WO2025168540A1

WO2025168540A1 - Process for producing a flexible plastic-copper layer composite by electrolytic deposition of copper

Info

Publication number: WO2025168540A1
Application number: PCT/EP2025/052780
Authority: WO
Inventors: Sven Lamprecht; Kai-Jens Matejat; Akif ÖZKÖK
Original assignee: Atotech Deutschland GmbH and Co KG
Current assignee: Atotech Deutschland GmbH and Co KG
Priority date: 2024-02-09
Filing date: 2025-02-04
Publication date: 2025-08-14
Anticipated expiration: 2026-08-09

Abstract

The invention relates to a process for producing a flexible plastic-copper layer composite wherein a copper layer is electrolytically deposited on a conductive, flexible plastic substrate to obtain the composite in a roll-to-roll coating process wherein the substrate is transported to a plating device comprising a plating tank, a cathode, an insoluble anode and an electrolyte solution in order to be deposited in the plating device; the substrate is immersed in the electrolyte solution contained in the plating tank and the substrate is in contact with the cathode; the insoluble anode is used as counter-electrode to the cathode and is placed next to the substrate within electrolyte solution in the plating tank; the electrolyte solution contains copper ions, organic additives and an Fe2+/Fe3+ redox system; the concentration of copper ions in the electrolyte solution is maintained constant by passing the electrolyte solution through a copper dissolution unit; in the copper dissolution unit, the electrolyte solution is in contact with an auxiliary anode and an auxiliary cathode; copper metal and an oxygen-containing gas are introduced into the copper dissolution unit; the auxiliary anode is in contact with the copper metal; the oxygen-containing gas is introduced such that bubbles thereof contact the surface of the copper metal; the copper metal continuously dissolves into the electrolyte solution by being oxidized by the Fe3+ component of the Fe2+/Fe3+ redox system and optionally the oxygen contained in the oxygen-containing gas.

Description

PROCESS FOR PRODUCING A FLEXIBLE PLASTIC-COPPER LAYER COMPOSITE BY ELECTROLYTIC DEPOSITION OF COPPER

DESCRIPTION

Field of the invention

The present invention relates to a process for producing a flexible plastic-copper layer composite by electrolytic deposition of copper layer on a conductive, flexible plastic substrate and, in particular to the means for dissolving the copper to be deposited in the process.

Prior art

The production of flexible plastic-copper layer composite as plastic-copper foils is well-known and starts with transferring the plastic folio into a conductive, plastic foil having a thin copper layer normally deposited by sputtering technology under vacuum. This sputtered copper layer is in the following electrically enforced with copper by electroplating.

CN 115700295 A discloses a continuous preparation technology of a PET composite copper foil roll comprises the steps: S1 - copper is sputtered on the surface of a PET film roll to obtain a primary PET composite copper foil roll; S2 - the primary PET composite copper foil roll is placed in an electrolyte for pulse electroplating, and a final PET composite copper foil roll is obtained. The electrolyte in step S2 was prepared by mixing a copper salt with further additives.

US 5,425,862 relates to an apparatus for the electroplating of thin plastic films, provided on one or both sides with a conductive coating which includes a device which serves for preparing the electrolyte.

During the production of composite copper foils large amounts of copper ions are needed in a continuous manner. In a typical conventional process, the used copper electrolyte is at least partly withdrawn from the plating tank and transferred to a large copper oxide dissolution tank wherein the copper oxide is dissolved under vigorous agitation in order to replenish the used copper electrolyte with copper ions. The dissolution of copper oxide leads to the entry of unwanted further ions as zinc, tin or antimony ions which can lead to unacceptable plating results. Due to oxygen development at the anode in the plating tank during plating, oxygen entry into the electrolyte during dissolution of copper oxide, as well as heat development during the copper oxide dissolution process, the organic compounds contained in the electrolyte solution are destroyed and exist as undefined organic degradation compounds which need to be removed. Therefore, further steps are needed to take care of the destroyed organics and unwanted further ions as metal ions. Here e.g. active carbon is mixed into the solution. The active carbon then absorbs the organic compounds and is subsequently removed by filtration. The spent active carbon must then be disposed of. After filtering, the electrolyte is replenished also with missing organic electrolyte compounds before the solution is transferred back into the plating tank. Thus, providing copper ions by a copper oxide dissolution tank is complex in view of equipment and costs. Beside this, the received copper deposits are showing unwanted high roughness values of the copper surface.

WO 95/18251 A1 describes a process and device for the electrolytic deposition of metallic layers wherein insoluble anodes are used for the electrolytic deposition of uniform metallic layers having determined physico-mechanical properties, in particular copper layers. In the process, compounds of a redox system, comprising e.g. Fe²⁺/Fe³⁺, are added to the deposition solution and react at the insoluble anodes during deposition. The resulting compounds draw new metal ions out of part of a reservoir that contains the metal to be deposited in order to replace the metal ions deposited from the solution. In the process, the additive compounds are not destroyed (to a larger extent).

