Solder joint thermal fatigue life prediction method based on image data and accelerated degradation modeling

Abstract

The present invention discloses a method for predicting the thermal fatigue life of solder joints based on image data and accelerated degradation modeling. The method comprises: obtaining solder joint fatigue crack length image data through accelerated thermal fatigue life testing of circuit board solder joints, calculating the solder joint fatigue crack length at different times under each test stress; performing accelerated degradation modeling analysis on the solder joint fatigue crack length at different times under each test stress, and calculating the solder joint thermal fatigue reliable life for each test stress; solving an accelerated model based on the solder joint thermal fatigue reliable life at each test stress, and deriving the solder joint thermal fatigue reliable life under normal operating stress; and fitting the solder joint thermal fatigue life model to obtain the solder joint thermal fatigue life distribution under normal operating stress. The present invention's accelerated stress testing can predict the thermal fatigue life of circuit board solder joints under normal operating stress, providing data support for circuit board manufacturers to develop effective after-sales solutions.

Description

Technical Field

[0001] The present invention relates to the technical field of integrated circuits, and more particularly to a method for predicting solder joint thermal fatigue life based on image data and accelerated degradation modeling. Background Art

[0002] During the use of circuit board products, solder joints are periodically subjected to periodic transient currents during operation. When the current passes through the solder joints, they rapidly heat the solder joints, and after the current passes through the solder joints, the solder joints rapidly cool down. Therefore, the solder joints on circuit boards are in a state of thermal fatigue during operation. Under thermal fatigue, at the microscopic level, the solder joints can undergo internal recrystallization through a continuous recrystallization mechanism involving subgrain rotation, weakening the structure of the recrystallized region of the solder joint. Cracks can easily initiate and propagate between recrystallized grains, even penetrating the entire solder joint to form intergranular fractures, causing the solder joint to fail. At the macroscopic level, the different thermal expansion coefficients of the materials surrounding the solder joints result in mismatched thermal strains generated by the various materials during thermal expansion or contraction. This creates stress concentration at the point of strain mismatch, leading to crack initiation and propagation, and thus thermal fatigue damage to the solder joints.

[0003] To develop effective after-sales solutions, PCB manufacturers need to fully understand the thermal fatigue life of PCB solder joints. This refers to the percentage of products from a batch that remain functional after a specific period of use. Because fatigue cracks in PCB solder joints are difficult to detect after they are put into use, PCB solder joint testing is necessary. This data can be analyzed to assess the thermal fatigue life of PCB solder joints.

[0004] The thermal fatigue life of PCB solder joints under normal working stress is long. If conventional stress tests are carried out, the test time will be long and the test cost will be too high for manufacturers to bear. Therefore, accelerated stress tests are needed to shorten the test time while ensuring that the PCB solder joints meet the working requirements.

[0005] Failure of PCB solder joints is a degenerative failure, meaning that fatigue cracks in the solder joints gradually expand from initiation during the test until the fatigue crack length is too large to meet operational requirements. Therefore, regular monitoring of the fatigue crack length of the solder joints is necessary during the test. Conventional methods cannot be used to measure the fatigue crack length of solder joints. The only way to obtain image data is to slice and photograph the solder joints.

[0006] The thermal fatigue life cannot be directly obtained from the image data of the fatigue crack length of the solder joint. It is necessary to use the accelerated degradation modeling method to perform mathematical analysis on the image data to finally obtain the thermal fatigue life of the circuit board solder joint under normal working stress.

[0007] CN201610520419 discloses a method for predicting the thermal fatigue life of electronic package solder joints based on pulsed eddy current thermal imaging. However, this method only predicts the life of solder joints during service, and does not consider the fact that fatigue cracks in most circuit board solder joints are difficult to monitor during use. It also does not involve accelerated degradation modeling. CN20170073143 discloses a method for analyzing the fatigue life of electronic package solder joints, but this method does not involve accelerated degradation modeling and is unrelated to image data.

