Film laminate

Abstract

The film laminate is characterized in that a metallic copper layer is laminated on one surface or both surfaces of a fluororesin film, and an amorphous oxide layer is formed between the fluororesin film and the metallic copper layer. The thickness of the amorphous oxide layer is preferably within the range of 10 nm to 100 nm (inclusive). The oxide constituting the amorphous oxide layer preferably contains one or more elements selected from the group consisting of Ge, Si, Al, Ti, Ta, Zr, and Cr.

Description

Technical Field

[0001] The present invention relates to a film laminate in which a metal copper layer is laminated on one or both sides of a fluororesin film.

[0002] This application claims priority based on Japanese Patent Application No. 2023-052692 filed on March 29, 2023, and incorporates its content herein. Background Art

[0003] Generally, as a wiring substrate for electronic / electrical devices, a film laminate in which a metal copper layer as a conductive layer or a heat conductive layer is laminated on the surface of an insulating resin layer is used.

[0004] Here, for a wiring substrate for high-frequency signal transmission devices such as antennas or radars in the GHz band and above, low transmission loss when used in the high-frequency region is required.

[0005] Therefore, for example, as shown in Patent Documents 1 and 2, a film laminate using a fluororesin film is provided. Since the fluororesin has a low dielectric constant and a low dielectric loss, it is particularly suitable as a resin film constituting a wiring substrate for high-frequency signal transmission.

[0006] However, since the surface chemical properties of the fluororesin film are very stable, the adhesion to other materials tends to be low.

[0007] Therefore, in Patent Document 1, by forming protrusions on the surface of the fluororesin and roughening the metal foil, and optimizing the conditions for press-bonding lamination, the improvement of the adhesion between the copper film and the fluororesin based on the anchoring effect is achieved.

[0008] And, in Patent Document 2, by forming a metal thin film (nickel film or titanium film) on the surface of the fluororesin using a physical vapor deposition method and performing copper plating on the metal thin film to form a copper film, the improvement of the adhesion between the copper film and the fluororesin is achieved.

[0009] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2014-006668

[0010] Patent Document 2: International Publication No. 2018 / 179904

[0011] However, there is a problem in Patent Document 1 that the interface between the fluororesin and the metal foil is roughened and the transmission loss deteriorates.

[0012] And, in Patent Document 2, when used in a high-temperature environment, the metal thin film formed on the surface of the fluororesin is oxidized, which may cause a decrease in adhesion and thus insufficient heat resistance. Summary of the Invention

[0013] The present invention has been completed in view of the foregoing circumstances, and an object thereof is to provide a film laminate that has low transmission loss in a high-frequency region, particularly excellent adhesion between a fluororesin film and a copper metal layer, and whose adhesion does not significantly decrease even when used in a high-temperature environment, and is particularly suitable for a wiring substrate for high-frequency signal transmission.

[0014] In order to solve the above problems, the film laminate of aspect 1 of the present invention has a copper metal layer laminated on one or both sides of a fluororesin film, and is characterized in that an amorphous oxide layer is formed between the fluororesin film and the copper metal layer.

[0015] According to the film laminate of aspect 1 of the present invention, since an amorphous oxide layer is formed on the surface of the fluororesin film, a chemical bond mediated by O (oxygen) can be formed on the outermost surface of the fluororesin, and a strong bond between the fluororesin film and the amorphous oxide layer can be achieved. Moreover, the bonding property between the amorphous oxide layer and the copper metal layer is good, so the adhesion between the fluororesin film and the copper metal layer is particularly excellent.

[0016] In addition, since the amorphous oxide layer has chemical stability, the reaction between free F (fluorine) or adsorbed O (oxygen) present on the surface of the fluororesin and the amorphous oxide layer can be suppressed, and even when used in a high-temperature environment, a decrease in adhesion can be suppressed. Further, since it is set as an amorphous oxide layer, there are no grain boundaries and the barrier property is excellent, and even when used in a high-temperature environment, mutual diffusion between the fluororesin and the copper metal layer can be suppressed, thereby suppressing a decrease in adhesion caused by fluorination / oxidation of copper.

[0017] The film laminate of aspect 2 of the present invention is characterized in that, in the film laminate described in aspect 1, the thickness of the amorphous oxide layer is in the range of 10 nm or more and 100 nm or less.

