TWI829033B - High-frequency composite substrate and preparation method thereof - Google Patents

Abstract

The invention provides a high-frequency composite comprising a first copper foil layer, a first high-frequency resin adhesive layer, a composite laminate structure, a second high-frequency resin adhesive layer, and a second copper foil layer; wherein the composite laminate structure is an odd-numbered structure, and is composed of at least two third high- frequency resin adhesive layers and at least one low-dielectric thin film layer alternately laminated, and each third high-frequency resin adhesive layer serves as a layer adjacent to the first high-frequency resin adhesive layer and the second high-frequency resin adhesive layer. The present invention further provides a method for preparing the above-mentioned high-frequency composite substrate. Through the composite structure, the composite substrate of the present invention has advantages of good electrical properties, extremely low transmission loss, low thermal expansion coefficient, and good dimensional stability. It also has advantages in terms of cost and manufacturing process; even when exposed to high temperatures and high humidity environment, the composite substrate of the present invention can also provide the benefits of stable Dk/Df performance, ultra-low water absorption, excellent mechanical properties, high bonding strength, and the characteristics of a thick and low-dielectric dielectric layer.

Description

A composite high-frequency substrate and its preparation method

The present invention relates to the technical field of printed circuit boards, and in particular to a composite high-frequency substrate.

With the rapid development of information technology, high-speed transmission technologies such as 5G are being widely promoted around the world, and millimeter-wave transmission is accelerating. In order to meet the high-frequency and high-speed signal transmission and reduce the production cost of terminal equipment, various forms of mixed-voltage structures have appeared on the market. Multilayer board design and applications. Printed circuit boards are an indispensable material in electronic products. As the demand for consumer electronic products increases, the demand for printed circuit boards is also increasing day by day. Because Flexible Printed Circuit (FPC) has the characteristics of flexibility and three-dimensional wiring, scientific and technological electronic products emphasize light, thin, short, flexible, and thus require high-frequency and high-speed development in information technology. Driven by this trend, FPC has been widely used in computers and peripheral equipment, communication products, consumer electronics and other products.

The high-frequency boards currently used in the industry are mainly LCP (Liquid crystal polymer) boards, fluorine resin fiber boards, and MPI (Modified polyimide) boards. Although the substrate made of LCP film has better processability and due to its low water absorption, it is difficult to pass under high temperature and high humidity environment. The transmission loss performance has also become stable, but the problem is that its dielectric properties are difficult to reduce and adjust. Although its loss factor can reach 0.002 to 0.003, its dielectric constant is approximately between 3.2 and 4.0, which is different from the fluorine series. Compared with other materials, substrates made of LCP films are limited in the application of high-speed transmission; similar to fluorine-based materials, due to their surface characteristics, they also face insufficient adhesion and loss of metal conductors, and it is difficult to make further progress. Problems such as reducing and adjusting; the melting point of LCP films currently on the market is about 300°C, which can easily cause poor thickness uniformity in subsequent high-temperature assembly processes. In addition, the cost of LCP films remains high, so there are few large-scale suppliers in the market, and their supply cannot meet industry demand.

Therefore, the industry is still eager to develop a high-frequency substrate with good electrical properties, extremely low transmission loss, low thermal expansion coefficient, good dimensional stability, ultra-low water absorption, excellent mechanical properties and high bonding strength.

The main technical problem solved by the present invention is to provide a composite high-frequency substrate, which is a stacked structure including a low-dielectric film layer, a high-frequency resin adhesive layer and a copper foil layer. The advantage of this stack is to utilize the low CTE of thin films (such as modified polyimide films) and the symmetry of CTE under biaxial extension of thick films to support the thermal expansion characteristics and processability of the entire substrate, making the substrate have Low and uniform thermal expansion coefficient, good dimensional stability and low warpage height, and generally film systems have better and more stable mechanical properties and drilling processing properties than resin coatings. The high-frequency resin adhesive layer has strong adhesion, so low-roughness copper foil can be used to effectively reduce the impact of conductor loss during high-frequency signal transmission. It requires a lower temperature than the process of directly laminating copper foil with a thin film (due to the thin film The melting point is greater than 300°C, thus requiring a higher lamination temperature), which also reduces the cost of equipment requirements. this In addition, the composite film stack of low dielectric film and high-frequency resin glue is used to replace the traditional low dielectric film such as LCP film, polyimide film or modified polyimide film as the dielectric layer. In addition to being easy to manufacture thick The composite film stack is used as a low-dielectric dielectric layer to make the substrate with better hygroscopicity and electrical properties, which can also reduce costs and increase its competitive advantage.

