Printed circuit board and preparation method thereof

Abstract

The invention discloses a printed circuit board and a preparation method thereof, and the method comprises the steps: forming a bottom conductor layer and a surface transmission structure of a first micro-coaxial transmission structure on a first surface of a circuit substrate, forming an inner conductor, a support body and a side wall conductor layer on the bottom conductor layer, and forming a conductive connector for connecting the inner conductor with a first signal transmission line. And finally, forming a top cover conductor layer on the side wall conductor layer to obtain the printed circuit board integrated with the first micro coaxial transmission structure. Compared with the prior art, the micro-coaxial transmission structure is directly formed on the circuit substrate of the printed circuit board, so that the operation of stripping the micro-coaxial transmission structure from the substrate and integrating the micro-coaxial transmission structure on the printed circuit board through processes of surface mounting, embedding and the like is omitted, the process complexity and cost are reduced, the processing efficiency is improved, and the production cost is reduced. And meanwhile, the micro coaxial transmission structure is prevented from being damaged and the function of the micro coaxial transmission structure is prevented from being reduced in stripping, integration and other processes, link loss and crosstalk are reduced when high-speed signals are transmitted through a printed circuit board, and the transmission quality of the signals is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of integrated design of printed circuit boards and high-frequency and high-speed rectangular cavity microtransmission structures, and particularly relates to a printed circuit board and a preparation method thereof. Background Art

[0002] With the continuous increase in the signal transmission rate of high-speed interconnection links, as the carrier of devices and signal transmission, the signal integrity of printed circuit boards has an increasingly prominent impact on the electrical performance of communication systems.

[0003] In order to achieve high-frequency and high-speed signal transmission, high-frequency and high-speed rectangular cavity microtransmission structures are commonly used in printed circuit boards. To apply this high-frequency and high-speed rectangular cavity microtransmission structure, it is necessary to first process an array of rectangular cavity microtransmission structures on a substrate. After cutting the substrate, the rectangular cavity microtransmission structures are peeled off from the substrate and integrated into the printed circuit board by means of surface mounting or embedding. The process is complex, the processing efficiency is low, and the production operation is difficult. Moreover, during the processes of cutting, peeling, surface mounting, or embedding, it is very easy to cause damage and functional degradation of the rectangular cavity microtransmission structures, resulting in link loss and crosstalk when high-speed signals are transmitted through the printed circuit board, and the transmission quality is poor. Summary of the Invention

[0004] The present application provides a printed circuit board and a preparation method thereof to solve the technical problems of complex process, low processing efficiency, and difficulty in ensuring signal transmission quality after integration when processing high-frequency and high-speed rectangular cavity microtransmission structures on printed circuit boards using existing processes.

[0005] In view of the above problems, the present application is proposed to provide a printed circuit board and a preparation method thereof that overcome the above problems or at least partially solve the above problems.

[0006] In a first aspect, a preparation method of a printed circuit board is provided. The printed circuit board includes a circuit substrate and a first microcoaxial transmission structure disposed on a first surface of the circuit substrate. The first microcoaxial transmission structure includes: an outer conductor, an inner conductor, and a support. The outer conductor includes a bottom conductor layer, a sidewall conductor layer, and a top cover conductor layer. The bottom conductor layer, the sidewall conductor layer, and the top cover conductor layer form a cavity surrounding the inner conductor. The support is disposed between the inner conductor and the bottom conductor layer for supporting the inner conductor. The method includes:

[0007] Providing a circuit substrate of the printed circuit board;

[0008] Forming a bottom conductor layer and a surface transmission structure on the first surface of the circuit substrate. The surface transmission structure includes a first signal transmission line, and the first signal transmission line is insulated from the bottom conductor layer;

[0009] Form an inner conductor, a support, a sidewall conductor layer on the bottom conductor layer, and form a conductive joint connecting the inner conductor and the first signal transmission line;

[0010] Form a top cover conductor layer on the sidewall conductor layer to obtain a printed circuit board integrated with a first micro coaxial transmission structure.

[0011] Optionally, forming an inner conductor, a support, a sidewall conductor layer, and a conductive joint connecting the inner conductor and the first signal transmission line on the bottom conductor layer includes:

[0012] Form a first conductor sub-layer on the bottom conductor layer, and form a first conductive segment on the first signal transmission line. The first conductive segment is electrically connected to the first signal transmission line and is insulated from the first conductor sub-layer;

[0013] Form a support on the first conductor sub-layer;

[0014] Form a second conductor sub-layer on the first conductor sub-layer, and form a second conductive segment on the first conductive segment. The second conductive segment is electrically connected to the first conductive segment and is insulated from the second conductor sub-layer;

[0015] Form an inner conductor and a third conductor sub-layer on the support, and form a third conductive segment on the second conductive segment; the third conductive segment is electrically connected to the second conductive segment and the inner conductor and is insulated from the third conductor sub-layer. The first conductor sub-layer, the second conductor sub-layer, and the third conductor sub-layer constitute the sidewall conductor layer, and the first conductive segment, the second conductive segment, and the third conductive segment constitute the conductive joint.

[0016] Optionally, a metal layer is provided on the first surface of the circuit board. Forming a bottom conductor layer and a surface transmission structure on the first surface of the circuit board includes:

[0017] Etch the metal layer to form the bottom conductor layer and the surface transmission structure.

[0018] Optionally, the first surface of the circuit board is an insulating surface. Forming a bottom conductor layer and a surface transmission structure on the first surface of the circuit board includes:

[0019] Form a photoresist layer on the first surface of the circuit board;

[0020] By patterning the photoresist layer, form a first patterned window corresponding to the pattern of the bottom conductor layer and a second patterned window corresponding to the pattern of the surface transmission structure in the photoresist layer;

[0021] Deposit a metal material layer on the photoresist layer having the first patterned window and the second patterned window. The metal material layer covers the partial area of the first surface exposed from the first patterned window and the second patterned window and the photoresist layer;

[0022] Abrade the metal material layer until the photoresist layer is exposed;

[0023] Remove the photoresist layer.

[0024] Optionally, before or after forming the bottom conductor layer and the surface transmission structure on the first surface of the circuit board, the method further includes:

[0025] Provide a temporary carrier board;

[0026] Bond the temporary carrier board to the second surface of the circuit board, the second surface being opposite to the first surface;

[0027] After obtaining the printed circuit board integrated with the first micro coaxial transmission structure, the method further includes:

[0028] Separate the temporary carrier board from the second surface of the circuit board.

[0029] Optionally, the printed circuit board further includes a second micro coaxial transmission structure disposed on the second surface of the circuit board, the second surface being opposite to the first surface;

[0030] After obtaining the printed circuit board integrated with the first micro coaxial transmission structure, it further includes:

[0031] Form a second micro coaxial transmission structure on the second surface of the circuit board to obtain a printed circuit board integrated with the first micro coaxial transmission structure and the second micro coaxial transmission structure.

