A method for manufacturing a multi-layer circuit board with embedded profiled metal base

Abstract

The present application relates to a kind of multilayer circuit board manufacturing method of embedding special-shaped metal base, provide integrally formed special-shaped metal base, it includes main part and expansion part, expansion part is protruding on at least two opposite sides, increase the overall volume of metal base and the contact area with multilayer board under the premise of not invading device layout space;Subsequently, milling groove processing is carried out to multilayer core plate and prepreg, first groove body matching the outer contour of expansion part is milled on the bottom layer core plate, and second groove body matching the outer contour of main part is milled on each layer above it;After special-shaped metal base is embedded in corresponding groove body, hot pressing is carried out, so that the upper surface of main part is flush with the upper surface of top layer core plate, prepreg flows and solidifies as PP flow glue layer by heat, PP flow glue layer fills the gap between interface continuously, significantly improve the interface bonding strength;Finally, electroplating treatment is carried out, and electroplating layer is formed on the upper surface of main part and top layer core plate, with electrical conduction and secondary reinforcement function.

Description

Technical Field

[0001] This invention relates to the field of circuit board technology, and more specifically, to a method for manufacturing a multilayer circuit board with an embedded irregular metal substrate. Background Technology

[0002] Multilayer printed circuit board (PCB) technology is one of the core foundations of the modern electronics industry, widely used in communications, computing, industrial control, automotive electronics, and consumer electronics. As electronic devices rapidly evolve towards higher integration, higher power density, and thinner designs, more stringent requirements are being placed on PCBs in terms of heat dissipation, structural strength, and high-frequency, high-speed signal transmission performance. To meet these demands, embedding metal substrates within multilayer PCBs to enhance thermal conductivity and improve rigidity has become an important technological focus in the industry.

[0003] Existing metal substrate embedding technologies typically use standard rectangular metal blocks as embedding units. Due to the uniform cross-sectional shape of traditional metal substrates, the bonding force between the side of the metal substrate and the inner wall of the groove is limited after embedding. Especially when subjected to thermal shock, thermal cycling, or mechanical vibration, this interface is prone to cracking and delamination, leading to displacement or even detachment of the metal substrate, resulting in low reliability. When the circuit board operates at high power and the temperature of the metal substrate rises significantly, the difference in thermal expansion coefficient between the metal substrate and the surrounding copper-clad laminate material will generate large thermal mismatch stress at the interface, significantly increasing the risk of the metal substrate floating or detaching.

[0004] On the other hand, in existing technologies, the electrical connection between the upper surface of the metal substrate and the upper surface of the top core board is usually achieved by means of conductive adhesive bonding or partial welding. These methods have defects such as poor process stability, large fluctuations in contact resistance, and low reliability of thermal cycling, which make it difficult to meet the requirements of electrical connection quality for high reliability application scenarios.

[0005] The above problems are worth solving. Summary of the Invention

[0006] In order to overcome the problems of existing metal substrates having a single cross-sectional shape, insufficient bonding force between the embedded side and the inner wall of the groove, and easy cracking and delamination of the interface leading to metal detachment, the present invention provides a method for manufacturing a multilayer circuit board with an embedded irregular metal substrate.

[0007] The technical solution of this invention is as follows: A method for manufacturing a multilayer circuit board with an embedded irregular metal substrate includes the following steps: Step S1, irregular metal base preparation step: Provide an integrally formed irregular metal base, the irregular metal base including a main body part and an expanded part, the expanded part is located on one side of the main body part, and at least two opposite sides of the expanded part protrude relative to the main body part; Step S2, Layered milling step: Milling grooves is performed on at least two core boards and the prepreg disposed between adjacent core boards. Specifically, a first groove matching the outer contour shape of the expanded portion is milled on the bottom core board, and a second groove matching the outer contour shape of the main body is milled on the prepreg and core board above the bottom core board. Step S3, Metal base embedding step: Place the irregular metal base into the receiving space formed by the first groove and the second groove, so that the expanded part is embedded in the first groove and the main body part is embedded in the second groove; Step S4, Pressing Step: Hot press each core board and prepreg to make the end face of the main body away from the expansion part flush with the upper surface of the top core board, and make the prepreg flow and solidify to form a PP flow layer. The PP flow layer fully fills the interface between the top surface of the expansion part and the upper core board, as well as the gap between the side of the main body and the inner wall of the second groove. Step S5, Electroplating and Conductive Step: Electroplating is performed on the pressed board to form an electroplating layer on the upper surface of the main body and the upper surface of the top core board. The electroplating layer enables the upper surface of the main body and the upper surface of the top core board to be electrically connected and structurally connected.

[0008] As a preferred embodiment of the present invention, in step S1, the expansion portion protrudes from the main body portion only on two opposite sides in the first direction, and is flush with the main body portion on two opposite sides in the second direction perpendicular to the first direction, so that the longitudinal section of the irregular metal base is T-shaped.