In order to solve the above technical problems, the present invention provides a composite high-frequency substrate, which includes a first copper foil layer, a first high-frequency resin adhesive layer, a composite film stack, a second high-frequency resin adhesive layer, and a second copper foil layer. ; Among them, the composite film stack is an odd-layer structure, which is composed of a low dielectric film layer and a third high-frequency resin adhesive layer alternately, and the two low-dielectric film layers are adjacent to the first high-frequency resin adhesive layer and The second high-frequency resin glue layer.

In a specific implementation, the Dk value (10G Hz) of each of the first high-frequency resin glue layer, the second high-frequency resin glue layer, and the third high-frequency resin glue layer is 2.00 to 3.50, and the Df value (10G Hz) is 0.001 to 0.010.

In a specific implementation, the first copper foil layer and the second copper foil layer are independently selected from one of the group consisting of ED copper foil, RA copper foil, HA copper foil and HA-V2 copper foil.

In a specific implementation, the total thickness of the composite high-frequency substrate is 43 to 700 μm, wherein the thickness of the first copper foil layer and the second copper foil layer are both 6 to 70 μm; the first high frequency The thickness of the resin glue layer, the second high-frequency resin glue layer and the third high-frequency resin glue layer is 5 to 50 μm; the thickness of the low dielectric film layer is 8 to 100 μm.

In a specific implementation, the first copper foil layer and the second copper foil layer are both copper foil layers with a matte surface roughness (RZ, ten-point average roughness) of 0.4 to 2.0 μm.

In a specific implementation, the Dk value (10G Hz) of the low dielectric film layer is 2.0 to 3.5, and the Df value (10G Hz) is 0.002 to 0.020; the material forming the low dielectric film layer The system is selected from polyimide, ethylene fluoride-propylene copolymer, tetrafluoroethylene-perfluorovinyl ether copolymer, polytetrafluoroethylene, liquid crystal polymer, polyether ether ketone, polyphenylene ether and polyphenylene sulfide At least one polymer in the group.

In a specific implementation, the materials forming the first high-frequency resin glue layer, the second high-frequency resin glue layer and the third high-frequency resin glue layer are independently selected from fluorine resin, epoxy resin, and acrylic resin. , urethane resin, thermosetting polyimide resin, silicone rubber resin, parylene resin, polycarbonate resin, isocyanate, polystyrene resin, bismaleimide resin, polyethylene resin Ethernet, liquid crystal polymer, polyether ether ketone, polyethylene, polystyrene, bismaleimide Triazine Resin (BT resin), polyphenylene ether, polyolefin and polytetrafluoroethylene At least one polymer from the group consisting of vinyl fluoride.

In a specific implementation, the overall water absorption rate of the composite high-frequency substrate is in the range of 0.1 to 1.0%, and the overall CTE is in the range of 5 to 50 ppm/°C.

The invention further provides a method for preparing a composite high-frequency substrate, which includes:

Forming the third high-frequency resin adhesive layer on the low dielectric film layer;

Laminate another low-dielectric film layer on the third high-frequency resin adhesive layer to obtain the composite film stack;

The first copper foil layer is pressed together by forming the first high-frequency resin adhesive layer on one side of the composite film stack; and

The second high-frequency resin adhesive layer is formed on the opposite side of the composite film stack, and the second copper foil layer is pressed to produce the composite high-frequency substrate.

In a specific implementation, the preparation method of the composite high-frequency substrate further includes: before laminating the first copper foil layer and the second copper foil layer, respectively borrowing two holes on the opposite surfaces of the composite film stack. The two low-dielectric film layers are laminated by a third high-frequency resin glue layer.

