Non-pressure sensitive photosensitive coverlay film, method of making, method of using, and applications thereof

Abstract

The application discloses a non-pressure-sensitive photosensitive cover film, a preparation method and application thereof and a use method, relates to the technical field of photosensitive cover films, and sequentially comprises a carrier layer, a photosensitive resin layer without or with low adhesion in a temperature A range, and a protective layer; the photosensitive resin layer has fluidity in a temperature B range; 25 DEG C <= A <= 80 DEG C, 80 DEG C < B <= 120 DEG C, and the application has the beneficial effects that the photosensitive resin layer is designed to be without or with low adhesion in the temperature A range, so that the photosensitive resin layer does not form a closed space with a copper-clad plate base material surface during initial pressing; in combination with a two-step non-vacuum pressing process in the use method, gas can be effectively discharged during pressing; experimental data show that the peeling force between the photosensitive resin layer of an initial copper-clad plate and the base material is less than 0.5 N / cm, which proves that only slight adhesion is achieved in the pre-pressing stage, and the existence of the exhaust passage is ensured; and the peeling force can reach 10 N / cm-20 N / cm after final curing, and the bonding strength is ensured.

Description

Technical Field

[0001] This invention relates to the field of photosensitive cover film technology, and in particular to a non-pressure-sensitive photosensitive cover film, its preparation method, its usage method, and its application. Background Technology

[0002] In the manufacturing process of printed circuit boards (PCBs), photosensitive cover films are widely used to form a permanent protective layer on the surface of the circuit board. Traditional photosensitive cover films typically have a certain degree of pressure-sensitive adhesion to allow them to bond with the substrate during lamination. However, this adhesion also brings a series of problems.

[0003] First, during the lamination process, the adhesive photosensitive cover film easily forms a sealed space with the substrate surface, trapping air and creating bubbles. To eliminate these bubbles, the industry generally uses expensive vacuum lamination equipment, increasing equipment investment and production energy consumption.

[0004] Secondly, viscous photosensitive coatings easily attract dust and impurities during handling and operation, affecting the yield of the final product.

[0005] Furthermore, for rigid PCBs that do not have special requirements for flexural strength, the solder mask layer does not need to possess excellent flexibility. Therefore, it is necessary to develop a non-pressure-sensitive photosensitive cover film specifically for rigid PCBs, its preparation method, application method, and its applications. Summary of the Invention

[0006] The purpose of this invention is to disclose a non-pressure-sensitive photosensitive cover film, its preparation method, its usage method, and its applications.

[0007] The first objective of this invention is to develop a non-pressure-sensitive photosensitive cover film.

[0008] The second objective of this invention is to develop a method for preparing a non-pressure-sensitive photosensitive cover film.

[0009] The third objective of this invention is to develop a method for using a non-pressure-sensitive photosensitive cover film.

[0010] The fourth objective of this invention is to develop an application of a non-pressure-sensitive photosensitive cover film in the fabrication of rigid PCBs.

[0011] To achieve the first objective mentioned above, the present invention provides a non-pressure-sensitive photosensitive cover film, which, from bottom to top, comprises a carrier layer, a photosensitive resin layer that is non-adhesive or low-adhesive in the temperature range A, and a protective layer. The photosensitive resin layer has fluidity in the temperature range B; 25℃≤A≤80℃, 80℃<B≤120℃.

[0012] Preferably, the photosensitive resin layer comprises a thermosetting resin, a photopolymerizable compound, and a photoinitiator, and the photosensitive resin layer contains no or only trace amounts of pressure-sensitive adhesive resin.

[0013] Preferably, the photosensitive resin layer comprises the following components: High Tg temperature epoxy acrylate resin, 80 parts by weight - 110 parts by weight; Trimethylolpropane triacrylate: 20-35 parts by weight; Photoinitiator: 3-5 parts by weight; Thermosetting accelerator: 1 part by weight to 3 parts by weight; Leveling agent: 0.5 parts by weight to 1 part by weight; Solvent: 45 parts by weight - 65 parts by weight.

[0014] Preferably, the Tg temperature is 65℃-70℃.

