Preparation method and system of soldering paste

Abstract

The invention relates to the technical field of solder paste preparation, in particular to a solder paste preparation method and system.The method comprises the steps that 1, metal particles of different shapes are obtained, and the feature sizes of the metal particles of different shapes are measured; 2, according to the measured feature sizes of the metal particles in different shapes and the mass ratio of the metal particles in different shapes, corresponding compactness is obtained through calculation; 3, during preparation of the soldering paste, selecting a mass ratio corresponding to the maximum approximate density from the calculated densities to prepare metal particles in different shapes; and 4, the prepared mixed metal particles and a preset solvent are evenly mixed, and the soldering paste is prepared. According to the preparation method of the soldering paste, a better proportion of the metal particle materials can be obtained, and then the soldering paste with higher quality is prepared.

Description

Technical Field

[0001] The present invention relates to the technical field of solder paste preparation, and in particular to a method and system for preparing solder paste. Background Art

[0002] The third generation of wide bandgap semiconductor devices (such as SiC and GaN) are characterized by high frequency, high power density and high junction temperature, and their full load operating temperature is expected to exceed 200°C. This temperature is far higher than the maximum temperature (150°C) that traditional Si-based packaging technology can withstand. Therefore, it is urgent to develop new process methods and interconnection materials that meet the heat-resistant interconnection requirements of wide bandgap semiconductor devices.

[0003] Low-temperature silver / copper sintering interconnection technology has become the preferred interconnection material for heat-resistant packaging of wide-bandgap semiconductor devices, and has been studied and applied more and more widely. The sintered silver / copper interconnection layer is a porous structure, and the pores in it will limit the conductivity of the interconnection layer to a certain extent. Compared with the traditional single-peak spherical silver / copper solder paste, the multi-peak silver / copper non-spherical solder paste can greatly increase the density of the particles, thereby effectively reducing the porosity of the sintered silver / copper structure and improving the mechanical properties and electrical and thermal conductivity of the sintered connection joint.

[0004] Admittedly, there is a certain research foundation for multi-modal silver / copper solder paste at home and abroad, but it is based on repeated experiments and tests to obtain the optimal ratio of multi-modal micro-nano particle materials under specific sizes, and there is still a lack of effective theoretical guidance. Therefore, it is necessary to conduct in-depth research on the ratio of micro-nano particles in the preparation method of solder paste. Summary of the invention

[0005] To this end, the technical problem to be solved by the present invention is to overcome the problem that the ratio of micro-nano particles in the preparation method of solder paste in the prior art is obtained based on experiments or tests, and there is a lack of in-depth research on the ratio of micro-nano particles.

[0006] In order to solve the above technical problems, the present invention provides a method for preparing a solder paste, comprising:

[0007] Step 1: Obtain metal particles of different shapes and measure the characteristic sizes of metal particles of different shapes;

[0008] Step 2: According to the characteristic size of metal particles of different shapes and the mass ratio between metal particles of different shapes obtained by measurement, the corresponding density is calculated. The density calculation method includes:

[0009] Mix and add metal particles of different shapes, or combine metal particles of different shapes in a preset ratio;

[0010] Setting basic parameters of metal particles; the basic parameters include: three-dimensional space boundary, particle characteristic size, preset step length, target movement direction and number of particles;

[0011] Based on the sum of the Z-axis coordinate of the highest point of the existing particles and the preset distance, generate the three-dimensional coordinates of the target particles on the current height plane where the sum of the Z-axis coordinate of the highest point and the preset distance is located;

[0012] Within the three-dimensional space boundary, the target particle is moved along the target movement direction with a preset step length, the three-dimensional coordinates of the target particle are updated, and the target particle and the existing particles are judged according to preset conditions until all the target particles to be placed are placed, and then the density is calculated by using the Monte Carlo method to solve pi;

[0013] Step 3: When configuring solder paste, select the mass ratio corresponding to the maximum density from the calculated density to configure metal particles of different shapes;

[0014] Step 4: Evenly mix the prepared mixed metal particles with a preset solvent to obtain solder paste.

[0015] In one embodiment of the present invention, performing a preset condition judgment on the target particle and the existing particle includes:

[0016] Determine whether the target particle overlaps with the existing particle; if not, determine the particle stability;

[0017] If the particle meets the stability condition, the target particle is added to the existing particle sequence, and it is determined whether all the target particles to be placed have been placed; if all have been placed, the cycle ends and density calculation is performed.

[0018] In one embodiment of the present invention, if it is determined that the target particle overlaps with the existing particle, the target particle is discarded, and the three-dimensional coordinates of a new target particle are generated on the current height plane based on the sum of the Z-axis coordinate of the highest point of the existing particle and the preset distance.

