Method for producing vertical pad circuit board for 5g communication device

Abstract

The application provides a vertical pad circuit board production method of a 5G communication device, comprising the following steps: a vertical pad module manufacturing step, an L2-L3 layer flowable prepreg slotting step, an L1-L2 and L3-L4 layer manufacturing step, and an L1-L4 layer manufacturing step. The vertical pad module is manufactured by using a thick copper core plate laminated substrate, the two sides of the vertical pad module are placed upward and downward with the sidewall metallized (so that the thick copper layer is vertical), the vertical pad module is embedded in the board by using a local mixed pressing method, then drilling, copper deposition, milling of the metal groove hole is performed to expose the vertical thick copper layer, and then graphic plating and gold deposition are performed to manufacture the vertical pad PCB structure. The vertical pad design is diversified, the bottleneck of the conventional pad planarization is broken, the space saving requirement of the customer for the vertical welding component is met, and mass production can be realized.

Description

Technical Field

[0001] This invention relates to the field of circuit board manufacturing, and in particular to a method for producing a vertical pad circuit board for 5G communication equipment. Background Technology

[0002] As PCB electronic products increasingly trend towards miniaturization, high integration, and high frequency, some 5G communication equipment PCB products are beginning to adopt vertical pad designs for mounting components, thereby improving overall product integration or saving space. Existing pad designs, due to their small width and limitations in equipment and processing methods, restrict the pads to planar designs, which consumes significant space when soldering components onto planar pads. Some products, to save space, require component mounting within the sidewalls of slots, necessitating a 90° vertical design of the PCB pads to the sidewalls. Currently, there is no method in the industry to manufacture pads for this vertical sidewall position. Summary of the Invention

[0003] This invention provides a method for manufacturing a vertical pad circuit board for 5G communication devices to solve at least one of the aforementioned technical problems.

[0004] To address the aforementioned problems, as one aspect of the present invention, a method for manufacturing a vertical pad circuit board for a 5G communication device is provided, comprising: a vertical pad module fabrication step, a slotting step for L2-L3 layer flowable prepreg, a fabrication step for L1-L2 and L3-L4 layers, and a fabrication step for L1-L4 layers. The steps for fabricating a vertical pad module include: Step 11, First lamination: Under certain temperature and pressure, the resin in the prepreg flows and solidifies when the temperature reaches a certain level, bonding together 9 core boards with a thickness of 0.13mm and 6oz copper on both sides, 2 copper foils, and 10 prepreg sheets. Step 12, Milling slot 1: As required, use a 1.0mm milling cutter to mill slots into the plate using a milling machine.

