Side chain modified polyimide alkali-soluble resin as well as preparation method and application thereof

Abstract

The invention discloses side chain modified polyimide alkali-soluble resin, which is prepared from the following raw materials in parts by weight: 6 to 8 parts of tetrahydrophthalimide, 5 to 18 parts of styrene, 1 to 2 parts of free radical initiators, 0.5 to 0.9 part of mercaptopropionic acid, 7 to 10 parts of glycidyl methacrylate, 0.2 to 0.6 part of triethylamine, 7 to 10 parts of dicarboxylic anhydride, 0.5 to 0.9 part of triphenylphosphine, 0.02 to 0.04 part of polymerization inhibitors and 40 to 60 parts of solvents. According to the invention, the styrene-tetrahydrophthalimide copolymer is used as a main chain of the resin, so that the resin shows excellent heat resistance, and can meet the harsh requirements of IC carrier solder resist ink on line width precision and thermal deformation resistance. The invention further discloses a preparation method and application of the side chain modified polyimide alkali-soluble resin.

Description

Technical Field

[0001] The invention belongs to the technical field of polymer materials, and particularly relates to a side chain modified polyimide alkali-soluble resin and a preparation method and application thereof. Background Art

[0002] IC substrate technology originated in Japan in the 1980s and has a history of over 30 years. Early on, it coexisted with integrated IC packaging technology. Currently, high-end ICs largely utilize substrate packaging technology, serving as the precise connection between the core chip and conventional printed circuit boards (PCBs). IC substrates are manufactured from copper-clad laminates through processes such as photolithography, solder mask development, and gold plating. They differ from traditional copper laminates in several ways. First, the substrate used for IC substrates differs from the epoxy / glass fiber composites used in traditional copper-clad laminates. Instead, the copper-clad laminates (films) primarily utilize BT resin, ABF insulation film (Ajinomoto Build-up Film), and MIS polymers. Second, IC substrate production begins with specialized copper-clad laminates (films), and the circuit etching and solder mask development processes required require more sophisticated techniques than those used in conventional PCB production. This means higher resolution etching and solder mask development, with line widths typically controlled within tens of microns. Third, as a permanent, fine, protective thin layer of material, solder mask photosensitive developing ink is required to have strict heat resistance, thermal expansion resistance, hardness, scratch resistance, and impact resistance on the IC substrate. Some applications even require the solder mask layer to have a low dielectric constant to meet the requirements of high-frequency communications. Fourth, the back-end processing of IC substrates mostly uses chemical gold plating (abbreviated as chemical gold in the industry) rather than electroplating. Chemical gold solutions are generally highly acidic or alkaline, which requires the IC substrate solder mask layer to have a high resistance to chemical gold (i.e., corrosion resistance) to avoid defects such as discoloration, denaturation, and easy peeling of the solder mask layer. In short, because IC substrates are directly involved in IC bare chip packaging, in order to ensure the working reliability of the packaged chip, there are high requirements for the performance reliability and dimensional precision of various materials on the substrate (especially the solder mask material).

[0003] In the prior art, there is still a lack of an IC substrate solder resist material with excellent properties such as photosensitivity, etching resistance, electroplating resistance, and film stripping resistance. Summary of the Invention

[0004] According to a first aspect of the present invention, a side chain modified polyimide alkali-soluble resin is provided, the raw material composition of which includes, in parts by weight: 6-8 parts of tetrahydrophthalimide, 5-18 parts of styrene, 1-2 parts of a free radical initiator, 0.5-0.9 parts of mercaptopropionic acid, 7-10 parts of glycidyl methacrylate, 0.2-0.6 parts of triethylamine, 7-10 parts of dicarboxylic acid anhydride, 0.5-0.9 parts of triphenylphosphine, 0.02-0.04 parts of a polymerization inhibitor, and 40-60 parts of a solvent.

[0005] In some embodiments, the molar ratio of tetrahydrophthalimide to styrene is (1-3):1.

[0006] In some embodiments, the free radical initiator may be selected from at least one of dibenzoyl peroxide, lauroyl peroxide, t-butyl perbenzoate, and t-butyl pervalerate.

