Surface-treated copper foil for high-frequency circuits and its manufacturing method

Abstract

The present invention proposes a surface-treated copper foil for high frequency circuits and a corresponding method for treating the copper foil. The copper foil (12) comprises two opposite faces (12.1, 12.2), in which the first face (12.2) is coated with a treatment layer (14) comprising, in this order: a first layer (16) comprising oxides of Mo and Zn, deposited on said first face (12.2), said first layer being free of Ni; a second layer (18) of Cr oxide; and a binder layer (20); the first layer (16) comprises between 5 and 30 mg / m2 calculated as Mo and Zn. 2 the treated layer (14) has a roughness RzJIS of 0.7 μm or less; and the first surface is not subjected to a roughening treatment.

Description

[Technical field]

[0001] The present invention relates to a surface-treated copper foil for use in high-frequency circuits, and more specifically to a surface-treated copper foil having excellent adhesion to insulating substrates for use in high-frequency circuits and excellent transmission characteristics in the high-frequency range. [Background technology]

[0002] Data is growing exponentially, and the momentum is unrelenting, not only due to social media and video sharing platforms, but also due to the proliferation of information terminals such as smartphones and laptops. This increases the demand for transmitting large amounts of data, which requires ever-increasing signal transmission speeds between components on a circuit board. To achieve these speeds, the frequency range is inevitably increasing from the MHz range to 1 GHz, 10 GHz, or even higher. In these higher ranges, current flows primarily near the surface of a conductor, due to the well-known "skin effect," which is the tendency for high-frequency current density to be highest at the surface of a conductor and decay exponentially toward the center. The skin depth, where approximately 67% of the signal is transmitted, is inversely proportional to the square root of the frequency.

[0003] Thus, at 1 MHz the skin depth is 65 μm, at 1 GHz it is 2.1 μm, while at 10 GHz the skin depth is only 0.65 μm. At higher frequencies the topography or roughness of the conductor becomes increasingly important, as roughness has a similar or greater effect on signal transmission due to scattering as the skin depth.

[0004] In this context, conventional printed circuit boards (PCBs) intentionally roughen the surfaces of conductor tracks to improve their adhesion properties to the resin layers used in the laminate PCB construction. Rough surfaces typically have a surface roughness Rz of a few μm, which affects any transmission in the GHz range. Conventional designs are therefore limited by the conflicting needs of high roughness to ensure adhesion and low roughness to minimize transmission losses. Conventional roughening treatments include the deposition of nodules on the copper foil surface (nodule treatment); or etching the copper surface with acidic solutions to form the so-called brown-oxide.

[0005] Many techniques have been developed to produce copper foils for HF applications: US 10,772,199, JPS 61288095 A, and EP 3882378 A1 disclose copper foils with micro-scale nodule treatment to ensure high adhesion to the substrate.

[0006] In US2021 / 0321514A1, it is proposed to increase the microroughness of the foil to ensure high adhesion. In JP6083619B2, a copper foil with heat-resistant treatment by metal content is disclosed. In US2021029823, a copper foil with an adhesive layer for high signal transmission is disclosed.

[0007] Although various prior art approaches have been proposed, there remains a need for copper foils that exhibit good adhesion, heat resistance and chemical resistance while having controlled properties for HF circuits, particularly desirably low transmission loss. Summary of the Invention

[0008] The present invention provides a surface-treated copper foil for high-frequency circuits as recited in claim 1 and a method for treating the copper foil as recited in claim 13. In accordance with the present invention, a surface treated copper foil includes two opposing sides, a first side having: a first layer comprising an oxide of molybdenum and zinc deposited on said first surface, said first layer being nickel-free; - a second layer of chromium oxide; and - preferably a coupling agent layer; and coated with a treatment layer including, in this order, The first layer is 5-30 mg / m2 calculated as molybdenum and zinc. 2 containing molybdenum and zinc oxides in an amount of; The surface-treated copper foil has a roughness RzJIS of 0.7 μm or less; and The first surface is not subjected to a roughening treatment.

[0009] According to a first result, the present invention proposes a surface-treated copper foil which meets the requirements for high-frequency circuit applications, especially in terms of adhesion, heat resistance, chemical resistance and low transmission loss.

[0010] In other words, the present invention is based on the finding that by performing a specified surface treatment directly on the surface of the copper foil, i.e., by not performing a roughening treatment on the surface of the copper foil, it is possible to minimize transmission loss at high frequencies without adversely affecting the adhesion, heat resistance, and chemical resistance of the surface-treated copper foil, and to achieve the low transmission loss required for applications at frequencies of 1 GHz or higher, such as fifth-generation mobile communications (5G).

[0011] Surprisingly, this is contrary to the common practice in the field of roughening copper foils to improve their bonding and adhesion properties, as disclosed in JPS 61288095 A and EP 3882378 A1, but such roughening affects the profile roughness of the foil and adversely affects signal quality at high frequencies.

