A production process of PCB side edge embedded test pads

Abstract

The application relates to the technical field of PCB manufacturing, in particular to a production process of a PCB side edge embedded test pad, which comprises the following steps: S1, presetting a test base point on an inner layer of a PCB; S2, milling a blind groove inward at a position corresponding to the inner layer test point base on the side edge of the PCB; S3, performing activation treatment on the blind groove to make palladium metal particles uniformly adhere to all inner wall surfaces of the blind groove; S4, depositing a uniform copper layer on the inner wall of the blind groove, so that the inner wall of the blind groove is completely formed into a conductive copper surface; and S5, performing electroplating, so that the inside of the blind groove is completely filled with metal copper; under the premise that an additional connecting via hole is not needed on the inner layer functional circuit, the physical bearing position of the test point is directly transferred from the surface layer of the PCB to the side edge embedded space, the available wiring area of the surface layer of the PCB is improved, and the technical problems of recess, substrate crack and pad falling caused by vertical extrusion of rigid probes on the surface of the PCB during electrical test of an ultrathin PCB are solved.

Description

Technical Field

[0001] This invention relates to the field of PCB manufacturing technology, and in particular to a production process for embedded test pads on the side of a PCB. Background Technology

[0002] Currently, almost all test pads in the PCB industry are located on the surface or bottom layer of the PCB board. This approach presents intractable technical problems in the production of high-density HDI boards and ultra-thin PCB boards: surface test pads occupy a large amount of valuable surface routing space, forcing designers to connect inner layer test points to the surface layer through additional blind vias. This not only increases the cost of drilling and electroplating processes but also occupies inner layer routing resources, further compressing the already limited circuit design space. At the same time, in the electrical testing process, rigid probes directly and vertically press against the surface pads, which can easily cause defects such as board surface dents, pad detachment, and substrate cracks for ultra-thin PCB boards with a thickness of less than 0.4mm.

[0003] Although existing technologies address the aforementioned technical problems by setting test points on the edge of the PCB board, most of these methods simply extend ordinary circuits to the exposed side of the board without making specific structural and process optimizations for the side pads. As a result, issues such as poor pad adhesion, easy oxidation, unstable test contact, and pad detachment after multiple probe penetrations still exist. Based on this, this application proposes a manufacturing process for embedded test pads on the side of the PCB board. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the purpose of this application is to provide a manufacturing process for embedded test pads on the side of a PCB board, thereby solving the technical problems mentioned in the background art.

[0005] The above-mentioned objective of this application is achieved through the following technical solution: a manufacturing process for embedded test pads on the side of a PCB board, comprising the following steps: S1, inner layer test point pre-setting: during the inner layer circuit pattern fabrication stage of the PCB board, according to the design file, a square copper block is reserved as the test point base at the corresponding inner layer board edge position. A preset distance is left between the outer edge of the square copper block and the side distance of the final PCB board product. The square copper block is directly connected to the inner layer functional circuit. S2. Blind slot pre-processing: After all lamination and outer layer circuit fabrication processes are completed on the PCB board, a blind slot with a convex cross-section is milled inward on the side of the PCB board corresponding to the position of the inner layer test point base. The bottom of the blind slot completely exposes the outer edge of the square copper block reserved in the inner layer. S3. In-tank activation treatment: Immerse the PCB board in acidic colloidal palladium activation solution and use ultrasonic-assisted vibration treatment to make palladium metal particles evenly adhere to the entire inner wall surface of the blind tank. Then rinse the board surface with deionized water to remove the activation solution remaining outside the tank. S4. Chemical copper plating filling: The activated PCB board is placed in the chemical copper plating solution, and a uniform copper layer is deposited on the inner wall of the blind trench, so that the inner wall of the blind trench is completely formed as a conductive copper surface, and the copper layer is completely connected to the test point substrate reserved in the inner layer. S5. Electroplating Thickening Forming: The PCB board is placed in an acidic copper plating bath for electroplating, so that the inside of the blind tank is completely filled with metallic copper. After electroplating, the copper surface on the outside of the blind tank is flush with the side reference surface of the PCB board, forming a complete embedded side test pad.

[0006] By adopting the above technical solution, without the need to add additional connection vias to the inner functional circuits, the physical bearing position of the test point is directly transferred from the PCB surface to the side embedded space, which increases the available wiring area on the PCB surface. This solves the technical problems of indentation, substrate cracking, and pad detachment caused by rigid probes perpendicularly pressing the board surface during electrical testing of ultra-thin PCBs.

[0007] Furthermore, after step S5, the process also includes: S6, pad surface passivation: the PCB board is immersed in an organic solder resist solution to generate an organic protective layer on the outer surface of the side-embedded test pads. After completion, it is rinsed with deionized water and dried with hot air to obtain the final product.

[0008] By adopting the above technical solution, without damaging the original high adhesion structure of the side embedded pads, a uniform organic protective layer is constructed on the exposed copper surface, which completely isolates the copper layer of the pads from direct contact with the outside air and moisture, thus avoiding the oxidation and blackening problem that is very easy to occur in bare copper pads during turnover and storage.

