Polyimide resin for positive photoresist and preparation method and application thereof

Abstract

The invention provides a polyimide resin for positive photoresist, which comprises 75-92.5% of a polyimide precursor (PAA), 11.5-15.5% of a hyperbranched chain prepolymer, and 1.2-4.5% of a photoacidifier by weight percentage; the polyimide precursor (PAA) is prepared by polymerizing a fluorine-containing diamine monomer and a fluorine-containing dianhydride monomer; the hyperbranched chain prepolymer is a chain hyperbranched alkenyl tert-butyl ester, and the chain hyperbranched alkenyl tert-butyl ester is prepared by polymerizing a polyol and an alkenyl tert-butyl ester. Two chain-structured low Tg values ​​and chemical-resistant fluorine-containing polyimide resins are obtained by hyperbranched polymerization of PAA, hyperbranched chain prepolymer / blended photoacidifier or hyperbranched polymerization of PAA, photoacidifier, and hyperbranched chain prepolymer.

Description

Technical Field

[0001] The invention relates to the technical field of photosensitive materials, and in particular to a polyimide resin for positive photoresist and a preparation method and application thereof. Background Art

[0002] Polyimide has high heat resistance, high strength, and excellent dielectric properties. More importantly, polyimide can be converted into stable polyimide by heating in the form of various precursors, such as polyamic acid, polyamide ester, and polyisoimide. In this way, photosensitive groups can be introduced in the form of salts or esters and converted into a stable polyimide layer by heating after exposure and development.

[0003] At present, commercial positive photosensitive polyimide resin mainly uses polyamic acid (PAA) precursor, which has the advantages of: the monomer source is relatively wide, and it can be developed in alkaline solution (2.38% tetramethylammonium hydroxide aqueous solution), which is environmentally friendly, such as Toray's PW series. However, polyamic acid precursor contains a large number of hydrophilic groups, and the dissolution rate in alkaline developer is extremely fast. The difference in dissolution rate between the exposed area and the non-exposed area is small, resulting in low film retention rate and contrast, and the development process is difficult to accurately control. In the post-baking process, the conversion of the precursor polyamic acid (PAA) to PI not only requires high-temperature treatment, generally greater than 320°C, but also in this process, PAA has to remove water molecules, which can easily cause film shrinkage, cause stress between the film and the substrate, and affect the reliability of the product. Summary of the invention

[0004] In order to solve the technical problems in the exposure and development of positive photoresist in the prior art, the present invention provides a polyimide resin for positive photoresist and a preparation method and application thereof.

[0005] In a first aspect, the present invention provides a polyimide resin for positive photoresist, which comprises, by weight percentage, 75-92.5% of a polyimide precursor (PAA), 11.5-15.5% of a hyperbranched chain precursor, and 1.2-4.5% of a photoacid agent.

[0006] The polyimide precursor is prepared by polymerizing a fluorine-containing diamine monomer and a fluorine-containing dianhydride monomer.

[0007] Preferably, the fluorine-containing diamine monomer is 2,2′-bistrifluoromethyl-4,4-biphenylenediamine.

[0008] Preferably, the fluorine-containing dianhydride monomer is 4,4'-(hexafluoroisopropylene) diphthalic anhydride.

[0009] The hyperbranched chain precursor is chain hyperbranched alkenyl tert-butyl ester, and the chain hyperbranched polytert-butyl acrylate is prepared by polymerizing polyol and alkenyl tert-butyl ester.

[0010] Preferably, the alkenyl tert-butyl ester is tert-butyl acrylate.

[0011] The photoacid generator is at least one of an onium salt photoacid generator, a dicarboximide N-sulfonyl group, and a fluorine-containing oxime ester.

[0012] The onium salt photoacid agent and dicarboximide N-sulfonyl group can form monomers, which are hyperbranched and polymerized at the end groups of the hyperbranched chain precursors, and then blended and polymerized with the polyimide precursors to graft the polyimide precursors.

[0013] Preferably, the onium salt photoacid generator is at least one of a sulfonium salt photoacid generator or an iodonium salt photoacid generator.

[0014] The onium salt photoacid agent and dicarboximide N-sulfonyl group are grafted and polymerized on the hyperbranched chain precursor, which can enhance the conversion of the tert-butyl ester group in the hyperbranched chain precursor into a carboxyl group after absorbing exposure energy, thereby enhancing the dissolution rate of the resin in the exposed area of ​​the polyimide resin for positive photoresist in an alkaline developer.