[0012] Conversely, since the copper foil of the present invention is not roughened, signal transmission loss at high frequencies is minimized.

[0013] Again, it should be appreciated that the low surface roughness of the treated layer, reflecting the low surface roughness of the copper foil on the low surface, results in less signal loss in high speed / high frequency applications. This is due to the fact that at high frequencies, signals propagate only on the surface of the conductor (skin effect). Thus, a smooth conductor provides a shorter path for the signal to propagate, resulting in lower losses. This makes it possible to build effective transmission lines for applications at frequencies above 1 GHz (e.g. 5G).

[0014] Surprisingly, the mechanical properties, especially the adhesion, of the surface-treated copper foil are not adversely affected even in the absence of a roughening treatment due to the specific combination of layers and the given composition that forms the treatment layer.

[0015] In this document, the term "roughening treatment" is to be understood as a treatment designed to increase the roughness of the copper foil, which is applied to the copper foil after removal from the electrodeposition bath in which the formation of the copper foil has been completed. In particular, the roughening treatment can be called a nodular treatment, i.e. the electrodeposition of fine copper nodules (sometimes called dendritic copper) onto the base copper foil, or a so-called brown oxide treatment or black oxide treatment. During the brown / black oxide treatment, the surface of the copper foil is micro-etched to a depth of about 1-2 μm in order to generate a micro-roughness on the copper surface, and at the same time the surface copper is converted into a layer of organometallic structures that are favorable for adhesion.

[0016] The first layer comprises or consists of oxides of Mo and Zn, and provides a first passivation layer formed directly on one side of the copper foil. The first layer may be formed by an electrolytic co-deposition process. The first layer may include various oxide forms (various oxidation states), i.e., oxides of Zn, oxides of Mo, or mixed oxide forms of Zn and Mo. In particular, oxides may be formed that include at least one oxygen atom bonded to each of Mo and Zn in one or more oxidation states. Without intending to be limiting, in the first analysis, the oxides include oxides of zinc, primarily Zn, oxides of Mo, and oxides of Zn, primarily Zn. 2+ , and Mo for molybdenum6+ , Mo 5+ and / or Mo 4+ It has been shown that the first layer contains Mo, which can improve the heat resistance of the copper foil. Zn is used to enable the deposition of Mo, i.e. to perform the simultaneous deposition of Mo and Zn in the electrolytic bath. In other words, the first layer is a layer of binary alloys, mainly of Zn oxide and Mo oxide, with mixed oxides in which Zn and Mo can be found in one or more oxidation states.

[0017] The amounts of Mo and Zn specified herein in the first layer (referring to Mo and Zn, respectively, as the elements themselves, i.e., not in oxide form) are selected to provide good thermal resistance and high chemical resistance. In embodiments, the weight ratio of Mo to Zn in said first layer is between 0.3 and 1.5.

[0018] The first layer does not contain Ni. In fact, Ni is not desired in the first layer and there is no spontaneous addition of Ni in the bath. However, typically 0.2 mg / m 2 The following impurities or traces may be present:

[0019] Similarly, the first layer preferably does not contain Co. However, it typically contains less than 0.05 mg / m 2 The following impurities or traces may be present:

[0020] Preferably, the first layer comprises more than 85% by weight, in particular more than 90% or 95% by weight, of oxides of Mo and Zn. The use of oxide forms of Mo and Zn provides thermal and chemical resistance as well as reduced insertion loss compared to the metallic forms (metal passivation).

[0021] In some embodiments, the first layer may contain small amounts of other metals, such as Cr, especially in the oxide form.

[0022] The first layer contains traces of species other than the desired Mo and Zn oxides, possibly originating from the electrolyte solution.

[0023] The second layer provides a second passivation, usually formed directly on the first layer. This second layer is provided to provide for the deposition of a binder and also to further improve the chemical stability of the first layer. The second layer may contain 80-100% by weight, in particular 95-100% chromium oxide. The second layer may contain Cr in one or more oxide forms, in particular having Cr in oxidation state III and / or other oxidation states.

[0024] The third layer, i.e., coupling agent layer, is usually formed directly on the second layer to provide desired adhesion properties to the resin / polymer substrate during lamination. In that regard, it will be understood that the above-mentioned first layer and second layer, by their predetermined design, provide good adhesion to the third coupling agent layer, which in turn provides adhesion to the resin / polymer substrate. This is reasonable because there is no roughening treatment to improve adhesion to the resin / polymer substrate.

[0025] The surface roughness RzJIS of this surface-treated copper foil is very low, less than 0.7 μm. The roughness shown is the roughness of the free surface of the treatment layer (i.e., the free surface of the binder layer opposite the second layer).

