CN114818387A - Performance evaluation method of nonlinear conductive material - Google Patents
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- 238000011156 evaluation Methods 0.000 title claims abstract description 98
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Abstract
The invention provides a performance evaluation method of a nonlinear conductive material, which comprises the following steps: s1) taking the electrical performance, the thermal performance and the mechanical performance of the nonlinear conductive material as performance evaluation indexes, and obtaining the weight of the performance evaluation indexes by using an AHP method; s2) adopting a TOPSIS model, carrying out forward normalization processing on the measurement data of the electrical performance, the thermal performance and the mechanical performance of the nonlinear conductive material, combining the weight of the performance evaluation index to obtain the distance between the nonlinear conductive material and the optimal solution and the worst solution, and carrying out comprehensive distance grading to obtain a comprehensive performance evaluation result. Compared with the prior art, the method provided by the invention comprehensively evaluates the nonlinear conductive material added with the fillers with different doping quality fractions under the condition of simultaneously considering the electrical, thermal and mechanical characteristics, so that the evaluation result is more in line with the actual engineering requirement, and the method has certain guiding significance for the optimization design of the doping quality fractions in the nonlinear conductive packaging material.
Description
Technical Field
The invention belongs to the technical field of semiconductors, and particularly relates to a performance evaluation method of a nonlinear conductive material.
Background
The active metal brazing process in high temperature and high pressure silicon carbide module packaging is easy to produce metal protrusions at the bottom of a module metallization layer, namely three bonding points of an aluminum nitride ceramic substrate, a copper metallization layer and a packaging material. The high field strength created by such metallic bump triple junctions at high voltages tends to create partial discharges in the module, resulting in insulation degradation and even module failure. The nonlinear conductive material can be used for homogenizing high field intensity generated by the triple junction, so that partial discharge in a module packaging structure is inhibited, and the safety and reliability of the silicon carbide module in long-term operation in a high-temperature and high-pressure environment are improved.
Epoxy resin is a common insulating material for packaging high-voltage equipment and power electronic modules, and silicon carbide whisker is a semiconductive filler with a large length-diameter ratio, and can have nonlinear conductivity characteristics at a low doping mass fraction when being doped with epoxy resin, so that the epoxy resin/silicon carbide whisker composite material is a nonlinear conductivity material with a low doping mass fraction.
However, as the doping fraction of the nonlinear electrically conductive material increases, its dielectric strength, thermal properties, and mechanical properties are degraded or optimized to varying degrees, although its nonlinear electrical conductivity characteristics increase. For the high-temperature high-pressure silicon carbide module, the insulating packaging material of the high-temperature high-pressure silicon carbide module needs higher electrical, thermal and mechanical properties, so that the electrical, thermal and mechanical properties of the nonlinear conductive material under different doping quality fractions are comprehensively evaluated, a comprehensive evaluation system and indexes are established, and the selection significance for the optimal doping quality fraction of the nonlinear conductive material of the high-temperature high-pressure silicon carbide device is great.
However, the performance index of the nonlinear conductive packaging material of the power electronic module is more, such as electrical performance (nonlinear conductivity coefficient: (non-linear conductivity coefficient) (ii))α) Dielectric constant ofε') Dielectric loss (tan)δ e ) Dielectric strength of the resin compositionB d ) Thermal properties (glass transition temperatureT g ) Thermal decomposition temperature (CT d ) Mechanical properties (coefficient of thermal expansion (CTE), storage modulus: (E')). For nonlinear electrically conductive materials of different doping mass fractions,the trade-off relationship exists between different performance indexes (for example, although the nonlinear conductivity coefficient of the nonlinear conductive material with different doping weight fractions is high, the glass transition temperature is low, and the quality cannot be judged), and it is difficult to evaluate the quality of the nonlinear conductive material with different doping weight fractions based on a plurality of performance indexes, so as to select the optimal doping weight fraction for package insulation.
Therefore, at present, the relevant documents or patents of the nonlinear conductive material as the power electronic module packaging material only remain in the analysis of electrical, thermal and mechanical properties, but do not perform comprehensive evaluation on the electrical, thermal and mechanical properties, and establish and calculate comprehensive evaluation coefficients through evaluation indexes.