[0015] The fluorine-containing oxime ester is blended with a polyimide precursor and a hyperbranched chain precursor polymer, but is not polymerized in the chain structure of the polyimide precursor and the hyperbranched chain precursor polymer. The structural formula of the fluorine-containing oxime ester is:

[0016] ; Rf group is C3F7, C4F8H.

[0017] The fluorine-containing oxime ester introduces fluorine element, thereby enhancing the light transmittance and hydrophobicity of the resin. Meanwhile, by enhancing the hydrophobicity of the resin, the dissolution rate in the alkaline developer is inhibited, thereby enhancing the resolution and contrast of the graphics.

[0018] The polyimide precursor (PAA) in the positive photoresist polyimide resin is grafted and polymerized on the end group of the hyperbranched chain precursor, and the photoacid agent is mixed, so that the glass transition temperature of the formed positive photoresist polyimide resin is 280°C-315°C.

[0019] The photoacid agent in the positive photoresist polyimide resin is graft polymerized on the end group of the hyperbranched chain precursor and graft polymerized on the polyimide precursor (PAA). The glass transition temperature of the formed positive photoresist polyimide resin is 270°C-295°C.

[0020] In a second aspect, the present invention provides a method for preparing a polyimide resin for a positive photoresist:

[0021] S100: Preparation of polyimide precursor:

[0022] Under the protection of inert gas, the fluorine-containing diamine monomer and the fluorine-containing dianhydride monomer are dissolved in an organic solvent, dispersed by ultrasonic wave, a mixture of triethylamine and acetic anhydride is slowly added dropwise, and the reaction is continued in a water bath for 8-15 hours to obtain the polyimide precursor;

[0023] S200: Preparation of hyperbranched chain precursors:

[0024] S2001: dissolving polyol and ethyl 2-[bis(2-hydroxyethyl)amino]acetate in an organic solvent, fully reacting, adding tert-butyl acrylate and initiator azobisisobutyronitrile under the protection of inert gas, ultrasonically dispersing, oil bathing, fully reacting for 5-8 hours, and diluting with an organic solvent to obtain the first hyperbranched chain precursor polymer;

[0025] S2002: Prepare a dicarboximide N-sulfonyl monomer or an onium salt photoacid monomer, and add it to a flask, then add the first hyperbranched chain precursor and initiator azobisisobutyronitrile in step S2001, ultrasonically disperse, oil bath, fully react for 3-5 hours, dilute with an organic solvent, and obtain a second hyperbranched chain precursor.

[0026] S300: Preparation of polyimide:

[0027] S3001: 75-92.5% of the polyimide precursor (PAA) is grafted polymerized on 11.5-15.5% of the first hyperbranched chain precursor obtained in step S2001, and an initiator azobisisobutyronitrile is added, ultrasonic dispersion is performed, and an oil bath is used for full reaction for 12-15 hours, and then mixed with 1.2-4.5% of the photoacid agent to obtain the polyimide;

[0028] S3002: Calculated by weight percentage, 75-92.5% of the polyimide precursor (PAA) is grafted onto 12.7%-20% of the second hyperbranched chain precursor obtained in step S2002, an initiator azobisisobutyronitrile is added, ultrasonic dispersion is performed, an oil bath is used, and the reaction is fully reacted for 8-10 hours to obtain the polyimide.

[0029] By adjusting the weight percentage of the hyperbranched chain precursor to the first hyperbranched chain precursor, the dielectric constant of the polyimide prepared in step S3001 is controlled to be 2.5-3.1, and the glass transition temperature is 280° C.-315° C.

[0030] By adjusting the weight percentage of the hyperbranched chain precursor and the second hyperbranched chain precursor, the dielectric constant of the polyimide prepared in step S3002 is controlled to be 1.7-2.6, and the glass transition temperature is 270° C.-295° C.

[0031] The formed symmetrical chain polyimide resin has symmetrical molecular groups in the internal structure, which is beneficial to reducing the molecular polarization caused by the stretching vibration of the asymmetric structure molecules under heat, thereby obtaining a polyimide resin with a low dielectric constant.

[0032] In a third aspect, the present invention provides an application of a polyimide resin for positive photoresist in electronic packaging.