[0019] In one embodiment of the present invention, the operation of determining overlap includes:

[0020] When the target particle and the existing particle are both spheres, calculating the distance between the center of the moving sphere and the existing sphere;

[0021] When the particles are a mixture of non-spherical and spherical particles, there are three cases:

[0022] The first case is: when judging the overlap between spheres, the distance between the center of the moving sphere and the existing sphere is calculated;

[0023] The second case is: when judging the overlap between the sphere and the elliptical sheet, the target particle is transformed into a new three-dimensional coordinate system using the oblique ellipse in space through the spatial coordinate conversion formula, and other particles are transformed into the new three-dimensional coordinate system for judgment: in the new three-dimensional coordinate system x'O'y' plane, the circle is circumscribed to the ellipse, and the center trajectory forms an envelope; by judging whether the center of the sphere projected on the new three-dimensional coordinate system x'O'y' plane falls inside the outer ellipse, it is preliminarily judged whether the sphere and the elliptical sheet overlap; the relationship between the sphere center Z' and the half thickness of the elliptical sheet is used for target judgment, and the specific formula is:

[0024]

[0025] The third case is: when judging the overlap between elliptical slices, the target particle is transformed into a new three-dimensional coordinate system using an oblique ellipse in space through a spatial coordinate conversion formula, and other particles are transformed into the new three-dimensional coordinate system for judgment. When judging, the outer surface operation of the elliptical slice is described by multiple scattered points; and whether an overlap occurs is judged by judging whether the scattered points fall into other elliptical slices. The oblique ellipse is an elliptical slice tilted in three-dimensional space.

[0026] In one embodiment of the present invention, the stable conditions include:

[0027] The number of contact points between any spherical particle and other particles or boundaries is not less than three;

[0028] When the elliptical piece moves, it does not participate in the collision, and only the gravity effect is considered;

[0029] When the elliptical sheet is stable, a displacement of a target length is applied to the elliptical sheet along a preset direction so that the elliptical sheet reaches a relative lowest potential energy position.

[0030] In one embodiment of the present invention, if it is determined that the particle does not meet the stability condition, a force analysis is performed on the target particle, the target movement direction is updated, and the target particle is returned to be moved along the target movement direction with a preset step length.

[0031] In one embodiment of the present invention, if the center of the projection of the sphere on the new system x′O′y′ plane falls between the outer ellipse and the central ellipse, the direction of the force on the sphere is along the negative direction of the thickness of the elliptical sheet; if the center of the projection falls inside the central ellipse, the direction of the force on the sphere is along the major axis, minor axis and direction, and obliquely downward.

[0032] In one embodiment of the present invention, if all current particles are not placed, the three-dimensional coordinates of new target particles are generated on the current height plane based on the sum of the Z-axis coordinates of the highest point of the existing particles and the preset distance.

[0033] In one embodiment of the present invention, the preset solvent is any one of ethylene glycol, polyethylene glycol 200, polyethylene glycol 300, glycerol, and diethylene glycol.

[0034] The present invention also provides a system for preparing solder paste, which adopts the above-mentioned method for preparing solder paste, comprising:

[0035] Acquisition and measurement module: used to acquire metal particles of different shapes and measure the characteristic dimensions of metal particles of different shapes;

[0036] Calculation module: used to calculate the corresponding density based on the characteristic size of metal particles of different shapes and the mass ratio between metal particles of different shapes. The calculation method of density includes:

[0037] Mix and add metal particles of different shapes, or combine metal particles of different shapes in a preset ratio;

[0038] Setting basic parameters of metal particles; the basic parameters include: three-dimensional space boundary, particle characteristic size, preset step length, target movement direction and number of particles;

[0039] Based on the sum of the Z-axis coordinate of the highest point of the existing particles and the preset distance, generate the three-dimensional coordinates of the target particles on the current height plane where the sum of the Z-axis coordinate of the highest point and the preset distance is located;

[0040] Within the three-dimensional space boundary, the target particle is moved along the target movement direction with a preset step length, the three-dimensional coordinates of the target particle are updated, and the target particle and the existing particles are judged according to preset conditions until all the target particles to be placed are placed, and then the density is calculated by using the Monte Carlo method to solve pi;

[0041] Selection module: used to select the mass ratio corresponding to the maximum density from the calculated density to configure metal particles of different shapes when configuring solder paste;

[0042] Preparation module: used to evenly mix the configured mixed metal particles with the preset solvent to prepare solder paste.

[0043] The above technical solution of the present invention has the following beneficial effects compared with the prior art:

[0044] The method and system for preparing solder paste described in the present invention can use the obtained better particle ratio for the preparation of multi-peak silver / copper solder paste. Compared with the traditional method of using a solver to solve the lowest potential energy position for continuous accumulation, the optimal particle ratio calculated by the present invention (obtained by density calculation) is greatly reduced in running time under the condition of the same number of particles, and the particles are more dense.

[0045] When calculating the optimal particle ratio, the present invention assumes particle stability conditions, collision force and gravity, and the calculation is simple and the running time is fast.

[0046] The silver and / or copper particles of the present invention are not limited to fixed sizes. The size of each spherical particle can be different, and the size of the long and short diameters of elliptical pieces can also be changed, for example.

