Thermocuring bending-resistant modified resin for FPC (Flexible Printed Circuit) golden finger, preparation method and cured product of thermocuring bending-resistant modified resin

Abstract

The invention provides thermocuring bending-resistant modified resin for an FPC (Flexible Printed Circuit) golden finger. The composition comprises modified polyimide, wherein polymeric monomers of the modified polyimide comprise an aromatic dianhydride component, a multi-benzene ring multi-ammonia structure aromatic diamine component and an ether bond-containing aromatic diamine component; the preparation method comprises the following steps: reacting a bisphenol aromatic compound with substituted nitro aryl halide under an alkaline condition, introducing a multi-benzene-ring structural unit, and converting nitro into amino through a hydrazine reduction reaction to prepare the aromatic diamine monomer with a multi-benzene-ring and multi-amino structure. The monomer is matched with an ether-bond-containing aromatic diamine component, the proportion is controlled, the monomer is compounded for preparing a polyimide material, the high temperature resistance, the bending fatigue resistance and the electrical property stability of the material can be remarkably improved, and the monomer is particularly suitable for a golden finger structure of a flexible printed circuit board.

Description

Technical Field

[0001] This invention relates to the technical field, and in particular to a thermosetting, flexurally resistant modified resin for FPC gold fingers, its preparation method, and its cured product. Background Technology

[0002] Flexible printed circuit boards (FPCs) are widely used in consumer electronics, automotive electronics, industrial control, and high-end equipment due to their advantages such as thinness, flexibility, and space adaptability. Among these components, the gold fingers of the FPC are crucial for enabling pluggable electrical connections between the FPC and connectors or motherboards; their material properties directly determine the reliability, lifespan, and system stability of the electrical connection.

[0003] Existing FPC gold fingers typically use polyimide film as the substrate, with copper conductors formed on its surface and further plated with nickel or gold. Because gold fingers need to withstand repeated insertion and removal, localized stress concentration, high-frequency signal transmission, and high-temperature welding or long-term high-temperature environments during use, comprehensive requirements are placed on the polyimide substrate for low resistance transmission stability, high heat resistance, and excellent bending fatigue resistance.

[0004] Currently, most industrially used polyimide materials are produced by the polycondensation of aromatic dianhydrides and conventional aromatic diamines (such as p-phenylenediamine, 4,4′-diaminodiphenyl ether, etc.). Although these materials possess high heat resistance and good film-forming properties, they still have the following shortcomings in gold finger applications. For example, existing diamine structures are mostly based on a single benzene ring or a simple biphenyl structure, with regular molecular chain arrangement and dense packing. Under repeated bending or insertion / extraction stress, microcracks are easily generated, leading to a decline in mechanical properties. At the same time, the gold finger area has high requirements for signal integrity and contact resistance stability, while traditional polyimides are prone to local structural relaxation or interface failure under microscopic interface stress concentration and long-term thermal aging conditions, thus indirectly affecting resistance stability.

[0005] Improving the high-temperature resistance of polyimide usually relies on increasing the rigidity of the molecular chain and the degree of aromatization, but excessive rigidity will reduce the bending resistance of the material; while simply introducing flexible segments can improve bending performance, it will significantly reduce the glass transition temperature and thermal dimensional stability of the material, making it difficult to meet the long-term high-temperature use requirements of gold fingers.

[0006] Therefore, how to significantly improve the bending fatigue resistance of polyimide through molecular structure design while maintaining its high heat resistance, and also take into account low resistance and electrical performance stability, has become an urgent technical problem to be solved in the field of polyimide materials for gold fingers. Summary of the Invention

[0007] Purpose of the invention: In view of the above-mentioned deficiencies in the prior art, the purpose of the present invention is to provide a thermosetting flexurally resistant modified resin suitable for FPC gold fingers. The modified resin includes modified polyimide. By directional structural design of aromatic diamine, the resulting polyimide material simultaneously possesses low resistance, high temperature resistance and excellent flexural mechanical properties.