[0009] As a preferred embodiment of the present invention, in step S1, the expansion portion protrudes relative to the main body portion on all four circumferential sides.

[0010] As a preferred embodiment of the present invention, in step S2, the milling dimensions of the first groove and the second groove are 0.1 mm to 0.2 mm larger on each side than the corresponding outer contour dimensions of the expansion portion and the main body portion, so as to form a preset gap for the PP adhesive layer to be filled.

[0011] As a preferred embodiment of the present invention, in step S4, the thickness of the PP adhesive layer is 0.1 mm to 0.2 mm.

[0012] As a preferred technical solution of the present invention, in step S1, the irregular metal base is an integrally formed copper-based structure or aluminum-based structure, and the main body is a cylinder or a rectangle.

[0013] As a preferred embodiment of the present invention, in step S2, the thickness of the bottom core board is equal to the thickness of the expansion portion, so that after the expansion portion is embedded in the bottom core board in step S3, the bottom surface of the expansion portion is flush with the lower surface of the bottom core board and exposed to the lower surface of the multilayer board structure.

[0014] As a preferred technical solution of the present invention, in step S5, the electroplating process includes copper immersion and copper electroplating processes, the electroplating layer is a copper electroplating layer, and the copper electroplating layer covers the upper surface of the main body and at least part of the upper surface of the top core board.

[0015] As a preferred embodiment of the present invention, the method further includes the following step after step S5: Step S6, Pattern Making Step: Etching the electroplated layer to form a surface circuit pattern; Step S7, Surface Coating Step: Use chemical deposition or displacement methods to complete the surface coating of the circuit board.

[0016] As a preferred technical solution of the present invention, after step S3 and before step S4, step S3a, a metal substrate surface treatment step, is further included: the surface of the irregular metal substrate is activated by plasma treatment or chemical roughening treatment to form a micro-rough structure on the surface of the irregular metal substrate, so as to enhance the bonding force between the irregular metal substrate and the PP adhesive layer.

[0017] According to the above-described solution, the beneficial effects of this invention are as follows: The present invention employs an integrally molded irregular metal substrate, which includes a main body and an expansion portion. The expansion portion protrudes from the main body on at least two opposite sides. This structure allows the metal substrate to maintain its original design on the device mounting surface side without encroaching on the device layout space. On the other hand, the protrusion of the expansion portion effectively increases the overall volume of the metal substrate and the contact area with the multilayer board structure.

[0018] This invention involves milling a first groove on the bottom core board that matches the outer contour of the expanded portion, and milling a second groove on the prepreg and core board above the bottom core board that matches the outer contour of the main body. The thickness of the expanded portion is equal to the thickness of the bottom core board, avoiding poor bonding caused by thickness differences. The height of the main body is flush with the upper surface of the top core board, and the upper surface of the main body is connected to the upper surface of the top core board through an electroplating layer. The electroplating layer forms an integrated connection between the main body of the metal substrate and the top circuit layer of the multilayer board structure on the surface, which not only achieves electrical conductivity but also provides secondary structural reinforcement to the metal substrate.

[0019] In the hot pressing step, PP adhesive is used to fully fill the interface between the top surface of the expanded part and the upper core board, as well as the gap between the side of the main part and the inner wall of the second tank, so that the interface between the shaped metal base and the surrounding core board forms a continuous and dense insulating bonding layer, which greatly improves the bonding strength of the interface. Attached Figure Description

[0020] Figure 1 This is a flowchart of the method of the present invention; Figure 2 A flowchart of a preferred embodiment of the method; Figure 3 This is a schematic diagram of the implantation process of an irregularly shaped metal substrate; Figure 4 This is a schematic diagram of the structure after the core board, prepreg, and irregularly shaped metal substrate are laminated together; Figure 5 A schematic diagram of the structure of a multilayer circuit board after electroplating on the component mounting side; Figure 6 This is a schematic diagram of the multilayer circuit board structure of the present invention; Figure 7 This is a schematic diagram of the irregular metal-based structure of the present invention; Figure 8 This is a schematic diagram of an irregular metal-based structure for other alternative embodiments.

[0021] In the diagram, 1 is the core board; 11 is the device mounting surface; 2 is the prepreg; 21 is the PP adhesive layer; 101 is the first tank; 102 is the second tank; 3 is the irregular metal base; 31 is the main body; 32 is the expanded part; 4 is the electroplated layer; and 41 is the surface circuit pattern. Detailed Implementation

[0022] To better understand the purpose, technical solution, and technical effects of this invention, the invention will be further explained and described below in conjunction with the accompanying drawings and embodiments. It should be noted that similar reference numerals and letters in the following drawings indicate similar items; therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings. It is also stated that the embodiments described below are only for explaining this invention and are not intended to limit this invention.

