Laminated welding spot bending torsion combined stress optimization method based on genetic algorithm

Abstract

The invention discloses a laminated welding spot bending torsion combined stress optimization method based on a genetic algorithm, and the method comprises the following steps: designing a corresponding combination based on a Box-Behnken test, and building a bending torsion combined stress mathematical model of a laminated welding spot through IBM SPSS; optimizing the structural parameters of the laminated welding spots on the stress mathematical model by using a genetic algorithm; according to the method, the structural parameters of the laminated welding spots are better, and the bending torsion combined stress of the laminated welding spots can be reduced through the obtained parameters.

Description

Technical Field

[0001] This invention relates to a method for optimizing the combined bending and torsional stress of laminated solder joints based on genetic algorithms, which relates to the optimization of the mechanical properties of laminated solder joints and belongs to the technical field of electronic packaging. Background Technology

[0002] For the novel type of laminated solder joint, the use of electronic products involves uncertainties such as drops and vibrations. The PCB board is subjected to pressure exceeding its design capacity, which can cause relative displacement and torsion. This may lead to solder joint breakage due to excessive stress, resulting in electrical interconnection failure between the chip and the PCB board, system malfunction, and ultimately, product inoperability. Furthermore, a large temperature difference between the two sides of the PCB board may cause it to bend, further compromising solder joint reliability. Therefore, to ensure the widespread application of this novel solder joint, it is necessary to conduct stress optimization research on laminated solder joints under combined bending and torsional loads. Summary of the Invention

[0003] The purpose of this invention is to address the aforementioned problems by providing a genetic algorithm-based optimization method for the combined bending and torsional stress of laminated solder joints. This method solves for the structural parameters of the laminated solder joints, minimizing the stress under combined bending and torsional loads. This invention overcomes the limitations of existing technologies and provides a more comprehensive and effective optimization method for the field of electronic packaging technology.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] A method for optimizing the combined bending and torsional stress of laminated weld joints based on genetic algorithms includes the following steps:

[0006] Step 1: Establish a finite element model of the laminated weld joint that takes into account good mechanical properties, design the test group using the response surface methodology, and obtain data through simulation.

[0007] Step 2: Based on the above data, fit the independent and dependent variable data to obtain the mathematical model of the stress of the laminated weld joint after IBM SPSS analysis.

[0008] Step 3: Based on the above mathematical model, with the goal of minimizing the combined bending and torsional stress of the laminated weld joint, the optimal solution of the structural parameters and stress of the laminated weld joint is obtained by using a genetic algorithm.

[0009] Step 1 includes the following specific methods:

[0010] Step 1-1: A geometric model of the stacked solder joint interconnect structure was established using ANSYS software. The model is an 8×8 full array, and its specific package dimensions are as follows: chip size (8mm×8mm×1mm), PCB size (132mm×77mm×1.2mm), and the main structural parameters of the stacked solder joint are: solder ball diameter 0.55mm, solder joint height 0.36mm, pad diameter 0.4mm, and solder joint spacing 0.8mm.

[0011] Steps 1-2: Based on the Box-Behnken Design (BBD) in the response surface methodology, 17 sets of horizontal combinations of stacked weld joint structural parameters are designed according to the factor level table, and corresponding simulation models are established to perform stress analysis under bending and torsional combined loads, and the stress results of each set of horizontal combinations are obtained.

[0012] The specific process of establishing the model described in step 2 is as follows:

[0013] Based on IBM SPSS software, a fitting equation was established between the structural parameters of the laminated solder joint and the combined bending and torsional stress. The solder ball diameter, solder joint height and solder pad diameter were selected as independent variables X and the stress was selected as the dependent variable Y to obtain a mathematical model of the stress of the laminated solder joint. The relevant conditions of the model were then constrained.

[0014] The mathematical expression for the stress Y model of the laminated weld joint is:

[0015]

[0016] In the formula: X1 is the diameter of the solder ball; X2 is the height of the solder joint; X3 is the diameter of the solder pad;

[0017] The model constraints are as follows:

[0018]

[0019] In the formula: X1 is the diameter of the solder ball; X2 is the height of the solder joint; X3 is the diameter of the solder pad;

[0020] Step 3, which uses a genetic algorithm to obtain the optimal solution for the structural parameters and stress of the laminated weld joint, includes the following steps:

[0021] a. Set the relevant parameters: solder ball diameter X1, solder joint height X2, and solder pad diameter X3. The objective function to be solved is 1. The population size is 100, the crossover probability is 0.6, and the maximum number of iterations is 5000.

