A method for manufacturing a stepped line printed circuit board

Abstract

The application discloses a manufacturing method of a stepped circuit printed circuit board, which comprises the following steps: pasting a film on a production board, sequentially performing exposure and development to form a circuit pattern, the circuit pattern comprising a thin copper circuit pattern corresponding to a thin copper circuit and a thick copper circuit pattern corresponding to a thick copper circuit; electroplating copper on the production board to plate a copper layer at the circuit pattern to a thickness required by the thin copper circuit; electroplating gold on the production board to plate a gold layer on the copper surface at the circuit pattern; pasting a film on the production board, sequentially performing exposure and development to perform windowing at positions corresponding to the thick copper circuit; sequentially electroplating copper and electroplating a layer of resist protective layer on the production board to plate the copper at the windowing position to a thickness required by the thick copper circuit; removing the film on the production board, and then performing etching treatment on the production board to obtain a required stepped circuit. The method solves the problem of opening and notch of the circuit during film pasting and etching in the later period due to the height difference of the copper thickness at the stepped circuit on the board surface.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of printed circuit board manufacturing, and particularly relates to a manufacturing method of a stepped circuit printed circuit board. BACKGROUND

[0002] With the diversified development of the circuit board industry, the circuit board develops towards the direction of carrying more functional requirements. Different finished copper thickness lines (i.e. stepped lines) are designed in a network line to achieve the performance requirements that the thick copper region in the network line transmits signals and the thin copper region in the network line realizes filtering. However, in the traditional circuit board production process, it is difficult to realize the process conditions of two kinds of copper thickness in the network due to the limitation of process capacity.

[0003] In the traditional process, the whole board is plated with copper, and then the dry film is used to protect the thin copper region, and the thick copper region is locally electroplated to form a stepped line. However, due to the difference in copper thickness of the board surface, there is a gradient difference at the junction of the two different thickness board surfaces, which causes the dry film to be poorly attached to the board surface during etching. During etching, the etching solution will seep into the gap between the dry film and the board surface, causing the board surface circuit to be open and have a gap. The existing method for manufacturing a stepped circuit board is as follows: after whole board electroplating, the pattern circuit is etched on the board surface, then the dry film is used to cover the circuit that does not need to be thickened, and the circuit pattern that needs to be thickened is subjected to pattern electroplating. However, this method has obvious disadvantages: during electroplating, it is difficult to ensure the uniformity of the copper thickness of the same line due to the thinness of the circuit. In addition, it is very difficult to ensure good connection of the stepped circuit, which requires very high technology and high cost, and is not suitable for mass production. SUMMARY

[0004] The present application provides a manufacturing method of a stepped circuit printed circuit board to solve the problem of open circuit and gap caused by the height difference of copper thickness at the stepped circuit of the board surface during later film etching.

[0005] In order to solve the above technical problems, the present application provides a manufacturing method of a stepped circuit printed circuit board, wherein the stepped circuit includes a thin copper circuit and a thick copper circuit with a thickness greater than the thin copper circuit, and the manufacturing method comprises the following steps:

[0006] S1, film is attached to the production board, and then line patterns are formed by exposure and development in sequence, wherein the line patterns include a thin copper circuit pattern corresponding to the thin copper circuit and a thick copper circuit pattern corresponding to the thick copper circuit;

[0007] S2, electroplating copper on the production board to plate the copper layer at the line pattern to the required thickness of the thin copper circuit;

[0008] S3, electroplating gold on the production board to plate a gold layer on the copper surface at the circuit pattern;

[0009] S4, pasting a film on the production board, and then sequentially performing exposure, development and windowing at the position corresponding to the thick copper circuit;

[0010] S5, sequentially electroplating copper and electroplating a protective layer of resist on the production board to thicken the copper at the windowed position to the thickness required by the thick copper circuit;

[0011] S6, removing the film on the production board, and then performing etching treatment on the production board to obtain the required stepped circuit.

