Hole processing method of circuit board and multilayer circuit board

Abstract

The invention discloses a hole processing method of a circuit board and a multilayer circuit board, the multilayer circuit board comprises a circuit board body, the circuit board body is provided with a conductive hole, and the inner wall of the conductive hole is provided with an annular conductive layer; a resin ceramic composite part is arranged on the inner wall of the conductive layer, and the inner ring surface of the conductive layer is filled with the resin ceramic composite part; and the ceramic powder concentration of the resin ceramic composite part is gradually increased along the axis direction close to the conductive hole. Specifically, the content of resin in the resin-ceramic composite part close to the inner wall area of the conductive layer is high, the content of ceramic powder is low, the high proportion of the resin ensures excellent interface adhesiveness with the copper layer, and the phenomenon of interface separation is effectively prevented; and the concentration of the ceramic powder is gradually increased along the direction close to the axis of the conductive hole, so that the thermal expansion coefficient of the composite material is gradually reduced and is close to the thermal expansion coefficient of a copper layer, stress accumulation in the thermal cycle process is reduced, cracks and hole blasting are prevented, and the composite material has good interface adhesiveness and thermal expansion coefficient matching performance.

Description

Technical Field

[0001] The present invention relates to the technical field of multi-layer printed circuit board structures, and particularly to a method for processing holes in a printed circuit board and a multi-layer printed circuit board. Background Art

[0002] A multi-layer printed circuit board is a printed circuit board formed by alternately laminating multiple conductive pattern layers and insulating layers, and is widely used in fields such as computers, communication devices, consumer electronics, and aerospace. With the development of electronic products towards being thinner, lighter, shorter, faster, higher frequency, and more reliable, the design and manufacturing technologies of multi-layer printed circuit boards are constantly innovating. In particular, the filling technology of conductive holes has become a key factor affecting product performance and reliability. In a multi-layer printed circuit board, a conductive hole is an important channel connecting different conductive layers, and its inner wall is usually plated with a layer of copper to form a ring-shaped conductive layer to achieve the function of electrical interconnection. In high-density interconnection and high-frequency high-speed application scenarios, it is usually necessary to perform filling treatment (i.e., "hole plugging") on the conductive holes to improve the mechanical strength, flatness, heat dissipation performance, and electrical performance of the multi-layer printed circuit board.

[0003] Currently, the commonly used conductive hole filling treatments in industry mainly include the following methods: One is pure resin filling, using organic polymer materials such as epoxy resin and polypropylene to fill the conductive holes. The resin has good adhesion to the copper layer, but has low thermal conductivity and a large difference in thermal expansion coefficient from the copper layer, and is prone to stress concentration under thermal cycling conditions, resulting in cracks and hole explosions; The other is conductive material filling, using conductive paste (such as conductive silver paste) to fill the conductive holes. This method can achieve electrical conduction of the conductive holes and has a small difference in thermal expansion coefficient, but there is an easy problem of poor contact at the interface between the conductive paste and the copper layer, that is, it is easy for the interface between the conductive paste and the copper layer to detach.

[0004] In summary, the scheme of using resin filling is prone to cracks and hole explosions, and the scheme of using conductive materials is prone to interface detachment. Therefore, the hole processing technology in the prior art is difficult to simultaneously solve the technical problems of being prone to cracks and easy interface detachment. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for processing holes in a printed circuit board and a multi-layer printed circuit board, which solves the problem that it is difficult to simultaneously solve the problems of being prone to cracks and easy interface detachment in the filling area of conductive holes in the prior art.

[0006] To achieve this purpose, the present invention adopts the following technical solutions: A multi-layer printed circuit board includes a printed circuit board body, conductive holes are provided on the printed circuit board body, and a ring-shaped conductive layer is provided on the inner wall of the conductive holes; Wherein, a resin-ceramic composite part is arranged on the inner wall of the conductive layer, and the resin-ceramic composite part fills the inner ring surface of the conductive layer; the ceramic powder concentration of the resin-ceramic composite part increases along the direction close to the axis of the conductive hole.

[0007] Optionally, the resin-ceramic composite part includes a resin-ceramic column and a plurality of resin-ceramic rings sleeved outside the resin-ceramic column in sequence from inside to outside.

[0008] Optionally, the conductive layer includes an integrally formed conductive outer layer and a conductive inner layer. The height of the conductive outer layer is the same as the depth of the conductive hole, and the height of the conductive inner layer is less than the height of the conductive outer layer, so as to form a connection groove between the conductive inner layer and the hole edge of the conductive hole.