[0032] Optionally, the first signal transmission line includes a first pad and a first planar transmission line, and the first planar transmission line is electrically connected to the first pad; forming a conductive joint connecting the inner conductor and the first signal transmission line includes:

[0033] Form a conductive joint connecting the inner conductor and the first pad on the first pad, or

[0034] Form a conductive joint connecting the inner conductor and the first planar transmission line on the first planar transmission line.

[0035] Optionally, the surface transmission structure further includes a second signal transmission line, the second signal transmission line includes a second pad and a second planar transmission line, the second pad is electrically connected to the second planar transmission line and is insulated from the first pad, and before forming the inner conductor, the support, the sidewall conductor layer, and the conductive joint connecting the inner conductor and the first signal transmission line on the bottom conductor layer, the method further includes:

[0036] Form a solder mask layer on the first surface formed with the bottom conductor layer and the surface transmission structure, and the solder mask layer exposes the first pad, the second pad, the bottom conductor layer, and the connection end of the first planar transmission line and the conductive joint.

[0037] Optionally, the surface transmission structure further includes a grounding line, which is electrically connected to the bottom conductor layer.

[0038] In a second aspect, an embodiment of the present application further provides a printed circuit board prepared by the method of the first aspect. The printed circuit board includes:

[0039] A circuit substrate;

[0040] A surface transmission structure disposed at least on a first surface of the circuit substrate. The surface transmission structure includes a first signal transmission line;

[0041] A micro coaxial transmission structure disposed at least on the first surface of the circuit substrate. The micro coaxial transmission structure includes: an outer conductor, an inner conductor, and a support. The outer conductor includes a bottom conductor layer, a sidewall conductor layer, and a top cover conductor layer. The bottom conductor layer, the sidewall conductor layer, and the top cover conductor layer form a cavity surrounding the inner conductor. The support is disposed between the inner conductor and the bottom conductor layer for supporting the inner conductor. Among them, the bottom conductor layer is in contact with the first surface of the circuit substrate, the outer conductor is insulated from the first signal transmission line, and the inner conductor is electrically connected to the first signal transmission line

[0042] The technical solution provided by the present application has at least the following technical effects or advantages:

[0043] For the printed circuit board and its manufacturing method provided by the present application, by forming the bottom conductor layer of the first micro coaxial transmission structure and the surface transmission structure on the first surface of the circuit substrate, then forming the inner conductor, the support, the sidewall conductor layer, and a conductive joint connecting the inner conductor and the first signal transmission line on the bottom conductor layer, and finally forming the top cover conductor layer on the sidewall conductor layer, a printed circuit board integrated with the first micro coaxial transmission structure is obtained. The present application directly forms the micro coaxial transmission structure on the circuit substrate of the printed circuit board. Compared with the prior art, it saves the operations of peeling the micro coaxial transmission structure from the substrate and then integrating it into the printed circuit board through processes such as surface mounting and embedding, reduces the process complexity and cost, improves the processing efficiency, and at the same time avoids damage and functional degradation of the micro coaxial transmission structure during processes such as peeling and integration, reduces the link loss and crosstalk when high-speed signals are transmitted through the printed circuit board, and improves the signal transmission quality.

[0044] The above description is only an overview of the technical solution of the present application. In order to be able to understand the technical means of the present application more clearly, it can be implemented according to the content of the specification. And in order to make the above and other purposes, features, and advantages of the present application more obvious and understandable, the specific embodiments of the present application are specifically given below. Description of the Drawings

[0045] Upon reading the following detailed description of the preferred embodiments, various other advantages and benefits will become clear to those of ordinary skill in the art. The accompanying drawings are only for the purpose of illustrating the preferred embodiments and are not considered to be a limitation of the present application. Moreover, throughout the drawings, the same reference numerals are used to represent the same components. In the drawings:

[0046] Figure 1 is the cross-sectional structure of the printed circuit board in the embodiment of the present application Figure 1 ;

[0047] Figure 2 is the flowchart of the method for preparing the printed circuit board in the embodiment of the present application;

[0048] Figure 3 is the cross-sectional structure of the printed circuit board in the embodiment of the present application Figure 2 ;

[0049] Figure 4 is the process diagram of the preparation of the bottom conductor layer in the embodiment of the present application;

[0050] Figure 5 is the process diagram of the preparation of the first micro coaxial transmission structure in the embodiment of the present application;

[0051] Figure 6 is the schematic diagram of the differential structure micro coaxial transmission structure in the embodiment of the present application;

[0052] Figure 7 is the example diagram of the preparation of the printed circuit board using a temporary carrier in the embodiment of the present application;

[0053] Figure 8 is the schematic diagram of processing the micro coaxial transmission structure on both sides of the circuit substrate in the embodiment of the present application;

[0054] Figure 9 is the schematic diagram of two inner conductor structures of the micro coaxial transmission structure in the embodiment of the present application;

[0055] Figure 10 is the schematic diagram of the planar transmission structure and the high-frequency and high-speed rectangular cavity micro transmission structure in the embodiment of the present application;

[0056] Figure 11 is the bonding schematic diagram of a temporary carrier and a circuit substrate provided by the embodiment of the present application;

[0057] Figure 12 is another bonding schematic diagram of a temporary carrier and a circuit substrate provided by the embodiment of the present application;

[0058] Figure 13 is the schematic diagram of processing the micro coaxial transmission structure on the bottom metal layer provided by the embodiment of the present application;

[0059] Figure 14 Another schematic diagram of a micro coaxial transmission structure processed on the bottom metal layer provided by an embodiment of the present application;

[0060] Figure 15 A schematic diagram of an integrated structure of a printed circuit board and a high-frequency and high-speed interconnection transmission line prepared by using the method provided by an embodiment of the present application. Detailed implementation manners

[0061] Exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings.

[0062] Schematic diagrams of various structures according to embodiments of the present application are shown in the accompanying drawings. These figures are not drawn to scale, and for the purpose of clear expression, some details are enlarged and some details may be omitted. The shapes of various regions and layers shown in the figures, as well as their relative sizes and positional relationships, are merely exemplary. In practice, there may be deviations due to manufacturing tolerances or technical limitations, and those skilled in the art can design regions / layers with different shapes, sizes, and relative positions according to actual needs.

[0063] In order to facilitate a clear description of the technical solutions of the embodiments of the present application, in the embodiments of the present application, terms such as "first" and "second" are used to distinguish identical or similar items with basically the same functions and effects. For example, the first value and the second value are only used to distinguish different values, and do not limit their order. Those skilled in the art can understand that terms such as "first" and "second" do not limit the quantity and execution order, and "first", "second", etc. do not necessarily mean different.

[0064] It should be noted that in the present application, words such as "exemplary" or "for example" are used to represent examples, illustrations, or explanations. Any embodiment or design solution described as "exemplary" or "for example" in the present application should not be construed as being more preferred or having more advantages than other embodiments or design solutions. Rather, the use of words such as "exemplary" or "for example" is intended to present related concepts in a specific manner.