WO 01/68953 A1 describes a method and device for the regulation of the concentration of metal ions in an electrolyte for the electrolytic deposition of metals, the electrolyte containing additional substances of an electrochemically reversible redox system. According to the method at least a part of the electrolyte is passed through an auxiliary cell, comprising an insoluble auxiliary anode and at least one auxiliary cathode, between which a flow of current is generated by application of a voltage. Excess amounts of the oxidized material from the redox system are thus reduced at the auxiliary cathode and the formation of ions of the metal to be deposited is avoided. According to the method, pieces of the metal to be deposited are used as the auxiliary cathode.

The above conventional method to produce plastic-copper foils is disadvantageous in that it does not provide a sufficient amount of copper ions to be deposited in copper plating applications with high productivity as the production of high volume of flexible resin-copper layer composites, which can be used in particular for battery production. The known copper dissolution unit is relatively complex, large in dimension and expensive.

Thus, it is an object of the invention to provide a continuous process for the production of a flexible, plastic-copper layer composite wherein copper layer is electrolytical ly deposited on a conductive, flexible plastic substrate, which process avoids the disadvantages of the prior art, in particular, which consumes lower amount of organic plating additives and provides high amounts of copper ions to be deposited while leading to improved copper layer deposits. The produced copper layer shall be a high purity copper layer with constant physical properties as a glossy, dense and pores-free surface and which can be carried out by means of a relatively simple device requiring reduced maintenance effort.

Summary of the invention

The invention relates to a continuous process for producing a flexible plastic-copper layer composite wherein

- a copper layer is electrolytical ly deposited on a conductive, flexible plastic substrate to obtain the flexible plastic-copper layer composite in a roll-to-roll coating process wherein the substrate is transported to a plating device comprising a plating tank, a cathode, an insoluble anode and an electrolyte solution, in order to be deposited in the plating device;

- the substrate is immersed in the electrolyte solution contained in the plating tank and the substrate is in contact with the cathode;

- the insoluble anode is used as counter-electrode to the cathode and is placed next to the substrate within the electrolyte solution in the plating tank;

- the electrolyte solution contains copper ions, organic additives and an Fe²⁺/Fe³⁺ redox system;

- the concentration of copper ions in the electrolyte solution is maintained constant by passing a part of the electrolyte solution withdrawn from the plating tank through a copper dissolution unit;

- in the copper dissolution unit, the part of the electrolyte solution is in contact with an auxiliary anode and an auxiliary cathode;

- copper metal and an oxygen-containing gas are introduced into the copper dissolution unit;

- the auxiliary anode is in contact with the copper metal;

- the oxygen-containing gas is introduced such that bubbles thereof contact the surface of the copper metal;

- the copper metal continuously dissolves into the part of the electrolyte solution by being oxidized by the Fe³⁺ component of the Fe²⁺/Fe³⁺ redox system and optionally the oxygen contained in the oxygen-containing gas. The object of the invention is achieved by the process according to claim 1 ; preferred embodiments thereof are defined in the dependent claims.

The invention is in particular achieved by the means for dissolving the copper metal to be deposited in the process; the process consumes low amounts of energy and organic additives wherein no significant amounts of active carbon is used. The process can be carried out by means of a relatively simple device requiring reduced maintenance effort. The process provides a flexible plastic-copper layer composite having a high purity and glossy, dense and pores-free copper layer. In the context of the invention, the use of the singular form shall also cover plural forms e.g. if the use of a cathode or an anode is described, the use of more than one cathode or anode is comprised.

In the context of the invention, the term “conductive, flexible plastic substrate cathode” is understood in the sense that the conductive, flexible plastic substrate is in contact with cathode in the plating device and therefore the substrate is cathodic charged to get plated with copper.

In one embodiment of the invention, the conductive, flexible plastic substrate is preferable a flexible plastic foil preferably having a first metal layer, preferably a copper (Cu) or nickel (Ni) layer, onto the surface of the plastic foil wherein the first metal layer provides the conductivity. Preferably the plastic foil has a first metal layer on both sides of the plastic foil. The flexible plastic foil is preferably made of polyethylene terephthalate (PET), polycarbonate (PC), polyimide (PI) and the like or mixture thereof. In a preferred embodiment flexible plastic-copper layer composite can be a flexible copper-coated PET-based foil or a flexible nickel-coated Plbased foil.

The thickness of the plastic substrate (e.g. plastic foil) is preferably from 3.5 to 5 pm, more preferably 4.5 pm.

The first metal layer has preferably a thickness from 20 nm to 0.3 pm, preferably 20 nm to 60 nm.

In one embodiment of the invention, the first copper layer is deposited by known sputtering technology preferably on both sides of the plastic foil e.g. as disclosed in CN 115700295 A in the description and examples which is incorporate here with this reference.

In another embodiment of the invention, the first copper layer can be provided preferably on both sides of the plastic foil by known galvanic processes, wherein a flexible plastic foil is at least wet-chemical treated with an activator solution as a palladium containing solution to obtain an activated flexible plastic foil. This activated flexible plastic foil is wet-chemical treated with an electroless copper plating solution to obtain a flexible plastic foil having a first copper layer onto the surface of the foil.