[0005] Step 13, sidewall metallization: Plating copper: The sidewalls of the plate after milling are metallized. The main purpose of the treatment is to form a conductive layer in the sidewall substrate area, and the resulting copper layer is about 0.02um. Negative plating: After copper plating, the copper layer of the board is thickened by electroplating to a thickness of about 10-12um, so that the sidewalls are metallized and conductive with the thick copper layer. Step 14, External Light Imaging 1: Under certain temperature and pressure conditions, a dry film is applied to the board surface, then the film is aligned, and finally, ultraviolet light is used in the exposure machine to cause the dry film not covered by the film to react and form the required circuit pattern on the board surface. Then, in the developing section, the film that has not been exposed to light is dissolved by the developing solution, exposing the areas that need to be tin-plated. Step 15, Tin plating: Tin ions are dissolved at the anode in the tin plating bath and move to the cathode under the action of an electric field. They gain electrons and form an etch-resistant protective tin layer on the copper layer surrounding the sidewall. Step 16, Outer layer etching 1: Under the action of alkaline solution, the film is removed to expose the copper surface to be etched. In the etching tank, copper reacts with copper ions to produce copper sub-metal, thus achieving the etching effect. The top and bottom copper layers are etched away to expose the substrate. In the desoldering tank, nitric acid reacts with the tin surface to remove the tin plating layer and expose the copper layer on the sidewall. Step 17, Milling plate 1: As required, a 1.0mm milling cutter was used to mill the board into vertical pad modules, thus completing the fabrication of the vertical pad modules. The grooving step of the L2-L3 layer fluid prepreg includes: according to the requirements, using a 1.0mm milling cutter to perform milling on the fluid prepreg to mill out a square groove of the same size as the L1-L2 and L3-L4 core board layers, in order to facilitate the subsequent stacking with the L1-L2 and L3-L4 layers. The steps for creating layers L1-L2 and L3-L4 include: Step 21, Cutting materials: The L1-L2 and L3-L4 layers of copper-clad laminate are cut to the design size using a cutting machine; Step 22, Internal Light Imaging: Under certain temperature and pressure conditions, a dry film is applied to the board surface, then the film is aligned, and finally, ultraviolet light is used in the exposure machine to cause the dry film not covered by the film to react and form the required circuit pattern on the board surface. Then, in the developing section, the film that has not been exposed to light is dissolved by the developing solution, exposing the areas of L2 and L3 layers that need to be etched, while the copper surfaces of L1 and L4 layers are protected by dry film. Step 23, Inner layer etching: In the etching tank, copper reacts with copper ions to produce copper sub-cubic membrane, thus achieving the etching effect and creating the L2 and L3 layer circuits. Then, in the stripping tank, the film is dissolved under the action of alkaline solution to expose the desired circuits. Step 24, Milling slot 1: As required, a milling machine is used to process the core board of layers L1-L2 and L3-L4 with a 0.8mm milling cutter to mill a groove whose length and width are 0.2mm larger than the length and width of the vertical pad module, in order to facilitate the subsequent stacking with layers L2-L3. The steps for creating layers L1-L4 include: Step 31, Lamination: The core boards of layers L1-L2 and L3-L4 are browned. Then, the flowable prepregs of L2-L3 are stacked and riveted together with tube pins. Then, vertical pad modules are placed in the slots (the top and bottom of the metallized sidewalls of the vertical pad modules are placed up and down so that the thick copper layer is vertical). Under certain temperature and pressure, the resin of the prepregs flows and fills the circuit and substrate. When the temperature reaches a certain level, curing occurs, bonding the interlayer and the vertical pad modules together to form layers L1-L4. Step 32, Drilling: According to the customer's requirements, drilling is performed on the board to prepare for the connection between the inner and outer layers in subsequent processes.

[0006] Step 33, Hole Metallization (Immersion Copper, Plate Plating): Plating copper: This process involves metallizing the holes in the board after drilling. The main purpose of this process is to form a conductive layer in the substrate area in the middle of the board, resulting in a copper layer of about 0.02um. Plate plating: After copper plating, the copper layer on the board is thickened by electroplating, with a thickness of about 5-8 μm. Step 34, Milling metal slots: As required, a 1.0mm milling cutter is used to mill the board with a milling machine to create an open slot that is 4mm smaller than the "milling slot 1" slot (i.e., leaving a 2mm vertical solder pad module on one side of the substrate), exposing the vertical thick copper layer. Step 35, External Light Imaging: Under certain temperature and pressure conditions, a dry film is applied to the board surface, then the film is aligned, and finally, ultraviolet light is used in the exposure machine to cause the dry film not covered by the film to react and form the required circuit pattern on the board surface. Then, in the developing section, the film that has not been exposed to light is dissolved by the developing solution, exposing the areas that need to be plated with copper and tin. Step 36, Pattern Electroplating: The pretreatment process cleans the board surface. Copper and tin ions are dissolved at the anode in the copper and tin plating baths. Under the action of an electric field, they move to the cathode, gain electrons, and are plated with a layer of metallic copper and a layer of tin for etching protection on the conductive areas of the board. Step 37, outer layer etching: Under the action of alkaline solution, the film is removed to expose the copper surface to be etched. In the etching tank, copper reacts with copper ions to produce copper sub-metal, thus achieving the etching effect. In the desoldering tank, nitric acid reacts with the tin surface to remove the tin plating layer, exposing the copper surface of the circuit pads and the etched vertical pads. Step 38, Solder Mask / Character: Solder resist: Solder resist paste is screen-printed onto the board surface using a screen printing machine. Pre-baking removes volatiles, forming a semi-cured film. Through alignment and exposure, the solder resist film undergoes cross-linking reactions in the exposed areas, while the unexposed areas are developed and removed under alkaline conditions. At high temperature, the solder resist fully cures and adheres to the board surface. Characters: The manufacturing method is similar to that of solder mask; Step 39, Immersion Gold: A layer of nickel and a layer of gold are deposited on the copper surface and vertical pads of the board through a chemical displacement reaction.

