A method for improving gold precipitation efficiency

Abstract

The application discloses a method for improving gold plating efficiency, which comprises the following steps: adding sodium persulfate into an oil removing cylinder in a gold plating process, so that the tank solution in the oil removing cylinder comprises an oil removing agent and the sodium persulfate; and after a production plate to be plated with gold sequentially undergoes oil removing, water washing, pre-impregnation, activation, nickel plating, water washing and gold plating processes, a nickel-gold layer is formed on the production plate; wherein the oil removing process is carried out by using the oil removing cylinder with the sodium persulfate added in step S1, so as to simultaneously perform oil removing and micro-etching treatment on the production plate. By optimizing the process flow, the method reduces the micro-etching process and the second water washing process after the micro-etching in the gold plating process, thereby effectively improving the gold plating efficiency.

Description

Technical Field

[0001] This invention relates to the field of printed circuit board manufacturing technology, and specifically to a method for improving the efficiency of immersion gold plating. Background Technology

[0002] With the rapid development of the electronics industry, the PCB industry has increasingly higher requirements for efficiency and cost. So-called lean production requires greater research and development and innovation. In the PCB industry, the commonly used immersion gold (ENIG) surface treatment process is generally carried out using a gantry line. The specific immersion gold process is as follows: board loading - degreasing - three water washes - micro etching - two water washes - pre-immersion - water wash - activation - water wash - nickel immersion - water wash - immersion gold - recovery - water wash - drying - board unloading, a total of 16 processes. The overall immersion gold process takes 15 minutes.

[0003] The above-mentioned immersion gold process involves many steps and takes a long time. Immersion gold production line equipment occupies a large area and has low efficiency, so there is an urgent need to improve efficiency and reduce costs. Summary of the Invention

[0004] To address the aforementioned shortcomings of existing technologies, this invention provides a method for improving the efficiency of gold immersion. By optimizing the process flow, the micro-etching step and the second water washing step after micro-etching are reduced in the gold immersion process, thereby effectively improving the gold immersion efficiency.

[0005] To address the aforementioned technical problems, this invention provides a method for improving the efficiency of gold plating, comprising the following steps:

[0006] S1. Add sodium persulfate to the degreasing tank in the immersion gold process so that the tank solution contains both degreasing agent and sodium persulfate.

[0007] S2. After the production board to be immersed in gold undergoes degreasing, water washing, pre-immersion, activation, nickel immersion, water washing and immersion gold immersion processes in sequence, a nickel-gold layer is formed on the production board in sequence. The degreasing process uses a degreasing tank with sodium persulfate added in step S1 to degrease the production board at the same time as degreasing and micro-etching.

[0008] Furthermore, in the bath solution of step S1, the volume percentage of the degreasing agent is 8-12%.

[0009] Furthermore, in step S1, the sodium persulfate content in the bath is controlled at 40-60 g / L.

[0010] Furthermore, in step S1, sulfuric acid with a concentration of 3-5% is used as a solvent in the bath solution.

[0011] Furthermore, in step S2, the production plate is immersed in the degreasing tank for 3-4 minutes during the degreasing process.

[0012] Furthermore, the amount of micro-etching during degreasing treatment is controlled at 30-50 uinch.

[0013] Furthermore, in step S2, a water washing step is also included between pre-dip and activation, and between activation and nickel plating.

[0014] Furthermore, in step S2, after the gold immersion, the steps of washing with water and drying are also included in sequence.

[0015] Furthermore, the production board is a multilayer board with a solder resist layer already fabricated.

