Low-dielectric non-flowing prepreg for rigid-flex printed circuit board and preparation method thereof

Abstract

The application discloses a low-dielectric non-flow prepreg for soft and hard combination plates and a preparation method thereof. The low-dielectric epoxy adhesive suitable for the low-dielectric non-flow prepreg comprises the following components in the following amount: 8-10 mass parts of epoxy resin with a biphenyl structure; 5-8 mass parts of a rubber toughening agent; 2-6 mass parts of a benzoxazine; 4.9-5.5 mass parts of a low-molecular polyphenyl ether; 0.1-0.5 mass parts of a thixotropic agent; and 70-80 mass parts of a solvent. The non-flow prepreg obtained based on the low-dielectric epoxy adhesive has the performance characteristics of low dielectric constant, high bonding strength, reflow soldering at 288 DEG C, low dust drop rate and low thermal expansion coefficient.

Description

Technical Field

[0001] This invention relates to a low-dielectric non-flowing prepreg for rigid-flex PCBs and its preparation method, belonging to the field of electronic chemicals. Background Technology

[0002] With the rapid development of consumer electronics, the requirements for circuit boards in electronic products are becoming increasingly stringent, leading to the emergence of a special type of circuit board – the rigid-flex PCB. Rigid-flex PCBs combine the advantages of both rigid and flexible boards. They allow for the soldering of complex electronic components onto rigid boards while retaining the thinness, foldability, bendability, and space-saving characteristics of flexible boards, effectively reducing the size of electronic products. Rigid-flex PCBs utilize non-flowing prepreg, a special adhesive material used in the PCB manufacturing process to tightly connect the rigid and flexible boards through a specific pressing process. Non-flowing prepreg for rigid-flex PCBs typically refers to a semi-cured solid film prepared by impregnating epoxy resin adhesive onto fiberglass cloth as a carrier and then undergoing a semi-curing treatment. Currently, the dielectric constant of non-flowing prepregs on the market is generally between 4.2 and 4.8, which clearly cannot meet the high-speed, high-frequency requirements of current 5G communication. Circuit board manufacturers have explicitly requested low-dielectric non-flowing prepregs.

[0003] The purpose of this invention is to develop a rigid-flex PCB using a low-dielectric, non-flowing prepreg to meet the material requirements of 5G communication technology. This prepreg is mainly used in rigid-flex PCBs in consumer electronics products such as smartphones and tablet modules for bonding flexible and rigid boards, serving as an adhesive or connector within the rigid-flex PCB. Summary of the Invention

[0004] The purpose of this invention is to provide a low-dielectric non-flowing prepreg for rigid-flex PCBs and its preparation method. The non-flowing prepreg has properties such as low dielectric constant, high bonding strength, ability to pass reflow soldering at 288℃, low dust shedding rate and low coefficient of thermal expansion. The preparation process is simple and the operation performance is good.

[0005] To achieve the above-mentioned objectives, the technical solution adopted by this invention is as follows:

[0006] The low-dielectric epoxy resin adhesive used for low-dielectric non-flowing prepreg in rigid-flex PCBs has the following component dosages:

[0007]

[0008] According to the above scheme, the epoxy resin with a biphenyl structure has the following chemical structural formula:

[0009]

[0010] The epoxy equivalent of the biphenyl epoxy resin is 260-340.

[0011] The epoxy resin with the biphenyl structure can be a product of the NC-3000 series from Nippon Kayaku Co., Ltd., and the NC-3000H biphenyl structure epoxy resin can be selected.

[0012] According to the above scheme, the dielectric constant of the rubber toughening agent is 1.5-2.4.

[0013] According to the above scheme, the rubber toughening agent can be hydrogenated SBS rubber. Specifically, it can be selected from the KRATON SEBS series products, with KRATON SEBS A1536H being a representative product.

[0014] According to the above scheme, the dielectric constant of the benzoxazine is 2.68-3.5.

[0015] According to the above scheme, the chemical structural formula of benzoxazine is as follows:

[0016]

[0017] In the formula, R1 and R2 are fluorine-containing alkylphenyl or siloxane, and n is 2.

[0018] Specifically, benzoxazine containing a fluorine structure can be selected, with the structural formula:

[0019]

[0020] R is phenyl, and the characteristics of this benzoxazine structure are: dielectric constant of 2.8-3.2 and thermal decomposition temperature of 380-400℃.

[0021] According to the above scheme, the dielectric constant of the low molecular weight polyphenylene ether modifier is 2.45-2.65, preferably with a molecular weight of less than 2300.

[0022] The structural formula of low molecular weight polyphenylene ether:

[0023]

[0024] In the formula, R1 can be methyl, and R2 can be methyl, ethyl, isopropyl, tert-butyl, phenyl, or methoxy. Specifically, it can be SA9000 product from Sabiq Corporation.

[0025] According to the above scheme, the thixotropic agent is silicon dioxide, specifically QS-102 Deshan fumed silicon dioxide.

