Method for improving burrs and copper nodules in holes of CEM-3 plate

Abstract

The invention discloses a method for improving burrs and in-hole copper nodules of a CEM-3 board, which comprises the following steps of: carrying out precise polish-brush on a production board after drilling to remove the burrs at the hole opening; performing high-pressure water washing on the production board; carrying out sand blasting treatment on the production board so as to wash the interiors of the holes; the production board is subjected to copper deposition treatment, the production board does not pass through the bulking section but passes through the chemical degumming section during copper deposition, and hole wall glass fibers are cleaned through the chemical degumming section; and full-board electroplating is carried out on the production board, the thickness of hole copper and the thickness of a board surface copper layer are increased, and the current density during full-board electroplating is 1.15 ASD. According to the method disclosed by the invention, the quality problems of poor appearance and small aperture caused by drilling burrs and copper nodules in the hole in the prior art are solved by adjusting and improving the mode and parameters of each process step.

Description

Technical Field

[0001] The invention relates to the technical field of printed circuit board manufacturing, and in particular to a method for improving the flash of a CEM-3 plate and copper nodules in holes. Background Art

[0002] PCB (Printed Circuit Board), also known as printed circuit board in Chinese, is an important electronic component, a support for electronic components, and a carrier for electrical connection of electronic components. Because it is made by electronic printing, it is called a "printed" circuit board.

[0003] Among them, electroless copper plating is the abbreviation of electroless copper plating, also called plated through hole (PTH), which is a self-catalyzed redox reaction. The PTH process must be carried out after the two layers or production boards are drilled.

[0004] At present, due to the characteristics of the material itself, CEM-3 plates are prone to hole burr during production. When drilling, there are fine glass fibers in the hole that are pulled on the hole wall. When copper is deposited, the glass fibers are deposited on copper, and copper nodules appear in the holes after electroplating. In order to improve the quality, the drill speed is reduced during drilling to reduce the hole burr and the amount of glass fibers in the hole. The plate is ground once after drilling, and chemical glue is removed during copper deposition. VCP line is used for electroplating.

[0005] The existing process flow is generally as follows: cutting - baking - drilling - copper plating pre-treatment - copper plating - electroplating - graphics - etching - AOI inspection - solder mask - characters - surface treatment - molding - testing - FQC - FQA - packaging - shipment; among them, copper plating pre-treatment includes sharp grinding (using 800 mesh sandpaper to grind the plate once), precision grinding (using 320# grinding brush and 500# grinding brush to grind the plate once each) and high-pressure water washing (pressure 70-80kg / cm 2 Wash with water once), do not expand and chemically remove the glue during copper deposition, and control the parameters during electroplating at 2.8ASD*50min.

[0006] Although the above-mentioned processes have been adjusted during the drilling and copper electroplating processes, in actual processing, the defective ratios of slot holes, round hole burrs and copper nodules in the holes after electroplating are still over 20%, and the burrs at the hole mouths and copper nodules in the holes are greater than 50μm, resulting in poor appearance and poor holes. In severe cases, the aperture may be too small, making it difficult for subsequent customers to plug in components. Summary of the invention

[0007] In view of the above-mentioned existing technical defects, the present invention provides a method for improving the flash and copper nodules in the holes of CEM-3 plates, thereby solving the quality problems of poor appearance and small hole diameter caused by the flash and copper nodules in the holes.

[0008] In order to solve the above technical problems, the present invention provides a method for improving the flash and copper nodules in the holes of CEM-3 plates, comprising the following steps:

[0009] S1. After drilling, the production plate is precisely brushed to remove the flash at the hole mouth;

[0010] S2, high pressure water washing of the production board;

[0011] S3, sandblasting the production plate to flush the inside of the hole;

[0012] S4, copper deposition is performed on the production board. When copper deposition is performed, the production board does not pass through the bulking section but passes through the chemical degumming section, so as to clean the hole wall glass fiber through the chemical degumming section;

[0013] S5. Full-plate electroplating is performed on the production board to thicken the hole copper and board surface copper layer. The current density during full-plate electroplating is 1.15ASD.

[0014] Furthermore, in step S1, when the production plate is drilled, a phenolic pad is placed underneath it and a coated aluminum sheet is placed above it.

[0015] Furthermore, in step S1, 500-mesh sandpaper is used for precision grinding.

[0016] Furthermore, in step S1, the production plate is precision-brushed twice.

[0017] Furthermore, in step S1, the directions of the two brushing operations are perpendicular to each other.

[0018] Furthermore, in step S2, the pressure during high pressure water washing is controlled at 70-80 kg / cm 2 .

[0019] Furthermore, in step S4, the production board only passes through a chemical debonding section.

[0020] Furthermore, in step S5, during full-board electroplating, the leveler concentration in the electroplating solution is controlled at 15-20 ml / L, and the brightener concentration is controlled at 2-3 ml / L.

[0021] Furthermore, in step S5, the time for full-plate electroplating is controlled within 120 minutes.

