Device and method for testing out-of-plane dielectric constant based on quasi-optical cavity

Abstract

The invention provides an out-of-plane dielectric constant testing device and method based on a quasi-optical cavity, and belongs to the technical field of electromagnetic parameter testing of microwave and millimeter wave materials. According to the device, a cavity form is innovatively designed, a traditional spherical cavity is replaced by a hemispherical cavity, and the hemispherical cavity is placed on a metal short-circuit plate, so that an electric field on the surface of the metal short-circuit plate is strictly perpendicular to a short-circuit surface, a dielectric substrate to be measured is flatly placed in the center of a quasi-optical cavity, and the thickness direction is the same as the direction of the electric field; therefore, the in-cavity electric field can be ensured to be vertically distributed on the dielectric substrate, and the out-of-plane dielectric constant can be tested based on the quasi-optical-cavity method. According to the testing device, the dielectric substrate can be tested under high frequency, and a solid foundation is laid for development of high-frequency devices.

Description

Technical Field

[0001] The present invention belongs to the technical field of microwave and millimeter wave material electromagnetic parameter testing, and in particular relates to an out-of-plane dielectric constant testing device and method based on a quasi-optical cavity. Background Art

[0002] Driven by technological innovation in the field of electronic manufacturing, dielectric substrates, as the core carrier material of electronic devices, are becoming increasingly important in circuit boards, chip packaging and semiconductor processes. With the popularization of high-frequency devices, the stability of the dielectric properties of dielectric materials has become a key indicator. At present, in order to meet the needs of low-loss transmission, the industry generally adopts a variety of material composite technologies to prepare dielectric substrates. Due to the characteristics of the composite structure, the dielectric constant of such materials exhibits anisotropy, that is, there is a significant difference between the in-plane (horizontal) and out-of-plane (vertical) directions. This characteristic poses new challenges to the characterization of electromagnetic parameters of materials. Accurate measurement of dielectric parameters of anisotropic materials has become a key technical link to ensure the performance of high-frequency electronic devices.

[0003] Most of the dielectric constant test methods are to test the dielectric constant in the horizontal direction, and few methods can test the dielectric properties of the dielectric substrate in the vertical direction. At present, the commonly used test methods for testing the dielectric properties of the dielectric substrate in the vertical direction are mainly the flat plate capacitor method, the whole board test method and the stripline resonator method. IPC Standard (The Institute for Interconnecting and Packaging Electronic Circuits 2215 Sanders Road •Northbrook, IL 60062. IPC-TM-650 TEST METHODS MANUAL-2.5.5.6 Non-Destructive Full Sheet Resonance Test for Permittivity of Clad Laminates[S].) uses the whole board test method to connect the upper and lower metal surfaces of the double-sided copper-clad laminate with the inner and outer conductors of the coaxial connector, and the whole copper-clad laminate is used to form a resonator for testing. The test frequency is generally below 0.5GHz and is often used for product quality monitoring; Zhang Yonghua et al. (Zhang Yonghua, Liu Liguo. Research on the stripline method for testing the complex dielectric constant of high-frequency printed circuit board substrates [J]. Printed Circuit Information, 2018, 26(08): 21-26.) use the stripline resonator method to make the material into a stripline resonator, and measure the resonant frequency and quality factor. To calculate the dielectric constant, this method has high requirements on sample flatness, and due to the large edge effect error, the applicable frequency range is 0.5~20GHz; Zhao Wuyin et al. (Zhao Wuyin, Chen Xinwei, Ma Runbo. Design of a portable parallel plate structure dielectric constant measuring instrument [J]. Instrument Technology and Sensor, 2023, (06): 40-43.) used the flat plate capacitance method to test the dielectric sample, placing the material to be tested between two electrodes to form a capacitor, and calculating the dielectric constant by measuring the capacitance value, but this method has a low test frequency and is usually only used for tests below 1GHz. The aforementioned test method is only used for low-frequency testing, and has high requirements on the structure of the dielectric substrate to be tested. With the emergence of more and more high-frequency scenarios at the application level, it is necessary to expand the out-of-plane dielectric test of the dielectric substrate to high frequencies.

