) contacting the substrate with the electroless copper metallizing solution such that a first copper layer is deposited on the enhanced surface.

[0048] The objectives mentioned above are further solved by a method for metallizing an electroless deposited copper surface of a non-conductive or carbon-fibres containing substrate, the method comprising the steps:

[0049] (A) providing the non-conductive or carbon-fibres containing substrate with the electroless deposited copper surface obtained by the method above; and

[0050] (B) metallizing the electroless deposited copper surface by contacting the electroless deposited copper surface with metallizing solution such that a second metallization layer is electrically deposited on the electroless deposited copper surface. Own experiments show that using of an electroless copper metallizing solution by directly contacting the activated surface with the solution in step (III) can lead to passivation and corrosion of the palladium-free activated surface as a side reaction due to a delayed copper deposition.

[0051] Surprisingly it could be found that by using the methods according to the present invention, the inner layer connection reliability of electroless copper plated substrates is improved.

[0052] With other words, the reliability of the whole process can be improved with the result that the rejection rate of insufficient formed copper-to-copper interconnections could be significantly reduced. In particular, the method of the present invention provides a very good and stable performance in the standard solder shock test at 288°C.

[0053] Furthermore, with the method of the present invention also solder shock test at 326°C were passed with significant lower defect rates, which secures higher reliability of the formed interconnects even in a high thermal stress situation. Moreover, at 326°C solder temperature the ICD results are comparable to the Pd reference as “Standard Reference”.

[0054] Without to be bound by theory, it is believed that the enhancer treatment in step (II) seems to protect the activated surface of the substrate and helps to accelerate the starting behavior of the electroless copper metallization solution in the electroless copper deposition step (III). The accelerated starting behavior can be seen therein that the enhanced surface will be covered very fast directly after contacting the enhanced surface with the electroless copper metallizing solution in step (I I l)(c) wherein the total enhanced surface is converted to a black shinny surface comprising probably first small copper particles. This black shinny surface is than converted to a salmon pink copper surface. In consequence, undesired side-reactions as a passivation and / or corrosion is avoided or strongly suppressed by the enhanced surface. Additionally, the faster starting of the copper deposition reduces the overall process time which saves costs and time.

[0055] The respective method does not require expensive noble metals but can be carried out with low-priced transition metals, preferably with copper ions.

[0056] Further, the additional step does not interfere with the subsequent steps after step (III) and leads to an overall performance which is near or same of standard electroless copper deposition processes using a palladium-based activation. Detailed of the Invention

[0057] In the context of the present invention, “continuous”, “continuously”, and “continually”, respectively, denote a constantly ongoing doing of a respective action without significant interruptions of the action while e.g. a respective method or aspect of the invention is carried out.

[0058] In the context of the present invention, “semi-continuous”, “semi-continuously”, and, “semi- continually”, respectively, denote a doing of a respective action with one or more than one even significant interruption of the action while e.g. a respective method or aspect of the invention is carried out. The interruptions are in some cases longer than the time during the action is carried out. It includes even only temporary and brief actions.

[0059] In the context of the present invention, “species” denotes a chemical element, wherein “a first species of dissolved transition metal ions” denotes dissolved copper ions.

[0060] In the context of the present invention, “a first species of dissolved transition metal ions and additionally metal particles thereof” denotes dissolved copper ions as first species and additionally copper particles of this first species, e.g. in the aqueous, palladium-free activation composition. Preferable, the aqueous, palladium-free activation composition does not comprise any other reducible metal ions (in particular transition metals) and metal particles. Consequently, the reducing agent is used in a suitable concentration to reduce copper ions and is intended to reduce only these copper ions.

[0061] The substrate:

[0062] In step (l)(a) of the method of the present invention, a non-conductive or carbon-fibres containing substrate with a non-conductive or carbon-fibres surface is provided. Such a substrate inherently cannot be successfully metallized and therefore needs an activation.

[0063] The substrate can also comprise a surface with a conductive area. Preferably, the substrate can also comprise through hole vias (THVs) and / or blind micro vias (BMVs) within the non- conductive or carbon-fibres containing substrate, wherein the surface of the substrate comprises the surface of the through hole vias (THVs) and blind micro vias (BMVs). The substrate can further comprise inner metal layers. The surface of the through hole vias (THVs) and / or blind micro vias (BMVs) can further comprise conductive areas, preferably metallic areas, more preferably copper areas. These areas are derived from inner metal layers, preferably from copper layers within the non-conductive or carbon-fibres containing substrate.

[0064] In the context of the present invention, activating means to modify the surface of the non- conductive or carbon-fibres containing substrate in such a way that it comprises copper as the transition metal after the respective activation step with sufficient adhesion for subsequent metallization. Furthermore, the deposited transition metal is sufficiently adherent to the surface such that a subsequent metallization layer (i) can be deposited thereon and (ii) is altogether also sufficiently adherent to the surface of the non-conductive or carbon-fibres containing substrate.

[0065] Preferred is a method of the present invention, wherein the non-conductive substrate comprises, preferably is, selected from the group consisting of plastics, resin-containing laminates, glasses, ceramics, semi-conductors, and mixtures thereof.

[0066] Preferred plastics comprise, preferably are, thermoplastics, more preferably comprise, preferably are, polyacrylates, polyamides, polyimides, polyesters, polycarbonates, polyalkylenes, polyphenylenes, polystyrenes, polyvinyls, or mixtures thereof.

[0067] Preferred polyacrylates comprise poly(methyl methacrylate) (PMMA).

[0068] Preferred polyimides comprise polyetherimide (PEI).

[0069] Preferred polyesters comprise polylactic acid (PLA).

[0070] Preferred polycarbonates comprise polycarbonate obtained with bisphenol A (PC).

[0071] Preferred polyalkylenes comprise polyethylene (PE), polypropylene (PP), polytetrafluoroethylene (PTFE), polyoxymethylene (POM), or mixtures thereof.

[0072] Preferred polyphenylenes comprise poly(phenylene oxide) (PPO), poly(phenylene ether) (PPE), or mixtures thereof.

[0073] Preferred polystyrenes comprise polystyrene (PS), acrylonitrile butadiene styrene (ABS), styrene / butadiene rubber (SBR), styrene-acrylonitrile (SAN).

[0074] Preferred polyvinyls comprise polyvinyl chloride (PVC), poly(ethylene-vinyl acetate) (PEVA), polyvinylidene difluoride (PVDF), or mixtures thereof.

[0075] Preferred resin-containing laminates comprise, preferably are, fiber-enforced resin-containing laminates, most preferably glass-fiber-enforced laminates.

[0076] Very preferably, the resin-containing laminates comprise as resin one or more than one polymer of epoxys, vinylesters, polyesters, amides, imides, phenols, alkylenes, sulfones, or mixtures thereof, most preferably epoxy, imides, or mixtures thereof.

[0077] A very preferred resin-containing laminate comprises, preferably is, FR4.

[0078] Preferred glasses comprise, preferably are, silica glass, soda-lime glass, float glass, fluoride glass, aluminosilicate glass, phosphate glass, borate glass, borosilicate glass, chalcogenide glass, aluminium oxide glass, or mixtures thereof. Preferred ceramics comprise, preferably are, glass-ceramics, aluminium oxide ceramics, or mixtures thereof.

