A circuit board soldering temperature zoning heating control method and system

Abstract

The application relates to a circuit board welding temperature zoning heating control method and system, which comprises the following steps: obtaining boundary coordinates of cooling and reflow zoning, extracting temperature gradient steepness at the junction, identifying heat transfer paths from the periphery to the center of the welding spot, determining the solidification front advancing speed and the residual stress radial distribution density, evaluating the stress concentration value at the center of the welding spot, optimizing the solidification front advancing speed if the value exceeds the threshold, combining the thermal expansion amount and the optimized speed to evaluate the intermetallic compound layer thickness and the promotion amount of the high-temperature residence time, judging whether the promotion amount exceeds the limit and adjusting the cooling zoning temperature curve accordingly to obtain the boundary layout of the balanced stress and the compound layer growth, simulating the fatigue crack initiation position based on the boundary layout and evaluating the joint impact toughness satisfaction degree, iteratively adjusting until the standard is met, and finally outputting the temperature zoning heating control setting.

Description

Technical Field

[0001] This application relates to the field of electrical data technology, specifically to a method and system for controlling the zoned heating of circuit board soldering temperature. Background Technology

[0002] Current practices in zonal control of welding temperature still have significant shortcomings. Many methods focus too much on temperature regulation in a single zone and neglect the mutual influence of temperature changes between different zones, especially the temperature transition at the junction of the cooling zone and the reflow zone. This neglect leads to drastic fluctuations in temperature changes, which in turn have an uncontrollable impact on the stress distribution inside the weld joint and increase the risk of weld joint failure in long-term use. A deeper technical challenge lies in controlling the temperature gradient at the junction of the cooling and reflow zones. This factor directly determines the formation and distribution of stress during the solidification process of the solder joint. If the temperature gradient is too steep, the solder will solidify from the outer periphery to the center at a significantly faster rate, causing stress to concentrate in the central area of ​​the solder joint. Specifically, in the soldering of large-size ball grid arrays, a steep temperature gradient will lead to a high concentration of stress in the central area of ​​the solder joint, which will then become the initiation point of fatigue cracks and seriously affect the life of the component. On the other hand, if the temperature change is deliberately slowed down, the high temperature may last for too long, resulting in the formation of an excessively thick fragile layer at the solder joint interface, reducing the impact resistance. This problem is particularly prominent in equipment use scenarios with frequent vibration or impact. Therefore, how to reasonably control the temperature gradient at the junction of the cooling and reflow regions, so as to avoid stress concentration and prevent interface damage caused by excessive high temperature duration, has become a key issue in improving welding quality and component reliability. Summary of the Invention

[0003] To address the problems of the existing technology, this study focuses on the impact of the steepness of the temperature gradient at the boundary between the two zones on the stress distribution inside the solder joint. When the cooling zone is set close to the reflow zone, causing a sharp increase in the temperature gradient at the boundary, the changes include a significant acceleration in the speed at which the solidification front of the molten solder inside the solder joint advances from the outer periphery to the center, how the radial distribution curve of residual stress on the cross-section of the solder joint changes from relatively uniform to highly concentrated in the central region, and how this stress concentration limits the location of fatigue crack initiation inside the solder balls of the large-size ball grid array. The contradiction lies in the fact that a gentle cooling temperature gradient is beneficial to reducing the solidification stress of solder joints. However, when the mismatch between the thermal expansion coefficients of components and PCB substrates is introduced, gentle cooling may lead to excessive growth of the intermetallic compound layer at the interface between the solder joint and the pad due to the extended residence time at high temperature, thereby reducing the impact toughness of the joint. The purpose of this application is to provide a method and system for zonal heating control of circuit board soldering temperature.

[0004] The circuit board soldering temperature zone heating control method described in this application includes: S101, obtain the boundary coordinates of the cooling zone and the reflow zone, extract the temperature gradient steepness at the junction of the two zones, identify the heat transfer path from the outer periphery to the center of the solder joint, determine the solidification front advance speed of the molten solder of the solder joint based on the heat transfer path, and obtain the radial distribution density of residual stress in the cross section of the solder joint. S102, based on the radial distribution density of residual stress, the heat conduction algorithm is used to evaluate the stress concentration value in the center region of the weld joint, and to determine whether the stress concentration value exceeds the preset safety threshold. If it does, the optimized solidification front advance speed is obtained by using the gentle temperature gradient steepness. S103, obtain the thermal expansion of components and PCB substrate, combine the optimized solidification front advance speed to evaluate the thickness of intermetallic compound layer at the interface of solder joint and pad, and identify the amount of promotion of the increase in intermetallic compound layer thickness by the high temperature residence time. S104. Based on the amount of heat promotion and thermal expansion during the high-temperature residence time, a zone heating control algorithm is used to determine whether the amount of heat promotion exceeds the preset thickness limit. If it does, the temperature curve of the cooling zone is adjusted to obtain the boundary position layout that balances solidification stress and intermetallic compound layer growth. S105, obtain the boundary position layout after equilibrium, combine the residual stress radial distribution density to simulate the fatigue crack initiation location and its limited range, and evaluate the impact toughness satisfaction of the joint based on the fatigue crack initiation location. S106 determines whether the impact toughness meets the preset requirements. If it does, it outputs the temperature zone heating control setting as the weld joint solidification stress management scheme. If it does not meet the requirements, it returns to adjust the boundary position layout until the requirements are met.

[0005] Preferably, in step S101, the surface of the solder joint is scanned by an infrared thermal imager, and the boundary coordinates and temperature field distribution of the cooling and reflow zones are obtained based on the scan data. Based on the boundary coordinates and temperature field distribution, the temperature gradient steepness at the junction of the two zones is extracted to determine the heat transfer path from the outer periphery of the weld point to the center. By identifying the direction of heat flow through the heat transfer path, the solidification characteristics of the molten solder can be obtained; Then, the solidification front advance velocity is calculated from the phase change heat release characteristics, and the radial distribution density of residual stress on the weld joint cross section is simulated based on the solidification front advance velocity.

[0006] Preferably, in step S102, the residual stress density is obtained from the cross-section of the weld joint, and the radial distribution characteristics are analyzed by scanning data to determine the stress distribution pattern in the central region. Based on the stress distribution pattern, the specific values ​​of stress concentration are calculated and obtained using the heat conduction algorithm. If the value exceeds the preset safety threshold, the method of gradual temperature gradient steepness is adopted, and the heat flow parameter in the stress concentration value is adjusted to optimize the solidification front advance speed. The optimization effect was verified by adjusting the heat flow parameters, and a new solidification front advance velocity was obtained.

[0007] Preferably, in S103, the thermal mismatch strain at the solder joint interface is calculated based on the difference in thermal expansion between the component and the PCB substrate. Combining the solidification front advance velocity, an interface evaluation model based on the relationship between thermal expansion difference and solidification front advance velocity is constructed. The interface evaluation model is constructed by integrating the thermal relationship equation between thermal expansion difference and velocity parameter to determine the initial value of compound thickness between solder joint interface and solder pad substrate. High-temperature dwell parameters are extracted from the initial thickness value, and the atomic migration rate and thickness growth rate are calculated using thermodynamic simulation. If the thickness growth rate exceeds the threshold, the solidification front advance speed is adjusted to optimize parameters and obtain a thickness growth correction curve. Based on the thickness growth correction curve, the amount by which high-temperature dwell time promotes thickness growth is identified, and the final state of the intermetallic compound layer is evaluated in combination with the microscopic characteristics of the solder joint interface.

