An off-plane dielectric constant testing device and method based on a quasi-optical cavity

Abstract

The present invention provides an out-of-plane dielectric constant testing device and method based on a quasi-optical cavity, belonging to the technical field of electromagnetic parameter testing of microwave and millimeter-wave materials. The device innovatively designs the cavity form. By replacing the traditional spherical cavity with a hemispherical cavity and placing the hemispherical cavity on a metal short-circuit plate, the electric field on the surface of the metal short-circuit plate is strictly perpendicular to the short-circuit surface. At this time, the dielectric substrate to be measured is placed flat at the center of the quasi-optical cavity, and the thickness direction is the same as the electric field direction, so as to ensure that the electric field in the cavity is vertically distributed on the dielectric substrate, realizing the testing of the out-of-plane dielectric constant based on the quasi-optical cavity method. 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.

Description

Technical Field

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

[0002] Driven by the technological innovation in the field of electronic manufacturing, as the core carrier material of electronic devices, the importance of dielectric substrates is becoming increasingly prominent in circuit boards, chip packaging, and semiconductor processes. With the popularization and development of high-frequency devices, the stability of the dielectric properties of dielectric materials has become a key indicator. Currently, to meet the requirements of low-loss transmission, the industry generally uses various material composite technologies to prepare dielectric substrates. Due to the characteristics of the composite structure of such materials, their dielectric constants show anisotropy, that is, significant differences exist in the in-plane (horizontal) and out-of-plane (vertical) directions. This characteristic poses new challenges to the characterization of the electromagnetic parameters of materials, and achieving accurate measurement of the dielectric parameters of anisotropic materials has become a key technical link to ensure the performance of high-frequency electronic devices.

[0003] Most of the test methods for dielectric constants are used to measure the dielectric constant in the horizontal direction, and there are few methods to test the dielectric properties in the vertical direction of the dielectric substrate. Currently, the commonly used test methods for the dielectric properties in the vertical direction of the dielectric substrate mainly include the parallel-plate capacitor method, the full-board test method, and the stripline resonator method. The 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].) adopts the full-board test method, connecting the upper and lower metal surfaces of the double-sided copper-clad laminate to the inner and outer conductors of the coaxial connector, and using the whole copper-clad laminate as a resonator for testing. Its test frequency is generally below 0.5 GHz and is commonly used for product quality monitoring; Zhang Yonghua et al. (Zhang Yonghua, Liu Liguo. Research on the Measurement of the Complex Dielectric Constant of High-Frequency Printed Circuit Board Substrates by the Stripline Method[J]. Printed Circuit Information, 2018, 26(08): 21-26.) adopted the stripline resonator method, making the material into a stripline resonator and calculating the dielectric constant by measuring the resonance frequency and quality factor. However, this method has high requirements for the flatness of the sample and has large errors due to edge effects, and the applicable frequency range is 0.5-20 GHz; Zhao Wuyin et al. (Zhao Wuyin, Chen Xinwei, Ma Runbo. Design of a Portable Parallel-Plate Structure Dielectric Constant Measuring Instrument[J]. Instrument Technique and Sensor, 2023, (06): 40-43.) used the parallel-plate capacitor method to test the dielectric sample, placing the material to be measured between two electrodes to form a capacitor and calculating the dielectric constant by measuring the capacitance value. However, this method has a low test frequency and is usually only used for tests below 1 GHz. The aforementioned test methods are only used for low-frequency tests and have high requirements for the structure of the dielectric substrate to be measured. 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 operate at high frequencies. However, currently, the electric field in the quasi-optical cavity follows a Gaussian beam distribution, and most samples are placed in parallel, that is, both the electric field and the magnetic field are parallel to the sample. Therefore, only the horizontal direction can be tested, and it is inconvenient to disassemble and assemble the sample in most test systems. CN118624992A discloses an out-of-plane dielectric constant test device and method based on a quasi-optical cavity. By innovatively designing a sample placement fixture and mechanically adjusting the position of the sample to make the electric field in the cavity strictly perpendicular to the sample, the out-of-plane dielectric constant of the sample can be tested. However, this device completely relies on mechanical limiting methods, and has extremely high requirements for the accuracy of the adjusted position, because even a slight difference between the electric field direction and the out-of-plane direction will have a great impact on the test.

