CN112946412B - Selection method of screening stress of capacitor - Google Patents
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- 239000003990 capacitor Substances 0.000 title claims abstract description 293
- 238000012216 screening Methods 0.000 title claims abstract description 54
- 238000010187 selection method Methods 0.000 title abstract description 9
- 238000012360 testing method Methods 0.000 claims abstract description 280
- 230000015556 catabolic process Effects 0.000 claims abstract description 44
- 238000006731 degradation reaction Methods 0.000 claims abstract description 44
- 238000010277 constant-current charging Methods 0.000 claims abstract description 33
- 230000007613 environmental effect Effects 0.000 claims description 39
- 238000000034 method Methods 0.000 claims description 33
- 238000005457 optimization Methods 0.000 claims description 13
- 230000015572 biosynthetic process Effects 0.000 claims description 7
- 238000004364 calculation method Methods 0.000 claims description 4
- 230000035882 stress Effects 0.000 description 68
- GUVRBAGPIYLISA-UHFFFAOYSA-N tantalum atom Chemical compound [Ta] GUVRBAGPIYLISA-UHFFFAOYSA-N 0.000 description 13
- 238000001514 detection method Methods 0.000 description 11
- 229910052715 tantalum Inorganic materials 0.000 description 11
- 230000007547 defect Effects 0.000 description 8
- 230000007246 mechanism Effects 0.000 description 8
- 239000002131 composite material Substances 0.000 description 7
- 230000008569 process Effects 0.000 description 7
- 230000000694 effects Effects 0.000 description 5
- 238000005259 measurement Methods 0.000 description 5
- 230000008859 change Effects 0.000 description 4
- 230000008439 repair process Effects 0.000 description 4
- 238000011160 research Methods 0.000 description 3
- 230000001133 acceleration Effects 0.000 description 2
- 230000003679 aging effect Effects 0.000 description 2
- 230000001174 ascending effect Effects 0.000 description 2
- 230000001976 improved effect Effects 0.000 description 2
- 239000012535 impurity Substances 0.000 description 2
- 238000004519 manufacturing process Methods 0.000 description 2
- BPUBBGLMJRNUCC-UHFFFAOYSA-N oxygen(2-);tantalum(5+) Chemical group [O-2].[O-2].[O-2].[O-2].[O-2].[Ta+5].[Ta+5] BPUBBGLMJRNUCC-UHFFFAOYSA-N 0.000 description 2
- 238000007873 sieving Methods 0.000 description 2
- PBCFLUZVCVVTBY-UHFFFAOYSA-N tantalum pentoxide Inorganic materials O=[Ta](=O)O[Ta](=O)=O PBCFLUZVCVVTBY-UHFFFAOYSA-N 0.000 description 2
- 238000010998 test method Methods 0.000 description 2
- 230000009471 action Effects 0.000 description 1
- 230000032683 aging Effects 0.000 description 1
- 238000004458 analytical method Methods 0.000 description 1
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 238000012512 characterization method Methods 0.000 description 1
- 239000003153 chemical reaction reagent Substances 0.000 description 1
- 238000002425 crystallisation Methods 0.000 description 1
- 230000008025 crystallization Effects 0.000 description 1
- 238000007405 data analysis Methods 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 230000002950 deficient Effects 0.000 description 1
- 230000000593 degrading effect Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 230000002349 favourable effect Effects 0.000 description 1
- 230000001939 inductive effect Effects 0.000 description 1
- 229910052760 oxygen Inorganic materials 0.000 description 1
- 239000001301 oxygen Substances 0.000 description 1
- 230000000630 rising effect Effects 0.000 description 1
- 238000005245 sintering Methods 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 239000007784 solid electrolyte Substances 0.000 description 1
- 230000005676 thermoelectric effect Effects 0.000 description 1
Classifications
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/003—Environmental or reliability tests
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
- Y02E40/30—Reactive power compensation
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- Environmental & Geological Engineering (AREA)
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- Fixed Capacitors And Capacitor Manufacturing Machines (AREA)
- Testing Electric Properties And Detecting Electric Faults (AREA)
Abstract
The application provides a selection method of screening stress of a capacitor, and belongs to the technical field of device screening. The selection method comprises the following steps: the capacitors are divided into a plurality of groups with different preset conditions for constant current charging, wherein the preset conditions comprise various test voltages and various test environment conditions, and the test environment conditions comprise various test temperatures. And measuring the capacitor at intervals of preset time to obtain leakage current parameters, and dividing the capacitor into a normal capacitor and a failure capacitor according to the leakage current parameters. And determining degradation voltage boundary conditions of the capacitor, which are respectively degraded under different test environment conditions, according to test data of the normal capacitor. And determining the boundary conditions of failure voltages of the capacitors, which are respectively failed under different test environment conditions, according to the test data of the failed capacitors. The voltage condition that is higher than the failure voltage boundary condition and not higher than the degradation voltage boundary condition is selected as the voltage stress condition. The selection method can effectively prevent the problems of screening stress and undersize stress.
Description
Technical Field
The application relates to the technical field of device screening, in particular to a method for selecting screening stress of a capacitor.
Background
The chip solid electrolyte tantalum capacitor is widely applied to various high-end electronic equipment due to the advantages of small volume, large capacity, good temperature characteristics, high stability and reliability and the like. In the practical use process, the capacitor is required to be subjected to stress screening so as to ensure the use reliability of the capacitor.
The current screening stress is selected according to the multiple of rated voltage, and as the conventional chip tantalum electrolytic capacitor is subjected to multiple process innovations, the product performance and reliability are improved, the conventional screening stress condition can not well meet the screening requirement of the conventional capacitor, and the screening stress and the under-screening stress are usually generated. Wherein, screening stress can lead to product damage, while under-screening stress can lead to failure to reject defective products.