[0023] like Figures 1 to 6 As shown, this embodiment provides a method for manufacturing a multilayer circuit board with an embedded irregular metal substrate, including the following steps: Step S1: Provide a one-piece molded irregular metal base 3; The irregularly shaped metal base 3 is manufactured using a one-piece molding process, and is a single solid metal structure without any splicing seams or joint interfaces, exhibiting excellent overall mechanical properties and thermal conductivity continuity. Structurally, the irregularly shaped metal base 3 is divided into two functional regions: a main body 31 and an expanded portion 32, which are integrally formed in the same molding process.

[0024] The main body 31 is the upper section of the irregularly shaped metal base 3, and its outer contour dimensions correspond to the design dimensions of one side of the device mounting surface 11. After being embedded in the multilayer board, the planar dimensions of the upper surface of the main body 31 remain unchanged and do not encroach on the adjacent device layout space. The expansion portion 32 is located below the main body 31, i.e., on the side opposite to the device mounting surface 11. At least two of its opposite sides protrude relative to the main body 31, forming a boss structure in the lateral direction, making the cross-sectional dimension of the expansion portion 32 larger than that of the main body 31. Due to the protrusion of the expansion portion 32, the overall volume of the irregularly shaped metal base 3 is significantly larger than that of a regular column with the same cross-section as the main body 31, and the contact area with the multilayer board structure also increases accordingly. Thus, without changing the dimensions of the device mounting surface 11, the heat dissipation capacity of the metal base is effectively improved.

[0025] The integral molding method of the irregular metal base 3 includes, but is not limited to, mechanical milling, precision casting, and forging followed by finishing. Since the main body 31 and the expanded part 32 are integrally molded structures, there is no joint interface between them, and no interlayer separation will occur due to thermal stress during subsequent use, resulting in excellent structural integrity.

[0026] Step S2: Mill grooves on each core board 1 and the prepreg 2. like Figure 3 As shown, at least two core boards 1 are provided, each core board 1 is a copper-clad laminate, the copper foil and insulating substrate of which have been pre-processed into inner layer circuit patterns and a prepreg 2 (PP sheet) disposed between adjacent core boards 1. The above-mentioned boards are milled to form a receiving space for embedding a shaped metal base 3.

[0027] When designing the laminated structure, the thickness of the bottom core board 1 is selected to be equal to the thickness of the expansion portion 32 to ensure that the bottom surface of the expansion portion 32 is flush with the lower surface of the bottom core board 1 after insertion, avoiding poor bonding caused by thickness differences. On the bottom core board 1, located at the bottommost layer, a first groove 101 is milled through the entire thickness of the bottom core board 1 using a CNC milling machine, according to the outer contour shape of the expansion portion 32. Its planar shape matches the outer contour of the cross-section of the expansion portion 32, allowing the expansion portion 32 to be precisely inserted. On each layer of prepreg 2 and core board 1 above the bottom core board 1, a second groove 102 is milled, matching the outer contour of the cross-section of the main body portion 31. The positions of the second grooves 102 in each layer are aligned, and after being stacked, they together form the upper receiving space for the insertion of the main body portion 31. It should be noted that... Figure 3 The dashed line indicates the portion that has been milled away.

[0028] Since the planar dimensions of the first groove 101 match those of the expansion portion 32 and are significantly larger than those of the second groove 102, which matches those of the main body 31, the two grooves, when stacked together, form a stepped accommodating space. The stepped surface of this space corresponds to the plane containing the upper surface of the bottom core board 1. This stepped surface supports the top surface of the expansion portion 32 and provides a gap for the subsequent filling of the PP adhesive layer 21. After milling, the edges of the grooves must be deburred to ensure that the inner walls are smooth and clean.

[0029] In the laminated design, the total height of each core board 1 and the prepreg 2 must meet the following requirement: the top surface of the main body 31 is flush with the upper surface of the top core board 1 after pressing, so as to ensure that the two are on the same plane reference during subsequent electroplating, providing conditions for the continuous and uniform coverage of the electroplating layer 4.

[0030] Step S3: Place the irregular metal base 3 into the receiving space. The integrally formed irregular metal base 3 is placed into the receiving space formed by the first groove 101 and the second groove 102. In specific operation, the bottom core board 1 is first laid flat, and the expanded part 32 of the irregular metal base 3 is placed vertically with the first groove 101 facing downward, so that the expanded part 32 is embedded in the first groove 101; then the semi-cured sheets 2 and the core board 1 are stacked in sequence according to the designed stacking order, so that the main body 31 is inserted into the second groove 102 of each layer.