Disclosure of Invention
In view of the above, the present invention provides a method for evaluating the performance of a nonlinear conductive material, which can integrate a plurality of performance indexes to establish a comprehensive evaluation index, thereby realizing selection of an optimal doping quality score.
The invention provides a performance evaluation method of a nonlinear conductive material, which comprises the following steps:
s1) taking the electrical performance, the thermal performance and the mechanical performance of the nonlinear conductive material as performance evaluation indexes, and obtaining the weight of the performance evaluation indexes by using an AHP method;
s2) adopting a TOPSIS model, carrying out forward normalization processing on the measurement data of the electrical performance, the thermal performance and the mechanical performance of the nonlinear conductive material, combining the weight of the performance evaluation index to obtain the distance between the nonlinear conductive material and the optimal solution and the worst solution, and carrying out comprehensive distance grading to obtain a comprehensive performance evaluation result.
Preferably, the nonlinear electrically conductive material comprises nonlinear electrically conductive materials with different inorganic particle doping amounts.
Preferably, the electrical properties include nonlinear conductivity coefficient, dielectric constant, dielectric loss and dielectric strength; the thermal properties include a glass transition temperature and a thermal decomposition temperature; the mechanical properties include coefficient of thermal expansion and storage modulus.
Preferably, in the step S2), the dielectric constant, the dielectric loss, the thermal expansion coefficient and the storage modulus are used as cost indexes; the nonlinear conductivity coefficient, the dielectric strength, the glass transition temperature and the thermal decomposition temperature are used as benefit indexes.
Preferably, the weight of the performance evaluation index obtained by using the AHP method in step S1) is specifically:
and (3) sorting the importance of the performance evaluation indexes to obtain a pair comparison matrix A:
wherein,a ij representing the importance of the ith individual performance evaluation index compared with the jth individual performance evaluation index;
obtaining the weight of the performance evaluation index by using the formula (1):
whereinλ max Is the largest eigenvalue of the matrix a,Iis a vector of the unit,wthe eigenvector of the matrix a is the weight of the performance evaluation index.
Preferably, the step S1) further includes performing weight check using formula (2):
c.i. is a consistency index, and when c.i. is less than 0.1, the calculated weight is considered reasonable.
Preferably, the forward normalization in step S2) is specifically:
the measurement data matrix of the electrical property, the thermal property and the mechanical property of the nonlinear conductive material is converted into a maximum index according to a formula (3):
where x is the measured data matrix, f (x) is the forward value, M = max | x-x best |，x best Is an optimum value;
the forward matrix is then normalized to eliminate the dimensional effect according to equations (4) and (5):
wherein x is ij Is the jth individual performance evaluation index of the ith nonlinear conductive material, N matrix represents the normalized matrix of the forward values of the jth individual performance evaluation indexes of the m nonlinear conductive materials, N ij Is the normalized result of the forward value of the j individual performance evaluation index of the i nonlinear conductive material, f (x) ij ) And the positive value of the j individual performance evaluation index of the ith nonlinear conductive material is represented.
Preferably, in the step S2), the distances between the nonlinear conductive material and the optimal solution and the worst solution are obtained according to equations (6) and (7):
wherein D is i + Is the distance of the ith nonlinear conductive material from the optimal solution, D i - Is the distance of the ith nonlinear conductive material from the worst solution, N j + Is the maximum value, N, in the jth individual performance evaluation index j - Is the minimum value in the jth individual performance evaluation index; w is a j Is the weight corresponding to the performance evaluation index.
Preferably, in the step S2), a comprehensive distance score is performed according to formula (8):
wherein,F i is the firstiA composite distance score for each nonlinear conductive material; d i + Distance of ith nonlinear conductive material from optimal solution, D i - The distance of the ith nonlinear electrically conductive material from the worst solution.
The invention also provides application of the performance evaluation method of the nonlinear conductive material in the selection of the nonlinear conductive material for the encapsulation of the high-temperature and high-pressure silicon carbide module.
