Manufacturing method of printed circuit board with stepped groove

Abstract

The invention relates to a method for manufacturing a printed circuit board with a stepped groove, which comprises the following steps of: (a) providing a laminated structure comprising at least one core board and prepregs arranged on two sides of the core board; (b) forming step grooves in the prepregs and the core plate, wherein the size of each step groove is expanded by a preset margin on a single side; (c) pre-arranging a detachable supporting insert block in the stepped groove before pressing; (d) carrying out pressing operation to enable the prepreg to flow glue and form; and (e) removing the covering layer on the stepped groove through a depth-controlled milling process after pressing, and taking out the supporting insert block. A traditional pure prepreg lamination is replaced by the core plate, the material cost is remarkably reduced, the structure is simplified, the structural reliability, the overflowing glue controllability and the economical efficiency are considered, the method has wide application prospects in the high-added-value fields of communication equipment, intelligent terminals and the like, and a reliable technical path is provided for manufacturing of the precise stepped groove circuit board.

Description

Technical Field

[0001] This invention relates to the field of printed circuit board manufacturing technology, specifically to a method for manufacturing a printed circuit board with stepped grooves and the application of a support structure, which is particularly suitable for solving the problems of adhesive overflow control and structural collapse in the stepped groove area. Background Technology

[0002] In the field of printed circuit board manufacturing, stepped slot structures are widely used in devices such as high-frequency communication and mobile payment terminals to accommodate antenna modules or microelectronic components. Traditional manufacturing processes typically rely on stacking multiple layers of non-flowing prepreg to form the slot, but this method has several inherent drawbacks: Risk of uncontrolled adhesive overflow: It is difficult to precisely control the adhesive flow behavior of prepreg during the lamination process. Excess adhesive can easily overflow to the bottom of the stepped groove, forming an unexpected insulating layer or contaminants, which can lead to subsequent component placement misalignment or electrical contact failure.

[0003] Insufficient structural integrity: The stepped groove area is suspended during lamination, lacking an internal support system. Under high temperature and pressure, the material undergoes plastic deformation, and after cooling, the groove area shows depressions or edge warping, affecting the overall flatness and dimensional stability of the circuit board.

[0004] Material cost pressures: To compensate for adhesive flow losses and maintain the designed thickness, the amount of non-flowing prepreg needs to be increased. These specialty materials are significantly more expensive than ordinary types, and their supply chain flexibility is limited, hindering cost control in large-scale production.

[0005] Existing improvement solutions attempt to alleviate the above problems by filling with auxiliary materials or optimizing the stacking design, but with limited success: Filling solution: The stepped groove is temporarily filled with a high-temperature stable material. Although it can partially prevent glue overflow, it cannot provide uniform mechanical support. Local collapse still occurs after pressing. In addition, the filler and the glue may stick together and are easy to remain in the groove when removed.

[0006] Layered solution: Adding a protective structure to the bottom layer of the stepped groove can improve milling accuracy, but it does not solve the problems of uncontrollable glue flow and structural instability during the pressing stage, and still relies on high-cost non-flowing glue materials.

[0007] The aforementioned defects collectively lead to fluctuations in the yield of stepped slot circuit boards and an increase in production costs, necessitating the development of new methods that balance structural reliability, controllable adhesive overflow, and economy. Summary of the Invention

[0008] In view of this, the present invention provides a method for manufacturing a printed circuit board with stepped grooves. By replacing the traditional pure prepreg laminate with a core board, the material cost is significantly reduced and the structure is simplified. It takes into account structural reliability, controllable glue overflow and economy, and has broad application prospects in high value-added fields such as communication equipment and smart terminals, providing a reliable technical path for the manufacturing of precision stepped groove circuit boards.

[0009] The objective of this invention is achieved through the following technical solution: A method for manufacturing a printed circuit board with stepped grooves includes the following steps: (a) A laminated structure comprising a core board, the laminated structure comprising at least one core board and prepregs disposed on both sides of the core board; (b) A stepped groove is formed on the prepreg and the core board, wherein the size of the stepped groove is increased by a preset allowance on one side; (c) Before pressing, a removable support block is pre-placed in the stepped groove; (d) Perform a pressing operation to mold the prepreg into shape; (e) After pressing, the cover layer on the stepped groove is removed by controlled depth milling process, and the support block is taken out.