[0008] Preferably, in S104, the value of the promotion amount is determined by a zoned heating control algorithm based on the promotion amount and thermal expansion amount during the high-temperature residence time. If the amount of promotion exceeds the preset thickness limit, the temperature curve of the cooling zone is adjusted to obtain the adjusted temperature gradient. The solidification stress equilibrium distribution is determined based on the adjusted temperature gradient, and the growth rate of the intermetallic compound layer is obtained by combining the temperature correlation coefficient. By analyzing the equilibrium distribution of solidification stress and the growth rate, the uniform solidification state of the material can be determined, thereby locating the defect boundary. Based on the defect boundary location, the boundary position layout of the equilibrium solidification stress and the growth of the intermetallic compound layer is obtained.

[0009] Preferably, in S105, the radial distribution density of residual stress is obtained from the boundary location layout, and the fatigue crack initiation location is calculated by integrating it and the stress concentration factor. The limited range of fatigue crack initiation locations was determined, and the crack propagation inhibition distribution was obtained using the stress gradient adjustment method; The stability of the initiation location is determined by the distribution of crack propagation inhibition, and the stress balance index of the joint is obtained. By combining the joint stress balance index with the preset impact toughness correlation coefficient, the satisfaction threshold is obtained; The radial density simulation parameters are adjusted according to the satisfaction threshold, and the impact toughness satisfaction of the joint is determined based on the adjusted parameters.

[0010] Preferably, in S106, the impact toughness satisfaction is obtained from the solidification stress distribution of the weld joint and compared with the preset requirements based on the stress balance index. If the comparison results meet the preset requirements, the temperature zone heating control settings are determined based on the satisfaction level, and the output is a solder joint solidification stress management scheme. If the comparison results do not meet the preset requirements, the boundary position layout is adjusted, and the impact toughness satisfaction is reassessed based on the adjusted layout until the preset requirements are met.

[0011] The circuit board soldering temperature zone heating control system described in this application includes: The boundary position acquisition module is used to acquire the boundary position coordinates of the cooling zone and the reflow zone, extract the temperature gradient steepness at the junction of the two zones, identify the heat transfer path from the outer periphery to the center of the solder joint, determine the solidification front advancement speed of the molten solder at the solder joint based on the heat transfer path, and obtain the radial distribution density of residual stress in the cross section of the solder joint. The stress concentration assessment module is used to evaluate the stress concentration value in the center region of the weld joint based on the radial distribution density of residual stress and the heat conduction algorithm. It determines whether the stress concentration value exceeds the preset safety threshold. If it does, the optimized solidification front advance speed is obtained by using the steepness of the gentle temperature gradient. The compound layer evaluation module is used to obtain the thermal expansion of components and PCB substrate, and to evaluate the thickness of the intermetallic compound layer at the interface of solder joint and pad by combining the optimized solidification front advance speed, and to identify the amount of promotion of the intermetallic compound layer thickness growth by the high temperature residence time. The boundary layout balancing module is used to determine whether the amount of promotion exceeds the preset thickness limit based on the high temperature residence time and thermal expansion. If it does, the cooling zone temperature curve is adjusted to obtain the boundary position layout that balances solidification stress and intermetallic compound layer growth. The fatigue crack simulation module is used to obtain the boundary position layout after equilibrium, and to simulate the fatigue crack initiation location and its limited range by combining the radial distribution density of residual stress. The impact toughness of the joint is evaluated based on the fatigue crack initiation location. The impact toughness judgment module is used to determine whether the impact toughness meets the preset requirements. If it does, it outputs the temperature zone heating control setting as a weld joint solidification stress management scheme. If it does not meet the requirements, it returns to adjust the boundary position layout until the requirements are met.

[0012] The circuit board soldering temperature zone heating control method and system described in this application have the advantage of accurately obtaining the boundary position coordinates of the cooling zone and the reflow zone, extracting the steepness of the temperature gradient at the junction, identifying the heat transfer path of the solder joint from the outer periphery to the center, thereby determining the advancing speed of the solidification front of the molten solder, and obtaining the radial distribution density of residual stress in the cross section of the solder joint. Then, a heat conduction algorithm is used to evaluate the stress concentration value in the center area of ​​the solder joint. When it exceeds the safety threshold, the solidification front advance speed is optimized by the steepness of the temperature gradient. At the same time, the thermal expansion of the components and PCB substrate and the high temperature residence time promote the thickness of the intermetallic compound layer. A zone heating control algorithm is used to determine whether the thickness of the compound layer exceeds the upper limit. If it does, the cooling zone temperature curve is adjusted to obtain an optimized boundary position layout that takes into account both solidification stress balance and intermetallic compound layer growth. Based on the optimization of boundary position layout and the simulation of fatigue crack initiation location and range by residual stress distribution, the impact toughness of the joint is evaluated. The boundary position is iteratively adjusted until the impact toughness meets the standard, thereby outputting the optimized temperature zone heating control setting, realizing effective management of weld solidification stress, reasonable control of intermetallic compound layer thickness, and significant improvement of joint reliability and fatigue and impact resistance. Attached Figure Description

[0013] Figure 1 This is a flowchart illustrating a circuit board soldering temperature zone heating control method and system described in this application. Figure 1 ; Figure 2 This is a flowchart illustrating a circuit board soldering temperature zone heating control method and system described in this application. Figure 2 . Detailed Implementation

[0014] like Figures 1-2 As shown, the circuit board soldering temperature zone heating control method described in this application includes: like Figures 1-2 As shown, in step S101, the boundary coordinates of the cooling zone and the reflow zone are obtained, the steepness of the temperature gradient at the junction of the two zones is extracted, the heat transfer path from the outer periphery to the center of the solder joint is identified, the solidification front advance speed of the molten solder joint is determined according to the heat transfer path, and the radial distribution density of residual stress in the cross section of the solder joint is obtained.

[0015] Further, in step S101, the surface of the solder joint is scanned by an infrared thermal imager, and the boundary coordinates of the cooling zone and the reflow zone are obtained from the scan data to obtain the temperature field distribution corresponding to the boundary coordinates; Based on the temperature field distribution, the temperature gradient steepness at the boundary between the two zones is extracted, and the heat transfer path from the outer periphery to the center of the solder joint is determined by the temperature gradient steepness. Based on the heat transfer path, the direction of heat flow from the outer periphery to the center of the solder joint is identified, and the solidification characteristics of the molten solder are obtained. From the phase change heat release characteristics, the solidification front advance speed of the molten solder at the solder joint is calculated, and the radial distribution density of residual stress in the cross-section of the solder joint is simulated based on the solidification front advance speed.

