A method for local surface treatment of inner layer of circuit board

Abstract

The present invention discloses a method for local surface treatment of the inner layer of a circuit board, comprising the following steps: making an inner layer circuit on an inner layer board, and making a connection position to be surface treated at the same time; silk-screening solder resist ink at the corresponding step platform on the inner layer board and curing it to form an isolation layer, wherein the solder resist ink is an ink without a curing agent; laminating the inner layer board and the outer layer copper foil in sequence through a prepreg to form a production board; the production board is sequentially subjected to drilling, copper deposition, full-board electroplating, outer layer circuit production and solder resist production processes; deep milling grooves are controlled inwardly at the position of the corresponding step platform on the production board to the isolation layer, and a step platform is formed after the cover is opened, and the isolation layer is removed together with the waste material to expose the connection position of the inner layer; the production board is surface treated. The method of the present invention adopts solder resist ink that is easy to fall off instead of protective tape, which can effectively improve production efficiency and alignment accuracy, and is not limited by irregular shapes and has a wide range of applications.

Description

Technical Field

[0001] The invention relates to the technical field of printed circuit board manufacturing, and in particular to a method for performing local surface treatment on an inner layer of a circuit board. Background Art

[0002] During the production process of some printed circuit boards with special requirements, it is necessary to design a stepped platform on the circuit board, and the immersion gold pattern needs to be exposed at the stepped platform. For such products that require local surface treatment at the stepped platform on the inner layer, the usual method is to perform the surface treatment of the inner and outer layers separately, that is, perform a surface treatment process on the inner and outer layers respectively, resulting in a long production process and low production efficiency.

[0003] At present, there is also a way to perform surface treatment of the inner and outer layers at the same time. The production process includes: cutting → inner layer graphics → inner layer etching → inner layer AOI → corresponding step platform area with protective tape (protective tape model FN-PI25015) → rapid pressing → browning → pressing → outer layer drilling → copper immersion → full board electroplating → outer layer graphics → graphic electroplating → outer layer etching → outer layer AOI → silk screen solder mask → silk screen characters → SET shape → SET platform → protective tape removal → FQC1 → micro-etching → immersion gold → testing → FQC → FQA → packaging; in this way, for boards that need to be surface treated locally on the inner layer, protective tape is usually applied to the step platform area that needs to be surface treated before pressing, and the protective tape is used to protect the inner layer's immersion gold graphics, as shown in the published patents CN201810949433.X and CN201810045409.3. However, applying protective tape has the following disadvantages:

[0004] 1) The protective tape needs to be applied manually, which is inefficient;

[0005] 2) The limitations are large and the graphics are irregular, which is not conducive to production;

[0006] 3) Large alignment deviation. Summary of the Invention

[0007] In response to the above-mentioned existing technical defects, the present invention provides a method for local surface treatment of the inner layer of a circuit board. The method uses easily removable solder mask ink instead of protective tape, which can effectively improve production efficiency and positioning accuracy, is not restricted by irregular shapes, and has a wide range of applications.

[0008] In order to solve the above technical problems, the present invention provides a method for performing local surface treatment on the inner layer of a circuit board, comprising the following steps:

[0009] S1. Make inner layer circuits on the inner layer board and make connection points to be surface treated at the corresponding step platforms;

[0010] S2. Screen-printing solder resist ink on the corresponding step platform of the inner layer board and curing it to form an isolation layer, wherein the solder resist ink is an ink without a curing agent;

[0011] S3, the inner layer board and the outer copper foil are stacked in sequence through the prepreg and pressed together to form a production board; during the pressing, the prepreg is combined with the solder mask ink of the inner layer;

[0012] S4, then the production board goes through the processes of drilling, copper deposition, full board electroplating, outer layer circuit making and solder mask making;

[0013] S5. Mill a deep groove inward at the position corresponding to the step platform on the production board to the solder mask ink of the inner layer. After removing the cover, a step platform is formed. The solder mask ink of the inner layer is removed together with the waste material to expose the connection position of the inner layer.

[0014] S6. Perform surface treatment on the production board.