[0015] Preferably, the weight content of the pressure-sensitive adhesive resin is 0-3 parts.

[0016] Based on the same inventive principle, in order to achieve the second inventive objective mentioned above, the present invention also provides a method for preparing a non-pressure-sensitive photosensitive coating film, comprising the following steps: Step S1: Under yellow light conditions, mix the following components evenly to form a composition: High Tg temperature epoxy acrylate resin, 80 parts by weight - 110 parts by weight; Trimethylolpropane triacrylate: 20-35 parts by weight; Photoinitiator: 3-5 parts by weight; Thermosetting accelerator: 1 part by weight to 3 parts by weight; Leveling agent: 0.5 parts by weight to 1 part by weight; Solvent: 45-65 parts by weight; Pressure-sensitive adhesive resin: 0 parts by weight - 3 parts by weight; Step S2: The composition formed in step S1 is uniformly coated on a carrier film with a thickness of 15μm-30μm and dried to form a base film; Step S3: A protective layer is attached to the surface of the base film to form a photosensitive cover film.

[0017] Based on the same inventive principle, and to achieve the third inventive objective mentioned above, this invention also provides a method for using a non-pressure-sensitive photosensitive cover film, comprising the following steps: Step A1: Remove the protective layer of the non-pressure-sensitive photosensitive cover film described in the first invention; Step A2: Under non-vacuum conditions, temperature range A, and pressure conditions of 0.8MPa-1.5MPa, the flatbed press presses the exposed photosensitive resin layer onto the surface of the copper-clad laminate substrate. The pressing time is 20s-35s. The gas between the photosensitive resin layer and the copper-clad laminate substrate is discharged. After pressing, the substrate is cooled to room temperature to obtain the initial copper-clad laminate. Step A3: Under non-vacuum conditions, temperature range B, and pressure conditions of 0.8MPa-1.5MPa, the initial copper-clad laminate is hot-pressed by a flatbed press for 20s-35s. After pressing, it is cooled to room temperature to obtain the copper-clad laminate.

[0018] Preferably, in step A2, the peel force between the photosensitive resin layer of the initial copper-clad laminate and the copper-clad laminate substrate is less than 0.5 N / cm.

[0019] Preferably, in step A3, the peel force between the photosensitive resin layer of the copper-clad laminate and the copper-clad laminate substrate is 10N / cm-20N / cm.

[0020] Based on the same inventive principle, in order to achieve the fourth inventive objective mentioned above, the present invention also provides an application of a non-pressure-sensitive photosensitive cover film in the preparation of rigid PCBs. The non-pressure-sensitive photosensitive cover film described in the first invention is used to prepare rigid PCBs.

[0021] Compared with the prior art, the beneficial effects of the present invention are: (1) Significantly reduces bubble generation, eliminates the need for vacuum pressing equipment, and saves costs; This invention designs the photosensitive resin layer to be non-sticky or low-sticky within the temperature range A (25℃-80℃), ensuring that it does not form a sealed space with the copper-clad laminate substrate surface during initial pressing; Combined with the two-step non-vacuum pressing process in the method, gas can be effectively discharged during the pressing process; Experimental data shows that the peel force between the initial photosensitive resin layer of the copper-clad laminate and the substrate is less than 0.5N / cm, proving that only slight adhesion is achieved in the pre-pressing stage, ensuring the existence of venting channels; The peel force after final curing can reach 10N / cm-20N / cm, ensuring bonding strength. This process eliminates the need for expensive vacuum pressing equipment, significantly reducing equipment investment and production energy consumption.

[0022] (2) Improve the cleanliness of operation and increase the product yield. Since the photosensitive resin layer of the present invention has no pressure-sensitive adhesive or contains only a trace amount (0.5-3 parts by weight) of pressure-sensitive adhesive resin, the cover film is not easy to adsorb dust and impurities in the environment during handling, cutting, alignment and other operations. This effectively avoids defects in the solder resist layer caused by foreign matter contamination, thereby improving the final yield of rigid PCB.