[0010] By replacing traditional pure prepreg stacks with a core board, material costs are significantly reduced and the structure is simplified. Compared to traditional solutions that rely on stacking multiple layers (e.g., 5 sheets) of high-cost, non-flowing prepreg, this invention significantly reduces the amount of expensive specialty materials (especially non-flowing types) by introducing a rigid core board to replace part of the prepreg stack, which is one of the main ways to achieve cost reduction. Simultaneously, the enlarged groove design and the application of support blocks reduce the stringent requirements for prepreg flowability, making it possible to use lower-cost, ordinary flowable prepreg in certain application scenarios, further expanding the scope for cost reduction. The design of an enlarged stepped groove with a pre-set margin provides redundant space for prepreg flow, effectively preventing overflow and contamination of the bottom pads, ensuring the reliability of electronic component installation. Pre-installed removable support blocks provide physical support during the pressing process, eliminating collapse and warping deformation in the stepped area due to lack of support, and improving product flatness. The staged controlled-depth milling process removes the cover layer first and then takes out the support blocks, avoiding damage to the underlying circuitry during one-time processing while ensuring groove wall precision.

[0011] This combined solution addresses three major industry challenges: adhesive overflow control, structural support, and cost optimization. The core board structure reduces the amount of expensive prepreg used; the support inserts are reusable and leave no residue; and the widened groove design is compatible with ordinary flowable prepregs, breaking through the reliance of traditional processes on non-flowing materials. Step-by-step operations after lamination reduce processing difficulty and improve yield, making it particularly suitable for mass production of high-precision stepped groove printed circuit boards.

[0012] Preferably, the support block is fixed to the bottom of the stepped groove by an adhesive layer.

[0013] The adhesive layer ensures that the support insert does not shift during the pressing process, preventing local support failure or uneven adhesive distribution due to insert misalignment. This fixing method is simple to operate, does not increase additional equipment costs, and the adhesive layer remains stable after high-temperature pressing, preventing the insert from falling off and contaminating the prepreg.

[0014] Preferably, the adhesive layer is a double-sided adhesive layer.

[0015] The double-sided adhesive layer combines strong adhesion with easy peeling, maintaining its bond strength under high-temperature pressing conditions to ensure the support insert is fixed, while allowing for residue-free separation during the cap removal stage. Its elastic properties buffer pressing stress, reducing the risk of core board deformation. The double-sided adhesive is inexpensive and its thickness is controllable, avoiding any impact on the accuracy of the stepped groove depth, while also accommodating the rapid placement needs of inserts of different sizes.

[0016] Preferably, the thickness of the core board is not greater than the total thickness of the adjacent prepreg sheets.

[0017] The design of the core board thickness not exceeding the total thickness of adjacent prepreg sheets ensures that the prepreg adhesive fully fills the gaps between the core board and adjacent layers during lamination, avoiding interface voids. Simultaneously, this thickness relationship makes the core board the primary load-bearing structure, with the prepreg serving as the adhesive medium, optimizing material mechanical properties and reducing board warping after lamination.

[0018] Preferably, the prepreg is a common flowable prepreg.

[0019] The choice of prepreg is flexible. In certain embodiments, ordinary flowable prepregs can be used, which are significantly less expensive than non-flowable types. Regardless of the flowable type of prepreg chosen, its flow behavior can be effectively controlled by the redundant space of the aforementioned expansion tank design and the physical restraint of the support blocks, guiding the adhesive to be evenly distributed within the preset area and avoiding disorderly overflow that contaminates the functional area at the bottom of the tank.

[0020] Preferably, the depth of the controlled-depth milling process covers the thickness of the overlay layer on the stepped groove.

[0021] Limiting the milling depth to cover only the thickness of the overlay layer ensures precise removal of the target layer without damaging the underlying functional circuitry. This depth control avoids the risk of milling through due to depth errors in traditional depth control processes, protects the integrity of the pads at the bottom of the stepped groove, and reduces electrical performance loss.

