Improved polymer packaging material viscoelastic constitutive model testing and fitting method
By using dynamic mechanical analysis and fitting of the generalized Maxwell model, the shift factor was optimized, which solved the problems of instability and low accuracy in existing viscoelastic tests, and realized a more accurate viscoelastic model, thereby improving the predictive ability and reliability of packaging materials.
Patent Information
- Application Number
- CN202511776365.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-28
- Publication Date
- 2026-03-20
AI Technical Summary
Existing viscoelasticity testing methods are unstable and have low fitting accuracy, failing to accurately describe the stress state and warpage of polymers over a wide temperature range, leading to packaging reliability issues.
The storage modulus and relaxation modulus were tested at multiple temperatures using a dynamic mechanical analyzer. The curves were fitted using a generalized Maxwell model, and the shift factor was optimized by interpolation to reduce test errors and improve the accuracy of the viscoelastic model.
The accuracy of viscoelasticity testing has been improved over a wider temperature range, reducing errors, enhancing the predictive power of packaging materials, and improving product yield and reliability.
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Figure CN121709104A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of viscoelastic constitutive model testing technology for polymer encapsulation materials, and particularly to an improved method for testing and fitting viscoelastic constitutive models of polymer encapsulation materials. Background Technology
[0002] Polymers such as epoxy molding compounds, underfills, conductive adhesives, and polyamide-imide are widely used in microelectronic packaging, and viscoelasticity is one of the important properties of polymers. Due to the complexity and time-consuming nature of viscoelasticity testing, most packaging stress studies use elastic models to replace viscoelasticity. However, the specific response of polymers to thermal mismatch stress caused by temperature changes differs significantly from the linear elastic response. In the manufacturing process, mismatches in the coefficients of thermal expansion of different materials can lead to thermal stress. For highly compact microelectronic packages, enormous stress can cause severe material cracking, interface delamination, and other reliability issues. Therefore, high-precision testing and application of viscoelasticity are essential for accurately predicting package stress distribution and optimizing package warpage.
[0003] Currently, the testing methods for viscoelastic constitutive models mainly include the following four types: The first method is based on oscillatory rheology, which measures the viscoelastic modulus (storage modulus and loss modulus) of the material by applying periodic strain or stress. This method is often used to test the viscoelasticity of complex fluids and soft materials such as hydrogels. The second method is to perform stress relaxation tests, which measure the stress of the material over time under constant strain. This method is often used to extend the viscoelasticity of rubber elasticity theory to simulate time- and rate-dependent effects. The third method is based on dynamic mechanical analysis, which measures the storage modulus, loss modulus, and loss factor of the material by applying oscillatory force within a certain frequency and temperature range. This method is particularly suitable for studying the viscoelasticity of polymers and composite materials. The fourth method is to measure the mechanical properties of the material in a very small-scale region using nanoindentation technology. Combined with a vibrating indenter, dynamic nanoindentation can be performed to test the viscoelasticity of local regions of polymer materials. After the test, a constitutive model is used for fitting. The generalized Maxwell model is currently a commonly used viscoelastic constitutive model, which consists of multiple Maxwell units (springs and dampers connected in series) in parallel, and can capture a wider range of viscoelastic behavior. Actual testing is limited by equipment service capabilities and time costs, and is often conducted within a narrow range of frequencies or times. In order to expand the frequency or time range of the viscoelastic response of materials, data at different temperatures are often superimposed using the time-time superposition (TTS) principle to obtain a wider range of viscoelastic master curves.
[0004] Current mainstream TTS (Traction Theory System) principle models include the Williams-Landel-Ferry (WLF) equation, the Arrhenius equation, and the Vogel-Fulcher-Tammann (VFT) equation. In general, existing testing methods primarily rely on vibration testing, but without accuracy verification and optimization. The stress-strain relationship of the viscoelastic constitutive model only closely approximates experimental measurements within a small temperature range near the reference temperature, making it unsuitable for direct and widespread application in the research and design of actual products. Furthermore, due to errors in the model fitting process, the resulting viscoelastic constitutive model and TTS principle equations cannot accurately describe the modulus levels at various temperatures and time points, thus underestimating or overestimating the stress state and warpage. Summary of the Invention
[0005] The purpose of this invention is to provide an improved method for testing and fitting viscoelastic constitutive models, which aims to solve the problems of instability and low fitting accuracy in existing viscoelastic tests.
