Circuit board selective dry film process and circuit board

Abstract

The invention discloses a circuit board selective dry film technology and a circuit board, and the technology comprises the steps: feeding a target circuit board semi-finished product into character jet printing equipment, carrying out the jet printing of characters on the surface of the target circuit board semi-finished product, and carrying out the pre-curing of the characters through a first ultraviolet lamp disposed in the character jet printing equipment, and obtaining a first semi-finished product; the first semi-finished product is sent into an oven to be baked, the characters are solidified for the second time, and a second semi-finished product is obtained; the characters of the second semi-finished product are cured for the third time through a second ultraviolet lamp, a third semi-finished product is obtained, the energy density of the second ultraviolet lamp is 600 + / -50 mJ / cm < 2 >, and the curing time is 60 seconds; a dry film is attached to the third semi-finished product, and after selection treatment is conducted, a fourth semi-finished product is obtained; and the fourth semi-finished product is fed into a film stripping assembly line, the dry film is subjected to film stripping treatment, a fifth semi-finished product is obtained, and the linear speed of the film stripping assembly line is larger than or equal to 2.0 m / min. Dry film residues can be effectively avoided, and the appearance quality of a product is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of circuit board, in particular to a circuit board selective dry film process and a circuit board. BACKGROUND

[0002] With the continuous development of technology, the cost control requirement of the printed circuit board industry is increasingly improved. In order to effectively control the cost, the circuit board (especially high-density interconnection board, HDI board) adopts a selective dry film process. The process uses a dry film to realize selective chemical treatment, such as selective electroplating or surface treatment, which is usually performed after character printing is completed. However, it is found in actual application that the dry film may still remain in the character and its surrounding area after the film is removed, which causes adverse effects on the appearance quality of the product. SUMMARY

[0003] The present application aims to at least solve one of the technical problems existing in the prior art. To this end, the present application provides a circuit board selective dry film process and a circuit board, which can effectively avoid dry film residue and improve the appearance quality of the product.

[0004] In one aspect, the present application provides a circuit board selective dry film process, comprising: sending a target circuit board semi-finished product into a character jet printing device to jet print characters on the surface of the target circuit board semi-finished product, and pre-curing the characters by using a first ultraviolet lamp built in the character jet printing device to obtain a first semi-finished product; sending the first semi-finished product into an oven for baking to perform second curing on the characters, to obtain a second semi-finished product; performing third curing on the characters of the second semi-finished product by using a second ultraviolet lamp to obtain a third semi-finished product, the energy density of the second ultraviolet lamp being 600±50 mJ / cm 2 , and the curing time being 60 seconds; after attaching a dry film on the third semi-finished product and performing selective treatment, obtaining a fourth semi-finished product; sending the fourth semi-finished product into a film removal assembly line to perform film removal treatment on the dry film to obtain a fifth semi-finished product, the line speed of the film removal assembly line being ≥2.0 m / min.

[0005] According to some embodiments of the present application, the energy density of the first ultraviolet lamp is 200-500 mJ / cm 2 , and the curing time is 6 seconds.

[0006] According to some embodiments of the present application, the baking temperature of the oven is 80-150℃, and the baking time is 3 hours.

[0007] According to some embodiments of the present application, the spray pressure value of the film removal assembly line is 2.5±0.5 kg / cm 2temperature value is 55±5℃.

[0008] According to some embodiments of the present application, the attaching the dry film on the third semi-finished product comprises: attaching the dry film on the third semi-finished product based on a hot-pressing process, the hot-pressing temperature of the hot-pressing process being 120±10℃, and the pressure value being 3kg / cm 2 .

[0009] In another aspect, the embodiments of the present application provide a circuit board prepared by the above circuit board selective dry film process.

[0010] In yet another aspect, the embodiments of the present application provide a circuit board comprising: a circuit board body provided with a plurality of target pads; a solder resist layer covering a surface of the circuit board body, the solder resist layer being provided with a first windowing position, the first windowing position being adapted to the target pads; a character layer provided on the solder resist layer, the character layer forming a dense protective interface after multiple solidifications, the multiple solidifications comprising pre-solidification based on a first ultraviolet lamp, second solidification based on an oven, and third solidification based on a second ultraviolet lamp, the energy density of the second ultraviolet lamp being 600±50mJ / cm 2 , and the solidification time length being 60 seconds; a dry film layer covering the solder resist layer and the character layer, the dry film layer being provided with a second windowing position adapted to the target pads; a surface treatment layer provided on the target pads.

[0011] According to some embodiments of the present application, the energy density of the first ultraviolet lamp is 200-500mJ / cm 2 , and the solidification time length is 6 seconds.

