A high heat-resistant high-frequency coating film for multilayer boards and its preparation method

Abstract

This invention discloses a high-heat-resistant high-frequency cover film for multilayer boards and its preparation method. The high-heat-resistant high-frequency cover film for multilayer boards includes an adhesive film layer and a release layer. The adhesive film layer includes a substrate layer and an adhesive layer. The adhesive layer is disposed on the lower surface of the substrate layer and contains adhesive. The release layer is pressed onto the lower surface of the adhesive layer. The adhesive is composed of the following components in weight percentage: 15-45 parts of high-Tg polyimide resin; 5-40 parts of maleimide resin; 0.5-2.0 parts of latent curing agent; 0.5-1.5 parts of silane coupling agent; 30-60 parts of low-dielectric inorganic filler; and 5-15 parts of flame retardant. The high-heat-resistant high-frequency cover film for multilayer boards provided by this invention has excellent high-temperature solderability, excellent dielectric properties, highly precise controlled characteristic impedance, low water absorption, and good machinability and dimensional stability.

Description

Technical Field

[0001] This invention relates to the field of flexible electronic materials technology, and in particular to a high heat-resistant high-frequency cover film for multilayer boards and its preparation method. Background Technology

[0002] With the rapid development of 5G communication, the Internet of Things, and automotive electronics, the application scenarios of flexible printed circuit boards (FPCs) and rigid-flex multilayer boards are becoming increasingly complex. Coverlays, as key materials protecting the insulation and mechanical properties of FPC surface circuitry, directly determine the reliability and signal transmission quality of the circuit board. In high-frequency and high-speed applications, coverlays need to possess low dielectric constant (Dk) and low dielectric loss (Df) to reduce signal transmission delay and loss. While existing polyimide (PI)-based coverlays have good heat resistance, their dielectric properties (Dk approximately 3.5, Df approximately 0.008) are insufficient to meet the requirements of the 5G millimeter-wave band. Although polytetrafluoroethylene (PTFE) or liquid crystal polymer (LCP) materials possess excellent high-frequency characteristics, PTFE has low surface energy and is difficult to bond, while LCP is expensive and has weak interlayer adhesion. In addition, with the popularization of lead-free soldering processes, multilayer boards need to withstand instantaneous thermal shocks of 260°C or even higher (288°C) during reflow soldering. Existing high-frequency cover films are prone to delamination, blistering, warping, or a significant decrease in adhesive strength after experiencing multiple high-temperature thermal shocks. Summary of the Invention

[0003] The purpose of this invention is to provide a high heat resistance high frequency cover film for multilayer boards, so as to solve the problem that existing cover films are difficult to have both high frequency performance and high heat resistance.

[0004] This invention is achieved through the following technical solution: A high-heat-resistant high-frequency cover film for multilayer boards includes an adhesive film layer and a release layer. The adhesive film layer includes a substrate layer and an adhesive layer. The adhesive layer is disposed on the lower surface of the substrate layer and contains an adhesive. The release layer is pressed onto the lower surface of the adhesive layer. The adhesive is composed of the following components in weight percentage: 15-45 parts of high Tg polyimide resin; 5-40 parts of maleimide resin; 0.5–2.0 parts of latent curing agent; 0.5–1.5 parts of silane coupling agent; 30-60 parts of low-dielectric inorganic filler; 5-15 parts flame retardant; The sum of the mass percentages of the above components is 100%.

[0005] Furthermore, the adhesive is prepared by the following method: S11: Add high Tg polyimide resin, maleimide resin, curing agent, coupling agent, and flame retardant to the solvent according to the mass percentage, and stir to dissolve; S12: Then add low dielectric inorganic filler, disperse and grind at high speed to a fineness of <5μm to obtain adhesive.

[0006] Furthermore, in step S12, at a test temperature of 25°C, the viscosity of the adhesive is 800–1200 mPa·s.

