CN114141319A - Method for rapidly and accurately characterizing viscoelastic parameters of material - Google Patents
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- CN114141319A CN114141319A CN202111137548.7A CN202111137548A CN114141319A CN 114141319 A CN114141319 A CN 114141319A CN 202111137548 A CN202111137548 A CN 202111137548A CN 114141319 A CN114141319 A CN 114141319A
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Abstract
A method for rapidly and accurately characterizing the viscoelasticity parameters of a material belongs to the technical field of viscoelasticity materials. The method comprises the following steps: (1) preparing a viscoelastic material sample strip, and performing mechanical test; (2) performing a stress relaxation test to obtain a stress relaxation curve A; (3) simulating and constructing a constitutive model according to the sample structure of the sample band and the experimental conditions of the mechanical test; (4) inputting Prony series coefficients in simulation modeling software, setting loading conditions, and performing finite element simulation calculation to obtain a stress relaxation curve B; (5) comparing the stress relaxation curve B with the stress relaxation curve A, if the stress relaxation curve B is different from the stress relaxation curve A, adjusting the Prony series coefficient, and repeating the step (4) to perform finite element simulation calculation; if the same, the constitutive parameters are obtained. The method has high result accuracy, and the simulated calculation result has almost no deviation from the actual stress condition.
Description
Technical Field
The invention belongs to the technical field of viscoelastic materials, and particularly relates to a method for rapidly and accurately characterizing viscoelastic parameters of a material.
Background
With the development of information technology and the demand of national economy, electronic products are continuously developing toward miniaturization, light weight, high performance, multiple functions, low cost and the like, and the power consumption of chips is continuously increasing. The thermal interface material is used for reducing the interface thermal resistance, effectively guiding out the heat generated by the chip, reducing the working temperature of the chip and being necessary for ensuring the long-term effective work of the chip.
In a classical flip chip package structure, a thermal interface material is located between the chip and the metal lid, as shown in fig. 1. In the actual operation and reliability test process of the chip, due to different material characteristics of each component of the package structure, such as thermal expansion coefficient, young modulus and other physical parameters, the whole package may deform under the state of temperature change, and stress may be generated at each connection interface, welding spot and other parts. Thermal interface materials are also subject to package thermal stresses, which can lead to failure phenomena such as body cracking or interface delamination once the stresses exceed the threshold that the material and interface can withstand. The thermal physical parameters of the thermal interface material, such as modulus, thermal expansion coefficient, poisson's ratio, etc., can be the main factors affecting its thermo-mechanical reliability.
Thermal stress of package structures can generally be evaluated by finite element simulation methods, but this relies on accurate input of material parameters. In a typical simulation, the thermal interface material is provided as a linear elastic material. In practice, however, the thermal interface material is a viscoelastic material, i.e., its modulus has a significant dependence on temperature and time. Thus, the use of a linear elastic thermal interface material may cause a large deviation between the calculated results of the simulation and the actual stress conditions.
The thermal interface material (usually named as TIM1) of the thermal conductive gel type is mainly composed of a silicone polymer matrix and an inorganic high thermal conductive filler, and is a typical viscoelastic material, but its viscoelastic material structure is generally of less interest. The viscoelastic constitutive structure has various expressions, and a common mathematical model is a generalized Maxwell model, which can be regarded as that a viscoelastic material is formed by connecting an elastic element and a viscous element in series and is expressed by a Prony series, and the equation is shown as follows.
In the formula, the overall elastic modulus is decomposed into the sum of several elastic or viscous elements. Modulus data of the material at different temperatures and different frequencies can be obtained by testing methods such as constant temperature frequency sweep test, constant frequency temperature change and the like. And determining a final viscoelastic constitutive model through data processing, model fitting and other modes, and providing the final viscoelastic constitutive model for finite element simulation as initial material parameter input.
Although the existing method can obtain more accurate viscoelastic material parameters of the thermal interface material, it needs a large number of samples (more than 10 samples) and a very long testing time (10-20 hours), and it also needs much time for processing and analyzing the testing data. In addition, the constitutive parameters obtained by this method are generally complex, and the calculation amount of subsequent finite element analysis is increased.
