Film-forming resin and preparation method thereof, resin composition and solder resist dry film

Abstract

The invention relates to the technical field of resin synthesis, in particular to film-forming resin and a preparation method thereof, a resin composition and a dry solder mask. The preparation raw materials of the film-forming resin comprise acrylic resin and photosensitive molecules; the acrylic resin is prepared from the following raw materials in parts by weight: 5-50 parts of an acrylic monomer, 6-10 parts of anhydride, 5-10 parts of a styrene compound, 0.1-1 part of an initiator and 20-40 parts of a solvent I; the photosensitive molecule is an isocyanate compound containing a carbon-carbon double bond in a molecular structure. The invention focuses on researching the film-forming resin applied to the solder resist dry film, and effectively optimizes the film-forming characteristic and mechanical property of the solder resist dry film by elaborately designing the molecular structure and composition of the film-forming resin; by adding specific monomer molecules and selecting a curing accelerator, filler and the like, the physical strength, the reaction activity, the chemical resistance, the heat resistance and the photosensitivity of the solder resist dry film are improved at the same time.

Description

Technical Field

[0001] This invention relates to the field of resin synthesis technology, and in particular to a film-forming resin and its preparation method, resin composition, and solder resist dry film. Background Technology

[0002] As electronic devices continue to evolve towards greater precision and performance, higher demands are being placed on solder resist layers. Traditional liquid solder resist inks are gradually showing significant limitations in terms of coating uniformity, precise thickness control, and environmental performance. To effectively address these issues, dry film solder resist technology has emerged. This technology first pre-forms the resin into a film, and then directly coats it onto the substrate via lamination, simplifying the production process and significantly improving coating efficiency and quality. For solder resists using alkaline-developable photosensitive resin compositions, the formation method of the film-forming resin is typically as follows: First, a photosensitive resin composition is coated onto the substrate surface and dried to form a resin layer; then, the resin layer is irradiated with patterned light, followed by development in an alkaline developer to finally form the solder resist layer.

[0003] The current market requirements for the performance of solder resist dry film mainly include: (1) It must be able to withstand the lamination softening temperature of 100–110℃; (2) It must not expand or peel off for 10 seconds in a soldering environment of 260℃; (3) Its glass transition temperature (Tg) is higher than 100℃, its coefficient of thermal expansion (CTE) is lower than 100ppm / k, and it can withstand the corrosion of cleaning agents, acids and alkalis without discoloration, blistering and peeling; (4) The solder resist dry film should have high line resolution; (5) It should have strong adhesion, good flexibility and mechanical strength, and be not easily scratched or damaged.

[0004] As the electronics industry places increasingly stringent demands on the performance of solder resist dry films, engineers have reportedly attempted to research the various components of solder resist dry films to meet these requirements. Chinese invention patent application CN120230289A discloses an alkali-soluble photocurable resin, its preparation method, and a photocurable resin composition. By introducing an imide structure into the alkali-soluble photocurable resin, it solves the problems of insufficient thermomechanical properties and compatibility with polyimide resins, achieving improved thermodynamic properties and better overall performance. Chinese invention patent application CN119039569A discloses a method for preparing a modified epoxy photocurable resin. This method involves reacting polyetheramine with acryloyl chloride to generate an amine-modified prepolymer, followed by chain extension with a polymerization inhibitor. This solves the problems of high viscosity and poor toughness in existing modified epoxy acrylates, producing a modified epoxy photocurable resin with low viscosity and high toughness, maintaining hardness and heat resistance while improving the flexibility and gloss of the cured film. However, these existing technologies have not solved the aforementioned technical problems, especially failing to simultaneously possess high adhesion, reliable chemical resistance, and photosensitivity (high resolution), thus failing to meet application requirements.