[0033] 1) The prepared bare chip is encapsulated with polyimide having a high Tg value to expose the chip electrodes;

[0034] 2) Spin-coating the positive photoresist polyimide resin on the chip electrode surface, pre-baking, exposing, and developing with alkaline solution to form a first resin pattern layer;

[0035] 3) Ion implantation, electroplating or metal evaporation of the resin pattern layer to form metal pillars and RDL rewiring layers that conduct the chip electrodes;

[0036] 4) Spin-spray high Tg polyimide again, pre-bake, expose, and develop with alkaline solution to form a second resin pattern layer, and then electroplate and evaporate metal to form a ball pad;

[0037] 5) Solder paste ball planting, connecting the chip electrodes and forming a heat transfer channel at the same time, transferring the chip heat through the metal column and ball planting pad to the solder paste ball planting.

[0038] Preferably, the Tg value of the high Tg polyimide is at least 325°C.

[0039] Preferably, the Tg value of the polyimide resin for positive photoresist is 270-290°C.

[0040] The beneficial effects achieved by the present invention are:

[0041] 1) The tert-butyl ester group is subjected to super-differentiation polymerization with PAA to introduce a photoacid group, which generates a proton acid after absorbing energy. The proton acid reacts the tert-butyl ester group into a carboxyl group. The carboxyl group increases the dissolution rate of polyimide in the developed area in the alkaline developer, thereby enhancing the contrast and resolution with the non-exposed area;

[0042] 2) Superdifferentiation of polymerized alkenyl tert-butyl ester groups and grafting of PAA makes PAA arranged in a chain, which reduces the entanglement of macromolecules and lowers the glass transition temperature;

[0043] 3) The terminal PAA group accounts for a high proportion in the polymerization, which can isolate the base of the alkaline developer from the tert-butyl ester group, inhibit the hydrolysis of the tert-butyl ester group, and reduce the dissolution rate of the alkaline developer on the non-exposed area;

[0044] 4) Super-differentiated polymerized alkenyl tert-butyl ester groups, then grafted with photoacid monomers, and then polymerized with PAA. By adjusting the proportion of PAA in polyimide, the protonic acid is encapsulated, and the acid diffusion capacity of the protonic acid can be easily adjusted, thereby controlling the LER;

[0045] 5) Blending the photoacid generator, by adjusting the proportion of PAA in the polyimide, the proton acid generated by the photoacid generator is separated from the end group PAA, thereby adjusting the generation rate of the carboxyl group and further adjusting the chemical resistance of the polyimide;

[0046] 6) PAA is polymerized from fluorine-containing diamine monomers and fluorine-containing dianhydride monomers. By introducing the fluorine element, the transmittance and hydrophobicity of the resin are enhanced. At the same time, by enhancing the hydrophobicity of the resin, the dissolution rate in alkaline developer is inhibited, thereby enhancing the resolution and contrast of the graphic. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0048] Figure 1 This is the DSC test diagram of the polyimide resin in Example 3;

[0049] Figure 2 The figure is a schematic diagram of the application process of the polyimide resin prepared in Example 1 and Example 2 in electronic packaging. DETAILED DESCRIPTION

[0050] In order to more clearly understand the above-mentioned purpose, features and advantages of the present invention, the present invention is further described below in conjunction with the accompanying drawings and embodiments. It should be noted that the embodiments of the present application and the features in the embodiments can be combined with each other without conflict.

[0051] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0052] Example 1: The present invention provides a method for preparing a polyimide resin for positive photoresist: (hyperbranched grafted PAA + photoacid agent)

[0053] S100: Preparation of polyimide precursor:

[0054] Under nitrogen protection, 1.5 mol of the fluorinated diamine monomer and 1.5 mol of the fluorinated dianhydride monomer are dissolved in an organic solvent, acetone, and ultrasonically dispersed for 30 minutes. A mixture of triethylamine and acetic anhydride is slowly added dropwise within 10 minutes, and the reaction is continued in a water bath at 65-75° C. for 8-15 hours. After the reaction, a highly viscous polymer solution is slowly poured into methanol, and the precipitated solid is repeatedly washed with an organic solvent for 3 times and dried in a vacuum oven.