[0022] Preferably, when the support block is placed in the stepped groove, the distance between its edge and the inner wall of the stepped groove is uniform.

[0023] The uniform gap design ensures symmetrical distribution of the prepreg adhesive within the tank, preventing localized adhesive buildup or loss. The gaps act as overflow buffers, working in conjunction with the expanded tank design to further accommodate adhesive flow. Uniform support force distribution reduces stress concentration during bonding, improving the thickness uniformity of the stepped areas and enhancing product reliability.

[0024] Preferably, a compressible buffer layer is added to the hot press chassis during pressing.

[0025] The compressible buffer layer absorbs vibrations and pressure fluctuations from the laminating machine, reducing the risk of interlayer misalignment. Its elastic deformation compensates for sheet thickness tolerances, ensuring that pressure is evenly transmitted to the laminated structure and avoiding poor bonding or material damage caused by insufficient or excessive local lamination.

[0026] Preferably, the circuit surface in the stepped groove area is covered with a solder resist layer, and the middle solder pad area has a window.

[0027] The solder mask protects the stepped slot sidewalls from environmental corrosion, while the windowed design precisely exposes the pad areas for easy component soldering. This combination strikes a balance between solder mask protection and soldering reliability, reducing short-circuit risk and improving the stability of high-frequency signal transmission.

[0028] Preferably, after the controlled depth milling process, the exposed copper pads of the stepped groove are subjected to surface metallization treatment.

[0029] Surface metallization enhances the oxidation resistance and solderability of the pads, ensuring high component soldering yield. This treatment is only performed after controlled-depth milling to prevent damage to the pre-metallization layer during lamination and milling processes, thus guaranteeing coating integrity and functional reliability.

[0030] The advantages of this invention compared to the prior art are: 1. Synergistic Improvement of Material Structure and Glue Overflow Control: By replacing part of the prepreg laminate with a rigid core plate, the amount of special materials used is reduced while a basic support framework for the stepped groove is constructed. As a non-flowing entity, the core plate reduces the total amount of flowable adhesive during the pressing stage, effectively suppressing glue overflow. Enlarged stepped grooves are created on the core plate and prepreg, providing directional expansion space for the limited flow of adhesive, promoting uniform distribution of the adhesive within a predetermined area, preventing disorderly spread to critical functional areas at the bottom of the groove, and significantly reducing the risk of solder pad contamination. Pre-installed detachable support blocks form a dynamic physical isolation barrier during pressing. Their sidewalls and the gaps in the expansion grooves work together to form a flow buffer, guiding the adhesive to fill along a predetermined path. The top surface of the blocks simultaneously bears the pressing pressure, preventing excessive seepage of the prepreg, achieving multi-dimensional constraints on glue overflow behavior.

[0031] 2. Dual Enhancement of Structural Stability and Process Compatibility: The support insert and core board jointly construct a three-dimensional mechanical balance network: the insert provides local rigid support in the groove area, offsetting the deformation potential energy caused by the pressing pressure; the core board, as a continuous carrier, disperses edge stress concentration and collaboratively maintains the overall flatness of the laminate. The phased processing strategy avoids accidental damage to the underlying circuitry caused by traditional single milling by first removing the top cover layer of the groove through controlled-depth milling, and then completely removing the support insert, while reducing the processing accuracy tolerance requirements. The application of the core board architecture reduces the sensitivity to the flowability of the prepreg, allowing ordinary flowable materials to replace expensive non-flowing types; the removable nature of the support insert avoids the introduction of new contaminants, ensuring the cleanliness of the groove and process compatibility.

[0032] 3. Comprehensive Benefit Optimization: The synergistic improvement in the controllability of adhesive overflow and structural stability directly enhances the component placement yield and product lifespan in the stepped groove area. Large-scale application of common materials combined with reduced use of specialty materials lowers direct material costs; step-by-step milling strategies shorten precision machining time and improve production line turnaround efficiency. The buffer layer design is compatible with press parameter fluctuations and supports flexible adjustment of insert dimensions according to the groove shape, further expanding the rapid changeover capability for multi-specification products and providing a reliable and economical technical path for the manufacturing of high-value-added electronic equipment. Attached Figure Description

[0033] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0034] Figure 1 This diagram illustrates the overflow contamination at the bottom of the stepped groove in a traditional process caused by uncontrolled flow of prepreg from the semi-cured sheet.