[0005] Against this backdrop, in order to meet the ever-evolving needs of the electronics industry, it is imperative to develop high-performance film-forming resins suitable for IC substrates and improve the overall performance of dry films (such as adhesion, solderability, chemical resistance, developability, resolution, etc.). Summary of the Invention

[0006] To address the practical application problems of existing solder resist dry films, such as low hardness, poor chemical resistance and solderability, insufficient developability and heat resistance, this invention focuses on researching a film-forming resin for use in solder resist dry films. By carefully designing the molecular structure and composition of the film-forming resin, the film-forming characteristics and mechanical properties of the solder resist dry film are effectively optimized. By adding specific monomer molecules and selecting curing accelerators and fillers, the physical strength, reactivity, chemical resistance, heat resistance and photosensitivity of the solder resist dry film are also improved.

[0007] The first aspect of the present invention provides a film-forming resin, wherein the raw materials for preparing the film-forming resin include acrylic resin and photosensitive molecules.

[0008] Optionally, the photosensitive molecule is an isocyanate compound containing carbon-carbon double bonds in its molecular structure.

[0009] Further optionally, the photosensitive molecule is an isocyanate compound containing an acryloyl group in its molecular structure. Examples of isocyanate compounds containing an acryloyl group include 2-acryloyloxyethyl isocyanate, methacryloyl isocyanate, and methacryloyloxyethyl isocyanate; 2-acryloyloxyethyl isocyanate (CAS No.: 13641-96-8) is a further option.

[0010] Optionally, the molecular structure of the photocurable resin contains reactive groups; the reactive groups include one or more combinations of carboxyl groups, double bonds, and hydroxyl groups.

[0011] Optionally, the raw materials for preparing the acrylic resin, by weight, include: 5-50 parts of acrylic monomers, 6-10 parts of acid anhydrides, 5-10 parts of styrene compounds, 0.1-1 parts of initiator, and 20-40 parts of solvent.

[0012] The acrylic monomers may include methyl methacrylate, ethyl methacrylate, butyl methacrylate, lauryl methacrylate, acrylic acid, methacrylic acid, methyl acrylate, ethyl acrylate, butyl acrylate, lauryl acrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxymethylacrylamide, glycidyl methacrylate, acrylamide, etc.

[0013] Optionally, the acrylic monomers include methacrylates and acrylates, wherein the mass ratio of methacrylates to acrylates is (20-30):(5-10).

[0014] The methacrylates mentioned may include methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-pentyl methacrylate, n-hexyl methacrylate, cyclohexyl methacrylate, n-octyl methacrylate, tetradecyl methacrylate, phenyl methacrylate, etc.

[0015] Optionally, the methacrylate includes methyl methacrylate.

[0016] The acrylates may include ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, 2-ethylhexyl acrylate, n-octyl acrylate, tetradecyl acrylate, phenyl acrylate, vinyl acrylate, etc.

[0017] Optionally, the acrylate includes ethyl acrylate.

[0018] The styrene compounds include one or more combinations of styrene, stilbene, vinylnaphthalene, vinylphenanthrene, and anthracene; further optionally, styrene.

[0019] The acid anhydride may include maleic anhydride, phthalic anhydride, pyromellitic anhydride, etc.; optionally, the acid anhydride includes maleic anhydride; further optionally, the amount of acid anhydride added is 9-10 parts by weight (the acid anhydride accounts for 8-10% of the total mass of the film-forming resin).

[0020] The initiator may include benzoyl peroxide, hydrogen peroxide of benzoic acid, tert-butylhydrogen peroxide, dicumyl peroxide, boron trifluoride, potassium persulfate, ammonium persulfate, azobisisobutyronitrile, azobisisoheptane, azobiscyanocyclohexane, azobisisobutyramidine hydrochloride, etc.; azobisisobutyronitrile may be selected as the initiator.

[0021] The solvent can include, for example, hydrocarbon solvents, ketone solvents, halogenated hydrocarbon solvents, ether solvents, alcohol solvents, ester solvents, and water.

[0022] Optionally, the solvent one includes one or more combinations of toluene, acetone, butanone, dichloromethane, dichloroethane, trichloroethane, chloroform, dioxane, methyl ethyl ketone, methanol, ethanol, ethyl acetate, butyl acetate, xylene, diethyl ether, propylene glycol methyl ether, ethylene glycol methyl ether, and water; further optionally, the solvent one includes butanone.

[0023] Optionally, the mass ratio of the acrylic resin to the photosensitive molecule is (6-10):1.