[0031] like Figure 4As shown, after embedding, the expanded portion 32 is completely located within the space of the first groove 101, with its bottom surface flush with the lower surface of the bottom core board 1; the main body portion 31 is located within the upper receiving space formed by the second groove 102, with its top surface flush with the upper surface of the top core board 1. Since the lateral dimension of the expanded portion 32 is larger than that of the main body portion 31, the top protrusion area of ​​the expanded portion 32 will be covered by the layers above the bottom core board 1, thus structurally limiting the irregular metal base 3 vertically. Pre-set gaps are left at each interface for subsequent PP adhesive filling, ensuring the overall stable positioning of the irregular metal base 3 and providing an accurate positional reference for the hot pressing process.

[0032] Step S4: Hot pressing treatment The stacked core board 1 and prepreg 2 are subjected to hot pressing. The stacked boards are placed in a hot press and pressed under the set temperature, pressure and time parameters.

[0033] During the hot-pressing process, the resin system in the prepreg 2 melts and softens as the temperature rises, significantly reducing its viscosity and exhibiting good fluidity. Under pressure, the molten resin fully permeates into the surrounding gaps: on the one hand, it fills the interface gap between the top surface of the expanded portion 32 (i.e., the upper surface of the protruding step of the expanded portion 32) and the lower surface of the adjacent core board 1 above; on the other hand, it fills the annular gap between the side of the main body portion 31 and the inner wall of the second groove 102. As the temperature further increases, the resin undergoes cross-linking and curing, forming a continuous and dense PP adhesive layer 21, which completely seals and fills the aforementioned interface gaps. As a result, the shaped metal substrate 3 forms a strong insulating bond with the surrounding core board 1 material, and the interfacial bonding strength is greatly improved.

[0034] After hot pressing, the upper surface of the main body 31 remains flush with the upper surface of the top core board 1, meeting the requirements of subsequent electroplating for a flattened reference surface.

[0035] Step S5: Electroplating treatment like Figure 5 As shown, the hot-pressed plates are electroplated to form an electroplating layer 4 on the upper surface of the main body 31 and the upper surface of the top core plate 1. The electroplating layer 4 enables the upper surface of the main body 31 and the upper surface of the top core plate 1 to achieve electrical conductivity and form a structural connection.

[0036] Before electroplating, necessary pretreatment of the board surface is required, including grinding, degreasing, and micro-etching, to remove residual resin and oxide layer from the board surface after lamination, expose a clean metal surface, and ensure that the electroplated layer 4 has good adhesion to the upper surface of the metal substrate and the copper foil surface of the core board 1.

[0037] The electroplated layer 4 forms a continuous cover between the upper surface of the main body 31 and the upper surface of the top core board 1, forming an integrated connection between the main body 31 of the metal substrate and the top circuit layer of the multilayer board structure on the surface. On the one hand, it realizes the electrical conduction between the main body 31 and the upper surface of the top core board 1, and the conductivity of the metal substrate can be directly incorporated into the surface circuit design to meet the requirements of high current transmission or functional electrical connection. On the other hand, the electroplated layer 4 forms a covering structure connection on the upper surface of the metal substrate, which is equivalent to a secondary reinforcement of the metal substrate on the basis of hot pressing and fixing. When subjected to shear force in the direction of the board surface, the electroplated layer 4, the metal substrate and the top copper foil share the load, further improving the fixing reliability of the metal substrate in the multilayer board.

[0038] In this embodiment, the steps work together to achieve the integrated functionality of heat dissipation, electrical, and structural functions. The irregularly shaped metal substrate 3 prepared in step S1, through the protruding structure of the expanded portion 32, increases the overall heat dissipation volume and contact area while maintaining the same dimensions of the device mounting surface 11. The differential milling groove design in step S2, where the bottom core board 1 and the expanded portion 32 have the same thickness, ensures fitting accuracy and eliminates the risk of poor bonding caused by thickness differences. The precise embedding in step S3 lays the foundation for the uniform filling of the PP adhesive layer 21 in step S4. The hot pressing in step S4, through the dense filling of the PP adhesive layer 21, significantly improves the interfacial bonding strength between the metal substrate and the multilayer board. The electroplating process in step S5 incorporates the metal substrate into the surface circuit and forms a secondary structural reinforcement of the metal substrate, achieving a synergistic enhancement of electrical conductivity and structural retention.

[0039] like Figure 7 As shown, in step S1 of an optional embodiment, the expansion portion 32 protrudes from the main body portion 31 only on two opposite sides in the first direction, while its two opposite sides in the second direction perpendicular to the first direction are flush with the main body portion 31, making the longitudinal section of the irregular metal base 3 T-shaped. Specifically, with the axial direction of the main body portion 31 as the height direction and the first direction as the width direction, the horizontal and vertical segments of the T-shaped section correspond to the expansion portion 32 and the main body portion 31, respectively: the expansion portion 32 forms the transverse flange of the "T" and forms a protruding step on each side in the width direction; the main body portion 31 forms the longitudinal web of the "T," the width of which is smaller than that of the expansion portion 32. In the second direction, the expansion portion 32 and the main body portion 31 have the same dimensions and there is no additional protrusion.

