A structure for suppressing electromagnetic interference of a circuit board and a circuit board

Abstract

The present invention relates to the technical field of circuit boards. The present invention discloses a structure for suppressing electromagnetic interference of a circuit board. The circuit board is a multi-layer circuit board, which at least includes a pair of power layers and ground layers. The substrate medium is between the power layer and the ground layer. The structure further includes a plurality of noise suppression units spacedly embedded in the substrate medium. The noise suppression units are periodically distributed in the substrate medium. The noise suppression unit includes a thin film unit with a high dielectric constant and a metal column. The first surface of the thin film unit is connected to the power layer or the ground layer. The second surface of the thin film unit is connected to the first end face of the metal column. The second end face of the metal column is connected to the ground layer or the power layer. The present invention constitutes an enhanced dielectric EBG (electromagnetic bandgap) structure, enhances the capacitance of the EBG dielectric unit, reduces the requirement for the dielectric constant of the thin film unit, increases the electromagnetic interference suppression bandwidth, and can effectively suppress the propagation of noise electromagnetic waves between the power layer and the ground layer.

Description

Technical Field

[0001] The present invention belongs to the technical field of circuit boards, and particularly relates to a structure and a circuit board for suppressing electromagnetic interference of a circuit board. Background Art

[0002] With the rapid popularization and application of 5G technology, the electronic information system is about to enter the millimeter wave era. The high-frequency and high-speed, high-density characteristics of high-speed digital systems such as integrated circuits (ICs) and high-speed printed circuit boards (PCBs) make the problem of electromagnetic interference very important. In high-speed multi-layer PCBs, the sources of electromagnetic interference noise are relatively extensive, among which simultaneous switching noise (SSN) plays a dominant role and is the main source of electromagnetic interference noise. The power distribution network (PDN) of multi-layer PCBs generally adopts a planar structure, that is, a pair of adjacent power planes and ground planes. Since the power / ground planes are the largest conductors in multi-layer PCBs, they are also the antennas that are most likely to emit and receive noise. At the same time, the power / ground planes carry the largest current, which will generate serious SSN. When the frequency of the noise electromagnetic wave reaches the resonance frequency of the power / ground plane, a resonance phenomenon will occur, which will exacerbate electromagnetic interference phenomena such as crosstalk and radiation emission, and will cause serious signal integrity (SI) and power integrity (PI) problems. Electromagnetic interference will not only degrade the system performance of the PCB board, resulting in reliability problems, but also interfere with the external system of the PCB. Therefore, appropriate measures must be taken to suppress the electromagnetic interference on the PCB board to meet the requirements of relevant electromagnetic compatibility standards.

[0003] The common method for suppressing electromagnetic interference is to use discrete decoupling capacitors, including traditional decoupling capacitors, surface mount technology (SMT) capacitors, and embedded capacitors, etc. Due to the existence of parasitic equivalent series inductance (ESL) and equivalent series resistance (ESR), discrete decoupling components are prone to resonance, and the operating frequency is not high. The traditional decoupling capacitor can only reach dozens of megahertz, and the operating frequency of SMT capacitors can reach several hundred megahertz. Embedded capacitors have very small ESR and ESL, but their upper limit operating frequency is generally not higher than 1 GHz. Due to the influence of parasitic effects, discrete components cannot meet the noise suppression requirements of high-speed and high-frequency PCB boards. In addition, numerous discrete components will occupy a large amount of space, which is difficult to arrange for high-density and miniaturized PCB boards. Decoupling above 1 GHz can use distributed capacitors, such as embedded capacitors. The power layer and ground layer of embedded capacitors have a very small spacing, and a dielectric with a high dielectric constant is filled between the power layer and the ground layer. Although the embedded capacitor has a wide frequency range for noise suppression, its disadvantage is that it requires a specific layer stack technology, its cavity structure will cause resonance phenomena, and the isolation degree of noise suppression is not high enough.

