Photosensitive composition of circuit ink and preparation method thereof

Abstract

The invention provides a photosensitive composition of circuit ink and a preparation method thereof. The alkali-soluble resin with high glass transition temperature is introduced on the basis that the small-particle-size filler is adopted to guarantee the image resolution and the image side edge definition, due to the fact that the glass transition temperature of the resin is high, after the resin is pre-dried and recovered to the room temperature, a stable glass state can be formed on the film surface, and the resin has enough mechanical strength and also can be used as a high-temperature-resistant film. Scraping and abrasion in the machining process can be effectively resisted, and plate sticking or other sticking problems can be avoided; meanwhile, the surface tension of the alkali-soluble resin is in a proper range, so that the problems that the coating uniformity of a photosensitive composition substrate is poor and the composition is difficult to be thoroughly removed by a film stripping solution to remain a glue film due to the fact that the surface tension is too high are avoided, and the problems that the adhesive force of a copper surface is insufficient due to the fact that the surface tension is too low and the adhesive force is not enough are solved. And the whole film surface falls off during developing.

Description

Technical Field

[0001] This invention relates to the field of ink technology, specifically to a photosensitive composition for circuit ink and its preparation method. Background Technology

[0002] Circuit ink is an alkaline-soluble negative photoresist. Through exposure and development, it transfers the pattern from a photomask to a circuit board, completing the fabrication of fine copper lines on the printed circuit board. Circuit ink must meet the following requirements: high resolution, clear lines with minimal burrs (small jagged edges), excellent processing performance, no sticking after pre-baking, and complete removal by stripping solution without residue after copper line fabrication.

[0003] Circuit inks are mainly composed of alkali-soluble acrylic resins, photoinitiators, and fillers. To ensure the surface dryness of the circuit ink after pre-baking and to prevent abnormalities such as sticking during actual use, a common method is to add a large amount of inorganic fillers (commonly talc, barium sulfate, silica, calcium carbonate, etc.).

[0004] To improve the resolution of circuit inks and create patterns with clear edges and minimal jagged edges (small serrations), common existing techniques involve reducing the particle size of fillers and decreasing the amount of filler added. The particle size of the filler directly affects the resolution and clarity of the circuit ink. However, simply reducing the particle size or the amount of filler added significantly impacts the surface drying properties of the ink after pre-baking, leading to abnormalities such as sticking to the printing plate. This severely affects the operability of subsequent processing on the production line, further reducing yield.

[0005] In conclusion, a new technical solution is urgently needed to address the problems existing in the current technology. Summary of the Invention

[0006] Based on this, the present invention provides a photosensitive composition for circuit ink and its preparation method. The photosensitive composition of the present invention improves the resolution of circuit ink and the clarity of the edges of the pattern, while ensuring the dryness of the ink surface after pre-baking and excellent processability. After the copper circuit fabrication process is completed, it can be completely removed by stripping solution without residue, and will not cause abnormalities such as sticking to the board.

[0007] One object of the present invention is to provide a photosensitive composition for circuit ink, the photosensitive composition for circuit ink comprising the following components: alkali-soluble acrylic resin, photoinitiator, filler, and alkali-soluble resin; in, The particle size of the filler is less than 8 μm; The alkali-soluble resin has a glass transition temperature greater than 60°C and a surface tension in the range of 50-80 mN / m.

[0008] Furthermore, the alkali-soluble acrylic resin is selected from polymers or mixtures thereof formed by copolymerizing two or more monomers selected from methacrylic acid, benzyl methacrylate, hydroxyethyl methacrylate, 2-ethylhexyl acrylate, glycidyl methacrylate, and styrene.

[0009] Furthermore, the photoinitiator is selected from one or more of benzoyl derivative photoinitiators, acylphosphine oxide photoinitiators, isopropylthioxanthone, and benzophenone.

[0010] Furthermore, the filler is selected from one or more of barium sulfate, silicon dioxide, talc, calcium carbonate, aluminum oxide, boron nitride, mica, or kaolin.

[0011] Furthermore, the amount of filler added is 10-70 wt% of the photosensitive composition of the circuit ink.

[0012] Furthermore, the filler preferably has a particle size of less than 8 μm, more preferably less than 5 μm, and most preferably less than 3 μm; the amount of filler added is preferably greater than 10 wt%, more preferably greater than 15 wt%, and most preferably greater than 20 wt%; the filler is not limited to whether it is surface modified; the shape of the filler is not limited to whether it is spherical, plate-like, cubic, or irregular.