[0040] From a heat dissipation perspective, the expanded portion 32 of the T-section increases the lateral volume in the first direction compared to a regular column with a uniform cross-section. This effectively expands the overall heat dissipation volume of the metal substrate and correspondingly increases the contact area with the multilayer board structure, improving heat dissipation capacity without changing the dimensions of the main body 31. Simultaneously, compared to a design with protrusions on all four sides of the circumference, the T-section has no protrusions in the second direction, reducing the total area occupied by the first groove 101 on the bottom core board 1. This allows for more ample wiring space for adjacent inner layer circuits on the bottom core board 1, achieving a reasonable balance between enhanced heat dissipation and wiring density. Furthermore, the milling of the T-section only requires differentiating groove widths in two directions, simplifying the process and improving processing efficiency and dimensional accuracy.

[0041] like Figure 8 As shown, in step S1 of an optional embodiment, the expansion portion 32 protrudes relative to the main body portion 31 on all four circumferential sides, so that the expansion portion 32 forms a four-way expansion structure around the outer periphery of the main body portion 31 in cross-section. Viewed from any side direction, the longitudinal section of the irregular metal base 3 is inverted T-shaped, and the circumferential protruding steps of the expansion portion 32 completely surround the bottom side of the main body portion 31.

[0042] From a heat dissipation perspective, compared to the T-shaped cross section which expands only in the first direction, the circumferentially convex structure increases the volume of the expansion portion 32 in all directions, resulting in a larger expansion of the overall heat dissipation volume of the metal base. The PP flow adhesive contact interface area between the top surface of the expansion portion 32 and the upper core plate 1 is also larger, further improving the overall heat dissipation efficiency. It is especially suitable for high power density devices or applications with extremely stringent heat dissipation requirements.

[0043] From a holding perspective, the circumferentially protruding expansion portion 32 is held in all directions by the material of the upper plate, which has a stronger ability to resist vertical pull-out force. At the same time, it has anti-lateral displacement constraint in any horizontal direction, further enhancing the holding reliability. It is suitable for occasions with large metal base size or harsh working environment vibration and shock conditions.

[0044] In step S1 of an optional embodiment, the irregular metal substrate 3 is an integrally formed copper-based structure or aluminum-based structure, and the main body 31 is a cylinder or rectangle. When a copper-based structure is used, the thermal conductivity of copper is approximately 385 W / (m·K), which is much higher than that of conventional copper-clad laminate insulating substrates (approximately 0.3–1 W / (m·K)). This provides excellent vertical heat dissipation channels for high-power components, efficiently conducting the heat generated by the devices to the outer surface of the multilayer board for dissipation. The expansion portion 32 of the copper-based structure increases the heat dissipation volume, and its high thermal conductivity further enhances the heat dissipation capacity. When an aluminum-based structure is used, the thermal conductivity of aluminum is approximately 205 W / (m·K), also exhibiting good thermal conductivity. Moreover, the density of aluminum (approximately 2.7 g / cm³) is only about 1 / 3 that of copper, giving it a significant advantage in lightweight applications with strict weight constraints (such as avionics and mobile devices). The design concept of increasing the heat dissipation volume through the expansion portion 32 can also be fully utilized in aluminum-based structures.

[0045] In step S2 of an optional embodiment, the milled groove dimensions of the first groove 101 and the second groove 102 are 0.1 mm to 0.2 mm larger on each side than the corresponding outer contour dimensions of the expansion portion 32 and the main body portion 31, respectively, to form a preset gap for the PP adhesive layer 21 to be filled.

[0046] Specifically, if the outer dimension of the expanded portion 32 in a certain direction is L, then the corresponding dimension of the first groove 101 in that direction is L+0.2mm to L+0.4mm (increased by 0.1mm to 0.2mm on each side, and increased by 0.2mm to 0.4mm on both sides). The preset gap is set based on the following considerations: the gap needs to be large enough to ensure that the resin of the prepreg 2 can flow smoothly and completely fill all interface gaps during hot pressing, without generating pores or voids, and ensuring that the PP adhesive layer 21 forms a continuous and dense bonding layer; at the same time, the gap should not be too large. If it exceeds 0.2mm, the increased thickness of the PP adhesive layer 21 will lead to an increase in thermal resistance, weakening the thermal conductivity of the metal base, and the mechanical strength of an excessively thick resin layer is relatively low, affecting the bonding reliability.

[0047] Therefore, controlling the single-sided gap within the range of 0.1mm to 0.2mm takes into account both the requirements of sufficient PP adhesive filling and efficient heat conduction, providing a clear standard for process consistency in mass production.

