TWI849341B - Composite fluorine-based substrate - Google Patents

Abstract

Provided is a composite fluorine-based substrate includes a first copper foil layer, a first fluorine-based resin layer, a composite polyimide layer, a second fluorine-based resin layer, and a second copper foil layer laminated in sequence, wherein the composite polyimide layer has an odd-numbered layer structure composed of alternating polyimide sublayers and high-frequency resin adhesive sublayers, and the outermost layer of the odd-numbered layer structure is the polyimide sublayer. The present disclosure also provides a method for preparing the composite fluorine-based substrate. The composite fluorine-based substrate of the present disclosure has low Dk/Df, low CTE, good dimensional stability, low water absorption, and excellent mechanical properties.

Description

Composite fluorine-based substrate

This disclosure is about a high-frequency, high-speed, low-loss flexible printed circuit (FPC) double-sided board for millimeter wave transmission, which is made by combining a composite polyimide (PI) layer structure with a fluorine resin layer. It is mainly used in the high-transmission field and can improve the transmission loss, processing and cost in the FPC field.

With the rapid development of information technology, the global 5G and other high-speed transmission technologies are being promoted in large quantities, and millimeter wave transmission is being accelerated. In order to meet the high-frequency and high-speed signal transmission and reduce the production cost of terminal equipment, various forms of mixed pressure structure multi-layer board design and application are in the ascendant in the market. Printed circuit boards are indispensable materials in electronic products, and with the growth of demand for consumer electronic products, the demand for printed circuit boards is also increasing day by day. Among them, because FPC has the characteristics of flexibility and three-dimensional wiring, so in the technological electronic products emphasize light, thin, short, flexible, and the development trend of information technology requiring high-frequency and high-speed transmission, FPC has been widely used in computers and their peripheral equipment, communication products, and consumer electronic products, etc.

The high-frequency boards currently used in the industry are mainly liquid crystal polymer (LCP) boards, fluorine resin fiber boards, and modified polyimide (MPI) boards. However, although the substrate made of LCP film has better processability and stable transmission loss performance due to low water absorption in high temperature and high humidity environments, it faces the problem that it is difficult to further improve and reduce the dielectric performance. Although its loss factor can reach 0.002~0.003, the dielectric constant is mostly between 3.2~4.0, which is more limited in the field of high-speed transmission compared to fluorine materials. Moreover, like fluorine-based materials, it has low adhesion due to surface properties, and it is difficult to reduce the loss of metal conductors. The melting point of LCP films currently produced in the market is around 300°C, which will cause poor thickness uniformity in subsequent high-temperature assembly processes. In addition, there are currently few manufacturers on the market that have the ability to supply LCP films, so the supply cannot meet industry demand and the cost remains high.

Secondly, fluorinated resins have excellent electrical properties such as low dielectric constant (Dk) and low dielectric loss. For example, the dielectric constant of polytetrafluoroethylene (PTFE) fluorinated substrate at a frequency of 10GHz is about 2.1, and the dielectric loss factor (Df) is about 0.0004. It also has the excellent property of low water absorption of only about 0.03%. However, it has a high coefficient of thermal expansion (CTE) of about 200ppm/℃, which can easily lead to poor dimensional stability, excessive shrinkage during laser drilling, resulting in difficulty in metallization, and circuit breakage. The change in size will directly affect the production of conductor circuits and alignment issues, especially with the requirements of high density. The impact is more obvious when the circuits are getting finer and finer. Therefore, if fluorine-based polymers are directly made into substrates, although extremely low Dk/Df can be obtained, it is not feasible for practical application. Generally, other materials with low thermal expansion coefficients are used to compound the structure or composition to improve processability.

