Low-loss microstrip transmission line based on substrate stacking and bonding

Abstract

The invention provides a low-loss microstrip transmission line based on substrate stacking and bonding. The low-loss microstrip transmission line comprises an upper carrier plate layer, a hollow transmission layer, a lower carrier plate layer, a first bonding layer and a second bonding layer, a first metal layer is arranged on the lower surface of the upper carrier plate layer, and a second metal layer is arranged on the upper surface of the lower carrier plate layer; the first metal layer, the second metal layer and the hollow-out area of the hollow-out transmission layer jointly form a transmission area; electromagnetic waves are propagated in the transmission area in a quasi-TEM mode form; the upper carrier plate layer, the first bonding layer, the hollow transmission layer, the second bonding layer, the second metal layer and the lower carrier plate layer are stacked and bonded in parallel in sequence; and therefore, the interlayer is tightly bonded, the structure is flat and stable, and displacement and height change between the layers are avoided. The invention has the advantages of low cost and low loss, and is suitable for the field of microwave communication transmission. In addition, the antenna also has the characteristics of easy processing, high integration and wide frequency band, so that the antenna is widely applied to scenes using a multilayer board integration technology.

Description

Technical Field

[0001] The present invention relates to the technical field of microwave transmission lines, and in particular to a low-loss microstrip transmission line based on substrate stacking bonding. Background Art

[0002] As an important component of microwave integrated circuits, microstrip transmission lines have developed into the most commonly used transmission line technology in radio frequency circuits since they were first proposed by Gr ieg and Engelmann in the 1950s. Its structure consists of a single conductor strip on a dielectric substrate and a grounded metal plate at the bottom. Microstrip lines have been widely used in high-speed circuits and microwave integrated circuits due to their simple manufacturing, low cost, small size and light weight. Especially in the fields of mobile communications, satellite communications, radar systems, etc., microstrip transmission lines have significantly improved the integration and reliability of circuits with their excellent transmission characteristics and the ability to be easily integrated with active devices.

[0003] The application advantages of microstrip transmission lines are mainly reflected in the planarity of their structure, which allows them to be integrated with microwave components and systems and also supports the use of wideband. In addition, microstrip lines have high design flexibility and can control characteristic impedance by adjusting their width and the thickness of the dielectric substrate to meet the needs of different circuit designs. Secondly, microstrip lines have relatively low losses, especially in the lower microwave frequency bands, which makes them very effective in RF transmission and signal processing.

[0004] However, in higher microwave frequency bands, microstrip transmission lines face some inevitable disadvantages. With the increase of frequency, the loss of microstrip lines increases significantly. The loss mainly comes from three sources: radiation loss, conductor loss, and dielectric loss. Since microstrip lines are similar to antennas, they radiate electromagnetic energy outward along the propagation path, and the loss caused is called radiation loss. Correctly designing the transmission line size according to the operating frequency of the transmission line can suppress radiation loss to a certain extent. The increase in frequency leads to a decrease in the skin depth of the microstrip line, thereby increasing the conductor loss. In addition, a large part of the loss comes from dielectric loss. In the millimeter wave frequency band, dielectric loss is particularly critical because the signal wavelength in this frequency band is shorter and the effect of dielectric loss on transmission characteristics is more significant. In high-frequency applications such as 5G communications and automotive radars, dielectric loss will significantly affect the transmission efficiency of signals. In order to reduce dielectric loss, the first method is to select substrate materials with low dielectric constant and low loss, but this will lead to a sharp increase in processing costs and difficulty. In addition, most substrate materials are tested in the range of 2GHz to 15GHz, and electromagnetic behavior at higher frequencies is difficult to predict, which will increase the difficulty of system design and the instability of system operation. It is difficult to apply to the field of high-frequency microwave communications, which is currently widely used and has more abundant spectrum resources. Summary of the invention

[0005] The main technical problem to be solved by the present invention is to provide a low-loss microstrip transmission line based on substrate stacking bonding, and the water electrolysis module can be easily disassembled and cleaned.

[0006] In order to solve the above technical problems, the present invention provides a low-loss microstrip transmission line based on substrate stacking bonding, comprising an upper board layer, a hollow transmission layer, a lower board layer, a first bonding layer and a second bonding layer;

[0007] A first metal layer is provided on the lower surface of the upper loading board layer, and a second metal layer is provided on the upper surface of the downloading board layer; the first metal layer, the second metal layer and the hollow area of ​​the hollow transmission layer together constitute a transmission area; electromagnetic waves propagate in the transmission area in the form of a quasi-TEM mode;

[0008] The upper board layer, the first bonding layer, the hollow transmission layer, the second bonding layer, the second metal layer and the lower board layer are stacked in parallel and bonded in sequence.

