Film removing process for avoiding residues in circuit board holes

Abstract

The invention relates to a film removing process for avoiding residues in holes of a circuit board. The film removing process comprises the steps of plate preparation, vacuum film pressing, patterning, preliminary film removing, pressurized flushing and drying. According to the invention, drying is not carried out after preliminary film removal, so that the photosensitive resin in the hole is kept in a state of being infiltrated by the film stripping solution, the photosensitive resin stuck in the hole can be better removed in the step of pressurizing and washing, the cleaning is more targeted, the cost and time are saved, and the product quality is ensured.

Description

Technical Field

[0001] The present invention relates to the field of photovoltaic technology, and in particular to a film removal process for avoiding residue in a circuit board hole. Background Art

[0002] As the aperture diameter of flexible printed circuits (FPCs) continues to decrease, the height differences formed after copper plating become increasingly significant. For products with such pronounced surface differences, vacuum lamination is often required during the surface patterning process. This involves first forming photosensitive resin onto one side of a protective film, then applying a vacuum to adhere the photosensitive resin to the circuit board surface. In the absence of air, the protective film ensures that the photosensitive resin adheres to the circuit board surface regardless of the height difference. However, for boards with holes, there is a problem of residual photosensitive resin remaining in the holes after stripping. This is because the photosensitive resin can be trapped in the holes due to suction, making it more difficult to remove mechanically or chemically than from the protective film exposed on the board surface. This unremoved photosensitive resin can cause problems in subsequent processing at the holes, ultimately affecting product quality, reliability, and stability. While vacuum lamination technology has improved in terms of dry film filling, completely removing the photosensitive resin from the holes remains a challenge. This problem leads to residual dry film in the holes during FPCB production, seriously impacting the quality and reliability of subsequent processes.

[0003] Chinese patent CN106937481A discloses a process for wiring PCBs with high-molecular conductive polymers, which includes numerous cleaning steps to ensure PCB quality. However, this process significantly increases equipment costs, has limited impact on product quality, and can also lead to increased production costs.

[0004] Chinese patent CN110035619A discloses a method for producing an inner layer dry film, which discloses the use of a hot pressing wheel to apply the dry film. However, when the height difference of the copper layer on the board surface is relatively obvious, it is difficult to ensure that the entire film surface is tightly attached to the board surface.

[0005] Therefore, it is necessary to design a new film removal process to avoid the above problems. Summary of the Invention

[0006] The main purpose of the present invention is to provide a film removal process that avoids residue in the circuit board hole, which can use relatively simple process steps to complete the film removal work in a targeted manner, not only saving cost and time, but also ensuring product quality.

[0007] The present invention achieves the above-mentioned object through the following technical solution: a film removal process to avoid residue in the circuit board hole, comprising the following steps: S1. Board preparation: Prepare a circuit board with a plurality of through holes; S2. Vacuum lamination: Prepare two dry films that are larger than the circuit board. The dry films are coated with a photosensitive resin on one side using a protective film as a carrier. With the photosensitive resin facing the circuit board, the two dry films are tightly attached to the two sides of the circuit board by vacuum lamination. S3, circuit: remove the protective film, use conventional exposure, development, and etching processes to remove excess copper, leaving a copper ring area around the through hole, and the copper ring area is still covered with a cured photosensitive resin; S4, preliminary film removal: using a film stripping solution to preliminarily remove the residual photosensitive resin to obtain an exposure plate with a wet surface; S5, pressure washing: the exposure plate is pressure washed to remove the residual photosensitive resin in the through hole to obtain a debonded plate; S6, drying: drying the surface of the debonded board.

[0008] Specifically, the circuit board is a hard board or a soft board.

[0009] Furthermore, the circuit board includes a substrate and copper layers located on both sides of the substrate, the basic thickness of the substrate is not less than 20um, the basic thickness of the copper layer is not less than 12um, and the total thickness of the copper ring area is not more than 29um.

