CN114340186A

CN114340186A - FPC and preparation method thereof

Info

Publication number: CN114340186A
Application number: CN202210012127.XA
Authority: CN
Inventors: 潘丽; 魏旭光; 李泰巍; 吴育炽
Original assignee: Akm Electronics Technology Suzhou Co ltd
Current assignee: Akm Electronics Technology Suzhou Co ltd
Priority date: 2022-01-06
Filing date: 2022-01-06
Publication date: 2022-04-12

Abstract

The invention relates to an FPC and a preparation method thereof, relating to the technical field of circuit boards. The preparation method comprises the following steps: film pressing, namely performing film pressing treatment on the dry film and the FPC board of the circuit to be manufactured, wherein the film pressing surface of the FPC board is a copper layer surface, and thus obtaining a dry film board; ablation, namely ablating the dry film plate by adopting laser to expose the copper surface to obtain an ablated plate; etching and stripping the film, etching the ablation plate, and washing the dry film to obtain the final product. According to the preparation method, the dry film is attached to the copper layer, then the dry film is ablated by laser, and the traditional pattern transfer processes such as exposure, development and the like are replaced, so that the processing time of the product can be shortened, special requirements on the dry film and laser equipment are avoided, and the fine circuit can be manufactured at extremely low production cost.

Description

FPC and preparation method thereof

Technical Field

The invention relates to the technical field of circuit boards, in particular to an FPC (flexible printed circuit) and a preparation method thereof.

Background

The existing FPC and PCB circuit manufacturing method comprises two major types, one type is a traditional addition and subtraction method, the method comprises the steps of firstly attaching a layer of photosensitive dry film with a specified thickness on a copper surface, then using an ultraviolet exposure machine and matching with a specified graphic film to irradiate the dry film, so that the dry film is subjected to photopolymerization reaction to form an anti-corrosion layer; and finally, developing, etching and stripping the exposed board to obtain a circuit pattern. The CCD exposure machine, the laser exposure machine and the pattern electroplating process which are commonly used at present are all manufactured based on the method, and are the mainstream circuit manufacturing process method in the circuit board industry (including PCB and FPC).

The other type is laser etching, which uses a laser to directly etch away the unwanted copper surface of the board, leaving the desired lines, in conjunction with the corresponding line laser data. The method saves the whole process flow of film pasting, exposure, development, etching and film stripping, and can greatly shorten the processing time of products.

However, as the density of the circuit increases, the line width spacing is also being changed to be finer, the mainstream line width in the PCB industry has been made 50 × 50 μm, and the mainstream line width in the FPC industry has been made 40 × 40 μm. The dry film exposure and development steps in the conventional addition and subtraction method have the following technical problems: 1. the thin dry film (with the thickness of 20-30 μm) has good exposure resolution and is more suitable for processing fine circuits, but when the thickness of the surface copper exceeds 40 μm or the step height difference of the board surface exceeds 20 μm, the dry film is thin and cannot completely fill the steps, so that the notches are opened after etching; 2. the thick dry film (thickness 35-50 μm) can fill the steps on the board surface, but because the dry film is thick, the exposure resolution is not good, and residual copper and short circuit occur after etching. Particularly in the FPC industry, a hole ring copper plating step can appear in the current common electroplating hole process, so that the circuit manufacturing yield is influenced.

The other laser etching method is limited by the type of the produced product, only can process the product with a thicker interlayer dielectric layer, is influenced by the processing mode, and is easy to cause the phenomena of damage and breakdown of the dielectric layer after the copper surface is etched away, so that the laser etching method is suitable for the PCB product with a thicker partial dielectric layer, and the FPC product with the average dielectric thickness within 50 mu m is not suitable for the laser etching process.

Disclosure of Invention

Aiming at the problems, the invention provides a preparation method of FPC, which adopts a dry film to attach a copper layer, then uses laser to ablate the dry film to replace the traditional pattern transfer processes such as exposure, development and the like, can shorten the processing time of the product, has no special requirements on the dry film and laser equipment, and can manufacture fine circuits with extremely low production cost.