[0007] Furthermore, the thickness of the substrate layer is 8–50 μm, the thickness of the adhesive layer is 8–50 μm, and the thickness of the release layer is 110–150 μm.

[0008] Furthermore, the substrate layer is a polyimide film, and the release layer is release paper.

[0009] Furthermore, the high Tg polyimide resin is SP1T05H polyimide resin produced by Yinxing Technology; the maleimide resin is BMI-200 resin produced by Daika Ruion; the latent curing agent is 2E4MZ-CN produced by Shikoku Chemical; the silane coupling agent is KH-560 produced by Shin-Etsu Chemical; the low dielectric inorganic filler is Admafine SO series, hydrophobically treated spherical silica; and the flame retardant is magnesium hydroxide produced by Dongguan Hongtai Flame Retardant Materials Co., Ltd.

[0010] To address the problem that existing cover films cannot simultaneously possess high-frequency performance and high heat resistance, the present invention aims to provide a high-heat-resistant high-frequency cover film for multilayer boards. Accordingly, a method for preparing the aforementioned high-heat-resistant high-frequency cover film for multilayer boards is provided. The specific steps are as follows: S1: Preparation of adhesive: S11: Add high Tg polyimide resin, maleimide resin, curing agent, coupling agent, and flame retardant to the solvent by mass percentage and stir to dissolve; S12: Add low-dielectric inorganic filler according to the mass percentage, disperse and grind at high speed until the fineness is <5μm to obtain the adhesive; The total mass percentage of high Tg polyimide resin, maleimide resin, curing agent, coupling agent, flame retardant and low dielectric inorganic filler is 100%. S2: The prepared adhesive is evenly coated from the inside to the outside onto the lower surface of the substrate layer, and after drying, an adhesive film layer is obtained. S3: Apply release paper to the underside of the adhesive layer and press it together.

[0011] Further, in step S1, the high Tg polyimide resin, maleimide resin, curing agent, coupling agent, flame retardant, and low dielectric inorganic filler are expressed as follows by mass percentage: 15-45 parts of high Tg polyimide resin; 5-40 parts of maleimide resin; 0.5–2.0 parts of latent curing agent; 0.5–1.5 parts of silane coupling agent; 30-60 parts of low-dielectric inorganic filler; 5-15 parts flame retardant; The sum of the mass percentages of the above components is 100%.

[0012] Furthermore, in step S11, one of butanone or cyclohexanone is used as a solvent.

[0013] Further, in step S2, the coating speed is 10-30 m / min and the drying temperature is 140-180℃; in step S3, the pressing temperature is 40-100℃, the pressing pressure is 0.1-0.4 MPa, and the high-temperature pressing linear speed is 10-30 m / min.

[0014] The advantages of this technical solution are: High heat-resistant high-frequency cover film for multilayer boards has excellent high-temperature solderability and can improve problems such as delamination, blistering, warping or significant decrease in bond strength that easily occur in multilayer boards.

[0015] High heat-resistant high-frequency cover film for multilayer boards has excellent dielectric properties, with low dielectric constant (Dk) and dielectric loss tangent (Df), and can maintain its stability when environmental conditions such as temperature, frequency, and humidity change. The high heat-resistant high-frequency cover film for multilayer boards has a high-precision controlled characteristic impedance. The high heat-resistant high-frequency cover film for multilayer boards has low water absorption, good machinability and dimensional stability, copper foil peel strength (1 / 2OZ) > 1.0 N / mm, and flame retardancy reaches UL94V-0 level. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1This is a schematic diagram of the structure of a high heat-resistant high-frequency cover film for multilayer boards according to an embodiment of the present invention; Figure 2 This is a flowchart of a method for preparing a high heat-resistant high-frequency cover film for multilayer boards according to an embodiment of the present invention. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] Example 1: As Figure 1 As shown, this high heat-resistant high-frequency cover film for multilayer boards includes an adhesive film layer 1 and a release layer 2. The adhesive film layer 1 includes a substrate layer 11 and an adhesive layer 12. The adhesive layer 12 is disposed on the lower surface of the substrate layer 11 and contains adhesive. The release layer 2 is pressed onto the lower surface of the adhesive layer 12. The adhesive is composed of the following components by mass percentage: 15-45 parts of high Tg polyimide resin; 5-40 parts of maleimide resin; 0.5–2.0 parts of latent curing agent; 0.5–1.5 parts of silane coupling agent; 30-60 parts of low-dielectric inorganic filler; 5-15 parts flame retardant; The sum of the mass percentages of all components is 100%.

