Liquid crystal polymer film, preparation method therefor and use thereof

Abstract

The present invention relates to the technical field of liquid crystal polymers (LCPs). Disclosed are an LCP film, a preparation method therefor and a use thereof. The LCP film of the present invention has a surface roughness from 350 nm to 850 nm, and a high-temperature storage modulus G' from 10,000 Pa to 25,000 Pa. By controlling the high-temperature storage modulus and the surface roughness of the LCP film, the LCP film has a certain deformation capability during copper-clad lamination. Meanwhile, a "rivet" effect that occurs when a low-roughness copper foil is laminated with the LCP film is maximized, thereby increasing the adhesion strength between the film and the copper foil. The LCP film has high copper-clad peel force, the peel strength is above 0.7 N / mm, meeting industry standard, and therefore, the LCP film can be applicable to the fields such as flexible printed circuit boards.

Description

Liquid crystal polymer film and its preparation method and application Technical Field

[0001] The present invention relates to the technical field of liquid crystal polymers, and more particularly to a liquid crystal polymer film and a preparation method and application thereof. Background Art

[0002] Liquid crystal polymer (LCP) boasts excellent high-frequency dielectric properties, processing fluidity, high heat resistance, and dimensional stability, making it widely used in the electronics and electrical fields. The 5G commercial era will feature higher electromagnetic wave transmission speeds and reduced signal propagation loss, requiring materials with minimal dielectric constant and dielectric loss. Liquid crystal polymer (LCP) precisely meets these stringent requirements. Therefore, flexible printed circuits (FPCs) based on LCP film have become the optimal material for 5G terminal antennas.

[0003] The high-frequency characteristics of copper foil used for transmission lines, namely transmission loss, depend on the skin effect (surface resistance) and the surface roughness Rz of the copper foil. High-roughness copper foil with a larger Rz exhibits greater transmission loss, meaning poorer high-frequency characteristics. Reducing the Rz of the copper foil helps maintain its excellent high-frequency characteristics. However, if low-roughness copper foil is used to reduce transmission loss by reducing the resistance of the "skin effect," the adhesion strength between the copper foil and the thermoplastic liquid crystal polymer film, namely the copper peel strength, will be insufficient. Improving the copper peel strength between the LCP film and the low-roughness copper foil is a technical difficulty in developing flexible circuit boards using LCP film as a substrate that meet the requirements of high-frequency communications.

[0004] Prior art discloses a method for manufacturing a high-frequency flexible substrate for 5G communications. The method involves plasma-activating an LCP film and copper foil, respectively, and laminating the two to produce the high-frequency flexible substrate. While plasma activation of the LCP film effectively improves the contact angle characteristics of the film surface, it also requires improving the contact angle and roughness of the copper foil. With a copper foil roughness of 1.1 μm, the copper peel strength only reaches 0.5 to 0.7 N / mm, failing to significantly improve the peel strength between the LCP film and the low-roughness copper foil. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the defects and shortcomings of low copper clad peeling strength between the existing LCP film and the low-roughness copper foil, and to provide a liquid crystal polymer film.

[0006] Another object of the present invention is to provide a method for preparing a liquid crystal polymer film.

[0007] Another object of the present invention is to provide an application of a liquid crystal polymer film in the preparation of a flexible circuit board.

[0008] Another object of the present invention is to provide a copper clad laminate.

[0009] The above-mentioned purpose of the present invention is achieved through the following technical solutions:

[0010] A liquid crystal polymer film has a surface roughness of 350nm-850nm, a high-temperature storage modulus G' of 10000-25000Pa, and a test temperature of the high-temperature storage modulus is the melting point of the film.

[0011] Among them, it should be noted that:

[0012] The surface roughness of the liquid crystal polymer film of the present invention is determined by measuring the surface of the LCP film using an atomic force microscope (AFM), yielding Figure 1. The difference d between the maximum and minimum surface roughness values ​​of the film is obtained. The average of the d values ​​obtained from testing five different areas of each sample represents the surface roughness of the LCP film.