[0012] According to some embodiments of the present application, the baking temperature of the oven is 80-150℃, and the baking time length is 3 hours.

[0013] According to some embodiments of the present application, the dry film layer is separated from the solder resist layer and the character layer after a film stripping treatment, the line speed of the flow line of the film stripping treatment being ≥2.0m / min, the spraying pressure value being 2.5±0.5kg / cm 2 , and the temperature value being 55±5℃.

[0014] The embodiments of the present application have at least the following beneficial effects: The character is multiple-cured before the dry film selection and curing process, so that a dense protective interface is formed on the surface of the character, the character and the dry film after exposure are prevented from sticking and adhering, the bonding force between the dry film and the character is reduced, the dry film residue can be effectively avoided during the film stripping process, the appearance quality of the product is improved, the line speed of the film stripping line can reach 2.0 m / min or more, and the production efficiency is improved.

[0015] Additional aspects and advantages of the present application will be set forth in part in the description which follows, and in part will become apparent to those having ordinary skill in the art upon examination of the following or can be learned from practice of the application. BRIEF DESCRIPTION OF DRAWINGS

[0016] The above and / or additional aspects and advantages of the present application will become apparent and be readily appreciated from the following description, taken in conjunction with the accompanying drawings, in which: Figure 1 is a partial schematic view of a circuit board semi-finished product of an embodiment of the present application; Figure 2 is a step flow chart of a circuit board dry film selection and curing process of an embodiment of the present application; Figure 3 is a partial schematic view of a circuit board semi-finished product of an embodiment of the present application; Figure 4 is a partial schematic view of a circuit board semi-finished product of an embodiment of the present application; Figure 5 is a partial schematic view of a circuit board semi-finished product of an embodiment of the present application; Figure 6 is a partial schematic view of a circuit board semi-finished product of an embodiment of the present application; Figure 7 is a schematic view of a laminated structure of a circuit board semi-finished product of an embodiment of the present application.

[0017] REFERENCE NUMERALS circuit board body 100, target pad 101, solder resist layer 110, first windowing position 111, character layer 120, dry film layer 130, second windowing position 131, surface treatment layer 140. DETAILED DESCRIPTION

[0018] Embodiments of the present application are described in detail below with reference to the attached drawings, which show by way of example, embodiments in which like numerals indicate like elements or elements having the same or similar function. The embodiments described below with reference to the attached drawings are illustrative of the present application and are not intended to limit the present application.

[0019] In the description of this invention, it should be understood that the orientation descriptions, such as up, down, front, back, left, right, etc., are based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention.

[0020] In the description of this invention, "several" means one or more, "multiple" means two or more, "greater than," "less than," "exceeding," etc. are understood to exclude the stated number, and "above," "below," "within," etc. are understood to include the stated number. If "first," "second," etc. are used in the description, they are only for the purpose of distinguishing technical features and should not be construed as indicating or implying relative importance or implicitly indicating the number of indicated technical features or the order of the indicated technical features.

[0021] In the description of this invention, unless otherwise explicitly defined, terms such as "set", "install", and "connect" should be interpreted broadly, and those skilled in the art can reasonably determine the specific meaning of the above terms in this invention in conjunction with the specific content of the technical solution.

[0022] In existing technologies, the selective dry film process is typically performed after the character printing process. However, this process has a significant drawback: even after the film removal operation is completed, some dry film material may still remain in the characters and their adjacent areas (e.g., Figure 1 As shown in the center circle (position A1), this significantly damages the appearance quality of the final product. Currently, the industry commonly uses two main improvement methods: one is to introduce a dedicated stripping solution for pre-soaking, and simultaneously reduce the conveyor speed of the stripping line to 1.0~1.3 m / min; the other is to repeat the stripping process multiple times. While the first method can improve the stripping effect to some extent, it relies on a specific stripping solution, leading to a significant increase in raw material costs. Simultaneously, during the soaking process, the stripping solution may undergo unnecessary chemical reactions with the solder resist layer in non-covered areas, causing surface matte finish and potentially leading to the scrapping of the entire board. Furthermore, the reduced line speed decreases the overall efficiency of the production line, forcing a longer production cycle. The second method, implementing multiple stripping processes, while relatively simple, also prolongs the production cycle due to process repetition and exacerbates the risk of solder resist damage or matte finish during multiple chemical treatments, which is also detrimental to quality and cost control.

