Manufacturing method for circuit board

Abstract

Disclosed in the present invention is a manufacturing method for a circuit board, comprising the following treatment steps: cutting; inner-layer patterning; lamination; outer-layer wet film coating: roughening a copper surface of a production board with a chemical solution, coating the surface of the production board with photosensitive ink, and sequentially carrying out pre-baking, film alignment and exposure to obtain a production board with the surface covered with protective ink; drilling; copper deposition: depositing thin copper on the surface and in holes of the production board by means of chemical deposition; board plating; developing and etching; solder mask and text formation; and surface treatment and molding. The use of the method of the present invention to manufacture a circuit board has the advantages of lowering the cost, reducing circuit scratches, omitting the outer-layer AOI process and reducing the number of solder mask times for thick copper plates.

Description

Method for manufacturing a circuit board Technical Field

[0001] The present invention relates to the technical field of printed circuit board manufacturing, and in particular to a method for manufacturing a circuit board. Background Art

[0002] At present, the production process of circuit boards is: cutting - inner layer graphics - lamination - drilling - copper plating, full board electroplating - outer layer graphics - outer layer AOI - solder mask, text - surface treatment - molding - electrical testing - FQC.

[0003] Wet film coating is more cost-effective than dry film coating for producing circuit patterns. However, traditional wet film coating is primarily used for inner-layer circuits. During the production of outer-layer circuits, due to the presence of various through-holes, wet film coating can easily lead to ink seeping into the holes, causing blockage or ink buildup within the holes, impacting customer weldments and causing serious quality issues. Therefore, dry film coating is often used for outer-layer circuits.

[0004] Chinese patent CN103826391B discloses a method for applying a wet film coating to the outer layers of a circuit board. This method, by simply adding a tin stripping step, can separate any remaining oil in the hole from the hole walls, eliminating the formation of an ink resist during subsequent copper electroplating. This method also ensures that the defect rate for wet film coating lines in the through-hole plating process is similar to that of dry film coating. However, this method is effective for small amounts of residual ink, but cannot completely remove large amounts.

[0005] Summary of the Invention

[0006] The purpose of the present invention is to overcome the above technical deficiencies and propose a method for manufacturing a circuit board to solve the technical problem in the prior art of wet film manufacturing of outer layer circuits resulting in a high outer layer AOI defect rate.

[0007] The present invention provides a method for manufacturing a circuit board, which includes the following processing steps in sequence:

[0008] Cutting: Cut out the core board, PP sheet and outer copper foil according to the size requirements of the product drawing;

[0009] Inner layer pattern: produce inner layer circuit pattern on the core board;

[0010] Lamination: The core board, PP sheet and outer copper foil are stacked and fixed, and then pressed into production board;

[0011] Outer wet film: After the copper surface of the production board is roughened with chemical solutions, photosensitive ink is coated on the surface of the production board, and then pre-baking, film alignment and exposure are carried out in sequence to obtain a production board covered with protective ink;

[0012] Drilling: Drill holes at corresponding positions on the production board according to the design data;

[0013] Copper deposition: depositing thin copper on the surface of the production board and in the holes by chemical deposition;

[0014] Plate electroplating: electroplating the production board after copper deposition;

[0015] Development and etching: The production board after electroplating is developed and etched in sequence to remove the ink from the non-photosensitive part of the production board surface and etch away the excess copper outside the board circuit to obtain a circuit pattern covered with protective ink on the surface;

[0016] Solder mask and text: solder mask and text are formed on the surface of the production board after development and etching;

[0017] Surface treatment and molding: The production board is subjected to surface treatment and molding to obtain a circuit board.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] The present invention adopts wet film to make the outer layer circuit, and applies ink before drilling, so there is no quality problem of wet film ink entering the hole. At the same time, the outer layer circuit is covered with a layer of protective ink in advance, which can effectively protect the outer layer circuit before drilling, copper deposition, board electricity and printing solder mask to avoid scratches on the circuit, so there is no need for outer layer AOI, which simplifies the production process. After the wet film ink is developed and etched, the film does not fade, so that the circuit is covered with ink, and then the solder mask process is carried out. For thick copper plates, the number of solder masks and the amount of solder mask ink used can be reduced, and production costs can be reduced. At the same time, because the circuit is covered with a layer of protective ink in advance, there will be no quality abnormalities such as thin circuit oil and copper leakage. In addition, the cost of making circuits with wet film is lower than that of dry film, which is also conducive to reducing production costs. It can be seen that the method of the present invention has the advantages of lower cost, less circuit scratches, and the ability to save the outer layer AOI process and reduce the number of solder masks on thick copper plates. DETAILED DESCRIPTION

[0020] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0021] The present invention provides a method for manufacturing a circuit board, which includes the following processing steps in sequence:

[0022] S1. Cutting: Cut the core board, PP sheet, and outer copper foil according to the product drawing dimensions. The core board is a copper-clad laminate. The thickness of the core board and PP sheet can be selected based on design requirements and is not limited by this invention. The outer copper foil thickness should be ≥ 2 oz, preferably ≥ 3 oz. It should be noted that thicker outer copper foil is preferred to facilitate forming outer circuit patterns that meet the required thickness.