For example, US 3676566 A proposed a composite layered structure of polyimide and fluorocarbon polymer; TW M531056 U, CN 103096612 B, CN 202276545 U, TW M422159 U1, TW M436933 U1, CN 202773176 U, etc. proposed a high-frequency substrate structure; CN 105269884 B proposed a composite high-frequency double-sided copper foil substrate and its manufacturing method; TW I645977 B proposed a PI type high-frequency high-speed transmission double-sided copper foil substrate and its preparation method; CN 207772540 U proposed a LCP or fluorine-based polymer high-frequency high-transmission double-sided copper foil substrate; CN 207744230 U proposed a composite fluorine-based polymer high-frequency high-transmission double-sided copper foil substrate and preparation method; CN 105295753 B proposed a high-frequency adhesive glue layer structure and preparation method; CN 105282959 B proposed a high-frequency cover film with low Dk and Df characteristics and preparation method. None of the above-mentioned previous patents disclosed a fluorine-based polymer substrate with the same structure and properties as the following disclosure.

In view of the above, the present disclosure provides a composite fluorine-based substrate, comprising a first copper foil layer, a first fluorine-based resin layer, a composite polyimide layer, a second fluorine-based resin layer and a second copper foil layer stacked in sequence, wherein the composite polyimide layer is an odd-numbered layer structure composed of alternating polyimide sublayers and high-frequency resin sublayers, and the outermost layer of the odd-numbered layer structure is the polyimide sublayer.

In a specific embodiment, the first copper foil layer and the second copper foil layer are each electrolytic copper foil, rolled copper foil, HA foil or HA-V2 foil.

In one specific embodiment, the thickness of the first copper foil layer and the second copper foil layer is between 6 and 70 μm. In another specific embodiment, the thickness of the first copper foil layer and the second copper foil layer is between 12 and 18 μm.

In a specific embodiment, the Dk value of the first fluorine-based resin layer and the second fluorine-based resin layer is between 2.00 and 3.50 (10 GHz), and the Df value is between 0.0001 and 0.005 (10 GHz).

In one specific embodiment, the thickness of the first fluorine-based resin layer and the second fluorine-based resin layer is between 2 and 50 μm. In another specific embodiment, the thickness of the first fluorine-based resin layer and the second fluorine-based resin layer is between 5 and 38 μm.

In a specific embodiment, the material of the first fluorine-based resin layer and the second fluorine-based resin layer is selected from at least one of the group consisting of polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyvinyl fluoride (PVF), fluoroethylene and vinyl ether copolymer, tetrafluoroethylene and ethylene copolymer, polytrifluorochloroethylene (PCTFE or PTFCE) and ethylene-chlorotrifluoroethylene copolymer (CTFE), ethylene-tetrafluoroethylene copolymer (ETFE), fluoroethylene-propylene copolymer (FEP), tetrafluoroethylene-perfluorovinyl ether copolymer (PFA), polyvinyl chloride, tetrafluoroethylene-hexafluoropropylene copolymer, ethylene-fluoroethylene copolymer, and tetrafluoroethylene-hexafluoropropylene-trifluoroethylene copolymer.

In one embodiment, the polyimide sublayer has a Dk value between 2.00 and 3.50 (10 GHz), and a Df value between 0.002 and 0.020 (10 GHz).

In one embodiment, the thickness of the polyimide sublayer is between 8 and 100 μm. In another embodiment, the thickness of the polyimide sublayer is between 25 and 90 μm.

In one embodiment, the Dk value of the high frequency resin sublayer is between 2.00 and 3.50 (10 GHz), and the Df value is between 0.001 and 0.010 (10 GHz).

In one embodiment, the thickness of the high-frequency resin sublayer is between 5 and 50 μm. In another embodiment, the thickness of the high-frequency resin sublayer is between 10 and 25 μm.

In a specific embodiment, the material of the high-frequency resin sublayer is at least one selected from the group consisting of fluorine resin, epoxy resin, acrylic resin, urethane resin, silicone rubber resin, polyparaxylene resin, dimaleimide resin and polyimide resin.

