METHOD FOR MANUFACTURING COMPOSITE COPPER FOIL AND COMPOSITE COPPER FOIL OBTAINED THEREFROM

Abstract

The present invention relates to a method for producing a peelable composite copper foil, comprising: providing a carrier foil; depositing a release layer, which is an amorphous layer comprising a ternary alloy of nickel, molybdenum, and tungsten, on the carrier foil using an acidic electrolyte comprising nickel, molybdenum, and tungsten; cleaning the exposed side of the release layer on the carrier foil with a cleaning solution having a pH between 2.5 and 4.5; and electroplating an ultra-thin copper foil onto the release layer. The present invention also relates to a composite copper foil comprising, in this order, a carrier foil, a release layer, and an ultra-thin copper foil, wherein the release layer comprises a ternary alloy of nickel, molybdenum, and tungsten formed as an amorphous layer, and wherein the release force of the release layer is between 30 and 120 N / m after lamination at 170°C for 1 hour.

Description

[Technical Field]

[0001] The present invention relates generally to the field of composite copper foils, and more particularly to composite copper foils having a release layer and methods for making the same. [Background technology]

[0002] As electronic devices become more compact, ultra-thin copper foils with thicknesses of approximately 5 μm or less have been used as electronic materials for printed circuit boards (PCBs). However, these ultra-thin copper foils are generally not self-supporting, making them difficult to use. To address this issue, composite copper foils, in which an ultra-thin copper layer is attached to a carrier (support) layer, are being used.

[0003] Composite foils are generally divided into two types: foils with a peelable carrier and foils with an etchable carrier. Simply put, the difference between these two types of composite foils is the method by which the carrier layer is removed. In peelable composite foils, the carrier layer is removed by peeling, while in etchable composite foils, the carrier layer is removed by etching.

[0004] Peelable composite foils are generally preferred over etchable composite foils because they allow easier and more precise preparation of copper clad laminates. In fact, chemical etching of the carrier—due to its relatively large thickness—takes a long time, necessitating several changes of the etching bath, and results in a rough surface. In addition, the choice of carrier layer is limited, since etching of very thin copper layers is not permitted.

[0005] Therefore, peelable composite foils are much easier to use than etchable foils. However, a frequent problem with conventional peelable composite foils is that it is difficult to control the peel strength, i.e., the force required to separate the carrier foil and the ultra-thin copper foil after lamination.

[0006] A conventional composite copper foil and its manufacturing method, in which a carrier foil and a functional foil are bonded via a release layer formed using an electroplating bath containing hexavalent chromium, are known from US 3,998,601. However, such composite copper foils are subject to the REACH regulation, and the use of hexavalent chromium will make them unsuitable for production after 2023.

[0007] To overcome this limitation, alternative manufacturing processes have been developed. For example, WO 2020 / 173574 A1 discloses a method for producing a peelable composite copper foil without using chromium. The peel layer is formed as an amorphous layer of a binary or ternary nickel alloy. Such composite copper foils have a low peel force, typically between 5 and 30 N / m, during lamination and are perfectly suited to some applications where the composite foil undergoes a lamination process at a relatively high temperature (usually about 220°C) and the carrier layer is peeled off after the lamination process. Note that the applied temperature during the lamination process has the effect of increasing the bond between the carrier layer and the functional foil. That is, during lamination, the temperature increases the initially low peel force, thereby improving the stability of the assembly and preventing unintended separation of the peelable foil.

[0008] In contrast, European industry typically uses processes involving lamination at low temperatures below 180°C. Tests performed on the composite copper foil of WO2020 / 173574A1 show that after low-temperature lamination, the peel force approaches zero. It is therefore not possible to ensure satisfactory sticking of the carrier layer, which cannot act as a protection during further processing of the copper clad laminate. Therefore, the composite copper foil disclosed in WO2020 / 173574A1 is not suitable for use in low-temperature lamination processes.

[0009] The object of the present invention is to provide a method for producing a composite copper foil that has a high demolding force and is compatible with low temperature lamination while complying with REACH regulations. Summary of the Invention

[0010] In order to achieve the above object, the present invention provides a method for manufacturing a composite copper foil, which includes a carrier foil, a release layer, and an ultra-thin copper foil, wherein the ultra-thin copper foil is peelable from the carrier foil, the method comprising: Provide carrier foil; depositing an amorphous release layer comprising a ternary alloy of nickel, molybdenum and tungsten on one side of the carrier foil using an acidic electrolyte comprising nickel, molybdenum and tungsten; Cleaning the exposed side of the release layer on the carrier foil with a cleaning solution having a pH between 2.5 and 4.5; Electroplating an ultra-thin copper foil onto the release layer; We propose a method that includes:

[0011] The present method allows for the production of composite copper foils that, upon cold lamination, have a peel force in the range of 30 to 120 N / m, preferably between 40 and 120 N / m. Obviously, the peel force can be adapted to a given application. Thus, in embodiments, the peel force may range from 40 to 80, 90, or 100 N / m, and in other embodiments, the peel force may range from 70 or 80 to 120 N / m. Nevertheless, in other embodiments, the peel force may range from 70 to 90 N / m.