[0013] The high-temperature deformation ability of the liquid crystal polymer film LCP film of the present invention is reflected by the high-temperature storage modulus, which is measured by the following method:

[0014] The test was carried out using a rotational rheometer.

[0015] The sample was kept at the film melting point for 3 minutes before measurement. The test temperature was the copper cladding pressing temperature, i.e. the film melting point, and the test frequency was 50 rad / s.

[0016] By controlling the high-temperature storage modulus G' of the LCP film to be between 10000-25000Pa, the bonding strength between the LCP film and the copper foil can be improved. It is speculated that the reason is that by controlling the high-temperature rough energy modulus G' of the LCP film (that is, controlling the high-temperature deformation ability of the LCP film), the deformation degree of the LCP film can be within a certain range when it is at the copper cladding pressing temperature. The purpose of controlling the degree of deformation is to allow the LCP film and the copper foil to fit better when pressed together. If the degree of deformation is too large, the fluidity will be too good, which will affect the maintenance of roughness, and thus affect the matching of the surface morphology of the copper foil and the LCP film. In addition, if the degree of deformation is too large, it will also cause changes in the thickness of the film, resulting in poor local thickness uniformity, and ultimately affecting the signal transmission stability of the subsequent circuit board.

[0017] The purpose of controlling the surface roughness of the LCP film is to ensure that the low-roughness copper foil and the LCP film surface can be more firmly bonded during the copper lamination process through a "rivet" effect. If the roughness is too small, the "rivet" effect will not work. If the roughness is too large, the surface morphology of the low-roughness copper foil and the LCP film will not match, the "rivet" effect will be weakened, and the bonding strength between the LCP film and the copper foil will also deteriorate.

[0018] The present invention controls the high-temperature storage modulus and surface roughness of the LCP film so that the LCP film has a certain deformation ability when copper cladding is pressed. At the same time, the "rivet" effect when the low-roughness copper foil is pressed against the LCP film is maximized, thereby increasing the bonding strength between the film and the copper foil, and realizing the preparation of an LCP film with high copper cladding peeling force.

[0019] The liquid crystal polymer film of the present invention has a specific LCP film surface roughness and high-temperature deformation ability, can achieve high peel strength between the LCP film and high-frequency copper foil, and the peel strength can reach up to 0.95N / mm, and can be applied to fields such as flexible circuit boards.

[0020] In a specific embodiment, the surface roughness of the liquid crystal polymer film of the present invention can be 360 ​​nm, 400 nm, 450 nm, 500 nm, 550 nm, 600 nm, 650 nm, 700 nm, 750 nm, 800 nm, 50 nm, etc.

[0021] In a specific embodiment, the high temperature storage modulus G' of the liquid crystal polymer film of the present invention can be 12000Pa, 14000Pa, 16000Pa, 18000Pa, 20000Pa, 22000Pa, 24000Pa, etc.

[0022] Preferably, the surface roughness of the liquid crystal polymer film is 450-750 nm, more preferably 590-680 nm.

[0023] Preferably, the high temperature storage modulus G' of the liquid crystal polymer film is 14000-21000 Pa, more preferably 14500-16000 Pa.

[0024] The high temperature of the high temperature storage modulus of the liquid crystal polymer film of the present invention is the melting point of the liquid crystal polymer film, which ranges from 270-320°C, more preferably 283-310°C, for example, 270°C, 280°C, 290°C, 300°C, 310°C or 320°C.

[0025] The liquid crystal polymer film of the present invention has a melting point of 270-320° C. and has a wide melting point range, which can meet the requirements of LCP films with different melting points in downstream applications.

[0026] In a specific embodiment, the polymerization monomers of the liquid crystal polymer film of the present invention are p-hydroxybenzoic acid HBA and 2-hydroxy-6-naphthoic acid HNA, wherein the molar ratio of HBA to HNA is (65-85): (15-35).

