Laminate and transmission circuit using same

Abstract

A laminate according to the present disclosure includes a base material layer, a dielectric layer, and a first conductor. The base material layer contains a thermoplastic resin, and the dielectric layer contains a thermosetting resin. The dielectric layer is layered on at least one surface of the base material layer via the first conductor.

Description

Laminate and transmission circuit using same

[0001] The present disclosure relates to a laminate and a transmission circuit using the same.

[0002] In recent years, flexible substrates have been in demand as wiring substrates used in electronic components, as described in Patent Document 1. Unlike rigid substrates, flexible substrates can be bent. Therefore, flexible substrates can be installed in curved areas, etc., improving the degree of freedom in installation locations. Furthermore, by bending a flexible substrate, the directivity of radio waves can be controlled, making it easier to estimate the direction of radio waves.

[0003] Japanese Patent Application Laid-Open No. 2023-29306

[0004] The laminate according to the present disclosure includes a base layer, a dielectric layer, and a first conductor. The base layer includes a thermoplastic resin. The dielectric layer includes a thermosetting resin. The dielectric layer is laminated on at least one surface of the base layer with the first conductor interposed therebetween.

[0005] A transmission circuit according to the present disclosure includes the laminate described above and a second conductor. The second conductor is located on a surface of a dielectric layer included in the laminate. The first conductor included in the laminate includes a ground conductor. The second conductor includes a patch conductor.

[0006] Fig. 4 is an explanatory diagram for explaining a laminate according to an embodiment of the present disclosure. Fig. 5 is an explanatory diagram for explaining a laminate according to another embodiment of the present disclosure. Fig. 6 is a schematic diagram showing a transmission circuit according to an embodiment of the present disclosure. Fig. 7 is an enlarged explanatory diagram for explaining region X shown in Fig. 3. Fig. 8 is an explanatory diagram for explaining a cross section when cut along line A-A shown in Fig. 4.

[0007] Flexible substrates are often subject to cracks or breakage when used in a curved state, and therefore there is a demand for a laminate that reduces the occurrence of cracks and breakage even when curved.

[0008] The laminate according to the present disclosure has a configuration as described in the section on means for solving the above problems, and thus reduces the occurrence of cracks and breaks even when bent.

[0009] A laminate according to an embodiment of the present disclosure will be described with reference to Fig. 1. Fig. 1 is an explanatory diagram for describing a laminate 10 according to an embodiment of the present disclosure. The laminate 10 according to an embodiment of the present disclosure includes a base layer 1, a dielectric layer 2, and a first conductor 31.

[0010] The substrate layer 1 is a base layer of the laminate 10 and contains a thermoplastic resin. Examples of the thermoplastic resin include, but are not limited to, liquid crystal polymer, polytetrafluoroethylene, and polyether ether ketone (PEEK). Only one type of thermoplastic resin may be used, or two or more types may be used in combination. The thermoplastic resin may be at least one selected from the group consisting of liquid crystal polymer and polytetrafluoroethylene. By using at least one selected from the group consisting of liquid crystal polymer and polytetrafluoroethylene, cracks and breakage are less likely to occur even when the laminate 10 is bent.

[0011] The liquid crystal polymer may be a thermotropic liquid crystal polymer that exhibits liquid crystallinity within a specific temperature range. The liquid crystal polymer is not particularly limited, and examples thereof include liquid crystal aromatic polyester resins and liquid crystal aromatic polyester amide resins. More specifically, examples of the liquid crystal polymer include Vecstar (manufactured by Kuraray Co., Ltd.).

[0012] In addition to the thermoplastic resin, the base layer 1 may contain additives such as an antioxidant, an ultraviolet absorber, a colorant, a stress relaxation agent, an inorganic filler, and a flame retardant. The additives may be used alone or in combination of two or more.

[0013] Furthermore, the base layer 1 may contain a reinforcing material. Examples of the reinforcing material include insulating fabric materials such as glass fiber, glass nonwoven fabric, aramid nonwoven fabric, aramid fiber, and polyester fiber. Only one type of reinforcing material may be used, or two or more types may be used in combination.