[0012] As used herein, the term "peel force" refers to the force required to separate the carrier foil from the ultra-thin copper foil. Because the bond between the ultra-thin copper foil and the carrier foil is via a release layer, the peel force is sometimes referred to in the art as the "release strength." In practice, the peel force is usually measured after lamination.

[0013] It will be appreciated that the inventors have discovered that a cleaning step applied to the exposed side of the release layer can control the oxidation of the surface of the release layer, thereby controlling the release force of the composite copper foil. The cleaning step only affects the surface of the release layer, leaving the majority of it unaffected. Because the ultra-thin copper foil is formed on the cleaned side of the release layer, there are oxides of the components / elements of the ternary alloy at the interface with the ultra-thin copper foil, which affect / control the release force.

[0014] The inventors have discovered that the carrier foil remains peelable during the lamination process at temperatures up to 170°C, while surprisingly increasing the peel force during the cleaning process to a higher extent compared to the composite copper foil of WO2020 / 173574A1.

[0015] In other words, the present invention is based on the discovery by the inventors that a composite copper foil suitable for lamination at low temperatures can be produced that exhibits a peel force between -30 and 120 N / m after lamination at -170°C for 1 hour by certain process steps including cleaning of the release layer with an acidic cleaning solution.

[0016] The present invention relies on the use of a cleaning solution to clean the release layer to control the release force of the composite copper foil. In fact, the inventors discovered that cleaning the release layer with a cleaning solution induces the formation of oxides on the surface of the release layer. The presence and amount of oxides adjusts (i.e., controls) the release force of the composite copper foil. Therefore, the release force, i.e., the bonding strength between the carrier and the ultra-thin copper foil, can be controlled by fine-tuning the cleaning process, thereby controlling the formation of oxides.

[0017] Furthermore, because the release layer is formed as an amorphous alloy layer, it exhibits a smooth surface that is substantially free of irregularities due to grain boundaries, thereby preventing the formation of structural defects such as pinholes in the foil deposited thereon. In other words, by forming the release layer as an amorphous layer, it is possible to manufacture a composite copper foil that is free of structural defects such as pinholes.

[0018] In an embodiment, the pH of the cleaning solution is between 2.5 and 4.0, preferably between 2.5 and 3.5. According to the same or a different embodiment, the cleaning solution comprises water and any suitable acid, preferably an inorganic acid, such as, for example, H2SO4, HCl, etc.

[0019] In a preferred embodiment, cleaning the exposed side of the release layer (i.e., the cleaning step) comprises spraying a cleaning liquid onto the exposed side of the release layer and / or immersing the carrier foil with the release layer deposited thereon in the cleaning liquid. More preferably, the cleaning step comprises spraying the cleaning liquid onto the exposed side of the release layer, immersing the carrier foil together with the release layer in the cleaning liquid, and again spraying the exposed side of the release layer with the cleaning liquid, in that order.

[0020] In embodiments, cleaning of the exposed side of the release layer (i.e., the cleaning step) is carried out for a period of between 10 and 50 seconds, preferably between 10 and 30 seconds. In embodiments where the cleaning step includes both spraying with the cleaning solution and immersion in the cleaning solution, the immersion is preferably carried out for a period of time corresponding to 20 to 25% of the total time of the cleaning step.

[0021] In embodiments, the cleaned release layer can be wiped off by passing it through a rotating roller, such as a nip roller. According to the same or other embodiments, the cleaned release layer may be left in air for 10 to 40 seconds to dry the cleaned release layer.

[0022] According to the same or other embodiments, the acidic electrolyte comprises nickel at a concentration between 5.0 and 9.0 g / L, preferably between 7.0 and 9.0 g / L, more preferably between 7.5 and 8.5 g / L, molybdenum at a concentration between 5.0 and 9.0 g / L, preferably between 5.0 and 7.0 g / L, more preferably between 5.5 and 6.5 g / L, and tungsten at a concentration between 1.0 and 5.0 g / L, preferably between 2.0 and 4.0 g / L, more preferably between 2.5 and 3.5 g / L.