[0022] b. Use Matlab software to write genetic algorithm code, and after multiple iterations of optimization, finally obtain the optimized solution.

[0023] This invention addresses the issue of minimizing stress in multilayer solder joints of chips subjected to loads such as drops and vibrations. It provides a genetic algorithm-based optimization method for combined bending and torsional stress in multilayer solder joints. This method combines IBM SPSS with a genetic algorithm to optimize the structural parameters of multilayer solder joints. Attached Figure Description

[0024] Figure 1 This is an overall flowchart of the optimization method of the present invention;

[0025] Figure 2 This is a finite element model diagram of the laminated weld joint of the present invention;

[0026] Figure 3 This is the iterative result of the genetic algorithm of this invention;

[0027] Figure 4 This is a stress verification diagram of the laminated weld joints based on the iterative results of this invention; Detailed Implementation

[0028] The invention will now be described in further detail with reference to the accompanying drawings:

[0029] This invention relates to a method for optimizing the combined bending and torsional stress of laminated weld joints based on a genetic algorithm. It studies the stress of laminated weld joints under combined bending and torsional loads and solves for a set of parameter combinations that minimize the combined bending and torsional stress. First, a corresponding combination is designed based on Box-Behnken experiments. Then, a mathematical model of the combined bending and torsional stress of the laminated weld joint is established using IBM SPSS. Finally, a genetic algorithm is used to optimize the structural parameters of the laminated weld joint using the stress mathematical model, aiming to minimize the combined bending and torsional stress of the laminated weld joint. The main steps and model solution steps are as follows: Figure 1 As shown.

[0030] The method specifically includes the following steps:

[0031] 1. Establish a finite element model of the laminated weld joint that takes into account good mechanical properties, such as... Figure 2 As shown;

[0032] 2. Using IBM SPSS analysis, a mathematical model of the combined bending and torsional stress of the laminated weld joints was obtained;

[0033] 3. Using a genetic algorithm, the structural parameters of the laminated weld joint with the minimum bending and torsional stress are obtained.

[0034] The specific steps for establishing the finite element simulation model of the stacked weld joint considering good mechanical properties, as described in step 1, are as follows:

[0035] (1) A geometric model of the stacked solder joint interconnection structure was established using ANSYS software. The model is an 8×8 full array, and its specific package dimensions are as follows: chip size (8mm×8mm×1mm), PCB (132mm×77mm×1.2mm), and the main structural parameters of the stacked solder joint are: solder ball diameter 0.55mm, solder joint height 0.36mm, pad diameter 0.4mm, and solder joint spacing 0.8mm.

[0036] (2) Based on the Box-Behnken Design (BBD) in the response surface methodology, 17 sets of horizontal combinations of stacked solder joint structural parameters were designed according to the factor level table, and corresponding simulation models were established to perform stress analysis under bending and torsion combined loads. The load loading details are as follows: a 0.3 mm displacement load (causing the PCB to torsion) is applied to the loading point of the model, and then a 0.5 mm displacement load (causing the PCB to bend) is applied. Bending and torsion simulation analysis is performed, and the stress results of each horizontal combination are shown in Table 1.

[0037]

[0038]

[0039] After obtaining the simulation data, the independent and dependent variables need to be fitted to obtain the mathematical model of the stress of the laminated weld joints after IBM SPSS analysis. The specific establishment process of step 2 is as follows:

[0040] Based on IBM SPSS software, a fitting equation was established between the structural parameters of the laminated solder joint and the combined bending and torsional stress. The solder ball diameter, solder joint height and solder pad diameter were selected as independent variables X and the stress was selected as the dependent variable Y to obtain a mathematical model of the stress of the laminated solder joint. The relevant conditions of the model were then constrained.

[0041] The mathematical expression for the stress F model of the laminated weld joint is:

[0042]

[0043] In the formula: X1 is the diameter of the solder ball; X2 is the height of the solder joint; X3 is the diameter of the solder pad;

[0044] The model constraints are as follows:

[0045]

[0046] In the formula: X1 is the diameter of the solder ball; X2 is the height of the solder joint; X3 is the diameter of the solder pad;

[0047] Based on the above mathematical model, with the goal of minimizing the stress of the laminated weld joints under combined bending and torsion loads, the optimal solution of the structural parameters and stress of the laminated weld joints is obtained by using a genetic algorithm.