A roll-to-roll coating process according to the invention means, that the conductive, flexible plastic substrate is provided as a substrate roll from which the substrate is released and transported to the plating device to be deposited in the plating device. After a copper layer is electrolytical ly deposited on the conductive, flexible plastic substrate, preferably onto the first copper layer of the flexible plastic substrate, the obtained flexible plastic-copper layer composite is collected onto a take-up roll.

In the process according to the invention, relatively large amounts of copper per unit time are removed from the electrolyte solution due to deposition on the conductive, flexible plastic substrate and drag out. The transport speed can be in the range from 1 to 10 m/min, preferably 3 to 8 m/min, more preferably 3 to 5 m/min.

The current density at the substrate in the plating tank which is in contact with the cathode and the electrolyte solution is typically 0.1 to 5 A/dm², preferably 0.5 to 4 A/dm².

The amount of deposited copper on the conductive, flexible plastic substrate is typically 2 to 30 kg/h, preferably 5 to 20 kg/h.

For example, when the substrate to be plated in the plating device, has a width of 1 .22 m and a transport speed of 10 m/min, i.e. a surface area of 732 m² has to be plated per hour. That means, with a targeted electrolytic deposited copper layer thickness of approximately 0.9 pm, about 12 kg of copper will be deposited per hour; furthermore, at a relatively high transport speed of typically 10 m/min, a significant amount of electrolyte solution is dragged out of the plating tank due to adhesion to the substrate transported through the electrolyte solution (typically, about 100 ml/m²).

In order to keep the copper ion concentration in the electrolyte solution constant, fresh copper metal is continuously dissolved into the electrolyte solution by passing the electrolyte solution through the dissolution unit, into which copper metal is introduced. That means, the concentration of copper ions in the electrolyte solution is maintained constant by passing a part of the electrolyte solution withdrawn from the plating tank through the copper dissolution unit. In the copper dissolution unit, the part of the electrolyte solution is in contact with the auxiliary anode and the auxiliary cathode. The copper metal may be introduced into the dissolution unit as copper pieces e.g. in the form of copper clippings. The copper metal (e.g. clippings) may be placed in a basket made of an inert metal such as titanium. The basket then functions as the auxiliary anode. The part of the electrolyte solution withdrawn from the plating tank can be introduced into the copper dissolution unit at a location that is closer to the auxiliary cathode than to the auxiliary anode so that the part comes into contact with the auxiliary cathode first.

The copper metal continuously dissolves into the electrolyte solution by being oxidized by the Fe³⁺ component of the Fe²⁺/Fe³⁺ redox system. This dissolution process is described by the following chemical equation:

Cu° + 2 Fe³⁺ — > Cu²⁺ + 2 Fe²⁺

The Fe³⁺ is generated predominantly by oxidation of Fe²⁺ at the insoluble anode used as counter-electrode to the cathode contacting the conductive, flexible plastic substrate as in the plating tank.

An oxygen-containing gas, e.g. air, is introduced into the dissolution unit such that bubbles thereof contact the surface of the copper metal, for example by bubbling the oxygen-containing gas, into the dissolution unit at a location beneath a basket containing the copper metal in the form of copper clippings to generate moderate gas agitation around the surface of copper metal.

This has two effects. First, turbulence at the copper metal surface increases, therefore the dissolving reaction increases in speed. Second, oxygen from the oxygen-containing gas acts as additional oxidizer (beside the anodic potential of the auxiliary anode which contacts the copper metal) to oxidize further Fe²⁺ to Fe³⁺, which then dissolves additional copper metal.

However, the generation of excessive amounts of Fe³⁺, which does not react with the copper metal and which is then transferred to the plating tank, should be avoided because Fe³⁺ contacting the cathode would reduce the copper deposition efficiency. Therefore, all Fe³⁺ should be transformed into Fe²⁺ after passing the copper metal in the copper dissolution unit.

To ensure this, the copper metal (e.g. copper clippings) in the dissolution unit is in electrical contact with the auxiliary anode. As the cathodic potential during copper deposition becomes higher, the anodic potential during copper dissolution increases. When entering and preferably additional when leaving the dissolution unit, the electrolyte solution passes the auxiliary cathode and additional auxiliary cathode respectively, i.e. a metallic device (e.g., mesh), which has a positive potential; this potential has to be lower than the positive potential for copper deposition within the dissolving tank. Both, the copper metal at a negative potential and the auxiliary cathode with a positive potential will eliminate any existing Fe³⁺ ions. The current efficiency at the cathode being in contact with the conductive, flexible plastic substrate in the plating device will thus remain close to 100 %.

Both, (i) the anodic potential of the copper metal introduced into the dissolution unit and (ii) the gas agitation created by the introduction of the oxygen-containing gas such that bubbles thereof contact the surface of the copper metal, speed up the dissolution reaction of the copper metal. Thus, the copper concentration in the electrolyte solution can be effectively controlled and thereby kept within a narrow and high concentration range required for efficient and constant deposition of copper on the conductive, flexible plastic substrate contacted by the cathode by (i) controlling the potential applied to the auxiliary anode (i.e. the voltage between the auxiliary anode and the auxiliary cathode) and (ii), to a lesser extent, by controlling the intensity of the gas agitation.

