Substrate dielectric constant testing device based on a cylindrical cavity with a centrally inserted metal disc.

Abstract

The purpose of this invention is to provide a substrate dielectric constant testing device based on a cylindrical cavity with a centrally inserted metal disc, belonging to the field of electromagnetic parameter testing technology for microwave and millimeter-wave materials. This device is designed with a centrally divided cylindrical resonant cavity. The substrate to be tested, the metal disc, and the substrate to be tested are sequentially placed within the divided area. The electric field within the cavity is vertically distributed on the substrate, thereby enabling the testing of the dielectric constant of the substrate in the vertical direction.

Description

Technical Field

[0001] This invention belongs to the field of electromagnetic parameter testing technology for microwave and millimeter-wave materials, specifically relating to a substrate dielectric constant testing device based on a cylindrical cavity with a centrally inserted metal disc. Background Technology

[0002] With the continuous development of printed circuit boards (PCBs), dielectric substrates have also evolved. As supporting materials for circuit components, dielectric substrates are widely used in PCBs, chips, and semiconductors. As device operating frequencies increase, dielectric substrates require more stable performance. Therefore, many low-loss dielectric substrates are currently composed of composite materials. Due to the combination of materials with different properties, the dielectric constant of the substrate is anisotropic, meaning the dielectric constant differs in the horizontal and vertical directions. Currently, most dielectric constant testing methods focus on the horizontal direction, with few methods capable of testing the vertical dielectric properties at high frequencies. Therefore, testing the vertical dielectric properties of the substrate to obtain the vertical dielectric constant is crucial for accurately determining the dielectric constant of anisotropic dielectric substrates.

[0003] Currently, the commonly used testing methods for the dielectric properties of dielectric substrates in the vertical direction are mainly the planar capacitance method, the whole-board testing method, and the stripline resonator method. Reference [1] uses the planar capacitance method to test dielectric samples, placing the material to be tested 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 IPC standard [2] uses the whole-board testing method, which connects the upper and lower metal surfaces of the double-sided copper-clad board to the inner and outer conductors of the coaxial connector, and uses the whole copper-clad board to form a resonator for testing. Its test frequency is generally below 0.5 GHz and is commonly used for product quality monitoring. Reference [3] uses the stripline resonator method, which makes the material into a stripline resonator and calculates the dielectric constant by measuring the resonant frequency and quality factor. However, this method has high requirements for sample flatness and large errors due to edge effects, and the applicable frequency range is 0.5 to 20 GHz.

[0004] The aforementioned testing methods are typically only used for low-frequency testing and require a high degree of structural integrity of the substrate under test. Therefore, it is urgent to develop a method for testing the dielectric constant of a substrate in the vertical direction at high frequencies.

[0005] [1] Zhao Wuyin, Chen Xinwei, Ma Runbo. Design of portable parallel plate structure dielectric constant measuring instrument [J]. Instrumentation Technology and Sensors, 2023, (06): 40-43.

[0006] [2]The Institute for Interconnecting and Packaging Electronic Circuits 2215Sanders Road·Northbrook, IL 60062.IPC-TM-650TEST METHODS MANUAL-2.5.5.6Non-Destructive Full Sheet Resonance Test for Permittivity of CladLaminates[S].

[0007] [3] Zhang Yonghua, Liu Liguo. Study on the complex permittivity of high frequency printed circuit board substrate by stripline method [J]. Printed Circuit Information, 2018, 26(08):21-26. Summary of the Invention

[0008] To address the problems existing in the background technology, the present invention aims to provide a substrate dielectric constant testing device based on a cylindrical cavity with a centrally inserted metal disc. This device is designed with a centrally divided cylindrical resonant cavity. The substrate to be tested, the metal disc, and the substrate to be tested are sequentially placed within the divided area. The electric field within the cavity is vertically distributed on the substrate, thereby enabling the testing of the dielectric constant of the substrate in the vertical direction.