The invention provides a performance evaluation method of a nonlinear conductive material, which comprises the following steps: s1) taking the electrical performance, the thermal performance and the mechanical performance of the nonlinear conductive material as performance evaluation indexes, and obtaining the weight of the performance evaluation indexes by using an AHP method; s2) adopting a TOPSIS model, carrying out forward normalization processing on the measurement data of the electrical performance, the thermal performance and the mechanical performance of the nonlinear conductive material, combining the weight of the performance evaluation index to obtain the distance between the nonlinear conductive material and the optimal solution and the worst solution, and carrying out comprehensive distance grading to obtain a comprehensive performance evaluation result. Compared with the prior art, the method provided by the invention comprehensively evaluates the nonlinear conductive material added with the fillers with different doping quality fractions under the condition of simultaneously considering the electrical, thermal and mechanical characteristics, so that the evaluation result is more in line with the actual engineering requirement, and the method has certain guiding significance for the optimization design of the doping quality fractions in the nonlinear conductive packaging material.
Drawings
FIG. 1 is a diagram of a power electronic power module model and its dimensions provided in an embodiment of the present invention;
FIG. 2 is a diagram of a power electronic power module model after being processed and produced in an embodiment of the present invention;
FIG. 3 is a diagram of a mold encapsulated with 4 wt% epoxy/silicon carbide whisker composite in accordance with an embodiment of the invention;
FIG. 4 is a graph of a partial discharge spectrum at 30 ℃ in an example of the present invention;
FIG. 5 is a graph of a partial discharge spectrum at 90 ℃ in an example of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The invention provides a performance evaluation method of a nonlinear conductive material, which comprises the following steps: s1) taking the electrical performance, the thermal performance and the mechanical performance of the nonlinear conductive material as performance evaluation indexes, and obtaining the weight of the performance evaluation indexes by using an AHP method; s2) adopting a TOPSIS model, carrying out forward normalization processing on the measurement data of the electrical performance, the thermal performance and the mechanical performance of the nonlinear conductive material, combining the weight of the performance evaluation index to obtain the distance between the nonlinear conductive material and the optimal solution and the worst solution, and carrying out comprehensive distance grading to obtain a comprehensive performance evaluation result.
In the present invention, the nonlinear electrically conductive material preferably includes nonlinear electrically conductive materials of different inorganic particle doping amounts; the doping amount of the inorganic particles in the nonlinear conductive material is preferably 0-10%, more preferably 0-8%, and further preferably 0-5%; the doping amount of the inorganic particles in the nonlinear conductive material with different inorganic particle doping amounts is preferably changed in a gradient manner by taking 1%; the nonlinear conductive material is not particularly limited as long as it is a nonlinear conductive material well known to those skilled in the art, and in the present invention, the polymer matrix of the nonlinear conductive material is preferably an epoxy resin; the inorganic particles in the nonlinear conductive material are preferably one or more of barium titanate, titanium dioxide and silicon carbide.
The nonlinear conductive material can be commercially available or self-made, and is preferably prepared according to the following method in the invention: modifying the inorganic particles by using a silane coupling agent to obtain modified inorganic particles; mixing the modified inorganic particles, the polymer matrix, the curing agent and the curing accelerator, and curing to obtain the nonlinear conductive material; wherein, the silane coupling agent is preferably a silane coupling agent KH 560; the temperature of the modification is preferably 35-45 ℃, and more preferably 40 ℃; the mass ratio of the silane coupling agent to the inorganic particles is preferably 1: (0.5 to 2), more preferably 1: (0.8 to 1.5), and more preferably 1: 1; the modification is preferably carried out in water; the mass concentration of the silane coupling agent in the modification system is preferably 10-40%, more preferably 20-30%, and further preferably 25%; the modification time is preferably 0.5-2 h, and more preferably 1-1.5 h; the mass ratio of the polymer matrix to the curing agent to the curing accelerator is preferably 100: (80-90): (1-3), more preferably 100:85: 2; the curing agent may be selected according to the kind of the polymer matrix, and in the present invention, methylhexahydrophthalic anhydride is preferable; the curing accelerator may be selected according to the kind of the polymer matrix, and in the present invention, tris (dimethylaminomethyl) phenol is preferable; the mixing is preferably carried out by ultrasonic treatment for 0.5-2 h, more preferably ultrasonic treatment for 1-1.5 h, and then stirring is carried out for 5-20 min, preferably stirring is carried out for 10-15 min; before the solidification, degassing treatment is preferably carried out; the degassing treatment is preferably carried out under vacuum conditions; the degassing treatment temperature is preferably 40-60 ℃, and more preferably 50 ℃; the time of the degassing treatment is preferably 10-50 min, more preferably 20-40 min, and further preferably 30 min; after degassing treatment, preferably, pre-curing is carried out firstly and then curing is carried out; the pre-curing temperature is preferably 70-90 ℃, and more preferably 80 ℃; the pre-curing time is preferably 1-5 h, more preferably 2-4 h, and further preferably 3 h; the curing temperature is preferably 110-150 ℃, more preferably 120-140 ℃ and most preferably 130 ℃; the curing time is preferably 1-4 hours, and more preferably 2-3 hours.