[0027] The present invention further specifically protects a method for preparing a liquid crystal polymer film, comprising the following steps:

[0028] The LCP film-grade resin is blown into a film to obtain an LCP original film, and then the LCP film is laminated with an aluminum foil, subjected to a high-temperature heat treatment, the aluminum foil is peeled off, and the liquid crystal polymer film is obtained through surface treatment.

[0029] Among them, it should be noted that:

[0030] In the method for preparing a liquid crystal polymer film of the present invention, the surface treatment is performed to further adjust the surface roughness of the LCP film. The method for adjusting the surface roughness of the film is not particularly limited, and generally, surface treatment methods that can be used include sandblasting, grinding, alkaline etching, or laser treatment.

[0031] In a specific embodiment, the liquid crystal film meeting the high-temperature storage modulus of the present invention can be controlled by any method known in the art, such as adjusting the die flow channel structure, stretch ratio, and blow-up ratio during the LCP raw film forming stage, the heat treatment process during the film heat treatment stage, or adjusting the formulation, such as adding a toughening agent. The stretch ratio refers to the ratio of the speed of the traction roller to the speed of the LCP film bubble leaving the forming die during the blow molding process of the LCP raw film, and the blow-up ratio refers to the ratio of the diameter of the LCP raw film to the diameter of the die.

[0032] Specifically, the high-temperature storage modulus liquid crystal polymer film of the present invention can be prepared by the following process: extruding a molten LCP resin to form a film bubble, which is then drawn, extruded, pulled out, and wound to form an LCP film. The LCP film is then laminated to aluminum foil at a temperature 20-80°C below the film's melting point, at a lamination pressure of 2-4 MPa, to form an LCP / Al laminate. The Al layer is then removed after heat treatment, and both surfaces of the LCP film are roughened.

[0033] Preferably, the stretching ratio in the LCP original film preparation stage is 2.5-5.5, the heat treatment temperature is Tm-8°C to Tm+20°C, where Tm is the melting point of the film, and the heat treatment time is 0.02 to 20 minutes.

[0034] More preferably, the stretching ratio in the LCP original film preparation stage is 3 to 4.5.

[0035] More preferably, the heat treatment temperature is Tm to Tm+15° C., wherein Tm is the melting point of the film.

[0036] More preferably, the heat treatment time is 1 to 10 minutes.

[0037] LCP film-grade resin is a mixture of one or more liquid crystal polymer polyesters and processing aids, wherein the liquid crystal polymer polyesters have different melting points.

[0038] The processing aid of the present invention may include an antioxidant, a lubricant, a toughening agent, a light stabilizer, etc., and the content of the processing aid is 0.2 to 5 wt%.

[0039] The amount of the high molecular weight liquid crystal polyester is preferably ≥90 wt%, more preferably 99-100 wt%. The melting point of the liquid crystal polyester is generally 270-320°C, and in some embodiments, 280-310°C.

[0040] The liquid crystal high molecular weight polyester used in the present invention has the following repeating units, wherein Ring A can be formed by condensing a 6-membered aromatic group with a 6-membered aromatic group, such as 2-hydroxy-6-naphthoic acid. R1 and R2 can be C=O, C=O-NH, O, or NH-C=O. Examples of aromatic ester repeating units include, for example, aromatic dicarboxyl repeating units (terephthalic acid, terephthalic acid, etc.), aromatic dihydroxy repeating units (biphenol, hydroquinone, etc.), aromatic hydroxycarboxyl repeating units (p-hydroxybenzoic acid, 2-hydroxy-6-naphthoic acid, etc.), and various combinations thereof.

[0041] n is 50-200, preferably 80-150.

[0042] Particularly preferred monomers are the aromatic hydroxycarboxyl monomers p-hydroxybenzoic acid (HBA) and 2-hydroxy-6-naphthoic acid (HNA). When HBA and HNA are used as the main polymeric units, the molar content of the aromatic hydroxycarboxyl monomer is about 40 mol %, about 75 mol % or higher in some embodiments, and about 90 mol % or higher in some embodiments.

