Printed circuit board welding spot temperature cyclic acceleration test profile design method

Abstract

The invention relates to a printed circuit board welding spot temperature cycle acceleration test profile design method, which takes welding spots on an aging test board carrying a test device as research objects, and utilizes simulation software to carry out finite element simulation on a target circuit board under multiple groups of temperature cycle stress conditions. A plurality of groups of fatigue life are calculated through an Engelmaier fatigue life model in combination with a simulation result, the fatigue life obtained through calculation is substituted into a Coffin-Manson acceleration model for fitting calculation of an acceleration factor calculation formula, finally, the acceleration factor calculation formula is utilized, required acceleration time is substituted into the formula for calculation to obtain actual condition design acceleration test section parameters, and the acceleration test section parameters are calculated according to the actual condition design acceleration test section parameters. The obtained acceleration test profile can complete the temperature cycle acceleration test of the printed circuit board within a given time, and the process of the method is as shown in Figure 8. The method belongs to the technical field of reliability evaluation of microelectronics and components.

Description

(I) Technical field:

[0001] The present invention relates to a method for designing a profile of a temperature cycle accelerated test of a solder joint of a printed circuit board. The method takes the solder joints on an aging test board equipped with a test device as a research object, performs finite element simulation of a target circuit board under multiple groups of temperature cycle stress conditions by using simulation software, calculates multiple groups of fatigue life by using an Engelmaier fatigue life model in combination with the simulation results, and brings the calculated fatigue life into a Coffin-Manson acceleration model fitting calculation acceleration factor calculation formula, and finally uses the above acceleration factor calculation formula to bring the required acceleration time into the formula to calculate and obtain the actual condition design acceleration test profile parameters, and the obtained acceleration test profile can complete the temperature cycle accelerated test of the printed circuit board within a given time. This method belongs to the technical field of microelectronics and component reliability evaluation. (II) Background technology:

[0002] Printed circuit boards (PCBs) have high component density and are multi-layered. Their reliability is greatly affected by environmental stress, and the reliability of printed circuit boards determines the reliability of electronic products. Failure of printed circuit board solder joints is a common problem in electronic assembly. Surveys show that solder joint failure (including solder joint cracking caused by overstress and failure caused by solder joint corrosion during the welding process) accounts for 49% of the failure causes of printed circuit boards. Therefore, solder joint reliability is an important part of the study of weak structures of printed circuit boards. Sn-Pb solder is widely used as a solder joint material for printed circuit boards because of its low melting point, good working performance, and good adhesion to copper. Therefore, under the condition that modern printed circuit board solder joints generally have the characteristics of long life and high reliability, it is necessary to study how to set up accelerated tests for printed circuit board solder joints and analyze the reliability of solder joints under temperature cycling stress.

[0003] Although there is a certain foundation for the accelerated test profile design of printed circuit board solder joints, the existing methods for accelerated test profile design of printed circuit board solder joints are mainly based on engineering experience and lack corresponding theoretical and simulation guidance. Based on this, this paper proposes a method for accelerated test profile design of printed circuit board solder joints by temperature cycle, which realizes the design of accelerated test profile of printed circuit board solder joints by temperature cycle. (III) Summary of the invention:

[0004] 1. Purpose: The purpose of the present invention is to provide a method for designing a profile of a temperature cycle accelerated test of a solder joint of a printed circuit board. The method takes into account the failure problem that may occur in the solder joint of the printed circuit board under temperature cycle conditions, and uses the fitted acceleration factor calculation formula and given actual conditions to design the accelerated test profile, so that the design of the accelerated test profile is more accurate and practical. Compared with the traditional method for designing a profile of an accelerated test of a solder joint of a printed circuit board, the method provides a theoretical basis for the design of the accelerated test profile, and can design the accelerated test profile more accurately.

[0005] 2. Technical solution: A method for designing a profile of a temperature cycle accelerated test for a printed circuit board solder joint is invented, which comprises the following steps:

[0006] Step 1: Establishment of PCB solder joint simulation model

[0007] In order to obtain simulation data of printed circuit board solder joints, it is necessary to establish a simulation model of printed circuit board solder joints. First, use instruments to measure the appearance parameters of the printed circuit board and the size and position of the solder joints, and investigate the material parameters of the target printed circuit board. Ignore tiny components such as resistors and capacitors, build a model, and add material properties to each material in the model.