[0079] Preferred semi-conductors comprise, preferably are, silicon-based semi-conductors, more preferably silicon-based semi-conductors comprising silicon dioxide and / or silicon.

[0080] Very preferred semi-conductors are wafers.

[0081] Preferred is a method of the present invention, wherein the carbon-fibres containing substrate comprise, preferably are, carbon-fibre composites and / or arrangements of carbon- fibre filaments.

[0082] Preferred carbon-fibre composites comprise, preferably are, carbon-fibre reinforced polymers and / or carbon-fibre containing fabrics, more preferably carbon-fibre reinforced polymers and / or woven carbon-fibre containing fabrics.

[0083] Preferred arrangements of carbon-fibre filaments comprise, preferably are, fabrics made of carbon-fibres, most preferably woven fabrics made of carbon-fibres.

[0084] An in particularly preferred carbon-fibres containing substrate is a carbon-fibre containing felt.

[0085] Pre-treatment

[0086] Optionally one or more of the following pre-treatment steps (Pre-(l), Pre-(la), Pre-(lb)) can be processed before the activation step (I), which improves further the overall performance of the inventive method in view of reliability of the deposited metal layers. Furthermore, the overall stability of the inventive method can be improved. These steps are:

[0087] Pre-(l) conditioning the surface of a non-conductive or carbon-fibres containing substrate, the conditioning method comprising the steps of

[0088] (a) providing said substrate;

[0089] (b) providing a conditioning composition comprising a nitrogen-containing compound; and

[0090] (c) contacting the substrate with the conditioning composition to receive a conditioned surface.

[0091] Pre-(la) rinsing the surface of a non-conductive or carbon-fibres containing substrate, the rinsing method comprising the steps of

[0092] (a) providing the substrate treated according to step (I);

[0093] (b) providing an aqueous acidic rinsing composition; and (c) contacting the substrate with the aqueous acidic rinsing composition to receive a rinsed surface.

[0094] Pre-(lb) a selector treatment of the surface of a non-conductive or carbon-fibres containing substrate, the selector treatment method comprising the steps of

[0095] (a) providing the substrate treated according to step (la);

[0096] (b) providing a selector composition which

[0097] (i) comprises a nitrogen-containing compound, and

[0098] (ii) has a pH of from 9 to 14;

[0099] (c) contacting the substrate with the selector composition.

[0100] Preferably, at least a Pre-(l) conditioning is processed before step (I).

[0101] In a more preferred embodiment, Pre-(lb) will be processed after Pre-(l) before step (I).

[0102] Most preferably, all pre-steps (I), (la) and (lb) are processed in the shown order above before step (I).

[0103] Pre-(l) Conditioning:

[0104] Preferably, the conditioning solution has an alkaline pH, preferably a pH in a range from 9.0 to 14.0, more preferably in a range from 10.0 to 13.5, even more preferably in a range from 10.5 to 13.0, most preferably in a range from 11.0 to 12.5.

[0105] Preferred is a method of the present invention, wherein in the conditioning solution the ni- trogen-containing compound is a polymer, preferably a water-soluble polymer.

[0106] More preferred is a method of the present invention, wherein in the conditioning solution the nitrogen-containing compound is a polymer comprising pyrrolidine moieties.

[0107] Preferably, the polymer is cationic.

[0108] Preferably, the nitrogen-containing compound consists of carbon atoms, nitrogen atoms, and hydrogen atoms.

[0109] Preferred is a method of the present invention, wherein in the conditioning solution the ni- trogen-containing compound comprises quaternary nitrogen atoms.

[0110] Most preferred is a method of the present invention, wherein the nitrogen-containing compound comprises, preferably is, Polyquaternium 6.

[0111] Another preferred method of the present invention is a method, wherein the nitrogen-con- taining compound comprises, preferably is, a polymer which results from the polyaddition and / or polycondensation of at least one nitrogen-containing compound. Examples are polyamides such as Nylon 6, Nylon 6,6, Nylon 6,16, and polyurethanes. Most preferred is a method of the present invention, wherein the nitrogen-containing compound comprises, preferably is, a polymer of methylamine and epichlorohydrin.

[0112] Preferred is a method of the present invention, wherein the concentration of the nitrogencontaining compound is of from 0.1 g / L to 4 g / L, preferred of from 0.2 g / L to 2 g / L, more preferred of from 0.25 g / L to 1 .5 g / L, more preferred of from 0.3 g / L to 1 g / L.

[0113] Preferred is a method of the present invention, wherein the conditioning solution during step (l)(c) has a temperature in a range from 20°C to 90°C, preferably in a range from 25°C to 80°C, more preferably in a range from 30°C to 70°C, most preferably in a range from 40°C to 60°C.

[0114] Preferred is a method of the present invention, wherein step (l)(c) is carried out for 1 minute to 10 minutes, preferably for 2 minutes to 8 minutes, more preferably for 3 minutes to 6 minutes, most preferably for 3.5 minutes to 5 minutes.

[0115] Pre-(la) Rinsing the conditioned surface

[0116] If the rinsing step Pre-(la) is used in the sequence of the pre-treatment steps, the rinsing step is used after the conditioner step and will support the following selector treatment step Pre-(lb). Without to be bound by theory, the rinsing step mildly attacks the conditioner film without removing it, but the attack enables an improved removal of the conditioner film from e.g. inner metal layers of the substrate. The conditioner film is not removed from the surface of the non-conductive or carbon-fibres containing substrate. In this way, the quality of cop- per-to-copper interconnections between inner metal layers is improved. Further, the rinsing step also improved the stability of the solder shock test results.

[0117] Beside this, it could be shown that the use of the rinsing step after the selector treatment step leads to bad coverage of the substrate layers resulting in worse backlight test results.

[0118] Preferred is a method of the present invention, wherein the aqueous acidic rinsing composition comprises or consist of water and sulfuric acid. More preferred is a method wherein the aqueous acidic rinsing composition doesn't comprise any other mineral or organic acid or salts thereof. Own experiments show that other mineral or organic acid or salts thereof are not working or inserting inorganic anions which disturb the subsequent method steps and results in insufficient solder shock tests and / or backlight tests.

[0119] Preferred is a method of the present invention, wherein the aqueous acidic rinsing composition has a pH from 2 to 4.5, preferably from 2.5 to 4, more preferably 2.5. Preferred is a method of the present invention, wherein step (la)(c) - contacting the substrate with the aqueous acidic rinsing composition - is conducted for a time period of 0.5 to 2 min.

[0120] Pre-(lb) Selector Treatment:

[0121] Pre-treatment step Pre-(lb) can be used after the pre-treatment step Pre-(l) or Pre(la), preferably after Pre(la).

[0122] Preferred is a method of the present invention, wherein the selector composition has an alkaline pH, preferably a pH in a range from 9.0 to 14.0, more preferably in a range from 10.0 to 13.5, even more preferably in a range from 10.5 to 13.0, most preferably in a range from 11.0 to 12.5. pH values can be easily adjusted with a pH adjuster, preferably the pH adjuster is selected from the group consisting of hydrochloric acid, sulfuric acid, sodium hydroxide and potassium hydroxide.

[0123] Preferred is a method of the present invention, wherein in the selector composition the ni- trogen-containing compound is an amine of the formula

[0124] NHx[(CH2)nOH]3-x with x = 0, 1 , 2 or 3 and n = 1 , 2, 3 or 4.