[0013] Furthermore, the alkali-soluble resin is selected from one or more of bisphenol A epoxy acrylate compounds, bisphenol F epoxy acrylate compounds, phenolic epoxy acrylate compounds, and aliphatic epoxy acrylates.

[0014] Furthermore, the amount of alkali-soluble resin added is 3-30 wt% of the photosensitive composition of the circuit ink.

[0015] Furthermore, to improve the resolution of circuit inks and the clarity of graphic edges, the formulation of circuit inks requires controlled addition of fillers with a particle size of less than 8 μm. To simultaneously ensure the dryness of the ink surface after pre-drying and prevent abnormalities such as sticking, the amount of fillers smaller than 8 μm should be greater than 10% of the total mass, and the amount of alkali-soluble resins with a glass transition temperature (Tg) greater than 60℃ and a surface tension in the range of 50-80 mN / m should be greater than 3% of the total mass. While adding small-particle-size micron-sized fillers alone can achieve sufficient high resolution, insufficient dryness of the ink after pre-drying severely affects subsequent processing and the yield of the final product.

[0016] Furthermore, the alkali-soluble resin with a glass transition temperature greater than 60°C and a surface tension in the range of 50-80 mN / m is crucial for maintaining the dryness of the ink surface after pre-baking and ensuring thorough removal of residue by the stripping solution. The presence of a high-Tg resin allows it to accumulate on the surface of the ink during pre-baking as the solvent evaporates and heat is applied. Its high Tg characteristic ensures that the pre-baked ink film remains in the glassy state of the resin at room temperature, providing sufficient strength and dryness, preventing abnormalities such as sticking, and ensuring the operability of subsequent ink processing. Simultaneously, a surface tension in the range of 50-80 mN / m ensures sufficient adhesion of the photosensitive composition to the substrate, while also allowing for thorough removal of residue by the stripping solution after the copper circuit fabrication is completed.

[0017] Furthermore, the alkali-soluble groups of the alkali-soluble resin may include carboxyl groups, phenolic hydroxyl groups, sulfonic acid groups, hydroxyl groups, etc., but are not limited to these.

[0018] Furthermore, the amount of alkali-soluble resin added is preferably greater than 3 wt%, more preferably greater than 5 wt%, and most preferably greater than 7 wt%.

[0019] Another object of the present invention is to provide a method for preparing the photosensitive composition of the above-mentioned circuit ink, comprising the following steps: Alkali-soluble acrylic resin, photoinitiator, filler, and alkali-soluble resin are mixed, stirred and dispersed, and then further dispersed using a ball mill or emulsifier, filtered and degassed to obtain a photosensitive composition for circuit ink.

[0020] The present invention has the following beneficial effects: This invention provides a photosensitive composition for circuit ink and its preparation method. The photosensitive composition for circuit ink includes the following components: alkali-soluble acrylic resin, photoinitiator, filler, and alkali-soluble resin; wherein the particle size of the filler is less than 8 μm; the glass transition temperature of the alkali-soluble resin is greater than 60°C, and the surface tension is in the range of 50-80 mN / m. This invention, while using small-particle-size fillers to ensure image resolution and graphic edge clarity, introduces an alkali-soluble resin with a high glass transition temperature. Due to its high glass transition temperature, this type of resin, after pre-baking and returning to room temperature, can form a stable glassy state on the film surface, possessing sufficient mechanical strength to effectively resist scratches and wear during processing, and avoiding board adhesion or other sticking problems. Simultaneously, the surface tension of the alkali-soluble resin used in this invention is within a suitable range, avoiding the defects of poor substrate coating uniformity and insufficient adhesion to the copper surface (easily leading to shrinkage or peeling) caused by excessively high surface tension, and also solving the problem of the composition being difficult to completely remove with stripping solution and leaving residual film caused by excessively low surface tension.

[0021] Meanwhile, the uniform dispersion and stable storage of small-particle fillers in ink compositions is also one of the current challenges. The addition of alkali-soluble resin with a surface tension within a specific suitable range can fully wet the surface of small-particle fillers, accelerating the uniform dispersion of fillers during ball milling or emulsification. Furthermore, this resin with a specific surface energy can act as a spacer and support between fillers, ensuring that the ink composition is not prone to agglomeration and sedimentation during long-term storage. This further ensures the clarity of the side edges of the pattern after exposure and development, preventing uneven side patterns caused by the agglomeration of small-particle fillers. Through the synergistic effect of the above properties, the photosensitive composition of the circuit ink of the present invention achieves a synergistic balance of the three core properties of circuit ink: image resolution, pattern side clarity, and dryness of the film surface after pre-baking. Its comprehensive application effect is significantly better than the best solution in the prior art. Detailed Implementation

[0022] To more clearly illustrate the technical solution of the present invention, the following embodiments are provided. Unless otherwise stated, the raw materials, reactions, and post-processing methods appearing in the embodiments are all commercially available raw materials and technical methods well known to those skilled in the art.