[0048] Relevant parameter settings:

[0049] The solder ball diameter is X1, the solder joint height is X2, and the pad diameter is X3. The objective function to be solved is 1. The population size is 100, the crossover probability is 0.6, the maximum number of iterations is 5000, and the iteration results are as follows. Figure 3 As shown.

[0050] Find the optimal solution:

[0051] Genetic algorithm code was written using Matlab software. After multiple iterations and optimizations, the optimal solution was finally obtained as X1 = 0.60 mm, X2 = 0.35 mm, X3 = 0.42 mm, and Y = 16.661 MPa.

[0052] verify:

[0053] To determine whether the obtained optimal parameter level combination can effectively reduce the bending and torsional stress of the laminated weld joint, under the condition that other factors remain unchanged, a new laminated weld joint model with the same parameter level combination was established, and a bending and torsional combined loading simulation analysis was performed. The stress distribution results of the laminated weld joint are as follows: Figure 4 As shown.

[0054] Depend on Figure 4 As can be seen from the simulation, the maximum stress in the laminated weld joint under the combined bending and torsional load of the optimized parameter combination is 16.626 MPa, which is 0.556 MPa less than the minimum maximum stress of 17.182 MPa among all the combined weld joints shown in Table 3. The maximum bending and torsional stress is reduced by 3.24%. This verifies that the maximum bending and torsional stress of the laminated weld joint obtained by using the optimal structural parameter level combination obtained by IBM SPSS-genetic algorithm is effectively reduced.

Claims

1. A genetic algorithm-based method for optimizing the bending-torsion composite stress of a laminated solder joint, characterized by, It comprises the following steps: Step 1, a finite element model of a laminated solder joint considering good mechanical properties is established, a test group is designed by using Box-Behnken test, and data are obtained by simulation; Step 2, according to the above data, the independent variable and dependent variable data are fitted to obtain the mathematical model of the laminated solder joint stress analyzed by IBM SPSS; Step 3, on the basis of the above mathematical model, the bending and torsional composite stress of the laminated solder joint is minimized as the target, and the optimal solution of the laminated solder joint structure parameters and stress is obtained by using genetic algorithm.

2. The method of claim 1, wherein the method is a genetic algorithm-based method for optimizing the combined bending and torsional stresses in a solder joint in a flip chip package. The specific method of step 1 comprises: Step 1-1, a geometric model of a laminated solder joint interconnection structure is established by using ANSYS software, the model is an 8x8 full array, and the specific packaging size is as follows: the chip size is (8mmx8mmx1mm), the PCB is (132mmx77mmx1.2mm), and the main structure parameters of the laminated solder joint are: solder ball diameter 0.55mm, solder joint height 0.36mm, pad diameter 0.4mm, and solder joint spacing 0.8mm. Step 1-2, based on the BBD (Box-Behnken Design) design in the response surface method, 17 groups of laminated solder joint structure parameter level combinations are designed according to the factor level table, and the corresponding simulation model is established to analyze the stress under the bending and torsional composite load, and the stress results of each group of level combinations are obtained.

3. The method of claim 1, wherein the method is characterized by: The laminated solder joint bending and torsional composite stress mathematical model in step 2 is constructed based on the data obtained in step 1, and the related conditions of the model are constrained; The mathematical expression of the laminated solder joint bending and torsional composite stress is: In the formula, X1 is the solder ball diameter; X2 is the solder joint height; X3 is the pad diameter; The constraint condition of the model is: In the formula, X1 is the solder ball diameter; X2 is the solder joint height; X3 is the pad diameter.

4. The method of claim 1, wherein the method is a genetic algorithm-based method for optimizing the combined bending and torsional stresses in a solder joint. The optimal solution of the laminated solder joint structure parameters and stress obtained by using genetic algorithm in step 3 comprises the following steps: a. Set the related parameters, the solder ball diameter X1, the solder joint height X2 and the pad diameter X3, the target function to be solved is 1, the population size is 100, the crossover probability is 0.6, and the maximum iteration number is 5000. b. Genetic algorithm code is written by using Matlab software, and after multiple iteration optimization, the optimal solution is finally obtained.

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