[0023] The inventors have unexpectedly discovered that electrodepositing a release layer from an electrolytic bath with such a predetermined composition, in combination with a cleaning step, is particularly effective in achieving the desired release force during lamination at low temperatures.

[0024] In an embodiment, electroplating of ultra-thin copper foil comprises: electroplating a first copper layer directly onto the release layer using an alkaline copper electrolyte; and electroplating a second copper layer onto the first copper layer using an acidic copper electrolyte; This includes:

[0025] Preferably, the alkaline bath may contain pyrophosphate, cyanate and / or sulfamate ions.

[0026] According to another aspect, the present invention relates to a composite copper foil comprising, in that order, a carrier foil, a release layer and an ultra-thin copper foil, the composite copper foil having a peel force between 30 and 120 N / m after lamination at 170°C for 1 hour.

[0027] In embodiments, the peel force may range from 40 to 80, 90 or 100 N / m, and in other embodiments, the peel force may range from 70 or 80 to 120 N / m. Nevertheless, in other embodiments, the peel force may range from 70 to 90 N / m. The release layer comprises an amorphous ternary alloy of nickel, molybdenum, and tungsten.

[0028] In an embodiment, the release layer comprises nickel in an oxidized form, wherein the nickel in the +II oxidation state represents at least 30 wt. % of the total amount of nickel at the surface. In an embodiment, the amount of Ni(+II) can be between 30 and 50 wt. % of the total amount of nickel at the surface. Initial testing indicates that such a proportion of Ni in the oxidized form can produce copper foils with desirable release force characteristics.

[0029] With regard to the method of the present invention, as mentioned above, the present invention is based on the inventor's discovery that the presence of components / elements of the ternary alloy, particularly oxides in the oxidized form of nickel, at the interface with the ultra-thin copper foil influences / controls the peel force of the composite copper foil.

[0030] The presence and amount of nickel in oxidized form (i.e., nickel oxide) adjusts (i.e., controls) the peel force of the composite copper foil. Thus, the peel force, i.e., the bonding strength between the carrier and the ultra-thin copper foil, can be controlled by fine-tuning the amount of nickel oxide. Furthermore, since the release layer includes an amorphous alloy layer, it exhibits a smooth surface with substantially no irregularities due to grain boundaries, thereby preventing the formation of structural defects such as pinholes in the foil deposited thereon. In other words, the release layer including an amorphous layer can ensure that the composite copper foil is free of structural defects such as pinholes.

[0031] The other advantages listed for the method of the present invention apply mutatis mutandis to the composite copper foil of the present invention. According to the same or other embodiments, the release layer has a thickness between 5 and 50 nm, preferably between 30 and 50 nm, more preferably between 35 and 50 nm.

[0032] Advantageously, the thickness of the ultra-thin copper foil may be between 0.5 and 10 μm, in particular between 5 and 9 μm, depending on the intended use of the composite copper foil. According to yet another aspect, the present invention relates to a copper clad laminate comprising a substrate with a resin and the disclosed composite copper foil, wherein an ultra-thin copper foil is laminated to an exposed surface of the substrate, wherein the resin of the substrate has a Tg of less than 170°C and the peel force of the release layer after lamination at 170°C for 1 hour is between 30 and 120 N / m.

[0033] Advantageously, the composite copper foil is manufactured using the method according to the invention or the composite copper foil is a composite copper foil according to the invention. What has been said regarding the advantages and embodiments of the composite copper foil of the invention applies mutatis mutandis to the copper clad laminate of the invention.

[0034] "Amorphous," as used herein, refers to the case where broad diffraction peaks appear when measured by grazing incidence X-ray diffraction (GIXRD), or where hollow patterns appear at the peaks when electron beam diffraction is measured using a transmission electron microscope (TEM).

[0035] In the present context, any given numerical value includes a numerical range of -10% to +10% of said value, preferably a numerical range of -5% to +5% of said value, more preferably a numerical range of -1% to +1% of said value.

