Surface treatment process for production of multi-layer PCB (Printed Circuit Board)

Abstract

The invention discloses a surface treatment process for multi-layer PCB production, and particularly relates to the technical field of PCB production, and the surface treatment process comprises the following eleven steps: step 1, checking whether a PCB is complete or not, removing burrs on the surface of the PCB, then cleaning to remove stains on the surface, and finally drying; 2, spraying a protective coating on the surface of the dried PCB; 3, reducing copper ions in the solution into metal copper and depositing the metal copper on the surface of the PCB; step 4, pattern electroplating is carried out on the PCB after copper deposition and drying; and 5, printing characters, marks and the like on the surface of the PCB in a silk-screen manner. According to the method, the perfume is added into the solution into which the PCB needs to be immersed, so that the PCB carries the fragrance after completing the reaction, the PCB is cleaned until the fragrance is dissipated, and the fragrance can be used as a basis for judging whether the PCB is cleaned up, and in this way, whether the PCB is cleaned up or not can be judged more intuitively, and the probability of solution residue is greatly reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of PCB production, and in particular to a surface treatment process for producing multi-layer PCBs. Background Art

[0002] A multi-layer PCB refers to a printed circuit board with more than two layers. Common specifications include four layers, six layers, and even up to thirty-two layers. Due to its small size, high reliability, and strong anti-interference ability, it is widely used in high-speed, high-frequency, and high-reliability circuit design.

[0003] Generally speaking, the production and processing of PCB boards usually requires multiple steps and is very complicated. For example, a PCB board production surface treatment process with publication number CN117677071A in the prior art requires the PCB board to be immersed in a chemical solution in multiple steps such as electroplating, tin plating, and copper plating.

[0004] Since PCBs need to be immersed in different solutions repeatedly, they need to be cleaned each time after being taken out of the previous solution before being immersed in the next solution. However, it is difficult to visually determine whether the solution has been cleaned thoroughly by visual observation alone, so it is easy for solution residue to occur, which may interfere with the surface treatment process. Summary of the Invention

[0005] The present invention aims to provide a surface treatment process for the production of multi-layer PCBs. By cleaning the PCBs until the fragrance dissipates, it can be used as a basis for judging whether the PCBs have been cleaned. This allows for a more intuitive judgment of whether the PCBs have been cleaned, greatly reduces the probability of solution residue, and avoids interference with the surface treatment process.

[0006] In order to achieve the above object, the present invention provides the following technical solution: a surface treatment process for producing multi-layer PCB boards, the specific steps of which are as follows:

[0007] Step 1: Preparation: Check whether the PCB board is intact. PCB boards with cracks, scratches, etc. will be directly removed without further processing. Remove burrs on the surface of the PCB board, then clean and remove surface stains, and finally dry;

[0008] Step 2: Coating: Spray a protective coating on the dried PCB surface to improve the waterproofness and corrosion resistance of the PCB board, improve its surface adhesion, and extend its service life;

[0009] Step 3: Copper deposition: Immerse the PCB in a solution containing copper ions, such as copper sulfate, and add a reducing agent, such as formaldehyde. Meanwhile, add fragrance to the solution, preferably water-soluble essential oils, such as lavender essential oil and lemongrass essential oil. The reducing agent reduces the copper ions in the solution to metallic copper, which is deposited on the PCB surface. After copper deposition, clean the residual solution on the PCB surface until there is no fragrance odor on the surface of the PCB, indicating that the residual solution has been cleaned. Finally, dry the PCB.

[0010] Step 4: After copper deposition and drying, the PCB board is pattern-plated. First, a cover layer is sprayed on the PCB board. Then, part of the cover layer is removed according to the pre-designed pattern. Chemical etching or laser exposure can be used to remove the cover layer, exposing the area to be plated, while other areas remain protected. The circuit board is then immersed in the plating solution for electroplating. Fragrance is also added to the plating solution for the same purpose as in step 3. After electroplating, the remaining plating solution is cleaned until the fragrance is completely dissipated.

[0011] Step 5: Print characters and marks on the surface of the PCB board by silk screen printing, including component numbers and nominal values, component outlines, manufacturer logos, production dates, etc., as well as various annotation characters. This information helps with circuit installation, maintenance, and plug-in operations during the production process. Fluorescent agents are added to the printing coating to enable identification of relevant information in dim light.