The electrical property, the thermal property and the mechanical property of the nonlinear conductive material are taken as performance evaluation indexesThe method comprises the steps of marking, obtaining the weight of a performance evaluation index by using an AHP method; the nonlinear conductive materials with different inorganic particle doping amounts preferably take the electrical performance, the thermal performance and the mechanical performance at the same temperature as performance evaluation indexes; the electrical property preferably comprises a non-linear conductivity coefficient (c:α) Dielectric constant ofε') Dielectric loss (tan)δ e ) And dielectric strength ofB d ) (ii) a The thermal properties preferably include a glass transition temperature of (CT g ) With a thermal decomposition temperature ofT d ) (ii) a The mechanical properties preferably include a Coefficient of Thermal Expansion (CTE) and a storage modulus: (E') (ii) a In the present invention, the weight preference for obtaining the performance evaluation index by using the AHP method is specifically:
and (3) sorting the importance of the performance evaluation indexes to obtain a pair comparison matrix A:
wherein,a ij representing the importance of the ith individual performance evaluation index compared with the jth individual performance evaluation index; in the invention, the importance degree is preferably assigned according to a 1-9 comparison scale, wherein the scale 1 represents that two performance indexes have the same importance compared with each other; scale 3 indicates that the former is slightly more important than the latter in comparison to the two performance indicators; scale 5 indicates that the former is significantly more important than the latter in comparison to the two performance indicators; the scale 7 indicates that the former is more important than the latter in comparison to the two performance indicators; scale 9 indicates that the former is extremely important compared to the latter performance index; the scales 2, 4, 6, 8 represent the median of the above described adjacent decisions; the ratio of the importance of the reciprocal number performance index i to the performance index j is a ij The ratio of the importance of the performance index j to the performance index i is then a ji =1/a ij 。
Obtaining the weight of the performance evaluation index by using the formula (1):
whereinλ max Is the largest eigenvalue of the matrix a,Iis a vector of the unit,wthe eigenvector of the matrix a is the weight of the performance evaluation index.
To further determine whether the weights are reasonable, a weight check is preferably also performed using equation (2):
c.i. is a consistency index, and when c.i. is less than 0.1, the calculated weight is considered reasonable.
According to the invention, the weight calculation is carried out according to the actual situation by the AHP method, and the optimal impurity doping amount fraction of the nonlinear conductive material can be selected from multiple angles.
The TOPSIS model is adopted to carry out forward normalization processing on the measurement data of the electrical property, the thermal property and the mechanical property of the nonlinear conductive material, and the optimization is as follows: the measurement data matrix of the electrical property, the thermal property and the mechanical property of the nonlinear conductive material is converted into a maximum index according to a formula (3):
where x is the measured data matrix, f (x) is the forward value, M = max | x-x best |，x best Is the optimum value.
The forward matrix is then normalized to eliminate the dimensional effect according to equations (4) and (5):
wherein,x ij is the jth individual performance evaluation index of the ith nonlinear conductive material, N matrix represents the normalized matrix of the forward values of the jth individual performance evaluation indexes of the m nonlinear conductive materials, N ij Is the normalized result of the positive value of the j individual performance evaluation index of the ith nonlinear conductive material, f (x) ij ) And the positive value of the j individual performance evaluation index of the ith nonlinear conductive material is represented.