[0036] Further details and advantages of the invention will become apparent from the following detailed description of some non-limiting embodiments, with reference to the accompanying drawings. [Brief explanation of the drawings]

[0037] The invention will now be described, by way of example, with reference to the accompanying drawings, in which: [Figure 1] 1 is a cross-sectional view of a composite copper foil according to an embodiment of the present invention. [Figure 2] FIG. 2 is a cross-sectional view of the functional foil of FIG. [Figure 3] 1 is a graph of intensity (arbitrary units—CPS) versus binding energy (electron volts (eV)) showing the results of X-ray photoelectron spectroscopy (XPS) analysis of the Ni region of the release layer surface of two composite copper foils produced according to the present invention. [Figure 4] 1 is a graph of intensity (arbitrary units—CPS) versus binding energy (electron volts (eV)) showing the results of X-ray photoelectron spectroscopy (XPS) analysis of the Ni region of the release layer surface of two comparative composite copper foils. [Figure 5] 1 is a principle diagram of a production line for carrying out the method. Detailed Description of the Preferred Embodiments

[0038] An embodiment of the method and the resulting composite copper foil will now be described. For ease of explanation, the composite copper foil will be shown first.

[0039] Composite Copper Foil FIG. 1 is a cross-sectional view of a composite copper foil 10 obtained by this method. The composite copper foil 10 includes a carrier layer 1, a release layer 2, and an ultra-thin functional layer 3, in that order. The carrier layer 1 and the functional layer 3 may also be conventionally referred to as the carrier foil and the functional foil, respectively. The release layer 2 includes a ternary alloy containing nickel, molybdenum, and tungsten, and is preferably formed as an amorphous layer. The functional foil 3 is an ultra-thin copper foil having a predetermined thickness depending on the application. As shown by the arrows in FIG. 1 , the ultra-thin copper foil 3 may peel from the carrier foil 1, and this separation occurs at the interface with the release layer 2. Each layer of the composite copper foil according to an embodiment of the present invention will now be described.

[0040] Carrier foil According to one embodiment of the present invention, the carrier foil 1 is a support layer that supports the ultra-thin functional foil 3. The carrier foil 1 acts as a stiffener or support for the functional foil 3 until it is bonded to a substrate.

[0041] As is known in the art, the surface roughness of the carrier layer 1 has a strong influence on the adhesive strength between the ultrathin copper layer 3 and the resin substrate. For example, when high adhesive strength is required, it is preferable that the surface roughness of the carrier layer 1 is large. On the other hand, when fine circuits need to be formed, it is preferable that the surface roughness of the carrier layer 1 is small. In an embodiment of the present invention, the surface roughness Rz (JIS) of the carrier layer on the side where the release layer 2 and ultra-thin copper foil 3 are formed is preferably 2.5 μm or less, and more preferably about 2.0 μm. The thickness of the carrier foil 1 is not particularly limited, but a self-supporting thickness is usually sufficient. For example, the carrier foil may have a thickness of 12 μm to 70 μm, taking into account cost, process, and properties. The material of the carrier layer 1 is not particularly limited, but copper foil is preferred in consideration of cost, process, and properties.

[0042] peeling layer The release layer 2 is a layer designed to allow convenient peeling of the functional foil 3 (i.e. the ultra-thin copper foil) from the carrier foil 1. Thanks to the release layer 2, the carrier layer 1 can be easily and cleanly separated from the functional foil 3. When the carrier foil 1 and the functional foil 3 are separated from each other, the separation essentially occurs at the interface between the release layer 2 and the functional foil 3. That is to say, the release layer 2 is separated from the functional foil 3 together with the carrier foil 1 and therefore remains on the carrier foil 1.

[0043] The release layer 2 comprises a ternary alloy including nickel, and more preferably the release layer comprises (or consists of) a ternary alloy of nickel, molybdenum and tungsten. In an embodiment, the ternary alloy layer of the release layer has a ternary alloy content of 1000 μg / dm 2 to 3000 μg / dm 2 Ni content in the range of 300μg / dm 2 to 1600 μg / dm 2 Mo content in the range of 5μg / dm 2 The W content is equal to or greater than 1000 ppm.

[0044] In the majority of the release layer, Ni, Mo, and W are essentially in metallic form. However, it should be noted that the side of the release layer facing / supporting the functional copper foil contains oxidized forms of the components / elements of the ternary alloy. The release force of the surface of the release layer 2 in contact with the ultra-thin copper foil 3 can be controlled by controlling the amount of oxide. The release layer 2 is formed as an amorphous layer, i.e., the alloy of this release layer is preferably an amorphous alloy.

[0045] Amorphous alloys, also known as non-crystallizing alloys, are alloys with an irregular atomic structure similar to that of a liquid. Because the exfoliation layer 2 is amorphous, crystal growth in a specific direction is unlikely to occur, and the exfoliation layer 2 contains almost no grain boundaries. In addition, the release layer 2 is amorphous and has almost no crystalline structure even when observed down to the molecular level, resulting in higher rigidity and a more uniform surface than typical metal materials. In other words, the release layer 2 has a smooth surface. The amorphous release layer 2 can be formed by any conventional method, such as vapor deposition, sputtering, or plating, but plating is preferred. In particular, wet plating, i.e., electrodeposition, is more preferred.