[0023] (3) Optimized for rigid PCBs, with suitable heat resistance and rigidity, this invention uses epoxy acrylate resin with a high Tg temperature (65℃-70℃) as the main resin, and combines it with components such as trimethylolpropane triacrylate. The resulting photosensitive resin layer has a high glass transition temperature and crosslinking density after thermal curing. This characteristic is specifically designed for rigid PCBs without special folding resistance requirements. The solder mask layer can provide good hardness, heat resistance and adhesion without the need for flexibility, thus achieving a precise match between material properties and application scenarios.

[0024] (4) High process tolerance and wide operating window. In the photosensitive cover film application method provided by the present invention, good results can be obtained under non-vacuum and pressure conditions of 0.8MPa-1.5MPa, whether it is low temperature pre-pressing (20s-35s) or high temperature hot pressing (20s-35s). The wide temperature range (A range: 25-80℃, B range: 80-120℃) and pressure range give operators more room for process adjustment, reduce the difficulty of production control, and make it easy to realize industrial mass production.

[0025] (5) The composition is reasonably designed and has good storage stability. The photosensitive resin layer contains no or only a trace amount of pressure-sensitive adhesive resin. Combined with the protective layer structure, it avoids the viscosity changes caused by long-term contact with the carrier layer or air in traditional photosensitive cover films. At the same time, the combination of high Tg resin with active diluent, photoinitiator and thermosetting accelerator ensures that the photosensitive resin layer can form a stable solder resist protective layer after exposure, development and thermosetting. Attached Figure Description

[0026] Figure 1 This is a cross-sectional schematic diagram of the non-pressure-sensitive photosensitive cover film of the present invention.

[0027] Figure 2 This is a schematic diagram of the preparation method of the non-pressure-sensitive photosensitive cover film of the present invention.

[0028] Figure 3 This is a schematic diagram of the process for using the non-pressure-sensitive photosensitive cover film of the present invention.

[0029] The structure consists of: 1. Carrier layer; 2. Photosensitive resin layer; 3. Protective layer. Detailed Implementation

[0030] The present invention will now be described in detail with reference to the embodiments shown in the accompanying drawings. However, it should be noted that these embodiments are not intended to limit the present invention. Equivalent changes or substitutions in function, method, or structure made by those skilled in the art based on these embodiments are all within the scope of protection of the present invention.

[0031] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used 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.

[0032] The specific implementation process of the present invention will be described below through several embodiments. Example 1

[0033] See Figure 1 This embodiment discloses a non-pressure-sensitive photosensitive cover film, which includes, from bottom to top, a carrier layer 1, a photosensitive resin layer 2 with no or low viscosity in the temperature range A, and a protective layer 3; the photosensitive resin layer 2 has fluidity in the temperature range B; 25℃≤A≤80℃, 80℃<B≤120℃.

[0034] Specifically, the photosensitive resin layer comprises a thermosetting resin, a photopolymerizable compound, and a photoinitiator, and contains little or no pressure-sensitive adhesive resin. The photosensitive resin layer 2 comprises the following components: 80-110 parts by weight of epoxy acrylate resin with a high Tg temperature (65℃-70℃); 20-35 parts by weight of trimethylolpropane triacrylate; 3-5 parts by weight of photoinitiator; 1-3 parts by weight of thermosetting accelerator; 0.5-1 part by weight of leveling agent; and 45-65 parts by weight of solvent. Thermosetting resins, such as epoxy acrylate resins with a molecular weight exceeding 100,000, contain epoxy groups in their molecules. Under the action of a thermosetting accelerator, they can undergo a cross-linking and curing reaction upon heating, forming a three-dimensional network structure, thus functioning as thermosetting resins. Photopolymerizable compounds, such as trimethylolpropane triacrylate, contain acrylate double bonds in their molecules. Under the presence of a photoinitiator and irradiation with ultraviolet light, they can rapidly undergo a free radical polymerization reaction to achieve photocuring. In this embodiment, the high proportion of epoxy acrylate resin and its molecular weight exceeding 100,000 can adjust the viscosity of the photosensitive resin layer 2 within the temperature range A, making it low-viscosity or non-viscosity. It should also be noted that if a non-viscosity photosensitive resin layer 2 at room temperature (25°C) is desired, the weight content of the pressure-sensitive adhesive resin can be 0; if a low-viscosity photosensitive resin layer 2 at room temperature (25°C) is desired, the weight content of the pressure-sensitive adhesive resin can be 0.5-3 parts.