[0010] Furthermore, the inner diameter of the through hole is 3 to 10 times the thickness of the substrate.

[0011] Specifically, during the pressurized flushing, the debonded board is transported horizontally by a conveying roller, and the flushing direction is perpendicular to the board surface.

[0012] Furthermore, the water pressure during the pressurized flushing is 1.6±0.3kg / cm 2 .

[0013] Specifically, the specific operation process of the drying step is to first suck dry, then blow dry with strong wind, then dry with hot air, and finally cool.

[0014] The beneficial effects of the technical solution of the present invention are: The present invention does not perform drying after the initial film stripping, so that the photosensitive resin in the hole remains in a state of being soaked in the film stripping solution, so that the pressurized flushing step can better remove the photosensitive resin stuck in the hole, and the cleaning is more targeted, which not only saves cost and time, but also ensures product quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 Schematic diagram of the local changes of the circuit board during the film removal process.

[0016] The following are marked in the figure: 1-circuit board, 11-through hole, 12-substrate, 13-copper layer, 131-circuit copper area; 2-dry film, 21-protective film, 22-photosensitive resin. DETAILED DESCRIPTION

[0017] The present invention is further described in detail below with reference to specific embodiments.

[0018] Example: like Figure 1 As shown, the following steps are used to remove the film from the circuit board 1: S1. Board preparation: Prepare a circuit board 1 having a plurality of through holes 11 .

[0019] The circuit board 1 can be a hard board (ie, PCB) or a flexible board (ie, FPC). This is because whether the substrate of the circuit board 1 is hard or soft does not affect the process.

[0020] Circuit board 1 includes a substrate 12 and copper layers 13 on both sides of substrate 12. The base thickness of substrate 12 is no less than 20 μm, and the base thickness of copper layer 13 is no less than 12 μm. A copper ring 131 surrounds through-hole 11, and the total thickness of copper ring 131 is no more than 29 μm. The inner diameter of through-hole 11 is 3 to 10 times the thickness of substrate 12.

[0021] In this embodiment, the copper ring area 131 is at least 17 μm higher than the rest of the copper layer 13. This height difference in the copper layer 13 necessitates vacuum lamination to attach the photosensitive resin 22. Otherwise, conventional hot press lamination is more effective. If the inner diameter of the through-hole 11 is too small, the flushing effect will be poor. If the inner diameter is too large, impurities will not easily accumulate in the through-hole 11, and special treatment is unnecessary.

[0022] S2. Vacuum lamination: Prepare two dry films 2 that are larger than the circuit board 1. The dry films 2 are supported by a protective film 21 and coated with a photosensitive resin 22 on one side. With the photosensitive resin 22 facing the circuit board 1, the two dry films 2 are placed tightly against both sides of the circuit board 1 by vacuum lamination. S3. Patterning: Remove the protective film 21 and use conventional exposure, development, and etching processes to remove excess copper, leaving a copper ring area 131 around the through hole 11. The copper ring area 131 is still covered with a cured photosensitive resin 22.

[0023] The photosensitive resin 22 is partially exposed according to the circuit pattern, so that the exposed portion of the photosensitive resin 22 is solidified and the unexposed portion remains in a fluid state. The fluidized photosensitive resin 22 is removed and the exposed copper surface is etched away, leaving a copper ring area 131.

[0024] S4. Preliminary film removal: using a film stripping solution to preliminarily remove the residual photosensitive resin 22 to obtain an exposure plate with a wet surface.

[0025] S5. Pressurized washing: The exposure plate is pressurized and washed to remove the photosensitive resin 22 remaining in the through-holes 11 to obtain a debonded plate.

[0026] The present invention does not dry after the initial film stripping, so that the photosensitive resin 22 in the hole remains soaked in the film stripping solution, so that the pressurized flushing step can better remove the photosensitive resin 22 stuck in the hole, and the cleaning is more targeted, which not only saves cost and time, but also ensures product quality.