[0022] Furthermore, after step S5, the following steps are also included:

[0023] S6. On the production board, outer layer circuit production, solder mask production, surface treatment and molding processes are sequentially performed to obtain a circuit board.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The present invention first grinds the hole mouth to remove the burr by precision grinding and brushing, and the precision grinding and brushing method can reduce the damage to the hole mouth on the basis of ensuring the burr is ground off, thereby improving the burr problem of the hole mouth. Then, the hole is rinsed by adding sandblasting to reduce the fine glass fibers in the hole. When copper is deposited, the production board passes through a chemical degumming section to further clean the glass fibers on the hole wall, make the hole wall smooth, and improve the problem of copper nodules in the hole. Finally, a small current is used for full-board electroplating to further improve the problem of small hole diameter, thereby solving the existing quality problems of poor appearance and small hole diameter caused by drilling burr and copper nodules in the hole. DETAILED DESCRIPTION

[0026] 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.

[0027] Example

[0028] A method for manufacturing a circuit board shown in this embodiment includes the following processing steps in sequence:

[0029] (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.

[0030] (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). After development, the inner layer circuit pattern is formed; inner layer etching, the exposed and developed core board is etched to etch the inner layer circuit, and the inner layer line width is measured to be 3mil; inner layer AOI, and then check the inner layer circuit for defects such as open short circuits, circuit gaps, and circuit pinholes. Defective products are scrapped, and non-defective products are sent to the next process.

[0031] (3) Lamination: The browning speed is based on the browning thickness of the bottom copper. The core board, prepreg, and outer copper foil are laminated in sequence as required. Then, appropriate lamination conditions are selected according to the Tg of the sheet material to laminate the laminated board to form a production board.

[0032] (4) Drilling: Based on the existing drilling technology, drilling processing is performed on the production board according to the design requirements.

[0033] In the above, when drilling the production board, a phenolic pad is placed underneath and a coated aluminum sheet is placed above the production board to reduce the problem of flashing during drilling.

[0034] (5) Plate grinding: The production plate is precision-brushed to remove the burrs at the hole mouth. The process of grinding the burrs before precision brushing is not enough. The sandpaper used for grinding the burrs is relatively rough, which can easily cause deformation of the plate at the hole mouth.

[0035] In the above, 500-mesh sandpaper is used for precision brushing twice. Compared with the existing method of using 320-mesh brush and 500-mesh brush once each, the damage to the hole opening can be reduced while ensuring that the flash is removed. The 320-mesh sandpaper used in the existing method is relatively rough, which can easily cause deformation of the hole opening grinding plate.

[0036] In the above, the directions of the two brushings are perpendicular to each other, that is, the production board is brushed once horizontally and once vertically, that is, the production board is brushed once in the long side direction and once in the short side direction in sequence.

[0037] (6) Water washing: The production board is washed with high pressure water once, and the pressure during high pressure water washing is controlled at 70-80kg / cm 2 .

[0038] (7) Sandblasting: Sandblast the production board to flush the holes and reduce the fine glass fibers in the holes.

[0039] (8) Copper plating: A thin layer of copper is deposited on the board surface and hole wall by chemical copper plating. The backlight test is level 10, and the thickness of the copper plating in the hole is 0.5μm.

[0040] In the above, the existing process generally includes a bulking section (treating the hole wall with a bulking agent to make it bulky and softened for subsequent processing) and multiple chemical degumming sections (using chemical agents such as potassium permanganate to remove glue residue on the hole wall) before chemical copper deposition; but in this embodiment, the production board does not pass through the bulking section before chemical copper deposition to avoid generating more glass fibers on the hole wall due to bulking, and only passes through one chemical degumming section (i.e., only one chemical degumming cylinder is used to immerse and degumming the production board) to clean the glass fibers on the hole wall, make the hole wall smooth, and improve the copper nodules in the hole.

[0041] (8) Full-board electroplating: The full-board electroplating is performed at a current density of 1.15ASD for 120 minutes to thicken the hole copper and the board surface copper layer; here, a small current and long-term electroplating method is adopted to improve the electroplating uniformity and further avoid the problem of small hole diameter.

[0042] At present, the plating solution used for electroplating generally includes:

[0043] Accelerators (also known as brighteners) are usually small molecule sulfur-containing compounds. Their function is to accelerate the reduction of copper ions in blind holes. At the same time, they can form new copper plating nuclei to make the copper layer structure more delicate. They mainly include SPS (sodium polydisulfide propane sulfonate) and MPS (sodium 3-thiopropane sulfonate).

[0044] Inhibitors (also called carriers) are mostly polyether compounds, which are easily adsorbed on the active points of grain growth, can increase the resistance of electrochemical reactions, and enhance electrochemical polarization, thereby achieving the effect of refining grains and inhibiting the growth of plate coatings. Commonly used ones include polyethylene glycol, aromatic polyoxyethylene ethers, and nonylphenol and ethylene oxide reactants.

