A guided SiP reflow soldering process modeling simulation method

Abstract

The application discloses a guide type SiP reflow soldering process modeling and simulation method, relates to the simulation analysis technical field of the cross field of electronic packaging manufacturing process and multi-physical field finite element simulation, and the method comprises the following steps: parameterized geometric modeling, substrate equivalent simplification and automatic mesh division based on metal proportion, batch configuration of material constitutive model, automatic setting of contact interface, reflow soldering process timing modeling and solder life and death unit control, thermal-solid coupling simulation solving and result post-processing automation. The application automatically splits the reflow soldering process into heating, cooling and cooling sub-analysis steps with the solder melting point as the critical value, simulates the "melting-solidification" state change of the solder through the automatic timing control of the life and death unit, greatly reduces the grid scale under the premise of reserving mechanical and thermal characteristics through the substrate equivalent simplification, and realizes full-process automatic modeling through the guide type operation. High-fidelity and high-efficiency simulation of the reflow soldering full process is realized.

Description

Technical Field

[0001] This invention relates to the field of simulation analysis technology at the intersection of electronic packaging manufacturing processes and multiphysics finite element simulation, and more specifically to the field of a guided SiP reflow soldering process modeling and simulation method. Background Technology

[0002] Reflow soldering is a core process in electronic packaging and surface mount manufacturing. With the rapid development of advanced packaging technology towards multi-chip stacking and high-density integration, complex structures such as 2.5D / 3D packaging, Chiplet, and RF SiP commonly adopt multi-step reflow soldering processes. By using a preset temperature profile to melt and then solidify the solder paste, mechanical interconnection and electrical conduction between the chip, passive device, and substrate are achieved. Its essence is a thermo-mechanical coupling process involving heterogeneous matching of multiple materials, multi-phase transformation coupling, strong temperature nonlinearity, and transient throughout the entire process. Its process stability directly determines the mass production yield and life-cycle reliability of electronic devices. The core physical contradiction of the reflow soldering process is the mismatch of the coefficient of thermal expansion (CTE) of heterogeneous materials and the abrupt change in the stiffness of the solder melting-solidification phase transition. Multi-step thermal cycling directly causes thermal warping of the package and PCB, interface stress concentration, solder joint failure, and accumulation of residual stress in multiple processes. It is the core root cause of reliability failures in advanced miniaturized, high-power, multi-chip stacked devices and has become a core bottleneck restricting the mass production of advanced packaged devices.

[0003] As advanced packaging moves towards higher density, more stacked layers, and smaller solder ball sizes, the reflow soldering process window continues to narrow. Traditional modeling methods have two drawbacks: Firstly, physical modeling is inefficient and cannot keep up with the demands of rapid process iteration. Traditional modeling methods require complete reproduction of microscopic geometric details such as substrate wiring and vias, and preprocessing modeling for a single complex SiP device can take tens of hours, with the solution time for a single operating condition being even more difficult to estimate. Furthermore, when iterating on process parameters, the entire modeling process must be repeated, which cannot match the design rhythm of rapid iteration and multi-solution comparison and optimization for advanced packaging products.

[0004] Secondly, the fragmented logic of multi-process time-series modeling makes it impossible to accurately reproduce the physical essence of the actual process. Reflow soldering is a transient time-series process involving multiple steps: heating, holding, melting, cooling, solidification, and cooling. The solder undergoes solid-liquid-solid phase transitions, and the multi-step welding process results in the accumulation of residual stress. Traditional methods require engineers to manually break down the process states, which is not only time-consuming but also fails to accurately match the temporal relationship between the solder melting point and temperature curves. This makes it difficult to simulate the real strain evolution of the solder during melting and solidification, leading to significant discrepancies between simulation results and actual processes, and thus failing to support failure prediction.

[0005] Accurate reflow soldering process simulation is the only digital means to predict failure risks in advance, optimize process parameters, and reduce trial and error costs. High-quality, high-fidelity modeling methods are the core prerequisites for determining the accuracy and engineering practicality of reflow soldering simulation. Traditional modeling methods can no longer meet the core engineering requirements of "process physical fidelity, simulation accuracy, controllable computational efficiency, and adaptability to operational thresholds," nor can they adapt to the process design requirements of advanced packaging with multiple processes, high precision, and rapid iteration. Therefore, there is an urgent need to research an innovative modeling method for the entire reflow soldering process. Summary of the Invention

[0006] The purpose of this invention is to address the technical problems of low modeling efficiency and distorted process timing simulation in traditional precise reflow soldering process simulation. This invention provides a guided SiP reflow soldering process modeling and simulation method.

