Resin composition and low-flow prepreg prepared using the same

Abstract

The application develops a resin composition and a low-flow prepreg prepared by applying the resin composition. While ensuring that the low-flow prepreg has excellent toughness and a low powder loss rate, the adhesion and the apparent flatness of the low-flow prepreg are significantly improved, and finally, a low-flow prepreg with excellent comprehensive performance such as overflow amount, toughness / powder loss rate, interlayer adhesion of the bonded sheet, apparent flatness of the bonded sheet, heat resistance and the like is obtained, and the low-flow prepreg can be well used in rigid-flex combined printed circuit boards.

Description

TECHNICAL FIELD

[0001] The application relates to a low-flow prepreg for use as a bonding layer material in rigid-flex printed circuit board production, and belongs to the technical field of printed circuit boards. BACKGROUND

[0002] Rigid-flex printed circuit board, also known as rigid-flex board, is a combination of soft board and hard board, which combines a thin layer of flexible bottom layer and rigid bottom layer, and is laminated into a single component to form a circuit board. Rigid-flex board changes the traditional flat design concept to a three-dimensional 3D space concept, which brings great convenience to product design, but also brings great challenges. Rigid-flex printed circuit board is a kind of printed circuit board in great demand and development at present, and its application range mainly includes: consumer electronics field such as mobile phones, wireless earphones and AR glasses, and application fields such as automobiles, military industry, industrial control and medical treatment.

[0003] In the prior art, a typical (four-layer) rigid-flex printed circuit board has a polyimide core, and copper foils are coated on the upper and lower surfaces of the core. The outer rigid layers are composed of single-sided FR4 (glass fiber board), which are laminated on both sides of the flexible core to form a multi-layer PCB. When manufacturing a multi-layer rigid-flex board, the processing technology of the flexible layer is completely different from that of the outer FR4 layer. Each layer made of different materials must be gathered together by lamination, and then drilled and electroplated. When manufacturing rigid-flex printed circuit boards, adhesive materials are needed to bond the soft board and the hard board together. The most commonly used adhesive material at present is low-flow prepreg (also known as low-flow prepreg, low-flow adhesive sheet). Compared with conventional FR-4 prepreg, low-flow prepreg needs to have the characteristics of extremely small or almost no flow under high temperature and high pressure, and also needs to have good adhesion, excellent toughness and low powder dropping, and excellent apparent flatness. Due to the characteristics of extremely small or almost no flow of low-flow prepreg under high temperature and high pressure, it is usually necessary to improve the reaction degree of the resin system, which will lead to the decrease of the bonding capacity of the adhesive sheet, which becomes a pair of contradictions. Therefore, how to ensure that the low-flow prepreg has extremely small or almost no flow while having excellent bonding capacity has become a major technical problem of low-flow prepreg.

[0004] To solve the above technical problems, the early low-flow prepreg realizes low-flow by increasing the baking time to improve the reaction degree on the basis of conventional FR-4, and has the problems of insufficient adhesion, insufficient toughness and high powder loss rate. In order to improve the toughness and powder loss rate of the low-flow prepreg, the prior art usually adds rubber to the resin system for toughening, such as core-shell rubber and carboxyl-terminated butyronitrile rubber, to improve the toughness and powder loss rate of the low-flow prepreg. However, there are certain technical difficulties in using rubber for toughening modification: if the amount of rubber component is too small, the toughening effect cannot be achieved to improve the toughness and reduce the powder loss rate, and if the amount of rubber component is too large, the adhesion of the low-flow prepreg will be reduced. Due to the characteristics of the low-flow prepreg that the flow is extremely small or almost no flow under high temperature and high pressure, the low-flow prepreg cannot have good flowability and wettability under high temperature and high pressure like ordinary FR-4 prepreg, and the adhesion of the bonded sheet is particularly reduced when the amount of rubber component is too large.