[0007] This invention first uses a thick copper core board laminated substrate to create a vertical pad module. Then, the two metallized sides of the vertical pad module are placed face up and down (making the thick copper layer vertical). A localized mixed-lamination method is used to embed the vertical pad module within the board for lamination. Next, holes are drilled, electroplated copper is applied, and metal slots are milled to expose the vertical thick copper layer. Finally, through plating and immersion gold treatment, a vertical pad PCB structure is created. This allows for diversified pad design, breaking through the bottleneck of conventional planar pads, meeting customers' space-saving needs for vertically soldering components, and enabling mass production. Attached Figure Description

[0008] Figure 1 A cross-sectional view of the invention is shown schematically; Figure 2 A schematic diagram of the structure of the present invention is shown. Figure 3 A schematic diagram of step 11 is shown; Figure 4 A schematic diagram of step 12 is shown; Figure 5 A schematic diagram of step 13 is shown; Figure 6 A schematic diagram of step 14 is shown; Figure 7 A schematic diagram of step 15 is shown; Figure 8 A schematic diagram of step 16 is shown; Figure 9 A schematic diagram of step 17 is shown; Figure 10 A schematic diagram illustrating the grooving steps of the L2-L3 layer flowable prepreg; Figure 11A schematic diagram of step 22 is shown; Figure 12 A schematic diagram of step 23 is shown; Figure 13 A schematic diagram of step 24 is shown; Figure 14 A schematic diagram of step 31 is shown; Figure 15 A schematic diagram of step 32 is shown; Figure 16 A schematic diagram of step 34 is shown; Figure 17 A schematic diagram of step 35 is shown; Figure 18 A schematic diagram of step 36 is shown; Figure 19 A schematic diagram of step 37 is shown. Detailed Implementation

[0009] The embodiments of the present invention will be described in detail below, but the present invention can be implemented in many different ways as defined and covered by the claims.

[0010] Figure 1 In the diagram, "1" represents the L1 layer of the PCB board; "2" represents the L2 layer of the PCB board; "3" represents the L3 layer of the PCB board; "4" represents the L4 layer of the PCB board; "5" represents the copper surface after metallization of the sidewall of the vertical pad module; and "6" represents the vertical thick copper layer in the vertical pad module. Figure 2 In the diagram, "7" represents the vertical pad, "8" represents the solder mask, "9" represents the thick copper layer, "10" represents the base copper, "11" represents the plate copper plating, "12" represents the pattern copper plating, "13" represents the sidewall metallized copper, and "14" represents the slot.

[0011] This invention first uses a substrate laminated with a thick copper core board to create a vertical pad module. Then, the two sides of the vertical pad module with metallized sidewalls are placed face up and down (so that the thick copper layer is vertical). The vertical pad module is built into the board and laminated using a local mixed pressing method. Then, holes are drilled, electroplated copper is applied, and metal slots are milled to expose the vertical thick copper layer. Finally, after plating and immersion gold, a vertical pad PCB structure is created.

[0012] This invention first uses a substrate laminated with a thick copper core board to create a vertical pad module. Then, the two sides of the vertical pad module with metallized sidewalls are placed face up and down (so that the thick copper layer is vertical). The vertical pad module is built into the board and laminated using a local mixed pressing method. Then, holes are drilled, electroplated copper is applied, and metal slots are milled to expose the vertical thick copper layer. Finally, after plating and immersion gold, a vertical pad PCB structure is created.

[0013] Vertical pad module manufacturing process 1. Single lamination: Under certain temperature and pressure, the resin in the prepreg flows and solidifies when the temperature reaches a certain level, bonding 9 0.13mm copper-free boards, 2 copper foils, and 10 prepregs together.

[0014] 2. Milling slot 1 As required, use a 1.0mm milling cutter to mill slots into the plate using a milling machine.

[0015] 3. Sidewall metallization Plating copper: The sidewalls of the plate after milling are metallized. The main purpose of the treatment is to form a conductive layer in the sidewall substrate area, and the resulting copper layer is about 0.02um. Negative plating: After copper plating, the copper layer on the board is thickened by electroplating to a thickness of about 10-12um, so that the sidewalls are metallized and conductive with the thick copper layer.