[0009] Furthermore, step S3 also includes sub-step S31, which includes the following steps: before activation treatment, acid and alkali resistant PET solder resist film is pre-applied to the upper and lower surfaces of the PCB board, exposing only the side blind slot area, so as to prevent palladium particles from adhering to the board surface.

[0010] Furthermore, step S4 also includes sub-step S41, which includes the following steps: after the chemical copper plating is completed, the board surface is quickly sprayed with ammonium persulfate weak etchant to remove any possible residual copper spots.

[0011] By adopting the above technical solution, although the in-tank activation treatment can remove the residual activation solution outside the tank by rinsing the board surface with ionized water, relying solely on ionized water rinsing may leave trace amounts of palladium particles on the surface of the solder mask layer during mass production. In the subsequent chemical copper plating process, this may generate sporadic copper spots in the non-pad areas of the board surface, causing micro-short circuit defects in the outer layer circuitry. The S31 and S41 steps solve this technical problem. The acid and alkali resistant PET solder mask film uses a 25μm specification with silicone pressure-sensitive adhesive, and after application, it adheres tightly to the board surface without any lifting edges. After activation, the plating solution can be completely removed without any residue on the board surface. It does not damage the original solder mask layer or the outer circuit pattern, and it also isolates palladium particles from adhering to the board surface. The subsequent ammonium persulfate weak corrosion spray only takes 10 seconds to complete. While completely removing the scattered copper spots on the board surface, it does not cause any corrosion damage to the copper plating layer inside the blind slot or the side pad structure. This blocks the adhesion path of the palladium activation solution to non-target areas on the upper and lower surfaces of the PCB, and solves the technical problem of scattered copper spots in chemical copper plating caused by residual palladium particles on the board surface.

[0012] Furthermore, in step S3, while the ultrasonic-assisted oscillation treatment is being performed, a small amount of compressed air is introduced into the activation liquid to bubble it, ensuring that the inner wall deep inside the blind tank can also be fully in contact with the activation liquid.

[0013] By adopting the above technical solution, the high-frequency micro-vibration of ultrasound and the liquid flow disturbance of bubbling work together to break up the tiny bubbles remaining inside the blind tank, allowing the activation liquid to continuously circulate and renew to the deepest part of the blind tank, thus avoiding the problem of uneven adhesion of palladium particles and incomplete activation in the dead corners of the tank.

[0014] Furthermore, in the electroplating thickening process in step S5, a shielding fixture is used to hold the PCB board. The shielding fixture only exposes the blind slot position on the side of the PCB board to shield the surface and bottom layers of the PCB board and prevent abnormal growth in the copper thickness of the outer layer during the electroplating process.

[0015] Furthermore, the shielding fixture includes a shielding frame, which is divided into multiple placement spaces for placing PCB boards. All the placement spaces are arranged in two rows within the shielding frame. One side of the shielding frame has an opening that extends through the entire length of the shielding frame, so that the top of all the placement spaces is open, which facilitates the quick handling of PCB boards. The number of exposed through holes is the same as the placement space and each one corresponds to a placement space. The exposed through holes are opened on the outside of the shielding frame, and their specific positions correspond to the blind slots on the side of the PCB board, ensuring that the electroplating solution enters the blind slots only through the exposed through holes. The lid is used to cover the opening on the shielding frame, thus completing the closure of the shielding frame.

[0016] By adopting the above technical solution, when electroplating thickening is required in step S5, multiple PCB boards are first placed into multiple placement spaces, ensuring that the blind slots of the PCB boards are opposite to the exposed through holes. Then, the box cover is closed to completely cover the opening, forming a closed cavity with the shielding frame. The upper and lower surface layers and the bottom layer circuits of the PCB board are sealed inside the cavity, and the electroplating solution cannot come into contact with any area of ​​the board surface, thereby preventing the problem of abnormal growth of copper thickness of the outer layer circuits during the electroplating process, ensuring that the copper layer in the side blind slots grows uniformly, and will not have any impact on the original circuits on the board surface.

[0017] Furthermore, the PCB board is provided with marking arrows indicating the location of blind slots.

[0018] By adopting the above solution, when operators load PCB boards into the placement space of the shielding frame, they can directly align the relative positions of the exposed through holes and blind slots by the marking arrows on the board surface, without the need for repeated alignment and calibration, thus reducing the error rate of placing PCB boards in the placement space. This is especially suitable for batch clamping scenarios of PCB boards with multiple blind slot arrays.