[0009] Optionally, a resin connection part is arranged in the connection groove, and the resin connection part is connected to the conductive layer and the resin-ceramic composite part respectively.

[0010] A hole processing method for a circuit board, used to prepare the multi-layer circuit board as described above, includes: Step S100: Provide a circuit board body, a conductive hole is formed on the circuit board body, and a ring-shaped conductive layer is arranged on the inner wall of the conductive hole; Step S200: Arrange a resin-ceramic composite part on the inner wall of the conductive layer, and the ceramic powder concentration of the resin-ceramic composite part increases along the direction close to the axis of the conductive hole.

[0011] Optionally, the step S200 includes: Step S201: Prepare mixtures of resin powder and ceramic powder with multiple different ratios, wherein the concentration of ceramic powder increases sequentially in different mixtures; Step S202: Through a stencil, fill the mixture with the lowest ceramic powder concentration in the area close to the inner wall of the conductive layer; Step S203: Perform mild curing on the filled first layer of mixture, and the mild curing temperature is 75-85°C; Step S204: Through a stencil, fill the area close to the axis direction of the conductive hole with the next group of mixtures with a higher ceramic powder concentration; Step S205: Perform mild curing on the newly filled mixture layer, and the mild curing temperature is 75-85°C; Step S206: Repeat steps S204 to S205 to sequentially complete the filling of all mixture layers, and form a resin-ceramic composite part with the ceramic powder concentration increasing along the direction close to the axis of the conductive hole; Step S207: Perform hot pressing treatment on the completed filled resin-ceramic composite part.

[0012] Optionally, the step S100 includes: Step S101: Perform first electroplating on the circuit board body provided with conductive holes to form a conductive outer layer on the inner wall of the conductive holes, and the height of the conductive outer layer is the same as the depth of the conductive holes; Step S102: Perform second electroplating on the inner wall of the conductive outer layer to form a conductive inner layer on the inner wall of the conductive outer layer, obtaining a conductive layer; wherein, the height of the conductive inner layer is less than the height of the conductive outer layer, so as to form a connection groove between the conductive inner layer and the hole edge of the conductive hole; The step S200 includes: Step S211: Set a solvent transmission part on the connection groove; Step S212: Provide a uniform mixture of resin powder and ceramic powder, and fill the uniform mixture into the conductive holes; Step S213: Inject cyclohexane solvent into the solvent transmission part, and use capillary action to make the cyclohexane solvent penetrate in the axial direction to form a solvent concentration gradient, and the solvent concentration gradient decreases along the direction close to the axis, so that the resin powder migrates in the direction away from the axis; Step S214: Remove the cyclohexane solvent and the solvent transmission part to obtain a resin-ceramic composite part.

[0013] Optionally, the process of removing the cyclohexane solvent includes: Step S221: Place the processed circuit board body in a volatile environment for 2 - 4 h; Step S222: Slowly raise the temperature to 55 - 65 °C and maintain it for 1 - 2 h; Step S223: Place the circuit board body in a vacuum environment and maintain the temperature at 40 - 50 °C for 30 - 60 min.

[0014] Optionally, the material of the solvent transmission part is modified polyvinyl alcohol; The process of removing the solvent transmission part includes: Step S231: Immerse the circuit board body in deionized water at 35 - 45 °C and stir gently to promote the dissolution of the modified polyvinyl alcohol; Step S2�2: Rinse the circuit board multiple times with deionized water at 40 - 50 °C; Step S233: Place the washed circuit board in an oven or dry it with nitrogen to perform drying treatment.

[0015] Optionally, the step S200 further includes: Step S215: After the resin-ceramic composite part is formed and the solvent transmission part is removed, set a resin connection part in the connection groove.