[0043] The liquid crystal polymer polyester used in the present invention can be purchased or prepared by existing technology, or can be prepared by the following method:

[0044] The polymer monomers HBA and HNA are mixed, acetic anhydride acylating agent is added, reflux reaction is carried out, and the reaction by-product acetic acid begins to be produced.

[0045] After the acylation reaction is completed, the temperature is raised to 200°C to 400°C at a heating rate of 0.5-6°C / min, and the acetic acid and unreacted raw material small molecules are discharged from the distillation column. Then, the internal pressure of the reactor is reduced to below 10kPa, and this pressure is maintained. The material is discharged and pelletized to obtain LCP resin.

[0046] The present invention also specifically protects a use of the liquid crystal polymer film in preparing a flexible circuit board.

[0047] After the liquid crystal polymer film of the present invention is hot-pressed and copper-clad with high-frequency copper foil, the copper-clad peeling force of the LCP film is above 0.7 N / mm, which meets the industry application standards and can be widely used in the flexible circuit board industry.

[0048] The present invention also specifically protects a copper clad laminate, which comprises the liquid crystal polymer film and copper foil laminated together.

[0049] The roughness Rz of the copper foil is ≤ 1.0 μm and / or the thickness of the copper foil is 13 to 15 μm. Rz may preferably be 0.9 μm, 0.6 μm, etc.

[0050] In a specific embodiment, the liquid crystal polymer film of the present invention has a thickness of 25-100 μm and has good copper clad peel strength. It can also have good adhesion strength to copper foil with low roughness, such as high-frequency copper foil with Rz of 0.9 to 1.0 μm, thereby improving the adhesion strength between the LCP film and the high-frequency copper foil and reducing the high-frequency transmission loss of the prepared circuit board.

[0051] The thickness of the liquid crystal polymer film can be measured by the following method:

[0052] Using a digital thickness meter (manufactured by Mitutoy Co., Ltd.), the thickness of the LCP film was measured at intervals of 1 cm along the flow direction (TD) and the direction perpendicular to the flow direction (MD). The film thickness was measured at 30 points along the MD and TD directions, and the average value of 10 points was arbitrarily selected and set as the average film thickness.

[0053] The copper-clad laminate of the present invention can be selectively etched to remove the copper foil to obtain a flexible circuit board. Based on the copper-clad laminate prepared by the present invention, the flexible circuit board obtained by further processing can be widely used in 5G mobile terminals, such as mobile phones, communication radars and antennas required for base stations.

[0054] Compared with the prior art, the present invention has the following beneficial effects:

[0055] The liquid crystal polymer film of the present invention has a surface roughness of 350nm-850nm and a high-temperature storage modulus G' of 10,000-25,000Pa. By controlling the high-temperature storage modulus and surface roughness of the LCP film, the LCP film has a certain deformation ability when copper-clad and pressed. At the same time, the "rivet" effect when the low-roughness copper foil is pressed with the LCP film is maximized, thereby increasing the bonding strength between the film and the copper foil. The film has a high copper-clad peeling force, and the peeling strength can reach up to 0.95N / mm. The film is suitable for fields such as flexible circuit boards. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 is the AFM surface morphology of the LCP film.

[0057] Figure 2 is a schematic diagram of the LCP film manufacturing process. DETAILED DESCRIPTION

[0058] The present invention will be further described below in conjunction with specific embodiments, but the examples do not limit the present invention in any form. Unless otherwise specified, the raw materials and reagents used in the examples of the present invention are conventionally purchased raw materials and reagents.

[0059] The specific methods for testing various properties in the embodiments and comparative examples of the present invention are as follows:

[0060] 1: The melting point of the above-mentioned liquid crystal polymer is 260-320°C. The melting point is measured using DSC200F3 manufactured by NETZSCH Company at a heating rate of 20°C / min. The temperature is raised to 30°C above the melting point and then kept for 5 minutes to eliminate the thermal history. The melting point Tm is obtained by taking the curve of the second heating.

[0061] 2. Film surface roughness measurement method: The surface of the LCP film was measured using a Bruker Dimension FastScan Bio atomic force microscope (AFM), as shown in Figure 2. The measurement range was 90 x 90 x 10 μm, and the scanning speed was 0.5 Hz.