[0009] To achieve the above objectives, the technical solution of the present invention is as follows:

[0010] A substrate dielectric constant testing device based on a cylindrical cavity with a centrally inserted metal disc includes a coaxial feeding structure 1, a cylindrical resonant cavity 2 divided in the middle, a substrate of dielectric material under test 3, a metal disc 4, a microwave cable 5, a vector network analyzer 6, and a flange 7.

[0011] The cylindrical resonant cavity 2, which is divided in the middle, consists of a first semi-cylindrical cavity and a second semi-cylindrical cavity. The dielectric substrate to be tested includes two identical first dielectric substrates and second dielectric substrates. The cavity structure from top to bottom is as follows: first semi-cylindrical cavity, first dielectric substrate, metal disc, second dielectric substrate, and second semi-cylindrical cavity. An opening is made at the center of the short surface of the two semi-cylindrical cavities to provide a coaxial feeding structure. The metal disc, the cylindrical resonant cavity divided in the middle, and the feeding structure are coaxial in the vertical direction. A flange 7 is provided on the open surface of the cylindrical resonant cavity for fixing and connecting the cavity structure.

[0012] Furthermore, the diameter of the metal disc should be larger than the cavity diameter of the cylindrical resonant cavity.

[0013] Furthermore, the dielectric substrate has a regular or irregular shape; the regular shape is specifically a circle, rectangle, etc., and the shortest distance between any two sides of the dielectric substrate should be greater than 1.3 times the diameter of the metal disc to prevent leakage of the electric field inside the cavity.

[0014] Furthermore, the substrate dielectric constant testing device also includes a moving unit, which is used to move the first semi-cylindrical cavity up and down to facilitate the replacement of the substrate to be tested.

[0015] Furthermore, the thickness of the dielectric substrate and the disk determines the highest frequency of the test. The greater the height of the cylindrical cavity, the higher the Q value, and the higher the accuracy of the resonant frequency and quality factor test. To test the dielectric constant in the vertical direction, it is necessary to ensure that the electric field is perpendicular to the dielectric substrate. Therefore, the height of the cylindrical cavity must be limited so that no extraneous modes can appear in the cylindrical cavity.

[0016] Furthermore, the operating frequency of the substrate dielectric constant testing device is: Where c0 is the speed of light in vacuum, μ and ε are the dielectric constant and magnetic permeability of the substrate to be tested, and d is the gap between the two flange faces.

[0017] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0018] 1. This invention alters the electric field distribution within a cylindrical cavity divided in the middle by inserting a metal disc, making the electric field within the dielectric substrate perpendicular to both the substrate and the metal disc. This allows for the testing of the dielectric constant of the substrate in the vertical direction. Furthermore, the testing device of this invention exhibits high sensitivity and operates at frequencies up to 110 GHz, enabling testing of dielectric substrates at high frequencies and laying a solid foundation for the development of high-frequency devices.

[0019] 2. The device of the present invention does not require a specific shape for the dielectric substrate during use; it can adopt circular, rectangular, or other structures. During testing, it is necessary to ensure that the metal disc, cylindrical resonant cavity, and feeding structure are coaxial, thereby ensuring that the electric field within the dielectric substrate is vertically distributed. This allows the testing device to test dielectric substrates with different structures. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the substrate dielectric constant testing device of the present invention.

[0021] Figure 2 The figure shows the simulation results of Embodiment 1 of the present invention.

[0022] In the figure, 1 is a coaxial coupling device, 2 is a cylindrical resonant cavity, 3 is the substrate of the dielectric material under test, 4 is a metal disc, 5 is a cable, 6 is a vector network analyzer, and 7 is a flange. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings.

[0024] A substrate dielectric constant testing device based on a cylindrical cavity with a centrally inserted metal disc is shown in the schematic diagram below. Figure 1 As shown, it includes a coaxial feed structure 1, a cylindrical resonant cavity 2 with a middle section, a substrate of dielectric material under test 3, a metal disc 4, a microwave cable 5, a vector network analyzer 6, and a flange 7.