[0048] Based on the groove width of the above embodiment, in step S4, the thickness of the PP adhesive layer 21 formed after hot pressing is 0.1mm to 0.2mm. The thickness of the PP adhesive layer 21 is directly determined by the preset gap in step S2, and the two correspond numerically. Within the thickness range of 0.1mm to 0.2mm, the PP adhesive layer 21 can simultaneously meet the performance requirements of adhesive strength and electrical insulation. Firstly, the cured PP adhesive layer 21 within this thickness range can provide sufficient interfacial bonding shear strength, significantly improving the bonding force between the irregular metal substrate 3 and the surrounding core board 1, and meeting the reliability requirements for the retention of the metal substrate in the multilayer board. Secondly, the cured resin layer with a thickness of 0.1 mm or more has sufficient breakdown voltage, which can effectively ensure the electrical insulation between the three sides of the irregular metal substrate and the adjacent inner copper foil.

[0049] In step S2 of an optional embodiment, the thickness of the bottom core board 1 is equal to the thickness of the expansion portion 32, such that after the expansion portion 32 is embedded into the bottom core board 1 in step S3, the bottom surface of the expansion portion 32 is flush with the lower surface of the bottom core board 1 and exposed to the lower surface of the multilayer board structure.

[0050] If the thickness of the bottom core board 1 is inconsistent with the thickness of the expanded portion 32, a vertical gap or excess will form between the first groove 101 and the expanded portion 32. This will result in uneven gap width between the top surface of the expanded portion 32 and the upper core board 1, or even localized gaps. The PP adhesive layer 21 will then be unable to uniformly and densely fill this interface during hot pressing, leading to poor interface adhesion. By setting their thicknesses to be equal, the expanded portion 32 perfectly matches the first groove 101 vertically, ensuring the geometric uniformity of the interface gap and creating favorable conditions for dense filling of the PP adhesive. Therefore, precisely matching the thickness of the bottom core board 1 and the expanded portion 32 is a direct means of avoiding poor bonding caused by thickness differences.

[0051] Based on this, the bottom surface of the expansion portion 32 is exposed on the lower surface of the multilayer board, allowing the expansion portion 32 to directly contact the heat dissipation module (such as heat sink, heat sink, liquid cooling plate, etc.). The metal base forms a continuous metal heat conduction path from the top surface to the bottom surface, running through the thickness direction of the multilayer board, with minimal thermal resistance. At the same time, the flushness between the bottom surface and the lower surface ensures the flatness of the overall lower surface of the multilayer board, which is beneficial for tight contact with the heat dissipation base plate during subsequent assembly, without generating additional contact thermal resistance or installation stress.

[0052] When the main body 31 is cylindrical, its cross-section is circular, exhibiting geometric symmetry in all directions of the plane. Milling the groove requires only a single pass with a circular milling cutter, simplifying the process. Furthermore, the circular cross-section has no sharp corners, preventing localized cracking caused by stress concentration and improving mechanical reliability. When the main body 31 is rectangular, its cross-section is rectangular or square. Milling the groove can be performed using a standard square milling cutter, resulting in high positioning accuracy. This is suitable for high-density layouts where multiple metal substrates need to be closely arranged on a circuit board.

[0053] In step S5 of an optional embodiment, the electroplating process includes copper immersion and copper electroplating processes, wherein the electroplating layer 4 is a copper electroplating layer, and the copper electroplating layer covers the upper surface of the main body 31 and at least part of the upper surface of the top core board 1.

[0054] The electroless copper plating (ECC) process is a crucial preliminary step for achieving continuous coverage of the electroplated layer 4. After hot pressing, there is an insulating resin top surface area of ​​the PP adhesive layer 21 between the upper surface of the main body 31 and the copper foil of the top core board 1. This area is non-conductive and cannot be directly electroplated. Through the ECC process, a thin layer of copper (approximately 0.3–1.0 μm thick) is uniformly deposited on the surface of the insulating resin using a palladium catalyst and a chemical reduction reaction. This gives the entire board surface, including the resin area, continuous conductivity, laying the foundation for the subsequent copper electroplating process.

[0055] The copper plating process thickens the copper layer to the design requirements through electrochemical deposition on top of the immersion copper layer, typically to 20–35 μm or more, forming a copper plating layer with sufficient strength and conductivity. The copper plating layer continuously covers the upper surface of the main body 31 and the copper foil surface of the top core board 1, forming an integrated connection between the metal-based main body 31 and the top circuit layer of the multilayer board. The copper plating layer provides a conductive bridge between the two, enabling electrical conduction; simultaneously, it forms a metallic coating on the upper surface of the main body 31, providing secondary structural reinforcement to the metal substrate. The copper-copper metallurgical bond exhibits excellent peel strength and thermal cycling reliability. Compared to conductive adhesives or welding methods, it offers lower contact resistance and higher connection stability, fully meeting the requirements of high-reliability applications.