[0026] It is noted that the treatment layers do not substantially change the surface roughness of the copper foil surface on which they are formed. In other words, each layer of the treatment layer tends to conform / replicate the surface roughness of the layer below, and ultimately, the surface roughness of the base copper foil. The functional layers of the treatment layer are fairly thin layers that do not noticeably alter the surface roughness of the treated copper foil, which is determined primarily by the initial roughness of the base copper foil.

[0027] In an embodiment, the treatment layer has a roughness of 0.6 μm or less, for example RzJIS 0.5 or 0.4 μm. The SDR of the treatment layer can be 0.3% or less, in particular 0.2 or 0.1 or less. It should be noted that the treatment layer does not essentially change the roughness of the base copper layer.

[0028] Such a low SDR indicates that the treatment layer is a smooth layer and the copper foil does not contain a roughened layer. Therefore, the bondability / adhesion properties of the surface-treated copper foil of the present invention are guaranteed by the treatment layers, especially the third (bonding agent) layer.

[0029] In this context, 3D parameters, especially the surface developpe ratio (SDR), are believed to be suitable for accurately characterizing the surface roughness of treated copper foils, especially surface-treated copper foils that can be used in high frequency applications and have lower insertion loss than two-dimensional (or 2D) surface parameters.

[0030] Surface development ratio (SDR), or developed interfacial area ratio, also called surface complexity, corresponds to the ratio of the actual developed surface area to the projected surface area. The actual surface is the interfacial area of ​​the surface-treated copper foil, while the projected surface is the corresponding flat and perfectly smooth foil surface. SDR can be calculated based on the following formula (or an equivalent calculation): SDR = ((real developed surface - projected surface) / projected surface) x 100

[0031] In other words, SDR is expressed as the percentage of additional surface area contributed by texture (the presence of peaks and valleys on the surface of the copper foil, in addition to copper nodules and / or dendritic copper filaments) compared to an ideal flat surface. Because SDR is affected by both the texture (number and size of peaks and valleys, number and size of nodules and / or dendritic copper filaments) and their spatial arrangement, this parameter more advantageously distinguishes between surfaces of similar roughness described using a 2D parameter, such as Rz. Typically, SDR increases with the spatial complexity of the texture, regardless of whether Rz changes or not.

[0032] In this regard, it should be noted that copper foil that has been subjected to a roughening treatment such as the electrodeposition of fine copper nodules or dendritic copper may exhibit a surface roughness RzJIS similar to that of unroughened (surface-treated) copper foil, but the roughened (surface-treated) copper foil will have a much higher SDR value.

[0033] Preferably, the copper foil on which the treatment layer is formed is an electrodeposited copper foil. The treatment layer is typically applied to the electrolyte side, but can also be applied to the drum side. The side of the electrodeposited copper foil on which the treatment layer is formed is preferably a low-roughness side, with a roughness RzJIS of 0.7 μm or less, for example 0.6, 0.5 or 0.4 μm. The SDR of the same side is usually 0.3% or less, in particular 0.2 or 0.1% or less. Preferably, the second side of the copper foil opposite to the side bearing the treatment layer has a surface roughness in the same range.

[0034] In summary, the present invention provides a surface treated copper foil including a first layer of Zn and Mo oxides that provides a first passivation with a non-metallic alloy, which has the advantage of improving thermal resistance without affecting signal quality at high frequencies.

[0035] In comparison with prior art foils, the surface treatment of the surface-treated copper foil of the present invention does not include nodules / nodular treatment or other types of roughening treatment. Moreover, the treatment layer has a very smooth roughness profile; the treatment layer does not essentially change the surface roughness of the copper foil surface formed thereon. In this regard, this low surface roughness is reflected by the Rz and SDR values.

[0036] The present invention proposes a copper foil that, whatever the roughening treatment, is smooth to ensure low insertion loss at high frequencies and exhibits good performance with respect to criteria such as peel strength, chemical resistance and heat resistance (blistering).

[0037] As an added benefit, smooth copper foil passivation typically requires less material than copper foil with nodules.

[0038] The present invention thus solves the problem of high transmission loss at high frequencies by applying a non-metallic passivation treatment to a copper foil with low roughness, and by surface treatment using the combination of layers defined herein, without applying a nodule / roughening treatment.

[0039] According to another aspect, the present invention relates to a method of treating a copper foil, the method comprising: coating a first surface of a copper foil with a treatment layer to provide a copper foil having two opposing surfaces; Coverage: - electrodepositing a first layer of Mo and Zn oxides in a first bath containing 1.5-7 g / L Mo and 1-5 g / L Zn, but no Ni; - electrodepositing a second layer of Cr oxide onto the first layer in a second bath; - forming a binder layer on the second layer in a third bath; This includes:

[0040] The method is adapted to provide a treatment layer on a copper foil as disclosed hereinabove. The technical features, explanations and advantages disclosed with respect to the surface-treated copper foil disclosed herein apply mutatis mutandis to the method.