In the process according to the invention, the electrolyte solution contains an Fe²⁺/Fe³⁺ redox system, i.e. a combination of ferrous and ferric compounds. Fe³⁺ ions are generated predominantly by oxidation of Fe²⁺ at the insoluble anode in the plating tank and, after they are transferred to the dissolution unit, then act as an oxidant to oxidize copper metal to Cu²⁺ and thereby dissolve the copper metal into the electrolyte solution.

Thus, there is a continuous process in which copper metal is oxidized by Fe³⁺ in the dissolution unit, then transferred to the plating tank and reduced again to copper metal at the conductive, flexible plastic substrate which is in contact with the cathode while, at the same time, Fe³⁺ is reduced to Fe²⁺ by the copper metal as well as the auxiliary cathode in the dissolution unit and, after the Fe²⁺ has been transferred to the plating tank, it is oxidized to Fe³⁺ again.

This use of an Fe²⁺/Fe³⁺ redox system as a means to dissolve copper metal in the large amounts required in a process for producing a flexible plastic-copper layer composite as plastic-copper foil and in a well-controlled manner has the following advantages compared to conventional processes for producing the composite:

Firstly, the oxidization of Fe²⁺ to Fe³⁺ at the insoluble anode competes with, and thus suppresses oxygen evolution and organic additive burning at the anode. Thus, consumption of organic additives (and the ensuing generation of contaminating decomposition products) is only due to the copper deposition processes at the conductive, flexible plastic substrate. Thereby, the total organic content (TOC) of the electrolyte solution remains low and extends the plating bath lifetime. Additionally, due to avoiding oxygen development at the anode, the lifetime of the anode is greatly increased. Secondly, due to the oxidation of Fe²⁺ to Fe³⁺ at the insoluble anode and Fe³⁺ being an efficient oxidant for copper metal, there is no need to use a copper oxide dissolution process as is necessary in the conventional processes for producing a plastic-copper composite foil. The Fe³⁺ generated at the insoluble anode will act as oxidant together with the oxygen-containing gas introduced into the dissolution unit and dissolves the copper metal. The temperature can remain at preferably lower temperature, i.e. the same as in the plating tank.

Thirdly, as lower amounts of organic compounds are destroyed and no disturbing metal ions were introduced, the use of additional filtering steps as active carbon use to remove decomposition products becomes redundant. Further lower amounts of organic compound must be replenished.

Fourthly, as the copper clippings within the dissolving unit are in contact with an auxiliary anode for copper dissolution, the amount of copper clippings, and therefore the copper surface area which reacts with the Fe³⁺ ions, can be reduced by 70% (weight) and therefore less organic decomposition products are formed as a reaction product of brightener with the copper clipping surface.

Fifthly, the electrolytically deposited copper layer is a high purity copper layer having a copper content of 98 weight-% or more, preferably 99 weight-% or more.

Sixthly, the surface roughness of the electrolytically deposited copper layer is significantly reduced and glossy and pore-free surfaces are provided.

Brief description of the drawings

Figure 1 is a diagrammatic depiction of an apparatus for producing a flexible plastic-copper layer composite by the process according to the invention.

Description of embodiments

In the continuous process for producing a flexible plastic-copper layer composite according to the invention, copper is electrolytically deposited on a conductive, flexible plastic substrate which is transported through the plating device and is immersed in an electrolyte solution (the substrate on which the copper layer is deposited can be partly or fully immersed into the electrolyte solution during deposition (not shown)); the electrolyte solution contains at least copper ions, organic additives and an Fe²⁺/Fe³⁺ redox system. The invention is explained by referring to an apparatus shown in Fig. 1 , which can be used with the inventive process. The apparatus in Fig. 1 can be seen as an example. The apparatus is not necessarily limiting the inventive process. In another embodiment of the invention, e.g. the conductive, flexible plastic substrate transported to the plating device is fully immersed in the electrolyte solution in the plating tank during the electrically deposition of copper wherein the substrate is contacted by a plurality of clamps as cathodes. At least the cathodic contacting points of the clamps and also the insoluble anodes can be arranged within the electrolyte solution.

As the electrolyte solution, an aqueous acidic copper plating bath is used. Such baths are known from the prior art, for example from WO 95/18251 A1 , which is incorporate here by reference.

The basic composition of the electrolyte solution bath can vary within relatively large boundaries. In general, an aqueous solution of the following composition is used: copper ions: 5-65 g/l, preferably 15-50 g/l, more preferably 20-35 g/l (e.g. as copper sulfate (CuSO4 ■ 5x H2O): 20-250 g/l, preferably 80-140g/l or 180-220g/l); cone, sulfuric acid: 50-350 g/l, preferably 50-240 g/l, more preferably 90-210 g/l; iron(ll) iron ions: 0.2-40 g/l (e.g. iron sulfate (FeSCU 7x H2O): 1-200 g/l, preferably 15-150 g/l, more preferably 20-120 g/l, most preferably 25-75 g/l); chloride ions (added for example as NaCI): 0.01-0.18 g/l, preferably 0.03-0.1 g/l or 0.50-0.09 g/l. Instead of copper sulfate, other copper salts can be used at least in part. Even the sulfuric acid can be partly or wholly replaced by fluoroboric acid, methanesulfonic acid or other acids. That is, the electrolyte solution can be free or substantially free of sulfuric acid and/or sulfate salts. In particular, the electrolyte solution can contain methanesulfonic acid and the iron and/or copper salts thereof without containing sulfuric acid. In this case the electrolyte solution contains copper ions in form of copper methyl sulfonic acid: 65 - 110 g/l.