[0004] In the past decade or more, extensive research has been carried out at home and abroad on noise suppression structures based on metamaterial technologies such as the high-impedance surface (HIS) method, coplanar electromagnetic bandgap (EBG) structures, and dielectric EBG structures. These structures utilize the characteristic of periodic metamaterial structures having frequency bandgaps, thereby achieving relatively high noise isolation. However, the HIS method requires complex via connections, is complex to process, and has a high cost. Moreover, etching patterns on the power / ground plane in coplanar EBG structures will damage the integrity of the conductor surface and cause signal integrity problems. The dielectric EBG structure embeds periodically arranged high-K materials in a low-K (dielectric constant) medium. It combines the advantages of capacitance and EBG, can ensure good signal integrity, and is a good noise suppression solution. However, the currently studied dielectric EBG requires a very small interval between the power / ground planes. Otherwise, the dielectric material needs to have a very high dielectric constant, with a relative dielectric constant reaching or even exceeding 5000. High-dielectric-constant materials will lead to an increase in dielectric loss. Another problem with the dielectric EBG structure is that a circuit board with a certain periodic dielectric structure can only be used to suppress electromagnetic noise in a specific frequency range, and its versatility is not high. Summary of the Invention

[0005] The object of the present invention is to provide a structure and a circuit board for suppressing electromagnetic interference of a circuit board to solve the above-mentioned existing technical problems.

[0006] To achieve the above object, the technical solution adopted by the present invention is: a structure for suppressing electromagnetic interference of a circuit board. The circuit board is a multi-layer circuit board, at least including a pair of power layers and ground layers. The substrate dielectric is between the power layer and the ground layer. The structure further includes a plurality of noise suppression units spacedly embedded in the substrate dielectric. The noise suppression units are periodically distributed in the substrate dielectric. The noise suppression unit includes a thin film unit with a high dielectric constant and a metal column. The first surface of the thin film unit is connected to the power layer or the ground layer. The second surface of the thin film unit is connected to the first end face of the metal column. The second end face of the metal column is connected to the ground layer or the power layer.

[0007] Further, the noise suppression units are equally spaced and periodically distributed in the substrate dielectric.

[0008] Further, the thin film unit is circular or regular polygonal.

[0009] Further, the thin film units of multiple noise suppression units are all connected to the power layer or all connected to the ground layer.

[0010] Further, the thin film units of multiple noise suppression units are alternately connected to the power layer and the ground layer.

[0011] Further, the relative dielectric constant of the thin film unit is 50 - 500.

[0012] Furthermore, the metal column is a metallized electroplated blind via, and the bottom surface of the blind via in contact with the thin film unit is metallized.

[0013] Furthermore, the metal column is a solid metal pin.

[0014] Furthermore, the thin film unit has a circular structure, and the diameters of both the thin film unit and the metal column are 1-2 mm.

[0015] Furthermore, vias can be accommodated inside the noise suppression unit, including signal vias, ground vias, power vias, etc., and the diameter of the vias is less than 0.25 mm.

[0016] Furthermore, the noise suppression unit is also evenly arranged around the noise source area of the substrate medium to form an annular structure.

[0017] The present invention also provides a circuit board provided with the above structure for suppressing electromagnetic interference of the circuit board.

[0018] The present invention also provides a reconfigurable noise suppression circuit board, which only has a periodic thin film unit array in the above noise suppression unit.

[0019] Advantageous technical effects of the present invention:

[0020] The present invention uses a thin film unit with a high dielectric constant and a metal column structure to form small noise suppression units with a relatively large capacitance value. The periodic arrangement of these small noise suppression units further forms a dielectric EBG structure. This EBG structure reduces the requirement for the dielectric constant of the thin film unit and increases the noise suppression performance at the same time.

[0021] The present invention can pre-cure a thin film unit with a high dielectric constant on the circuit board, and then reprocess the metal column according to needs to reconstruct and manufacture an EBG structure with a new periodic structure, expanding the application range and flexibility.

[0022] The thin film unit and metal column structure of the present invention are arranged around the signal via, providing a good low-impedance current return path, which can improve the signal integrity of interconnect structures such as via conversion, effectively suppress the propagation of noise electromagnetic waves and reduce resonance.