[0012] Step 6: Immersion nickel gold: Palladium is replaced on the copper surface through a chemical reaction, and a nickel-phosphorus alloy layer is chemically plated on the palladium core. The PCB board is then immersed in a solution containing nickel ions, causing nickel to be deposited where the palladium is attached. A layer of gold is then plated on the nickel surface through a replacement reaction. The PCB board is immersed in a solution containing gold ions, causing the gold to precipitate and cover the nickel surface. Flavoring is added to the solution during the nickel gold immersion process, and its function is the same as in step 3. After the PCB board is removed from each solution, it needs to be cleaned until the fragrance is completely dissipated. This operation not only improves the conductivity of the PCB board but also plays a protective role and extends its service life. A too low pH value will lead to excessive hydrogen precipitation, affecting the quality of the coating; while a too high pH value will increase the porosity and brittleness of the coating, resulting in a decrease in coating performance.

[0013] Step 7: Carbon oil printing: A layer of conductive carbon oil is printed on the PCB surface using silk screen printing. This can be used as a contact conductor for key positions or as a conductor with a certain resistance requirement. Carbon oil can replace some metal circuits, providing good conductivity while offering greater flexibility, making it suitable for complex design requirements. In addition, carbon oil can also serve as an electromagnetic shielding layer to block external electromagnetic interference and improve the PCB's anti-interference ability.

[0014] Step 8: Spray tin: Immerse the PCB board in molten solder, and then use hot air to blow off the excess solder on its surface and in the metallized holes, so as to obtain a smooth, uniform and bright solder coating layer. Its function is to prevent oxidation and corrosion, and improve welding quality and reliability.

[0015] Step 9: Use silk screen printing to print a layer of peelable oil pattern on the surface of the circuit board, which is mainly used for the selective assembly needs of the later assembly factory. It is required that the connected peelable pattern can be completely torn off after curing or after wave soldering without residue;

[0016] Step 10: Immersion silver and immersion tin: Immerse the PCB in a solution containing silver ions to precipitate metallic silver and deposit it on the PCB surface. Then, immerse it in a solution containing tin ions to precipitate metallic tin and deposit it on the PCB surface. Flavoring is added to the solutions during the immersion silver and tin processes, and its function is the same as in step 3. After removing the PCB from each solution, it needs to be cleaned until the fragrance completely dissipates. The functions of immersion silver and immersion tin are to improve conductivity, enhance solderability, protect the copper layer, and enhance product reliability and durability.

[0017] Step 11: Print multiple dot-shaped indicator marks on the surface of the PCB board. The diameter of each mark point is 3-5mm. The mark points are distributed throughout the PCB board and do not block the original annotation information on the PCB board. Use three different colors of paint to print three times in a superimposed manner. After the previous print paint is completely dry, print the next one. After the three prints are completed and the paint is completely dry, the surface treatment process of the PCB board is completed.

[0018] Furthermore, the main components of the protective coating in step 2 include acrylic resin, fluorocarbon resin, stabilizer and anti-corrosion agent.

[0019] Furthermore, in step 3, the water temperature and pH value are monitored in real time during the copper deposition process, and the water temperature is maintained at 60° C. and the pH value is maintained at 12-13.5.

[0020] Furthermore, in step six, before nickel-gold plating, it is necessary to clean the dirt on the surface of the circuit board, and then immerse the PCB board in a solution containing palladium ions, maintaining it at 20-30°C, and the palladium ion concentration is controlled at 20-40ppm, so that a layer of palladium is precipitated on the copper surface. During the nickel plating process, the temperature is controlled at 55-60°C and the pH value is 3-4. During the gold plating process, the temperature is controlled at 85-90°C and the pH value is 4-5.

[0021] Furthermore, in step eight, the OSP process can also be used to replace the traditional tin-spraying process. By immersing the bare copper printed circuit board in an aqueous solution, a 0.2-0.5um thick hydrophobic organic protective film is formed on the copper surface through a chemical reaction. This film can protect the copper surface from oxidation, has a flux function, is compatible with various fluxes and can withstand more than three thermal shocks. The operating cost is 25-50% lower than the hot air leveling process, the shelf life can reach one year, and it is easy to repair.

[0022] Furthermore, during the silver precipitation process in step ten, the solution temperature is maintained at 25-35°C and the pH value is maintained at 8-9. During the tin precipitation process, the temperature is maintained at around 35°C. The pH required for complete precipitation in the form of Sn(OH)2 and Sn(OH)4 ([Sn]≤10^(-5)mol / l) are 2.6 and 1.25 respectively.

