Finite element-based multilayer ceramic dielectric capacitor plate bending mechanical failure analysis method

Abstract

The invention relates to the field of electronic components, and particularly discloses a finite element-based multilayer ceramic capacitor board bending mechanical failure analysis method, which comprises the following steps of: establishing an MLCC board bending simulation geometric model according to geometric parameters of an MLCC, a PCB (Printed Circuit Board) and a pressure head in combination with a board bending test standard; the ceramic body is partitioned according to the distribution characteristics of the inner electrodes, and equivalent mechanical parameters of the ceramic body are calculated; establishing an equivalent plate bending finite element model of the MLCC in finite element software ANSYS; determining a stress index reference point, and eliminating adverse effects of singular points; obtaining failure strain of the plate bending test and an MLCC failure mode; and verifying the finite element model and carrying out failure mode analysis. Compared with a traditional physical test failure analysis method, the method has the advantages that the requirements for cost, time, equipment and the like are greatly reduced, and development of MLCC failure analysis and structural design is promoted.

Description

Technical Field

[0001] The invention relates to an analysis method, in particular to a finite element-based multilayer ceramic dielectric capacitor plate bending mechanical failure analysis method, belonging to the field of electronic components. Background Art

[0002] MLCC is a basic component of electronic systems. Due to its high capacitance density, small size, and easy installation, it has been used in almost all electronic engineering fields. Due to its large and wide range of applications in engineering, MLCC is the component with the highest failure rate and is more likely to cause system failures than other components. Therefore, mechanical analysis of MLCC to reveal the mechanical mechanism behind its failure mode has important theoretical research and practical application value.

[0003] The brittleness of ceramic dielectrics determines that the most common failure mode of MLCC is fracture. Crack failure of ceramic bodies caused by deformation of PCB boards due to bending, temperature, vibration, installation and other loads is particularly common. This failure mode will cause an open circuit, resulting in capacitor loss and failure, becoming one of the main problems affecting the reliability of electronic systems. MLCC is made of ceramic dielectrics and internal electrodes stacked and sintered in an interlaced manner. The structure is complex and the sizes of each component vary greatly, making it difficult to conduct cross-scale research using conventional theoretical analysis methods. At present, the mechanical properties evaluation of MLCC is mainly completed through plate bending tests. However, physical tests face many difficulties such as high cost, long cycle, cumbersome process, and limitations of experimental instruments. It is impossible to intuitively obtain the stress state of MLCC and cannot meet the needs of fast, low-cost and accurate failure analysis. In recent years, simulation technology has gradually been introduced into the research of MLCC, but the numerical models established by existing research institutes are too simple to fully characterize the distribution characteristics of the internal electrodes of MLCC, do not consider the anisotropy of the material, and do not eliminate the adverse effects of singular points during the solution process, resulting in distortion of the numerical solution and significant deviation between the simulation results and the physical test results.

[0004] Therefore, it is urgent to develop a finite element-based MLCC board bending mechanical failure analysis method. According to the distribution characteristics of the electrodes in the MLCC, combined with the theory of composite materials, a fine MLCC equivalent finite element model is established, mechanical simulation under board bending load is carried out, stress index reference points are determined to eliminate the adverse effects of singular points, and corresponding failure analysis is performed according to the stress and strain distribution of the MLCC. This method can intuitively provide key information such as MLCC stress and strain distribution, greatly saving time and cost, and improving the efficiency of failure analysis. Summary of the invention

[0005] In response to the problems in the prior art, the present invention provides a finite element-based multilayer ceramic capacitor plate bending mechanical failure analysis method, which is used to intuitively and accurately simulate the stress and strain distribution of MLCC under plate bending load, greatly saving time and cost and improving the efficiency of failure analysis.

[0006] The purpose of the present invention can be achieved through the following technical solutions:

[0007] A finite element-based bending mechanical failure analysis method for multilayer ceramic capacitor plates comprises the following steps:

[0008] S1: Select the MLCC to be evaluated, and establish the MLCC board bending simulation geometric model based on the geometric parameters of the MLCC, PCB board and indenter, combined with the board bending test standard;

[0009] S2: Obtain material parameters, partition the ceramic body according to the internal electrode distribution characteristics and calculate its equivalent mechanical parameters;

[0010] S3: Establish an equivalent plate bending finite element model of MLCC in the finite element software ANSYS;

[0011] S4: Solve the finite element model, determine the stress index reference point, and eliminate the adverse effects of singular points;

[0012] S5: Carry out plate bending test to obtain the failure strain of plate bending test and MLCC failure mode;

[0013] S6: Compare test results, validate finite element model and perform failure mode analysis.