[0016] Furthermore, the production board is a multilayer board in which the inner core board and the outer copper foil are pressed together by a prepreg, and before the solder mask layer is made, the processes of drilling, copper plating, full-board electroplating and outer circuit fabrication are carried out on the multilayer board in sequence.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] This invention adds sodium persulfate to the degreasing tank, so that the tank solution not only has degreasing properties but also sodium persulfate has micro-etching properties. This transforms the degreasing tank into a degreasing-micro-etching tank, integrating the micro-etching process after degreasing into the existing process. This reduces the need for a post-degreasing micro-etching process and a second water washing process, resulting in a total reduction of three processes. After degreasing and water washing, the product can directly enter the pre-immersion process, effectively improving the time and efficiency of the immersion gold process. Furthermore, it reduces the need for a micro-etching tank and a subsequent second water washing tank in the immersion gold production line, thus improving the overall production efficiency. Compared to existing technologies, this new line equipment can save approximately 2.4 meters, reducing the space occupied by the equipment. Furthermore, it controls the sodium persulfate content in the degreasing cylinder to 40-60 g / L, which is lower than the 60-80 g / L sodium persulfate content in the existing separate micro-etching process. This is mainly because the existing separate micro-etching process takes 1.5-2 minutes, while the degreasing process takes 3-4 minutes. Therefore, the micro-etching process in the degreasing cylinder in this invention would extend the micro-etching time. To ensure the micro-etching amount meets the requirements, it is necessary to reduce the amount of sodium persulfate used.

[0019] In the method of this invention, sodium persulfate with micro-etching effect is added directly to the degreasing cylinder, rather than adding a micro-etching agent containing sodium persulfate. This is mainly because the degreasing solution and micro-etching agent in the degreasing cylinder generally use sulfuric acid with a concentration of 3-5% as a solvent. That is, sulfuric acid is present in the micro-etching agent in addition to sodium persulfate. If the micro-etching agent is added directly, it will change the concentration of sulfuric acid and degreasing agent in the degreasing cylinder. Therefore, by directly adding sodium persulfate in the method of this invention, the degreasing effect and micro-etching effect of the degreasing cylinder can be maintained well, thus improving the production quality. Detailed Implementation

[0020] To better understand the technical content of this invention, the technical solution of this invention will be further introduced and explained below in conjunction with specific embodiments.

[0021] Example

[0022] The current traditional immersion gold process is as follows: plate loading - degreasing - three water washes - micro-etching - two water washes - pre-immersion - water wash - activation - water wash - nickel immersion - water wash - immersion gold - recovery - water wash - drying - plate unloading. The entire production process takes about 15 minutes, meaning that it takes about 15 minutes to complete the immersion gold production of one batch of production plates. The daily production time of the immersion gold production line is calculated as 22 hours, excluding maintenance. In this immersion gold process, the daily production capacity of plates is 22 * ​​60 / 15 = 88 batches.

[0023] The optimized immersion gold process in this embodiment is as follows: plate loading - degreasing and micro-etching - three water rinses - pre-immersion - water rinse - activation - water rinse - nickel immersion - water rinse - immersion gold - recovery - water rinse - drying - plate unloading. Since the degreasing and micro-etching processes generally use sulfuric acid with a concentration of 3-5% as a solvent, the characteristic that the same solvent can be combined can be taken advantage of to combine the degreasing tank and the micro-etching tank into one tank, thereby reducing the steps of the micro-etching tank and the second water rinse. The optimized entire production process takes about 13.5 minutes, that is, the immersion gold production line can complete the immersion gold production of one batch of production plates every 13.5 minutes. The daily production time of the immersion gold production line is calculated as 22 hours, excluding maintenance. In this immersion gold process, the daily production volume of plates is 22*60 / 13.5=97 batches. Therefore, compared with the existing process, the production efficiency of the optimized process is increased by (97-88) / 88=10.2%.

[0024] This embodiment illustrates a method for manufacturing a circuit board, which can effectively improve the efficiency of immersion gold plating, and includes the following processing steps in sequence:

[0025] (1) Cutting: Cut out several core boards according to the panel size of 520mm×620mm. The thickness of the core board is 0.5mm, and the copper layer thickness on both surfaces of the core board is 0.5oz.