[0005] Therefore, how to achieve the test of the dielectric constant in the strictly vertical direction of the dielectric substrate at high frequencies and make the test process simple and easy to operate is very important. Summary of the Invention

[0006] Aiming at the problems 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 a quasi-optical cavity. This device innovatively designs the cavity form. By replacing the traditional spherical cavity with a hemispherical cavity and placing the hemispherical cavity on a metal short-circuit plate, the electric field on the surface of the metal short-circuit plate is strictly perpendicular to the short-circuit surface. At this time, the dielectric substrate to be tested is placed flat at 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 and realize the test of the out-of-plane dielectric constant based on the quasi-optical cavity method.

[0007] To achieve the above purpose, 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, comprising a coupling loop feeding unit, a hemispherical cavity, and a base;

[0009] The base is a metal flat plate, and the 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 concave surfaces of the two hemispherical mirrors face each other; the hemispherical cavity and the base form an improved double-concave quasi-optical cavity, and the base is the short-circuit surface of the quasi-optical cavity;

[0010] A coupling hole is opened at the center of the spherical surface of the quasi-optical cavity for setting the coupling loop feeding unit; by adjusting the depth of the coupling loop in the coupling hole in the coupling loop feeding unit, the coupling amount can be adjusted;

[0011] The dielectric substrate to be tested is placed on the upper surface of the base, and the center of the dielectric substrate to be tested coincides with the central axis of the quasi-optical cavity. The dielectric substrate to be tested is perpendicular to the plane where the coupling loop is located, so that the out-of-plane direction of the dielectric substrate to be tested 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 includes a sample fixture; the sample fixture is used to make the sample to be tested closely adhere to the upper surface of the base and make the sample to be tested straight.

[0013] Furthermore, the dielectric substrate to be tested is strip-shaped, and the sample size should meet the usage conditions of the perturbation method;

[0014] The usage conditions of the perturbation method are: , is the resonant frequency measured after the dielectric substrate to be tested is placed in the quasi-optical cavity, is the cavity resonant frequency.

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

[0016] Furthermore, when placing the sample, the long side should be parallel to the hemispherical mirror.

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

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

[0019] Step 1. Do not place the dielectric substrate to be tested in the quasi-optical cavity, and then test the cavity resonant frequency f0 and quality factor Q0 of the quasi-optical cavity at this time;

[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 s and quality factor Q s ;

[0021] Step 3. Based on the frequencies and quality factors measured in Step 1 and Step 2, use the perturbation method to inversely obtain the relative dielectric constant .

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

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

[0024] ;

[0025] Among them, 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 a free-space beam, z is the direction of the length of the quasi-optical cavity in the rectangular coordinate system, is the additional phase shift, R is the radius of curvature of the wavefront, j is the imaginary part, is the permittivity of air, is the permeability of air, is the radial mode number of the Gaussian beam field; , , , , , , ;

[0026] Among them, is the length of the quasi-optical cavity, is the radius of curvature of the spherical mirror, is the wavelength of the electromagnetic wave, is the imaginary displacement of the Gaussian beam, is the radius of curvature of the equiphase surface. A rectangular coordinate system is constructed with x, y, and z,

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

[0028] ,

[0029] is the relative permittivity of the substrate of the medium to be measured, is the resonant frequency measured when the substrate of the medium to be measured is placed in the quasi-optical cavity, is the cavity resonant frequency, is the conjugate form of the electric field, is the electric field, v is the cavity volume, is the perturbed volume.

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

[0031] 1. The device of the present invention innovatively changes the structure of the quasi-optical cavity, changing from a conventional complete double-sphere cavity to a hemispherical cavity, that is, only half of the spherical mirror is retained, and at the same time, the spherical mirror is arranged on the short-circuit plane, so that the electric field lines at the center of the quasi-optical cavity are strictly perpendicular to the short-circuit plane; during the test, the substrate of the medium to be measured is placed on the short-circuit plane, 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 substrate of the medium to be measured, thus enabling the device of the present invention to simply realize the measurement of the permittivity in the vertical direction of the substrate of the medium to be measured.