[0065] In this application, "at least one" means one or more, and "a plurality" means two or more. "And / or" describes the association relationship of associated objects and indicates that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone, where A and B can be singular or plural. The character " / " generally indicates that the associated objects before and after are in an "or" relationship. "At least one (item)" or its similar expression refers to any combination of these items, including any combination of single item(s) or plural item(s). For example, at least one (item) of a, b, or c can represent: a, b, c, a - b, a - c, b - c, or a - b - c, where a, b, and c can be single or multiple.

[0066] In the context of the present disclosure, when a layer / component is referred to as being "on" another layer / component, the layer / component can be directly on the other layer / component, or there can be an intermediate layer / component between them. Additionally, if a layer / component is "on" another layer / component in one orientation, then when the orientation is reversed, the layer / component can be "under" the other layer / component. In the context of the present disclosure, similar or identical components may be represented by the same or similar reference numerals.

[0067] To better understand the above technical solutions, the above technical solutions will be described in detail below in conjunction with specific embodiments. It should be understood that the embodiments of the present disclosure content and the specific features in the embodiments are detailed descriptions of the technical solutions of the present application, rather than limitations on the technical solutions of the present application. Without conflict, the technical features in the embodiments of the present application and the embodiments can be combined with each other.

[0068] With the continuous increase in the signal transmission rate of high-speed interconnect links, as the carrier of devices and signal transmission, the signal integrity of printed circuit boards has an increasingly prominent impact on the electrical performance of communication systems. Especially with the rapid development and large-scale commercialization of technologies such as the Internet of Things, big data, artificial intelligence, and 5G communication, the monitoring of the insertion loss of printed circuit boards is an important indicator for the research and development of high-speed products and mass production control.

[0069] Traditional planar transmission line structures, such as microstrip lines, striplines, coplanar waveguides, etc., are highly dependent on the materials of printed circuit board substrates; while waveguide structures, due to their high-pass transmission characteristics, can only be applicable to a certain specific frequency band and are unable to handle the interconnection of high-speed signals. For high-frequency and high-speed printed circuit boards, when designing, it is necessary to consider whether the material selection and design meet the signal integrity requirements, which requires minimizing the signal transmission loss as much as possible. The transmission loss of printed circuit boards mainly consists of three parts: dielectric loss, conductor loss, and radiation loss. The mainstream in the development of high-frequency and high-speed printed circuit boards is to use a certain type of resin.

[0070] In the current market, a certain type of high-frequency and high-speed board can only be competent for a certain characteristic frequency band. Moreover, the resin-based substrate has poor long-term stability and serious aging at high temperatures. At high frequencies, the insertion loss is large, resulting in a serious deterioration of signal quality and even causing the system to malfunction.

[0071] Therefore, there is an urgent need for a new type of high-frequency and high-speed transmission interconnection structure and architecture to relieve the pressure on the transmission performance of high-frequency and high-speed boards, so as to achieve a high-frequency, high-bandwidth, low-loss, and high-integration high-frequency and high-speed electrical interconnection structure.

[0072] The high-frequency and high-speed rectangular cavity microtransmission structure in the prior art needs to be processed on a silicon substrate / / other carrier boards. After cutting and peeling, it is integrated onto the circuit board by means of surface mounting or embedding. The method of using such a high-frequency and high-speed rectangular cavity microtransmission structure as an independent device and then surface mounting it on a printed circuit board has a complex process and a low yield, and cannot adapt to large-scale production.

[0073] In view of this, the embodiments of the present application provide a printed circuit board and a preparation method thereof. Figure 1 For the structural diagram of the printed circuit board in the embodiments of the present application, as Figure 1 shown, the printed circuit board provided by some embodiments of the present application may include a circuit substrate 100 and a first micro coaxial transmission structure 200 disposed on the first surface of the circuit substrate 100. The first micro coaxial transmission structure 200 includes: an outer conductor 201, an inner conductor 202, and a support 203. The outer conductor includes a bottom conductor layer 2011, a sidewall conductor layer 2012, and a top cover conductor layer 2013. The bottom conductor layer 2011, the sidewall conductor layer 2012, and the top cover conductor layer 2013 form a cavity surrounding the inner conductor 202. The support 203 is disposed between the inner conductor 202 and the bottom conductor layer 2011 for supporting the inner conductor 202.

[0074] Figure 2 For the flowchart of the preparation method of the printed circuit board provided by the embodiments of the present application, please refer to Figure 2 . This method at least includes the following steps S201 to step S204.

[0075] Step S201, provide the circuit substrate 100 of the printed circuit board.

[0076] In the operation of step S201, the circuit substrate 100 includes at least one insulating dielectric layer and at least one transmission layer, and vias connecting the functions of the upper and lower layers; the insulating dielectric layer and the transmission line layer are alternately arranged. A metal layer may be provided on the first surface of the circuit substrate 100, or it may also be an insulating surface.

[0077] Step S202: Form a bottom conductor layer 2011 and a surface transmission structure on the first surface of the circuit board 100. The surface transmission structure includes a first signal transmission line, and the first signal transmission line is insulated from the bottom conductor layer 2011.

[0078] The surface transmission structure is located on the first surface of the circuit board 100 and undertakes the wiring and connection tasks to ensure that signals can be transmitted accurately. The processing methods of the bottom conductor layer 2011 and the surface transmission structure include etching and electroplating.

[0079] In some examples, if a metal layer is provided on the first surface of the circuit board 100, during the operation of step S202, the metal layer is etched to form the bottom conductor layer 2011 and the surface transmission structure. The etching can adopt wet etching (acid etching, alkaline etching), laser etching, plasma etching, reactive ion etching (RIE), inductively coupled plasma etching (ICP), drilling etching, mechanical etching, electric spark etching and other processes, which are not limited here.

[0080] In other examples, if the first surface of the circuit board 100 is an insulating surface, the operation of step S202 specifically includes the following three steps:

[0081] The first step: Form a photoresist layer on the first surface of the circuit board 100.

[0082] The second step: By patterning the photoresist layer, a first patterned window corresponding to the pattern of the bottom conductor layer 2011 and a second patterned window corresponding to the pattern of the surface transmission structure are formed in the photoresist layer.

[0083] The third step: Deposit a metal material layer on the photoresist layer with the first patterned window and the second patterned window. The metal material layer covers the partial areas of the first surface exposed from the first patterned window and the second patterned window and the photoresist layer.

[0084] The fourth step: Grind the metal material layer until the photoresist layer is exposed.

[0085] The fifth step: Remove the photoresist layer, and thus the bottom conductor layer 2011 and the surface transmission structure formed on the first surface of the circuit board 100 are obtained.

[0086] For example, the damascene process can be used to form a copper metal layer in the first patterned window and the second patterned window, and then the chemical mechanical polishing process is used to process the surface of the copper metal layer to expose the photoresist layer and flatten the surface of the copper metal layer, so as to obtain accurate patterns of the bottom conductor layer 2011 and the surface transmission structure.

[0087] It can be understood that the second graphical window includes a window corresponding to the first signal transmission line. Since the first signal transmission line and the bottom conductor layer 2011 are insulated from each other, there is a gap between the window corresponding to the first signal transmission line and the first graphical window.