[0007] In some embodiments, the dicarboxylic acid anhydride may be selected from at least one of tetrahydrophthalic anhydride, methyltetrahydrophthalic anhydride, and hexahydrophthalic anhydride.

[0008] In some embodiments, the polymerization inhibitor may be selected from at least one of hydroquinone, p-tert-butylcatechol, 2,6-di-tert-butyl-p-methylphenol, and catechol.

[0009] In some embodiments, the solvent may be selected from at least one of N,N-dimethylformamide, dimethyl sulfoxide, and ethylene glycol methyl ether acetate.

[0010] According to a second aspect of the present invention, there is provided a method for preparing a side chain modified polyimide alkali-soluble resin, comprising the following steps: S1. Tetrahydrophthalimide and a solvent are mixed to obtain a first mixed solution. Styrene, mercaptopropionic acid, a free radical initiator, and a solvent are mixed to obtain a second mixed solution. The second mixed solution is added dropwise to the first mixed solution at 70-90° C. and stirred for 0.5-1 h. The mixed solution is then heated to 120-140° C. and stirred for 3-5 h. After the reaction is completed, the mixture is cooled to room temperature. The product is then purified and dried to obtain a tetrahydrophthalimide-styrene polymer. S2. Tetrahydrophthalimide-styrene polymer, triethylamine, a polymerization inhibitor, and a solvent are mixed, glycidyl methacrylate is added dropwise to the mixed system at 40-60° C., and stirred for 0.5-1 h. The reaction system is then heated to 80-100° C. and stirred for 6-8 h. After the reaction is completed, a brown-black viscous liquid is obtained; S3. Mix the brown-black viscous liquid, triphenylphosphine and dicarboxylic acid anhydride, and stir the mixture at 70-90° C. for 6-8 h to obtain the product.

[0011] It should be noted that mercaptopropionic acid is used as a chain transfer agent to regulate the molecular weight and prevent implosion.

[0012] It should be noted that in step S1, a staged heating method is adopted to prepare the tetrahydrophthalimide-styrene polymer. The purpose is to first allow all the reaction raw materials to be evenly mixed at a lower temperature (70-90°C) to avoid local implosion during the subsequent high temperature (120-140°C) reaction.

[0013] It should be noted that in step S2, the role of triethylamine is to provide an alkaline environment, making it easier for the imide group to undergo a nucleophilic reaction with the epoxy group.

[0014] The preparation method of the side chain modified polyimide alkali-soluble resin of the present invention comprises the following steps: firstly subjecting styrene and tetrahydrophthalimide to free radical polymerization to obtain a polymer having an imide structure on the side chain; then utilizing the structure to react with an epoxy group for grafting to generate a polymer having a hydroxyl group; and finally utilizing the hydroxyl group to react with an acid anhydride monomer to ultimately obtain an alkali-soluble resin having both an acrylic acid double bond and a carboxylic acid group.

[0015] In some embodiments, in step S1, the structural formula of the tetrahydrophthalimide-styrene polymer is as shown in formula (I): Formula (I); In formula (I), the ratio of a to b is 1:1-1:3, and n is 8-21.

[0016] In some embodiments, in step S1, the mass ratio of the solvent in the first mixed liquid to the solvent in the second mixed liquid is (1-1.1):1.

[0017] In some embodiments, the mass ratio of the solvent used in step S1 to the solvent used in step S2 is (1-1.15): 1. It should be noted that the solvent used in step S1 includes the solvent in the first mixed liquid and the solvent in the second mixed liquid.

[0018] In some embodiments, in step S1, the time taken to add the second mixed solution dropwise to the first mixed solution is 20-40 minutes, in order to prevent subsequent reactions from being too rapid and causing implosion.

[0019] In some embodiments, in step S2, the molar ratio of glycidyl methacrylate to the imide group in the tetrahydrophthalimide-styrene polymer is (1-1.1):1.

[0020] According to a third aspect of the present invention, there is provided the use of the above-mentioned side chain modified polyimide alkali-soluble resin in the preparation of IC substrate solder resist ink, printed circuit board solder resist ink, and chip photoresist.

