Method for manufacturing printed circuit board with integrated surface treatment and printed circuit board

Abstract

The present application relates to the field of printed circuit board manufacturing, more particularly, to a printed circuit board manufacturing method integrating multiple surface treatments and a printed circuit board. The method comprises: S100, manufacturing a multi-layer board; S200, exposing a electroplated hard gold area through a first selective exposure, plating nickel and gold-cobalt alloy to form a hard gold layer; S300, forming an outer layer circuit; S400, exposing a thick gold plating area through a second selective exposure, chemically plating nickel and gold to form a thick gold plating layer; S500, exposing a nickel-palladium-gold plating area through a third selective exposure, chemically plating nickel, palladium and gold to form a nickel-palladium-gold plating layer; S600, forming and testing; S700, exposing a silver plating area through a fourth selective exposure, chemically plating silver to form a silver plating layer; S800, final inspection and delivery. Through four selective exposures, the electroplated hard gold, thick gold plating, nickel-palladium-gold plating and silver plating are sequentially integrated on the same printed circuit board, so that the printed circuit board has the functions of wear-resistant plugging, gold wire bonding, fine pitch soldering and high-frequency signal transmission.

Description

Technical Field

[0001] This invention relates to the field of printed circuit board manufacturing, and more specifically, to a method for manufacturing a printed circuit board integrating multiple surface treatments and a printed circuit board thereof. Background Technology

[0002] As the carrier of electronic components and the provider of electrical connections, the surface treatment process of printed circuit boards (PCBs) directly determines the solderability, contact reliability, environmental resistance, and applicable scenarios of the pads. With the development of electronic devices towards multifunctionality, miniaturization, and high integration, a single circuit board often needs to integrate multiple different functional modules, such as central processing units, memory, RF front-ends, power management units, and input / output interfaces. These different functional modules have varying requirements for the surface treatment of the pads.

[0003] In existing technologies, electroplating hard gold is widely used in gold fingers, button contacts, and connectors that are frequently plugged and unplugged due to the high hardness and good wear resistance of the gold layer; immersion gold plating is suitable for gold wire bonding pads due to the high purity and controllable thickness of the gold layer; immersion nickel-palladium-gold plating is suitable for fine-pitch BGA, CSP and other package pads because the palladium layer on the nickel layer can effectively block excessive nickel-gold reaction and prevent "black pad" defects; immersion silver plating is suitable for high-frequency signal areas such as radio frequency circuits and antennas due to its excellent conductivity and high-frequency characteristics.

[0004] However, due to the mutual influence between different surface treatment processes during cross-production, and the significant differences in the protection methods and process windows required for each process, it is difficult to manufacture the above four surface treatment processes compatiblely on the same PCB. When a product needs to have multiple functions simultaneously, designers usually design the circuits of different functions on multiple independent PCBs and then interconnect them through connectors or ribbon cables. However, this approach leads to increased device size, weight, power consumption, and signal transmission paths, limiting the miniaturization and high performance of the device, especially failing to meet the stringent space and power consumption requirements of applications such as AI accelerator cards, high-performance servers, and mobile terminals. Summary of the Invention

[0005] The present invention aims to overcome at least one of the defects (deficiencies) of the prior art and provide a method for manufacturing a printed circuit board that integrates multiple surface treatments, aiming to integrate four surface treatment processes—hard gold plating, thick gold plating, nickel-palladium-gold plating, and silver plating—on the same printed circuit board.

[0006] The technical solution adopted in this invention is a method for manufacturing a printed circuit board integrating multiple surface treatments, comprising the following steps:

[0007] S100, Fabrication of multilayer boards: Multilayer boards with conductive lines and multilayer interconnection structures are fabricated through inner layer lamination, drilling, copper plating and pattern plating processes.

[0008] S200, Electroplating hard gold fabrication: On the multilayer board, through the first selective exposure, a predetermined electroplating hard gold area is exposed, and nickel plating and electroplating gold-cobalt alloy treatment are performed to form an electroplating hard gold layer.

[0009] S300, Outer Layer Circuit Forming: Etching is performed on the multilayer board that has been electroplated with hard gold to form the outer layer circuit.

[0010] S400, Thick Gold Plating: On a multilayer board with the outer circuit pattern formed, a second selective exposure is performed to expose the predetermined thick gold plating area, and chemical nickel-gold plating is performed to form a thick gold plating layer.

[0011] S500, Immersion Nickel Palladium Gold Fabrication: On a multilayer board that has completed the immersion thick gold fabrication, a third selective exposure is performed to protect the formed electroplated hard gold layer and immersion thick gold layer, while exposing the predetermined immersion nickel palladium gold area for chemical immersion nickel, immersion palladium, and immersion gold treatment to form an immersion nickel palladium gold layer.

[0012] S600, Forming and Testing: Performing shape processing and electrical testing on multilayer boards that have completed the nickel-palladium-gold plating process;

[0013] S700, Immersion Silver Production: On the multilayer board that has been molded and tested, through the fourth selective exposure, the formed electroplated hard gold layer, thick gold layer and immersion nickel palladium gold layer are completely wrapped and protected with protective material, leaving only the predetermined immersion silver area exposed, and chemical immersion silver treatment is performed to form the immersion silver layer.

[0014] S800, Final Inspection and Shipment: After all surface treatments are completed, final inspection and anti-oxidation packaging are carried out.