[0019] Furthermore, all of the aforementioned placement spaces are equipped with spring-loaded elements, which are used to press the PCB board within the placement space so that the blind slots of the PCB board are accurately aligned with the exposed through holes. The spring-loaded element includes: multiple spring-loaded springs, which are respectively arranged on the side walls of the placement space where no exposed through holes are opened. The spring force of the spring-loaded springs points inward into the placement space and is used to apply continuous elastic pressure to the PCB board. At least three flexible protective strips are provided, which are respectively installed on the side walls of the placement space where no exposed through holes are opened. The flexible protective strips are fixedly connected to the inner end of the spring compression spring and are made of acid and alkali resistant silicone material. They directly contact the PCB board surface, providing elastic support while preventing the hard spring from scratching the board surface circuit.

[0020] While the shielding fixture prevents abnormal copper thickness growth in the outer layer during electroplating, gaps inevitably exist between the PCB board and the inner wall of the frame in the actual production process. If the PCB board shifts in the electroplating solution, the blind slots and exposed vias will not align precisely, potentially causing the electroplating solution to seep into the board surface through the gaps or uneven filling of the blind slots. The spring-loaded components solve this problem. Multiple spring-loaded springs are arranged on the side walls of the placement space where no exposed vias are opened, and their spring force is uniformly directed towards the placement space. Inside, a stable elastic pressure is continuously applied to the PCB board. The flexible protective strip is fixedly connected to the inner end of the spring and directly contacts the PCB board surface. While providing elastic support, it prevents the hard spring from scratching the circuitry on the board surface. It always keeps the PCB board stably against the side wall with exposed through holes, ensuring that the blind groove and the exposed through holes are precisely aligned. The electroplating solution only enters the blind groove through the exposed through holes, thus preventing the PCB board from shifting in the electroplating solution. If the blind groove and the exposed through holes are not precisely aligned, the electroplating solution may seep into the board surface from the gaps or the blind groove may not be filled evenly.

[0021] Furthermore, after the electroplating in step S5 is completed, a nylon abrasive brush is used to lightly grind the sides of the PCB board to remove the slight oxide layer on the surface of the pads and ensure the flatness of the outer surface of the pads.

[0022] By adopting the above technical solution, after electroplating, a nylon abrasive brush is used to lightly grind the sides of the PCB board, which can effectively remove the slight oxide layer generated on the surface of the pads due to exposure to air after electroplating. At the same time, it will not damage the already formed copper layer structure inside the blind slot, ensuring the flatness and cleanliness of the outer surface of the pads, making the copper surface of the pads completely flush with the reference surface of the side of the PCB board, with the height difference controlled within 0.05mm.

[0023] In summary, this application includes at least one of the following beneficial technical effects: Without requiring additional vias for the inner functional circuitry, the physical bearing position of the test points is directly transferred from the PCB surface to the side embedded space, increasing the available wiring area on the PCB surface. This solves the technical problems of indentation, substrate cracking, and pad detachment caused by rigid probes perpendicularly pressing the board surface during electrical testing of ultra-thin PCBs. Secondly, the blind slot with a convex cross-section creates a physical locking structure similar to a "mortise and tenon" between the subsequently filled copper and the PCB, completely different from the existing technology where exposed side pads rely solely on the adhesion of the copper layer surface for fixation. The final formed side test pads have a significantly higher average pull-out force than those of exposed side pads in the existing technology, and can withstand probe pressure. The pads exhibit extremely strong impact resistance, ensuring they remain secure and undisturbed, thus stabilizing contact resistance and meeting the long-term testing requirements of the product. Furthermore, the selective activation process design within the blind groove, combined with ultrasonic-assisted oscillation and subsequent board rinsing, guarantees that palladium metal particles are uniformly adhered to the entire inner wall of the blind groove, preventing issues such as localized plating omissions and poor conductivity. Finally, the production process path of this embodiment is compatible with mass production, eliminating the need to develop dedicated processes for PCBs of different thicknesses. By simply adjusting milling parameters and electroplating time, it can be adapted to both ultra-thin flexible PCBs and thick copper power PCBs, solving the technical problems of poor mass production consistency and narrow applicability of existing side pad solutions. Attached Figure Description

[0024] Figure 1 This is a detailed flow chart of the production process for an example; Figure 2 This is a schematic diagram of the specific structure of the PCB board; Figure 3 This is an exploded view of the specific structure of the shielding fixture.

[0025] Reference numerals: 1. PCB board; 10. Test pad; 11. Marking arrow; 2. Shielding fixture; 20. Shielding frame; 201. Placement space; 21. Exposed through hole; 22. Box cover; 3. Spring-loaded component; 30. Spring-loaded spring; 31. Flexible protective strip. Detailed Implementation

[0026] To make the technical problems, technical solutions, and beneficial effects to be solved by this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and are not intended to limit the scope of this application.

[0027] It should be noted that when a component is referred to as being "fixed to" or "set on" another component, it can be directly on or indirectly on that other component. When a component is referred to as being "connected to" another component, it can be directly connected to or indirectly connected to that other component.

[0028] It should be understood that the terms "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application 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. Therefore, they should not be construed as limitations on this application.

[0029] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0030] The present application will be further described in detail below with reference to the accompanying drawings.