In a specific embodiment, the high-frequency resin sublayer is a thermosetting polyimide-based rubber layer and includes a thermosetting polyimide resin content of 40 to 95 weight percent.

In one specific embodiment, the overall water absorption rate of the composite fluorine-based substrate is between 0.1% and 10%. In another specific embodiment, the overall water absorption rate of the composite fluorine-based substrate is between 0.1% and 0.4%.

In one specific embodiment, the overall thermal expansion coefficient of the composite fluorine-based substrate is between 5 and 40 ppm/°C. In another specific embodiment, the overall thermal expansion coefficient of the composite fluorine-based substrate is between 10 and 20 ppm/°C.

In one specific embodiment, the total thickness of the composite fluorine-based substrate is between 35 and 700 μm. In another specific embodiment, the total thickness of the composite fluorine-based substrate is between 85 and 300 μm.

The present disclosure further provides a method for preparing a composite fluorine-based substrate, comprising:

The first fluorine-based resin layer and the second fluorine-based resin layer are formed on different surfaces of the polyimide sublayer and dried;

Forming the high frequency resin sublayer on the other surface of one of the polyimide sublayers and bonding it to the other surface of another polyimide sublayer; and

High temperature pressing is performed to press the first copper foil layer onto the first fluorine resin layer, and the second copper foil layer onto the second fluorine resin layer.

For high-frequency and high-speed transmission, it is crucial to select materials with low Dk/Df. While meeting the conditions of low transmission loss at millimeter-wave frequencies, it is also necessary to consider how to match materials to facilitate FPC process production and reduce costs. Therefore, the composite fluorine-based substrate disclosed herein, in addition to a fluorine-based resin layer and a copper foil layer, also includes a composite polyimide layer, which is composed of alternating polyimide sublayers and high-frequency resin sublayers. The advantage of this structure is that the low CTE of polyimide can be used to support the overall thermal expansion value of the substrate, so that the substrate has a low thermal expansion coefficient and good dimensional stability. In addition, compared with substrates using only polyimide layers, since the hygroscopicity and Dk/Df of the high-frequency resin in the composite polyimide layer are lower, if the composite polyimide layer is used to replace the polyimide layer as the core layer, in addition to the feature of easily manufacturing a thicker dielectric layer, a substrate with better hygroscopicity and electrical properties can be produced, which can also reduce costs and increase competitive advantages. Therefore, the significant effects brought by the present disclosure include: low cost, short process steps, good electrical properties of the substrate (especially extremely low transmission loss), low CTE, good dimensional stability, stable Dk/Df performance in high temperature and humidity environments, ultra-low water absorption, excellent mechanical properties, and the ability to provide a thicker low-dielectric dielectric layer, etc.

1: Copper foil layer

2: Fluorine resin layer

3: Composite polyimide layer

30: Polyimide sublayer

31: High frequency resin layer

Figure 1 is a schematic diagram of the structure of an embodiment of the composite fluorine-based substrate disclosed herein.

Figure 2 is a schematic structural diagram of another embodiment of the composite fluorine-based substrate disclosed herein.

The following is a specific embodiment to illustrate the implementation of the present disclosure. A person with ordinary knowledge in the technical field to which the present disclosure belongs can easily understand the scope and efficacy of the present disclosure based on the content described in this article. However, the specific embodiments described in this article are not intended to limit the present disclosure. The listed technical features or solutions can be combined with each other. The present disclosure can also be implemented or applied through other different implementation methods. The details described in this article can also be given different changes or modifications based on different viewpoints and applications without deviating from the present disclosure.

