Gold melting process of micro-spacing printed circuit board

Abstract

The invention provides an electroless gold plating process for a micro-spacing printed circuit board, which comprises the following steps of: (1) immersing a PCB (Printed Circuit Board) in a cleaning solution for cleaning, adding the cleaned PCB into an activating agent for activating treatment, and forming a layer of uniform activated film on the surface of the PCB; (2) adding the activated PCB into a post-immersion agent for cleaning; and (3) adding the PCB treated in the step (2) into a nickel sulfate solution for nickel melting to obtain a finished product. According to the chemical gold process of the micro-spacing printed circuit board, through the improved pretreatment process and the optimized chemical gold solution formula, the phenomenon that palladium remains on a base material and nickel gold remains on the base material in the chemical gold process is effectively reduced, the risk of gold permeation is reduced, the electrical performance and reliability of the micro-spacing printed circuit board are improved, and through experimental verification, the chemical gold process has good application prospects. The PCB gold infiltration reject ratio of the technology is reduced to below 1% from above 5% of the traditional technology.

Description

Technical Field

[0001] This invention relates to the field of printed circuit board technology, and in particular to a chemical gold plating process for micro-pitch printed circuit boards. Background Art

[0002] With the rapid development of electronic technology, various electronic devices have increasingly higher requirements for PCB integration. In order to achieve higher integration, PCB circuit design is constantly moving towards miniaturization, with line width and line spacing gradually decreasing, currently reaching a level of a few micrometers or even smaller. This miniaturized design can increase the number of lines and the layout density of electronic components within a limited space, thereby improving the performance and functionality of electronic devices. Due to the continuous iteration and updating of technical requirements, the requirements for electroless gold plating processes are becoming more stringent. Due to the limitations of existing electroless gold plating processes, the fine lines cannot fully meet the increasingly demanding product requirements. Therefore, the expectation of upgrading electroless gold plating processes is imminent, leading to the development of new technologies to improve this situation.

[0003] Traditional electroless gold plating processes have the following problems when dealing with fine-pitch circuitry: 1. Gold seepage problem: In the fine-pitch circuits, the chemical solution is not easy to be washed off during the gold plating process, which can easily cause the gold layer to deposit in non-target areas, i.e., gold seepage. Gold seepage may cause short circuits between adjacent circuits, which seriously affects the functionality and reliability of the PCB.

[0004] 2. Gold Adhesion Issues: Due to the traditional chemical gold plating process, the cleaning effect of the chemicals on the substrate and ink residue is not good, resulting in the residue of activated palladium on the substrate and ink surface. According to the principle of chemical reaction, the areas with activated palladium residue will undergo a catalytic reaction and deposit nickel in the nickel bath, resulting in abnormal gold adhesion on the substrate and ink surfaces. This can easily cause quality problems during the soldering process, seriously affecting the normal use of the soldering process, and consequently affecting the overall performance and stability of the PCB.

[0005] 3. Difficult to clean: The gaps between the fine-pitch lines are narrow, making it difficult to completely clean the solution after gold plating. The residual solution is not easy to clean completely, which can cause gold penetration and short circuit abnormalities when starting the plating in the nickel bath. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a chemical gold plating process for micro-pitch printed circuit boards, effectively solving the problems of traditional chemical gold plating processes on micro-pitch lines.

[0007] The technical solution adopted in the present invention is: A gold plating process for micro-pitch printed circuit boards, comprising the following steps: (1) Immerse the PCB board in the cleaning solution for cleaning, and add the cleaned PCB board to the activator for activation treatment to form a uniform activation film on the surface of the PCB board. (2) The activated PCB board is then cleaned in a post-immersion solution; (3) Add the PCB board processed in step (2) into a nickel sulfate solution to dissolve nickel and obtain the finished product.

[0008] Preferably, the electroplating process of the micro-pitch printed circuit board includes, by mass percentage, the cleaning solution in step (1) comprising 8-10% quaternary ammonium salt, 25-30% diethylene glycol and 60-67% water.