[0006] To achieve the above objectives, this invention provides an improved method for testing and fitting a viscoelastic constitutive model of polymer encapsulation materials, comprising the following steps:
[0007] The curves of energy storage modulus versus frequency and relaxation modulus versus time at multiple temperatures were obtained using a dynamic mechanical analyzer.
[0008] Using the lowest temperature in the experimental storage modulus data as the reference temperature, keeping the curve of the reference temperature unchanged, and shifting the storage modulus curves of other temperatures left and right, we obtain the viscoelastic master curve. The amount of shifting of each temperature curve is the shift factor.
[0009] The viscoelastic master curve of storage modulus-frequency is fitted by a generalized Maxwell model, and the viscoelastic master curve of relaxation modulus-time is plotted using all parameters in the fitting results.
[0010] The experimental relaxation modulus curves at different temperatures are shifted left and right respectively. The shift amount is the optimized shift factor at the corresponding temperature, and it is defined by interpolation.
[0011] The mean value of all relaxation modulus-time curves under the optimal overlap state is calculated to obtain the optimized master curve, and then refitted to obtain the optimized viscoelastic parameters.
[0012] In the section "The curves of energy storage modulus versus frequency and relaxation modulus versus time at multiple temperatures were obtained by testing with a dynamic mechanical analyzer", the frequencies for testing the energy storage modulus were set to 0.05, 0.1, 0.2, 0.5, 1, 2, 5, 10, 20, and 100 Hz, with an amplitude of 3 μm; the temperatures were set to 30~300℃, with each 10℃ representing a node.
[0013] In the section "The curves of energy storage modulus versus frequency and relaxation modulus versus time at multiple temperatures were obtained by testing with a dynamic mechanical analyzer", the temperature nodes for testing the relaxation modulus were 30, 50, 80, 120, 150, and 180℃, the initial strain was 0.1% or 0.05%, and the relaxation time was 2h or 1h; the initial strain was applied after holding the temperature at the corresponding temperature node for 1h.
[0014] The step of "shifting the experimental relaxation modulus curves at different temperatures left and right respectively, and obtaining the shift amount as the optimized shift factor at the corresponding temperature" includes the following steps:
[0015] Take several points evenly on the experimental relaxation modulus curve;
[0016] Calculate the difference between the x-coordinate of the relaxation modulus at these points on the principal curve of relaxation modulus and the x-coordinate of these points;
[0017] The mean of these differences is used as the optimized shift amount, which is the optimized shift factor at the corresponding temperature in the time domain, and is defined by interpolation.
[0018] Replace the frequency domain shift factor obtained by shifting the energy storage modulus with this shift factor.
[0019] The step of "calculating the mean value of all relaxation modulus-time curves under the optimal overlap state to obtain the optimized master curve, and refitting to obtain the optimized viscoelastic parameters" includes the following steps:
[0020] The average relaxation modulus at each time point is calculated by taking all relaxation modulus-time curves under the optimal overlap condition, and the viscoelastic master curve of average relaxation modulus-time is obtained.
[0021] The optimized viscoelastic parameters were obtained by refitting the model using the generalized Maxwell model.
[0022] This invention provides an improved method for testing and fitting viscoelastic constitutive models of polymer encapsulation materials. This method is applicable to the testing and fitting of viscoelastic constitutive models for various engineering materials. The actual stress relaxation curve is a direct standard for verifying the accuracy of the viscoelastic model. By calculating the mean value of the actual stress relaxation curve and the master relaxation modulus curve under optimal overlap, and then re-fitting the nonlinear curve, the shape of the master viscoelastic curve and its fitting parameters can be optimized. Using the translation of the relaxation modulus curve instead of the translation of the storage modulus curve as the shift factor allows for optimization of the shift factor. In numerical calculations, interpolation is used instead of the Williams-Landel-Ferry (WLF) equation method to define the shift factor, thus improving the input method. By optimizing the viscoelastic master curve and shift factor using the time-domain relaxation modulus curve, improvements were made from multiple perspectives, including testing, fitting, and numerical calculation. This reduced random errors introduced by test samples and conditions. Using the storage modulus master curve as a translation reference reduced human experience errors caused by curve translation overlap. Furthermore, the shift factor input method was improved using interpolation, eliminating the influence of WLF equation fitting accuracy. This resulted in a more accurate viscoelastic model over a wider temperature range. Effective closed-loop verification of viscoelastic testing was performed, improving testing accuracy and providing an engineering approach for high-precision material testing in advanced electronic packaging technology R&D, reducing production losses. It also helps improve the predictive ability of packaging signals, heat transfer, stress, and moisture changes, significantly improving product yield, lifespan, and long-term reliability. This solves the problems of unstable testing and low prediction accuracy in existing viscoelastic methods. Attached Figure Description
[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0024] Figure 1 This is a flowchart of the improved viscoelastic constitutive model testing and fitting method for polymer encapsulation materials provided by the present invention.