[0021] According to a fourth aspect of the present invention, a dry film is provided, which is prepared by photocuring or thermally curing the above-mentioned side chain modified polyimide alkali-soluble resin. The dry film can be used to prepare IC carriers or printed circuit boards.

[0022] The beneficial effects of the present invention include: The side chain modified polyimide alkali-soluble resin of the present invention adopts styrene-tetrahydrophthalimide copolymer as the main chain of the resin and exhibits excellent heat resistance. At the same time, due to the presence of a large number of imide structures, after double bond cross-linking and curing, it becomes a polyimide cured film, so it has excellent heat resistance, thermal expansion resistance, and dimensional stability, and can meet the stringent requirements of IC substrate solder mask ink for line width accuracy and thermal deformation resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Schematic diagram of the synthetic route of Examples 1-4 of the present invention; Figure 2 These are the infrared spectroscopy characterization results of tetrahydrophthalimide, styrene-tetrahydrophthalimide copolymer and side chain modified polyimide alkali-soluble resin in Example 1 of the present invention. DETAILED DESCRIPTION

[0024] The present invention will be further described in detail below with reference to the accompanying drawings, but the embodiments of the present invention are not limited thereto. The raw materials and reagents involved in the following examples can all be obtained from commercial channels.

[0025] One of the synthetic routes of the present invention is shown in Figure 1 . Figure 1 In the process, tetrahydrophthalimide and styrene are firstly reacted by free radical polymerization to obtain a styrene-tetrahydrophthalimide copolymer represented by formula (I).

[0026] Formula (I); In formula (I), the ratio of a to b is 1:1-1:3, and n is 8-21.

[0027] The imide group (-CO-NH-CO-) of the styrene-tetrahydrophthalimide copolymer then reacts with the epoxy group of glycidyl methacrylate. The lone pair of electrons on the nitrogen acts as a nucleophile, attacking the less hindered β-carbon of the epoxy group, causing the epoxy ring to open, forming a new C-N bond and a hydroxyl group (-OH). Glycidyl methacrylate is successfully grafted onto the styrene-tetrahydrophthalimide copolymer. Subsequently, tetrahydrophthalic anhydride undergoes an esterification reaction with the hydroxyl group generated by the ring-opening of glycidyl methacrylate, yielding a side-chain-modified polyimide alkali-soluble resin.

[0028] It should be noted that in Figure 1 In the synthesis route, in addition to tetrahydrophthalic anhydride, the dicarboxylic anhydride can also be selected from hydrogenated phthalic anhydride, such as methyltetrahydrophthalic anhydride and hexahydrophthalic anhydride.

[0029] Example 1 This embodiment provides a method for preparing a side chain modified polyimide alkali-soluble resin, comprising the following steps: (1) Under the condition of 90℃ oil bath, add 7.55 g of tetrahydrophthalimide and 11.3 g of ethylene glycol methyl ether acetate to a 250 mL three-necked flask with nitrogen protection, then mix 15.6 g of styrene, 0.82 g of 3-mercaptopropionic acid, 1.03 g of tert-butyl peroxybenzoate and 11.3 g of ethylene glycol methyl ether acetate, and slowly add the mixed solution dropwise to the three-necked flask. After the addition is complete, heat to 120℃ and react for 3.5 hours. After the reaction is completed, wait for the system to cool to room temperature, wash with anhydrous ethanol three times, filter and dry to obtain styrene-tetrahydrophthalimide copolymer. The obtained product is in the form of solid powder. (2) In a 50°C oil bath, 23.15 g of the styrene-tetrahydrophthalimide copolymer solid powder prepared in step (1), 0.05 g of hydroquinone, 0.25 g of triethylamine and 20 g of ethylene glycol methyl ether acetate were added to a 250 mL three-necked flask, and the mixture was stirred evenly. 7.81 g of glycidyl methacrylate was slowly added dropwise to the three-necked flask. After the addition was completed, the temperature was raised to 80°C and the reaction was carried out for 6 h. (3) Add 0.655 g of triphenylphosphine and 8.36 g of tetrahydrophthalic anhydride to the three-necked flask used in step (2), stir evenly, and react for 12 hours to obtain a side chain modified polyimide alkali-soluble resin.