[0023] The diameter of the metal column in the present invention is larger than the diameter of the via, so that the via can be arranged inside the noise suppression unit, avoiding the spatial conflict between the noise suppression unit and the via. By appropriately selecting the spacing of the noise suppression units, the structural integration of the via and the noise suppression unit can be achieved. Description of the Drawings

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the accompanying drawings required for the description of the embodiments. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other accompanying drawings can be obtained based on these drawings.

[0025] Figure 1 Structural schematic diagram of Embodiment 1 of the present invention;

[0026] Figure 2 Cross-sectional view of Embodiment 1 of the present invention;

[0027] Figure 3 Cross-sectional view of Embodiment 2 of the present invention;

[0028] Figure 4 Structural schematic diagram of Embodiment 3 of the present invention;

[0029] Figure 5 Cross-sectional view of Embodiment 3 of the present invention;

[0030] Figure 6 Cross-sectional view of the circuit board without metal posts of the present invention;

[0031] Figure 7 Suppression simulation effect diagram using a dielectric column array;

[0032] Figure 8 Suppression simulation effect diagram of the present invention. Specific embodiments

[0033] To further illustrate each embodiment, the present invention provides accompanying drawings. These accompanying drawings are part of the public disclosure of the present invention, mainly used to illustrate the embodiments, and can be used in conjunction with the relevant descriptions in the specification to explain the operating principles of the embodiments. With reference to these contents, those of ordinary skill in the art should be able to understand other possible implementation manners and the advantages of the present invention. The components in the figures are not drawn to scale, and similar component symbols are usually used to represent similar components.

[0034] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0035] Embodiment 1

[0036] As Figure 1 and 2As shown in the figure, a structure for suppressing electromagnetic interference of a circuit board. The circuit board 1 is a multi-layer circuit board, including at least a pair of power layers 2 and ground layers 3. Between the power layer 2 and the ground layer 3 is a substrate dielectric 4. It also includes a plurality of noise suppression units 5 spaced and embedded in the substrate dielectric 4. The noise suppression units 5 are periodically distributed in the substrate dielectric 4. The noise suppression unit 5 includes a thin film unit 51 with a high dielectric constant and a metal column 52. The first surface ( Figure 2 in the figure is the lower surface) of the thin film unit 51 is connected to the ground layer 3. The second surface ( Figure 2 in the figure is the upper surface) of the thin film unit 51 is connected to the first end face ( Figure 2 in the figure is the lower end face) of the metal column 52. The second end face ( Figure 2 in the figure is the upper end face) of the metal column 52 is connected to the power layer 2.

[0037] A plurality of noise suppression units 5 are arranged in a periodic array to form an electromagnetic bandgap structure, which blocks the propagation of noise electromagnetic waves within a specific frequency stopband, reducing the resonance phenomenon between the power layer 2 and the ground layer 3 of the circuit board 1. It can not only effectively suppress electromagnetic interferences such as crosstalk and radiation emission, but also the thin film unit 51 and the metal column 52 form a capacitive structure unit with a relatively large capacitance value, increasing the overall capacitance of the circuit board 1 at the same time. This not only reduces the requirement for the dielectric constant of the thin film unit 51, but also enables the circuit board 1 to have the advantages of suppressing electromagnetic interference by using both capacitors and electromagnetic bandgap structures.

[0038] Of course, in other embodiments, it can also be that the first surface of the thin film unit 51 is connected to the power layer, the second surface of the thin film unit 51 is connected to the first end face of the metal column 52, and the second end face of the metal column 52 is connected to the ground layer 2.

[0039] In this specific embodiment, a plurality of noise suppression units 5 are equally spaced and periodically distributed in the substrate dielectric 4, resulting in a smaller inductance and a more uniform distribution, improving the suppression effect of electromagnetic interference.

[0040] In this specific embodiment, the shape of the thin film unit 51 is preferably circular. Correspondingly, the cross-sectional shape of the metal column 52 is also circular, which is easy to process. However, this is not limited to this. In some embodiments, the shape of the thin film unit 51 can also be a regular polygon such as a square or a regular hexagon, or any other arbitrary shape, which can be specifically selected according to actual needs.

