Insulation and voltage resistance testing method suitable for integrally-formed inductor or magnetic powder core

Abstract

The invention relates to the technical field of electronic component testing, and discloses an insulation and voltage resistance testing method suitable for an integrally-formed inductor or a magnetic powder core, which comprises the following steps: (1) connecting a high-voltage output end of an insulation and voltage resistance tester with a high-voltage electroprobe, electrically connecting a high-voltage input end with a to-be-tested sample, setting test parameters of the insulation and voltage resistance tester, comprising the following steps: setting a leakage current threshold value between 0.1 mA and 1mA; (2) applying voltage to the to-be-tested sample, wherein the high-voltage electroprobe is in close contact with the surface of the to-be-tested sample in a point type contact mode; and (3) carrying out statistical analysis on the collected breakdown voltage data by adopting a mathematical distribution statistical method, and calculating to obtain a fitting insulation voltage resistance value. According to the method, the test efficiency is effectively improved, the accuracy and credibility of a test result are enhanced, the test cost is reduced, and the magnetic performance of a tested product is prevented from being remarkably reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of electronic component testing, and in particular to an insulation withstand voltage test method applicable to an integrally formed inductor. The test method aims to accurately test the insulation withstand voltage performance of the integrally formed inductor through a specific test process, parameter setting and statistical method, so as to accurately evaluate the reliability and safety of electronic components in practical applications. Background Art

[0002] With the rapid development of electronic technology, the performance requirements for electronic components are getting higher and higher. Especially in the fields of mobile communications, automotive electronics, computers and consumer electronics, more stringent requirements are placed on the size, efficiency and reliability of inductors. One-piece molded inductors refer to inductors that use powder metallurgy technology to integrate magnetic powder cores and wire coils. Because of their high density and good heat and shock resistance, they can provide high current carrying capacity and good frequency characteristics, and have become an indispensable component in the above fields.

[0003] As the core electromagnetic component in electronic devices, the insulation performance and voltage resistance level of the one-piece molded inductor are crucial to ensure the stability of the entire system and extend its service life. During the SMD packaging and reflow soldering process, the one-piece molded inductor will be affected by thermal stress and mechanical stress, which may cause the powder insulation coating to fall off or change its physical and chemical properties, thereby reducing its insulation performance. In addition, in actual applications, the one-piece molded inductor needs to frequently withstand the impact of high voltage and ripple circuits, resulting in local internal heating and uneven distribution of electric field strength, which also poses a challenge to the breakdown resistance of the one-piece molded inductor.

[0004] At present, in the field of one-piece molded inductor testing, there is no unified insulation withstand voltage test standard. Usually, based on the breakdown resistance requirements of one-piece molded inductors, a method of rapid withstand voltage screening is adopted, that is, a specified high voltage is directly applied to both ends of the sample through block electrodes. Although this method is easy to operate, it cannot fully evaluate the insulation performance of the material under variable conditions such as voltage amplitude, frequency, and holding time. In addition, the magnetic properties of the sample are significantly attenuated after the experiment, and it cannot meet the subsequent use requirements. In recent years, with the frequent occurrence of inductor insulation failure events, researchers have continuously improved the test method to achieve a better match between the test conditions and the actual working conditions. In the field of inductor withstand voltage testing, patent CN 110658426 A shortens the inductor leads, detects the insulation resistance change to confirm the withstand voltage failure mode, and uses the inflection point of the volt-ampere characteristic curve as the insulation withstand voltage value, thereby effectively simplifying the test process. However, this method requires the disassembly of the inductor and has certain requirements on the operator's skills. At the same time, due to the rapid change of the breakdown current, it is difficult to accurately reflect the withstand voltage strength of the inductor. Patent CN 110007199 B characterizes the voltage tolerance index of the sample by designing the insulation damage curve of the solid material, which significantly improves the accuracy of the test results. However, the mathematical theory used is relatively complex and requires specific equipment and software, which is not conducive to promotion and efficient application. In addition, Patent CN 116819246A proposes to use the Weibull function to test the insulation life of the material under constant voltage. However, this test method involves a complex withstand voltage evaluation mechanism and is only applicable to the long-term low-voltage tolerance of the sample. It cannot judge the situation where the inductor encounters a voltage pulse peak or local electric field enrichment under actual working conditions. It can be seen that the existing test methods have their own advantages and disadvantages, and cannot meet the comprehensive evaluation of the insulation withstand voltage performance of the inductor and the standardized test requirements that adapt to actual working conditions.