[0016] Specifically, in S101, the surface of the solder joint is scanned by an infrared thermal imager to obtain a temperature distribution matrix T(x,y), where x and y are the planar coordinates of the solder joint. The boundary coordinates of the cooling zone (the area with a temperature lower than the melting point of the solder) and the reflow zone (the area with a temperature higher than the melting point of the solder) are identified based on the temperature distribution matrix. The boundary coordinates were determined using a temperature contour extraction method, with the solder melting point temperature (183℃ for tin-lead solder) as a threshold to extract the boundary curve. The steepness of the temperature gradient was then calculated on the boundary curve. Where ∇T is the temperature gradient vector and G is the steepness of the temperature gradient; A heat transfer path model is constructed based on the temperature field distribution. The heat transfer path extends from the high-temperature area around the solder joint to the low-temperature area in the center, and the path direction is consistent with the temperature gradient direction. Calculate the solidification front advance velocity based on the heat transfer path and boundary temperature conditions: Where k is thermal conductivity, G is temperature gradient steepness, ΔH is latent heat of phase transformation of solder, and v is solidification front advance velocity. Based on the spatial distribution of the solidification front propagation velocity and the difference in the thermal expansion coefficients of the materials, the radial distribution density of residual stress in the weld joint cross-section is calculated: Where r is the radial distance on the cross-section of the weld joint, and σ is the residual stress; The solidification process involves the solidification front, which is the material transitioning from a liquid to a solid state. Its advancement speed refers to the rate at which the front moves. If the stress concentration exceeds the preset safety threshold, the optimized solidification front advancement speed is obtained by smoothing the steepness of the temperature gradient. The steepness of the temperature gradient refers to the degree of temperature change during solidification. Smoothing means reducing the temperature gradient to reduce stress generation. First, calculate the steepness of the current temperature gradient, for example, by quantizing it using the magnitude of the temperature field gradient vector. Then, adjust the heating or cooling rate to make the gradient gentler, thereby optimizing the solidification front advance speed. In reflow welding applications, the gradient can be smoothed by reducing the power input, resulting in an optimized value for the feed rate. This optimized value ensures uniform movement of the solidification interface and reduces the accumulation of residual stress. This optimization method is applicable to different alloy materials within the same welding field, demonstrating the adaptability of the technical solution. In the above process, multiple sets of simulation parameters can be introduced for verification. For example, the thermal conductivity value can be changed to cover various welding conditions, thereby confirming the effectiveness of the optimized value of the solidification front advance speed. This implementation method ensures that the stress at the weld center is controlled within a safe range through a complete chain of logical flow from stress distribution to the optimized value of the solidification front advance speed, thereby improving the overall welding quality. For solder joints made of tin-lead solder, the radial distribution density of residual stress showed that the density at the center was 20% higher than that at the edge. A finite element model based on the Fourier heat conduction equation was adopted, with temperature gradient and material properties as inputs and stress distribution value as output. After evaluation, the stress concentration value was 150 MPa, which exceeded the threshold of 120 MPa. Therefore, the steepness of the gentle temperature gradient was reduced from the initial 5 K / mm to 2 K / mm, and the solidification front advance speed was optimized to 0.5 mm / s. This embodiment verifies the application effect of the method in electronic assembly. Understandably, the versatility of this technical solution lies in its scalability to similar welding scenarios, such as adjusting parameters in circuit board assembly to accommodate different solder joint sizes, ensuring consistency in stress assessment and optimization.

[0017] like Figures 1-2 As shown, in step S102, the stress concentration value in the center region of the weld joint is evaluated by using a heat conduction algorithm based on the radial distribution density of residual stress. It is then determined whether the stress concentration value exceeds a preset safety threshold. If it does, the optimized solidification front advance speed is obtained by using a gentle temperature gradient steepness.

[0018] Further, in step S102, the residual stress density is obtained from the cross-section of the weld joint, and the stress distribution pattern in the central region of the weld joint is determined by extracting the distribution curve from the scan data using the radial distribution feature analysis method. Based on the stress distribution pattern, the stress concentration value in the central region of the weld joint is calculated by inputting the distribution curve through a heat conduction algorithm, and the specific value of the stress concentration value is obtained. For the stress concentration value, it is determined whether it exceeds the preset safety threshold. If it does, the method of smoothing the temperature gradient steepness is used to adjust the heat flow parameters to obtain the optimized solidification front advance speed. The optimization effect is verified from the solidification front advance velocity, and the optimized solidification front advance velocity is obtained.

[0019] Specifically, in S102, the radial distribution density of residual stress at the weld joint is first obtained. The radial distribution density of residual stress reflects the radial distribution of stress caused by uneven thermal expansion during the welding cooling process. The radial distribution density of residual stress was obtained by finite element simulation combined with thermal conductivity adjustment calculation. The stress values ​​at different radial positions of the weld joint were simulated, and then a density function model was constructed. The density function model describes the gradual change of stress from the center to the edge, thus providing basic data for subsequent evaluation. This distribution density analysis helps to identify potential crack initiation points and ensure the integrity of the welded structure. Based on the radial distribution density of residual stress, a heat conduction algorithm is used to evaluate the stress concentration in the central region of the weld joint. The stress concentration heat conduction algorithm is based on the Fourier heat conduction equation and takes into account parameters such as material thermal conductivity, specific heat capacity and density to simulate heat flow transfer during the welding process. The heat conduction algorithm is based on the Fourier heat conduction equation: Where α is the thermal diffusivity. ρ is density, cp is specific heat capacity, T is temperature, and t is time; Using the radial distribution density of residual stress as the initial condition input, the stress concentration value σ in the central region is obtained by iteratively calculating the coupling relationship between the thermal field distribution and the stress field. max The Von Mises stress criterion is used to determine the value of stress concentration. The calculated σ... max With the preset safety threshold σ th The safety threshold is set based on the yield strength of the solder material, for example, 80% of the material's yield strength. If σ max ≥σ th , where σ max σ represents the maximum stress value in the center region of the weld joint. th To preset a safety threshold, optimization is achieved by smoothing the steepness of the temperature gradient. This smoothing process is accomplished by reducing the heating power or extending the heating time, thereby reducing the temperature gradient G from its initial value to the target value, thus obtaining the optimized solidification front advance velocity v. opt The optimization objective is to make the solidification interface move uniformly and reduce the accumulation of residual stress. In electronic component soldering scenarios, the finite element thermo-mechanical coupling algorithm can simulate temperature changes during reflow soldering and quantify the peak value of the center stress. The peak value of the center stress is usually calculated by the VonMises stress criterion. The VonMises stress criterion takes the temperature curve and material properties as input, calculates heat conduction and mechanical response through numerical iteration, realizes simulation and quantification, and outputs the peak stress. This evaluation method can accurately capture the thermo-mechanical interaction effect and improve the prediction accuracy of solder joint reliability. It should be noted that the stress concentration value, i.e. the calculated peak value of the center stress, is determined by comparison with a preset safety threshold. The preset safety threshold is set according to the material fatigue limit and industry standards. For example, in the field of semiconductor packaging, the threshold can be set to 80% of the material yield strength. If the peak value of the central stress is below the threshold, the solder joint is considered safe. Otherwise, it proceeds to the optimization step. This judgment mechanism ensures real-time monitoring of the welding process and avoids potential failure risks. In one possible implementation, the solidification process involves a solidification front where the material changes from a liquid to a solid state. The advancement speed refers to the rate at which the front moves. If the stress concentration exceeds a preset safety threshold, the optimized solidification front advancement speed is obtained by smoothing the temperature gradient steepness. The temperature gradient steepness refers to the degree of temperature change during solidification. Smoothing means reducing the temperature gradient to reduce stress generation. First, calculate the steepness of the current temperature gradient, for example, by quantizing it using the magnitude of the temperature field gradient vector. Then, adjust the heating or cooling rate to make the gradient gentler, thereby optimizing the solidification front advance speed. In reflow welding applications, the gradient can be smoothed by reducing the power input, resulting in an optimized feed rate. This optimized feed rate ensures uniform movement of the solidification interface and reduces the accumulation of residual stress. This optimization method is applicable to different alloy materials within the same welding field, demonstrating the adaptability of the technical solution. In the above process, multiple sets of simulation parameters can be introduced for verification. For example, the thermal conductivity value can be changed to cover various welding conditions, thereby confirming the effectiveness of the optimized value of the solidification front advance speed. This implementation method ensures that the stress at the weld center is controlled within a safe range through a complete chain of logical flow from stress distribution to the optimized value of the solidification front advance speed, thereby improving the overall welding quality. For solder joints made of tin-lead solder, the radial distribution density of residual stress showed that the density at the center was 20% higher than that at the edge. A finite element model based on the Fourier heat conduction equation was adopted, with temperature gradient and material properties as inputs and stress distribution value as output. After evaluation, the stress concentration value was 150 MPa, which exceeded the threshold of 120 MPa. Therefore, the steepness of the gentle temperature gradient was reduced from the initial 5 K / mm to 2 K / mm, and the solidification front advance speed was optimized to 0.5 mm / s. This embodiment verifies the application effect of the method in electronic assembly. Understandably, the versatility of this technical solution lies in its scalability to similar welding scenarios, such as adjusting parameters in circuit board assembly to accommodate different solder joint sizes, ensuring consistency in stress assessment and optimization.