[0026] According to the above scheme, the solvent is preferably a mixture of methyl ethyl ketone (MEK), butyl acetate, and toluene.

[0027] A low-dielectric non-flowing prepreg for rigid-flex boards is provided, which is obtained by impregnating the aforementioned low-dielectric epoxy grease adhesive with glass fiber cloth as a carrier and then performing a semi-curing treatment.

[0028] According to the above scheme, the curing temperature of the low dielectric non-flowing prepreg used in the rigid-flex PCB is 170-190℃, and the curing time is 60-120min.

[0029] A method for preparing low-dielectric epoxy ester adhesive is provided: dissolve the rubber toughening agent in a solvent, heat to dissolve, and after the rubber toughening agent is completely dissolved, add low molecular weight polyphenylene ether, disperse and mill at high speed for 60-90 minutes, filter and pour into a mixing tank, slowly add the formulated amount of biphenyl-structured epoxy resin, benzoxazine and thixotropic agent, and stir evenly for 20-24 hours to obtain the low-dielectric epoxy ester adhesive solution.

[0030] A method for preparing a low-dielectric non-flowing prepreg is provided: using glass fiber cloth as a support carrier, the above-mentioned dielectric epoxy ester adhesive solution is impregnated on a vertical impregnation machine, semi-cured, and then wound up to prepare a low-dielectric non-flowing prepreg.

[0031] According to the above scheme, the semi-curing treatment is as follows: the oven temperature is controlled at 70℃~85℃, the winding speed is 3~5m / min, and the dry adhesive content is maintained at 50-55%.

[0032] According to the above scheme, the preparation method of the prepreg also includes: further baking the prepreg (low dielectric non-flowing prepreg) in an oven, and controlling the amount of adhesive overflow of the prepreg to obtain the low dielectric non-flowing prepreg product. The specific processing steps are: oven baking temperature of 40℃~55℃, baking time of 20-40h, and controlling the amount of adhesive overflow to 0.1-0.2mm.

[0033] This invention provides a low-dielectric epoxy resin adhesive suitable for low-dielectric non-flowing prepregs used in rigid-flex PCBs, and the resulting low-dielectric non-flowing prepreg. The invention uses a biphenyl-structured epoxy resin with a low dielectric constant as the main resin, low-molecular-weight polyphenylene ether with a low dielectric constant, and benzoxazine with excellent high-temperature resistance and dielectric constant as the curing agent. It also incorporates low-molecular-weight polyphenylene ether and a rubber toughening agent, preferably hydrogenated SBS rubber. Through formulation optimization experiments, a special low-dielectric epoxy resin adhesive suitable for low-dielectric non-flowing prepregs used in rigid-flex PCBs is formulated. Electronic-grade fiberglass cloth is then used as a support material, and the adhesive is impregnated to form a non-flowing prepreg.

[0034] This non-flowing semi-cured film has a curing temperature of 170-190℃. At this curing temperature, the oxazine ring in benzoxazine can undergo a ring-opening crosslinking reaction with the epoxy groups in the epoxy resin to form a network structure. Simultaneously, with the synergistic effect of toughening agents and low-molecular-weight polyphenylene ether, a dielectric constant range of 3.2-3.5 is achieved, resulting in low dielectric loss, high bonding strength, low dust shedding rate and coefficient of thermal expansion, and high-temperature resistance. This non-flowing semi-cured film can withstand reflow soldering at 288℃. It can be applied to components in consumer electronics products such as smartphones, tablets, and digital camera modules. Detailed Implementation

[0035] The present invention will be further described in detail below with reference to specific embodiments. In the following embodiments, the dosage of each component involved in the preparation process of the low dielectric epoxy grease adhesive is shown in Appendix 1, and the unit of dosage is kg.

[0036] Example 1

[0037] Referring to the formulation ratio of Example 1 in Appendix 1, the rubber toughening agent is dissolved in a solvent and heated appropriately to dissolve it. After the rubber toughening agent is completely dissolved, low molecular weight polyphenylene ether is added and placed in the grinding jar of a high-speed ball mill. The mixture is dispersed and ground at high speed for 60-90 minutes. After filtering with a 300-mesh filter, it is poured into a mixing tank. The epoxy resin, benzoxazine and thixotropic agent measured in the formulation are slowly added, and then the mixture is stirred evenly for 20-24 hours to obtain the low dielectric epoxy ester adhesive solution.

[0038] Using fiberglass cloth as a support, the prepared low-dielectric epoxy grease adhesive solution was impregnated in a vertical impregnation machine. The oven temperature was controlled at 70℃~85℃, the speed at 3~5m / min, and the dry adhesive content was maintained at 50-55%. The mixture was then wound up to prepare a low-dielectric non-flowing prepreg. The prepared low-dielectric non-flowing prepreg was placed in an oven at 40℃ for treatment, controlling the amount of adhesive overflow within a suitable range to produce a qualified low-dielectric non-flowing prepreg product. Rigid and flexible boards were then bonded together, subjected to rapid pressing at 2MPa and 170℃ for 3 minutes, and then baked at 170℃ for 60~120 minutes to prepare test samples of the non-flowing prepreg. The test performance of the samples is shown in Appendix Table 2.