[0047] The present invention can improve the computational simulation efficiency of stacking and construct a model of multi-modal non-spherical particles, can quickly and effectively obtain the density of multi-modal non-spherical particles, provide theoretical guidance for the development of high-performance multi-modal silver / copper solder paste, and accelerate the research progress of new materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] In order to make the content of the present invention more clearly understood, the present invention is further described in detail below according to specific embodiments of the present invention in conjunction with the accompanying drawings, wherein:

[0049] Figure 1 A flow chart of a method for preparing solder paste provided in a preferred embodiment of the present invention;

[0050] Figure 2 A diagram of the delivery process of equal-diameter balls / mixed balls provided in a preferred embodiment of the present invention;

[0051] Figure 3 The stable conditions and force analysis diagram for judging the number of contact points provided in the preferred embodiment of the present invention;

[0052] Figure 4 A schematic diagram of Monte Carlo solution to pi provided in a preferred embodiment of the present invention;

[0053] Figure 5 A diagram of the mixed delivery process of spheres and elliptical tablets provided in a preferred embodiment of the present invention;

[0054] Figure 6 A schematic diagram of using a corresponding number of scattered points to replace an ellipse boundary provided in a preferred embodiment of the present invention;

[0055] Figure 7 A schematic diagram of the elliptical sheets provided in the preferred embodiment of the present invention being stacked together at a certain location;

[0056] Figure 8 The changes (x) provided in the preferred embodiment of the present invention 0 ,y 0 ) Schematic diagram of adjusting the position of the ellipse;

[0057] Fig. 9 A schematic diagram of the position of a sphere relative to an elliptical piece after spatial coordinate transformation provided in a preferred embodiment of the present invention;

[0058] Fig.10 The elliptical envelope diagram provided in the preferred embodiment of the present invention;

[0059] Fig.11 Four cross-sectional views of small particles with a size of r=1 provided in a preferred embodiment of the present invention;

[0060] Fig.12 It is a three-dimensional diagram corresponding to the specific embodiment 1 provided in the preferred embodiment of the present invention;

[0061] Fig.13 The density corresponding to each size in the specific implementation example 1 provided in the preferred embodiment of the present invention;

[0062] Fig.14 A cross-sectional view of one of the cases where r1 / r2=0.2 is provided in a preferred embodiment of the present invention;

[0063] Fig.15 It is a three-dimensional diagram corresponding to the specific embodiment 2 provided in the preferred embodiment of the present invention;

[0064] Fig.16 It is a density diagram corresponding to each mass proportion under three size ratios in the specific implementation example 2 provided in the preferred embodiment of the present invention;

[0065] Fig.17 It is a two-dimensional cross-sectional view of a simulation in the specific embodiment 3 provided in the preferred embodiment of the present invention;

[0066] Fig.18 It is a three-dimensional diagram corresponding to the specific embodiment 3 provided in the preferred embodiment of the present invention;

[0067] Fig.19 A comprehensive graph of density at various mass ratios in the specific embodiment 3 provided in the preferred embodiment of the present invention;

[0068] Fig. 20 A three-dimensional graph corresponding to a certain operation in the specific embodiment 4 provided in the preferred embodiment of the present invention;

[0069] Fig.21 It is a density diagram corresponding to each mass proportion in the specific embodiment 4 provided in the preferred embodiment of the present invention;

[0070] Fig. 22 A three-dimensional stacking diagram of bimodal spherical and non-spherical particles when σ=80% provided in a preferred embodiment of the present invention;

[0071] Fig.23 A schematic diagram of particle density variation under different sphere / elliptical flake mass ratios provided in a preferred embodiment of the present invention;

[0072] Fig.24 A schematic diagram of the microscopic morphology of sintered copper patterns with different ratios provided in a preferred embodiment of the present invention;

[0073] Fig.25 It is a schematic diagram showing the variation of the resistivity of the sintered copper pattern with the content of submicron particles provided in the preferred embodiment of the present invention. DETAILED DESCRIPTION

[0074] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it, but the embodiments are not intended to limit the present invention.

[0075] In order to overcome the problems existing in the prior art, the present invention proposes a method for preparing a solder paste. This embodiment mainly improves the calculation method of the density of multi-peak non-spherical particles. By calculating and simulating the particles' own gravity and the mutual collisions between particles during the packing process, the random delivery process of equal-diameter balls, two different-diameter balls, three different-diameter balls... in space is realized. On this basis, a random delivery method that can achieve the mixing of different particles is designed using the spatial coordinate conversion formula and the idea of ​​digital image processing. Based on the simulation results, the Monte Carlo idea is used to design a corresponding algorithm to calculate the density. In this way, the relationship between the density and the mass ratio of various particles when multiple particles are delivered is obtained. Finally, the obtained preferred particle ratio is used for the preparation of multi-peak silver / copper solder paste.

[0076] A method for preparing solder paste in this embodiment specifically includes the following steps:

[0077] Step 1: Obtain metal particles of different shapes (such as spherical or elliptical flakes) and measure the characteristic dimensions of the metal particles of different shapes;

[0078] It should be noted that the types of metal particles (such as silver particles, copper particles, etc.) can be the same or different, and the characteristic dimensions of metal particles of different shapes can include, for example: the radius of spherical particles, the major diameter, minor diameter, and thickness of elliptical flake particles;

[0079] Step 2: According to the characteristic sizes of metal particles of different shapes and the mass ratios between metal particles of different shapes obtained by measurement, the corresponding densities are calculated;

[0080] Step 3: When configuring solder paste, select the mass ratio corresponding to the maximum density from the calculated density to configure metal particles of different shapes;

[0081] Step 4: Evenly mix the prepared mixed metal particles with a preset solvent to prepare a multi-peak solder paste.

[0082] The metal particles in step 1 may be, for example, silver and / or copper particles, and the silver and / or copper particles may be all silver particles, or all copper particles, or a combination of silver / copper particles.