[0004] Due to the structure of the quasi-optical cavity itself, it is determined that it can work at high frequencies. However, the electric field of the current quasi-optical cavity method is distributed according to the Gaussian beam, and most samples are placed in parallel, that is, the electric field and the magnetic field are parallel to the sample, so only horizontal tests can be achieved, and most test systems have the inconvenience of disassembling and assembling samples. CN118624992A discloses an out-of-plane dielectric constant test device and method based on a quasi-optical cavity. Through an innovative sample placement fixture, the electric field in the cavity is strictly perpendicular to the sample by mechanically adjusting the sample position, thereby achieving the test of the out-of-plane dielectric constant of the sample. However, the device is completely based on the method of mechanical limiting, and the requirements for the accuracy of adjusting the position are too high, because the slight difference between the direction of the electric field and the out-of-plane direction will have a great impact on the test.

[0005] Therefore, it is very important to test the dielectric constant of the dielectric substrate in a strict vertical direction at high frequencies and to make the test process simple and easy to operate. Summary of the invention

[0006] In view of the problems existing in the background technology, the purpose of the present invention is to provide an out-of-plane dielectric constant test device and method based on quasi-optical cavity. The device innovatively designs the cavity form, replaces the traditional spherical cavity with a hemispherical cavity, and places the hemispherical cavity on a metal short-circuit plate, thereby constructing an electric field on the surface of the metal short-circuit plate that is strictly perpendicular to the short-circuit surface. At this time, the dielectric substrate to be tested is placed flatly in the center of the quasi-optical cavity, and the thickness direction is the same as the electric field direction, which can ensure that the electric field in the cavity is vertically distributed on the dielectric substrate, thereby realizing the test of the out-of-plane dielectric constant based on the quasi-optical cavity method.

[0007] To achieve the above object, the technical solution of the present invention is as follows:

[0008] An out-of-plane dielectric constant test device based on a quasi-optical cavity comprises a coupling ring feeding unit, a hemispherical cavity and a base;

[0009] The base is a metal flat plate, and a hemispherical cavity is vertically arranged on its upper surface; the hemispherical cavity is composed of two hemispherical mirrors, and the hemispherical mirrors are halves of a conventional spherical mirror, and the inner concave surfaces of the two hemispherical mirrors are opposite; the hemispherical cavity and the base constitute an improved double concave quasi-optical cavity, and the base is a short-circuit surface of the quasi-optical cavity;

[0010] A coupling hole is provided at the center of the spherical surface of the quasi-optical cavity for setting a coupling ring feeding unit; the coupling amount is adjusted by adjusting the depth of the coupling ring in the coupling ring feeding unit entering the coupling hole;

[0011] The medium substrate to be measured is placed on the upper surface of the base, and the center of the medium substrate to be measured coincides with the central axis of the quasi-optical cavity. The medium substrate to be measured and the plane where the coupling ring is located are perpendicular to each other, so that the out-of-plane direction of the medium substrate to be measured is consistent with the direction of the electric field line at the center of the quasi-optical cavity.

[0012] Furthermore, the out-of-plane dielectric constant testing device of the present invention further comprises a sample fixture; the sample fixture is used to make the sample to be tested close to the upper surface of the base and to make the sample to be tested straight.

[0013] Furthermore, the medium substrate to be tested is in the shape of a long strip, and the sample size should meet the use conditions of the perturbation method;

[0014] The conditions for using the perturbation method are: , is the resonant frequency measured after the medium substrate to be tested is placed in the quasi-optical cavity. is the cavity resonance frequency.

[0015] Furthermore, the medium substrate to be tested is a thin sample with a thickness not greater than 1 mm.

[0016] Furthermore, the long side should be parallel to the hemispherical mirror during the lofting.

[0017] Furthermore, the aperture of the hemispherical mirror should be greater than 5 times the diameter of the light spot at the mirror surface to contain almost all electromagnetic wave energy.

[0018] The present invention also provides a testing method based on the above testing device, comprising the following steps:

[0019] Step 1. No dielectric substrate to be tested is placed in the quasi-optical cavity, and then the cavity resonance frequency f0 and quality factor Q0 of the quasi-optical cavity are tested;

[0020] Step 2. Place the dielectric substrate to be tested at the center of the quasi-optical cavity, and then test the resonant frequency f of the quasi-optical cavity at this time. s and quality factor Q s ;

[0021] Step 3. Based on the frequency and quality factor measured in steps 1 and 2, the relative dielectric constant of the dielectric substrate to be measured is obtained by inversion using the perturbation method. .