[0014] The thickness and size of the base layer 1 are not limited and are set appropriately depending on the application of the laminate 10. Specifically, the base layer 1 may have a thickness of 25 μm or more and 125 μm or less.

[0015] The dielectric layer 2 is a layer that forms the surface of the laminate 10 and contains a thermosetting resin. Examples of thermosetting resins include, but are not limited to, cyclic olefin copolymers, polyphenylene ethers, and cyanate resins. Only one type of thermosetting resin may be used, or two or more types may be used in combination. The thermosetting resin may be at least one selected from the group consisting of cyclic olefin copolymers and polyphenylene ethers. By using at least one selected from the group consisting of cyclic olefin copolymers and polyphenylene ethers, cracks and breakage are less likely to occur even when the laminate 10 is bent.

[0016] A cyclic olefin copolymer is a polyolefin copolymer having a cyclic structure. The cyclic olefin copolymer is obtained by polymerizing a cyclic olefin and another monomer copolymerizable with the cyclic olefin. The ratio of the cyclic olefin to the other monomer is not particularly limited. For example, the other monomer may be contained in an amount of 1 part by mass or more and 100 parts by mass or less per 100 parts by mass of the cyclic olefin.

[0017] Examples of cyclic olefins include norbornene-based monomers, cyclic diene-based monomers, and vinyl alicyclic hydrocarbon-based monomers. Specific examples of cyclic olefins include norbornene, vinylnorbornene, phenylnorbornene, dicyclopentadiene, tetracyclododecene, cyclopropene, cyclobutene, cyclopentene, cyclohexene, cyclohexadiene, and cyclooctadiene. These cyclic olefins may be used alone or in combination of two or more.

[0018] Examples of other monomers copolymerizable with cyclic olefins include linear olefins, acrylic acid, methacrylic acid, acrylic acid esters, methacrylic acid esters, aromatic vinyl compounds, unsaturated nitriles, and aliphatic conjugated dienes. Specific examples of such monomers include ethylene, propylene, butene, acrylic acid, methacrylic acid, fumaric acid, fumaric anhydride, maleic acid, maleic anhydride, methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, styrene, vinyltoluene, acrylonitrile, methacrylonitrile, 1,3-butadiene, 2-methyl-1,3-butadiene, and 2,3-dimethyl-1,3-butadiene. These other monomers may be used alone or in combination of two or more.

[0019] The cyclic olefin copolymer may have a tan δ peak of 100° C. or higher when measured using a dynamic mechanical analyzer (DMA). If the tan δ peak is 100° C. or higher, cracks and fractures are less likely to occur even when the laminate 10 is bent.

[0020] In addition to the thermosetting resin, the dielectric layer 2 may contain additives such as an antioxidant, an ultraviolet absorber, a colorant, a stress relief agent, an inorganic filler, and a flame retardant. The additives may be used alone or in combination of two or more.

[0021] The thickness and size of the dielectric layer 2 are not limited and are set appropriately depending on the application of the laminate 10. Specifically, the dielectric layer 2 may have a thickness of 20 μm or more and 200 μm or less.

[0022] In the laminate 10 according to one embodiment, the dielectric layer 2 is laminated on both sides of the base layer 1 via first conductors 31. The first conductors 31 are not particularly limited as long as they are conductors, and examples thereof include metals such as copper, nickel, gold, platinum, silver, aluminum, and brass. The thickness and size of the first conductors 31 are not limited and are set appropriately depending on the application of the laminate 10. Specifically, the first conductors 31 may have a thickness of 12 μm or more and 40 μm or less. The thickness of the first conductors 31 may be smaller than the thickness of the dielectric layer 2.

[0023] The laminate 10 according to one embodiment includes the above-described base material layer 1, dielectric layer 2, and first conductor 31, and has a structure in which the base material layer 1 and the dielectric layer 2 are laminated via the first conductor 31. By having such a laminate structure, the laminate 10 according to one embodiment tends to distribute the force evenly when bending, and the force applied to each layer is reduced. Furthermore, by having such a laminate structure, the layers support each other, thereby distributing the load.