[0007] To achieve the above objectives, the present invention specifically adopts the following technical solution: This invention provides a guided SiP reflow soldering process modeling and simulation method, comprising the following steps: Step 1: Parametric geometric modeling: Based on the SiP design file, import the substrate ECAD file in the layer sequence, automatically extract geometric information and configure layer thickness and physical properties; import the component model and configure its size and spatial position, and automatically complete the Z-axis assembly; Step 2, Geometric Equivalence Simplification and Mesh Generation: The layered structure of the substrate is discretized into a regular mesh, the local metal ratio is calculated to solve the equivalent material properties and mapped to the substrate model; the global mesh size is controlled by coarse / medium / fine levels, mesh parameters are configured for different components, and a hybrid mesh is automatically generated; Step 3: Batch configuration of material constitutive models: Build a SiP material library, complete the batch configuration of material constitutive models through the wizard, and complete the material assignment by component; Step 4: Automated setup of contact interfaces: Automatically traverse the entire model to identify all physical contact interfaces and generate a list of contact pairs. Automatically configure contact parameters and generate binding constraints according to preset contact types. Step 5: Time-sequential modeling of reflow soldering process and control of solder cell life and death: Import furnace temperature curve and plot temperature-time curve; create new process steps based on furnace temperature curve, and automatically divide a single reflow soldering process into three sub-analysis steps: heating, cooling, and deheating, using the solder melting point as the critical value; automatically configure cell life and death attributes for the solder components in each reflow soldering step, killing cells during the heating stage and activating cells during the cooling stage; map the thermal analysis temperature results to the structural model to achieve temperature field-structural field coupling. Step 6, Thermal-Structure Coupling Solution and Post-processing: Automatically generate thermal and structural analysis solution tasks and complete parameter configuration to achieve unidirectional thermal-structure coupling solution; automatically generate displacement contour maps, stress contour maps and plastic strain contour maps, extract warping deformation and draw warping curves.

[0008] In one embodiment, in step two, the mesh generation is as follows: for the substrate, solder balls, chip, and frame, respectively configure the mesh type, cell order, mesh size, and minimum number of layers in the thickness direction, the system automatically generates a hybrid mesh with hexahedrons as the main component.

[0009] In one embodiment, in step two, the equivalent material properties are calculated using a series-parallel spring model to determine the equivalent Young's modulus, coefficient of thermal expansion, and thermal conductivity, including separate calculations of the metal proportions in the in-plane and thickness directions.

[0010] In one implementation, in step three, for the solder material of the reflow soldering core, multiple constitutive models such as linear elasticity, bilinearity, and Anand viscoplasticity are used to quasi-adapt the mechanical behavior simulation of the solder at different temperatures, and the material constitutive model is configured in batches. Specifically targeting the mechanical behavior of lead-free solder under high temperature, large deformation, and creep-dominated conditions during reflow soldering, it adopts the Anand unified viscoplastic constitutive model: which fully describes the mechanical properties of the entire process of melting, softening, hardening, and creep, and is the only high-precision model for predicting solder joint stress and fatigue life. Flow equations: ; Evolution of internal variables: ; in: Equivalent plastic strain; This is the equivalent stress (i.e., Mises equivalent stress); A This is the frequency factor (i.e., the material structure constant); It is the thermal activation energy for plastic deformation; This is the universal gas constant (typically 8.314). ); T Absolute temperature; It is the stress constant; It is a strain rate sensitivity index; It is the hardening modulus constant; The hardening index; The rate of change of deformation resistance; Resistance to saturated deformation; It is a hyperbolic sine function; It is a symbolic function.

[0011] In one implementation, in step three, batch material assignment is completed on a component-by-component basis, material parameters in the geometric modeling stage are automatically synchronized, and the addition and modification of custom material properties are supported. The ECAD layered structure of the substrate is discretized into a regular mesh, the in-plane and thickness metal ratio of each mesh unit is calculated, the equivalent material properties are calculated through a series and parallel spring model, the equivalent material properties are mapped to the substrate geometric model, the equivalent material properties of the substrate are assigned, the macroscopic equivalent characterization of the substrate micro-wiring details is completed, and the model size is greatly simplified while retaining the mechanical properties of the substrate.