[0016] Compared with the prior art, the present invention has the following beneficial effects: The hole processing method for a circuit board and the multi-layer circuit board provided by the present invention adopt a resin-ceramic composite part with the ceramic powder concentration increasing along the axial direction of the conductive hole. In the resin-ceramic composite part near the inner wall area of the conductive layer, the resin content is relatively high and the ceramic powder content is relatively low. The high proportion of resin ensures excellent interfacial adhesion with the copper layer and effectively prevents the phenomenon of interfacial detachment. As it extends along the axial direction of the conductive hole, the ceramic powder concentration gradually increases, making the coefficient of thermal expansion of the composite material gradually decrease and match the coefficient of thermal expansion of the copper layer, thereby reducing the stress accumulation during the thermal cycle and effectively preventing the generation of cracks and via explosion. It can be seen that the hole processing method for a circuit board and the multi-layer circuit board provided by the present invention simultaneously solve the problems of cracks, via explosion, and interfacial detachment that are prone to occur in the conventional via filling process, enabling the multi-layer circuit board to simultaneously have good interfacial adhesion and coefficient of thermal expansion matching. Description of the Drawings

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0018] The structures, proportions, sizes, etc. shown in the drawings of this specification are only used to cooperate with the content disclosed in the specification for those familiar with this technology to understand and read, and are not used to limit the limited conditions for the implementation of the present invention. Therefore, they do not have technical essential significance. Any modification of the structure, change in the proportional relationship, or adjustment of the size, without affecting the effects that the present invention can produce and the purposes that can be achieved, should still fall within the scope that can be covered by the technical content disclosed by the present invention.

[0019] Figure 1 It is a schematic structural diagram of the first state of the multi-layer circuit board provided by the embodiment of the present invention; Figure 2 It is a schematic structural diagram of the second state of the multi-layer circuit board provided by the embodiment of the present invention; Figure 3 It is a schematic structural diagram of the third state of the multi-layer circuit board provided by the embodiment of the present invention; Figure 4 It is a schematic structural diagram of the fourth state of the multi-layer circuit board provided by the embodiment of the present invention; Figure 5 It is a schematic structural diagram of the fifth state of the multi-layer circuit board provided by the embodiment of the present invention; Figure 6 It is a schematic structural diagram of the sixth state of the multi-layer circuit board provided by the embodiment of the present invention; Figure 7 Schematic diagram of the seventh state structure of the multi-layer circuit board provided by the embodiment of the present invention; Illustration: 100, circuit board body; 110, conductive hole; 120, conductive layer; 121, outer conductive layer; 122, inner conductive layer; 130, connection groove; 200, resin-ceramic composite part; 210, resin-ceramic column; 220, resin-ceramic ring; 300, resin connection part; 400, solvent transmission part. Specific embodiments

[0020] In order to make the object, features, and advantages of the present invention more obvious and understandable, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the embodiments described below are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0021] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "upper", "lower", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention. It should be noted that when a component is considered to be "connected" to another component, it may be directly connected to the other component or there may be an intermediate component present at the same time.

[0022] The technical solutions of the present invention will be further described below with reference to the accompanying drawings and through specific embodiments.

[0023] Embodiment 1: The multi-layer circuit board in this embodiment mainly covers the fields of high-frequency, high-speed electronic products and high-reliability requirements; especially in products that require the circuit board to have excellent thermal stability, stress resistance, and long service life, this multi-layer circuit board has broad application prospects. The multi-layer circuit board provided by this embodiment can effectively solve the problems of cracks, burst holes, and interface detachment in the prior art, greatly improving the stability of the multi-layer circuit board in harsh environments such as high frequency and thermal cycling, so as to meet the requirements of high-performance electronic devices for multi-layer circuit boards.

[0024] As Figure 7As shown in the figure, the multi-layer circuit board in this embodiment includes a circuit board body 100. A conductive hole 110 is formed in the circuit board body 100, and an annular conductive layer 120 is provided on the inner wall of the conductive hole 110. Among them, a resin-ceramic composite part 200 is arranged on the inner wall of the conductive layer 120, and the resin-ceramic composite part 200 fills the inner ring surface of the conductive layer 120; the ceramic powder concentration of the resin-ceramic composite part 200 increases along the direction close to the axis of the conductive hole 110. In this embodiment, the resin-ceramic composite part 200 is composed of polypropylene powder and ceramic powder, and the conductive layer 120 is a copper plating layer.

[0025] Specifically, by using the resin-ceramic composite part 200 with the ceramic powder concentration increasing along the direction close to the axis of the conductive hole 110, the resin-ceramic composite part 200 in the area close to the inner wall of the conductive layer 120 has a higher resin content and a lower ceramic powder content. The high proportion of resin ensures excellent interfacial adhesion with the copper layer and effectively prevents the phenomenon of interfacial detachment. As it extends towards the axis direction of the conductive hole 110, the ceramic powder concentration gradually increases, making the coefficient of thermal expansion of the composite material gradually decrease and match the coefficient of thermal expansion of the copper layer, thereby reducing the stress accumulation during the thermal cycle and effectively preventing the generation of cracks and blowholes. It can be seen that the multi-layer circuit board provided in this embodiment simultaneously solves the problems of cracks, blowholes, and interfacial detachment that are prone to occur in the conventional plug hole process, enabling the multi-layer circuit board to simultaneously have good interfacial adhesion and coefficient of thermal expansion matching.