After normalization processing, combining the weight of the performance evaluation index to obtain the distance between the nonlinear conductive material and the optimal solution and the worst solution, and obtaining the distance between the nonlinear conductive material and the optimal solution and the worst solution according to the formulas (6) and (7):
wherein D is i + Is the distance of the ith nonlinear conductive material from the optimal solution, D i - Is the distance of the ith nonlinear conductive material from the worst solution, N j + Is the maximum value, N, in the jth individual performance evaluation index j - Is the minimum value in the jth individual performance evaluation index; w is a j Is the weight corresponding to the performance evaluation index.
And finally, carrying out comprehensive distance grading, preferably carrying out comprehensive distance grading according to a formula (8), and obtaining a comprehensive performance evaluation result.
Wherein,F i is the firstiA composite distance score for each nonlinear conductive material; d i + Distance of ith nonlinear conductive material from optimal solution, D i - Distance of ith nonlinear conductive material from worst solutionAnd (5) separating.
The TOPSIS is applied to the comparison of the nonlinear conductive packaging materials of the high-temperature and high-pressure silicon carbide module, and then the nonlinear conductive material with the optimal doping quality fraction is selected.
The method provided by the invention comprehensively evaluates the nonlinear conductive material added with the fillers with different doping mass fractions under the condition of simultaneously considering the electrical, thermal and mechanical characteristics, so that the evaluation result is more in line with the actual requirements of engineering, and the method has certain guiding significance on the optimization design of the doping mass fractions in the nonlinear conductive packaging material.
The invention also provides application of the performance evaluation method of the nonlinear conductive material in the selection of the nonlinear conductive material for the encapsulation of the high-temperature and high-pressure silicon carbide module.
In order to further illustrate the present invention, the following will describe the performance evaluation method of a nonlinear conductive material provided by the present invention in detail with reference to the examples.
The reagents used in the following examples are all commercially available.
Examples
1. The invention considers the influence of different temperatures and different performance index weights on the comprehensive evaluation index of the nonlinear conductive material, and prepares the epoxy resin/silicon carbide whisker (EP/SiCw) composite materials with the doping mass fractions of 0 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt% and 5 wt%, which are respectively marked as EP0, EP1, EP2, EP3, EP4 and EP5, and the preparation process is as follows:
the sample preparation process is divided into four main steps: (a) firstly, carrying out hydration reaction at 40 ℃ for 1 hour, carrying out ultrasonic treatment (the ultrasonic power is 800W) on the surface of silicon carbide whiskers (KH 560: silicon carbide whiskers =1:1, the mass fraction of KH560 is 25 wt%, and the mass fraction of silicon carbide whiskers is 25 wt%) in a deionized water environment by using a silane coupling agent KH560, drying the modified silicon carbide whiskers at 130 ℃ for 2 hours, and then grinding; (b) in the second step, modified silicon carbide whiskers with corresponding mass fractions (0 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt% and 5 wt%) were mixed with epoxy resin E-51 (EP-51), methylhexahydrophthalic anhydride (MHHPA) curing agent and tris (dimethylaminomethyl) phenol (DMP-30) accelerator by ultrasonication for 1 h and magnetic stirring for 10 min, wherein the mass ratio of EP-51, MHHPA, DMP-30 was 100:85: 2; (c) the third step, degassing the stirred mixture in a vacuum oven at 50 ℃ for 30 min, preheating a mold for 1 h by using a release agent at 130 ℃, and then cooling to room temperature, and the last step, pre-curing the sample at 80 ℃ for 3 h, and then post-curing at 130 ℃ for 2, so as to obtain the epoxy resin/silicon carbide whisker composite material.
2. The direct conductivity of EP0, EP1, EP2, EP3, EP4, EP5 was measured by a direct conductivity measurement system at 30 ℃ and 90 ℃. The direct current conductivity measurement system consisted of a three electrode system and a Keithley 6517B electrometer. The diameter of the measuring electrode was 30 mm and a temperature controlled oven was used to control the temperature. Measuring direct current at 30 deg.C and 90 deg.C, field intensity is 0.5-10 kV/mm, time is 30 min, calculating direct current conductivity with last 20 s direct current steady state current, and calculating to obtain nonlinear conductivity coefficient by formula (9) ((α) As shown in table 1.
In the formula,Eis a certain field strength in the interval of the non-linear conductance,σfor field strength in the interval of non-linear conductanceEThe corresponding electrical conductivity of the conductive material,E b the switching field strength being a non-linear conductance,σ b is composed ofE b The corresponding conductivity.