[0012] In one embodiment, in step four, the contact type includes metal dry contact, silicone grease, thermal pad, and solder equivalent thermal resistance, with each type having three preset high / medium / low contact thermal resistance and friction coefficients for selection or customization.

[0013] In one implementation, in step five, the furnace temperature curve management includes: wizard-driven import of CSV format curve files, automatic identification of the time nodes corresponding to peak temperature and melting point, and support for curve editing, saving, and reuse; The transient heat conduction control equation is: ; in: For material density, For specific heat capacity, Thermal conductivity, For temperature field distribution, For time, The latent heat of the solid-liquid phase transition of the solder is a core parameter for reproducing the true temperature field.

[0014] In one implementation, in step five, the activated units of the multi-step reflow soldering remain activated in subsequent processes to reduce the residual stress accumulation effect. In thermal analysis, the furnace temperature curve is applied to the outer surface of the model as a convection boundary condition. In structural analysis, inertial release constraints are applied and binding constraints are added to the welded components to match the actual connection state after welding.

[0015] In one implementation, in step six, the thermo-structure coupling solution involves first solving the transient temperature field, and then mapping the temperature field to the structural model to sequentially solve for thermal strain, thermal stress, and residual stress. Thermal strain: ; Thermal stress: ; In the formula, Thermal strain; The coefficient of linear expansion; This refers to the change in temperature. Equivalent stress; Here is the elastic stiffness matrix; For total strain; Thermal strain; This is plastic strain.

[0016] In one implementation, step six further includes a post-processing module that automatically extracts the geometric model, mesh information, material parameters, process settings, and simulation results to generate a standardized simulation analysis report in Word format.

[0017] The beneficial effects of this invention are as follows: 1. Significantly improves modeling efficiency and shortens simulation cycles. This invention achieves fully automated modeling from geometric modeling to result output through a wizard-driven operation process, replacing the tedious operations of traditional manual analysis steps, configuring birth and death elements, and defining contact pairs. This improves pre-processing modeling efficiency, effectively matching the design pace of rapid iteration and multi-solution comparison and optimization for advanced packaging products.

[0018] 2. Realistically reproduces the physical essence of the reflow soldering process. This invention uses a time-sequential modeling method driven by the solder melting point to accurately match the physical state changes of the solder during the "melting-solidification" process. Through automated time-sequential control of birth and death units, it realistically reproduces the residual stress accumulation effect of multi-step reflow soldering, overcoming the problems of fragmented multi-physics modeling and inability to simulate the real strain evolution of solder melting-solidification in traditional methods.

[0019] 3. Achieving a balance between simulation accuracy and computational efficiency. This invention utilizes a simplified modeling method based on the equivalent metal ratio of the substrate. While preserving core mechanical and thermal properties, it reduces the number of model meshes and improves solution efficiency. Compared to purely detailed modeling, it significantly reduces computational resource requirements; compared to coarse homogenization equivalence, it significantly improves the accuracy of warpage and stress prediction.

[0020] 4. Lowering the barrier to simulation operation. Through a wizard-driven parametric modeling and simulation process, complex low-level operations such as finite element theory, birth and death element control, and contact algorithms are encapsulated, enabling process engineers to complete high-fidelity reflow soldering simulations without a deep background in finite element theory, which is conducive to the promotion and application of the technology in the field of engineering.

[0021] 5. Supports closed-loop management throughout the entire process. By automatically generating standardized simulation analysis reports, it achieves closed-loop management from model building to result output, providing strong digital support for reliability design, failure prediction, and parameter optimization of system-level packaging reflow soldering processes. Attached Figure Description

[0022] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained from these drawings without creative effort.

[0023] Figure 1 This is a flowchart of a guided SiP reflow soldering process modeling and simulation method according to the present invention.

[0024] Figure 2 This is a schematic diagram of the SiP parametric modeling results in Implementation Example 1 of the present invention.

[0025] Figure 3 This is a schematic diagram of the equivalent simplified model of the substrate structure in Embodiment 1 of the present invention.

[0026] Figure 4 This is a mesh model diagram after automatic mesh generation in Implementation Example 1 of the present invention.

[0027] Figure 5 This is a schematic diagram of the automated setting of the contact surface in Embodiment 1 of the present invention.

[0028] Figure 6 This is a furnace temperature curve management diagram of the process in Embodiment 1 of the present invention.

[0029] Figure 7 This is a warping cloud map of a single weld in Embodiment 1 of the present invention.