[0083] The mass ratio of metal particles of different shapes (taking silver and / or copper particles as an example) in step 2 includes at least two silver and / or copper particles of different shapes, for example, the following situations:

[0084] (1) It can be the mass ratio between two spherical silver particles with different radii (a total of two types); or the mass ratio between two elliptical flake copper particles with different radii (a total of two types).

[0085] (2) The mass ratio between the spherical silver particles and the elliptical flake copper particles (two types in total) may also be used.

[0086] (3) Alternatively, it may be the mass ratio between two elliptical silver particles of different sizes and one spherical copper particle (three in total).

[0087] In step 3, when selecting the mass ratio corresponding to the maximum density from the calculated densities to configure metal particles of different shapes (taking silver and / or copper particles as an example), it is assumed that step 2 uses the mass ratio between two spherical silver particles of different radii (a total of two types), and there are three mass ratios assumed to be: 2:1, 3:1, and 4:1. If 3:1 corresponds to the maximum density, then the mass ratio of 3:1 is selected.

[0088] The preset solvent in step 4 includes, but is not limited to, any one of ethylene glycol (EG), polyethylene glycol 200, polyethylene glycol 300, glycerol, and diethylene glycol.

[0089] The following is an example to illustrate: micron copper (elliptical sheet, major axis 2±0.05 μm, minor axis 1.6±0.04 μm, thickness 0.3±0.03 μm) and submicron copper (sphere, diameter 0.2±0.02 μm), in the multi-peak non-spherical particle accumulation simulation algorithm, according to the principle of proportional scaling, the parameters of the spherical particles are set to r1=0.5, the parameters of the elliptical particles are set to a=5 (half of the major axis of the elliptical sheet), b=4 (half of the minor axis of the elliptical sheet), d=0.75 (half of the thickness of the elliptical sheet), θ max =10°, num_point=16, the mass proportion of submicron spherical particles σ ranges from 50 to 100%. Fig. 22 This is a three-dimensional overlay diagram when σ = 80%. Fig.23 From the simulated density diagram, when σ=70%, the density curve reaches its maximum value.

[0090] In order to verify the feasibility of computer-aided design of multi-modal non-spherical copper solder paste, different proportions of micron copper flakes, submicron copper particles and PEG 300 solvent were mechanically mixed to prepare multiple groups of multi-modal non-spherical copper solder paste. Then, the copper solder paste was printed on a glass sheet by steel screen printing and sintered in a nitrogen environment at 280℃ for 30min. Finally, the surface morphology and microstructure of the sintered copper pattern were observed by scanning electron microscopy (SEM, EVO18, CarlZeiss-Ag), and the resistivity of the sintered copper pattern was evaluated by a four-probe resistivity tester (ST2263, Suzhou Lattice Electronics). Fig.24 The surface microstructures of sintered copper patterns with different submicron particle contents are shown. As can be seen from the figure, with the increase of submicron particle content, the surface of sintered copper becomes denser and the porosity decreases significantly. Fig.25 The change in resistivity of the sintered copper pattern with different submicron particle contents is shown. When the submicron particle content is 70%, the resistivity of the sintered copper pattern is the lowest. However, when the submicron particle content exceeds 70%, macro cracks appear in the sintered pattern, resulting in a relatively high macro resistivity even though the local micromorphology is particularly dense. The reason for the macro cracks may be that there are more submicron particles, the sintering activity is stronger, and the particle density is low, resulting in uneven densification shrinkage during the sintering process. Therefore, this embodiment believes that the sintering test results of the multi-peak non-spherical copper solder paste are consistent with the optimal ratio of the computer-aided design.

[0091] The calculation method of density in step 2 includes:

[0092] S201: Mix and add metal particles of different shapes, or combine metal particles of different shapes according to a preset ratio. In this embodiment, the metal particles include but are not limited to round pieces, elliptical pieces, equal-diameter balls (several metal particles with the same radius), mixed balls (several metal particles with different radii), and triangular pieces;

[0093] S202: Setting basic parameters of metal particles; the basic parameters include: three-dimensional space boundary, particle characteristic size, preset step length, target movement direction and number of particles;

[0094] S203: based on the sum of the Z-axis coordinate of the highest point of the existing particles and the preset distance, generating the three-dimensional coordinates of the target particle on the current height plane where the sum of the Z-axis coordinate of the highest point and the preset distance is located;

[0095] S204: within the three-dimensional space boundary, the target particle is moved along the target movement direction with a preset step length, the three-dimensional coordinates of the target particle are updated, and the target particle and the existing particles are judged according to preset conditions until all the target particles to be placed (the number of target particles to be placed is set in advance) are placed, and the density is calculated by using the Monte Carlo method to solve pi, and the result after the calculation is completed is saved to the target file;

[0096] S205: Draw a three-dimensional graph or a two-dimensional cross-sectional graph according to the calculation result.

[0097] In some possible implementations, performing a preset condition judgment on the target particle and the existing particle includes:

[0098] Determine whether the target particle overlaps with the existing particle; if not, determine the particle stability;

[0099] If the particle meets the stability condition, the target particle is added to the existing particle sequence, and it is determined whether all the target particles to be placed have been placed; if all have been placed, the cycle ends and density calculation is performed.