In order to achieve the above object, the present invention provides a method for producing an FPC, comprising the steps of:

film pressing: carrying out film pressing treatment on the dry film and an FPC board of a circuit to be manufactured, wherein the film pressing surface of the FPC board is a copper layer surface, and obtaining a dry film board;

ablation: the dry film plate is ablated by laser, and a copper surface is exposed to obtain an ablated plate;

etching and film stripping: and etching the ablation plate, and washing a dry film to obtain the material.

The inventor finds that the traditional addition and subtraction method is to manufacture a circuit by film sticking → exposure → development → etching → film removal, as shown in fig. 1, while the fine circuit has extremely high requirements on the thickness of the dry film, and the circuit with the line width spacing of 40 μm/40 μm to 75 μm/75 μm can be manufactured only by using a special dry film with the thickness of 15-25 μm, and the special dry film has extremely high cost and low filling capability, and needs to be matched with exposure equipment with extremely high precision, and no matter the production cost and the technical capability have limitations. On the other hand, since the laser etching method directly ablates the copper layer by using the fine capability of the laser spot, it takes a long time if the laser energy is low, while the energy is high, the substrate is easily scratched or broken by the laser, as shown in fig. 2, and there is a risk of short-circuiting of carbon black generated by laser ablation. Therefore, the inventor protects the copper layer through the thick dry film, correspondingly captures the ablation parameters of the laser according to the thicknesses of different dry films, enables the laser to ablate the dry film without damaging the copper layer, and then completes the circuit manufacturing of the FPC by etching and film stripping.

By adopting the preparation method, the copper surface can be filled and protected through the dry film, then the dry film is ablated by laser, a required pattern is processed, the circuit is etched on the basis of ensuring that the copper layer is not damaged, and then the film is removed to show a fine circuit.

In one embodiment, the preparation method further comprises an idle exposure step between the film pressing step and the ablation step, wherein the idle exposure step is to expose the dry film plate to enable the dry film to generate photopolymerization.

Through the above-mentioned idle exposure step, can make the dry film through photopolymerization and harden, increase the hardness of dry film, be convenient for going on of follow-up ablation step more, increase laser ablation's stability.

In one embodiment, the thickness of the dry film is 20-50 μm.

In one embodiment, the laser is a UV ultraviolet laser.

The above preparation method is not limited to the type of laser because the copper layer is not directly ablated, and CO can be used₂Infrared laser or UV ultraviolet laser, and the conventional laser etching is limited by the reason that the absorption rate of copper metal to infrared wavelength is low, so that only UV ultraviolet laser can be used.

In one embodiment, in the ablation step, the thickness of the dry film is less than 35 μm and less than 20 μm, the laser energy is 10W, and the ablation is carried out for 1-2 times.

In one embodiment, in the ablation step, the thickness of the dry film is less than or equal to 35 μm and less than or equal to 50 μm, the laser energy is 15W, and the ablation is carried out for 2-3 times.

By adopting the laser and the ablation frequency within the energy range, the dry film covered on the part, which does not need to keep the copper layer, on the FPC is ablated according to the preset design after the laser ablation, and the copper layer is not damaged.

In one embodiment, the laser is a UV laser, the dry film thickness is 20 μm, the laser energy is 10W, and the number of ablations is 1.

In one embodiment, the laser is a UV laser, the dry film thickness is 25 μm, the laser energy is 10W, and the number of ablations is 1.

In one embodiment, the laser is a UV laser, the dry film thickness is 40 μm, the laser energy is 15W, and the number of ablations is 2.

In one embodiment, the laser is a UV laser, the dry film thickness is 50 μm, the laser energy is 15W, and the number of ablations is 2.

In one embodiment, the reaction conditions of the lamination step are as follows: the film pressing temperature is 100 plus or minus 5 ℃, the pressure is 0.55 plus or minus 0.05MPa, and the speed is 1.4 plus or minus 0.2 m/min.

By adopting the preparation method of the invention, the extremely high requirement on the thickness of the dry film as the traditional addition and subtraction method is not required, and a special dry film is not required.

In one embodiment, the reaction conditions of the etching step are: three-stage etching is carried out by adopting an acid etching line, the etching speed is 2.8m/min, and the etching temperature is 50 +/-5 ℃.