The chloride ions are added as alkali chlorides, for example sodium chloride or in the form of hydrochloric acid. The addition of sodium chloride can be dispensed with wholly or partly if halogen ions are already contained in the supplements.

The electrolyte solution contains an Fe²⁺/Fe³⁺ redox system. The ratio of Fe²⁺/Fe³⁺ varies from high to low and back, depending on the situation and location in the plating tank or in the Cu dissolution unit as described below. Preferably, the total concentration of Fe²⁺/Fe³⁺ ions of the electrolyte solution is from 0.2-40 g/l, preferably 3-30 g/l, more preferably 4-24 g/l or 5-15 g/l. The Fe²⁺/Fe³⁺ redox system can be formed from iron (II) sulfate heptahydrate to prepare the electrolyte. It is particularly suited to regenerating copper ions in aqueous, acidic copper baths. However, other water-soluble iron salts, for example the iron salt of methanesulfonic acid and iron (III) sulfate nonahydrate, can also be used as long as the salts contain no biologically non- degradable (hard) complexing agents in the compound since the latter present problems during waste disposal (e.g. iron ammonium alum).

The organic additives contained in the electrolyte solution comprise, in particular, at last one brightener, preferably an organic sulfur-containing compound, at least one levelling agent, preferably a nitrogen-containing compound, and at least one carrier. Thus, the electrolyte solution generally contains copper ions (preferably, Cu²⁺ ions), Fe²⁺ ions, an acid, chloride ions, a brightener, a levelling agent and a carrier.

The organic sulfur-containing compound as brightener compound is preferably selected from one or more compounds selected from the group consisting of organic thiol, sulfide, disulfide and polysulfide compounds, preferably selected from the group consisting of 3-(benzthiazolyl- 2-thio)-propylsulfonic acid, 3-mercaptopropane-1 -sulfonic acid, ethylendithiodipropylsulfonic acid, bis-(p-sulfophenyl)-disulfide, bis-(w-sulfobutyl)-disulfide, bis-(w-sulfohydroxypropyl)- disulfide, bis-(w-sulfopropyl)-disulfide, bis-(w-sulfopropyl)-sulfide, methyl-(w-sulfopropyl)- disulfide, methyl-(w-sulfopropyl)-trisulfide, O-ethyl-dithiocarbonic acid S-(w-sulfopropyl) ester, thioglycol acid, thiophosphoric acid O-ethyl-bis-(w-sulfopropyl) ester, 3-N,N- dimethylaminodithiocarbamoyl-1 -propanesulfonic acid, 3, 3’-thio-bis(1 -propanesulfonic acid), thiophosphoric acid tris-(w-sulfopropyl)-ester and their corresponding salts. The concentration of all brightener compounds (in total) present in the electrolyte solution preferably ranges from 0.01 mg/l to 100 mg/l, more preferably from 0.05 mg/l to 10 mg/l still more preferably from 0.1 to 5 mg/l.

The nitrogen-containing compound as levelling agent compound is preferably selected from one or more compounds selected from the group consisting of a ureylene polymer, polyethyleneimine, alkoxylated polyethyleneimine, alkoxylated lactams and polymers thereof, diethylenetriamine and hexamethylenetetramine, polyethylenimine bearing peptides, polyethylenimine bearing amino acids, polyvinylalcohol bearing peptides, polyvinylalcohol bearing amino acids, polyalkyleneglycol bearing peptides, polyalkyleneglycol bearing amino acids, aminoalkylene bearing pyrroles and aminoalkylene bearing pyridines, organic dyes such as Janus Green B, Bismarck Brown Y and Acid Violet 7, sulfur containing amino acids such as cysteine, and phenazinium salts. The concentration of the levelling agent compound added to the electrolyte solution (in total) ranges from 0.5 mg/l to 400 mg/l, preferably from 0.1 mg/l to 100 mg/l.

The oxygen-containing compound as carrier compound is preferably selected from one or more compounds selected from the group consisting of polyvinylalcohol, carboxymethylcellulose, polyethylenglycol, polypropylenglycol, stearic acid polyglycol ester, alkoxylated naphtoles, oleic acid polyglycol ester, stearylalcoholpolyglycol ether, nonylphenolpolyglycol ether, octanolpolyalkylenglycol ether, octanediol-bis-(polyalkylenglycol ether), poly(ethylenglycol-ran-propylenglycol), poly(ethylenglycol)-block-poly(propylenglycol)- block-poly(ethylenglycol), and poly(propylenglycol)-block-poly(ethylenglycol)-block- poly(propylenglycol). The concentration of the carrier compound (in total), added to the electrolyte solution ranges from 0.005 g/l to 20 g/l, more preferably from 0.01 g/l to 20 g/l, still more preferably from 0.01 g/l to 5 g/l.