[0088] Step S203: Form an inner conductor 202, a support 203, a sidewall conductor layer 2012 on the bottom conductor layer 2011, and form a conductive joint 304 connecting the inner conductor 202 and the first signal transmission line.

[0089] As Figure 3 shown, the sidewall conductor layer 2012 includes a first conductor sub-layer 301, a second conductor sub-layer 302, and a third conductor sub-layer 303, and the conductive joint 304 includes a first conductive segment 3041, a second conductive segment 3042, and a third conductive segment 3043. The operations in step S203 specifically include the following operations:

[0090] The first step is to form a first conductor sub-layer on the bottom conductor layer 2011 and form a first conductive segment on the first signal transmission line. The first conductive segment is electrically connected to the first signal transmission line and is insulated from the first conductor sub-layer.

[0091] Exemplarily, as Figure 4 shown in, on the surface of the circuit board 100 where the first signal transmission line 401 and the bottom conductor layer 2011 have been processed as shown in (a) figure, spin-coat the photosensitive dry film 402 as shown in (b) figure, perform exposure and development processing on the photosensitive dry film 402 to obtain the first circuit groove 403 and the second circuit groove 404 as shown in (c) figure. The bottom conductor layer 2011 is exposed in the first circuit groove 403, and a part of the first signal transmission line is exposed in the second circuit groove 404.

[0092] Deposit a seed layer on the photosensitive dry film 402 having the first circuit groove 403 and the second circuit groove 404. The seed layer covers the photosensitive dry film 402, the bottom conductor layer 2011, and the first signal transmission line exposed from the first circuit groove 403 and the second circuit groove 404. Use the damascene process to form a metal material layer 405 as shown in (d) figure on the seed layer.

[0093] Use a mechanical research process to grind the metal material layer 405 until the photosensitive dry film 402 is exposed, obtaining the first conductor sub-layer 301 and the first conductive segment 3041 as shown in (e) figure. It can be seen that the first conductor sub-layer 301 is electrically connected to the bottom conductor layer 2011, and the first conductive segment 3041 is electrically connected to the first signal transmission line 401.

[0094] It can be understood that the bottom conductor layer 2011 is arranged along the extending direction of the first micro coaxial transmission structure 200. The first line groove 403 is composed of two grooves arranged along the extending direction of the bottom conductor layer 2011. The first conductor sub-layer 301 is composed of two convex ribs arranged along the extending direction of the bottom conductor layer 2011, and these two convex ribs cover the two side edges of the bottom conductor layer 2011.

[0095] Second, form a support 203 on the first conductor sub-layer.

[0096] The specific forming process of the support 203 generally includes: spin-coating an insulating material layer on the surface of the circuit board 100 on which the first conductor sub-layer has been processed, and patterning the insulating material layer to form the support 203 as shown in (a) of Figure 5 Figure, which is used to support the metal inner conductor 202. The two ends of the support 203 are supported by the inner sides of the two convex ribs of the first conductor sub-layer 301.

[0097] Third, form a second conductor sub-layer on the first conductor sub-layer, and form a second conductive segment on the first conductive segment.

[0098] Referring to the operation in the first step, obtain the second conductor sub-layer 302 and the second conductive segment 3042 as shown in (b) of Figure 5 Figure. The second conductor sub-layer 302 is located on both sides of the support 203 and is electrically connected to the first conductor sub-layer 301. The second conductive segment 3042 is electrically connected to the first conductive segment 3041 and is insulated from the second conductor sub-layer 302.

[0099] Fourth, form an inner conductor 202 and a third conductor sub-layer on the support 203, and form a third conductive segment on the second conductive segment.

[0100] Similarly referring to the operation in the first step, obtain the inner conductor 202, the third conductor sub-layer 303 and the third conductive segment 3043 as shown in (c) of Figure 5 Figure. The inner conductor 202 is located in the middle of the support 203. The third conductor sub-layer 303 is located on both sides of the inner conductor 202 and is electrically connected to the second conductor sub-layer 302. The third conductive segment 3043 is electrically connected to the second conductive segment 3042 and the inner conductor 202 and is insulated from the third conductor sub-layer 303.

[0101] It can be understood that the first conductor sub-layer 301, the second conductor sub-layer 302 and the third conductor sub-layer 303 constitute the sidewall conductor layer 2012 as shown in Figure 3 Figure, and the first conductive segment 3041, the second conductive segment 3042 and the third conductive segment 3043 constitute the conductive joint 304.

[0102] It should be noted that, for the convenience of clearly showing the connection relationship between the third conductive segment 3043 and the inner conductor 202, in Figure 5 in figure (c) of Figure 5 , the third conductive segment 3043 obscures part of the third conductor sub-layer 303. The overall structure of the third conductor sub-layer 303 is actually two convex ribs covering the second conductor sub-layer 302. Figure 5 (c) does not limit the relative position of the conductive joint 304 formed by the first conductive segment 3041, the second conductive segment 3042, and the third conductive segment 3043 with respect to the first micro coaxial transmission structure 200. In actual operation, the conductive joint 304 can be positioned at a suitable location that can conduct the first signal transmission line 401 and the inner conductor 202 of the first micro coaxial transmission structure 200 according to actual requirements.

[0103] Step S204: Form a top cover conductor layer 2013 on the sidewall conductor layer 2012 to obtain a printed circuit board integrated with the first micro coaxial transmission structure 200.

[0104] Similarly referring to the operation of the first step, the top cover conductor layer 2013 as shown in Figure 2 is obtained. It can be understood that the top cover conductor layer 2013 has two layers. The first layer is the part located on the third conductor sub-layer 303, and the second layer is the topmost part.

[0105] The inner conductor 202 of the first micro coaxial transmission structure 200 has various types. Only one of them is given in the above embodiments. In some other embodiments, the inner conductor 202 of the first micro coaxial transmission structure 200 can also be a differential transmission structure as shown in Figure 6 . The inner conductor 202 of this structure includes two mutually insulated sub-conductors 601, and the support 203 is supported at the lower ends of the two sub-conductors 601. Thus, the manufacturing process of the inner conductor of the differential transmission structure and the support 203 is: first form the support 203, and then form two sub-conductors 601 on the support 203. The specific process can be the same as the process used in the above embodiments.

[0106] The support 203 can also pass through the two sub-conductors 601 in sequence to support the two sub-conductors 601. Thus, in the operation of the above step S203, the manufacturing process of the inner conductor of the differential transmission structure and the support 203 is: first form the lower half of the two sub-conductors 601, then form the support 203, and then form the upper half of the two sub-conductors 601. The specific process can be the same as the process used in the above embodiments.

[0107] In the method for preparing the circuit board 100 provided in the above embodiments, a temporary carrier plate can be further used for fixation to facilitate subsequent processing operations. Therefore, in some other alternative embodiments, before or after the operation of step S202, the method further includes:

[0108] Provide a temporary carrier 701; Figure 7 As shown, the temporary carrier 701 is bonded to the second surface of the circuit substrate 100, and the second surface is arranged opposite to the first surface. After the operation of step S204, the temporary carrier 701 is further separated from the second surface of the circuit substrate 100.