Disclosure of Invention
The purpose of the application is to provide a screening stress selection method of a capacitor, which can effectively prevent the problems of screening stress and undersize stress.
Embodiments of the present application are implemented as follows:
the embodiment of the application provides a method for selecting screening stress of a capacitor, which comprises the following steps:
dividing the capacitors into a plurality of groups with different preset conditions for testing, and carrying out constant current charging on each group of capacitors under the corresponding preset conditions, wherein the preset conditions comprise various test voltages and various test environmental conditions, and the test environmental conditions comprise various test temperatures;
measuring the leakage current of each capacitor at intervals of preset time to obtain leakage current parameters, and dividing the capacitors into normal capacitors and failure capacitors according to the leakage current parameters;
determining degradation voltage boundary conditions of the capacitor, which are respectively degraded under different test environment conditions, according to preset conditions of a normal capacitor and corresponding leakage current parameters, wherein the degradation voltage boundary conditions are ratios of corresponding test voltages and capacitor formation voltages when the capacitor is degraded;
determining a failure voltage boundary condition of the capacitor, which is a ratio of corresponding test voltage to capacitor forming voltage when the capacitor fails, under different test environment conditions according to preset conditions of the failed capacitor and corresponding leakage current parameters;
voltage conditions above the failure voltage boundary condition and not above the degradation voltage boundary condition are correspondingly selected as voltage stress conditions according to the test environmental conditions.
The method for selecting the screening stress of the capacitor has the beneficial effects that:
in the method, the voltage boundary condition is selected through the ratio of the test voltage to the capacitor formation voltage, and the influence factors of the formation voltage on the capacitor are combined, so that the voltage condition can be determined more accurately. And determining a failure voltage boundary condition according to test data of the failure capacitor, and selecting a voltage condition higher than the failure voltage boundary condition as a voltage stress condition to effectively prevent the problem of undersize stress. And determining a degradation voltage boundary condition according to test data of a normal capacitor, and selecting a voltage condition which is not higher than the degradation voltage boundary condition as a voltage stress condition, so that the problem of sieving stress selection is effectively prevented.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings that are needed in the embodiments will be briefly described below, it being understood that the following drawings only illustrate some embodiments of the present application and therefore should not be considered limiting the scope, and that other related drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a flow chart of a method for selecting screening stress of a capacitor according to an embodiment of the present disclosure;
fig. 2 is a schematic diagram of a trend of capacitor leakage current according to an embodiment of the present application;
FIG. 3 is a graph showing the trend of leakage current of sample No. 2 in group A101 capacitor;
FIG. 4 is a nonlinear regression plot of a non-linear fit to group A101 capacitors with equation I without rejecting sample number 2 from group A101 capacitors;
FIG. 5 is a non-linear residual plot of a non-linear fit to the A101 set of capacitors equation I without rejecting sample number 2 in the A101 set of capacitors;
FIG. 6 is a nonlinear regression plot of a nonlinear fit to group A101 capacitors with equation I, with sample number 2 removed from group A101 capacitors;
FIG. 7 is a non-linear residual plot of a non-linear fit to the A101 set of capacitors equation I with sample number 2 removed from the A101 set of capacitors;
FIG. 8 is a graph showing the trend of leakage current for sample No. 3 in group A102 capacitors;
FIG. 9 is a nonlinear regression plot of a non-linear fit to group A102 capacitors with equation I, with sample number 3 removed from group A102 capacitors;
FIG. 10 is a non-linear residual plot of a non-linear fit to the A102 set of capacitors equation I with sample number 3 removed from the A102 set of capacitors;
FIG. 11 is a graph of a linear fit of the β value fit to the test voltage conditions under test environmental conditions with a test temperature of 85℃and a test humidity of room air humidity;
FIG. 12 is a graph comparing a sensitive parameter degradation model and a composite stress failure model under the same experimental environmental conditions.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present application more clear, the technical solutions in the embodiments of the present application will be clearly and completely described below. The specific conditions are not noted in the examples and are carried out according to conventional conditions or conditions recommended by the manufacturer. The reagents or apparatus used were conventional products commercially available without the manufacturer's attention.
In this application, "and/or" such as "feature 1 and/or feature 2" means that "feature 1" alone, and "feature 2" alone, and "feature 1" plus "feature 2" alone, are all possible.
In addition, in the description of the present application, unless otherwise specified, the range of "numerical value a to numerical value b" includes both the end values "a" and "b", and "measurement unit" in "numerical value a to numerical value b+ measurement unit" represents "measurement unit" of both "numerical value a" and "numerical value b"; the meaning of "plural" in "one or more" means two or more.
The selection method of the screening stress of the capacitor according to the embodiment of the present application is specifically described below.
The present application provides a method of selecting screening stress for a capacitor, which is exemplarily applicable to a chip tantalum electrolytic capacitor. Referring to fig. 1, the selection method of screening stress in the present application includes:
s1, dividing a plurality of capacitors into a plurality of groups with different preset conditions for testing, and carrying out constant current charging on each group of capacitors under the corresponding preset conditions, wherein the preset conditions comprise various test voltages and various test environment conditions, and the test environment conditions comprise various test temperatures.
S2, measuring the leakage current of each capacitor at intervals of preset time to obtain leakage current parameters, and dividing the capacitors into normal capacitors and failure capacitors according to the leakage current parameters.
S3, (a) determining degradation voltage boundary conditions of the capacitor respectively degrading under different test environment conditions according to preset conditions of a normal capacitor and corresponding leakage current parameters, wherein the degradation voltage boundary conditions are ratios of corresponding test voltages and capacitor formation voltages when the capacitor is degraded.