The composite high-frequency substrate of the present invention solves the transmission loss problem of millimeter wave transmission and solves the common processability problems of LCP substrates, fluorine-based substrates, and MPI substrates through the composite structure. It has extremely low dielectric loss and dielectric constant, uniform It has a low thermal expansion coefficient and has excellent transmission performance in high temperature or high humidity environments. It can be effectively thickened through the composite structure to achieve low transmission loss requirements. The use of high-frequency resin adhesive layer can effectively reduce the processing temperature. Therefore, it has excellent thickness uniformity and cost advantages.

100, 100’: Composite high-frequency substrate

101: First copper foil layer

101’: Second copper foil layer

102: The first high frequency resin adhesive layer

102’: The second high frequency resin glue layer

103,103’: Composite membrane stacking

1031: Low dielectric film layer

1032: The third high frequency resin adhesive layer

200:LCP substrate

201, 301: Copper foil layer

202:LCP thin film layer

300:Fluorine based substrate

302: Fluorine resin layer

303:Polyimide layer

The embodiments of the present invention are described with reference to the accompanying drawings:

Figure 1 is a schematic structural diagram of the composite high-frequency substrate of the present invention, in which the composite film stack is a three-layer structure;

Figure 2 is a schematic structural diagram of the composite high-frequency substrate of the present invention, in which the composite film stack is a five-layer structure;

Figure 3 is a schematic structural diagram of Comparative Example 1 and Comparative Example 2; and

Figure 4 is a schematic structural diagram of Comparative Example 3 and Comparative Example 4.

The following describes the implementation of the present invention through specific embodiments. Those skilled in the art can easily understand the advantages and effects of the present invention from the content disclosed in this specification.

It should be noted that the structures, proportions, sizes, etc. shown in the drawings attached to this specification are only used to coordinate with the content disclosed in the specification for the understanding and reading of those familiar with the art, and are not used to limit the implementation of the present invention. Therefore, it has no technical substantive significance. Any structural modifications, changes in proportions, or adjustments in size shall still fall within the scope of this invention without affecting the effects that can be produced and the purposes that can be achieved. The technical content disclosed by the invention must be within the scope that can be covered. At the same time, words such as "a", "lower" and "upper" cited in this specification are only for the convenience of description and are not used to limit the scope of the present invention. Changes or adjustments to their relative relationships will not occur without Substantial changes in the technical content shall also be deemed to be within the scope of the present invention. In addition, all ranges and values herein are inclusive and combinable. Any value or point that falls within the range described in this article, such as any integer, can be used as a minimum or maximum value to derive a lower range, etc.

As shown in Figure 1, a composite high-frequency substrate 100 of the present invention is shown, which includes a first copper foil layer 101, a first high-frequency resin adhesive layer 102, a composite film stack 103, and a second high-frequency resin adhesive layer 102. 'and the second copper foil layer 101'; wherein, the composite film stack 103 is an odd-numbered layer structure, and the odd-numbered layer structure is alternately composed of a low dielectric film layer 1031 and a third high-frequency resin glue layer 1032, and is The outermost low-dielectric film layer 1031 serves as a layer adjacent to the first high-frequency resin glue layer 102 and the second high-frequency resin glue layer 102'. In addition, as shown in Figure 2, the composite film stack 103' of the composite high-frequency substrate 100' is composed of a five-layer structure alternately composed of a low dielectric film layer 1031 and a third high-frequency resin glue layer 1032.

In the composite high-frequency substrate of the present invention, the first high-frequency resin glue layer, the second high-frequency resin glue layer and the third high-frequency resin glue layer all have Dk values (10G Hz) of 2.00 to 3.50 and Df Low dielectric glue layer with a value (10G Hz) of 0.001 to 0.010. In other specific implementations, the Dk value (10G Hz) is 2.00, 2.10, 2.20, 2.30, 2.40, 2.50, 2.60, 2.70, 2.80, 2.90, 3.00, 3.10, 3.20, 3.30, 3.40 or 3.50; the Df value ( 10G Hz) is 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009 or 0.010.