In one embodiment, the reaction conditions of the film removing step are as follows: the dry film is washed by a film stripping solution with the concentration of 12 +/-4 percent.

The invention also provides the FPC prepared by the preparation method, and the line width/space of the FPC is 40 mu m/40 mu m to 75 mu m/75 mu m.

In one embodiment, the FPC board to be wired is a double-sided board or a multilayer board.

In one embodiment, the FPC board to be wired is made of 5G high-frequency materials.

Compared with the prior art, the invention has the following beneficial effects:

the invention provides a preparation method of FPC, which adopts a thick dry film to attach a copper layer of an FPC board of a circuit to be manufactured, then adopts low-energy laser to ablate the dry film to expose a copper surface which does not need to be reserved without damaging the copper layer, and then carries out etching and film removing treatment to obtain the FPC board with a fine circuit with the line width/space of 40 mu m/40 mu m to 75 mu m/75 mu m. The preparation method adopts laser ablation to replace the traditional pattern transfer processes such as exposure, development and the like, not only can shorten the processing time of products, but also has no special requirements on dry films and laser equipment, and can manufacture fine circuits with extremely low production cost. In the preparation process, a special dry film is not needed, a thick dry film with low cost can be used, special requirements on laser equipment are avoided, a copper layer is not needed to be ablated by using overhigh energy, the cost for manufacturing a fine circuit on the FPC board is reduced, the circuit manufacturing difficulty caused by electroplating hole steps can be perfectly solved, the requirements of the circuit manufacturing on the height difference of the electroplating hole steps are reduced, and the applicability of the FPC product for etching the circuit by using laser is improved.

Drawings

FIG. 1 is a process flow diagram of a conventional addition and subtraction method in the summary of the invention;

FIG. 2 is a schematic illustration of a laser etching process in accordance with the present invention;

FIG. 3 is a process flow chart for preparing FPC in example 1;

FIG. 4 is a schematic view of a film laminating step in example 1;

FIG. 5 is a schematic view of an air-exposure step in example 1;

FIG. 6 is a schematic view of an ablation step in example 1;

FIG. 7 is a schematic view showing the etching and film-removing steps in example 1;

FIG. 8 is a schematic diagram of FPC with copper surface damage exceeding 1/2 in comparative example 1;

fig. 9 is a schematic view of FPC in comparative example 2 where the dry film is not completely ablated clean.

Wherein, 1 is a copper layer, 2 is a high-frequency material, 3 is a thin dry film (the thickness is 15-25 μm), 4 is an FPC after an LDI exposure and development step, 5 is an FPC after an etching step, 6 is an FPC after a film stripping step, 7 is an FPC after high-energy laser ablation, 8 is a thick dry film (the thickness is 50 μm), 9 is an FPC after an idle exposure step, 10 is an FPC after an ablation step, and 11 is a thick dry film (the thickness is 40 μm).

Detailed Description

To facilitate an understanding of the invention, the invention will now be described more fully with reference to the accompanying drawings. Preferred embodiments of the present invention are shown in the drawings. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

Defining:

the dry film of the invention: the material is a high molecular material which can generate a polymerization reaction after being irradiated by ultraviolet rays to form a stable substance to be attached to the board surface, thereby achieving the functions of blocking electroplating and etching.

Double-sided board: refers to a printed circuit board with copper coated on both sides, including a top layer and a bottom layer.

Multilayer board: the circuit board with a plurality of conductive layers is obtained by laminating a double-sided board and an adhesive.

5G high-frequency material: the material is suitable for fifth generation mobile communication technology and frequency bands above 10 GHz.

The source is as follows:

reagents, materials and equipment used in the present example are all commercially available sources unless otherwise specified; unless otherwise specified, all the experimental methods are routine in the art.

Example 1

An FPC is prepared by the following method, and the process flow of the preparation method is shown in figure 3.