[0015] This invention employs a four-stage selective exposure process design to integrate four surface treatment processes—electroplating hard gold, immersion gold, immersion nickel-palladium-gold, and immersion silver—onto a single printed circuit board (PCB). This allows a single PCB to simultaneously perform four functions: wear-resistant insertion and removal, gold wire bonding, fine-pitch soldering, and high-frequency signal transmission. This overcomes the limitation of existing technologies that require multiple PCBs to achieve various functionalities. Single-board integration significantly reduces the PCB's footprint and overall weight, providing technical support for the miniaturization and weight reduction of electronic devices. Simultaneously, it shortens the signal transmission path, improves signal transmission performance, and reduces energy consumption. It is particularly suitable for applications with stringent requirements for space, power consumption, and performance, such as AI accelerator cards, high-performance servers, and mobile terminals, providing a feasible technical path for further miniaturization and functional enhancement of these high-end electronic products.

[0016] Step S200 includes:

[0017] S210, First Selective Exposure: A dry film is applied to the surface of the multilayer board after S100 is completed, and the predetermined electroplated hard gold pads are exposed by exposure and development.

[0018] S220, Desoldering: Removes the protective tin layer from the exposed surface of the electroplated hard gold pads to expose the fresh copper surface;

[0019] S230, Electroplating Hard Gold Treatment: The exposed copper surface of the electroplating hard gold pads is treated with nickel plating and electroplating gold-cobalt alloy to form an electroplating hard gold layer.

[0020] By selectively exposing the pads in the first stage, the areas requiring hard gold plating are precisely revealed, ensuring that hard gold plating only occurs in predetermined locations. This avoids plating gold in non-hard gold areas, saving on precious metal costs and ensuring clear separation between different surface treatment processes. A desoldering step is added before hard gold plating to remove the protective tin layer from the surface of the hard gold plating pads, exposing fresh copper. This avoids defects such as poor nickel-copper bonding and gold peeling (gold flaking) caused by tin residue, significantly improving the adhesion and reliability of the hard gold plating layer.

[0021] Step S230 includes:

[0022] S231, Copper surface activation treatment: Activation treatment for copper surface after detinning;

[0023] S232, Nickel plating treatment: Electroplating a nickel layer onto the activated copper surface;

[0024] S233, Hard gold plating treatment: Electroplating a gold-cobalt alloy layer onto a nickel layer.

[0025] By breaking down the hard gold plating process into three steps—copper surface activation treatment, nickel plating treatment, and hard gold plating treatment—a complete hard gold plating process chain was constructed. Among them, the copper surface activation treatment removes any tin-copper compound layer that may remain on the copper surface after tin stripping, giving the copper surface a high degree of cleanliness and appropriate micro-roughness, providing a solid foundation for the subsequent nickel plating layer to achieve a strong metal bond with the copper surface.

[0026] Specifically, step S231 includes:

[0027] S2311, Acid Immersion Pre-protection: Pre-immersion treatment of the exposed copper surface using H2SO4 solution with a mass concentration of 3-7%;

[0028] S2312 Degreasing treatment: Use a degreasing solution with a mass concentration of 8-12% to remove oil stains from the copper surface;

[0029] S2313, Micro-etching treatment: Micro-etching is performed on the copper surface, with an etching depth of 30-70 microinches;

[0030] S2314, Acid washing and activation: Acid washing is performed using an H2SO4 solution with a mass concentration of 5-15%.

[0031] Step S400 includes:

[0032] S410, Printing solder resist ink: Printing solder resist ink on the surface of a multilayer board after the outer layer circuit is formed, and forming a solder resist layer by exposure and development, wherein the solder resist layer covers the non-soldering area;

[0033] S420, Second selective exposure: A dry film is applied to the surface of the solder resist layer, and then exposed and developed to reveal the predetermined thick gold pads;

[0034] S430, Thick Gold Plating: Thick gold plating is applied to the exposed thick gold pads to form a thick gold layer.

[0035] By breaking down the process of applying thick gold plating into three steps—printing solder resist ink, secondary selective exposure, and thick gold plating treatment—a complete thick gold plating process chain was constructed. The solder resist ink printing step forms a permanent solder resist layer on the board surface after the outer layer circuitry is formed, covering non-soldered areas and exposing all pads requiring soldering. These pads include: pads that have already undergone hard gold plating, pads awaiting thick gold plating, pads awaiting nickel-palladium-gold plating, pads awaiting silver plating, and other ordinary solder pads. The secondary selective exposure step involves applying a dry film to the solder resist layer. Through exposure and development, only the areas requiring thick gold plating are exposed, while other pads are covered and protected with the dry film. This ensures that thick gold plating only occurs in predetermined locations, preventing gold plating in non-thick gold areas, saving precious metal costs, and ensuring clear separation between different surface treatment processes. The thick gold plating treatment involves chemically immersing nickel-gold on the exposed thick gold plating pads to form a thick gold plating layer.

[0036] During the thick gold plating process, the chemical gold plating solution has a high temperature and strong permeability. A single dry film protective layer may develop micro-cracks or edge lifting during prolonged immersion, causing the solution to seep beneath the dry film and corrode the pads and circuitry in areas not covered by the thick gold plating. To solve this problem, in step S420, after exposing the predetermined thick gold plating pads, a layer of adhesive tape is applied to the surface of the dry film, forming a double protective structure of dry film and adhesive tape.

[0037] Step S430 includes:

[0038] S431, Pretreatment of thick gold plating: Degreasing, micro-etching, pre-dipping and activation treatment of exposed thick gold plating pads;

[0039] S432, Chemical Nickel Plating: The entire board is immersed in chemical nickel plating solution to form a nickel plating layer on the exposed surface of the thick gold pads.

[0040] S433, Chemical Immersion Gold Treatment: The entire board after nickel immersion is immersed in chemical immersion gold solution to form a thick gold layer on the nickel immersion layer.