[0035] Figure 2 This diagram illustrates the creation of stepped grooves on a core board according to the dimensional requirements of a unilaterally expanded preset allowance.

[0036] Figure 3 This diagram illustrates the pressing indentation defect that occurs in the stepped groove area due to lack of support when no support block is set during the pressing process.

[0037] Figure 4 This diagram shows a structure where the circuit surface in the stepped groove area is covered with a solder resist layer and the middle pad area has a window. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. The components of the embodiments of this application described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0039] Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments of the application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0040] It should be noted that similar reference numerals and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. In the description of the embodiments of this application, it should be understood that the terms "upper," "lower," "left," "right," "vertical," "horizontal," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the figures, or the orientation or positional relationship commonly used when the product of this application is in use, or the orientation or positional relationship commonly understood by those skilled in the art. 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.

[0041] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other.

[0042] The technical solutions in this application will now be described with reference to the accompanying drawings. Example 1

[0043] This embodiment provides a method for manufacturing a printed circuit board with stepped grooves, including the following steps: (a) Provide a laminated structure including a core board, the laminated structure including at least one core board and prepregs disposed on both sides of the core board; (b) Stepped grooves are made in the prepreg and the core board, with the size of the stepped grooves being increased by a preset allowance on one side; (c) Before pressing, a removable support block is pre-placed in the stepped groove; (d) Perform a pressing operation to mold the prepreg into shape; (e) After pressing, the cover layer on the stepped groove is removed by controlled depth milling process, and the support block is taken out.

[0044] Replacing traditional pure prepreg laminates with core boards significantly reduces material costs and simplifies the structure. The stepped groove design with an increased pre-set margin provides redundant space for prepreg flow, effectively preventing adhesive overflow from contaminating the bottom pads and ensuring reliable electronic component mounting. Pre-installed removable support blocks provide physical support during lamination, eliminating collapse and warping in the stepped area due to lack of support, and improving product flatness. A staged, controlled-depth milling process removes the cover layer before removing the support blocks, avoiding damage to the underlying circuitry during single-processing while ensuring groove wall precision.

[0045] This combined solution addresses three major industry challenges: adhesive overflow control, structural support, and cost optimization. The core board structure reduces the amount of expensive prepreg used; the support inserts are reusable and leave no residue; and the widened groove design is compatible with ordinary flowable prepregs, breaking through the reliance of traditional processes on non-flowing materials. Step-by-step operations after lamination reduce processing difficulty and improve yield, making it particularly suitable for mass production of high-precision stepped groove printed circuit boards.

[0046] In this embodiment, the support block is fixed to the bottom of the stepped groove by an adhesive layer.

[0047] The adhesive layer ensures that the support insert does not shift during the pressing process, preventing local support failure or uneven adhesive distribution due to insert misalignment. This fixing method is simple to operate, does not increase additional equipment costs, and the adhesive layer remains stable after high-temperature pressing, preventing the insert from falling off and contaminating the prepreg.

[0048] In this embodiment, the adhesive layer is a double-sided adhesive layer.

[0049] The double-sided adhesive layer combines strong adhesion with easy peeling, maintaining its bond strength under high-temperature pressing conditions to ensure the support insert is fixed, while allowing for residue-free separation during the cap removal stage. Its elastic properties buffer pressing stress, reducing the risk of core board deformation. The double-sided adhesive is inexpensive and its thickness is controllable, avoiding any impact on the accuracy of the stepped groove depth, while also accommodating the rapid placement needs of inserts of different sizes.

[0050] In this embodiment, the thickness of the core board is no greater than the total thickness of the adjacent prepreg sheets.

[0051] The design of the core board thickness not exceeding the total thickness of adjacent prepreg sheets ensures that the prepreg adhesive fully fills the gaps between the core board and adjacent layers during lamination, avoiding interface voids. Simultaneously, this thickness relationship makes the core board the primary load-bearing structure, with the prepreg serving as the adhesive medium, optimizing material mechanical properties and reducing board warping after lamination.

