Copper-clad laminate and printed circuit board

Abstract

A copper-clad laminate is provided, in which copper foil and resin are bonded with high heat-resistant adhesion even when using fluoropolymers, which are thermoplastic resins with low dielectric constants. The copper-clad laminate comprises: a surface-treated copper foil having a copper foil and a zinc-containing layer disposed on at least one side of the copper foil; and a sheet-like fluoropolymer disposed on the zinc-containing layer side of the surface-treated copper foil. The zinc-containing layer is composed of Zn and transition elements M with a melting point above 1200°C. When elemental analysis of the interface between the copper foil and the zinc-containing layer is performed using glow discharge emission spectrometry (GD-OES), the luminescence intensity I of Zn is... Zn Luminous intensity I relative to Cu Cu The ratio of luminous intensity to I Zn / I Cu 3.0×10 ‑3 Below, and the luminescence intensity I of Zn Zn Luminous intensity I relative to transition element M M The ratio of luminous intensity to I Zn / I M It is above 0.30 and below 0.50.

Description

Technical Field

[0001] This invention relates to copper-clad laminates and printed circuit boards. Background Technology

[0002] With the increasing functionality of portable electronic devices in recent years, and the advancement of high-frequency signals to process large amounts of information at high speeds, printed circuit boards (PCBs) suitable for high-frequency applications such as base station antennas are needed. For such high-frequency PCBs, reducing transmission loss is desirable in order to transmit high-frequency signals without degrading their quality. PCBs consist of copper foil with a wiring pattern and an insulating resin substrate. Transmission loss is primarily caused by conductor loss due to the copper foil and dielectric loss due to the insulating resin substrate. Therefore, using a thermoplastic resin with a low dielectric constant is ideal to reduce dielectric loss caused by the insulating resin substrate. However, unlike thermosetting resins, thermoplastic resins with low dielectric constants, such as fluoropolymers like polytetrafluoroethylene (PTFE), have low chemical reactivity, resulting in poor adhesion to the copper foil. Therefore, techniques to improve the adhesion between the copper foil and the thermoplastic resin have been proposed.

[0003] For example, Patent Document 1 (International Publication No. 2017 / 150043) discloses a method for ensuring adhesion to fluoropolymers by using copper foil with micro-uneven textures formed by oxidation and reduction treatments.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: International Publication No. 2017 / 150043 Summary of the Invention

[0007] However, in the copper-clad laminate disclosed in Patent Document 1, where copper foil and a fluoropolymer substrate are bonded together, the decrease in adhesion between the copper foil and the substrate at high temperatures remains significant. Therefore, further improvements in heat-resistant adhesion are required to enhance reliability in applications where heat resistance is also necessary. In particular, printed circuit boards using fluoropolymers are sometimes exposed to harsh environments such as high temperatures, and high adhesion between the copper foil and the resin substrate is desirable even after exposure to such conditions. In fact, printed circuit boards using fluoropolymers such as PTFE are sometimes used in aerospace and other applications, and from this perspective, further improvements in adhesion at high temperatures are also desired. The current situation is that ensuring adhesion strength and reliability can only be achieved by increasing the roughness of the bonding surface between the copper foil and the resin, which cannot prevent increased transmission losses in high-frequency applications. Therefore, a novel method is needed to balance adhesion and heat resistance between the copper foil and the fluoropolymer substrate.

[0008] The inventors have obtained the following insight: by sandwiching a zinc-containing layer with a specified interface between a copper foil and a fluororesin, a copper-clad laminate can be provided that not only has high adhesion, but also excellent heat resistance that makes the adhesion difficult to deteriorate at high temperatures. In other words, the copper foil and the fluororesin are bonded with high heat-resistant adhesion.

[0009] Therefore, the object of the present invention is to provide a copper-clad laminate in which the copper foil and the resin are bonded with high heat-resistant adhesion even when using a fluoropolymer resin, which is a thermoplastic resin with a low dielectric constant.

[0010] According to one aspect of the present invention, a copper-clad laminate is provided, comprising:

[0011] A surface-treated copper foil comprising a copper foil and a zinc-containing layer disposed on at least one side of the copper foil; and

[0012] A sheet-like fluororesin is disposed on the zinc-containing layer side of the aforementioned surface-treated copper foil.