[0012] Further, in step S1, a dry film of resist is pasted on the production board; and in step S4, a dry film is pasted on the production board.

[0013] Further, in step S3, the thickness of the gold layer is 0.025-0.05 μm.

[0014] Further, in step S5, the protective layer of resist is a tin layer.

[0015] Further, the thickness of the tin layer is 3-5 μm.

[0016] Further, when the stepped circuit to be made on the production board is three steps or more, the protective layer in step S5 is a gold layer, and steps S4 and S5 are repeated between steps S5 and S6 to sequentially window and electroplate the positions after the third step circuit to obtain a stepped circuit of three steps or more.

[0017] Further, after step S6, the following steps are further included:

[0018] S7, sequentially making a solder resist layer, surface treatment and forming treatment on the production board to obtain a printed circuit board.

[0019] Further, the production board is a multilayer board in which an inner core board and an outer copper foil are pressed together by a prepreg, and the multilayer board has sequentially undergone a drilling and copper plating process.

[0020] Further, the production board is a double-sided copper-clad core board, and the double-sided copper-clad core board has sequentially undergone a drilling and copper plating process.

[0021] Compared with the prior art, the present application has the following beneficial effects:

[0022] The method thickens the whole circuit pattern to the required thickness of the thin copper circuit by graphic electroplating, and then continues to thicken the copper thickness at the thick copper circuit; a gold layer and a resist protective layer are plated respectively after the first electroplating and the second electroplating, the copper thickness of the circuit is thickened by plating copper on the gold surface, the different copper thicknesses are realized, the required circuit is protected by the corrosion resistance of the gold layer and the resist protective layer, the surface of the base copper outside the circuit pattern is not protected by the gold layer and the resist protective layer, so that the film need not be attached when etching the copper surface outside the circuit pattern in the later stage, only the circuit protected by the gold layer and the resist protective layer is left after etching the base copper, the production of the stepped circuit is realized, and the problems of poor film adhesion to the board surface due to the height difference of the copper thickness of the stepped circuit on the board surface in the prior art, the gap, and the line opening and notch caused by the penetration of etching chemicals in the etching process are solved. DETAILED DESCRIPTION

[0023] In order to more fully understand the technical content of the present application, the technical solutions of the present application will be further introduced and described below in combination with specific embodiments.

[0024] Embodiment 1

[0025] The production method of the stepped circuit printed circuit board shown in this embodiment is a two-step circuit, specifically including a thin copper circuit and a thick copper circuit with a thickness greater than that of the thin copper circuit, and the production method sequentially includes the following processing procedures:

[0026] (1) Cutting: cut the core plate according to the size of the assembled board 520mmx620mm, the thickness of the core plate is 0.5mm, and the thickness of the copper layer on both surfaces of the core plate is 0.5oz.

[0027] (2) Production of inner layer circuit (negative film process): inner layer pattern transfer, use a vertical coating machine to coat a photosensitive film, control the film thickness of the photosensitive film to 8μm, use a full-automatic exposure machine to complete the exposure of the inner layer circuit with a 5-6 grid exposure ruler (21 grid exposure ruler), and form the inner layer circuit pattern after development; inner layer etching, etch the core plate after exposure and development to form the inner layer circuit, and the inner layer AOI, then check the defects of the inner layer circuit such as open circuit, line gap, line pinhole, etc., and the defective products are treated, and the products without defects are output to the next process.

[0028] (3) Laminating: according to the bottom copper thickness, the core plate, the semi-solid sheet and the outer layer copper foil are laminated according to the requirements, and then the laminated plate is laminated according to the Tg of the plate material to form the production plate.

[0029] (4) Drilling: according to the existing drilling technology, drilling is carried out on the production plate according to the design requirements.

[0030] (5) Copper deposition: a thin copper layer is deposited on the surface of the board and the hole wall by using the method of electroless copper plating, the back light test is 10 levels, and the thickness of the copper layer in the hole is 0.5 μm.