[0052] In this embodiment, the prepreg is a regular flowable prepreg.

[0053] The choice of prepreg is flexible. In certain embodiments, ordinary flowable prepregs can be used, which are significantly less expensive than non-flowable types. Regardless of the flowable type of prepreg chosen, its flow behavior can be effectively controlled by the redundant space of the aforementioned expansion tank design and the physical restraint of the support blocks, guiding the adhesive to be evenly distributed within the preset area and avoiding disorderly overflow that contaminates the functional area at the bottom of the tank.

[0054] In this embodiment, the depth of the controlled-depth milling process covers the thickness of the overlay layer on the stepped groove.

[0055] Limiting the milling depth to cover only the thickness of the overlay layer ensures precise removal of the target layer without damaging the underlying functional circuitry. This depth control avoids the risk of milling through due to depth errors in traditional depth control processes, protects the integrity of the pads at the bottom of the stepped groove, and reduces electrical performance loss.

[0056] In this embodiment, when the support block is placed in the stepped groove, the distance between its edge and the inner wall of the stepped groove is uniform.

[0057] The uniform gap design ensures symmetrical distribution of the prepreg adhesive within the tank, preventing localized adhesive buildup or loss. The gaps act as overflow buffers, working in conjunction with the expanded tank design to further accommodate adhesive flow. Uniform support force distribution reduces stress concentration during bonding, improving the thickness uniformity of the stepped areas and enhancing product reliability.

[0058] In this embodiment, a compressible buffer layer is added to the hot press chassis during pressing.

[0059] The compressible buffer layer absorbs vibrations and pressure fluctuations from the laminating machine, reducing the risk of interlayer misalignment. Its elastic deformation compensates for sheet thickness tolerances, ensuring that pressure is evenly transmitted to the laminated structure and avoiding poor bonding or material damage caused by insufficient or excessive local lamination.

[0060] In this embodiment, the circuit surface in the stepped groove area is covered with a solder resist layer, and the middle pad area has a window.

[0061] The solder mask protects the stepped slot sidewalls from environmental corrosion, while the windowed design precisely exposes the pad areas for easy component soldering. This combination strikes a balance between solder mask protection and soldering reliability, reducing short-circuit risk and improving the stability of high-frequency signal transmission.

[0062] In this embodiment, after the controlled depth milling process, the exposed copper pads of the stepped groove are subjected to surface metallization treatment.

[0063] Surface metallization enhances the oxidation resistance and solderability of the pads, ensuring high component soldering yield. This treatment is only performed after controlled-depth milling to prevent damage to the pre-metallization layer during lamination and milling processes, thus guaranteeing coating integrity and functional reliability. Example 2

[0064] This embodiment details a method for fabricating a stepped-groove printed circuit board (PCB) for use in a pseudo-four-layer board (adopting a Core+Core structure, i.e., including L1 / 2 and L3 / 4 layers, where L2 is a 0.3mm thick plain core board without patterns). The core challenge of this design lies in precisely controlling adhesive overflow in the stepped-groove area and preventing structural collapse. Traditional methods rely on stacking a large number (e.g., 5 sheets, each 0.1mm thick) of high-cost non-flow prepreg (PP) sheets (theoretically about 0.4mm thick after lamination). However, due to the large amount of adhesive overflow in the open areas of the stepped groove, the thickness of the surrounding areas is often reduced, and the risk of adhesive overflow is high.

[0065] I. Innovative Optimization Scheme of this Embodiment 1. Material stacking optimization: Instead of the traditional multi-layer non-adhesive PP stacking, a 0.3mm thick bare board (without copper core) is sandwiched between two non-adhesive PP sheets. This combination aims to achieve the target lamination thickness while utilizing the rigidity of the core board to provide basic support.