[0024] Optionally, the acid value of the film-forming resin is ≥60mg KOH / g; more preferably, the acid value of the film-forming resin is 72-80mg KOH / g.

[0025] A second aspect of the present invention provides a method for preparing the film-forming resin, wherein the preparation steps of the film-forming resin include: Acrylic monomers, acid anhydrides, styrene compounds, initiators and solvents are mixed and reacted to obtain resin precursors. Photosensitive molecules are grafted onto the resin precursor to obtain a film-forming resin.

[0026] In some embodiments, the preparation steps of the film-forming resin include: S1. Add 60-80% of the solvent amount of the formula into the reaction apparatus, and set the temperature of the reaction apparatus to 80-95℃; S2. Mix the acid anhydride, acrylic monomer, styrene compound, 20-50% of the initiator and 5-15% of the solvent to obtain mixture one; set the temperature of the reaction apparatus to 70-80℃, add mixture one, and keep the reaction at 80-90℃ for 1-4 hours. S3. Mix the remaining initiator and the remaining solvent one evenly to obtain mixture two; add mixture two into the reaction apparatus and keep it at 80-95℃ for 2-8 hours to obtain the resin precursor; S4. Add the photosensitive molecules to the reaction apparatus to perform a grafting reaction with the resin precursor to obtain the film-forming resin.

[0027] Optionally, the mixture is added to the reaction apparatus dropwise.

[0028] Optionally, the time for adding the mixture dropwise is controlled to be 1-5 hours; more preferably, it is 2-3 hours.

[0029] Optionally, the mixture 2 is added to the reaction apparatus by dripping.

[0030] Optionally, the time for adding the mixture is controlled to be 2-6 hours; more preferably, it is 4 hours.

[0031] Optionally, the grafting reaction is carried out at 80-95℃ for 5-15 hours; more preferably at 90℃ for 8 hours.

[0032] A third aspect of the present invention provides a resin composition, wherein the raw materials for preparing the resin composition include: the film-forming resin, photopolymerization monomer, curing accelerator, photoinitiator, colorant, filler and solvent II as described above.

[0033] In some embodiments, the raw materials for preparing the resin composition, by weight, include: 20-60 parts of the film-forming resin as described above, 10-40 parts of the photopolymerizable monomer, 5-30 parts of the curing accelerator, 5-12 parts of the photoinitiator, 1-30 parts of the colorant, 5-30 parts of the filler, and 20-60 parts of the solvent.

[0034] Optionally, the photopolymerizable monomer includes hydroxyl-containing acrylates.

[0035] Optionally, the photopolymerizable monomer is selected from one or more combinations of pentaerythritol triacrylate, pentaerythritol tetraacrylate, dipentaerythritol hexaacrylate, trimethylolpropane triacrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, isooctyl acrylate, and hydroxyethyl methacrylate; further, it may be selected as pentaerythritol tetraacrylate.

[0036] Optionally, the curing accelerator is selected from one or more combinations of imidazole or its derivatives, amine compounds, hydrazine compounds, and phosphorus compounds.

[0037] The imidazole or its derivatives may include imidazole, 2-methylimidazolium, 2-ethylimidazolium, 2-ethyl-4-methylimidazolium, 2-phenylimidazolium, 4-phenylimidazolium, 1-cyanoethyl-2-phenylimidazolium, and 1-(2-cyanoethyl)-2-ethyl-4-methylimidazolium, etc.

[0038] Examples of the amine compounds mentioned include dicyandiamide, benzyl dimethylamine, 4-(dimethylamino)-N,N-dimethylbenzylamine, 4-methoxy-N,N-dimethylbenzylamine, and 4-methyl-N,N-dimethylbenzylamine.

[0039] The hydrazine compounds may include adipate dihydrazide or sebacic dihydrazide. Phosphorus compounds may include triphenylphosphine.

[0040] Optionally, the curing accelerator includes imidazole or its derivatives.

[0041] Optionally, the photoinitiator includes one or more combinations of 1-hydroxycyclohexylphenyl ketone (photoinitiator 184), diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide, phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, 2,4-diethylthioxanthrone, 2-hydroxy-2-methylphenylacetone, triphenylthionium hexafluorophosphate, benzoin dimethyl ether, benzophenone, and 3-methyl-4-phenylbenzophenone.