[0018] According to the film laminate of aspect 2 of the present invention, the thickness of the amorphous oxide layer is set to 10 nm or more, so that the barrier property can be ensured and the mutual diffusion between the fluororesin and the copper metal layer can be accurately suppressed. On the other hand, the thickness of the amorphous oxide layer is set to 100 nm or less, so that film warping caused by film stress can be suppressed.

[0019] The film laminate of aspect 3 of the present invention is characterized in that, in the film laminate described in aspect 1 or aspect 2, the oxide constituting the amorphous oxide layer contains one or more selected from Ge, Si, Al, Ti, Ta, Zr, and Cr.

[0020] The film laminate according to aspect 3 of the present invention is such that the oxide constituting the amorphous oxide layer contains one or more selected from Ge, Si, Al, Ti, Ta, Zr, and Cr. Therefore, the amorphous oxide layer has higher chemical stability, and can further suppress the reaction between free F (fluorine) or adsorbed O (oxygen) present on the surface of the fluororesin and the amorphous oxide layer. Also, barrier properties can be sufficiently ensured, and the mutual diffusion between the fluororesin and the metal copper layer can be suppressed, thereby accurately suppressing the decrease in adhesion caused by the fluorination / oxidation of copper.

[0021] The film laminate according to aspect 4 of the present invention is characterized in that, in the film laminate according to aspect 1 or aspect 2, the oxide constituting the amorphous oxide layer contains In and Zn. The film laminate according to aspect 4 of the present invention is such that the oxide constituting the amorphous oxide layer contains In and Zn. Therefore, the amorphous oxide layer has higher chemical stability, and can further suppress the reaction between free F (fluorine) or adsorbed O (oxygen) present on the surface of the fluororesin and the amorphous oxide layer. Also, barrier properties can be sufficiently ensured, and the mutual diffusion between the fluororesin and the metal copper layer can be suppressed, thereby accurately suppressing the decrease in adhesion caused by the fluorination / oxidation of copper.

[0022] The film laminate according to aspect 5 of the present invention is characterized in that, in the film laminate according to any one of aspects 1 to 4, the thickness of the metal copper layer is in the range of 2 μm or more and 20 μm or less.

[0023] In the film laminate according to aspect 5 of the present invention, the thickness of the metal copper layer is set to 2 μm or more, so the influence of radiation loss can be suppressed, and the transmission loss can be reliably controlled to be low. On the other hand, the thickness of the metal copper layer is set to 20 μm or less, so pattern formation can be effectively and precisely performed by etching.

[0024] The film laminate according to aspect 6 of the present invention is characterized in that, in the film laminate according to any one of aspects 1 to 5, the conductivity of the metal copper layer is 80% IACS or more.

[0025] In the film laminate according to aspect 6 of the present invention, the conductivity of the metal copper layer is set to 80% IACS or more, so the transmission characteristics are particularly excellent.

[0026] According to the present invention, a film laminate can be provided, which has low transmission loss in the high-frequency region, particularly excellent adhesion between the fluororesin film and the metal copper layer, and the adhesion does not significantly decrease even when used in a high-temperature environment, and is particularly suitable for a wiring substrate for high-frequency signal transmission. Brief Description of the Drawings

[0027] Figure 1This is a schematic cross-sectional view of the film laminate of the present embodiment.

[0028] Figure 2 This is a flowchart showing an example of the manufacturing method of the film laminate of the present embodiment.

[0029] Figure 3 This is a graph showing an example of the XRD measurement results in the examples.

[0030] Figure 4 This is a perspective view of the peel test in the examples. Detailed Embodiment

[0031] Hereinafter, a film laminate according to an embodiment of the present invention will be described.

[0032] The film laminate according to an embodiment of the present invention is used as a wiring substrate for high-frequency signal transmission.

[0033] As Figure 1 As shown, the film laminate 10 of the present embodiment has the following structure: it includes a fluororesin film 11 and a metallic copper layer 12 laminated on the fluororesin film 11, and an amorphous oxide layer 13 is formed between the fluororesin film 11 and the metallic copper layer 12.