[0046] The thickness of the release layer varies depending on the manufacturing method, and is not particularly limited, but is in the range of 30 nm to 50 nm. However, the thickness of the release layer 2 is most preferably in the range of 35 to 50 nm, regardless of the method for forming the release layer. In a preferred embodiment, the release layer is electroplated onto the carrier foil 1, and the thickness of the release layer can be adjusted (i.e., controlled) by changing the composition of the electrolyte and the electroplating conditions (e.g., the current density and temperature of the electrolyte, etc.).

[0047] Furthermore, because the release layer 2 is formed on an amorphous alloy layer, the oxide film formed on the release layer 2 has almost no minute irregularities due to grain boundaries. This allows the oxide film to have a smooth and dense surface, thereby significantly reducing pinhole defects.

[0048] Functional Foil The functional copper foil is an ultra-thin layer of copper that is detached from the carrier and remains on the substrate, especially to form a copper clad laminate. In other words, the ultra-thin copper layer (functional foil) is peelable (i.e., separable) from the carrier layer 1. Advantageously, the functional foil is formed in a two-step process and therefore comprises a first copper layer 4 (or cover layer) and a second copper layer 5, as shown in FIG.

[0049] The two layers 4, 5 are formed on top of each other to obtain a functional foil 3 (or ultra-thin copper foil or layer) of the desired thickness. The resulting functional foil 3 is a coherent foil that is formed in two steps but behaves as a single layer. As previously indicated, separation from the carrier foil occurs at the interface with the release layer, not within the functional foil 3. That is, the two copper layers 4, 5 do not separate when the carrier foil is detached.

[0050] The thickness of the ultra-thin copper layer 3 varies depending on its manufacturing method and is not particularly limited, but is in the range of 0.5 to 10 μm. However, the thickness of the ultra-thin copper layer 3 is most preferably in the range of 5 μm to 9 μm, regardless of the method of forming the ultra-thin copper layer. Although the method of forming the ultra-thin copper layer 5 is not particularly limited, the copper layer is preferably formed by electroplating. The covering layer 4 is typically a very thin layer of copper or copper alloy plated in an alkaline bath. The microstructure of the covering copper layer 4 is very thin compared to most functional foils 3, making it more compact and allowing for the covering layer to be formed.

[0051] In a subsequent step, the exposed surface of the ultra-thin copper foil 3 (i.e., the surface opposite to the surface in contact with the release layer) may be subjected to an electrochemical or chemical surface treatment, such as a bond enhancing treatment and / or a passivation treatment (not shown).

[0052] Resin layer An embodiment of the present invention provides a copper clad laminate in which a substrate containing a resin is laminated on an ultra-thin copper foil. In this specification, the resin of the substrate can be of any type as long as the glass transition temperature (Tg) of the resin is lower than the temperature of the lamination process performed to form the copper clad laminate. In an embodiment, the Tg of the resin is less than 170°C, preferably less than 160°C or less than 150°C.

[0053] The resin of the substrate may include an epoxy-based resin, a polyimide-based resin, a maleimide-based resin, a triazine-based resin, a polyphenylene-based resin, or a polybutadiene-based resin.

[0054] Manufacturing method Next, the manufacturing method will be described with reference to FIG. As mentioned above, the carrier foil can be any suitable self-supporting layer. Preferably, the carrier foil 1 is an electrodeposited copper foil. Typically, electrodeposited carrier foils are continuously produced using an electroforming cell 12 (known in the industry as a plating machine). In the electroforming cell, an electrolyte (an acidic copper bath with additives) passes through an apparatus including a tank 18 with a tank inlet 18.1 and a tank outlet 18.2, a rotating drum-shaped cathode 14 (whose surface is made of stainless steel or titanium), and a stationary anode 16 (a titanium electrode coated with lead or a noble metal oxide) facing the cathode. A current is passed through both electrodes to deposit a desired thickness of copper on the cathode surface to form an electrodeposited copper foil. The electrodeposited copper foil 1 is then peeled from the surface of the cathode 14 and can be coiled onto a storage reel or directly transferred to a first processing bath. Processes for producing such electrodeposited copper foils are well known and can be used to produce copper carrier foils suitable for the present process.

[0055] Deposition of peeling layer The release layer is formed on one side of the electrodeposited copper carrier foil, usually the drum side. Prior to deposition of the release layer 2, it is preferable, but not always necessary, to pretreat the surface of the carrier layer 1 on which the release layer is to be formed. The pretreatment method is not particularly limited, and generally, methods such as acid cleaning, alkaline degreasing, and electrolytic cleaning are used.