[0013] The aforementioned zinc-containing layer is composed of Zn and transition elements M with a melting point above 1200°C.

[0014] When performing elemental analysis on the interface between the aforementioned copper foil and the aforementioned zinc-containing layer using glow discharge emission spectroscopy (GD-OES), the luminescence intensity I of Zn was... Zn Luminous intensity I relative to Cu Cu The ratio of luminous intensity to I Zn / I Cu 3.0×10 -3 Below, and the luminescence intensity I of Zn Zn The luminescence intensity I relative to the aforementioned transition element M M The ratio of luminous intensity to I Zn / I M It is above 0.30 and below 0.50.

[0015] In another aspect of the present invention, a printed circuit board manufactured using the aforementioned copper-clad laminate is provided. Attached Figure Description

[0016] Figure 1 This is an example of depth curves showing the luminescence intensity of various elements based on glow discharge emission spectroscopy (GD-OES). The horizontal axis represents sputtering time, corresponding to the depth direction from the copper foil in the copper foil laminate to the resin, while the vertical axis represents the luminescence intensity of each element: Si, Cu, Zn, Ni, and Cr. Detailed Implementation

[0017] Copper-clad laminate

[0018] The copper-clad laminate of the present invention comprises: a surface-treated copper foil; and a sheet-like fluororesin disposed on the zinc-containing layer side of the surface-treated copper foil. The surface-treated copper foil includes: a copper foil and a zinc-containing layer disposed on at least one side of the copper foil. The zinc-containing layer is composed of Zn and a transition element M with a melting point of 1200°C or higher. Furthermore, when elemental analysis of the interface between the copper foil and the zinc-containing layer is performed using glow discharge emission spectrometry (GD-OES), the luminescence intensity I of Zn is... Zn Luminous intensity I relative to Cu Cu The ratio of luminous intensity to I Zn / I Cu 3.0×10 -3 Below, and the luminescence intensity I of Zn Zn Luminous intensity I relative to transition element M M The ratio of luminous intensity to I Zn / I M The value is 0.30 or higher and 0.50 or lower. In this way, by sandwiching a zinc-containing layer with a specified interface composition between the copper foil and the fluororesin, a copper-clad laminate can be provided that not only has high adhesion, but also excellent heat resistance that makes it difficult for the adhesion to deteriorate at high temperatures. In other words, the copper foil and the fluororesin are bonded with high heat-resistant adhesion.

[0019] That is, as mentioned above, unlike thermosetting resins, thermoplastic resins with low dielectric constants, such as polytetrafluoroethylene (PTFE), have low chemical activity, and therefore inherently have low adhesion to copper foil. Even in the copper-clad laminate disclosed in Patent Document 1, which addresses this problem, the reduction in adhesion between the copper foil and the substrate at high temperatures remains significant. Historically, to ensure adhesion strength and reliability, the roughness of the bonding surface between the copper foil and the resin has been increased, which cannot prevent increased transmission losses in high-frequency applications. In response, the copper-clad laminate of this invention achieves a balance between adhesion strength and heat resistance between the copper foil and the fluororesin by sandwiching a zinc-containing layer with a defined interface composition at the interface.

[0020] The surface-treated copper foil used in this invention comprises a copper foil and a zinc-containing layer disposed on at least one side of the copper foil. The copper foil is preferably a roughened copper foil having roughening particles on at least one surface, and more preferably, the surface of the copper foil on the zinc-containing layer side is a roughened surface. Known roughened copper foils can be used. The thickness of the copper foil is not particularly limited, but is preferably 0.1 μm or more and 70 μm or less, more preferably 0.5 μm or more and 18 μm or less.