[0041] Step S500 includes:

[0042] S510, Third Selective Exposure: Selective oil is printed on the multilayer board after the thick gold plating is completed, and the predetermined nickel-palladium-gold solder pads are exposed by exposure and development.

[0043] S520, Immersion Nickel Palladium Gold Treatment: The exposed immersion nickel palladium gold pads are sequentially treated with immersion nickel, immersion palladium, and immersion gold to form an immersion nickel palladium gold layer.

[0044] By breaking down the immersion nickel-palladium plating process into two steps—a third selective exposure and immersion nickel-palladium plating treatment—a complete immersion nickel-palladium plating process chain was constructed. The third selective exposure involves printing selective ink on a multilayer board and then exposing and developing it to precisely expose the predetermined immersion nickel-palladium plating pads. Simultaneously, the selective ink is retained on the already formed electroplated hard gold layer, the thick gold layer, and the area to be silvered, forming a temporary protective layer to prevent corrosion or contamination by subsequent chemical immersion nickel-palladium plating solutions. The area to be silvered is effectively protected in this process by the selective ink, preventing accidental deposition of the immersion nickel-palladium plating solution and preserving a clean copper surface for the subsequent silvering process, ensuring that each surface treatment area does not interfere with each other and is formed independently. The immersion nickel-palladium plating treatment sequentially performs chemical nickel plating, palladium plating, and gold plating on the exposed immersion nickel-palladium plating pads to form a nickel-palladium-palladium plating layer with a palladium layer barrier structure. This palladium layer effectively blocks excessive reaction between nickel and gold, eliminating the "black pad" defect and meeting the stringent requirements for soldering reliability of fine-pitch BGA and CSP package pads.

[0045] In step S510, after printing the selective ink, a layer of adhesive paper is then applied to the surface of the selective ink, forming a double protective structure of selective ink and adhesive paper. By further applying adhesive paper to the surface of the selective ink to form a double protective structure, the reliability and density of the protection are greatly improved. This double protection effectively blocks the risks of penetration, corrosion, and seepage of the nickel-palladium-gold plating solution, completely avoiding problems such as corrosion and abnormal thickness of the electroplated hard gold layer or thick gold layer caused by pinholes, edge omissions, or solution penetration in a single selective ink, as well as the accidental deposition of nickel-palladium-gold in the area to be plated with silver. This fully ensures the integrity of the formed plating layer and the cleanliness of the area to be treated.

[0046] The printed circuit board (PCB) manufactured using the above method integrates four surface treatment processes—hard gold plating, thick gold plating, nickel-palladium-gold plating, and silver plating—onto a single board. This allows a single PCB to simultaneously perform four functions: wear-resistant insertion and removal, gold wire bonding, fine-pitch soldering, and high-frequency signal transmission. This overcomes the limitation of existing technologies that require multiple PCBs to achieve multiple functions. The single-board integration significantly reduces the PCB's footprint and overall weight, providing technical support for the miniaturization and weight reduction of electronic devices. It also shortens the signal transmission path, improves signal transmission quality, and reduces system power consumption. This PCB is particularly suitable for applications with stringent requirements for space, power consumption, and performance, such as AI accelerator cards, high-performance servers, and mobile terminals, providing a practical technical solution for further miniaturization and performance improvement of high-end electronic products.

[0047] Compared with existing technologies, the advantages of this invention are as follows: Through a precise process design involving four selective exposures, four surface treatment processes—hard gold plating, thick gold plating, nickel-palladium-gold plating, and silver plating—are successfully integrated onto a single printed circuit board. This allows a single printed circuit board to simultaneously perform four functions: wear-resistant insertion and removal, gold wire bonding, fine-pitch soldering, and high-frequency signal transmission. This effectively solves the limitation of existing technologies where multiple functional requirements must be achieved using multiple PCBs. Specifically, the first selective exposure precisely positions the hard gold plating area, combined with tin removal and copper surface activation treatments, avoiding defects such as weak plating adhesion and gold layer peeling caused by tin residue. This significantly improves the adhesion and reliability of the hard gold plating layer while saving on precious metal costs. The second selective exposure, through a dual protective structure of dry film and adhesive tape, completely blocks the penetration and corrosion risks of high-temperature, high-permeability thick gold plating solutions, ensuring the integrity of pads and circuits in non-thick gold plating areas. Furthermore, the permanent solder resist layer formed by the printed solder resist ink provides full protection for non-soldering areas. The third selective exposure employs a dual-protection design using both chemical oil and adhesive tape, significantly enhancing the reliability and density of the protection. This effectively prevents corrosion of the already formed plating by the immersion nickel-palladium-gold solution and avoids accidental deposition in areas requiring immersion silver. The palladium layer barrier structure formed by the immersion nickel-palladium-gold treatment eliminates "black pad" defects, meeting the stringent requirements for soldering reliability in fine-pitch package pads. Through single-board integration, the PCB's footprint and overall weight are significantly reduced, providing technical support for the miniaturization and weight reduction of electronic devices. Simultaneously, it shortens the signal transmission path, improves signal transmission quality, and reduces system power consumption. This is particularly suitable for applications with stringent requirements for space, power consumption, and performance, such as AI accelerator cards, high-performance servers, and mobile terminals, providing a practical technical solution for further miniaturization and performance improvement of high-end electronic products. Attached Figure Description

[0048] Figure 1 This is a process flow diagram of the manufacturing method of the present invention. Detailed Implementation

[0049] The accompanying drawings are for illustrative purposes only and should not be construed as limiting the invention. To better illustrate the following embodiments, some parts in the drawings may be omitted, enlarged, or reduced, and do not represent the actual product dimensions; it is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0050] In the description of this invention, it should be noted that the terms "upper," "lower," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of this invention is in use, or the orientation or positional relationship commonly understood by those skilled in the art. These terms are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention. In addition, the terms "first," "second," etc., are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0051] Example 1

[0052] like Figure 1 As shown in the figure, this embodiment describes a method for manufacturing a printed circuit board integrating multiple surface treatments, including the following steps:

[0053] S100, Fabrication of multilayer boards: Multilayer boards with conductive lines and multilayer interconnection structures are fabricated through inner layer lamination, drilling, copper plating and pattern plating processes.