[0055] S200: Preparation of hyperbranched chain precursors:

[0056] Dissolve 0.1 mol of tetrakisene tetraol and 0.4 mol of ethyl 2-[bis(2-hydroxyethyl)amino]acetate in acetone solvent, fully react for 30 minutes, add tert-butyl acrylate and initiator azobisisobutyronitrile under nitrogen protection, ultrasonically disperse for 1 hour, and fully react for 5-8 hours in an oil bath at 75-85°C, dilute with organic solvent acetone, wash 3 times, and dry to obtain the hyperbranched chain precursor polymer;

[0057] S300: Preparation of polyimide:

[0058] Calculated by weight percentage, 75-92.5% of polyimide precursor (PAA) and 11.5-15.5% of hyperbranched chain precursor are blended, initiator azobisisobutyronitrile is added, ultrasonic dispersion is performed for 1 hour, oil bath is performed at 75-85°C, and fully reacts for 5-8 hours, and then onium salt photoacid agent, dicarboximide N-sulfonyl or fluorine-containing oxime ester are added and blended to form three types of positive photoresist polyimide resins (PR1, PR2, PR3). PR1 is a blended onium salt polyimide resin, PR2 is a blended dicarboximide N-sulfonyl polyimide resin, and PR3 is a blended fluorine-containing oxime ester polyimide resin.

[0059] Example 2: The present invention provides a method for preparing a polyimide resin for positive photoresist: (hyperbranched grafted PAA / hyperbranched grafted photoacid agent)

[0060] S400: polymerizing an onium salt photoacid agent and a dicarboximide N-sulfonyl group at the end group of the hyperbranched chain precursor, the specific steps are as follows:

[0061] (1) Preparation of dicarboximide N-sulfonyl monomer

[0062] Provide a three-necked flask, dissolve sodium vinylbenzenesulfonate in 200 mL of DMF aqueous solution, disperse by ultrasonic for 10 minutes, slowly dropwise add thionyl chloride solution within 10 minutes to obtain an intermediate product, vinylbenzenesulfonyl chloride, dissolve the obtained vinylbenzenesulfonyl chloride in catalysts pyridine and acetonitrile, add N-hydroxyphthalimide, and react fully to obtain dicarboximide N-sulfonyl monomer;

[0063] (2) Preparation of onium salt photoacid monomer

[0064] Sodium p-vinylbenzenesulfonate is dissolved in a DMF aqueous solution, and ultrasonic dispersion is performed for 10 minutes. A diaryl iodonium salt or triaryl sulfonium salt aqueous solution is added dropwise, and the reaction is fully carried out to obtain an onium salt photoacid agent monomer.

[0065] (3) End-group grafting of the photoacid agent

[0066] Provide a three-necked flask, add the hyperbranched chain precursor described in step S200 of Example 1 and the initiator azobisisobutyronitrile into the flask, disperse by ultrasonic for 1 hour, and fully react for 5 hours in an oil bath at 75-85° C., and dilute with an organic solvent acetone.

[0067] S500: Calculate by weight percentage, blend the polyimide precursor and the hyperbranched chain precursor obtained in step S400, add initiator azobisisobutyronitrile, ultrasonically disperse for 1 hour, and fully react for 5-8 hours in an oil bath at 75-85°C to form two polyimide resins (PR4 and PR5) for positive photoresist. PR4 is a polyimide resin grafted with an onium salt monomer, and PR5 is a polyimide resin grafted with a dicarboximide N-sulfonyl monomer.

[0068] Example 3: DSC test of polyimide resin

[0069] The three polyimide resins of the blend system (PR1, PR2, PR3) prepared in Example 1 and the two polyimide resins of the graft modification system (PR4, PR5) prepared in Example 2 were set as the experimental group. The same weight ratio of polyimide precursor (PAA), tert-butyl acrylate, and photoacid agent were polymerized to form a linear polyimide resin, which was set as the control group PR0. The test results are shown in FIG. Figure 1 :

[0070] The Tg values ​​of the five chain polyimide resins synthesized by hyperbranching are all lower than that of the linear polyimide resin, and the reduction in Tg value is at least 30°C. This is mainly because the chain structure formed by hyperbranching helps to reduce the entanglement of macromolecular chains. At the same time, the higher the degree of branching, the more active branching points there are, and more monomers will participate in the branching reaction, resulting in a shorter average molecular segment length of the polymer, a smaller molecular weight, and an increase in the internal free volume of the polymer, resulting in a decrease in the Tg of the polymer.

[0071] At the same time, by comparing the three polyimide resins in the blending system (PR1, PR2, PR3) and the two polyimide resins in the grafting modification system (PR4, PR5), it can be seen that the Tg value decreases when the onium salt monomer and the dicarboximide N-sulfonyl monomer are grafted into the polyimide resin. This is because more monomers participate in the branching reaction, the average molecular segment length becomes shorter, and the Tg of the polymer is reduced.