[0008] Therefore, how to provide a method for predicting the thermal fatigue life of circuit board solder joints based on image data and accelerated degradation modeling is an urgent problem that needs to be solved by those skilled in the art. Summary of the Invention

[0009] In view of this, the present invention provides a solder joint thermal fatigue life prediction method based on image data and accelerated degradation modeling. Accelerated thermal fatigue life tests of circuit board solder joints are carried out to obtain image data of solder joint fatigue crack lengths. By preprocessing the data and performing accelerated degradation modeling, the thermal fatigue life distribution of circuit board solder joints under normal working stress is calculated. The proportion of circuit board products in the same batch that can still work normally after a specific period of use is predicted, providing data support for circuit board manufacturers to formulate practical and effective after-sales plans.

[0010] In order to achieve the above object, the present invention adopts the following technical solutions:

[0011] Solder joint thermal fatigue life prediction method based on image data and accelerated degradation modeling, including:

[0012] The solder joint fatigue crack length image data is obtained by conducting accelerated thermal fatigue life test on the solder joint of the circuit board, and the solder joint fatigue crack length image data is preprocessed to calculate the solder joint fatigue crack length at different test stress moments;

[0013] The fatigue crack length of the solder joint at different times under each test stress is modeled and analyzed for accelerated degradation of the solder joint thermal fatigue performance. The thermal fatigue reliability of the solder joint under each test stress is calculated. Based on the thermal fatigue reliability of the solder joint under each test stress, the thermal fatigue reliable life of the solder joint under each test stress is calculated.

[0014] By solving the accelerated model of the solder joint thermal fatigue reliable life under various test stresses, the solder joint thermal fatigue reliable life under normal working stress is derived;

[0015] The thermal fatigue life model of the solder joint is fitted by the thermal fatigue reliable life of the solder joint under normal working stress, and the thermal fatigue life distribution of the solder joint under normal working stress is obtained.

[0016] Preferably, the specific process of obtaining the fatigue crack length of the weld is:

[0017] Collect the solder joints under various test stresses t1, t2,…, t m Image data of fatigue crack length of weld spot after time preprocessing;

[0018] For weld fatigue cracks with simple shapes, they are treated as straight lines; for weld fatigue cracks with complex shapes, they are treated as broken lines or multiple straight lines superimposed. The measured weld fatigue crack length and the scale length are converted to obtain the actual weld fatigue crack length.

[0019] Preferably, the fatigue crack length of the solder joint at different times under each test stress is subjected to accelerated degradation modeling analysis of the solder joint thermal fatigue performance, and the specific process is as follows:

[0020] The maximum likelihood estimation is used to obtain the t j Estimated value of the mean fatigue crack length of the weld at time and the estimated standard deviation of fatigue crack length of welds

[0021]

[0022]

[0023] Among them, S y (t j ) is the sample standard deviation, t j The mean of the performance degradation of all samples at the moment, n represents the total number of samples, y ij Indicates t j The performance degradation of the i-th sample at time moment;

[0024] Calculate t1, t2, ..., t under each test stress m Estimated value of the mean fatigue crack length of the weld corresponding to time and standard deviation estimates Thus, the estimated value of the mean fatigue crack length of the weld spot at all measurement moments under each test stress and the estimated value of the standard deviation of the fatigue crack length of the weld spot at all measurement moments under each test stress are obtained;

[0025] The function μ of the average value of fatigue crack length of solder joints at all measurement moments under each test stress is simulated as a function of the number of temperature cycles. y (t), the function of the standard deviation of fatigue crack length of the weld at all measurement moments under each test stress and the number of temperature cycles σ is simulated by estimating the standard deviation of the fatigue crack length of the weld at all measurement moments under each test stress y (t);

[0026] Assume that the performance degradation amount is y, and the performance degradation amount y obeys the mean μ y (t), standard deviation is σ y Normal distribution of (t);

[0027] If y≥C, the relationship between solder joint thermal fatigue reliability and performance degradation distribution is as follows:

[0028]

[0029] Where, R(t) represents the thermal fatigue reliability of the solder joint, C represents the fatigue crack length failure threshold, μ y (t) represents the functional relationship between the mean fatigue crack length and the number of temperature cycles, σ y (t) represents the functional relationship between the standard deviation of fatigue crack length and the number of temperature cycles, and Φ(·) represents the standard normal distribution.

