Potting type thin film capacitor screening method based on moisture diffusion

Abstract

The invention discloses an encapsulation type film capacitor screening method based on moisture diffusion, and belongs to the technical field of film capacitors, and the method comprises the steps: obtaining the linear period time of capacitance loss of a capacitor under different test conditions (temperature, humidity and voltage); measuring to obtain a capacitance loss curve and a mass gain curve of each group of test elements, and obtaining a linear segment rate coefficient in the capacitance loss curve according to the capacitance and mass curves; calculating a temperature coefficient, a humidity coefficient and a voltage coefficient so as to obtain a failure criterion alpha under different test conditions; and if the capacitance loss during cut-off of the linear section of the to-be-screened encapsulation type thin film capacitor or the capacitance loss during saturation weight increment is smaller than alpha, the capacitor passes the test, and screening is successful, otherwise, the capacitor does not pass the test, and screening fails. The method is rigorous in derivation and accurate and feasible in calculation, and has important significance for capacitor element failure criterion evaluation, encapsulation type film design optimization and product quality improvement.

Description

Technical Field

[0001] The present invention belongs to the technical field of thin film capacitors, and more specifically, relates to a screening method for potted thin film capacitors based on moisture diffusion. Background Art

[0002] According to the research on the capacitance loss characteristics, the capacitance loss process of potted capacitors is divided into a linear section and an accelerating section. The main characteristic of the linear section is that the rate is gentle and the dispersion is relatively small, while the accelerating section is the opposite. Currently, the reliability criterion for thin film capacitors is usually a fixed value, without considering the staged characteristics of the capacitance loss caused by electrode oxidation due to moisture intrusion under high temperature and high humidity conditions. If the reliability criterion falls within the accelerating section of the capacitance loss with large dispersion, the actual working life of the capacitor may be significantly lower than the expected life, which will cause a large deviation between the expected life and the actual life of the capacitance, threatening the stability of the system or equipment. The comparative analysis of the capacitance loss of potted and unpotted capacitors shows that the linear section of the capacitance loss is closely related to the process of moisture intrusion into potted thin film capacitors. Therefore, it is necessary to establish a connection between the two at the level of characteristic parameters, and further propose a failure criterion and screening technology for potted thin film capacitors. Summary of the Invention

[0003] Aiming at the defects of the prior art, the purpose of the present invention is to provide a screening method for potted thin film capacitors based on moisture diffusion, aiming to propose a method of selecting the moisture diffusion coefficient or the saturation weight gain time of the potting material to characterize the potting effect of the potting material and further characterize the suppression of capacitance loss, and further provide a failure criterion and screening method for potted capacitors.

[0004] To achieve the above purpose, the present invention provides a screening method for potted thin film capacitors based on moisture diffusion, including the following steps:

[0005] Obtain the linear section time t c (T), t c (RH), t c (U) of the capacitance loss curve of potted thin film capacitors under different temperature, humidity, and voltage test conditions;

[0006] According to the difference in capacitance loss on the linear section of the capacitance loss curve and the ratios of the linear section time t c (T), t c (RH), t c (U), calculate the linear section rate coefficients k(T), k(RH), k(U);

[0007] According to the exponential of the temperature coefficient E aD and the proportional relationship with k(T), fit the temperature coefficient E aD; Take the preset temperature value as the reference temperature T A , and obtain the temperature acceleration factor α T and the relationship with temperature T U . where k B is a constant;

[0008] According to the proportional relationship between the log value of the humidity coefficient n and the linear segment rate coefficient k(RH), fit the humidity coefficient n from k(RH), and take the preset humidity value as the reference humidity RH A , and obtain the humidity acceleration factor α RH and the relationship with humidity RH U .