[0022] Furthermore, the specific process of the perturbation method is:

[0023] The quasi-optical cavity adopts a double-concave quasi-optical cavity, which works in the even mode. The equivalent form of the main vector field inside the cavity is:

[0024] ;

[0025] in, is the electric field, is the magnetic field, is the waist radius of the Gaussian beam in the hemispherical cavity, is the spot radius, is the radial coordinate parameter in the cylindrical coordinate system, is the free space beam, z is the length direction of the quasi-optical cavity in the rectangular coordinate system, is the additional phase shift, R is the wavefront curvature radius, j is the imaginary part, is the dielectric constant of air, is the magnetic permeability of air, is the radial mode number of the Gaussian beam field; , , , , , , ;

[0026] in, is the cavity length of the quasi-optical cavity, is the radius of curvature of the spherical mirror, is the wavelength of electromagnetic waves, is the virtual displacement of the Gaussian beam, is the radius of curvature of the equal phase surface, and a rectangular coordinate system is constructed using x, y, and z.

[0027] x is the direction of the electric field on the surface of the medium substrate to be measured, y is the direction of the long side of the medium substrate to be measured, and z is the direction of the length of the quasi-optical cavity;

[0028] ,

[0029] is the relative dielectric constant of the dielectric substrate to be measured, The resonant frequency is measured by placing the dielectric substrate to be tested into the quasi-optical cavity. is the cavity resonant frequency, is the electric field conjugate form, is the electric field, v is the cavity volume, is the perturbation volume.

[0030] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0031] 1. The device of the present invention innovatively changes the cavity structure of the quasi-optical cavity, from a conventional complete double-spherical cavity to a hemispherical cavity, that is, only retains a hemispherical mirror, and at the same time sets the spherical mirror on the short-circuit surface, so that the electric field lines at the center of the quasi-optical cavity are strictly perpendicular to the short-circuit surface; during the test, the dielectric substrate to be tested is placed on the short-circuit surface, and the thickness direction is parallel to the electric field direction, so that the electric field lines at the center are strictly consistent with the out-of-plane direction of the dielectric substrate to be tested, so that the device of the present invention can easily realize the test of the dielectric constant of the dielectric substrate to be tested in the vertical direction.

[0032] 2. The testing device of the present invention can realize the testing of dielectric substrates at high frequencies, laying a solid foundation for the development of high-frequency devices.

[0033] 3. The sample clamp used in the device of the present invention makes the sample to be tested close to the short road surface of the bottom plate, and the sample to be tested is stretched straight; the lateral size of the sample clamped by the sample clamp is fixed, so that the lateral position of the sample to be tested is limited, and the sample position is always symmetrically centered relative to the cavity, which improves the test accuracy. While ensuring the placement of the sample, it greatly improves the portability of sample equipment and disassembly, and improves the test efficiency to a certain extent. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 Schematic diagram of the three-dimensional structure of the testing device based on the double-concave hemispherical quasi-optical cavity according to Example 1 of the present invention.

[0035] Figure 2 Schematic diagram of the two-dimensional structure of the testing device based on the dual-cavity hemispherical quasi-optical cavity according to Example 1 of the present invention.

[0036] Figure 3 Schematic diagram of the fixture structure in the testing device of Example 1 of the present invention.

[0037] Figure 4 Schematic diagram of the relationship between the electric field vector and the sample position of the present invention.

[0038] Reference numerals: 1 is a coupling ring feeding unit, 2 is a hemispherical mirror, 3 is a sample fixture, 4 is a medium substrate to be tested, and 5 is a base. DETAILED DESCRIPTION

[0039] In order to make the objectives, technical solutions and advantages of the present invention more clear, the present invention is further described in detail below in conjunction with the implementation modes and the accompanying drawings.

[0040] Example 1

[0041] An out-of-plane dielectric constant test device based on a quasi-optical cavity, the three-dimensional structure diagram is shown in Figure 1 As shown, it includes a coupling ring feeding unit 1, a quasi-optical cavity, a base 5 and a sample fixture 3; an xyz space coordinate system is constructed with the cavity length direction of the quasi-optical cavity as the z-axis, the out-of-plane direction of the medium substrate to be tested as the x-axis, and the long side direction of the medium substrate to be tested as the y-axis; a top view of the two-dimensional structure of the test device is shown in Figure 2 As shown, the biconcave hemispherical quasi-optical cavity is composed of two hemispherical mirrors 2 and a short-circuit surface of a base 5;