[0014] Optionally, in S1:

[0015] The geometric parameters of MLCC include length, width, height, terminal electrode thickness, flange width, protective layer thickness, overlap, stacking, number and thickness of internal electrodes;

[0016] The geometric parameters of the PCB board include length, width and thickness;

[0017] The geometric parameter of the indenter is the indenter radius size;

[0018] The board bending test standard includes clarifying the placement area of ​​MLCC on the PCB board and the span between the support rods on both sides;

[0019] The MLCC board bending simulation geometric model is established in the following way:

[0020] According to the geometric parameters of MLCC, PCB board and indenter and the board bending test standard, a 1 / 4 geometric model of MLCC board bending simulation is established.

[0021] Optionally, the material parameters obtained in S2 are specifically:

[0022] Obtain the mechanical material parameters of MLCC components, PCB boards, and fixtures, including density, elastic modulus, shear modulus, Poisson's ratio, yield strength, and tangent modulus.

[0023] Optionally, the MLCC ceramic body in S2 is divided into an active area, a protective layer, a side source area and a shell area;

[0024] The calculation of equivalent mechanical parameters is based on the material composition and volume ratio of the active area and the side source area using the composite material homogenization method to perform parameter equivalent processing. The formula for the homogenization method is:

[0025] ρ=ρ f V f +ρ m V m

[0026]

[0027] E z =V f E f +V m E m

[0028]

[0029] ν xz =v yz =V f ν f +V m ν m

[0030]

[0031] Wherein, subscripts f and m represent the inner electrode and ceramic dielectric, respectively; E x , E y , E z are the equivalent elastic modulus in the x, y, and z directions respectively; G xy , G xz , G yz , ν xy , ν xz , ν yz are the equivalent shear modulus and Poisson's ratio in the xy, xz, and yz planes respectively; ρ f , ρ m , E f ,E m ,G f ,G m ,ν f ,ν mare the density, elastic modulus, shear modulus and Poisson's ratio of the inner electrode and ceramic medium respectively; ρ is the equivalent density; V f , V m are the volume fractions of the inner electrode and the ceramic dielectric, respectively.

[0032] Optionally, in S3, the process of establishing the equivalent plate bending finite element model of MLCC includes: selecting an analysis module, assigning material parameters to each part of the model, setting symmetry conditions and contact, dividing the grid, and applying loads and boundary conditions.

[0033] Optionally, the specific process of S4 is:

[0034] The finite element model is solved, and the stress singularity area and the local stress concentration area are distinguished according to the stress gradient change trend of the preset key focus area. The intersection point between the two is selected as the reference point of the stress index to eliminate the adverse effects of the singularity point.

[0035] Optionally, the specific process of S5 is:

[0036] Conduct MLCC board bending test, use LCR tester to monitor the capacitance change of MLCC during the test, use strain gauge to record the strain change of PCB board during the test, and use the corresponding PCB board strain when MLCC fails as the failure strain of board bending test; perform destructive physical analysis on MLCC to obtain failure mode.

[0037] Optionally, comparing the test results, verifying the finite element model and conducting failure mode analysis in S6 includes the following steps:

[0038] Extract the failure strain of the PCB board in the finite element method and compare it with the test results to verify the validity of the finite element model;

[0039] Extract the maximum principal stress distribution of the MLCC ceramic body, determine the initial failure position based on the maximum tensile stress distribution, and predict the crack propagation direction based on the tensile stress vector distribution direction;

[0040] The equivalent plastic strain of the MLCC solder foot is extracted, and the failure location and trend are determined based on the plastic strain distribution.

[0041] Beneficial effects of the present invention:

[0042] The present invention provides a finite element-based MLCC plate bending mechanical failure analysis method, which can intuitively and comprehensively obtain the stress and strain distribution of MLCC under bending load, and accurately and quickly implement failure analysis according to its force characteristics, and explain the failure mechanism. The equivalent finite element simulation model constructed by the present invention fully considers the distribution characteristics of the electrodes inside the MLCC and the anisotropy of the PCB board, overcomes the cross-scale problem faced by the theoretical model, and effectively eliminates the adverse effects caused by singular points in the numerical model. The finite element simulation results are very consistent with the actual test results. Compared with the traditional physical test failure analysis method, it greatly reduces the requirements for cost, time, equipment, etc., which helps to promote the development of MLCC failure analysis and structural design. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to facilitate understanding by those skilled in the art, the present invention is further described below with reference to the accompanying drawings.