[0054] S200, Electroplating hard gold fabrication: On the multilayer board, through the first selective exposure, a predetermined electroplating hard gold area is exposed, and nickel plating and electroplating gold-cobalt alloy treatment are performed to form an electroplating hard gold layer.

[0055] S300, Outer Layer Circuit Forming: Etching is performed on the multilayer board that has been electroplated with hard gold to form the outer layer circuit.

[0056] S400, Thick Gold Plating: On a multilayer board with the outer circuit pattern formed, a second selective exposure is performed to expose the predetermined thick gold plating area, and chemical nickel-gold plating is performed to form a thick gold plating layer.

[0057] S500, Immersion Nickel Palladium Gold Fabrication: On a multilayer board that has completed the immersion thick gold fabrication, a third selective exposure is performed to protect the formed electroplated hard gold layer and immersion thick gold layer, while exposing the predetermined immersion nickel palladium gold area for chemical immersion nickel, immersion palladium, and immersion gold treatment to form an immersion nickel palladium gold layer.

[0058] S600, Forming and Testing: Performing shape processing and electrical testing on multilayer boards that have completed the nickel-palladium-gold plating process;

[0059] S700, Immersion Silver Production: On the multilayer board that has been molded and tested, through the fourth selective exposure, the formed electroplated hard gold layer, thick gold layer and immersion nickel palladium gold layer are completely wrapped and protected with protective material, leaving only the predetermined immersion silver area exposed, and chemical immersion silver treatment is performed to form the immersion silver layer.

[0060] S800, Final Inspection and Shipment: After all surface treatments are completed, final inspection and anti-oxidation packaging are carried out.

[0061] Step S100 includes the following procedures:

[0062] S110, Inner Layer Stacking and Pressing: Based on the preset press plate structure design, the P sheet and the inner core board are precisely stacked according to the number of layers and arrangement requirements and then transferred to the press. Pressing is carried out according to the set temperature, pressure and time parameters. After pressing, irregular board edges and burrs are trimmed and trimmed. Four positioning holes are cut into the board edge for subsequent fixing. Inner layer inspection is carried out on defects such as board thickness consistency, residual glue on the board surface, dents, and wrinkles to obtain multilayer board semi-finished products.

[0063] S120, Chemical Copper Reduction: The chemical micro-etching process is used to uniformly thin the copper layer on the surface of the multilayer board, so that the surface copper thickness reaches the preset requirements, providing a suitable thin copper base for subsequent etching.

[0064] S130. Drilling and Hole Wall Treatment: Based on the design data, a special drill tape is made to perform mechanical and laser drilling on the multilayer board. Plasma cleaning and chemical cleaning are used to remove residual adhesive and oxide layer at the bottom of the hole. After drilling, defects such as crooked holes, hole burrs, multiple holes, and missing holes are checked by inspection and counting. Before copper plating, the board surface is ground to remove drilling powder and hole burrs. The board is then baked to remove moisture. Plasma adhesive removal is used to remove the adhesive layer on the hole wall to ensure a strong bond between the copper layer on the hole wall and the inner copper layer during subsequent copper plating.

[0065] S140, Copper Plating and Board Surface Electroplating: Chemical copper plating process is implemented for through holes and blind holes to deposit a uniform conductive copper layer on the hole wall; the copper plating layer is used as a conductive path for board surface electroplating to ensure that the copper layer thickness on the board surface and inside the holes meets the design requirements; after electroplating, defects such as copper nodules, copper wire residue, and hole blockage are checked by counting holes.

[0066] S150, Pattern Plating and Circuit Forming: The circuit is fabricated layer by layer through multiple outer dry film and pattern plating processes. The first outer dry film is used to create the basic circuit layer. A thicker copper layer is electroplated on the exposed copper area. After the film is removed, the designated holes are filled with resin using a vacuum filling process. The board surface is smoothed by grinding to remove excess resin. The second outer dry film and pattern plating process is repeated on the newly added layers. A 1-2 mil thick copper layer is electroplated on the exposed copper surface and tin is plated as an anti-corrosion protective layer to complete the outer circuit fabrication.

[0067] After the multilayer board is fabricated, it undergoes hard gold plating. Step S200, hard gold plating, includes:

[0068] S210, First Selective Exposure: A dry film is applied to the surface of the multilayer board after S100 is completed, and the predetermined electroplated hard gold pads are exposed by exposure and development.

[0069] Specifically, the multilayer boards fabricated using S100 are subjected to DI washing and drying. The washing speed is controlled at 1.2-1.8 m / min, and the drying temperature is 55-65℃. Conventional dry film micro-etching and grinding processes are not performed. After washing and drying, a dry film is precisely applied. The areas requiring hard gold plating are exposed through exposure and development, while the remaining areas (including those protected by a tin layer) are covered and protected with the dry film. During this step, the tin surface in the non-hard gold plating areas must not have any mechanical scratches; otherwise, the underlying copper traces will be etched away during subsequent etching. The operation must be supervised by professionals, handling the boards gently to ensure the tin surface remains intact.