[0041] In this specific embodiment, the relative dielectric constant of the thin film unit 51 is preferably 50 - 500, which can not only achieve the purpose of suppressing electromagnetic interference, but also avoid large dielectric losses caused by too large a dielectric constant. However, this is not limited to this. In other embodiments, the relative dielectric constant of the thin film unit 51 can be selected according to the actual stopband frequency.

[0042] Preferably, in this embodiment, the thin film unit 51 is preferably made of a ceramic material. The dielectric constant of the ceramic material has a wide range and good electrical properties. Of course, in some embodiments, the material of the thin film unit 51 can also be other materials with high dielectric constants.

[0043] In this specific embodiment, the metal column 52 is a solid metal pin and can be made of a metal material such as copper. Of course, in other embodiments, the metal column 52 can also be a metallized blind hole, and the bottom surface of the blind hole in contact with the thin film unit 51 is metallized.

[0044] In this specific embodiment, the diameters of the thin film unit 51 and the metal column 52 can be 1-2 mm to accommodate necessary vias, thereby avoiding spatial conflicts between the vias and the metal column. However, this is not limited thereto. In other embodiments, the specifications of the thin film unit 51 and the metal column 52 can be selected according to actual needs.

[0045] Specifically, the number and the spacing between the noise suppression units 5 can be selected according to the frequency bandwidth of the noise suppression, which will not be elaborated here.

[0046] The circuit board 1 can be various existing multi-layer circuit boards as long as it has a power layer 2, a ground layer 3, and a substrate dielectric 4 between the power layer 2 and the ground layer 3.

[0047] Embodiment Two

[0048] As Figure 3 shown, the difference between this embodiment and Embodiment One is that the thin film units 51 of the multiple noise suppression units 5 in this embodiment are alternately connected to the power layer 2 and the ground layer 3, that is, the thin film units 51 and the metal columns 52 of the adjacent noise suppression units 5 are arranged up and down in a staggered manner. Such a structure has a more complex periodic structure and is a highly non-linear structure, which can regulate the performance of the electromagnetic structure in a wider frequency band.

[0049] Embodiment Three

[0050] As Figure 4 and 5 shown, the difference between this embodiment and Embodiment One is that the noise suppression units 5 are also uniformly arranged around the outside of the noise source area to form an annular structure. In this specific embodiment, the noise source area is the signal via 6, and an anti-pad 7 is provided around the outside of the signal via 6. Multiple noise suppression units 5 are uniformly arranged around the outside of the anti-pad 7 to form an annular structure.

[0051] Multiple noise suppression units 5 form a one-dimensional electromagnetic bandgap structure in cylindrical coordinates, preventing the noise electromagnetic wave from propagating radially. At the same time, the thin film unit 51 and the metal column 52 provide a good low-impedance return path for the return current of the signal via 6, enhancing the signal integrity of the signal via 6.

[0052] Of course, in other embodiments, the noise source region may also be an integrated circuit or the like.

[0053] In this specific embodiment, the number of noise suppression units 5 is 4, but it is not limited thereto. In other embodiments, the number of noise suppression units 5 can be set according to relevant parameters such as the sizes of the thin film unit 51 and the metal column 52, and the size of the signal via 6.

[0054] Preferably, in this specific embodiment, the 4 noise suppression units 5 are arranged at equal intervals from each other, so that the capacitance and inductance are more evenly distributed, improving the suppression effect of electromagnetic interference.

[0055] In this specific embodiment, the signal via 6 has a circular structure, and the 4 noise suppression units 5 form an annular structure, that is, the 4 noise suppression units 5 are evenly distributed on the same circle with the center of the signal via 6 as the center of the circle, adapting to the shape of the outer peripheral surface of the signal via 6, further improving the suppression effect of electromagnetic interference. However, it is not limited thereto. In other embodiments, the shape of the annular structure may also be other shapes such as square and triangle.

[0056] The present invention also provides a circuit board provided with the above structure for suppressing electromagnetic interference of the circuit board.