[0072] Example 4: Polyimide resin sensitivity and contrast test

[0073] The three polyimide resins of the blend system (PR1, PR2, PR3) prepared in Example 1 and the two polyimide resins of the graft modification system (PR4, PR5) prepared in Example 2 were set as the experimental group. The same weight ratio of polyimide precursor (PAA), tert-butyl acrylate, and photoacid agent were polymerized to form a linear polyimide resin, which was set as the control group PR0. The test results are shown in Table 1 below:

[0074]

[0075] Table 1

[0076] In the sensitivity test, since the three polyimide resins in the blend system (PR1, PR2, and PR3) form proton acids when exposed to photoacid, and the proton acids enter the interior of the chain polyimide and react with tert-butyl ester to hydrolyze, they are affected by the steric hindrance of the polyimide precursor at the end group, and the exposure energy is higher than that of the PR0 control group. However, the two polyimide resins in the graft modification system (PR4 and PR5) have proton acids generated by the grafting polymerization of the photoacid groups on the alkenyl tert-butyl ester groups, and the exposure energy to promote the hydrolysis of the tert-butyl ester groups is significantly reduced.

[0077] In the contrast test, the three polyimide resins in the blend system (PR1, PR2, PR3) and the two polyimide resins in the graft modification system (PR4, PR5) all had stronger dissolution inhibition ability in alkaline solution development than the control group PR0. Among them, due to the introduction of fluorine element, the polyimide resin prepared in the PR3 experimental group has strong hydrophobicity, and the fluorine element inhibits the dissolution of the resin in the alkaline developer and enhances the contrast.

[0078] Example 5: Application of polyimide resin in electronic packaging

[0079] Process such as Figure 2 :

[0080] 1) The prepared bare chip is encapsulated with polyimide PSPI with a high Tg value (at least 325°C) to expose the chip electrodes;

[0081] 2) Spin-coating the positive photoresist polyimide resin (Tg value is 270-290° C.) on the chip electrode surface, pre-baking, exposing, and developing with alkaline solution to form a first resin pattern layer;

[0082] 3) Ion implantation, electroplating, or evaporation of copper metal into the resin pattern layer to form copper pillars and RDL layers that conduct the chip electrodes;

[0083] 4) Spin-spray polyimide PSPI with high Tg value (at least 325°C) again, pre-bake, expose, and develop with alkaline solution to form a second resin pattern layer, and then electroplate and evaporate metal to form a ball pad;

[0084] 5) Solder paste ball planting, connecting the chip electrodes and forming a heat transfer channel at the same time, transferring the chip heat through the metal column and ball planting pad to the solder paste ball planting.

[0085] In the chip working state, heat is transferred from the chip electrode to the copper pillar, and the copper pillar transfers the heat to the copper pillar ball pad, forming a thermal bump in the solder paste. Correspondingly, in the chip area where heat is concentrated, polyimide PSPI with a high Tg value (at least 325°C) is used for plastic sealing, and the solder paste layer of the thermal bump also uses polyimide PSPI with a high Tg value as a dielectric layer. In the chip area where heat is not concentrated, that is, the corresponding layer of the copper pillar and the RDL layer uses the hyperbranched polyimide PSPI prepared in Example 1 or 2 as a dielectric layer, and the RDL layer and copper pillar for making fine lines can be formed by the photosensitive hyperbranched polyimide PSPI with high resolution and contrast, reducing the dissolution of the film layer in the non-exposed area due to the inability of PAA to tolerate alkaline developer.

[0086] Through the above specific implementations, those skilled in the art can easily implement the present invention. However, it should be understood that the present invention is not limited to the above specific implementations. On the basis of the disclosed implementations, those skilled in the art can arbitrarily combine different technical features to achieve different technical solutions.