[0020] The adhesive uses high-Tg polyimide as the base resin, avoiding the complex effects of fine-tuning the ratio between various resins on viscosity and rheology, eliminating compatibility issues, and ensuring high uniformity of the adhesive during storage and coating processes.

[0021] Among them, optimizing the ratio of high Tg polyimide to maleimide can form a highly dense three-dimensional network structure. The thermal decomposition temperature (Td5%) of the three-dimensional network structure exceeds 370℃, which is much higher than the peak temperature of lead-free reflow soldering (260-288℃).

[0022] In Example 1 of this invention, the adhesive is prepared by the following method: S11: Add high Tg polyimide resin, maleimide resin, curing agent, coupling agent, and flame retardant to the solvent according to the mass percentage, and stir to dissolve; S12: Then add low dielectric inorganic filler, disperse and grind at high speed to a fineness of <5μm to obtain adhesive.

[0023] In Embodiment 1 of the present invention, in step S12, at a test temperature of 25°C, the viscosity of the adhesive is 800-1200 mPa·s.

[0024] In Embodiment 1 of the present invention, the thickness of the substrate layer 11 is 8-50 μm, the thickness of the adhesive layer 12 is 8-50 μm, and the thickness of the release layer 2 is 110-150 μm.

[0025] In Embodiment 1 of the present invention, the substrate layer 11 is a polyimide film and the release layer 2 is release paper.

[0026] In Example 1 of this invention, the high Tg polyimide resin selected is SP1T05H polyimide resin produced by Yinxing Technology.

[0027] In Example 1 of this invention, the maleimide resin used is BMI-200 resin produced by Daika Ruiweng.

[0028] In Example 1 of this invention, the latent curing agent selected is model 2E4MZ-CN manufactured by Shikoku Chemical.

[0029] In Example 1 of this invention, the silane coupling agent selected is KH-560 produced by Shin-Etsu Chemical.

[0030] In Embodiment 1 of this invention, the low-dielectric inorganic filler selected is Admafine SO series, spherical silica that has undergone hydrophobic treatment.

[0031] In Example 1 of this invention, the flame retardant used is magnesium hydroxide produced by Dongguan Hongtai Flame Retardant Materials Co., Ltd.

[0032] Embodiment 1 of the present invention also provides a method for preparing a high heat-resistant high-frequency cover film for multilayer boards, used to prepare a high heat-resistant high-frequency cover film for multilayer boards, such as... Figure 2 As shown, the preparation method includes the following steps: S1: Preparation of adhesive: S11: Add high Tg polyimide resin, maleimide resin, curing agent, coupling agent, and flame retardant to the solvent by mass percentage and stir to dissolve; S12: Add low-dielectric inorganic filler according to the mass percentage, disperse and grind at high speed until the fineness is <5μm to obtain the adhesive; The total mass percentage of high Tg polyimide resin, maleimide resin, curing agent, coupling agent, flame retardant and low dielectric inorganic filler is 100%. S2: The prepared adhesive is uniformly coated from the inside to the outside onto the lower surface of the substrate layer 11, and after drying, an adhesive film layer 1 is obtained. S3: Apply release paper to the lower surface of adhesive layer 12 and press it together to obtain release layer 2.