Disclosure of Invention
In view of the above problems in the prior art, the present invention is directed to a method for rapidly and accurately characterizing viscoelastic parameters of a material. The method combines a tensile stress relaxation experiment and finite element simulation analysis, obtains viscoelasticity material constitutive parameters by backstepping by comparing stress relaxation curves obtained by actual test and simulation, and is used for calculating the stress condition of the viscoelasticity material in the thermal interface material in a packaging structure by finite element simulation. Not only needs less experiments, but also the data processing process and the subsequent calculation are simple and convenient, and meanwhile, the calculation result still has higher precision.
A method for rapidly and accurately characterizing the viscoelastic parameters of a material is characterized by comprising the following steps:
(1) preparing a viscoelastic material sample strip, and performing mechanical test;
(2) performing a stress relaxation test at room temperature to obtain a stress relaxation curve A;
(3) simulating and constructing a constitutive model in simulation modeling software according to the sample structure of the viscoelastic material spline in the step (1) and the experimental conditions of the mechanical test;
(4) inputting Prony series coefficients in simulation modeling software, setting loading conditions the same as those of the mechanical test in the step (1), and performing finite element simulation calculation to obtain a stress relaxation curve B;
(5) comparing the stress relaxation curve B with the stress relaxation curve A, if the stress relaxation curve B is different from the stress relaxation curve A, adjusting the Prony series coefficient, and repeating the step (4) to perform finite element simulation calculation; if the values are the same, the input Prony series coefficient is correct, namely the constitutive parameters of the viscoelastic material based on the Prony series are obtained.
The method for rapidly and accurately characterizing the viscoelastic parameters of the material is characterized in that the mechanical test in the step (1) comprises the following steps: tensile testing, compression testing, shear testing, and three-point bend testing.
The method for rapidly and accurately characterizing the viscoelastic parameters of the material is characterized in that the tensile test is completed by using a dynamic thermomechanical analyzer.
The method for rapidly and accurately characterizing the viscoelastic parameters of the material is characterized in that the experimental conditions of the mechanical test in the step (3) comprise a stretching rate.
The method for rapidly and accurately characterizing the viscoelastic parameters of the material is characterized in that the simulation modeling software in the step (3) comprises Abaqus.
The method for rapidly and accurately characterizing the viscoelastic parameters of the material is characterized in that the constitutive model in the step (3) is in a form containing 1-3 Prony series, and the equation of the constitutive model is as follows:
the method for rapidly and accurately characterizing the viscoelastic parameters of the material is characterized in that the coefficients of the Prony series in the steps (4) and (5) comprise a characteristic modulus and a relaxation time.
The method for rapidly and accurately characterizing the viscoelastic parameters of the material is characterized in that the loading condition in the step (4) comprises a stretching speed.
The method for rapidly and accurately characterizing the viscoelasticity parameters of the material is characterized in that the viscoelasticity material is a polymer-based high polymer material with viscoelasticity, and mainly comprises a thermal interface material, an epoxy molding compound and underfill.
The use of the method for obtaining constitutive parameters of a viscoelastic material.
The invention has the following beneficial effects:
(1) the invention provides a rapid, simple and low-cost reverse analysis method, which obtains the constitutive parameters of the viscoelastic material through the reverse extrapolation of a tensile stress relaxation experiment and can be effectively used for finite element simulation calculation. The result accuracy is high, the data acquisition process verifies the data accuracy, and the simulated calculation result almost has no deviation from the actual stress condition.
(2) Compared with the traditional viscoelastic parameter characterization scheme, the method has the advantage that the cost is greatly reduced.
Drawings
FIG. 1 is a schematic diagram of a flip chip package structure;
FIG. 2 is a stress relaxation curve;
FIG. 3 is a flow chart of the method of the present invention;
fig. 4 is an application example of the viscoelastic constitutive structure of the thermal interface material obtained by the present invention, wherein a is a flip chip model structure, b is a vertical deformation result of the package structure using the viscoelastic constitutive structure, and c is a vertical deformation result of the package structure using the linear elastic constitutive structure.
Detailed Description
The invention will be further illustrated by the following figures and examples.
Example 1:
in this embodiment 1, taking tensile test and simulation of a thermal interface material as an example, the following technical scheme is adopted to characterize viscoelasticity constitutive parameters of a multi-thermal interface material:
(1) and (5) preparing a sample through an experiment. Thermal interface material bars were prepared for tensile testing in a dynamic thermomechanical analyzer.
(2) And (5) performing experimental characterization. Stress relaxation tests were performed at room temperature to obtain stress relaxation curves, as shown in fig. 2.