[0035] Table 1. Main components of non-pressure-sensitive photosensitive cover film and their peel strength with copper clad laminate. According to the ASTM D3330 test method, the initial peel force between the photosensitive resin layer and the copper-clad laminate surface of the non-pressure-sensitive photosensitive cover film prepared according to the main components in Table 1 is less than 0.5 N / cm, indicating that the photosensitive resin layer of the non-pressure-sensitive photosensitive cover film prepared in serial numbers 1 to 5 is in a low-tack or non-tack state in the temperature range A; while the initial peel force of Comparative Example 1 reached 6 N / cm, showing obvious adhesion.

[0036] Through this embodiment, the non-pressure-sensitive photosensitive cover film has the following technical effects: (1) It significantly reduces the generation of bubbles, eliminates the need for vacuum pressing equipment, and saves costs; In this embodiment, the photosensitive resin layer is designed to be non-sticky or low-sticky within the temperature range A (25℃-80℃), so that it will not form a sealed space with the surface of the copper-clad laminate substrate during the initial pressing; Combined with the two-step non-vacuum pressing process in the method, the gas can be effectively discharged during the pressing process; Experimental data show that the peel force between the photosensitive resin layer and the substrate of the initial copper-clad laminate is less than 0.5N / cm, proving that only slight adhesion is achieved in the pre-pressing stage, ensuring the existence of the exhaust channel; The peel force after final curing can reach 10N / cm-20N / cm, ensuring the bonding strength. This process does not require expensive vacuum pressing equipment, which significantly reduces equipment investment and production energy consumption.

[0037] (2) Improve the cleanliness of operation and increase the product yield. Since the photosensitive resin layer in this embodiment has no pressure-sensitive adhesive or contains only a small amount (0.5-3 parts by weight) of pressure-sensitive adhesive resin, the cover film is not easy to adsorb dust and impurities in the environment during handling, cutting, alignment and other operations. This effectively avoids defects in the solder resist layer caused by foreign matter contamination, thereby improving the final yield of rigid PCB.

[0038] (3) Optimized for rigid PCBs, with suitable heat resistance and rigidity, this embodiment uses epoxy acrylate resin with high Tg temperature (65℃-70℃) as the main resin, and combines it with components such as trimethylolpropane triacrylate. The resulting photosensitive resin layer has a high glass transition temperature and crosslinking density after thermal curing. This characteristic is specifically designed for rigid PCBs without special folding resistance requirements. The solder mask layer can provide good hardness, heat resistance and adhesion without the need for flexibility, thus achieving a precise match between material properties and application scenarios. Example 2

[0039] See Figure 2 This embodiment discloses a method for preparing a non-pressure-sensitive photosensitive cover film, including the following steps: Step S1: Under yellow light conditions, mix the following components evenly to form a composition: high Tg temperature epoxy acrylate resin, 80-110 parts by weight; trimethylolpropane triacrylate: 20-35 parts by weight; photoinitiator: 3-5 parts by weight; thermosetting accelerator: 1-3 parts by weight; leveling agent: 0.5-1 part by weight; solvent: 45-65 parts by weight; pressure-sensitive adhesive resin: 0-3 parts by weight; specifically, the thermosetting resin, for example, is an epoxy acrylate resin with a molecular weight exceeding 100,000. This resin molecule contains epoxy groups, and under the action of the thermosetting accelerator, it can undergo a cross-linking curing reaction when heated to form a three-dimensional network structure, thereby playing the role of a thermosetting resin; the photopolymerizable compound, for example, trimethylolpropane triacrylate, which contains acrylate double bonds in its molecule, can rapidly undergo a free radical polymerization reaction under ultraviolet light irradiation in the presence of a photoinitiator to achieve photocuring; in this embodiment, the high proportion of epoxy acrylate resin and its molecular weight exceeding 100,000 can adjust the viscosity of the photosensitive resin layer 2 in the temperature range A, keeping it in a low-viscosity state.