[0027] During pressure washing, the debonded board is transported horizontally by the conveyor roller, and the washing direction is perpendicular to the board surface. The water pressure during pressure washing is 1.6±0.3kg / cm 2 .

[0028] The conveying mechanism here is composed of many conveying rollers with the same height and conveying direction. The conveying rollers are basically in point contact with the bottom of the degumming board, so the lower part of the through hole 11 of the degumming board will not be blocked all the time during the conveying process. The water used for flushing is sprayed from top to bottom by a high-pressure nozzle onto the board surface, which can effectively act on the impurities inside the through hole 11, so that the impurities falling out of the through hole 11 can pass through the gaps between the conveying rollers and prevent them from sticking to the board again. When the circuit board 1 is a soft board, it is necessary to consider both the effective removal of impurities in the through hole 11 and the avoidance of quality problems such as broken holes in the soft board during pressurized flushing, so the water pressure is preferably within the above range.

[0029] S6. Drying: Dry the surface of the debonded board. The specific operation process of the drying step is to first suck it dry, then blow it dry with strong air, then dry it with hot air, and finally cool it.

[0030] The ultimate goal of drying is to ensure the board's surface is dry, clean, and free of foreign matter, making it easier to add additional circuitry to the outermost layer. Blotting involves using absorbent materials to quickly remove any solution or moisture from the board's surface. The remaining moisture evaporates rapidly under the influence of strong airflow. Finally, the hot air raises the board's temperature, evaporating the last trace of moisture. The remaining heat then needs to cool before the board can be processed into the next step.

[0031] The above are only some embodiments of the present invention. For those skilled in the art, several modifications and improvements can be made without departing from the inventive concept of the present invention, which all fall within the scope of protection of the present invention.

Claims

1. A film removal process to avoid residue in the circuit board hole, characterized in that the steps include: S1. Board preparation: Prepare a circuit board with a plurality of through holes; S2. Vacuum lamination: Prepare two dry films that are larger than the circuit board. The dry films are coated with a photosensitive resin on one side using a protective film as a carrier. With the photosensitive resin facing the circuit board, the two dry films are tightly attached to the two sides of the circuit board by vacuum lamination. S3, circuit: remove the protective film, use conventional exposure, development, and etching processes to remove excess copper, leaving a copper ring area around the through hole, and the copper ring area is still covered with a cured photosensitive resin; S4, preliminary film removal: using a film stripping solution to preliminarily remove the residual photosensitive resin to obtain an exposure plate with a wet surface; S5, pressure washing: the exposure plate is pressure washed to remove the residual photosensitive resin in the through hole to obtain a debonded plate; S6, drying: drying the surface of the debonded board.

2. The film removal process for preventing residue in circuit board holes according to claim 1, characterized in that: The circuit board is a hard board or a soft board.

3. The film removal process for preventing residue in circuit board holes according to claim 2, characterized in that: The circuit board includes a substrate and copper layers located on both sides of the substrate. The basic thickness of the substrate is not less than 20um, the basic thickness of the copper layer is not less than 12um, and the total thickness of the copper ring area is not more than 29um.

4. The film removal process for preventing residue in circuit board holes according to claim 3, characterized in that: The inner diameter of the through hole is 3 to 10 times the thickness of the substrate.

5. The film removal process for preventing residue in circuit board holes according to claim 1, characterized in that: During the pressurized flushing, the debonded board is horizontally transported by the conveying roller, and the flushing direction is perpendicular to the board surface.

6. The film removal process for preventing residue in circuit board holes according to claim 1, characterized in that: The water pressure during pressurized flushing is 1.6±0.3 kg / cm 2 .

7. The film removal process for preventing residue in circuit board holes according to claim 1, characterized in that: The specific operation process of the drying step is to first suck dry, then blow dry with strong wind, then dry with hot air, and finally cool.

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