[0008] The technical solution of the present invention: In some embodiments, the present invention provides a thermosetting flexurally resistant modified resin for FPC gold fingers, the composition comprising a modified polyimide; wherein the polymer monomers of the modified polyimide comprise an aromatic dianhydride component, a polyphenyl ring polyamine structure aromatic diamine component, and an aromatic diamine component containing an ether bond.

[0009] In some embodiments, the aromatic dianhydride component is selected from one or more combinations of 3,3′,4,4′-biphenyltetracarboxylic dianhydride, 4,4′-oxobiphenyltetracarboxylic dianhydride, pyromellitic dianhydride, and benzophenonetetracarboxylic dianhydride.

[0010] In some embodiments, the preparation method of the polyphenyl ring polyamine aromatic diamine component includes the following steps: Step 1: Add bisphenol A to the reactor, then add salt and solvent, heat to reflux and react. After the reaction is complete, cool down, then add 2-benzyloxy-5-chloronitrobenzene, continue the reaction and cool after the reaction is complete. Post-process to obtain product 1. Step 2: Add product 1, catalyst and solvent to the reactor, heat and stir to dissolve, then cool to 70°C, start adding hydrazine hydrate dropwise from the dropping funnel, continue the reaction, and after the reaction is completed, obtain the aromatic diamine component with the polybenzene ring polyamine structure through post-treatment.

[0011] In some embodiments, the salt in S1 is selected from potassium carbonate and sodium carbonate; the solvent is selected from N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide and toluene; and the reflux reaction temperature is 90-150°C and the reaction time is 4-16 h.

[0012] In some embodiments, the ratio of bisphenol A, salt and 2-benzyloxy-5-chloronitrobenzene added in S1 is 1 mol: 1.5-3.0 mol: 1-2.5 mol.

[0013] In some embodiments, the catalyst in S2 is selected from one of Pd / C, Ni-Al alloy, Fe powder / FeCl3 system, and Cu-Ni composite catalyst; the solvent in S2 is selected from one of ethanol, isopropanol, n-butanol, tetrahydrofuran, and ethanol / water mixed system.

[0014] In some embodiments, the molar ratio of product 1 and hydrazine hydrate added in S2 is 1:6-16.

[0015] In some embodiments, the reaction temperature of the reaction described in S2 is 70-110°C, and the reaction time is 2-10 h.

[0016] In some embodiments, the aromatic diamine component containing an ether bond is 4,4′-diaminodiphenyl ether.

[0017] In some embodiments, the molar ratio of the aromatic dianhydride component, the polyphenylene ring polyamine structure aromatic diamine component, and the ether-containing aromatic diamine component is 6-10:3-7:3-7; further, the molar ratio of the aromatic dianhydride component, the polyphenylene ring polyamine structure aromatic diamine component, and the ether-containing aromatic diamine component is 7-9:3-6:4-6.

[0018] In a second aspect, the present invention provides a method for preparing the thermosetting, flexurally resistant modified resin for FPC gold fingers, comprising the following steps: Solvent is added to a dry reactor, and aromatic diamine components with polyphenyl ring and polyamine structure and aromatic diamine components containing ether bonds are added under nitrogen protection. The mixture is heated and stirred until completely dissolved. The reaction system is cooled, and then aromatic dianhydride components are added. After the addition is complete, the temperature is raised to continue the reaction to obtain a polymer solution. After vacuum degassing and filtration through a filter membrane, the solution is formed into a film and cured under a nitrogen atmosphere to obtain a modified resin.

[0019] In some embodiments, the heating temperature during the heating and stirring until complete dissolution is 20-50°C; the heating temperature for continuing the reaction after the addition is 20-40°C, and the reaction time is 4-40°C.

[0020] In some embodiments, the heating and curing process includes: a first stage of 80-120°C for 30-90 min; a second stage of 140-180°C for 30-60 min; a third stage of 200-250°C for 60-120 min; and a fourth stage of 280-330°C for 30-90 min.

[0021] In a third aspect, the present invention provides a thermosetting, flexurally resistant resin composition for FPC gold fingers prepared as described above.