[0026] Specifically, the resin-ceramic composite part 200 includes a resin-ceramic column 210 and a plurality of resin-ceramic rings 220 sleeved on the outside of the resin-ceramic column 210 in sequence from the inside to the outside. In this embodiment, three resin-ceramic rings 220 are sequentially sleeved on the outside of the resin-ceramic column 210, and their sizes increase in sequence, and the proportion of resin powder continuously increases. As other optional implementation manners, the number of resin-ceramic rings 220 is four or five, which is not limited in this embodiment.

[0027] Furthermore, the conductive layer 120 includes an integrally formed conductive outer layer 121 and a conductive inner layer 122. The height of the conductive outer layer 121 is the same as the depth of the conductive hole 110, and the height of the conductive inner layer 122 is less than the height of the conductive outer layer 121, so that a connection groove 130 is formed between the conductive inner layer 122 and the hole edge of the conductive hole 110. Through the above setting, the top of the conductive layer 120 is disconnected from the resin-ceramic composite part 200, and the disconnection is limited to the top layer, while maintaining the connection between the bottom of the conductive layer 120 and the resin-ceramic composite part 200 to ensure the structural stability between the conductive layer 120 and the resin-ceramic composite part.

[0028] A resin connection part 300 is provided in the connection groove 130, and the resin connection part 300 is respectively connected to the conductive layer 120 and the resin-ceramic composite part 200. Among them, the resin connection part 300 is arranged in the connection groove 130, which helps to improve the mechanical stability between the conductive layer 120 and the resin-ceramic composite part 200. Specifically, the resin connection part 300 can be made of epoxy resin material. Epoxy resin has excellent interfacial adhesion performance, can form a stable chemical bond with the conductive layer 120 and the resin-ceramic composite part 200, and has a low coefficient of thermal expansion, and can maintain good thermal expansion matching with other materials (such as the conductive layer 120 and the resin-ceramic composite part 200) during the thermal cycle process, reducing the accumulation of thermal stress; thus, the setting of the resin connection part 300 can not only effectively avoid the interfacial detachment between the conductive layer 120 and the resin-ceramic composite part, but also reduce the stress accumulation caused by the difference in the coefficient of thermal expansion.

[0029] Embodiment 2: The hole processing method of the circuit board provided in this embodiment is used to prepare the multi-layer circuit board in Embodiment 1, and includes: As Figures 1 to 2 shown, in step S100, a circuit board body 100 is provided, a conductive hole 110 is formed in the circuit board body, and a ring-shaped conductive layer 120 is provided on the inner wall of the conductive hole 110; As Figures 3 to 7 shown, in step S200, a resin-ceramic composite part 200 is provided on the inner wall of the conductive layer 120, and the ceramic powder concentration of the resin-ceramic composite part 200 increases along the direction close to the axis of the conductive hole 110.

[0030] Specifically, for the resin-ceramic composite part 200 with the ceramic powder concentration increasing along the direction close to the axis of the conductive hole 110, the resin-ceramic composite part 200 in the area close to the inner wall of the conductive layer 120 has a higher resin content and a lower ceramic powder content. The high proportion of resin ensures excellent interfacial adhesion with the copper layer and effectively prevents interfacial detachment; as it extends along the axis direction of the conductive hole 110, the ceramic powder concentration gradually increases, so that the coefficient of thermal expansion of the composite material gradually decreases and matches the coefficient of thermal expansion of the copper layer, thereby reducing the stress accumulation during the thermal cycle process and effectively preventing the generation of cracks and blowholes. It can be seen that the hole processing method of the circuit board provided in this embodiment can simultaneously solve the problems of cracks, blowholes, and interfacial detachment that are prone to occur in the conventional plug hole process, so that after the multi-layer circuit board is processed by the hole processing method, it can simultaneously have good interfacial adhesion and coefficient of thermal expansion matching.