(b) And determining the boundary conditions of the failure voltage of the capacitor, which are respectively failed under different test environment conditions, according to the preset conditions of the failed capacitor and the corresponding leakage current parameters, wherein the boundary conditions of the failure voltage are the ratio of the corresponding test voltage to the capacitor forming voltage when the capacitor fails.
S4, correspondingly selecting a voltage condition which is higher than the failure voltage boundary condition and not higher than the degradation voltage boundary condition as a voltage stress condition according to the test environment condition.
The inventor researches that the current screening stress is usually selected according to the multiple of the rated voltage of the capacitor, and the influence of the applied voltage on the capacitor is more closely related to the forming voltage in the manufacturing process, so that the current screening stress usually has the problems of screening stress and undersize stress.
In the method, the influence of the forming voltage on the capacitor in the manufacturing process is considered, the voltage boundary condition is selected through the ratio of the test voltage to the capacitor forming voltage, and the influence factor of the forming voltage on the capacitor is combined, so that the voltage condition can be determined more accurately.
In the selection method, considering that the sample parameters of the failed capacitor can effectively reflect the relation between the capacitor failure condition and the voltage boundary condition, and the sample parameters of the normal capacitor can effectively reflect the relation between the capacitor degradation condition and the voltage boundary condition, the capacitors are divided into the normal capacitor and the failed capacitor according to the leakage current parameters. And determining a failure voltage boundary condition according to the preset condition of the failure capacitor and the corresponding leakage current parameter, and selecting a voltage condition higher than the failure voltage boundary condition as a voltage stress condition, thereby effectively preventing the problem of undersize stress. And a voltage condition which is not higher than a degradation voltage boundary condition is selected as a voltage stress condition, so that the problem of sieving stress selection is effectively prevented.
It will be appreciated that in embodiments of the present application, parameters such as test voltage, test environmental conditions, period of leakage current detection interval, and time of constant current charging of the capacitor may be selected based on capacitor model specifications, capacitor application requirements, and reference standards known in the art. In embodiments of the present application, the degraded voltage boundary conditions and degraded voltage boundary conditions may also be analyzed, generalized, and calculated by statistical means well known in the art. Some alternative embodiments will be exemplified below.
Regarding step S1:
considering that stress conditions of different severity have different ageing effects on the capacitor, the effect on inducing product failure is also different. And selecting some stress conditions with higher severity, and distributing the stress conditions within a certain range according to the application requirements and the product performance of the capacitor, so that the relation between the preset conditions and the aging effect of the product can be reflected more accurately, and the reliability of the degradation voltage boundary condition and the failure voltage boundary condition obtained according to the test preset conditions and the corresponding leakage current parameters is higher.
Optionally, the capacitor is rated at a voltage U, and the various test voltages are selected from the range of 0.5 to 1.5U, such as, but not limited to, a plurality of point values including 0.5U, 0.6U, 0.7U, 0.8U, 0.9U, 1.0U, 1.1U, 1.2U, 1.3U, 1.4U, and 1.5U.
As one example, the plurality of test voltages includes 1.0U, 1.2U, and 1.4U.
Alternatively, the test completion time for constant current charging of the capacitor is selected to be in the range of 4 to 2000 hours, or 480 to 1920 hours, or 720 to 1920 hours, or 960 to 1920 hours.
As one example, the test completion time for constant current charging of the capacitor includes 960h, 1200h, 1680h, and 1920h. The test completion time refers to the total time period used for each capacitor to complete the test of constant current charging.
It should be noted that, the description of C test conditions including C1, C2 and C3 in the present application means: among the sets of capacitors having different preset conditions, the test conditions a when the capacitors of different sets are tested are C1, C2 and C3, respectively. By way of example, descriptions of test voltages including 1.0U, 1.2U, and 1.4U refer to: among the respective sets of capacitors having different preset conditions, the test voltage at the time of the test of the respective sets of capacitors was 1.0U, the test voltage at the time of the test of the respective sets of capacitors was 1.2U, and the test voltage at the time of the test of the respective sets of capacitors was 1.4U.
In consideration of different environmental conditions in different application scenes, a plurality of groups of different test environmental conditions are correspondingly selected according to the application of the capacitor, and voltage boundary conditions under different test environmental conditions are respectively obtained so as to perform stress screening under the corresponding test environmental conditions, thereby realizing more accurate capacitor screening.
Alternatively, the various test temperatures may be selected in the range of 25 to 175 ℃. As one example, the plurality of test temperatures includes 85 ℃ and 125 ℃. In view of the high temperatures in some special use environments, further, the various test temperatures also include 175 ℃ to better embody the extreme stress condition at the high temperature to better realize stress screening under different applications and requirements.
The inventors have found that temperature, voltage and humidity are all central factors affecting the failure condition of the capacitor. Under the application scene that the environmental humidity is higher, the influence of the environmental humidity on the capacitor failure also needs to be considered during stress screening, so that the qualified capacitor is ensured to have better working reliability under the severe condition.
Optionally, the test environmental conditions further comprise a plurality of test humidities.
As an example, the various test humidities may be selected from the range of 20-95% RH, such as, but not limited to, a plurality of spot values in 20% RH, 30% RH, 40% RH, 50% RH, 60% RH, 70% RH, 80% RH, 85% RH, and 95% RH.
As an example, the plurality of test humidities include conditions approaching indoor air humidity, which is suitable for capacitor stress screening for conventional applications, and conditions of higher humidity, such as 20% rh and 85% rh, which is suitable for capacitor stress screening under severe environmental humidity conditions.
In some exemplary embodiments, in a test group with a test temperature of 85 ℃, the test voltages include 1.0U, 1.2U, and 1.4U, the test humidity includes room air humidity and 85% rh, and the test completion time for constant current charging of the capacitor includes 960h and 1920h.