The first copper foil layer and the second copper foil layer are independently selected from the group consisting of ED copper foil, RA copper foil, HA copper foil and HA-V2 copper foil.

The total thickness of the composite high-frequency substrate is 43 to 700 μm, wherein the thickness of the first copper foil layer and the second copper foil layer are both 6 to 70 μm; the first high-frequency resin adhesive layer, the second high-frequency The thickness of the resin glue layer and the third high-frequency resin glue layer is 5 to 50 μm; the thickness of the low dielectric film layer is 8 to 100 μm. In other embodiments, the total thickness of the composite high-frequency substrate is 85 to 300 μm, wherein the thickness of the first copper foil layer and the second copper foil layer is both 12 to 18 μm; The thickness of the three high-frequency resin adhesive layers is 10 to 25 μm; the thickness of the low dielectric film layer is 12 to 50 μm.

The first copper foil layer and the second copper foil layer are both copper foil layers with a matte surface roughness (RZ, ten-point average roughness) of 0.4 to 2.0 μm.

The low dielectric film layer has a Dk value (10G Hz) of 2.0 to 3.5 and a Df value (10G Hz) of 0.002 to 0.020. In other specific implementations, the Dk value (10G Hz) is 2.00, 2.10, 2.20, 2.30, 2.40, 2.50, 2.60, 2.70, 2.80, 2.90, 3.00, 3.10, 3.20, 3.30, 3.40 or 3.50; the Df value ( 10G Hz) is 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009, 0.010, 0.011, 0.012, 0.013, 0.014, 0.015, 0.016, 0.017, 0.018, 0.019 or 0.02. The material forming the low dielectric thin film layer is selected from polyimide, ethylene fluoride-propylene copolymer, tetrafluoroethylene-perfluorovinyl ether copolymer, polytetrafluoroethylene, liquid crystal polymer, and polyether ether ketone. , at least one polymer in the group consisting of polyphenylene ether and polyphenylene sulfide, among which the polyimide film layer is particularly preferred.

The materials forming the first high-frequency resin glue layer, the second high-frequency resin glue layer and the third high-frequency resin glue layer are independently selected from fluorine resin, epoxy resin, acrylic resin, urethane resin, Thermosetting polyimide-based resin, silicone rubber-based resin, parylene-based resin, polycarbonate resin, isocyanate, polystyrene resin, bismaleimide-based resin, polyether styrene, liquid crystal polymer, polyether At least one of the group consisting of ether ketone, polyethylene, polystyrene, bismaleimide Triazine Resin (BT resin), polyphenylene ether, polyolefin and polytetrafluoroethylene A polymer. Preferably, the third high-frequency resin adhesive layer is a thermosetting polyimide-based resin adhesive layer, and the polyimide content thereof is 40 to 95% by weight. For example, the polyimide content is 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90 or 95% by weight.

The overall water absorption rate of the composite high-frequency substrate is between 0.1 and 1.0%, such as 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 1.0; the overall CTE of the composite high-frequency substrate is between 5 to 50ppm/℃, such as 5, 6, 7, 8, 9, 10, 15, 20, 25, 30, 35, 40, 45 or 50ppm/℃. In other embodiments, the overall water absorption rate ranges from 0.3 to 0.8%, and the overall CTE ranges from 5 to 15 ppm/°C.

In a specific implementation, when the composite film is stacked into three layers, the preparation method of the composite high-frequency substrate includes the following steps:

Step 1: Prepare a composite structural film by first coating a low-dielectric film layer with a third high-frequency resin adhesive layer and then laminating another low-dielectric film layer and drying and solidifying;

Step 2: Coat the material obtained in Step 1 with the first high-frequency resin adhesive layer, laminate the first copper foil layer, and dry and solidify; and

Step 3: Coat the second high-frequency resin adhesive layer on the side of the material obtained in Step 2 that is not the first copper foil layer, then press the second copper foil layer and dry and solidify to obtain the composite high-frequency substrate of the present invention.