[0033] Specifically, in step S1, the high Tg polyimide resin, maleimide resin, curing agent, coupling agent, flame retardant, and low dielectric inorganic filler are expressed as follows by mass percentage: 15-45 parts of high Tg polyimide resin; 5-40 parts of maleimide resin; 0.5–2.0 parts of latent curing agent; 0.5–1.5 parts of silane coupling agent; 30-60 parts of low-dielectric inorganic filler; 5-15 parts flame retardant; The sum of the mass percentages of the above components is 100%.

[0034] In step S11, one of butanone or cyclohexanone is used as a solvent.

[0035] In step S2, the coating speed is 10-30 m / min and the drying temperature is 140-180℃.

[0036] In step S3, the pressing temperature is 40–100℃, the pressing pressure is 0.1–0.4 MPa, and the high-temperature pressing line speed is 10–30 m / min.

[0037] In this specific embodiment 1, the thickness of the adhesive layer 12 is 15-20 μm, and the substrate layer 11 is a PI film with a thickness of 12.5 μm produced by SKC.

[0038] In this specific embodiment 1: In step S1: the mass percentages of high Tg polyimide resin, maleimide resin, curing agent, coupling agent, and flame retardant are as follows: 20 parts high Tg polyimide resin, 35 parts maleimide resin, 30 parts low dielectric inorganic filler, 2 parts latent curing agent, 1 part coupling agent, and 12 parts flame retardant. Using methyl ethyl ketone (MEK) as a solvent, the solid content of the adhesive is 40%. In step S2: the adhesive is uniformly applied to the substrate layer 11 in one go using a coating machine at a coating speed of 10-30 m / min and a drying temperature of 140-180℃. In step S3: the pressing temperature is 40-100℃, the pressing pressure is 0.1-0.4 MPa, and the high-temperature pressing line speed is 10-30 m / min.

[0039] Embodiment 1 of the present invention mainly involves configuring a multilayer board with a high heat-resistant high-frequency cover film in a top-to-bottom stacked manner, comprising a substrate layer, an adhesive layer, and a release layer. The adhesive layer contains an adhesive, which is composed of the following components by mass percentage: 15-45 parts of high Tg polyimide resin; 5-40 parts of maleimide resin; 0.5–2.0 parts of latent curing agent; 0.5–1.5 parts of silane coupling agent; 30-60 parts of low-dielectric inorganic filler; 5-15 parts flame retardant; The sum of the weight percentages of all components is 100%. The resulting high-heat-resistant high-frequency cover film for multilayer boards exhibits excellent high-temperature solderability, improving issues such as delamination, blistering, warping, or significant decrease in bond strength that often occur in multilayer boards. It also possesses excellent dielectric properties, with low dielectric constant (Dk) and dielectric loss tangent (Df), maintaining stability under varying environmental conditions such as temperature, frequency, and humidity. Furthermore, it features highly precise characteristic impedance control, low water absorption, good machinability and dimensional stability, copper foil peel strength (1 / 2OZ) > 1.0 N / mm, and flame retardancy reaching UL94V-0 level. Its superior overall performance fully meets the production requirements of millimeter-wave radar substrates.

[0040] Example 2 differs from Example 1 in that: The adhesive is composed of the following components by weight percentage: 25 parts high Tg polyimide resin, 20 parts maleimide resin, 45 parts low dielectric inorganic filler, 2 parts latent curing agent, 1.0 part coupling agent, and 7 parts flame retardant.

[0041] Example 3 differs from Example 1 in that: The adhesive is composed of the following components by weight percentage: 30 parts high Tg polyimide resin, 7 parts maleimide resin, 60 parts low dielectric inorganic filler, 2 parts latent curing agent, 1 part coupling agent, and 5 parts flame retardant.

[0042] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that the adhesive used in Comparative Example 1 consists of the following components by mass percentage: 15 parts high Tg polyimide resin, 37 parts maleimide resin, 30 parts low dielectric inorganic filler, 2 parts latent curing agent, 1.0 part coupling agent, and 15 parts flame retardant. All other components are the same as in Example 1.