Claims

1. A polyimide resin for positive photoresist, characterized in that: By weight percentage, it includes polyimide precursor PAA 75-92.5%, hyperbranched chain precursor polymer 11.5-15.5%, and photoacid agent 1.2-4.5%; The polyimide precursor PAA is prepared by polymerizing a fluorine-containing diamine monomer and a fluorine-containing dianhydride monomer; The hyperbranched chain precursor is a chain hyperbranched alkenyl tert-butyl ester, and the chain hyperbranched alkenyl tert-butyl ester is prepared by polymerizing a polyol with an alkenyl tert-butyl ester; The fluorine-containing diamine monomer is 2,2'-bistrifluoromethyl-4,4-biphenyl diamine, and the fluorine-containing dianhydride monomer is 4,4'-(hexafluoroisopropylene) diphthalic anhydride; The photoacidifier is at least one of an onium salt photoacidifier, a dicarboximide N-sulfonyl, and a fluorine-containing oxime ester; The onium salt photoacid generator is at least one of a sulfonium salt photoacid generator or an iodonium salt photoacid generator; The structural formula of the fluorine-containing oxime ester is: ； The Rf group is C3F7, C4F8H; Preparation method of polyimide resin for positive photoresist: S100: Preparation of polyimide precursor: Under the protection of inert gas, the fluorine-containing diamine monomer and the fluorine-containing dianhydride monomer are dissolved in an organic solvent, dispersed by ultrasonic wave, a mixture of triethylamine and acetic anhydride is slowly added dropwise, and the reaction is continued in a water bath for 8-15 hours to obtain the polyimide precursor; S200: Preparation of hyperbranched chain precursors: S2001: dissolving polyol and ethyl 2-[bis(2-hydroxyethyl)amino]acetate in an organic solvent, fully reacting, adding tert-butyl acrylate and initiator azobisisobutyronitrile under the protection of inert gas, ultrasonically dispersing, oil bathing, fully reacting for 5-8 hours, and diluting with an organic solvent to obtain the first hyperbranched chain precursor polymer; S2002: preparing a dicarboximide N-sulfonyl monomer or an onium salt photoacid monomer, and adding it to a flask, and then adding the first hyperbranched chain precursor polymer and the initiator azobisisobutyronitrile in step S2001, ultrasonically dispersing, oil bathing, fully reacting for 3-5 hours, and diluting with an organic solvent to obtain a second hyperbranched chain precursor polymer; S300: Preparation of polyimide: S3001: 75-92.5% of the polyimide precursor PAA is grafted onto 11.5-15.5% of the first hyperbranched chain precursor obtained in step S2001 by weight percentage, an initiator azobisisobutyronitrile is added, ultrasonic dispersion is performed, an oil bath is used, and the reaction is fully performed for 12-15 hours, and then mixed with 1.2-4.5% of the photoacid agent to obtain the polyimide; S3002: Calculated by weight percentage, 75-92.5% of the polyimide precursor PAA is grafted onto 12.7%-20% of the second hyperbranched chain precursor obtained in step S2002, an initiator azobisisobutyronitrile is added, ultrasonic dispersion is performed, an oil bath is used, and the reaction is fully reacted for 8-10 hours to obtain the polyimide.

2. A polyimide resin for positive photoresist as claimed in claim 1, characterized in that: The alkenyl tert-butyl ester is tert-butyl acrylate.

3. A polyimide resin for positive photoresist as claimed in claim 1, characterized in that: The positive photoresist uses a polyimide precursor PAA in a polyimide resin to graft polymerize the end group of the hyperbranched chain precursor and mixes the photoacid agent.

4. A polyimide resin for positive photoresist as claimed in claim 3, characterized in that: The glass transition temperature of the polyimide resin for positive photoresist is 280° C.-315° C.

5. A polyimide resin for positive photoresist as claimed in claim 1, characterized in that: The photoacidifier in the positive photoresist polyimide resin is graft polymerized on the end group of the hyperbranched chain precursor polymer, and is graft polymerized on the polyimide precursor PAA.

6. A polyimide resin for positive photoresist as claimed in claim 5, characterized in that: The glass transition temperature of the polyimide resin for positive photoresist is 270° C.-295° C.

7. Application of a polyimide resin for positive photoresist in electronic packaging, characterized in that: Providing a polyimide resin for positive photoresist according to any one of claims 1 to 6, 1) The prepared bare chip is encapsulated with polyimide having a Tg value of at least 325°C to expose the chip electrodes; 2) Spin-coating the positive photoresist polyimide resin with a Tg value of 270-290° C. on the electrode surface of the bare chip, pre-baking, exposing, and developing with alkaline solution to form a first resin pattern layer; 3) ion implantation, electroplating or evaporation of metal into the first resin pattern layer to form metal pillars and RDL rewiring layers that conduct the chip electrodes; 4) Spin-spray polyimide with a Tg value of at least 325°C again, pre-bake, expose, and develop with alkaline solution to form a second resin pattern layer, and then electroplate and evaporate metal to form a ball pad; 5) Solder paste ball planting, connecting the chip electrodes and forming a heat transfer channel, transferring the heat of the chip to the solder paste ball planting through the metal column and the ball planting pad.

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