[0009] Preferably, the electroplating process of the micro-pitch printed circuit board includes the following steps: the cleaning temperature in step (1) is 40℃-50℃ and the cleaning time is 4-6min.

[0010] Preferably, the gold plating process of the micro-pitch printed circuit board includes: in step (1), the activator is palladium sulfate, the palladium content in the palladium sulfate is 10-18 ppm, the activation time is 2-4 min, and the activation temperature is 23-28℃.

[0011] Preferably, the gold plating process of the micro-pitch printed circuit board includes the following steps: the cleaning temperature in step (2) is 20℃-25℃ and the time is 1-3min.

[0012] Preferably, the gold plating process of the micro-pitch printed circuit board includes, by mass percentage, the post-immersion agent in step (2) comprising 0.5-1% sodium sulfate, 4-6% sodium chloride, 0.1%-0.2% organic ether, and 92.8-95.4% water.

[0013] Preferably, in the electroless gold process of the micro-pitch printed circuit board, the temperature of nickel plating in step (3) is 75°-85°C and the time is 20-30 min.

[0014] Preferably, in the electroless gold plating process of the micro-pitch printed circuit board, the mass concentration of the nickel sulfate solution in step (3) is 4.6-5.2 g / l.

[0015] Advantages of this invention: (1) The gold plating process of the micro-pitch printed circuit board of the present invention effectively reduces the phenomenon of residual palladium on nickel gold on the substrate during the gold plating process by improving the pretreatment process and optimizing the gold plating solution formula, thereby reducing the risk of gold penetration and improving the electrical performance and reliability of the micro-pitch circuit of the PCB. After experimental verification, the gold penetration defect rate of the PCB board using the process of the present invention is reduced from more than 5% in the traditional process to less than 1%.

[0016] (2) The electroplating process of the micro-pitch printed circuit board of the present invention, with precise parameter control and optimized post-immersion solution, makes the palladium layer deposition on the micro-pitch circuit more uniform, so that no activation agent remains on the substrate and ink surface, and palladium is uniformly deposited on the circuit and PAD, which significantly improves the overall performance and stability of the PCB.

[0017] (3) The gold plating process of the micro-pitch printed circuit board of the present invention activates the uniformity of palladium deposition, so that during nickel plating, nickel is uniformly deposited on the circuit and pads by catalytic reaction, with uniform thickness, significantly improving reliability and extending the service life of the PCB; under the premise of ensuring quality, this patented process greatly reduces the gold plating defect rate by optimizing the process flow and parameters, and at the same time reduces rework and scrap caused by defective products, thus reducing production costs; compared with the traditional process, the production efficiency is increased by more than 20%, and the production cost is reduced by about 15%. Attached Figure Description

[0018] Figure 1 This is a microscope image of the PCB sample after processing in Embodiment 1 of the present invention.

[0019] Figure 2 This is a microscope image of the PCB sample after processing in Embodiment 2 of the present invention.

[0020] Figure 3 This is a microscope image of the PCB sample after processing in Comparative Example 1 of this invention. Detailed Implementation

[0021] The present invention will be further described below with reference to specific embodiments.

[0022] The process of this invention first involves immersing the PCB in a cleaning solution, which contains effective substances such as quaternary ammonium salt and diethylene glycol (defined as Y). - It has good permeability and adsorption properties, and can fill the micropores on the plate surface, reducing the need for Pd activation in subsequent processes. 2+ It can also react with residual Pd in ​​the micropores. 2+ The reaction generates PdY2, which deactivates the PdY2 and prevents further reaction in the nickel bath, thus preventing plating penetration. Meanwhile, residual cleaning solution in the micropores of the copper surface is effectively removed through micro-etching. Ultrasonic cleaning removes surface impurities such as oil, dust, and oxides. The cleaning solution effectively dissolves and removes various contaminants without damaging the PCB surface. Then, an activation treatment is performed to form a uniform activation film on the PCB surface, providing excellent active centers for subsequent gold plating reactions. The concentration of the activator and the treatment time are precisely controlled to ensure consistent activation results.