[0056] Following step S5 of the present invention, the following process steps S6 and S7 are also included to complete the fabrication of the surface circuit pattern and surface protection treatment of the multilayer circuit board.

[0057] Specifically, step S6: Etching the electroplated layer 4 to form the surface circuit pattern. After the deposition of the electroplated copper layer is completed, the electroplated copper layer on the upper surface of the top core board 1 is subjected to pattern transfer and chemical etching according to the circuit design pattern. The specific process flow is as follows: First, a photosensitive dry film or liquid photosensitive ink is coated on the surface of the electroplated layer 4. The circuit pattern is transferred to the photosensitive layer through exposure and development processes to form a patterned etching protective mask. Then, the copper layer not covered by the mask is selectively dissolved and removed using an etching solution. After etching, the photosensitive layer is stripped off to form a precise surface copper circuit pattern. The etching solution is such as copper chloride or alkaline ammonia etching solution.

[0058] The electroplated copper layer on the upper surface of the main body 31 can be incorporated into the circuit pattern according to design requirements, forming a conductive pattern in which the metal base directly participates in circuit connections. Alternatively, it can be etched away to leave the exposed metal base surface as a heat dissipation contact surface, depending on the product's electrical design. This step integrates the surface layer signal transmission, power distribution, and heat dissipation functions of the multilayer board.

[0059] Step S7: Surface coating is applied to the circuit board surface using chemical deposition or displacement methods. After the circuit pattern is fabricated, the copper traces on the circuit board surface are coated to improve their solderability, oxidation resistance, and contact reliability. Commonly used surface coating methods include: electroless nickel-gold plating (ENIG), electroless nickel-palladium-gold plating (ENEPIG), and organic solderability protection film (OSP). Taking electroless nickel-gold plating as an example: First, a nickel layer with a thickness of approximately 35 μm is deposited on the copper trace surface through chemical plating as a barrier layer to prevent copper from diffusing into the gold layer; then, a thin gold layer with a thickness of approximately 0.05-0.1 μm is deposited on the nickel layer surface through a displacement reaction. The gold layer is chemically stable, oxidation-resistant, and has excellent solderability and contact conductivity. The above chemical deposition and displacement methods do not require external current and are suitable for uniform coating on boards with existing fine circuit patterns. The coating uniformity is good, making it suitable for high-density fine circuit designs.

[0060] Through steps S6 and S7, the manufacturing method of the present invention can provide a complete multilayer circuit board manufacturing solution from structural integration to surface treatment.

[0061] In a preferred embodiment, a step S3a—a metal substrate surface treatment step—is added after step S3 and before step S4. Step S3a involves activating the surface of the irregularly shaped metal substrate 3 using plasma treatment or chemical roughening treatment, creating a micro-roughened structure on the surface of the irregularly shaped metal substrate 3 to enhance the bonding force between the irregularly shaped metal substrate 3 and the PP adhesive layer 21. This step activates the surface of all interface areas on the irregularly shaped metal substrate 3 that will contact the PP adhesive layer 21 (including the sides of the main body 31, the top surface and sides of the expanded portion 32), aiming to further improve the interfacial adhesion strength between the PP adhesive layer 21 and the metal substrate. This, combined with the filling and curing of the PP adhesive layer 21 in step S4, significantly enhances the interfacial adhesion strength.

[0062] When plasma treatment is used, the metal substrate surface is bombarded with low-temperature plasma (such as oxygen plasma, argon plasma, or air plasma). The highly reactive ions and free radicals in the plasma produce a dual effect of physical sputtering and chemical etching on the metal substrate surface. Physical sputtering creates a uniform micron-nano-scale roughened morphology on the metal substrate surface, providing mechanical engagement anchoring points. Chemical etching removes organic contaminants and oxide layers from the surface, while simultaneously introducing oxygen-containing functional groups (such as hydroxyl-OH, carboxyl-COOH, etc.) into the metal substrate surface, changing the surface from a hydrophobic state to a hydrophilic active state, significantly improving the wettability of the metal substrate surface to the molten PP resin. These effects together promote the full wetting and spreading of the molten resin on the metal substrate surface during hot pressing, and form a "riveting effect" physical locking between the cured PP adhesive layer 21 and the metal substrate surface, significantly improving the interfacial adhesion strength.

[0063] When using chemical roughening treatment, a micro-etching solution (such as a sodium persulfate-sulfuric acid mixture or a hydrogen peroxide-sulfuric acid system) is typically used to selectively dissolve the copper-based surface, forming a uniform micro-undulating rough structure on the copper surface (the surface roughness Ra value can usually be increased to 0.5–2.0 μm). For aluminum-based structures, an alkaline etching solution (such as sodium hydroxide solution) can be used for moderate roughening, forming a fine uneven morphology on the aluminum-based surface, which also increases the effective bonding contact area and produces a mechanical anchoring effect. After treatment, the metal-based surface is kept clean and active through water washing and drying steps, ready for the hot pressing process.