[0045] Leveling agents are usually nitrogen-containing heterocyclic compounds. They are more likely to be adsorbed on the protruding areas of the board surface, that is, the high current density areas, which slows down the electroplating speed there and inhibits the deposition of copper in the high current density areas. However, they are less adsorbed in the concave areas of the board surface and in the micro blind holes, so that the copper deposition effect here is not affected, thereby achieving the effect of leveling the board surface.

[0046] In this embodiment, the leveling agent concentration in the plating solution is controlled at 15-20 ml / L, and the brightener concentration is controlled at 2-3 ml / L during full-board electroplating. By improving the concentrations of the leveling agent and the brightener, the electroplating quality can be further improved.

[0047] (9) Production of outer circuits (positive film process): Transfer of outer pattern, using fully automatic exposure machine and positive circuit film, with 5-7 grid exposure ruler (21 grid exposure ruler) to complete the exposure of outer circuit, after development, the outer circuit pattern is formed on the production board; electroplating of outer pattern, and then copper plating and tin plating respectively on the production board, setting the electroplating parameters according to the required copper thickness, copper plating is 1.8ASD current density electroplating for 60 minutes on the whole board, tin plating is 1.2ASD current density electroplating for 10 minutes, tin thickness 3-5μm; then stripping, etching and tin stripping in turn, etching the outer circuit on the production board; outer layer AOI, using automatic optical inspection system, by comparing with CAM data, to detect whether the outer circuit has defects such as open circuit, gap, incomplete etching, short circuit, etc.

[0048] (10) 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.

[0049] (11) Surface treatment (nickel-gold immersion): The copper surface of the pad at the solder mask opening is chemically treated to uniformly deposit nickel and gold layers of a certain required thickness. The thickness of the nickel layer is 3-5 μm; the thickness of the gold layer is 0.05-0.1 μm.

[0050] (12) Electrical test: Test the electrical conductivity of the finished board. The test method used for this board is: flying probe test.

[0051] (13) Molding: According to the existing technology and design requirements, the circuit board is manufactured with a shape tolerance of + / -0.05mm.

[0052] (14) 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.

[0053] (15) FQA: Re-test the circuit board’s appearance, hole copper thickness, dielectric layer thickness, green oil thickness, inner layer copper thickness, etc. to see if they meet customer requirements.

[0054] (16) Packaging: According to the packaging method and packaging quantity required by the customer, the circuit boards are sealed and packed with desiccant and humidity card before shipment.

[0055] 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 will be changes in the specific implementation methods and application scopes. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A method for improving the flash and copper nodules in the holes of CEM-3 plates, characterized in that: The following steps are involved: S1. After drilling, the production plate is precisely brushed to remove the flash at the hole mouth; S2, high pressure water washing of the production board; S3, sandblasting the production plate to flush the inside of the hole; S4, copper deposition is performed on the production board. When copper deposition is performed, the production board does not pass through the bulking section but passes through the chemical degumming section, so as to clean the hole wall glass fiber through the chemical degumming section; S5. Full-plate electroplating is performed on the production board to thicken the hole copper and board surface copper layer. The current density during full-plate electroplating is 1.15ASD.

2. The method for improving the flash and copper nodules in the holes of CEM-3 sheet according to claim 1, characterized in that: In step S1, when the production board is drilled, a phenolic backing plate is placed underneath and a coated aluminum sheet is placed above.

3. The method for improving the flash and copper nodules in the holes of CEM-3 sheet according to claim 1, characterized in that: In step S1, 500-mesh sandpaper is used for precision grinding.

4. The method for improving the flash and copper nodules in the holes of CEM-3 sheet according to claim 1 or 3, characterized in that: In step S1, the production plate is precision-brushed twice.

5. The method for improving the flash and copper nodules in the holes of CEM-3 sheet according to claim 4, characterized in that: In step S1, the directions of the two brushing operations are perpendicular to each other.

6. The method for improving the flash and copper nodules in the holes of CEM-3 sheet according to claim 1, characterized in that: In step S2, the pressure during high pressure water washing is controlled at 70-80 kg / cm 2 .

7. The method for improving the flash and copper nodules in the holes of CEM-3 sheet according to claim 1, characterized in that: In step S4, the production board only passes through a chemical debonding section.

8. The method for improving the flash and copper nodules in the holes of CEM-3 sheet according to claim 1, characterized in that: In step S5, during full-board electroplating, the leveler concentration in the electroplating solution is controlled at 15-20 ml / L, and the brightener concentration is controlled at 2-3 ml / L.

9. The method for improving the flash and copper nodules in the holes of CEM-3 sheet according to claim 1, characterized in that: In step S5, the time for full-plate electroplating is controlled at 120 minutes.

10. The method for improving the flash and copper nodules in the holes of CEM-3 sheet according to claim 1, characterized in that: After step S5, the following steps are also included: S6. On the production board, outer layer circuit production, solder mask production, surface treatment and molding processes are sequentially performed to obtain a circuit board.