[0022] Beneficial effects: This invention introduces a polybenzene ring structural unit by reacting a bisphenol-type aromatic compound with a substituted nitro halogen under alkaline conditions. The nitro group is then converted to an amino group via hydrazine reduction, resulting in an aromatic diamine monomer with a polybenzene ring and polyamino structure. This monomer, combined with an aromatic diamine component containing an ether bond and with controlled proportions, can be used to prepare polyimide materials. This significantly improves the material's high-temperature resistance, bending fatigue resistance, and electrical stability, making it particularly suitable for the gold finger structure of flexible printed circuit boards. Detailed Implementation

[0023] The present invention will be described below with reference to specific embodiments. It should be noted that the following embodiments are examples of the present invention and are used only to illustrate the invention, not to limit it. Other combinations and various modifications within the scope of the present invention can be made without departing from its spirit or scope.

[0024] Unless otherwise specified, all chemical reagents used in this invention are commercially available analytical grade reagents.

[0025] Preparation examples of aromatic diamine components with polybenzene ring and polyamine structures Step 1: Add 5 mol of bisphenol A to the reactor, then add 10 mol of potassium carbonate and 600 ml of dimethyl sulfoxide, heat to reflux for 4 h, after the reaction is completed, cool to 25 °C, then add 2.2 mol of 2-benzyloxy-5-chloronitrobenzene, continue to heat to 120 °C, after the reaction is completed for 4 h, cool to room temperature, pour the solution in the three-necked flask into 500 ml of 1% sodium hydroxide solution, stir, let stand, filter to obtain product 1; Step 2: Add 5 mol of product 1, 1.2 mol of Pd / C, and 600 ml of ethanol to the reactor. Heat and stir until uniformly dispersed. Then adjust the temperature to 70°C and begin adding 30 mol of hydrazine hydrate dropwise from a dropping funnel. Continue the reaction. After the reaction is complete, filter while hot to recover Pd / C. Let the filtrate stand, filter again to obtain brown crystals, and dry to obtain the aromatic diamine component with the polybenzene ring polyamine structure. (Yield: 72.17%) Example 1 800 ml of NMP was added to a dry reactor. Under nitrogen protection, 3 mol of the polyphenylene ring polyamine aromatic diamine component and 4 mol of the aromatic diamine component containing ether bonds (4,4′-diaminodiphenyl ether) were added. The mixture was heated and stirred at 40 °C until it was uniformly dispersed. The reaction system was cooled to 10 °C, and then 7 mol of the aromatic dianhydride component (3,3′,4,4′-biphenyltetracarboxylic dianhydride) were added in batches. After the addition was complete, the temperature was raised to 40 °C and the reaction was continued for 10 h to obtain a polymer solution. After vacuum degassing for 2 h and filtration through a 1 μm filter membrane, the solution was cast into a film. The solvent was removed at 80 °C for 60 min, and the film was further densified at 120 °C for 30 min. Then, the film was imidized under a nitrogen atmosphere (the four stages were: 150 °C × 1 h, 200 °C × 1 h, 250 °C × 1 h, and 300 °C × 0.1 h) to obtain the modified resin film 1.

[0026] Example 2 The preparation steps are basically the same as in Example 1, except that the ratio of the amount of the polyphenylene ring polyamine structure aromatic diamine component, the aromatic diamine component containing ether bonds (4,4′-diaminodiphenyl ether), and the aromatic dianhydride component (3,3′,4,4′-biphenyltetracarboxylic dianhydride) added is 3 mol: 5 mol: 8 mol, and the modified resin film 2 is prepared.

[0027] Example 3 The preparation steps are basically the same as in Example 1, except that the ratio of the amount of the polyphenylene ring polyamine structure aromatic diamine component, the aromatic diamine component containing ether bonds (4,4′-diaminodiphenyl ether), and the aromatic dianhydride component (3,3′,4,4′-biphenyltetracarboxylic dianhydride) added is 5 mol: 4 mol: 9 mol, and the modified resin film 3 is prepared.

[0028] Comparative Example 1 The preparation steps are basically the same as in Example 1, except that the ratio of the amount of the polyphenylene ring polyamine structure aromatic diamine component, the aromatic diamine component containing ether bonds (4,4′-diaminodiphenyl ether), and the aromatic dianhydride component (3,3′,4,4′-biphenyltetracarboxylic dianhydride) added is 0 mol: 7 mol: 7 mol, and the modified resin film 4 is prepared.