[0005] On the other hand, due to the characteristics of the low-flow prepreg that the flow is extremely small or almost no flow, when the low-flow prepreg is used as a bonding material to prepare a rigid-flex combined board laminate, the flow of the low-flow prepreg is very small, and even if there is only a small defect on the surface of the low-flow prepreg, the low-flow prepreg cannot flow flat during lamination. Therefore, the low-flow prepreg requires very good surface flatness and cannot have any defects. The surface defects of the low-flow prepreg are the same as those of the ordinary FR-4 prepreg, which can be classified as bubbles, flow marks, fish eyes, stripes and cracks. Once the surface of the low-flow prepreg has defects, the flatness cannot meet the requirements, which will cause defects such as adhesion, voids and bubbles in the circuit board substrate after pressing, thereby greatly reducing the reliability of the circuit board.

[0006] Therefore, it is necessary to further improve the above problems and develop a new rubber-toughened resin composition and a low-flow prepreg made of the same, which can improve the adhesion of the low-flow prepreg, especially the interlayer adhesion of the low-flow prepreg, while ensuring that the low-flow prepreg has excellent toughness and low powder loss rate, and at the same time, improve the surface flatness of the low-flow prepreg, which obviously has positive practical significance. SUMMARY

[0007] The application aims to provide a resin composition and a low-flow prepreg prepared by using the same.

[0008] To achieve the above application purpose, the technical scheme adopted by the application is as follows: a resin composition, including the following components in terms of organic solid weight parts:

[0009] (a) epoxy resin, 100 parts by weight;

[0010] (b) an epoxy curing agent, 2-100 parts by weight;

[0011] (c) a curing accelerator, 0.05-1 parts by weight;

[0012] (d) a carboxyl nitrile rubber, 1-10% of the total amount of the above components (a), (b) and (c);

[0013] (e) a carbodiimide compound, the carbodiimide compound being added in an amount of 5-40% of component (d);

[0014] The method for preparing the resin composition is as follows:

[0015] S1, mixing the dissolved components (a) epoxy resin, (b) epoxy resin curing agent, (d) carboxyl nitrile rubber, (e) carbodiimide compound in proportion to prepare a resin mixture;

[0016] S2, pre-reacting the resin mixture at a temperature of 30-70°C for 2-48 hours to obtain a pre-reactant;

[0017] S3, adding the dissolved component (c) curing accelerator to the pre-reactant and stirring to mix uniformly to obtain the resin composition.

[0018] In the above, the component (d) carboxyl nitrile rubber can be solid carboxyl nitrile rubber or liquid carboxyl nitrile rubber, and is preferably solid carboxyl nitrile rubber.

[0019] In the above, the resin composition is used to prepare a low-flow prepreg, and the low-flow prepreg is used to prepare a rigid-flex printed circuit board.

[0020] In the above, the temperature for pre-reaction in step S2 is preferably 40-60°C, more preferably 45-50°C, and can also be 35°C, 55°C, 65°C or 68°C. The pre-reaction time is preferably 10-30 hours, more preferably 15-20 hours, and can also be 3 hours, 7 hours, 12 hours, 18 hours, 22 hours, 25 hours, 28 hours, 35 hours, 40 hours or 45 hours.

[0021] Preferably, the epoxy resin is selected from one or more of bisphenol A epoxy resin, bisphenol F epoxy resin, tetraphenyl ethane epoxy resin, triphenyl methane epoxy resin, biphenyl type epoxy resin, naphthalene ring type epoxy resin, dicyclopentadiene type epoxy resin, isocyanate type epoxy resin, aralkyl linear phenolic epoxy resin, bisphenol A phenolic type epoxy resin, polyphenyl ether modified epoxy resin, alicyclic epoxy resin, glycidyl amine type epoxy resin, glycidyl ester type epoxy resin, phosphorus-containing epoxy resin, nitrogen-containing epoxy resin, and multifunctional epoxy resin.

[0022] If the low flow adhesive prepreg has high heat resistance requirement, then the composition should be made of biphenyl type epoxy resin, naphthalene ring type epoxy resin, aralkyl linear phenolic aldehyde epoxy resin and other high heat resistance resins; if the low flow adhesive prepreg has low dielectric property requirement, then the composition should be made of dicyclopentadiene type epoxy resin, polyphenyl ether modified epoxy resin and other special epoxy resins.