In the test group with the test temperature of 125 ℃, the test voltage comprises 1.0U, 1.2U and 1.4U, the test humidity is the indoor air humidity, and the test completion time of constant-current charging of the capacitor comprises 1200h and 1680h.
In the test group with the test temperature of 175 ℃, the test voltage comprises 1.0U and 1.2U, the test humidity is the indoor air humidity, and the test completion time of constant-current charging of the capacitor comprises 960h and 1200h.
As one example, the plurality of capacitors is divided into a first group of capacitors, a second group of capacitors, a third group of capacitors, a fourth group of capacitors, a fifth group of capacitors, a sixth group of capacitors, a seventh group of capacitors, an eighth group of capacitors, a ninth group of capacitors, and a tenth group of capacitors.
In the first group of capacitors, the test completion time of constant current charging of each capacitor is 1920h, and the preset conditions are as follows: the test temperature was 85 ℃, the test voltage was 1.0U and the test humidity was room air humidity.
In the second group of capacitors, the test completion time of constant current charging of each capacitor is 1920h, and the preset conditions are as follows: the test temperature was 85 ℃, the test voltage was 1.2U and the test humidity was room air humidity.
In the third group of capacitors, the test completion time of constant current charging of each capacitor is 1920h, and the preset conditions are as follows: the test temperature was 85 ℃, the test voltage was 1.4U and the test humidity was room air humidity.
In the fourth group of capacitors, the test completion time of constant current charging of each capacitor is 1680h, and the preset conditions are as follows: the test temperature was 125 ℃, the test voltage was 1.0U and the test humidity was room air humidity.
In the fifth group of capacitors, the test completion time of constant current charging of each capacitor is 1680h, and the preset conditions are: the test temperature was 125 ℃, the test voltage was 1.2U and the test humidity was room air humidity.
In the sixth group of capacitors, the test completion time of constant current charging of each capacitor is 1200h, and the preset conditions are as follows: the test temperature was 125 ℃, the test voltage was 1.4U and the test humidity was room air humidity.
In the seventh group of capacitors, the test completion time of constant current charging of each capacitor is 1200h, and the preset conditions are as follows: the test temperature was 175 ℃, the test voltage was 1.0U and the test humidity was room air humidity.
In the eighth group of capacitors, the test completion time of constant current charging of each capacitor is 960h, and the preset conditions are: the test temperature was 175 ℃, the test voltage was 1.2U and the test humidity was room air humidity.
In the ninth group of capacitors, the test completion time of constant current charging of each capacitor is 960h, and the preset conditions are: the test temperature was 85 ℃, the test voltage was 1.2U and the test humidity was 85% rh.
In the tenth group of capacitors, the test completion time of constant current charging of each capacitor is 960h, and the preset conditions are: the test temperature was 85 ℃, the test voltage was 1.4U and the test humidity was 85% rh.
Regarding step S2:
when detecting leakage current, a certain time interval is favorable for ensuring that the change condition of the leakage current can be better reflected in two adjacent detection processes, so that the preset time of the interval for detecting the leakage current is required to have a certain time length so as to ensure the effectiveness of each detection and the efficiency of the whole detection process. Meanwhile, considering that the shorter the interval preset time for detecting the leakage current is, more detection data can be obtained under the same sample condition, and the accuracy of data analysis is improved, so that the interval preset time for detecting the leakage current is preferably reduced as much as possible under the condition of meeting the requirement of a certain time interval.
Optionally, in order to better achieve both the detection efficiency and the detection data amount, the preset time is 240h.
In this application, the detection method of the leakage current parameter may be performed in a manner known in the art. As an example, in the present application, when the leakage current of each capacitor is measured at every preset time, the test environment condition of the capacitor is kept the same as that in the constant current charging test process, and the rated dc voltage leakage current of the capacitor is measured by using the same meter and the same test method. At the time of detection, optionally, the leakage current value is read at 120 s. In order to ensure the effectiveness and accuracy of data acquisition, optionally, a special machine is adopted for data acquisition.
It is understood that normal and failed capacitors may be divided according to criteria well known in the art. As an example, since some capacitors have a problem in that a short circuit phenomenon or a leakage current exceeds a standard value after a test for constant current charging is performed on the capacitors, the capacitors having a short circuit phenomenon or a leakage current exceeding a standard value are classified as failed capacitors, and the remaining capacitors are classified as normal capacitors.
Regarding step S3 (a):
the inventor researches degradation characterization parameters of a mixed stress acceleration test of the tantalum capacitor, and discovers that the leakage current of the capacitor can have an ascending trend or a descending trend under different conditions. It shows that under the influence of different stresses, different mechanisms of the chip tantalum capacitor can be excited, and leakage current parameters which directly show the quality of the oxide film are influenced.
In the first aspect, the dielectric oxide film of the chip tantalum capacitor is tantalum pentoxide, and the quality of the oxide film depends largely on the purity of the tantalum core. A small amount of impurities are always present in the tantalum powder and are difficult to completely remove by high-temperature sintering, so that when a tantalum pentoxide film is formed, these impurities occupy the position of the oxide film, forming dielectric layer defects. Due to the defects, when the chip tantalum capacitor works, the current passing through the defect positions is larger, the current passing through other positions is smaller, so that the current distribution is uneven, heat is concentrated at the defect positions, and particularly under the environment condition of higher temperature, the heat crystallization is caused, and the leakage current is increased.
In the second aspect, when current is concentrated through the defect, high temperature occurs at the defect site due to thermoelectric effect, mnO at the high temperature 2 Start to release oxygen to become Mn 2 O 3 . Due to Mn 2 O 3 The resistivity is high, and the points are isolated, so that the repairing effect is realized. This effect is known as self-healing in solid tantalum capacitors, the self-healing mechanism causing leakage current to drop.