[0023] During the research, we also attempted to optimize the film removal effect by opening windows in the dry film of the character area. The core of this method lies in adjusting the photoplotting data used for dry film exposure and designing windows in the dry film of the character area so that it is not processed during the exposure stage and can be completely removed during the development stage. However, in practical applications, it was found that the single-sided coverage of conventional dry films is usually not less than 100μm, while most characters on HDI circuit boards are located in high-density areas, such as the periphery of BGA pads and OSP surface-treated pads (e.g., Figure 1 As shown in position A2 (circled in the middle), the spacing between the characters and pads at these locations is generally 75μm or less, which fails to meet the basic spacing requirements of the windowing process. Insufficient dry film coverage can easily lead to plating penetration in the pad area, severely impacting soldering reliability. Furthermore, from a production implementation perspective, creating standardized dry film windowing data is challenging. Current processes still rely on manual adjustments to photoplot files, which is not only time-consuming and inefficient but also lacks process error prevention mechanisms, easily leading to batch quality anomalies. Therefore, this approach is difficult to practically apply to the optimization of dry film processes for HDI boards.

[0024] Based on an understanding of existing conventional improvement methods, and utilizing limited production resources, this study attempted to focus on parameter control in the film stripping process, such as adjusting key variables like stripping solution concentration, pre-soaking time, and stripping temperature. Systematic controlled variable experiments were conducted. However, the results showed that neither single-factor adjustments nor multi-parameter synergistic optimization consistently resolved issues like dry film residue or character damage. This indicates that simply adjusting the stripping process parameters cannot fundamentally eliminate the causes of dry film residue.

[0025] A deeper study of the mechanism revealed that a cross-linking reaction may occur between the dry film and the character ink during exposure, significantly enhancing their adhesion. This not only makes it difficult to completely peel off the dry film during delamination but may also cause the characters themselves to be torn off, resulting in incomplete or severely damaged character outlines. Based on this finding, improvements can be made by effectively weakening the adhesion between the dry film and the character surface. For example, an isolation coating could be added to the character surface to reduce the adhesion strength of the dry film. However, the development of coating materials requires significant resources for formulation screening and performance verification. Even if successfully developed, the addition of materials and processes will increase overall costs, weakening the product's price competitiveness in the market.

[0026] Therefore, the method proposed in this embodiment, under the premise of fully considering production cost and efficiency constraints, is committed to fundamentally suppressing the formation of dry film residue, significantly improving the appearance quality of products, and has strong engineering applicability and industrialization potential.

[0027] Example 1 Please refer to Figure 2The embodiment discloses a kind of circuit board selective dry film processes, including steps S100~S500.It needs to be explained, the step of this embodiment is labeled only for the convenience of review understanding, and not the execution order of step is limited.The content of each step is described in detail as follows: S100, the target circuit board semi-finished product is sent to the character jet printing equipment to jet print characters on the surface of the target circuit board semi-finished product, and the first ultraviolet lamp built-in character jet printing equipment is used to pre-cure the characters, to obtain the first semi-finished product; Illustratively, the target circuit board semi-finished product is an intermediate product formed in the production and processing process, and the structure mainly includes a circuit board body and a solder resist layer covering the surface of the circuit board body. The circuit board body is a multi-layer composite structure, which is usually composed of multiple layers, such as an inner layer circuit layer, an outer layer circuit layer, and a first insulating layer filled and solidified between different inner layer circuit layers by a prepreg pressing process, and a second insulating layer between the inner layer circuit layer and the outer layer circuit layer formed by the same process. These insulating layers not only play an electrical isolation role, but also enhance the mechanical stability of the overall structure.

[0028] A target pad is provided on the outer layer circuit layer for subsequent component assembly or electrical connection. The solder resist layer is coated on the surface of the outermost circuit layer, and its main function is to prevent solder short circuit and protect the circuit, and according to customer or process requirements, a windowing process is performed at the position corresponding to the target pad to expose the pad area, facilitating subsequent selective surface treatment (such as gold plating, tin spraying or OSP treatment, etc.). The solder resist layer can be selected from different materials according to actual application, such as green, black and other colors, to meet the requirements of appearance recognition or optical detection, etc.