1. Film pressing: carrying out film pressing treatment on an FPC board to be manufactured with a fine circuit by using a low-cost dry film to obtain a dry film board, wherein the FPC board is made of a 5G high-frequency material, and the thickness of the dry film is 20-50 μm as shown in figure 4; the dry film thickness used in this example was 50 μm, and the parameter indices of the lamination step were: the film pressing temperature is 100 plus or minus 5 ℃, the pressure is 0.55 plus or minus 0.05MPa, and the speed is 1.4 plus or minus 0.2 m/min.

2. And (3) empty exposure: exposing the dry film plate to make the dry film generate photopolymerization reaction, as shown in figure 5; the exposure energy satisfies the 5-7 lattices of the exposure ruler.

3. Ablation: the dry film board after the air exposure is ablated by laser according to a preset design, a copper surface which does not need to be reserved is exposed, and an ablated board is obtained, as shown in fig. 6, the preset design can be adjusted according to the circuit design to be manufactured, and the damage to a copper layer is guaranteed to be less than or equal to 1/2 copper layer thickness by adopting UV laser and controlling the laser energy in the ablation process; adopt UV ultraviolet laser in this embodiment, through carrying out a lot of ablations to first piece, then confirm the copper face condition of ablating after the sample of longitudinal section, and then snatch and obtain best ablation parameter, promptly: a large group HRT500A picosecond laser cutter was used to ablate 2 times with a laser power of 15W.

4. Etching: etching the ablation plate to obtain an etching plate, wherein the etching step adopts an acid etching line (DES) and carries out parameter adjustment according to the line width, the interval and the copper thickness of the preset design; in this embodiment, the parameter indexes of the etching step are: the etching speed is 2.8m/min, the etching temperature is 50 +/-5 ℃, and three-stage etching is counted.

5. Removing the film: removing the film of the etching board to obtain the FPC board, wherein the film removing comprises the following specific steps: and (3) washing the exposed dry film by adopting a special film stripping solution with the concentration of 12 +/-4%.

The steps of etching and film stripping are shown in fig. 7. The line width/space of the FPC board is 40 mu m/40 mu m to 75 mu m/75 mu m.

Comparative example 1

An FPC was ablated 3 times using a large HRT500A picosecond laser cutter with a laser power of 15W, and the other preparation steps were the same as in example 1.

As shown in fig. 8, the damage of the copper surface of the prepared FPC exceeds 1/2, and the FPC has a risk of breakdown.

Comparative example 2

An FPC was prepared by using a dry film having a thickness of 40 μm, subjecting the film to the same lamination and space exposure steps as in example 1, and then ablating the film 2 times with a laser cutter of a Dai HRT500A picosecond laser with a laser power of 10W, in which the other steps were the same as in example 1.

As shown in fig. 9, the dry film of the prepared FPC is not completely ablated, and copper cannot be removed during etching, so that a circuit cannot be formed.

The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.

The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.

Claims

1. A preparation method of FPC is characterized by comprising the following steps:

2. The method according to claim 1, further comprising an idle exposure step between the lamination step and the ablation step, wherein the idle exposure step is exposing the dry film plate to photopolymerize the dry film.

3. The method according to claim 1, wherein the thickness of the dry film is 20 to 50 μm.

4. The method of claim 1, wherein the laser is a UV ultraviolet laser.

5. The method according to claim 4, wherein in the ablation step, the thickness of the dry film is 20 μm or less and less than 35 μm, the laser energy is 10W, and the ablation is performed 1 to 2 times.

6. The method according to claim 4, wherein in the ablation step, the thickness of the dry film is 35 μm or less and 50 μm or less, the laser energy is 15W, and the ablation is performed 2 to 3 times.

7. The manufacturing method according to claim 1, wherein the film pressing step is performed under the following reaction conditions: the film pressing temperature is 100 plus or minus 5 ℃, the pressure is 0.55 plus or minus 0.05MPa, and the speed is 1.4 plus or minus 0.2 m/min.

8. The FPC produced by the production method as claimed in any one of claims 1 to 7, wherein the FPC has a line width/space of 40 μm/40 μm to 75 μm/75 μm.

9. The FPC according to claim 8, wherein the FPC board to be wired is a double-sided board or a multilayer board.

10. The FPC of claim 8, wherein the FPC board to be wired is made of a 5G high frequency material.