[0005] Electrical breakdown is a complex phenomenon caused by the combined action of multiple factors. This phenomenon involves internal factors such as Joule heat and impact ionization, as well as external factors such as processing defects, material flaws and micropores. Under specific conditions and environments, these factors synergistically promote the diffusion of charges, causing changes in the dielectric properties of the material, and ultimately leading to irreversible damage to certain physical properties of the material. Therefore, in order to accurately evaluate the voltage resistance of the material, a large amount of breakdown test data must be statistically analyzed to ensure the reliability and accuracy of the test results. Among them, there are two key issues worthy of attention: one is how to efficiently obtain a large amount of breakdown data; the other is how to reduce material waste while ensuring the acquisition of large-scale breakdown data, that is, to avoid as much as possible the substantial attenuation of the magnetic properties of the inductor due to the insulation withstand voltage test, so that it can still meet the subsequent use requirements.

[0006] In view of the limitations of the prior art, the present invention proposes an insulation withstand voltage test method suitable for one-piece molded inductors. This method uses a self-designed test fixture and a precisely controlled test process to ensure that the insulation withstand voltage performance of the one-piece molded inductor can be accurately and efficiently tested without damaging the magnetic properties of the sample or minimizing the damage. Specifically, this method uses a point-type local contact method to gradually increase the voltage, and performs an insulation breakdown test on the one-piece molded inductor based on an adjustable test mode, parameter setting, and loading voltage time. At the same time, combined with Weibull statistical analysis, the test process is optimized and key parameters that can effectively reflect the breakdown characteristics are obtained. This not only improves the accuracy and efficiency of the test, but also ensures the reliability of the test results, provides technical support for the manufacture and quality control of electronic components, and is conducive to improving the overall performance and reliability of electronic systems. Summary of the invention

[0007] The main purpose of the present invention is to solve the shortcomings of the prior art insulation withstand voltage test method of an integrally molded inductor and to provide an insulation withstand voltage test method of an integrally molded inductor that can improve the test efficiency and the accuracy of the test results.

[0008] The purpose of the present invention is achieved through the following technical solutions:

[0009] A method for dielectric withstand voltage testing of an integrally formed inductor or a magnetic powder core comprises the following steps:

[0010] (1) Connect the high voltage output terminal of the insulation withstand voltage tester to the high voltage pen, and electrically connect the high voltage input terminal to the sample to be tested, and set the test parameters of the insulation withstand voltage tester, including setting the leakage current threshold between 0.1 mA and 1 mA, and selecting the alternating current (AC) or direct current (DC) test mode;

[0011] (2) applying voltage to the sample to be tested, the high-voltage electric pen is in close contact with the surface of the sample to be tested in point contact mode, selecting multiple non-adjacent points of the same sample to be tested for testing, and collecting the breakdown voltage data of each point; wherein, multiple samples are randomly selected from each batch of inductors or magnetic powder cores for insulation withstand voltage test;

[0012] (3) The collected breakdown voltage data are statistically analyzed using mathematical distribution statistics methods to calculate the fitted insulation withstand voltage value.