It should be noted that the structures, proportions, sizes, etc. depicted in the drawings attached to this specification are only used to match the contents disclosed in the specification for understanding and reading by people familiar with this technology, and are not used to limit the restrictive conditions for the implementation of the present invention. Therefore, they have no substantial technical significance. Any modification of the structure, change of the proportion relationship or adjustment of the size should still fall within the scope of the technical content disclosed by the present invention without affecting the effects and purposes that can be achieved by the present invention. At the same time, the terms such as "above", "first" and "second" used in this specification are only for the convenience of description, and are not used to limit the scope of implementation of the present invention. Changes or adjustments to their relative relationships, without substantial changes to the technical content, should also be regarded as the scope of implementation of the present invention.

When "includes", "comprising" or "having" a specific element in this article, unless otherwise stated, it may also include other elements, components, structures, regions, parts, devices, systems, steps or connections, rather than excluding such other elements.

Unless otherwise expressly stated herein, the singular forms "a", "an" and "the" mentioned herein also include the plural forms, and "or" and "and/or" mentioned herein can be used interchangeably.

The numerical ranges described herein are inclusive and combinable. Any numerical value falling within the numerical range described herein can be used as the maximum or minimum value to derive the sub-range; for example, the numerical range of "2.00 to 3.50" should be understood to include any sub-range between a minimum value of 2.00 and a maximum value of 3.50, such as: 2.00 to 3.00, 2.50 to 3.50, and 2.50 to 3.00. In addition, if a numerical value falls within the ranges described herein (such as between the maximum and minimum values), it should be considered to be included in the scope of the present disclosure.

The composite fluorine-based substrate disclosed herein includes a first copper foil layer, a first fluorine-based resin layer, a composite polyimide layer, a second fluorine-based resin layer, and a second copper foil layer stacked in sequence.

In a specific embodiment, the stacked structure is shown in FIG. 1. The composite fluorine-based substrate includes a copper foil layer 1, a fluorine-based resin layer 2, and a composite polyimide layer 3. The composite polyimide layer 3 in FIG. 1 includes alternating polyimide sublayers 30, high-frequency resin sublayers 31, and polyimide sublayers. In another specific embodiment, the stacked structure is shown in FIG2 , wherein the composite polyimide layer 3 includes five layers of alternating polyimide sublayer 30, high frequency resin rubber sublayer 31, polyimide sublayer 30, high frequency resin rubber sublayer 31 and polyimide sublayer 30.

In the composite fluorine-based substrate disclosed herein, the copper foil layer may be electrolytic copper foil (ED), rolled copper foil (RA), HA foil or HA-V2 foil, and the thickness may be between 6 and 70 μm, or between 12 and 18 μm, such as 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 22, 25, 30, 35, 40, 45, 50, 55, 60, 65, or 70 μm.

In the composite fluorine-based substrate disclosed herein, the Dk value of the fluorine-based resin layer may be between 2.00 and 3.50 (10 GHz), for example, the Dk value may be 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 of the fluorine resin layer may be between 0.0001 and 0.005 (10 GHz), for example, 0.0001, 0.0002, 0.0003, 0.0004, 0.0005, 0.0006, 0.0007, 0.0008, 0.0009, 0.001, 0.0015, 0.002, 0.0025, 0.003, 0.0035, 0.004, 0.0045, or 0.005.

The thickness of the fluorine resin layer can be between 2 and 50 μm, or between 5 and 38 μm, for example, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25, 30, 35, 40, 45, 50 μm.

In order to provide a fluorine-based resin layer with the desired electrical properties, the fluorine-based resin disclosed herein may be selected from at least one of the group consisting of polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyvinyl fluoride (PVF), vinyl fluoride and vinyl ether copolymers, tetrafluoroethylene and ethylene copolymers, polytrifluorochloroethylene (PCTFE or PTFCE) and ethylene-trifluorochloroethylene copolymers (CTFE), ethylene-tetrafluoroethylene copolymers (ETFE), fluoroethylene-propylene copolymers (FEP), tetrafluoroethylene-perfluorovinyl ether copolymers (PFA), polytrifluorochloroethylene, polyvinyl chloride, tetrafluoroethylene-hexafluoropropylene copolymers, ethylene-vinyl fluoride copolymers, and tetrafluoroethylene-hexafluoropropylene-trifluoroethylene copolymers.