[0009] In a preferred embodiment, a hollow strip-shaped hole is provided in the middle of the hollow transmission layer, and the hollow strip-shaped hole, the first metal layer and the second metal layer constitute the transmission area.

[0010] In a preferred embodiment, the first metal layer and the second metal layer are both thin metal layers; the first metal layer has a certain line width, and the first metal layer is attached to the upper carrier layer;

[0011] The second metal layer covers the entire upper surface of the download board layer; the first metal layer and the second metal layer together form a low-loss microstrip line.

[0012] In a preferred embodiment, the line width of the first metal layer is set at 66um-67um; the thickness of the hollow transmission layer is set at 30um-30.5um;

[0013] The width of the hollow area of ​​the hollow transmission layer is set to 2.6 times the width of the first metal line.

[0014] In a preferred embodiment, the thickness of the first metal layer and the second metal layer is set to 17um or 35um.

[0015] In a preferred embodiment, the upper carrier layer and the hollow transmission layer are bonded via the first bonding layer;

[0016] The hollow transmission layer and the download board layer are bonded via the second bonding layer.

[0017] In a preferred embodiment, the upper board layer, the hollow transmission layer and the lower board layer are all made of FR4 substrate material.

[0018] In a preferred embodiment, the thickness of the upper board layer and the lower board layer is set to 160um-200um.

[0019] In a preferred embodiment, the first bonding layer and the second bonding layer are made of dry film ABF GL102 material.

[0020] In a preferred embodiment, the thickness of the first bonding layer and the second bonding layer is set to 5um-15um.

[0021] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0022] 1. The first metal layer, the second metal layer and the hollow area of ​​the hollow transmission layer are arranged to form a transmission area, and the upper board layer, the first bonding layer, the hollow transmission layer, the second bonding layer, the second metal layer and the lower board layer are stacked and bonded in parallel in sequence, so that the layers can be tightly bonded, the structure is flat and stable, and no displacement or height change occurs between the layers. The present invention has the advantages of low cost and low loss, and is suitable for the field of microwave communication transmission. Because it also has the characteristics of easy processing, high integration and wide bandwidth, it is widely used in scenarios using multilayer board integration technology.

[0023] 2. The transmission line structure proposed in the present invention can achieve a significant reduction in dielectric loss in the millimeter wave frequency band, and can significantly reduce material costs and processing costs, while having the characteristics of wide bandwidth, high integration, and easy processing. It can be widely used in the field of microwave communication transmission, especially in application scenarios using multilayer board integration technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 A schematic diagram of the decomposed structure of a low-loss microstrip transmission line based on substrate stacking bonding in a preferred embodiment of the present invention;

[0025] Figure 2 A schematic diagram of the cross-sectional electric field distribution of a low-loss microstrip transmission line in a preferred embodiment of the present invention;

[0026] Figure 3 A cross-sectional detail diagram of a low-loss microstrip transmission line in a preferred embodiment of the present invention;

[0027] Figure 4 A characteristic impedance curve diagram of a low-loss microstrip transmission line in a preferred embodiment of the present invention;

[0028] Figure 5 A reflection coefficient curve diagram of a low-loss microstrip transmission line in a preferred embodiment of the present invention;

[0029] Figure 6 This is a comparison curve of the unit transmission loss between the low-loss microstrip transmission line and the traditional dielectric-filled microstrip transmission line in the preferred embodiment of the present invention. DETAILED DESCRIPTION

[0030] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention; it is obvious that the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments, and all other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making creative work are within the scope of protection of the present invention.

[0031] In the description of the present invention, it should be noted that the terms "upper", "lower", "inner", "outer", "top / bottom" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific position, be constructed and operated in a specific position, and therefore cannot be understood as limiting the present invention. In addition, the terms "first" and "second" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance.

[0032] In the description of the present invention, it should be noted that, unless otherwise clearly stipulated and limited, the terms "installed", "provided with", "mounted / connected", "connected", etc. should be understood in a broad sense. For example, "connection" can be a wall-mounted connection, a detachable connection, or an integral connection. It can be a mechanical connection or an electrical connection. It can be a direct connection or an indirect connection through an intermediate medium. It can be the internal connection of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0033] refer to Figure 1-Figure 6 This embodiment provides a 50 ohm low-loss microstrip transmission line based on dry film bonding stacking in the 26 GHz-100 GHz band.