[0013] Preferably, the mathematical distribution statistics method is a two-parameter Weibull distribution statistics, the number of data collected in the same batch is between 10 and 50, and the shape parameter β and scale parameter V are calculated. I , with V IThe insulation withstand voltage value is used as the evaluation value of the sample's withstand voltage strength, and the shape parameter β is used to evaluate the uniformity of the sample. The larger the β value, the more uniform the sample composition is, and the higher the reliability of the insulation withstand voltage fitted by the measured results.

[0014] Wherein, the formula for calculating the Weibull parameter is:

[0015] ln[-ln(1-P b )]=β(lnV b -lnV I ) (1)

[0016]

[0017] In the formula, β represents the shape parameter, V I Indicates the scale parameter, namely, insulation withstand voltage, P b is the statistical probability of breakdown.

[0018] Preferably, in the point contact test mode, the spacing between the selected contact points of the same sample is greater than 2 mm. If, during breakdown, the insulation withstand voltage tester displays the breakdown form as "Short Fail", the data cannot be included in the mathematical distribution statistics.

[0019] Preferably, setting the test parameters of the insulation withstand voltage tester also includes selecting an alternating current (AC) test mode.

[0020] Preferably, the voltage applied to the sample to be tested is to first apply a starting voltage, and then gradually increase the voltage according to a preset step voltage, and each voltage loading is tested in a cycle of boosting-maintaining-reducing voltage; when the surface leakage current of the sample to be tested exceeds the preset leakage current threshold, the insulation withstand voltage tester displays "High fail" and records the breakdown voltage and the actual leakage current at this time.

[0021] Preferably, the cycle of pressure increase-pressure maintenance-pressure reduction is 0.5 seconds for pressure increase, 4.0 to 60.0 seconds for pressure maintenance, and 0.5 seconds for pressure reduction.

[0022] Preferably, the output end of the insulation withstand voltage tester is connected to a test fixture, and the sample to be tested is placed on a conductive copper bar of the test fixture for testing.

[0023] Preferably, the test fixture comprises insulating bakelite, two conductive copper bars for clamping the sample to be tested, a high-voltage input end and a high-voltage output end electrically connected to the two conductive copper bars, and the conductive copper bars are fixed to the insulating bakelite by screws; the output end of the insulation withstand voltage tester is connected to the high-voltage input end of the test fixture.

[0024] The present invention is based on an insulation withstand voltage tester, and a test fixture is designed for matching application. The test fixture allows the copper bar thereon to be adjusted through threads to achieve surface contact or point contact with the sample to be tested. In the point contact mode, the relevant parameters of the insulation withstand voltage tester can be set, the voltage is applied, and then the voltage is increased step by step until the surface leakage current of the inductor sample monitored by the insulation withstand voltage tester exceeds the set threshold value, at which time it is determined that the sample has a high-voltage breakdown. The breakdown voltage data of multiple samples of the same batch are analyzed using a mathematical distribution statistical method, and the calculated value is used as the insulation withstand voltage of the batch of one-piece molded inductors.

[0025] The insulation withstand voltage tester used in the test can be selected from the TH9310, TH2683 and other series models produced by Changzhou Tonghui Electronics Co., Ltd. to ensure the accuracy and consistency of the test.

[0026] When conducting insulation withstand voltage tests, the fixture can realize two contact modes between the applied voltage and the sample to be tested: one is the surface contact test mode clamped by copper bars, in which the input and output cables are connected to two copper bars respectively; the other is the point contact test mode with high-voltage pen input and output from the copper bars. Through these two modes, the breakdown statistics of the sample to be tested under different contact modes can be obtained respectively.