[0009] According to the proportional relationship between the exponent of the voltage coefficient λ and the linear segment rate coefficient k(U), fit the humidity coefficient λ from k(U), and take the preset voltage value as the reference voltage U A , and obtain the voltage acceleration factor α U and the relationship with voltage U U α U = exp[λ(U A - U U )];

[0010] Take the product of the temperature acceleration factor α T , the humidity acceleration factor α RH , and the voltage acceleration factor α U as the failure criterion α. If the capacitance loss when the linear segment of the capacitor to be screened is cut off or the capacitance loss when saturated weight gain is less than α, the capacitor passes the test and the screening is successful; otherwise, the capacitor fails the test and the screening fails.

[0011] Furthermore, t c (T), t c (RH), t c (U) are obtained from the product data of the capacitor to be screened or through tests. The tests include dividing the capacitors to be screened into 3 groups, with the number of capacitors in each group being n, and performing accelerated aging tests under different test conditions. At the same moment, take the average value of the capacitances of n capacitors to obtain the capacitance loss curve of each group of capacitors to be screened, and obtain the linear segment time t c (T), t c (RH), t c (U) of their respective capacitance loss curves respectively.

[0012] Furthermore, obtain the linear segment time t c (T), tc (RH), t c (U), comprising: obtaining the capacitor weight gain curves of potted film capacitors under different temperature, humidity, and voltage test conditions, where the saturation weight gain times in the curves are t m (T), t m (RH), t m (U), and making t c (T), t c (RH), t c (U) and t m (T), t m (RH), t m (U) be equal to each other one by one.

[0013] The present invention also provides an electronic device, comprising: a computer-readable storage medium and a processor;

[0014] The computer-readable storage medium is used to store executable instructions;

[0015] The processor is used to read the executable instructions stored in the computer-readable storage medium and execute the above method.

[0016] The present invention also provides a computer-readable storage medium, which stores computer instructions for causing a processor to execute the above method.

[0017] The present invention also provides a computer program product, comprising a computer program or instructions, and when the computer program or instructions are executed by a processor, the above method is implemented.

[0018] Through the above technical solution conceived by the present invention, compared with the prior art, the present invention determines the reliable working time period of the capacitor according to the capacitance loss curve of the potted film capacitor. Aiming at the problem that moisture intrusion accelerates the capacitance loss, it is proposed to limit the capacitance loss in the linear segment. In this stage, the temperature acceleration factor, humidity acceleration factor, and voltage acceleration factor are more stable, and can accurately reflect the failure time of the potted film capacitor, thereby providing an accurate method for determining the failure criterion of the potted film capacitor and a capacitor screening technology. The derivation of the present invention is rigorous, the calculation is accurate and easy to implement, simple and reliable, and is of great significance for evaluating the failure criterion of capacitor components, optimizing the design of potted film, and improving product quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is a schematic diagram of a screening method for potted film capacitors based on moisture diffusion according to the present invention.

[0020] Figure 2 is the determination of the linear segment time in the capacitance loss curve of the potted capacitor.

[0021] Figure 3 It is to determine the saturation weight gain time in the moisture absorption weight gain curve of the potting material for potting capacitors. Specific embodiments

[0022] 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 with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0023] The present invention provides a screening method for potted film capacitors based on moisture diffusion, as Figure 1 shown, including the following steps:

[0024] Obtain the linear segment time t of the capacitance loss curve of the potted film capacitor under different temperature, humidity, and voltage test conditions c (T), t c (RH), t c (U);

[0025] According to the difference in capacitance loss on the linear segment of the capacitance loss curve and the ratio of the linear segment time t c (T), t c (RH), t c (U), calculate the linear segment rate coefficients k(T), k(RH), k(U);

[0026] According to the exponential proportional relationship between the temperature coefficient E aD and k(T), fit the temperature coefficient E from k(T) aD ; Take the preset temperature value as the reference temperature T A , and obtain the temperature acceleration factor α T and the temperature T U relationship where k B is a constant;