TABLE 1 nonlinear conductivity coefficients
Measuring the dielectric constant of the epoxy resin/silicon carbide whisker composite material at 0.1 Hz at 30 ℃ and 90 ℃ by using a Novocontrol Concept 40 broadband dielectric spectrum analyzer (theε') And dielectric loss (tan)δ e ) The results are shown in tables 2 and 3, respectively.
TABLE 2 dielectric constant
TABLE 3 dielectric loss
Measuring the DC breakdown field strength of the epoxy resin/silicon carbide whisker composite material at 30 ℃ and 90 ℃ by adopting a ball plate electrode through an ASTM D-149 standard (B d ) The boosting rate was 1 kV/mm, and the results are shown in Table 4.
TABLE 4 DC breakdown field strength
Measuring and measuring the glass transition temperature of the epoxy resin/silicon carbide whisker composite material by adopting a differential scanning calorimeter TA Q200 (T g ) The temperature range is 25 ℃ to 200 ℃, the heating rate is 10 ℃/min, the test atmosphere is nitrogen, and the results are shown in table 5.
TABLE 5 glass transition temperature
Measuring the thermal decomposition temperature of the epoxy resin/silicon carbide whisker composite material by adopting a thermogravimetric analyzer TA Q500 (T d ) The temperature range is 25 ℃ to 600 ℃, the heating rate is 10 ℃/min, the test atmosphere is nitrogen, and the results are shown in table 6.
TABLE 6 thermal decomposition temperature
Dynamic thermo-mechanical analyzer TA Q800 with environment regulation and control for measuring epoxy resin/carbonCoefficient of Thermal Expansion (CTE) and maximum storage modulus at 30 ℃ and 90 ℃ for silicon carbide whisker compositesE'The temperature increase rate was 5 ℃/min, and the results are shown in tables 7 and 8, respectively.
TABLE 7 coefficient of thermal expansion
TABLE 8 maximum storage modulus
3. And determining the weight of the 8 performance indexes by adopting an AHP method:
(a) the importance of different performance indexes is ranked,a ij is shown asiThe index is compared withjAnd (4) assigning importance degrees of the importance of each index according to a comparison scale of 1-9. Matrix a is a pair-wise comparison matrix.
(b) And solving the weights of different performance indexes by using the formula (1).λ max Is the largest eigenvalue of the matrix a,Iis a vector of the unit,wis the eigenvector of matrix a, i.e. the weight of the performance indicator.
(c) The weight check is performed using equation (2). Calculating a consistency index C.I. whenC.I.Less than 0.1, the calculated weight is considered reasonable.
For the epoxy resin/silicon carbide whisker composite materials with different doping mass fractions studied by the invention, 4 importance orderings are carried out on the performance indexes, as shown in table 9, and according to the steps, the weights of the following 4 performance indexes are calculated, as shown in table 10. For weight 1, the importance of each performance indicator is set to be the same. For weight 2, consider the electrical property, e.g.α、ε'And tanδ e Specific heat and mechanical properties are more important, andB d the composite material is set to be the least important, because the breakdown strength of the epoxy resin/silicon carbide whisker composite material with the doping mass fraction of 1-5 wt% is higher than the lower limit (10 kV/mm) of the breakdown field strength required by the electronic packaging material. For weight 3, thermal behavior is considered, e.g.T g AndT d more important than the electrical and mechanical properties. For weight 4, consider the mechanical properties, e.g. CTE andE'more important than electrical and thermal performance.
TABLE 9 four ranking of importance
TABLE 10 four weight cases
4. Adopting a TOPSIS model to solve comprehensive evaluation indexes:
(a) the original data matrix is converted into a maximum index in a forward mode:
wherein x is a measured value of the index, f (x) is a value after the index is normalized, and M = max | x-x in interval type index calculation best |，x best Is the optimum value.
(b) Normalizing the matrix after the forward normalization to eliminate the influence of the dimension:
wherein x is ij Is the jth index of the ith option, the N matrix represents m options (different evaluation objects), each option has N indexes (evaluation indexes) to be evaluated, f (x) ij ) The values representing the normalization are all benefit-type indicators, meaning that larger values represent better performance.