[0024] Specifically, because the layers are in close contact with each other, when the laminate 10 is bent, a load is applied to the entire laminate 10, not just one layer. As a result, the stress and load applied when the laminate 10 is bent are more likely to be distributed evenly, reducing the force applied to each layer. Therefore, in the laminate 10 according to one embodiment, the stress applied to the interior of each layer is reduced even when the laminate 10 is bent, reducing the occurrence of cracks and fractures. In the laminate 10 according to one embodiment, the dielectric layer 2 is located on both sides of the base layer 1. However, it is sufficient that the dielectric layer 2 is located on at least one side of the base layer 1.

[0025] The dielectric layer 2 may be thicker than the base layer 1. When the dielectric layer 2 is thicker than the base layer 1, the laminate 10 can be used as an antenna substrate that has flexibility and high radiation efficiency. The thickness of the dielectric layer 2 may be 0.5 to 2.0 times the thickness of the base layer 1.

[0026] The surface roughness Sz of the first conductors 31 is not limited. The surface roughness Sz of the first conductors 31 on the substrate layer 1 side may be 1.7 μm or less, or may be 0.5 μm or more and 1.0 μm or less. When the surface roughness Sz of the substrate layer 1 side is such a surface roughness Sz, the adhesion between the substrate layer 1 and the first conductors 31 is improved. In particular, when the surface roughness Sz of the substrate layer 1 side is 0.5 μm or more and 1.0 μm or less, the adhesion to the substrate layer 1 is ensured and cracks in the substrate layer 1 caused by stress concentration on the substrate layer 1 during bending can be reduced. Furthermore, when the first conductors 31 are used as a signal layer, such a surface roughness Sz of the substrate layer 1 side can provide both good signal characteristics and adhesion to the substrate layer 1.

[0027] The surface roughness Sz of the first conductor 31 on the dielectric layer 2 side may be 3.0 μm or more, or may be 4.2 μm or more and 6.0 μm or less. When the surface roughness Sz of the dielectric layer 2 side is such a surface roughness Sz, the adhesion between the dielectric layer 2 and the first conductor 31 is improved. In particular, when the surface roughness Sz of the dielectric layer 2 side is 4.2 μm or more and 6.0 μm or less, the adhesion to the dielectric layer 2 is ensured and cracks in the base layer 1 caused by stress concentration on the base layer 1 during bending can be reduced.

[0028] In the first conductor 31, the surface roughness Sz on the dielectric layer 2 side may be larger than the surface roughness Sz on the base material layer 1 side. When the first conductor 31 has such a relationship in the surface roughness Sz, the adhesion between the base material layer 1 and the dielectric layer 2 is improved, and bending resistance is also improved.

[0029] Next, a laminate 20 according to another embodiment of the present disclosure will be described with reference to Fig. 2. In the laminate 20 according to the other embodiment, the same components as those in the laminate 10 according to the first embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted. Fig. 2 is an explanatory diagram for describing the laminate 20 according to the other embodiment of the present disclosure.

[0030] In the laminate 10 according to one embodiment, the dielectric layer 2 has a single-layer structure. On the other hand, in the laminate 20 according to the embodiment, the dielectric layer 2 has a two-layer structure. In this manner, the dielectric layer 2 may have a multi-layer structure. When the dielectric layer 2 has a multi-layer structure, the number of layers included in the laminate 20 increases, and the force applied to each layer is further reduced. As a result, the occurrence of cracks and fractures is further reduced.

[0031] When the dielectric layer 2 has a multilayer structure, the number of dielectric layers 2 is not limited as long as it is two or more layers, and may be, for example, two to six layers. When the dielectric layer 2 has a multilayer structure, the thickness of the dielectric layer 2 mentioned above does not refer to the thickness of each layer, but refers to the total thickness. Furthermore, when the dielectric layers 2 are located on both sides of the base layer 1, the number of layers in each dielectric layer 2 may be the same or different. For example, one dielectric layer 2 may have a single-layer structure, and the other dielectric layer 2 may have a multilayer structure.