[0031] (6) Manufacturing the outer layer circuit (positive process): specifically comprising the following steps:

[0032] a. The anti-chemical gold dry film is pasted on the production board, and then the outer layer circuit pattern is formed by exposure and development in sequence, which includes the thin copper circuit pattern corresponding to the thin copper circuit and the thick copper circuit pattern corresponding to the thick copper circuit;

[0033] b. Copper is electroplated on the production board, that is, the entire outer layer circuit pattern is thickened as a whole to plate the copper layer at the outer layer circuit pattern to the required thickness of the thin copper circuit, thereby completing the manufacturing of the thin copper circuit in the stepped circuit;

[0034] c. Gold is electroplated on the production board to plate a 0.025-0.05 μm thick gold layer on the copper surface at the circuit pattern, the gold layer is plated on the surface of the copper layer after copper plating as a circuit surface protection layer during the final etching of the base copper, and the thickness of the gold layer can provide etching protection to the circuit while avoiding excessive thickness of the gold layer to increase the cost; and the anti-chemical gold dry film pasted in the front avoids the problem of etching quality and circuit short circuit caused by penetration plating of the part other than the outer layer circuit pattern;

[0035] d. The ordinary dry film is pasted on the production board, and then the windowing is performed at the position corresponding to the thick copper circuit by exposure and development in sequence;

[0036] e. Copper and a 3-5 μm thick tin layer are electroplated in sequence on the production board, so that a copper layer is first electroplated on the gold surface at the windowing to plate the copper at the windowing to the required thickness of the thick copper circuit, the copper thickness at the thick copper circuit is controlled to meet the requirement of signal transmission of the thick copper area, and the tin is directly plated on the surface of the copper layer after copper plating as an etching protection layer to protect the circuit.

[0037] f. The dry film and the anti-chemical gold dry film on the production board are removed in sequence to expose the base copper of the part other than the outer layer circuit pattern, and then the production board is subjected to alkaline etching treatment to remove the exposed base copper, thereby obtaining the required stepped circuit.

[0038] g. Outer layer AOI: using an automatic optical detection system, the outer layer circuit is detected for defects such as open circuit, gap, incomplete etching, and short circuit by comparison with the CAM data

[0039] In the above, during the manufacturing of the outer layer circuit, different circuit compensation is adopted according to different circuit copper thickness (i.e. thin copper circuit and thick copper circuit) to ensure that the same outer layer circuit has the same line width after one-time etching in different copper thickness areas.

[0040] (7) Solder resist, silk-screen character: after silk-screening solder resist ink on the surface of the production board, and sequentially going through pre-curing, exposure, development and thermal curing treatment, the solder resist ink is cured into a solder resist layer; specifically, TOP face solder resist ink, TOP face character adding "UL mark", thereby coating a protective layer on the lines and substrates which do not need to be welded, preventing the bridging between lines during welding, providing permanent electrical environment and anti-chemical corrosion, and beautifying the appearance.

[0041] (8) Surface treatment (nickel-gold plating): through chemical principle, the copper surface of the solder pad window is uniformly deposited with a nickel layer and a gold layer with a thickness of 3-5 μm and 0.05-0.1 μm respectively.

[0042] (9) Electrical test: testing the electrical conduction performance of the finished board, and the test method is flying probe test.

[0043] (10) Shaping: according to the existing technology and the design requirements, the outer shape is shaped with an outer shape tolerance of + / - 0.05 mm, and the circuit board is obtained.

[0044] (11) FQC: according to the customer acceptance standard and the company's inspection standard, the appearance of the circuit board is checked, and if there is a defect, it is repaired in time to ensure that the customer is provided with excellent quality control.

[0045] (12) FQA: the appearance, hole copper thickness, dielectric layer thickness, green oil thickness, inner layer copper thickness, etc. of the circuit board are re-measured to see if they meet the customer's requirements.

[0046] (13) Packaging: according to the customer's required packaging method and packaging quantity, the circuit board is sealed and packaged, and then shipped with desiccant and humidity card.