[0021] The zinc-containing layer is not particularly limited in its composition as long as it is composed of Zn and a transition element M with a melting point of 1200°C or higher. An alloy of Zn and M, i.e., a zinc alloy, is preferred. Preferred examples of transition elements M with a melting point of 1200°C or higher include Co, Fe, Ni, Mo, W, and combinations thereof; more preferably, Co, Ni, Mo, and combinations thereof; even more preferably, Ni and / or Mo; and particularly preferably, Ni. Therefore, the zinc-containing layer is preferably composed of Zn-Co alloy, Zn-Fe alloy, Zn-Ni alloy, Zn-Mo alloy, Zn-W alloy, Zn-Ni-Mo alloy, or combinations thereof; more preferably, it is composed of Zn-Co alloy, Zn-Ni alloy, Zn-Mo alloy, or Zn-Ni-Mo alloy; even more preferably, it is composed of Zn-Ni alloy, Zn-Mo alloy, or Zn-Ni-Mo alloy; and particularly preferably, it is composed of Zn-Ni alloy.

[0022] As mentioned earlier, for copper-clad laminates, when performing elemental analysis of the interface between the copper foil and the zinc-containing layer using GD-OES, the luminescence intensity I of Zn is... Zn Luminous intensity I relative to Cu Cu The ratio of luminous intensity to I Zn / I Cu 3.0×10 -3 The preferred value is 1.5 × 10⁻⁶. -3 Above and 3.0×10 -3 Hereinafter, 2.0 × 10 is preferred. -3 Above and 3.0×10 -3 Below. Additionally, when performing elemental analysis on the interface between the copper foil and the zinc-containing layer using GD-OES, the luminescence intensity I of Zn... Zn Luminous intensity I relative to transition element M M The ratio of luminous intensity to I Zn / I M The luminous intensity I is 0.30 or higher and 0.50 or lower, preferably 0.30 or higher and 0.45 or lower, more preferably 0.33 or higher and 0.45 or lower, and even more preferably 0.35 or higher and 0.45 or lower. Cu and I Zn The interface between the copper foil and the zinc-containing layer is defined, but this interface refers to the portion of the zinc-containing layer directly above the copper foil. This portion is considered to be resistant to surface oxidation and other factors, and is important for imparting adhesion and heat resistance.

[0023] Elemental analysis based on GD-OES can be performed as follows: Elemental analysis is conducted simultaneously by sputtering from the copper foil side of the copper-clad laminate down into the resin, thereby obtaining, for example,... Figure 1 The depth curves of the luminescence intensity of various elements are shown. Figure 1The horizontal axis of the depth curve shown corresponds to the sputtering time from the copper foil in the copper foil laminate to the resin depth, while the vertical axis corresponds to the luminescence intensity of each element such as Cu, Zn, Ni, and Cr. For example... Figure 1 As shown, in the depth curve of the copper-clad laminate of the present invention, broad peaks of rust-preventing elements such as Zn, Ni, and Cr (hereinafter referred to as rust-preventing element peaks) originating from rust-preventing layers such as zinc-containing layers and chromate layers will inevitably be observed. Therefore, it is inferred that in the depth direction from the copper foil side towards the resin (the direction of increasing sputtering time), there exists an interface between the copper foil and the zinc-containing layer in a protruding portion slightly ahead of the rust-preventing element peak (slightly shorter sputtering time). In fact, in the depth direction from the copper foil side towards the resin, the Cu depth curve (even with slight variations or height differences) maintains a roughly constant luminescence intensity until slightly ahead of the rust-preventing element peak, and then decreases linearly with a certain slope in the region corresponding to the rust-preventing element peak. By utilizing such characteristics of the Cu depth curve, the interface between the copper foil and the zinc-containing layer can be determined without doubt. Specifically, the interface between the copper foil and the zinc-containing layer is defined as follows: On the Cu depth curve, the first tangent line L1 is drawn at a position slightly before the rust-inhibiting element peak (with a slightly shorter sputtering time), using the highest correlation coefficient. Furthermore, the second tangent line L2 is drawn at a position slightly beyond the rust-inhibiting element peak (with a slightly longer sputtering time), using the highest correlation coefficient. The intersection point X of the two tangent lines L1 and L2 is defined as the interface between the copper foil and the zinc-containing layer. Thus, the luminescence intensity I of Cu at the sputtering time (depth) determined by the intersection point X is read from the depth curve of the luminescence intensity of each element. Cu The luminescence intensity I of Zn Zn And the luminescence intensity I of transition element M M That's all.