The inventive process can be conducted in an apparatus, comprising a plating device 1 having a plating tank 2, a cathode 3, an insoluble anode 14 and an electrolyte solution 4 wherein a conductive, flexible plastic substrate 15 can be deposited; and a Cu dissolution unit 5 having a part of the electrolyte solution 4 an auxiliary anode 7 and an auxiliary cathode 6; copper metal 10 as copper clippings, and an air blower 12 for introducing oxygen-containing gas into the part of the electrolyte solution 4 of the copper dissolution unit 5. The plating device 1 and the Cu dissolution unit 5 are connected with conduits through which used electrolyte solution is pumped from the plating device to the Cu dissolution unit and refreshed electrolyte solution from Cu dissolution unit to the plating device as shown in Fig. 1.

In the process for producing a flexible plastic-copper layer composite 16 according to the invention, a copper layer is electrolytically deposited on a conductive, flexible plastic substrate 15, which is immersed in an electrolyte solution 4 contained in a plating tank 2. The conductive, flexible plastic substrate 15 is released from a substrate roll (not shown) and transported to the plating tank and the obtained flexible plastic-copper layer composite 16 is transported out of the plating tank 2 and coiled to a composite take-up roll (not shown).

The cathode 3 can be formed as roller in order to transport and electrically contact the substrate 15 within the electrolyte solution 4 and/or outside the electrolyte solution 4 within the plating device 1. In one embodiment, the cathode 3 is preferable contacting the substrate only outside the electrolyte solution 4 in the plating device 1. In this case, the roller as shown as 3 in Fig. 1 within the electrolyte solution 4 is only used for transporting the substrate 15 through the electrolyte solution 4. In still another embodiment, only the roller as shown as 3 in Fig. 1 within the electrolyte solution 4 functions as cathode, while the roller shown as 3 in Fig. 1 outside the electrolyte solution 4 only function as transport rollers.

The current density at the substrate in the plating tank which is in contact with the cathode and the electrolyte solution is typically 0.1 to 5 A/dm², preferably 0.5 to 4 A/dm². The transport speed of the conductive, flexible plastic substrate is typically 1 to 10 m/min, preferably 3 to 8 m/min, more preferably 3 to 5 m/min. The amount of copper deposited on the conductive, flexible plastic substrate is typically 2 to 30 kg/h, preferably 5 to 20 kg/h.

The total thickness of the deposited metal layer, preferable of a copper or nickel layer, of the composite produced by the process according to the invention is typically 100 to 2000 nm, preferably 300 to 1000 nm, more preferably 400 to 900 nm. The thickness can be determined by known techniques as X-ray fluorescence spectroscopy (XRF).

The value of the arithmetic average of the roughness profile Ra is preferably < 500 nm, more preferably < 300 nm, most preferably 100 nm to 200 nm. The maximum peak to vally height of profile Rz is preferably < 1.5 pm, more preferably < 1.0 pm. Ra and Rz can be determined by standard measurement with e.g. a profilometer. The determination of profile roughness parameters is included in ISO 21920.

The value of the arithmetic average of the 3D roughness Sa is preferably < 40 nm, more preferably < 30 nm, most preferably 10 nm to 20 nm. The determination of areal roughness parameters is included in ISO 25178.

The process can be used in particular to provide flexible plastic-copper layer composite having surface roughness values as explained above.

In the process for producing a flexible plastic-copper layer composite according to the invention, an insoluble anode 14 is used as counter-electrode to the cathode 3. The anode is preferably placed next to the substrate within the electrolyte solution 4 in the plating tank 1 .

The current density at the insoluble anode is typically >0.5 A/dm², preferred from 0.8 to 5 A/dm².

In the process for producing a flexible plastic-copper layer composite according to the invention, a copper layer is electrolytically deposited on a conductive, flexible plastic substrate, typically at a temperature of the electrolyte solution of 15 to 50°C, preferably 20 to 40 °C, more preferably 25 to 35°C.

In the process for producing a flexible plastic-copper layer composite according to the invention, the concentration of copper ions in the electrolyte solution is maintained constant by passing the electrolyte solution through a copper dissolution unit. Thereby, the concentration of copper ions in the electrolyte solution present in the plating tank is typically 5 to 65 g/l. In one embodiment, the concentration of copper ions in the electrolyte solution from 22 to 35 g/l. A constant concentration of the copper ions is achieved wherein a part of the electrolyte solution present in the plating tank is continuously or periodically withdrawn from the plating tank and transferred to the dissolution unit.

While the auxiliary anode is in electrical contact with the copper metal, the auxiliary cathode is not in electrical contact with the copper metal, but the auxiliary anode and the auxiliary cathode are in contact with the part of the electrolyte solution withdrawn from the plating tank.

The part of the electrolyte solution withdrawn from the plating tank can be introduced into the copper dissolution unit having a concentration of the Fe³⁺ ions which is higher than the concentration of the Fe³⁺ ions which leaves the copper dissolution unit back into the plating tank.