[0016] 4. External light imaging 1 Under certain temperature and pressure conditions, a dry film is applied to the board surface, then the film is aligned, and finally, ultraviolet light is used in the exposure machine to cause the dry film not covered by the film to react and form the required circuit pattern on the board surface. Then, in the developing section, the film that was not exposed to light is dissolved by the developing solution, exposing the areas that need to be tin-plated.

[0017] 5. Tin plating Tin ions dissolve at the anode in the tin plating bath and migrate to the cathode under the influence of an electric field. They gain electrons and deposit an etch-resistant protective tin layer onto the copper layer surrounding the sidewall. 6. Outer layer etching 1 Under the action of alkaline solution, the film is removed to expose the copper surface to be etched. In the etching tank, copper reacts with copper ions to produce copper sub-metal, achieving the etching effect and etching away the top and bottom copper layers to expose the substrate. In the desoldering tank, nitric acid reacts with the tin surface to remove the tin plating layer, exposing the copper layer surrounding the sidewalls. 7. Milling plate 1 As required, a 1.0mm milling cutter was used to mill the board into vertical pad modules, thus completing the fabrication of the vertical pad modules.

[0018] L2-L3 layers: Grooved semi-cured sheet with fluidity: As required, a 1.0mm milling cutter is used to mill square grooves of the same size as the L1-L2 and L3-L4 core board layers on the flow semi-cured surface. This is to prepare for subsequent stacking with the L1-L2 and L3-L4 layers.

[0019] Key manufacturing processes for L1-L2 and L3-L4 layers: 1. Material cutting: The L1-L2 and L3-L4 layers of copper-clad laminate are cut to the design size using a cutting machine.

[0020] 2. Internal light imaging Under certain temperature and pressure conditions, a dry film is applied to the board surface, then the film is aligned, and finally, ultraviolet light is used in the exposure machine to cause the unmasked dry film to react, forming the required circuit pattern on the board surface. Then, in the developing section, the film that has not been exposed to light is dissolved by the developing solution, exposing the areas of L2 and L3 layers that need to be etched, while the copper surfaces of L1 and L4 layers are protected by the dry film.

[0021] 3. Inner layer etching In the etching tank, copper reacts with copper ions to produce copper sub-cubic membrane, thus achieving the etching effect and creating the L2 and L3 layers of circuitry. Then, in the stripping tank, the film is dissolved under the action of alkaline solution to expose the desired circuitry.

[0022] 4. Milling slot 1 As required, a milling machine is used to mill the core boards of layers L1-L2 and L3-L4 with a 0.8mm milling cutter to create grooves whose length and width dimensions are 0.2mm larger than those of the vertical pad module, in order to facilitate subsequent stacking with layers L2-L3.

[0023] Key production process for layers L1-L4: 1. Lamination: The core boards of layers L1-L2 and L3-L4 are browned. Then, the flowable prepregs of L2-L3 are stacked and riveted together with pins. Then, vertical pad modules are placed in the slots (the top and bottom of the metallized sidewalls of the vertical pad modules are placed face up and down so that the thick copper layer is vertical). Under certain temperature and pressure, the resin of the prepregs flows and fills the circuit and substrate. When the temperature reaches a certain level, curing occurs, bonding the interlayer and vertical pad modules together to form layers L1-L4.

[0024] 2. Drilling: According to the customer's requirements, drilling is performed on the board to prepare for the connection between the inner and outer layers in subsequent processes.

[0025] 3. Hole metallization (electroplating, plate plating): Plating copper: This process involves metallizing the holes in the board after drilling. The main purpose of this process is to form a conductive layer in the substrate area in the middle of the board, resulting in a copper layer of about 0.02um. Plate plating: After copper plating, the copper layer on the board is thickened by electroplating, with a thickness of about 5-8 μm.

[0026] 4. Milling metal slots As required, a 1.0mm milling cutter is used to mill a slot on the board, which is 4mm smaller than the "milling slot 1" slot (i.e., leaving a 2mm vertical solder pad module on one side of the substrate), exposing the vertical thick copper layer.

[0027] 5. External light imaging Under certain temperature and pressure conditions, a dry film is applied to the board surface, then the film is aligned, and finally, ultraviolet light is used in the exposure machine to cause the dry film not covered by the film to react and form the required circuit pattern on the board surface. Then, in the developing section, the film that was not exposed to light is dissolved by the developing solution, exposing the areas that need to be plated with copper and tin.