[0034] The fluororesin film 11 is made of a fluororesin such as PFA (perfluoroalkoxy alkane), PTFE (polytetrafluoroethylene), ETFE (ethylene-tetrafluoroethylene copolymer), FEP (tetrafluoroethylene-hexafluoropropylene copolymer), PCTFE (polychlorotrifluoroethylene), etc. Since the fluororesin has a low dielectric constant and a low dielectric loss, it is particularly suitable as the resin film constituting the wiring substrate for high-frequency signal transmission.

[0035] Here, the thickness t1 of the fluororesin film 11 is not particularly limited, and it is preferably in the range of 5 μm or more and 200 μm or less.

[0036] The metallic copper layer 12 is made of copper or a copper alloy having excellent conductivity and thermal conductivity, and functions as a conductive layer or a heat conductive layer.

[0037] Here, the conductivity of the metallic copper layer 12 is preferably 80% IACS or more, more preferably 85% IACS or more.

[0038] Moreover, the thickness t2 of the metallic copper layer 12 is preferably in the range of 2 μm or more and 20 μm or less.

[0039] If the thickness t2 of the metallic copper layer 12 is 2 μm or more, the influence of radiation loss can be ignored without reaching the same level as the skin effect. On the other hand, if the thickness t2 of the metallic copper layer 12 is 20 μm or less, when forming a circuit pattern on the metallic copper layer 12 by etching, the etching can be carried out efficiently and precisely.

[0040] In addition, the lower limit of the thickness t2 of the copper metal layer 12 is more preferably 5 μm or more, and further preferably 10 μm or more. Moreover, the upper limit of the thickness t2 of the copper metal layer 12 is more preferably 18 μm or less, and further preferably 15 μm or less.

[0041] Moreover, an amorphous oxide layer 13 composed of an amorphous oxide is formed between the fluororesin film 11 and the copper metal layer 12.

[0042] Due to this amorphous oxide layer 13, the fluororesin film 11 and the amorphous oxide layer 13 are firmly bonded through a chemical bond C-O-M (where M is a component element contained in the amorphous oxide layer 13) with O (oxygen) as a medium.

[0043] Moreover, the amorphous oxide layer 13 has chemical stability, thereby suppressing the reaction between free F (fluorine) or adsorbed O (oxygen) present on the surface of the fluororesin film 11 and the amorphous oxide layer 13.

[0044] In addition, since the amorphous oxide layer 13 has no grain boundaries and excellent barrier properties, it can suppress the interdiffusion between the fluororesin film 11 and the copper metal layer 12, thereby suppressing the decrease in adhesion caused by the fluorination / oxidation of copper.

[0045] Here, the oxide constituting the amorphous oxide layer 13 preferably contains one or more selected from Ge, Si, Al, Ti, Ta, Zr, and Cr.

[0046] When these metal oxides are formed into a film by sputtering or the like, an amorphous oxide film is formed, thereby being able to sufficiently ensure the barrier properties.

[0047] Alternatively, the oxide constituting the amorphous oxide layer 13 preferably contains In and Zn.

[0048] When these metal oxides are formed into a film by sputtering or the like, an amorphous oxide film is formed, thereby being able to sufficiently ensure the barrier properties.

[0049] Moreover, the thickness t3 of the amorphous oxide layer 13 is preferably in the range of 10 nm or more and 100 nm or less.

[0050] If the thickness t3 of the amorphous oxide layer 13 is 10 nm or more, the barrier properties can be sufficiently ensured. On the other hand, if the thickness t3 of the amorphous oxide layer 13 is 100 nm or less, film warping due to film stress can be suppressed.

[0051] In addition, the lower limit of the thickness t3 of the amorphous oxide layer 13 is more preferably 15 nm or more, and further preferably 20 nm or more. Also, the upper limit of the thickness t3 of the amorphous oxide layer 13 is more preferably 80 nm or less, and further preferably 50 nm or less.

[0052] Next, with reference to Figure 2 the flowchart of, the manufacturing method of the film laminate 10 according to the present embodiment will be described.

[0053] (Fluororesin film preparation step S01)

[0054] First, a fluororesin film 11 is prepared. In addition, surface treatment such as plasma treatment may be performed for the purpose of introducing a functional group onto the surface of the fluororesin film 11.

[0055] (Amorphous oxide layer formation step S02)

[0056] Next, on the surface of the fluororesin film 11, the amorphous oxide layer 13 is formed by sputtering to a prescribed thickness.