[0041] The first bath may be an acidic aqueous solution containing predetermined amounts of Mo and Zn, or may contain only Mo and Zn in addition to an acidic species (usually sulfuric acid or equivalent).

[0042] The first bath does not contain Ni. Indeed, Ni is not desirable in the first layer formed by the present method, and nickel is not optionally added to the bath. However, typically, 0.5 mg / m 2 The following impurities or traces may be present:

[0043] In an embodiment, the first tank may contain 2.5-5.5 g / L Mo and 1.5-4 g / L Zn. The first tank may have a pH of 3.0-4.5, preferably 3.5-4.

[0044] The electrodeposition process in the first bath can be carried out using two different anodes applying different current densities. This allows more flexible control of the co-deposition process. It should be noted that Mo alone is difficult to deposit in aqueous solution, whereas the present proposal relying on co-deposition provides a viable solution for forming Mo and Zn oxide layers. Thus, the present invention is in contrast to the state of the art where Mo has been co-deposited with ferromagnetic elements such as Ni or Co, which are adversely affected at high frequencies.

[0045] Electrodeposition in the first bath is advantageously achieved with a concentration of 5-30 mg / m, calculated as Mo and Zn elements. 2 , preferably 15 to 25 mg / m 2 A first layer is formed that includes oxides of Mo and Zn in an amount of 1000 nm.

[0046] The second tank preferably contains 0.5-4 g / L, more preferably 1-2 g / L Cr. The second tank is usually an acidic solution (sulfuric acid) to which chromium oxide (e.g. CrO3) has been added to meet a desired concentration. The pH of the second tank can be 1-4.

[0047] In an embodiment, the electrodeposition process in the second bath is such that the second layer has a concentration of 4-10 mg / m2 calculated as Cr (not in oxide form). 2 The method is carried out so as to include an amount of Cr oxide.

[0048] In an embodiment, the third bath contains a functionalized silane coupling agent at a concentration of 0.5-5 wt.%, preferably an aminosilane, an epoxy-silane, a vinyl-silane, a methacrylate silane, or a mixture thereof. Preferably, the third bath has a pH of 9-12, particularly about 10.5, for aminosilane coupling agents.

[0049] Prior to immersion in the first bath, the copper foil is advantageously subjected to a cleaning step to remove oxides, grease, etc. The cleaning step may, for example, involve immersing the copper foil in an acid bath.

[0050] The side of the copper foil on which the treatment layer is formed has a surface roughness RzJIS of 0.7 μm or less, in particular 0.6, 0.5, 0.4 μm or even less. Preferably, both sides have a surface roughness in that range.

[0051] This process does not include nodule treatment or other types of roughening treatment of the surface of the copper foil on which the treatment layer is formed. This process is performed to have a smooth surface treatment surface. The surface-treated copper foil has a roughness RzJIS of 0.7 μm or less, particularly 0.6, 0.5 or 0.4 μm or less, measured from the exposed surface of the treatment layer (i.e., the surface not in contact with the copper foil).

[0052] According to another aspect, the present invention relates to a copper clad laminate comprising a surface treated copper foil as disclosed herein laminated onto a substrate at 200° C. for 2 hours. The substrate can generally be a polymer, particularly a resin, or a prepreg. Such a copper clad laminate exhibits the following properties: The copper foil has a peel strength of 0.40 N / mm or more, preferably at least 0.45 or 0.50 N / mm; a peel strength loss of 10% or less after HCl (chemical resistance) testing; and is capable of withstanding a blister (heat resistance) test at a temperature of 270°C or 275°C or higher.

[0053] As used herein, any given numerical value covers a range of values ​​from -10% to +10% of said numerical value, preferably from -5% to +5% of said numerical value, and more preferably from -1% to +1% of said numerical value. [Brief description of the drawings]

[0054] The invention will now be described, by way of example, with reference to the accompanying drawings, in which: [Figure 1] FIG. 2 is a diagram showing the principle of an embodiment of the surface-treated copper foil. [Diagram 2] FIG. 1 is a schematic diagram of a surface treatment line for carrying out the present process. [Diagram 3] 1 is an XPS spectrum of a treated layer. [Figure 4] 1 is an XPS spectrum of a treated layer. Description of the Preferred Embodiments

[0055] The present invention addresses challenges unique to copper foils for high frequency circuits. Specifically, the present invention provides an electrodeposited copper foil that provides improved signal quality at high frequencies by combining low roughness electrodeposited copper foil, no roughening treatment (particularly no nodular free treatment) and no metallic free passivation, while ensuring high thermal resistance, chemical resistance and high peel strength in PPE / PPO and PTFE materials, in the following embodiments.