[0040] Step S2: The composition formed in step S1 is uniformly coated on a carrier film with a thickness of 15μm-30μm and dried to form a base film; Step S3: A protective layer is attached to the surface of the base film to form a photosensitive cover film.

[0041] This embodiment prepares the non-pressure-sensitive photosensitive cover film as described in Example 1. For the parts that are the same as in Example 1, please refer to Example 1, and will not be repeated here. Example 3

[0042] See Figure 3 This embodiment discloses a method for using a non-pressure-sensitive photosensitive cover film, including the following steps: Step A1: Remove the protective layer of the non-pressure-sensitive photosensitive cover film described in Example 1; Step A2: Under non-vacuum conditions, temperature range A, and pressure of 0.8MPa-1.5MPa, a flatbed press presses the exposed photosensitive resin layer onto the surface of the copper-clad laminate substrate for 20-35 seconds. Gas between the photosensitive resin layer and the copper-clad laminate substrate is expelled. After pressing, the surface is cooled to room temperature to obtain the initial copper-clad laminate. Specifically, by designing the photosensitive resin layer to be non-sticky or low-sticky within temperature range A (25℃-80℃), it is prevented from forming a sealed space with the copper-clad laminate substrate surface during initial pressing. Combined with the two-step non-vacuum pressing process described in the method, gas can be effectively expelled during pressing. Experimental data shows that the peel force between the photosensitive resin layer and the substrate of the initial copper-clad laminate is less than 0.5N / cm, proving that only slight adhesion is achieved in the pre-pressing stage, ensuring the existence of an exhaust channel. Step A3: Under non-vacuum conditions, temperature range B, and pressure of 0.8MPa-1.5MPa, the initial copper-clad laminate is hot-pressed using a flatbed laminator for 20-35 seconds. After lamination, it is cooled to room temperature to obtain the copper-clad laminate. Specifically, within temperature range B, the peel strength after final curing can reach 10N / cm-20N / cm, ensuring bonding strength. This process eliminates the need for expensive vacuum lamination equipment, significantly reducing equipment investment and production energy consumption.

[0043] The non-pressure-sensitive photosensitive cover film described in Example 1 has high process tolerance and a wide operating window. In the application method of the photosensitive cover film provided in this example, good results can be obtained under non-vacuum, pressure conditions of 0.8MPa-1.5MPa, whether it is low-temperature pre-pressing (20s-35s) or high-temperature hot pressing (20s-35s). The wide temperature range (A range: 25-80℃, B range: 80-120℃) and pressure range give operators more room for process adjustment, reduce the difficulty of production control, and facilitate industrial mass production. The photosensitive cover film was prepared according to the main components in Table 1 of Example 1. After hot pressing and cooling according to the application method of this example, microscopic observation showed that there were no bubbles between the non-pressure-sensitive photosensitive cover film (numbers 1-5) and the copper-clad laminate, while there were bubbles between the photosensitive cover film and the copper-clad laminate in Comparative Example 1.

[0044] The method of using the non-pressure-sensitive photosensitive cover film disclosed in this embodiment has the same technical solution as that in Embodiment 1. Please refer to Embodiment 1 for details, which will not be repeated here. Example 4

[0045] This embodiment discloses the application of a non-pressure-sensitive photosensitive cover film in the fabrication of rigid PCBs. The non-pressure-sensitive photosensitive cover film described in Embodiment 1 is used to fabricate rigid PCBs. Optimized for rigid PCBs, it possesses suitable heat resistance and rigidity. A high Tg temperature (65℃-70℃) epoxy acrylate resin is used as the main resin, combined with components such as trimethylolpropane triacrylate. The resulting photosensitive resin layer exhibits a high glass transition temperature and crosslinking density after thermosetting. This characteristic is specifically designed for rigid PCBs without special folding resistance requirements. The solder mask layer provides good hardness, heat resistance, and adhesion without requiring flexibility, achieving a precise match between material properties and application scenarios.

