Exposure method of anti-soldering ink and application thereof

Abstract

The application relates to an exposure method of anti-soldering ink and application, and belongs to the technical field of flexible circuit boards. The exposure method of the application converts one-time high-energy exposure into two-time exposure with a dislocation, keeps the window size unchanged, and reduces the visible joint marks on the anti-soldering ink at the joint of the digital micromirror strip due to the difference in exposure energy distribution.

Description

Technical Field

[0001] This invention relates to the field of flexible circuit board technology, and in particular to a method and application of solder resist ink exposure. Background Technology

[0002] As flexible circuit boards continue to develop towards higher density and higher precision, the requirements for alignment accuracy and appearance quality in solder resist exposure processes are becoming increasingly stringent. Traditional automatic film alignment exposure machines can no longer meet the demands. Solder resist direct imaging (DI) exposure machines have gained widespread application due to their high-precision charge-coupled device (CCD) alignment and digital micromirror (DMD) digital image projection technology.

[0003] Solder resist DI exposure machines utilize a DMD (Digital Masking Device) to project ultraviolet light onto the solder resist ink layer on the circuit board surface in a digital pattern. Due to the limited area of ​​a single exposure, multiple strip scans must be spliced ​​together to achieve full-board exposure. At the strip splicing points, differences in exposure energy distribution can easily create visible splicing marks, leading to color differences in the exposed solder resist ink and causing the solder resist window size to deviate from the design value, even exceeding the ±20μm accuracy requirement. When using photosensitive solder resist inks such as black, the color difference is even more pronounced, severely affecting product quality. To address this issue, current methods typically use the grayscale template function in the equipment program to adjust the gap width of the splicing area and the laser energy, striving to make the energy in the splicing area as uniform as possible with the non-splicing area. While this method can alleviate the severity of color differences to some extent, it cannot completely eliminate splicing marks, and the problems of solder resist ink exposure color differences and window size deviations still cannot meet the requirements of high-quality production.

[0004] Therefore, there is an urgent need to provide a new method that can effectively improve the color difference of solder resist ink exposure. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method and application for exposing solder resist ink that can reduce color difference after exposure.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: In a first aspect, the present invention provides a method for exposing solder resist ink, comprising the following steps: S1. Use a digital micromirror to emit ultraviolet A light to perform the first exposure treatment on the substrate coated with solder resist ink. S2. Keep the substrate coated with solder resist ink stationary and move the digital micromirror in a direction perpendicular to the ultraviolet scanning direction. S3. Use a digital micromirror to emit ultraviolet B light to perform a second exposure treatment on the substrate coated with solder resist ink; Wherein, the width of the digital micromirror is w mm; in step S2, the displacement is 5 mm to w mm, preferably 5 to 10 mm; the energy of ultraviolet A is a, the energy of ultraviolet B is b, the energy of the ultraviolet light required for the complete exposure and curing of the solder resist ink in one step is E, a+b=E, |ab|≤400 mJ / m 2 .

[0007] This invention transforms the solder resist ink into two low-energy exposures during the exposure process of a solder resist DI (Digital Dissolved Metal) device. First, the solder resist ink is exposed to ultraviolet light for the first time. During the second exposure, all DMDs are staggered at a distance perpendicular to the ultraviolet light scanning direction from their starting points. The solder resist patterns overlap in both exposures, and the total energy of the two exposures equals the energy required for a single exposure, thus achieving a transition from high-energy to low-energy exposure. Higher energy exposure of the solder resist ink results in more pronounced color differences in the printed color, while lower energy exposure results in less noticeable color differences. This invention converts one high-energy exposure into two low-energy exposures. Simultaneously, during the second exposure, all DMDs are staggered at a distance perpendicular to the ultraviolet light scanning direction, distributing the DMD splicing areas to different locations. These areas do not overlap with the splicing areas of the DMDs exposed in the first exposure, resulting in a smaller energy difference between the splicing and non-splicing areas in the two exposures, leading to a more uniform overall exposure effect and reduced color differences.

[0008] In a preferred embodiment of the solder resist ink exposure method of the present invention, the exposure scale number of the first exposure process and the second exposure process is the same as the exposure scale number of the solder resist ink for complete curing in one exposure. Having the same exposure scale number ensures that the energy required for complete ink curing matches the light source output of the DI exposure machine, guaranteeing the accuracy of the window size and the uniformity of the film properties.