As shown in fig. 2, based on the basic structure and principle analysis of the chip tantalum capacitor, the mechanism and phenomenon affecting the rise and fall of the leakage current coexist, and whether the leakage current finally appears to rise or fall depends on which mechanism is the dominant factor.
Based on the above mechanism, the change of the leakage current can be regarded as the sum of the change trend of the two directions, and the research discovers that the nonlinear regression fitting is performed by using a logarithmic generalized linear model, and the optimal parameter is iterated by combining the Gaussian-Newton algorithm, so that the method is more in accordance with the leakage current degradation rule, can better reflect the relation between the test environment condition of the capacitor and the degradation condition of the capacitor, and can more accurately determine the degradation voltage boundary conditions under different test environment conditions.
In some exemplary embodiments, determining degradation voltage boundary conditions for each capacitor that degrade under different test environmental conditions based on preset conditions for a normal capacitor and corresponding leakage current parameters includes:
first, a formula based on formula I is selected, wherein formula I is y=e (α+βx) . The y value is a leakage current parameter, which is exemplified by μA number of leakage current; the x value is the test time, which is illustratively the number of hours of the test time.
The test time in the present application refers to the time corresponding to each time the leakage current measurement is performed, in which the test is performed; the y value in formula I also refers to the leakage current parameter in one-to-one correspondence with the test time.
Secondly, nonlinear fitting is carried out on leakage current parameters of the normal capacitor and corresponding test time under the same preset condition on the basis of a formula I, and optimal parameters are iterated through a Gaussian-Newton algorithm to obtain an alpha value fitting result and a beta value fitting result through calculation.
It can be understood that performing nonlinear fitting on a normal capacitor under the same preset condition refers to performing nonlinear fitting on a leakage current parameter and a corresponding test time of the normal capacitor under the same preset condition, and obtaining a nonlinear fitting formula corresponding to the preset condition. When M groups of normal capacitors with different preset conditions exist, nonlinear fitting is carried out on the normal capacitors under each group of preset conditions, and M nonlinear fitting formulas matched with the corresponding preset conditions are obtained.
And then, performing linear fitting on the beta value fitting result of the normal capacitor under the same test environment condition and the test voltage condition to obtain a beta value linear fitting formula, wherein the test voltage condition is the ratio of the test voltage of the normal capacitor to the capacitor forming voltage.
Under the condition of the same test environment conditions, different test voltages can generate different stresses, so that different leakage current phenomena are caused. The linear fitting based on the beta value fitting result and the test voltage condition is carried out on a plurality of groups of capacitors with the same test environment condition and different test voltage conditions, so that the linear relation between the beta value fitting result and the test voltage condition under a certain test environment condition can be accurately reflected.
It can be understood that the linear fitting is performed on the normal capacitors under the same test environment condition, that is, under the condition that the test environment condition is the same, the normal capacitors with the same test voltage condition are taken as a group, and the test voltage conditions of the normal capacitors in each group under different test voltage conditions are respectively fitted in one-to-one correspondence with the corresponding beta value fitting results. When N (N is a positive integer less than or equal to M) test environmental conditions exist in the normal capacitors with different preset conditions in the M (M is an integer greater than or equal to 1), N beta value linear fitting formulas which are respectively matched with the corresponding test environmental conditions are obtained through linear fitting.
And finally, obtaining a voltage condition fitting value of the test voltage condition when the beta value is 0 according to a beta value linear fitting formula, and taking the voltage condition fitting value as a degraded voltage boundary condition.
According to a nonlinear fitting formula, positive and negative values of the beta value can reflect the rising and falling conditions of leakage current, wherein: leakage current shows a decreasing trend when the beta value is negative; leakage current shows an ascending trend when the beta value is a positive value; the leakage current remains unchanged when the beta value is equal to 0, which indicates that the repair rate is the same as the oxide film defect degradation rate. And taking the voltage condition fitting value corresponding to the beta value of 0 as a degradation voltage boundary condition, establishing a one-to-one correspondence between the test environment condition and the degradation voltage boundary condition, and taking the voltage condition fitting value as a sensitive parameter degradation model for defining the degradation of the capacitor, so that the voltage boundary condition of the capacitor, which is degraded due to the comprehensive influence of the sensitive parameter, under a certain test environment condition can be defined more accurately.
Regarding step S3 (b):
it is considered that capacitor failure is mainly due to composite stress, and temperature, voltage and humidity are all core factors affecting the capacitor failure condition. When the failure capacitor is analyzed, the failure number of the capacitor is taken as a vector function of the combination of the stress element groups such as time, temperature, humidity and voltage, and the corresponding relation between the failure condition of the capacitor tested for the preset time under certain test environment conditions and the voltage stress can be more accurately determined.
In some exemplary embodiments, determining a failure voltage boundary condition for a capacitor to fail under different test environmental conditions, respectively, based on test parameters of the failed capacitor, comprises:
first, based on equation II, equation II is A is the failure number 0 And a j Is constant (I)>Is a stress vector.
The stress vector includes test voltage conditions, test environmental factors, and test time. The test voltage condition is the ratio of the test voltage of the failed capacitor to the capacitor forming voltage. The test environmental factor is the product of the acceleration factor in the Arrhenius model and the Peck model of the test environmental condition. It will be appreciated that the test environmental factor is a test temperature factor in the case where the test environmental conditions do not include test humidity; in the case where the test environmental conditions also include test humidity, the test environmental factor is a test temperature and humidity factor.