[0030] Figure 8 This is a warping cloud diagram of the secondary welding in Embodiment 1 of the present invention.

[0031] Figure 9 This is a warping cloud map of the three welding operations in Embodiment 1 of the present invention.

[0032] Figure 10 This is a residual stress cloud diagram after welding is completed in Embodiment 1 of the present invention. Detailed Implementation

[0033] To make the technical problems, technical solutions, and technical effects of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0034] This invention provides a guided SiP reflow soldering process modeling and simulation method, which fully covers the entire process from geometric model construction to simulation result output. It is divided into 6 key steps, focusing on the timing and high-fidelity modeling of the reflow soldering process. The specific implementation method is as follows: Step 1: Parametric geometric modeling The main goal of this step is to rapidly construct the SiP geometric structure model and perform equivalent simplified modeling of the substrate based on metal ratio. Based on SiP design files (such as ECAD files like DXF / ODB++ and component files), a wizard is created to automatically generate geometric models by loading design files. The substrate ECAD file is imported layer by layer, automatically extracting the geometric information of metal layers, dielectric layers, vias, and pads, and parameterizing the thickness and physical properties of each layer. Component models such as chips, capacitors, frames, solder balls, and bond wires are imported, and their dimensions and spatial positions are parameterized. Finally, the precise Z-axis assembly of components and their corresponding substrates is automatically completed.

[0035] Step 2: Geometric Simplification and Automated Mesh Generation The high precision of the detailed modeling achieved through the design file in step one directly leads to low computational efficiency. To resolve the contradiction between precision and efficiency in substrate modeling, a simplified modeling of the substrate based on the metal ratio is proposed. By discretizing the ECAD layered structure of the substrate into a regular mesh, the local metal ratio is calculated to solve for the equivalent material properties. This transforms the micro-wiring details of the substrate into macro-equivalent material parameters, replacing the traditional geometric detail reproduction. While preserving the mechanical and thermal properties of the substrate, the model mesh size is significantly reduced, serving as an auxiliary means for balancing simulation precision and computational efficiency in this invention.

[0036] The wizard-driven mesh generation allows for global mesh size settings to be controlled at three levels: coarse, medium, and fine. For different functional components such as substrates, solder balls, chips, and frames, the mesh type, cell order, mesh size, and minimum number of layers in the thickness direction can be configured interactively. The system automatically generates a high-quality hybrid mesh with hexahedrons as the main component for the entire model.

[0037] Step 3: Batch configuration of material constitutive models: A comprehensive SiP (System-in-Package) materials library is built, covering all categories of packaging materials, including substrates, metal conductors, solders, chips, and interface materials. A design wizard enables batch configuration of material constitutive models. For solder materials, a core component of reflow soldering, multiple constitutive models are provided, including linear elastic, bilinear, and Anand viscoplastic models, accurately simulating the mechanical behavior of solders at different temperatures. For lead-free solders exhibiting high-temperature, large-deformation, and creep-dominated mechanical behavior during reflow soldering, the Anand unified viscoplastic constitutive model is employed to fully describe the mechanical properties throughout the melting, softening, hardening, and creep stages. This model is the only high-precision model for predicting solder joint stress and fatigue life. Flow equations: ; Evolution of internal variables: ; in: Equivalent plastic strain; This is the equivalent stress (i.e., Mises equivalent stress); A This is the frequency factor (i.e., the material structure constant); It is the thermal activation energy for plastic deformation; This is the universal gas constant (typically 8.314). ); T Absolute temperature; It is the stress constant; It is a strain rate sensitivity index; It is the hardening modulus constant; The hardening index; The rate of change of deformation resistance; Resistance to saturated deformation; It is a hyperbolic sine function; It is a symbolic function; Batch material assignment is performed on a component-by-component basis, automatically synchronizing material parameters during the geometric modeling stage, and supporting the addition and modification of custom material properties. The substrate ECAD layered structure is discretized into a regular mesh, and the in-plane and thickness metal ratio of each mesh unit is calculated. Key parameters such as equivalent Young's modulus, coefficient of thermal expansion, and thermal conductivity are calculated using a series-parallel spring model. Equivalent material properties are mapped to the substrate geometric model, achieving the assignment of equivalent material properties to the substrate. This completes the macroscopic equivalent characterization of the substrate's micro-wiring details, significantly simplifying the model size while preserving the substrate's mechanical properties.