[0031] As an optional implementation manner, step S200 includes: Step S201: Prepare multiple groups of mixtures of resin powder and ceramic powder with different ratios, where the concentration of the ceramic powder increases sequentially in different mixtures; Step S202: Through a stencil, fill the mixture with the lowest ceramic powder concentration in the area close to the inner wall of the conductive layer; among them, the stencil has different sizes corresponding to mixtures with different ceramic powder concentrations. In step S202, the stencil has a ring structure with the largest size, which can be sleeved on the inner wall of the conductive layer. There is a gap between the ring structure with the largest size and the inner wall of the conductive layer, and this gap enables the subsequent first-layer mixture to be formed into the outermost resin-ceramic ring 220; Step S203: Mildly cure the filled first-layer mixture, and the mild curing temperature is 75 - 85 °C; the method of mild curing is not limited, and infrared heating, oven heating, etc. can be selected, as long as the first-layer mixture can be heated at the specified temperature; Step S204: Through a stencil, fill the area close to the axis direction of the conductive hole with the next group of mixtures with a higher ceramic powder concentration; among them, the stencil has different sizes corresponding to mixtures with different ceramic powder concentrations. In step S204, the size of the ring structure of the stencil gradually decreases, so as to sequentially form resin-ceramic rings 220 with continuously decreasing sizes, and finally, with a stencil without a ring structure, a resin-ceramic column 210 is obtained; Step S205: Mildly cure the newly filled mixture layer, and the mild curing temperature is 75 - 85 °C; Step S206: Repeat steps S204 to S205 to sequentially complete the filling of all mixture layers, and form a resin-ceramic composite part with the ceramic powder concentration increasing along the direction close to the axis of the conductive hole; Exemplarily, taking a three-layer structure as an example, after the first-layer mixture is mildly cured, cooperate with another stencil with the second-largest ring structure to fill the second-layer mixture (the ceramic powder concentration of the second-layer mixture decreases correspondingly) inside the first-layer mixture (the outermost resin-ceramic ring 220); after the second-layer mixture is mildly cured, cooperate with a stencil without a ring structure to fill the third-layer mixture inside the second-layer mixture (the middle resin-ceramic ring 220), and after mild curing, a resin-ceramic column 210 is obtained.

[0032] Step S207: Perform a hot pressing treatment on the filled resin-ceramic composite part. The hot pressing treatment is implemented by a double-sided hot press, and its hot pressing principle is well-known to those skilled in the art and will not be specifically elaborated in this embodiment. During the hot pressing process, the first-layer mixture (the outermost resin-ceramic ring 220) is connected to the conductive layer 120.

[0033] As another optional implementation manner, as Figure 3 shown, step S100 includes: Step S101: Perform first electroplating on the circuit board body provided with conductive holes 110 to form a conductive outer layer 121 on the inner wall of the conductive holes 110, and the height of the conductive outer layer 121 is the same as the depth of the conductive holes 110; Step S102: Perform second electroplating on the inner wall of the conductive outer layer 121 to form a conductive inner layer 122 on the inner wall of the conductive outer layer 121, obtaining a conductive layer 120; wherein, the height of the conductive inner layer 122 is less than the height of the conductive outer layer 121, so that a connection groove 130 is formed between the conductive inner layer 122 and the hole edge of the conductive hole 110; Step S200 includes: As Figures 3 to 4 shown, Step S211: Set a solvent transmission part 400 on the connection groove 130; As Figure 5 shown, Step S212: Provide a uniform mixture of resin powder and ceramic powder, and fill the uniform mixture into the conductive holes 110; Step S213: Inject cyclohexane solvent into the solvent transmission part 400, and use capillary action to make the cyclohexane solvent penetrate in the axial direction to form a solvent concentration gradient, and the solvent concentration gradient decreases along the direction close to the axis, so that the resin powder migrates in the direction away from the axis; As Figure 6 shown, Step S214: Remove the cyclohexane solvent and the solvent transmission part 400 to obtain a resin-ceramic composite part 200.

[0034] Among them, the solvent transmission part 400 is made of materials such as modified polyvinyl alcohol and polyacrylamide. Taking modified polyvinyl alcohol as an example, it has solvent transmission ability and structural stability, and has excellent water-soluble characteristics for easy subsequent removal; modified polyvinyl alcohol is formed into a ring block by means of chemical cross-linking method, extrusion molding, molding, etc., so as to be easily set on the connection groove 130. Then, injection process, impregnation process and other methods can be used to make the solvent transmission part 400 filled with cyclohexane solvent.