By X t The test time is the number of hours of the test time; by X e Representing the experimental environment factor variable in X e The test time can be expressed as the above formula IIWherein a is 0 、a t 、a e And a v Are all constants; n (X) t ，X e ，X v ) Is the failure number and is related to the stress vector.
Then, substituting the preset condition of the failure capacitor and the corresponding leakage current parameter into a formula II, and calculating by Gaussian-NewtonThe method iterates out the optimal parameters to calculate and obtain a 0 Value sum a j The value, i.e. obtain a 0 Value, a t Value, a e Value sum a v Value of X t 、X e And X e The formula is optimized for the failure number of the variable.
And finally, for the failure capacitors under different test environment conditions, respectively acquiring voltage condition optimization values when the test time is preset time and the failure number is 1 according to a failure number optimization formula, and taking the voltage condition optimization values as failure voltage boundary conditions.
In the failure number optimization formula, the failure number is 1, so that the condition that the capacitor starts to fail can be accurately defined. Under the condition that the test environment condition and the preset time are certain, the voltage boundary condition of capacitor degradation under certain test environment condition can be accurately determined through the failure number optimization formula, the one-to-one correspondence relation between the test environment condition and the failure voltage boundary condition is established, and the voltage boundary condition of the capacitor, which is invalid due to the composite stress under certain test environment condition, can be accurately defined as the composite stress failure model for defining the capacitor failure.
In some possible embodiments, the preset time is a test completion time corresponding to a capacitor with the shortest constant current charging time, so that the stress screening can be realized in a shorter time under the determined voltage boundary condition. Of course, in the embodiment of the present application, the preset time may also be selected according to the actual screening or the application requirement.
In this application, (a) and (b) in the step S3 do not indicate the order of execution of the steps, the step S3 (a) may be executed before the step S3 (b), the step S3 (a) may be executed simultaneously with the step S3 (b), and the step S3 (a) may be executed after the step S3 (b).
Regarding step S4:
considering that the closer the voltage condition is to the degraded voltage boundary condition, the better screening effect can be realized by applying larger stress action while avoiding the occurrence of screening stress.
Optionally, a voltage condition close to or equal to the degradation voltage boundary condition is selected as the voltage stress condition according to the actual situation, so that a better stress screening effect is ensured.
The features and capabilities of the present application are described in further detail below in connection with the examples.
A method of selecting screening stress for a capacitor, comprising:
s1, 500 capacitors with two specifications of CAK45-E-16V-47 mu F-K and CAK45-C-25V-10 mu F-K are selected. The formation voltage of the CAK45-E-16V-47 mu F-K capacitor is 71V, and the rated voltage U is 25V; the formation voltage of the CAK45-C-25V-10 mu F-K capacitor is 101V, and the rated voltage U is 16V.
The CAK45-E-16V-47 mu F-K capacitor is marked as A1, the A1 capacitor is divided into 10 groups, 50 capacitors in each group are subjected to constant current charging corresponding to 10 groups of different preset conditions in sequence, and the codes of test samples are A101, A102, A103, A104, A105, A106, A107, A108, A109 and A110 in sequence. The CAK45-C-25V-10 mu F-K capacitor is marked as A2, the A2 capacitor is divided into 10 groups, 50 capacitors in each group are subjected to constant current charging corresponding to 10 groups of different preset conditions in sequence, and the codes of test samples are A201, A202, A203, A204, A205, A206, A207, A208, A209 and A210 in sequence. The group of test capacitors and the test conditions are shown in Table 1.
TABLE 1 groups of test capacitors and test conditions
S2, measuring the leakage current of each capacitor every 240h to obtain leakage current parameters. During detection, the test environment condition of the capacitor is kept to be the same as that in the constant current charging test process, the same instrument and the same test method are used for measuring rated direct current voltage leakage current of the capacitor, and the leakage current value is read in 120s by adopting a special machine mode.
And dividing the capacitor with short circuit phenomenon or leakage current exceeding the standard value into failure capacitors according to the leakage current parameters, and dividing the rest capacitors into normal capacitors. As for the capacitor whose leakage current exceeds the standard value, description will be made below by way of a specific example.
The sample No. 2 in the A101 group is a failure capacitor, and the situation that the individual oxide film has obvious defects occurs, namely, the self-healing mechanism of the tantalum capacitor cannot repair the damage of the electrical stress in the test process, so that the situation that the leakage current continuously rises occurs.
Referring to fig. 3, fig. 3 is a graph showing the leakage current trend of sample No. 2 in the a101 group capacitor. As can be seen from fig. 3, the leakage current of sample No. 2 in group a101 increases substantially linearly, and the degradation rate is greater than the repair rate.
FIG. 4 is a nonlinear regression plot of a non-linear fit to group A101 capacitors with equation I without rejecting sample number 2 from group A101 capacitors; FIG. 5 is a non-linear residual plot of a non-linear fit to the A101 set of capacitors equation I without rejecting sample number 2 in the A101 set of capacitors; FIG. 6 is a nonlinear regression plot of a nonlinear fit to group A101 capacitors with equation I, with sample number 2 removed from group A101 capacitors; fig. 7 is a non-linear residual plot of a non-linear fit to a101 bank capacitor equation I with sample No. 2 removed from the a101 bank capacitor.
As can be seen from fig. 4 and 5, the fit is less reasonable without rejecting sample No. 2 in the a101 group capacitor. As can be seen from fig. 6 and 7, the fit is reasonable with the sample No. 2 in the a101 group capacitor removed. After the failure capacitor is removed, a more reliable sensitive parameter degradation model can be obtained by fitting the A101 group of normal capacitors.