[0023] Preferably, the epoxy curing agent is selected from one or more of aliphatic amine, aromatic amine, alicyclic amine, heterocyclic amine, aromatic anhydride, alicyclic anhydride, aliphatic anhydride, polyamide resin, linear phenolic aldehyde resin and polyphenol resin, arylamine formaldehyde resin, polysulfide compound, polyester resin, latent curing agent, flame-retardant curing agent and active ester curing agent.

[0024] Preferably, the epoxy curing agent is selected from one or more of dicyandiamide, polyamide, linear phenolic aldehyde resin and aromatic diamine curing agent.

[0025] Preferably, the reaction temperature of the component (b) epoxy curing agent and epoxy resin is above 100℃, so as to ensure that the epoxy resin and epoxy curing agent react as little as possible in the pre-reaction stage and react more in the subsequent semi-curing or curing process. The epoxy curing agent can be dicyandiamide, linear phenolic aldehyde resin, aromatic amine and the like. If the low flow adhesive prepreg has high heat resistance requirement, then the curing agent is preferably aromatic amine, linear phenolic aldehyde resin and aromatic anhydride; if the low flow adhesive prepreg has low dielectric property requirement, then the curing agent is preferably active ester or anhydride.

[0026] Preferably, the curing accelerator is selected from one or more of imidazole accelerator, amine accelerator, tin accelerator and DBN / DBU. The DBN / DBU respectively refers to 1,8-diazabicyclo- bicyclo(5,4,0)-7-undecene(DBU) and 1,5-diazabicyclo(4,3,0)non-5-ene(DBN).

[0027] The imidazole accelerator can be 2-methylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole and the like. The amine accelerator can be triethylenediamine, N-amino morpholine, boron trifluoride ethylamine and the like. The tin accelerator can be dibutyltin dilaurate, stannous octoate and the like.

[0028] Preferably, the carbodiimide compound has a molecular structure containing Preferably, the carbodiimide compound has a molecular structure containing

[0029] Preferably, the carbodiimide compound has a molecular structure containing

[0030] Preferably, the carbonized diimine compound is added in an amount of 10-30% of component (d). To obtain better adhesive strength and apparent flatness, more preferably 15-20%. It can also be 12%, 18%, 22%, 25%, 28%.

[0031] Preferably, the resin composition further comprises component (f): a filler selected from one or several of crystalline silica, fused silica, spherical silica, aluminum oxide, aluminum hydroxide, aluminum nitride, boron nitride, titanium dioxide, strontium titanate, barium titanate, barium sulfate, talc, calcium silicate, calcium carbonate, mica, polytetrafluoroethylene, graphene;

[0032] The filler is added in an amount of 5-80% of the total amount of the resin composition. More preferably 7-20%. It can also be 10%, 15%, 20%, 25%, 30%, 40%, 45%, 55%, 60%, 65%, 70%, 75%.

[0033] In the above, the filler is added in an amount of 5-80% of the total amount of the resin composition, specifically: in terms of weight parts, relative to the total amount of the resin composition being 100 parts by weight, the filler is added in an amount of 5-80 parts by weight. The filler can be surface treated with a silane coupling agent, can be directly put into or pre-prepared into a filler dispersion or into a paste into the resin composition; the particle size of the filler is preferably 0.5-10 microns.

[0034] The resin composition can further comprise flame retardants, other toughening agents, heat-resistant modifiers, etc. according to actual needs.

[0035] The present application also claims a low-flow prepreg made of the above resin composition, the resin composition is dissolved with a solvent to form a glue solution, then the reinforcing material is immersed in the glue solution, and the immersed reinforcing material is heated and dried to obtain the low-flow prepreg.