[0029] After completing the solder resist treatment, the target circuit board semi-finished product is sent to the character jet printing equipment, and the specified characters are sprayed on the surface of the solder resist layer according to the pre-set production data, such as boundary lines for identifying the position of components, and "VBAT" and "NTC" numbers for identifying the position and attributes of components. To improve the visual contrast, the characters usually use white ink. The character ink exists in a liquid state during jet printing, and the first ultraviolet lamp built-in character jet printing equipment emits ultraviolet light of a specific wavelength (usually 365 nm or 395 nm band) to irradiate the ink to start the photocuring process, wherein the energy density of the first ultraviolet lamp is 200~500mJ / cm 2 , and the curing time is 6 seconds. The curing mechanism mainly includes the following steps: Light initiator absorbs ultraviolet light: the light initiator (or photosensitizer) in the ink absorbs light energy under ultraviolet light irradiation, the chemical bond breaks, and a free radical or cation with high reactivity is generated; Initiation of polymerization: these active species react with the unsaturated bonds in the monomer and prepolymer molecules in the character ink system, triggering chain growth polymerization. Monomers continuously join the polymer chain, and prepolymers crosslink between them, increasing the molecular weight; Curing molding: as the reaction proceeds, the character ink system gradually transforms from a linear structure to a three-dimensional network solid. The transition from liquid to solid is achieved in a very short time (usually within a few seconds), forming a character pattern with high mechanical strength, firm adhesion, excellent wear resistance and chemical resistance.

[0030] S200, the first semi-finished product is sent into the oven for baking to perform the second curing of the characters, obtaining the second semi-finished product; For example, although the ultraviolet curing technology can quickly form a hardened film layer on the surface of the ink within seconds, its curing mechanism has inherent physical limitations. Due to the limited penetration ability of ultraviolet light in matter, especially for character ink containing pigments (such as titanium dioxide), it is difficult for light to fully reach the bottom layer of the ink, resulting in insufficient curing degree in the bottom area. This uneven curing phenomenon will further affect the adhesion between the ink and the substrate, and reduce the overall mechanical durability and long-term reliability of the coating.

[0031] In addition, the ultraviolet curing mechanism mainly relies on the rapid polymerization reaction of photoinitiators on the surface layer, and the support for the complete reaction of solvent volatilization and deep active components in the ink system is limited. There may be residual solvents or uncrosslinked oligomers in the ink that do not participate in the reaction, affecting the density and performance stability of the final cured layer. To overcome the above limitations of ultraviolet curing, introducing thermal energy assisted curing becomes an effective strategy. Thermal energy can promote the overall temperature rise of the ink, accelerate molecular motion, and make reaction groups collide and crosslink further, thereby significantly improving the completion degree of deep curing and achieving more thorough molecular-level reaction. In this process, a tunnel oven is usually used to heat and bake the second semi-finished product that has completed ultraviolet pre-curing and subsequent controlled cooling, so that its temperature decreases to room temperature when it is taken out of the oven, completing the entire curing process. The baking temperature of the oven is 80°C to 150°C, and the baking time is 3 hours, so that the character ink achieves good curing effect.

[0032] However, the current character process in the manufacture of circuit boards has gradually adopted inkjet printing technology instead of traditional screen printing technology, and the ink used in inkjet printing is mainly ultraviolet curing ink, whose curing mechanism relies on ultraviolet light source (built-in light source) to induce photopolymerization reaction, which is fundamentally different from traditional heat-curable ink. In actual process research, it is found that even after the above baking treatment, the curing degree of the character ink is usually only about 80%, and there are still unreacted monomers and oligomers remaining in the ink system, resulting in incomplete curing and low molecular crosslinking degree, which leads to a low level of character ink surface hardness. If the dry film is attached to the surface of the character ink in this state, and then the dry film exposure process is carried out, additional chemical crosslinking reactions may occur between the dry film and the interface of the incompletely cured ink, forming a strong interaction interface. After subsequent various surface treatments (such as nickel gold plating, nickel palladium gold plating or chemical tin, etc.) and the action of alkaline stripping solution (such as sodium hydroxide solution), the dry film and the character ink both swell and soften, but lack sufficient mechanical stability to resist stress, and the interface strengthening effect between the dry film and the character will cause the dry film to be difficult to completely peel off from the surface of the character during the stripping stage, resulting in problems such as residue or excessive peeling force, which affects the appearance quality of the product.

[0033] S300, using a second ultraviolet lamp to perform a third curing on the characters of the second semi-finished product to obtain a third semi-finished product, the energy density of the second ultraviolet lamp being 600±50 mJ / cm 2 , and the curing time being 60 seconds; For example, based on the interface interaction mechanism between the character ink and the dry film, and based on the ultraviolet curing characteristics of the character ink, a hardening protective layer with high crosslinking degree is constructed on the surface of the ink by a secondary ultraviolet curing process (i.e. a third curing) in this embodiment. The hardening layer can effectively inhibit the chemical bonding between the dry film and the ink surface, significantly reduce the bonding strength between them, and thus provide good interface separation conditions for the subsequent stripping process.