[0066] 2. Stepped Groove Size Design (Key to Prevent Adhesive Overflow): Stepped grooves are pre-cut on the pre-cured sheet (PP) and the polished sheet before lamination. The size of this pre-cut groove is 0.5mm larger on each side than the final designed stepped groove size, thus reserving space to accommodate adhesive flow during the lamination process. For example: Final stepped groove design dimensions: 64mm*56mm.

[0067] Pre-grooving dimensions on PP and bare plates: 64.5mm*56.5mm.

[0068] 3. Application of removable support inserts (key to preventing collapse): Before the pressing process, a small plate (support insert) cut from the blank plate, smaller than the pre-grooved slot, is precisely placed in the center of each stepped groove pre-grooved window. To ensure it does not shift during the pressing process: Apply double-sided tape to the bottom of the support block (the side that contacts the L3 layer).

[0069] After placing the insert into the pre-opened window, press it down appropriately to ensure it adheres firmly to the surface of the L3 layer circuit board using double-sided adhesive.

[0070] When placing the support block, ensure that the distance between the edge of the support block and the inner wall of the pre-opened window remains uniform to provide a symmetrical buffer for the glue flow.

[0071] 4. Pressing Buffer Design: To absorb vibrations and pressure fluctuations in the pressing machine, ensure uniform pressure transmission, and compensate for sheet thickness tolerances, 20 sheets of kraft paper are placed on the hot press base of the pressing machine as a compressible buffer layer. When arranging the steel sheets, after two layers are filled, 5 new sheets of kraft paper are placed as a false buffer layer, and then the arranging continues until the machine is full.

[0072] II. Process Design Ideas Considering the differences and parallel processing capabilities between layers L1 / 2 (including the light-emitting plate) and L3 / 4, this embodiment divides the process flow into three sub-processes to optimize efficiency: Process 1 is responsible for the preparation of L1 / 2 layers and the support structure of the light board (material cutting, L1 layer circuit / positioning, light board etching, stepped pre-grooving milling).

[0073] Process 2 is responsible for the independent processing of L3 / 4 layers (material cutting, drilling / electroplating / resin plugging, L3 / 4 layer circuitry, AOI, solder mask covering and windowing in the stepped groove area).

[0074] Process 3 is responsible for overall lamination, outer layer treatment and final molding of stepped grooves (integrating the output of processes 1 & 2, pretreatment / browning, lamination - including insert placement / buffer layer, drilling / electroplating - L1 / 4 holes, outer layer circuitry, AOI, solder mask / text, depth control for insert removal, electroless gold plating, final molding, electrical testing, FQC, and packaging).

[0075] III. Detailed Process Flow Design Process 1: Cutting → Inner layer (L1-2, plain board) → Molding 1 (curling board, PP).

[0076] Process 2: Material cutting → Drilling (L3 / 4) → Electroplating → Resin plugging → Resin grinding → Circuit → Circuit AOI → Solder resist.

[0077] Process 3: Inner layer pretreatment → browning → lamination → drilling → electroplating → outer layer circuit → circuit AOI → solder mask → text → molding 2 (uncapping) → chemical gold treatment → molding 3 (rod set) → electrical testing → FQC → packaging.

[0078] IV. Detailed Implementation Methods 1. Material cutting: Process 1: Cut the L1 / 2 layer (including the bare board that serves as the L2 layer). Select double-sided copper-clad laminate for cutting.

[0079] Step 2: Cutting L3 / 4 layers. Double-sided copper-clad laminate is also selected for cutting.

[0080] 2. Inner layer fabrication (process 1): Fabricate the tooling positioning holes and target around the PNL on the L1 core board.

[0081] Prepare a 0.3mm thick light board for use as the L2 layer: completely etch the copper foil on both sides of the board and set it aside.

[0082] 3. Molding Step 1 (Stepped Pre-grooving - Process 1): On the prepared PP sheet and the 0.3mm smooth plate as the L2 layer, using a 1.8mm diameter milling cutter, a stepped groove pre-grooving is machined according to the dimensional requirement of 0.5mm enlargement on one side (e.g., 64.5mm * 56.5mm in the previous example). The result of this step is as follows... Figure 2 As shown (slotted on the core board at an enlarged size).