[0057] In addition, as the sputtering target, an oxide target of a prescribed composition may be used, or a metal target may be used to introduce oxygen for film formation.

[0058] (Seed layer formation step S03)

[0059] Next, on the amorphous oxide layer 13, a copper layer is formed by sputtering as a plating seed layer. The thickness of the seed layer (sputtered copper layer) is preferably in the range of 10 nm or more and 1000 nm or less.

[0060] The seed layer is preferably formed continuously without being exposed to the atmosphere after the formation of the amorphous oxide layer 13.

[0061] (Copper plating layer formation step S04)

[0062] Next, after the formation of the seed layer, a copper plating layer of a prescribed thickness is formed by electroplating. The metal copper layer 12 is constituted by the seed layer and the copper plating layer.

[0063] Through the above-described respective steps, the film laminate 10 according to the present embodiment is manufactured. In addition, when the metal copper layers 12 are formed on both sides of the fluororesin film 11, it is only necessary to perform the amorphous oxide layer formation step S02 and the seed layer formation step S03 on one side of the fluororesin film 11, and then, after performing the amorphous oxide layer formation step S02 and the seed layer formation step S03 on the opposite side, perform the copper plating layer formation step S04.

[0064] According to the film laminate 10 of the present embodiment configured as described above, an amorphous oxide layer 13 is formed on the surface of the fluororesin film 11. Therefore, a chemical bond mediated by O (oxygen) is formed on the outermost surface of the fluororesin film 11, enabling the fluororesin film 11 and the amorphous oxide layer 13 to be firmly bonded. Moreover, the bonding property between the amorphous oxide layer 13 and the metal copper layer 12 is good, so the adhesion between the fluororesin film 11 and the metal copper layer 12 is particularly excellent.

[0065] Furthermore, the amorphous oxide layer 13 has chemical stability, thereby suppressing the reaction between free F (fluorine) or adsorbed O (oxygen) present on the surface of the fluororesin film 11 and the amorphous oxide layer 13. Even when used in a high-temperature environment, a decrease in adhesion can be suppressed. In addition, the amorphous oxide layer 13 without grain boundaries functions as a barrier layer. Even when used in a high-temperature environment, mutual diffusion between the fluororesin film 11 and the metal copper layer 13 can be suppressed, thereby suppressing a decrease in adhesion caused by the fluorination / oxidation of copper.

[0066] In the film laminate 10 of the present embodiment, when the thickness t3 of the amorphous oxide layer 13 is in the range of 10 nm or more and 100 nm or less, barrier properties can be ensured, mutual diffusion between the fluororesin and the metal copper layer can be accurately suppressed, and film warping caused by film stress can be suppressed.

[0067] In the film laminate 10 of the present embodiment, when the oxide constituting the amorphous oxide layer 13 contains one or more selected from Ge, Si, Al, Ti, Ta, Zr, and Cr, the amorphous oxide layer 13 has greater chemical stability and can further suppress the reaction between free F (fluorine) or adsorbed O (oxygen) present on the surface of the fluororesin and the amorphous oxide layer 13.

[0068] Moreover, the amorphous oxide film can be formed by sputtering, thereby enabling the barrier properties in the amorphous oxide layer 13 to be sufficiently ensured.

[0069] In the film laminate 10 of the present embodiment, when In and Zn are included, the amorphous oxide layer 13 has greater chemical stability and can further suppress the reaction between free F (fluorine) or adsorbed O (oxygen) present on the surface of the fluororesin and the amorphous oxide layer 13.

[0070] Moreover, the amorphous oxide film can be formed by sputtering, thereby enabling the barrier properties in the amorphous oxide layer 13 to be sufficiently ensured.

[0071] In the film laminate 10 of the present embodiment, when the thickness t2 of the metallic copper layer 12 is in the range of 2 μm or more and 20 μm or less, the influence of radiation loss can be suppressed, the transmission loss can be reliably controlled to be low, and patterning can be effectively and precisely performed by etching.

[0072] In addition, in the film laminate 10 of the present embodiment, when the conductivity of the metallic copper layer 13 is 80% IACS or more, the transmission characteristics are particularly excellent.

[0073] As described above, the embodiments of the present invention have been described, but the present invention is not limited thereto, and modifications can be appropriately made without departing from the technical idea of the present invention.