[0038] Step 4: Automating the touch interface settings: The system is designed for one-click automatic traversal of all components in the entire model, intelligently identifying all physical contact interfaces such as chip-substrate, solder-pad, substrate-substrate, and frame-cover, and automatically generating a contact pair list. It includes preset contact types commonly used in engineering, such as metal-to-metal dry contact, silicone grease application, thermal pads, and solder equivalent thermal resistance. Each type provides high, medium, and low levels of contact thermal resistance and friction coefficient parameters, which users can directly select or customize to adapt to the actual processes of different interfaces. Based on the configured contact parameters, it automatically generates contact conditions, adds contact thermal resistance settings for thermal analysis, generates binding constraints for structural analysis, and completes the batch automated setting of all contact conditions for the entire model.

[0039] Step 5: Reflow soldering process timing modeling and solder birth / death cell control: Achieving high-fidelity digital mapping of the entire reflow soldering process specifically includes: 1) Furnace temperature curve management and analysis: The furnace temperature curve file in CSV format is automatically imported through the curve manager wizard and the temperature-time curve is automatically plotted. The key time nodes corresponding to the peak temperature and solder melting point are automatically identified. It supports the editing, saving and reuse of multiple temperature curves and realizes the matching of the furnace temperature curve of the simulation and the actual production line.

[0040] 2) Multi-step process step timing definition: Based on the furnace temperature curve, total process duration, cooling termination temperature, and corresponding temperature curves, a new reflow soldering process step is created for each reflow soldering step. The termination time of the previous step is automatically inherited as the start time of this step. Using the solder melting point as the critical value, the single-step reflow soldering process is automatically divided into three sub-analysis steps: heating, cooling, and cooling. The stage with the temperature above the melting point is the heating step, the stage with the temperature below the melting point is the cooling step, and the stage of holding at room temperature is the cooling step, to match the actual reflow soldering process stages. The reflow soldering simulation fully considers three core terms: heat conduction, temperature change, and latent heat of phase change. The transient heat conduction control equation is the core control equation for solving the temperature field. ; in: For material density, For specific heat capacity, Thermal conductivity, For temperature field distribution, For time, The latent heat of the solid-liquid phase transition of the solder is a core parameter for reproducing the true temperature field.

[0041] 3) Automated configuration of solder unit life and death status: For the solder components corresponding to each reflow soldering step, the life and death attributes of the units are automatically configured: During the heating stage, the solder temperature is higher than the melting point and is in a molten state, so the unit is set to the "killed" state and does not transfer structural stress (stiffness ≈ 0, simulating melting); During the cooling stage, the solder temperature is lower than the melting point and begins to solidify, so the unit is automatically "activated" to realistically simulate the strain state of cooling and contraction during the solder melting and solidification process (restoring stiffness, simulating solidification) and accurately capture residual stress; The state inheritance of the welded components in multi-step reflow soldering directly maps the temperature results of the transient thermal analysis to the transient structural mechanics model, realizing full-cycle synchronous coupling of temperature field and structural field. The activated units remain activated in subsequent processes, accurately restoring the residual stress accumulation effect of multi-step welding.

[0042] 4) Automated setting of boundary conditions: In thermal analysis, the system automatically applies the furnace temperature curve to the outer surface of the model in the form of convective boundary conditions, which can be customized by the user according to the actual parameters of the furnace body; In structural analysis, the system automatically applies inertial release constraints to limit the displacement of the rigid body of the structure, avoiding the introduction of additional constraint stress, and automatically adds binding constraints to the welded components to match the actual connection state after welding.

[0043] Step Six: Automated Solution and Post-processing of Thermo-Structure Coupling Simulation Results: The setup wizard enables full configuration of process timing definition and reflow soldering thermo-mechanical coupling simulation. It automatically generates two solution tasks: transient thermal analysis and transient structural analysis. It also completes full parameter configuration for sub-analysis steps, birth and death elements, boundary conditions, loads, and output requests, establishing automated data linkage between thermal and structural analyses. The full-time-step transient temperature field results obtained from the thermal analysis are mapped to the temperature loads of the structural analysis according to spatial location and time nodes, achieving seamless linkage in unidirectional thermo-mechanical coupling to solve for thermal strain, thermal stress, warpage, and residual stress. First, the transient temperature field solution for the entire reflow cycle is completed, then the full-time-step temperature field is accurately mapped to the structural mechanics model for solution, achieving sequential thermo-mechanical coupling solution.