[0027] Preferably, the present invention uses a high-voltage electric pen to perform insulation breakdown test of point contact, which is easier to operate. The test fixture can hold 4 to 7 samples for testing at the same time, which effectively saves sample change time and greatly improves test efficiency. During the test, samples of the same batch of one-piece molded inductors are randomly selected, voltage is applied, and a high-voltage test pen is used to randomly contact the surface of the sample at a lower voltage, with the position where the maximum leakage current value appears as the first point selected for the test (breakdown weak point). The voltage is increased step by step at this point until breakdown is reached, and the insulation withstand voltage tester displays "Highfail", indicating that the sample has broken down at this point. Thereafter, a second test point is selected on the sample, and the spacing between the test points of each sample should be greater than 2mm. More specifically, if a breakdown occurs during the test, the instrument displays "Shortfail", indicating that the breakdown path partially overlaps with the breakdown path, then the breakdown data of this point cannot be included in the mathematical statistics, and a new test point needs to be selected. The selection principle of the breakdown point of the sample in point contact can be referred to. Figure 4 . Usually, 3 to 5 different test points are selected for each sample for testing. By determining the number of samples in the same batch for insulation breakdown testing, the total number of data points collected in the same batch can be controlled between 10 and 50, thereby ensuring the accuracy and reliability of the test results.

[0028] The beneficial effects of the present invention are that, through the testing method of the present invention, the insulation withstand voltage of the one-piece molded inductor can be accurately tested without damaging it; the parameter setting defined in the present invention is adopted to optimize the distribution characteristics of the sample breakdown data, which can better reflect the insulation characteristics of the batch of one-piece molded inductors or magnetic powder cores; mathematical statistical methods are used to analyze the test data, thereby improving the accuracy and reliability of the test results; and a special test fixture and point contact test mode are adopted, so that the test process is simple and efficient, which reduces potential damage to the product, reduces the test cost, and at the same time improves the test efficiency and the accuracy of data processing. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for describing the embodiments are briefly introduced below.

[0030] Figure 1 This is a flow chart of the insulation withstand voltage test of the one-piece molded inductor of the present invention.

[0031] Figure 2 Schematic diagram of the structure of the test fixture of the present invention.

[0032] Figure 3 This is a sample placement diagram of the test fixture of the present invention when performing insulation withstand voltage tests in two contact modes: surface type (left figure) and point type (right figure).

[0033] Figure 4 This is a schematic diagram of selecting test points for the test sample when using the point contact test mode.

[0034] Figure 5 The Weibull distribution statistics of the breakdown voltage of the FeSiCr one-piece molded inductor using the point contact test mode.

[0035] Figure 6 The insulation withstand voltage and position parameter V obtained when the FeSiCr one-piece molded inductor is subjected to insulation withstand voltage test under different leakage current thresholds and AC / DC test modes I , the relationship between leakage current.

[0036] In the figure: 1. Insulating bakelite; 2. Screws; 3. Conductive copper strip; 4. Limiting slide groove; 5. High-voltage input port; 6. High-voltage output port; 7. Insulating base. DETAILED DESCRIPTION

[0037] The present invention is further described in detail below in conjunction with specific implementations and with reference to the accompanying drawings. It should be noted that the following description is only exemplary and is not intended to limit the scope of the present invention and its application.

[0038] In order to more accurately test the insulation withstand voltage of the integrated molded inductor, refer to the attached Figure 1 The present invention provides an insulation withstand voltage test method applicable to an integrally formed inductor, comprising the following steps:

[0039] S1. According to the test requirements, accurately set the test parameters of the insulation withstand voltage tester. This includes selecting the AC or DC test mode, and setting a reasonable leakage current threshold range (recommended 0.1mA to 1mA) to balance the sensitivity of the test and the potential damage to the sample. In AC mode, the AC frequency must also be set to ensure that the test conditions meet the actual working environment requirements.

[0040] S2. Perform insulation withstand voltage test using point contact method. First, clean the copper strip on the test fixture with alcohol to remove any impurities that may affect the test results. After cleaning, wait for the copper strip to dry completely to ensure good electrical contact. Then, connect the high-voltage output end of the insulation withstand voltage tester through a high-voltage electric pen, and connect the input end to the special test fixture described in the present invention.