[0023] S2. Inner layer graphics: produce inner layer circuit graphics on the core board. The inner layer circuit graphics can be produced by wet film or dry film process, which is the existing technology and will not be described in detail in the present invention. In order to reduce production costs, the present invention adopts a wet film process. In some specific embodiments of the present invention, the step of producing the inner layer circuit graphics on the core board includes: roughening the surface copper surface of the core board with chemical solutions, coating the surface of the core board with photosensitive ink (i.e., wet film), and then performing pre-baking, film alignment, exposure, development, etching, and film stripping in sequence to form the inner layer circuit graphics. Among them, the photosensitive ink is preferably transparent. In some more specific embodiments of the present invention, the photosensitive ink is Rongda liquid photosensitive circuit ink A-9060C.

[0024] S3, lamination: Use rivets or hot melt to stack and fix the inner core board, PP sheet and outer copper foil, and then press them into production board. This step is prior art and will not be described in detail in this invention.

[0025] S4, outer wet film: After the copper surface of the production board is roughened with chemical solutions, a photosensitive ink (i.e., wet film) is coated on the surface of the production board, and then pre-baking, film alignment, and exposure are carried out in sequence to obtain a production board with a surface covered with protective ink. It should be noted that development, etching, and film stripping processes are not performed in this process. In the scheme of the present invention, a layer of protective ink is covered on the outer layer of the circuit in advance, which can effectively protect the outer layer of the circuit before drilling, copper deposition, board electricity, and silk screen solder mask ink to avoid scratches on the circuit, so there is no need for an outer layer AOI, which simplifies the production process. Among them, the photosensitive ink is preferably transparent. In some specific embodiments of the present invention, the photosensitive ink is Rongda liquid photosensitive circuit ink A-9060C.

[0026] S5, drilling: drilling holes at corresponding positions of the production board according to the design data. This step is a prior art and will not be described in detail in the present invention.

[0027] S6, copper deposition: deposit thin copper on the surface of the production board and in the holes by chemical deposition, in preparation for subsequent copper electroplating. It should be noted that although the outer wet film covers the board surface, a thin layer of copper will also be deposited on the board surface after copper deposition. It is necessary to further adopt a grinding process to grind off the thin copper deposited on the ink surface and retain the thin copper in the holes to avoid the formation of a thick copper layer on the board surface after the plate electroplating step, which affects the smooth progress of the subsequent development and etching process. In the copper deposition step, the thickness of the chemical thin copper formed is 0.3-0.8um; in the grinding process of the present invention, a nylon needle roller brush is used, and the grinding current is 0.2-1A. Here, it is only necessary to slightly grind the board surface to remove the thin copper on the ink surface. It should be noted that in the prior art, before copper deposition, it is often necessary to roughen the surface copper surface of the production board through a grinding process. At this time, the grinding current used is 2.6-3.2A, which is significantly higher than the grinding current of 0.2-1A of the present application; while using the manufacturing method of the present application, there is no need to adopt a grinding process before copper deposition.

[0028] S7, board electroplating: The copper-plated production board is electroplated to add another layer of hole wall copper. It should be noted that in this step, since the outer wet film covers the board surface, only a layer of metal copper is electroplated on the inner wall of the hole.

[0029] S8, development, etching (non-fading film): the production board after the plate is developed and etched in sequence to remove the ink on the non-photosensitive part of the production board surface to form a circuit pattern, and the excess copper outside the board circuit is etched away to obtain the circuit pattern, and the circuit pattern is covered with exposed ink.

[0030] S9, solder mask, text: forming a solder mask layer and text on the surface of the production board after development and etching. In some specific embodiments of the present invention, the step of forming a solder mask layer and text on the surface of the production board after development and etching includes: performing solder mask pre-treatment, screen printing of solder mask ink, pre-baking, exposure, and development on the surface of the production board after development and etching, and printing characters on the corresponding positions of the board surface according to customer needs after the solder mask ink is developed, and then post-baking to form the solder mask layer and text. Among them, the solder mask pre-treatment includes at least one of grinding or sandblasting, preferably sandblasting, to reduce damage to the ink on the circuit pattern. It should be noted that when the thickness of the outer copper foil is ≥2oz, due to the large height difference between the outer circuit pattern and the substrate, it is easy to cause thin circuit oil and copper leakage. Therefore, the existing process often requires multiple solder masking (taking two solder masking (outer copper foil thickness is 2-3.5oz) as an example: solder mask pre-treatment - screen printing of the first ink - pre-baking - exposure - development - post-baking - screen printing of the second ink - pre-baking - exposure - development - post-baking). However, in the solution of the present invention, the outer layer of wet film ink does not fade after development and etching, and the circuit is covered with ink, which is equivalent to covering the circuit with a layer of protective ink in advance. The ink can be screen-printed once less, the number of solder mask times and the amount of solder mask ink used can be reduced, and the production cost can be reduced. At the same time, there will be no quality abnormalities such as thin circuit oil and copper leakage.