[0056] In conventional processes, low profile copper foil is treated with either micro-scale nodule or roughening processes to ensure high adhesion to the substrate, which affects signal transmission at high frequencies.

[0057] Indeed, the skin effect is experienced by resistors at high frequencies. At low frequencies, the current distribution is uniform throughout the resistor. However, as the frequency increases, the current distribution becomes non-uniform and is concentrated at the surface of the resistor. The current is only confined to the surface at RF frequencies. At high frequencies, AC currents have a higher current density at the edges of the conductor and the current flows within the "skin depth". Thus, in these frequency ranges, the signal quality is mainly affected by the foil profile.

[0058] Thus, loss of signal quality at high frequencies is associated with a high profile of the foil. Reducing the foil profile improves signal quality at high frequencies, but can affect adhesion. While some prior art processes include deposition of micro-scale nodules or roughening processes that affect the foil profile, the present process does not alter or affect the profile of a low roughness copper foil (base) while maintaining adhesion.

[0059] Improvements in heat resistance are usually achieved by depositing metallic elements such as Ni and Co, which are deposited in the metallic state, but this has a negative effect on signal quality at high frequencies. While some patents teach the use of these elements to improve heat resistance, the present invention uses only the non-metallic forms of the alloys that do not adversely affect signal transmission at high frequencies.

[0060] 1 shows a schematic diagram of a surface treated copper foil 10 according to one embodiment of the present invention, which comprises a copper foil 12, specifically an electrodeposited copper foil having two opposing surfaces, a drum surface 12.1 and an electrolyte surface 12.2 (also referred to as a matte surface).

[0061] The electrolyte surface 10.2 consists of three layers: a first layer 16 comprising an oxide of Mo and Zn; - a second layer 18 of chromium oxide; and - coated with treatment layers generally designated 14, including a third layer 20 called the binder layer.

[0062] The first and second layers 14, 16 are passivation layers, while the third layer 18 is provided to improve adhesion to polymers / resins.

[0063] Note that in reality, the three layers are built up one after the other on the copper foil surface (one on top of the other, so to speak), and therefore they are described and represented here as three separate layers, although there may be some intermixing due to the small amount of material deposited in each layer.

[0064] The manufacture of the copper foil is not the object of the present invention. Any suitable copper foil can be used. The copper foil is preferably an electrodeposited copper foil. Preferred properties of the copper foil are: - thickness from 9 to 70 μm; -Roughness RzJIS: Drum surface: 0.8-1.2μm - Electrode surface: 0.4-0.7μm -SDR: electrolyte surface: <0.3%. Preferably, the foil has a copper purity of at least 99.8%. The tensile strength is typically 31 to 38 kgf / mm 2 The range may be:

[0065] The surface-treated copper foil 10 of the present invention is obtained from a specific combination of layers having a predetermined composition, which has good results in terms of heat resistance, peel strength, chemical resistance, and exhibits low transmission loss.

[0066] <Surface treatment process> The copper foil is obtained by subjecting the foil to a treatment process that includes three baths 22, 24, 26 contained in separate recipients 28i - called treaters, one for forming one of the layers 16, 18, and 20. The process is usually continuous, i.e. the copper foil is dipped successively through a series of treaters 28. This is shown in Figure 2. The untreated (as-manufactured) copper foil 12 is unrolled from a support drum 30 and guided through the various treaters 28 by guide rolls 32. The resulting surface-treated copper foil 10 is finally wound up on a receiving drum 34.

[0067] During storage of untreated copper foil 12, copper oxides may form locally. It is therefore preferable to clean copper foil 12 before forming a treatment layer. This optional cleaning step may be performed by immersion in an acid bath 36 of first treatment device 281. Acid bath 36 may contain sulfuric acid at a concentration of 60-100 g / L.

[0068] The cleaned copper foil 12 then enters a second processing unit 18.2 which contains a first passivating bath 22. The first bath 22 is an acidic solution containing 1.5-7 g / L Mo and 1-5 g / L Zn. It can be prepared from Na2MoO4·2H2O and ZnSO4·7H2O. The concentrations given here for the various baths relate to the metal ions in solution.

[0069] The first bath 22 is an electrodeposition bath in which Zn and Mo are co-deposited in oxide form. Various oxide forms of Zn and Mo are deposited, possibly also mixed oxides. Deposition of Mo in aqueous solutions is difficult, but the present proposal based on co-deposition allows the formation of coherent layers of Zn and Mo oxides.

[0070] The pH can be adjusted by adding sulfuric acid and / or sodium hydroxide to between 3.0 and 4.5. At pH above 4.5, Zn tends to precipitate. At pH < 3, the amount of Zn deposited is lower.

[0071] The electrodeposition process consisted of a first layer of 5 and 30 mg / m 2 The specific mass is calculated for Zn and Mo metals only.