[0083] 4. Drilling (Process 2): Drill through holes in the L3 / 4 layer slab (connecting L3 and L4 layers), located in the middle of the stepped window area. The designed hole diameter is 0.25mm.

[0084] 5. Electroplating (Process 2): Electroplat the drilled through holes in L3 / 4 layer. The minimum copper thickness in the holes is 20μm.

[0085] 6. Resin plugging (process 2): Fill the through holes after L3 / 4 layer electroplating with resin to a full extent.

[0086] 7. Circuit Fabrication (Process 2): Fabricate the inner layer circuitry of L3 / 4, including design drawings for coil modules with a line width / spacing of 4 / 4 mil. Perform automated optical inspection (AOI) of the circuitry.

[0087] 8. Solder Mask (Solder Mask - Process 2): Cover the trace surface in the L3 / 4 layer stepped slot window area with black solder mask ink. Pay special attention to creating windows in the central pad areas where components will be installed to expose the copper surface. Cover or create windows in other areas according to the design. Structural diagram as shown below. Figure 4 (Showing solder mask coverage and solder pad openings).

[0088] 9. Inner layer pretreatment (process 3): Perform pretreatment on the L3 / 4 layer board surface that has been solder masked to remove the oxide layer and prevent poor browning in the future.

[0089] 10. Browning (Process 3): The treated L3 / 4 and L1 / 2 layers (including the light-colored layer) are browned to enhance interlayer bonding.

[0090] 11. Pressing (Core Step - Process 3): Stack the layers in the following order: L4 layer down -> L3 layer -> 1 sheet of non-adhesive PP -> 0.3mm smooth board (pre-grooved) as L2 layer -> 1 sheet of non-adhesive PP -> L1 layer (L2 / 1 layer base facing up).

[0091] Key procedure: Before placing the L1 / 2 layer, carefully place the small pieces (support inserts) cut from the polished plate in step 3, smaller than the pre-grooved slots, into the center of each pre-grooved window on the polished plate using the double-sided adhesive attached to their bottoms, and press to ensure they are firmly bonded to the L3 layer. Ensure the gaps around the inserts are uniform. Figure 3 This demonstrates the inevitable indentation defect that occurs in the stepped area after pressing when no support insert is placed.

[0092] After the plates are stacked, check that the four corners of the plates are concentric. Once they pass the inspection, transfer them to the press.

[0093] Buffer layer application: Lay 20 sheets of kraft paper as the bottom buffer on the hot press chassis of the press. After arranging two layers of boards on the steel plate, place 5 new sheets of kraft paper as a false buffer, and then continue arranging boards until the machine is fully loaded.

[0094] A pressing operation is performed to allow the PP to melt and flow into shape. Support blocks provide localized rigid support, and the enlarged pre-grooved space accommodates the flowing adhesive.

[0095] 12. Drilling (Process 3 - L1 / 4 through holes): Drill through holes on the laminated integral plate (connecting layers L1 and L4).

[0096] 13. Electroplating (process 3): Electroplat the drilled through holes in L1 / 4 layer. The minimum copper thickness in the holes is 18μm, and the average is 20μm.

[0097] 14. Outer Layer Circuit Fabrication (Process 3): Fabricate the outer layer circuitry for layers L1 and L4, with a line width / spacing of 12 / 10 mil, and connect the vias from layers L1 to L4. Perform automated optical inspection (AOI) of the circuitry.

[0098] 15. Solder Mask & Text (Process 3): Apply a layer of black solder mask ink to the surface of the L1 / 4 layer circuitry. Then print the text.

[0099] 16. Molding 2 (Depth Control Screw - Lid Uncovering & Insert Removal - Process 3): Using controlled depth milling (milling) technology, the L1 / 2 layer of material covering the stepped groove is precisely removed (i.e., "uncovering").

[0100] Routing depth requirement: 0.4-0.5mm (covering the thickness of L1 / 2 layer).

[0101] Key control point: Strictly control the soldering depth, remove only the target overlay, and absolutely avoid soldering through to the third layer (L3 layer). Soldering through will damage the black solder resist on the surface of the L3 layer circuit, exposing the copper surface, which will lead to abnormal gold adhesion in subsequent gold plating processes (contamination of the gold plating bath).