In another specific implementation, when the composite film stack is more than 3 layers, the preparation method of the composite high-frequency substrate includes the following steps:

Step 1: Prepare a low-dielectric film layer, coat it with a third high-frequency resin adhesive layer, and then attach it to another low-dielectric film layer;

Step 2: Coat the material obtained in the previous step with a third high-frequency resin adhesive layer and attach it to another low-dielectric film layer. Repeat this step N times, where N is a positive integer not less than 1, to obtain the composite. The membrane structure is then dried and solidified;

Step 3: Coat the material obtained in Step 2 with the first high-frequency resin adhesive layer, laminate the first copper foil layer, and dry and solidify; and

Step 4: Coat the second high-frequency resin adhesive layer on the side of the material obtained in Step 3 that is not the first copper foil layer, then press the second copper foil layer and dry and solidify to obtain the composite high-frequency substrate of the present invention.

Examples 1 to 2:

Preparation of composite high-frequency substrate:

First, the third high-frequency resin adhesive layer is formed on the low-dielectric film layer through coating lines; then, another low-dielectric film is laminated at a temperature of 90 to 130°C. Put it on the third high-frequency resin adhesive layer, and bake it in an oven from room temperature to a maximum of 180° C. for 21 hours to completely solidify to prepare the composite film stack.

Finally, through the coating line, the first high-frequency resin adhesive layer is formed on one side of the composite film stack, the first copper foil layer is pressed at 110 to 130°C, rolled up and put into a non-oxidation oven for drying After curing at a maximum temperature of 60°C for 12 to 30 hours (18 hours in this embodiment), the second high-frequency resin adhesive layer is formed on the opposite side of the composite film stack, and the second high-frequency resin adhesive layer is pressed at 130°C. The two copper foil layers are then baked in a non-oxidizing oven from room temperature to a maximum of 180°C for 21 hours to completely cure the high-frequency resin adhesive layer to prepare the composite high-frequency substrate.

Examples 3 to 4:

Preparation of composite high-frequency substrate:

First, prepare a low-dielectric film layer, apply a third high-frequency resin adhesive layer through a coating line, and then laminate another low-dielectric film layer on the above-mentioned layer at a temperature of 90 to 130°C. On the third high-frequency resin adhesive layer, the material obtained in the previous step is coated with the third high-frequency resin adhesive layer through a coating line. After that, the above-mentioned layer is heated at a temperature of 90 to 130°C. , after being attached to another low-dielectric film layer, put it into an oven and bake it from room temperature to a maximum of 180°C for 21 hours to completely solidify to prepare the composite film stack. If the composite structural membrane part has a 2n+3 (n is a positive integer) layer structure of no less than five layers, then the steps of coating and laminating the upper coating line are repeated n times (step 2, step 2-2, step 2-3,..., step 2-n), bake and completely solidify in the last step. This example is the case where n=1;

Furthermore, the material obtained in the previous step is coated with the first high-frequency resin glue layer through the coating line; then, the first copper foil layer is laminated to the first high-frequency resin under the temperature condition of 110 to 130°C. The adhesive layer is dried and cured in a non-oxidizing oven at the highest temperature of 60°C for 18 hours.

Finally, the second high-frequency resin adhesive layer is coated on the surface of the material obtained in the previous step other than the first copper foil layer through the coating line; then, the second copper foil is laminated at a temperature of 110 to 130°C. The second high-frequency resin adhesive layer is placed in an oven and the temperature is raised from room temperature to a maximum of 180° C. and baked for 21 hours to completely solidify to prepare the composite high-frequency substrate.

Comparative Examples 1 to 4:

The LCP substrates of Comparative Examples 1 and 2 are commercially available substrates (R-F705S EC series) made by Panasonic using a liquid crystal polymer (LCP) film (Kuraray, Vecstar CT-Z). The fluorine-based substrates of Comparative Example 3 and Comparative Example 4 are respectively commercially available substrates of Dupont (TK series) and Shirre (PT series, PT100) from the same industry.