[0024] The sheet-like fluoropolymer used in the copper-clad laminate of the present invention can be a cut sheet or a strip drawn from a roller, and the method is not particularly limited. Preferred examples of fluoropolymers include polytetrafluoroethylene (PTFE), tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene / hexafluoropropylene copolymer (FEP), tetrafluoroethylene-ethylene copolymer (ETFE), and any combination thereof.

[0025] Surface-treated copper foil can be applied to one side or both sides of the sheet-like fluororesin. The sheet-like fluororesin only needs to contain fluororesin, but may further contain other materials. Therefore, the sheet-like fluororesin can also be a prepreg. Prepreg refers to a general term for composite materials made by impregnating synthetic resin into substrates such as synthetic resin boards, glass boards, glass fabrics, glass nonwovens, and paper. Furthermore, from the viewpoint of improving insulation, the fluororesin may also contain filler particles formed from various inorganic particles such as silica and alumina. The thickness of the sheet-like fluororesin is not particularly limited, but is preferably 1–1000 μm, more preferably 2–400 μm, and even more preferably 3–200 μm. The fluororesin layer may also consist of multiple layers.

[0026] Manufacturing method of copper clad laminate

[0027] The copper-clad laminate of the present invention can be manufactured by (1) preparing a surface-treated copper foil and (2) attaching a sheet-like fluororesin to the zinc-containing layer side of the surface-treated copper foil.

[0028] (1) Preparation of surface-treated copper foil

[0029] The surface-treated copper foil used in the manufacture of the copper-clad laminate of the present invention can have a zinc-containing layer that provides the interface composition described above.

[0030] For the surface-treated copper foil used in the manufacture of copper-clad laminates, when performing elemental analysis of the interface between the copper foil and the zinc-containing layer using X-ray photoelectron spectroscopy (XPS), the Zn content is preferably 10% by weight or less, more preferably 1.0% by weight or more and 10.0% by weight or less, further preferably 2.0% by weight or more and 8.0% by weight or less, particularly preferably 2.1% by weight or more and 7.5% by weight or less, and most preferably 2.1% by weight or more and 7.0% by weight or less. Furthermore, when performing elemental analysis of the interface between the copper foil and the zinc-containing layer using XPS, the weight ratio of Zn to the content of transition element M, i.e., the Zn / M ratio, is preferably 0.2 or more and 0.6 or less, more preferably 0.22 or more and 0.58 or less, and further preferably 0.25 or more and 0.55 or less.

[0031] The Zn content and Zn / M weight ratio are determined at the interface between the copper foil and the zinc-containing layer, which refers to the portion of the zinc-containing layer directly above the copper foil. This portion is considered to be less susceptible to surface oxidation and is important for imparting adhesion and heat resistance. The location (depth) of the interface between the copper foil and the zinc-containing layer is defined as the inflection point of the curve formed by the depth (horizontal axis) and Cu content (vertical axis) in an XPS-based elemental analysis performed from the zinc-containing layer to the depth of the copper foil. Specifically, it is determined using steps i) to vi) below.

[0032] i) Set the surface opposite the copper foil containing the zinc layer as the measurement depth D1 = 0 nm. Simultaneously perform XPS-based elemental analysis by sputtering downwards towards the depth of the copper foil. Elemental analysis is performed at the measurement depth D1 = 0 nm at the start of the XPS measurement. Afterwards, starting from the start of the measurement, elemental analysis is performed at the measurement depth D1 = 0 nm every specified sputtering time (e.g., 20 seconds). n Elemental analysis is performed at locations (n ​​represents the measurement point). For example, measurements are performed at equal time intervals, such as measurement point D2 20 seconds after the start of the measurement and measurement point D3 40 seconds after the start of the measurement. A preferred example of XPS measurement conditions is shown below (more specific measurement conditions are shown in the examples described later).

[0033] (Measurement conditions)

[0034] -Ion gun settings: Ar gas, 1kV, 2mm×2mm

[0035] - Sputtering rate: 3.43 nm / min

[0036] ii) Following i) above, determine the Cu content C at measurement point n. n (weight%).

[0037] iii) To determine depth D n The horizontal axis represents the Cu content (C). n Create a graph for the vertical axis, and calculate the slope S of the tangent line at the measured point n for the obtained curve. n =(C n+1 -C n ) / (D n+1 -D n ).