[0109] The materials of the temporary carrier 701 include glass, stainless steel, copper plate, etc. Before bonding with the circuit substrate 100, the surface of the temporary carrier 701 is degreased and plasma dry-treated, and a layer of photosensitive dry film is spin-coated on the surface of the temporary carrier 701 as a temporary bonding adhesive. The first surface of the circuit substrate 100 is fixed on the temporary carrier 701 through the bonding adhesive.

[0110] It is understood that the temporary bonding adhesive can be subsequently debonded by chemical, optical, etc. If the mechanical support of the printed circuit board itself is sufficient, the temporary carrier board 701 may not be required.

[0111] In some optional embodiments, after obtaining the printed circuit board integrated with the first micro-coaxial transmission structure 200, the method further includes:

[0112] On the second surface of the circuit substrate 100, a Figure 8 The second micro-coaxial transmission structure 801 shown is a printed circuit board integrated with the first micro-coaxial transmission structure 200 and the second micro-coaxial transmission structure.

[0113] If the printed circuit board needs to be processed with an integrated high-frequency and high-speed rectangular cavity micro-transmission structure on both sides, then after the operation of the above-mentioned step S204, the temporary carrier is temporarily bonded to one side of the first surface of the circuit substrate 100 to process the surface transmission structure and the micro-coaxial transmission structure on the second surface of the circuit substrate 100.

[0114] In some optional embodiments, the first planar transmission line is conductively connected to the first pad, and the first pad is connected to the first planar transmission line; forming a conductive joint 304 connecting the inner conductor 202 and the first signal transmission line in step S203 includes:

[0115] A conductive joint 304 is formed on the first pad to connect the inner conductor 202 and the first pad, or

[0116] A conductive joint 304 is formed on the first planar transmission line to connect the inner conductor 202 and the first planar transmission line.

[0117] In some optional embodiments, the surface transmission structure further includes a grounding line, which is conductively connected to the bottom conductor layer 2011 .

[0118] In some alternative embodiments, the surface transmission structure further includes a second signal transmission line, and the second signal transmission line includes a second pad and a second planar transmission line. The second pad is electrically connected to the second planar transmission line and is insulated from the first pad. Before the operation of step S203, the method further includes:

[0119] A solder mask layer is formed on the first surface of the bottom conductor layer 2011 and the surface transmission structure, and the solder mask layer exposes the first pad, the second pad, the bottom conductor layer 2011, and the connection end of the first planar transmission line and the conductive joint.

[0120] In this way, most of the circuit board except for some pads is covered by the solder mask layer, which will not cause damage to the board material and metal of the circuit board 100.

[0121] In summary, in the present application, the micro coaxial transmission structure is directly formed on the circuit board of the printed circuit board. Compared with the prior art, it saves the operations of peeling the micro coaxial transmission structure from the substrate and then integrating it into the printed circuit board through processes such as surface mounting and embedding, reduces the process complexity and cost, improves the processing efficiency, and at the same time avoids damage and function degradation of the micro coaxial transmission structure during processes such as peeling and integration, reduces the link loss and crosstalk when high-speed signals are transmitted through the printed circuit board, and improves the signal transmission quality.

[0122] Next, in conjunction with Figures 9 to 15 , the preparation method of the printed circuit board provided by the embodiments of the present application is introduced on how to be applied to the integration of the high-frequency and high-speed rectangular cavity micro transmission structure and the printed circuit board to solve the technical problems existing in the processing of the high-frequency and high-speed rectangular cavity micro transmission structure on the printed circuit board by the existing process, such as complex process, low processing efficiency, and difficulty in ensuring signal transmission quality after integration.

[0123] In the prior art, to integrate the high-frequency and high-speed rectangular cavity micro transmission structure with the printed circuit board, it is necessary to completely peel the high-frequency and high-speed rectangular cavity micro transmission processed by silicon-based / plate-level precision from the silicon wafer or the board-level substrate. However, due to the tiny features of the high-frequency and high-speed rectangular cavity micro transmission, its handling and surface mounting still require extra care; the thermal stress introduced by the inconsistent thermal expansion coefficients of the high-frequency and high-speed rectangular cavity micro transmission and the printed circuit board substrate during the reflow temperature, the mechanical impact on the micro structure by the substrate cleaning process after surface mounting, the removal of residues trapped in the high-frequency and high-speed rectangular cavity micro transmission structure, and uncertain factors such as the alignment of precision devices result in complex processes, low processing efficiency, and difficulty in ensuring signal transmission quality after integration.

[0124] Next, how to integrally integrate the high-frequency and high-speed rectangular cavity micro transmission structure with the printed circuit board by using the method provided by the embodiments of the present application to solve the above problems is introduced. The specific operation steps are as follows:

[0125] S10. Provide a circuit substrate of a printed circuit board, a temporary carrier, and prepare a temporary bonding adhesive.

[0126] Degrease and perform dry plasma treatment on the surface of the temporary carrier for cleaning. Spin-coat a layer of temporary photosensitive dry film on the first surface of the temporary carrier, and fix the circuit substrate of the printed circuit board on the temporary carrier.

[0127] Step S20. Prepare the first layer structure of the planar transmission structure and the high-frequency and high-speed rectangular cavity microtransmission structure, that is, the bottom conductor layer described above.

[0128] As Figure 9 shown, the high-frequency and high-speed rectangular cavity microtransmission structure generally includes an outer conductor 901, an inner conductor 902, and an insulating support 903. The outer conductor encloses the inner conductor and is insulated from the inner conductor. The insulating support is used to support the inner conductor. There is an air medium between the inner conductor 902 and the outer conductor 901. The outer conductor includes a bottom metal layer 9011, a sidewall metal layer 9012, and a top cover metal layer 9013. The first layer of the high-frequency and high-speed rectangular cavity microtransmission structure, that is, the bottom metal layer 9011 of the outer conductor.

[0129] It can be understood that the bottom metal layer 9011 is the bottom conductor layer described above, the sidewall metal layer 9012 is the sidewall conductor layer described above, and the top cover metal layer 9013 is the top cover conductor layer described above.

[0130] The inner conductor 902 can be the single-ended structure shown in Figure (a). The inner conductor of the single-ended structure 902 can be a square cross-section shown in Figure (b), or a rectangular cross-section shown in Figure (c). Among them, when the inner conductor 902 is as shown in Figure (b), it can be called a full-height high-frequency and high-speed microcavity coaxial, which has a larger impedance transformation range and power capacity, while resulting in a larger transmission line volume. When the inner conductor 902 is as shown in Figure (c), it can be called a half-height high-frequency and high-speed microcavity coaxial, which has a general impedance transformation range and power capacity, while the manufacturing process is less difficult.

[0131] The inner conductor 902 can also be the differential structure shown in Figure (d), and the inner conductor 902 uses two mutually insulated conductors. The inner conductor 902 of this structure includes two mutually insulated sub-conductors 904. The insulating support 903 can support the lower ends of the two sub-conductors 904 as shown in Figure (e), or can pass through the two sub-conductors 904 in sequence for support.