[0062] The difference d between the maximum and minimum values ​​of the film surface undulation. The average value of d obtained from testing 5 different areas of each sample is the surface roughness of the LCP film.

[0063] 3: High-temperature storage modulus testing was performed using a rotational rheometer (Discovery DHR 2, TA Co., Ltd.). The fixed strain was 0.5%. The heat-treated LCP film was cooled to room temperature. The sample was then held at the film's melting point for 3 minutes before measurement. The test temperature was the film's melting point, and the test frequency was 50 rad / s.

[0064] 4: Copper clad peel strength test: LCP film and high-frequency copper foil (Rz = 1.0μm) were hot-pressed near the film melting point to form a copper-clad laminate at a composite pressure of 3MPa. Five 10mm wide strips were cut from the copper-clad laminate and the copper peel strength of the copper-clad laminate was tested according to GB / T 13542.2-2009.

[0065] According to the peel force F, LCP films are classified as follows:

[0066] F≥0.85 is “excellent”, 0.7≤F<0.85 is “good”, 0.6≤F<0.7 is “qualified”, and F<0.6 is “unqualified”.

[0067] Example 1

[0068] A liquid crystal polymer film has a surface roughness of 510 nm, a high-temperature storage modulus G' of 16300 Pa, and a melting point of 283°C.

[0069] The preparation process of the liquid crystal polymer film is shown in FIG2 . The preparation method includes the following steps:

[0070] The LCP molten resin with a Tm of 283°C is extruded from an annular die to form a bubble. Under the action of traction rollers, the bubble is flattened after reaching the herringbone plate and pulled out and guided by guide rollers to finally obtain an LCP film with a stretch ratio of 4.1 and a film thickness of 50 microns. The LCP film is then laminated to aluminum foil at 80°C below the film's melting point and a lamination pressure of 3 MPa to obtain an LCP / Al laminate. After heat treatment in a high-temperature furnace, the Al layer is peeled off, and both sides of the LCP film are treated by a grinding surface treatment method at a heat treatment temperature of Tm + 5°C for 4 minutes.

[0071] The results were as follows:

[0072] The resulting LCP film had a high-temperature storage modulus of 16,300 Pa and a surface roughness of 510 nm. The polished surface of the LCP film was laminated to a high-frequency copper foil at a lamination temperature equal to the LCP film's melting point and a lamination pressure of 3 MPa. Testing revealed a peel force of 0.86 N / mm. The copper foil had a roughness Rz of 0.9 μm.

[0073] Wherein, the preparation method of LCP resin is as follows:

[0074] The molar ratio of the polymerized monomers HBA and HNA was adjusted from 65:35 to 80:20 to obtain LCP film-grade resins with different melting points. After the two monomers were blended, acetic anhydride acylating agent was added and the mixture was refluxed at 240°C for 2 hours to start the production of the reaction byproduct acetic acid.

[0075] After the acylation reaction is completed, the temperature is increased to 300°C at a heating rate of 3°C / min to discharge acetic acid and unreacted raw material small molecules from the distillation column. Then, the internal pressure of the reactor is reduced to below 10 kPa and maintained at this pressure. The material is discharged and pelletized to obtain LCP resin.

[0076] The LCP film-grade resins having melting points of 270°C, 283°C and 310°C respectively adopt liquid crystal polymer polyesters having melting points of 270°C, 283°C and 310°C.

[0077] The preparation methods of LCP resins with different melting points are the same. The difference lies in the different molar ratios of the polymerization monomers HBA and HNA, specifically:

[0078] The molar ratio of the polymerized monomers HBA and HNA of the LCP film-grade resin with a melting point of 270°C is 69:31;

[0079] The molar ratio of the polymerized monomers HBA and HNA of the LCP film-grade resin with a melting point of 283°C is 73:27;

[0080] The molar ratio of the polymerized monomers HBA and HNA of the LCP film-grade resin with a melting point of 310°C is 79:21;

[0081] The LCP film-grade resin with a melting point of 293° C. is a composition of two liquid crystal polymer polyester resins with melting points of 283° C. and 310° C., which are mixed in a mass ratio of 80%:20%.