[0125] More preferred is a method of the present invention, wherein in the selector composition the nitrogen-containing compound is selected from ammonia, monoethanolamine, triethanolamine, guanidine, guanidine derivates such as guanidinium salts or mixtures thereof. In this context “guanidine derivates” are understood as guanidine compounds, which are preferably guanidine in which one or more hydrogen is substituted by functional groups preferably as hydroxy, halogen, amino or C1-C4 alkyl and / or wherein these guanidine compounds are chosen from guanidinium salts.

[0126] Preferred is a method of the present invention, wherein in the selector composition the concentration of the nitrogen-containing compound is of from 1 g / L to 50 g / L, preferred of from 2 g / L to 40 g / L, more preferred of from 3 g / L to 35 g / L, more preferred of from 5 g / L to 30 g / L.

[0127] Even more preferred is a method of the present invention, wherein in the selector composition

[0128] (i) comprises a) a first nitrogen-containing compound which is selected from ammonia, monoethanolamine, triethanolamine or mixtures thereof; and b) a second nitrogen-containing compound which is selected from guanidine, guanidine compounds such as guanidinium salts, or mixtures thereof; and

[0129] (ii) has a pH of from 9 to 12.

[0130] Even more preferred is a method of the present invention, wherein in the selector composition

[0131] (i) comprises a) a first nitrogen-containing compound which is selected from ammonia, monoethanolamine, triethanolamine or mixtures thereof; and b) a second nitrogen-containing compound which is selected from guanidine, guanidine compounds such as guanidinium salts, or mixtures thereof; and

[0132] (ii) has a pH of from 9 to 12, wherein in the selector composition the concentration of the first nitrogen-containing compound is of from 1 g / L to 50 g / L, preferred of from 2 g / L to 40 g / L, more preferred of from 3 g / L to 35 g / L, more preferred of from 5 g / L to 30 g / L, and in the selector composition the concentration of the second nitrogen-containing compound is of from 1 g / L to 10 g / L, preferred of from 2 g / L to 8 g / L, more preferred of from 3 g / L to 7 g / L, more preferred of from 4 g / L to 6 g / L.

[0133] Preferred is a selector composition which

[0134] (i) comprises a) a first nitrogen-containing compound which is selected from ammonia, monoethanolamine, triethanolamine or mixtures thereof; and b) a second nitrogen-containing compound which is selected from guanidine, guanidine compounds such as guanidinium salts, or mixtures thereof; and

[0135] (ii) has a pH of from 9 to 12, wherein in the selector composition the concentration of the first nitrogen-containing compound is of from 1 g / L to 50 g / L, preferred of from 2 g / L to 40 g / L, more preferred of from 3 g / L to 35 g / L, more preferred of from 5 g / L to 30 g / L, and in the selector composition the concentration of the second nitrogen-containing compound is of from 1 g / L to 10 g / L, preferred of from 2 g / L to 8 g / L, more preferred of from 3 g / L to 7 g / L, more preferred of from 4 g / L to 6 g / L..

[0136] Preferred is a method of the present invention, wherein the selector composition during step Pre-(lb)(c) has a temperature in a range from 20°C to 90°C, preferably in a range from 25°C to 80°C, more preferably in a range from 30°C to 70°C, most preferably in a range from 40°C to 60°C.

[0137] Preferred is a method of the present invention, wherein step Pre-(lb)(c) is carried out for 1 minute to 10 minutes, preferably for 2 minutes to 8 minutes, more preferably for 3 minutes to 7 minutes, even more preferably for 3.5 minutes to 6 minutes, most preferably for 4 minutes to 5.5 minutes.

[0138] Step (I) activating the surface of a non-conductive or carbon-fibres containing substrate

[0139] Step (l)(b) providing an agueous, palladium-free activation composition

[0140] In step (l)(b) of the method of the present invention, an agueous, palladium-free activation composition is provided.

[0141] In view of the palladium-free activation, the activation, as part of the method of the present invention, relies on the fact, that the particles are formed again and again in situ, which renders any stabilization or stabilizer compounds obsolete. For that, the dissolved transition metal ions, and the metal particles thereof are present in a reversible eguilibrium. As a result, a very effective and strong activation can be achieved because fresh particles without a shell of stabilizer compounds around them are formed with a relatively short lifetime. Subse- guently, they are reacted back into their ionic form by oxidation. Upon adding further reducing agent fresh particles are formed again, i.e. in situ. In the palladium-free activation, a transition metal is deposited on the surface of said substrate and an activated surface for subseguent metallization is obtained. This means that the concentration of dissolved metal ions of the first species decreases over time due to deposition. However, replenishment of the first species is easily achieved by simply adding ions of that species. Therefore, replenishment is extremely easy and simple. This furthermore, significantly increases the lifetime of a respective activation composition and a thereto related method.

[0142] The agueous composition utilized in the method of the present invention is an agueous composition, which means that water is the primary component. Thus, more than 50 wt.-% of the composition is water, based on the total weight of the aqueous composition, preferably at least 70 wt.-%, even more preferably at least 90 wt.-%, most preferably 95 wt.-% or more. Only in rare cases it is preferred that the composition comprises one or more than one solvent (other than water) that is miscible with water. However, most preferred (for ecological reasons) is a method, wherein water is the only solvent, and, thus, most preferably the composition is substantially free of or does not comprise organic solvents at all.

[0143] In the context of the present invention, the term “substantially free of or does not comprise” of a subject-matter (e.g. a compound, a chemical, a material, etc.) independently denotes that said subject-matter is not present at all (“does not comprise”) or is present only in (to) a very little and non-disturbing amount (extent) without affecting the intended purpose of the invention (“substantially free of”). For example, such a subject-matter might be added or utilized unintentionally, e.g. as unavoidable impurity, “substantially free of or does not comprise” preferably denotes 0 (zero) ppm to 5 ppm, based on the total weight of e.g. the activation composition, preferably 0 ppm to 3 ppm, more preferably 0 ppm to 1.5 ppm, even more preferably 0 ppm to 1 ppm, most preferably 0 ppm to 0.5 ppm, even most preferably 0 ppm to 0.1 ppm. This principle applies likewise to other subject-matters, e.g. to the total weight of the transition metal obtained in step (l)(c) of the method of the present invention.

[0144] The activation composition has an acidic pH, a neutral pH, or an alkaline pH, preferably an acidic or neutral pH, most preferably an acidic pH.

[0145] Preferred is a method of the present invention, wherein the pH of the activation composition is in a range from > 2.0 to < 13.0, preferably in a range from > 3.0 to < 12.0, more preferably in a range from > 4.0 to < 11 .0, most preferably in a range from > 4.5 to < 10.0.

[0146] In some cases, a method of the present invention is preferred, wherein the pH of the activation composition is in a range from > 3.0 to < 6.5, preferably in a range from > 4.0 to < 6.0. Preferably this applies with the proviso that the one or more than one reducing agent comprises a borohydride.

[0147] The pH in the activation composition is typically a result of the presence of (i) to (iii). If an adjustment of the pH is necessary, it is carried out by typical means. Preferred acids are mineral acids and organic acids. A preferred mineral acid is sulfuric acid. A preferred organic acid is the acid form of the one or more than one complexing agent. A preferred alkaline compound is an alkaline hydroxide, preferably NaOH, an alkaline carbonate, preferably sodium carbonate, and ammonia.