[0025] The cylindrical resonant cavity 2, which is divided in the middle, is composed of a first semi-cylindrical cavity and a second semi-cylindrical cavity. The dielectric substrate includes two identical first dielectric substrates and second dielectric substrates. The cavity structure from top to bottom is as follows: first semi-cylindrical cavity, first dielectric substrate, metal disc 4, second dielectric substrate and second semi-cylindrical cavity. An opening is made at the center of the short surface of the two semi-cylindrical cavities to provide a coaxial feeding structure. The metal disc, the cylindrical resonant cavity divided in the middle, and the feeding structure are coaxial in the vertical direction. A flange 7 is provided on the short surface of the cylindrical resonant cavity for fixing and connecting the cavity structure.

[0026] Example 1

[0027] Based on the above dielectric constant testing device, wave ports were set at both ends of the coaxial feed structure for simulation.

[0028] The simulated cavity structure, from top to bottom, consists of: coaxial feed, first semi-cylindrical cavity, first dielectric substrate, metal disc, second dielectric substrate, second semi-cylindrical cavity, and coaxial feed. The coaxial feed structure is positioned at the center of the short path between the two semi-cylindrical cavities; the metal disc, the intermediately divided cylindrical resonant cavity, and the feed structure are coaxial in the vertical direction.

[0029] The simulation results of this embodiment are as follows: Figure 2 As shown, there are multiple resonance peaks with good resonance effects in the 5GHz-120GHz frequency band. The complex permittivity of the substrate under test can be obtained by the frequency and quality factor of each resonance peak.

[0030] The above description is merely a specific embodiment of the present invention. Any feature disclosed in this specification may be replaced by other equivalent or similar features unless otherwise specified. All disclosed features, or steps in all methods or processes, may be combined in any way except for mutually exclusive features and / or steps.

Claims

1. A substrate dielectric constant testing device based on a cylindrical cavity with a centrally inserted metal disc, characterized in that, It includes a coaxial feed structure, a cylindrical resonant cavity with a central segment, a dielectric substrate under test, a metal disc, a microwave cable, a vector network analyzer, and a flange; The cylindrical resonant cavity with the middle division consists of a first semi-cylindrical cavity and a second semi-cylindrical cavity, and the dielectric substrate under test includes two identical first dielectric substrates and second dielectric substrates. The cavity structure, from top to bottom, consists of: a first semi-cylindrical cavity, a first dielectric substrate, a metal disc, a second dielectric substrate, and a second semi-cylindrical cavity; An opening is made at the center of the short surface of each of the two semi-cylindrical cavities to house a coaxial power supply structure; the metal disc, the cylindrical resonant cavity divided in the middle, and the power supply structure are coaxial in the vertical direction; a flange is installed on the opening surface of the cylindrical resonant cavity to fix and connect the cavity structure.

2. The substrate dielectric constant testing device as described in claim 1, characterized in that, The diameter of the metal disc should be larger than the cavity diameter of the cylindrical resonant cavity.

3. The substrate dielectric constant testing device as described in claim 1, characterized in that, The dielectric substrate may be regular or irregular in shape; the shortest distance between any two sides of the dielectric substrate should be greater than 1.3 times the diameter of the metal disc.

4. The substrate dielectric constant testing device as described in claim 3, characterized in that, The specific regular shape is either a circle or a rectangle.

5. The substrate dielectric constant testing device as described in claim 1, characterized in that, The thickness of the dielectric substrate and the disk determines the highest frequency that can be tested.

6. The substrate dielectric constant testing apparatus as described in claim 1, characterized in that, The greater the height of the cylindrical cavity, the higher the Q value, and the higher the accuracy of the resonant frequency and quality factor test; however, if the height is too high, noxious modes will appear in the cylindrical cavity.

7. The substrate dielectric constant testing apparatus as described in claim 1, characterized in that, The operating frequency of the substrate dielectric constant testing device is f. Where c0 is the speed of light in vacuum, μ and ε are the dielectric constant and magnetic permeability of the substrate to be tested, and d is the gap between the two flange faces.

8. The substrate dielectric constant testing apparatus according to any one of claims 1-7, characterized in that, The substrate dielectric constant testing device also includes a moving unit, which is used to move the first semi-cylindrical cavity up and down to facilitate the replacement of the substrate to be tested.

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