[0029] Comparative Example 2 The preparation steps are basically the same as in Example 1, except that the ratio of the amount of the polyphenylene ring polyamine structure aromatic diamine component, the aromatic diamine component containing ether bonds (4,4′-diaminodiphenyl ether), and the aromatic dianhydride component (3,3′,4,4′-biphenyltetracarboxylic dianhydride) added is 7 mol: 2 mol: 9 mol, and the modified resin film 5 is prepared.

[0030] Comparative Example 3 The preparation steps are basically the same as in Example 1, except that the ratio of the amount of the polyphenylene ring polyamine structure aromatic diamine component, the aromatic diamine component containing ether bonds (4,4′-diaminodiphenyl ether), and the aromatic dianhydride component (3,3′,4,4′-biphenyltetracarboxylic dianhydride) added is 7 mol: 0 mol: 7 mol, and the modified resin film 6 is prepared.

[0031] Performance testing 1. Select a modified resin film with a thickness of 5μm, cut it into sheets of 100mm×15mm, and then fix the sheets perpendicular to the chuck of the high-speed rail tensile testing machine with the initial vertical height of the chuck 5cm. Set the tensile rate to 50mm / min and measure the maximum tensile force as F. Tensile strength = F / 9.8 / (15mm×T).

[0032] 2. Cut the modified resin film into samples 200mm in length and 15mm in width. Fix the samples onto a tensile testing machine (model AI7000), record the initial length L0, and start the tensile testing machine until the polyimide composite film sample breaks. Read the displacement distance L1 of the polyimide composite film sample at the time of breakage from the tensile testing machine. The average value of the two test results is the test result. Calculate the elongation at break using the formula: elongation at break = (L1 - L0) / L0 * 100%.

[0033] 3. The dielectric constant of the polyimide film prepared above was determined; the dielectric constant was obtained at a frequency of 10 GHz using the resonant cavity resonance method.

[0034] 4. The modified resin material was subjected to 80,000 bending tests in a bending tester (PT-604A). The film was then sent to a desktop scanning microscope to observe its surface and cross-section. The surface of the resin film was observed to ensure it remained flat and the cross-section was free of cracks.

[0035] The test results are shown in Table 1.

[0036] Table 1 Test Result Data Table

[0037] The polyimide material of this invention introduces a multi-benzene ring structure into the main chain and achieves full imidization, which suppresses the molecular chain polarization ability and thus exhibits a lower dielectric constant, which is beneficial to improving high-frequency signal transmission performance and electrical performance stability.

[0038] As can be seen from the comparison of the examples and comparative examples, when the amount of aromatic diamine component containing ether bonds is excessive, although the aromatic diamine containing ether bonds is itself relatively flexible, its excess will lead to insufficient chain length and a decrease in intermolecular entanglement density. While it may appear flexible in the initial stage of the bending test, it will rapidly fatigue and fail after repeated bending cycles, resulting in a decrease in the insertion and removal life of the flexible circuit board gold fingers. This is a "false flexibility" problem, which is extremely fatal in gold finger applications. Simultaneously, the proportion of aromatic rigid units in the material decreases, leading to increased dielectric loss, which is detrimental to its use in gold finger products.

[0039] When too much aromatic diamine component with polyphenyl ring and polyamine structure is added, the rigidity of the molecular chain increases sharply and the mobility of the chain segments decreases, resulting in poor leveling, easy formation of streaks, uneven film thickness, i.e., microcracks. Furthermore, the molecular chain is difficult to relax, internal stress is concentrated, and the stress cannot be released through chain segment rotation. After repeated bending, it is easy to break brittle. During repeated insertion and removal of the gold finger, the crack will expand rapidly, which is not conducive to improving the bending performance.