[0041] S3. When conducting the insulation withstand voltage test, first use an ear-cleaning ball to remove the attachments on the surface of the one-piece molded inductor sample to be tested, and then place the sample on the copper bar of the test fixture. Next, ensure that the high-voltage pen is in close contact with the sample to be tested. After the test starts, apply the starting voltage and gradually increase the voltage according to the preset step voltage scheme. This test follows the International Electrotechnical Commission standard IEC 60243-1:2013 or the Chinese national standard GB / T 1408.1-2016. The specific operation is to increase the voltage for 0.5 seconds, maintain the voltage for 4 to 60 seconds, and reduce the voltage for 0.5 seconds under each preset high voltage load. When the leakage current on the sample surface is detected to exceed the preset leakage current threshold, the instrument will alarm and display "Highfail", indicating that the sample has broken down. At this time, record the breakdown voltage value.

[0042] S4. In order to improve the accuracy of the test results, according to the method described in the invention content, 4 samples were selected from the same batch of one-piece molded inductors, and 3 to 5 points were selected for breakdown test for each sample. After collecting all the measured breakdown voltage data, the two-parameter Weibull distribution function was used for statistical analysis. The shape parameter β and scale parameter V were calculated by formula (1) and (2): I , with V I As the insulation withstand voltage of this batch of one-piece molded inductors.

[0043] In a series of embodiments of the present invention, different insulation treatment methods are used to treat soft magnetic alloy powders and then an integrally formed inductor is prepared, thereby demonstrating the effectiveness and accuracy of the method. The following is a detailed description of these embodiments:

[0044] Example 1: An integrally formed inductor is manufactured by insulating and coating with a blended organic resin.

[0045] Example 2: An integrally formed inductor is manufactured by using a blended organic resin composite phosphoric acid passivation process for composite insulation coating.

[0046] Example 3: An integrally formed inductor is manufactured by using a blended organic resin composite SiO2 insulation coating process.

[0047] Wherein, the alloy magnetic powder is FeSiCr magnetic powder, with an atomic percentage of 4.5-5.5at.% Si, 5-6at.% Cr, and the balance is Fe; the medium particle size D50 of the FeSiCr magnetic powder is 10.05μm. Purchased from Antai Special Powder Co., Ltd. The blended organic resin coating and phosphoric acid passivation process described in the embodiment is derived from the inventor's published patent CN202410153954.X, and the SiO2 coating method is derived from the inventor's paper work FeSiCr-Based Soft Magnetic Compositeswith SiO2 Insulation Coating Prepared Using the Elemental Silicon PowderHydrolysis Method (DOI: 10.3390 / met13081444). The one-piece inductor molding process is 600MPa pressure holding for 5.5s. The dimensions of the one-piece molded inductor are: length*width*height=6.7mm*6.7mm*2.8mm, and the coil specifications are: 0.4mm×2.8mm×7.5 (conductor diameter×center column diameter×number of turns). The one-piece molded inductor is subjected to a heat treatment process of 180°C for 2 hours after molding.

[0048] All samples were tested in AC mode, the leakage current threshold was set to 1mA, and 3 to 5 test points were selected for each sample for point contact insulation withstand voltage test.

[0049] Figure 5 The Weibull distribution statistics of the breakdown voltage of each embodiment are shown, which intuitively reflects the influence of different insulation treatments on the insulation withstand voltage performance. Through Weibull distribution fitting, the scale parameter V of each embodiment can be calculated by formulas (1) and (2): I and shape parameter β to evaluate the insulation withstand voltage level and the concentration of breakdown voltage distribution.

[0050] Example 3 exhibits the highest insulation withstand voltage, reaching 143V, showing its superior insulation performance. This is followed by Example 2, with an insulation withstand voltage of 135V, while the insulation withstand voltage of Example 1 is 130V. This result shows that different inorganic coating preparation methods have a significant effect on the insulation withstand voltage of the obtained one-piece molded inductor. The results of the shape parameter β also reflect the degree of concentration of the breakdown voltage distribution of each embodiment. The β value of Example 3 is 17, indicating that its breakdown voltage distribution is very concentrated and shows good uniformity. The β value of Example 2 is 13, while that of Example 1 is 12, indicating that their insulation performance and material uniformity are relatively weak.