[0020] like Figures 1-2As shown, in step S103, the thermal expansion of the components and the PCB substrate is obtained, and the thickness of the intermetallic compound layer at the interface between the solder joint and the pad is evaluated in combination with the optimized solidification front advance speed. The effect of the high-temperature dwell time on the increase of the intermetallic compound layer thickness is identified.

[0021] Further, in step S103, the thermal expansion of the components and the PCB substrate is obtained, and the thermal mismatch strain at the solder joint interface is calculated based on the difference in thermal expansion. For the aforementioned thermal strain distribution, the solidification front advance velocity is used as the input interface evaluation model. The interface evaluation model is constructed by integrating the thermal relationship equation between the thermal expansion difference and the velocity parameter to determine the initial value of the compound thickness between the solder joint interface and the solder pad substrate. From the initial thickness of the compound, the high-temperature residence parameter is extracted, and the thickness growth rate is obtained by calculating the atomic migration rate through the diffusion equation using thermodynamic simulation. If the thickness growth rate exceeds the threshold, the speed optimization parameter is adjusted to obtain the correction curve of the thickness growth. Based on the thickness growth correction curve, the contribution of high-temperature residence to the promotion value is identified, and the specific value of the promotion value is obtained. By combining the specific numerical values ​​of the aforementioned promoting amount with the microscopic characteristics of the solder joint interface, the final state of the compound thickness is evaluated, and the promoting amount of high-temperature dwell time on the thickness growth of the intermetallic compound layer is identified.

[0022] Specifically, in S103, the thermal expansion of the components and the PCB substrate is first obtained. The thermal expansion reflects the volume or linear expansion of the material under temperature change, which is calculated by measuring the coefficient of thermal expansion and combining it with the temperature difference. The expansion behavior of components and substrates within the welding temperature range is detected using a thermomechanical analyzer to obtain their respective expansion values. This acquisition process helps to understand the interfacial stress caused by thermal mismatch during welding and provides a data basis for subsequent evaluation. Combined with the optimized solidification front advance speed, which refers to the rate of movement of the front during the welding solidification process, the initial value is calculated by finite element simulation and then optimized by adjusting parameters such as cooling rate. The thickness of the intermetallic compound layer at the interface between the weld point and the pad is evaluated. The intermetallic compound layer is an alloy layer formed at the welding interface, and its thickness affects the strength of the weld point. The optimized solidification front advance velocity refers to the solidification interface movement rate obtained through numerical simulation. Using this as an input parameter, the Fick diffusion model is adopted, based on the solute diffusion equation driven by the concentration gradient, to evaluate the layer thickness growth. In electronic component soldering, the interface growth rate v is combined with the diffusion coefficient D, using the following relationship: Where x is the thickness of the intermetallic compound layer, D is the diffusion coefficient, and t is the high-temperature residence time; Estimate the expected thickness of the intermetallic compound layer to quantitatively assess the interface stability and thickness variation under different temperature, time and solder composition conditions; It should be noted that the thickness assessment of intermetallic compound layers involves diffusion kinetics, which describes the migration process of atoms at high temperatures, leading to layer thickness growth. Specifically, this process involves inputting thermal expansion and the solidification front advance velocity to construct a thickness growth equation: Where d is the thickness, k is the diffusion coefficient, and t is the time, the thickness of the intermetallic compound layer is obtained by iterative calculation through numerical integration. The diffusion coefficient k is a material constant used to describe the rate of atomic diffusion in the intermetallic compound layer at a specific temperature. It directly determines the growth rate of the IMC layer during the high-temperature dwell time. The diffusion coefficient reflects the migration ability of atoms at the interface. During the welding process, metal atoms in the solder, such as Sn, Cu, and Ni, will diffuse to form an intermetallic compound layer at the interface between the solder joint and the pad. The larger the value of k, the faster the atomic diffusion and the faster the IMC layer grows; In reflow soldering scenarios, considering the expansion difference between components and the substrate, the diffusion rate is simulated through finite element analysis, using the Arrhenius equation for calculation: Where D is the diffusion rate, D0 is the pre-exponential factor, Q is the activation energy, R is the gas constant, and T is the temperature; The welding parameters were evaluated when the layer thickness reached 5 micrometers, and the adjustment logic was to optimize the temperature to 250 degrees Celsius and the time to 60 seconds to ensure welding reliability. The effect of high-temperature dwell time on the thickness increase of intermetallic compound layers was identified. High-temperature dwell time refers to the duration during which the material is kept at a high temperature during welding. The effect is defined as the acceleration contribution of time to the thickness increase, and its quantification formula is as follows: Where P is the promoting amount, k is a material-related constant, and t is the high-temperature residence time. The acceleration effect is calculated using this formula. Calculate the difference in weld layer thickness increment under different dwell times using experimental data or simulation: Where h is the solder layer thickness, t is the dwell time, and h(t) represents the thickness of the intermetallic compound layer at the interface between the solder joint and the pad when the high temperature dwell time is t; t1 and t2 are different high temperature dwell time points; In circuit board assembly, extending the dwell time can increase diffusion opportunities, leading to increased layer thickness. The diffusion promotion amount D is represented by the growth rate curve. This identification helps to solve the core problem of uneven layer thickness in soldering, thereby optimizing process parameters. The above process can be applied to solder joint scenarios using tin-silver-copper solder. First, based on thermal expansion test data, the thermal expansion of the components is determined to be 5 micrometers, and that of the PCB substrate is 3 micrometers. Then, combined with the solidification front advance speed of 0.4 mm / s, the formula is used: Where T is the thickness of the IMC layer, k is the diffusion correlation coefficient, t is the high-temperature residence time, and v is the solidification front advance velocity; The thickness of the IMC layer was evaluated, and further, based on time-based experiments, it was found that every 10-second increase in dwell time promoted an increase of 0.1 micrometers in the thickness of the IMC layer. This method demonstrates the application of the technology in electronic assembly. In the laser welding process, based on the known thermal expansion of the components being 5 micrometers, optical measurement methods were used for real-time verification. Combined with speed to assess layer thickness, the promotion amount was identified and quantified through a time-thickness relationship graph to ensure consistency. Understandably, the versatility of this technical solution lies in its scalability to similar soldering materials, such as adjusting parameters for lead-free solder to maintain accurate evaluation. The effect of high-temperature residence on growth can be identified by comparing experiments of different durations to obtain the growth promotion coefficient value, which can be used for process control. For multilayer PCB soldering, the expansion amount is calculated using the coefficient of thermal expansion to assess the layer thickness, and the promotion amount is identified as a function of time. Where k is the slope and m is the intercept, obtained through experimental fitting; Through the above steps, a complete chain is formed from obtaining the expansion amount, evaluating the layer thickness, to identifying the promotion amount. The expansion amount data is transformed into the layer thickness input, and then the promotion amount is output to support the improvement of welding quality.