[0100] In some possible implementations, if it is determined that the target particle overlaps with the existing particle, the target particle is discarded, and the three-dimensional coordinates of a new target particle are generated on the current height plane based on the sum of the Z-axis coordinate of the highest point of the existing particle and the preset distance.

[0101] In some possible implementations, the operation of determining overlap includes:

[0102] When the target particle and the existing particle are both spheres, calculating the distance between the center of the moving sphere and the existing sphere;

[0103] When the particles are a mixture of non-spheres and spheres (this embodiment does not consider the mixture of non-spheres alone, it must be a mixture of spheres and non-spheres), there are three cases:

[0104] The first case is: when judging the overlap between spheres, the distance between the center of the moving sphere and the existing sphere is calculated;

[0105] The second case is: when judging the overlap between the sphere and the elliptical sheet, the target particle is transformed into a new three-dimensional coordinate system using the oblique ellipse in space through the spatial coordinate conversion formula, and other particles are transformed into the new three-dimensional coordinate system for judgment: in the new three-dimensional coordinate system x'O'y' plane, the circle is circumscribed to the ellipse, and the center trajectory forms an envelope; by judging whether the center of the sphere projected on the new three-dimensional coordinate system x'O'y' plane falls inside the outer ellipse, it is preliminarily judged whether the sphere and the elliptical sheet overlap; the relationship between the sphere center Z' and the half thickness of the elliptical sheet is used for target judgment, and the specific formula is:

[0106]

[0107] The third case is: when judging the overlap between elliptical slices, the target particle is transformed into a new three-dimensional coordinate system with an oblique ellipse in space through a spatial coordinate conversion formula, and other particles are transformed into the new three-dimensional coordinate system for judgment. When judging, the outer surface operation of the elliptical slice is described by multiple scattered points; and whether an overlap occurs is judged by judging whether the scattered points fall into other elliptical slices. The oblique ellipse is an elliptical slice that is tilted in three-dimensional space (not placed horizontally).

[0108] In some possible embodiments, the stabilizing conditions include:

[0109] The number of contact points between any spherical particle and other particles or boundaries is not less than three;

[0110] When the elliptical piece moves, it does not participate in the collision, and only the gravity effect is considered;

[0111] When the elliptical piece is stable, a displacement of a target length is applied to the elliptical piece along a preset direction so that the elliptical piece reaches a relative lowest potential energy position (the elliptical piece does not participate in the collision, but only falls down within the boundary of the three-dimensional space to reach a relative lowest potential energy position, which may not be the lowest potential energy position in the three-dimensional space).

[0112] In some possible implementations, if it is determined that the particle does not meet the stability condition, a force analysis is performed on the target particle, the target movement direction is updated, and the target particle is returned to be moved along the target movement direction with a preset step length.

[0113] In some possible embodiments, if the center of the projection of the sphere on the new system x′O′y′ plane falls between the outer ellipse and the central ellipse, the direction of the force on the sphere is along the negative direction of the thickness of the elliptical sheet; if the center of the projection falls inside the central ellipse, the direction of the force on the sphere is along the major axis, minor axis and direction, and obliquely downward.

[0114] In some possible implementations, if the current particles are not all placed, the three-dimensional coordinates of the new target particles are generated on the current height plane based on the sum of the Z-axis coordinates of the highest point of the existing particles and the preset distance.

[0115] It should be noted that, due to the particularity of the elliptical tablets, the present invention is divided into two parts, equal diameter spheres / mixed spheres and a mixture of elliptical tablets and spheres.

[0116] In one example, equal diameter spheres / hybrid spheres:

[0117] Considering the influence of gravity, in order to realize the random delivery process, the coordinates of the center point of the ball (x 0 ,y 0 ,z 0 ), denoted as O 0 The initial movement direction is downward, recorded as dir = [0,0,-1]. The ball moves at the initial position according to the set step size. Continuously iterate and update O 0 , dir, until the ball is stable.

[0118] See also Figure 2 , Figure 2 This is a diagram of the equal diameter ball / mixed ball delivery process.

[0119] Step 1: Set basic parameters:

[0120] Three-dimensional space boundary (taking a cuboid as an example, only its length and width need to be set, and the height is not limited. The size setting format is a one-dimensional vector, such as S = [a, b], where a and b represent half of the length and width);

[0121] Particle size: The radius of different spherical particles is represented by r1, r2, r3, etc.;

[0122] Step length: the total length of each movement of the particle, set to 0.1·r 1 ;

[0123] Movement direction (dir): Due to gravity, the initial movement direction dir = [0,0,-1]. Later, due to collisions with particles and space boundaries, dir is continuously updated during the subsequent movement;

[0124] The number of each particle: By setting the mass ratio between the particles and using the size relationship between the particles, the number of each particle is calculated. Use numbers to represent various balls and set them as a one-dimensional vector, called sequence p. The sequence is disrupted to achieve random delivery;

[0125] For example, in the case of double particles, the mass of the small particle: the mass of the large particle: ratio = [e, g]; where e + g = 10;

[0126] Number of small particles: Number of large particles: By setting the proportion of large particles to n0 large particles, the number of large particles can be calculated: n 2 =g·n 0 ; Number of small particles: n 1 =ra 1 ·n 2 ; So the number of particles: num 0 =[n 1 ,n 2 ]; use 0 to represent small particles and 1 to represent large particles, then p = [0,0,0,……,1,1,1,1,……]; where the p sequence contains n 1 0,n 2 1. Then shuffle.