[0056] The release layer is preferably formed by electroplating directly onto the surface of the carrier foil, which is therefore guided through a second electroplating cell 20 containing an electrolyte 22 containing nickel, molybdenum and tungsten, and the carrier foil is placed at a cathodic potential.

[0057] The electrolyte of the release layer is typically an acidic aqueous solution. Nickel compounds, molybdenum compounds, and tungsten compounds can be used as sources of nickel, molybdenum, and tungsten, respectively. For example, nickel sulfate hydrate can be used as the nickel compound. Sodium molybdenum or its hydrates, such as molybdenum dihydrate, can be used as the molybdenum compound; and tungsten or its hydrates, such as tungsten dihydrate, can be used as the tungsten compound. The solvent for the electrolyte is not particularly limited as long as it is a commonly used solvent, but water is generally used.

[0058] The concentrations of the metals used in the electrolyte cell can be appropriately selected depending on the type of metal. For example, to form an amorphous alloy layer of Ni, Mo, and W, the Ni concentration is preferably 5 g / L to 9 g / L, more preferably 7.0 to 9.0 g / L, the Mo concentration is preferably 5 g / L to 9 g / L, and the W concentration is preferably 1 to 5 g / L.

[0059] The temperature of the electrolyte is generally in the range of 5° C. to 70° C., preferably in the range of 10° C. to 50° C. The current density is generally 0.2 A / dm 2 from 10A / dm 2 The range is preferably 0.5A / dm 2 from 5A / dm 2 Advantageously, the tungsten compound can induce co-precipitation of the three metals of the ternary alloy, thus forming an amorphous layer.

[0060] The pH of the electrolyte may vary depending on the type of alloy-forming metal contained in the release layer. For example, to form a release layer containing an alloy of nickel, molybdenum, and tungsten, it is preferable to adjust the pH of the electrolytic bath to a range of 2.0 to 5.0, such as 2.5 to 4.5, because this is favorable for forming an amorphous alloy layer. If the pH of the electrolytic cell is less than 2.0, a crystalline alloy layer may be formed. If the pH of the electrolytic cell is greater than 5.0, only a thin film may be obtained because electroplating or deposition is difficult at such a pH.

[0061] The release layer may be formed in one or more passes, i.e., via single or multiple electrodeposition steps. Regardless of the manufacturing method, the release layer is formed to achieve a desired thickness or specific density (mass per surface unit).

[0062] Cleaning process It will be appreciated that after being formed (i.e., deposited) on the carrier foil, the release layer having the desired thickness or specific density is subjected to a cleaning step, in particular, using a cleaning solution (or rinse water) having a pH within a specified range.

[0063] The cleaning solution is typically an aqueous solution. It may have a pH between 2.5 and 4.5, preferably between 2.5 and 4.0, and more preferably between 2.5 and 3.5. For ease of implementation, the cleaning solution may contain a significant amount of water, for example, more than 90, 95, or 99% by weight of water based on the total weight of the cleaning solution.

[0064] In practice, the cleaning liquid is sprayed onto the exposed surface of the release layer (i.e., onto the side of the release layer opposite to the side in contact with the carrier foil) using a nozzle 30. The cleaning liquid may be sprayed onto the release layer in one or several steps for 10 to 50 seconds. In some embodiments, the cleaning steps are performed according to the following sequence: spray the cleaning liquid onto the release layer, immerse the carrier foil with the release layer thereon in a bath 32 of cleaning liquid, and spray the cleaning liquid onto the release layer emerging from the bath.

[0065] This cleaning step allows for the formation of an oxide on the surface of the release layer, which provides desirable release behavior in low temperature lamination processes.

[0066] After cleaning, the carrier foil with the release layer deposited thereon may be wiped, for example by passing it between pressure rollers (eg nip rollers), before being conveyed to a bath for electrodeposition of the functional foil.

[0067] Electrodeposition of functional foils As previously mentioned, the functional foil is formed in two steps. A first copper layer (copper or copper alloy) is formed directly on the release layer, ie, on the cleaned and dried side of the release layer.

[0068] The first copper layer is formed by electroplating in an alkaline copper plating bath 40. The alkaline bath preferably contains pyrophosphate, cyanate, and / or sulfamate ions. The current rate is controlled to form a thin, compact, and uniform cover layer. This first / cover copper foil is very thin and is designed as a strike layer, which helps avoid pinholes and promotes copper deposition at a higher rate.