[0031] Reference Figure 1 , Figure 2 A manufacturing process for embedded test pads on the side of a PCB board includes the following steps: S1, inner layer test point preset: during the inner layer circuit pattern production stage of PCB board 1, according to the design file, a square copper block is reserved at the corresponding inner layer board edge position as the test point base. A preset distance is left between the outer edge of the square copper block and the side distance of the final product of PCB board 1. The square copper block is directly connected to the inner layer functional circuit. S2. Blind Slot Pre-processing: After all lamination and outer layer circuit fabrication processes are completed on PCB board 1, a blind slot with a convex cross-section is milled inward on the side of PCB board 1 at the position corresponding to the inner layer test point base using a CNC milling machine. The bottom of the blind slot completely exposes the outer edge of the square copper block reserved in the inner layer. The CNC milling machine can be a PCB-specific CNC milling machine (forming machine), a desktop PCB engraving machine, a CNC milling cutter-type depaneling machine, or a dedicated CNC milling machine. S3. In-tank activation treatment: Immerse PCB board 1 in acidic colloidal palladium activation solution and use ultrasonic-assisted vibration treatment to allow palladium metal particles to evenly adhere to the entire inner wall surface of the blind tank. Then rinse the board surface with deionized water to remove the activation solution remaining outside the tank. Specifically: First, load PCB board 1 with completed blind tank pre-processing into the hanger, ensuring that all side blind tanks are completely facing the direction of activation solution flow and that no board surfaces are obstructed by each other. Then, immerse the entire hanger in the acidic colloidal palladium activation solution, ensuring that the activation solution completely fills the interior of all blind tanks without any air bubbles remaining. Then, turn on the ultrasonic transducer installed at the bottom of the activation tank, set the frequency to 40kHz, control the power density at 0.3W / L, and continuously assist vibration for 3 minutes. Finally, after vibration, remove PCB board 1 and spray the board surface with 25℃ deionized water for 1 minute to rinse away the activation solution remaining on the board surface outside the tank, leaving only the palladium metal particles adhering to the inner wall of the blind tank. S4. Chemical Copper Plating Filling: The activated PCB board 1 is placed in the chemical copper plating solution, and a uniform copper layer is deposited on the inner wall of the blind tank, so that the inner wall of the blind tank is completely formed as a conductive copper surface, and the copper layer is completely conductive with the test point substrate reserved in the inner layer. Regarding how to deposit a uniform copper layer on the inner wall of the blind tank for chemical copper plating filling, the specific steps are as follows: The activated board is first immersed in a 30°C dilute sulfuric acid pre-immersion tank for 1 minute to completely fill the inside of the blind tank with the solution, thoroughly remove the residual air in the tank, and avoid air bubbles blocking the inner wall and causing local incomplete plating. Then, a standard chemical copper plating solution of 15g / L copper sulfate and 12mL / L formaldehyde is used, with a constant temperature of 32°C and a pH stable at 12.5±0.1. Five minutes before plating, a 28kHz low-power ultrasonic wave with a power density of 0.2W / L is turned on to enhance the mass transfer efficiency of the plating solution in the depth of the blind tank. Finally, the thickness of the copper layer on the inner wall is uniform and stable at 5±0.5μm, with no local thickness difference. S5. Electroplating Thickening Forming: Place PCB board 1 into an acidic copper plating bath for electroplating, so that the inside of the blind groove is completely filled with metallic copper. After electroplating, the copper surface on the outside of the blind groove is flush with the side reference surface of PCB board 1, forming a complete embedded side test pad 10. Regarding how to ensure that the copper surface on the outside of the blind groove is flush with the side reference surface of PCB board 1 after electroplating thickening, the specific steps are as follows: First, use a universal fixture with silicone pressure strips to completely seal the upper and lower surfaces of the PCB, exposing only the side blind groove area. During electroplating, only the copper layer inside the tank grows in a directional manner, and no additional copper is plated on the board surface. Set the electroplating time according to the volume of the blind groove. For example, if the depth of the blind groove is 12μm, the length is 3mm, and the width is 1.6mm, electroplating at a current density of 2ASD for 30 minutes will just fill the blind groove with copper, and there will be no excessive protrusion. S6. Pad Surface Passivation: The PCB board 1 is immersed in an organic solder resist solution to generate an organic protective layer on the outer surface of the side-embedded test pads 10. After completion, it is rinsed with deionized water and dried with hot air to obtain the final product. Without damaging the original high adhesion structure of the side-embedded pads, a uniform organic protective layer is constructed on the exposed copper surface, completely isolating the copper layer of the pads from direct contact with the outside air and moisture, avoiding the oxidation and blackening problem that is very easy to occur in bare copper pads during turnover and storage. Secondly, the pad surface passivation fully reuses the mature OSP production line commonly used in the PCB industry, without the need for any additional special equipment. The process will not affect other functional lines or resistors on the PCB board 1. While the solder layer causes corrosion damage, the ultra-thin nature of the organic protective layer does not change the overall shape and size of the side pads. When the test probe contacts the protective layer, it can penetrate the protective layer to achieve stable conductivity, completely eliminating the probe contact problems caused by thick plating layers. Finally, the process parameters can be adjusted for different application scenarios: for consumer PCB products, the protective layer thickness can be controlled at 0.2~0.3μm, balancing oxidation resistance and conductivity efficiency; for high-reliability products such as servers and industrial control, the protective layer thickness can be increased to 0.3~0.5μm, which can withstand the high temperature impact of lead-free reflow soldering continuously, and the pad performance remains stable without the need to change to other high-cost surface treatment processes, thereby improving the product's adaptability to different scenarios while controlling production costs.