[0039] Example 2

[0040] According to the formulation ratio of Example 2 in Appendix 1, test samples were prepared in accordance with the glue preparation, impregnation and sample preparation methods in Example 1. The test performance of the samples is shown in Appendix 2.

[0041] Example 3

[0042] According to the formulation ratio of Example 3 in Appendix 1, test samples were prepared in accordance with the glue preparation, impregnation and sample preparation methods in Example 1. The test performance of the samples is shown in Appendix 2.

[0043] Example 4

[0044] According to the formulation ratio of Example 4 in Appendix 1, test samples were prepared in accordance with the glue preparation, impregnation and sample preparation methods in Example 1. The test performance of the samples is shown in Appendix 2.

[0045] Example 5

[0046] According to the formulation ratio of Example 5 in Appendix 1, test samples were prepared in accordance with the glue preparation, impregnation and sample preparation methods in Example 1. The test performance of the samples is shown in Appendix 2.

[0047] In the above embodiments, the epoxy resin with a biphenyl structure was selected from the NC-3000H biphenyl structure epoxy resin of Nippon Kayaku Co., Ltd.

[0048] The rubber toughening agent can be selected from KRATON SEBSA1536 H, a representative product in the KRATON SEBS series of products from the United States.

[0049] Benzoxazine is selected from:

[0050]

[0051] R stands for phenyl.

[0052] The low molecular weight polyphenylene ether is selected from SA9000 product of Sabiq Corporation.

[0053] The thixotropic agent selected is QS-102 Deshan fumed silica.

[0054] Table 1: Formulation Components of Low Dielectric Epoxy Grease Adhesives

[0055] Epoxy resin 8 8.5 9 9.5 10 Rubber toughening agent 5 5.5 6.7 7 8 Benzoxazine 2 3.8 4.8 5 6 Modifier 4.9 5 5.2 5.5 5.5 thixotropic agents 0.1 0.2 0.3 0.4 0.5 Butanone 12.5 11 10 8 9 Toluene 65 64 64 63 60 Butyl acetate 2.5 2 2 1.6 1

[0056] Table 2: Performance Test Table of Non-flowing Prepreg Samples

[0057]

[0058]

[0059] Acid and alkali resistance: tested according to GB / T 13357-2017 8.1.3.

Claims

1. A low-dielectric epoxy resin adhesive for use in low-dielectric non-flowing prepregs for rigid-flex PCBs, characterized in that: The components and dosages are as follows: 8-10 parts by weight of epoxy resin with biphenyl structure 5-8 parts by weight of rubber toughening agent 2-6 parts by weight of benzoxazine 4.9~5.5 parts by weight of low molecular weight polyphenylene ether Thixotropic agent 0.1~0.5 parts by weight Solvent 70-80 parts by weight, The low-molecular-weight polyphenylene ether modifier has a dielectric constant of 2.45-2.65 and a molecular weight below 2300; the rubber toughening agent has a dielectric constant of 1.5-2.4, and the rubber toughening agent is hydrogenated SBS rubber; the benzoxazine is selected from benzoxazines with a dielectric constant of 2.68-3.5, and its chemical structural formula is: wherein R is phenyl.

2. The low dielectric epoxy adhesive of claim 1, wherein: The epoxy resin with a biphenyl structure has the following chemical structural formula: The epoxy equivalent of the biphenyl epoxy resin is 260-340.

3. The low dielectric epoxy adhesive of claim 1, wherein: The epoxy resin with a biphenyl structure is a product of the NC-3000 series from Nippon Kayaku Co., Ltd.

4. The low dielectric epoxy adhesive of claim 1, wherein: The thixotropic agent is silicon dioxide; the solvent is a mixture of methyl ethyl ketone, butyl acetate, and toluene.

5. The method of making a low dielectric epoxy adhesive of claim 1, characterized by: Dissolve the rubber toughening agent in a solvent, heat to dissolve, and after the rubber toughening agent is completely dissolved, add low molecular weight polyphenylene ether, disperse and grind at high speed for 60-90 minutes, filter and pour into a mixing tank, slowly add the biphenyl-structured epoxy resin, benzoxazine and thixotropic agent measured in the formula, and stir evenly for 20-24 hours to obtain the low dielectric epoxy resin adhesive solution.

6. A low-dielectric non-flowing prepreg for rigid-flex PCBs, which is obtained by impregnating glass fiber cloth as a carrier with the low-dielectric epoxy resin adhesive of claim 1, followed by a semi-curing treatment.

7. The low dielectric non-flowing prepreg for rigid-flex printed circuit boards according to claim 6, characterized by: Its curing temperature is 170-190℃, and the curing time is 60-120min.

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