[0031] S10, surface treatment and molding: select the corresponding surface treatment process according to customer needs to perform surface treatment, and cut the PNL board (gong board) into the external dimensions required by the customer. This step is prior art and will not be described in detail in this invention.

[0032] Example 1

[0033] This embodiment provides a method for manufacturing a circuit board, which includes the following processing steps in sequence:

[0034] (1) Cutting: Cut the core board, PP sheet and outer copper foil according to the cutting size of 400mm×500mm, and use an edge grinder to remove the burrs and burrs on the edge of the board after cutting; among them, KB (Kingboard) TGI70 core board is selected, the core board thickness is 0.6mm, the core board copper thickness is 1oz, and the outer copper foil thickness is 3oz.

[0035] (2) Inner layer pattern: After the surface copper surface of the core board is roughened with chemical solutions, Rongda liquid photosensitive circuit ink A-9060C is coated on the surface of the core board with a coating machine, and then pre-baking, film alignment, exposure, development, etching, and film stripping are carried out in sequence to form the inner layer circuit pattern.

[0036] (3) Lamination: The inner core board, PP sheet and outer copper foil are laminated and fixed by hot melt method, and then pressed into production board by press machine.

[0037] (4) Outer wet film: After the copper surface of the production board is roughened with chemical solutions, Rongda liquid photosensitive circuit ink A-9060C is coated on its surface with a coating machine, and then pre-baking, film alignment and exposure are carried out in sequence to obtain a production board with a surface covered with protective ink.

[0038] (5) Drilling: Drill holes at the corresponding positions of the production board according to the design data.

[0039] (6) Copper deposition: A layer of chemically deposited copper with a thickness of approximately 0.5 μm is deposited on the surface of the production board and in the holes. A nylon needle roller brush is then used to grind away the thin copper deposited on the board surface, while the thin copper deposited in the holes remains. The grinding current is 0.5 A.

[0040] (7) Board electroplating: The production board after copper deposition is electroplated to add a layer of hole wall metal copper with a thickness of about 30um in the hole.

[0041] (8) Development and etching (non-fading film): The production board after electroplating is developed and etched in sequence to remove the ink on the non-photosensitive part of the production board surface to form a circuit pattern, and the excess copper outside the board circuit is etched away to obtain the circuit pattern, and the circuit pattern is covered with exposed ink, and the thickness of the ink after curing is 15um.

[0042] (9) Solder mask and text: After development and etching, the surface of the production board is subjected to solder mask pre-treatment, screen printing of solder mask ink, pre-baking, exposure, and development in sequence. After the solder mask ink is developed, characters are printed on the corresponding positions on the board surface according to customer needs, and then post-baking is performed to form the solder mask layer and text. Among them, the thickness of the base solder mask layer is 25um, and the thickness of the line surface solder mask layer is 10um (including the outer wet film on the circuit, the total line surface thickness is 25um).

[0043] (10) Surface treatment: Select the corresponding surface treatment process according to customer needs.

[0044] (11) Molding: According to the existing technology, the PNL plate is divided (gong plate) into the external dimensions required by the customer.

[0045] (12) Testing: Test the electrical conductivity of the finished board according to existing technology.

[0046] (13) Finished product inspection (FQC): Inspect the appearance of the finished PCB board according to the customer's acceptance standards and our inspection standards.

[0047] (14) Packaging: The finished PCB boards that have passed the inspection are packaged using vacuum packaging film under heating and vacuum conditions.

[0048] Comparative Example 1

[0049] Compared with Example 1, the only difference is that the following processing steps are adopted: cutting - inner layer patterning - lamination - drilling - copper deposition, board electroplating - outer layer patterning (copper surface roughening, wet film coating, pre-baking, film alignment, exposure, development, etching, and film stripping) - outer layer AOI - solder mask (two solder masks are used, the first solder mask thickness is: substrate solder mask thickness 28μm, line surface solder mask thickness 15μm; the second solder mask thickness is: substrate solder mask thickness 16μm, line surface solder mask thickness 10μm), text - surface treatment - molding - testing - FQC - packaging. In this process, unless otherwise specified, the process parameters and raw materials used are consistent with those of Example 1.