[0082] Examples 2 to 14

[0083] A liquid crystal polymer film. The surface roughness, high-temperature storage modulus and melting point of the liquid crystal polymer film are shown in Table 1.

[0084] In Example 13, the amount of the toughening agent added to the LCP film-grade resin composition is 4%. In the remaining examples, the amount of the toughening agent added to the LCP film-grade resin composition is 2%.

[0085] The preparation method of the above liquid crystal polymer film is basically the same as that of Example 1, wherein Example 13 uses an LCP film with a thickness of 100 μm, and the other examples use an LCP film with a thickness of 50 μm. Specific parameters are detailed in Table 1.

[0086] Example 15

[0087] A liquid crystal polymer film has a surface roughness of 510 nm, a high-temperature storage modulus G' of 16300 Pa, and a melting point of 283°C.

[0088] The preparation method of the above-mentioned liquid crystal polymer film includes the following steps: melting LCP particles with Tm=283°C to obtain an LCP melt, extruding the LCP melt through a T-shaped slit die, stretching it through a steel roller, and winding it to obtain an LCP film, thereby obtaining an LCP film with a stretch ratio of 2.2 and a thickness of 25 microns.

[0089] The LCP film and aluminum foil were then laminated at 80°C below the film's melting point, with a lamination pressure of 3 MPa, to form an LCP / Al laminate. After heat treatment in a high-temperature furnace, the Al layer was peeled off, and both sides of the LCP film were sandblasted. The heat treatment temperature used was 283°C for 10 minutes.

[0090] The peeling strength of the thin film copper coating was tested to be 0.86N / mm, which was rated as excellent.

[0091] Example 16

[0092] A liquid crystal polymer film has a surface roughness of 510 nm, a high-temperature storage modulus G' of 16300 Pa, and a melting point of 283°C.

[0093] The above-mentioned method for preparing a liquid crystal polymer film includes the following steps: dissolving LCP resin in a 100°C pentafluorophenol solvent to obtain a solution. This solution is then poured into a glass mold while still hot. The mold is then baked in a 150°C vacuum oven for 48 hours to remove the pentafluorophenol solvent. Finally, the film prepared by the casting method is peeled from the mold to obtain an approximately 25μm thick LCP film. Finally, both surfaces of the LCP film are sandblasted.

[0094] The copper cladding peeling force was tested to be 0.84N / mm, which was rated as excellent.

[0095] Comparative Example 1

[0096] A liquid crystal polymer film has a surface roughness of 576 nm, a high-temperature storage modulus G' of 9240 Pa, and a melting point of 283°C.

[0097] The method for preparing the liquid crystal polymer film comprises the following steps:

[0098] The LCP molten resin with a Tm of 283°C is extruded from an annular die to form a film bubble. Under the action of the traction roller, after reaching the herringbone plate, the film bubble is flattened and pulled out and guided by the guide roller for winding, finally obtaining an LCP film with a stretch ratio of 2.2 and a film thickness of 50 microns. The LCP film is then laminated to an aluminum foil film at 80°C below its melting point, with a lamination pressure of 3MPa, to obtain an LCP / Al laminate. After heat treatment in a high-temperature furnace, the Al layer of aluminum foil is peeled off, and then both sides of the LCP film are treated by a grinding surface treatment method. The heat treatment temperature used is Tm+25°C and the time is 4 minutes.

[0099] The results were as follows:

[0100] The resulting LCP film had a high-temperature storage modulus of 9240 Pa and a surface roughness of 576 nm. The LCP film was laminated to a high-frequency copper foil at a temperature equal to the LCP film's melting point and a pressure of 3 MPa. The peel strength of the copper foil was 0.54 N / mm.

[0101] The roughness Rz of the copper foil was 0.9 μm.