[0009] In a preferred embodiment of the solder resist ink exposure method of the present invention, E ≥ 400 mJ / m². The higher the exposure energy required for complete curing of the solder resist ink in a single exposure, the more pronounced the color difference after exposure. The exposure method of the present invention can effectively improve the color difference of solder resist inks requiring high exposure energy.

[0010] Secondly, the present invention provides a method for manufacturing a printed circuit board, comprising the following steps: S1. The substrate is subjected to ultra-roughening treatment; S2. Apply solder resist ink to the substrate, let it stand, and pre-bake to form a substrate coated with solder resist ink. S3. Expose the substrate coated with solder resist ink using the solder resist ink exposure method as described in any one of claims 1 to 3, and then let it stand. S4. Use developer to remove unexposed solder resist ink; S5. Use UV C to perform a third exposure treatment on the solder resist ink, followed by baking and curing.

[0011] When printing circuit boards, using the exposure method of this invention can eliminate color differences during splicing and obtain circuit boards with precise window sizes.

[0012] In a preferred embodiment of the printed circuit board fabrication method of the present invention, the substrate includes copper metal, and also includes one or more of aluminum metal, epoxy glass fiber, polyimide, alumina ceramic, aluminum nitride ceramic, and silicon nitride ceramic. The above-mentioned substrates cover major printed circuit board types such as rigid boards, flexible boards, rigid-flex boards, metal substrates, and ceramic substrates, enabling the fabrication method to be compatible with different application scenarios.

[0013] In a preferred embodiment of the printed circuit board manufacturing method of the present invention, in step S2, the thickness of the coated solder resist ink is 15~25 μm. Controlling the ink thickness within a suitable range ensures that the ultraviolet light penetration depth matches the ink's photosensitivity during exposure, resulting in a uniform curing effect.

[0014] In a preferred embodiment of the printed circuit board preparation method of the present invention, in step S2, the standing time is 0.25~4 h, the pre-baking temperature is 70~80℃, and the time is 30~40 min. Under these standing and pre-baking conditions, the solvent evaporates at a suitable rate, and the degree of pre-curing is appropriate, which ensures that the film surface maintains its photosensitive activity during subsequent exposure and prevents the image from sticking to the plate and damaging the integrity of the pattern.

[0015] In a preferred embodiment of the printed circuit board fabrication method of the present invention, the resting time in step S3 is 0.25~8 h. Setting an appropriate resting time after exposure helps the exposure-induced reaction to proceed fully, stabilizes the latent image, and improves the uniformity of the developed pattern.

[0016] In a preferred embodiment of the printed circuit board manufacturing method of the present invention, in step S5, the energy of the ultraviolet C is c, where c ≥ a and c ≥ b, and c ≤ E. Ultraviolet C within this range increases the photocuring rate of the solder resist ink and enhances its adhesion. In a preferred embodiment of the printed circuit board manufacturing method of the present invention, in step S5, the post-baking temperature is 150~160℃ and the time is 50~60 min. Under these conditions, the post-baking can make the ink crosslinking reaction more complete, fully release internal stress, obtain excellent hardness, adhesion and chemical resistance, and at the same time avoid the influence of thermal stress on the dimensional stability of the substrate.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention, through the method of misaligned secondary exposure, can make the splicing print lighter or eliminated while ensuring the alignment accuracy and integrity of the solder resist pattern, improve the exposure color difference and window size over-specification of the solder resist ink, improve the exposure quality of the solder resist ink, and reduce scrap costs. Attached Figure Description

[0018] Figure 1 This is a flowchart of the exposure method of the present invention, wherein the left side is the first exposure process and the right side is the second exposure process after misalignment; Figure 2 The diagram shows a method for fabricating a printed circuit board. A is a schematic diagram of a printed circuit board after ultra-roughening, B is a schematic diagram of a printed circuit board after coating with solder resist ink, and C is a schematic diagram of a printed circuit board after development.