[0032] The laminate 10 according to one embodiment and the laminate 20 according to another embodiment may be manufactured by any method, for example, as follows. First, a film (sheet material) made of a thermoplastic resin is prepared as the substrate layer 1. As such a film, a double-sided metal-clad laminate, such as a double-sided copper-clad laminate having metal layers laminated on both sides, is prepared. The metal layers of the double-sided metal-clad laminate correspond to the first conductors 31.

[0033] Next, films (sheet materials) formed of thermosetting resin are laminated on both sides of the double-sided metal-clad laminate as dielectric layers 2, and integrated by lamination press curing. Curing may be performed, for example, under pressure conditions of 2.5 MPa to 4.5 MPa, at 170°C to 190°C, for 90 minutes to 180 minutes. Two or more layers of films (sheet materials) formed of thermosetting resin may be used on each side.

[0034] By this procedure, the laminate 10 according to one embodiment and the laminate 20 according to another embodiment can be obtained. Instead of a double-sided metal-clad laminate, a film made of a thermoplastic resin may be used with metal layers formed on both sides.

[0035] Next, a transmission circuit according to the present disclosure will be described with reference to Figures 3 to 5. Figure 3 is a schematic diagram showing a transmission circuit 100 according to an embodiment of the present disclosure. The transmission circuit 100 according to the embodiment includes a laminate 10, a second conductor 32, and a third conductor 33.

[0036] As shown in Figures 4 and 5, the second conductor 32 is located on the surface of the laminate 10, i.e., on the surface of the dielectric layer 2 included in the laminate 10. Figure 4 is an enlarged explanatory view for explaining region X shown in Figure 3. Figure 5 is an explanatory view for explaining a cross section when cut along line A-A shown in Figure 4.

[0037] The second conductor 32 is not particularly limited as long as it is a conductor. Examples of the second conductor 32 include metals such as copper, nickel, gold, platinum, silver, aluminum, and brass. The thickness and size of the second conductor 32 are not limited and are set appropriately depending on the application of the transmission circuit 100. Specifically, the second conductor 32 may have a thickness of 18 μm or more and 36 μm or less.

[0038] The second conductor 32 includes a patch conductor. Since the second conductor 32 includes the patch conductor and the first conductor 31 functions as a ground conductor, the transmission circuit 100 functions as a microstrip patch antenna.

[0039] 4 and 5 , the third conductor 33 is located on the surface of the dielectric layer 2 included in the laminate 10 and electrically connects the second conductors 32. The third conductor 33 includes a linear conductor. That is, the third conductor 33 electrically connects the plurality of second conductors 32 located on the surface of the dielectric layer 2.

[0040] The third conductor 33 is not particularly limited as long as it is a conductor. Examples of the third conductor 33 include metals such as copper, nickel, gold, platinum, silver, aluminum, and brass. The thickness of the third conductor 33 is not limited and is set appropriately depending on the application of the transmission circuit 100. Specifically, the third conductor 33 may have a thickness of 18 μm or more and 36 μm or less, or may have the same thickness as the second conductor 32. The surface roughness Sz of the second conductor 32 and the third conductor 33 on the dielectric layer 2 side is not limited and may be, for example, 0.7 μm or more and 3 μm or less.

[0041] The manufacturing method of the transmission circuit 100 according to an embodiment is not limited, and for example, the second conductor 32 and the third conductor 33 may be formed on the surface (surface of the dielectric layer 2) of the laminate 10 according to an embodiment. The second conductor 32 and the third conductor 33 may be formed integrally or separately. Although the transmission circuit 100 according to an embodiment includes both the second conductor 32 and the third conductor 33, the transmission circuit according to the present disclosure is only required to include at least the second conductor.

[0042] The transmission circuit 100 according to an embodiment uses the laminate 10 according to an embodiment, and therefore the occurrence of cracks and breaks is reduced even when the circuit is bent. Furthermore, the first conductor 31 is located between the base layer 1 and the dielectric layer 2, which reduces variation in the radius of curvature when the circuit is bent. As a result, the transmission circuit 100 has excellent radiation characteristics.