[0051] According to the testing method adopted by the present invention, the voltage withstand capability of the one-piece molded inductors of the same batch and the consistency of the insulation performance of the samples under the action of voltage can be intuitively understood.

[0052] In addition, due to the lack of unified standards for the parameters set for the insulation withstand voltage test of one-piece molded inductors, we conducted comprehensive tests on the same batch of samples, covering both AC and DC modes, and conducted breakdown tests for different leakage current thresholds (from 0.1mA to 3mA). The test data was fitted with Weibull distribution to evaluate the relationship between insulation withstand voltage and leakage current threshold, such as Figure 6 shown.

[0053] The results show that the insulation withstand voltage measured in DC mode is generally higher than that in AC mode. As the leakage current threshold increases, the insulation withstand voltage shows a monotonically increasing trend. However, at high leakage current thresholds, the volatility of the test results is significantly enhanced. Specifically, at low leakage current thresholds (such as 0.2mA and 0.8mA in AC mode), the insulation withstand voltage shows a centralized trend, and the fitting values ​​are between 133V and 138V. At high leakage current thresholds (such as 2mA to 3mA in AC mode), the insulation withstand voltage fluctuates greatly, ranging from 161V to 193V. At the same time, the shape parameter β of the Weibull distribution is significantly reduced at high current thresholds, indicating that the randomness of the breakdown voltage data increases, which is not conducive to the accurate determination of the insulation withstand voltage of the one-piece molded inductor.

[0054] In summary, the insulation parameters of the AC mode and the DC mode show similar patterns, which indicates that the two as test parameters have little effect on the accuracy of the results. However, considering that the conductivity of the dielectric material is susceptible to change due to the polarization effect under the action of DC voltage; at the same time, the AC mode can better simulate the voltage fluctuations under actual working conditions, so it is more recommended to use the AC test mode in the present invention. In addition, setting too high a leakage current threshold will increase the volatility of the test results, so the present invention recommends setting the leakage current threshold within 1mA to ensure the stability and consistency of the test results.

[0055] Finally, by comparing with the traditional test method, the insulation withstand voltage test method of the one-piece molded inductor proposed in the present invention shows significant advantages:

[0056] In Example 2-1 to 2-3, samples from the same batch as Example 2 are parallel samples, and the insulation withstand voltage test method of the present invention is used.

[0057] Comparative Examples 1 to 3 are also parallel samples from the same batch as the above-mentioned Example 2, which use traditional surface contact to fix the samples and perform breakdown voltage tests by lateral loading of high voltage.

[0058] The measured insulation withstand voltage and magnetic properties of the samples before and after the insulation breakdown test in each case are shown in Table 2. According to the traditional test method, the control example only measures the insulation withstand voltage of a single sample and calculates the average value, and such data is less representative. Relatively speaking, this embodiment can more accurately reflect the average performance of the sample by performing multi-point measurements on the same number of samples. Specifically, in terms of the volatility of the measured breakdown data, the fluctuation range of the embodiment is 121 to 151, which is significantly smaller than 110 to 171 of the traditional method, which further shows that the insulation withstand voltage measured by the method of the present invention is more accurate. In terms of magnetic properties, the changes in magnetic permeability before and after the test are within 2%, indicating that neither test method will have a significant effect on the magnetic permeability of the sample. However, there are obvious differences between the two in the attenuation of the quality factor. The attenuation of the quality factor caused by the traditional test method is as high as 13% to 43%, while the method of the present invention controls the attenuation within 3%. This result shows that the method of the present invention can more effectively reduce the impact of the insulation withstand voltage test on the magnetic properties of the sample, thereby providing more reliable test results.