[0072] Preferably, two separate planar anodes are placed in the bath and different current densities are applied. The current density of each anode is adjusted depending on the desired amount of Zn and Mo to be deposited and the Zn / Mo ratio. Current densities are typically between 0.2 and 1.4 A / dm 2 Varies between.

[0073] At the exit of the treatment device 28.2, the copper foil is coated with the first layer 16 and enters the second bath 24 of the treatment device 28.3. The second bath 24 is a chromium plating bath, which usually contains a mixture of chromium trioxide (CrO3) and sulfuric acid. The concentration of Cr in the bath can be between 0.5 and 4 g / L. The pH of this passivation bath is preferably adjusted to about 2.0. The current density is about 2-6 A / dm2 It could be.

[0074] The deposition can be performed with one anode. A chromium oxide layer 18, also called a chromate layer, is formed on the first layer 16.

[0075] The copper foil with the first layer 16 and the second layer 18 then enters a final processing unit 28.4 which contains a third bath 26. The bath 26 is an aqueous solution containing a bonding agent, in particular a functionalized silane bonding agent, such as aminosilane, epoxy-silane, vinyl-silane, methacrylate silane, or mixtures thereof. The pH of the bath 26 is adapted depending on the type of bonding agent. For example, the bath 26 is a basic solution when it contains aminosilane.

[0076] The concentration of the binder in the third tank 26 may be 0.5-5% by weight. The pH of the aqueous solution may be adjusted by adding sulfuric acid or sodium hydroxide.

[0077] The copper foil emerging from the final treatment unit 28.4 is thus coated with the three layers 16, 18, 20 forming the present surface treated copper foil 10.

[0078] Prior to being wound on receiving drum 34, the surface treated copper foil 12 is dried in drying tunnel 40, typically for about 15, 20 or 30 seconds, or more.

[0079] It should be noted here that Figures 3 and 4 support the fact that the first passivation layer consists of oxides of zinc and molybdenum. In these first tests, the following oxidation states were observed: Zn2+, Mo4+, Mo5+, Mo6+.

[0080] <Example> Below we provide some examples and counterexamples. In all examples and counter examples, the original copper foil to be surface treated was an electrolytic copper foil produced with a thickness of 18 μm using a titanium electrolytic drum, a cathode and an insoluble anode and a cupric sulfate electrolyte. The surface roughness of the produced electrolytic copper foil was RzJIS of <0.7 μm on both sides.

[0081] Examples A1, A2 and A3 relate to copper foils surface treated by the present process. The first bath 22 contains 4.0 g / L Mo and 2.6 g / L Zn. For example A1, 0.4 A.dm -2 , 1.2A.dm at the second anode -2 The deposition was performed at a current density of 20 mg / m 2 A Mo+Zn density of 25 mg / m for examples A2 and A3, respectively, was achieved. 2 and 15 mg / m 2 A current density was applied to achieve a Mo+Zn specific gravity of 1000. The speed of the copper foil through the bath was 10-20 m / min.

[0082] The second tank 24 contained 2 g / L Cr. The deposition was performed at 3.5 A.dm -2 The experiment was carried out at a current density of 0.01 μm.

[0083] The third tank 26 contained 2% by weight of aminosilane as a binder.

[0084] <Test procedure> To characterize the resulting surface-treated copper foils, several tests were performed on the exemplary foils, which are well known in the art and are only briefly presented below.

[0085] Peel test The copper foil is laminated onto a resin substrate, i.e. PPE blend resin substrate such as resin Megtron 6, at 200C for 2 hours. The peel strength is measured at 90°. The test was performed according to IPC-TM-650 Method 2.4.8.5.

[0086] Roughness measurement The roughness RzJIS is measured with a perthometer according to IPC-TM-650 Method 2.2.17. The roughness of the surface-treated copper foil is measured from the exposed side of the treatment layer, i.e. the free side 21 of the binder layer 20 opposite the passivation layer 18, relative to the treatment layer.

[0087] SDR-Surface development rate SDR or developed interfacial area ratio represents the percentage of additional surface area of ​​a defined area provided by texture compared to the planar defined area. A perfectly flat surface has an SDR of 0. If a surface has peaks or slopes, its SDR value will be higher.

[0088] The SDR parameters are measured by non-contact measurement and may be measured using a non-contact 3D white light interferometer or a non-contact 3D laser interferometer.

[0089] Independent of the type of light used for the measurement (white light or laser source), the principle is to split a light beam into two paths, one directed to a reference mirror and the other to the sample surface. This measurement beam travels different distances depending on the surface profile. The two waveforms are then recombined and create specific interference patterns depending on the phase difference. These patterns are analyzed to calculate the height of the sample at each point (pixel) scanned. Roughness parameters such as SDR are calculated from this 3D profile.

[0090] The light source (laser or white light) can be of any type conventionally used in the field of surface roughness measurement, the laser can exhibit any desired wavelength, such as for example 408 nm or 658 nm.