[0030] The tetrahydrophthalimide (THPI), styrene-tetrahydrophthalimide copolymer (STI), and side chain modified polyimide alkali soluble resin (STI@G@T) in Example 1 were analyzed by Fourier transform infrared spectroscopy. The results are as follows: Figure 2 As shown. Figure 2 It can be seen that in the styrene-tetrahydrophthalimide copolymer, at 1706 cm -1 The characteristic peak at 1600-1450 cm -1 The benzene ring peak appeared at 3500cm, indicating that the styrene-tetrahydrophthalimide copolymer was successfully synthesized; in the infrared spectrum of the side chain modified polyimide alkali-soluble resin, the peak at 3500cm -1 The hydroxyl peak appears near 1640 cm -1 The carbon-carbon double bond peak appears at , proving that the synthesis of side chain modified polyimide alkali-soluble resin is successful.

[0031] Example 2 This embodiment provides a method for preparing a side chain modified polyimide alkali-soluble resin, comprising the following steps: (1) Under the condition of 90℃ oil bath, add 7.55 g of tetrahydrophthalimide and 11.3 g of N,N-dimethylformamide to a 250 mL three-necked flask with nitrogen protection, then mix 15.6 g of styrene, 0.82 g of 3-mercaptopropionic acid, 1.03 g of tert-butyl peroxybenzoate and 11.3 g of N,N-dimethylformamide, and slowly add the mixed solution dropwise to the three-necked flask. After the addition is complete, heat to 120℃ and react for 3.5 hours. After the reaction is completed, wait for the system to cool to room temperature, wash with anhydrous ethanol three times, filter and dry to obtain styrene-tetrahydrophthalimide copolymer. The obtained product is in the form of solid powder. (2) In a 50°C oil bath, 23.15 g of the styrene-tetrahydrophthalimide copolymer solid powder prepared in step (1), 0.05 g of hydroquinone, 0.25 g of triethylamine and 20 g of N,N-dimethylformamide were added to a 250 mL three-necked flask, and the mixture was stirred evenly. 7.81 g of glycidyl methacrylate was slowly added dropwise to the three-necked flask. After the addition was completed, the temperature was raised to 80°C and the reaction was carried out for 6 h. (3) Add 0.655 g of triphenylphosphine and 8.36 g of tetrahydrophthalic anhydride to the three-necked flask used in step (2), stir evenly, and react for 12 hours to obtain a side chain modified polyimide alkali-soluble resin.

[0032] Example 3 This embodiment provides a method for preparing a side chain modified polyimide alkali-soluble resin, comprising the following steps: (1) Under the condition of 90℃ oil bath, add 7.55g of tetrahydrophthalimide and 11.3g of ethylene glycol methyl ether acetate to a 250mL three-necked flask with nitrogen protection, then mix 10.4g of styrene, 0.82g of 3-mercaptopropionic acid, 1.03g of tert-butyl peroxybenzoate and 11.3g of ethylene glycol methyl ether acetate, and slowly add the mixed solution dropwise to the three-necked flask. After the addition is complete, heat to 120℃ and react for 3.5h. After the reaction is completed, wait for the system to cool to room temperature, wash with anhydrous ethanol three times, filter and dry to obtain styrene-tetrahydrophthalimide copolymer, the obtained product is in the form of solid powder; (2) In a 50°C oil bath, 23.15 g of the styrene-tetrahydrophthalimide copolymer solid powder prepared in step (1), 0.05 g of hydroquinone, 0.25 g of triethylamine and 20 g of ethylene glycol methyl ether acetate were added to a 250 mL three-necked flask, and the mixture was stirred evenly. 7.81 g of glycidyl methacrylate was slowly added dropwise to the three-necked flask. After the addition was completed, the temperature was raised to 80°C and the reaction was carried out for 6 h. (3) Add 0.655 g of triphenylphosphine and 8.36 g of tetrahydrophthalic anhydride to the three-necked flask used in step (2), stir evenly, and react for 12 hours to obtain a side chain modified polyimide alkali-soluble resin.