Referring to fig. 8, fig. 8 is a leakage current trend graph of sample No. 3 in the capacitor of group a 102. As can be seen from fig. 8, sample No. 3 in the a102 group capacitor had a sharp rise in leakage current from 0.187 μa to 0.741 μa at test 960h, followed by a gradual drop, but failed to repair by the self-healing mechanism until the abrupt change.
FIG. 9 is a nonlinear regression plot of a non-linear fit to group A102 capacitors with equation I, with sample number 3 removed from group A102 capacitors; fig. 10 is a non-linear residual plot of a non-linear fit to a102 bank capacitor equation I with sample No. 3 removed from the a102 bank capacitor.
As can be seen from fig. 9 and 10, the fit is reasonable with the sample No. 3 in the a102 group capacitor removed. After the failure capacitor is removed, a more reliable sensitive parameter degradation model can be obtained by fitting the normal capacitors of the A102 group.
In fig. 4 to 7 and fig. 9 to 10 of the present application, for simplicity and clarity of illustration, the points that are close to each other are integrated into one point, and the cited data are all corresponding data obtained by detection.
The failure of the test capacitors of the different groups was counted and the results are shown in table 2.
TABLE 2 failure statistics for test capacitors
Note that: it should be noted that, due to the self-healing mechanism of the tantalum capacitor, the total number of failures is not counted for the sample in which the leakage current is abnormally increased but the leakage current is reduced to the standard value after the subsequent repeated measurement and continuous aging. For example, sample No. 2 in the a101 group capacitor and sample No. 3 in the a102 group capacitor, so the total number of failures in both test group 1 and test group 2 is 0.
S3 (a), taking a formula I as a basic formula, respectively carrying out nonlinear fitting on leakage current parameters and corresponding test time of normal capacitors in each group of capacitors such as A101, A102, A103, A201, A202 and A203, and the like, and obtaining an alpha value fitting result and a beta value fitting result by iterating optimal parameters through a Gaussian-Newton algorithm. The results of the alpha value fitting result, the beta value fitting result, and the voltage data of the normal capacitors in each group of capacitors were counted, taking the capacitors of the groups a101, a102, a103, a201, a202, and a203 as examples, and the results thereof are shown in table 3.
TABLE 3 nonlinear fitting results and Voltage data for Normal capacitor
And performing linear fitting on the beta value fitting result of the normal capacitor under the same test environment condition and the test voltage condition to obtain a beta value linear fitting formula.
The test environment conditions of the capacitors of the groups A101, A102, A103, A201, A202 and A203 are the same, the test temperature is 85 ℃, and the test humidity is the indoor air humidity. Taking this experimental environmental condition as an example, the β value fitting results in the groups a101, a102, a103, a201, a202, and a203 were linearly fitted to the experimental voltage conditions. A linear fit plot of the β value fit versus test voltage conditions was obtained for the test environment conditions with a test temperature of 85 ℃ and a test humidity of room air humidity, as shown in fig. 11.
As can be determined from fig. 11, the linear fit formula for the β value is β= -0.000966+0.002911 x under the test environmental conditions where the test temperature is 85 ℃ and the test humidity is the indoor air humidity. Wherein X is the test voltage condition, i.e. the ratio of the test voltage to the capacitor forming voltage.
And obtaining a voltage condition fitting value of the test voltage condition when the beta value is 0 according to the beta value linear fitting formula, and taking the voltage condition fitting value as a degraded voltage boundary condition.
In combination with the linear fit formula of the beta value in fig. 11, under the test environment condition that the test temperature is 85 ℃ and the test humidity is the indoor air humidity, the test voltage condition is 0.3318 when the beta value is 0. The degradation voltage boundary conditions of all the groups of capacitors were confirmed in the same manner, and the results are shown in table 4.
TABLE 4 degradation Voltage boundary Condition under different test Environment conditions
S3 (b) substituting preset conditions of the failure capacitor and corresponding leakage current parameters into the formula II based on the formula II, and iterating out optimal parameters through a Gaussian-Newton algorithm to obtain a by calculation 0 Value, a t Value, a e Value sum a v Values. In the results obtained, a 0 ＝-12.7693，a t ＝0.00137589，a e ＝0.00164497，a v = 34.7825. Therefore, the failure number optimization formula is as follows:
taking the shortest test completion time (960 h) as preset time, for the failed capacitors under different test environment conditions, respectively obtaining voltage condition optimization values when the failure number is 1 according to a failure number optimization formula, and taking the voltage condition optimization values as failure voltage boundary conditions, wherein the results are shown in table 5.
TABLE 5 boundary conditions of failure voltages under different test environmental conditions
S4, establishing a one-to-one correspondence relation between test environmental conditions and degradation voltage boundary conditions, and using the one-to-one correspondence relation as a sensitive parameter degradation model for defining capacitor degradation; and establishing a one-to-one correspondence between the test environmental conditions and the failure voltage boundary conditions as a composite stress failure model for defining the capacitor failure.
Referring to FIG. 12, a comparison of a sensitive parameter degradation model and a composite stress failure model under different experimental environmental conditions is shown.
As can be seen from fig. 12, the voltage boundary conditions of the sensitive parametric degradation model are above those of the composite stress failure model.
Voltage conditions above the failure voltage boundary condition and not above the degradation voltage boundary condition are correspondingly selected as voltage stress conditions according to the test environmental conditions.
By adopting the method for selecting the screening stress of the capacitor, stress selection is carried out, then product screening is carried out, and early failure feedback caused by undersize stress and batch failure feedback caused by screening stress do not appear in the screened product in subsequent use.
The embodiments described above are some, but not all, of the embodiments of the present application. The detailed description of the embodiments of the present application is not intended to limit the scope of the application, as claimed, but is merely representative of selected embodiments of the application. All other embodiments, which can be made by one of ordinary skill in the art based on the embodiments herein without making any inventive effort, are intended to be within the scope of the present application.