[0025] Figure 2 This is a graph showing the change of energy storage modulus with frequency.
[0026] Figure 3 This is a graph showing the change of relaxation modulus over time.
[0027] Figure 4 It is the energy storage modulus translation method and the master curve.
[0028] Figure 5This is the relationship between the shift factor and temperature at a reference temperature of 40℃.
[0029] Figure 6 This is the fitting graph of the master curve of energy storage modulus.
[0030] Figure 7 This is the principal curve of the relaxation modulus calculated based on the generalized Maxwell model.
[0031] Figure 8 This is a diagram of the optimization method for the master curve of relaxation modulus.
[0032] Figure 9 It is the relationship between the optimized relaxation modulus shift factor and temperature, defined by the interpolation method.
[0033] Figure 10 This is the optimized mean value fitting plot of the relaxation modulus.
[0034] Figure 11 This is the result of the viscoelastic model before optimization.
[0035] Figure 12 This is the result of the optimized viscoelastic model. Detailed Implementation
[0036] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.
[0037] Please see Figures 1 to 12 This invention provides an improved method for testing and fitting a viscoelastic constitutive model of polymer encapsulation materials, comprising the following steps:
[0038] S1 used a dynamic mechanical analyzer to test the curves of the storage modulus versus frequency and the curves of the relaxation modulus versus time at multiple temperatures.
[0039] The frequencies for testing the energy storage modulus were set to 0.05, 0.1, 0.2, 0.5, 1, 2, 5, 10, 20, and 100 Hz, with an amplitude of 3 μm; the temperature was set to 30~300℃, with each 10℃ representing a node.
[0040] The temperature nodes for testing the relaxation modulus are 30, 50, 80, 120, 150, and 180℃, the initial strain is 0.1% or 0.05%, and the relaxation time is 2h or 1h. The initial strain is applied after holding the material at the corresponding temperature node for 1h.
[0041] Specifically, the experiments used DMA (DMAQ800, TA, USA) and its Tension-film fixture. Taking polyimide as an example, the sample size was 20×5×0.02mm, the gauge length was 10mm, and the dry nitrogen pressure was 60~65psi. To obtain the storage modulus versus frequency curves at multiple temperatures, the Temperature Step & Frequency Sweep method in Multi-Frequency-Strain mode was used; the frequencies were set to 0.05, 0.1, 0.2, 0.5, 1, 2, 5, 10, 20, and 100Hz; the amplitude was 3μm; and the temperature range was 30~300℃, with each 10℃ node representing a node. Furthermore, to obtain the relaxation modulus versus time curves at multiple temperatures, the Stress Relaxation mode was used; the temperature nodes were 30, 50, 80, 120, 150, and 180℃; the initial strain was 0.1% or 0.05%; and the relaxation time was 2h or 1h. To minimize the impact of sample storage temperature and humidity, as well as the test clamping condition, on the test results, the sample is typically held at the corresponding temperature node for 1 hour before the initial strain is applied, and then the test begins. Experimental results are as follows: Figure 2 and Figure 3 As shown.
[0042] S2 uses the lowest temperature in the experimental storage modulus data as the reference temperature. The curve of the reference temperature is kept still, and the storage modulus curves of other temperatures are shifted left and right to obtain the viscoelastic master curve. The amount of shifting of each temperature curve is the shift factor.