[0008] Step 2: Printed Circuit Board Solder Joint Software Simulation

[0009] Define the simulation conditions of the printed circuit board solder joints. After the study settings are completed, mesh the model. The setting of the temperature cycle profile of the printed circuit board solder joints used for simulation refers to IPC-9701A "Accelerated Reliability Test Methods and Qualification Requirements for Surface Mounted Welding Parts". After the above steps are completed, perform transient solution on the temperature cycle study, draw the equivalent viscoplastic strain diagram of the printed circuit board, and the stress cloud diagram of the printed circuit board, respectively, to obtain the equivalent viscoplastic strain of the solder joint under the preset temperature cycle profile of the printed circuit board solder joint. Change the value of the preset temperature cycle profile multiple times, and perform simulation according to the above steps to obtain the equivalent viscoplastic strain under different temperature cycle stress conditions.

[0010] Step 3: Calculation of printed circuit board solder joint life under simulation conditions

[0011] The life of the solder joints on the printed circuit board is analyzed based on the Engelmaier viscoplastic strain model under temperature cycling conditions. The preset temperature cycle profile parameters and the equivalent viscoplastic strain values ​​obtained by simulation are brought into the model for calculation. The life of the solder joints on the printed circuit board under different temperature cycle profiles is obtained.

[0012] Step 4: Acceleration factor formula fitting

[0013] For the selection of stress level under temperature cycle, the optimization model of Coffin-Manson acceleration model is applied to fit the acceleration factor model, and the simulation results of different temperature cycle profiles are brought in to fit the acceleration factor calculation formula.

[0014] Step 5: Temperature Cycle Accelerated Test Profile Design

[0015] According to the acceleration factor calculation formula obtained by fitting, by substituting the target acceleration time and normal working environment and conditions, the maximum temperature, minimum temperature, and cycle frequency of the accelerated test profile required to complete the accelerated test of the printed circuit board solder joints within the target time can be obtained. (IV) Description of the drawings:

[0016] Figure 1 This is a physical picture of a printed circuit board

[0017] Figure 2 It is a simulation model of printed circuit board solder joints

[0018] Figure 3 It is the simulated profile of the normal working environment temperature cycle of the printed circuit board

[0019] Figure 4 This is the strain cloud diagram of tin-lead solder joints under extremely high temperature conditions

[0020] Figure 5 This is the strain cloud diagram of tin-lead solder joints in extremely low temperature conditions

[0021] Figure 6 is the residual plot of the model cycle life

[0022] Figure 7 is the temperature accelerated test profile

[0023] Figure 8 This is the flow chart of the accelerated test profile design method (V) Specific implementation methods:

[0024] The present invention will be further described in detail below in conjunction with the accompanying drawings and a case of a profile design method for a printed circuit board solder joint temperature cycle accelerated test.

[0025] A method for designing a profile of a temperature cycle accelerated test of a solder joint of a printed circuit board is invented, and the specific steps are as follows:

[0026] Step 1: Establishment of PCB solder joint simulation model

[0027] In order to simulate the solder joints of the printed circuit board, a simulation model of the solder joints of the printed circuit board is established. First, according to the physical picture of the printed circuit board, such as Figure 1 As shown, the model is established. Combined with the PCB board in the actual test,

[0028] For the convenience of modeling and without affecting the temperature cycle simulation results, small components such as resistors and capacitors are ignored, and the resulting model is as follows: Figure 2 As shown in Table 1, add material properties to each material in the model. For the PCB board, set the material to FR4; for the solder joint, set the material to Sn60Pb40; for the package shell, set the material to tungsten copper alloy. The material parameters of the above materials are shown in Table 1.

[0029] Table 1 Tin-lead solder joint material parameters

[0030]

[0031] Step 2: Printed Circuit Board Solder Joint Software Simulation

[0032] The temperature cycle profile of the solder joint of the printed circuit board used for fitting is set according to IPC-9701 "Accelerated Reliability Test Methods and Qualification Requirements for Surface Mount Solder Parts". The daily working environment is -40℃ to 60℃, and the temperature profile is drawn, such as Figure 3 As shown.