[0044] Thermal strain: ; Thermal stress: ; in: Thermal strain; The coefficient of linear expansion; This refers to the change in temperature. Equivalent stress; Here is the elastic stiffness matrix; For total strain; Thermal strain; This is plastic strain.

[0045] After the solution is completed, the system automatically generates warpage displacement cloud maps, equivalent stress cloud maps, and solder equivalent plastic strain cloud maps for the entire reflow soldering process. It supports switching between results at different time frames and allows viewing the dynamic evolution of the entire process, including heating, melting, cooling, and quenching. It automatically extracts the Z-axis warpage deformation of the substrate along a specified path, plots the warpage curve, and accurately locates the maximum warpage position and value. Simultaneously, the post-processing module automatically extracts geometric models, mesh information, material parameters, process settings, simulation results, etc., and generates a standardized reflow soldering simulation analysis report in Word format, achieving fully closed-loop management of the simulation process.

[0046] Example 1 This embodiment uses a three-layer stacked radio frequency SiP device as an example. The radio frequency SiP device includes a DXF format double-sided board, two ODB++ format four-layer wiring boards, a total of 435 vias, three sets of BGA solder ball arrays, two radio frequency chips and supporting passive components, Kovar alloy frame and cover plate. In the first soldering, with the help of tooling fixtures, the substrate and frame are soldered to form a shell, where the solder melting point is 287°C. On the basis of the first soldering, a second soldering is performed to complete the interconnection between the lower circuit board and the shell, where the solder melting point is 250°C. On the basis of the second soldering, a third soldering is performed to complete the interconnection between the upper circuit board and the lower board, where the solder melting point is 217°C.

[0047] The accuracy of the traditional manual detailed modeling method and the wizard-guided reflow soldering process modeling method of this embodiment 1 were compared and verified.

[0048] This embodiment completes substrate equivalent modeling, process parameter configuration, and furnace temperature profile import via a wizard-guided workflow. The system automatically performs analysis step breakdown, solder birth and death cell configuration, contact condition setting, and thermo-solder coupling analysis generation to establish a reflow soldering simulation model. The complete operation process is as follows: Figure 1 As shown, the specific operation steps are as follows: Step 1: Parametric geometric modeling Following the design file import wizard, import DXF format double-sided boards and two ODB++ format 4-layer wiring substrates in layer order. The program automatically extracts the geometric information of metal layers, dielectric layers, vias, and pads. Configure the thickness and physical properties of each layer through the parameter setting window. Import component models such as chips, capacitors, frames, solder balls, and bonding wires through the wizard settings, configure their dimensions and spatial position parameters, and finally automatically complete the precise Z-axis assembly of components and corresponding substrates. Figure 2 As shown.

[0049] Step 2: Geometric Simplification and Automated Mesh Generation The program uses a wizard-guided dialog box to discretize the substrate's layered structure into a regular mesh. It automatically calculates the in-plane and thickness metal percentages of each mesh cell, and uses a series-parallel spring model to calculate key parameters such as equivalent Young's modulus, coefficient of thermal expansion, and thermal conductivity. This equivalent material property is then mapped to the substrate's geometric model. The simplified mesh model is shown below. Figure 3 As shown. The global mesh size is set to a medium coarseness using the mesh setup wizard. For different functional components such as the substrate, solder balls, chips, and frame, the mesh type, element order, mesh size, and minimum number of layers in the thickness direction are customized. The program automatically generates a high-quality hybrid mesh, primarily composed of hexahedrons, for the entire model. The overall model mesh is shown below. Figure 4 As shown.

[0050] Step 3: Batch setting of material models: The setup wizard allows users to select the corresponding materials from the software's built-in SiP professional material library and complete the setup. Materials such as substrate, metal conductor, solder, and chip are assigned values ​​in batches by component. For the solder material of the reflow soldering core, the Anand viscoplastic constitutive model is selected. The three soldering materials are Pb92.5Sn5Ag2.5 (melting point 287℃), SAC305 (melting point 217℃), and Sn63Pb37 (melting point 183℃) with different melting points to reflect the mechanical behavior of the solder at different temperatures.

[0051] Step 4: Automating the touch interface settings: In the wizard process tree, a right-click menu allows for a one-click traversal of all components in the entire model, automatically identifying chip-substrate, solder-pad, substrate-substrate, and frame-cover, generating all physical contact interfaces. The software automatically identifies the corresponding contact type based on the contact material properties, including metal-to-metal dry contact, silicone grease application, thermal pads, and solder equivalent thermal resistance. Each type is set with medium-level contact thermal resistance and friction coefficient parameters by default, and binding constraints are generated, such as... Figure 5 As shown.