[0057] Simulation verification:

[0058] A 100 mm × 60 mm circuit board is used for simulation comparison, and the power / ground plane is 0.25 mm thick. The EBG structure is composed of a 9×5 array of high-K dielectric columns embedded in the FR4 substrate dielectric, with a spacing of 10 mm between adjacent dielectric columns, a diameter of 2 mm for the dielectric columns, and a relative dielectric constant of ε r1 = 4.4 for FR4. The simulation frequency range is from 100 MHz to 5 GHz. Figure 7 are the S-parameter simulation results when the relative dielectric constants of the high-K dielectric columns are ε r2 = 100 and ε r2 = 500 respectively. As can be seen from Figure 7 (a) of, the frequency range where S 21 is less than -40 dB is approximately 2.38 - 5 GHz. As can be seen from Figure 7 (b) of, the frequency range where S 21 is less than -40 dB is approximately 0.9 - 5 GHz, but there are two obvious resonance points at 2.5 GHz and 4.22 GHz, and at the resonance points, S 21 is close to -40 dB.

[0059] Adopting the structure of the present invention, the dielectric columns are replaced with a 75-μm-thick dielectric film and a 0.175-mm-high metal column. Figure 8 are the relative dielectric constants of the high-K dielectric columns being ε r2= 100 and ε r2 S-parameter simulation results when = 500. From Figure 8 (a), it can be seen that S 21 The frequency range where S is less than -40 dB is approximately 1.2 - 5 GHz. From Figure 8 (b), it can be seen that within 0.7 - 5 GHz, S 21 is less than -60 dB.

[0060] From Figure 7 and Figure 8 the comparison of the calculation results, it can be seen that the use of the present invention significantly improves the noise suppression effect and reduces the requirement for the dielectric constant of the high-K medium.

[0061] The circuit board 1 of the present invention can be pre-cured with a high-density thin film unit 51 on the circuit board 1, as Figure 6 shown. Then, select some of the thin film units 51 as needed, perform secondary processing on the metal posts, and reconstruct and fabricate a noise suppression unit with a new periodic structure. Since different periodic structures have different bandgap characteristics, the application range and flexibility of the circuit board of the present invention are expanded.

[0062] Although the present invention has been specifically shown and described in conjunction with the preferred embodiments, those skilled in the art should understand that various changes can be made to the present invention in terms of form and details without departing from the spirit and scope of the present invention defined by the appended claims, and all such changes are within the protection scope of the present invention.

Claims

1. A structure for suppressing electromagnetic interference of a circuit board, the circuit board being a multi-layer circuit board, at least including a pair of power layers and ground layers, with a substrate medium between the power layer and the ground layer, characterized in that: It further includes a plurality of noise suppression units interspersed at intervals in the substrate medium, the noise suppression units being periodically distributed in the substrate medium. The noise suppression unit includes a thin film unit with a high dielectric constant and a metal column. The first surface of the thin film unit is connected to the power supply layer or the ground layer. The second surface of the thin film unit is connected to the first end face of the metal column. The second end face of the metal column is connected to the ground layer or the power supply layer. The relative dielectric constant of the thin film unit is 50 to 500, and it is made of a ceramic material. The metal column is a solid metal pin and is made of copper metal material.

2. The structure for suppressing electromagnetic interference of a circuit board according to claim 1, wherein: The noise suppression units are equally spaced and periodically distributed in the substrate medium.

3. The structure for suppressing electromagnetic interference of a circuit board according to claim 1, wherein: The thin film unit is circular or regular polygonal.

4. The structure for suppressing electromagnetic interference of a circuit board according to claim 1, wherein: The thin film units of multiple noise suppression units are all connected to the power supply layer or all connected to the ground layer.

5. The structure for suppressing electromagnetic interference of a circuit board according to claim 1, wherein: The thin film units of multiple noise suppression units are alternately connected to the power supply layer and the ground layer.

6. The structure for suppressing electromagnetic interference of a circuit board according to claim 1, wherein: The noise suppression units are also evenly arranged around the periphery of the noise source area of the substrate medium to form an annular structure.

7. A circuit board, characterized in that: There is provided a structure for suppressing electromagnetic interference of a circuit board according to any one of claims 1-6.

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