[0070] S220, Tin Removal Process: Remove the protective tin layer from the exposed hard gold plating pads to reveal the fresh copper surface. After step S210, the areas requiring hard gold plating will have exposed tin plating. The multilayer board will undergo tin removal at the tin removal section of the etching line, without the conventional etching process. The board speed during tin removal should be controlled at 1.2-1.8 m / min. After tin removal, the board surface will be washed and dried at a temperature controlled at 55-65℃. This step is crucial to completely remove the protective tin layer from the exposed hard gold plating pads to prevent residual tin from causing poor nickel-copper bonding and gold peeling defects. The tin removal process should ensure complete removal of the tin layer while avoiding excessive etching of the copper surface.

[0071] S230, Hard Gold Plating Treatment: The exposed copper pads for hard gold plating are plated with nickel and then with a gold-cobalt alloy to form a hard gold plating layer. This step includes the following processes:

[0072] S231. Copper Surface Activation Treatment: This treatment activates the copper surface after tin removal. It removes any residual tin-copper compound layer that may remain on the copper surface, resulting in a high degree of cleanliness and appropriate micro-roughness. This provides a solid foundation for a strong metallic bond between the subsequent nickel plating layer and the copper surface. This step specifically includes:

[0073] S2311, Acid Immersion Pre-protection: The exposed copper surface is pre-immersed in an H2SO4 solution with a mass concentration of 3-7% to form an acidic protective film on the copper surface and prevent secondary oxidation.

[0074] S2312 Degreasing treatment: Use a degreasing solution with a mass concentration of 8-12% to remove oil stains from the copper surface.

[0075] S2313. Micro-etching treatment: Perform horizontal micro-etching on the copper surface, with an etching depth of 30-70 microinches and a throughput speed of 1.6-2.0 m / min. This step is used to remove any residual tin-copper compound layer that may remain after tin stripping. The micro-etching solution composition is NPS 30-70 g / L, H2SO4 1-4% (v / v), and Cu²2... + Concentration below 20 g / L.

[0076] S2314. Pickling and Activation: Use a 5-15% H2SO4 solution for pickling to remove micro-etching residues.

[0077] S232, Nickel Plating Treatment: Electroplating a nickel layer onto the activated copper surface. The specific process parameters for the nickel plating solution in this step are controlled as follows: Ni²⁺ in the nickel plating solution... + The concentration is controlled at 55-75 g / L, the pH value is controlled at 3.8-4.8, and 5-20 ml / L of 3009R additive, 5-15 g / L of NiCl2, and 25-45 g / L of H3BO3 are added. During the electroplating process, the temperature is controlled at 50-60℃, and the current density is controlled at 5-20 ASF.

[0078] S233, Hard Gold Plating: Electroplating a gold-cobalt alloy layer onto a nickel layer. The process parameters for the gold plating solution are: Au concentration 2.5-3.5 g / L, pH value 3.8-4.6, specific gravity 1.05-1.15, and temperature 35-45℃.

[0079] Through the above processes, the electroplated hard gold layer is completed, ensuring that the electroplated hard gold pads have excellent wear resistance, low contact resistance and reliable bonding force, meeting the usage requirements of parts such as gold fingers, button contacts and frequently plugged-in connectors.

[0080] After the hard gold plating is completed, the outer layer circuitry is formed. Step S300, outer layer circuitry forming, includes drilling NPTH holes, outer layer etching, outer layer AOI inspection, outer layer in-process inspection and repair, current withstand test, and micro-resistance test. Specifically, firstly, non-plated through holes are drilled for subsequent mounting positioning or screw fixing; then, alkaline etching solution is used to remove the copper layer that does not need to be retained on the board surface, leaving only the copper pads and the pads that have been plated with hard gold, forming the outer conductive circuitry. After the circuitry is formed, an automatic optical inspection device is used to check for defects such as open circuits, short circuits, pad defects, jagged edges, dents, and copper particles. Repairable defects are repaired to ensure circuit quality. Subsequently, the network undergoes a current withstand test, applying a specified high current to verify the current carrying capacity and reliability of the high-current network; simultaneously, a four-wire milliohmmeter is used for micro-resistance testing, measuring the network's resistance value and analyzing resistance fluctuations to ensure that the conductivity meets design requirements.

[0081] Through the above processes, the outer layer circuitry is formed and its quality is verified, providing a qualified circuitry foundation for subsequent processes such as immersion gold, immersion nickel-palladium-gold, and immersion silver.

[0082] After the outer layer circuit is formed, a thick gold plating process is performed. Step S400, the thick gold plating process, includes:

[0083] S410, Printing Solder Resist Ink: Solder resist ink is printed on the surface of the multilayer board after the outer layer circuitry has been formed. After exposure and development, a solder resist layer is formed, covering the non-soldered areas. In this step, after the solder resist layer covers the non-soldered areas, all solder pads that need to be soldered are exposed. These pads include: pads that have been electroplated with hard gold, pads to be plated with thick gold, pads to be plated with nickel-palladium-gold, pads to be plated with silver, and other ordinary solder pads. This process provides a basis for subsequent selective processing.

[0084] S420, Second Selective Exposure: A dry film is applied to the surface of the solder resist layer, and then exposed and developed to reveal the predetermined gold plating pads. This step exposes only the pad areas requiring gold plating through exposure and development, while covering and protecting other pads with a dry film. This ensures that the gold plating only occurs at the predetermined locations, preventing non-gold plating areas from being gold-plated.