[0042] The base 5 is a metal flat plate in a "bow tie" shape, and two hemispherical mirrors of the quasi-optical cavity are vertically arranged on its upper surface, and the inner concave surfaces of the two hemispherical mirrors are opposite to each other; the sample clamps 3 are fixedly arranged on both sides of the center of the base 5, and the medium substrate 4 to be tested is fixed by the sample clamps 3; the medium substrate 4 to be tested is placed at the center of the base and is close to the short-circuit surface of the base 5, and the center of the medium substrate to be tested coincides with the central axis of the quasi-optical cavity; the schematic diagram of the clamp structure is shown in FIG. Figure 3As shown, the fixture includes a horizontal seat, a limit seat, two knobs and a clamping head. The limit seat is "U" shaped, and its opening surface is fixedly set on the horizontal seat. The first knob is set on the top of the limit seat. The clamping head is used to adjust the position of the medium substrate to be tested in the x direction so that the medium substrate to be tested is as close to the base as possible; the second knob is set on the side of the horizontal seat, and is used to adjust the position of the medium substrate to be tested in the y direction so that the medium substrate to be tested is straightened. The lateral size of the limit seat is fixed, so that the lateral (z direction) position of the medium substrate to be tested is limited, so that the position of the medium substrate to be tested is always symmetrically centered relative to the cavity, which ensures the placement of the sample while improving the portability of sample equipment and disassembly.

[0043] A coupling hole is provided at the center of the short-circuit surface of the hemispherical cavity for setting a coupling ring feeding unit; the coupling amount is adjusted by adjusting the depth of the coupling ring in the coupling ring feeding unit entering the coupling hole; the base 5 is perpendicular to the plane where the coupling ring is located.

[0044] Figure 4 The figure is a schematic diagram of the relationship between the electric field vector and the sample position of the present invention. As can be seen from the figure, the present invention uses the design of a hemispherical cavity plus a metal base, and utilizes the characteristic that the electric field is strictly perpendicular to the short-circuit surface, so that the electric field lines on the upper surface of the metal base are kept strictly perpendicular to the surface; and because the present invention uses a quasi-optical cavity for testing, and the test of the quasi-optical cavity generally requires that the sample to be tested be placed at the center position of the quasi-optical cavity, that is, the waist position of the Gaussian beam in the quasi-optical cavity, therefore, the sample to be tested of the present invention is placed horizontally on the upper surface of the metal base, and the center of the medium substrate to be tested coincides with the central axis of the quasi-optical cavity, so that the electric field lines at the center are in the same direction as the thickness direction of the medium substrate to be tested, that is, vertically pass through the medium substrate to be tested; this avoids the problem existing in the prior art of mechanically coordinating the position of the sample to be tested to make the electric field parallel to the thickness direction of the medium substrate to be tested to achieve the test outside the surface.

[0045] During conventional quasi-optical cavity testing, it is generally horizontally laid out. At this time, the thickness direction of the dielectric substrate to be tested is parallel to the electric lines of force on the surface of the dielectric substrate to be tested. When testing the dielectric constant in the horizontal direction, the field solution method is generally used to invert and solve the dielectric constant. At this time, the dielectric substrate to be tested is required to be infinite or at least larger than the size of the spherical mirror or the plane mirror, so that the electromagnetic field can act on the dielectric substrate to be tested as much as possible. When the dielectric constant outside the test surface needs to be tested, the electric field needs to be parallel to the thickness direction of the dielectric substrate to be tested. By controlling the size of the sample to be tested, the use conditions of the perturbation method can be met. However, if the size of the dielectric substrate to be tested is too large, it will have a great impact on the test field, making the resonance unstable and not meeting the perturbation conditions during inversion, so the perturbation method cannot be used to invert and obtain the dielectric constant. In addition, the present invention utilizes the characteristic that the electric field is strictly perpendicular to the short-circuit surface, so there are also requirements for the thickness of the sample to be tested, and it can only be used to test thin samples. Therefore, the size design of the dielectric substrate to be tested by the test device of the present invention is different from the requirements of the conventional quasi-optical cavity method.

[0046] The above description is only a specific implementation mode of the present invention. Any feature disclosed in this specification, unless otherwise stated, can be replaced by other alternative features that are equivalent or have similar purposes; all the disclosed features, or all the steps in the methods or processes, except for mutually exclusive features and / or steps, can be combined in any way.