[0127] Step 2: Based on the z-axis coordinate of the highest point of the existing particle, add the preset distance to the z-axis coordinate of the highest point to get a new z-axis coordinate, and randomly generate the coordinates of the center point (x 0 ,y 0 ,z 0 ), the particle is called a new particle. The specific size is determined by the sequence p. If there are 1000 particles and the 1001th number in the sequence p is 0, the size of the new particle is the particle size corresponding to the number 0.

[0128] Step 3: The new particle moves along the direction of motion dir with a fixed step length step, and updates the coordinates of the center point (x 0 ,y 0 ,z 0 ). Then calculate the distance dis between the new particle and the existing particle at this position. Then there are three judgments to be made;

[0129] Judgment 1: Determine whether the new particle overlaps with the existing particle. If so, discard the new particle and return to step 2. If not, proceed to judgment 2.

[0130] Conditions for determining non-overlapping: When the distance between two particles is dis=2·r, they are just in contact. However, when it is necessary to calculate the contact point and no large overlap occurs, it is considered that when dis≥1.9·r, the particles do not overlap.

[0131] Therefore, the non-overlap condition is dis ≥ 1.9·r; Where: (x 0 ,y 0 ,z 0 ) is the current coordinate of the new particle, (x i ,yi ,z i ) are the coordinates of the existing particles.

[0132] Judgment 2: Judgment of the number of contact points. If the number of contact points is not enough to meet the stability condition, the force analysis is performed on the new particle, the movement direction dir is updated, and step 3 is repeated. If the number of contact points meets the stability condition, the new particle is added to the existing particle sequence and judgment 3 is performed.

[0133] See also Figure 3 , Figure 3 To determine the stability conditions and force analysis diagram of the second, the stability conditions and force analysis notes for determining the second are as follows: Particle stability condition assumption: The number of contact points of any spherical particle with other particles or boundaries is not less than three; Particle collision force assumption: The force exerted on the particle by each contact point is the same; Particle resultant force assumption: The resultant force of each contact point on the particle is equal to the gravity.

[0134] It should be noted that the stability of the bottom layer of particles does not require three contact points. Generally speaking, the first layer often has only one contact point with the bottom of the space, but it can still be stable. Therefore, in order to avoid this situation, before the official launch, the grid is divided in the set space, the sequence is disrupted, and a layer of small particles is generated at the bottom layer (this layer does not participate in the particle counting).

[0135] For example, when the new particle has two contact points, and the direction of the force exerted by the two contact points on the new particle is tow 1 =(t x1 ,t y1 ,t z1 )、tow 2 =(t x2 ,t y2 ,t z2 ), based on the particle collision force assumption, under the vector composition law, we have tow 3 =(t x1 +t x2 ,t y1 +t y2 ,t z1 +t z2 ), after unitization tow 3 =(t x3 ,t y3 ,t z3 ), gravity unit vector tow 0 =(0,0,-1), based on the assumption that the particle is subject to the net force, dir is updated after the collision; dir = tow 3 +tow 0 .

[0136] Judgment 3: Have all particles been placed? If all have been placed, break the loop and proceed to step 4. If any particles have not been placed, return to step 2.

[0137] Step 4: Density calculation. The density calculation uses the Monte Carlo method to solve pi. Figure 4 To solve the Monte Carlo method for pi, generate T random points in a square with a side length of 1, and count the number of points that fall inside the circle. In order to avoid the influence of the space boundary during the delivery process, a core area is circled inside the space to calculate the density. After the calculation is completed, it is saved to the specified file.

[0138] Step 5: Automatically generate and save the three-dimensional graphics / two-dimensional cross-sectional diagram of the simulation results through autonomous coding.

[0139] In another example, spherical and elliptical slices are mixed:

[0140] See also Figure 5 , Figure 5 Diagram of the mixed delivery process of spherical and elliptical pieces.

[0141] Step 1, set the basic parameters: three-dimensional space boundary, step size (step), movement direction (dir), these three parameters are equal diameter ball / mixed ball; particle size, spherical particle radius r, elliptical slice major semi-axis a, minor semi-axis b, semi-thickness d; ellipse maximum allowable tilt angle θ: in actual situations, elliptical slices are not lying flat in space one by one, but have a certain tilt angle. Take θ = ±10°; num_point value. Select num_point scattered points on an ellipse to replace all the upper points. Since the distance calculation between the elliptical slice and other particles cannot be the same as the distance between the spheres, the only way to calculate the distance between the spheres is to use the upper, middle and lower elliptical surfaces to replace the entire elliptical slice, and each elliptical surface uses num_point points to replace the points on the entire elliptical slice. Therefore, an elliptical slice is actually described by 3·num_point scattered points. Substitute these scattered points into the equations of other particles. By judging whether these scattered points are located inside the existing particles, it can be judged whether the elliptical slice overlaps with other particles. The value of num_point can be based on Table 1, Figure 6 Make a selection, Figure 6 The ellipse boundary is replaced by a corresponding number of scattered points.