[0038] iv) Based on the slope S of the obtained tangent line n Calculate the rate of change ΔS of the slope of the tangent. n =S n+1 -S n .

[0039] v) Based on the rate of change ΔS of the slope of the obtained tangent line n Calculate curvature c n =ΔS n / (D n+1 -D n ).

[0040] vi) Curvature c n The measurement point where the value equals 0 is identified as the Cu inflection point, and the measurement depth D with this Cu inflection point is determined. n The location is determined to be the interface between the copper foil and the zinc-containing layer. It should be noted that, in order to avoid curvature c... n The random curvature c caused by positive / negative variationsn =0, Cu inflection point adopts curvature c n The curvature c in the region that stably begins to converge to 0 n The measurement point is 0. By using this method, the interface between the copper foil and the zinc-containing layer can be determined without any doubt.

[0041] The surface-treated copper foil preferably also has a chromate layer and / or a silane coupling agent layer on the zinc-containing layer side, and more preferably both a chromate layer and a silane coupling agent layer. By further including a chromate layer and / or a silane coupling agent layer, not only are the rust resistance, moisture resistance, and chemical resistance improved, but the combination with the zinc-containing layer also improves the adhesion to the fluoropolymer substrate.

[0042] (2) Fluoropolymer Adhesion

[0043] The application of fluororesin to the surface-treated copper foil can be performed according to the known manufacturing steps of copper-clad laminates, without particular limitation. Alternatively, a method of applying copper foil to the inner substrate using fluororesin can be employed, in which case a known method such as the so-called lamination method can be used. In summary, through the preferred manufacturing method of the copper-clad laminate of the present invention, an interface having a luminous intensity ratio within the above-mentioned range is selectively used as the surface-treated copper foil containing a zinc layer, and it is applied to the fluororesin. This allows the manufacture of a copper-clad laminate that not only possesses high adhesion between the copper foil and the fluororesin but also excellent heat resistance, where this adhesion is difficult to deteriorate at high temperatures. The application of fluororesin to the surface-treated copper foil is preferably performed by heating and pressing simultaneously. The pressing temperature can be appropriately determined according to the characteristics of the fluororesin used, without particular limitation, but is preferably 150–500°C, more preferably 180–400°C. The pressing pressure is also not particularly limited, but is preferably 1–10 MPa, more preferably 2–5 MPa.

[0044] Manufacturing method of surface-treated copper foil

[0045] The surface-treated copper foil based on the present invention can be manufactured by any method as long as a zinc-containing layer can be formed on the copper foil, but is preferably manufactured by zinc alloy plating. Hereinafter, an example of a preferred manufacturing method for the surface-treated copper foil based on the present invention will be described. This preferred manufacturing method includes: a step of preparing copper foil; and a step of zinc alloy plating the surface.

[0046] (1) Preparation of copper foil

[0047] Both electrolytic copper foil and rolled copper foil can be used in the manufacture of surface-treated copper foil, with electrolytic copper foil being more preferred. Furthermore, the copper foil preferably undergoes a roughening treatment, for example, by electroplating using an aqueous solution containing sulfuric acid and copper sulfate, a roughened surface with adhering roughening particles can be formed on the copper foil surface. The maximum height Sz of the roughened surface, as measured according to ISO 25178, is preferably 3.0 μm or more and 15.0 μm or less, more preferably 4.0 μm or more and 12.0 μm or less. When preparing the copper foil as a carrier-supported copper foil, the copper foil can be formed using wet film-forming methods such as electroless copper plating and electrolytic copper plating, dry film-forming methods such as sputtering and chemical vapor deposition, or combinations thereof.

[0048] (2) Formation of zinc-containing layer based on zinc alloy plating

[0049] Preferably, a zinc-containing layer is formed by applying a zinc alloy plating to the surface of the copper foil (e.g., a roughened surface). Examples of zinc alloy plating include Zn-Co alloy plating, Zn-Fe alloy plating, Zn-Ni alloy plating, Zn-Mo alloy plating, Zn-W alloy plating, Zn-Ni-Mo alloy plating, and combinations thereof. The zinc alloy plating solution is prepared in a manner that yields the desired zinc alloy composition, and the plating is performed using a known electroplating method. For example, when performing Zn-Ni alloy plating, an aqueous solution containing zinc oxide, nickel sulfate, and potassium diphosphate is preferably used for electroplating.