[0148] In the context of the present invention, the pH is determined at a temperature of 20°C, i.e. the defined pH is referenced to 20°C. Thus, only for the sake of pH determination the activation composition has a temperature of 20°C. This does not mean that the activation composition in itself is limited to the specific temperature of 20°C. For preferred temperatures of the activation composition see below.

[0149] If the pH is significantly below 2 or above 13 a mostly insufficient activation is obtained. If the pH is too acidic typically acid-sensitive reducing agents decompose too quickly. On the contrary, if the pH is too alkaline, alkaline-sensitive reducing agents decompose too quickly.

[0150] The aqueous composition utilized in the method of the present invention is palladium-free. Therefore, the activation composition is substantially free of or does not comprise palladium ions. This means that neither compounds comprising palladium are present nor palladium atoms / particles or palladium ions. Advantageously, the present invention is an excellent alternative to palladium-containing activation processes with identical or at least almost identical results in terms of activation.

[0151] Preferably, no other noble metals or at least expensive / rare metals are used in the activation composition, in particular no second species of dissolved metal ions being different from the first species are used which could be reduces with the reducing agent. Thus, preferred is a method of the present invention, wherein the activation composition is substantially free of or does not comprise platinum ions, gold ions, silver ions, rhodium ions, ruthenium ions, and iridium ions, preferably is substantially free of or does not comprise platinum, gold, silver, rhodium, ruthenium, and iridium.

[0152] The aqueous composition utilized in the method of the present invention comprises (i) copper ions as a first species of dissolved transition metal ions and additionally metal particles thereof, meaning copper particles.

[0153] Preferred is an activation composition, wherein said copper particles are nanoparticles.

[0154] Even more preferred is an activation composition, wherein the the copper particles have a particle diameter in a range from 0.1 nm to 500 nm, preferably in a range from 0.5 nm to 200 nm, more preferably in a range from 1 .0 nm to 100 nm, most preferably in a range from 3 nm to 50 nm, even most preferably in a range from 5 nm to 15 nm.

[0155] More preferred is a method of the present invention, wherein the copper particles as the first species in the activation composition are colloidal copper particles.

[0156] Thus, preferred is a method of the present invention, wherein the activation composition is a colloid, preferably a colloidal suspension. However, the activation composition is still a clear but colored solution depending on the coloring effect caused by the dissolved ions, primarily of the first species.

[0157] In the activation composition said dissolved copper ions as transition metal ions of the first species and said metal particles thereof form together a total amount of the metal of the first species. Preferred is a method of the present invention, wherein in the activation composition the metal ions of the first species and the metal particles thereof form a total concentration in a range from 0.05 g / L to 30.0 g / L, based on the total volume of the activation composition and based on an ionic, non-particular form, preferably in a range from 0.07 g / L to 18.0 g / L, more preferably in a range from 0.09 g / L to 12.0 g / L, even more preferably in a range from 0.11 g / L to 8.0 g / L, most preferably in a range from 0.15 g / L to 6.0 g / L, even most preferably in a range from 0.2 g / L to 3.0 g / L. This means that for determining said total concentration the transition metal particles of the first species are considered / calculated as dissolved metal ions.

[0158] Although the method of the present invention can be basically carried out with comparatively high concentrations of the first species, it turned out that surprisingly very low concentrations are already sufficient to obtain very efficient and excellent results (see examples). This is in particular advantageous in terms of waste-water treatment and is thus cost- and ecofriendly.

[0159] The method of the present invention, uses copper as the first species. Copper is a cost efficient metal compared to commonly used palladium but achieve sufficient activation on the surface of the non-conductive or carbon-fibres containing substrate. The aforementioned concentrations apply to copper.

[0160] Preferred is a method of the present invention, wherein the source of dissolved copper ions is selected from the group consisting of copper sulfate, copper chloride, copper nitrate, copper fluoroborate, copper acetate, copper citrate, copper phenyl sulfonate, copper para-tolu- ene sulfonate, and copper alkyl sulfonates. A preferred copper alkyl sulfonate is copper methane sulfonate. The most preferred copper source is copper sulfate, most preferably CuSCL * 5 H2O.

[0161] In addition to the first species, the aqueous, palladium-free activation composition comprises (ii) one or more than one complexing agent. Preferably, the one or more than one complexing agent is suitable to form complexes with the dissolved copper ions as transition metal ions of the first species.

[0162] Preferred is a method of the present invention, wherein the one or more than one complexing agent comprises or is an organic complexing agent, preferably a carboxylic acid and / or salts thereof, more preferably a di- or tricarboxylic acid and / or salts thereof, even more preferably a tricarboxylic acid and / or salts thereof, most preferably a hydroxy tricarboxylic acid and / or salts thereof, even most preferably citric acid, structural isomers, and / or salts thereof. A preferred structural isomer is iso-citric acid and salts thereof. Most preferably, the one or more than one complexing agent defined above (including the preferred variants) is the only complexing agent in the activation composition.

[0163] Preferred is a method of the present invention, wherein in the activation composition - the copper ions as metal ions of the first species and the metal particles thereof forming together a total concentration based on the total volume of the activation composition and based on an ionic, non-particular form, and

[0164] - the one or more than on complexing agent in a total concentration are present in a molar ratio in a range from 1 .0 : 0.2 to 1.0 : 100.0, preferably in a range from 1.0 : 0.5 to 1.0 : 50.0, more preferably in a range from 1.0 : 0.85 to 1.0 : 25.0, even more preferably in a range from 1.0 : 0.95 to 1.0 : 15.0, yet even more preferably in a range from 1.0 : 1.0 to 1.0 : 10.0, most preferably in a range from 1.0 : 1.1 to 1.0 : 5.0. This very preferably applies, if the one or more than one complexing agent comprises a tricarboxylic acid and / or salts thereof, more preferably a hydroxy tricarboxylic acid and / or salts thereof, most preferably citric acid, structural isomers, and / or salts thereof.

[0165] Preferred is a method of the present invention, wherein the one or more than one complexing agent in the activation composition is present in a total amount in a range from 0.01 mol / L to 0.5 mol / L, based on the total volume of the activation composition, preferably in a range from 0.015 mol / L to 0.35 mol / L, more preferably in a range from 0.02 mol / L to 0.3 mol / L, most preferably in a range from 0.023 mol / L to 0.275 mol / L.

[0166] In addition to the first species, and the one or more than one complexing agent, the aqueous, palladium-free activation composition comprises permanently or temporarily (iii) one or more than one reducing agent. The one or more than one reducing agent is essential for forming the copper particles as metal particles from the dissolved transition metal ions of the first species. For that, the dissolved transition metal ions are chemically reduced, continuous or semi-continuous, in order to form said particles. Thus, said particles are either formed continually or semi-continually, respectively, depending on the presence of the one or more than one reducing agent in the activation composition, which is permanent or temporary. However, when the one or more than one reducing agent is present, typically said particles will be formed until said reducing agent is used up or insufficiently present. Preferred is a method of the present invention, wherein the oxidation affects said particles and is in constant competition with the reduction. Typically, oxidation starts as soon as the one or more than one reducing agent is used up, which is explicitly desired in the context of the present invention.