[0044] Figure 1 It is a flow chart of a finite element-based MLCC plate bending mechanical failure analysis method in an embodiment of the present invention;

[0045] Figure 2 is a schematic diagram of the structure of an MLCC according to an embodiment of the present invention;

[0046] Figure 3 It is a schematic diagram of a 1 / 4 geometric model of an MLCC board bending test according to an embodiment of the present invention;

[0047] Figure 4 1. It is a schematic diagram of the partitioning of the MLCC ceramic body according to an embodiment of the present invention;

[0048] Figure 5 is a schematic diagram of mesh division of a finite element model according to an embodiment of the present invention;

[0049] Figure 6 is a schematic diagram of stress indicator reference point selection according to an embodiment of the present invention;

[0050] Figure 7 Schematic diagram of a MLCC board bending test sample according to an embodiment of the present invention;

[0051] Figure 8 Schematic diagram of an MLCC board bending test instrument according to an embodiment of the present invention;

[0052] Fig. 9 is a schematic diagram comparing the finite element results of the failure strain of a PCB board according to an embodiment of the present invention with the test data;

[0053] Fig.10 It is a schematic diagram of the stress distribution cloud diagram of the MLCC ceramic body and the actual test verification results of the embodiment of the present invention;

[0054] Fig.11 It is a plastic strain cloud diagram of the MLCC solder foot part according to an embodiment of the present invention. DETAILED DESCRIPTION

[0055] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0056] See also Figure 1-Figure 11 ;

[0057] like Figure 1 As shown, an MLCC plate bending mechanical failure analysis method based on finite element provided in an embodiment of the present invention comprises the following steps:

[0058] S1. Select the MLCC to be evaluated. This embodiment takes the 1206 model MLCC as an example. The MLCC geometric parameters include: MLCC length, width, height, terminal electrode thickness, flange width, protective layer thickness, overlap, overlap, number and thickness of internal electrodes. PCB board geometric parameters include: length, width, thickness. The geometric dimension of the indenter is the indenter radius. The detailed geometric parameters are shown in Table 1. The main structure of the MLCC is shown in Table 1. Figure 2 As shown in the figure. According to the three-point board bending test standard, the MLCC is placed in the center area of ​​the PCB board, and the span between the support rods on both sides is 90mm. Due to the symmetry of the MLCC board bending test structure and load, the following is established based on the above geometric parameter information: Figure 3 The 1 / 4 geometry model of the MLCC board bending test is shown.

[0059] Table 1 Geometric parameters

[0060]

[0061]

[0062] S2. Obtain the material parameters of MLCC, PCB board and fixture. In this example, the PCB board is made of FR4 material, the ceramic medium used in the 1206 model MLCC is barium titanate, the inner electrode is a silver electrode, and the external terminal electrode is three layers, the materials are silver, nickel and tin-lead alloy (Pb 37 Sn 63 ), the solder feet are tin-lead alloy (Pb 37 Sn 63 ), the relevant material parameters are shown in Table 2 and Table 3:

[0063] Table 2 Material parameters of MLCC and fixture

[0064]

[0065] Table 3 PCB material parameters

[0066]

[0067]

[0068] The ceramic body of MLCC is made of ceramic dielectric and internal electrodes stacked and fired alternately. Figure 4 As shown in the figure, the ceramic body of the MLCC is partitioned into an active area, a protective layer, a side source area, and a shell area according to the volume ratio of the internal electrode. The material parameters of the active area and the side source area are equivalent using the composite material homogenization method. The material homogenization formula is:

[0069] ρ=ρ f V f +ρ m V m

[0070]

[0071] E z =V f E f +V m E m

[0072]

[0073] ν xz =v yz =V f ν f +V m ν m

[0074]

[0075] Wherein, subscripts f and m represent the inner electrode and ceramic dielectric, respectively; E x , E y , E z are the equivalent elastic modulus in the x, y, and z directions respectively; G xy , G xz , G yz , ν xy , ν xz , ν yz are the equivalent shear modulus and Poisson's ratio in the xy, xz, and yz planes respectively; ρ f , ρ m , E f ,E m ,Gf ,G m ,ν f ,ν m are the density, elastic modulus, shear modulus and Poisson's ratio of the inner electrode and ceramic medium respectively; ρ is the equivalent density; V f , V m are the volume fractions of the inner electrode and the ceramic dielectric, respectively.

[0076] The equivalent material parameters of the active area and side source area after homogenization treatment are shown in Table 4.