[0050] (3) Chromate treatment

[0051] Preferably, the copper foil with a zinc-containing layer is subjected to chromate treatment to form a chromate layer. The chromate treatment preferably uses a chromate treatment solution with a chromic acid concentration of 0.5–8 g / L and a pH of 1–13, at a current density of 0.1–10 A / dm³. 2 Electrolysis is performed, preferably for 1 to 30 seconds.

[0052] (4) Silane coupling agent treatment

[0053] Preferably, the copper foil is treated with a silane coupling agent to form a silane coupling agent layer. The silane coupling agent layer can be formed by appropriately diluting and coating the silane coupling agent, followed by drying. Examples of silane coupling agents include (i) epoxy-functionalized silane coupling agents such as 4-epoxypropoxybutyltrimethoxysilane and 3-epoxypropoxypropyltrimethoxysilane; and (ii) 3-aminopropyltriethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, N-3-(4-(3-aminopropoxy)butoxy)propyl-3-aminopropyltrimethoxysilane, and N-phenyl-3-aminopropyltrimethoxysilane. Amino-functional silane coupling agents such as alkanes; (iii) mercapto-functional silane coupling agents such as 3-mercaptopropyltrimethoxysilane; (iv) olefin-functional silane coupling agents such as vinyltrimethoxysilane and vinylphenyltrimethoxysilane; (v) acrylic-functional silane coupling agents such as 3-methacryloyloxypropyltrimethoxysilane; (vi) imidazole-functional silane coupling agents such as imidazole silane; (vii) triazine-functional silane coupling agents such as triazine silane, etc. It should be noted that when the chromate layer and the silane coupling agent layer are formed on the surface of the zinc-containing layer, their formation order is not particularly limited.

[0054] Printed Circuit Board

[0055] The copper-clad laminate of the present invention is preferably used in the manufacture of printed circuit boards. Specifically, according to a preferred embodiment of the present invention, a printed circuit board manufactured using the aforementioned copper-clad laminate is provided. Specific examples relating to printed circuit boards include single-sided or double-sided printed circuit boards in which circuitry is formed on the copper-clad laminate of the present invention, and multilayer printed circuit boards in which these are multilayered. The multilayer printed circuit board may be one in which circuitry is formed on a multilayer copper-clad laminate in which copper foil is attached to an inner substrate using a thermoplastic resin (e.g., fluoropolymer), or it may be one in which additionally multilayered layers are formed. Furthermore, the circuit formation method may be a subtractive method or a semi-additive process (MSAP method). Printed circuit boards manufactured using the copper-clad laminate of the present invention can be suitably used as high-frequency substrates for applications such as automotive antennas, mobile phone base station antennas, high-performance servers, and impact-resistant radars used in high-frequency bands with signal frequencies above 10 GHz.

[0056] Example

[0057] The invention will be further illustrated by the following examples.

[0058] Examples 1 to 7

[0059] (1) Preparation of surface-treated copper foil

[0060] Various surface-treated copper foils with a zinc-containing layer on their surface were prepared using known methods. For these surface-treated copper foils, the electrode surface of the electrolytic copper foil (35 μm thick) was sequentially roughened, Zn-Ni alloy plating (Examples 1-5) or Zn-Ni-Mo alloy plating (Examples 6 and 7) was applied, followed by chromate treatment and silane coupling agent treatment using known methods. For each surface-treated copper foil, elemental analysis was performed using XPS while sputtering to penetrate the copper foil to its depth. This elemental analysis was conducted using a scanning dual-channel X-ray photoelectron spectrophotometer (XPS) (ULVAC-PHI Corporation, PHI Quantes) under the following measurement conditions.