[0023] In the above technical solution, the technical effects and advantages provided by the present invention are:

[0024] 1. By adding fluorescent agents when printing characters and marks, these characters and marks can glow in dim light. PCB boards are often installed in the casing of electrical equipment, where the environment is dim. Therefore, characters and marks with luminous function are easier to identify during subsequent use.

[0025] 2. By adding fragrance to the solution in which the PCB is immersed, the PCB will carry a fragrance after the reaction. Therefore, the PCB will be cleaned until the fragrance dissipates. This can be used as a basis for judging whether the PCB is clean. This method can more intuitively judge whether the PCB is clean, greatly reducing the probability of solution residue and avoiding interference with the surface treatment process.

[0026] 3. By printing three colors in succession to set the marking points, the degree of wear of the PCB board can be judged according to the exposed color. This can be used as a basis to more conveniently judge the wear of the PCB board. DETAILED DESCRIPTION

[0027] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention is further described in detail below.

[0028] The present invention provides a surface treatment process for producing multi-layer PCB boards, and the specific steps are as follows:

[0029] Step 1: Preparation: Check whether the PCB board is intact. PCB boards with cracks, scratches, etc. will be directly removed without further processing. Remove burrs on the surface of the PCB board, then clean and remove surface stains, and finally dry;

[0030] Step 2: Coating: Spray a protective coating on the dried PCB surface. The main components of the protective coating include acrylic resin, fluorocarbon resin, stabilizer and anti-corrosion agent, which are used to improve the waterproofness and corrosion resistance of the PCB board, improve its surface adhesion and extend its service life.

[0031] Step 3: Copper deposition: Immerse the PCB in a solution containing copper ions, such as copper sulfate, and add a reducing agent, such as formaldehyde. Meanwhile, add fragrance to the solution, preferably water-soluble essential oils, such as lavender essential oil and lemongrass essential oil. The reducing agent reduces the copper ions in the solution to metallic copper and deposits it on the surface of the PCB. During the copper deposition process, monitor the water temperature and pH value in real time, maintaining the water temperature at 60°C and the pH value at 12-13.5. After copper deposition, clean the residual solution on the surface of the PCB until there is no fragrance odor on the surface of the PCB, indicating that the residual solution has been cleaned. Finally, dry it.

[0032] Step 4: After copper deposition and drying, the PCB board is pattern-plated. First, a cover layer is sprayed on the PCB board. Then, part of the cover layer is removed according to the pre-designed pattern. Chemical etching or laser exposure can be used to remove the cover layer, exposing the area to be plated, while other areas remain protected. The circuit board is then immersed in the plating solution for electroplating. Fragrance is also added to the plating solution for the same purpose as in step 3. After electroplating, the remaining plating solution is cleaned until the fragrance is completely dissipated.

[0033] Step 5: Silkscreen characters and markings are printed on the surface of the PCB, including component numbers and nominal values, component outlines, manufacturer logos, production dates, and various annotations. This information facilitates circuit installation, maintenance, and plug-in operations during the production process. Fluorescent agents are added to the printed coating to facilitate identification of relevant information in dim light. The addition of fluorescent agents makes these characters and markings glow in dim light. PCBs are often installed in the housing of electrical equipment in dimly lit environments, so the luminescent characters and markings make them easier to identify during subsequent use.

[0034] Step 6: Nickel-gold plating: Palladium is replaced on the surface of copper through chemical reaction, and then a nickel-phosphorus alloy layer is chemically plated on the basis of the palladium core. The PCB board is then immersed in a solution containing nickel ions, so that nickel is deposited where the palladium is attached. Then, a layer of gold is plated on the surface of the nickel through a replacement reaction. The PCB board is immersed in a solution containing gold ions, so that gold is precipitated and covered on the nickel surface. Fragrance is added to the solution during the nickel-gold plating process, and its function is the same as step 3. After the PCB board is taken out of each solution, it needs to be cleaned until the fragrance is completely dissipated. This operation improves the conductivity of the PCB board while It also plays a protective role and prolongs the service life. Before immersing nickel gold, it is necessary to clean the dirt on the surface of the circuit board. Then immerse the PCB board in a solution containing palladium ions, maintain 20-30℃, and control the palladium ion concentration at 20-40ppm, so that a layer of palladium is precipitated on the copper surface. During the nickel immersion process, the temperature is controlled at 55-60℃ and the pH value is 3-4. Too low a pH value will cause excessive hydrogen precipitation, affecting the quality of the coating; while too high a pH value will increase the porosity and brittleness of the coating, resulting in a decrease in the coating performance. During the gold immersion process, the temperature is controlled at 85-90℃ and the pH value is 4-5.