[0034] refer to Figure 1 , its structure includes an upper loading board layer L1, a hollow transmission layer L2 and a downloading board layer L3; a first metal layer MS1 is provided on the lower surface of the upper loading board layer L1; a second metal layer MS2 is provided on the upper surface of the downloading board layer L3; a strip hole of a certain width is hollowed out in the middle of the hollow transmission layer L2 as a transmission area; the upper loading board layer L1, the hollow transmission layer L2 and the downloading board layer L3 are arranged in parallel from top to bottom, and the upper loading board layer L1 and the hollow transmission layer L2 are bonded by the first bonding layer B1, and the hollow transmission layer L2 and the downloading board layer L3 are bonded by the second bonding layer B2. Reference Figure 2 The first metal layer MS1, the second metal layer MS2 and the hollow area (strip-shaped holes) of the hollow transmission layer together constitute a transmission area, and electromagnetic waves propagate in the form of a quasi-TEM mode in the transmission area.

[0035] In the specific implementation, in order to better demonstrate the advantages of the wideband of this structure, the 26GHz-100GHz range in the millimeter wave frequency band is selected to demonstrate the effect. This frequency range covers many microwave communication application scenarios such as satellite communication, ground short-distance communication, and automotive radar.

[0036] In the specific implementation, in order to better demonstrate the advantages of low cost and low loss of this transmission line, the upper board layer L1, the hollow transmission layer L2 and the lower board layer L3 are all made of low-cost and high-loss FR4 substrate materials. Considering the miniaturization required for high-frequency applications, it is finally decided to use the S1000-2M model FR4 substrate developed by Shengyi Technology, which has a dielectric constant of 4.5 and a loss tangent of 0.02. The processing thickness of the substrate can be as small as 30um, which meets the design size requirements of this embodiment.

[0037] It should be noted that the substrate used by the upper board layer L1 and the lower board layer L3 does not specifically refer to a specific material substrate. In addition to the FR4 substrate material provided in this embodiment, various material substrates applicable to the field of microwave communication transmission and multilayer board integration technology can be used. The substrate used by the hollow transmission layer L2 does not specifically refer to a specific material substrate. In addition to the FR4 substrate material provided in this embodiment, various processable hollowed-out material substrates applicable to the field of microwave communication transmission and multilayer board integration technology can be used.

[0038] In the specific implementation, refer to Figure 2 and Figure 3 A small part of the transmitted electromagnetic wave will exist in the upper loading board layer L1, and it should be ensured that it has a certain height to eliminate the influence on other structures above. As a preferred embodiment, the thickness H1 of the upper loading board layer L1 is 200um. The downloading board layer L3 is mainly used as a bearing bonding platform, and its rigidity and stress requirements should be guaranteed. As a preferred embodiment, the thickness H3 of the downloading board layer L3 is 200um.

[0039] In the specific implementation, refer to Figure 3 , Figure 4 and Figure 5 , through design optimization to ensure the characteristic impedance of 50 ohms and good reflection coefficient of the transmission line, as a preferred embodiment, the line width W1 of the first metal layer MS1 is 66.5um, the thickness H2 of the hollow transmission layer L2 is 30.27um, and the width of the hollow area is 2.6 times the width W1 of the first metal MS1, specifically 172.9um. The design considerations of the width of the hollow area take into account both miniaturization requirements and transmission loss.

[0040] In the specific implementation, refer to Figure 3, the first metal layer MS1 and the second metal layer MS2 are attached to the bottom of the upper board layer L1 and the top of the lower board layer L3 respectively by substrate hot pressing process, and then the first metal layer MS1 is cut into the required line width W1 by photolithography. Combined with the actual process standards, the thickness H4 of the first metal layer MS1 and the thickness H5 of the second metal layer MS2 are both set to 17um, and can also be adjusted according to the actual process standards. The thickness H4 of the first metal layer MS1 and the thickness H5 of the second metal layer MS2 include two sizes, 17um or 35um.

[0041] In the specific implementation, refer to Figure 3 , the first bonding layer B1 and the second bonding layer B2 are realized using dry film ABF GL102 material, whose dielectric constant is 3.3 and loss tangent value is 0.009. A femtosecond laser is used to punch and hollow out the middle of the hollow transmission layer L2, and then the dry film ABF GL102 is vacuum laminated on both sides of the hollow transmission layer L2, and then an air gun is used to remove the dry film from the top of the hollow cavity to form the first bonding layer B1 and the second bonding layer B2. Combined with the actual material, as a preferred method, the thickness H6 of the first bonding layer B1 and the thickness H7 of the second bonding layer B2 are both set to 5um. It should be noted that the first bonding layer B1 and the second bonding layer B2 use different bonding methods depending on the material, including dry film bonding, mechanical bonding (screws, clamps), and hot pressing. Different bonding methods have different thicknesses. The dry film bonding thickness is set to 5um-15um, the mechanical bonding thickness is set to 10um-25um, and the hot pressing thickness is almost zero.