(3) And (5) simulation modeling. According to the structure and the stretching rate of an actual experimental sample, a simulation model is constructed in Abaqus or related software, and the viscoelastic constitutive model of the thermal interface material is in a form containing 1-3 Prony series.
(4) And (5) simulating iterative computation. The Prony series coefficients of the thermal interface material, such as the characteristic modulus, the relaxation time and the like, are input into Abaqus software, the loading conditions which are the same as those of the experiment are set, finite element simulation calculation is carried out, and a stress relaxation curve is obtained, as shown in figure 2. Comparing the stress relaxation curve obtained by simulation with the actual stress relaxation curve, if the stress relaxation curve and the actual stress relaxation curve are not consistent, properly adjusting the Prony series coefficient of the thermal interface material and submitting the coefficient for calculation; if the two are consistent, the input Prony series coefficient of the thermal interface material is correct, and the viscoelasticity constitutive parameter of the thermal interface material based on the Prony series can be obtained.
FIG. 3 shows a flow chart of the inventive method. The invention is feasible through simulation verification. The thermal interface viscoelastic material obtained by the scheme is used for evaluating the deformation and stress of the packaging structure, as shown in FIG. 4. The result calculated by adopting the viscoelasticity constitutive structure is different from the calculation result by adopting the linear elasticity, and can represent the actual stress and deformation mode of the packaging structure.
Claims (10)
1. A method for rapidly and accurately characterizing the viscoelastic parameters of a material is characterized by comprising the following steps:
(1) preparing a viscoelastic material sample strip, and performing mechanical test;
(2) performing a stress relaxation test at room temperature to obtain a stress relaxation curve A;
(3) simulating and constructing a constitutive model in simulation modeling software according to the sample structure of the viscoelastic material spline in the step (1) and the experimental conditions of the mechanical test;
(4) inputting Prony series coefficients in simulation modeling software, setting loading conditions the same as those of the mechanical test in the step (1), and performing finite element simulation calculation to obtain a stress relaxation curve B;
(5) comparing the stress relaxation curve B with the stress relaxation curve A, if the stress relaxation curve B is different from the stress relaxation curve A, adjusting the Prony series coefficient, and repeating the step (4) to perform finite element simulation calculation; if the values are the same, the input Prony series coefficient is correct, namely the constitutive parameters of the viscoelastic material based on the Prony series are obtained.
2. A method for rapidly and accurately characterizing the viscoelastic parameters of a material as claimed in claim 1, wherein the mechanical test in step (1) comprises: tensile testing, compression testing, shear testing, and three-point bend testing.
3. The method for rapidly and accurately characterizing the viscoelastic parameters of a material according to claim 2, wherein said tensile testing is performed using a dynamic thermomechanical analyzer.
4. The method for rapidly and accurately characterizing the viscoelastic parameters of the material as claimed in claim 1, wherein the experimental conditions of the mechanical test in the step (3) comprise a tensile rate, a compression rate and a shear rate.
5. The method for rapidly and accurately characterizing the viscoelastic parameters of the material as claimed in claim 1, wherein the simulation modeling software in the step (3) comprises Abaqus.
6. The method according to claim 1, wherein the constitutive model in the step (3) is in a form containing 1-3 Prony series, and the equation of the constitutive model is as follows:
7. a method for rapidly and accurately characterizing the viscoelastic parameters of a material according to claim 1, wherein the coefficients of the Prony series in steps (4) and (5) include the characteristic modulus and the relaxation time.
8. A method for rapidly and accurately characterizing the viscoelastic parameters of a material as claimed in claim 1, wherein the loading conditions in step (4) include a stretching rate, a compressing rate and a shearing rate.
9. The method of claim 1, wherein the viscoelastic material is a polymer-based polymeric material with viscoelastic properties, and comprises a thermal interface material, an epoxy molding compound, and an underfill.
10. Use of the method according to claim 1 for obtaining constitutive parameters of a viscoelastic material.
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| CN202111137548.7A CN114141319A (en) | 2021-09-27 | 2021-09-27 | Method for rapidly and accurately characterizing viscoelastic parameters of material |
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| CN202111137548.7A CN114141319A (en) | 2021-09-27 | 2021-09-27 | Method for rapidly and accurately characterizing viscoelastic parameters of material |
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