[0026] (2) Inner layer circuit fabrication (negative film process): Inner layer pattern transfer, photosensitive film is coated using a vertical coating machine, and the film thickness is controlled at 8μm. A fully automatic exposure machine is used to expose the inner layer circuit on the core board with 5-6 exposure rulers (21 exposure rulers). After development, the inner layer circuit pattern is formed; Inner layer etching, the inner layer circuit is etched out on the core board after exposure and development. The inner layer line width is measured to be 3mil; Inner layer AOI, and then the inner layer circuit is inspected for defects such as open circuits, short circuits, line gaps, and line pinholes. Defective products are scrapped, and defect-free products are sent to the next process.

[0027] (3) Lamination: The browning speed is based on the thickness of the bottom copper. The core board, prepreg, and outer copper foil are stacked in sequence as required. Then, according to the Tg of the board material, appropriate lamination conditions are selected to press the laminated board to form the production board.

[0028] (4) Drilling: Drilling is performed on the production board according to the design requirements based on existing drilling technology.

[0029] (5) Copper plating: A thin layer of copper is deposited on the board surface and hole walls using chemical copper plating. The backlight test is level 10, and the copper plating thickness in the hole is 0.5μm.

[0030] (6) Full-board electroplating: Electroplating the entire board for 120 minutes at a current density of 18ASF to thicken the copper layer in the holes and on the board surface.

[0031] (7) Fabrication of outer layer circuitry (positive film process): The outer layer pattern is transferred using a fully automatic exposure machine and positive film circuitry film. The outer layer circuitry is exposed using an exposure ruler of 5 to 7 divisions (or 21 divisions). After development, the outer layer circuitry pattern is formed on the production board. The outer layer pattern is 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 1.8 ASD for 60 minutes, and tin plating is performed at a current density of 1.2 ASD for 10 minutes, with a tin thickness of 3 to 5 μm. Then, the film is removed, etched, and tin is removed in sequence to etch the outer layer circuitry on the production board. The copper thickness of the outer layer circuitry is greater than or equal to 70 μm. The outer layer AOI is performed using an automatic optical inspection system. By comparing with the CAM data, the outer layer circuitry is inspected for defects such as open circuits, gaps, incomplete etching, and short circuits.

[0032] (8) Solder resist and screen printing: After screen printing solder resist ink on the surface of the production board, it is then subjected to pre-curing, exposure, development and heat curing treatments in sequence to cure the solder resist ink into a solder resist layer; specifically, the solder resist ink on the TOP side and the characters on the TOP side are added with "UL mark", thereby coating a layer on the lines and substrates that do not need to be soldered to prevent bridging between lines during soldering, provide a permanent electrical environment and chemical corrosion resistance, and at the same time beautify the appearance.

[0033] (9) Surface treatment (immersion nickel gold): including the following processes:

[0034] a. Sodium persulfate is added to the degreasing tank in the immersion gold process so that the tank solution includes degreasing agent and sodium persulfate, and the degreasing tank is formed into a degreasing and micro-etching tank that has both degreasing and micro-etching functions.

[0035] The aforementioned degreasing micro-etching tank also includes sulfuric acid with a volume percentage concentration of 3-5%, used as a solvent for the degreasing agent and sodium persulfate. Additionally, the volume percentage of the degreasing agent in the tank is 8-12%, consistent with the degreasing agent content in existing processes. The sodium persulfate content is controlled at 40-60 g / L, which is lower than the 60-80 g / L sodium persulfate content in the separate micro-etching step in existing processes. This is mainly because the separate micro-etching step in existing processes takes 1.5-2 minutes, while the degreasing step takes 3-4 minutes. Therefore, the simultaneous micro-etching process in the degreasing tank in this embodiment would lengthen the micro-etching time. To ensure the micro-etching amount meets requirements, it is necessary to reduce the amount of sodium persulfate used to reduce the micro-etching amount per unit time.