[0036] The organic solvent in the present application is not specifically limited. For example, the organic solvent can be selected from one or a combination of any of acetone, butanone, toluene, methyl isobutyl ketone, N, N-dimethylformamide, N, N-dimethylacetamide, ethylene glycol methyl ether, propylene glycol methyl ether, benzene, toluene, xylene, cyclohexane. The reinforcing material is natural fiber, organic synthetic fiber, organic fabric or inorganic fabric; preferably, the reinforcing material uses glass fiber cloth, and open fiber cloth or flat cloth is preferably used in the glass fiber cloth. In addition, when the reinforcing material uses glass fiber cloth, the glass fiber cloth generally needs to be chemically treated to improve the bonding between the interface of the resin composition and the glass fiber cloth. The main method of chemical treatment is coupling agent treatment. The coupling agent used is preferably epoxy silane or amino silane, etc. to provide good water resistance and heat resistance.

[0037] The specific preparation method of the prepreg is as follows: the resin composition is added into a glue mixing kettle, a diluent is added to adjust the solid content to 40-70%, the glue liquid is uniformly stirred, the reinforcing material is immersed in the glue liquid, and then the immersed reinforcing material is dried at 100-200 DEG C for 3-10 min to obtain the low-flow prepreg provided by the application.

[0038] The application also claims a rigid-flex printed circuit board comprising the low-flow prepreg.

[0039] Compared with the prior art, the application has the following advantages due to the technical scheme:

[0040] 1. The application develops a new low-flow prepreg which has excellent toughness and low powder loss rate, and significantly improves the adhesion and the flatness of the low-flow prepreg, and finally obtains a low-flow prepreg with excellent comprehensive performance such as glue overflow amount, toughness / powder loss rate, interlayer adhesion of the bonded sheet, apparent flatness of the bonded sheet, heat resistance, etc., which can be well used in rigid-flex printed circuit boards.

[0041] 2. In the preparation process of the resin composition, the components (a) epoxy resin, (b) epoxy resin curing agent, (d) carboxyl nitrile rubber, and (e) carbodiimide compound are pre-reacted, the reaction speed and process are controlled by controlling the pre-reaction temperature and time, and then a curing accelerator is added, so as to control the reaction process, so that the carboxyl nitrile rubber is inside the polymer after polymerization, which can play a toughening and powder loss rate reducing role, and the amount of carboxyl nitrile rubber is greatly reduced, so as to improve the adhesion and the apparent flatness, and finally obtain a low-flow prepreg with excellent comprehensive performance.

[0042] 3. The application uses a combination of carboxyl nitrile rubber and carbodiimide compound, and the adhesion and the apparent flatness of the composition and the prepreg are greatly optimized by strictly controlling the ratio of the two, which achieves unexpected effects.

[0043] 4. The preparation process of the application is simple and easy to implement, and the cost is low, which is suitable for popularization and application. DETAILED DESCRIPTION

[0044] The application will be further described below in combination with examples:

[0045] The formulations of examples 1-6 and comparative examples 1-6 are shown in the following table 1 and table 2; the preparation method is as follows:

[0046] S1, dissolve components (a) epoxy resin, (b) epoxy resin curing agent, (d) carboxyl nitrile rubber, (e) carbodiimide compound in proportion to prepare a resin mixture;

[0047] S2, the above resin mixture is pre-reacted at a temperature of 30-70°C for 2-48 hours; to obtain a pre-reaction product;

[0048] S3, the dissolved component (c) curing accelerator is added to the above pre-reaction product, and stirred and mixed uniformly to prepare the resin composition;

[0049] The above component (a) corresponds to A1 to A4 in the following table; component (b) corresponds to B1 to B2 in the following table; component (c) corresponds to C in the following table; component (e) corresponds to E1 to E2 in the following table;

[0050] Then, according to the specified pre-reaction conditions, a 55% resin solution is prepared, and electronic grade 2116 glass cloth is used as a reinforcing material to impregnate the resin solution, and then the prepreg is heated and cured in an oven for a certain time to obtain a low flow prepreg. Some prepregs are pressed into laminates according to the following conditions, and then the properties of the prepregs and laminates are evaluated by the following methods.

[0051] Low flow prepreg prepregging conditions: 165°C / 3-5min;

[0052] Laminated board parameters: stacked into 5*2116, the thickness of the board after forming is 0.6mm, and the board curing condition is 190°C / 2h;

[0053] Prepreg test items: excess glue amount, cutting edge quality, and powder loss rate.