[0030] Preferably, the specific process of deriving the thermal fatigue reliable life of the solder joint under normal working stress is:

[0031] Substitute the thermal fatigue reliable life of the solder joint under each test stress into the acceleration model formula to solve the unknown parameters. The acceleration model is:

[0032]

[0033] Where N is the reliable life, ΔT is the temperature range, Tmax is the maximum temperature, f is the frequency of temperature cycle, Ea is the activation energy, K is the Boltzmann constant, δ, β1, β2 are unknown parameters, for lead-free solder joints, β2 takes the empirical value

[0034] The normal working stress parameters of the solder joint are substituted into the accelerated model after solving the unknown parameters, and the thermal fatigue reliable life of the solder joint under normal working stress is obtained.

[0035] Preferably,

[0036] The thermal fatigue life model is:

[0037]

[0038] Where m and η are the shape parameter and scale parameter of the solder joint respectively, N f is the number of temperature cycles the solder joint experiences.

[0039] It can be seen from the above technical solution that, compared with the prior art, the present invention discloses a method for predicting the thermal fatigue life of solder joints based on image data and accelerated degradation modeling. By conducting accelerated thermal fatigue life tests on circuit board solder joints, image data of the fatigue crack length of solder joints is obtained. The image data is mathematically analyzed using the accelerated degradation modeling method to predict the thermal fatigue life of circuit board solder joints under normal working stress, providing data support for circuit board manufacturers to formulate practical and effective after-sales plans. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0041] Figure 1 The accompanying drawing is a flow chart of the solder joint thermal fatigue life prediction method based on image data and accelerated degradation modeling provided by the present invention.

[0042] Figure 2 The accompanying drawing is a schematic diagram of measuring the fatigue crack length of a weld provided by the present invention. Figure 2 (a) Schematic diagram of linear fatigue crack length measurement; Figure 2 (b) is a schematic diagram of the broken line fatigue crack length measurement; Figure 2 (c) is a schematic diagram of the weld diameter measurement. DETAILED DESCRIPTION

[0043] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0044] The embodiment of the present invention discloses a method for predicting the thermal fatigue life of solder joints based on image data and accelerated degradation modeling, such as Figure 1 Shown, including:

[0045] (1) The solder joint fatigue crack length image data is obtained through the accelerated test of the thermal fatigue life of the circuit board solder joint. The solder joint fatigue crack length image data is preprocessed and the solder joint fatigue crack length of each test stress is calculated.

[0046] In order to reproduce the thermal fatigue failure of the PCB solder joints, it is necessary to simulate their actual working environment and conduct high and low temperature cycle tests. In this case, a long test time is required. Therefore, the test time must be shortened and the idea of ​​accelerated degradation must be introduced to conduct high and low temperature cycle accelerated tests on the PCB solder joints.

[0047] In order to ensure the validity of the results of image data processing and analysis of fatigue crack length of solder joints, the stress levels of high and low temperature cycle acceleration test shall not be less than 3, and all stress intensities shall not exceed the ultimate working stress of the solder joint. The number of measurement points at each stress level shall not be less than 5, and the number of measurements at each measurement point does not have to be exactly the same, but at least 1 time. Since slicing and photographing solder joints is a destructive measurement, the test sample data shall not be less than the sum of all measurements. The test time under each test stress shall be determined by the manufacturer based on the product specifics and test equipment parameters. An empirical value: first estimate the approximate acceleration factor under each test stress, and then divide the expected thermal fatigue life of the solder joint under normal working stress by the respective acceleration factors to obtain the expected thermal fatigue life of the solder joint under each test stress. The test time under each test stress shall not be less than one-third of the corresponding expected thermal fatigue life.