[0059] It can be seen that the method of the present invention can not only accurately measure the insulation withstand voltage, but also significantly improve the test efficiency. At the same time, this method effectively avoids the substantial attenuation of the magnetic properties of the one-piece molded inductor when performing the insulation withstand voltage test, thereby ensuring that the material performance loss is minimized. This advantage not only improves the reliability of the test, but also reduces the loss of materials, showing good practical application value, and providing more reliable support for the performance evaluation of the one-piece molded inductor.

[0060] Table 2 Insulation withstand voltage and magnetic properties before and after breakdown of Example 2 and the control example

[0061]

[0062] Note: In Example 2, each sample was tested using point contact with 4 to 5 data points, which are not listed in detail in the table due to limited space.

[0063] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A method for dielectric withstand voltage testing of integrally formed inductors or magnetic powder cores, characterized in that: The following steps are involved: (1) Connect the high voltage output terminal of the insulation withstand voltage tester to a high voltage pen, connect the high voltage input terminal to the sample to be tested, and set the test parameters of the insulation withstand voltage tester, including setting the leakage current threshold between 0.1 mA and 1 mA; (2) applying voltage to the sample to be tested, the high-voltage electric pen is in close contact with the surface of the sample to be tested in point contact mode, selecting multiple non-adjacent points of the same sample to be tested for testing, and collecting the breakdown voltage data of each point; wherein, multiple samples are randomly selected from each batch of inductors or magnetic powder cores for insulation withstand voltage test; (3) The collected breakdown voltage data are statistically analyzed using mathematical distribution statistics methods to calculate the fitted insulation withstand voltage value.

2. The testing method according to claim 1, characterized in that: The mathematical distribution statistics method is a two-parameter Weibull distribution statistics. The number of data collected in the same batch is between 10 and 50. The shape parameter β and scale parameter V are calculated. I , with V I The insulation withstand voltage value is used as the evaluation value of the sample's withstand voltage strength, and the shape parameter β is used to evaluate the uniformity of the sample. The larger the β value, the more uniform the sample composition is, and the higher the reliability of the insulation withstand voltage fitted by the measured results.

3. The testing method according to claim 2, characterized in that: In the point contact test mode, if the distance between the contact points selected for the same sample is greater than 2mm, if the insulation withstand voltage tester displays the breakdown form as "Short fail" during breakdown, the data cannot be included in the mathematical distribution statistics.

4. The testing method according to claim 3, characterized in that: Set the test parameters of the insulation withstand voltage tester, including selecting the AC test mode.

5. The testing method according to claim 4, characterized in that: The voltage applied to the sample to be tested is to first apply a starting voltage, and then gradually increase the voltage according to a preset step voltage. Each voltage loading adopts a cycle of boosting-maintaining-reducing voltage for testing; when the surface leakage current of the sample to be tested exceeds the preset leakage current threshold, the insulation withstand voltage tester displays "High fail" and records the breakdown voltage and the actual leakage current at this time.

6. The testing method according to claim 5, characterized in that: The cycle of pressure increase-pressure maintenance-pressure reduction is 0.5 seconds for pressure increase, 4.0 to 60.0 seconds for pressure maintenance, and 0.5 seconds for pressure reduction.

7. The testing method according to any one of claims 1 to 6, characterized in that: The output end of the insulation withstand voltage tester is connected to the test fixture, and the sample to be tested is placed on the conductive copper bar of the test fixture for testing.

8. The testing method according to claim 7, characterized in that: The test fixture includes insulating bakelite, two conductive copper bars for clamping the sample to be tested, a high-voltage input end and a low-voltage output end electrically connected to the two conductive copper bars, and the conductive copper bars are fixed to the insulating bakelite by screws; the high-voltage input end of the insulation withstand voltage tester is connected to the low-voltage output end of the test fixture.

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