[0043] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that the adhesive used in Comparative Example 2 consists of the following components by mass percentage: 15 parts high Tg polyimide resin, 10 parts maleimide resin, 65 parts low dielectric inorganic filler, 2 parts latent curing agent, 1 part coupling agent, and 7 parts flame retardant. All other components are the same as in Example 1.

[0044] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that the adhesive formulation in Example 1 used a combination of high-Tg polyimide resin and maleimide resin as the base resin matrix, while Comparative Example 3 uses an epoxy resin system. The adhesive for the cover film in Comparative Example 3, by weight, includes 50 parts of bisphenol A type epoxy resin, 15 parts of phenolic curing agent, 20 parts of low-dielectric inorganic filler, 1 part of latent curing agent, 2 parts of coupling agent, and 12 parts of flame retardant. All other components are the same as in Example 1.

[0045] The performance of the cover films prepared in Examples 1-3 and Comparative Examples 1-3 was tested, including the surface morphology, heat resistance, peel strength, and dielectric properties of the adhesive film layer.

[0046] The surface morphology of the adhesive film layer was observed and recorded by the naked eye, and the results are shown in Table 1.

[0047] The coefficient of thermal expansion (CTE) was tested using a thermomechanical analyzer (TMA) according to the test method specified in IPC-TM-650, and the results are shown in Table 1.

[0048] Among them, peel strength, solder heat resistance and dielectric properties were tested according to the test method specified in IPC-TM-650, and the results are shown in Table 1.

[0049] Table 1 Performance test results of the examples and comparative examples

[0050] As can be seen from the data of Examples 1-3, the CTE significantly decreases with the synergistic increase of polyimide and filler, and the reduction in CTE effectively reduces the thermal expansion mismatch stress during high-temperature welding; the floating welding time is negatively correlated with CTE. The heat resistance of Example 3 reaches 370 degrees Celsius, which is slightly lower than that of Comparative Example 2. This is because the low resin ratio affects the interfacial bonding, while the dielectric properties are continuously improved due to the increase in the filler ratio.

[0051] Compared with Comparative Example 1 (low polyimide, low filler), the embodiments of the present invention significantly reduce CTE by synergistically increasing high Tg polyimide and low dielectric inorganic filler, thereby greatly improving the heat resistance of solder.

[0052] Compared with Comparative Example 2 (only filler was added, without adding polyimide), the Example improved peel strength and solder heat resistance while ensuring low dielectric loss. This shows that simply adding filler cannot balance heat resistance and bonding reliability, and the polyimide resin content must be increased in a coordinated manner.

[0053] Based on the above comparison and performance data, it can be seen that the high heat resistance high frequency cover film for multilayer boards prepared by this invention can better meet the quality requirements of IPC-4203B standard; and it meets the application requirements of high temperature resistance and high reliability, and has good prospects for industrial production and broad application prospects.

[0054] It should be understood that the terms "first," "second," etc., are used in this invention to describe various information, but this information should not be limited to these terms. These terms are only used to distinguish information of the same type from each other. For example, without departing from the scope of this invention, "first" information can also be referred to as "second" information, and similarly, "second" information can also be referred to as "first" information. In addition, the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention.

[0055] The above description provides one or more embodiments in conjunction with specific content, and does not imply that the specific implementation of the present invention is limited to these descriptions. Any methods or structures that are similar to or identical to those of the present invention, or any technical deductions or substitutions made based on the concept of the present invention, should be considered as protected by the present invention.

Claims

1. A high-heat-resistant high-frequency coating film for multilayer boards, characterized in that, The device includes an adhesive film layer and a release layer. The adhesive film layer comprises a substrate layer and an adhesive layer. The adhesive layer is disposed on the lower surface of the substrate layer and contains an adhesive. The release layer is pressed onto the lower surface of the adhesive layer. The adhesive consists of the following components in weight percentages: 15-45 parts of high Tg polyimide resin; 5-40 parts of maleimide resin; 0.5–2.0 parts of latent curing agent; 0.5–1.5 parts of silane coupling agent; 30-60 parts of low-dielectric inorganic filler; 5-15 parts flame retardant; The sum of the mass percentages of the above components is 100%.