[0074] Examples

[0075] The results of the confirmation experiments conducted to confirm the effectiveness of the present invention will be described below.

[0076] As the fluororesin film, a PFA film (thickness: 50 μm) manufactured by AGC Inc. was prepared. The oxide layers shown in Table 1 were formed on the surface of the fluororesin film by sputtering. In addition, the oxide layers were formed under the following conditions. In Comparative Example 3, a metallic Ti film was formed as an intermediate layer using a Ti target.

[0077] (Film formation conditions for oxide layers)

[0078] Target materials: Si, Al, Ti, Ta, Zr, Cr, Ge, Zn, In, Sn, IZO (85 at% In - 15 at% Zn composite oxide) (purity: 99.9 mass% or more)

[0079] Film formation start vacuum degree: 1.0×10 -4 Pa or less

[0080] Sputtering gas: Mixed gas of high-purity argon and high-purity oxygen

[0081] Sputtering gas pressure in the chamber: 0.2 Pa

[0082] DC power density: 7.5 W / cm 2 (Si, Al, Ti, Ta, Zr, Cr, Zn, In, Sn, IZO)

[0083] AC power density: 10.0 W / cm 2 (Ge)

[0084] Next, as a seed layer for plating, a 100-nm copper layer was formed by sputtering. The sputtering conditions are as described below. In addition, the seed layer was continuously formed without exposure to the atmosphere after the intermediate layer was formed.

[0085] (Film formation conditions for the seed layer)

[0086] Target material: Cu (purity 99.99 mass% or more)

[0087] Initial vacuum for film formation: 1.0×10 -4 Pa or less

[0088] Sputtering gas: High-purity argon

[0089] Sputtering gas pressure in the chamber: 0.2 Pa

[0090] DC power density: 7.5 W / cm 2

[0091] Next, electrolytic plating was performed on the seed layer under the following conditions to form a copper plating layer. In addition, the thickness of the metallic copper layer shown in Table 1 became the total thickness of the seed layer and the copper plating layer.

[0092] (Electrolytic plating conditions)

[0093] Pretreatment: Sulfuric acid cleaning

[0094] Liquid temperature: 25°C

[0095] Anode: Phosphorus-containing copper

[0096] Stirring conditions: Air 12.5 L / min

[0097] Plating conditions: 4 A, 45 minutes (for a film thickness of 15 μm)

[0098] Plating solution: CuSO4·5H2O 200 g / L

[0099] H2SO4 54 g / L

[0100] 1 mol HCl 1.37 mL / L

[0101] For the film laminate manufactured in the above manner, the crystallinity of the intermediate layer (oxide layer), the thickness of the intermediate layer, the thickness of the metallic copper layer, the conductivity of the metallic copper layer, the adhesion strength, and the heat resistance were evaluated as follows. The evaluation results are shown in Table 1.

[0102] (Crystallinity of the intermediate layer)

[0103] A 50-nm oxide film was formed as a single layer on the fluororesin film, and the crystallinity of the intermediate layer (oxide layer) was judged by measuring it by the GI-XRD method (Rigaku Corporation SmartLab). As the incident X-ray, Cu Kα ray was used, and the measurement was carried out at an X-ray incident angle ω = 0.5° and a detection range 2θ = 10 to 110°. An example of the XRD measurement result is shown in Figure 3 .

[0104] As Figure 3 shown, in Example 6, the same pattern as that of the fluororesin film (reference data) was presented, and no peak indicating crystallinity was confirmed. On the other hand, in Comparative Example 1, a peak indicating crystallinity was confirmed (arrow in Figure 3 ).

[0105] Regarding other examples and comparative examples, the XRD measurement was similarly carried out to confirm whether there was a peak indicating crystallinity, and thereby the crystallinity of the intermediate layer (oxide layer) was judged.

[0106] (Thickness of the intermediate layer)

[0107] The thickness of the intermediate layer was the target value obtained from the film formation rate. Regarding the film formation rate, the film thickness after forming a film on a blank substrate for a certain time was measured by using a step profiler (Dektak-XT manufactured by Bruker Corporation), and the film thickness was divided by the film formation time to calculate.

[0108] In addition, by observing the cross section of the film laminate by TEM (transmission electron microscope: JEM-2010F manufactured by JEOL Ltd.), the result of confirming the thickness of the intermediate layer showed the same value as the target value obtained from the film formation rate.