[0102] After removing the cover, carefully remove the support block (along with the double-sided adhesive on its bottom) completely from the stepped groove.

[0103] Check the bottom of the stepped slot window for excess adhesive contaminating the solder pads and assess its impact on the installation of electronic components.

[0104] 17. Electroless Gold Treatment (Process 3): Perform electroless nickel immersion gold (ENIG) surface treatment on the copper pads exposed after deep soldering in the stepped groove to enhance solderability and oxidation resistance.

[0105] 18. Forming 3 (Shape Processing - Process 3): Cut the whole plate into the final SET shipping size required by the customer.

[0106] 19. Electrical testing (process 3): Conduct electrical performance tests on the finished stepped slab.

[0107] 20. FQC (Final Quality Control - Process 3): Conduct final inspection (FQC), including visual inspection, cross-section analysis, and routine PCB reliability testing.

[0108] 21. Packaging (Process 3): Pack according to the customer's specific packaging requirements.

[0109] Key takeaways from this embodiment: This embodiment reduces material costs by replacing part of the non-adhesive PP with a core board (0.3mm smooth board); the pre-grooving design with a 0.5mm enlargement on one side provides redundant space for adhesive flow, effectively controlling overflow; the pre-placed removable support inserts with double-sided adhesive provide precise local support during pressing, completely eliminating collapse in the stepped area (e.g., Figure 3 (Defects shown); Step-by-step depth control (0.4-0.5mm) ensures safe opening and removal of the insert; The application of kraft paper buffer layers (20 sheets for the bottom layer + 5 sheets for the dummy layer) improves the uniformity of lamination. The process design adopts a three-process parallel / serial approach (Process 1: L1 / 2 + bare board; Process 2: L3 / 4 layers; Process 3: lamination + outer layer + forming) to optimize production efficiency. These measures based on raw data and features work synergistically to solve the core problems in the production of the dummy four-layer board stepped groove, achieving optimization of cost, quality, and reliability.

[0110] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for manufacturing a printed circuit board with stepped grooves, characterized in that, Includes the following steps: (a) A laminated structure comprising a core board, the laminated structure comprising at least one core board and prepregs disposed on both sides of the core board; (b) A stepped groove is formed on the prepreg and the core board, wherein the size of the stepped groove is increased by a preset allowance on one side; (c) Before pressing, a removable support block is pre-placed in the stepped groove; (d) Perform a pressing operation to mold the prepreg into shape; (e) After pressing, the cover layer on the stepped groove is removed by controlled depth milling process, and the support block is taken out.

2. The method for manufacturing a printed circuit board with stepped grooves according to claim 1, characterized in that, The support block is fixed to the bottom of the stepped groove by an adhesive layer.

3. The method for manufacturing a printed circuit board with stepped grooves according to claim 2, characterized in that, The adhesive layer is a double-sided adhesive layer.

4. The method for manufacturing a printed circuit board with stepped grooves according to claim 1, characterized in that, The thickness of the core board is no greater than the total thickness of the adjacent prepreg sheets.

5. The method for manufacturing a printed circuit board with stepped grooves according to claim 1, characterized in that, The prepreg is a common flowable prepreg.

6. The method for manufacturing a printed circuit board with stepped grooves according to claim 1, characterized in that, The depth of the controlled-depth milling process covers the thickness of the overlay layer on the stepped groove.

7. The method for manufacturing a printed circuit board with stepped grooves according to claim 1, characterized in that, When the support block is placed in the stepped groove, the distance between its edge and the inner wall of the stepped groove is uniform.

8. The method for manufacturing a printed circuit board with stepped grooves according to claim 1, characterized in that, A compressible buffer layer is added to the hot press chassis during the pressing process.

9. The method for manufacturing a printed circuit board with stepped grooves according to claim 1, characterized in that, The circuit surface in the stepped groove area is covered with a solder resist layer, and the middle solder pad area has a window.

10. The method for manufacturing a printed circuit board with stepped grooves according to claim 1, characterized in that, After the controlled-depth milling process, the exposed copper pads of the stepped groove are subjected to surface metallization treatment.

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