[0033] Example 4 This embodiment provides a method for preparing a side chain modified polyimide alkali-soluble resin, comprising the following steps: (1) Under the condition of 90℃ oil bath, add 7.55 g of tetrahydrophthalimide and 11.3 g of ethylene glycol methyl ether acetate to a 250 mL three-necked flask with nitrogen protection, then mix 5.2 g of styrene, 0.82 g of 3-mercaptopropionic acid, 1.03 g of tert-butyl peroxybenzoate and 11.3 g of ethylene glycol methyl ether acetate, and slowly add the mixed solution dropwise to the three-necked flask. After the addition is complete, heat to 120℃ and react for 3.5 hours. After the reaction is completed, wait for the system to cool to room temperature, wash with anhydrous ethanol three times, filter and dry to obtain styrene-tetrahydrophthalimide copolymer. The obtained product is in the form of solid powder. (2) In a 50°C oil bath, 23.15 g of the styrene-tetrahydrophthalimide copolymer solid powder prepared in step (1), 0.05 g of hydroquinone, 0.25 g of triethylamine and 20 g of ethylene glycol methyl ether acetate were added to a 250 mL three-necked flask, and the mixture was stirred evenly. 7.81 g of glycidyl methacrylate was slowly added dropwise to the three-necked flask. After the addition was completed, the temperature was raised to 80°C and the reaction was carried out for 6 h. (3) Add 0.655 g of triphenylphosphine and 8.36 g of tetrahydrophthalic anhydride to the three-necked flask used in step (2), stir evenly, and react for 12 hours to obtain a side chain modified polyimide alkali-soluble resin.

[0034] Next, the performance of the side chain modified polyimide alkali soluble resins prepared in Examples 1-4 was tested.

[0035] First, the molecular weight of the side chain modified polyimide alkali soluble resin prepared in Examples 1-4 was determined by using Waterse2695 gel chromatography. The test results are shown in Table 1. As shown in Table 1, in Example 2, N,N-dimethylformamide was selected as the solvent, and the number average molecular weight (M n ) and mass average molecular weight (M w) are significantly greater than those in other examples. This may be due to the fact that, at the reaction temperature, N,N-dimethylformamide is more volatile than ethylene glycol methyl ether acetate. Due to the nitrogen purge, a small amount of mercaptopropionic acid (mercaptopropionic acid has reached its boiling point at the reaction temperature) is lost along with the N,N-dimethylformamide, resulting in a decrease in chain transfer agent and an increase in molecular weight. Furthermore, as the amount of styrene used decreases, the molecular weight of the side-chain modified polyimide alkali-soluble resin increases. This may be because styrene is prone to chain transfer reactions (especially to monomers) during free radical polymerization, which limits molecular weight growth. Furthermore, the rigid benzene rings of styrene may hinder chain motion.

[0036] Table 1 Molecular weight of various side chain modified polyimide alkali soluble resins

[0037] Then, the side chain modified polyimide alkali soluble resin prepared in Examples 1-4 was made into a solder resist dry film and the performance was tested. The test method is as follows: 1. Pretreatment (1) Preparation of solder resist dry film: Use a coating machine to coat the solder resist dry film resin composition mixed according to the components in Table 2 on the surface of a PET support film with a thickness of 25 μm to obtain a photosensitive layer with a thickness of 25 μm, and cover the surface of the photosensitive layer with a PE protective film with a thickness of 25 μm; Table 2 Components of solder resist dry film resin composition

[0038] The weights of the components in Table 2 are calculated as mass percentages. The photoinitiator used was diphenyl (2,4,6-triformyl) phosphine oxide (photoinitiator TPO), the reactive diluent was bisphenol A dimethacrylate, the defoamer was a silyl ether copolymer defoamer, and the leveling agent was polyacrylate.