Claims (15)
1. A method of selecting screening stress for a capacitor, comprising:
dividing a plurality of capacitors into a plurality of groups with different preset conditions for testing, and carrying out constant current charging on each group of capacitors under the corresponding preset conditions, wherein the preset conditions comprise a plurality of test voltages and a plurality of test environmental conditions, and the test environmental conditions comprise a plurality of test temperatures;
measuring the leakage current of each capacitor at intervals of preset time to obtain leakage current parameters, and dividing the capacitors into normal capacitors and failure capacitors according to the leakage current parameters;
determining degradation voltage boundary conditions of degradation of the capacitor under different test environment conditions respectively according to the preset conditions of the normal capacitor and the corresponding leakage current parameters, wherein the degradation voltage boundary conditions are ratios of the corresponding test voltage and capacitor formation voltage when the capacitor is degraded;
determining a failure voltage boundary condition of the capacitor, which is a ratio of the corresponding test voltage to the capacitor forming voltage when the capacitor fails, under different test environment conditions according to the preset condition of the failure capacitor and the corresponding leakage current parameter;
voltage conditions above the failure voltage boundary condition and not above the degradation voltage boundary condition are correspondingly selected as voltage stress conditions for the test environmental conditions.
2. The method according to claim 1, wherein determining degradation voltage boundary conditions for degradation of the capacitor under different test environmental conditions according to the preset conditions and the corresponding leakage current parameters of the normal capacitor, respectively, comprises:
formula I is based on formula I, formula I being y=e (α+βx) The y value is the leakage current parameter, the x value is the test time, nonlinear fitting is carried out on the leakage current parameter of the normal capacitor under the same preset condition and the corresponding test time, and a beta value fitting result of the normal capacitor under each preset condition is obtained;
performing linear fitting on the beta value fitting result of the normal capacitor under the same test environment condition and a test voltage condition to obtain a beta value linear fitting formula, wherein the test voltage condition is the ratio of the test voltage of the normal capacitor to the capacitor forming voltage;
and obtaining a voltage condition fitting value of the test voltage condition when the beta value is 0 according to the beta value linear fitting formula, and taking the voltage condition fitting value as the degradation voltage boundary condition.
3. The method of selecting screening stress according to claim 2, wherein the β value fitting result is obtained by iterative calculation of a gaussian-newton algorithm.
4. The method according to claim 1, wherein determining a failure voltage boundary condition for the capacitor to fail under different test environmental conditions according to the preset condition of the failed capacitor and the corresponding leakage current parameter comprises:
based on formula II, formula II is A is the failure number 0 And a j Is constant (I)>The stress vector comprises a test voltage condition, a test environment factor and a test time, wherein the test voltage condition is the ratio of the test voltage of the failed capacitor to the capacitor forming voltage, the test environment factor is the product of an Arrhenius model of the test environment condition and a accelerating factor in a Peck model, and the preset condition of the failed capacitor and the corresponding leakage current parameter are substituted into the formula II to obtain a 0 Value sum a j Obtaining a failure number optimization formula;
and for the failure capacitors under different test environment conditions, respectively acquiring voltage condition optimization values when the test time is preset time and the failure number is 1 according to the failure number optimization formula, and taking the voltage condition optimization values as the failure voltage boundary conditions.
5. The method of selecting screening stress according to claim 4, wherein the preset time is a test completion time corresponding to the capacitor having the shortest constant current charging time.
6. The method of selecting screening stress according to claim 4, wherein a 0 Value sum a j The values were obtained by iterative calculations using a gauss-newton algorithm.
7. The method for selecting screening stress according to any one of claims 1 to 6, wherein the rated voltage of the capacitor is U, and the selection range of the plurality of test voltages is 0.5 to 1.5U;
and/or, the selection range of the plurality of test temperatures is 25-175 ℃.
8. The method of selecting screening stress according to claim 7, wherein the plurality of test voltages comprises 1.0U, 1.2U and 1.4U.
9. The method of selecting screening stress according to claim 7, wherein the plurality of test temperatures includes 85 ℃, 125 ℃ and 175 ℃.
10. The method of selecting screening stress according to any one of claims 1 to 6, wherein the preset time is 240 hours;
and/or the test completion time of the constant current charging of the capacitor is selected to be 4-2000 h.
11. The method of selecting screening stress according to claim 10, wherein the test completion time of constant current charging of the capacitor includes 960h, 1200h, 1680h and 1920h.
12. The method of selecting screening stress according to any of claims 1 to 6, wherein the test environmental conditions further comprise a plurality of test humidities.
13. The method of selecting screening stress according to claim 12, wherein the plurality of test humidities are selected in a range of 20 to 95% rh.
14. The method of selecting screening stress according to claim 12, wherein the plurality of test humidities comprises 20% rh and 85% rh.
15. The method of selecting screening stress according to any one of claims 1 to 6, wherein the capacitor rated voltage is U, the test environmental conditions further include test humidity, the test temperature includes 85 ℃ and 125 ℃ and 175 ℃;
in the test group with the test temperature of 85 ℃, the test voltage comprises 1.0U, 1.2U and 1.4U, the test humidity comprises indoor air humidity and 85% RH, and the test completion time of constant-current charging of the capacitor comprises 960h and 1920h;
in the test group with the test temperature of 125 ℃, the test voltage comprises 1.0U, 1.2U and 1.4U, the test humidity is the indoor air humidity, and the test completion time of constant-current charging of the capacitor comprises 1200h and 1680h;
in the test group with the test temperature of 175 ℃, the test voltage comprises 1.0U and 1.2U, the test humidity is the indoor air humidity, and the test completion time of constant-current charging of the capacitor comprises 960h and 1200h.
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