[0034] After the first ultraviolet curing and baking curing, the character ink surface has certain mechanical strength and chemical resistance, but the curing degree of the character ink is insufficient, and partial bonding may occur between the dry film and the character ink during the subsequent dry film coating and exposure, development and various surface treatment processes, resulting in excessive interface bonding force, and thus causing problems such as incomplete stripping, ink damage or increased surface roughness. By introducing a secondary ultraviolet curing process, the molecules in the surface layer and near-surface layer of the ink can be further crosslinked, forming a dense and high-crosslinking hardening film layer on the surface of the ink. The hardening film layer has excellent chemical inertness and low surface energy, and can effectively block the physical adsorption and chemical action between the dry film and the ink body.

[0035] In the subsequent dry film exposure and various surface treatment processes, due to the formation of a dense cross-linked structure on the surface of the ink, the physical bonding force between the character ink and the dry film is maintained at a low level. During the alkaline film stripping process, the stripping solution mainly acts on the dry film layer and is difficult to penetrate into the character ink, thereby ensuring that the surface of the character ink remains smooth, making the dry film more easily peeled off, and effectively improving the film stripping quality.

[0036] In order to balance the film stripping effect and production efficiency in actual production, the degree of curing of the character ink needs to be accurately controlled. Since the degree of curing is mainly controlled by the ultraviolet light energy density (unit: mJ / cm 2 ) and irradiation time (unit: seconds), this embodiment takes energy density as the key variable to carry out single-factor test, and the rest of the process parameters remain the same to ensure the comparability of the results. The rest of the process parameters include: ultraviolet curing time is 60 seconds; dry film pressing is carried out in the production line, the dry film pressing temperature is 110°C, the pressure is 3 kg / cm 2 , the line speed is 2.5 m / min; the dry film exposure energy is 8 grids; the film stripping process is carried out in the production line, and the film stripping line speed is controlled at 2 m / min. It is worth mentioning that in order to ensure the film stripping effect, the conventional improvement scheme will lower the transmission speed of the film stripping production line to 1.0-1.3 m / min, while this embodiment can still maintain a relatively high film stripping line speed, meeting the demand for production efficiency.

[0037] Please refer to Figure 3 , when the second ultraviolet curing (i.e. the third curing) is not implemented, a large range of film stripping unclean phenomenon occurs on the surface of the semi-finished product, and the dry film (blue-purple color) on the surface of the character ink (white color) is seriously retained (as shown by the circled position B1 in Figure 3 ), and even the dry film is retained on the solder mask layer (black color) (as shown by the circled position B2 in Figure 3 ), indicating that the initial curing state is not sufficient to resist the erosion of the stripping solution to the interface and achieve clean separation. Please refer to Figure 4 , Figure 4 , (a) to (d) respectively show the film stripping effect when the energy density of the second ultraviolet lamp is 100 mJ / cm², 200 mJ / cm², 300 mJ / cm² and 400 mJ / cm². From the figure, it can be observed that there is still obvious residue on the surface of the character ink, and the film stripping unclean problem has not been completely solved, indicating that the energy density is still insufficient to make the surface layer of the ink reach the required cross-linking density and surface inertness. Please refer to Figure 5 , when the energy density of the second ultraviolet lamp is increased to 500 mJ / cm 2 , the amount of dry film residue on the surface of the character ink after film stripping has been significantly reduced, and only sporadic or very thin layer of residue exists (as shown by the circled position B3 in Figure 5As shown in the middle circle (positions C1 and C2), the dry film is no longer obvious compared to the character ink, indicating that the curing degree and protective effect of the character ink surface layer have been greatly improved, but it has not yet fully met the requirements for high-quality mass production.

[0038] Please refer to Figure 6 When the energy density further reached 550 mJ / cm², no dry film residue was observed on the surface of the character ink after decoction (e.g., Figure 6 As shown in the middle circle (position D), the board surface is clean, and the character edges are clear, meeting the good product standard. This indicates that at this energy density, the secondary UV curing has successfully formed a sufficiently dense and stable hardened layer on the ink surface, completely blocking the strong forces between the dry film and the ink, and allowing the selective peeling effect of the stripping solution to be fully utilized. To verify the robustness of this process window, the energy density was further increased to 600 mJ / cm² and 650 mJ / cm² for further testing. The results also showed that no dry film residue was found on the character surface, the stripping effect was good, and no ink embrittlement, discoloration, or other negative phenomena caused by over-curing were observed, indicating that the process has good stability and reliability over a wide energy range of 550 mJ / cm² to 650 mJ / cm².