[0023] Secondly, after activation, when the PCB board enters the post-dip bath, the post-dip agent wets the PCB substrate and board surface. Because the surface tension of the post-dip agent is similar to that of the substrate and board surface, it can completely wet the substrate and board surface. The post-dip agent, through its free radical functional groups, chelates with the residual activated palladium on the substrate and board surface to form easily washable chelates. Through circulation and electrical vibration, the board is thoroughly cleaned, leaving no residual activated palladium solution on the substrate and board surface. The mechanism is as follows: a. Pd(OH) α → Pd 2＋ ; b. Pd 2＋ →Pd(XX) β ; c. Wash thoroughly The working principle of the post-dip agent is to enhance its surface wetting ability on the substrate, allowing it to fully penetrate the substrate and remove residual activating agents. This enhanced wetting ability requires the surface tension of the post-dip agent and the substrate to be nearly identical, meaning a reduction in the surface tension of the post-dip agent allows for better wetting, diffusion, and cleaning of the substrate surface, thus maximizing or even completely removing residual activating agents. Without residual activating agents on the substrate, there will be no plating points on the nickel plating substrate surface, preventing gold penetration and, in severe cases, short circuits, which affect PCB functionality, lead to scrap, and impact costs and efficiency. This invention's post-dip agent solves the problem of residual activating agents on the substrate between fine lines, avoiding the quality abnormalities caused by gold penetration and short circuits during nickel plating in the nickel bath. This invention achieves a perfect match between the post-dip agent and the surface tension of the substrate between the activating agents and fine lines, maximizing the complete removal of residual activating agents and controlling costs.

[0024] Finally, after the residual activated palladium on the substrate and board surface is completely cleaned by the post-immersion solvent, leaving no activated palladium residue on the substrate and board surface, the cleaned board enters the nickel bath for nickel plating. Nickel ions in the nickel sulfate solution react with palladium to produce elemental nickel, which is then deposited onto the copper surface. (Chemical nickel plating reaction:) a. Dehydrogenation of H2PO2 － →·HPO2 － + H; b. Oxidation of HPO2 － + OH － → H2PO3 － + e － ; c. Then combine H + H → H2; d. Oxidation of H₂ + OH⁻ － → H2O + e － ; e. Metal precipitation of Ni 2＋ + 2e － → Ni; f. Hydrogen gas is produced as 2H₂O + 2e⁻ － → H2 + 2OH － ; g. Phosphocoeluting mNi 2＋ + H2PO2 － + (2 m +1)e － → NimP + 2 OH － ; As can be seen from the nickel plating reaction mechanism, where there is activated palladium, a plating point will be formed. On the substrate and ink surface where there is no residual activated palladium, there will be no plating point for nickel plating. Nickel plating will only be carried out on the copper surface to meet the corresponding nickel thickness quality requirements. Nickel plating will not be carried out on the substrate and ink surface to ensure that the performance of the PCB is not affected.

[0025] Example 1 A gold plating process for micro-pitch printed circuit boards includes the following steps: (1) The PCB board with a line width of 3μm and a line spacing of 4μm was immersed in a cleaning solution for cleaning. The cleaning solution included 10% quaternary ammonium salt, 25% diethylene glycol and 65% water. The quaternary ammonium salt was sodium quaternary ammonium salt, and the chemical formula of sodium quaternary ammonium salt was [(CH3)4N]. + [CH3COO·Na] - The cleaning temperature was 40℃, the cleaning time was 4min, and the cleaned PCB board was added to palladium sulfate activator for activation treatment. Palladium was homogenized on the PCB board. The concentration of palladium in the activator was 10ppm, the activation time was 2min, and the activation temperature was 23℃, forming a uniform activation film on the PCB board surface. (2) The activated PCB board is added to the post-dip agent in the post-dip tank for cleaning. The cleaning temperature is 20°C and the time is 1 min. The post-dip agent includes 1% sodium sulfate, 5% sodium chloride, 0.1% diphenyl ether, and 93.9% water. The chemical formula of diphenyl ether is (C6H5)2O. It completely removes palladium from the surface of the ink on the PCB board and in the gaps in the activation tank. (3) Add the PCB board processed in step (2) into a nickel sulfate solution to nickel-metallize it. The mass concentration of the nickel sulfate solution is 4.6 g / L, the nickel-metallization temperature is 75°C, and the time is 20 min to obtain the finished product.