[0043] Specifically, at the same frequency, the storage modulus decreases with increasing temperature; at the same temperature, the storage modulus increases with increasing frequency. The rate of decrease in storage modulus reaches its peak at the glass transition temperature, and eventually stabilizes at a constant value with increasing relaxation time. Experimental results cannot be directly fitted to the generalized Maxwell model, such as... Figure 4 This paper uses 40℃ as the reference temperature. The curve at the reference temperature remains unchanged, and the TTS method is used to shift the storage modulus curves at other temperatures left and right. The results at 30℃ and 300℃ are discarded due to large errors. Finally, the curves are overlapped and connected to form a smooth curve, thus obtaining the viscoelastic master curve. See Table 1 and... Figure 5 As shown, the amount of shift in each temperature curve is the shift factor, and the shift factor logα is... T By fitting the WLF equation using formula (1), the coefficient of determination R is obtained. 2 The value is 0.9672, and the empirical constants C1 and C2 are 4.5927 × 10⁻⁶. 15 and 6.2308×10 16 .
[0044] (1)
[0045] Where logα T C1 and C2 are shift factors, C1 and C2 are empirical constants, and T is the test temperature. ref This is a reference temperature.
[0046] Table 1 Energy Storage Modulus Shift Factor
[0047] Temperature (°C) shift factor 40 0.0000 50 -0.0741 60 -0.5889 70 -1.2437 80 -1.9054 90 -2.6997 100 -3.3407 110 -4.0825 120 -4.7203 130 -5.2580 140 -5.7206 150 -6.2187 160 -7.1433 170 -8.1687 180 -9.3350 190 -10.5493 200 -12.1024 210 -13.5717 220 -14.5006 230 -15.5457 240 -16.4183 250 -16.5429 260 -16.7497 270 -17.1290 280 -17.6540 290 -18.5421
[0048] S3 fits the viscoelastic master curve of storage modulus-frequency using a generalized Maxwell model, and plots the viscoelastic master curve of relaxation modulus-time using all parameters in the fitting results.
[0049] Specifically, will Figure 4 The viscoelastic master curve of medium energy storage modulus-frequency is fitted by the Prony series form of the generalized Maxwell model energy storage modulus in the frequency domain according to formula (2), and the fitting result is as follows. Figure 6 As shown. Formula (3) is the Prony series form of the relaxation modulus of the generalized Maxwell model in the time domain. According to formulas (4), (5) and (6), formulas (2) and (3) can be transformed into formulas (7) and (8). Therefore, the fitting results of the storage modulus master curve are calculated as relaxation time and relative modulus, as shown in Table 2. By combining all the parameters in Table 2 with formula (8), the viscoelastic master curve of relaxation modulus-time is plotted, as shown in Table 2. Figure 7 As shown.
[0050] (2)
[0051] (3)
[0052] (4)
[0053] (5)
[0054] (6)
[0055] (7)
[0056] (8)
[0057] Where E' is the storage modulus, E is the relaxation modulus, and E ∞ Let E be the rubber modulus, i be the number of branches, and E be the rubber modulus. i τ is the relaxation coefficient, ω is the frequency, and τ is the τ frequency. i Let E0 be the relaxation time, E0 be the glass modulus, and μ be the glass modulus. ∞ μ is the relative rubber modulus.i It is the relative relaxation coefficient (i.e., the relative modulus).
[0058] Table 2. Fitting results of the master curve of energy storage modulus
[0059]
[0060] S4 shifts the experimental relaxation modulus curves at different temperatures to the left and right respectively. The shift amount is the optimized shift factor at the corresponding temperature, and it is defined by interpolation.
[0061] S41 uniformly selects several points on the experimental relaxation modulus curve;
[0062] S42 calculates the difference between the x-coordinate of the relaxation modulus at these points on the principal curve of relaxation modulus and the x-coordinate of these points.
[0063] S43 takes the mean of these differences as the optimized shift amount, which is the optimized shift factor at the corresponding temperature in the time domain, and defines it using interpolation.
[0064] S44 uses this shift factor to replace the frequency domain shift factor obtained by shifting the energy storage modulus.
[0065] Specifically, such as Figure 8 As shown, Figure 3 The experimental relaxation modulus curves at different temperatures were shifted left and right respectively to make them consistent with... Figure 7 The relaxation modulus-time viscoelastic master curves overlap. During translation, several points (generally 5-10) are uniformly selected from the experimental relaxation modulus curve. The difference between the x-coordinate of the relaxation modulus at these points and the x-coordinate of these points on the relaxation modulus master curve is calculated. The average of these differences is used as the optimized translation amount, which is the optimized shift factor at the corresponding temperature in the time domain (Table 3). This shift factor is used to replace the shift factor in the frequency domain obtained by translating the storage modulus (Table 1), improving the test accuracy of the shift factor. Figure 9 When calculating the shift factor input, the interpolation method is used to replace the Williams-Landel-Ferry (WLF) equation in the TTS principle model, thereby improving the input accuracy of the shift factor.