[0085] As a preferred solution, after the predetermined thick gold plating pads are exposed through exposure and development, a layer of adhesive tape is then applied to the dry film surface, forming a dual protective structure of dry film and adhesive tape. In subsequent thick gold plating processes, the chemical gold plating solution has high temperature and strong permeability. A single dry film protective layer may develop micro-cracks or edge lifting during prolonged immersion, causing the solution to seep beneath the dry film and corrode the pads and circuitry in areas not covered by thick gold plating. The dual protective structure of dry film and adhesive tape effectively avoids solution leakage caused by dry film cracking.

[0086] Traditional methods of manually applying adhesive tape have the following technical problems: First, alignment accuracy is difficult to guarantee; manual operation cannot ensure that the tape covers only the designated protected area, and the tape often covers non-target pads. Second, cutting the tape easily scratches the board surface; manually cutting the tape with a blade can easily damage circuits and pads, affecting product yield. To solve these technical problems, this solution adopts a laser-cut adhesive tape application process. Specifically, special adhesive tape is selected, and after the tape is applied to the entire board surface, a laser cutting device is used to precisely cut according to a preset pattern, accurately separating the protected area from the part to be removed. Then, the unwanted tape is peeled off, leaving only the tape in the protected area.

[0087] Through the combined operation of S410 and S420, a precise area for gold plating is formed on the board surface. S410's solder resist layer provides a permanent window for all pads, while S420's second selective exposure, using a dry film (and a preferred dual-protection structure), exposes only the gold plating pads to be processed in the current step, reliably protecting the other pads. This completes the preparation work for gold plating, providing a precise processing window for subsequent gold plating treatments.

[0088] S430, Thick Gold Plating: Exposed thick gold pads are subjected to thick gold plating to form a thick gold layer. This step includes pretreatment for thick gold plating, electroless nickel plating, and electroless gold plating, as detailed below:

[0089] S431. Pretreatment for Thick Gold Plating: Exposed thick gold plating pads undergo degreasing, micro-etching, pre-immersion, and activation treatments. Degreasing uses a UC.K degreasing solution with a mass concentration of 8-12%; micro-etching uses a micro-etching solution with an NPS concentration of 80-120 g / L and an H2SO4 concentration of 15-25 ml / L, controlling Cu²... + The concentration is below 20 g / L, and the micro-etching depth is controlled at 1.0-1.5 μm; after micro-etching, a post-immersion treatment is performed using a solution with an H2SO4 concentration of 40-60 ml / L; pre-immersion uses a solution with an H2SO4 concentration of 40-60 ml / L; activation uses a solution containing Pd²⁺. + An activation solution with a concentration of 35-55 ppm, containing H2SO4 at a concentration of 40-60 ml / l, is used to control Cu²⁺. + The concentration is below 500 ppm; after activation, a post-immersion treatment is performed using a solution with an H2SO4 concentration of 40-80 ml / l.

[0090] The pretreatment of thick gold plating involves a series of meticulous processes, including degreasing, micro-etching, pre-dip, and activation, to remove oil and oxides from the surface of the thick gold plating pads, achieving appropriate micro-roughness and cleanliness on the copper surface of the thick gold plating pads. The micro-etching amount is precisely controlled at 1.0-1.5μm, ensuring sufficient roughening effect while avoiding over-etching. The activation treatment ensures uniform initiation and rapid deposition of chemical nickel plating.

[0091] S432, Chemical Nickel Plating: The entire board is immersed in a chemical nickel plating solution to form a nickel plating layer on the exposed thick gold pads. Chemical nickel plating uses Ni²⁺. + An optimized formulation with a concentration of 5.6-6.2 g / L and a NaH2PO2 concentration of 20-35 g / L, combined with precise control of pH 4.6-5.0 and temperature 78-88℃, can yield a nickel layer with uniform thickness, no porosity, and low internal stress. This nickel layer acts as a barrier layer to effectively prevent copper-gold interdiffusion, while also providing an ideal bonding substrate for subsequent gold immersion.

[0092] S433. Chemical Immersion Gold Treatment: The entire board after nickel immersion is immersed in a chemical immersion gold solution to form a thick gold layer on top of the nickel layer. The chemical immersion gold treatment uses an alkaline immersion gold system with an Au concentration of 0.4-1.2 g / L and a pH value of 8.8-9.2, adding a bath builder MU at a concentration of 170-230 ml / L, and controlling the temperature at 80-84℃. This results in a high-purity, soft, and controllable thick gold layer, with a thickness reaching 0.05-1 μm, fully meeting the stringent requirements for gold wire bonding thickness. In addition, the immersion gold solution contains additives, including additive D 6-14 ml / L, additive C 12-25 ml / L, additive E 80-120 ml / L, and additive H 5-10 ml / L.

[0093] By employing three sub-steps—pre-treatment for thick gold plating, electroless nickel plating, and electroless gold plating—the thick gold plating pads are ensured to possess excellent solderability, gold wire bonding reliability, and long-term stability, meeting the stringent requirements of high-end packaging for bonding pads. This completes the thick gold plating process, resulting in thick gold plating pads with excellent bonding performance. After the thick gold plating is completed, the adhesive tape on the board is removed, and the dry film on the board is peeled off, exposing the plating pads and the areas to be processed, preparing them for subsequent electroless nickel-palladium plating.

[0094] After completing the thick gold plating process, the multilayer board undergoes a nickel-palladium plating process. Step S500, the nickel-palladium plating process, includes:

[0095] S510, Third Selective Exposure: Selective ink is printed on the multilayer board after the thick gold plating is completed, and the predetermined nickel-palladium-gold plating pads are exposed through exposure and development. While exposing the nickel-palladium-gold plating pads through exposure and development, the selective ink is retained on the already formed electroplated hard gold layer, the thick gold plating layer, and the areas to be subsequently silvered, forming a temporary protective layer to prevent the subsequent chemical nickel-palladium-gold plating solution from corroding or contaminating the above areas.