[0027] According to the proportional relationship between the log value of the humidity coefficient n and the linear segment rate coefficient k(RH), fit the humidity coefficient n from k(RH), and take the preset humidity value as the reference temperature RH A , and obtain the humidity acceleration factor α RH and the humidity RH U relationship

[0028] According to the proportional relationship between the exponent of the voltage coefficient λ and the linear segment rate coefficient k(U), the humidity coefficient λ is fitted from k(U), and the preset voltage value is taken as the reference temperature U. A , the voltage acceleration factor and the voltage U U relation α U = exp[λ(U A - U U )];

[0029] Taking the product of the temperature acceleration factor α T , the humidity acceleration factor α RH , and the voltage acceleration factor α U as the failure criterion α. If the capacitance loss at the cut-off of the linear segment or the capacitance loss during saturation weight gain of the encapsulated film capacitor to be screened is less than α, the capacitor passes the test and the screening is successful; otherwise, the capacitor fails the test and the screening fails.

[0030] Specifically, first, according to the product data of the encapsulated film capacitor, it is judged whether the capacitance loss curve of the capacitor sample and the water absorption rate curve of the potting material can be obtained, and then the linear segment time t c (T), t c (RH), t c (U) of the capacitance loss of the capacitor under different test conditions (temperature, humidity, voltage), or the saturation weight gain time t m (T), t m (RH), t m (U) in the weight gain curve of the capacitor, as shown in Figure 2 and 3 .

[0031] If it cannot be obtained, the test samples are divided into three groups, with the number of samples in each group being n, and accelerated aging tests are carried out under three conditions: (a) the same relative humidity, the same voltage, and different temperatures; (b) the same temperature, the same voltage, and different relative humidities; (c) the same temperature, the same relative humidity, and different voltages.

[0032] When carrying out aging tests under different temperature, humidity, and voltage conditions, monitor the mass of the test samples and calculate the moisture absorption weight gain ΔM (i.e., the moisture absorption rate):

[0033]

[0034] where m h is the weight of the test sample after moisture absorption, and m0 is the original weight of the test sample.

[0035] To reduce the random error of the test and improve the accuracy and reliability of the data, the average value of the moisture absorption rate of the test samples is used for numerical characterization, and ΔM mean is:

[0036]

[0037] wherein, ΔM(t i ) is the moisture absorption rate of the i-th sample at a certain measurement time. To measure the dispersion degree of a set of data and reflect the deviation of data points from the average value, standardization processing is performed during data processing. The standard deviation SD formula is:

[0038]

[0039] The capacitance loss rate is calculated in the same way as the standard deviation, and then the capacitance loss curve and mass gain curve after the accelerated aging test are obtained.

[0040] From ΔM(t m ) / M sat = 90%, when the potting compound of the potted capacitor reaches water absorption saturation, then the moment t m is called the saturation weight gain time, which is expressed as:

[0041]

[0042] where M sat is the weight when the weight gain of the test sample reaches saturation, D is the moisture diffusion coefficient, which is used to measure the speed of moisture diffusion in different potting materials; d ep is the thickness of the potting compound in the moisture diffusion direction.

[0043] The rate coefficient k of the linear segment in the curve is extracted from the capacitance loss curve:

[0044]

[0045] wherein, t0 is the initial test time, generally the 0th h; ΔC(t0) is the normalized capacitance value at the initial test, generally 0; t c is the end time of the linear segment test; ΔC(t c ) is the normalized capacitance value at the end of the linear segment test.

[0046] According to the accelerated life model, the failure criteria α T , α RH , α U under different test conditions (temperature, humidity, voltage) are calculated to obtain the temperature coefficient E aD , the humidity coefficient n and the voltage coefficient λ. The failure criterion α is the capacitance loss CL(t c ) or CL(t m ) at the end of the linear segment; among them, the accelerated life model is expressed as:

[0047]

[0048] In the formula, α T is the temperature acceleration factor, α RH is the humidity acceleration factor, α U is the voltage acceleration factor. The specific expressions for each item are as follows:

[0049]

[0050] α U = exp[λ(U A - U U )]

[0051] When the capacitance loss at the cut-off of the linear segment or the capacitance loss at saturation weight gain of the encapsulated film capacitor to be screened is less than α, the capacitor passes the test and the screening is successful; otherwise, the capacitor fails the test and the screening fails.