[0028] 6. Graphic electroplating The pretreatment process cleans the board surface. Copper and tin ions are dissolved at the anode in the copper and tin plating baths. Under the influence of an electric field, they move to the cathode, gain electrons, and are then plated with a layer of metallic copper and a layer of tin for etching protection on the conductive areas of the board.

[0029] 7. Outer layer etching Under the action of alkaline solution, the film is removed to expose the copper surface to be etched. In the etching tank, copper reacts with copper ions to produce copper sub-metal, thus achieving the etching effect. In the desoldering tank, nitric acid reacts with the tin surface to remove the tin plating layer, exposing the copper surface of the circuit pads and the etched vertical pads.

[0030] 8. Solder mask / characters Solder resist: Solder resist paste is screen-printed onto the board surface using a screen printing machine. Pre-baking removes volatiles, forming a semi-cured film. Through alignment and exposure, the solder resist film undergoes cross-linking reactions in the exposed areas, while the unexposed areas are developed and removed under alkaline conditions. At high temperature, the solder resist fully cures and adheres to the board surface.

[0031] Characters: The manufacturing method is similar to that of solder mask.

[0032] 9. Sinking Gold A layer of nickel and a layer of gold are deposited on the copper surface and vertical pads of the board through a chemical displacement reaction.

[0033] This invention first uses a thick copper core board laminated substrate to create a vertical pad module. Then, the two metallized sides of the vertical pad module are placed face up and down (making the thick copper layer vertical). A localized mixed-lamination method is used to embed the vertical pad module within the board for lamination. Next, holes are drilled, electroplated copper is applied, and metal slots are milled to expose the vertical thick copper layer. Finally, through plating and immersion gold treatment, a vertical pad PCB structure is created. This allows for diversified pad design, breaking through the bottleneck of conventional planar pads, meeting customers' space-saving needs for vertically soldering components, and enabling mass production.