The auxiliary cathode increases the concentration of Fe²⁺ ions in the part of electrolyte solution withdrawn from the plating tank by reduction Fe³⁺ ions entering the Cu dissolution unit.

The voltage applied between the auxiliary anode (7) and the auxiliary cathode (3) is preferably 1 to 9 V.

Preferably, a constant concentration of the copper ions in the electrolyte solution is done such that the part of the electrolyte solution withdrawn according to Fig. 1 from the plating tank is introduced into the Cu (copper) dissolution unit 5 through a conduit at a location that is closer to the auxiliary cathode 6 as a cathode mesh than to the auxiliary anode 7 as an anode mesh so that the withdrawn part comes into contact with the auxiliary cathode 6 first. It could be found that an undesired copper plating, in particular copper deposition in form of copper dendrites, onto the cathodic surface of the auxiliary cathode 6 during copper dissolution in the Cu dissolution unit 5 can be avoided.

The part of the electrolyte solution withdrawn from the plating tank which is introduced into the copper dissolution unit has a concentration of the Fe³⁺ ions which is higher than the concentration of the Fe³⁺ ions which leaves the copper dissolution unit back into the plating tank. With other words, the part of the electrolyte solution withdrawn from the plating tank through a conduit contains Fe³⁺ ions at a relatively high concentration (Fe³⁺rich electrolyte solution 8) and Fe²⁺ ions at a relatively low concentration compared to the electrolyte solution leaving the Cu dissolution unit 5 through another conduit where the concentration of Fe³⁺ ions is at a relatively low concentration (Fe³⁺low electrolyte solution 9) and Fe²⁺ ions is at a relatively high concentration. Preferably the concentration of the Fe³⁺ ions leaving the copper dissolution unit is less than 30 % of the total iron ions concentration, preferably less than 25 % or preferably in the range from 0.25 - 25 % of the total iron ions concentration. For example: In an electrolyte solution as explained above, 15 g/l of Fe²⁺ ions were added to the electrolyte plating solution. At this point of generating the electrolyte plating solution, the concentration of Fe³⁺ ions was zero, wherein the total iron ions concentration of Fe²⁺/Fe³⁺ ions of this Fe²⁺/Fe³⁺ redox system is consequently 15 g/L. During the plating process in the plating tank and during the Cu dissolution in the copper dissolution unit the concentration of the Fe²⁺ ions and Fe³⁺ ions changing, while the overall concentration remains constant. Good results in view of plating quality of the produced copper foil, time and energy consumption for copper deposition and dissolution were achieved if the concentration of the Fe³⁺ ions in the electrolyte solution withdrawn from the plating tank and introduced into the Cu dissolution unit was from 3-12 g/L and the concentration of the Fe³⁺ ions in the electrolyte solution leaving the Cu dissolution unit was 0.5 - 5 g/L.

The auxiliary cathode 6 slightly increases the concentration of Fe²⁺ ions in the part of electrolyte solution 4 withdrawn from the plating tank 2 by reduction Fe³⁺ ions entering the Cu dissolution unit 5 which helps to reduce organic additive burning at the anode in the Cu dissolution unit 5. The potential is adjusted to avoid copper deposition at the cathode mesh 6.

In the Cu dissolution unit, the Fe³⁺ ions contribute to the oxidation of copper metal (which thereby dissolves) and are thereby reduced to Fe²⁺ ions. Therefore, after it has passed through the Cu dissolution unit, the electrolyte solution contains Fe³⁺ ions at a relatively low concentration and Fe²⁺ ions at a relatively high concentration (Fe²⁺rich electrolyte solution 9).

In the copper dissolution unit 5, the electrolyte solution 4 is in contact with an auxiliary anode 7 and an auxiliary cathode 6. A voltage is applied between the auxiliary anode and the auxiliary cathode. This voltage is typically 1 to 9 V, preferably 2 to 4 V. The auxiliary anode is in contact with the copper metal 10. The application of this voltage and the copper metal being in contact with the auxiliary anode promotes the dissolution of the copper metal introduced into the dissolution unit such that relatively large amounts of copper can be dissolved per time unit. This dissolution is also promoted by the introduction of an oxygen-containing gas into the Cu dissolution unit such that bubbles 11 thereof contact the surface of the copper metal. The oxygen-containing gas can be air, preferably is air, more preferably hot air bubbles. The air can be introduced by an air blower 12.

In one embodiment (not shown) according to Fig. 1 the Cu dissolution unit 5 comprises an additional auxiliary cathode as an additional auxiliary cathode mesh which is close to the location where the electrolyte solution leaves the Cu dissolution unit to further reduce the concentration of the Fe³⁺ ions. The additional auxiliary cathode can be placed within the Cu dissolution unit 5 next to the beginning of the conduit through which the refreshed Fe²⁺rich electrolyte solution 9 containing newly dissolved copper ions leaves the Cu dissolution unit 5. This voltage is typically again from 1 to 9 V, preferably 2 to 4 V. The voltage of the additional auxiliary cathode is preferably lower than the voltage of the auxiliary cathode (6), preferably up to 50 percent lower. In the process of dissolution of copper metal in the Cu dissolution unit, the electrolyte solution in the Cu dissolution unit typically is at a temperature of 15 to 70°C, preferably 20 to 60 °C, more preferably 25 to 50°C. Preferably the temperature of electrolyte solution is the same in the plating tank and the Cu dissolution unit.