[0096] Preferably, after printing the selective ink and exposing and developing it, a layer of adhesive tape is then applied to the surface of the selective ink, forming a dual protective structure of selective ink and adhesive tape to further enhance the protection of non-immersion nickel-palladium-gold areas. The application of this adhesive tape also employs the aforementioned laser-cut adhesive tape application process to ensure protection precision and board surface integrity.

[0097] S520, Immersion Nickel-Palladium-Gold Treatment: The exposed immersion nickel-palladium-gold pads are sequentially treated with immersion nickel, immersion palladium, and immersion gold to form an immersion nickel-palladium-gold layer. Specifically, the exposed immersion nickel-palladium-gold pads are first pretreated, with process parameters and steps similar to those in S431, immersion gold pretreatment. Then, the entire board is sequentially immersed in chemical immersion nickel solution, chemical immersion palladium solution, and chemical immersion gold solution to form immersion nickel, immersion palladium, and immersion gold layers on the immersion nickel-gold pads, respectively.

[0098] The chemical nickel precipitate solution is composed of Ni²⁺. + The concentration of NaH₂PO₂ is 5.6-6.2 g / L, the concentration is 20-35 g / L, the pH is controlled at 4.6-5.0, and the temperature is controlled at 78-88℃. The chemical palladium precipitation solution has a palladium content of 0.4-0.7 g / L, a pH controlled at 5.5-6.5, and adds reducing agent 2 at a concentration of 120-180 ml / L. The chemical gold precipitation solution consists of Au²⁺. + The concentration is 0.4-1.2 g / l, the pH value is controlled at 5.8-6.2, and the concentration of bath supplement A is 3-5.5 g / l, the concentration of bath supplement B is 90-110 ml / l, and the concentration of bath supplement C is 270-330 ml / l.

[0099] Through the combined steps described above, a nickel-palladium-gold layer with a palladium barrier structure is formed, effectively preventing nickel-gold interdiffusion, eliminating "black pad" defects, and ensuring that the immersion nickel-palladium-gold pads possess excellent soldering reliability and long-term stability. After the immersion nickel-palladium-gold process is completed, the adhesive tape on the board surface is removed, and the selective ink is washed away, restoring the completed immersion nickel-palladium-gold pads and the areas to be processed to a bare state, preparing for subsequent immersion silver fabrication.

[0100] After the nickel-palladium-gold plating process is completed, the multilayer board is formed and tested. Step S600, forming and testing, specifically includes shape processing, electrical testing, and preliminary inspection.

[0101] During the shape processing stage, component reference numbers, logos, version numbers, and other identification characters are first silkscreened on the board surface; then countersunk holes are processed on the multilayer board to meet the installation requirements of countersunk screws; QR codes or barcodes are formed on the board surface using laser ablation to achieve product production and quality traceability; finally, a CNC milling machine is used to mill away excess board material according to the design shape to form a PCB single board of the final size.

[0102] Based on this, electrical performance tests are conducted: open-circuit and short-circuit tests are performed on all conductive networks on the board to ensure correct electrical connections; then, high voltage is applied to the board for high-voltage testing to verify its insulation reliability under high-voltage conditions.

[0103] Finally, an initial QC inspection is conducted manually or under magnification to verify the uniformity of surface treatment, the integrity of the green oil coverage, the clarity of characters, the accuracy of dimensions, and the appearance quality of the board surface. Defective products are screened out to provide qualified substrates for the subsequent silver plating process.

[0104] After molding and testing, the immersion silver fabrication process begins. Step S700 includes: first, a protective coating process is performed, using protective tape to completely encapsulate and protect the formed electroplated hard gold layer, thick gold layer, and nickel-palladium-gold layer, precisely exposing only the predetermined immersion silver area to prevent subsequent immersion silver solutions from corroding or contaminating other surface treatment layers; then, chemical immersion silver treatment is applied to the exposed clean copper surface, depositing a uniform immersion silver layer to meet the requirements of high-frequency signal transmission; after immersion silvering, the board surface is thoroughly rinsed with deionized water (DI water) to completely remove residual immersion silver solutions and impurities, ensuring the cleanliness and stability of the immersion silver layer surface. After rinsing, the protective tape is removed, restoring all solder pads to their bare state. Through these processes, the immersion silver surface treatment is completed, giving the immersion silver area of ​​the printed circuit board excellent high-frequency signal transmission performance.

[0105] After removing the adhesive tape, the printed circuit board undergoes final inspection and shipment processing. Step S800, final inspection and shipment, includes: first, a full inspection of the board surface, verifying all quality items such as surface treatment molding quality, pad integrity, board appearance, and dimensional accuracy; then, random sampling inspections are conducted according to quality control requirements to further verify product consistency and reliability; after passing inspection, the products undergo anti-oxidation packaging treatment, completing the finished product shipment.

[0106] Through the above processes, the entire process of manufacturing a printed circuit board integrating four surface treatments is completed.

[0107] Example 2

[0108] This embodiment provides a printed circuit board (PCB) manufactured using the method described in the above embodiment. The PCB integrates four surface treatment structures: electroplated hard gold, immersion gold, immersion nickel-palladium-gold, and immersion silver. It simultaneously enables wear-resistant insertion and removal, gold wire bonding, fine-pitch soldering, and high-frequency signal transmission, meeting the needs of high-end electronic products such as AI accelerator cards, high-performance servers, and mobile terminals.