[0077] Table 4 Equivalent material parameters

[0078]

[0079] S3. Import the established geometric model into the transient structural analysis module of ANSYS software, and assign corresponding material parameters to the model according to different parts. Add symmetry conditions to the model, and set the cross section to be symmetrical about the xz plane and the yz plane respectively. The contact between the PCB board and the indenter is achieved by setting rough contact, and the arc surface of the indenter with greater stiffness is set as the target surface, and the side of the PCB board with less stiffness is set as the contact surface. Figure 5 This is a schematic diagram of the mesh division of the finite element model. In order to balance the accuracy of the calculation results and the calculation efficiency, the entire model is divided into hexahedral meshes. The MLCC part uses a fine mesh with a small size, and the PCB board uses a coarse mesh with a large size. There is a cross-scale problem in the size of the MLCC and the PCB board, so a transition mesh is set in the contact area between the two, and all meshes are set to common nodes. Set the boundary conditions and set the support rod to fixed. Add a plate bending load, press the head down at a speed of 1mm / s, and set the maximum displacement to 2mm.

[0080] S4. Solve the finite element model. Figure 6 (a) is the geometric diagram of MLCC. Figure 6 (b) is the corresponding stress distribution cloud diagram of the ceramic body under the plate bending load. Point B is the junction of the ceramic body and the terminal electrode. Due to the sudden change of material properties, severe stress singularity will occur here. With the increase of grid density, the stress can increase infinitely. Therefore, it is necessary to determine the reference point of the stress index to eliminate the influence of stress singularity. Figure 6 As shown in (c), the stress value of path AC is extracted, and path AC is divided into a stress singularity region and a local stress concentration region according to the stress gradient change. The first point outside the stress singularity region, that is, the point corresponding to the maximum stress value in the local stress concentration region, is selected as the reference point, and its value can approximately represent the maximum stress on path AC.

[0081] S5, Figure 7For the board bending test sample, the MLCC is welded in the middle of the PCB board, and the strain gauges are arranged along the length direction near the MLCC. Figure 8 As shown in (a), the MLCC board bending test is carried out. The sample is placed on the universal testing machine and the distance between the fixture support rods is adjusted to 90mm. The displacement control method is used to apply the displacement load in multiple steps. In each step, the pressure head moves down 0.1mm at a speed of 1mm / s and remains in the specified position for 20 seconds. During this period, the pressure head is used to Figure 8 The LCR tester and strain gauge shown in (b) and (c) monitor the capacitance value of the MLCC and the strain value of the PCB board. Repeat the above process until the MLCC fails. The MLCC failure standard is that the measured capacitance value is 90% lower than the initial capacitance value. At this time, the recorded PCB board strain value is the failure strain of the MLCC board bending test.

[0082] S6. Extract the stress, strain and other results of MLCC under board bending load. Barium titanate ceramics are brittle materials, and tensile stress is selected as the failure indicator of the ceramic body. The failure strength of barium titanate ceramics is 100MPa. The strain value of the PCB board corresponding to the reference point of 100MPa in the finite element is the failure strain of the MLCC board bending test obtained by simulation. Fig. 9 The comparison results of the average failure strain of the MLCC plate bending test obtained by the physical test and the finite element method are as follows. The error between the finite element result and the test result is only 5.32%, indicating that the MLCC plate bending mechanical failure analysis method based on the finite element proposed in the present invention is effective. Fig.10 (a) and (b) are the maximum principal stress and its vector distribution cloud diagram of the MLCC ceramic body. The maximum principal stress is tensile stress, and the location of the maximum value is the initial location of the ceramic body cracking. The direction perpendicular to the principal stress vector is the crack extension direction. Fig.10 (c) is the failure analysis result of the physical test. The crack initiation position and crack propagation direction on the MLCC ceramic body are highly consistent with the results obtained by the finite element model. The weld foot is a ductile material, so the plastic strain is selected as its failure indicator. Fig.11 The plastic strain cloud diagram of the solder foot. The maximum plastic strain occurs at the edges and corners. These positions are the starting points for the solder foot to fall off. As the external load increases, the falling area continues to expand. When the crack area exceeds the threshold, the solder foot will fall off the PCB board.