[0039] (2) Laminating: Polish the copper surface of the copper clad laminate with a grinder, wash it with water, and dry it to obtain a bright and fresh copper surface. Peel off the PE protective film, and use a laminating machine to stick the solder resist dry film resin composition on the copper clad laminate. Place it in an oven at 100°C and bake it for 5 minutes. (3) Exposure: The test substrate obtained after lamination was left to stand for 15 min, and then exposed using a laser direct imaging (LDI) exposure machine with a wavelength of 365 nm. The photosensitivity test was then performed using a Stouffer 41-step exposure ruler. The number of exposure grids was controlled at 14-20 grids, and the exposure energy was 8-20 mJ / cm 2 ; (4) Development: After exposure, the sample was allowed to stand for 20 min, the PET support film was peeled off, and the sample was developed using an alkaline developer. A 1% by mass Na2CO3 aqueous solution was evenly sprayed onto the surface of the sample to be developed at 30°C for twice the development time (60 s). After development, the sample was washed with water and dried to obtain a substrate with a dry solder mask for evaluation, which was the test substrate.

[0040] 2. Performance Testing (1) Sensitivity evaluation A Stouffer 41-step scale was placed on the test substrate obtained after lamination to test sensitivity. After exposure and development, a solder resist dry film, obtained by curing the solder resist dry film resin composition, was formed on the surface of the test substrate. The exposure energy (mJ / cm2) obtained by the solder resist dry film when the scale had 20 remaining segments was obtained. 2 ), the sensitivity of the photosensitive resin composition was evaluated, and the smaller the value, the better the sensitivity.

[0041] (2) Minimum line width Tested according to GB / T 29846-2013 Photoimaging electroplating resists for printed circuit boards.

[0042] (3) Etching resistance evaluation The etching resistance is tested according to the method of GB / T 29846-2013 for photo-imaging electroplating resists for printed circuit boards. After etching, the pattern is visually intact, the line edges are neat, and there is no wrinkling, shedding or dog-tooth shape. The product is considered excellent if there is wrinkling but no shedding, and poor if there is shedding.

[0043] (4) Hardness evaluation The hardness will be measured according to GB / T1730-93.

[0044] (5) Flexibility evaluation After lamination, exposure, and development, the prepared dry film was folded in half 20 times at different angles to observe whether the dry film cracked. The number of cracks was counted. The larger the number, the better the flexibility of the dry film.

[0045] (6) Heat resistance evaluation Apply rosin flux to the surface of a high-temperature-baked printed circuit board and dip tin at 280±5°C for 10 seconds three times. Then, pull the surface three times with 3M tape (Type 600) to inspect the coating for blistering and oil loss. A coating with no oil loss is considered acceptable; a coating with oil loss is considered unacceptable.

[0046] Table 3 shows the performance test results of solder mask dry films prepared from various side-chain modified polyimide alkali-soluble resins. As can be seen from Table 3, the solder mask dry films prepared from the side-chain modified polyimide alkali-soluble resins of the present invention exhibit excellent properties such as sensitivity, etching resistance, hardness, flexibility, and heat resistance, meeting the application requirements of solder mask dry films. Specifically, each solder mask dry film had a hardness of 6H and cracked after 16 folds, indicating that the styrene dosage and solvent selection have little effect on the hardness and flexibility of the solder mask dry films. As the styrene dosage decreases, the sensitivity of the solder mask dry films increases, and the minimum line width and line spacing decrease. This is because the reduced styrene dosage increases the flexibility of the polymer segments, reduces shrinkage during film formation, and avoids line expansion-induced narrowing of the spacing. The minimum line spacing of the solder mask dry films of Examples 1-2 is 3 / 3 of the line width because benzene rings (styrene structural units) have strong absorption in the ultraviolet region (365 nm). The higher concentration of benzene rings in the solder mask dry films of Examples 1-2 allows for more efficient light absorption, reducing energy loss. At the same time, the solder mask dry film of Example 1-2 has a high styrene content and a large cross-linking density of the film layer after curing (synergistic effect of the imide structure and the acrylic double bond), which can effectively block the penetration of the etching solution and is rated as "excellent" in etching resistance. The solder mask dry film of Example 3-4 has a slightly lower cross-linking density of the film layer after curing, and slight "wrinkling" appears at the edge, and is rated as "good".