In the composite fluorine-based substrate disclosed herein, the Dk value of the polyimide sublayer may be between 2.00 and 3.50 (10 GHz) like the fluorine-based resin layer. For example, the Dk value may be 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 of the polyimide sublayer may be between 0.002 and 0.002 (10 GHz), for example, 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, 0.020.

The thickness of the polyimide sublayer may be between 8 and 100 μm, or between 25 and 90 μm, for example, 8, 9, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, or 100 μm.

In the composite fluorine-based substrate disclosed herein, the Dk value of the high-frequency resin sublayer may also be between 2.00 and 3.50 (10 GHz). For example, the Dk value may be 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. Since the Df of the high-frequency resin sublayer is lower than that of the polyimide sublayer, a Df value between 0.001 and 0.010 (10GHz) is selected to reduce the Df of the overall composite fluorine-based substrate, for example, 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009, or 0.010.

The thickness of the high frequency resin sublayer is between 5 and 50 μm, or between 10 and 25 μm, for example, 5, 10, 15, 20, 25, 30, 35, 40, 45, or 50 μm.

In order to provide a high-frequency resin sublayer with desired electrical properties, the material of the high-frequency resin disclosed herein is selected from at least one of the group consisting of fluorine resin, epoxy resin, acrylic resin, urethane resin, silicone rubber resin, polyparaxylene resin, dimaleimide resin and polyimide resin. In a specific embodiment, the high-frequency resin sublayer is a thermosetting polyimide-based rubber layer, and includes 40 to 95% by weight of polyimide, or 50 to 90% by weight, 60 to 80% by weight of polyimide, for example, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95% by weight of polyimide. The high-frequency resin sublayer may include other resin components and additives, and the other resin components include but are not limited to epoxy resins, fluorine resins, etc., and the additives may be known additives, such as sintered silica, flame retardants, etc.

The composite fluorine-based substrate disclosed herein has excellent low water absorption, specifically, its overall water absorption is between 0.1% and 10%, or 0.1% and 0.4%, for example, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.9%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%. The composite fluorine-based substrate disclosed herein also has excellent low thermal expansion coefficient, specifically, its overall thermal expansion coefficient is between 5 and 40ppm/℃, or 10 to 20ppm/℃, for example, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 20, 25, 30, 35, 40ppm/℃.

The total thickness of the composite fluorine-based substrate disclosed herein can be controlled by adjusting the thickness of each layer as required. Specifically, the total thickness can be between 35 and 700 μm, or between 85 and 300 μm, for example, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, or 700 μm.

In order to obtain the above-mentioned composite fluorine-based substrate, the present disclosure further provides a method for preparing the composite fluorine-based substrate, including:

The first fluorine-based resin layer and the second fluorine-based resin layer are formed on different surfaces of the polyimide sublayer and dried;

Forming the high frequency resin sublayer on the other surface of one of the polyimide sublayers and bonding it to the other surface of another polyimide sublayer; and

High temperature pressing is performed to press the first copper foil layer onto the first fluorine resin layer, and the second copper foil layer onto the second fluorine resin layer.

Taking the preparation of a composite fluorine-based substrate having three composite polyimide layers as shown in Figure 1 as an example, the steps may include:

1. Form a fluorine-based resin layer 2 on one surface of two different polyimide sublayers 30 respectively, and bake them;

2. Then, a high-frequency resin glue sublayer 31 is formed on the other surface of the polyimide sublayer 30 of one of the semi-finished products in step 1, and then the high-frequency resin glue sublayer 31 is bonded to the polyimide sublayer 30 of the other semi-finished product and dried; and

3. Finally, a high temperature pressing process is performed to press the copper foil layer 1 onto the fluorine resin layer 2 to obtain a composite fluorine substrate with a composite polyimide layer 3 as three layers.

