PCB structure for reducing crosstalk of high-speed signal via transition
By increasing the diameter of the return ground via and constructing an electromagnetic shielding cavity, the problem of crosstalk between vias during high-speed signal layer switching was solved, achieving more efficient signal transmission.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- EMDOOR ELECTRONICS TECH
- Filing Date
- 2025-05-06
- Publication Date
- 2026-06-05
AI Technical Summary
Existing technologies are insufficient in suppressing crosstalk at high-speed signal transceiver vias, especially in the high-frequency band where energy coupling between adjacent signal vias is difficult to effectively block, resulting in significant signal integrity issues.
By designing the return ground via with a diameter 1.2 times larger than the signal via diameter to form a fully or semi-enclosed structure, the electromagnetic shielding cavity is enhanced. Combined with conductive materials and optimized grounding structure, a low-impedance return path is constructed to reduce electromagnetic field diffusion and energy coupling.
It significantly reduces crosstalk in high-speed signal layer switching vias, improves system margin, and ensures the integrity and reliability of signal transmission.
Smart Images
Figure CN224329649U_ABST
Abstract
Description
Technical Field
[0001] This utility model relates to the field of high-speed printed circuit board design, specifically to a PCB structure that reduces crosstalk between vias for high-speed signal layer switching. Background Technology
[0002] In the field of high-speed printed circuit board (PCB) design, as the transmission rate of high-speed differential signals increases to 112Gbps and above, the crosstalk problem of high-speed signal layer-changing vias has an increasingly significant impact on signal integrity. Crosstalk is essentially the electromagnetic energy coupling between adjacent signal vias. When a high-frequency signal changes layers through a via, if the alternating electromagnetic field it generates is not effectively constrained, it will be transmitted to adjacent vias through spatial radiation or dielectric coupling, leading to problems such as distortion and increased noise in the affected signal.
[0003] To suppress crosstalk from high-speed signal vias, the main approach is to optimize the layout strategy of return ground vias. For example, multiple return ground vias can be densely arranged around signal vias to form a symmetrically distributed grounding structure, thereby shortening the signal return path and reducing loop inductance. It is evident that the existing design approach, based on the principle of "improving return current by increasing the number and uniform distribution of ground vias," can reduce electromagnetic noise caused by poor return current to a certain extent.
[0004] In traditional designs, the aperture of return ground vias is typically set to the same size as that of signal vias. This design fails to adequately consider the constraint requirements of high-frequency electromagnetic fields, allowing the high-frequency electromagnetic fields generated by signal vias to still diffuse into the external space. Furthermore, energy coupling between adjacent signal vias is difficult to effectively block. For example, in a 112Gbps high-speed signal transmission scenario, when using return ground vias with traditional aperture designs, the crosstalk amplitude of adjacent signals at the 29GHz base frequency can reach -38.0dB. This crosstalk level is close to the critical threshold for high-speed signal transmission, highlighting the problem of insufficient system margin.
[0005] Therefore, current technologies only focus on the number and distribution of return ground vias in high-speed signal layer switching scenarios. The electromagnetic field containment capability of several return ground vias for signal vias is limited, making it difficult to effectively suppress crosstalk at high frequencies. Therefore, how to further and effectively reduce crosstalk based on existing technologies is a problem that urgently needs to be solved in the industry. Utility Model Content
[0006] To address the limitations of existing technologies in terms of the electromagnetic field envelopment capability of ground vias on signal vias, the difficulty in effectively blocking energy coupling between adjacent signal vias in the high-frequency band, and the insufficient crosstalk suppression effect, this invention provides a PCB structure that reduces crosstalk between vias used for high-speed signal layer switching.
[0007] The technical solution of this utility model is as follows:
[0008] A PCB structure for reducing crosstalk between high-speed signal vias includes at least one pair of signal vias and a plurality of return ground vias surrounding the pair of signal vias. The diameter of the return ground vias is greater than or equal to 1.2 times the diameter of the signal vias, so as to increase the electromagnetic shielding cavity formed by the signal vias.
[0009] As a preferred embodiment of this utility model, the aperture range of the signal via is 6 to 10 mil, and the aperture range of the return ground via is 8 to 12 mil.
[0010] As a preferred embodiment of this utility model, a plurality of return ground holes are distributed on one side of each pair of signal vias to form a semi-enclosed structure; or a plurality of return ground holes are symmetrically distributed on both sides to form a fully enclosed structure.