[0035] Exemplarily, in the first stage, when the cyclohexane solvent is released to the pore wall region through the modified polyvinyl alcohol, the solvent molecules first contact the resin powder near the pore wall. Due to the strong affinity between the resin powder and the solvent, the solvent molecules quickly infiltrate and dissolve the resin powder near the pore wall. This process follows Fick's diffusion law, and the solvent molecules diffuse from the high-concentration region to the low-concentration region. In this stage, a high-concentration region of the solvent is formed in the pore wall region, while the pore center region has not yet contacted the solvent. The surface of the resin powder particles in the pore wall region begins to dissolve, forming a colloidal layer, and the boundaries between the particles begin to blur, but no obvious flow has occurred. This stage is mainly to establish an initial solvent concentration gradient to lay the foundation for subsequent material migration.

[0036] In the second stage, as time passes, the solvent continues to penetrate radially toward the center of the pore. However, due to capillary effects and diffusion resistance, the solvent's penetration rate gradually slows, and its concentration also decreases with increasing distance. At this point, a solvent concentration gradient is formed from the pore wall to the middle area to the center area, and the solvent concentration gradient shows a downward trend. Because the solvent concentration is set in a gradient at each location, the resin powder can migrate accordingly, resulting in the phenomenon of "more outside and less inside"; In the third stage, the solvent has penetrated all areas, forming a relatively stable concentration gradient. At this point, resin redistribution is essentially complete: For example, the hole wall region (corresponding to the outermost resin-ceramic ring 220) contains 95% resin and 5% ceramic powder, ensuring good adhesion to the copper layer. The intermediate transition region (corresponding to the intermediate resin-ceramic ring 220) has a mixture ratio of approximately 75% resin and 25% ceramic. The central core region (corresponding to the resin-ceramic pillar 210) has a mixture ratio of approximately 30% resin and 70% ceramic, providing a low coefficient of thermal expansion and excellent heat dissipation. This approach differs from conventional multilayer stacking methods. The migration of the resin powder follows the principle of self-organization, spontaneously forming a continuously changing composition distribution driven by the solvent concentration gradient. This avoids the obvious interfaces and stress concentration zones that can occur with traditional multilayer filling, thereby improving the overall performance and reliability of the filling structure. Furthermore, the process allows for a single-step molding process without repeated operations.

[0037] Specifically, the process of removing the cyclohexane solvent includes: Step S221: placing the processed circuit board body 100 in a volatile environment for 2 to 4 hours; Step S222, slowly raising the temperature to 55-65°C and maintaining it for 1-2 hours; Step S223 , placing the circuit board body 100 in a vacuum environment (20-30 Pa) and maintaining the temperature at 40-50° C. for 30-60 minutes.

[0038] Specifically, the material of the solvent transmission part 400 is modified polyvinyl alcohol; The process of removing the solvent transfer part 400 includes: Step S231: Soak the circuit board body 100 in deionized water at 35-45° C. and gently stir to promote the dissolution of the modified polyvinyl alcohol; Step S232: rinse the circuit board multiple times with deionized water at a temperature of 40-50°C; Step S233: Place the cleaned circuit board in an oven or blow dry it with nitrogen gas for drying.

[0039] It should be added that, Figure 7 As shown, step S200 also includes: Step S215: After the resin-ceramic composite part 200 is formed and the solvent transmission part 400 is removed, a resin connection part 300 is arranged in the connection groove 130. Specifically, the resin connection part 300 can be formed by injection and curing of epoxy resin. The above-mentioned forming method is well-known to those skilled in the art and will not be specifically elaborated in this embodiment.

[0040] As mentioned above, the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A multilayer circuit board, characterized in that, It includes a circuit board body (100), and a conductive hole (110) is formed on the circuit board body (100), and an annular conductive layer (120) is provided on the inner wall of the conductive hole (110); Wherein, a resin-ceramic composite part (200) is arranged on the inner wall of the conductive layer (120), and the resin-ceramic composite part (200) fills the inner ring surface of the conductive layer (120); the ceramic powder concentration of the resin-ceramic composite part (200) increases along the direction close to the axis of the conductive hole (110).

2. The multilayer circuit board according to claim 1, characterized in that, The resin-ceramic composite part (200) includes a resin-ceramic column (210) and a plurality of resin-ceramic rings (220) sleeved outside the resin-ceramic column (210) in sequence from inside to outside.