[0033] According to the literature, the strain value of the solder joint tends to be stable after the third cycle. In the "Solid Mechanics" module, set the fixed constraint to "PCB bottom surface fixed". In the "Solid Heat Transfer" module, set the heat flux to "Convection heat flux" and the heat transfer coefficient to 10W / (m2·K). Set the interpolation function describing the temperature cycle to the ambient temperature and select all boundaries. Define the initial temperature of the printed circuit board as room temperature 20℃.

[0034] After the research settings are completed, the model is meshed. Since the overall and solder joint sizes are small, the physical field control mesh is used for meshing. After the above steps are completed, the temperature cycle study is transiently solved, and the output range is set to 0-170min, that is, 5 temperature cycles, and the output step is 1min. The corresponding simulation results are obtained, and the equivalent viscoplastic strain diagram of the printed circuit board and the stress cloud diagram of the printed circuit board are drawn respectively.

[0035] The simulation results of the temperature cycle (-40℃~60℃) of the solder joints of the printed circuit board are analyzed. The results show that at the extreme temperature of each temperature cycle, the maximum value of the equivalent viscoplastic strain of the solder joint is located at the connection between the solder joint and the chip, such as Figure 4, as shown in Figure 5. Since the main damage causes of micro-bumps under temperature cycle load are creep deformation and fatigue, the most likely failure path of the solder joint is the maximum creep deformation position in the temperature cycle, and microcracks are generated near this position. Since the stress value near this position is also large, the crack may continue to extend along the junction between the solder joint and the chip, and finally the solder joint is completely cracked. The curve of the equivalent viscoplastic strain of the solder joint at the corner is extracted with time. The horizontal axis in the figure is time (min), the blue solid line is the temperature change curve of the solder joint under temperature cycle conditions, corresponding to the left vertical axis - solder joint temperature (degC), and the black solid line is the curve of the equivalent viscoplastic strain of the solder joint with time, corresponding to the right vertical axis - equivalent viscoplastic strain. After 150 minutes of temperature cycle load, the equivalent viscoplastic strain of the solder joint is accumulated to 0.022232, and after the 3rd to 5th temperature cycles, the increment of the equivalent viscoplastic strain remains stable at 0.003722.

[0036] By changing the preset temperature cycle profile conditions and performing simulation according to the above steps, the equivalent viscoplastic strain under different temperature cycle stress conditions is obtained, as shown in Table 2.

[0037] Table 2 Equivalent viscoplastic strain of printed circuit board solder joints under different temperature cycles

[0038]

[0039] Step 3: Calculation of printed circuit board solder joint life under simulation conditions

[0040] The life analysis under temperature cycling conditions is mainly based on the Engelmaier viscoplastic strain model, which is in the form of:

[0041]

[0042] c=-0.442-6×10 -4 T+1.74×10 -2 ×ln(1+f)

[0043] Δγ is the shear strain range, ε is the fatigue toughness parameter, c is the fatigue toughness index, T is the cycle average temperature, and f is the daily cycle frequency.

[0044] c=-0.442-6×10 -4 ×10+1.74×10 -2 ×ln48)=-0.38

[0045] Δγ=0.003722

[0046] ε=0.325

[0047]

[0048] The calculated cycle life of the solder joint is 397494 cycles.

[0049] According to the IPC-9701 surface mount solder performance test method and identification requirements, the upper limit of the accelerated profile setting temperature cannot exceed 125℃, the lower limit cannot exceed -55℃, the temperature dwell time is set to 10min, and the temperature change rate is set to 20℃ / min to avoid temperature shock. According to the above requirements, six temperature profiles are set, as shown in Table 3, so that the limit temperature is between -55℃ and 125℃.

[0050] Based on the above simulation method, these sections are applied to the printed circuit board model, and temperature cycle simulation is carried out to obtain the equivalent viscoplastic strain results. According to the Engelmaier viscoplastic strain model, the cycle life of the solder joints of the following six accelerated test sections is calculated, as shown in Table 3.

[0051] Table 3 Life of solder joints on printed circuit boards under different temperature cycles

[0052]

[0053] Step 4: Acceleration factor formula fitting

[0054] For the selection of stress level under temperature cycle, this paper applies the optimization model of Coffin-Manson acceleration model to fit the acceleration factor model, so as to obtain the accelerated stress level corresponding to the target test time.