[0167] Said oxidation is furthermore very relevant if in the method of the present invention after one or more than one first step (c) the method is interrupted for a comparatively long time. In order to prevent precipitating agglomerates during such a time, in the activation composition said oxidation is carried out until no particles are any longer present but rather only dissolved transition metal ions. Preferably, the oxidation is accelerated by adding an oxidizing agent, more preferably a peroxide, most preferably hydrogen peroxide. Upon resuming operation, particles are formed by adding continually or semi-continually the one or more than reducing agent to re-form particles. Afterwards, the method of the present invention is resumed.

[0168] Thus, preferably the one or more than one reducing agent is suitable for reducing copper ions as the dissolved transition metal ions of the first species.

[0169] In some cases, preferred is a method of the present invention, wherein the one or more than one reducing agent comprises one or more than one hydrogen atom such that hydrogen is released upon reducing said transition metal ions, which at least partly adsorbs on said activated surface.

[0170] In some cases, a method of the present invention is preferred, wherein the one or more than one reducing agent comprises an aldehyde, preferably formaldehyde, glyoxylic acid, salts of glyoxylic acid, or mixtures thereof, most preferably as the only reducing agent. In such a case formation of boric acid is avoided.

[0171] In some cases, a method of the present invention is preferred, wherein the one or more than one reducing agent comprises hydrazine, most preferably as the only reducing agent. Also, in such a case formation of boric acid is avoided.

[0172] Preferred is a method of the present invention, wherein the activation composition comprises the one or more than one reducing agent in a total concentration in a range from 0.2 mmol / L to 500.0 mmol / L, based on the total volume of the activation composition, preferably in a range from 0.4 mmol / L to 350.0 mmol / L, more preferably in a range from 0.6 mmol / L to 250.0 mmol / L, even more preferably in a range from 0.8 mmol / L to 150.0 mmol / L, most preferably in a range from 1.0 mmol / L to 80.0 mmol / L. An in particular preferred total concentration is in a range from 0.9 mmol / L to 50.0 mmol / L, very preferably in a range from 1.0 mmol / L to 30.0 mmol / L, most preferably in a range from 1.1 mmol / L to 10.0 mmol / L. Most preferably, this applies to the aforementioned preferred, more preferred, etc. reducing agents, most preferably to a borohydride.

[0173] Generally preferred is a method of the present invention, wherein in the activation composition

[0174] - the copper ions as metal ions of the first species and the metal particles thereof forming together a total concentration based on the total volume of the activation composition and based on an ionic, non-particular form, and

[0175] - the one or more than on reducing agent (if semi-continually added, in the moment of addition) in a total concentration are present in a molar ratio of more than 0.5, preferably of 1 or more, more preferably of 2 or more, even more preferably of 3 or more, most preferably of 3.5 or more. Very preferred is a molar ratio in the range from 1 to 20. Thus, in the activation composition the one or more than one reducing agent is preferably present (either permanently or temporarily) in such a total concentration that the dissolved transition metal ions of the first species are not quantitatively reduced into the respective particles. Furthermore, a method of the present invention is preferred, wherein the activation composition does not predominantly exhibit a reductive environment to prevent oxidation of the metal particles. On the contrary, as already mentioned, oxidation is required and desired. Thus, preferred is a method of the present invention, wherein the activation composition is predominantly kept in oxidizing condition to allow oxidation of the metal particles.

[0176] Particularly preferred is a method of the present invention, wherein in the activation composition

[0177] - the copper ions as metal ions of the first species and the metal particles thereof forming together a total concentration based on the total volume of the activation composition and based on an ionic, non-particular form, and

[0178] - the one or more than on reducing agent (if semi-continually added, in the moment of addition) in a total concentration are present in a molar ratio in a range from 0.3 to 60.0, preferably in a range from 0.5 to 30.0, more preferably in a range from 1 .0 to 20.0, even more preferably in a range from 1 .5 to 10.0, most preferably in a range from 1 .8 to 3.0.

[0179] In some cases, a method of the present invention is preferred, wherein in the aqueous, palladium-free activation composition the one or more than one reducing agent is permanently present. Thus, preferred is that the one or more than one reducing agent is added to the activation composition continually, preferably by a permanent flow of a respective liquid containing said one or more than one reducing agent. In this approach oxidation and reduction are taking place simultaneously over the time during step (c) of the method of the present invention is carried out. As a result, the metal particles are present in a comparatively constant concentration.

[0180] Alternatively, a method of the present invention is preferred, wherein in the aqueous, palladium-free activation composition the one or more than one reducing agent is temporarily present. Thus, preferably the one or more than one reducing agent is added semi-continuously; e.g. in consecutive portions with time-wise interruptions between each portion. This means that when the one or more than one reducing agent is added fresh particles are formed. However, during the interruptions the oxidation, creating the dissolved transition metal ions, is very dominant. As a result, the metal particles are present in a basically varying concentration. However, depending on the length of the time-wise interruptions and making sure that the interruptions are not too long, such an approach is fully sufficient to successfully activate surfaces of even a plurality of non-conductive or carbon-fibres containing substrates. Therefore, this approach is in particular preferred.

[0181] However, in either case preferred is a method of the present invention, wherein the one or more than one reducing agent is present in such a way that the equilibrium remains reversible. Thus, the reversible equilibrium is not only a side reaction or an undesired side reaction.

[0182] Upon oxidation, in the activation composition the total concentration of the dissolved transition metal ions basically increases as a result of the reversible equilibrium, wherein the total amount of said metal particles decreases. This reversible equilibrium is preferably monitored for a better process control. Therefore, preferred is a method of the present invention, wherein the reversible equilibrium is monitored by UV / VIS inspection. Preferably, said dissolved transition metal ions are monitored at a wavelength within a range from 700 nm to 800 nm, preferably within a range from 710 nm to 780 nm, more preferably within a range from 720 nm to 760 nm, most preferably within a range from 730 nm to 750 nm. Also preferred is that said metal particles are monitored at a wavelength within a range from 400 nm to 600 nm, preferably within a range from 450 nm to 550 nm. This allows determining when to add one of the one or more than one reducing agent in order to form, preferably re-form, said metal particles in order to increase their total amount.

[0183] Thus, preferred is a method of the present invention, wherein the one or more than one reducing agent is continually or semi-continually added to the activation composition such that further metal particles are continually or semi-continually, respectively, formed from the dissolved transition metal ions of the first species, preferably added after one or more than one step (c) is carried out.

[0184] Preferred is a method of the present invention, wherein the copper particles as metal particles of the first species are continually or semi-continually formed in situ in the activation composition by said reduction after and / or during one or more than one step (c) is carried out. This preferably defines that in the method of the present invention step (c) is carried out more than one time, preferably the method, including step (c), is carried out repeatedly. It is very preferred that after one, more than one, or each step (c) of the method of the present invention metal particles are freshly formed by said reduction. This is possible because said oxidation is allowed and desired, leading, preferably continually but at least semi-continually, to fresh dissolved transition metal ions ready for re-reduction. This is contrary to common approaches, wherein metal particles are formed (and stabilized) before the activation is carried out, which afterwards typically last as long as possible by particle stabilization until the respective activation composition is unstable and inoperable. As mentioned throughout the text, in the context of the present invention it is preferably necessary to add at least semi-continually a reducing agent. Typically, the reducing agent used for said reduction reacts with the dissolved transition metal ions and leads to a reducing agent degradation product, preferably boric acid and / or salts thereof. Usually, such degradation products accumulate in the activation composition, which is not preferred in the context of the present invention. Therefore, a method of the present invention is preferred, wherein the method is performed by bleed and feed. In such an approach, a certain volume of the activation composition is removed (e.g. by drag out; thereby removing also degradation products) and replaced by a replacement volume (e.g. by means of replenishment) in such a way that essential components in the activation composition have a sufficiently constant concentration. This means that the replacement volume typically does not comprise boric acid and / or salts thereof, preferably does not comprise the reducing agent degradation product. This is also beneficial for stabilizing the pH to a basically constant pH.