[0048] The specific steps include:

[0049] (11): Obtain solder joint fatigue crack length image data through accelerated thermal fatigue life test of circuit board solder joints;

[0050] (12) The weld fatigue crack length image data is preprocessed, and the preprocessed data can be directly used for accelerated degradation modeling analysis.

[0051] Since the format of the weld fatigue crack length image data is a picture, it is necessary to use image processing software to measure the fatigue crack length. The measurement principle is as follows: For fatigue cracks with simple shapes, they are processed as straight lines, such as Figure 2 (a) As shown; for fatigue cracks with complex shapes, they are processed as broken lines or multiple straight lines superimposed, such as Figure 2 (b)

[0052] The actual length of the fatigue crack can be obtained by converting the measured fatigue crack length and the ruler length.

[0053] For images that provide a complete solder joint structure, the solder joint diameter needs to be measured, and the solder joint fatigue crack length failure threshold is determined based on the solder joint diameter, such as Figure 2 (c) shown.

[0054] (2) The pre-processed weld fatigue crack length image data is used to perform accelerated degradation modeling analysis of the weld thermal fatigue performance.

[0055] The measured values ​​of the fatigue crack length of the solder joint under each measurement point obey the normal distribution, so the normal process model can be used to model the accelerated degradation of the thermal fatigue performance of the solder joint based on the fatigue crack length of the solder joint.

[0056] Collect solder joints at t1, t2,…, t mThe fatigue crack length data of the weld at each moment is used to perform a distribution hypothesis test on the fatigue crack length of the weld at each measurement moment using the graphical estimation method or other distribution hypothesis test methods. If the performance degradation amount y obeys the mean value μ y (t) (location parameter), standard deviation is σ y (t) (shape parameter) is normally distributed, and the normal process model should be used to model the performance degradation process of the solder joint. Specifically, the following steps are included:

[0057] When the solder joint failure criterion is performance degradation y ≥ C (C represents the failure threshold of the solder joint fatigue crack length), the relationship between the solder joint thermal fatigue reliability and performance degradation distribution is as follows:

[0058]

[0059] The degradation data of the i-th test sample is recorded as (t j ,y ij )(i=1,2,…,n;j=1,2,…,m), let t j The population mean at this moment is μ y (t j ), the population standard deviation is σ y (t j ), and use maximum likelihood estimation to get t j The point estimates of the mean and standard deviation of the fatigue crack length of the weld spot at time are

[0060]

[0061]

[0062] Among them, S y (t j ) is the sample standard deviation, t j The mean performance degradation of all samples at the moment.

[0063] In this way, we can get t1, t2, ..., t m Estimated value of the mean fatigue crack length of the weld at time and an estimate of the population standard deviation

[0064] Based on the estimated values ​​of the fatigue crack length mean and standard deviation of the solder joints, the functional relationship between them and time is established through degradation trend analysis and degradation model. Substituting them into Equation 1, the reliability function of the solder joint can be determined, and then the life distribution of the solder joint can be fitted.

[0065] The Darveaux model is a solder joint life prediction model based on the energy accumulation theory. When predicting the fatigue life of solder joints, it comprehensively utilizes the damage of hysteresis energy to solder joints. Its life prediction equation is as follows:

[0066]

[0067]

[0068]

[0069] Where k1, k2, k3, k4 are related constants, N0 is the number of temperature cycles experienced by the solder joint when the crack initiates, Δw ave is the accumulated strain energy density, α is the fatigue crack length, da / dN is the crack growth rate, N f is the number of temperature cycles the solder joint experiences.

[0070] The Darveaux model predicts the fatigue life of solder joints based on strain energy and takes into account the influence of hysteresis energy, so it can make a more accurate prediction of the fatigue life of solder joints.