[0047] In this embodiment, direct pattern electroplating can be performed after copper plating, reducing the previous full-board electroplating process and effectively improving the production efficiency.

[0048] Example 2

[0049] The manufacturing method of the stepped circuit printed circuit board shown in this embodiment is a two-step circuit, specifically including a thin copper circuit and a thick copper circuit with a thickness greater than the thin copper circuit, and the manufacturing method sequentially includes the following processing procedures:

[0050] (1) Cutting: cutting the core board according to the size of the assembled board 520mm x 620mm, the thickness of the core board is 0.5mm, and the thickness of the copper layer on both surfaces of the core board is 0.5oz.

[0051] (2) Drilling: according to the existing drilling technology, drilling is performed on the core board according to the design requirements.

[0052] (3) Copper deposition: a thin copper layer is deposited on the surface of the board and the hole wall by using the method of electroless copper plating, the back light test is 10 levels, and the thickness of the copper layer in the hole is 0.5 μm.

[0053] (4) Manufacturing the outer layer circuit (positive process): specifically comprising the following steps:

[0054] a. Pasting the anti-chemical gold dry film on the core board, and then forming the outer layer circuit pattern by exposure and development in sequence, the outer layer circuit pattern comprising a thin copper circuit pattern corresponding to the thin copper circuit and a thick copper circuit pattern corresponding to the thick copper circuit;

[0055] b. Electroplating copper on the core board, that is, the entire outer layer circuit pattern is thickened as a whole to plate the copper layer at the outer layer circuit pattern to the required thickness of the thin copper circuit, thereby completing the manufacturing of the thin copper circuit in the stepped circuit;

[0056] c. Electroplating gold on the core board to plate a 0.025-0.05 μm thick gold layer on the copper surface at the circuit pattern, the gold layer being plated on the surface of the copper layer after copper plating as a circuit surface protection layer during the final etching of the base copper, and the thickness of the gold layer being able to provide etching protection to the circuit while avoiding the increase of excessive cost caused by the excessive thickness of the gold layer; and the anti-chemical gold dry film pasted in the previous step avoiding the seepage plating of the parts other than the outer layer circuit pattern to cause the etching quality and circuit short circuit problems;

[0057] d. Pasting the ordinary dry film on the core board, and then performing windowing at the positions corresponding to the thick copper circuit by exposure and development in sequence;

[0058] e. Electroplating copper and a 3-5 μm thick tin layer on the core board in sequence, thereby electroplating a copper layer on the gold surface at the windowing part to plate the copper at the windowing part to the required thickness of the thick copper circuit, controlling the copper thickness at the thick copper circuit to meet the requirement of signal transmission of the thick copper area, and directly plating tin on the surface of the copper layer after copper plating as an etching protection layer to protect the circuit.

[0059] f. Removing the dry film and the anti-chemical gold dry film on the core board in sequence to expose the base copper of the parts other than the outer layer circuit pattern, and then performing alkaline etching treatment on the core board to remove the exposed base copper, thereby obtaining the required stepped circuit.

[0060] g. Outer layer AOI: using the automatic optical detection system to detect whether the outer layer circuit has defects such as open circuit, gap, incomplete etching, short circuit, etc. by comparison with the CAM data

[0061] In the above, during the manufacturing of the outer layer circuit, different circuit compensation is adopted according to different circuit copper thickness (i.e. thin copper circuit and thick copper circuit) to ensure that the same outer layer circuit has the same line width after one-time etching in different copper thickness areas.

[0062] (5) Solder resist, silk-screen character: after silk-screening solder resist ink on the surface of the core plate, and sequentially going through pre-curing, exposure, development and thermal curing treatment, the solder resist ink is cured into a solder resist layer; specifically, TOP surface solder resist ink, TOP surface character adding "UL mark", thus on the circuit and substrate which do not need to be welded, a protective layer is coated to prevent bridging between circuits during welding, to provide permanent electrical environment and anti-chemical corrosion, and to beautify the appearance.