[0054] Excess glue amount determination: PP is made into a square sample of 100mm*100mm, a 1-inch circular hole is punched in the middle position, and then the PP sample is stacked according to the stacking method of "steel plate + copper clad plate + PP sample + release film + buffer material + steel plate", and the press with set temperature / pressure / time is used for pressing. After pressing, the excess glue amount at the circular hole position of the sample is taken out to evaluate the glue flow size under hot pressing conditions.

[0055] Cutting edge quality determination: the prepreg is cut with a sampler for resin content test, and the cut sample is observed under a 10x magnifying glass to observe the whiteness of the edge. The more obvious the whiteness, the more resin powder is shed. In order to facilitate evaluation, the number of stars is used to represent the cutting edge quality, and five stars represent good cutting edge quality, and one star represents poor cutting edge quality.

[0056] Toughness (powder loss rate) determination: the degree of resin powder falling off after the prepreg was punched and sheared was used as the judgment basis. The specific test method was as follows: 4 pieces of prepreg with a size of 10 cm*10 cm were taken, weighed and recorded as m1. A 9 cm deep notch was cut on one side of each piece with scissors, and a total of 29 cuts were made, so that each piece of sample was made into 30 small strips with a length of 9 cm. The handled sample was shaken up and down 30 times with the wrist as the center, and one back and forth was recorded as one vibration. After completion, it was weighed again and recorded as m2, and the powder loss rate of the prepreg was calculated according to (m1-m2) / m1*100%.

[0057] Prepreg apparent defect: the appearance of the prepreg was observed.

[0058] Prepreg interlayer bonding strength: after two pieces of low-flow prepreg were pressed together and completely cured, the universal material testing machine was used to test the interlayer bonding strength of the low-flow prepreg at 90°.

[0059] Plate glass transition temperature Tg: according to the differential scanning calorimetry method, the DSC method specified in IPC-TM-650 2.4.25 was used for determination.

[0060] Table 1: Examples

[0061]

[0062] Table 2: Comparative examples

[0063]

[0064] Table 1 and Table 2 footnotes:

[0065] A1: phosphorus-modified epoxy resin, epoxy equivalent weight 265 g / eq, Dongcaistechnology;

[0066] A2: bisphenol A epoxy resin, epoxy equivalent weight 185 g / eq, Guodu Chemical;

[0067] A3: bisphenol A novolac epoxy resin, epoxy equivalent weight 205 g / eq, Shengquan New Material; A4: UV resin, epoxy equivalent weight 210 g / eq, Dongcaistechnology;

[0068] B1: Dicy, dicyandiamide, Ningxia Darong;

[0069] B2: PN, linear phenolic resin, Shengquan New Material;

[0070] C: 2-ethyl-4-methylimidazole;

[0071] D: carboxyl nitrile rubber, Nipol 1072, Japan Zeon;

[0072] E1: Carbodiimide compound, molecular weight 9000, Rhein Chemie, Germany;

[0073] E2: Carbodiimide compound, molecular weight 15000, Rhein Chemie, Germany;

[0074] F: Filler, DQ1028L, Jiangsu Lianrui;

[0075] From the results of Table 1 and Table 2, it can be seen that Example 1 has obviously higher interlaminar bonding strength of prepreg compared with Comparative Example 1, Comparative Example 2, Comparative Example 4 and Comparative Example 6. Example 1 has obviously better appearance of prepreg and higher interlaminar bonding strength of prepreg compared with Comparative Example 3 and Comparative Example 5. Examples 1-6 have improved interlaminar bonding strength of low flow prepreg, improved flatness of appearance of low flow prepreg and obtained low flow prepreg with excellent comprehensive performance while ensuring excellent toughness and low powder dropping rate of low flow prepreg compared with Comparative Examples 1-6.

[0076] Examples 1-2 have obviously better interlaminar bonding strength of low flow prepreg compared with Examples 3-4.

[0077] In summary, the resin composition of the present application and the low flow prepreg prepared by using the resin composition have low flow characteristics, excellent toughness, good edge quality of prepreg after mechanical cutting, less resin powder dropping, obviously improved appearance of low flow prepreg and excellent interlaminar bonding strength of prepreg. The problems of decreased bonding performance of low flow prepreg and appearance flatness of prepreg caused by excessive amount of rubber component are solved while ensuring good toughness and low powder dropping rate of low flow prepreg.