[0132] As Figure 10As shown, the planar transmission structure includes multiple pads, multiple planar transmission lines, conventional traces, a ground plane, vias, etc. Among them, the multiple pads include a first pad 1001 and a second pad 1202, and the multiple planar transmission lines include a first planar transmission line 1003 and a second planar transmission line 1004. The first-layer structure 1005 of the high-frequency and high-speed rectangular cavity microtransmission structure is the Figure 9 bottom metal layer 901 in

[0133] In the operation of step S20 above, the planar transmission line, the pads, and the first-layer structure of the high-frequency and high-speed rectangular cavity microtransmission structure are processed on the circuit substrate bonded to the temporary carrier.

[0134] In some examples, the specific operation of step S20 is as follows:

[0135] First step, degrease and perform dry plasma treatment on the circuit substrate of the circuit substrate for cleaning;

[0136] Second step, spin-coat a photosensitive material layer on the surface of the circuit substrate away from the temporary carrier. According to the pattern of the planar transmission structure and the high-frequency and high-speed rectangular cavity microtransmission structure, develop the photosensitive material for the first layer to obtain fine line grooves.

[0137] Third step, use the damascene process to fill the metal material in the line grooves, and use the chemical mechanical polishing process to process the surface of the filled metal material to remove the excess metal and make the surface flat, obtaining an accurate metal interconnection pattern. This method can avoid the residual contamination of the surface of the original circuit substrate and structures such as vias by the excess copper-nickel seed layer.

[0138] It can be understood that the operations of S10 and step SZ0 above have no sequence. It can be first as Figure 11 shown in FIGS. (a) and (b) of, bond the circuit substrate 1007 with only vias 1101 processed on the surface and without the first-layer structure of the planar transmission line, pads, and high-frequency and high-speed rectangular cavity microtransmission structure to the temporary carrier 1006 through the temporary bonding adhesive 1102. Then process the planar transmission line, pads, and the first-layer structure of the high-frequency and high-speed rectangular cavity microtransmission structure on the circuit substrate.

[0139] It can also be as Figure 12As shown, first process the planar transmission line 1201, pads 1202, vias 1101, and the first-layer structure 1005 of the high-frequency and high-speed rectangular cavity microtransmission structure on the surface of the circuit board 1007, and then bond the circuit board 1007 to the temporary carrier board 1006 through the temporary bonding adhesive 1102. It can be understood that the planar transmission line 1201 includes the above-mentioned first planar transmission line 1003 and the second planar transmission line 1004, and the pads 1202 include the above-mentioned first pad 1001 and the second pad 1202.

[0140] When adopting the scheme of first bonding the circuit board to the temporary carrier board and then processing the planar transmission structure and the first-layer structure of the high-frequency and high-speed rectangular cavity microtransmission structure on the circuit board of the circuit board, no Trace processing has been realized on the surface of the circuit board, including the first-layer structure of the high-frequency and high-speed rectangular cavity microtransmission structure, planar transmission lines, conventional traces, ground planes, vias, pads, etc. The surface of the circuit board is an insulating surface. After the operation in the second step, a stripping solution can be used to remove the photosensitive material layer, and then an insulating layer can be coated according to requirements, and a copper and titanium etching solution can be used to release the seed layer remaining from the electroplating process. It is also possible to choose to retain the photosensitive material layer as a solder mask layer and a protective layer.

[0141] When adopting the scheme of first processing the planar transmission structure and the first-layer structure of the high-frequency and high-speed rectangular cavity microtransmission structure on the circuit board of the circuit board and then bonding the circuit board to the temporary carrier board, the surface of the circuit board is usually a copper-clad surface. According to the manufacturing method of a conventional circuit board, planar transmission lines, conventional traces, ground planes, vias, pads, and Trace lines at the bottom layer of the outer conductor of the high-frequency and high-speed transmission line can be processed on the copper-clad surface, and a solder mask layer can be set as needed, but a necessary exposed copper layer must be left for the subsequent processing area, and the pads required for the subsequent welding devices need to be exposed. In this way, except for some pads, most are covered by the solder mask layer, and no damage will be caused to the board material and metal.

[0142] S30. Preparation of the high-frequency and high-speed rectangular cavity microtransmission structure.

[0143] In the operation of the above step S20, the preparation of the bottom metal layer of the outer conductor of the high-frequency and high-speed rectangular cavity microtransmission structure has been completed on the circuit board of the circuit board. Therefore, based on the bottom metal layer, a metal stacking process can be used to prepare the sidewall metal layer, insulating support, inner conductor, and top cover metal layer of the outer conductor.

[0144] When the insulating support of the high-frequency and high-speed rectangular cavity microtransmission structure adopts the structure in which the insulating support passes through the inner conductor as shown in Figure 9 (e) of the figure, the stacked structure of the bottom metal layer, sidewall metal layer, insulating support, inner conductor, and top cover metal layer forms a 7-layer stacked structure, as shown in Figure 13As shown in Figure (a), a laminated structure of a sidewall metal layer, an insulating support, an inner conductor, and a top cover metal layer (layers 2 to 7) is prepared on the bottom metal layer (layer 1) by a metal stacking process, thus obtaining the complete high-frequency and high-speed rectangular cavity microtransmission structure 1301 shown in Figure (b).

[0145] Or when the high-frequency and high-speed rectangular cavity microtransmission structure adopts a structure in which the bottom of the inner conductor is supported by the insulating supports shown in Figures (b), (c), and (f), the laminated structure of the bottom metal layer, the sidewall metal layer, the insulating support, the inner conductor, and the top cover metal layer forms a 6-layer laminated structure. A laminated structure of a sidewall metal layer, an insulating support, an inner conductor, and a top cover metal layer (layers 2 to 6) is prepared on the bottom metal layer (layer 1) by a metal stacking process, thus obtaining the complete high-frequency and high-speed rectangular cavity microtransmission structure. Figure 9 As shown in Figures (b), (c), and (f), the laminated structure of the bottom metal layer, the sidewall metal layer, the insulating support, the inner conductor, and the top cover metal layer forms a 6-layer laminated structure. A laminated structure of a sidewall metal layer, an insulating support, an inner conductor, and a top cover metal layer (layers 2 to 6) is prepared on the bottom metal layer (layer 1) by a metal stacking process, thus obtaining the complete high-frequency and high-speed rectangular cavity microtransmission structure.

[0146] Among them, the specific preparation processes of the sidewall metal layer, the inner conductor, and the top cover metal layer are as follows: Spin-coat a photosensitive dry film on the surface away from the temporary carrier substrate, perform exposure and development on the photosensitive dry film to obtain fine circuit grooves, and electroplate to form corresponding circuit structures.

[0147] Among them, the specific preparation process of the insulating support is as follows: Spin-coat an insulating material on the second layer on the surface away from the temporary carrier substrate and pattern it to form a film support to support the metal inner conductor.