[0023] The terms "preferred," "more preferably," and "more suitable" used in this invention refer to embodiments of the invention that provide certain beneficial effects under certain circumstances. However, other embodiments may also be preferred under the same or other circumstances. Furthermore, the description of one or more preferred embodiments does not imply that other embodiments are unavailable, nor is it intended to exclude other embodiments from the scope of this invention.

[0024] It should be understood that, except in any operational instance or otherwise indicated, the amounts or all figures representing ingredients used, for example, in the specification and claims, should be understood to be modified by the term "about" in all cases. Therefore, unless otherwise stated, the numerical parameters set forth in the following specification and appended claims are approximate values ​​varying according to the desired performance to be obtained according to the invention.

[0025] The present invention uses the following raw materials: Alkali-soluble acrylic resin: prepared from synthesis example 1.

[0026] Photoinitiator: Name is isopropylthioxanthone ITX, brand name is JRCure-1105, purchased from Jiuri New Materials.

[0027] Filler 1: Particle size < 8 μm, named spherical silica powder, grade SCG-1.0, purchased from Lianrui New Materials.

[0028] Filler 2: Particle size > 8 μm, named spherical silica powder, grade SC-10, purchased from Lianrui New Materials.

[0029] Alkali-soluble resin 1: Tg > 60℃, surface tension 50.3 mN / m, named KAYARAD ZFR-1122, purchased from Nippon Kayaku Co., Ltd.

[0030] Alkali-soluble resin 2: Tg > 60℃, surface tension 77.0 mN / m, named CYCLOMER P(ACA)Z-250, purchased from Daicel Co., Ltd.

[0031] Alkali-soluble resin 3: Tg > 60℃, surface tension 80.0 mN / m, named REPOXY SP-4621, purchased from Showa Denko Co., Ltd.

[0032] Alkali-soluble resin 4: Tg > 60℃, surface tension 42.5 mN / m, prepared from synthesis example 2.

[0033] Alkali-soluble resin 5: Tg > 60℃, surface tension 95.4 mN / m, prepared from synthesis example 3.

[0034] Alkali-soluble resin 6: Tg < 60℃, surface tension 58.0 mN / m, named KAYARAD FLX-2089, purchased from Nippon Kayaku Co., Ltd.

[0035] Alkali-soluble resin 7: Tg < 60℃, surface tension 65.0 mN / m, named GF-211LX, purchased from Guangzhou Starley Electronic Raw Materials Co., Ltd.

[0036] Alkali-soluble resin 8: Tg < 60℃, surface tension 77.8 mN / m, named GF-135, purchased from Guangzhou Starley Electronic Raw Materials Co., Ltd.

[0037] Cresol phenolic resin clear varnish type epoxy resin: brand name NPEL-128, purchased from Guangzhou Senmao New Materials.

[0038] Propylene glycol monomethyl ether acetate solvent: purchased from Jiangsu Hualun Chemical.

[0039] Synthesis example 1 Synthesis of alkali-soluble acrylic resins: In a 1 L four-necked flask, add 80.0 g of propylene glycol methyl ether acetate (PMA). Start stirring and purge with nitrogen, heating the oil bath to 85°C and maintaining a stable temperature. Mix methyl methacrylate (40.0 g), butyl acrylate (35.0 g), and hydroxyethyl acrylate (25.0 g) thoroughly to obtain a monomer mixture. Dissolve 2.0 g of azobisisobutyronitrile (2.0 g) in 40.0 g of PMA to obtain an initiator solution. Add the monomer mixture and initiator solution dropwise to the four-necked flask, maintaining a slight positive pressure of nitrogen and good stirring during the addition.

[0040] After the addition was complete, the reaction was continued at 85°C under reflux for 2 h. The temperature was then lowered to 60°C; toluene diisocyanate (TDI, 11.2 g) was added dropwise while stirring. After the addition was complete, dibutyltin dilaurate catalyst (0.03 g) was added. The reaction system temperature was maintained at (65±5)°C and the reaction was continued for 4 h.