[0185] Preferred is a method of the present invention, wherein the activation composition comprises boric acid and / or salts thereof in a total concentration of 5 g / L or less, based on the total volume of the activation composition, preferably of 3 g / L or less, more preferably of 2 g / L or less, most preferably of 1.2 g / L or less. This preferably applies with the proviso that (1) the one or more than one reducing agent comprises a borohydride and (2) step (c) is carried out more than one time.

[0186] Preferred is a method of the present invention, wherein the reversible equilibrium is not predominantly shifted to the metal particles over the majority of time during which step (c) is carried out.

[0187] Preferred is a method of the present invention, wherein during and / or after step (c) the majority of said metal particles is subjected to said oxidation. Majority preferably denotes more than 50% of the particles.

[0188] Preferred is a method of the present invention, wherein “repeatedly involved” explicitly includes at least more than once, preferably more than twice, even more preferably more than three times, most preferably more than four times, even most preferably over the entire lifetime of the activation composition.

[0189] Own experiments have shown that it is in particular the oxidation that prevents agglomeration. The copper particles as metal particles are oxidized back into their ionic / dissolved form. This means that there is not sufficient time for the particles to form higher aggregates and to even form agglomerates. Although each suitable oxidation agent is basically applicable, ambient air proved to be an excellent choice. It is sufficiently strong and ubiquitous available. Preferred is a method of the present invention, wherein the forming of precipitating agglomerates of said metal particles is prevented through said oxidation, preferably through oxidation by ambient air and / or oxygen gas. Preferred is a method of the present invention, wherein the dissolved transition metal ions are formed from the metal particles through oxidation by ambient air and / or oxygen gas. In both cases the preferred oxidizing agent is molecular oxygen. Most preferred is a method of the present invention, wherein the majority of the dissolved transition metal ions are formed from the majority of the metal particles through oxidation by ambient air and / or oxygen gas.

[0190] In some cases, a method of the present invention is preferred, wherein the continuous or semi-continuous oxidation is additionally or solely achieved through an oxidizing agent, which is not molecular oxygen, more preferably through a peroxide, most preferably hydrogen peroxide. In particular in addition to ambient air this preferably accelerates the oxidation of the particles if this is required, e.g. if an activation composition must be inactivated and stored for longer times.

[0191] In order to sufficiently facilitate the oxidation in the activation composition, preferred is a method of the present invention, wherein the activation composition continually or semi-continually circulates, preferably by shaking, stirring and / or pumping. This is preferred to ensure that the oxidation is equally distributed in the entire activation composition. In other words, this ensures that the metal particles are equally contacted with an oxidizing agent, which facilitates the oxidation.

[0192] The method of the present invention for providing the aqueous, palladium-free activation com- position(step (l)(b) is preferably using a method for preparing an aqueous, palladium-free activation composition for activating a surface of a non-conductive or carbon-fibres containing substrate for metallization (preferably an activation composition as utilized in the method of the present invention), the method of preparing the aqueous, palladium-free activation composition comprising the following steps:

[0193] (1) providing an aqueous starting solution comprising

[0194] - copper ions as a first species of dissolved transition metal ions, and

[0195] - one or more than one complexing agent; and

[0196] (2) continually or semi-continually adding one or more than one reducing agent to the starting solution such that copper particles as metal particles of copper ions as the first species of dissolved transition metal ions are continually or semi- continually, respectively, formed in the solution, with the proviso that said metal particles are continually or semi-continually oxidized to form dissolved transition metal ions of the first species, wherein the method is used to provide the aqueous, palladium-free activation composition according to the method of the present invention above.

[0197] With other words, this method for preparing an aqueous, palladium-free activation composition for activating a surface of a non-conductive or carbon-fibres is used for providing an aqueous, palladium-free activation composition used in the present invention.

[0198] The method for preparation is also directed to the use of continuous or semi-continuous reduction of dissolved copper ions as transition metal ions of a first species in combination with continuous or semi-continuous oxidation of copper particles as metal particles of the first species in a reversible equilibrium to continually or semi-continually form in situ metal particles in an aqueous, palladium-free activation composition to be used in the method for treating a surface of a non-conductive or carbon-fibres containing substrate according to the present invention.

[0199] Preferably, the activation composition used in the method of the present invention is obtained at and / or has a temperature in a range from 10°C to 90°C, preferably in a range from 14°C to 75°C, more preferably in a range from 16°C to 65°C, most preferably in a range from 18°C to 45°C, even most preferably in a range from 20°C to 32°C. In particular preferred is a temperature in a range from 18°C to 45°C, preferably in a range from 20°C to 32°C, with the proviso that the one or more than one reducing agent is a borohydride, preferably sodium borohydride. This in particular preferably also applies to the method for preparing said activation composition to be used in the method of the present invention.

[0200] More preferably, the activation composition used in the present invention is not obtained at and / or has not a temperature above 110°C, preferably above 100°C, more preferably above 95°C. Most preferably the activation composition of the present invention is not obtained at a temperature above 110°C. This likewise preferably applies to the method for preparing said activation composition to be used in the method of the present invention.

[0201] Step (l)(c) contacting the substrate with said activation composition

[0202] In step (l)(c) of the method of the present invention, the substrate is contacted with the aqueous, palladium-free activation composition in order to obtain an activated surface. Preferably step (I) is conducted after one or more of the pre-treatment steps (Pre-(l), Pre-(la), Pre-(lb)) as explained above. Preferred is a method of the present invention, wherein in step (l)(c) the contacting is carried out at a temperature in a range from 10°C to 90°C, preferably in a range from 14°C to 75°C, more preferably in a range from 16°C to 65°C, most preferably in a range from 18°C to 45°C, even most preferably in a range from 20°C to 32°C. In particular preferred is a temperature in step (lll)(c) in a range from 18°C to 45°C, preferably in a range from 20°C to 32°C, and wherein the reduction through the one or more than one reducing agent is a borohydride, preferably sodium borohydride.

[0203] Preferred is a method of the present invention, wherein in step (l)(c) the contacting is carried out for a time in a range from 1 minute to 10 minutes, preferably for 2 minutes to 8 minutes, more preferably for 3 minutes to 6 minutes, most preferably for 3.5 minutes to 5 minutes.

[0204] Preferred is a method of the present invention, wherein after step (l)(c) a rinsing step is carried out. In such a case a rinsed, activated surface for metallization is obtained. Preferably, the rinsing is carried out with water.

[0205] Preferred is a method of the present invention, wherein the method is carried out for 10 days or more, without replacing the majority of the activation composition in one step (i.e. more than 50 vol.-% of the composition), preferably 50 days or more, more preferably 200 days or more, even more preferably 1 year or more, most preferably 2 years or more, even most preferably 5 years or more.