[0015] Furthermore, in step S1, the connection position is a pad or a plurality of finger bodies.

[0016] Furthermore, in step S2, solder resist ink is firstly screen-printed on the entire surface of the inner layer board, and then the solder resist ink in the area outside the step platform position is removed after exposure and development, and then the solder resist ink is cured by baking.

[0017] Furthermore, in step S3, before laminating the laminates, the inner layer laminates are first subjected to a browning treatment.

[0018] Furthermore, in step S3, after the browning treatment, the solder mask ink on the first production board is tested for peeling using adhesive tape. Specifically, the solder mask ink is adhered to the adhesive tape and then the peeling test is performed by tearing off the adhesive tape. The solder mask ink is qualified if it is peeled off during the process of tearing off the adhesive tape.

[0019] Furthermore, in step S2, the outer periphery of the isolation layer is retracted by 2 mil relative to the outer periphery of the stepped platform.

[0020] Furthermore, the following steps are included between steps S5 and S6:

[0021] S50: After the cover is removed, a dielectric layer may remain on the periphery of the stepped platform. The dielectric layer remaining on the periphery of the stepped platform is removed by laser ablation.

[0022] Furthermore, the following steps are included between step S50 and step S6:

[0023] S51. Perform micro-etching on the production board to clean and roughen the solder mask window area and the step platform area.

[0024] Furthermore, in step S6, the production board is subjected to a nickel-gold deposition process so that a nickel-gold layer is deposited on both the solder mask window positions of the outer layer and the connection positions of the inner layer.

[0025] Furthermore, the inner layer board is a core board or a multilayer board in which an inner core board and an outer copper foil are pressed together by a prepreg.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] In the present invention, a solder resist ink without a curing agent is used to replace the protective function of the protective tape. After the solder resist ink is screen-printed and cured to form an isolation layer, the solder resist ink cannot be completely cured because it does not contain a curing agent. Under the action of high temperature, the isolation layer is easily separated from the inner layer board and falls off. Therefore, when the inner layer board and the outer copper foil are pressed together, the high temperature during pressing is used to separate the solder resist ink of the inner layer from the inner layer board. At the same time, the solder resist ink is combined with the semi-cured sheet, which makes it easy to remove the solder resist ink together with the waste when the cover is later opened. Compared with the method of manually applying protective tape, this method can effectively improve production efficiency, and the isolation layer formed by screen-printing the solder resist ink and then exposing and developing can effectively improve the positioning accuracy, is not limited by irregular shapes, and has a wide range of applications. DETAILED DESCRIPTION

[0028] In order to more fully understand the technical content of the present invention, the technical solution of the present invention will be further introduced and illustrated in conjunction with specific embodiments below.

[0029] Example

[0030] The present embodiment shows a method for manufacturing a circuit board, which includes a process of performing local surface treatment on the inner layer of the circuit board, and includes the following processing steps in sequence:

[0031] (1) Cutting: Cut the core board according to the panel size of 520mm×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.

[0032] (2) Inner layer circuit production (negative film process): Inner layer pattern transfer, use a vertical coating machine to coat the photosensitive film, the film thickness of the photosensitive film is controlled to 8μm, and a fully automatic exposure machine is used to complete the exposure of the inner layer circuit with a 5-6 grid exposure ruler (21 grid exposure ruler), and the inner layer circuit pattern is formed after development; inner layer etching, the exposed and developed core board is etched to etch the inner layer circuit, the inner layer line width is measured to be 3mil, and the connection position to be surface treated is made at the corresponding step platform; inner layer AOI, then check the inner layer circuit for defects such as open short circuit, circuit gap, circuit pinhole, etc., and the defective products will be scrapped, and the products without defects will be sent to the next process.

[0033] In one embodiment, the connection site may be a large copper surface, or a circular pad or a plurality of finger bodies, and the finger bodies will form gold fingers after subsequent surface treatment.

[0034] (3) Making an isolation layer: Screen print solder resist ink on the corresponding step platform of the inner layer board and solidify it to form an isolation layer. The solder resist ink does not contain a curing agent. Since the solder resist ink does not contain a curing agent, the isolation layer made by it cannot be completely solidified. Under the action of high temperature, the isolation layer is easy to separate from the inner layer board and fall off.