[0036] b. Immerse the production board with the solder mask layer already made in the degreasing and micro-etching tank in step a to perform degreasing and micro-etching treatments simultaneously. The purpose of degreasing is to wash away oil stains, fingerprints, etc. on the board surface, while the purpose of micro-etching is to obtain a fresh copper surface to facilitate the activation of palladium. The immersion time is 3-4 minutes, and the micro-etching amount is controlled at 30-50 uinch.

[0037] c. Then, the production board undergoes three water washing, pre-dip, water washing, activation, water washing and nickel plating processes in sequence, and a nickel layer is deposited on the copper surface of the solder pads at the solder mask opening position.

[0038] d. After the nickel layer is deposited, the production board undergoes a water washing and immersion gold process in sequence, and a gold layer is deposited on the nickel layer of the production board.

[0039] e. After immersion gold plating, the production boards undergo a series of water washing and drying processes to ensure that the surface of the production boards is clean and free of contamination, and to avoid the problem of gold surface oxidation.

[0040] (10) Electrical test: Test the electrical conductivity of the finished board. The test method used for this board is: flying probe test.

[0041] (11) Molding: Based on existing technology and design requirements, the circuit board is made with a shape tolerance of + / -0.05mm.

[0042] (12) FQC: Inspect the appearance of the circuit board according to the customer's acceptance standards and our company's inspection standards. If there are any defects, repair them in time to ensure excellent quality control for customers.

[0043] (13)FQA: Re-test the appearance of the circuit board, the thickness of the copper in the holes, the thickness of the dielectric layer, the thickness of the solder mask, the thickness of the inner copper layer, etc. to see if they meet the customer's requirements.

[0044] (14) Packaging: The circuit boards are sealed according to the packaging method and quantity required by the customer, and desiccant and humidity card are placed in the packaging before shipment.

[0045] The technical solutions provided by the embodiments of the present invention have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of the embodiments of the present invention. The descriptions of the embodiments above are only for helping to understand the principles of the embodiments of the present invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the embodiments of the present invention. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A method for improving gold deposition efficiency, characterized in that, Includes the following steps: S1. Add sodium persulfate to the degreasing tank in the immersion gold process so that the tank solution contains degreasing agent and sodium persulfate; the sodium persulfate content in the tank solution is controlled at 40-60g / L, and sulfuric acid with a concentration of 3-5% is used as solvent in the tank solution. S2. After the production board to be immersed in gold undergoes degreasing, water washing, pre-immersion, activation, nickel immersion, water washing and immersion gold immersion processes in sequence, a nickel-gold layer is formed on the production board in sequence. Among them, the degreasing process adopts the degreasing tank with sodium persulfate added in step S1 to degrease the production board at the same time to degrease and micro-etch. During the degreasing process, the production board is immersed in the degreasing tank for 3-4 minutes.

2. The method for improving gold precipitation efficiency according to claim 1, wherein, In the bath solution of step S1, the volume percentage of the degreasing agent is 8-12%.

3. The method for improving gold precipitation efficiency according to claim 1, wherein, The amount of micro-etching during degreasing treatment should be controlled at 30-50 uinch.

4. The method for improving gold precipitation efficiency according to claim 1, wherein, In step S2, a water washing step is also included between pre-dip and activation, and between activation and nickel plating.

5. The method for improving gold precipitation efficiency according to claim 1, wherein, In step S2, after immersion gold, the process also includes washing with water and drying.

6. The method for improving gold precipitation efficiency according to claim 1, wherein, The production board is a multilayer board with a solder resist layer already fabricated.

7. The method for improving the efficiency of immersion gold plating according to claim 6, characterized in that, The production board is a multilayer board in which the inner core board and the outer copper foil are pressed together by a prepreg. Before the solder mask layer is made, the multilayer board is first drilled, copper plating is performed, the whole board is electroplated, and the outer circuit is made.