The auxiliary cathode and anode can be made of any kind of conductive and dimensionally stable material, whereas the cathode can also be made of copper. The size of the dissolution unit is not particularly limited and can be adapted to the requirements of the process for producing the composite, especially the amount of the composite as plastic-copper foil to be produced per time unit.

Claims

1. A continuous process for producing a flexible plastic-copper layer composite (16), wherein

- a copper layer is electrolytical ly deposited on a conductive, flexible plastic substrate (15) to obtain the flexible plastic-copper layer composite (16) in a roll-to-roll coating process wherein the substrate (15) is transported to a plating device (1) comprising a plating tank (2), a cathode (3), an insoluble anode (14) and an electrolyte solution (4), in order to be deposited in the plating device (1);

- the substrate (15) is immersed in the electrolyte solution (4) contained in the plating tank (1) and the substrate (15) is in contact with the cathode (3);

- the insoluble anode (14) is used as counter-electrode to the cathode (3) and is placed next to the substrate (15) within the electrolyte solution (4) in the plating tank (1);

- the electrolyte solution (4) contains copper ions, organic additives and an Fe²⁺/Fe³⁺ redox system;

- the concentration of copper ions in the electrolyte solution (4) is maintained constant by passing a part of the electrolyte solution (4) withdrawn from the plating tank (2) through a copper dissolution unit (5);

- in the copper dissolution unit (5), the part of the electrolyte solution (4) is in contact with an auxiliary anode (7) and an auxiliary cathode (6);

- copper metal and an oxygen-containing gas are introduced into the copper dissolution unit (5);

- the auxiliary anode (7) is in contact with the copper metal;

- the oxygen-containing gas is introduced such that bubbles (11) thereof contact the surface of the copper metal;

- the copper metal continuously dissolves into the part of the electrolyte solution (4) by being oxidized by the Fe³⁺ component of the Fe²⁺/Fe³⁺ redox system and optionally the oxygen contained in the oxygen-containing gas.

2. The process according to claim 1 wherein the organic additives contained in the electrolyte solution comprise at last one organic sulfur-containing compound as brightener, at least one nitrogen-containing compound as levelling agent, and at least one oxygen-containing compound as carrier.

3. The process according to any one of the preceding claims wherein the electrolyte solution contains 5-65 g/l of copper ions, 50-350 g/l of sulfuric acid, 0.2 - 40 g/l of iron ions, 0.01-0.18 g/l of chloride ions.

4. The process according to any one of the preceding claims wherein the electrolyte solution contains methanesulfonic acid and the iron and/or copper salts thereof.

5. The process according to any one of claims 1 , 2 or 4, wherein the electrolyte solution is substantially free of sulfuric acid and/or sulfate salts.

6. The process according to claim 2 wherein the total concentration of brightener compound present in the electrolyte solution is from 0.01 mg/l to 100 mg/l.

7. The process according to claim 2 wherein the total concentration of levelling agent compound present in the electrolyte solution is from 0.5 mg/l to 400 mg/l.

8. The process according to claim 2 wherein the total concentration of carrier compound present in the electrolyte solution is from 0.005 g/l to 20 g/l.

9. The process according to any one of the preceding claims wherein the current density at the cathode is from 0.1 to 5 A/dm², preferably from 0.5 to 4 A/dm².

10. The process according to any one of the preceding claims wherein the amount of copper deposited on the conductive, flexible plastic substrate is from 2 to 30 kg/h.

11. The process according to any one of the preceding claims wherein copper is dissolved in the copper dissolution unit at a temperature of from 15 to 70°C.

12. The process according to any one of the preceding claims wherein the concentration of copper ions in the electrolyte solution present in the plating tank is from 5 to 65 g/, preferably from 22 to 35 g/l.

13. The process according to any one of the preceding claims wherein the part of the electrolyte solution withdrawn from the plating tank (2) is introduced into the copper dissolution unit (5) at a location that is closer to the auxiliary cathode (6) than to the auxiliary anode (7) so that the part comes into contact with the auxiliary cathode (6) first.

14. The process according to any one of the preceding claims wherein the auxiliary cathode (6) increases the concentration of Fe²⁺ ions in the part of electrolyte solution (4) withdrawn from the plating tank (2) by reduction Fe³⁺ ions entering the Cu dissolution unit (5). .

15. The process according to any one of the preceding claims wherein the part of the electrolyte solution withdrawn from the plating tank is introduced into the copper dissolution unit (5) having a concentration of the Fe³⁺ ions which is higher than the concentration of the Fe³⁺ ions which leaves the copper dissolution unit (5) back into the plating tank.

16. The process according to any one of the preceding claims wherein the voltage applied between the auxiliary anode (7) and the auxiliary cathode (3) is 1 to 9 V.