[0061] (Measurement conditions)

[0062] -Power: 200μmφ, 50W

[0063] X-ray type: Monochromatic Al Kα lines

[0064] - Ion gun settings: Ar gas, 1kV (Examples 1-5) or 2kV (Examples 6 and 7), 2mm × 2mm

[0065] - Sputtering rate (SiO2 conversion): 3.43 nm / min (Examples 1-5) or 12.3 nm / min (Examples 6 and 7)

[0066] - Determined elements and orbitals: C 1s, O 1s, Si 2p, Cr 3p, Ni 2p3, Cu 2p3, Zn 2p3, Mo 3d (Examples 6 and 7 only)

[0067] - Measurement surface: Measurement from the zinc-containing layer towards the interface

[0068] Based on the obtained elemental analysis results, the Cu inflection point was determined according to the aforementioned definitions and procedures, thereby determining the location (depth) of the interface between the copper foil and the zinc-containing layer. Although the copper foil underwent roughening treatment, the roughening layer (roughening particles) was also considered to be included in the copper foil when determining the interface location. Next, at this interface, the Zn content (wt%) was calculated as the percentage of Zn in the total weight of the measured elements, and the M content (wt%) was calculated as the percentage of transition elements M (here referring to Ni and Mo) in the total weight of the measured elements. Furthermore, the Zn / M weight ratio was calculated using the obtained Zn and M contents. The results are shown in Table 1A.

[0069] (2) Fabrication of copper-clad laminate

[0070] As a fluoropolymer substrate, a PTFE substrate (RO3003 Bondply, manufactured by ROGERS Corporation, 125 μm thick, 1-ply) is prepared. On this PTFE substrate, the aforementioned surface-treated copper foil is laminated with its zinc-containing side abutting against the substrate. The laminate is then pressed using a vacuum press at a pressure of 2.4 MPa, a temperature of 370°C, and a pressing time of 30 minutes to produce a copper-clad laminate.

[0071] (3) Evaluation of copper clad laminate

[0072] The following evaluations are given for the fabricated copper-clad laminate.

[0073] Elemental analysis of the interface between copper foil and zinc-containing layer

[0074] Elemental analysis based on GD-OES was performed while sputtering from the copper foil side of the copper-clad laminate into the PTFE substrate in the depth direction. This elemental analysis was performed using a glow discharge luminescence analyzer (JOBIN YVON, JY-5000RF) under the following measurement conditions.

[0075] (Measurement conditions)

[0076] - Power: 30W

[0077] -Atmospheric pressure: 665Pa (Gas type: Ar)

[0078] - Sputtering rate: 7 μm / min (Cu conversion)

[0079] -DS(duty / cycle) = 0.0625 (the ratio of the time sputtering is in the ON state to the total time sputtering is in the ON state and the time sputtering is in the OFF state)

[0080] - Frequency: 100Hz

[0081] -step(sec) / point: 0.1 (interval between measurement points; 1 measurement every 0.1 seconds)

[0082] - Measurement mode: After measuring for 140 seconds in normal mode, switch to pulse mode to perform the measurement (in order to shorten the measurement time).

[0083] - Elemental determination: C, O, N, Si, Cr, Ni, Cu, Zn, Mo (Examples 6 and 7 only)

[0084] Based on the obtained depth curve of Cu luminescence intensity, two tangent lines L1 and L2 are drawn according to the aforementioned definitions and steps, and their intersection point X is determined, thereby identifying the interface between the copper foil and the zinc-containing layer. Thus, from the depth curve of each element's luminescence intensity, the luminescence intensity I of Cu at the sputtering time (depth) corresponding to the interface determined by the intersection point X is read. Cu The luminescence intensity I of Zn Zn And the luminescence intensity I of transition element M M (In this example, this corresponds to the total luminescence intensity of Ni and Mo). Based on these luminescence intensities, calculate the luminescence intensity ratio I. Zn / I Cu and I Zn / I M The results are shown in Table 1A. It should be noted that... Figure 1 The depth curve of the luminescence intensity shown is obtained from Example 2.

[0085] <Peel strength relative to PTFE>

[0086] A 0.4 mm wide straight circuit was formed on a copper-clad laminate using a subtraction method with copper chloride etching solution, resulting in a test substrate with a straight circuit for peel strength testing. The straight circuit was peeled off from the PTFE substrate according to Method A (90° peel) of JIS C 5016-1994, and the normal peel strength (kgf / cm) was measured. This measurement was performed using a desktop precision universal testing machine (AGS-50NX, manufactured by Shimadzu Corporation). The results are shown in Table 1B.