[0040] The polyimide material for gold fingers described in this invention uses aromatic dianhydrides and aromatic diamines as raw materials. The aromatic diamines include aromatic diamines with polyphenyl ring and polyamine structures and aromatic diamines containing ether bonds. Through the synergistic ratio of the two, while ensuring the high heat resistance of polyimide, the bending fatigue resistance and electrical stability of the material are significantly improved, making it particularly suitable for high-reliability applications of FPC gold fingers.

[0041] The present invention can also be implemented in various other ways. Without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and modifications according to the present invention, but these corresponding changes and modifications should all fall within the protection scope of the appended claims.

Claims

1. A thermosetting, flexurally resistant modified resin for FPC gold fingers, characterized in that, The composition comprises a modified polyimide, wherein the polymeric monomers of the modified polyimide include an aromatic dianhydride component, a polycyclic aromatic diamine component with a polyamine ring structure, and an aromatic diamine component containing an ether bond.

2. The thermosetting, flexurally resistant modified resin for FPC gold fingers according to claim 1, characterized in that, The aromatic dianhydride component is selected from one or more combinations of 3,3′,4,4′-biphenyltetracarboxylic dianhydride, 4,4′-oxobiphenyltetracarboxylic dianhydride, pyromellitic dianhydride, and benzophenonetetracarboxylic dianhydride.

3. The thermosetting, flexurally resistant modified resin for FPC gold fingers according to claim 1, characterized in that, The preparation method of the polyphenyl ring polyamine aromatic diamine component includes the following steps: Step 1: Add bisphenol A to the reactor, then add salt and solvent, heat to reflux and react. After the reaction is complete, cool down, then add 2-benzyloxy-5-chloronitrobenzene, continue the reaction and cool after the reaction is complete. Post-process to obtain product 1. Step 2: Add product 1, catalyst and solvent to the reactor, heat and stir to dissolve, then cool to 70°C, start adding hydrazine hydrate dropwise from the dropping funnel, continue the reaction, and after the reaction is completed, obtain the aromatic diamine component with the polybenzene ring polyamine structure through post-treatment.

4. The thermosetting, flexurally resistant modified resin for FPC gold fingers according to claim 1, characterized in that, The salt in S1 is selected from potassium carbonate and sodium carbonate; the solvent is selected from N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide and toluene; the reflux reaction temperature is 90-150℃ and the reaction time is 4-16h.

5. The thermosetting, flexurally resistant modified resin for FPC gold fingers according to claim 3, characterized in that, The ratio of bisphenol A, salt, and 2-benzyloxy-5-chloronitrobenzene added in S1 is 1 mol: 1.5-3.0 mol; 1-2.5 mol.

6. The thermosetting, flexurally resistant modified resin for FPC gold fingers according to claim 3, characterized in that, The molar ratio of product 1 to hydrazine hydrate in S2 is 1:6-16; the reaction temperature in S2 is 70-110℃, and the reaction time is 2-10 h.

7. The thermosetting, flexurally resistant modified resin for FPC gold fingers according to claim 3, characterized in that, The aromatic diamine component containing an ether bond is 4,4′-diaminodiphenyl ether.

8. The thermosetting, flexurally resistant modified resin for FPC gold fingers according to claim 1, characterized in that, The molar ratio of the aromatic dianhydride component, the polyphenyl ring polyamine structure aromatic diamine component, and the ether-containing aromatic diamine component is 6-10:3-7:3-7.

9. The method for preparing the thermosetting, flexurally resistant modified resin for FPC gold fingers according to claims 1-8, characterized in that, Includes the following steps: Solvent is added to a dry reactor, and aromatic diamine components with polyphenyl ring and polyamine structure and aromatic diamine components containing ether bonds are added under nitrogen protection. The mixture is heated and stirred until completely dissolved. The reaction system is cooled, and then aromatic dianhydride components are added. After the addition is complete, the temperature is raised to continue the reaction to obtain a polymer solution. After vacuum degassing and filtration through a filter membrane, the solution is formed into a film and cured under a nitrogen atmosphere to obtain a modified resin.

10. The cured product of the thermosetting flexurally resistant modified resin for FPC gold fingers according to any one of claims 1-8, or the cured product of the modified resin product prepared by the preparation method according to claim 9.

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