[0026] The processed PCB samples were inspected under a microscope, and no gold penetration was found. The gold layer thickness was measured, and the deviation at different locations was within ±0.1μm. Surface resistance testing showed uniform resistance with no significant differences. (See details...) Figure 1.

[0027] Example 2 A gold plating process for micro-pitch printed circuit boards includes the following steps: (1) Immerse the PCB board with a line width of 2μm and a line spacing of 3μm in the cleaning solution for cleaning. The cleaning solution includes 10% quaternary ammonium salt, 25% diethylene glycol and 65% water. The quaternary ammonium salt is sodium quaternary ammonium salt, and the chemical formula of sodium quaternary ammonium salt is [(CH3)4N]. + [CH3COO·Na] - The cleaning temperature was 45℃, the cleaning time was 4.5 min, and the cleaned PCB board was then added to palladium sulfate activator for activation treatment. The concentration of palladium in the activator was 15 ppm, the activation time was 2.5 min, and the activation temperature was 25℃, forming a uniform activation film on the surface of the PCB board. (2) The activated PCB board is added to the post-immersion agent for cleaning. The cleaning temperature is 24℃ and the time is 1.5min. The post-immersion agent includes 1% sodium sulfate, 5% sodium chloride, 0.1% diphenyl ether, and 93.9% water. The chemical formula of diphenyl ether is (C6H5)2O. It completely removes palladium from the surface of the ink on the PCB board and in the gaps of the activation tank. (3) Add the PCB board processed in step (2) into a nickel sulfate solution to nickel-metallize it. The mass concentration of the nickel sulfate solution is 5 g / L, the nickel-metallization temperature is 80℃, and the time is 25 min to obtain the finished product.

[0028] The processed PCB samples were inspected under a microscope, and no gold penetration was found. The gold layer thickness was measured, and the deviation at different locations was within ±0.1μm. Surface resistance testing showed uniform resistance with no significant differences. (See details...) Figure 2 .

[0029] Example 3 A gold plating process for micro-pitch printed circuit boards includes the following steps: (1) Immerse the PCB board with a line width of 2μm and a line spacing of 3μm in the cleaning solution for cleaning. The cleaning solution includes 10% quaternary ammonium salt, 25% diethylene glycol and 65% water. The quaternary ammonium salt is sodium quaternary ammonium salt, and the chemical formula of sodium quaternary ammonium salt is [(CH3)4N]. + [CH3COO·Na] - The cleaning temperature was 50℃, the cleaning time was 6 minutes, and the cleaned PCB board was then added to palladium sulfate activator for activation treatment. The concentration of palladium in the activator was 18 ppm, the activation time was 4 minutes, and the activation temperature was 28℃, forming a uniform activation film on the surface of the PCB board. (2) The activated PCB board is added to the post-immersion agent for cleaning. The cleaning temperature is 25℃ and the time is 3min. The post-immersion agent includes 1% sodium sulfate, 5% sodium chloride, 0.1% diphenyl ether, and 93.9% water. The chemical formula of diphenyl ether is (C6H5)2O. It completely removes palladium from the surface of the ink on the PCB board and in the gaps of the activation tank. (3) Add the PCB board processed in step (2) into a nickel sulfate solution to nickel ionize. The concentration of the nickel sulfate solution is 5 g / L, the nickel ionization temperature is 85℃, and the time is 30 min to obtain the finished product.