[0032] Through the aforementioned manufacturing process, without requiring additional vias for the inner functional circuitry, the physical bearing position of the test points is directly transferred from the surface of PCB 1 to the side embedded space, increasing the available wiring area on the surface of PCB 1. This solves the technical problems of indentation, substrate cracking, and pad detachment caused by rigid probes perpendicularly pressing the board surface during electrical testing of ultra-thin PCB 1. Secondly, the blind slot with a convex cross-section creates a physical locking structure similar to a "mortise and tenon" between the subsequently filled copper and PCB 1, completely different from the existing technology where exposed side pads rely solely on the adhesion of the copper layer surface for fixation. The average pull-out force of the final formed side test pad 10 is significantly higher than that of exposed side pads in the existing technology. Furthermore, it has extremely strong resistance to probe impact, ensuring that the pads remain secure and do not detach, thus stabilizing the contact resistance and meeting the long-term testing requirements of the product. Moreover, the selective activation process design within the blind groove, combined with ultrasonic-assisted oscillation and subsequent board rinsing, ensures that palladium metal particles are uniformly adhered to the entire inner wall of the blind groove, avoiding localized plating omissions and poor conductivity. Finally, the production process path of this embodiment is compatible with mass production, eliminating the need to develop dedicated processes for PCBs of different thicknesses. It can be adapted to both thin flexible PCBs and thick copper power PCBs simply by adjusting milling parameters and electroplating time, solving the technical problems of poor mass production consistency and narrow applicability of existing side pad solutions.

[0033] Although the in-tank activation treatment can remove residual activation solution outside the tank by rinsing the board surface with deionized water, if only deionized water is used for rinsing, trace amounts of palladium particles may remain on the surface of the solder mask layer of the board during mass production. In the subsequent chemical copper plating process, sporadic copper spots will be generated in the non-pad area of ​​the board surface, causing micro-short circuit defects in the outer layer circuit. In order to solve this technical problem, this embodiment also sets up a sub-step S31 in step S3 and a sub-step S41 in step S4. Sub-step S31 includes the following steps: Before the activation treatment, acid and alkali resistant PET solder mask film is pre-applied to the upper and lower surfaces of the PCB board 1, with only the side blind slot area exposed, to prevent palladium particles from adhering to the board surface; Sub-step S41 includes the following steps: After the chemical copper plating is completed, the board surface is quickly sprayed with ammonium persulfate weak etchant to remove any possible residual sporadic copper spots.

[0034] Regarding the acid and alkali resistant PET solder resist film, it is specifically used in PCB factories using a manual / semi-automatic dry film placement machine. The 25μm acid and alkali resistant PET film with silicone pressure-sensitive adhesive is aligned with the edge of the board. The roller temperature is set to 40℃, and the film is rolled at a uniform speed with a pressure of 0.2MPa. The film layer is completely adhered to the board surface, with only the blind groove area on the side exposed.

[0035] Through the S31 and S41 sub-steps, the acid and alkali resistant PET solder mask, using a 25μm ultra-thin specification with silicone pressure-sensitive adhesive, adheres tightly to the board surface without any lifting edges after application. After activation treatment, it can be completely peeled off without any adhesive residue on the board surface, without damaging the original solder mask layer and outer circuit pattern, while also isolating palladium particles from adhering to the board surface. The subsequent ammonium persulfate weak corrosion spray only takes 10 seconds to complete, completely removing sporadic copper spots on the board surface without causing any corrosion damage to the copper plating layer inside the blind slot or the side pad structure. This blocks the adhesion path of the palladium activation solution to non-target areas on the upper and lower surfaces of the PCB, solving the technical problem of sporadic copper spots in chemical copper plating caused by residual palladium particles on the board surface.

[0036] In this embodiment, while performing ultrasonic-assisted oscillation treatment in step S3, a small amount of compressed air is introduced into the activation liquid to bubble it, ensuring that the inner wall deep in the blind tank can also be fully in contact with the activation liquid.

[0037] As for how compressed air is introduced into the activation liquid, it can be achieved simply by adding a common bubbling pipe to the bottom of the existing activation tank; The high-frequency micro-vibration of ultrasound and the turbulent liquid flow of bubbling work together to break up the tiny air bubbles remaining inside the blind tank, allowing the activation liquid to continuously circulate and renew to the deepest part of the blind tank, thus avoiding the problem of uneven palladium particle adhesion and incomplete activation in the dead corners of the tank.