[0041] The reaction system temperature was adjusted to 50°C; hydroxyethyl acrylate (7.8 g) and hydroquinone (0.05 g) were premixed and added to the reaction system. After the addition was complete, the reaction was continued at 50°C for 3 h.

[0042] The reaction system was allowed to cool naturally to below 40°C. 10.0 g of propylene glycol methyl ether acetate was added to adjust the viscosity and solids content. After thorough mixing, the mixture was filtered to obtain a light yellow, transparent, viscous liquid, which is the alkali-soluble acrylic resin.

[0043] Synthesis example 2 Synthesis of alkali-soluble resin 4: 214 g of cresol-phenolic varnish-type epoxy resin was added to a 2 L three-necked flask, along with 103 g of carbitol acetate and 150 g of propylene glycol monomethyl ether acetate solvent. The mixture was heated until fully dissolved, and then 0.1 g of hydroquinone and 2.0 g of triphenylphosphine were added to obtain a mixture. This mixture was heated to 100 °C, and 96 g of acrylic acid was slowly added dropwise, allowing the reaction to proceed for 8 h. The mixture was then cooled to 90 °C, and 90 g of tetrahydrophthalic anhydride was added, allowing the reaction to proceed for 4 h. After cooling, the resulting carboxyl-containing unsaturated resin was identified as alkali-soluble resin 4, with an internal Tg of 107 °C and a surface tension of 42.5 mN / m.

[0044] Synthesis example 3 Synthesis of alkali-soluble resin 5: To a 2 L three-necked flask, add 220 g of cresol phenolic varnish-type epoxy resin, 218 g of carbitol acetate, and 150 g of propylene glycol monomethyl ether acetate solvent. Heat to dissolve, then add 0.4 g of methylhydroquinone and 1.5 g of triphenylphosphine to obtain a mixture. Heat the mixture to 100 °C, and slowly add 50.4 g of acrylic acid and 60.5 g of p-hydroxyphenylethanol dropwise, allowing the reaction to proceed for 8 h. Cool to 90 °C, add 60 g of tetrahydrophthalic anhydride, and allow the reaction to proceed for 4 h. After cooling, remove the resulting carboxyl-containing unsaturated resin, which is alkali-soluble resin 5. Internal testing shows its Tg is 96 °C and its surface tension is 95.4 mN / m.

[0045] The components and amounts of the photosensitive compositions of the circuit inks in Examples 1-3 and Comparative Examples 1-6 are shown in Table 1.

[0046] Table 1. Components and dosages of Examples 1-3 and Comparative Examples 1-6 The preparation method of the above-mentioned photosensitive composition of the circuit ink includes the following steps: According to the above mass fractions, alkali-soluble acrylic resin, photoinitiator, filler, and alkali-soluble resin are mixed, stirred and dispersed, and then ball-milled for 1 h with 2 mm diameter zirconium dioxide grinding balls to further disperse evenly. After filtration and degassing, the photosensitive composition of the circuit ink is obtained.

[0047] Test case The circuit ink was prepared according to the composition in Table 1 above, and then its performance was tested.

[0048] Fabrication of the test substrate: Substrate: Printed wiring substrate (glass epoxy board "FR-4", board thickness 1.6 mm, conductor (Cu foil) thickness 50 μm). Substrate surface treatment: Ultra-roughened treatment. Coating method: Screen printing. Wet film thickness: 20 μm. Pre-baking: 80℃, 30 min.

[0049] After pre-drying, test the dryness of the dry film surface, and stack multiple layers to determine whether sticking occurs.

[0050] Exposure: Irradiate the photosensitive resin composition with 300 mJ / cm 2 Ultraviolet light (wavelength 300-400 nm) (exposure device: ORC MANUFACTURING CO.,LTD. "HMW-680GW"). Alkali development: 1 wt% Na2CO3 solution, liquid temperature 30℃, jet pressure 0.2 MPa, development time 60 s.

[0051] After exposure and development, observe the resolution and edge sharpness of the image under a microscope.

[0052] Film removal: In a horizontal spray system, rinse with a 4 wt% NaOH stripping solution at 45°C for 60-180 seconds. Finally, rinse thoroughly with clean water.

[0053] After removing the film, observe and inspect the residual film / adhesive on the substrate surface.

[0054] Test method: Image resolution: After pre-baking, the dry film thickness is 10 μm. After exposure and development, the image resolution is: line width and line spacing <40 μm: indicated by ○; >40 μm: indicated by ×.