[0042] Further optionally, the photoinitiator includes photoinitiator 184.

[0043] The colorant may include phthalocyanine green, carbon black, titanium dioxide, etc.; optionally, the colorant includes phthalocyanine green.

[0044] Optionally, the filler includes inorganic fillers; examples of inorganic fillers include barium sulfate, barium titanate, silica, talc, clay, magnesium carbonate, calcium carbonate, alumina, aluminum hydroxide, and mica.

[0045] To improve the thermal stability and adhesion of the resin composition, the filler may optionally include barium sulfate.

[0046] Optionally, the second solvent includes an organic solvent; examples of organic solvents include butanone, cyclohexanone, ethyl acetate, butyl acetate, propylene glycol methyl ether acetate, toluene, xylene, ethanol, isopropanol, propylene glycol monomethyl ether, etc.

[0047] Further optionally, the solvent two includes propylene glycol methyl ether acetate.

[0048] In some embodiments, the raw materials for preparing the resin composition may also include additives; the additives may be added flexibly according to the usage requirements, such as leveling agents, defoamers, antibacterial agents, etc.

[0049] A fourth aspect of the present invention provides a dry solder resist film (also known as DFSR), wherein the dry solder resist film is formed by stacking a carrier film, a photosensitive layer and a release film in sequence from bottom to top; the photosensitive layer is formed by curing the resin composition as described above.

[0050] In some embodiments, the preparation steps of the solder resist dry film include: The resin composition is coated onto the surface of a carrier film and dried to form a photosensitive layer. A release film is applied to the surface of the photosensitive layer to obtain a solder resist dry film.

[0051] Optionally, the drying temperature is 40-150°C.

[0052] Optionally, the thickness of the photosensitive layer is 10-100 μm.

[0053] Optionally, the resolution of the solder resist dry film is ≤80μm; further optionally, the resolution of the solder resist dry film is ≤50μm.

[0054] The fifth aspect of the present invention provides an application of the film-forming resin as described above, wherein the film-forming resin is applied to photoresist, which can improve the resolution, photosensitivity, chemical resistance and developability of the photoresist.

[0055] The sixth aspect of the present invention provides a method of using the solder resist dry film as described above, the method of using the solder resist dry film comprising: Film application: Peel off the outer release film of the solder resist dry film, and use a hot roller laminator to evenly adhere the solder resist dry film to the substrate surface; Exposure: Using negative film technology, the substrate carrying the solder resist dry film is placed under an exposure machine for exposure. The exposed area undergoes a photocuring reaction, completing the transfer of the solder resist dry film circuitry. During the exposure stage, unsaturated functional groups such as film-forming resin and photopolymerizable monomers cross-link to form a dense layer. Development: The solder mask dry film is placed in the developer solution for development. The unexposed areas of the solder mask dry film are developed, and the solder mask lines are preserved. Post-curing: The developed solder resist dry film undergoes post-curing treatment to fully cross-link the remaining photosensitive components. The post-cured solder resist material exhibits excellent solderability and hardness, meeting the requirements for use in electronic components.

[0056] In some embodiments, the substrate is typically a PCB circuit board core board.

[0057] In some embodiments, the range of process parameters during the use of the solder resist dry film is shown in Table 1.

[0058] Table 1

[0059] This invention introduces maleic anhydride monomers into the film-forming resin to synthesize a film-forming resin (PSPI, photosensitive polyimide). The anhydride ring of maleic anhydride can react with isocyanate to obtain acidic polyamic acid (PAA), solving the problem of poor developability of traditional polyimide (PI). The resulting resin composition achieves high-performance PI through ring closure during the post-curing stage, improving the physical properties of the solder resist dry film without affecting the material's developability. The introduction of maleic anhydride enhances the polarity of the resin molecules and increases the resin's acid value. By adjusting the proportion of maleic anhydride monomers in the resin, the acid value can be precisely controlled. The alkali solubility of the resin increases accordingly with the increase of the acid value, further improving the development speed, thereby achieving control over the development window of the solder resist dry film. When the alkali solubility of the resin is poor, the unexposed areas of the final dry film are not fully developed; while excessive alkali solubility may overdevelop the exposed areas, causing erosion. This invention, by preparing a resin with a suitable acid value and imparting an appropriate dissolution rate, results in a solder resist dry film that helps form high-efficiency lines with vertical edges, no undercut, and clear development lines.