(c) Calculating the distance of each scheme from the optimal solution and the worst solution:
wherein D is i + Is the distance of the ith nonlinear conductive material from the optimal solution, D i - Is the distance of the ith nonlinear conductive material from the worst solution, N j + Is the maximum value, N, in the jth individual performance evaluation index j - Is the minimum value in the jth individual performance evaluation index; w is a j Is the weight corresponding to the performance evaluation index.
(d) And grading according to the comprehensive distance of each option:
wherein,F i is the firstiThe composite distance score for an option is a score that takes into account the distance of the option from both the optimal solution and the worst solution.
For the epoxy resin/silicon carbide whisker composites of different doping mass fractions studied in the present invention, the data were normalized in the forward direction according to the steps 4 (a) and 4 (b), and the results are shown in tables 11 and 12.
TABLE 11 normalization of performance index of epoxy/silicon carbide whisker composites at 30 deg.C
TABLE 12 normalization of performance index of epoxy/silicon carbide whisker composites at 90 deg.C
According to the steps of 4 (c) and 4 (d), the evaluation indexes for 4 kinds of weight at 30 ℃ and 90 ℃ were calculated, and the results are shown in tables 13 and 14.
Comprehensive evaluation index at 1330 ℃ in table
TABLE 1490 deg.C comprehensive evaluation index
As can be seen from tables 13 and 14, EP1 (epoxy resin/silicon carbide whisker composite material with a doping content fraction of 1 wt%) has the highest overall score at 30 ℃ and 90 ℃ under the weight of 1 (the importance of each performance index is set to be the same), i.e., the electrical, thermal and mechanical overall performance is the best, and EP1 (epoxy resin/silicon carbide whisker composite material with a doping content fraction of 1 wt%) has the highest overall score under the weights of 2, 3 and 4 (the breakdown field strength is reduced) under the weights of 3 and 4B d Weight of (c) EP4 (epoxy/silicon carbide whisker composite with a doping level fraction of 4 wt%) has the highest overall score at 30 ℃ and 90 ℃, i.e. the electrical, thermal and mechanical overall properties are optimal.
Further, the power electronic power module model shown in fig. 1 and its dimensions are designed. The physical diagram after processing and production is shown in FIG. 2.
The mold of figure 2 was encapsulated with 4 wt% epoxy/silicon carbide whisker composite as shown in figure 3.
In the practical process of 4 wt% of epoxy resin/silicon carbide whisker composite material, the composite material bears the action of electric stress, thermal stress and mechanical stress at the same time, and the electric-thermal-mechanical comprehensive performance can be reflected by measuring the strength of the electric performance, such as the partial discharge resistance, under the action of various stresses, so that the effectiveness of the comprehensive performance evaluation method provided by the invention is proved.
In this embodiment, a power electronic power module model encapsulated by 4 wt% of epoxy resin/silicon carbide whisker composite material is subjected to Partial Discharge measurement at 30 ℃ and 90 ℃ respectively by using an alternating current Partial Discharge (PD) measurement circuit, and Phase Resolved Partial Discharge (PRPD) spectra within 2 min from the beginning of Partial Discharge are shown in fig. 4 and 5 respectively. The effective value of the externally applied alternating voltage is 6 kV, and the frequency is 50 Hz.
As can be seen from FIGS. 4 and 5, when the temperature was 30 ℃, the maximum release amount of the model was 36.39 pC, the average release amount was 26.72 pC, and the partial discharge repetition rate was 29.8 PDS/S; when the temperature is 90 ℃, the maximum partial discharge of the model is 47.84 pC, the average partial discharge is 31.07 pC, the repetition rate of partial discharge is 73.74 PDS/S, although the partial discharge of the power electronic power module encapsulated by 4 wt% of epoxy resin/silicon carbide whisker composite material is more serious than 30 ℃ at 90 ℃, the maximum partial discharge is still less than 100 pC and is at a low level of partial discharge, and the partial discharge resistance characteristic at high temperature is still strong, so that the 4 wt% of epoxy resin/silicon carbide whisker composite material is selected as a nonlinear conductive encapsulating material, and the nonlinear conductive encapsulating material has better practicability, namely stronger electro-thermal-mechanical comprehensive performance, thereby proving that the method provided by the invention is reasonable and effective and has stronger practical value.