[0052] Step 5: Reflow soldering process timing modeling and solder birth / death cell control: First, the actual furnace temperature curve data from the production line was recorded as a CSV file. This file was then imported using a curve manager wizard to automatically plot the furnace temperature curve. For the three-layer welding materials Pb92.5Sn5Ag2.5, SAC305, and Sn63Pb37, three welding steps were set up, with each welding step lasting 400 seconds and a total process time of 1200 seconds, fully simulating the entire process from room temperature to peak temperature and then cooling back to room temperature. Reflow soldering process steps were created for each welding step, such as... Figure 6 As shown, in a single welding step, the melting point of the solder is used as the critical value to automatically divide the process into three sub-analysis steps: heating, cooling, and cooling, and automatically configure the birth and death cell attributes. Step Six: Automated Solution and Post-processing of Thermo-Structure Coupling Simulation Results: After completing the above settings, start the simulation solution with one click in the process wizard. The software will complete the solution calculations for the three welding steps in sequence. In the thermal analysis, the system will automatically apply the furnace temperature curve to the outer surface of the model in the form of convection boundary conditions. In the structural analysis, the system will automatically apply inertial release constraints to limit the rigid body displacement of the structure, and at the same time automatically add binding constraints to the welded components to simulate the connection state after actual welding.

[0053] After the solution is completed, warp displacement contour plot, equivalent stress contour plot, and solder equivalent plastic strain contour plot for the entire reflow soldering process are automatically generated, such as Figures 7 to 10As shown. Simultaneously, it generates a dynamic evolution animation of the entire process, including heating, melting, cooling, and quenching, and produces a standardized reflow soldering simulation analysis report in Word format.

[0054] Step 7: Comparison with traditional modeling and simulation: Traditional manual detailed modeling method: manually complete modeling and assembly, manually generate meshes, configure material properties, manually break down into 9 sub-analysis steps, configure the life and death states, contact pairs and boundary conditions of all solder elements one by one, manually complete the temperature field mapping of thermal-structural analysis, establish a reflow soldering thermal-structure coupling simulation model, and complete the simulation of each sub-analysis step in sequence.

[0055] In this case, the preprocessing process according to the method of the present invention takes more than 10 hours using the traditional method, while the preprocessing time of the present invention using the wizard-style simulation method is about 1 hour, and the preprocessing effect is improved by more than 10 times. By simplifying the modeling through substrate equivalence, the simulation accuracy and computational efficiency are balanced. While retaining the core mechanical and thermal properties, the number of model meshes is reduced by more than 85%, and the solution efficiency is improved by more than 10 times. For simulation of multiple welding processes in reflow soldering, traditional methods fragment multiphysics modeling into multiple independent simulation processes, failing to directly inherit the boundary conditions and accumulated stress of previous process steps. This invention employs a time-sequential modeling method driven by the solder melting point, accurately matching the "melting-solidification" physical state changes of the solder during reflow soldering. Through automated time-sequential control of birth and death units, it realistically reproduces the residual stress accumulation effect of multi-step reflow soldering. Automated data mapping of thermo-solid coupling enables efficient simulation of the reflow soldering process.