[0060] Beneficial effects: This invention provides a film-forming resin and its preparation method, a resin composition, and a solder resist dry film, which have the following advantages: (1) The present invention uses acrylic resin and photosensitive molecules to synthesize film-forming resin, which comprehensively improves the mechanical strength, heat resistance, chemical stability and adhesion of solder resist dry film, while improving the resolution, photosensitivity and resolution of solder resist dry film.

[0061] (2) In this invention, a monomer with a specific function is introduced into the film-forming resin. By controlling the selection of acrylic monomers and the amount of acid anhydride monomers added, the acid value of the film-forming resin can be controlled within the range of 72-80 mg KOH / g. The resulting film-forming resin has suitable alkali solubility and can be used to prepare a solder resist dry film with excellent development performance.

[0062] (3) The film-forming resin obtained by the present invention has good compatibility. When used with a specific ratio of photopolymerizable monomers, photoinitiators, colorants, fillers, curing accelerators and solvents, it can further improve the mechanical properties, chemical resistance and heat resistance of the solder resist dry film.

[0063] (4) The solder resist dry film obtained by the present invention helps to form a high-efficiency circuit with vertical edges, no undercut, and clear development lines. The resolution of the product can be accurate to below 50μm, which can meet the requirements of electronic components.

[0064] (5) The film-forming resin of the present invention imparts excellent comprehensive performance to the solder resist dry film, which can meet the high-quality requirements of electronic component application scenarios, improve customer satisfaction and production efficiency in actual application, and has broad application prospects. Detailed Implementation

[0065] The following describes the implementation of the present invention with reference to specific embodiments. Those skilled in the art can understand the technical concept of the present invention based on the content disclosed in this specification. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0066] Example 1 This embodiment provides a film-forming resin and its preparation method, a resin composition, and a solder resist dry film.

[0067] The raw materials for preparing the film-forming resin include acrylic resin and photosensitive molecules (2-acryloyloxyethyl isocyanate); the mass ratio of the acrylic resin to the photosensitive molecules is 94.45:10.

[0068] The raw materials for preparing the acrylic resin, by weight, include: 27 parts acrylic monomers (5 parts ethyl acrylate, 22 parts methyl methacrylate), 6 parts acid anhydride (maleic anhydride), 5 parts styrene compounds (styrene), 0.45 parts initiator (azobisisobutyronitrile), and 56 parts solvent one (butanone).

[0069] The preparation steps of the film-forming resin include: S1. Add 40 parts of solvent to the flask, turn on the stirrer, and set the flask temperature to 90°C; S2. Mix the acid anhydride, acrylic monomer, styrene compound, 0.3 parts of initiator and 7 parts of solvent one evenly to obtain mixture one; set the flask temperature to 75℃, and add mixture one dropwise into the flask through a dropper (complete the dropwise addition in 3 hours); after the dropwise addition is completed, keep the temperature at 85℃ for 2 hours. S3. Mix 1.5 parts of initiator and 9 parts of solvent one evenly to obtain mixture two; add mixture two dropwise into the flask through a dropper, and after the addition is completed, keep the temperature at 90°C for 4 hours to obtain the resin precursor; S4. Add the photosensitive molecules to the flask and perform a grafting reaction with the resin precursor (react at 90℃ for 8 hours) to obtain the film-forming resin.

[0070] The raw materials for preparing the resin composition are shown in Table 2.

[0071] Table 2

[0072] The resin composition is prepared by mixing the photopolymerizable monomer, curing accelerator, photoinitiator, colorant, filler, and solvent evenly.

[0073] The solder resist dry film is composed of a carrier film, a photosensitive layer and a release film stacked sequentially from bottom to top; the photosensitive layer is formed by curing the resin composition as described above.