[0038] In this embodiment, during the electroplating thickening process in step S5, a shielding fixture 2 is used to clamp the PCB board 1, as shown in the reference. Figure 3The shielding fixture 2 exposes only the blind slot on the side of the PCB board 1 to shield the surface and bottom layers of the PCB board 1, preventing abnormal growth in the copper thickness of the outer layers during electroplating. The shielding fixture 2 includes a shielding frame 20, exposed through holes 21 on the shielding frame 20, and a cover 22. The shielding frame 20 is divided into multiple placement spaces 201 for placing the PCB board 1. All placement spaces 201 are arranged in two rows within the shielding frame 20. One side of the shielding frame 20 has an opening that extends through the shielding fixture. The entire length of the frame 20 ensures that the top of all placement spaces 201 are open, facilitating the quick placement and removal of the PCB board 1. The number of exposed through holes 21 is the same as that of the placement spaces 201, and each one corresponds to a placement space 201. The exposed through holes 21 are located on the outside of the shielding frame 20, and their specific positions correspond to the blind slots on the upper side of the PCB board 1, ensuring that the electroplating solution enters the blind slots only through the exposed through holes 21. The cover 22 is used to close the shielding frame 20 and block the openings, thus completing the closure of the shielding frame 20.

[0039] When electroplating thickening is required in step S5, multiple PCB boards 1 are first placed into multiple placement spaces 201, ensuring that the blind slots of PCB boards 1 are aligned with the exposed through holes 21. Then, the cover 22 is closed to completely cover the opening, forming a closed cavity with the shielding frame 20. The upper and lower surface layers and bottom layer circuits of PCB boards 1 are sealed inside the cavity, and the electroplating solution cannot come into contact with any area of ​​the board surface, thereby preventing the problem of abnormal copper thickness growth of the outer layer circuits during electroplating and ensuring uniform copper layer growth in the side blind slots without affecting the original circuits on the board surface. Secondly, the multiple placement spaces 201 inside the shielding frame 20 are arranged in two parallel rows, allowing multiple PCB boards 1 to be processed simultaneously in a single electroplating, improving electroplating efficiency. At the same time, the design of the opening extending through the entire length direction, combined with the cover 22, allows for quick and complete sealing of the shielding frame 20, eliminating the need for operators to shield each board individually, greatly shortening the preparation cycle before electroplating.

[0040] It should be noted that during the process of using the shielding fixture 2 to thicken the blind plating tank, the existing air pumping system of the copper plating tank should be used. The cycle of "positive pressure bubbling for 3 seconds → static pressure holding for 2 seconds → negative pressure extraction for 2 seconds" should be repeated to squeeze and replace the residual old liquid in the blind tank. This intermittent pressure difference change can also bring out the tiny air bubbles remaining in the blind tank, avoiding plating defects caused by air bubbles.

[0041] Although the exposed through-hole 21 is positioned to correspond to the blind slot on the upper side of the PCB board 1, ensuring that the electroplating solution enters the blind slot only through the exposed through-hole 21, in actual production, when the PCB board 1 is loaded into the placement space 201, the operator needs to observe the position of the blind slot on the PCB board 1 each time and then adjust the PCB board 1 before placing it in the placement space 201 so that the exposed through-hole 21 corresponds to the blind slot position, which is very inconvenient. To solve this technical problem, this embodiment provides an indicator arrow 11 on the PCB board 1 to mark the position of the blind slot. When the operator loads the PCB board 1 into the placement space 201 of the shielding frame 20, they can directly align the exposed through-hole 21 with the relative position of the blind slot through the indicator arrow 11 on the board surface, without repeated alignment and calibration, reducing the error rate of placing the PCB board 1 in the placement space 201, and is especially suitable for the scenario of batch clamping of multiple PCB boards 1. Secondly, the marking arrow 11 can be produced simultaneously during the solder mask printing process of PCB board 1 without the need for additional special processing steps such as etching and laser engraving, thus not increasing the manufacturing cost of PCB board 1. It can also serve as a positioning mark for sampling and testing of blind groove plating in the subsequent electroplating quality inspection process, helping quality inspectors to quickly and accurately find the corresponding blind groove to complete the thickness test, thereby improving production efficiency and quality inspection efficiency.

[0042] The solder mask printing process is a core process in PCB manufacturing. By covering the non-soldering areas of the board with insulating ink, only the designated solder pads are exposed, which avoids short circuits during soldering and protects the circuits from oxidation and corrosion.