[0019] In the diagram, the markings are: 3-substrate; 4-solder resist ink layer; 11-first cover film substrate; 12-first cover film adhesive; 13-first copper layer; 21-second cover film substrate; 22-second cover film adhesive; 23-second copper layer. Detailed Implementation

[0020] To better illustrate the purpose, technical solution, and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0021] The solder mask DI exposure machine used in the following embodiments is a CFMEE NEX2T-08L40-25, whose digital micromirror scanning strip width is 20 mm.

[0022] Unless otherwise specified, all other materials and reagents used in the examples are commercially available.

[0023] Examples 1-12 and Comparative Examples 1-18 The exposure methods for the solder resist inks in Examples 1-12 and Comparative Examples 1-18 are as follows: S1. The energy emitted using a digital micromirror is a mJ / m 2 The substrate coated with solder resist ink is subjected to a first exposure treatment using ultraviolet A. S2. Keep the substrate coated with solder resist ink stationary, and move the digital micromirror x mm in a direction perpendicular to the ultraviolet scanning direction. S3, to make the solder mask DI exposure machine emit energy of b mJ / m 2 The substrate coated with solder resist ink is subjected to a second exposure treatment using ultraviolet B. S4. The color difference between the splicing surfaces of the solder resist ink was observed under a 40x microscope, and the color difference ΔE value was measured using an internal spectrophotometer CM-700d.

[0024] The exposure method process for S1~S3 is as follows: Figure 1 As shown.

[0025] The UV energy required for complete curing of the solder resist inks used in Examples 1-12 and Comparative Examples 1-18 in a single exposure was 1400 mJ / m². 2 The exposure scale number is 8; the scale number of the first and second exposures is 8, and the energy a, b, |ab|, displacement x, and splicing color difference are shown in Table 1.

[0026] Table 1 As can be seen from Table 1, the energy difference and displacement between the first and second exposure processes under the exposure method of the present invention can reduce the splicing color difference after the solder resist ink is exposed.

[0027] By comparing Examples 1, 4, 7, 10 and Comparative Examples 5 and 18, it was found that the amount of misalignment displacement affects the color difference after exposure and can reduce the color difference during splicing within the scope of this invention.

[0028] By comparing Examples 2, 5, 8, 11 and Comparative Examples 4 and 17, it was found that the amount of misalignment displacement affects the color difference after exposure and can reduce the color difference during splicing within the scope of this invention.

[0029] By comparing Examples 3, 6, 9, 12 and Comparative Examples 3 and 16, it was found that the amount of misalignment displacement affects the color difference after exposure and can reduce the color difference during splicing.

[0030] By comparing Examples 1-3 and Comparative Examples 6-7, it was found that the difference between the two exposures affects the color difference after splicing. The greater the difference between the two exposures, the greater the color difference after splicing.

[0031] By comparing Examples 4-6 and Comparative Examples 8-9, it was found that the difference between the two exposures affects the color difference after splicing. The greater the difference between the two exposures, the greater the color difference after splicing.

[0032] By comparing Examples 7-9 and Comparative Examples 10-11, it was found that the difference between the two exposures affects the color difference after splicing. The greater the difference between the two exposures, the greater the color difference after splicing.

[0033] By comparing Examples 10-12 and Comparative Examples 12-13, it was found that the difference between the two exposures affects the color difference after splicing. The greater the difference between the two exposures, the greater the color difference after splicing.

[0034] As can be seen from Examples 1-3, Comparative Examples 1-7, and Comparative Examples 14-18, when the displacement is too large, the DMD mirror will be outside the scanning range and cannot be exposed; when the displacement is too small, it is insufficient to eliminate the splicing color difference.