2. The high heat resistance high frequency coating film for multilayer boards according to claim 1, characterized in that, The adhesive is prepared by the following method: S11: Add high Tg polyimide resin, maleimide resin, curing agent, coupling agent, and flame retardant to the solvent according to the mass percentage, and stir to dissolve; S12: Then add low dielectric inorganic filler, disperse and grind at high speed to a fineness of <5μm to obtain adhesive.

3. The high heat resistance high frequency coating film for multilayer boards according to claim 2, characterized in that, In step S12, at a test temperature of 25°C, the viscosity of the adhesive is 800–1200 mPa·s.

4. The high heat resistance high frequency coating film for multilayer boards according to claim 1, characterized in that, The thickness of the substrate layer is 8–50 μm, the thickness of the adhesive layer is 8–50 μm, and the thickness of the release layer is 110–150 μm.

5. The high heat-resistant high-frequency cover film for multilayer boards according to claim 1, characterized in that, The substrate layer is a polyimide film, and the release layer is release paper.

6. The high heat resistance high frequency coating film for multilayer boards according to claim 1, characterized in that, The high Tg polyimide resin used is SP1T05H polyimide resin produced by Yinxi Technology. The maleimide resin used is BMI-200 resin produced by Daika Ruiweng. The latent curing agent used is model 2E4MZ-CN manufactured by Shikoku Chemicals. The silane coupling agent used is KH-560 produced by Shin-Etsu Chemical. The low-dielectric inorganic filler used is Admafine SO series, hydrophobically treated spherical silica. The flame retardant used is magnesium hydroxide produced by Dongguan Hongtai Flame Retardant Materials Co., Ltd.

7. A method for preparing a high-heat-resistant high-frequency coating film for multilayer boards, characterized in that, It is used to prepare a high heat-resistant high-frequency coating film for multilayer boards as described in any one of claims 1 to 6, the method comprising the following steps: S1: Preparation of adhesive: S11: Add high Tg polyimide resin, maleimide resin, curing agent, coupling agent, and flame retardant to the solvent by mass percentage and stir to dissolve; S12: Add low-dielectric inorganic filler according to the mass percentage, disperse and grind at high speed until the fineness is <5μm to obtain the adhesive; The total mass percentage of high Tg polyimide resin, maleimide resin, curing agent, coupling agent, flame retardant and low dielectric inorganic filler is 100%. S2: The prepared adhesive is evenly coated from the inside to the outside onto the lower surface of the substrate layer, and after drying, an adhesive film layer is obtained. S3: Apply release paper to the underside of the adhesive layer and press it together.

8. The method for preparing a high heat-resistant high-frequency coating film for multilayer boards according to claim 7, characterized in that, In step S1, the high Tg polyimide resin, maleimide resin, curing agent, coupling agent, flame retardant, and low dielectric inorganic filler are expressed as follows by mass percentage: 15-45 parts of high Tg polyimide resin; 5-40 parts of maleimide resin; 0.5–2.0 parts of latent curing agent; 0.5–1.5 parts of silane coupling agent; 30-60 parts of low-dielectric inorganic filler; 5-15 parts flame retardant; The sum of the mass percentages of the above components is 100%.

9. The method for preparing a high heat-resistant high-frequency coating film for multilayer boards according to claim 7, characterized in that, In step S11, one of butanone or cyclohexanone is used as a solvent.

10. The method for preparing a high heat-resistant high-frequency coating film for multilayer boards according to claim 7, characterized in that, In step S2, the coating speed is 10-30 m / min, and the drying temperature is 140-180℃; In step S3, the pressing temperature is 40–100℃, the pressing pressure is 0.1–0.4 MPa, and the high-temperature pressing linear speed is 10–30 m / min.

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