Claims

1. An out-of-plane dielectric constant test device based on a quasi-optical cavity, characterized in that: It includes a coupling ring feeding unit, a hemispherical cavity and a base; The base is a metal flat plate, and a hemispherical cavity is vertically arranged on its upper surface; the hemispherical cavity is composed of two hemispherical mirrors, and the hemispherical mirror is half of a conventional spherical mirror, and the inner concave surfaces of the two hemispherical mirrors are opposite; the hemispherical cavity and the base constitute an improved double concave quasi-optical cavity, and the base is a short-circuit surface of the quasi-optical cavity; A coupling hole is provided at the center of the spherical surface of the quasi-optical cavity for setting a coupling ring feeding unit; the coupling amount is adjusted by adjusting the depth of the coupling ring in the coupling ring feeding unit entering the coupling hole; The medium substrate to be measured is placed on the upper surface of the base, and the center of the medium substrate to be measured coincides with the central axis of the quasi-optical cavity. The medium substrate to be measured and the plane where the coupling ring is located are perpendicular to each other, so that the out-of-plane direction of the medium substrate to be measured is consistent with the direction of the electric field line at the center of the quasi-optical cavity.

2. The out-of-plane dielectric constant testing device according to claim 1, characterized in that: The out-of-plane dielectric constant testing device also includes a sample fixture; the sample fixture is used to make the sample to be tested close to the upper surface of the base and to make the sample to be tested straight.

3. The out-of-plane dielectric constant testing device according to claim 1, characterized in that: The medium substrate to be tested is in the shape of a long strip, and the sample size should meet the use conditions of the perturbation method; The conditions for using the perturbation method are: , is the resonant frequency measured after the medium substrate to be tested is placed in the quasi-optical cavity. is the cavity resonance frequency.

4. The out-of-plane dielectric constant testing device according to claim 1, characterized in that: The thickness of the medium substrate to be tested is not greater than 1 mm.

5. The out-of-plane dielectric constant testing device according to claim 1, characterized in that: When laying out, the long side should be parallel to the hemispherical mirror.

6. The out-of-plane dielectric constant testing device according to claim 1, characterized in that: The aperture of the hemispherical mirror should be greater than 5 times the diameter of the light spot at the mirror surface.

7. A testing method based on the out-of-plane dielectric constant testing device according to any one of claims 1 to 6, characterized in that: The following steps are involved: Step 1. No dielectric substrate to be tested is placed in the quasi-optical cavity, and then the cavity resonance frequency f0 and quality factor Q0 of the quasi-optical cavity are tested; Step 2. Place the dielectric substrate to be tested at the center of the quasi-optical cavity, and then test the resonant frequency f of the quasi-optical cavity at this time. s and quality factor Q s ; Step 3. Based on the frequency and quality factor measured in steps 1 and 2, the relative dielectric constant of the dielectric substrate to be measured is obtained by inversion using the perturbation method. .

8. The testing method according to claim 7, characterized in that: The specific process of the perturbation method is: The quasi-optical cavity adopts a double-concave quasi-optical cavity, which works in the even mode. The equivalent form of the main vector field inside the cavity is: ； in, is the electric field, is the magnetic field, is the waist radius of the Gaussian beam in the hemispherical cavity, is the spot radius, is the radial coordinate parameter in the cylindrical coordinate system, is the free space beam, z is the length direction of the quasi-optical cavity in the coordinate system, is the additional phase shift, R is the wavefront curvature radius, j is the imaginary part, is the dielectric constant of air, is the magnetic permeability of air, is the radial mode number of the Gaussian beam field; ， ， ， ， ， ， ； in, is the cavity length of the quasi-optical cavity, is the radius of curvature of the spherical mirror, is the wavelength of electromagnetic waves, is the virtual displacement of the Gaussian beam, is the radius of curvature of the equal phase surface, and a rectangular coordinate system is constructed using x, y, and z. x is the direction of the electric field on the surface of the medium substrate to be measured, y is the direction of the long side of the medium substrate to be measured, and z is the direction of the length of the quasi-optical cavity; ， is the relative dielectric constant of the dielectric substrate to be measured, The resonant frequency is measured by placing the dielectric substrate to be tested into the quasi-optical cavity. is the cavity resonant frequency, is the electric field conjugate form, is the electric field, v is the cavity volume, is the perturbation volume.

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