[0063] (6) Surface treatment (nickel-gold plating): through chemical principle, the solder pad copper surface of the solder resist window is uniformly deposited with a nickel layer and a gold layer with a required thickness; the thickness of the nickel layer is 3-5 μm; the thickness of the gold layer is 0.05-0.1 μm.

[0064] (7) Electrical test: testing the electrical conduction performance of the finished plate, the test method of the plate is flying probe test.

[0065] (8) Forming: according to the existing technology and the design requirements, the outer shape is punched with an outer shape tolerance of + / - 0.05 mm, and the circuit board is prepared.

[0066] (9) FQC: according to the customer acceptance standard and the inspection standard of the company, the appearance of the circuit board is checked, and if there is a defect, it is repaired in time to ensure that the excellent quality control is provided for the customer.

[0067] (10) FQA: the appearance, hole copper thickness, dielectric layer thickness, green oil thickness, inner layer copper thickness, etc. of the circuit board are re-measured to see if they meet the requirements of the customer.

[0068] (11) Packaging: according to the packaging method and packaging quantity required by the customer, the circuit board is sealed and packaged, and then shipped with desiccant and humidity card.

[0069] The technical solutions provided by the embodiments of the present application are described in detail above, and specific examples are applied to describe the principles and implementation modes of the embodiments of the present application; the above description of the embodiments is only applicable to help understand the principles of the embodiments of the present application; meanwhile, for those skilled in the art, according to the embodiments of the present application, the specific implementation modes and application scope will be changed, and the above description should not be understood as a limitation of the present application.

Claims

1. A method of manufacturing a stepped line printed circuit board, wherein the stepped line includes a thin copper line and a thick copper line having a thickness greater than that of the thin copper line, characterized by, The manufacturing method comprises the following steps: S1, pasting a film on a production board, and then forming a circuit pattern by exposure and development in sequence, wherein the circuit pattern comprises a thin copper circuit pattern corresponding to a thin copper circuit and a thick copper circuit pattern corresponding to a thick copper circuit; S2, electroplating copper on the production board to plate the copper layer at the circuit pattern to a thickness required by the thin copper circuit; S3, electroplating gold on the production board to plate a gold layer on the copper surface at the circuit pattern; S4, pasting a film on the production board, and then performing windowing at positions corresponding to the thick copper circuit by exposure and development in sequence; S5, electroplating copper and then electroplating a resist protective layer on the production board in sequence to plate the copper at the window to a thickness required by the thick copper circuit; S6, removing the film on the production board, and then performing etching treatment on the production board to obtain the required stepped circuit.

2. The method of claim 1, wherein In step S1, a dry gold film is pasted on the production board; and in step S4, a dry film is pasted on the production board.

3. The method of claim 1, wherein In step S3, the thickness of the gold layer is 0.025-0.05 μm.

4. The method of claim 1, wherein In step S5, the resist protective layer is a tin layer.

5. The method of claim 4, wherein the step of forming the stepped circuit board is performed by a subtractive process. The thickness of the tin layer is 3-5 μm.

6. The method of claim 1, wherein When the stepped circuit to be manufactured on the production board is three steps or more, the protective layer in step S5 is a gold layer, and steps S4 and S5 are repeated between steps S5 and S6 to sequentially perform windowing and electroplating thickening at positions after the third step circuit to obtain a three-step or more stepped circuit.

7. The method of claim 1, wherein After step S6, the following step is further included: S7, sequentially manufacturing a solder mask layer, a surface treatment layer and a forming treatment layer on the production board to obtain a printed circuit board.

8. The method of claim 1, wherein The production board is a multilayer board in which an inner core board and an outer copper foil are pressed together by a prepreg, and the multilayer board has been subjected to a drilling and copper plating process in sequence.

9. The method of claim 1, wherein The production board is a double-sided copper-clad core board, and the double-sided copper-clad core board has been subjected to a drilling and copper plating process in sequence.