[0102] Comparative Examples 2 to 5

[0103] A liquid crystal polymer film. The surface roughness, high-temperature storage modulus and melting point of the liquid crystal polymer film are shown in Table 2.

[0104] The preparation method of the above liquid crystal polymer film is basically the same as that of Comparative Example 1. The thickness of the LCP film is 50 μm. Specific parameters are shown in Table 2.

[0105] As can be seen from the data in Tables 1 and 2, the present invention significantly enhances the "rivet" effect when laminating the LCP film to the high-frequency copper foil by controlling the surface roughness of the LCP film to 350nm-850nm and the high-temperature storage modulus G' to 10,000-25,000Pa. This improves the interfacial bonding strength between the LCP film and the copper foil and enhances the copper peel force between the LCP film and the copper foil. The copper peel force between the LCP film and the high-frequency copper foil exceeds 0.7N / mm, reaching 0.71-0.95N / mm, meeting industry standards.

[0106] However, the high-temperature storage modulus G' of the liquid crystal polymer film in Comparative Example 1 is lower than 10,000 Pa, and the high-temperature storage modulus G' of the liquid crystal polymer film in Comparative Example 2 is higher than 25,000 Pa. Therefore, the final copper peeling force of the film can only reach 0.54 to 0.67 N / mm, and cannot reach a copper peeling force of 0.7 N / mm or above.

[0107] The surface roughness of the liquid crystal polymer films in Comparative Examples 3 and 5 was too low or too high, and the copper peeling force of the present invention could not be achieved. The copper peeling force was only 0.57 to 0.63 N / mm.

[0108] The surface roughness and high-temperature storage modulus G' of the liquid crystal polymer film in Comparative Example 4 both exceeded the protection range, and the final copper cladding peeling force thereof was the lowest, only 0.43 N / mm.

[0109] Obviously, the above embodiments of the present invention are merely examples for the purpose of clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description. It is not necessary and impossible to enumerate all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the claims of the present invention.

Claims

1. A liquid crystal polymer film, characterized in that, The surface roughness of the liquid crystal polymer film is 350 nm - 850 nm, and the high-temperature storage modulus G' is 10,000 - 25,000 Pa, where the high temperature is the melting point of the film.

2. The liquid crystal polymer film according to claim 1, wherein The surface roughness of the liquid crystal polymer film is 450 - 750 nm, more preferably 590 - 700 nm.

3. The liquid crystal polymer film according to claim 1, wherein, The high-temperature storage modulus G' of the liquid crystal polymer film is 14,000 - 21,000 Pa, more preferably 14,800 - 16,000 Pa.

4. The liquid crystal polymer film according to claim 1, wherein, The melting point of the liquid crystal polymer film is 270 - 320 °C.

5. The liquid crystal polymer film according to claim 1, wherein, The polymerization monomers of the liquid crystal polymer film are p-hydroxybenzoic acid (HBA) and 2-hydroxy-6-naphthoic acid (HNA), and the molar ratio of HBA to HNA is (65 - 85):(15 - 35).

6. A method for preparing the liquid crystal polymer film according to any one of claims 1 to 5, characterized in that, It includes the following steps: Blow-mold the LCP film-grade resin to obtain the LCP original film, then laminate the LCP original film with aluminum foil, and then perform high-temperature heat treatment, peel off the aluminum foil, and obtain the liquid crystal polymer film through surface treatment.

7. The preparation method of the liquid crystal polymer film according to claim 6, characterized in that, The surface treatment includes any one of sandblasting treatment, grinding treatment, alkali etching, or laser treatment.

8. Use of the liquid crystal polymer film according to any one of claims 1 to 5 in the preparation of a flexible printed circuit board.

9. A copper clad laminate, characterized in that, The copper-clad laminate comprises the liquid crystal polymer film according to any one of claims 1 to 5 laminated with copper foil.

10. The copper clad laminate according to claim 11, wherein, The roughness Rz of the copper foil is ≤ 1.0 μm and / or the thickness of the copper foil is 13 - 15 μm.

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