[0206] Step (II) an enhancer treatment of the activated surface of a non-conductive or carbon-fibres containing substrate

[0207] Preferred is a method of the present invention, wherein in step (l)(b) - providing an alkaline aqueous enhancer composition comprising water and a formaldehyde compound, wherein the formaldehyde compound is formaldehyde or a water-soluble formaldehyde precursor. A formaldehyde precursor is understood as a source of formaldehyde that is converted into formaldehyde in the aqueous enhancer composition, e.g. sodium formaldehyde bisulfite and hexamethylenetetramine. Formaldehyde is most preferred.

[0208] Preferably the concentration of the formaldehyde in the alkaline aqueous enhancer composition is from 3 g / l to 30 g / l, preferably from 10 g / L to 20 g / L.

[0209] Preferably the alkaline aqueous enhancer composition has a pH preferable from 8 to 13, more preferably from 10.5 to 12.5 (at 20°C).

[0210] In a preferred embodiment of the present invention, the concentration of the formaldehyde in the alkaline aqueous enhancer composition is from 10 g / l to 20 g / L and the alkaline aqueous enhancer composition has a pH from 10.5 to 12.5 (at 20°C). pH values can be easily adjusted with a pH adjuster, preferably the pH adjuster is selected from the group consisting of hydrochloric acid, sulfuric acid, sodium hydroxide and potassium hydroxide.

[0211] In step (I l)(c) of the method of the present invention, the substrate is contacted with the alkaline aqueous enhancer composition in order to obtain an enhanced surface for subsequent electroless metallization. Preferred is a method of the present invention, wherein in step (I l)(c) the contacting is carried out at a temperature in a range from 10°C to 50°C, preferably in a range from 20°C to 40°C, more preferably in a range from 25°C to 35°C. In particular preferred is a temperature in step (I l)(c) in a range from 25C to 35°C, and the enhancer composition has a pH from 10.5 to 12,

[0212] Preferred is a method of the present invention, wherein in step (I l)(c) the contacting is carried out for a time in a range from 0.5 minute to 4 minutes, preferably for 0.5 minutes to 2 minutes, more preferably 1 to 1.5 min.

[0213] Preferably step (II) is directly, more preferred without any further treatment steps, processed after step (I).

[0214] Step (III) an electroless copper depositing of the enhanced surface of a non-conductive or carbon-fibres containing substrate

[0215] Preferred is a method of the present invention, wherein in step (III) the electroless copper metallization layer (also mentioned as first metallization solution) is a distinct layer deposited on the transition metal obtained in step (l)(c) and additionally treated in the step (II) of the method of the present invention.

[0216] Preferred is a method of the present invention, wherein in step (III) the electroless copper metallization solution comprises a reducing agent or does not comprise a reducing agent, preferably comprises a reducing agent.

[0217] Preferred is a method of the present invention (for metallizing), wherein step (III) is carried out at a temperature in a range from 10°C to 95°C, preferably in a range from 15°C to 85°C, more preferably in a range from 20°C to 65°C, even more preferably in a range from 25°C to 55°C, most preferably in a range from 30°C to 45°C.

[0218] Preferred is a method of the present invention, wherein step (I ll)(c) is carried out for 30 seconds to 180 minutes, preferably for 45 seconds to 120 minutes, more preferably for 1 minutes to 60 minutes, most preferably for 1.5 minutes to 45 minutes.

[0219] Preferred is a method wherein the enhanced surface of the substrate is almost (means more than 90 %, preferably more than 95 %) completely black shining within 90 seconds, preferably within 60 seconds, more preferably shorter than 60 seconds in step (I ll)(c).

[0220] More preferred is a method of the present invention, wherein in step (III) the electroless copper metallizing solution of step (III) is an autocatalytic type metallization solution comprising copper ions and a reducing agent capable to reduce copper ions to metallic copper that a first copper layer is deposited on the enhanced surface. The reducing agent can be preferably selected from the group consisting of formaldehyde, hypophosphite, dimethylamine borane, glyoxylic acid and 2,2'-dialkoxyacetaldehydes. The aldehyde has the advantage that it is inexpensive, provides a strong reduction potential in alkaline aqueous solutions and generally leads to copper deposits of high quality. The reducing agent can successfully be used in combination with various complexing agents, such as EDTA, triethanolamine (TEA), quadrol, tartrate, citrate, different carbohydrates and carbohydrate derivatives.

[0221] In principle, electroless copper metallization compositions are known to the skilled person. E.g. Printoganth® MV Plus Electroless Copper can be used as electroless copper metallization composition.

[0222] Preferably step (III) is directly processed after step (II).

[0223] Use of the inventive method

[0224] The inventive method for electroless copper depositing onto a surface of a non-conductive or carbon-fibres containing substrate can be used for subsequent metallization of first copper layer.

[0225] Thus, a method of the present invention for metallizing an electroless deposited copper surface of a non-conductive or carbon-fibres containing substrate is preferred, the method comprising the steps:

[0226] (A) providing the non-conductive or carbon-fibres containing substrate with the electroless deposited copper surface obtained by a method according to method above; and

[0227] (B) metallizing the electroless deposited copper surface by contacting the electroless deposited copper surface with metallizing solution such that a second metallization layer is electrically deposited on the electroless deposited copper surface.

[0228] The method for metallizing an electroless deposited copper surface can be preferably used in the manufacturing of SAP applications.

[0229] Preferred is a method of the present invention (for metallizing), wherein in step (B) the second metallizing solution is an acidic copper solution comprising copper ions and optional alloying metal ions, more preferred no alloying metal ions.

[0230] Preferred is a method of the present invention (for metallizing), wherein in step (B) the second metallization layer is electrolytical deposited within 0.5 hour to 2.5 hours, preferably within 1 to 2 hours wherein a current is applied between an anode and the cathodic substrate. This most preferably applies if the second metallization layer comprises copper; preferably is a copper layer.

[0231] The used metallizing solution for depositing a second metallization layer are typically used and known to the skilled person.

[0232] The present invention is described in more detail by the following non limiting examples.

[0233] Examples

[0234] Test methods:

[0235] Solder shock test:

[0236] Following electroless copper plating, the electrical reliability coupons were immersed for 10 s in a 10% H2SO4 solution at room temperature and then 40 pm of copper were electrolyti- cally plated onto the coupons. The coupons were then annealed for 6 hours at 140 °C and, after cooling to room temperature, were subjected to a solder shock test, in which the coupons were floated for 10 s on molten solder at 288 °C or 326 °C and then allowed to cool to room temperature again. This floating and cooling procedure was repeated a further 6 times at 288 °C and 9 times at 326 °C. Solder shock test performance is given in percent [%] (mean) of interconnect defects. Equipment and general test procedure could be found e.g. in norm the IPC-TM-650 (No. 2.6.8) of the Association Connecting Electronics Industries®.

[0237] Visual inspection after step (B)

[0238] The treated coupons after step (B) were visual inspected with naked eye for appearance. Good results show a copper surface having a salmon pink color and are blister-free and were evaluated from “+” to “+++”.

[0239] Visual inspection after 60 seconds of step (III)

[0240] The treated coupons after 60 seconds of step (III) were visual inspected with naked eye for appearance and coverage. Good results show a completely black covered surface and were evaluated from “+” to “+++” and bad results show a partly covered yellow to greyish surface and were evaluated from

[0241] Test coupons

[0242] Bare FR4 test coupons (Panasonic MC100EX) were used for the assessment of the quality of the copper deposits. The parameters tested were appearance, blistering, and electrical reliability. The test coupons were treated in different sets to show the invention in different aspects. In some sets, a palladium standard was also processed as reference.