[0109] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the technical solution of the present invention, and are not intended to limit the specific implementation of the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the claims of the present invention should be included within the protection scope of the claims of the present invention.

Claims

1. A method for manufacturing a printed circuit board integrating multiple surface treatments, characterized in that, Includes the following steps: S100, Fabrication of multilayer boards: Multilayer boards with conductive lines and multilayer interconnection structures are fabricated through inner layer lamination, drilling, copper plating and pattern plating processes. S200, Electroplating hard gold fabrication: On the multilayer board, through the first selective exposure, a predetermined electroplating hard gold area is exposed, and nickel plating and electroplating gold-cobalt alloy treatment are performed to form an electroplating hard gold layer. S300, Outer Layer Circuit Forming: Etching is performed on the multilayer board that has been electroplated with hard gold to form the outer layer circuit. S400, Thick Gold Plating: On a multilayer board with the outer circuit pattern formed, a second selective exposure is performed to expose the predetermined thick gold plating area, and chemical nickel-gold plating is performed to form a thick gold plating layer. S410, Printing solder resist ink: Printing solder resist ink on the surface of a multilayer board after the outer layer circuit is formed, and forming a solder resist layer by exposure and development, wherein the solder resist layer covers the non-soldering area; S420, Second selective exposure: A dry film is applied to the surface of the solder resist layer, and the predetermined thick gold pads are exposed by exposure and development; after the predetermined thick gold pads are exposed, a layer of adhesive tape is applied to the surface of the dry film to form a double protective structure of dry film and adhesive tape. S430, Thick Gold Plating: Thick gold plating is applied to the exposed thick gold pads to form a thick gold layer. S500, Immersion Nickel Palladium Gold Fabrication: On a multilayer board that has completed the immersion thick gold fabrication, a third selective exposure is performed to protect the formed electroplated hard gold layer and immersion thick gold layer, while exposing the predetermined immersion nickel palladium gold area for chemical immersion nickel, immersion palladium, and immersion gold treatment to form an immersion nickel palladium gold layer. S600, Forming and Testing: Performing shape processing and electrical testing on multilayer boards that have completed the nickel-palladium-gold plating process; S700, Immersion Silver Production: On the multilayer board that has been molded and tested, through the fourth selective exposure, the formed electroplated hard gold layer, thick gold layer and immersion nickel palladium gold layer are completely wrapped and protected with protective material, leaving only the predetermined immersion silver area exposed, and chemical immersion silver treatment is performed to form the immersion silver layer. S800, Final Inspection and Shipment: After all surface treatments are completed, final inspection and anti-oxidation packaging are carried out.

2. The method for manufacturing a printed circuit board integrating multiple surface treatments according to claim 1, characterized in that, Step S200 includes: S210, First Selective Exposure: A dry film is applied to the surface of the multilayer board after S100 is completed, and the predetermined electroplated hard gold pads are exposed by exposure and development. S220, Desoldering: Removes the protective tin layer from the exposed surface of the electroplated hard gold pads to expose the fresh copper surface; S230, Electroplating Hard Gold Treatment: The exposed copper surface of the electroplating hard gold pads is treated with nickel plating and electroplating gold-cobalt alloy to form an electroplating hard gold layer.

3. The method for manufacturing a printed circuit board integrating multiple surface treatments according to claim 2, characterized in that, Step S230 includes: S231, Copper surface activation treatment: Activation treatment for copper surface after detinning; S232, Nickel plating treatment: Electroplating a nickel layer onto the activated copper surface; S233, Hard gold plating treatment: Electroplating a gold-cobalt alloy layer onto a nickel layer.

4. The method for manufacturing a printed circuit board integrating multiple surface treatments according to claim 3, characterized in that, Step S231 includes: S2311, Acid Immersion Pre-protection: Pre-immersion treatment of the exposed copper surface using H2SO4 solution with a mass concentration of 3-7%; S2312 Degreasing treatment: Use a degreasing solution with a mass concentration of 8-12% to remove oil stains from the copper surface; S2313, Micro-etching treatment: Micro-etching is performed on the copper surface, with an etching depth of 30-70 microinches; S2314, Acid washing and activation: Acid washing is performed using an H2SO4 solution with a mass concentration of 5-15%.

5. The method for manufacturing a printed circuit board integrating multiple surface treatments according to claim 1, characterized in that, Step S430 includes: S431, Pretreatment of thick gold plating: Degreasing, micro-etching, pre-dipping and activation treatment of exposed thick gold plating pads; S432, Chemical Nickel Plating: The entire board is immersed in chemical nickel plating solution to form a nickel plating layer on the exposed surface of the thick gold pads. S433, Chemical Immersion Gold Treatment: The entire board after nickel immersion is immersed in chemical immersion gold solution to form a thick gold layer on the nickel immersion layer.

6. The method for manufacturing a printed circuit board integrating multiple surface treatments according to any one of claims 1-4, characterized in that, Step S500 includes: S510, Third Selective Exposure: Selective ink is printed on the multilayer board after the thick gold plating is completed, and the predetermined nickel-palladium-gold solder pads are exposed by exposure and development. S520, Immersion Nickel Palladium Gold Treatment: The exposed immersion nickel palladium gold pads are sequentially treated with immersion nickel, immersion palladium, and immersion gold to form an immersion nickel palladium gold layer.

7. The method for manufacturing a printed circuit board integrating multiple surface treatments according to claim 6, characterized in that, In step S510, after printing the selective ink, a layer of adhesive paper is then applied to the surface of the selective ink to form a double protective structure of selective ink and adhesive paper.

8. A printed circuit board, characterized in that, It is manufactured using the manufacturing method described in any one of claims 1-7.

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