[0069] A second copper layer is then electroplated onto the first copper layer using a copper acid bath 42, typically a copper sulfate bath. This second copper layer is allowed to grow until the desired thickness of the ultra-thin copper foil is achieved. The resulting composite copper foil is finally wound onto a receiving drum 50.

[0070] Example Composite copper foils were produced using either a method according to the present invention (Example) or a comparative method not forming part of the present invention (Comparative Example), which differ from the inventive method in at least one of the release layer cleaning step and the release layer deposition conditions. In both the example and the comparative example, the same copper foil was used as the carrier foil and was first subjected to acid cleaning.

[0071] Next, in both the examples and comparative examples, an alloy release layer was formed on the carrier layer by electroplating using an electrolyte containing nickel (Ni), molybdenum (Mo), and tungsten (W). The amounts of Ni, Mo, and W in each bath are shown in Table 1. The release layer was deposited using an electrolyte with a pH between 2 and 5 and a temperature between 15 and 60°C, with a current of 0.8 and 8 A / dm 2 The release layer of the foils according to the examples was washed with a cleaning solution having a pH between 2.5 and 4.5 to oxidize the surface and form an oxide. The release layer of some of the foils according to the comparative examples was also washed with a cleaning solution having a pH between 2.5 and 5.0.

[0072] The pH of each of the cleaning solutions for the foils according to the invention, if applicable to the comparative foils, is given in Table 1. In practice, the cleaning process is carried out by spraying the carrier foil supporting the release layer with a cleaning solution as it emerges from the electrolytic bath for release before entering the next electroplating bath for the ultra-thin copper foil, immersing it in a bath of cleaning solution, and then spraying the cleaning solution on top of it.

[0073] The plating of the ultra-thin copper foil was carried out in two steps: first, a cover layer was plated onto the release layer (i.e., its cleaned / oxidized surface) using an alkaline plating bath to form a very thin, continuous cover layer.

[0074] A second copper layer was then plated onto the first layer using an acidic copper sulfate bath to the required thickness to obtain the desired thickness of the ultra-thin copper foil. The main characteristics of the composite copper foils according to the present invention and comparative examples are shown in Table 1.

[0075] The resulting composite copper foils (both according to the present invention and the comparative example) were then laminated onto substrates and the peel force was measured. The lamination process and peel force measurement are generally known in the art and only a brief description will be given below.

[0076] Lamination Process To determine the foil behavior during lamination, the foil is laminated at 170°C: Composite copper foil is laminated to epoxy resin FR4 at 170°C for 1 hour.

[0077] Peel force measurement The peel force (or demold force) between the carrier and the ultra-thin copper foil is measured at 90°. The test is performed according to IPC-TM-650 method 2.4.8.5. The peel force values ​​are shown in Table 1.

[0078] As can be seen from Table 1, all of the composite copper foils according to the present invention (Examples 1 to 4) exhibit a peel force between 30 and 120 N / m after lamination at 170°C for 1 hour. The composite copper foils of the present invention can be peeled at a convenient peel force after low-temperature lamination. Therefore, the carrier layer of the composite copper foils produced according to the present invention adheres to the ultra-thin copper layer even after lamination at 170°C, with a peel force between 30 and 120 N / m. The copper layer can be further processed (drilled, etc.) before peeling off the carrier layer.

[0079] [Table 1]

[0080] In contrast, without the cleaning process (Comparative Examples 1 and 2), the composite copper foil exhibits a peel force of less than -5 N / m after lamination at -170°C for 1 hour, which means that the carrier foil is very easy to separate immediately after lamination. The carrier foil cannot act as a protective measure in the various subsequent manufacturing steps of the printed circuit board, and the ultra-thin copper foil cannot be further processed. In other words, the composite foils of Comparative Examples 1 and 2 are not suitable for low-temperature lamination processes.

[0081] Furthermore, if the cleaning process is performed using a cleaning solution with a pH of 5.0, that is, a cleaning solution outside the specified range, the peeling force becomes too high and the ultra-thin copper foil cannot be peeled off from the carrier foil.

[0082] Furthermore, when the release layer is deposited using an acidic electrolyte containing Ni, Mo, or W outside the specified range (e.g., high in Ni—Comparative Example 3, low in W—Comparative Example 4, or low in Mo—Comparative Example 5), the release force is significantly higher than in Comparative Examples 1 and 2, sufficient to ensure cohesion of the composite copper foil in subsequent manufacturing steps, but not as high as that of the copper foil of the present invention, being less than 30 N / m.