[0071] Under the condition that the temperature cycle stress remains unchanged, N0 and da / dN are constants, and the fatigue crack length α of the solder joint is related to the number of temperature cycles N experienced by the solder joint. f are unknown variables, α and N f There is a linear relationship, that is

[0072]

[0073] Equation 4 is the thermal fatigue performance degradation model equation of the solder joint under specific temperature cycle stress, which can be used as μ in Equation 1. y (t) and σ y (t) is the fitting objective function.

[0074] The principle of data fitting analysis is as follows: data scatter points with small data volume and large deviation are removed as outliers; for measurement data at the end of fatigue crack failure, the corresponding data scatter points are no longer suitable for data fitting analysis and should all be removed as outliers.

[0075] After completing the data fitting analysis, the reliability function of the solder joint under each test stress can be obtained (see Formula 1). Let R be 0.99, 0.95, 0.9, 0.8, 0.7 and 0.6 respectively, substitute them into Formula 1, and calculate the reliable life corresponding to each test stress.

[0076] (3) Solve the accelerated model of the solder joint thermal fatigue reliable life under various test stresses and derive the solder joint thermal fatigue reliable life under normal working stress;

[0077] The Coffin-Manson model reflects the fatigue failure of products caused by thermal cycling stress and has also been successfully used to simulate the crack growth process of solder joints after being subjected to temperature shock. Therefore, it can be applied to the accelerated model of temperature cycling stress.

[0078] The general form of the Coffin-Manson model is

[0079]

[0080] Among them, N is the reliable life (the unit of product reliable life expressed by the number of temperature cycles), ΔT is the temperature range, Tmax is the maximum temperature, f is the frequency of temperature cycle, E a is the activation energy (related to the product), K is the Boltzmann constant (8.62×10-5eV / K), δ, β1, and β2 are unknown parameters. For lead-free solder joints, β2 is an empirical value.

[0081] Substitute 0.99, 0.95, 0.9, 0.8, 0.7 and 0.6 reliable life under each test stress into formula 5 respectively, solve the unknown parameters, and obtain the acceleration models corresponding to 0.99, 0.95, 0.9, 0.8, 0.7 and 0.6 reliable life respectively. Then substitute the normal working stress parameters of the solder joint into the acceleration model after solving the unknown parameters, and the thermal fatigue reliable life of 0.99, 0.95, 0.9, 0.8, 0.7 and 0.6 solder joints under normal working stress can be obtained respectively.

[0082] (4) The thermal fatigue life model of the solder joint is fitted by the thermal fatigue reliable life of the solder joint under normal working stress, and the thermal fatigue life distribution of the solder joint under normal working stress is obtained.

[0083] The thermal fatigue life model of the solder joint is fitted using the reliable life of 0.99, 0.95, 0.9, 0.8, 0.7 and 0.6 under normal working stress, and the thermal fatigue life distribution of the solder joint under normal working stress is obtained.

[0084] The Weibull distribution includes models with a constant failure rate, as well as models with a decreasing (early failure) or increasing (wear-out failure) failure rate over time. Therefore, it can describe more complex failure processes, including fatigue failures of products. Based on the experience of using the Weibull distribution to describe product life characteristics, the location parameter in the three-parameter Weibull distribution can often be assumed to be 0, in which case it becomes a two-parameter Weibull distribution. Therefore, the two-parameter Weibull model can be used to describe the thermal fatigue life distribution of solder joints. Its reliability function is

[0085]

[0086] Where m and η are the shape parameter and scale parameter of the solder joint, respectively.

[0087] Taking the natural logarithm of both sides of equation 6, we get

[0088]

[0089] According to Formula 7, the reliable life of 0.99, 0.95, 0.9, 0.8, 0.7 and 0.6 under normal working stress is fitted to obtain the thermal fatigue life distribution of the solder joint under normal working stress.