[0055] The accelerated life model proposed by Coffin and Manson is mainly used to describe the fatigue behavior of materials or components under temperature cycling conditions. This model is particularly suitable for materials that experience thermal expansion and contraction under temperature changes, especially solder joints, which are common structures in electronic packaging and assembly. During temperature cycling, solder joints are subjected to thermomechanical stress caused by mismatched thermal expansion coefficients, which may lead to fatigue damage and eventual failure of solder joints.

[0056] The basic assumption of the Coffin-Manson acceleration model is that there is a power law relationship between the plastic strain amplitude generated in each cycle and the fatigue life of the material; during the temperature cycle, due to the different thermal expansion coefficients of the materials, the solder joints will be subjected to shear and tensile stresses; as the number of temperature cycles increases, the plastic strain will accumulate, eventually leading to fatigue failure of the solder joints.

[0057] The mathematical expression of the Coffin-Manson acceleration model is usually as follows:

[0058]

[0059] Δε pis the plastic strain amplitude, which represents the difference between the maximum and minimum plastic strain in one cycle. f is the fatigue life, i.e. the number of cycles a material can withstand at a specific stress or strain level until it breaks. C and β are material-specific constants that can be obtained by fitting experimental data.

[0060] In practical applications, the Coffin-Manson accelerated model can be used to predict the fatigue life of solder joints under specific temperature cycling conditions. The fatigue life of solder joints can be predicted by experimentally determining the model parameters (C and β) and combining them with the plastic strain amplitude data obtained from finite element analysis. Although the Coffin-Manson model has a certain accuracy in predicting fatigue life caused by temperature cycling, it also has limitations. For example, the model focuses on the effect of plastic strain on fatigue life and may not fully consider other factors such as the microstructure of the solder joint, the creep behavior of the material, and interface stress concentration. In addition, the parameters of the model may be affected by factors such as loading rate, temperature range, and environmental conditions, and need to be calibrated through experiments.

[0061] In some applications, fatigue life is also a function of cycle frequency and high temperature. For example, in their papers by Ghaffarian, Teng and Brillhart and Shohji et al., Norris and Landzberg (1969) modified the traditional Coffin-Manson accelerated model to take into account the influence of these thermal cycle variables. The modified model is as follows:

[0062]

[0063] Where:

[0064] L is the number of cycles to failure; A, B, C are material characteristic constants; T max — is the absolute maximum temperature; f— is the cycle frequency; E a —activation energy in electron volts (eV); k—Boltzmann constant, 8.6171×10-5eV / ℃; T—absolute temperature (273.15℃).

[0065] In order to facilitate data analysis, the above formula will become a linear model

[0066]

[0067] In the formula, a=ln(A); b=-B; c=C; d=Ea / k;

[0068] Substitute the simulation results into Table 4 for regression analysis:

[0069] Table 4 Life of printed circuit board solder joints under different temperature cycles

[0070]

[0071]

[0072] The model regression equation is as follows:

[0073]

[0074] The residuals conform to the normal distribution, such as Figure 6 As shown, they lie roughly along a straight line with no discernible pattern or trend.

[0075] Table 4.2 Model correlation coefficients

[0076]

[0077] The model correlation coefficients are shown in Table 4.2.

[0078] The target printed circuit board has a lifespan of 397,494 cycles under normal operating limits (-40°C to 60°C).

[0079] Therefore, the acceleration factor calculation model of the target circuit board can be obtained:

[0080]

[0081] A f Indicates the temperature cycle acceleration factor, ΔT0 working environment temperature difference, f0 working environment temperature cycle frequency, T 0max The highest temperature of the working environment, ΔT, the temperature difference of the accelerated test profile, f, the temperature cycle frequency of the accelerated test profile, T max Maximum temperature of the accelerated test section.

[0082] Step 5: Temperature Cycle Accelerated Test Profile Design

[0083] This section simulates the acceleration requirements of the printed circuit board acceleration test in daily life by setting the target acceleration time of the research circuit board. The target printed circuit board is an aging test board equipped with key components, and its operating temperature is -40℃ to 60℃. First, set the required acceleration factor to 100, the maximum value of the accelerated test temperature to 100℃, and the high and low temperature residence time to 10 minutes.