[0109] (Thickness of the copper metal layer)

[0110] The thickness of the copper metal layer (seed layer and copper plating layer) was confirmed by the eddy current method.

[0111] (Conductivity of the copper metal layer)

[0112] The conductivity σ of the copper metal layer was measured by the four-probe method using a low resistivity measuring instrument (Loresta GP manufactured by Mitsubishi Chemical Corporation) A (S / m). Then, it was converted to %IACS by the following formula.

[0113] σ (%IACS) = σ A / (5.8×10 7 )

[0114] (Adhesion strength)

[0115] As Figure 4 shown, the intermediate layer and the metallic copper layer formed on the fluororesin film were cut into a width of 5 mm, and the adhesion strength of the film laminate was evaluated using a TENSILON universal testing machine (RTF-1310) manufactured by A&D Company, Limited under the conditions of a peeling angle of 90 degrees and a peeling speed of 50 mm / min. Regarding the adhesion strength of the film laminate, measurements were made before and after the heat resistance test described below.

[0116] (Heat Resistance Test)

[0117] As the heat resistance test, the film laminate was stored in a clean oven under the conditions of 150 °C × 240 h. Regarding the film laminate after storage, the adhesion strength was measured as described above. Then, the change rate of the adhesion strength before and after the heat resistance test was calculated.

[0118] (Change Rate) = (Adhesion Strength after Test - Adhesion Strength before Test) / Adhesion Strength before Test × 100 (%)

[0119]

[0120] In Comparative Example 1, a crystalline Zn oxide layer was formed as an intermediate layer between the fluororesin film and the metallic copper layer, but the adhesion strength decreased significantly after the heat resistance test. It is speculated that this is because mutual diffusion occurred between the fluororesin sheet and the metallic copper layer, resulting in the fluorination and oxidation of copper.

[0121] In Comparative Example 2, a crystalline In-Sn oxide layer (ITO layer) was formed as an intermediate layer between the fluororesin film and the metallic copper layer, but the adhesion strength decreased significantly after the heat resistance test. It is speculated that this is because mutual diffusion occurred between the fluororesin sheet and the metallic copper layer, resulting in the fluorination and oxidation of copper.

[0122] In Comparative Example 3, a metallic Ti layer was formed as an intermediate layer between the fluororesin film and the metallic copper layer, but the adhesion strength decreased significantly after the heat resistance test. It is speculated that this is because the metallic Ti layer as the intermediate layer was fluorinated and oxidized.

[0123] In Comparative Example 4, without forming an intermediate layer, a metallic copper layer was directly formed on the fluororesin film, but the initial adhesion strength was low and the adhesion strength decreased significantly after the heat resistance test.

[0124] In contrast, in Examples 1 to 22, an amorphous oxide layer was formed as an intermediate layer between the fluororesin film and the metallic copper layer, the initial adhesion was excellent, and the adhesion strength did not decrease significantly after the heat resistance test, thus showing excellent heat resistance.

[0125] As confirmed above, according to the embodiment, it is possible to provide a film laminate that has low transmission loss in the high-frequency region, particularly excellent adhesion between the fluororesin film and the copper metal layer, and whose adhesion does not significantly decrease even when used in a high-temperature environment, and is particularly suitable for a wiring substrate for high-frequency signal transmission.

Claims

1. A film laminate having a metal copper layer laminated on one or both sides of a fluororesin film, characterized in that an amorphous oxide layer is formed between the fluororesin film and the metal copper layer.

2. The film laminate according to claim 1, characterized in that the thickness of the amorphous oxide layer is in the range of 10 nm or more and 100 nm or less.

3. The film laminate according to claim 1 or 2, characterized in that the oxide constituting the amorphous oxide layer contains one or more selected from Ge, Si, Al, Ti, Ta, Zr, and Cr.

4. The film laminate according to claim 1 or 2, characterized in that the oxide constituting the amorphous oxide layer contains In and Zn.

5. The film laminate according to claim 1 or 2, characterized in that the thickness of the metal copper layer is in the range of 2 μm or more and 20 μm or less.

6. The film laminate according to claim 1 or 2, characterized in that the conductivity of the metal copper layer is 80% IACS or more.

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