[0043] Therefore, the transmission circuit 100 according to the embodiment can be installed in curved portions such as the curved portion of a pole or the instrument panel of an automobile, improving the flexibility of the installation location. Furthermore, by bending the transmission circuit 100 according to the embodiment, the directivity of radio waves can be controlled, making it easier to estimate the direction of radio waves.

[0044] Hereinafter, embodiments of the present disclosure will be specifically described with reference to examples, but the embodiments of the present disclosure are not limited to these examples.

[0045] First, a double-sided copper-clad laminate (manufactured by Panasonic Industries Co., Ltd.) was prepared, in which copper foil was laminated on both sides of a film formed from a liquid crystal polymer (LCP). The surface roughness Sz of the copper foil on the base layer side was 1.7 μm or less. Next, the surface of the double-sided copper-clad laminate was roughened so that the surface roughness Sz of the copper foil on the dielectric layer side was 4.2 μm or more.

[0046] Next, a sheet of thermosetting cyclic olefin copolymer (COC, manufactured by Mitsui Chemicals, Inc.) was laminated on both sides of the double-sided copper-clad laminate as a dielectric layer. Furthermore, a metal foil (copper foil) was laminated on one surface of the COC sheet. The surface roughness Sz of the copper foil on the sheet side was 0.8 μm.

[0047] Thereafter, the laminate was subjected to lamination press curing at 180°C for 2 hours under a pressure of 3.5 MPa to obtain a laminate. The base layer had a thickness of 100 μm. The copper foil corresponding to the first conductor had a thickness of 18 μm. The dielectric layer had a thickness of 100 μm. The copper foil located on the outermost surface had a thickness of 18 μm.

[0048] Next, the copper foil located on the outermost surface was processed to form a microstrip structure. Specifically, it was processed into a patch conductor (second conductor) and a linear conductor (third conductor) that electrically connected the patch conductors. Using this procedure, a transmission circuit (Sample No. 1) was obtained. The resulting Sample No. 1 measured 100 mm long and 100 mm wide.

[0049] The obtained sample No. 1 was cut into a length of 40 mm and a width of 10 mm to obtain a test piece. The obtained test piece did not develop cracks or breaks even when bent to a curvature radius of 16 mm. When the test piece was then placed in the bent state, it returned to its original flat state in less than 1 second.

[0050] A transmission circuit (Sample No. 2) was obtained using the same procedure as Sample No. 1, except that a double-sided copper-clad laminate (manufactured by Dupont) using polytetrafluoroethylene (PTFE) instead of LCP was used as the substrate layer, polyphenylene ether (PPE, manufactured by Panasonic Industries Co., Ltd.) was used as the dielectric layer instead of thermosetting COC, and the surface roughness Sz of the metal foil (copper foil) sheet side was set to 2.2 μm. Furthermore, a transmission circuit (Sample No. 3) was obtained using the same procedure as Sample No. 2, except that a double-sided copper-clad laminate (manufactured by Ube Industries, Ltd.) using polyimide instead of PTFE was used.

[0051] The resulting samples No. 2 and No. 3 were also cut into test pieces 40 mm long and 10 mm wide. The resulting test pieces did not develop cracks or breaks even when bent to a curvature radius of 16 mm. When the test pieces were then placed in the bent state, they all returned to their original flat state, although it took longer than sample No. 1.

[0052] Furthermore, a transmission circuit (Sample No. 4) was obtained in the same manner as Sample No. 1, except that a sheet formed of thermosetting COC was laminated as a dielectric layer on only one of the two surfaces of the double-sided copper-clad laminate as the base layer.