3. A multi-layer circuit board according to claim 1, characterized in that, The conductive layer (120) includes an integrally formed conductive outer layer (121) and a conductive inner layer (122), the height of the conductive outer layer (121) is the same as the depth of the conductive hole (110), and the height of the conductive inner layer (122) is less than the height of the conductive outer layer (121), so that a connection groove (130) is formed between the conductive inner layer (122) and the hole edge of the conductive hole (110).

4. A multi-layer circuit board according to claim 3, characterized in that, A resin connection part (300) is arranged in the connection groove (130), and the resin connection part (300) is respectively connected with the conductive layer (120) and the resin-ceramic composite part (200).

5. A method for hole processing of a circuit board, characterized in that, For preparing the multi-layer circuit board according to any one of claims 1-4, including:[[]] Step S100: Provide a circuit board body, a conductive hole is formed on the circuit board body, and an annular conductive layer is provided on the inner wall of the conductive hole; Step S200: Arrange a resin-ceramic composite part on the inner wall of the conductive layer, and the ceramic powder concentration of the resin-ceramic composite part increases along the direction close to the axis of the conductive hole.

6. The hole processing method of a circuit board according to claim 5, wherein, The step S200 includes:[[]] Step S201: Prepare mixtures of resin powder and ceramic powder with multiple different ratios, wherein the concentration of ceramic powder increases sequentially in different mixtures; Step S202: Through a stencil, fill the mixture with the lowest ceramic powder concentration in the area close to the inner wall of the conductive layer; Step S203: Mildly cure the first filled mixture, and the mild curing temperature is 75-85 °C; Step S204: Through a stencil, fill the area close to the axis direction of the conductive hole with the next group of mixtures with a higher ceramic powder concentration; Step S205: Mildly cure the newly filled mixture layer, and the mild curing temperature is 75-85 °C; Step S206: Repeat steps S204 to S205 to complete the filling of all mixture layers in sequence, and form a resin-ceramic composite part with the ceramic powder concentration increasing along the direction close to the axis of the conductive hole; Step S207: Perform hot pressing treatment on the completed filled resin-ceramic composite part.

7. A method for hole processing of a circuit board according to claim 5, characterized in that, The step S100 includes:[[]] Step S101: Perform the first electroplating on the circuit board body provided with the conductive hole, and form a conductive outer layer on the inner wall of the conductive hole, and the height of the conductive outer layer is the same as the depth of the conductive hole; Step S102: Perform second electroplating on the inner wall of the conductive outer layer to form a conductive inner layer on the inner wall of the conductive outer layer, thereby obtaining a conductive layer; wherein, the height of the conductive inner layer is less than that of the conductive outer layer, so as to form a connection groove between the conductive inner layer and the hole edge of the conductive hole. The step S200 includes: Step S211: Set a solvent transmission part on the connection groove; Step S212: Provide a uniform mixture of resin powder and ceramic powder, and fill the uniform mixture into the conductive hole; Step S213: Inject cyclohexane solvent into the solvent transmission part, and utilize capillary action to make the cyclohexane solvent penetrate in the axial direction to form a solvent concentration gradient, which decreases along the direction close to the axis, so that the resin powder migrates away from the axis; Step S214: Remove the cyclohexane solvent and the solvent transmission part to obtain a resin-ceramic composite part.

8. A method for hole processing of a circuit board according to claim 7, characterized in that, The process of removing the cyclohexane solvent includes: Step S221: Place the processed circuit board body in a volatile environment for 2 - 4 h; Step S222: Slowly raise the temperature to 55 - 65 °C and maintain it for 1 - 2 h; Step S223: Place the circuit board body in a vacuum environment and maintain the temperature at 40 - 50 °C for 30 - 60 min.

9. A method for hole processing of a circuit board according to claim 7, characterized in that, The material of the solvent transmission part is modified polyvinyl alcohol; The process of removing the solvent transmission part includes: Step S231: Immerse the circuit board body in deionized water at 35 - 45 °C and stir gently to promote the dissolution of the modified polyvinyl alcohol; Step S232: Rinse the circuit board with deionized water at 40 - 50 °C for multiple times; Step S233: Place the cleaned circuit board in an oven or dry it with nitrogen for drying treatment.

10. A method for hole processing of a circuit board according to claim 7, characterized in that, The step S200 further includes: Step S215: After the resin-ceramic composite part is formed and the solvent transmission part is removed, set a resin connection part in the connection groove.

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