[0090] The method of the present invention will be further described below with reference to specific embodiments:

[0091] Accelerated thermal fatigue life testing of solder joints on a certain type of circuit board was conducted under three temperature cycling stress levels: -15°C to 65°C (low temperature 15°C, high temperature 65°C), -15°C to 75°C, and -15°C to 85°C. All tests were conducted at the same heating and cooling rate of 10°C / min, with a temperature cycling period of 1 hour. The data obtained after preprocessing the fatigue crack length image data are shown in Tables 1 to 3. The normal operating stress for the solder joints was 12 temperature cycles per 24-hour day, with the lowest temperature cycle being room temperature (25°C) and the highest temperature being 55°C.

[0092] Table 1 - Fatigue crack length data under test stress at 15℃~65℃

[0093]

[0094]

[0095]

[0096] Table 2 - Fatigue crack length data under test stress at 15℃~75℃

[0097]

[0098]

[0099]

[0100]

[0101]

[0102] Table 3 Fatigue crack length data under test stress at -15℃~85℃

[0103]

[0104]

[0105]

[0106]

[0107]

[0108]

[0109]

[0110] The data in Tables 1 to 3 were fitted and analyzed according to the following principle: scattered points with small data volume and large deviation were removed as outliers. For the scatter plots under the test stress of -15℃ to 75℃ and -15℃ to 85℃, after the number of temperature cycles reached 700 and 600, respectively, many fatigue cracks had reached the end of failure, and the corresponding scattered points were no longer suitable for data fitting analysis.

[0111] The thermal fatigue performance degradation model of the solder joint obtained after data fitting analysis is shown in Table 4.

[0112] Table 4 Thermal fatigue performance degradation model of solder joints of a certain type of circuit board

[0113]

[0114]

[0115] Convert all measured solder joint diameters to actual solder joint diameters according to the ruler length and calculate the average value. Failure threshold of fatigue crack length Combined with the data in Table 4, substitute them into formula 1 together, and assume that the thermal fatigue reliability life of the solder joint under the i-th test stress level is R Then there is

[0116]

[0117]

[0118]

[0119] Let R be 0.99, 0.95, 0.9, 0.8, 0.7 and 0.6 respectively, and the calculated reliable life is shown in Table 5.

[0120] Table 5 Thermal fatigue reliability life of solder joints under test stress (unit: number of temperature cycles)

[0121]

[0122]

[0123] Substitute the thermal fatigue reliable life of the solder joint with a given reliability under the test stress in Table 5 into Formula 5 to obtain the accelerated models of the reliable life of 0.99, 0.95, 0.9, 0.8, 0.7 and 0.6, respectively.

[0124]

[0125]

[0126]

[0127]

[0128]

[0129]

[0130] where N f is the point estimate of the average life of the solder joint thermal fatigue, N f0.99 、N f0.95 、N f0.9 、N f0.8 、N f0.7 and N f0.6 The thermal fatigue reliable life of the solder joint is taken as 0.99, 0.95, 0.9, 0.8, 0.7 and 0.6 for the given reliability R respectively.

[0131] Substituting the normal working stress parameters of the solder joint into the above acceleration model, the reliable lifespans of 0.99, 0.95, 0.9, 0.8, 0.7 and 0.6 under normal working stress can be calculated respectively, as shown in Table 6.

[0132] Table 6 Reliable life of solder joints under working stress due to thermal fatigue

[0133]

[0134]

[0135] By fitting the data in Table 6 according to Equation 7, we can obtain the reliability function of the solder joints under working stress and the reliability and corresponding failure probability of the solder joints of this model circuit board every month within one year of use, as shown in Tables 7 and 8, respectively.

[0136] Table 7 Solder joint reliability function under working stress

[0137]

[0138] Table 8 Monthly reliability and failure probability of solder joints

[0139]

[0140] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. Reference can be made to the common and similar parts between the various embodiments. For the devices disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple, and the relevant parts can be referred to the method description.