[0074] The preparation steps of the solder resist dry film include: T1. Using a doctor blade coater, the above resin composition is uniformly coated onto the surface of a carrier film (made of polyethylene terephthalate), and then dried in an oven at 100°C to form a film (film thickness 25μm), thus forming a photosensitive layer; T2. Apply a release film to the surface of the photosensitive layer to obtain a dry solder resist film.

[0075] Example 2 This embodiment provides a film-forming resin and its preparation method, a resin composition and a solder resist dry film, with the specific implementation method being the same as in Embodiment 1; the difference is that the amount of maleic anhydride added is 7 parts.

[0076] Example 3 This embodiment provides a film-forming resin and its preparation method, a resin composition and a solder resist dry film, with the specific implementation method being the same as in Embodiment 1; the difference is that the amount of maleic anhydride added is 8 parts.

[0077] Example 4 This embodiment provides a film-forming resin and its preparation method, a resin composition and a solder resist dry film, with the specific implementation method being the same as in Embodiment 1; the difference is that the amount of maleic anhydride added is 9 parts.

[0078] Example 5 This embodiment provides a film-forming resin and its preparation method, a resin composition and a solder resist dry film, with the specific implementation method being the same as in Embodiment 1; the difference is that the amount of maleic anhydride added is 10 parts.

[0079] Comparative Example 1 This comparative example provides a film-forming resin and its preparation method, a resin composition and a solder resist dry film, with the specific implementation method being the same as in Example 1; the difference is that the amount of maleic anhydride added is 0.

[0080] Performance testing 1. Film-forming resin properties The film-forming resins prepared in Examples 1-5 and Comparative Example 1 were used as test samples and the following tests were performed; the test results are shown in Table 3.

[0081] 1) Solid content The test was conducted using the weighing method.

[0082] 2) Viscosity Test method: The viscosity of the resin to be tested was measured using a rotational viscometer at a temperature of 25°C. The unit is Ps.

[0083] 3) Acid value Test method: Take 1 ± 0.05 g of the resin to be tested, add 10 g of anhydrous ethanol and 40 g of butanone, stir until completely dissolved, add an appropriate amount of phenolphthalein solution, and titrate with KOH standard solution; the calculation method is Equation 2: Acid value = C KOH ×V KOH ×56.1 / m 样品质量 The acid value is expressed in mg KOH / g.

[0084] 4) Tg value Test method: The resin to be tested is made into a thin sheet and stamped to obtain a test strip of a specific size (2cm long and 0.5cm wide); the test strip is precisely and vertically mounted on the fixture (ensuring that the contact point between the test strip and the fixture is accurate and the clamping force is consistent to avoid slippage or stress concentration), and Tg is tested using a dynamic thermomechanical analyzer; during analysis, the peak point on the tanδ curve is determined by the loss factor peak method, and the temperature corresponding to the peak point is the Tg value, with the unit of Tg being ℃.

[0085] 5) Weight-average molecular weight Test method: Take an appropriate amount of film-forming resin, add 1.5 ml of tetrahydrofuran to dissolve and stir; take 1 ml of solution, put it into a sampling bottle and label it, put it into GPC (gel permeation chromatography) for testing, turn on the instrument and computer, set the relevant parameters, use the standard sample to make a standard curve, and analyze to obtain the weight average molecular weight of the resin.

[0086] Table 3

[0087] 2. Properties of the resin composition The resin compositions prepared in Examples 1-5 and Comparative Example 1 were used as test samples to test solid content, viscosity, and fineness (the test methods for solid content and viscosity are as described above); the test results are shown in Table 4.

[0088] Fineness testing method: Ensure the sample to be tested is uniform and free of sediment, and keep the fineness meter and scraper clean and dry; pour a sufficient amount of sample into the deeper end of the wedge groove of the fineness meter, avoiding the generation of air bubbles; hold the scraper and scrape the sample smoothly towards the shallower end of the groove at a uniform speed and with appropriate pressure within 1-2 seconds; after the scraping is completed, observe the surface of the fineness meter plate at a 20-30 degree overhead angle within 3 seconds to find the position where particles aggregate or scratches begin to appear, and read the corresponding scale. The fineness unit is μm.