[0047] Table 3 Performance test results of solder mask dry films of various side chain modified polyimide alkali soluble resins

[0048] The above are only some embodiments of the present invention. For those skilled in the art, several modifications and improvements can be made without departing from the inventive concept of the present invention, which all fall within the scope of protection of the present invention.

Claims

1. Side chain modified polyimide alkali soluble resin, characterized in that, The raw material composition includes, by weight, 6-8 parts of tetrahydrophthalimide, 5-18 parts of styrene, 1-2 parts of free radical initiator, 0.5-0.9 parts of mercaptopropionic acid, 7-10 parts of glycidyl methacrylate, 0.2-0.6 parts of triethylamine, 7-10 parts of dicarboxylic acid anhydride, 0.5-0.9 parts of triphenylphosphine, 0.02-0.04 parts of polymerization inhibitor, and 40-60 parts of solvent.

2. The side chain modified polyimide alkali-soluble resin according to claim 1, characterized in that The free radical initiator is at least one selected from dibenzoyl peroxide, lauroyl peroxide, tert-butyl perbenzoate, and tert-butyl pervalerate.

3. The side chain modified polyimide alkali-soluble resin according to claim 1, characterized in that The dicarboxylic anhydride is selected from at least one of tetrahydrophthalic anhydride, methyltetrahydrophthalic anhydride and hexahydrophthalic anhydride.

4. The side chain modified polyimide alkali-soluble resin according to claim 1, characterized in that The polymerization inhibitor is selected from at least one of hydroquinone, p-tert-butylcatechol, 2,6-di-tert-butyl-p-methylphenol, and catechol; and the solvent is selected from at least one of N,N-dimethylformamide, dimethyl sulfoxide, and ethylene glycol methyl ether acetate.

5. The method for preparing the side chain modified polyimide alkali soluble resin according to any one of claims 1 to 4, characterized in that: The following steps are involved: S1. Tetrahydrophthalimide and a solvent are mixed to obtain a first mixed solution. Styrene, mercaptopropionic acid, a free radical initiator, and a solvent are mixed to obtain a second mixed solution. The second mixed solution is added dropwise to the first mixed solution at 70-90° C. and stirred for 0.5-1 h. The mixed solution is then heated to 120-140° C. and stirred for 3-5 h. After the reaction is completed, the mixture is cooled to room temperature. The product is then purified and dried to obtain a tetrahydrophthalimide-styrene polymer. S2. Tetrahydrophthalimide-styrene polymer, triethylamine, a polymerization inhibitor, and a solvent are mixed, glycidyl methacrylate is added dropwise to the mixed system at 40-60° C., and stirred for 0.5-1 h. The reaction system is then heated to 80-100° C. and stirred for 6-8 h. After the reaction is completed, a brown-black viscous liquid is obtained; S3. Mix the brown-black viscous liquid, triphenylphosphine and dicarboxylic acid anhydride, and stir the mixture at 70-90° C. for 6-8 h to obtain the product.

6. The method for preparing the side chain modified polyimide alkali soluble resin according to claim 5, wherein In step S1, the structural formula of the tetrahydrophthalimide-styrene polymer is shown in formula (I): Formula (I); In formula (I), the ratio of a to b is 1:1-1:3, and n is 8-21.

7. The method for preparing the side chain modified polyimide alkali soluble resin according to claim 5, wherein: In step S1, the mass ratio of the solvent in the first mixed liquid to the solvent in the second mixed liquid is (1-1.1):1; In step S2, the molar ratio of glycidyl methacrylate to the imide group in the tetrahydrophthalimide-styrene polymer is (1-1.1):

1.

8. Use of the side chain modified polyimide alkali-soluble resin according to any one of claims 1 to 4 in the preparation of IC substrate solder resist ink, printed circuit board solder resist ink, and chip photoresist.

9. A dry film, characterized in that The side chain modified polyimide alkali soluble resin is prepared by photocuring or thermal curing.

10. Use of the dry film according to claim 9 in the preparation of IC substrates or printed circuit boards.

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