Claims (10)
1. A method for evaluating the performance of a nonlinear conductive material is characterized by comprising the following steps:
s1) taking the electrical performance, the thermal performance and the mechanical performance of the nonlinear conductive material as performance evaluation indexes, and obtaining the weight of the performance evaluation indexes by using an AHP method;
s2) adopting a TOPSIS model, carrying out forward normalization processing on the measurement data of the electrical performance, the thermal performance and the mechanical performance of the nonlinear conductive material, combining the weight of the performance evaluation index to obtain the distance between the nonlinear conductive material and the optimal solution and the worst solution, and carrying out comprehensive distance grading to obtain a comprehensive performance evaluation result.
2. The method of claim 1, wherein the nonlinear electrically conductive material comprises nonlinear electrically conductive materials with different inorganic particle doping levels.
3. The performance evaluation method according to claim 1, wherein the electrical properties include a nonlinear conductivity coefficient, a dielectric constant, a dielectric loss, and an insulation strength; the thermal properties include a glass transition temperature and a thermal decomposition temperature; the mechanical properties include coefficient of thermal expansion and storage modulus.
4. The method of evaluating performance according to claim 3, wherein in step S2), the dielectric constant, the dielectric loss, the thermal expansion coefficient and the storage modulus are used as cost-type indexes; the nonlinear conductivity coefficient, the insulation strength, the glass transition temperature and the thermal decomposition temperature are taken as benefit indexes.
5. The performance evaluation method according to claim 1, wherein the weight of the performance evaluation index obtained by the AHP method in step S1) is specifically:
and (3) sorting the importance of the performance evaluation indexes to obtain a pair comparison matrix A:
wherein,a ij representing the importance of the ith individual performance evaluation index compared with the jth individual performance evaluation index;
obtaining the weight of the performance evaluation index by using the formula (1):
whereinλ max Is the largest eigenvalue of the matrix a,Iis a vector of the unit,wthe eigenvector of the matrix a is the weight of the performance evaluation index.
6. The performance evaluation method according to claim 5, wherein the step S1) further comprises performing weight check using formula (2):
c.i. is a consistency index, and when c.i. is less than 0.1, the calculated weight is considered reasonable.
7. The performance evaluation method according to claim 1, wherein the forward normalization in step S2) specifically comprises:
the measurement data matrix of the electrical property, the thermal property and the mechanical property of the nonlinear conductive material is converted into a maximum index according to a formula (3):
where x is the measured data matrix, f (x) is the forward value, M = max | x-x best |，x best Is an optimum value;
the forward matrix is then normalized to eliminate the dimensional effect according to equations (4) and (5):
wherein x is ij Is the jth individual performance evaluation index of the ith nonlinear conductive material, N matrix represents the normalized matrix of the forward values of the jth individual performance evaluation indexes of the m nonlinear conductive materials, N ij Is the normalized result of the positive value of the j individual performance evaluation index of the ith nonlinear conductive material, f (x) ij ) And the positive value of the j individual performance evaluation index of the ith nonlinear conductive material is represented.
8. The method for evaluating performance of claim 1, wherein the distances between the nonlinear conductive material and the optimal solution and the worst solution are obtained according to equations (6) and (7) in step S2):
wherein D is i + Is the distance of the ith nonlinear conductive material from the optimal solution, D i - Is the distance of the ith nonlinear conductive material from the worst solution, N j + Is the maximum value, N, in the jth individual performance evaluation index j - Is the minimum value in the jth individual performance evaluation index; w is a j Is the weight corresponding to the performance evaluation index.
9. The performance evaluation method according to claim 1, wherein in step S2), a composite distance score is performed according to formula (8):
wherein,F i is the firstiA composite distance score for each nonlinear conductive material; d i + Distance of ith nonlinear conductive material from optimal solution, D i - The distance of the ith nonlinear electrically conductive material from the worst solution.
10. The method for evaluating the performance of the nonlinear conductive material according to any one of claims 1 to 9, applied to the selection of the nonlinear conductive material in the packaging of the high-temperature and high-pressure silicon carbide module.
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