The steps for preparing a composite fluorine-based substrate having 5 composite polyimide layers (as shown in Figure 2) may include:

1. Form a fluorine-based resin layer 2 on one surface of two different polyimide sublayers 30 respectively, and bake them;

2. Then, a high-frequency resin sublayer 31 is formed on the other surface of the polyimide sublayer 30 of the semi-finished product in step 1, and the polyimide sublayer 30 is bonded to the high-frequency resin sublayer 31 of one semi-finished product, and then bonded to the high-frequency resin sublayer 31 of the other semi-finished product, and dried; and

3. Finally, a high temperature pressing process is performed to press the copper foil layer 1 onto the fluorine resin layer 2 to obtain a composite fluorine substrate having 5 layers of composite polyimide layer 3.

When preparing a composite polyimide layer with more than 5 layers, the steps may include:

1. Form a fluorine-based resin layer 2 on one surface of two different polyimide sublayers 30 respectively, and bake them;

2. Then, a high frequency resin sublayer 31 is formed on the other surface of the polyimide sublayer 30;

3. Prepare a polyimide sublayer 30 separately, form a high-frequency resin glue sublayer 31 on one surface thereof, adhere an additional polyimide sublayer 30, and dry;

4. If necessary, form a high-frequency resin sublayer 31 on the semi-finished polyimide sublayer 30 of step 3 and adhere an additional polyimide sublayer 30, and dry it. This step can be repeated n times, where n is 0 and a positive integer;

5. Lay the semi-finished product of step 2 to both sides of the semi-finished product of step 4 with a high-frequency resin adhesive sublayer 31 and dry; and

6. Finally, a high temperature pressing process is performed to press the copper foil layer 1 onto the fluorine resin layer 2 to obtain the composite fluorine substrate disclosed herein.

From the above, it can be seen that the composite fluorine-based substrate disclosed in the present invention has the following beneficial effects: in order to solve the transmission loss problem of millimeter wave transmission and solve the common processing problems of LCP substrates, fluorine-based substrates, and composite substrates through a composite structure, a composite polyimide layer is designed to replace the known polyimide film, and a composite fluorine-based substrate with extremely low dielectric loss and dielectric constant (low transmission loss), uniform and low thermal expansion coefficient, excellent transmission performance, and suitable for high temperature or high humidity environment can be obtained. At the same time, the composite fluorine-based substrate can be effectively thickened.

This disclosure will be described in further detail with reference to the following embodiments, however, these embodiments are by no means intended to limit the scope of this disclosure.

Examples 1 to 4 and Comparative Examples 1 to 4

Examples 1 to 4 are composite fluorine-based substrates disclosed herein, and the stacked structures are sequentially a first copper foil layer (product of Futian Company, CF-T49A-DS-HD2), a first fluorine-based resin layer (product of AGC Company, EA-2000), a composite polyimide layer, a second fluorine-based resin layer (product of AGC Company, EA-2000), and a second copper foil layer (product of Futian Company, CF-T49A-DS-HD2).

The composite polyimide layer of Examples 1 and 3 is a three-layer structure of polyimide sublayer/high frequency resin rubber sublayer/polyimide sublayer. The high frequency resin rubber sublayer (Dk=2.9/Df=0.0026) contains 60 wt% of thermosetting polyimide resin, 10 wt% of tetraglycidylamine type epoxy resin, and 20 wt% of Flame retardant (Clariant's product, OP935), 8% by weight of sintered silica (Denka's product, FB-3SDX) and 2% by weight of fluorine resin (DuPont's product, 300AS), and the polyimide sublayer is a product of PIAM (FS, Dk=3.2/Df=0.0038). The thickness of each polyimide sublayer and high-frequency resin sublayer is 25μm.