[0055] Image side sharpness: After pre-baking, the average size of the tiny jagged edges (dog teeth) appearing in the lines after exposure and development is <8 μm: indicated by ○; >8 μm: indicated by ×.

[0056] Surface dryness after pre-baking: If the area of ​​the pre-baked circuit board stacked in 10 layers is less than 1%, it is indicated by ○; if the area of ​​the pre-baked circuit board stacked in 1 layer is greater than 1% or the film is stuck and falls off when the stacked boards are separated, it is indicated by ×.

[0057] Pattern stripping in the exposed area after development: The area ratio of the stripped area < 1% is indicated by ○; the area ratio of the stripped area > 1% is indicated by ×.

[0058] Residual adhesive after film removal: The substrate surface is clean and free of any adhesive residue after film removal: indicated by ○; The substrate surface has a matte finish or adhesive residue after film removal: indicated by ×.

[0059] The test results are shown in Table 2.

[0060] Table 2 Performance test results of Examples 1-3 and Comparative Examples 1-6 The test results above show that fillers with a particle size of less than 8 μm are required to ensure image resolution and edge clarity. Furthermore, by adding an alkali-soluble resin with a glass transition temperature >60℃, a stable glassy state can be formed on the film surface after pre-baking and returning to room temperature, effectively reducing board adhesion or other sticking problems. Simultaneously, the alkali-soluble resin used in this invention has a surface tension in the range of 50-80 mN / m, which avoids the problems of poor uniformity of the photosensitive composition substrate coating and difficulty in completely removing the composition by the stripping solution, resulting in residual adhesive film, caused by excessively high surface tension. It also solves the defects of insufficient adhesion to the copper surface caused by excessively low surface tension, leading to the entire film surface peeling off during development. Correspondingly, Comparative Example 6, with filler particle size greater than 8 μm, showed insufficient image resolution and clarity; Comparative Examples 3, 4, and 5, with alkali-soluble resin Tg less than 60℃, showed insufficient surface dryness after pre-baking and peeling of the image area after development; and Comparative Example 1, with alkali-soluble resin surface tension less than 50 mN / m, showed large-area peeling of the image in the exposed area, while Comparative Example 2, with alkali-soluble resin surface tension greater than 80 mN / m, showed various problems such as severe residual film after film removal.

[0061] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

[0062] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A photosensitive composition for circuit ink, characterized in that, The photosensitive composition of the circuit ink includes the following components: alkali-soluble acrylic resin, photoinitiator, filler, and alkali-soluble resin; in, The particle size of the filler is less than 8 μm; The alkali-soluble resin has a glass transition temperature greater than 60°C and a surface tension in the range of 50-80 mN / m.

2. The photosensitive composition of the circuit ink according to claim 1, characterized in that, The alkali-soluble acrylic resin is selected from polymers or mixtures thereof formed by copolymerizing two or more monomers selected from methacrylic acid, benzyl methacrylate, hydroxyethyl methacrylate, 2-ethylhexyl acrylate, glycidyl methacrylate, and styrene.

3. The photosensitive composition of the circuit ink according to claim 1, characterized in that, The photoinitiator is selected from one or more of benzoyl derivative photoinitiators, acylphosphine oxide photoinitiators, isopropylthioxanthone, and benzophenone.

4. The photosensitive composition of the circuit ink according to claim 1, characterized in that, The filler is selected from one or more of barium sulfate, silicon dioxide, talc, calcium carbonate, aluminum oxide, boron nitride, mica, or kaolin.

5. The photosensitive composition of the circuit ink according to claim 1, characterized in that, The amount of filler added is 10-70 wt% of the photosensitive composition of the circuit ink.

6. The photosensitive composition of the circuit ink according to claim 1, characterized in that, The alkali-soluble resin is selected from one or more of bisphenol A epoxy acrylate compounds, bisphenol F epoxy acrylate compounds, phenolic epoxy acrylate compounds, and aliphatic epoxy acrylates.

7. The photosensitive composition of the circuit ink according to claim 1, characterized in that, The amount of alkali-soluble resin added is 3-30 wt% of the photosensitive composition of the circuit ink.

8. A method for preparing the photosensitive composition of the circuit ink according to any one of claims 1-7, characterized in that, Includes the following steps: Alkali-soluble acrylic resin, photoinitiator, filler, and alkali-soluble resin are mixed, stirred and dispersed, and then further dispersed using a ball mill or emulsifier, filtered and degassed to obtain a photosensitive composition for circuit ink.

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