[0011] Optionally, five return ground vias are symmetrically distributed on the side of each pair of signal vias away from the trace, with the middle return ground via located on the perpendicular bisector of the line connecting the centers of the two signal vias.
[0012] Furthermore, the edge spacing between two adjacent return holes is less than or equal to twice the diameter of the return hole.
[0013] As a preferred embodiment of this utility model, the edge spacing between the signal via and the return ground via is less than or equal to 1 times the diameter of the return ground via.
[0014] As a preferred embodiment of this utility model, the width of the pad of the return ground hole is greater than or equal to the width of the pad of the signal via.
[0015] As a preferred embodiment of this utility model, the return flow holes all penetrate and connect at least two ground planes.
[0016] In a preferred embodiment of this invention, the walls of the return ground hole are filled using an electroplating process, with the filling material being a conductive paste or a copper resin composite with a conductivity greater than or equal to 5.8 × 10⁻⁶. 7 S / m.
[0017] As a preferred embodiment of this utility model, the distance between the signal layer where the signal via is located and the adjacent ground plane is less than or equal to 10 mil.
[0018] The advantages of this utility model based on the above solution are as follows:
[0019] This invention designs the return ground hole diameter around the signal via to be at least 1.2 times that of the signal via diameter. Compared with the existing structure, the increased return ground hole diameter enhances the electromagnetic field envelopment capability of the return ground hole on the signal via, forming a superior electromagnetic shielding cavity around the signal via. This restricts the diffusion of the high-frequency electromagnetic field generated by the signal via into the surrounding space, thereby reducing energy coupling between two adjacent signal vias and further reducing crosstalk between two signal vias in differential signals. Attached Figure Description
[0020] Figure 1 This is a schematic diagram of the structure of this utility model;
[0021] Figure 2 The results show the crosstalk between adjacent signals measured under different aperture return borehole conditions;
[0022] Figure 3 In one optional embodiment, the return ground via is fully surrounded by the signal via.
[0023] In the diagram, 1 is a signal via; 2 is a return ground via; and 3 is a differential trace. Detailed Implementation
[0024] To better understand the purpose, technical solution, and technical effects of this utility model, the following description, in conjunction with the accompanying drawings and embodiments, will provide further explanation. It should be noted that similar reference numerals and letters in the following drawings indicate similar items; therefore, once an item is defined in one drawing, it does not need further definition and explanation in subsequent drawings. It is also stated that the embodiments described below are only for explaining this utility model and are not intended to limit it.
[0025] It should be noted that when a component is referred to as "fixed to" or "set on" another component, it can be directly on the other component or there may be an intermediate component. When a component is referred to as "connected to" another component, it can be directly connected to the other component or there may be an intermediate component.
[0026] The indicated orientation or positional relationship is based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product is in use, or the orientation or positional relationship commonly understood by those skilled in the art, and is only for the convenience of describing this application and simplifying the description, and is not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on this application. The term "several" means two or more, unless otherwise expressly and specifically defined.
[0027] like Figure 1As shown, a PCB structure for reducing crosstalk between high-speed signal vias includes at least one pair of signal vias 1 and a plurality of return ground vias 2 surrounding the pair of signal vias 1. The diameter of the return ground vias 2 is greater than or equal to 1.2 times the diameter d of the signal vias 1, so as to increase the electromagnetic shielding cavity formed by the signal vias 1.
[0028] In this configuration, the structure in which several return ground vias "surround" a pair of signal vias can be either a fully enclosed structure or a semi-enclosed structure. Figure 1 The diagram shows a semi-enclosed structure. When differential traces fan out through the inner layer board, a structure can be created by arranging several return ground vias to fully enclose a pair of signal vias, as shown in the reference diagram. Figure 3 .
[0029] In one embodiment of a semi-enclosed structure, five return ground vias 2 are symmetrically distributed on the side of each pair of signal vias 1 away from the differential trace 3. The middle return ground via 2 is located on the perpendicular bisector of the line connecting the centers of the two signal vias 1. The five return ground vias 2 are symmetrically arranged on the side of the signal via 1 away from the trace, forming a semi-enclosed structure with the perpendicular bisector as the axis of symmetry, ensuring that the ground plane around the signal via 1 is spatially uniformly closed. The middle return ground via 2 is located on the perpendicular bisector of the line connecting the centers of the two signal vias 1, which is exactly in the "coupling sensitive area" between the two signal vias 1. By directly grounding, it forms a physical barrier, blocking the near-field coupling path between the two signal vias 1, and has a particularly significant effect on suppressing odd and even mode noise in differential signals. The symmetrical return ground vias 2 on both sides form a mirror return structure, balancing the return current of the differential pair and suppressing common mode noise caused by return imbalance, thereby reducing the coupling of common mode noise to adjacent vias.