[0066] Table 3 Optimized relaxation modulus shift factor
[0067]
[0068] S5 calculates the mean value of all relaxation modulus-time curves under the optimal overlap state to obtain the optimized master curve, and then refits it to obtain the optimized viscoelastic parameters.
[0069] S51 calculates the mean value of the relaxation modulus at each time point for all relaxation modulus-time curves under the optimal overlap state, and obtains the viscoelastic master curve of the mean relaxation modulus-time.
[0070] S52 was refitted using the generalized Maxwell model to obtain the optimized viscoelastic parameters.
[0071] Specifically, will Figure 7 By calculating the average relaxation modulus at each time point using all relaxation modulus-time curves under the optimal overlap state, the viscoelastic master curve of the average relaxation modulus-time is obtained. For example... Figure 10 As shown, the optimized viscoelastic parameters (Table 4) are obtained by refitting the Prony series form of the relaxation modulus of the generalized Maxwell model in the time domain using formula (3).
[0072] Table 4. Fitting results of the optimized relaxation modulus mean.
[0073] i Relaxation time (s) relative modulus 1 1.00E-02 2.50E-03 2 1.00E-01 2.98E-02 3 1.00E+00 3.61E-02 4 1.00E+01 1.28E-02 5 1.00E+02 4.53E-02 6 1.00E+03 4.51E-02 7 1.00E+04 4.47E-02 8 1.00E+05 3.12E-02 9 1.00E+06 5.75E-02 10 1.00E+07 7.14E-02 11 1.00E+08 2.36E-02 12 1.00E+09 6.46E-02 13 1.00E+10 6.65E-02 14 1.00E+11 1.85E-02 15 1.00E+12 1.18E-01 16 1.00E+13 3.31E-02 17 1.00E+14 8.50E-02 18 1.00E+15 2.04E-02 19 1.00E+16 5.26E-02 20 1.00E+17 6.23E-02 21 1.00E+18 2.61E-02 22 1.00E+19 1.74E-02 23 1.00E+20 1.93E-02 24 1.00E+21 9.44E-03 25 1.00E+22 2.18E-03 26 1.00E+23 2.87E-04 27 1.00E+24 2.83E-04 28 1.00E+25 4.28E-05
[0074] The following two viscoelasticity testing and fitting methods are compared with experimental results to compare the parameter accuracy before and after optimization. Method 1 (before optimization): Fitting results of the WLF equation ( Figure 5 ) and the fitting results of the master curve of energy storage modulus (Table 2); Method 2 (after optimization): shift factor defined by interpolation method ( Figure 9 The results of fitting the mean of the optimized relaxation modulus are shown in Table 4. Figure 11 and 12 As shown, conventional viscoelasticity testing and fitting methods are clearly only accurate in predicting near the reference temperature, while the improved method maintains high prediction accuracy over a wider temperature range.
[0075] Wherein: Dynamic Mechanical Analyzer, DMA: Dynamic Mechanical Analyzer;
[0076] Time-Temperature Superposition (TTS): Temperature-Time Superposition;
[0077] Williams-Landel-Ferry, WLF;
[0078] Vogel-Fulcher-Tammann, VFT.
[0079] Beneficial effects:
[0080] This invention proposes an improved method for testing and fitting viscoelastic constitutive models of polymer encapsulation materials, applicable to the testing and fitting of viscoelastic constitutive models for various engineering materials. The actual stress relaxation curve is a direct standard for verifying the accuracy of the viscoelastic model. By calculating the mean value of the actual stress relaxation curve and the master relaxation modulus curve under optimal overlap, and then re-fitting the nonlinear curve, the shape of the master viscoelastic curve and its fitting parameters can be optimized. Using the translation of the relaxation modulus curve instead of the translation of the storage modulus curve as the shift factor optimizes the shift factor. In numerical calculations, interpolation is used instead of the Williams-Landel-Ferry (WLF) equation method to define the shift factor, improving the input method. By optimizing the viscoelastic master curve and shift factor using the time-domain relaxation modulus curve, improvements were made from multiple perspectives, including testing, fitting, and numerical calculation. This reduced random errors introduced by test samples and conditions. Using the storage modulus master curve as a translation reference reduced human experience errors caused by curve translation overlap. Furthermore, the shift factor input method was improved using interpolation, eliminating the influence of WLF equation fitting accuracy. This resulted in a more accurate viscoelastic model over a wider temperature range. Effective closed-loop verification of viscoelastic testing was performed, improving testing accuracy and providing an engineering approach for high-precision material testing in advanced electronic packaging technology R&D, reducing production losses. This also helps improve the predictive ability of packaging signals, heat transfer, stress, and moisture changes, significantly contributing to improved product yield, lifespan, and long-term reliability.