[0034] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for manufacturing a vertical pad circuit board for a 5G communication device, characterized in that, include: Vertical pad module fabrication steps, L2-L3 layer flowable prepreg grooving steps, L1-L2 and L3-L4 layer fabrication steps, L1-L4 layer fabrication steps: The steps for fabricating a vertical pad module include: Step 11, First lamination: Under certain temperature and pressure, the resin in the prepreg flows and solidifies when the temperature reaches a certain level. This binds together 9 core boards with a substrate thickness of 0.13mm and a double-sided copper thickness of 6oz, 2 copper foils, and 10 prepreg sheets. Step 12, Milling slot 1: As required, use a 1.0mm milling cutter to perform milling on the plate to create slots; Step 13, sidewall metallization: Plating copper: The sidewalls of the plate after milling are metallized. The main purpose of the treatment is to form a conductive layer in the substrate area of ​​the sidewalls. The resulting copper layer is about 0.02um. Negative plating: After copper plating, the copper layer of the board is thickened by electroplating to a thickness of about 10-12um, so that the sidewalls are metallized and conductive with the thick copper layer. Step 14, External Light Imaging 1: Under certain temperature and pressure conditions, a dry film is applied to the board surface, then the film is aligned, and finally, ultraviolet light is used in the exposure machine to cause the dry film not covered by the film to react and form the required circuit pattern on the board surface. Then, in the developing section, the film that has not been exposed to light is dissolved by the developing solution, exposing the areas that need to be tin-plated. Step 15, Tin plating: Tin ions are dissolved at the anode in the tin plating bath and move to the cathode under the action of an electric field. They gain electrons and form an etch-resistant protective tin layer on the copper layer surrounding the sidewall. Step 16, Outer layer etching 1: Under the action of alkaline solution, the film is removed to expose the copper surface to be etched. In the etching tank, copper reacts with copper ions to produce copper sub-metal, thus achieving the etching effect. The top and bottom copper layers are etched away to expose the substrate. In the desoldering tank, nitric acid reacts with the tin surface to remove the tin plating layer and expose the copper layer on the sidewall. Step 17, Milling plate 1: As required, a 1.0mm milling cutter was used to mill the board into vertical pad modules, thus completing the fabrication of the vertical pad modules. The grooving step of the L2-L3 layer fluid prepreg includes: according to the requirements, using a 1.0mm milling cutter to perform milling on the fluid prepreg to mill out a square groove of the same size as the L1-L2 and L3-L4 core board layers, in order to facilitate the subsequent stacking with the L1-L2 and L3-L4 layers. The steps for creating layers L1-L2 and L3-L4 include: Step 21, Cutting materials: The L1-L2 and L3-L4 layers of copper-clad laminate are cut to the design size using a cutting machine; Step 22, Internal Light Imaging: Under certain temperature and pressure conditions, a dry film is applied to the board surface, then the film is aligned, and finally, ultraviolet light is used in the exposure machine to cause the dry film not covered by the film to react and form the required circuit pattern on the board surface. Then, in the developing section, the film that has not been exposed to light is dissolved by the developing solution, exposing the areas of L2 and L3 layers that need to be etched, while the copper surfaces of L1 and L4 layers are protected by dry film. Step 23, Inner layer etching: In the etching tank, copper reacts with copper ions to produce copper sub-cubic membrane, thus achieving the etching effect and creating the L2 and L3 layer circuits. Then, in the stripping tank, the film is dissolved under the action of alkaline solution to expose the desired circuits. Step 24, Milling slot 1: As required, a milling machine is used to process the core board of layers L1-L2 and L3-L4 with a 0.8mm milling cutter to mill a groove whose length and width are 0.2mm larger than the length and width of the vertical pad module, in order to facilitate the subsequent stacking with layers L2-L3. The steps for creating layers L1-L4 include: Step 31, Lamination: The core boards of layers L1-L2 and L3-L4 are browned. Then, the flowable prepregs of L2-L3 are stacked and riveted together with tube pins. Then, vertical pad modules are placed in the slots with the top and bottom of the metallized sidewalls of the vertical pad modules facing up and down, so that the thick copper layer is vertical. Under certain temperature and pressure, the resin of the prepreg flows and fills the circuit and substrate. When the temperature reaches a certain level, curing occurs, bonding the interlayer and vertical pad modules together to form layers L1-L4. Step 32, Drilling: According to the customer's requirements, drilling is performed on the board to prepare for the connection between the inner and outer layers in subsequent processes; Step 33, hole metallization with copper plating, plate plating: Plating copper: This process involves metallizing the holes in a board after drilling. The main purpose of this process is to form a conductive layer in the substrate area in the middle of the board, resulting in a copper layer of about 0.02um. Plate plating: After copper plating, the copper layer on the board is thickened by electroplating, with a thickness of about 5-8 μm. Step 34, Milling metal slots: As required, a 1.0mm milling cutter is used to mill the board, creating an open slot that is 4mm smaller than the slot width in step 24, leaving a 2mm vertical solder pad module on one side of the substrate to expose the vertical thick copper layer. Step 35, External Light Imaging: Under certain temperature and pressure conditions, a dry film is applied to the board surface, then the film is aligned, and finally, ultraviolet light is used in the exposure machine to cause the dry film not covered by the film to react and form the required circuit pattern on the board surface. Then, in the developing section, the film that has not been exposed to light is dissolved by the developing solution, exposing the areas that need to be plated with copper and tin. Step 36, Pattern Electroplating: The pretreatment process cleans the board surface. Copper and tin ions are dissolved at the anode in the copper and tin plating baths. Under the action of an electric field, they move to the cathode, gain electrons, and are plated with a layer of metallic copper and a layer of tin for etching protection on the conductive areas of the board. Step 37, outer layer etching: Under the action of alkaline solution, the film is removed to expose the copper surface to be etched. In the etching tank, copper reacts with copper ions to produce copper sub-metal, thus achieving the etching effect. In the desoldering tank, nitric acid reacts with the tin surface to remove the tin plating layer, exposing the copper surface of the circuit pads and the etched vertical pads. Step 38, Solder Mask / Character: Solder resist: Solder resist paste is screen-printed onto the board surface using a screen printing machine. After pre-baking to remove volatiles, a semi-cured film layer is formed. Through alignment and exposure, the solder resist film undergoes cross-linking reaction in the areas exposed to light, while the unexposed areas are developed and removed under the action of alkaline solution. At high temperature, the solder resist is completely cured and adheres to the board surface. character; Step 39, Immersion Gold: A layer of nickel and a layer of gold are deposited on the copper surface and vertical pads of the board through a chemical displacement reaction.

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