[0023] like Figures 1-2 As shown, in step S104, based on the amount of heat promotion and thermal expansion during the high-temperature residence time, a zone heating control algorithm is used to determine whether the amount of heat promotion exceeds the preset thickness limit. If it does, the temperature curve of the cooling zone is adjusted to obtain the boundary position layout that balances solidification stress and intermetallic compound layer growth.

[0024] Further, in step S104, the thermal expansion promotion amount is obtained from the high temperature residence time, and the promotion amount value is determined by the zone heating control algorithm, wherein the zone heating control algorithm is based on the feedback of regional temperature difference and calculates the thermal expansion promotion amount by comparing the difference between the temperature value of each zone and the reference temperature. The value of the promotion amount is determined to see if it exceeds the preset upper limit of the thickness. If it does, the temperature curve of the cooling zone is adjusted to obtain the adjusted temperature gradient. The solidification stress equilibrium distribution is determined based on the adjusted temperature gradient, and the growth rate of the intermetallic compound layer is obtained through the correlation coefficient between the solidification stress equilibrium distribution and temperature, wherein the growth rate is calculated based on the effect of the temperature gradient on the compound diffusion rate. By using the solidification stress equilibrium distribution and the growth rate of the intermetallic compound layer, the uniform solidification state of the material is determined, and the defect boundary is located. The boundary location layout is obtained from the defect boundary location, and the growth thickness monitoring results are determined.

[0025] Specifically, in S104, this method is applied to temperature control during the metal welding process. First, the promotion amount is calculated by monitoring the high-temperature dwell time. The promotion amount refers to the amount of diffusion or growth that occurs at the material interface under high temperature conditions, such as the amount of thickening of the intermetallic compound layer at the solder joint interface caused by high-temperature dwell in circuit board reflow soldering. The promoting effect of high-temperature residence time can be calculated based on the Arrhenius time integral model. The input of the time integral model is the residence time t (in seconds) and the temperature function T(t) (in degrees Celsius), and the output is the cumulative promoting effect: Where E is the cumulative promoting effect, τ is the time integral variable, f(T) is the temperature activation function, Q is the activation energy (200 kJ / mol), and R is the gas constant (8.314 J / mol Kelvin), used to quantify the accumulation of thermal effects; Simultaneously, the thermal expansion is combined with the thermal expansion, which is obtained by multiplying the material's thermal expansion coefficient by the temperature change and is used to evaluate the thermal stress distribution. Using these parameters, a zoned heating control algorithm is used for analysis. The zoned heating control algorithm divides the welding area into multiple heating zones, and each zone independently controls the heat source input. The adjustment process of the zoned heating control algorithm is implemented as follows: Where, ΔT cool (t) represents the adjustment amount of the cooling zone temperature curve, in °C, with positive values ​​indicating the temperature drop. K is an adjustment coefficient, dimensionless, used to balance stress and IMC growth; E represents the increase in the thickness of the intermetallic compound layer due to the current high-temperature residence time, in μm, calculated by the Arrhenius time integral model in step S103. E max This is the preset upper limit for the thickness of the intermetallic compound layer, in μm; The rate of change of the baseline temperature curve, in °C / s, is the original cooling rate, used to convert excess promotion amount into temperature adjustment. T cool , old (t): Original cooling zone temperature profile, unit: °C; T cool , new (t): Adjusted cooling zone temperature profile, unit: ℃, i.e., optimized temperature setting; The specific logic for implementing the zoned heating control algorithm is as follows: When the promotion amount E(t) does not exceed the upper limit E max When, ΔT cool (t)=0, maintaining the original curve; When E(t)>E max At that time, based on the degree of exceeding the limit EE max Accelerate cooling proportionally (i.e., reduce the temperature profile) and shorten the high-temperature dwell time to inhibit excessive IMC growth; Adjusted temperature gradient G new =∇T cool , new (t) is used as the output for solidification stress balance analysis and boundary position layout optimization in step S105.

[0026] For example, the core of the partitioned heating control algorithm is to determine whether the amount of promotion, that is, the thickness of the alloy layer formed during the heating process, exceeds the preset thickness limit. The preset thickness limit is preset according to the material type. For example, for copper-aluminum composite materials, the upper limit is set to 2 micrometers to avoid excessive embrittlement. If the amount of promotion exceeds the upper limit, the algorithm triggers the adjustment mechanism. The adjustment mechanism involves modifying the temperature curve of the cooling zone, for example, by reducing the cooling rate of a specific zone to alleviate the thermal gradient. The specific process includes first collecting real-time temperature data, then using a feedback loop to calculate the deviation. If the deviation is positive, the slope of the temperature curve is gradually reduced to achieve uniformity in the solidification process. It should be noted that solidification stress refers to the internal stress generated when a material changes from a liquid to a solid state. Balancing solidification stress aims to minimize the distribution of residual stress through temperature control. The equilibrium solidification stress is achieved through the gradient descent method. The gradient descent algorithm takes as input the initial temperature curve parameters T0 and the stress simulation function S, and outputs the optimized curve parameters. The specific process is as follows: initialize T0, simulate the stress field S, and if it is not in equilibrium, calculate the stress gradient ∇σ, where ∇σ represents the rate of stress change, and adjust the parameters accordingly. Iterate until |∇σ| is less than the threshold ε=0.01. This process ensures the optimization of the boundary position layout of the intermetallic compound layer growth. The intermetallic compound layer refers to the alloy layer formed at the welding interface, and its growth is affected by temperature and time. The boundary position layout represents the geometric configuration of the layer thickness and distribution. For circuit board soldering scenarios using tin-silver-copper lead-free solder, assuming a high-temperature dwell time of 10 seconds, the acceleration is calculated by multiplying the thermal expansion by the time factor. The time factor is defined as the ratio of the high-temperature dwell time t to the standard dwell time of 10 seconds. If it exceeds the upper limit of 1.5 micrometers, the cooling zone temperature curve is adjusted to linearly decrease from 800 degrees Celsius to room temperature, with an adjustment slope of 5 degrees Celsius per second. This achieves a balanced solidification stress, ensuring a uniform distribution of the balanced solidification stress and preventing crack formation. Simultaneously, the growth boundary of the intermetallic compound layer is positioned at the center of the interface, with the layer thickness controlled within 1 micrometer. This adjustment effectively improves the mechanical strength of the solder joint. In another embodiment, applied to reflow soldering of multilayer PCBs, the amount of high-temperature dwell time promoted is monitored in real time by a sensor. If the amount of thermal expansion causes the promotion to exceed the standard, the algorithm automatically divides the cooling into zones. For example, the front zone is cooled quickly to suppress the excessive growth of the compound layer, and the back zone is cooled slowly to balance the stress. Finally, the boundary position layout forms a gradient layer structure to improve corrosion resistance. Understandably, the technical goal of this method is to achieve stability of the material interface through precise control, which can bring about improved welding quality in business, such as reducing the defect rate. The accuracy of the algorithm is improved by introducing a multi-zone sensor enhancement algorithm. The multi-zone sensor enhancement algorithm is defined as an optimization method based on multi-sensor data. Its input includes temperature data collected by infrared sensors in each zone, and the output is a fine-grained temperature adjustment command. The construction process involves real-time analysis of temperature curve changes and parameter adjustment through feedback loop. For example, infrared sensors are used to monitor the temperature curve changes of each zone to further refine the adjustment process. The boundary location layout for the growth of the intermetallic compound layer is obtained using a thickness growth equation: Where d is the thickness of the intermetallic compound layer, k is the diffusion correlation coefficient, and t is time; In circuit board soldering, the contribution of high-temperature dwell time to the increase in the thickness of the intermetallic compound layer is expressed in micrometers. If it exceeds the upper limit threshold of 2μm, after adjusting the cooling curve, the solidification stress balance is shown to be a 20% reduction in the peak stress, the boundary of the intermetallic compound layer is clearly located, and the risk of interlayer delamination is avoided. The thickness growth equation can be extended to batch soldering production lines. Through software platform integration, automated judgment and adjustment can be achieved, thereby improving production efficiency.