[0043] Although the shielding fixture 2 prevents abnormal copper thickness growth in the outer layer during electroplating, gaps inevitably exist between the PCB board 1 in the placement space 201 and the inner wall of the frame during actual production. If the PCB board 1 shifts in the electroplating solution, the blind slots and exposed through holes 21 will not be accurately aligned, potentially causing the electroplating solution to seep into the board surface through the gaps or uneven filling of the blind slots. To solve this technical problem, this embodiment provides spring-loaded elements 3 inside all placement spaces 201. The spring-loaded elements 3 are used to press the PCB board 1 in the placement space 201 to ensure that the blind slots of the PCB board 1 are accurately aligned with the exposed through holes 21. The spring-loaded elements 3 include... The PCB board 1 includes a spring 30 and a flexible protective strip 31. Multiple springs 30 are provided and are respectively arranged on the side walls of the placement space 201 where no exposed through holes 21 are opened. The spring force of the springs points inward into the placement space 201 and is used to apply continuous elastic pressure to the PCB board 1. At least three flexible protective strips 31 are provided. The three flexible protective strips 31 are respectively arranged on the side walls of the placement space 201 where no exposed through holes 21 are opened. The flexible protective strips 31 are fixedly connected to the inner end of the springs and are made of acid and alkali resistant silicone material. They directly contact the surface of the PCB board 1 and provide elastic support while preventing the hard spring from scratching the circuit on the board surface.

[0044] The flexible protective strip 31 can be made of acid and alkali resistant silicone, EPDM rubber, fluororubber or polyurethane elastomer.

[0045] Multiple compression springs 30 are respectively arranged on the side walls of the placement space 201 where there are no exposed through holes 21. Their elastic force is uniformly directed towards the inside of the placement space 201, continuously applying stable elastic pressure to the PCB board 1. The flexible protective strip 31 is fixedly connected to the inner end of the compression springs 30 and directly contacts the surface of the PCB board 1. While providing elastic support, it prevents the hard springs from scratching the circuitry on the board surface. It always keeps the PCB board 1 stably against the side wall with exposed through holes 21, ensuring that the blind slot and the exposed through hole 21 are precisely aligned. The electroplating solution only enters the blind slot through the exposed through hole 21, thereby preventing the PCB board 1 from being blocked. If misalignment occurs in the electroplating solution, the blind groove and the exposed through hole 21 will not be accurately aligned, which may lead to the electroplating solution seeping into the board surface from the gap or uneven filling of the blind groove. Secondly, when facing PCB boards 1 of different sizes, the spring 30 can automatically compress or rebound according to the gap between the PCB board 1 and the inner wall of the frame, always keeping the PCB board 1 stably against the side wall with the exposed through hole 21, ensuring that the blind groove and the exposed through hole 21 are accurately aligned, and the electroplating solution only enters the blind groove through the exposed through hole 21. This adapts to the mixed-line mass production needs of PCB boards 1 of different sizes, without the need to customize fixtures for each size.

[0046] In other embodiments, the spring-loaded element 3 can be replaced by an elastic rubber pad instead of the combination of the spring-loaded spring 30 and the flexible protective strip 31. The elastic rubber pad is directly pasted on each side wall of the placement space 201 where there is no exposed through hole 21. The elastic deformation of the rubber itself applies a continuous and stable elastic pressure to the PCB board 1. The surface of the rubber pad is in direct contact with the PCB board 1, which also serves to prevent hard components from scratching the circuit on the board surface. The spring element 3 can also use an inflatable airbag instead of a spring spring. The airbag is placed on each side wall of the placement space 201 where there is no exposed through hole 21. The pressure is adjusted by manually inflating the airbag with an airbag pump. The surface of the airbag is covered with an acid and alkali resistant silicone film that directly contacts the PCB board 1. The inflation volume can be flexibly adjusted according to the gap of PCB boards 1 of different sizes, with a higher degree of adaptability, and is especially suitable for mass production scenarios with large size differences in mixed lines.

[0047] In this embodiment, after electroplating is completed in step S5, a nylon abrasive brush is used to lightly grind the side of the PCB board 1 to remove the slight oxide layer on the surface of the pads and ensure the flatness of the outer surface of the pads.

[0048] The nylon grinding brush is made of soft material and has no metal contamination. The bristle diameter is controlled to be less than 0.1mm. During the light grinding process, it will not scratch the solder mask layer and surrounding circuits on the board surface. It only works on the side pad area. The light grinding time of a single board is no more than 5 seconds, which is fully compatible with the mass production rhythm.

[0049] After electroplating, a nylon abrasive brush is used to lightly grind the side of PCB board 1. This effectively removes the slight oxide layer generated on the surface of the pads due to exposure to air after electroplating, without damaging the already formed copper layer structure inside the blind slot. This ensures the flatness and cleanliness of the outer surface of the pads, making the copper surface of the pads completely flush with the reference surface of the side of PCB board 1, with the height difference controlled within 0.05mm.