The composite polyimide layer of Examples 2 and 4 is a five-layer structure of polyimide sublayer/high frequency resin rubber sublayer/polyimide sublayer/high frequency resin rubber sublayer/polyimide sublayer, and the high frequency resin rubber sublayer (Dk=2.9/Df=0.0026) contains 60 wt% of thermal conductivity based on the total weight of each layer. Solid polyimide resin, 20% by weight flame retardant, 10% by weight tetraglycerolamine epoxy resin, 8% by weight sintered silica and 2% by weight fluorine resin, and the polyimide sublayer is a product of PIAM (FS, Dk=3.2/Df=0.0038). The thickness of each polyimide sublayer is 12.5μm, and the thickness of the high-frequency resin sublayer is 25μm.

Comparative Examples 1 and 2 are commercially available LCP substrates (Panasonic products, R-F705S series), which are substrates with two copper foil layers sandwiching an LCP layer, and the laminate does not include a fluorine resin layer, a polyimide sublayer, or a high-frequency resin sublayer. Comparative Examples 3 and 4 are commercially available PI substrates containing a modified fluorine resin layer (Comparative Example 3 is a DuPont TK series substrate, and Comparative Example 4 is a Shirre PT series substrate), which replace the composite polyimide layer of the embodiment with a polyimide (PI) layer, that is, the laminate does not include a high-frequency resin sublayer.

The thickness of each layer, bonding strength, Dk/Df (10GHz), water absorption rate of Examples 1 to 4 and Comparative Examples 1 to 4, and the overall Dk/Df (10GHz), water absorption rate, insertion loss, thermal expansion coefficient, dimensional stability, solder resistance, and maximum shrinkage during laser drilling are all recorded in Table 1 below. The method for obtaining the above values is as follows.

1. Then use a tensile testing machine for strength testing and test according to the IPC-TM-650 2.4.9D standard;

2. The Dk/Df test uses a network analyzer and a resonant cavity and is tested according to the IPC-TM-650 2.5.5.13 standard;

3. The insertion loss test uses a network analyzer and a probe platform and is conducted in accordance with the IPC-TM-650 2.5.5.12 standard;

4. The water absorption test uses the weighing method and is conducted in accordance with the standard of IPC-TM-650 2.6.2;

5. The thermal expansion coefficient test is conducted using a thermomechanical analyzer in accordance with the test specification IPC-TM-650 2.4.41.3;

6. The dimensional stability test uses a two-dimensional coordinate measuring instrument and is conducted in accordance with the IPC-TM-650 2.6.2C standard;

7. The solder resistance test is conducted using a lead-free soldering furnace in accordance with IPC-TM-650 2.4.13; and

8. The maximum shrinkage of the laser drilling hole is observed and recorded using an optical microscope.

Table 1

From the results in Table 1, it can be seen that the composite fluorine-based substrate disclosed in the present invention is configured with a fluorine-based resin layer, a polyimide sublayer, and a high-frequency resin sublayer, combining the advantages of each, and can maintain or have a better Dk/Df value, water absorption, insertion loss, solder resistance, and maximum shrinkage during laser drilling than the comparative example.

1: Copper foil layer

2: Fluorine resin layer

3: Composite polyimide layer

30: Polyimide sublayer

31: High frequency resin layer

Claims (21)