[0142] Table 1

[0143]

[0144] Since the size of the elliptical slices measured in the laboratory is too different from the size of the sphere, and the elliptical slices do not have the regularity of the sphere, the number of elliptical slices is fixed in the actual simulation (usually set to 20), and the corresponding number of balls is calculated according to the set mass ratio, ball:elliptical slice=ratio[e,g]. Other operations are equal diameter balls / mixed balls.

[0145] For example, sphere: elliptical slice (the number of elliptical slices is set to nu), ratio = [e, g], then the number of spheres num: Use 0 to represent elliptical pieces and 1 to represent spherical particles, then p = [0,0,0,...,1,1,1,1,...11], and shuffle the sequence p (the sequence p contains nu 0s and num 1s).

[0146] Step 2: Based on the z-axis coordinate of the highest point of the existing particle and the preset distance, randomly generate the coordinates of the center point (x 0 ,y 0 ,z 0 ), the particle is called a new particle. The specific size is determined by the sequence p. If there are 1000 particles and the 1001th number in the sequence p is 0, the size of the new particle is the particle size corresponding to the number 0.

[0147] Step 3: The new particle moves along the direction dir with a fixed step length and updates the center point coordinates. Then three judgments need to be made:

[0148] Judgment 1: Determine whether the new particle overlaps with the existing particle. If so, discard the new particle and return to step 2. If not, proceed to judgment 2.

[0149] Non-overlapping conditions: The non-overlapping conditions between spheres are equal diameter spheres / mixed spheres, which will not be described here; the non-overlapping judgment between ellipses is essentially the judgment of whether the point is inside the ellipse.

[0150] To determine the position of the spatial elliptical patch, 12 parameters are required. 0 ,y 0 ,z 0 ,n 1 ,n 2 ,n 3 ,v 1 ,v 2 ,v 3 ,u,u 2 ,u 3 ].

[0151] Where: (x 0 ,y 0 ,z 0) is the coordinate of the center point of the ellipse; (n 1 ,n 2 ,n 3 is the direction of half thickness; (v 1 ,v 2 ,v 3 ) is the direction of the major semi-axis; (u,u 2 ,u 3 ) is the direction of the minor semi-axis.

[0152] The parametric equation of the central elliptical surface of the space elliptical sheet is:

[0153] Parametric equations of the upper and lower elliptical surfaces of the space elliptical sheet:

[0154] After the new ellipse is determined, the coordinate values ​​of the 3·num_point scattered points are determined according to the above two parametric equations.

[0155] Space coordinate transformation formula:

[0156] Exemplary, the overlap between the new ellipse and the first ellipse slice is determined as follows:

[0157] Since the first ellipse is tilted at a certain angle in space, it is not conducive to judgment. Therefore, a new coordinate system is established with its major semi-axis, minor semi-axis, half thickness, center point as x', y', z' axis, and coordinate origin o', and the 3·num_point scattered points representing the new ellipse are converted to the new coordinate system using the above-mentioned spatial coordinate conversion formula. Judgment is performed. The judgment process is as follows:

[0158] First, take the absolute value of the z' coordinates of the 3·num_point scattered points, and only consider the case where they are above the x'o'y' plane. Then take the coordinate of the smallest z' value. If z' min ≥d, it means that the ellipses do not overlap. If z′ is not satisfied min ≥dContinue to perform overlap judgment.

[0159] Secondly, if z′ is not satisfied min ≥d, select all the scattered points that do not satisfy z′≥d from 3·num_point scattered points. At this time, the z' axis can be ignored, and the problem is converted into a plane problem. That is, whether these scattered points fall inside the ellipse with a as the major semi-axis, b as the minor semi-axis, and the center at the origin. If it does not satisfy This means that the new ellipse does not overlap with the existing ellipse, and the loop returns to step 3. This means that the new ellipse overlaps with the existing ellipse. In this case, the core parameters of the new ellipse (x 0 ,y 0 ,z0 ) returns to the value in the previous loop and performs the ellipse position adjustment operation.

[0160] Ellipse position adjustment operation: Since the ellipse is too special, it does not participate in the collision during the simulation and only follows the principle of minimum potential energy. From the previous operation to here, it means that without changing (x 0 ,y 0 ) under the premise that z 0 It is already the minimum value, so (x 0 ,y 0 ,z 0 )Save to (x t ,y t ,z min ). Then change (x 0 ,y 0 ), repeat step 3, if the final result is z 0 <z min , then save the new ellipse. If not satisfied, then (x t ,y t ,z min )save.

[0161] Change (x 0 ,y 0 ) method: Randomly select in the four directions [1,0,0], [-1,0,0], [0,1,0], [0,-1,0], (x 0 ,y 0 ) is offset by a certain distance in the selected direction to become a new (x 0 ,y 0 ). If you do not add this operation, Figure 4 In this case, the elliptical pieces are stacked up at certain positions, while other positions are left empty. Figure 7 This is a schematic diagram of the elliptical pieces stacked together at a certain location. Figure 8 To change (x 0 ,y 0 )Diagram of adjusting the ellipse position.

[0162] When the generated moving particles are spheres, the moving spheres are iterated in the same way as in the random stacking algorithm of spheres. The iterative process is not described here. The difference is the overlap, contact, and force analysis between the moving spheres and the elliptical cylinders.