Claims

1. A guided SiP reflow soldering process modeling and simulation method, characterized in that, Includes the following steps: Step 1: Parametric geometric modeling: Based on the SiP design file, import the substrate ECAD file in the layer sequence, automatically extract geometric information and configure layer thickness and physical properties; import the component model and configure its size and spatial position, and automatically complete the Z-axis assembly; Step 2, Geometric Equivalence Simplification and Mesh Generation: The layered structure of the substrate is discretized into a regular mesh, the local metal ratio is calculated to solve the equivalent material properties and mapped to the substrate model; the global mesh size is controlled by coarse / medium / fine levels, mesh parameters are configured for different components, and a hybrid mesh is automatically generated; Step 3: Batch configuration of material constitutive models: Build a SiP material library, complete the batch configuration of material constitutive models through the wizard, and complete the material assignment by component; Step 4: Automated setup of contact interfaces: Automatically traverse the entire model to identify all physical contact interfaces and generate a list of contact pairs. Automatically configure contact parameters and generate binding constraints according to preset contact types. Step 5: Time-sequential modeling of reflow soldering process and control of solder cell life and death: Import furnace temperature curve and plot temperature-time curve; create new process steps based on furnace temperature curve, and automatically divide a single reflow soldering process into three sub-analysis steps: heating, cooling, and deheating, using the solder melting point as the critical value; automatically configure cell life and death attributes for the solder components in each reflow soldering step, killing cells during the heating stage and activating cells during the cooling stage; map the thermal analysis temperature results to the structural model to achieve temperature field-structural field coupling. Step 6, Thermal-Structure Coupling Solution and Post-processing: Automatically generate thermal and structural analysis solution tasks and complete parameter configuration to achieve unidirectional thermal-structure coupling solution; automatically generate displacement contour maps, stress contour maps and plastic strain contour maps, extract warping deformation and draw warping curves; The system completes batch material assignment by component, automatically synchronizes material parameters in the geometric modeling stage, and supports the addition and modification of custom material properties. It discretizes the ECAD layered structure of the substrate into regular meshes, calculates the in-plane and thickness metal ratio of each mesh unit, calculates equivalent material properties through a series and parallel spring model, maps the equivalent material properties to the substrate geometric model, realizes the assignment of equivalent material properties of the substrate, completes the macroscopic equivalent characterization of the substrate's micro-wiring details, and greatly simplifies the model size while preserving the mechanical properties of the substrate.

2. The method according to claim 1, characterized in that, In step two, the mesh generation is as follows: for the substrate, solder balls, chip, and frame, respectively configure the mesh type, cell order, mesh size, and minimum number of layers in the thickness direction, the system automatically generates a hybrid mesh with hexahedrons as the main component.

3. The method according to claim 1, characterized in that, In step two, the equivalent material properties are calculated using a series and parallel spring model, including the equivalent Young's modulus, coefficient of thermal expansion, and thermal conductivity, as well as the separate calculations of the metal proportions in the in-plane and thickness directions.

4. The method according to claim 1, characterized in that, In step three, linear elastic, bilinear, and Anand viscoplastic constitutive models are used for the solder material of the reflow solder core to simulate the mechanical behavior of the solder at different temperatures, and batch configuration of the material constitutive model is completed. To address the mechanical behavior of lead-free solder under high temperatures, large deformations, and creep-dominated conditions during reflow soldering, the Anand unified viscoplastic constitutive model is adopted: Flow equations: ； Evolution of internal variables: ； in: Equivalent plastic strain; Equivalent stress; A For frequency factors; It is the thermal activation energy for plastic deformation; This is the universal gas constant; T Absolute temperature; It is the stress constant; It is a strain rate sensitivity index; It is the hardening modulus constant; The hardening index; The rate of change of deformation resistance; Resistance to saturated deformation; It is a hyperbolic sine function; It is a symbolic function.

5. The method according to claim 1, characterized in that, In step four, the contact types include metal dry contact, silicone grease, thermal pad, and solder equivalent thermal resistance. Each type has three preset contact thermal resistance and friction coefficient settings (high / medium / low) for selection or customization.

6. The method according to claim 1, characterized in that, In step five, furnace temperature curve management includes: wizard-driven import of CSV format curve files, automatic identification of the time nodes corresponding to peak temperature and melting point, and support for curve editing, saving, and reuse; The transient heat conduction governing equation is: ； in: For material density, For specific heat capacity, Thermal conductivity, For temperature field distribution, For time, The latent heat of the solid-liquid phase transition of the solder is a core parameter for reproducing the true temperature field.

7. The method according to claim 1, characterized in that, In step five, the activated units of the multi-step reflow soldering process remain activated in subsequent processes to reduce the residual stress accumulation effect. In thermal analysis, the furnace temperature curve is applied to the outer surface of the model as a convection boundary condition. In structural analysis, inertial release constraints are applied and binding constraints are added to the welded components to match the actual connection state after welding.

8. The method according to claim 1, characterized in that, In step six, the thermo-structure interaction solution involves first solving the transient temperature field, and then mapping the temperature field onto the structural model to sequentially solve for thermal strain, thermal stress, and residual stress. Thermal strain: ； Thermal stress: ； In the formula, Thermal strain; The coefficient of linear expansion; This refers to the change in temperature. Equivalent stress; Here is the elastic stiffness matrix; For total strain; This is plastic strain.

9. The method according to claim 1, characterized in that, Step six also includes a post-processing module that automatically extracts geometric models, mesh information, material parameters, process settings, and simulation results to generate a standardized simulation analysis report in Word format.

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