[0064] The introduction of this step significantly improves the interfacial bonding strength between the PP adhesive layer and the irregular metal substrate, effectively reducing the risk of interfacial cracking and delamination under thermal shock, thermal cycling and mechanical stress conditions, and further improving the long-term reliability of multilayer circuit boards with embedded irregular metal substrates.

[0065] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0066] The above embodiments merely illustrate several implementation methods of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for manufacturing a multilayer circuit board with an embedded irregular metal substrate, characterized in that, Includes the following steps: Step S1: Provide an integrally formed irregular metal base, the irregular metal base including a main body and an expanded portion, the expanded portion being located on one side of the main body, and at least two opposite sides of the expanded portion protruding relative to the main body; Step S2: Mill grooves on at least two core boards and the prepreg disposed between adjacent core boards, wherein a first groove matching the outer contour shape of the expanded portion is milled on the bottom core board, and a second groove matching the outer contour shape of the main body is milled on the prepreg and core board above the bottom core board. Step S3: Place the irregular metal base into the receiving space formed by the first groove and the second groove, so that the expanded part is embedded in the first groove and the main body is embedded in the second groove; Step S4: Hot-press each core board and prepreg together so that the end face of the main body away from the expansion part is flush with the upper surface of the top core board, and the prepreg is heated and flows and solidifies to form a PP flow adhesive layer. The PP flow adhesive layer fully fills the interface between the top surface of the expansion part and the upper core board, as well as the gap between the side of the main body and the inner wall of the second groove. Step S5: Electroplating is performed on the pressed board to form an electroplating layer on the upper surface of the main body and the upper surface of the top core board. The electroplating layer enables the upper surface of the main body and the upper surface of the top core board to be electrically connected and structurally connected.

2. The method for manufacturing a multilayer circuit board with an embedded irregular metal substrate according to claim 1, characterized in that, In step S1, the expansion portion protrudes from the main body portion only on two opposite sides in the first direction, and is flush with the main body portion on two opposite sides in the second direction perpendicular to the first direction, so that the longitudinal section of the irregular metal base is T-shaped.

3. The method for manufacturing a multilayer circuit board with an embedded irregular metal substrate according to claim 1, characterized in that, In step S1, the expanded portion protrudes relative to the main body portion on all four circumferential sides.

4. The manufacturing method according to claim 1, characterized in that, In step S2, the milling dimensions of the first groove and the second groove are 0.1 mm to 0.2 mm larger on each side than the corresponding outer contour dimensions of the expansion portion and the main body portion, so as to form a preset gap for the PP adhesive layer to be filled.

5. The method for manufacturing a multilayer circuit board with an embedded irregular metal substrate according to claim 4, characterized in that, In step S4, the thickness of the PP adhesive layer is 0.1 mm to 0.2 mm.

6. The method for manufacturing a multilayer circuit board with an embedded irregular metal substrate according to claim 1, characterized in that, In step S1, the irregular metal base is an integrally formed copper-based structure or aluminum-based structure, and the main body is a cylinder or a rectangle.

7. The method for manufacturing a multilayer circuit board with an embedded irregular metal substrate according to claim 1, characterized in that, In step S2, the thickness of the bottom core board is equal to the thickness of the expansion portion, so that after the expansion portion is embedded in the bottom core board in step S3, the bottom surface of the expansion portion is flush with the lower surface of the bottom core board and exposed to the lower surface of the multilayer board structure.

8. The method for manufacturing a multilayer circuit board with an embedded irregular metal substrate according to claim 1, characterized in that, In step S5, the electroplating process includes copper immersion and copper electroplating processes. The electroplated layer is a copper electroplated layer, which covers the upper surface of the main body and at least part of the upper surface of the top core board.

9. The method for manufacturing a multilayer circuit board with an embedded irregular metal substrate according to any one of claims 1 to 8, characterized in that, The process after step S5 also includes: Step S6: Etch the electroplated layer to form a surface circuit pattern; Step S7: Apply a chemical deposition or displacement method to the surface coating of the circuit board.

10. The method for manufacturing a multilayer circuit board with an embedded irregular metal substrate according to any one of claims 1 to 8, characterized in that, After step S3 and before step S4, step S3a, a metal substrate surface treatment step, is also included: the surface of the irregular metal substrate is activated by plasma treatment or chemical roughening treatment to form a micro-rough structure on the surface of the irregular metal substrate, so as to enhance the bonding force between the irregular metal substrate and the PP adhesive layer.

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