[0035] Example of effect This example examines the influence of the energy difference and displacement between different first and second exposure processes under the exposure method of the present invention on the window size of the printed circuit board. The fabrication method of the printed circuit board in this example is as follows: S1. A copper circuit board is used as the substrate. The substrate is composed of a first cover film substrate 11, a first cover film adhesive 12, a first copper layer 13, a base layer 3, a second cover film substrate 21, a second cover film adhesive 22, and a second copper layer 23. Degreasing is performed using a 10.5% (w / w) BTH-2111 solution at 40°C, followed by micro-etching using a BTH-2085 solution with a copper ion concentration of 16 g / L at 30°C. Antioxidant treatment is then performed using a 4% (v / v) HCl solution at 30°C, and finally, drying is carried out at 85°C. The resulting printed circuit board is shown below. Figure 2 As shown in A; S2. Apply a 20 μm thick layer of solder resist ink to the copper circuit board using screen printing. After standing for 15 minutes, pre-bake at 73℃ for 35 minutes to form solder resist ink layer 4. The resulting printed circuit board is shown below. Figure 2 As shown in B; S3. Expose the solder resist inks using the exposure method described in Examples 1-12 and Comparative Examples 1-13, and let them stand for 15 minutes. S4. Rinse and develop using a 1.1% K2CO3 solution at 30°C, then dry at 80°C. The resulting printed circuit board is as follows: Figure 2 As shown in C; S5. After development, use a flexible circuit board UV curing machine (model: ASIA NEO TECH NUVTI-384ETSX-HU) to light-cur the solder resist ink. The UV energy is 1200 mJ / m². 2 Then bake at 155℃ for 60 minutes.

[0036] S6. Use a 3D measuring instrument to measure the window opening size. The original design window opening size is 195 μm in length and 185 μm in width. The window opening size requirements are: window length 195±20μm and window width 185±20μm.

[0037] The window dimensions of Examples 1-12 and Comparative Examples 1-15 are shown in Table 2.

[0038] Table 2 As can be seen from Tables 1 and 2, the technical solution of the present invention can reduce the splicing color difference of the solder resist ink after exposure while keeping the window size unchanged. The displacement and color difference before and after the exposure outside the scope of the present invention will not only cause color difference at the splicing of the solder resist ink, but also make the window size smaller.

[0039] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for exposing solder resist ink, characterized in that, Includes the following steps: S1. Use a digital micromirror to emit ultraviolet A light to perform the first exposure treatment on the substrate coated with solder resist ink. S2. Keep the substrate coated with solder resist ink stationary and move the digital micromirror in a direction perpendicular to the ultraviolet scanning direction. S3. Use a digital micromirror to emit ultraviolet B light to perform a second exposure treatment on the substrate coated with solder resist ink; Wherein, the scanning strip width of the digital micromirror is w mm; in step S2, the displacement is 5 mm to w mm; the energy of ultraviolet A is a, the energy of ultraviolet B is b, the energy of ultraviolet light required for complete exposure and curing of the solder resist ink in one step is E, a+b=E, |ab|≤400 mJ / m 2 .

2. The solder resist ink exposure method as described in claim 1, characterized in that, The exposure scale number of the first exposure treatment and the second exposure treatment is the same as the exposure scale number of the solder resist ink when it is fully exposed and cured in one exposure.

3. The solder resist ink exposure method as described in claim 1, characterized in that, E≥400 mJ / m 2 。 4. A method for manufacturing a printed circuit board, characterized in that, Includes the following steps: S1. The substrate is subjected to ultra-roughening treatment; S2. Apply solder resist ink to the substrate, let it stand, and pre-bake to form a substrate coated with solder resist ink. S3. Expose the substrate coated with solder resist ink using the solder resist ink exposure method as described in any one of claims 1 to 3, and then let it stand. S4. Use developer to remove unexposed solder resist ink; S5. Use UV C to perform a third exposure treatment on the solder resist ink, followed by baking and curing.

5. The method for manufacturing a printed circuit board as described in claim 4, characterized in that, The substrate includes copper metal, and also includes one or more of aluminum metal, epoxy glass fiber, polyimide, alumina ceramic, aluminum nitride ceramic, and silicon nitride ceramic.

6. The method for preparing a printed circuit board as described in claim 4, characterized in that, In step S2, the thickness of the coated solder resist ink is 15~25μm.

7. The method for preparing a printed circuit board as described in claim 4, characterized in that, In step S2, the resting time is 0.25~4 h, the pre-baking temperature is 70~80℃, and the time is 30~40 min.

8. The method for manufacturing a printed circuit board as described in claim 4, characterized in that, In step S3, the settling time is 0.25~8 h.

9. The method for manufacturing a printed circuit board as described in claim 4, characterized in that, In step S5, the energy of the ultraviolet C is c, where c ≥ a and c ≥ b, and c ≤ E.

10. The method for manufacturing a printed circuit board as described in claim 4, characterized in that, In step S5, the post-baking temperature is 150~160℃ and the time is 50~60 min.

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