[0148] Matters needing attention in the above processes are as follows:

[0149] 1. The seed layers in the electroplating process are all stacked by Ti / TiN / CU (titanium, titanium nitride, copper).

[0150] 2. The thickness of the photosensitive dry film is 15 - 50 μm, and the material is an epoxy resin-based photoresist such as SU8.

[0151] 3. After each electroplating is completed, degrease the surface and perform dry plasma treatment for cleaning

[0152] 4. The processing of the high-frequency and high-speed rectangular cavity microtransmission structure is divided into seven copper plating processes. For the first layer of the high-frequency and high-speed rectangular cavity microtransmission structure and the third layer for processing the inner conductor, the damascene and CMP processes are adopted. By using this process, the width of the copper plating can be precisely controlled. On this basis, a photosensitive polymer and electroplated copper method are used.

[0153] 5. The seed layer is deposited on the side of the photoresist on the temporary carrier substrate away from the temporary carrier substrate by physical vapor deposition. Specifically, it is heated under a high vacuum state to remove moisture and contaminants on the intermediate product, and then a seed layer with high conductivity, uniform thickness, and high adhesion is prepared by physical vapor deposition.

[0154] 6. Select a photoresist and apply it evenly on the side of the seed layer facing away from the temporary carrier through a coater, and then form a uniform photosensitive film layer by baking to improve the resolution of exposure.

[0155] 7. Use an LDI exposure machine to transfer the required image data to the photoresist film layer through UV or laser light, and obtain the required patterning through development processing.

[0156] 8. After each layer of electroplating is completed, polish the surface of the thick photoresist layer by chemical mechanical polishing (CMP) to remove the excess copper layer and make the surface of the thick photoresist layer flat. When electroplating again, keep the circuit surface clean and improve the bonding force of the re-electroplating.

[0157] Thus, after the operations of S10 to S30 above, the circuit substrate is debonded from the temporary carrier, and the operation of preparing the planar transmission structure and the high-frequency and high-speed rectangular cavity microtransmission structure on the circuit substrate of the circuit substrate is completed. If it is still necessary to form the planar transmission structure and the high-frequency and high-speed rectangular cavity microtransmission structure on the circuit substrate, continue to perform the following operations:

[0158] S40. Debond the board-level high-frequency and high-speed rectangular cavity microtransmission integrated structure and the temporary carrier.

[0159] The circuit substrate, the high-frequency and high-speed rectangular cavity microtransmission structure integrated structure and the temporary carrier are debonded by using a chemical agent.

[0160] Specifically, a wet process is adopted, and the chemical agent reacts fully with the temporary photoresist, causing the chemical bonds of the materials in the temporary photoresist to break, and realizing the debonding of the temporary carrier and the integrated structure of the prepared circuit substrate and the high-frequency and high-speed rectangular cavity microtransmission structure.

[0161] S50. Use a stripping solution to remove the photosensitive dry film, leaving only the circuit substrate, the planar transmission line, the conventional trace, the ground plane, the via, the pad, and the high-frequency and high-speed rectangular cavity microtransmission structure of the metal structure.

[0162] As a preferred solution of the preparation method, step S50 specifically includes:

[0163] After debonding the transmission structure and the temporary carrier, use a stripping solution to remove the photosensitive dry film, and use a copper and titanium etching solution to release the residual seed layers of each layer. Finally, only the high-isolation high-frequency and high-speed rectangular cavity microtransmission structure of the metal structure remains.

[0164] Specifically, a wet process is adopted, and the chemical agent reacts fully with the photosensitive dry film, causing the chemical bonds of the materials in the photosensitive dry film to break and dissolve in the chemical agent. However, at this time, the chemical agent damages the substrate and metal pads of the circuit board.

[0165] Adopt the TAMO cleaning process to perform surface treatment on the board-level high-frequency and high-speed integrated processing circuit, effectively removing the residual impurities of the photosensitive dry film and the seed layer, improving the welding performance and corrosion resistance of the circuit board, and ensuring the quality and reliability of the circuit board and the high-frequency and high-speed rectangular cavity microtransmission structure.

[0166] After performing the operations of S40 and S50 above, as Figure 14 shown, remove the photosensitive dry film 1402 around the high-frequency and high-speed rectangular cavity microtransmission structure 1401 shown in (a) figure, and debond the circuit board 1007 from the temporary carrier 1006 to obtain the integrated structure of the printed circuit board and the high-frequency and high-speed interconnect transmission line shown in (b) figure.

[0167] S60. Prepare the high-frequency and high-speed rectangular cavity microtransmission structure on the bottom layer of the printed circuit board as needed.

[0168] For the specific operation, reference can be made to the operations of S10 to S50 above, and no further elaboration will be made here.

[0169] The integrated structure of the printed circuit board and the high-frequency and high-speed interconnect transmission line prepared by the method of the above embodiment, as Figure 15 shown, may include multiple high-frequency and high-speed rectangular cavity microtransmission structures 1501, multiple first pads 1502, second pads 1503, ground plane, first planar transmission line 1504, and second planar transmission line 1505 formed on the circuit board 1500 as shown in (a) figure. Among them, the first pad 1502 can be directly connected to the high-frequency and high-speed rectangular cavity microtransmission structure 1501, and the first pad 1502 can also be directly connected to the high-frequency and high-speed rectangular cavity microtransmission structure 1501 through the first planar transmission line 1504.

[0170] Multiple second pads 1503 are connected to each other through the second planar transmission line 1505. When in use, as shown in (b) figure, the chip 1506 can be connected to the first pad 1502 and the second pad 1503.

[0171] Thus, the above examples provide a method for manufacturing a printed circuit board according to the embodiments of the present application. By directly manufacturing a board-level high-frequency and high-speed rectangular cavity microtransmission structure on a circuit substrate, an integrated design of a board-level high-frequency and high-speed transmission interconnection structure is proposed. Without using complex process flows, the required high-frequency and high-speed cavity microtransmission structure is directly processed on the top / bottom transmission line layer of the required printed circuit board or directly with the printed circuit board substrate as the base. This solves the complex processing flow of the conventional application of this hollow high-frequency and high-speed rectangular cavity microtransmission structure, effectively improves the processing efficiency, reduces the production operation difficulty, effectively reduces the link loss and crosstalk when high-speed signals are transmitted through the printed circuit board, and improves the signal transmission quality.

[0172] Based on the same inventive concept, the embodiments of the present application also provide a printed circuit board, which is prepared by the method provided in the above embodiments, as Figure 1 and 3 shown. The printed circuit board includes:

[0173] A circuit substrate 100; a surface transmission structure, which is at least provided on the first surface of the circuit substrate 100, and the surface transmission structure includes a first signal transmission line 401; a microcoaxial transmission structure, which is at least provided on the first surface of the circuit substrate 100, and the microcoaxial transmission structure includes: an outer conductor 201, an inner conductor 202, and a support 203. The outer conductor 201 includes a bottom conductor layer 2011, a sidewall conductor layer 2012, and a top cover conductor layer 2013. The bottom conductor layer 2011, the sidewall conductor layer 2012, and the top cover conductor layer 2013 form a cavity surrounding the inner conductor 202. The support 203 is disposed between the inner conductor 202 and the bottom conductor layer 2011 for supporting the inner conductor 202. Among them, the bottom conductor layer 2011 is in contact with the first surface of the circuit substrate 100, the outer conductor 201 and the first signal transmission line 401 are insulated from each other, and the inner conductor 202 is conducted with the first signal transmission line 401.