[0078] The above description of disclosed embodiments enables a person skilled in the art to implement or use the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to these embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A resin composition, characterized by comprising: By weight of organic solid, comprising the following components: (a) epoxy resin, 100 parts by weight; (b) epoxy curing agent, 2-100 parts by weight; (c) curing accelerator, 0.05-1 parts by weight; (d) carboxyl nitrile rubber, 1-10% of the total amount of the above components (a), (b) and (c); (e) carbodiimide compound, the addition amount of the carbodiimide compound is 5-40% of component (d); The preparation method of the resin composition is as follows: S1, the dissolved components (a) epoxy resin, (b) epoxy resin curing agent, (d) carboxyl nitrile rubber, (e) carbodiimide compound are mixed according to the proportion to prepare a resin mixture; S2, the above resin mixture is pre-reacted at a temperature of 30-70℃ for 2-48 hours; to obtain a pre-reaction product; S3, the dissolved component (c) curing accelerator is added to the above pre-reaction product, and stirred and mixed uniformly to prepare the resin composition.

2. The resin composition according to claim 1, characterized by The epoxy resin is selected from one or more of bisphenol A epoxy resin, bisphenol F epoxy resin, tetraphenyl ethane epoxy resin, triphenyl methane epoxy resin, biphenyl type epoxy resin, naphthalene ring type epoxy resin, dicyclopentadiene type epoxy resin, isocyanate type epoxy resin, aralkyl linear phenolic aldehyde epoxy resin, bisphenol A aldehyde type epoxy resin, polyphenyl ether modified epoxy resin, alicyclic epoxy resin, glycidyl amine type epoxy resin, glycidyl ester type epoxy resin, phosphorus-containing epoxy resin, nitrogen-containing epoxy resin.

3. The resin composition according to claim 1, characterized by The epoxy resin is selected from a multifunctional epoxy resin.

4. The resin composition according to claim 1, characterized by The epoxy curing agent is selected from one or more of aliphatic amine, aromatic amine, alicyclic amine, heterocyclic amine, aromatic anhydride, alicyclic anhydride, aliphatic anhydride, polyamide resin, linear phenolic aldehyde resin, arylamine formaldehyde resin, polysulfide compound, polyester resin, latent curing agent, flame-retardant curing agent, active ester curing agent.

5. The resin composition according to claim 4, characterized by The epoxy curing agent is selected from one or more of dicyandiamide, polyamide, linear phenolic aldehyde resin, aromatic diamine curing agent.

6. The resin composition according to claim 1, characterized by The epoxy curing agent is selected from a polyphenol resin.

7. The resin composition according to claim 1, characterized by The curing accelerator is selected from one or more of imidazole accelerator, amine accelerator, tin accelerator, DBN / DBU.

8. The resin composition according to claim 1, characterized by The carbodiimide compound has a molecular structure containing Structure; wherein: R represents an aromatic group.

9. The resin composition according to claim 1, characterized by The addition amount of the carbodiimide compound is 10-30% of component (d).

10. The resin composition according to claim 1, characterized by The resin composition further comprises component (f): filler, which is selected from one or more of crystalline silica, fused silica, spherical silica, aluminum oxide, aluminum hydroxide, aluminum nitride, boron nitride, titanium dioxide, strontium titanate, barium titanate, barium sulfate, talc, calcium silicate, calcium carbonate, mica, polytetrafluoroethylene, graphene; The addition amount of the filler is 5-80% of the total amount of the resin composition.

11. A low flow prepreg made using the resin composition according to any one of claims 1 to 10, characterized by: The resin composition is dissolved with a solvent to prepare a glue solution, then the reinforcing material is immersed in the above glue solution, and after heating and drying the immersed reinforcing material, the low-flow glue semi-cured sheet is obtained.

12. A rigid-flex printed circuit board, characterized by: Containing the low-flow glue semi-cured sheet according to claim 11.

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