[0089] Table 4

[0090] 3. Solder resist dry film performance The solder resist dry films prepared in Examples 1-5 and Comparative Example 1 were tested. The samples were prepared by the following treatment before the test; the test results are shown in Table 6.

[0091] (1) Film application: Peel off the outer release film of the solder resist dry film and use a hot roller laminator to evenly apply the solder resist dry film to the substrate surface; (2) Exposure: Using negative film process, the substrate carrying solder resist dry film is placed under the exposure machine for exposure. Photocuring reaction occurs in the exposed area to complete the transfer of solder resist dry film lines. (3) Development: The solder resist dry film is placed in the developing solution for development. The unexposed areas of the solder resist dry film are developed, and the solder resist lines are preserved. (4) Post-curing: The developed solder resist dry film is post-cured using an oven to completely cross-link the remaining photosensitive components and obtain the solder resist dry film sample to be tested.

[0092] The range of process parameters in steps (1) to (4) is shown in Table 5 below.

[0093] Table 5

[0094] The test parameters and test methods for the solder resist dry film samples to be tested are as follows.

[0095] 1) Hardness The test method is as follows: Fix the solder resist dry film sample to be tested on a horizontal platform. Use a set of pencils from soft to hard (4B, 3B, 2B, B, HB, F, H, 2H, 3H, 4H, 5H, 6H) to scratch the surface of the solder resist dry film at a 45-degree angle with a force of 10N. Record the highest hardness level that does not scratch the film layer, which is the hardness of the solder resist dry film.

[0096] 2) Adhesion Test method: Use a special cross-cut tester to draw a 1mm×1mm grid on each sample film layer (it needs to cut through to the substrate); clean up the debris with a soft brush, apply special tape and press it firmly; hold one end of the tape and quickly peel it off at a 60-degree angle, observe the coating peeling at the edge of the grid, and evaluate the grade according to the standard cross-cut test chart (0 is the best, 5 is the worst, and ≤1 is usually required).

[0097] 3) Weldability Test method: The dry solder resist sample to be tested is pre-baked at 125℃ for 1 hour, and then immersed in a molten solder bath at 270±10℃ for 10 seconds. After removal, it is rinsed with isopropanol and the appearance is visually inspected to observe whether there is any swelling, peeling or discoloration.

[0098] 4) Chemical resistance Test method: Immerse the dry film sample of the solder resist to be tested in chemical reagents (10% sulfuric acid aqueous solution, 10% sodium hydroxide aqueous solution) for 30 minutes at room temperature; after immersion, take out the sample, rinse it clean, blow it dry, and check whether there is any loss of gloss, discoloration, bubbling, softening or peeling.

[0099] 5) Imaging properties and resolution Test method: Take the solder resist dry film sample after development and observe the development results; observe whether the non-pattern area is clean and free of residual adhesive, and whether the edge of the pattern is sharp and free of side etching and peeling; and use film with different line widths and line spacings for exposure. After development, observe under a metallographic microscope to determine the clear, complete, and unblemished finest pattern. Record the smaller value of the line width or line spacing of the finest pattern, which is the resolution of the solder resist dry film.

[0100] Table 6

[0101] The data in Table 3 show that the amount of maleic anhydride added has a significant impact on the acid value and the Tg of the resin. As the amount of maleic anhydride monomer added to the film-forming resin increases, the acid value of the film-forming resin gradually increases, while the acid value of the film-forming resin without maleic anhydride monomer is relatively low. Furthermore, the addition of maleic anhydride monomer can increase the Tg value of the film-forming resin, while the Tg value decreases when maleic anhydride monomer is not added or added in small amounts.