[0046] The application of the non-pressure-sensitive photosensitive cover film disclosed in this embodiment has the same technical solution as that in Embodiment 1. Please refer to Embodiment 1 for details, which will not be repeated here.

Claims

1. A non-pressure-sensitive photosensitive cover film, characterized in that, From bottom to top, it includes a carrier layer, a photosensitive resin layer that is non-sticky or low-sticky in the temperature range A, and a protective layer. The photosensitive resin layer has fluidity in the temperature range B; 25℃≤A≤80℃, 80℃<B≤120℃.

2. The non-pressure-sensitive photosensitive cover film as described in claim 1, characterized in that, The photosensitive resin layer comprises a thermosetting resin, a photopolymerizable compound, and a photoinitiator, and contains no or only trace amounts of pressure-sensitive adhesive resin.

3. The non-pressure-sensitive photosensitive cover film as described in claim 2, characterized in that, The photosensitive resin layer comprises the following components: High Tg temperature epoxy acrylate resin, 80 parts by weight - 110 parts by weight; Trimethylolpropane triacrylate: 20-35 parts by weight; Photoinitiator: 3-5 parts by weight; Thermosetting accelerator: 1 part by weight to 3 parts by weight; Leveling agent: 0.5 parts by weight to 1 part by weight; Solvent: 45 parts by weight - 65 parts by weight.

4. The non-pressure-sensitive photosensitive cover film as described in claim 3, characterized in that, The Tg temperature is 65℃-70℃.

5. The non-pressure-sensitive photosensitive cover film as described in claim 3, characterized in that, The weight content of the pressure-sensitive adhesive resin is 0-3 parts.

6. A method for preparing a non-pressure-sensitive photosensitive cover film, characterized in that, Includes the following steps: Step S1: Under yellow light conditions, mix the following components evenly to form a composition: High Tg temperature epoxy acrylate resin, 80 parts by weight - 110 parts by weight; Trimethylolpropane triacrylate: 20-35 parts by weight; Photoinitiator: 3-5 parts by weight; Thermosetting accelerator: 1 part by weight to 3 parts by weight; Leveling agent: 0.5 parts by weight to 1 part by weight; Solvent: 45-65 parts by weight; Pressure-sensitive adhesive resin: 0 parts by weight - 3 parts by weight; Step S2: The composition formed in step S1 is uniformly coated on a carrier film with a thickness of 15μm-30μm and dried to form a base film; Step S3: A protective layer is attached to the surface of the base film to form a photosensitive cover film.

7. A method of using a non-pressure-sensitive photosensitive cover film, characterized in that, Includes the following steps: Step A1: Remove the protective layer of the non-pressure-sensitive photosensitive cover film as described in any one of claims 1-5; Step A2: Under non-vacuum conditions, temperature range A, and pressure conditions of 0.8MPa-1.5MPa, the flatbed press presses the exposed photosensitive resin layer onto the surface of the copper-clad laminate substrate. The pressing time is 20s-35s. The gas between the photosensitive resin layer and the copper-clad laminate substrate is discharged. After pressing, the substrate is cooled to room temperature to obtain the initial copper-clad laminate. Step A3: Under non-vacuum conditions, temperature range B, and pressure conditions of 0.8MPa-1.5MPa, the initial copper-clad laminate is hot-pressed by a flatbed press for 20s-35s. After pressing, it is cooled to room temperature to obtain the copper-clad laminate.

8. The method of using the non-pressure-sensitive photosensitive cover film as described in claim 7, characterized in that, In step A2, the peel force between the photosensitive resin layer of the initial copper-clad laminate and the copper-clad laminate substrate is less than 0.5 N / cm.

9. The method of using the non-pressure-sensitive photosensitive cover film as described in claim 7, characterized in that, In step A3, the peel force between the photosensitive resin layer of the copper-clad laminate and the copper-clad laminate substrate is 10N / cm-20N / cm.

10. The non-pressure-sensitive photosensitive cover film according to any one of claims 1-5 is used to prepare a rigid PCB.

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