[0030] Comparative Example 1 A gold plating process for micro-pitch printed circuit boards includes the following steps: (1) The PCB board with a line width of 3μm and a line spacing of 4μm was immersed in the cleaning solution for cleaning. The cleaning solution was a sulfuric acid solution with a mass concentration of 4%, the cleaning temperature was 40℃, the cleaning time was 4min, and the cleaned PCB board was added to palladium sulfate activator for activation treatment. Palladium was homogenized on the PCB board. The concentration of palladium in the activator was 10ppm, the activation time was 2min, the activation temperature was 23℃, and a uniform activation film was formed on the surface of the PCB board. (2) The activated PCB board is cleaned in a 4% sulfuric acid solution at a temperature of 20°C for 1 minute. (3) Add the PCB board processed in step (2) into a nickel sulfate solution to nickel ionize. The concentration of the nickel sulfate solution is 5 g / L, the nickel ionization temperature is 85℃, and the time is 30 min to obtain the finished product.

[0031] Multiple PCB samples of the same specifications as in Example 1 were selected and treated using a traditional electroless gold plating process. The treated samples were then subjected to performance testing and comparison. The results showed that the samples using the traditional electroless gold plating process had a gold penetration defect rate of 8%, a gold layer thickness deviation of over ±0.3μm, and uneven surface resistance. In contrast, the samples using the patented process had a gold penetration defect rate of only 0.5%, a gold layer thickness deviation within ±0.1μm, and uniform surface resistance. All performance characteristics were significantly superior to the traditional process. See details below. Figure 3 .

[0032] The comparison between Examples 1-3 and Comparative Example 1 fully demonstrates the effectiveness and superiority of the electroplating process for micro-pitch printed circuit boards proposed in this patent.

[0033] Finally, it should be noted that the above specific embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A gold plating process for micro-pitch printed circuit boards, characterized in that: The following steps are involved: (1) Immerse the PCB board in the cleaning solution for cleaning, and add the cleaned PCB board to the activator for activation treatment to form a uniform activation film on the surface of the PCB board. (2) The activated PCB board is then cleaned in a post-immersion solution; (3) Add the PCB board processed in step (2) into a nickel sulfate solution to dissolve nickel and obtain the finished product.

2. The electroless gold plating process for micro-pitch printed circuit boards according to claim 1, characterized in that: The cleaning solution in step (1) comprises 8-10% quaternary ammonium salt, 25-30% diethylene glycol and 60-67% water by mass percentage.

3. The electroless gold plating process for micro-pitch printed circuit boards according to claim 1, characterized in that: The cleaning temperature in step (1) is 40℃-50℃, and the cleaning time is 4-6 minutes.

4. The electroless gold plating process for micro-pitch printed circuit boards according to claim 1, characterized in that: In step (1), the activator is palladium sulfate, the palladium content in palladium sulfate is 10-18 ppm, the activation time is 2-4 min, and the activation temperature is 23-28℃.

5. The electroless gold plating process for micro-pitch printed circuit boards according to claim 1, characterized in that: The cleaning temperature in step (2) is 20℃-25℃, and the time is 1-3min.

6. The electroplating process for micro-pitch printed circuit boards according to claim 1, characterized in that: By mass percentage, the post-immersion agent in step (2) includes 0.5-1% sodium sulfate, 4-6% sodium chloride, 0.1%-0.2% organic ether, and 92.8-95.4% water.

7. The electroless gold plating process for micro-pitch printed circuit boards according to claim 1, characterized in that: In step (3), the temperature for nickel plating is 75°-85°C and the time is 20-30 min.

8. The electroplating process for micro-pitch printed circuit boards according to claim 1, characterized in that: The mass concentration of the nickel sulfate solution in step (3) is 4.6-5.2 g / L.

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