[0087] <Relative to heat peel strength of fluoropolymer (PTFE)>

[0088] The test substrate with a 0.4 mm wide linear circuit for peel strength testing was placed in an oven and heated at 150°C for 4 hours, then floated in a solder bath at 288°C for 10 seconds. Otherwise, the heat-resistant peel strength (kgf / cm) relative to PTFE was measured using the same procedure as described above for the normal peel strength relative to PTFE. The results are shown in Table 1B.

[0089] <Heat resistance degradation rate>

[0090] The rate (%) of decrease in heat-resistant peel strength relative to normal peel strength was calculated as the heat resistance degradation rate. The results are shown in Table 1B.

[0091] <Overall Evaluation>

[0092] For each case, a comprehensive evaluation is conducted based on the following criteria.

[0093] • Acceptable: Normal peel strength is above 1.2 kgf / cm and heat resistance degradation rate is below 10%.

[0094] • Unacceptable: Meeting at least one of the following conditions: normal peel strength less than 1.2 kgf / cm, or heat resistance degradation rate greater than 10%.

[0095] [Table 1A]

[0096]

[0097] [Table 1B]

[0098] Table 1B

[0099]

[0100] * Indicates a comparative example.

[0101] According to the results shown in Tables 1A and 1B, the luminous intensity ratio I is satisfied at the interface between the copper foil and the zinc-containing layer. Zn / I Cu 3.0×10 -3 The following and the luminous intensity ratio I Zn / I M Examples 1, 2, 6, and 7, which have a peel strength of 0.30 or higher and 0.50 or lower under the conditions of the present invention, have higher overall peel strength (i.e., higher adhesion) and exceptionally low heat resistance degradation rate (i.e., excellent heat resistance) compared to comparative examples 3 to 5, which do not meet these conditions.

Claims

1. A copper-clad laminate, comprising: A surface-treated copper foil comprising a copper foil and a zinc-containing layer disposed on at least one side of the copper foil; and A sheet-like fluororesin is disposed on the zinc-containing layer side of the surface-treated copper foil. The zinc-containing layer is composed of Zn and transition elements M with a melting point above 1200°C. When performing elemental analysis on the interface between the copper foil and the zinc-containing layer using glow discharge emission spectroscopy (GD-OES), the luminescence intensity I of Zn was... Zn Luminous intensity I relative to Cu Cu The ratio of luminous intensity to I Zn / I Cu 3.0×10 -3 Below, and the luminescence intensity I of Zn Zn The luminescence intensity I relative to the transition element M M The ratio of luminous intensity to I Zn / I M It is above 0.35 and below 0.

42. The interface between the copper foil and the zinc-containing layer is defined as follows: on the Cu depth curve, the first tangent line L1 is drawn at a position slightly ahead of the rust-inhibiting element peak (with a slightly shorter sputtering time) with the highest correlation coefficient, and the second tangent line L2 is drawn at a position slightly beyond the rust-inhibiting element peak (with a slightly longer sputtering time) in the descending portion with the highest correlation coefficient. The intersection point X of the two tangent lines L1 and L2 is defined as the interface between the copper foil and the zinc-containing layer.

2. The copper-clad laminate according to claim 1, wherein, The transition element M is selected from at least one of the group consisting of Co, Fe, Ni, Mo and W.

3. The copper-clad laminate according to claim 1 or 2, wherein, The transition element M is Ni and / or Mo.

4. The copper-clad laminate according to claim 1 or 2, wherein, The luminous intensity ratio I Zn / I Cu 1.5×10 -3 Above and 3.0×10 -3 the following.

5. The copper-clad laminate according to claim 1 or 2, wherein, The fluororesin is at least one selected from the group consisting of polytetrafluoroethylene, tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer, tetrafluoroethylene / hexafluoropropylene copolymer, and tetrafluoroethylene-ethylene copolymer.

6. The copper-clad laminate according to claim 1 or 2, wherein, The surface of the zinc-containing layer side of the copper foil is roughened.

7. A printed circuit board manufactured using any one of claims 1 to 6.

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