A composite fluorine-based substrate includes a first copper foil layer, a first fluorine-based resin layer, a composite polyimide layer, a second fluorine-based resin layer and a second copper foil layer stacked in sequence, wherein the composite polyimide layer is an odd-numbered layer structure composed of alternating polyimide sublayers and high-frequency resin rubber sublayers, and the outermost layer of the odd-numbered layer structure is the polyimide sublayer, wherein the high-frequency resin rubber sublayer includes a thermosetting polyimide resin with a content of 40 to 95 weight %, and the high-frequency resin rubber sublayer includes a fluorine resin and an epoxy resin. The composite fluorine-based substrate as described in claim 1, wherein the first copper foil layer and the second copper foil layer are respectively electrolytic copper foil, rolled copper foil, HA foil or HA-V2 foil. The composite fluorine-based substrate as described in claim 1, wherein the thickness of the first copper foil layer and the second copper foil layer is between 6 and 70 μm. The composite fluorine-based substrate as described in claim 3, wherein the thickness of the first copper foil layer and the second copper foil layer is between 12 and 18 μm. The composite fluorine-based substrate as described in claim 1, wherein the Dk value of the first fluorine-based resin layer and the second fluorine-based resin layer is between 2.00 and 3.50 (10 GHz), and the Df value is between 0.0001 and 0.005 (10 GHz). The composite fluorine-based substrate as described in claim 1, wherein the thickness of the first fluorine-based resin layer and the second fluorine-based resin layer is between 2 and 50 μm. The composite fluorine-based substrate as described in claim 6, wherein the thickness of the first fluorine-based resin layer and the second fluorine-based resin layer is between 5 and 38 μm. The composite fluorine-based substrate as described in claim 1, wherein the materials of the first fluorine-based resin layer and the second fluorine-based resin layer are selected from at least one of the group consisting of polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyvinyl fluoride (PVF), vinyl fluoride and vinyl ether copolymer, tetrafluoroethylene and ethylene copolymer, polytrifluorochloroethylene (PCTFE or PTFCE) and ethylene-chlorotrifluoroethylene copolymer (CTFE), ethylene-tetrafluoroethylene copolymer (ETFE), fluoroethylene-propylene copolymer (FEP), tetrafluoroethylene-perfluorovinyl ether copolymer (PFA), polyvinyl chloride, tetrafluoroethylene-hexafluoropropylene copolymer, ethylene-vinyl fluoride copolymer, and tetrafluoroethylene-hexafluoropropylene-trifluoroethylene copolymer. The composite fluorine-based substrate as described in claim 1, wherein the Dk value of the polyimide sublayer is between 2.00 and 3.50 (10 GHz), and the Df value is between 0.002 and 0.020 (10 GHz). The composite fluorine-based substrate as described in claim 1, wherein the thickness of the polyimide sublayer is between 8 and 100 μm. The composite fluorine-based substrate as described in claim 9, wherein the thickness of the polyimide sublayer is between 25 and 90 μm. The composite fluorine-based substrate as described in claim 1, wherein the Dk value of the high-frequency resin sublayer is between 2.00 and 3.50 (10 GHz), and the Df value is between 0.001 and 0.010 (10 GHz). The composite fluorine-based substrate as described in claim 1, wherein the thickness of the high-frequency resin sublayer is between 5 and 50 μm. The composite fluorine-based substrate as described in claim 12, wherein the thickness of the high-frequency resin sublayer is between 10 and 25 μm. The overall water absorption rate of the composite fluorine-based substrate described in claim 1 is between 0.1% and 10%. The overall water absorption rate of the composite fluorine-based substrate described in claim 15 is between 0.1% and 0.4%. The composite fluorine-based substrate described in claim 1 has an overall thermal expansion coefficient of 5 to 40 ppm/℃. The composite fluorine-based substrate described in claim 17 has an overall thermal expansion coefficient between 10 and 20 ppm/°C. The total thickness of the composite fluorine-based substrate as described in claim 1 is between 35 and 700 μm. The total thickness of the composite fluorine-based substrate as described in claim 19 is between 85 and 300 μm. A method for preparing a composite fluorine-based substrate as described in claim 1, comprising: forming the first fluorine-based resin layer and the second fluorine-based resin layer on one surface of different polyimide sublayers and drying them; forming the high-frequency resin sublayer on the other surface of one of the polyimide sublayers and bonding it to the other surface of the other polyimide sublayer; and high-temperature pressing to press the first copper foil layer onto the first fluorine-based resin layer and the second copper foil layer onto the second fluorine-based resin layer.

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