[0083] In further comparison, the composite copper foil of the present invention was unable to be peeled off after high temperature lamination (220°C for 2 hours), whereas the composite copper foil of Comparative Example 1 showed a peel force of 15 N / m.

[0084] As a result, only the method for producing a composite copper foil according to the present invention, which includes the steps of depositing a release layer at a predetermined concentration using an acidic electrolyte consisting of Ni, Mo, and W, and then rinsing the release layer prior to the deposition of the ultra-thin copper foil, can produce a composite copper foil with a high release force suitable for low-temperature lamination.

[0085] To further characterize the different composite copper foils, X-ray photoelectron spectroscopy (XPS) measurements were performed on the surface of the release layer after peeling of the functional foil. Bond energy measurements were performed in the nickel (Ni) region for both the composite copper foil according to the present invention (FIG. 3—Examples 1 and 2) and the composite copper foil according to the comparative example (FIG. 4—Comparative Examples 1 and 2).

[0086] As can be seen, for both the release layer of the example and the release layer of the comparative example, the nickel is primarily metallic, and the nickel oxide is primarily in the oxidation state +II. 2+ is mainly in the oxide or hydroxide form. As shown in Figure 3, the amount of Ni(+II) is more important on the surface of the release layer of the example, i.e., the example with higher release force compared to the comparative example (Figure 4).

Claims

1. A method for producing a composite copper foil comprising a carrier foil, a release layer, and an ultrathin copper foil, wherein the ultrathin copper foil is peelable from the carrier foil, - Provide carrier foil; - An amorphous exfoliation layer containing a ternary alloy of nickel, molybdenum, and tungsten is deposited on a carrier foil using an acidic electrolyte containing nickel, molybdenum, and tungsten; - Wash the exposed side of the release layer on the carrier foil with a washing solution having a pH between 2.5 and 4.5; - An ultrathin copper foil is electroplated onto the release layer. A method that includes the act of doing so.

2. The method according to claim 1, wherein the pH of the washing solution is between 2.5 and 4.

0.

3. The method according to claim 1, wherein the cleaning solution comprises water and an acid, preferably an inorganic acid.

4. The method according to claim 1, wherein cleaning the exposed side of the peeling layer includes spraying and / or immersing it in a cleaning solution.

5. The method according to claim 1, wherein the cleaning of the exposed side of the peeling layer is performed for periods of 10 and 50 seconds.

6. The method according to claim 1, wherein the washed peeled layer is left in the air for 10 to 40 seconds.

7. The method according to claim 1, wherein the acidic electrolyte comprises nickel in concentrations between 5.0 and 9.0 g / L, molybdenum in concentrations between 5.0 and 9.0 g / L, and tungsten in concentrations between 1.0 and 5.0 g / L.

8. Electroplating of ultra-thin copper foil is Using an alkali copper electrolyte, the first copper layer is electroplated directly onto the stripping layer; and An acidic copper electrolyte is used to electroplate the second copper layer onto the first copper layer. The method described in claim 1.

9. The method according to claim 8, wherein the alkaline tank comprises pyrophosphate, cyanate and / or sulfamate ions.

10. A composite copper foil comprising a carrier foil, a release layer, and an ultrathin copper foil in this order, A composite copper foil in which the release layer contains a ternary alloy of nickel, molybdenum, and tungsten formed as an amorphous layer, and the release force of the release layer is between 30 and 120 N / m after lamination at 170°C for 1 hour.

11. The composite copper foil according to claim 10, wherein the release layer includes the oxidation form of the ternary alloy contained in the release layer at the interface with the ultrathin copper foil.

12. The composite copper foil according to claim 10, wherein the release layer contains nickel in an oxidized form at the interface with the ultrathin copper foil, and the nickel in the +II oxidized state accounts for at least 30% by weight of the total amount of nickel on the surface.

13. The composite copper foil according to claim 10, wherein the release layer has a thickness between 5 and 50 nm.

14. The composite copper foil according to claim 10, wherein the thickness of the ultrathin copper foil is between 5.0 and 9.0 μm.

15. The composite copper foil according to claim 10, wherein the composite copper foil is manufactured by the method described in claim 1.

16. The substrate resin has a Tg of less than 170°C, and the peel strength of the composite copper foil after lamination at 170°C for 1 hour is between 30 and 120 N / m. A copper-clad laminate comprising a resin-equipped substrate and carrier foil, a release layer and an ultrathin copper foil in this order, wherein the release layer includes a composite copper foil containing a ternary alloy of nickel, molybdenum and tungsten formed as an amorphous layer, and the ultrathin copper foil is laminated on the exposed surface of the substrate.

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