[0035] In one embodiment, the process of making the isolation layer is: first, screen-printing solder resist ink on the entire surface of the inner layer board, then removing the solder resist ink in the area outside the step platform position after exposure and development, and then curing the solder resist ink by baking.

[0036] In one embodiment, the outer periphery of the isolation layer is retracted by 2 mil relative to the outer periphery of the step platform to reduce the impact of the alignment error between the previous and subsequent processes, and avoid deviations between the alignment during the grooving and the alignment during the production of the isolation layer, which may result in the isolation layer not falling entirely on the step platform area, thereby ensuring that the entire isolation layer can be removed when the cover is later opened.

[0037] (4) Lamination: The browning speed is based on the browning thickness of the bottom copper. The core board, prepreg, and outer copper foil are stacked in sequence as required. Then, appropriate lamination conditions are selected according to the Tg of the sheet material to press the laminated board to form a production board. The high temperature during lamination is used to separate the inner layer of solder mask ink from the inner layer of the board, and the prepreg and the inner layer of solder mask ink are combined together during lamination.

[0038] In one embodiment, after the browning treatment, the solder mask ink on the first production board is tested for peeling using adhesive tape. Specifically, the solder mask ink is adhered to the adhesive tape and then the peeling test is performed by tearing off the adhesive tape. If the solder mask ink is peeled off during the process of tearing off the adhesive tape, it is qualified. After passing the test, mass production can be carried out.

[0039] (5) Drilling: Based on existing drilling technology, drilling is performed on the production board according to design requirements.

[0040] (6) Copper plating: A thin layer of copper is deposited on the board surface and the hole wall using the chemical copper plating method. The backlight test is level 10, and the thickness of the copper plating in the hole is 0.5μm.

[0041] (7) Full board electroplating: The production board is fully electroplated according to the design requirements to increase the thickness of the hole copper and the board surface copper layer.

[0042] (8) Production of outer layer circuits (positive film process): Transfer of outer layer graphics, using a fully automatic exposure machine and positive film circuit film, with a 5-7 grid exposure ruler (21 grid exposure ruler) to complete the outer layer circuit exposure, after development, the outer layer circuit graphics are formed on the production board; the outer layer graphics are electroplated, and then copper and tin are plated on the production board respectively. The electroplating parameters are set according to the required copper thickness. Copper plating is performed at a current density of 1.8ASD for 60 minutes on the entire board, and tin plating is performed at a current density of 1.2ASD for 10 minutes, with a tin thickness of 3-5μm; then the film is stripped, etched and tin stripped in sequence to etch the outer layer circuit on the production board; outer layer AOI, using an automatic optical inspection system, detects whether the outer layer circuit has defects such as open circuit, gap, incomplete etching, short circuit, etc. by comparing with the CAM data.

[0043] (9) Solder mask and silk screen characters: After silk screen printing solder mask ink on the surface of the production board, it is sequentially processed through pre-curing, exposure, development and heat curing to solidify the solder mask ink into a solder mask layer; specifically, the solder mask ink and the characters on the TOP surface are added with "UL mark", so that a layer is coated on the circuits and substrates that do not need to be soldered to prevent bridging between circuits during soldering, provide a permanent electrical environment and chemical corrosion resistance, and at the same time beautify the appearance.

[0044] (10) Gong platform: On the surface of the production board adjacent to the isolation layer, a deep milling groove is made inward to the solder mask ink of the inner layer (i.e., the milling groove is made to the isolation layer). After the cover is removed, a step platform is formed. The solder mask ink of the inner layer is removed together with the waste generated by the milling groove to expose the connection position of the inner layer.

[0045] (11) Laser ablation: Since the isolation layer is retracted 2 mil relative to the step platform, a dielectric layer will remain on the periphery of the step platform after the cover is removed. Laser ablation is used to remove the residual dielectric layer around the step platform.

[0046] (12) Micro-etching: Micro-etching is performed on the production board to clean and roughen the solder mask window area and the exposed step platform area.