[0035] Step 7: Carbon oil printing: A layer of conductive carbon oil is printed on the PCB surface using silk screen printing. This can be used as a contact conductor for key positions or as a conductor with a certain resistance requirement. Carbon oil can replace some metal circuits, providing good conductivity while offering greater flexibility, making it suitable for complex design requirements. In addition, carbon oil can also serve as an electromagnetic shielding layer to block external electromagnetic interference and improve the PCB's anti-interference ability.

[0036] Step 8: Spray tin: Immerse the PCB board in molten solder, and then use hot air to blow off the excess solder on its surface and in the metallized holes, so as to obtain a smooth, uniform and bright solder coating layer. Its function is to prevent oxidation and corrosion, improve welding quality and reliability. The OSP process can also replace the traditional spray tin process. By immersing the bare copper printed circuit board in an aqueous solution, a 0.2-0.5um thick hydrophobic organic protective film is formed on the copper surface through a chemical reaction. This film can protect the copper surface from oxidation, has a flux function, is compatible with various fluxes and can withstand more than three thermal shocks. The operating cost is 25-50% lower than the hot air leveling process, the shelf life can reach one year, and it is easy to repair;

[0037] Step 9: Use silk screen printing to print a layer of peelable oil pattern on the surface of the circuit board, which is mainly used for the selective assembly needs of the later assembly factory. It is required that the connected peelable pattern can be completely torn off after curing or after wave soldering without residue;

[0038] Step 10: Immersion silver and immersion tin: Immerse the PCB in a solution containing silver ions to precipitate metallic silver and deposit it on the surface of the PCB. During the silver immersion process, the solution temperature is maintained at 25-35°C and the pH value is maintained at 8-9. Then, immerse it in a solution containing tin ions to precipitate metallic tin and deposit it on the surface of the PCB. During the tin immersion process, the temperature is maintained at around 35°C. The pH required for complete precipitation of Sn(OH)2 and Sn(OH)4 ([Sn]≤10^(-5)mol / l) is 2.6 and 1.25 respectively. Fragrance is added to the solution during the silver and tin immersion processes, and its function is the same as in step 3. After the PCB is removed from each solution, it needs to be cleaned until the fragrance is completely dissipated. The functions of immersion silver and immersion tin are to improve conductivity, enhance solderability, protect the copper layer, and improve product reliability and durability.

[0039] In steps 3, 4, 6, and 10, whether electroplating or immersion copper, immersion gold, immersion tin, or immersion silver, fragrance is added to the solution in which the PCB board will be immersed. The fragrance plays an auxiliary role without interfering with the reaction. When the PCB board is contaminated with these solutions, it will inevitably be contaminated with the fragrance and acquire a fragrance. After each reaction is completed, the residual solution on the PCB board needs to be cleaned to prevent it from interfering with the next reaction. In this process, while cleaning the residual solution, the fragrance carried by the PCB board is also cleaned, thereby removing the fragrance it carries. Therefore, cleaning the PCB board until the fragrance dissipates can serve as a basis for judging whether the PCB board is clean. In this way, whether the PCB board is clean can be judged more intuitively, greatly reducing the probability of solution residue.

[0040] Step 11: Print multiple dot-shaped indicator marks on the surface of the PCB board. The diameter of each mark point is 3-5mm. The mark points are distributed throughout the PCB board and do not block the original annotation information on the PCB board. Use three different colors of paint to print three times in a superimposed manner. After the previous print paint is completely dry, print the next one. After the three prints are completed and the paint is completely dry, the surface treatment process of the PCB board is completed. Once the cover PCB board is worn during use, the mark points will be worn first. Since the mark points have three colors from the inside to the outside, the degree of wear of the PCB board can be judged according to the exposed color. Based on this, it is more convenient to judge the wear condition of the PCB board and then determine whether it needs to be repaired or replaced.

[0041] The above description is merely illustrative of certain exemplary embodiments of the present invention. It is understood that those skilled in the art will be able to modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the above description is illustrative in nature and should not be construed as limiting the scope of the claims.