The LCP substrate 200 of Examples 1 to 4 combined with the prior art is prepared through the steps of the above-mentioned composite high-frequency substrate preparation method (Comparative Example 1 and Comparative Example 2, as shown in Figure 3, are composed of a copper foil layer 201 and the LCP thin film layer 202 as a medium), the fluorine-based substrate 300 (Comparative Example 3 and Comparative Example 4, as shown in Figure 4, are composed of a polyimide layer 303, a modified fluorine-based resin layer 302 and a copper foil layer 301 substrate) for basic performance comparison and recorded in Table 1. The structures of Example 1 and Example 2 are as shown in Figure 1. The thickness of each low dielectric film layer in Example 1 is 25 microns. The thickness of each low dielectric film layer in Example 2 is 50 microns. The thickness of the three high-frequency resin glue layers is 25 microns; the structures of Examples 3 and 4 are as shown in Figure 2. The thickness of each low dielectric film layer in Example 3 is 12.5 microns. The thickness of each low dielectric film layer in Example 4 is 25 microns. The thickness of the electrical thin film layer is 25 microns, and the thickness of each third high-frequency resin glue layer is 25 microns.

In addition, the first copper foil layer and the second copper foil layer used in Examples 1 to 4 and Comparative Examples 1 to 4 are all electrolytic copper foils. In the composition of the third high-frequency resin glue layer, the first high-frequency resin glue layer and the second high-frequency resin glue layer of Examples 1 to 4, based on the total weight of each layer, the high frequency The resin adhesive layer contains 60% by weight of thermosetting polyimide resin, 10% by weight of tetraglycidylamine epoxy resin, and 20% by weight of flame retardant (Clariant product, OP935) based on the total weight of the layer. ), 8% by weight of sintered silica (product of Denka Company, FB-3SDX) and 2% by weight of fluorine resin (product of DuPont Company, 300AS). The low dielectric film layer in Examples 1 to 4 is a high-frequency polyimide film (PIAM, FS type). The LCP film layer of Comparative Examples 1 and 2 uses a liquid crystal polymer (LCP) film (Kuraray, Vecstar CT-Z). The fluorine-based substrates of Comparative Example 3 and Comparative Example 4 are respectively commercially available substrates of Dupont (TK series) and Shirre (PT series, PT100) from the same industry.

Then, the above substrate is tested according to the following methods: 1. Then strength test: use a tensile machine and test according to the IPC-TM-650 2.4.9D standard; 2. Dk/Df test: use a network analyzer and resonance cavity, and tested in accordance with the standards of IPC-TM-650 2.5.5.13; 3. Insertion loss test: using a network analyzer and probe platform, tested in accordance with the standards of IPC-TM-650 2.5.5.12; 4. Water absorption rate Test: Use the weighing method to test in accordance with IPC-TM-650 2.6.2; 5. Thermal expansion coefficient test: Use a thermal mechanical analyzer to test in accordance with the test specification IPC-TM-650 2.4.41.3; 6. Dimensional stability test: Use a two-dimensional coordinate instrument to test in accordance with the standards of IPC-TM-650 2.6.2C; 7. Solder resistance test: Use a lead-free tin furnace to test in accordance with the standards of IPC-TM-650 2.4.13 ; 8. Measurement of the maximum shrinkage of laser drilling: Use an optical microscope to observe the sample after laser drilling and record it.

Table 1

From the performance comparison results in Table 1, it can be seen that the composite high-frequency substrate of the present invention has the advantages of good electrical properties, extremely low transmission loss, low thermal expansion coefficient, and good dimensional stability. Even if it is placed in a high temperature and humidity environment, The composite substrate of the present invention can also provide the benefits of stable Dk/Df performance, ultra-low water absorption, excellent mechanical properties, high bonding strength, and has the characteristics of a thick and low dielectric layer.

The above embodiments are only illustrative and not intended to limit the present invention. Anyone skilled in the art can make modifications and changes to the above embodiments without departing from the spirit and scope of the invention. Therefore, the scope of rights protection of the present invention is defined by the scope of the patent application attached to the present invention. As long as it does not affect the effect and implementation purpose of the present invention, it should be covered by this disclosed technical content.