[0053] The obtained sample No. 4 was also cut to a length of 40 mm and a width of 10 mm to obtain a test piece. For the test pieces obtained from sample No. 1 and sample No. 4, a mandrel test was performed in accordance with JIS K5600-5-1, with a mandrel diameter of 2 mm or more and 5 mm or less, to determine the bending resistance of each sample. At this time, as reference samples, test pieces of 40 mm length and 10 mm width were also prepared for an LCP substrate layer alone having a total thickness of 100 μm (sample No. 5) and a COC alone having a total thickness of 100 μm (sample No. 6). A mandrel test was also performed on the test pieces obtained from sample No. 5 and sample No. 6 to determine their bending resistance. The results of the mandrel test are shown in Table 1.

[0054]

[0055] In Table 1, the test specimens in which no cracks occurred as a result of the mandrel test are indicated as "OK," and those in which cracks occurred are indicated as "NG." As shown in Table 1, Samples No. 1 and No. 4, like Sample No. 5, an LCP with excellent flexibility, did not experience cracks in the test specimens at any mandrel diameter. In other words, Samples No. 1 and No. 4 were found to have good bending resistance and to be easily installed in curved portions, etc. Therefore, it was found that antenna substrates using these samples can control the directivity of radio waves and facilitate the estimation of the direction of radio waves.

[0056] On the other hand, sample No. 6, which was made of only COC, exhibited good bending resistance only when the mandrel diameter was 5 mm, indicating that it could be used in curved sections with a limited radius of curvature.

[0057] The embodiments of the present disclosure have been described above. However, the invention according to the present disclosure is not limited to the above-described embodiments, and various modifications and improvements are possible within the scope of the present disclosure as shown in (1) to (7) below.

[0058] (1) A laminate according to the present disclosure includes a base layer, a dielectric layer, and a first conductor. The base layer includes a thermoplastic resin, and the dielectric layer includes a thermosetting resin. A dielectric layer is laminated on at least one surface of the base layer via the first conductor. (2) In the laminate according to (1) above, a dielectric layer is laminated on both surfaces of the base layer via the first conductor. (3) In the laminate according to (1) or (2) above, the thermoplastic resin includes at least one selected from the group consisting of a liquid crystal polymer and polytetrafluoroethylene. The thermosetting resin includes at least one selected from the group consisting of a cyclic olefin copolymer and polyphenylene ether. (4) In the laminate according to any one of (1) to (3) above, the dielectric layer is thicker than the base layer. (5) In the laminate according to any one of (1) to (4) above, the dielectric layer has a multilayer structure. (6) A transmission circuit according to the present disclosure includes the laminate according to any one of (1) to (5) above and a second conductor. The second conductor is located on a surface of a dielectric layer included in the laminate. The first conductor included in the laminate includes a ground conductor. The second conductor includes a patch conductor. (7) The transmission circuit according to (6) above further includes a third conductor, the third conductor including a linear conductor that electrically connects the patch conductors.

[0059] REFERENCE SIGNS LIST 1 substrate layer 2 dielectric layer 31 first conductor 32 second conductor 33 third conductor 10, 20 laminate 100 transmission circuit

Claims

1. A laminate comprising a base material layer, a dielectric layer, and a first conductor, wherein the base material layer contains a thermoplastic resin, the dielectric layer contains a thermosetting resin, and the dielectric layer is laminated on at least one surface of the base material layer via the first conductor.

2. The laminate according to claim 1, wherein the dielectric layer is laminated on both surfaces of the base material layer via the first conductor.

3. The laminate according to claim 1 or 2, wherein the thermoplastic resin contains at least one selected from the group consisting of liquid crystal polymers and polytetrafluoroethylene, and the thermosetting resin contains at least one selected from the group consisting of cyclic olefin copolymers and polyphenylene ethers.

4. The laminate according to any one of claims 1 to 3, wherein the dielectric layer is thicker than the base material layer.

5. The laminate according to any one of claims 1 to 4, wherein the dielectric layer has a multilayer structure.

6. A transmission circuit comprising the laminate according to any one of claims 1 to 5 and a second conductor, wherein the second conductor is located on the surface of the dielectric layer contained in the laminate, the first conductor contained in the laminate includes a ground conductor, and the second conductor includes a patch conductor.

7. The transmission circuit according to claim 6, further comprising a third conductor, wherein the third conductor includes a linear conductor that electrically connects the patch conductors.

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