[0030] This invention utilizes the electromagnetic field shielding properties of conductive structures, i.e., the Faraday cage effect, to construct a surrounding "grounding shielding ring" around the signal via by increasing the diameter of the return ground via. When the diameter of the return ground via is greater than or equal to 1.2 times the diameter of the signal via, the physical size advantage of the return ground via allows it to more tightly wrap around the signal via, confining the high-frequency electromagnetic field generated by the signal via inside the cavity and preventing it from diffusing to adjacent signal vias.
[0031] Increasing the diameter of the return via directly reduces the parasitic inductance and resistance of the grounding loop, providing a smoother, low-impedance return path for high-speed signals. The optimized return path reduces electromagnetic radiation caused by poor return flow. Furthermore, the larger diameter of the return via increases the coupling area between the signal via and the ground plane, further weakening the impact of via parasitic capacitance and inductance on high-frequency signals. This dual mechanism of "shielding + return flow" suppresses crosstalk.
[0032] The aperture d of signal via 1 ranges from 6 to 10 mil, and the aperture D of return ground via 2 ranges from 8 to 12 mil. The shielding effect increases with the increase of the aperture D of return ground via.
[0033] In one specific embodiment, the diameter d of signal via 1 is 6 mil, and the diameter D of return ground via 2 is 8 mil.
[0034] In one specific embodiment, the diameter d of signal via 1 is 7 mil, and the diameter D of return ground via 2 is 9 mil.
[0035] In one specific embodiment, the diameter d of signal via 1 is 8 mil, and the diameter D of return ground via 2 is 10 mil.
[0036] In one specific embodiment, the aperture d of signal via 1 is 9 mil, and the aperture D of return ground via 2 is 11 mil.
[0037] In one specific embodiment, the aperture d of signal via 1 is 10 mil, and the aperture D of return ground via 2 is 12 mil.
[0038] like Figure 2 The diagram shows a comparison of crosstalk measured with three different apertures: 8mil, 10mil, and 12mil. Under the same test conditions, when the aperture of the return ground is 8mil, the crosstalk between adjacent signals at the 29GHz base frequency is -38 dB; when the aperture is 10mil, the crosstalk decreases to -42.1dB; and when the aperture is 12mil, the crosstalk decreases to -45.1dB. It can be seen that the 12mil return ground via reduces the crosstalk between adjacent signals at the 29GHz base frequency by 7.1dB compared to the 8mil return ground via, which is equivalent to a 15.7% increase in system margin.
[0039] Existing technologies improve return current by increasing the number and optimizing the distribution of return ground vias, but they do not consider the impact of via size on shielding effectiveness, resulting in insufficient electromagnetic field confinement in the high-frequency band. This invention, however, uses an innovative combination of "via size ratio design + enclosing structure" to solve the core defect of limited electromagnetic field containment capability of return ground vias for signal vias, providing a highly efficient and practical technical approach for suppressing via crosstalk in high-speed PCB design.
[0040] In this invention, the edge spacing between two adjacent return ground holes 2 is less than or equal to twice the diameter of the return ground hole 2, ensuring that the physical gap between the return ground holes 2 is small enough so that the electromagnetic shielding areas of each return ground hole 2 overlap to form an approximately continuous "grounding shielding ring", further enhancing the lateral shielding effect of the shielding cavity.
[0041] The edge spacing between signal via 1 and return ground via 2 is less than or equal to one time the diameter of return ground via 2, ensuring that signal via 1 is completely within the strong shielding range of return ground via 2. For example, when the diameter of the signal via is 8 mil and the diameter of the return ground via is 12 mil, the edge spacing is ≤12 mil, ensuring that the electromagnetic field around the signal via is absorbed by the conductive layer of the ground via during the initial divergence stage, reducing the external radiated energy.
[0042] In a preferred embodiment, the pad width of the return via 2 is greater than or equal to the pad width of the signal via 1, resulting in a larger ground via pad. This forms a low-impedance conductive connection, enhances the grounding effectiveness of the electromagnetic shielding cavity, reduces current convergence effect, and allows the return current of high-frequency signals to be distributed more evenly on the grounding layer, thus avoiding electromagnetic field leakage caused by excessively high grounding impedance.