[0243] Examples

[0244] 1. Visual inspection and Solder shock test after step (B) A number of coupons was processed according to the conditions detailed in Table 1 , wherein the pH of the enhancer composition was varied, Table 2 (palladium standard), without certain steps of Table 1 and mentioned as inventive example - InvEx, and comparative example - Ex.

[0245] Table 1 Operating parameters are known to the one skilled in the art.

[0246] Some coupons (InvEx 3, 4) were processed wherein additionally to Table 1 between step Pre-(l) and step Pre-(lb), an acidic rinsing step (Pre-(la) was processed as follows:

[0247] Some Coupons (Ex 1 , 2) were processed according to the conditions detailed in Table 2 comprising a palladium activation as comparative example “Palladium Standard”.

[0248] Table 2 StepaBath Immersion Time [s]

[0249] 1 Securiganth® MV Cleaner PF 240

[0250] 2 Neoganth® MV Etch Cleaner SPS 60

[0251] 3 Neoganth® MV Pre Dip 60

[0252] 4 Neoganth® MV Activator (Palladium) 240

[0253] 5 Neoganth® MV Reducer S 180

[0254] 6 Printoganth® MV Plus Electroless Copper 1200aTap water rinse of approximately 60 s between each step, except between steps 3 and 4.

[0255] The following results were summarized in Table 3:

[0256] Table 3 n.t. - not tested

[0257] Solder shock test results at 288°C show already slight improvements by using the enhancer step. If solder shock tests are conducted at 326°C, the inventive effect is in particular strong to see. No solder shock tests were done for comparative example Ex 5 and 6, because the copper surface shows already strong blister and a greenish, irregular color. 2. Visual inspection after step (III) and Solder shock test after step (B)

[0258] A number of coupons was processed according to the conditions detailed in Table 4 without step (B), wherein the pH of the enhancer composition was varied from pH 5 to 12.5 including one example without enhancer step to show the starting behavior of the electroless copper depositing in step (III). In the test, the coupons were replaced from the electroless copper metallizing solution after

[0259] 60 seconds, rinsed with DI water and visual inspected.

[0260] Examples pH 5 and 11.5 with were processed in duplicates wherein one coupon was fully treated according to Table 1 and solder shock tests at 288°C and 326°C were conducted. The following results were summarized in Table 4:

[0261] Table 4

[0262] It can be seen that a fast coverage of the enhanced surface by using the inventive enhancer solution before the applying the electroless copper metallization solution leads to good sol- der shock test results in contrast to not using an enhancer solution or using an acidic enhancer solution.

Claims

C L A I M S1. A method for electroless copper depositing onto a surface of a non-conductive or carbon-fibres containing substrate, the method comprising the steps:(I) activating the surface of a non-conductive or carbon-fibres containing substrate for electroless copper depositing, the activation method comprising the steps of(a) providing the substrate;(b) providing an aqueous, palladium-free activation composition comprising(i) a first species of dissolved transition metal ions, wherein the first species are copper ions, and additionally metal particles thereof, wherein the metal particles are copper particles,(ii) one or more than one complexing agent, and(iii) permanently or temporarily one or more than one reducing agent.wherein- the first species of the dissolved transition metal ions and the metal particles thereof are present in a reversible equilibrium, with the proviso that- the metal particles are formed from the dissolved transition metal ions through a continuous or semi-continuous reduction through the one or more than one reducing agent,- the dissolved transition metal ions are formed from the metal particles through continuous or semi-continuous oxidation of said particles, and- the dissolved transition metal ions and the metal particles thereof, respectively, are repeatedly involved in said reduction and said oxidation such that no precipitating agglomerates of said metal particles are formed; and(c) contacting the substrate with said activation composition such that a transition metal is deposited on the surface of said substrate and an activated surface is obtained;(II) an enhancer treatment of the activated surface of a non-conductive or carbon- fibres containing substrate, the enhancer treatment method comprising the steps of(a) providing said substrate;(b) providing an alkaline aqueous enhancer composition comprising water and a formaldehyde or a water-soluble formaldehyde precursor, wherein the alkaline aqueous enhancer composition has a pH from 7.1 to 13; and(c) contacting the substrate with the alkaline aqueous enhancer composition such that an enhanced surface is obtained; and(III) an electroless copper depositing of the enhanced surface of a non-conductive or carbon-fibres containing substrate, the electroless copper depositing method comprising the steps of(a) providing said substrate;(b) providing an electroless copper metallizing solution; and(c) contacting the substrate with the electroless copper metallizing solution such that a first copper layer is deposited on the enhanced surface.

2. The method of claim 1 , wherein during and / or after step (l)(c) the majority of said metal particles is subjected to said oxidation.

3. The method of claim 1 or 2, wherein the metal particles of the first species in the activation composition are colloidal metal particles.

4. The method of any of the aforementioned claims, wherein the metal particles of the first species are continually or semi-continually formed in situ in the activation composition by said reduction after and / or during one or more than one step (l)(c) is carried out.

5. The method of any of the aforementioned claims, wherein the one or more than one reducing agent comprises a boron-containing reducing agent, preferably a borohy- dride.

6. The method of any of the aforementioned claims, wherein the one or more than one reducing agent is continually or semi-continually added to the activation composition such that further metal particles are continually or semi-continually, respectively, formed from the dissolved transition metal ions of the first species, preferably added after one or more than one step (l)(c) is carried out.

7. The method of any of the aforementioned claims, wherein the water-soluble formaldehyde precursor is sodium formaldehyde bisulfite or hexamethylenetetramine.

8. The method of any of the aforementioned claims, wherein the concentration of the formaldehyde in the alkaline aqueous enhancer composition is from 3 g / l to 30 g / l, preferably from 10 g / l to 20 g / L.

9. The method of any of the aforementioned claims, wherein the alkaline aqueous enhancer composition has a pH from 8 to 13, preferably from 10.5 to 12.5.

10. The method of any of the aforementioned claims, wherein the concentration of the formaldehyde in the alkaline aqueous enhancer composition is from 10 g / l to 20 g / L and wherein the alkaline aqueous enhancer composition has a pH from 10.5 to 12.5.11 . The method of any of the aforementioned claims, wherein the pH is adjusted with a pH adjuster, preferably the pH adjuster is selected from the group consisting of hydrochloric acid, sulfuric acid, sodium hydroxide and potassium hydroxide.

12. The method of any of the aforementioned claims, wherein step (I l)(c) contacting the substrate with the aqueous enhancer composition is conducted for a time period of 0.5 to 4 min, preferably 0.5 to 2 min.

13. The method of any of the aforementioned claims, wherein the electroless copper solution of step (III) is an autocatalytic type metallization copper solution comprising copper ions and a reducing agent.

14. A method for metallizing an electroless deposited copper surface of a non-conductive or carbon-fibres containing substrate, the method comprising the steps:(A) providing the non-conductive or carbon-fibres containing substrate with the electroless deposited copper surface obtained by a method according to any of claims 1 to 13; and(B) metallizing the electroless deposited copper surface by contacting the electroless deposited copper surface with metallizing solution such that a second metallization layer is electrically deposited on the electroless deposited copper surface.

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