[0174] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, and are not intended to limit them; although the present application 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 or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

[0175] In the specification provided here, a large number of specific details are described. However, it can be understood that the embodiments of the present application can be practiced without these specific details. In some instances, well-known methods, structures, and technologies are not shown in detail so as not to obscure the understanding of this specification.

Claims

1. A method for preparing a printed circuit board, characterized in that, The printed circuit board includes a circuit substrate and a first micro coaxial transmission structure disposed on a first surface of the circuit substrate. The first micro coaxial transmission structure includes: an outer conductor, an inner conductor, and a support. The outer conductor includes a bottom conductor layer, a sidewall conductor layer, and a top cover conductor layer. The bottom conductor layer, the sidewall conductor layer, and the top cover conductor layer form a cavity enclosing the inner conductor. The support is disposed between the inner conductor and the bottom conductor layer for supporting the inner conductor. The method includes: Providing the circuit substrate of the printed circuit board; Forming the bottom conductor layer and a surface transmission structure on the first surface of the circuit substrate. The surface transmission structure includes a first signal transmission line, and the first signal transmission line is insulated from the bottom conductor layer; Forming the inner conductor, the support, the sidewall conductor layer, and a conductive joint connecting the inner conductor and the first signal transmission line on the bottom conductor layer; Forming the top cover conductor layer on the sidewall conductor layer to obtain a printed circuit board integrated with the first micro coaxial transmission structure.

2. The method for preparing a printed circuit board according to claim 1, wherein The forming the inner conductor, the support, the sidewall conductor layer, and the conductive joint connecting the inner conductor and the first signal transmission line on the bottom conductor layer includes: Forming a first conductor sub-layer on the bottom conductor layer, and forming a first conductive segment on the first signal transmission line. The first conductive segment is electrically connected to the first signal transmission line and is insulated from the first conductor sub-layer; Forming the support on the first conductor sub-layer; Forming a second conductor sub-layer on the first conductor sub-layer, and forming a second conductive segment on the first conductive segment. The second conductive segment is electrically connected to the first conductive segment and is insulated from the second conductor sub-layer; Forming the inner conductor and a third conductor sub-layer on the support, and forming a third conductive segment on the second conductive segment. The third conductive segment is electrically connected to the second conductive segment and the inner conductor and is insulated from the third conductor sub-layer. The first conductor sub-layer, the second conductor sub-layer, and the third conductor sub-layer constitute the sidewall conductor layer. The first conductive segment, the second conductive segment, and the third conductive segment constitute the conductive joint.

3. The method for preparing a printed circuit board according to claim 1, wherein A metal layer is disposed on the first surface of the circuit substrate. The forming the bottom conductor layer and the surface transmission structure on the first surface of the circuit substrate includes: Etching the metal layer to form the bottom conductor layer and the surface transmission structure.

4. The method for preparing a printed circuit board according to claim 1, wherein The first surface of the circuit substrate is an insulating surface. The forming the bottom conductor layer and the surface transmission structure on the first surface of the circuit substrate includes: Forming a photoresist layer on the first surface of the circuit substrate; By performing a patterning process on the photoresist layer, a first patterned window corresponding to the pattern of the bottom conductor layer and a second patterned window corresponding to the pattern of the surface transmission structure are formed in the photoresist layer; Deposit a metal material layer on the photoresist layer having the first patterned window and the second patterned window, the metal material layer covering a partial area of the first surface exposed from the first patterned window and the second patterned window and the photoresist layer; Grind the metal material layer until the photoresist layer is exposed; Remove the photoresist layer.

5. The method for preparing a printed circuit board according to claim 1, wherein Before or after forming the bottom conductor layer and the surface transmission structure on the first surface of the circuit substrate, the method further includes: Provide a temporary carrier; Bond the temporary carrier to the second surface of the circuit substrate, the second surface being disposed opposite to the first surface; After obtaining the printed circuit board integrated with the first micro coaxial transmission structure, the method further includes: Separate the temporary carrier from the second surface of the circuit substrate.

6. The method for preparing a printed circuit board according to claim 1, wherein, The printed circuit board further includes a second micro coaxial transmission structure disposed on the second surface of the circuit substrate, the second surface being disposed opposite to the first surface; After obtaining the printed circuit board integrated with the first micro coaxial transmission structure, it further includes: Form the second micro coaxial transmission structure on the second surface of the circuit substrate to obtain a printed circuit board integrated with the first micro coaxial transmission structure and the second micro coaxial transmission structure.

7. The method for preparing a printed circuit board according to claim 1, wherein The first signal transmission line includes a first pad and a first planar transmission line, and the first planar transmission line is electrically connected to the first pad; Forming the conductive joint connecting the inner conductor and the first signal transmission line includes: Forming a conductive joint connecting the inner conductor and the first pad on the first pad, or Forming a conductive joint connecting the inner conductor and the first planar transmission line on the first planar transmission line.

8. The method for preparing a printed circuit board according to claim 1, wherein The surface transmission structure further includes a second signal transmission line, the second signal transmission line includes a second pad and a second planar transmission line, the second pad is electrically connected to the second planar transmission line and is insulated from the first pad, and before forming the inner conductor, the support, the sidewall conductor layer and the conductive joint connecting the inner conductor and the first signal transmission line on the bottom conductor layer, it further includes: Form a solder mask layer on the first surface where the bottom conductor layer and the surface transmission structure are formed, the solder mask layer exposing the first pad, the second pad, the bottom conductor layer and the connection end of the first planar transmission line and the conductive joint.

9. The method for preparing a printed circuit board according to claim 1, wherein The surface transmission structure further includes a ground line, and the ground line is electrically connected to the bottom conductor layer.

10. A printed circuit board, characterized in that, Prepared by the method according to any one of claims 1-9, the printed circuit board includes: A circuit substrate; A surface transmission structure, at least disposed on the first surface of the circuit substrate, the surface transmission structure including a first signal transmission line; A micro coaxial transmission structure is at least disposed on a first surface of the circuit board. The micro coaxial transmission structure includes: an outer conductor, an inner conductor, and a support. The outer conductor includes a bottom conductor layer, a sidewall conductor layer, and a top cover conductor layer. The bottom conductor layer, the sidewall conductor layer, and the top cover conductor layer form a cavity enclosing the inner conductor. The support is disposed between the inner conductor and the bottom conductor layer for supporting the inner conductor. Wherein, the bottom conductor layer is in contact with the first surface of the circuit board, the outer conductor is insulated from the first signal transmission line, and the inner conductor is electrically connected to the first signal transmission line.

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