[0081] The above-disclosed embodiments are merely preferred embodiments of the improved viscoelastic constitutive model testing and fitting method for polymer encapsulation materials of the present invention. Of course, they should not be construed as limiting the scope of the present invention. Those skilled in the art can understand that all or part of the processes of the above embodiments can be implemented, and equivalent changes made in accordance with the claims of the present invention are still within the scope of the invention.
Claims
1. An improved method for testing and fitting the viscoelastic constitutive model of polymer encapsulation materials, characterized in that, Includes the following steps: The curves of energy storage modulus versus frequency and relaxation modulus versus time at multiple temperatures were obtained using a dynamic mechanical analyzer. Using the lowest temperature in the experimental storage modulus data as the reference temperature, keeping the curve of the reference temperature unchanged, and shifting the storage modulus curves of other temperatures left and right, we obtain the viscoelastic master curve. The amount of shifting of each temperature curve is the shift factor. The viscoelastic master curve of storage modulus-frequency is fitted by a generalized Maxwell model, and the viscoelastic master curve of relaxation modulus-time is plotted using all parameters in the fitting results. The experimental relaxation modulus curves at different temperatures are shifted left and right respectively. The shift amount is the optimized shift factor at the corresponding temperature, and it is defined by interpolation. The mean value of all relaxation modulus-time curves under the optimal overlap state is calculated to obtain the optimized master curve, and then refitted to obtain the optimized viscoelastic parameters.
2. The improved viscoelastic constitutive model testing and fitting method for polymer encapsulation materials as described in claim 1, characterized in that, In the test of "the curves of energy storage modulus versus frequency and relaxation modulus versus time at multiple temperatures obtained by dynamic mechanical analyzer", the frequencies for testing the energy storage modulus were set to 0.05, 0.1, 0.2, 0.5, 1, 2, 5, 10, 20, and 100 Hz, with an amplitude of 3 μm; the temperatures were set to 30~300℃, with each 10℃ representing a node.
3. The improved viscoelastic constitutive model testing and fitting method for polymer encapsulation materials as described in claim 2, characterized in that, In the test of "the curves of energy storage modulus versus frequency and relaxation modulus versus time at multiple temperatures obtained by dynamic mechanical analyzer", the temperature nodes for testing the relaxation modulus were 30, 50, 80, 120, 150, and 180℃, the initial strain was 0.1% or 0.05%, and the relaxation time was 2h or 1h; the initial strain was applied after holding at the corresponding temperature node for 1h.
4. The improved viscoelastic constitutive model testing and fitting method for polymer encapsulation materials as described in claim 1, characterized in that, The step of "shifting the experimental relaxation modulus curves at different temperatures left and right respectively, and obtaining the shift amount as the optimized shift factor at the corresponding temperature" includes the following steps: Take several points evenly on the experimental relaxation modulus curve; Calculate the difference between the x-coordinate of the relaxation modulus at these points on the principal curve of relaxation modulus and the x-coordinate of these points; The mean of these differences is used as the optimized shift amount, which is the optimized shift factor at the corresponding temperature in the time domain, and is defined by interpolation. Replace the frequency domain shift factor obtained by shifting the energy storage modulus with this shift factor.
5. The improved viscoelastic constitutive model testing and fitting method for polymer encapsulation materials as described in claim 1, characterized in that, The step of "calculating the mean value of all relaxation modulus-time curves under the optimal overlap state to obtain the optimized master curve, and refitting to obtain the optimized viscoelastic parameters" includes the following steps: The average relaxation modulus at each time point is calculated by taking all relaxation modulus-time curves under the optimal overlap condition, and the viscoelastic master curve of average relaxation modulus-time is obtained. The optimized viscoelastic parameters were obtained by refitting the model using the generalized Maxwell model.