[0084]

[0085] According to the above temperature cycle acceleration factor calculation formula, the required temperature difference can be calculated, that is, 133.8℃. Taking the temperature difference of 135℃, it can be determined that the minimum temperature of the designed temperature cycle is -35℃, the high and low temperature residence time is 10min, and the temperature change rate is 20℃ / min. The temperature cycle acceleration test profile is drawn, as shown in Figure 7 shown.

Claims

1. The present invention relates to a method for designing a profile of a temperature cycle accelerated test of a solder joint of a printed circuit board. The method takes the solder joints on an aging test board equipped with a test device as a research object, performs finite element simulation of a target circuit board under multiple groups of temperature cycle stress conditions using simulation software, calculates multiple groups of fatigue lives using an Engelmaier fatigue life model in combination with the simulation results, and brings the calculated fatigue lives into a Coffin-Manson acceleration model to fit and calculate an acceleration factor calculation formula. Finally, using the above acceleration factor calculation formula, bringing the required acceleration time into the formula to calculate and obtain actual conditions to design accelerated test profile parameters. The obtained accelerated test profile can complete the temperature cycle accelerated test of the printed circuit board within a given time. The method has the following specific steps: Step 1: Establishment of printed circuit board solder joint simulation model; Step 2: Printed circuit board solder joint software simulation; Step 3: Calculation of printed circuit board solder joint life under simulation conditions; Step 4: Acceleration factor formula fitting. Step 5: Temperature cycle accelerated test profile design.

2. The method for designing a profile of a solder joint temperature cycle accelerated test of a printed circuit board according to claim 1, characterized in that: The specific process of establishing the printed circuit board solder joint simulation model described in step 1 is as follows: In order to obtain simulation data of printed circuit board solder joints, it is necessary to establish a simulation model of printed circuit board solder joints. First, use instruments to measure the appearance parameters of the printed circuit board and the size and position of the solder joints, and investigate the material parameters of the target printed circuit board. Ignore tiny components such as resistors and capacitors, build a model, and add material properties to each material in the model.

3. The method for designing a profile of a printed circuit board solder joint temperature cycle accelerated test according to claim 1, characterized in that: The specific process of the printed circuit board solder joint software simulation described in step 2 is as follows: Define the simulation conditions of the printed circuit board solder joints. After the study settings are completed, mesh the model. The setting of the temperature cycle profile of the printed circuit board solder joints used for simulation refers to IPC-9701A "Accelerated Reliability Test Methods and Qualification Requirements for Surface Mounted Welding Parts". After the above steps are completed, perform transient solution on the temperature cycle study, draw the equivalent viscoplastic strain diagram of the printed circuit board, and the stress cloud diagram of the printed circuit board, respectively, to obtain the equivalent viscoplastic strain of the solder joint under the preset temperature cycle profile of the printed circuit board solder joint. Change the value of the preset temperature cycle profile multiple times, and perform simulation according to the above steps to obtain the equivalent viscoplastic strain under different temperature cycle stress conditions.

4. The method for designing a profile of a printed circuit board solder joint temperature cycle accelerated test according to claim 1, characterized in that: The specific process of calculating the life of the printed circuit board solder joints under the simulation conditions described in step 3 is as follows: The life of the solder joints of the printed circuit board is analyzed based on the Engelmaier viscoplastic strain model under temperature cycling conditions. The temperature cycling profile parameters and the equivalent viscoplastic strain values ​​obtained by simulation are brought into the model for calculation. The life of the solder joints of the printed circuit board under different temperature cycling profiles is obtained.

5. The method for designing a profile of a printed circuit board solder joint temperature cycle accelerated test according to claim 1, characterized in that: The specific process of fitting the acceleration factor formula described in step 4 is as follows: For the selection of stress level under temperature cycle, the optimization model of Coffin-Manson acceleration model is applied to fit the acceleration factor model, and the simulation results of different temperature cycle profiles are brought in to fit the acceleration factor calculation formula.

6. A printed circuit board solder joint temperature cycle accelerated test profile design method according to claim 1, characterized in that: The specific process of the temperature cycle accelerated test profile design described in step 5 is as follows: According to the acceleration factor calculation formula obtained by fitting, by substituting the target acceleration time and normal working environment and conditions, the maximum temperature, minimum temperature, and cycle frequency of the accelerated test profile required to complete the accelerated test of the printed circuit board solder joints within the target time can be obtained.

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