[0091] In the context of the present invention, and for the examples and comparative examples, the SDR was measured using a 3D laser scanning microscope, model Nanoview 3D Profilometer NV2700, using white light as the light source.

[0092] thermal resistance The thermal resistance is measured by the so-called blistering test, the result of which indicates the maximum temperature at which no blisters or delamination are observed in the copper clad laminate.

[0093] Chemical resistance Chemical resistance is evaluated by the loss of peel strength measured after an HCl test. A surface-treated copper foil is laminated onto the resin, forming a 1.5 mm wide track. The peel strength is measured before and after immersion in a 12% HCl solution for 30 minutes.

[0094] Insertion Loss Measurement Insertion loss measurements were made on a PNA E8361C from 10 MHz to 67 GHz on a microstrip PCB design using the following characteristics: microstrip design on EM528 material (Dk=3.5); copper thickness: 1.8MIL-18μm; track width: 0.47μm; dielectric thickness: 8MIL; impedance=50Ω; no solder mask; no plating finish; track length: 20cm; connector ELF-67-002.

[0095] <Comparative Example> Starting with the same low roughness 18 μm copper foil used in Examples A1-A3, several comparative examples were prepared.

[0096] All comparative examples were surface treated to form treatment layers including a first passivation layer, a second chromium oxide layer, and an aminosilane layer, however, in some counter examples the surface treatment included a nodule layer on which the three layers were then deposited.

[0097] Comparative Example B. Copper foil was treated with a Nodular treatment followed by a first layer of standard Zn / Cr oxide passivation, followed by a second layer of chromium oxide and then a silane bond layer.

[0098] The nodule treatment was carried out in a copper sulfate bath ([Cu] = 2-15 g / L; [H2SO4] = 30-100 g / L; current density = 15-30 A / dm) to provide adhesive properties by mechanical fixation. 2 ) deposition takes place.

[0099] Comparative Example C. Copper foil was treated with a nodule process followed by a metallic Ni passivation (i.e., no oxide) where the first layer was deposited in a Ni-P bath. A second layer of chromium oxide and a silane bond layer were then deposited on the Ni layer.

[0100] Comparative Example D. The copper foil was treated without nodule treatment and then in a bath corresponding to Example A, but with a specific gravity of 60 mg / m 2 A first layer of Mo and Zn oxide was then treated with a silane bonded layer of chromium oxide on top of it.

[0101] Comparative Example F. Copper foil was treated without nodule treatment, but with a first layer of metallic Ni passivation (not oxide), followed by a second layer of chromium oxide, then a silane bonded layer.

[0102] The properties of the copper foils with various surface treatments are summarized in Table 1. The roughness Rz and SDR in Table 1 are for the free surface of the treatment layer. The foils of Examples A to F were subjected to a series of tests, the results of which are summarized in Table 2.

[0103] [Table 1]

[0104] [Table 2]

[0105] The surface treated copper foils according to the present invention, i.e. Examples A1 to A3, are treated with a non-metallic first layer of Zn and Mo oxides, and have a very smooth treated surface and excellent test results: excellent PS (0.5 N / mm), low HCL loss (less than 10%), high heat resistance (up to 275°C), and minimal insertion loss.

[0106] Regarding the comparative examples, the following comments are possible. The surface treated foil of the present invention of Example A provides similar roughness Rz parameters compared to the nodule treated foils (B and C), but the developed interfacial area ratio (SDR) is significantly lower.

[0107] The inventive foil of Example A provides similar adhesion to PPE / PPO as measured with the nodule treated foils (B and C). However, when the amount of Zn or Mo is too low (Comparative Example G), the adhesion to PPE / PPO is not sufficient.

[0108] The inventive foil of example A, thanks to the moderate passivation content deposition (case D), offers high chemical resistance, corresponding to a PS loss of <10% after HCl test observed for the nodule treated foils (B and C).

[0109] The inventive foil of example A provides better thermal resistance (up to 10-20°C) compared to the foils with nodule treatment and non-metallic passivation (B and C) and is similar to the foil without nodule treatment but with metallic passivation (F).

[0110] The inventive foil of Example A can improve signal quality at high frequencies compared to the nodule treated foils (B and C) and the metal passivated foils (C and F).

[0111] In summary, only the inventive foils of Examples A1-A3, relying on a low roughness base foil, nodule-free processing, and non-metallic passivation, can provide significant improvement in signal quality that meets all the requirements for use in HF circuits, i.e. low roughness, excellent thermal and chemical resistance, good peel strength, and low transmission loss.