[0039] Based on the above experimental results, in practical applications, it is recommended to set the target energy density for secondary UV curing to 600 mJ / cm², with an allowable process fluctuation range of ±50 mJ / cm² to accommodate equipment errors and changes in the production environment. For example, the energy density can be specifically controlled around values ​​such as 560 mJ / cm², 570 mJ / cm², 580 mJ / cm², 590 mJ / cm², 610 mJ / cm², 620 mJ / cm², 630 mJ / cm², and 640 mJ / cm². This process window ensures a stable, residue-free film removal effect, meeting yield standards, while also balancing production efficiency and process controllability, providing a clear and feasible parameter basis for improving the quality of the character processing segment in PCB manufacturing.

[0040] S400. After attaching a dry film to the third semi-finished product and performing a selection and chemical treatment, the fourth semi-finished product is obtained. To improve the adhesion between the dry film and the copper surface of the substrate, ensure the accuracy and reliability of the pattern transfer, the third semi-finished product needs to be pretreated before the dry film is attached. The core process of the pretreatment is micro-etching the copper surface. The purpose is to slightly etch the copper surface by chemical method to remove oxides, greases or other contaminants and form a uniform rough surface structure, thereby significantly increasing the physical adhesion between the pads and the dry film. The micro-etching amount is controlled within the range of 0.2-0.8 μm. If the micro-etching amount is too low, it is not enough to achieve effective roughening and cleaning effect, and the adhesion improvement is limited. If it is too high, it may cause the line width deviation to increase or the copper thickness loss to exceed the standard, affecting the circuit performance and reliability.

[0041] After the pretreatment is completed, the dry film attachment process is entered. The dry film is attached to the third semi-finished product based on the hot pressing process. The hot pressing temperature of the hot pressing process is 120±10℃, and the pressure value is 3kg / cm 2 Within this temperature range, the polymer bonding layer in the dry film can be fully activated and flow to achieve close contact and initial bonding with the roughened copper surface. The control of pressure is aimed to ensure that the dry film is uniformly pressed, effectively eliminates the interface bubbles, enhances the adhesion strength of the film layer and the substrate, and avoids the film layer wrinkling, peeling or pattern defects in the subsequent process.

[0042] After the dry film attachment is completed, selective exposure (selective exposure) is performed. This step uses a negative (mask) to transfer the target pattern to the dry film through ultraviolet light irradiation. The ultraviolet light causes the exposed area of the dry film to undergo a photochemical reaction, causing it to cross-link and solidify, while the unexposed area remains soluble. The exposure energy is usually controlled within the range of 8-10 grids (according to the display value of the light energy integrator). This range can ensure good pattern resolution, avoid poor development caused by insufficient energy, or side etching and line width deviation caused by excessive energy.

[0043] After exposure, the selective development process is entered. This process uses Na2CO3 aqueous solution as the developer, and the unexposed part of the dry film is dissolved and removed by spraying or soaking, so that the required pattern is revealed. The development point (i.e. the development degree) is controlled within the range of 50%-60% to ensure that the pattern edge is clear, without line thinning defects caused by residual film or overdevelopment, providing accurate pattern masking for subsequent etching or electroplating.

[0044] After development is completed, the surface of the board with the formed pattern needs to be subjected to selective surface treatment, such as electroless nickel gold plating (gold plating). This treatment aims to chemically deposit a layer of nickel and a layer of gold on the exposed pad copper surface in sequence. The nickel layer acts as a barrier layer to prevent copper diffusion and provides a reliable basis for intermetallic compound formation; the gold layer has good oxidation resistance, electrical conductivity and soldering performance, which can effectively protect the pads until the assembly and soldering stage, ensuring the reliability and long-term stability of the component soldering.

[0045] S500, send the fourth semi-finished product into a stripping line to perform stripping treatment on the dry film to obtain a fifth semi-finished product, and the line speed of the stripping line is greater than or equal to 2.0 m / min.

[0046] For example, the stripping process of the dry film is usually performed in a stripping line, and the alkaline stripping solution is uniformly sprayed on the surface of the fourth semi-finished product in a spraying manner under specific temperature and pressure conditions, and the stripping of the dry film is realized by using a chemical dissolution reaction. The spraying pressure value of the stripping line is 2.5±0.5 kg / cm 2 , and the temperature value is 55±5℃. The spraying pressure in this range can ensure that the stripping solution has sufficient mechanical impact force to effectively penetrate and flush each position on the surface of the board, accelerate the destruction of the bonding interface between the dry film and the board, and carry away the dissolved film residue. Too low pressure will result in weak spraying and difficulty in removing stubborn film layers; too high pressure may cause physical damage to fine lines or cause the chemical solution to splash. The temperature condition can ensure the reaction effect between the alkaline stripping solution and the dry film. Too high temperature may cause excessive evaporation of the stripping solution and accelerate the corrosion of the equipment and other metal layers on the board; too low temperature will significantly reduce the chemical reaction rate, resulting in incomplete stripping, low efficiency, and even residual film.