100: Composite high frequency substrate

101: First copper foil layer

101’: Second copper foil layer

102: The first high frequency resin adhesive layer

102’: The second high frequency resin glue layer

103: Composite membrane stacking

1031: Low dielectric film layer

1032: The third high frequency resin adhesive layer

Claims (9)

A composite high-frequency substrate includes: a first copper foil layer, a first high-frequency resin adhesive layer, a composite film stack, a second high-frequency resin adhesive layer, and a second copper foil layer; wherein, the composite film stack It is an odd-layer structure, consisting of at least two low-dielectric film layers and at least a third high-frequency resin glue layer alternately stacked, and the two low-dielectric film layers are adjacent to the first high-frequency resin glue layer and the second high-frequency resin glue layer. High-frequency resin glue layer; wherein, the Dk value (10G Hz) of each of the first high-frequency resin glue layer, the second high-frequency resin glue layer, and the third high-frequency resin glue layer is 2.00 to 3.50, and the Df value ( 10G Hz) is 0.002 to 0.010, and the Dk value (10G Hz) of the low dielectric film layer is 2.0 to 3.5, and the Df value (10G Hz) is 0.002 to 0.020. The composite high-frequency substrate as claimed in claim 1, wherein the first copper foil layer and the second copper foil layer are independently selected from the group consisting of ED copper foil, RA copper foil, HA copper foil and HA-V2 copper foil. One of the groups. The composite high-frequency substrate as claimed in claim 1 has a total thickness of 43 to 700 μm, wherein the thickness of the first copper foil layer and the second copper foil layer are both 6 to 70 μm, and the first high-frequency resin glue The thickness of the first layer, the second high-frequency resin glue layer and the third high-frequency resin glue layer is 5 to 50 μm, and the thickness of the low dielectric film layer is 8 to 100 μm. The composite high-frequency substrate according to claim 1, wherein the first copper foil layer and the second copper foil layer are both copper foil layers with a matte surface and a ten-point average roughness value of 0.4 to 2.0 μm. The composite high-frequency substrate as claimed in claim 1, wherein the material forming the low dielectric thin film layer is selected from the group consisting of polyimide, vinyl fluoride-propylene copolymer, and tetrafluoroethylene-perfluorovinyl ether copolymer. polymer, polytetrafluoroethylene, liquid crystal polymer, polyether ether ketone, polyphenylene ether and polyphenylene sulfide At least one polymer in the group. The composite high-frequency substrate as claimed in claim 1, wherein the materials forming the first high-frequency resin adhesive layer, the second high-frequency resin adhesive layer and the third high-frequency resin adhesive layer are independently selected from fluororesin, Epoxy resin, acrylic resin, urethane resin, thermosetting polyimide resin, silicone rubber resin, parylene resin, polycarbonate resin, isocyanate, polyurethane resin, bismale Imide resin, polyether ester, liquid crystal polymer, polyether ether ketone, polyethylene, polystyrene, bismaleimide-triazine resin, polyphenylene ether, polyolefin and polytetrafluoroethylene at least one polymer from the group formed. As claimed in claim 1, the composite high-frequency substrate has an overall water absorption rate of 0.1 to 1.0%, and an overall CTE of 5 to 50 ppm/℃. A method for preparing a composite high-frequency substrate as described in claim 1, which includes: forming the third high-frequency resin adhesive layer on the low-dielectric film layer; laminating another high-frequency resin adhesive layer on the third high-frequency resin adhesive layer. A low dielectric film layer to prepare the composite film stack; by forming the first high-frequency resin adhesive layer on one side of the composite film stack to laminate the first copper foil layer; and in the composite The second high-frequency resin adhesive layer is formed on the opposite side of the film stack, and the second copper foil layer is pressed to produce the composite high-frequency substrate. The preparation method of a composite high-frequency substrate as described in claim 8 further includes, before laminating the first copper foil layer and the second copper foil layer, respectively using a third-high layer on the opposite surfaces of the composite film stack. Frequency resin glue layer laminates two low dielectric film layers.

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