Claims

1. A surface treatment process for producing multi-layer PCBs, characterized by: The specific steps are as follows: Step 1: Preparation: Check whether the PCB board is intact, remove the burrs on the surface of the PCB board, then clean and remove the stains on the surface, and finally dry it; Step 2: Coating: Spray a layer of protective coating on the surface of the dried PCB board; Step 3: Copper deposition: Immerse the PCB in a solution containing copper ions, add a reducing agent, and add fragrance to the solution. The reducing agent reduces the copper ions in the solution to metallic copper and deposits it on the surface of the PCB. After copper deposition, clean the residual solution on the surface of the PCB until there is no fragrance smell on the surface of the PCB, indicating that the residual solution has been cleaned. The PCB board after copper deposition and drying is subjected to pattern electroplating. First, dry it. Step 4: Spray the cover layer on the PCB board, then remove part of the cover layer according to the pre-designed pattern to expose the area to be electroplated. Then immerse the circuit board in the plating solution for electroplating. Fragrance is also added to the plating solution, which has the same function as step 3. Step 5: Print characters and marks on the surface of the PCB board by silk screen printing, and add fluorescent agent to the printing coating; Step 6: Immersion nickel gold: Palladium is replaced on the surface of copper through a chemical reaction, and a nickel-phosphorus alloy layer is chemically plated on the basis of the palladium core. Then, a layer of gold is plated on the surface of nickel through a replacement reaction. The PCB board is immersed in a solution containing gold ions, so that gold is precipitated and covers the nickel surface. Flavoring is added to the solution during the process of immersion nickel gold, and its function is the same as step 3. Step 7: Carbon oil printing: Use silk screen printing to print a layer of conductive carbon oil pattern on the surface of the PCB board, which can be used as a contact conductor for key positions or as a wire with resistance requirements; Step 8: Spray tin: Immerse the PCB board in molten solder, and then use hot air to blow off the excess solder on its surface and in the metallized holes, so as to obtain a smooth, uniform and bright solder coating layer; Step 9: Print a layer of peelable oil pattern on the surface of the circuit board by silk screen printing; Step 10: Immersing silver and tin: Immersing the PCB into a solution containing silver ions to precipitate the silver metal and deposit it on the PCB surface. Then, immersing it into a solution containing tin ions to precipitate the tin metal and deposit it on the PCB surface. Fragrance is added to the solution during the immersion silver and tin processes, and the function is the same as in step 3. Step 11: Print multiple dot-shaped indicator marks on the surface of the PCB board using three different colors of paint in three overlapping layers. After the three printings are completed and the paint is completely dry, the surface treatment process of the PCB board is completed.

2. The surface treatment process for producing multi-layer PCBs according to claim 1, wherein: The components of the protective coating in step 2 include acrylic resin, fluorocarbon resin, stabilizer and anti-corrosion agent.

3. The surface treatment process for producing multi-layer PCBs according to claim 1, wherein: During the copper deposition process in step 3, the water temperature and pH value are monitored in real time, and the water temperature is maintained at 60°C and the pH value is maintained at 12-13.

5.

4. The surface treatment process for producing multi-layer PCBs according to claim 1, wherein: Before nickel-gold plating in step 6, the dirt on the surface of the circuit board needs to be cleaned. Then the PCB board is immersed in a solution containing palladium ions, maintained at 20-30°C, and the palladium ion concentration is controlled at 20-40ppm, so that a layer of palladium is precipitated on the copper surface. During the nickel plating process, the temperature is controlled at 55-60°C and the pH value is 3-4. During the gold plating process, the temperature is controlled at 85-90°C and the pH value is 4-5.

5. The surface treatment process for producing multi-layer PCBs according to claim 1, wherein: In step eight, the OSP process is used to replace the traditional tin spraying process. By immersing the bare copper printed circuit board in an aqueous solution, a hydrophobic organic protective film with a thickness of 0.2-0.5um is formed on the copper surface through a chemical reaction.

6. The surface treatment process for producing multi-layer PCBs according to claim 1, wherein: During the silver precipitation process in step 10, the solution temperature is maintained at 25-35°C and the pH value is maintained at 8-9. During the tin precipitation process, the temperature is maintained at 35°C, and Sn(OH)2 and Sn(OH)4 are completely precipitated, and the required pH values are 2.6 and 1.25 respectively.