[0050] Comparative Example 2

[0051] Compared with Comparative Example 1, the only difference is that the dry film process is used in the outer layer pattern production step. In this process, unless otherwise specified, the process parameters and raw materials used are the same as those in Comparative Example 1.

[0052] experimental group

[0053] The board developed and etched in step (8) of Example 1 of the present invention was further subjected to film stripping to obtain test board 1. The circuit boards (after film stripping) after forming the outer layer circuit patterns in Comparative Examples 1-2 were respectively recorded as test boards 2 and 3. 100 PNL test boards 1-3 were respectively taken and subjected to outer layer AOI scanning tests using a Condair AOI scanner. The OK and NG results of the PCs on each PNL test board were counted. The test results are shown in Table 1.

[0054] Table 1

[0055] As can be seen from Table 1, when the circuit board is manufactured by the solution of the present invention, the outer layer AOI yield rate after film stripping is 99.8%, which is significantly higher than the existing solution of using dry film or wet film to manufacture the outer layer circuit pattern. It can be seen that based on the method of the present invention, the outer layer circuit pattern is manufactured by using wet film, which can not only reduce the production cost, but also improve the outer layer AOI yield rate. In addition, during the production process of PCB boards, technical personnel in this field often repair the defective products of the outer layer AOI, so that they can enter the next process after passing the test, and test and inspect the finished products of the final formed PCB boards, and also repair the defective products after forming. Since the outer layer AOI yield rate of the present application is extremely high, taking into account the costs of labor, equipment, etc., the solution of the present application can save the outer layer AOI process, so that it only needs to be tested and inspected after forming, and the defective products after forming can be repaired.

[0056] The specific embodiments of the present invention described above do not limit the scope of protection of the present invention. Any other corresponding changes and modifications made based on the technical concept of the present invention should be included in the scope of protection of the claims of the present invention.

Claims

1. A method for manufacturing a circuit board, characterized in that: The following processing steps are included in sequence: Cutting: Cut out the core board, PP sheet and outer copper foil according to the size requirements of the product drawing; Inner layer pattern: making inner layer circuit pattern on the core board; Lamination: The core board, PP sheet and outer copper foil are stacked and fixed, and then pressed into a production board; Outer wet film: After the copper surface of the production board is roughened by chemical solution, photosensitive ink is coated on the surface of the production board, and then pre-baking, film alignment and exposure are performed in sequence to obtain a production board with a surface covered with protective ink; Drilling: Drill holes at corresponding positions of the production board according to the design data; Copper deposition: depositing thin copper with a thickness of 0.3-0.8um on the surface of the production board and in the holes by chemical deposition, and then grinding the thin copper deposited on the ink surface by a grinding process to retain the thin copper in the holes; Plate electroplating: electroplating the production plate after copper deposition; Development and etching: the production board after electroplating is developed and etched in sequence to remove the ink on the non-photosensitive part of the surface of the production board, and to etch away the excess copper outside the circuit on the board surface, so as to obtain a circuit pattern covered with protective ink on the surface; Solder mask and text: forming a solder mask layer and text on the surface of the production board after development and etching; Surface treatment and molding: Surface treatment and molding are performed on the production board to obtain a circuit board; wherein, In the outer wet film step, the photosensitive ink used is transparent; Before depositing thin copper on the surface of the production board and in the holes, no grinding process is used to roughen the surface copper surface; The plate grinding process adopts a nylon needle wheel grinding brush, and the plate grinding current is 0.2-1A.

2. The method for manufacturing a circuit board according to claim 1, characterized in that: The thickness of the outer copper foil is ≥2oz.

3. The method for manufacturing a circuit board according to claim 1, characterized in that: The steps of making the inner layer circuit pattern on the core board include: roughening the surface copper surface of the core board with chemical solutions, coating the surface of the core board with photosensitive ink, and then performing pre-baking, film alignment, exposure, development, etching, and film stripping in sequence to form the inner layer circuit pattern.

4. The method for manufacturing a circuit board according to claim 3, characterized in that: In the inner layer pattern step, the photosensitive ink used is transparent.

5. The method for manufacturing a circuit board according to claim 1, characterized in that: The step of forming a solder mask layer and text on the surface of the production board after development and etching includes: sequentially performing solder mask pre-treatment, silk screen solder mask ink, pre-baking, exposure, and development on the surface of the production board after development and etching, and printing characters at corresponding positions on the board surface according to customer needs after the solder mask ink is developed, and then post-baking to form the solder mask layer and text.

6. The method for manufacturing a circuit board according to claim 5, characterized in that: The solder resist pre-treatment includes at least one of grinding or sand blasting.

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