[0042] The performance characterization results of the 50 ohm low-loss microstrip transmission line based on dry film bonding stacking in the 26GH-100GHz band of this embodiment are as follows: Figure 4 , Figure 5 and Figure 6 As shown. Among them, Figure 4 The characteristic impedance of the structure fluctuates within the operating frequency range of 50±0.3 ohms. Figure 5 The reflection coefficient of the structure is characterized as being lower than -27.5dB within the operating frequency range. Figure 6 The structure is characterized in that compared with the traditional dielectric-filled microstrip transmission line in the operating frequency range, the black square is the transmission loss of the traditional dielectric-filled microstrip line, and the black triangle is the transmission loss of the microstrip transmission line described in Example 1, and its transmission loss is reduced by 0.08dB / mm-0.2dB / mm. And the transmission loss can be reduced by nearly 50% below 60GHz.

[0043] The design method and processing flow of a 50 ohm low-loss microstrip transmission line based on dry film bonding stacking in the 26 GHz-100 GHz band of this embodiment include the following steps:

[0044] Step 1: Determine the substrate material, bonding method, and certain fixed parameters such as metal layer thickness based on the design goals and processing requirements.

[0045] Step 2: Based on the required characteristic impedance, use TXLINE 2003 software to preliminarily determine the parameters; then use Ansys HFSS software to perform 3D modeling and full-wave simulation to further optimize the relevant parameters.

[0046] Step 3: According to the size of the structure and the characteristics of the material, the corresponding processing flow is adopted for processing, including metal hot pressing bonding, photolithography, laser hollowing, vacuum lamination, air gun blowing and other processes.

[0047] Compared with the traditional dielectric-filled microstrip transmission line, the low-loss microstrip transmission line based on substrate stacking bonding provided in this embodiment has the advantages of low-loss propagation characteristics and low cost, and has the characteristics of easy integration, miniaturization and wide bandwidth.

[0048] The above is only a preferred specific implementation of the present invention, but the design concept of the present invention is not limited to this. Any technician familiar with the technical field who uses this concept to make non-substantial changes to the present invention within the technical scope disclosed by the present invention shall be deemed to infringe the protection scope of the present invention.

Claims

1. A low-loss microstrip transmission line based on substrate stacking bonding, characterized in that: It includes an upload board layer, a hollow transmission layer, a download board layer, a first bonding layer and a second bonding layer; A first metal layer is provided on the lower surface of the upper loading board layer, and a second metal layer is provided on the upper surface of the downloading board layer; the first metal layer, the second metal layer and the hollow area of ​​the hollow transmission layer together constitute a transmission area; electromagnetic waves propagate in the transmission area in the form of a quasi-TEM mode; The upper board layer, the first bonding layer, the hollow transmission layer, the second bonding layer, the second metal layer and the lower board layer are stacked in parallel and bonded in sequence.

2. A low-loss microstrip transmission line based on substrate stacking bonding according to claim 1, characterized in that: A hollow strip-shaped hole is arranged in the middle of the hollow transmission layer, and the hollow strip-shaped hole, the first metal layer and the second metal layer constitute the transmission area.

3. A low-loss microstrip transmission line based on substrate stacking bonding according to claim 1, characterized in that: The first metal layer and the second metal layer are both thin metal layers; the first metal layer has a certain line width, and the first metal layer is attached to the upper carrier layer; The second metal layer covers the entire upper surface of the download board layer; the first metal layer and the second metal layer together form a low-loss microstrip line.

4. A low-loss microstrip transmission line based on substrate stacking bonding according to claim 3, characterized in that: The line width of the first metal layer is set at 66um-67um; the thickness of the hollow transmission layer is set at 30um-30.5um; The width of the hollow area of ​​the hollow transmission layer is set to 2.6 times the width of the first metal line.

5. A low-loss microstrip transmission line based on substrate stacking bonding according to claim 4, characterized in that: The thickness of the first metal layer and the second metal layer is set to 17um or 35um.

6. A low-loss microstrip transmission line based on substrate stacking bonding according to claim 1, characterized in that: The upper board layer and the hollow transmission layer are bonded via the first bonding layer; The hollow transmission layer and the download board layer are bonded via the second bonding layer.

7. A low-loss microstrip transmission line based on substrate stacking bonding according to claim 6, characterized in that: The upper board layer, the hollow transmission layer and the lower board layer are all made of FR4 substrate material.

8. A low-loss microstrip transmission line based on substrate stacking bonding according to claim 7, characterized in that: The thickness of the upper board layer and the lower board layer is set to 160um-200um.

9. A low-loss microstrip transmission line based on substrate stacking bonding according to claim 6, characterized in that: The first bonding layer and the second bonding layer are made of dry film ABF GL102 material.

10. A low-loss microstrip transmission line based on substrate stacking bonding according to claim 9, characterized in that: The thickness of the first bonding layer and the second bonding layer is set to 5um-15um.

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