[0102] This invention enhances the crosslinking ability of film-forming resin by adding maleic anhydride monomer. The anhydride groups in the system can react with various functional groups (e.g., forming ester bonds with hydroxyl groups and imide bonds with amino groups), thus acting as crosslinking points in the curing reaction. This effectively increases the crosslinking density of the coating, thereby improving the hardness, abrasion resistance, solderability, chemical resistance, and heat resistance of the coating film. Data from Table 6 shows that when the amount of maleic anhydride added is 9-10 parts, the resin exhibits the best alkali solubility, resulting in the best development effect (clean, no side etching or peeling) and high resolution of the final solder resist dry film. In contrast, the developability of the solder resist dry films in Examples 1-3 and Comparative Example 1 deteriorates, resulting in incomplete development, jagged edges, and poor resolution. In summary, this invention, by introducing a specific amount of maleic anhydride into the film-forming resin system, comprehensively improves the mechanical strength, heat resistance, chemical resistance, and adhesion of the solder resist dry film, and endows it with excellent resolution, developability, and overall resolution, thus meeting the requirements for electronic components.

Claims

1. A film-forming resin, characterized in that, The raw materials for preparing the film-forming resin include acrylic resin and photosensitive molecules; The raw materials for preparing the acrylic resin, by weight, include: 5-50 parts acrylic monomers, 6-10 parts acid anhydrides, 5-10 parts styrene compounds, 0.1-1 parts initiator and 20-40 parts solvent. The photosensitive molecule is an isocyanate compound containing carbon-carbon double bonds in its molecular structure.

2. The film-forming resin according to claim 1, characterized in that, The acrylic monomers include one or more combinations of methyl methacrylate, ethyl methacrylate, butyl methacrylate, lauryl methacrylate, acrylic acid, methacrylic acid, methyl acrylate, ethyl acrylate, butyl acrylate, lauryl acrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxymethylacrylamide, glycidyl methacrylate, and acrylamide.

3. The film-forming resin according to claim 1, characterized in that, The acrylic monomers include methacrylate and acrylate, wherein the mass ratio of methacrylate to acrylate is (20-30):(5-10).

4. The film-forming resin according to claim 1, characterized in that, The styrene compounds include one or more combinations of styrene, stilbene, vinylnaphthalene, vinylphenanthrene, and anthracene.

5. The film-forming resin according to claim 1, characterized in that, The acid anhydride includes maleic anhydride, and the amount of acid anhydride added is 9-10 parts by weight.

6. The film-forming resin according to claim 1, characterized in that, The photosensitive molecule is an isocyanate compound containing an acryloyl group in its molecular structure; The isocyanate compounds containing an acryloyl group in their molecular structure include one or more combinations of 2-acryloyloxyethyl isocyanate, methacryloyl isocyanate, and methacryloyloxyethyl isocyanate.

7. A method for preparing a film-forming resin according to any one of claims 1-6, characterized in that, The preparation steps of the film-forming resin include: Acrylic monomers, acid anhydrides, styrene compounds, initiators and solvents are mixed and reacted to obtain resin precursors. Photosensitive molecules are grafted onto the resin precursor to obtain a film-forming resin.

8. The preparation method according to claim 7, characterized in that, The preparation steps of the film-forming resin include: S1. Add 60-80% of the solvent amount of the formula into the reaction apparatus, and set the temperature of the reaction apparatus to 80-95℃; S2. Mix the acid anhydride, acrylic monomer, styrene compound, 20-50% of the initiator and 5-15% of the solvent to obtain mixture one; set the temperature of the reaction apparatus to 70-80℃, add mixture one, and keep the reaction at 80-90℃ for 1-4 hours. S3. Mix the remaining initiator and the remaining solvent one evenly to obtain mixture two; add mixture two into the reaction apparatus and keep it at 80-95℃ for 2-8 hours to obtain the resin precursor; S4. Add the photosensitive molecules to the reaction apparatus to perform a grafting reaction with the resin precursor to obtain the film-forming resin.

9. A resin composition, characterized in that, The raw materials for preparing the resin composition include: the film-forming resin according to any one of claims 1-6, a photopolymerizing monomer, a curing accelerator, a photoinitiator, a colorant, a filler, and a solvent.

10. A solder resist dry film, characterized in that, The solder resist dry film is composed of a carrier film, a photosensitive layer and a release film stacked from bottom to top; The photosensitive layer is formed by curing the resin composition according to claim 9; The resolution of the solder resist dry film is ≤80μm.

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