[0027] like Figures 1-2 As shown, in step S105, the boundary position layout after equilibrium is obtained, and the fatigue crack initiation location and its limited range are simulated by combining the radial distribution density of residual stress. The impact toughness of the joint is evaluated based on the fatigue crack initiation location.

[0028] Further, in step S105, the radial distribution density of residual stress is obtained from the equilibrium boundary location, and the fatigue crack initiation location is calculated by multiplying the distribution density integral by the stress concentration factor. A defined range is determined for the location of fatigue crack initiation, and a crack propagation suppression distribution is obtained by stress gradient adjustment, wherein the stress gradient adjustment is based on gradient difference feedback iterative calculation of the suppression distribution. Based on the crack propagation inhibition distribution, the stability of the initiation location is determined, and the joint stress balance index is obtained. The satisfaction threshold is obtained by using the joint stress balance index and the impact toughness correlation coefficient. If the satisfaction threshold exceeds the preset upper limit, the radial density simulation parameter is adjusted. The correlation coefficient is preset based on the correlation between stress balance and toughness historical data. The toughness satisfaction result is determined from the adjusted radial density simulation parameters, and the impact toughness satisfaction of the joint is obtained.

[0029] Specifically, in S105, the boundary position layout after equilibrium is first obtained, that is, the optimized distribution position of each boundary node is obtained by analyzing and calculating the actual constraint conditions and mechanical equilibrium requirements of the structural component. This process is for the field of welded joints and is achieved by analyzing the boundary conditions of the structural component. Boundary position layout refers to the edge distribution of a welded joint under mechanical equilibrium. For example, in a welded pipe structure, the location of the boundary points is determined after considering external loads and internal stresses. It should be noted that the balance of this layout is obtained through iterative calculations. For example, initial boundary data is collected first, and then the mechanical equilibrium equations are applied to adjust the position until the stability condition is met. The layout obtained in this way provides a basis for subsequent simulations and ensures the accuracy of the simulation. The key to this step is the accuracy of the data input to avoid deviations from affecting the overall evaluation. Furthermore, the radial distribution density of residual stress obtained through finite element analysis is used to simulate the location and limited range of fatigue crack initiation. The radial distribution density of residual stress refers to the stress value distribution density along the radial direction in the welded joint. For example, in a circular joint, it is the stress distribution gradient radiating outward from the center. The simulation process first establishes a residual stress model, which is based on thermodynamic principles and considers the thermal stress generated during welding and the residual effect after cooling. Simulation software generates radial density data, which represents the density as a numerical array, such as the density value ρ(r), where ρ is the density and r is the radial distance. This data is input into a finite element analysis tool to calculate stress peak regions, which are often potential crack initiation points, for example: The density distribution is represented as a Gaussian function. The function is constructed using the heat input and cooling rate data of the welding material. The parameters are derived from the experimentally measured density gradient. The path of crack propagation from the high-density area to the low-density area is simulated to determine the initiation location, such as the center point of the joint weld, and the range is limited to within 5 mm in the radial direction. This value is based on the typical radius of the stress concentration region in the finite element analysis. Non-uniformity of density distribution leads to stress concentration due to uneven welding heating. Combined with boundary layout, this affects fatigue life prediction. This method can accurately locate the crack initiation location and propagation boundary, providing quantitative evidence. The detailed implementation of this process helps to identify high-risk areas and achieve preventive maintenance. Its application in welded structures such as bridge joints can effectively reduce the risk of fatigue failure. When simulating the location of fatigue crack initiation, multi-layer stress density distribution analysis can be introduced, which is a method of calculating stress distribution by dividing the cross section into layers; First, the joint section is divided into multiple radial layers. The average stress density of each layer is calculated, which is defined as the stress integral within the layer divided by the layer area. For example, the average value is obtained by dividing the integral value by the area after obtaining the integral value through finite element software. Then, the data are integrated into an overall distribution map. A linear interpolation algorithm is used to superimpose the data of each layer to generate a continuous three-dimensional distribution map. This method enhances the accuracy of the simulation. Preferably, the impact toughness of the joint is evaluated based on the crack propagation path and energy absorption characteristics in the impact simulation. This evaluation is based on the dynamic fracture simulation results under impact load, and determines whether the toughness of the joint under high strain rate impact meets the design requirements, and whether the impact absorption energy is not less than 80% of the benchmark value or the crack propagation length is less than the limit value. The impact toughness satisfaction is used to evaluate the damage resistance of a structure at the crack initiation location under impact load. Its value is calculated by comparing the local maximum principal stress at the crack initiation location with a preset toughness threshold (300MPa): when the initiation location is in a low stress zone (local stress is below the threshold), the satisfaction is high (close to 1). When the threshold is approached or exceeded, the satisfaction level decreases, and structural optimization design is required to improve safety. In one embodiment, a quantitative index is used, defining the satisfaction as the ratio of position deviation to standard range, where position deviation refers to the distance difference between the actual weld center and the theoretical position, and the standard range is a process tolerance of ±0.5mm to ensure objective evaluation. The balanced boundary position layout obtained by this method, that is, the optimized distribution of coordinates of each key point, can be further extended to various welding types such as T-welding and lap welding. For butt welded joints, the boundary curvature is measured first, and then the layout is adjusted by applying a balancing algorithm. This extension demonstrates the versatility of the solution. Understandably, the simulation of radial distribution of residual stress involves an introduction to the underlying principles: Residual stress originates from the welding thermal cycle, leading to uneven shrinkage within the material and the formation of a radial gradient. During simulation, experimental data, such as stress values ​​measured by X-ray diffraction, are first collected, and then a distribution curve is constructed. For example, the stress decreases from a high value at the center to the edge. Through the finite element model, the distribution is calculated step by step to predict the crack initiation location, such as at the peak value, and the range is limited based on the stress attenuation threshold of 50 MPa. This detailed process ensures the reliability of the simulation. In actual welding, such as pressure vessel joints, fatigue risks can be assessed in advance to avoid sudden fractures. Furthermore, when assessing the impact toughness of the joint, scenario variations can be introduced. For example, under cyclic loading, the toughness index is calculated based on the initiation location. It is defined as the material's ability to resist crack propagation. The calculation process is as follows: Where TI is the toughness index, P is the coordinate of the initiation location, S is the coordinate of the center of the safe zone, and D is the density factor; If the position deviates from the safe zone by more than 5 mm, the satisfaction level decreases. This variant supports a variety of welding applications. The scope is defined as areas where the density of key facilities per unit area exceeds 5 per square kilometer. This method is implemented through data visualization technology, thereby significantly improving the practicality of the solution. In one embodiment, the entire process begins with acquiring boundary layout data, goes through analysis and processing, and continues until the resilience assessment is completed, forming a complete closed-loop process. First, the material layout is obtained. Then, crack locations are simulated through finite element analysis, i.e., potential crack points are randomly generated under a high-density distribution. Finally, the satisfaction level is evaluated, i.e., the toughness satisfaction level is calculated. Actual toughness is based on simulated stress calculations, requiring toughness to be at the standard threshold. The results show that under high density distribution, S can reach more than 90% of the required level (S≥85%). It should be noted that the application of this technical solution in the field of weld joint solidification stress management can achieve accurate prediction and evaluation, support the optimization of impact toughness through objective data, and avoid the uncertainty brought about by traditional reliance on experience.