Claims

1. It comprises two opposite faces (12.1, 12.2), where the first face (12.2) is: a first layer (16) comprising an oxide of Mo and Zn deposited on said first surface (12.2), said first layer (16) being free of Ni; a second layer (18) of Cr oxide; and a binder layer (20); A copper foil (12) coated with a treatment layer (14) comprising, in this order: The first layer (16) contains 5 and 30 mg / m calculated as Mo and Zn. ２ containing oxides of Mo and Zn in amounts between; The treatment layer (14) has a roughness RzJIS of 0.7 μm or less; and The first surface is not subjected to a roughening treatment. Surface-treated copper foil for high-frequency circuits.

2. 2. The surface treated copper foil of claim 1, wherein the weight ratio of Mo to Zn in the first layer (16) is between 0.3 and 1.

5.

3. 3. The surface-treated copper foil according to claim 1 or 2, wherein the first layer (16) comprises more than 80% by weight, in particular more than 85% or 90% by weight, of oxides of Mo and Zn.

4. 3. The surface treated copper foil of claim 1, wherein the binder layer (20) comprises a functionalized silane binder.

5. The third layer contains 0.5 and 5 mg / m2 calculated as Si. ２ 5. The surface treated copper foil of claim 4, comprising a bonding agent therebetween.

6. 3. The surface-treated copper foil according to claim 1, wherein the thickness of the copper foil (12) is in the range of 9 to 70 μm.

7. 3. The surface-treated copper foil according to claim 1, wherein the treatment layer (20) has a roughness RzJIS of 0.7, 0.6, 0.5 or 0.4 μm.

8. 3. The surface-treated copper foil according to claim 1, wherein the SDR of the treatment layer is 0.3% or less, in particular 0.2% or less or 0.1% or less.

9. 3. The surface-treated copper foil according to claim 1, wherein the second side (12.1) of the foil (12) is opposite to the first side having the treatment layer and has a roughness RzJIS of 0.7 or less, in particular 0.6, 0.5 or 0.4 μm.

10. 3. The surface-treated copper foil according to claim 1, wherein the copper foil (12) is an electrodeposited copper foil.

11. 3. The surface treated copper foil of claim 1 or 2, wherein the first side (12.2) is the electrolyte side of the copper foil.

12. The second layer (16) contains 4 and 10 mg / m2 calculated as Cr. ２ 3. The surface-treated copper foil according to claim 1, wherein the amount of Cr oxide is between 0.1 and 1.

0.

13. coating a first surface of a copper foil with a treatment layer to provide a copper foil (12) having two opposing surfaces; The coating comprises: - electrodepositing a first layer of oxides of Zn and Mo in a first bath (282) containing between 1.5 and 7 g / L Mo and between 1 and 5 g / L Zn, no Ni; - in a second bath (283), electrodepositing a second layer of Cr oxide onto said first layer; forming a binder layer on said second layer in a third bath (284), How to process copper foil.

14. 14. The method of claim 13, wherein the first bath contains between 2.5 and 5.5 g / L Mo and between 1.5 and 4 g / L Zn.

15. 15. A method according to claim 13 or 14, wherein the pH of the first tank is between 3.0 and 4.5, preferably between 3.5 and 4.

16. The electrodeposition in the first bath is preferably 0.2 to 1.4 A / dm ２ 15. The method according to claim 13 or 14, wherein the method is carried out using two different anodes to which different current densities are applied, in the range of 0.1 to 1.

5.

17. The electrodeposition in the first bath was carried out so that the first layer had a concentration of 5 and 30 mg / m, calculated as Mo and Zn. ２ 15. The method of claim 13 or 14, wherein the amount of Mo and Zn oxides is between 0.5 and 1.

0.

18. 15. The method of claim 13 or 14, wherein the second tank contains between 0.5 and 4 g / L of Cr.

19. 20. The method of claim 18, wherein the pH of the second bath is between 1 and 4.

20. The electrodeposition in the second bath was such that the second layer was between 4 and 10 mg / m, calculated as Cr. ２ 15. The method of claim 13 or 14, wherein the amount of Cr oxide is between 0.5 and 1.

0.

21. 15. The method of claim 13 or 14, wherein the third bath comprises a functionalized silane coupling agent at a concentration between 0.5 and 5 wt. %, wherein the functionalized silane coupling agent preferably comprises an aminosilane, an epoxysilane, a vinylsilane, a methacrylate silane, or a mixture thereof.

22. 15. A method according to claim 13 or 14, comprising a cleaning step before the first bath, in particular by immersing the copper foil in an acid bath.

23. 15. The method of claim 13 or 14, wherein the surface-treated copper foil (10) has a roughness RzJIS of 0.7 μm or less after the third bath.

24. 3. A copper clad laminate comprising the surface-treated copper foil according to claim 1 or 2, which is laminated onto a substrate at 200°C for 2 hours, wherein the peel strength of the copper foil is 0.40 N / mm or more; and the peel strength after an HCl test decreases by 10% or less, and the copper clad laminate can withstand a blister test at a temperature of 270°C or more.

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