[0047] Therefore, the character is solidified multiple times before the dry film selection process in this embodiment, so that a dense protective interface is formed on the surface of the character, the character is prevented from adhering to the dry film after exposure, the bonding force between the dry film and the character is reduced, the dry film residue can be effectively avoided during the stripping process, the appearance quality of the product is improved, and the line speed of the stripping line can be greater than or equal to 2.0 m / min, which is beneficial to improve the production efficiency.

[0048] This embodiment also provides a circuit board prepared by the above-mentioned circuit board dry film selection process, which can effectively avoid dry film residue and improve the appearance quality of the product while considering the cost and production efficiency.

[0049] Embodiment 2 For details, please refer to Figure 7 Based on the same technical concept as Embodiment 1, this embodiment provides a circuit board, which comprises a circuit board body 100, a solder mask layer 110, a character layer 120, a dry film layer 130, and a surface treatment layer 140. The contents not involved in this embodiment can be referred to Embodiment 1.

[0050] The circuit board body 100 is a multi-layer composite structure, which is usually composed of an inner circuit layer, an outer circuit layer, and first and second insulating layers filled and solidified by a prepreg lamination process, and has good electrical isolation performance and mechanical stability. The circuit board body 100 is provided with a plurality of target pads 101 for subsequent component assembly or electrical connection.

[0051] The solder resist layer 110 covers the surface of the circuit board body 100, and is provided with a first windowing position 111 adapted to the target pad 101 to expose the pad area, facilitating subsequent selective surface treatment such as electroless nickel immersion gold (ENIG) treatment, soldering or OSP (organic solderability preservative) treatment, etc.

[0052] The character layer 120 is disposed on the solder resist layer 110, and the forming process of the character layer 120 includes spraying designated characters (such as component boundary lines or identifiers such as “VBAT” and “NTC”) on the surface of the solder resist layer 110 by a character ink through a character inkjet printing device. After multiple curing, the character layer 120 forms a dense protective interface, and the multiple curing includes pre-curing based on a first ultraviolet lamp, second curing based on an oven, and third curing based on a second ultraviolet lamp.

[0053] In the pre-curing process based on the first ultraviolet lamp, the first ultraviolet lamp usually emits ultraviolet light in the 365 nm or 395 nm wave band, and the energy density is controlled at 200-500 mJ / cm², and the curing time is 6 seconds. In this process, the photoinitiator in the character ink absorbs ultraviolet light energy to generate free radicals or cationic active species, initiate chain polymerization of monomers and prepolymers, and rapidly convert the ink from a liquid state to a solid state to form a preliminary cured layer.

[0054] In the second curing process based on the oven, the oven baking temperature is controlled at 80-150°C, and the baking time is 3 hours. In this stage, the whole ink temperature is raised by heat energy to promote further crosslinking of deep layer molecules, solve the problem of insufficient curing of the bottom layer due to the limited penetration of ultraviolet light, significantly reduce the residual unreacted monomers and oligomers, and improve the ink adhesion and mechanical durability.

[0055] In the third curing process based on the second ultraviolet lamp, the energy density of the second ultraviolet lamp is strictly controlled at 600±50 mJ / cm², and the curing time is 60 seconds. Through high-energy ultraviolet irradiation, the molecules on the surface and near the surface of the character ink are deeply crosslinked to form a hard film layer with high crosslinking degree. The film layer has excellent chemical inertness and low surface energy, which can effectively block the physical adsorption and chemical bonding between the subsequent dry film layer 130 and the ink body, significantly reduce the interfacial bonding force, and create good separation conditions for the film stripping process.

[0056] A dry film layer 130 is applied over the solder mask layer 110 and the character layer 120 via a hot-pressing process. The hot-pressing temperature is typically 120±10℃, and the pressure is 3 kg / cm², to ensure uniform bonding of the film layers and eliminate interface bubbles. The dry film layer 130 has a second window position 131, the position and size of which are adapted to the target pad 101 to form a mask pattern for pattern transfer. After selective exposure and development, the dry film layer 130 serves as a mask to guide the formation of the subsequent surface treatment layer 140.