[0030] like Figures 1-2 As shown, in step S106, it is determined whether the impact toughness meets the preset requirements. If it does, the temperature zone heating control setting is output as the weld joint solidification stress management scheme. If it does not meet the requirements, the process returns to adjust the boundary position layout until the requirements are met.

[0031] Further, in step S106, the impact toughness satisfaction is obtained from the solidification stress distribution of the weld joint, and the satisfaction is compared with the preset requirements by combining the stress balance index to obtain the comparison result; If the comparison result meets the preset requirements, the temperature zone heating control setting is determined according to the satisfaction level, and the setting is output as a solder joint solidification stress management scheme. If the comparison result does not meet the preset requirements, the boundary position layout is adjusted according to the satisfaction level to obtain the adjusted layout; The impact toughness satisfaction is re-acquired through the adjusted layout, and it is determined whether the satisfaction meets the preset requirements.

[0032] Specifically, in S106, the process of judging the impact toughness satisfaction is first evaluated based on the mechanical property parameters of the weld joint material, including yield strength, tensile strength and fracture toughness. By collecting stress distribution data during the solidification process of the weld joint, combined with the formula: Where K is the toughness value, S is the stress data, and E is the material's elastic modulus; The toughness value was calculated and compared with the preset toughness threshold (50 MPa·m). 0.5 The preset toughness threshold is derived from material standards and specifications. If the calculated toughness value is greater than or equal to the preset requirement, it is determined to be satisfied, and the temperature zone heating control setting is output as a weld joint solidification stress management scheme. This setting includes the heating temperature (200 to 300 degrees Celsius) and time distribution (5 to 10 minutes per zone) of each zone. It is optimized and generated according to the stress distribution to ensure the structural integrity of the weld joint during the solidification stage and avoid the risk of crack propagation. Preferably, the temperature zone heating control includes dividing the welding area into zones and configuring the temperature parameters for each zone; In weld solidification management, i.e., controlling the weld cooling process to avoid defects such as cracks, the weld plate is divided into multiple heating zones. Each zone has a different heating temperature profile set according to the material's thermal conductivity. The specific process includes using the finite element method to analyze the thermal field distribution around the weld and calculating the heating power required for each zone. Where P is power, k is thermal conductivity, A is area, and T is... t For the target temperature, T a The ambient temperature is used to achieve a uniform solidification rate. This configuration scheme reduces thermal stress concentration through zoned control, thereby reducing the risk of solder joint fatigue. It can be applied to electronic circuit board assembly scenarios in actual soldering operations, improving the long-term reliability of solder joints. If the impact toughness satisfaction (the percentage calculated by impact test) does not reach the preset requirement of 80%, the step of adjusting the boundary position layout needs to be returned. This adjustment process emphasizes iterative optimization of the boundary layout, including adjusting the boundary position multiple times based on stress simulation until the stress distribution is uniform and the optimization converges to the preset threshold, in order to improve the overall stress distribution. First, identify the location of the stress peak at the weld point boundary, and then redistribute the load by adjusting the boundary point position or optimizing the layout geometry. Stress distribution can be simulated using finite element analysis. During the design phase, the position of the weld point boundary can be adjusted by software, or the welding layout can be changed using adjustable fixtures in the process to ensure stress dispersion. This method must be implemented within the strength limits of the welding material and the cost-benefit ratio of the equipment must be evaluated to ensure economic practicality. The finite element simulation tool is used to evaluate the toughness changes after adjustment until a preset threshold is met. This iterative mechanism plays a key role in welding process optimization and ensures the adaptability of the solution. It should be noted that the boundary position layout refers to the spatial arrangement of weld points or welds on the structural boundary. Its adjustment can cover multiple scenarios in the same welding field. For example, in the welding of metal frames, the spacing between weld points is adjusted first to balance the stress. During the adjustment process, the influence of the material expansion coefficient is considered, and the position parameters are gradually fine-tuned to avoid additional stress caused by excessive changes. This method not only improves the toughness satisfaction, but also provides a flexible implementation path for solidification stress management. In one embodiment, the entire judgment and output process can be integrated into an automated welding system. The system monitors the toughness index in real time. If the preset conditions are met, the temperature zone heating setting is automatically applied. Otherwise, the layout adjustment module is triggered. The module takes the solder joint stress distribution heat map as input and optimizes the position and spacing of the solder pads through finite element iteration. The goal is to reduce the local maximum stress to below 75% of the material yield strength. Iterative calculations are performed. This integration method demonstrates versatility on the circuit board production line. Closed-loop control is achieved through sensor feedback data, thereby effectively managing stress during the solidification stage. When processing aluminum alloy weld joints, the impact toughness assessment can be combined with impact test data as an auxiliary verification. The preset requirement is that the toughness value is not lower than a specific standard value. If the condition is not met after assessment, the boundary layout is adjusted, such as increasing the weld joint size or adopting an elliptical design to distribute stress evenly. This example demonstrates the application potential of the solution in welding lightweight materials. Understandably, the details of the temperature zone heating control setting include the segmented design of the heating curve, such as the temperature gradient control of the preheating stage, solidification stage and cooling stage. Through this zoned strategy, the internal stress of the weld joint can be uniformly released, which is suitable for precision instrument welding in actual operation and avoids thermal deformation problems. The process of iterating the boundary position layout until the requirements are met can be achieved through multiple simulation cycles. After each round of adjustment, the toughness satisfaction is recalculated. If the standard is not met for three consecutive times, auxiliary parameters such as adding support structures are introduced. This multi-round iteration enhances the robustness of the solution in welding optimization. In the weld solidification stress management scheme, after the output temperature zone heating control is set, its effect on improving toughness can be verified. After implementation, monitoring the performance indicators of the weld joints confirms the effectiveness of the stress management scheme. This verification step provides data support for subsequent welding process improvements. In one embodiment, when determining the impact toughness of high-strength steel weld joints, a crack propagation fatigue life model based on Paris's law can be referenced. This model describes the accumulation of fatigue damage using the relationship between the stress intensity factor range ΔK and the crack propagation rate da / dN. If the calculated weld joint fatigue life exceeds a set threshold of 10... 6 In the next cycle, the zone heating scheme is output, including the setting of high temperature in the central area and low temperature in the edge area; otherwise, the boundary layout is adjusted to optimize the stress path.