[0141] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A solder joint thermal fatigue life prediction method based on image data and accelerated degradation modeling, characterized in that: include: The solder joint fatigue crack length image data is obtained by accelerated thermal fatigue life test of the circuit board solder joint. The solder joint fatigue crack length image data is preprocessed to calculate the solder joint fatigue crack length at different test stress times. The specific process of obtaining the solder joint fatigue crack length is as follows: collect the solder joint fatigue crack length at each test stress t1, t2, ..., t m The image data of weld fatigue crack length after moment preprocessing; for weld fatigue cracks with simple shapes, they are processed as straight lines; for weld fatigue cracks with complex shapes, they are processed as broken lines or multiple straight lines superimposed, and the measured weld fatigue crack length is converted to the scale length to obtain the actual weld fatigue crack length; The fatigue crack length of the solder joint at different times under each test stress is fitted, and the thermal fatigue reliability function of the solder joint at each test stress is calculated through degradation trend analysis and degradation model. Based on the thermal fatigue reliability function of the solder joint at each test stress, the thermal fatigue reliable life of the solder joint at each test stress is calculated. The specific process is as follows: The maximum likelihood estimation is used to obtain the t j Estimated value of the mean fatigue crack length of the weld at time and the estimated standard deviation of fatigue crack length of welds Among them, S y (t j ) is the sample standard deviation, t j The mean of the performance degradation of all samples at the moment, n represents the total number of samples, y ij Indicates t j The performance degradation of the i-th sample at time moment; Calculate t1, t2, ..., t under each test stress m Estimated value of the mean fatigue crack length of the weld corresponding to time and standard deviation estimates Thus, the estimated value of the mean fatigue crack length of the weld spot at all measurement moments under each test stress and the estimated value of the standard deviation of the fatigue crack length of the weld spot at all measurement moments under each test stress are obtained; The function μ of the average value of fatigue crack length of solder joints at all measurement moments under each test stress is simulated as a function of the number of temperature cycles. y (t), the function of the standard deviation of fatigue crack length of the weld at all measurement moments under each test stress and the number of temperature cycles σ is simulated by estimating the standard deviation of the fatigue crack length of the weld at all measurement moments under each test stress y (t); Assume that the performance degradation amount is y, and the performance degradation amount y obeys the mean μ y (t), standard deviation is σ y Normal distribution of (t); If y≥C, the relationship between solder joint thermal fatigue reliability and performance degradation distribution is as follows: Where, R(t) represents the thermal fatigue reliability of the solder joint, C represents the fatigue crack length failure threshold, μ y (t) represents the functional relationship between the mean fatigue crack length and the number of temperature cycles, σ y (t) represents the functional relationship between the standard deviation of fatigue crack length and the number of temperature cycles, and Φ(·) represents the standard normal distribution; By solving the accelerated model of the solder joint thermal fatigue reliable life under various test stresses, the solder joint thermal fatigue reliable life under normal working stress is derived; The thermal fatigue life model of the solder joint is fitted by the thermal fatigue reliable life of the solder joint under normal working stress, and the thermal fatigue life distribution of the solder joint under normal working stress is obtained.

2. The solder joint thermal fatigue life prediction method based on image data and accelerated degradation modeling according to claim 1, characterized in that: The specific process of deriving the thermal fatigue reliable life of solder joints under normal working stress is: Substitute the thermal fatigue reliable life of the solder joint under each test stress into the acceleration model formula to solve the unknown parameters. The acceleration model is: Where N is the reliable life, ΔT is the temperature change range, T max is the maximum temperature, f is the frequency of temperature cycle, E a is the activation energy, K is the Boltzmann constant, δ, β1, and β2 are unknown parameters. For lead-free solder joints, β2 takes the empirical value. The normal working stress parameters of the solder joint are substituted into the accelerated model after solving the unknown parameters, and the thermal fatigue reliable life of the solder joint under normal working stress is obtained.

3. The solder joint thermal fatigue life prediction method based on image data and accelerated degradation modeling according to claim 1, characterized in that: The thermal fatigue life model is: Where h and η are the shape parameter and scale parameter of the solder joint respectively, N f is the number of temperature cycles the solder joint experiences.

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