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

[0033] 3. The sample fixture used in the device of the present invention makes the sample to be measured closely adhere to the short circuit surface of the bottom plate, and the sample to be measured is straightened; the transverse dimension of the sample clamped by the sample fixture is fixed, so that the transverse position of the sample to be measured is limited, and the position of the sample is always symmetric and centered relative to the cavity, improving the test accuracy. While ensuring the placement of the sample, the portability of sample equipment and disassembly is greatly improved, and the test efficiency is improved to a certain extent. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 FIG. is a three-dimensional structural schematic diagram of the test device based on the double concave hemispherical quasi-optical cavity in Embodiment 1 of the present invention.

[0035] Figure 2 FIG. is a two-dimensional structural schematic diagram of the test device based on the double cavity hemispherical quasi-optical cavity in Embodiment 1 of the present invention.

[0036] Figure 3 FIG. is a schematic diagram of the fixture structure in the test device of Embodiment 1 of the present invention.

[0037] Figure 4 FIG. is a 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 loop feeding unit, 2 is a hemispherical mirror, 3 is a sample fixture, 4 is a dielectric substrate to be measured, and 5 is a base. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0039] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the embodiments and the drawings.

[0040] Embodiment 1

[0041] A test device for out-of-plane dielectric constant based on a quasi-optical cavity, the three-dimensional structural schematic diagram of which is as Figure 1 shown, including a coupling loop feeding unit 1, a quasi-optical cavity, a base 5 and a sample fixture 3; taking the cavity length direction of the quasi-optical cavity as the z-axis, the out-of-plane direction of the dielectric substrate to be measured as the x-axis, and the long side direction of the dielectric substrate to be measured as the y-axis to construct an xyz space coordinate system; the top view two-dimensional structural schematic diagram of the test device is as Figure 2 shown, the double concave hemispherical quasi-optical cavity is composed of two hemispherical mirrors 2 and the short circuit surface of the base 5;

[0042] The base 5 is a metal flat plate in a "bow tie" shape, on the upper surface of which two hemispherical mirrors of the quasi-optical cavity are vertically arranged, and the concave surfaces of the two hemispherical mirrors face each other; on both sides of the center of the base 5, a sample fixture 3 is fixedly arranged, and the dielectric substrate 4 to be measured is fixed by the sample fixture 3; the dielectric substrate 4 to be measured is placed at the center of the base and closely adheres to the short circuit surface of the base 5, and the center of the dielectric substrate to be measured coincides with the central axis of the quasi-optical cavity; the schematic diagram of the fixture structure is as 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 the test of a conventional quasi-optical cavity, generally, it is laid out horizontally. At this time, the thickness direction of the dielectric substrate to be measured is parallel to the electric field lines on the surface of the dielectric substrate to be measured, and the dielectric constant in the horizontal direction is measured. Generally, the field solution method is used for inversion to solve the dielectric constant. At this time, it is required that the dielectric substrate to be measured should be infinitely large 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 measured as much as possible. When the out-of-plane dielectric constant needs to be measured, the electric field needs to be parallel to the thickness direction of the dielectric substrate to be measured. By controlling the size of the sample to be measured, the use conditions of the perturbation method can be satisfied. However, if the size of the dielectric substrate to be measured is too large, it will have too much influence on the test field, resulting in unstable resonance and not meeting the perturbation conditions during inversion, so the perturbation method cannot be used for inversion to obtain the dielectric constant. In addition, the present invention utilizes the characteristic that the electric field is strictly perpendicular to the short-circuit plane, so there are also requirements for the thickness of the sample to be measured and it can only be used for testing thin samples. Therefore, the size design of the dielectric substrate to be measured by the test device of the present invention is different from the requirements of the conventional quasi-optical cavity method.

[0046] As described above, the above is only the specific implementation manner of the present invention. Any feature disclosed in this specification, unless specifically described, can be replaced by other equivalent or similar-purpose alternative features; all the features disclosed, or all the steps in any method or process, 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.

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