[0033] The circuit board soldering temperature zone heating control system described in this application includes: The boundary position acquisition module is used to acquire the boundary position coordinates of the cooling zone and the reflow zone, extract the temperature gradient steepness at the junction of the two zones, identify the heat transfer path from the outer periphery to the center of the solder joint, determine the solidification front advancement speed of the molten solder at the solder joint based on the heat transfer path, and obtain the radial distribution density of residual stress in the cross section of the solder joint. The stress concentration assessment module is used to assess the stress concentration value in the central region of the weld joint based on the radial distribution density of the residual stress using a heat conduction algorithm, and to determine whether the stress concentration value exceeds a preset safety threshold. If it does, the optimized solidification front advance speed is obtained by using a gentle temperature gradient steepness. The compound layer evaluation module is used to obtain the thermal expansion of components and PCB substrate, and to evaluate the thickness of the intermetallic compound layer at the interface of solder joint and pad by combining the optimized solidification front advance speed, and to identify the amount of promotion of the intermetallic compound layer thickness growth by the high temperature residence time. The boundary layout balancing module is used to determine whether the amount of promotion exceeds the preset thickness limit based on the amount of promotion and thermal expansion during the high-temperature residence time using a zoned heating control algorithm. If it exceeds the limit, the cooling zone temperature curve is adjusted to obtain a boundary position layout that balances solidification stress and intermetallic compound layer growth. The fatigue crack simulation module is used to obtain the boundary position layout after equilibrium, combine the radial distribution density of residual stress to simulate the fatigue crack initiation location and its limited range, and evaluate the impact toughness satisfaction of the joint based on the fatigue crack initiation location. The impact toughness judgment module is used to determine whether the impact toughness meets the preset requirements. If it does, it outputs the temperature zone heating control setting as a weld joint solidification stress management scheme. If it does not meet the requirements, it returns to adjust the boundary position layout until the requirements are met.

[0034] For those skilled in the art, various other corresponding changes and modifications can be made based on the technical solutions and concepts described above, and all such changes and modifications should fall within the protection scope of the claims of this application.

Claims

1. A method for zoned heating control of circuit board soldering temperature, characterized in that, include: S101, obtain the boundary coordinates of the cooling zone and the reflow zone, extract the temperature gradient steepness at the junction of the two zones, identify the heat transfer path from the outer periphery to the center of the solder joint, determine the solidification front advance speed of the molten solder of the solder joint based on the heat transfer path, and obtain the radial distribution density of residual stress in the cross section of the solder joint. S102, based on the radial distribution density of residual stress, the heat conduction algorithm is used to evaluate the stress concentration value in the center region of the weld joint, and to determine whether the stress concentration value exceeds the preset safety threshold. If it does, the optimized solidification front advance speed is obtained by using the gentle temperature gradient steepness. S103, obtain the thermal expansion of components and PCB substrate, combine the optimized solidification front advance speed to evaluate the thickness of intermetallic compound layer at the interface of solder joint and pad, and identify the amount of promotion of the increase in intermetallic compound layer thickness by the high temperature residence time. S104. Based on the amount of heat promotion and thermal expansion during the high-temperature residence time, a zone heating control algorithm is used to determine whether the amount of heat promotion exceeds the preset thickness limit. If it does, the temperature curve of the cooling zone is adjusted to obtain the boundary position layout that balances solidification stress and intermetallic compound layer growth. S105, obtain the boundary position layout after equilibrium, combine the residual stress radial distribution density to simulate the fatigue crack initiation location and its limited range, and evaluate the impact toughness satisfaction of the joint based on the fatigue crack initiation location. S106 determines whether the impact toughness meets the preset requirements. If it does, it outputs the temperature zone heating control setting as the weld joint solidification stress management scheme. If it does not meet the requirements, it returns to adjust the boundary position layout until the requirements are met.

2. The circuit board soldering temperature zone heating control method according to claim 1, characterized in that, S101 includes: The surface of the solder joint is scanned by an infrared thermal imager, and the boundary coordinates and temperature field distribution of the cooling zone and reflow zone are obtained based on the scan data. Based on the temperature field distribution, the steepness of the temperature gradient at the boundary between the two zones is extracted to determine the heat transfer path from the outer periphery of the solder joint to the center. By identifying the direction of heat flow through the heat transfer path, the solidification characteristics of the molten solder can be obtained; The solidification front advance velocity is calculated from the solidification characteristics, and the radial distribution density of residual stress on the weld joint cross section is simulated accordingly.

3. The circuit board soldering temperature zone heating control method according to claim 2, characterized in that, S102 includes: The residual stress density is obtained from the cross-section of the weld joint, and the radial distribution characteristics are analyzed by scanning data to determine the stress distribution pattern in the central region. Based on the stress distribution pattern, the specific values ​​of stress concentration are calculated and obtained using a heat conduction algorithm. If the value exceeds the preset safety threshold, the gentle temperature gradient steepness method is adopted, and the heat flow parameter in the stress concentration value is adjusted to optimize the solidification front advance speed.

4. The circuit board soldering temperature zone heating control method according to claim 1, characterized in that, S103 includes: Calculate the thermal mismatch strain at the solder joint interface based on the difference in thermal expansion between the components and the PCB substrate. Combining the solidification front advance velocity, an interface evaluation model based on the relationship between thermal expansion difference and solidification front advance velocity is constructed. The interface evaluation model is constructed by integrating the thermal relationship equation between thermal expansion difference and velocity parameter to determine the initial value of compound thickness between solder joint interface and solder pad substrate. High-temperature dwell parameters are extracted from the initial thickness value, and the atomic migration rate and thickness growth rate are calculated using thermodynamic simulation. If the thickness growth rate exceeds the threshold, the solidification front advance speed is adjusted to optimize parameters and obtain a thickness growth correction curve. Based on the thickness growth correction curve, the amount by which high-temperature dwell time promotes thickness growth is identified, and the final state of the intermetallic compound layer is evaluated in combination with the microscopic characteristics of the solder joint interface.

5. The circuit board soldering temperature zone heating control method according to claim 1, characterized in that, S104 includes: The acceleration amount is determined by using a zoned heating control algorithm based on the acceleration amount and thermal expansion amount during high-temperature residence time. If the amount of promotion exceeds the preset thickness limit, the temperature curve of the cooling zone is adjusted to obtain the adjusted temperature gradient. The solidification stress equilibrium distribution is determined based on the adjusted temperature gradient, and the growth rate of the intermetallic compound layer is obtained by combining the temperature correlation coefficient. By analyzing the equilibrium distribution of solidification stress and the growth rate, the uniform solidification state of the material can be determined, thereby locating the defect boundary. Based on the defect boundary location, the boundary position layout of the equilibrium solidification stress and the growth of the intermetallic compound layer is obtained.

6. The circuit board soldering temperature zone heating control method according to claim 1, characterized in that, S105 includes: The radial distribution density of residual stress is obtained from the boundary location layout, and the location of fatigue crack initiation is calculated by integrating it and the stress concentration factor. The limited range of fatigue crack initiation locations was determined, and the crack propagation inhibition distribution was obtained using the stress gradient adjustment method; The stability of the initiation location is determined by the distribution of crack propagation inhibition, and the stress balance index of the joint is obtained. By combining the joint stress balance index with the preset impact toughness correlation coefficient, the satisfaction threshold is obtained; The radial density simulation parameters are adjusted according to the satisfaction threshold, and the impact toughness satisfaction of the joint is determined based on the adjusted parameters.

7. The circuit board soldering temperature zone heating control method according to claim 1, characterized in that, S106 includes: The impact toughness satisfaction is obtained from the solidification stress distribution of the weld joint and compared with the preset requirements based on the stress balance index. If the comparison results meet the preset requirements, the temperature zone heating control settings are determined based on the satisfaction level, and the output is a solder joint solidification stress management scheme. If the comparison results do not meet the preset requirements, the boundary position layout is adjusted, and the impact toughness satisfaction is reassessed based on the adjusted layout until the preset requirements are met.

8. A system for performing the circuit board soldering temperature zone heating control method according to claims 1-7, characterized in that, The boundary position acquisition module is used to execute S101; The stress concentration assessment module is used to perform S102; A compound layer evaluation module is used to perform S103; The boundary layout balancing module is used to execute S104; The fatigue crack simulation module is used to execute S105; The impact toughness determination module is used to execute S106.

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