[0052] Those skilled in the art can easily understand that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A screening method for encapsulated film capacitors based on moisture diffusion, characterized in that, comprising the following steps: Obtain the linear segment time t of the capacitance loss curve of the potted film capacitor under test conditions of different temperatures, humidities, and voltages c (T), t c (RH), t c (U); According to the difference in capacitance loss on the linear segment of the capacitance loss curve and the time t of the linear segment c (T), t c (RH), t c calculate the linear segment rate coefficients k(T), k(RH), k(U) according to the ratios of (T), t, (RH), t, (U); According to the proportional relationship between the exponent of the temperature coefficient E aD and k(T), the temperature coefficient E is fitted from k(T). aD Taking the preset temperature value as the reference temperature T A , the temperature acceleration factor α T is obtained as a relationship with the temperature T U . where k B is a constant. According to the proportional relationship between the log value of the humidity coefficient n and the linear segment rate coefficient k(RH), the humidity coefficient n is fitted from k(RH), and a preset humidity value is taken as the reference humidity RH A , and the humidity acceleration factor α RH is obtained with respect to the humidity RH U relationship According to the proportional relationship between the exponent of the voltage coefficient λ and the linear segment rate coefficient k(U), the humidity coefficient λ is fitted from k(U), and the preset voltage value is taken as the reference voltage U A , the voltage acceleration factor α is obtained U and the relationship between the voltage U U is α U = exp[λ(U A - U U )]; Take the product of the temperature acceleration factor α T , the humidity acceleration factor α RH , and the voltage acceleration factor α U as the failure criterion α. If the capacitance loss at the cut-off of the linear segment or the capacitance loss during saturation weight gain of the encapsulated film capacitor to be screened is less than α, the capacitor passes the test and the screening is successful; otherwise, the capacitor fails the test and the screening fails.

2. The screening method of the potted film capacitor according to claim 1, characterized in that t c (T), t c (RH), t c (U) is obtained from the product data of the capacitor to be screened or obtained through tests.

3. The method according to claim 2, wherein The test includes dividing the capacitors to be screened into three groups, with the number of capacitors in each group being n, and performing accelerated aging tests under different test conditions. At the same moment, the average value of the capacitance of n capacitors is taken to obtain the capacitance loss curve of each group of capacitors to be screened. The linear segment time t of the capacitance loss curve of each group of capacitors to be screened is obtained respectively from the capacitance loss curve of each group of capacitors to be screened c (T), t c (RH), t c (U).

4. The screening method of the potted film capacitor according to claim 1, wherein The time t of the linear segment of the capacitance loss curve of the potted film capacitor under different temperature, humidity, and voltage test conditions c (T), t c (RH), t c Obtaining the capacitor weight gain curve of the potted film capacitor under different temperature, humidity, and voltage test conditions, and the saturation weight gain times in the curves are t m (T), t m (RH), t m (U), and making t c (T), t c (RH), t c (U) and t m (T), t m (RH), t m correspond to each other equally.

5. An electronic device, characterized in that, including: a computer-readable storage medium and a processor; the computer-readable storage medium is used for storing executable instructions; the processor is used for reading the executable instructions stored in the computer-readable storage medium and executing the method according to any one of claims 1-4.

6. A computer-readable storage medium, characterized in that, the computer-readable storage medium stores computer instructions for causing the processor to execute the method according to any one of claims 1-4.

7. A computer program product comprising a computer program or instructions, characterized in that, when the computer program or instructions are executed by the processor, the method according to any one of claims 1-4 is implemented.

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