[0083] The preferred embodiments of the present invention disclosed above are only used to help illustrate the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to the specific implementation methods described. Obviously, many modifications and changes can be made according to the content of this specification. This specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can understand and use the present invention well. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A finite element-based method for analyzing the bending failure of multilayer ceramic capacitor plates, characterized in that: The following steps are involved: S1: Select the MLCC to be evaluated, and establish the MLCC board bending simulation geometric model based on the geometric parameters of the MLCC, PCB board and indenter, combined with the board bending test standard; S2: Obtain material parameters, partition the ceramic body according to the internal electrode distribution characteristics and calculate its equivalent mechanical parameters; S3: Establish the equivalent plate bending finite element model of MLCC; S4: Solve the finite element model, determine the stress index reference point, and eliminate the adverse effects of singular points; S5: Carry out plate bending test to obtain the failure strain of plate bending test and MLCC failure mode; S6: Compare test results, validate finite element model and perform failure mode analysis.

2. The method for flexural failure analysis of multilayer ceramic capacitor plates based on finite element analysis according to claim 1, characterized in that: In S1: The geometric parameters of MLCC include length, width, height, terminal electrode thickness, flange width, protective layer thickness, overlap, stacking, number and thickness of internal electrodes; The geometric parameters of the PCB board include length, width and thickness; The geometric parameters of the indenter are the indenter radius size; The board bending test standard includes clarifying the placement area of ​​MLCC on the PCB board and the span between the support rods on both sides; The geometric model of MLCC board bending simulation is established in the following way: According to the geometric parameters of MLCC, PCB board and indenter and the board bending test standard, a 1 / 4 geometric model of MLCC board bending simulation is established.

3. The method for flexural failure analysis of multilayer ceramic capacitor plates based on finite element analysis according to claim 1, characterized in that: The material parameters obtained in S2 are specifically: Obtain the mechanical material parameters of MLCC components, PCB boards, and fixtures, including density, elastic modulus, shear modulus, Poisson's ratio, yield strength, and tangent modulus.

4. The method for flexural failure analysis of multilayer ceramic capacitor plates based on finite element analysis according to claim 3, characterized in that: The MLCC ceramic body in S2 is divided into an active area, a protective layer, a side source area and a shell area; The calculation of equivalent mechanical parameters is based on the material composition and volume ratio of the active area and the side source area using the composite material homogenization method to perform parameter equivalent processing. The formula for the homogenization method is: p=p f V f +r m V m E z =V f E f +V m E m n xz =n yz =V f n f +V m n m Wherein, subscripts f and m represent the inner electrode and ceramic dielectric, respectively; E x , E y , E z are the equivalent elastic modulus in the x, y, and z directions respectively; G xy , G xz , G yz , ν xy , ν xz , ν yz are the equivalent shear modulus and Poisson's ratio in the xy, xz, and yz planes respectively; ρ f , ρ m , E f ,E m ,G f ,G m ,ν f ,ν m are the density, elastic modulus, shear modulus and Poisson's ratio of the inner electrode and ceramic medium respectively; ρ is the equivalent density; V f , V m are the volume fractions of the inner electrode and the ceramic dielectric, respectively.

5. The method for flexural failure analysis of multilayer ceramic capacitor plates based on finite element analysis according to claim 1, characterized in that: In S3, the process of establishing the equivalent plate bending finite element model of MLCC includes: selecting an analysis module, assigning material parameters to each part of the model, setting symmetry conditions and contact, dividing the grid, and applying loads and boundary conditions.

6. The method for flexural failure analysis of multilayer ceramic capacitor plates based on finite element according to claim 1, characterized in that: The specific process of S4 is as follows: The finite element model is solved, and the stress singularity area and the local stress concentration area are distinguished according to the stress gradient change trend of the preset key focus area. The intersection point between the two is selected as the reference point of the stress index to eliminate the adverse effects of the singularity point.

7. The method for flexural failure analysis of multilayer ceramic capacitor plates based on finite element according to claim 1, characterized in that: The specific process of S5 is as follows: Conduct MLCC board bending test, use LCR tester to monitor the capacitance change of MLCC during the test, use strain gauge to record the strain change of PCB board during the test, and use the corresponding PCB board strain when MLCC fails as the failure strain of board bending test; perform destructive physical analysis on MLCC to obtain failure mode.

8. The method for analyzing bending failure of multilayer ceramic capacitor plates based on finite element method according to claim 7, characterized in that: Comparing the test results in S6, verifying the finite element model and conducting failure mode analysis include the following steps: Extract the failure strain of the PCB board in the finite element method and compare it with the test results to verify the validity of the finite element model; Extract the maximum principal stress distribution of the MLCC ceramic body, determine the initial failure position based on the maximum tensile stress distribution, and predict the crack propagation direction based on the tensile stress vector distribution direction; The equivalent plastic strain of the MLCC solder foot is extracted, and the failure location and trend are determined based on the plastic strain distribution.

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