[0050] The embodiments described in this specific implementation are preferred embodiments of this application and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A manufacturing process for embedded test pads on the side of a PCB board, characterized in that, Includes the following steps: S1. Preset inner layer test points: During the inner layer circuit pattern production stage of the PCB board, according to the design file, a square copper block is reserved at the corresponding inner layer board edge position as the test point base. The outer edge of the square copper block is left with a preset distance from the side of the final PCB board. The square copper block is directly connected to the inner layer functional circuit. S2. Blind slot pre-processing: After all lamination and outer layer circuit fabrication processes are completed on the PCB board, a blind slot with a convex cross-section is milled inward on the side of the PCB board corresponding to the position of the inner layer test point base. The bottom of the blind slot completely exposes the outer edge of the square copper block reserved in the inner layer. S3. In-tank activation treatment: Immerse the PCB board in acidic colloidal palladium activation solution and use ultrasonic-assisted vibration treatment to make palladium metal particles evenly adhere to the entire inner wall surface of the blind tank. Then rinse the board surface with deionized water to remove the activation solution remaining outside the tank. S4. Chemical copper plating filling: The activated PCB board is placed in the chemical copper plating solution, and a uniform copper layer is deposited on the inner wall of the blind trench, so that the inner wall of the blind trench is completely formed as a conductive copper surface, and the copper layer is completely connected to the test point substrate reserved in the inner layer. S5. Electroplating Thickening Forming: The PCB board is placed in an acidic copper plating bath for electroplating, so that the inside of the blind tank is completely filled with metallic copper. After electroplating, the copper surface on the outside of the blind tank is flush with the side reference surface of the PCB board, forming a complete embedded side test pad.

2. The manufacturing process of the PCB board side-embedded test pad according to claim 1, characterized in that, Following step S5, the following is also included: S6. Pad Surface Passivation: Immerse the PCB board in an organic solder resist solution to generate an organic protective layer on the outer surface of the side-embedded test pads. After completion, rinse with deionized water and dry with hot air to obtain the final product.

3. The manufacturing process of the PCB board side-embedded test pad according to claim 1, characterized in that, Step S3 further includes sub-step S31, which includes the following steps: Before activation treatment, acid and alkali resistant PET solder resist film is pre-applied to the upper and lower surfaces of the PCB board, leaving only the side blind slot area exposed to prevent palladium particles from adhering to the board surface.

4. The manufacturing process of the PCB board side-embedded test pad according to claim 1, characterized in that, Step S4 further includes sub-step S41, which includes the following steps: After the chemical copper plating is completed, the board surface is quickly sprayed with a weak etchant solution of ammonium persulfate to remove any remaining copper spots.

5. The manufacturing process of the PCB board side-embedded test pad according to claim 1, characterized in that, In step S3, while the ultrasonic-assisted oscillation treatment is being performed, a small amount of compressed air is introduced into the activation liquid to bubble it, ensuring that the inner wall deep inside the blind tank can also be fully in contact with the activation liquid.

6. The manufacturing process of the PCB board side-embedded test pad according to claim 1, characterized in that, In step S5, during the electroplating thickening process, a shielding fixture is used to hold the PCB board. The shielding fixture only exposes the blind slot position on the side of the PCB board to shield the surface and bottom layers of the PCB board and prevent abnormal growth in the copper thickness of the outer layer during the electroplating process.

7. The manufacturing process of the PCB board side-embedded test pad according to claim 6, characterized in that, The shielding fixture includes a shielding frame, which is divided into multiple placement spaces for placing PCB boards. All the placement spaces are arranged in two rows within the shielding frame. One side of the shielding frame has an opening that extends through the entire length of the shielding frame, so that the top of all the placement spaces is open, which facilitates the quick handling of PCB boards. The number of exposed through holes is the same as the placement space and each one corresponds to a placement space. The exposed through holes are opened on the outside of the shielding frame, and their specific positions correspond to the blind slots on the side of the PCB board, ensuring that the electroplating solution enters the blind slots only through the exposed through holes. The lid is used to cover the opening on the shielding frame, thus completing the closure of the shielding frame.

8. The manufacturing process of the PCB board side-embedded test pad according to claim 7, characterized in that, The PCB board has marking arrows indicating the location of blind slots.

9. The manufacturing process of the PCB board side-embedded test pad according to claim 7, characterized in that, All of the aforementioned placement spaces are equipped with spring-loaded elements, which are used to press the PCB board within the placement space so that the blind slots of the PCB board are accurately aligned with the exposed through holes; The spring-loaded element includes: multiple spring-loaded springs, which are respectively arranged on the side walls of the placement space where no exposed through holes are opened. The spring force of the spring-loaded springs points inward into the placement space and is used to apply continuous elastic pressure to the PCB board. At least three flexible protective strips are provided, which are respectively installed on the side walls of the placement space where no exposed through holes are opened. The flexible protective strips are fixedly connected to the inner end of the spring compression spring and are made of acid and alkali resistant silicone material. They directly contact the PCB board surface, providing elastic support while preventing the hard spring from scratching the board surface circuit.

10. The manufacturing process of the PCB board side-embedded test pad according to claim 1, characterized in that, After electroplating is completed in step S5, a nylon abrasive brush is used to lightly grind the sides of the PCB board to remove the slight oxide layer on the surface of the pads and ensure the flatness of the outer surface of the pads.

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