[0057] A surface treatment layer 140 is disposed on the target pad 101, for example, formed by a chemical nickel-gold plating process. In some application examples, the surface treatment layer 140 includes a nickel layer and a gold layer, wherein the nickel layer acts as a barrier layer to prevent copper diffusion and provides a solder base, while the gold layer ensures good conductivity, oxidation resistance, and soldering reliability of the pad.

[0058] After the dry film layer 130 undergoes a stripping process, it detaches from the solder mask layer 110 and the character layer 120. The stripping process line has a line speed ≥ 2.0 m / min and a spray pressure of 2.5 ± 0.5 kg / cm². 2 The temperature is 55±5℃. Since the surface of the character layer 120 has been cured three times to form a dense protective interface, the adhesion between the dry film and the characters is significantly reduced. The stripping solution can effectively act on and remove the dry film, avoiding residue, while maintaining high production efficiency.

[0059] Thus, in this embodiment, the characters are cured multiple times before the dry film process, forming a dense protective interface on the surface of the characters. This prevents the characters from sticking to the exposed dry film after it is applied, reducing the bonding force between the dry film and the characters. As a result, dry film residue can be effectively avoided during the film removal process, improving the appearance quality of the product. Moreover, the line speed of the film removal line can reach more than 2.0 m / min, which is beneficial to improving production efficiency.

[0060] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A circuit board selective dry film process, characterized by, The method comprises the following steps: sending a target circuit board semi-product into a character jet printing device to jet print characters on the surface of the target circuit board semi-product, and pre-curing the characters by using a first ultraviolet lamp built in the character jet printing device to obtain a first semi-product; sending the first semi-product into an oven to bake and perform second curing on the characters to obtain a second semi-product; A third curing is performed on the characters of the second semi-finished product by using a second ultraviolet lamp, to obtain a third semi-finished product, wherein the energy density of the second ultraviolet lamp is 600±50 mJ / cm 2 , and the curing time length is 60 seconds. attaching a dry film on the third semi-product and performing a photoresist treatment to obtain a fourth semi-product; sending the fourth semi-product into a dry film stripping assembly line to perform a dry film stripping treatment on the dry film to obtain a fifth semi-product, and the line speed of the dry film stripping assembly line is greater than or equal to 2.0 m / min.

2. The circuit board photo-definition dry film process according to claim 1, wherein, The energy density of the first ultraviolet lamp is 200-500 mJ / cm 2 , and the curing time is 6 seconds.

3. The circuit board patterning dry film process according to claim 1 or 2, characterized by, The baking temperature of the oven is 80-150 DEG C, and the baking time is 3 hours.

4. The circuit board photo-definition dry film process according to claim 1, wherein, The spraying pressure value of the demolding flow line is 2.5±0.5kg / cm 2 , and the temperature value is 55±5℃.

5. The circuit board photo-definition dry film process according to claim 1, wherein, The method for attaching the dry film on the third semi-product comprises the following steps: attaching a dry film on the third semi-finished product based on a hot-pressing process, a hot-pressing temperature of the hot-pressing process being 120±10℃, a pressure value being 3kg / cm 2 .

6. A wiring board, characterized by The method is prepared by the circuit board photoresist dry film process according to any one of claims 1 to 5.

7. A wiring board, characterized by The method comprises the following steps: A circuit board body is provided with a plurality of target pads; A solder resist layer is covered on the surface of the circuit board body, and the solder resist layer is provided with a first windowing position which is adapted to the target pads; A character layer is arranged on the solder resist layer, and the character layer forms a dense protective interface after multiple solidifications, the multiple solidifications including pre-solidification based on a first ultraviolet lamp, second solidification based on an oven, and third solidification based on a second ultraviolet lamp, the energy density of the second ultraviolet lamp being 600±50 mJ / cm 2 , and the solidification time being 60 seconds. A dry film layer is covered on the solder resist layer and the character layer, and the dry film layer is provided with a second windowing position which is adapted to the target pads; A surface treatment layer is arranged on the target pads.

8. The circuit board according to claim 7, characterized by The energy density of the first ultraviolet lamp is 200-500 mJ / cm 2 , and the curing time is 6 seconds.

9. The circuit board according to claim 7, wherein The baking temperature of the oven is 80-150 DEG C, and the baking time is 3 hours.

10. The circuit board of claim 7, wherein The dry film layer is separated from the solder resist layer and the character layer after the film stripping treatment, the line speed of the film stripping treatment pipeline is greater than or equal to 2.0 m / min, the spray pressure value is 2.5±0.5 kg / cm 2 , and the temperature value is 55±5℃.

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