[0043] In one specific embodiment, the wall of the return ground via 2 is filled with electroplating material, which is a conductive paste or a copper resin composite with a conductivity greater than or equal to 5.8 × 10⁷ S / m. This reduces the resistance of the return ground via 2. Signal return requires a low-impedance path, and the reduced resistance decreases energy loss during signal return, allowing the signal to return more efficiently through the return ground via 2. This reduces signal distortion and reflection caused by poor return flow, ensuring signal integrity. Furthermore, due to the good conductivity of the return ground via, it can better guide the electromagnetic field generated by the signal via 1, confining it more tightly within the shielded area formed by the return ground via 2 and the ground plane, reducing electromagnetic field leakage into the surrounding space.
[0044] In this invention, the return ground holes 2 are all connected through at least two ground planes, which can play the role of isolation and shielding between different layers. When the signal is transmitted, the return current can be more smoothly distributed to multiple ground planes, significantly reducing the grounding impedance.
[0045] The distance between the signal layer where signal via 1 is located and the adjacent ground plane is less than or equal to 10 mil. This shortens the distance between signal via 1 and the ground plane, enhancing the shielding effect of the ground plane on the electromagnetic field generated by signal via 1. When signal via 1 transmits signals, the electromagnetic field generated by signal via 1 will be absorbed and guided by the adjacent ground plane more quickly, reducing the radiation of the electromagnetic field into the surrounding space, thereby reducing crosstalk to adjacent signal vias and traces.
[0046] In one specific embodiment, each pair of signal vias 1 connects to a pair of differential traces 3, and the signal rate is not less than 12.5Gbps. In high-speed scenarios, the low impedance matching characteristics of the differential traces and the connection method of the signal vias work together to ensure that the signal maintains good electrical performance during layer switching, providing a reliable signal transmission foundation for applications such as high-speed data communication and high-performance computing.
[0047] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.
[0048] The above embodiments only illustrate several implementation methods of this utility model, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the utility model patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this utility model, and these all fall within the protection scope of this utility model. Therefore, the protection scope of this utility model patent should be determined by the appended claims.
Claims
1. A PCB structure for reducing crosstalk vias during high-speed signal layer switching, characterized in that, It includes at least one pair of signal vias and a plurality of return ground vias surrounding the pair of signal vias, wherein the diameter of the return ground vias is greater than or equal to 1.2 times the diameter of the signal vias, so as to increase the electromagnetic shielding cavity formed by the signal vias.
2. The PCB structure for reducing crosstalk between vias for high-speed signal layer switching according to claim 1, characterized in that, The diameter of the signal via ranges from 6 to 10 mil, and the diameter of the return ground via ranges from 8 to 12 mil.
3. The PCB structure for reducing crosstalk between vias for high-speed signal layer switching according to claim 1, characterized in that, Each pair of signal vias has several return ground vias distributed on one side to form a semi-enclosed structure; or several return ground vias distributed symmetrically on both sides to form a fully enclosed structure.
4. The PCB structure for reducing crosstalk between vias for high-speed signal layer switching according to claim 3, characterized in that, In the semi-enclosed structure, five return ground vias are symmetrically distributed on the side of each pair of signal vias away from the trace, with the middle return ground via located on the perpendicular bisector of the line connecting the centers of the two signal vias.
5. The PCB structure for reducing crosstalk between vias for high-speed signal layer switching according to claim 1, characterized in that, The edge spacing between two adjacent return holes is less than or equal to twice the diameter of the return hole.
6. The PCB structure for reducing crosstalk of high-speed signal layer switching vias according to claim 1 or 5, characterized in that, The edge spacing between the signal via and the return ground via is less than or equal to 1 times the diameter of the return ground via.
7. The PCB structure for reducing crosstalk between vias for high-speed signal layer switching according to claim 1, characterized in that, The width of the pad of the return ground via is greater than or equal to the width of the pad of the signal via.
8. The PCB structure for reducing crosstalk between vias for high-speed signal layer switching according to claim 1, characterized in that, The return flow holes all penetrate and connect at least two ground planes.
9. The PCB structure for reducing crosstalk between vias for high-speed signal layer switching according to claim 1, characterized in that, The walls of the return ground vias are filled using an electroplating process, with the filling material being a conductive paste or a copper resin composite with a conductivity greater than or equal to 5.8 × 10⁻⁶. 7 S / m.
10. The PCB structure for reducing crosstalk between high-speed signal layer switching vias according to claim 1, characterized in that, The distance between the signal layer where the signal via is located and the adjacent ground plane is less than or equal to 10 mil.