[0047] (13) Surface treatment (nickel-gold plating): The copper surface of the connection position and the solder mask window position is chemically deposited with a nickel layer and a gold layer of a certain required thickness. The thickness of the nickel layer is 3-5μm; the thickness of the gold layer is 0.05-0.1μm.

[0048] (14) Electrical test: Test the electrical conductivity of the finished board. The test method used for this board is: flying probe test.

[0049] (15) Molding: According to the existing technology and the design requirements, the circuit board is manufactured with a shape tolerance of + / -0.05mm.

[0050] (16) FQC: Inspect the appearance of the circuit board according to the customer's acceptance standards and our inspection standards. If there are any defects, repair them in time to ensure that we provide customers with excellent quality control.

[0051] (17) FQA: Retest the appearance of the circuit board, hole copper thickness, dielectric layer thickness, green oil thickness, inner layer copper thickness, etc. to see if they meet customer requirements.

[0052] (18) Packaging: According to the packaging method and packaging quantity required by the customer, the circuit boards are sealed and packed, and desiccant and humidity card are placed before shipment.

[0053] The technical solutions provided by the embodiments of the present invention are introduced in detail above. Specific examples are used herein to illustrate the principles and implementation methods of the embodiments of the present invention. The description of the above embodiments is only applicable to help understand the principles of the embodiments of the present invention. At the same time, for those skilled in the art, according to the embodiments of the present invention, there may be changes in the specific implementation methods and application scopes. In summary, the contents of this specification should not be understood as limiting the present invention.

Claims

1. A method for local surface treatment of the inner layer of a circuit board, characterized in that: The following steps are involved: S1. Make inner layer circuits on the inner layer board and make connection points to be surface treated at the corresponding step platforms; S2. Screen-print solder resist ink on the inner layer board at the corresponding step platform and cure it to form an isolation layer. The solder resist ink does not contain a curing agent. The periphery of the isolation layer is indented 2 mil relative to the periphery of the step platform. S3, the inner layer board and the outer copper foil are stacked in sequence through the prepreg and pressed together to form a production board; during the pressing, the prepreg is combined with the solder mask ink of the inner layer; S4, then the production board goes through the processes of drilling, copper deposition, full board electroplating, outer layer circuit making and solder mask making; S5. Mill a deep groove inward at the position corresponding to the step platform on the production board to the solder mask ink of the inner layer. After removing the cover, a step platform is formed. The solder mask ink of the inner layer is removed together with the waste material to expose the connection position of the inner layer. S50: After the cover is removed, a dielectric layer may remain on the periphery of the stepped platform, and the dielectric layer remaining around the stepped platform is removed by laser ablation. S51. Perform micro-etching on the production board to clean and roughen the solder mask window area and the step platform area; S6. Perform nickel-gold immersion treatment on the production board, so that a nickel-gold layer is deposited on the solder mask opening position of the outer layer and the connection position of the inner layer.

2. The method for local surface treatment of the inner layer of a circuit board according to claim 1, characterized in that: In step S1 , the connection location is a pad or a plurality of finger bodies.

3. The method for local surface treatment of the inner layer of a circuit board according to claim 1, characterized in that: In step S2, solder resist ink is firstly screen-printed on the entire surface of the inner layer board, and then the solder resist ink in the area outside the step platform position is removed after exposure and development, and then the solder resist ink is cured by baking.

4. The method for local surface treatment of the inner layer of a circuit board according to claim 1, characterized in that: In step S3, before laminating the laminates, the inner layer laminates are first subjected to a browning treatment.

5. The method for local surface treatment of the inner layer of a circuit board according to claim 4, characterized in that: In step S3, after the browning treatment, the solder mask ink on the first production board is tested for peeling using adhesive tape. Specifically, the solder mask ink is adhered to the adhesive tape and then the adhesive tape is removed to perform the peeling test. The solder mask ink is qualified if it is peeled off during the process of tearing off the adhesive tape.

6. The method for local surface treatment of the inner layer of a circuit board according to claim 1, characterized in that: The inner layer board is a core board or a multilayer board in which an inner core board and an outer copper foil are pressed together by a prepreg.