[0163] Whether the sphere and the elliptical cylinder overlap each other needs to be judged no matter whether the moving particle is a sphere or an elliptical cylinder. However, the contact and force between the sphere and the elliptical cylinder are only required when the moving particle is a sphere.

[0164] Elliptical O 0The x′, y′, z′, and O′ of the new coordinate system are converted into the coordinates of the center of the spherical particle [x 0 ,y 0 ,z 0 ] is transformed to the new coordinate system [x', y', z']. The relationship between the sphere and the elliptical cylinder after the transformation is shown in Fig. 9 .

[0165] First, ignore z', that is, project all particles onto the x'o'y' plane. Since the projection of a sphere to any surface is a circle with the same radius as the sphere, the elliptical cylinder is projected into an ellipse with a as the major semi-axis, b as the minor semi-axis, and the center at the origin. So the problem is temporarily transformed into determining whether the circle on the plane overlaps with the ellipse.

[0166] Assuming that on a plane, if a circle is always tangential to an ellipse, the trajectory of the center of the circle will form an envelope outside the ellipse (such as Fig.10 ). Then there will be:

[0167] Parametric equation of an ellipse:

[0168] Parametric equation of a circle:

[0169] Where [x′, y′] is the coordinates of the center of the sphere projected on the x'o'y' plane, and r is the radius of the corresponding circle.

[0170] If the circle is always tangent to the ellipse, then the equation of the center of the circle (the equation of the envelope) is:

[0171] from Fig.10 As can be seen from the figure, the envelope is actually a quasi-ellipse, so the ellipse equation is used to approximate it. The approximate ellipse equation of the outer envelope is:

[0172] The approximate ellipse equation of the outer envelope is:

[0173] Therefore, only the spherical coordinates need to satisfy It can be considered that there is no overlap between the sphere and the elliptical cylinder, where r 0 is the radius of the moving sphere.

[0174] Although the above operation can preliminarily determine that there is no overlap between some spheres and ellipsoids, this is not enough. It is necessary to further determine the spheres whose projection centers fall within the envelope. 0 The coordinate values ​​are taken as absolute values, and only the case where they are above the c'o'y' plane is considered.

[0175] If |z′|>d+r 0, then there is no contact between the sphere and the ellipse, where r 0 is the radius of the moving sphere;

[0176] If |z′|>d+r is not satisfied 0 , then proceed to make a judgment;

[0177] If the formula d+r is satisfied at the same time 0 -step≤|z′|≤d+r 0 , This indicates that the moving sphere is in contact with the upper elliptical surface of the elliptical cylinder. The contact force is along the major axis, minor axis and direction, and is guaranteed to be obliquely downward. (For the moving sphere, it can only be in contact with the upper elliptical surface, not the lower elliptical surface. When it is used to judge the moving ellipse and the sphere, the contact situation does not need to be considered.)

[0178] If the formula d+r is not satisfied 0 -step≤|z′|≤d+r 0 Satisfied This means that there is an overlap between the sphere and the elliptical cylinder. The remaining cases are all that the sphere is between the elliptical cylinder and the outer envelope. At this time, it can be simply assumed that this part of the sphere is in contact with the side of the elliptical cylinder. The contact force is in the negative direction of the half-thickness d of the elliptical cylinder. You can also make the following judgment:

[0179]

[0180] If d≤|z′| <d+r 0 , the upper elliptical surface is needed to intercept the ball. If d>|z′| is satisfied, the elliptical surface with the same height as the center of the ball is needed to intercept the ball. Regardless of the case, the height of the plane used to intercept the ball is Q. At this time, the radius of the intercepted circle r′ is obtained:

[0181]

[0182] With the above operations, the problem is transformed into judging the relationship between the circle and the ellipse on the plane. Here we refer to the above operations.

[0183] The approximate ellipse equation of the outer envelope is:

[0184] At this time, the ellipse and the cut circle intersect (the sphere and the ellipse overlap) only need to satisfy:

[0185] The contact between the ball and the ellipse only needs to satisfy (the balls judged as in contact in this part are considered to be in contact with the arc of the side of the ellipse, and the contact force is simply considered to be along the negative direction of the thickness d):

[0186]

[0187] Judgment 2: When the new particle is a ball, the particle stability judgment is performed. If the number of contact points is not enough to meet the stability condition, the force analysis is performed on the new ball, the movement direction dir is updated, and step 3 is repeated. If the number of contact points meets the stability condition, the new particle is added to the existing particle sequence and judgment 3 (same diameter ball / mixed ball) is performed.

[0188] Judgment 3: Have all particles been placed? If all have been placed, break the loop and proceed to step 4. If any particles have not been placed, return to step 2.

[0189] Step 4: Density calculation: whether the point is inside the elliptical slice is determined by referring to the elliptical slice and elliptical slice judgment. The rest is the same as the equal diameter ball / mixed ball.

[0190] Step 5: Automatically generate and save the three-dimensional graphics / two-dimensional cross-sectional diagram of the simulation results through autonomous coding.

[0191] In the first specific implementation, for equal diameter spheres: set the space boundary S = [20, 20], the small particle size r = 1, and the number of particles is 8000; set the space boundary S = [20, 20], the small particle size r = 2, and the number of particles is 1000; set the space boundary S = [20, 20], the small particle size r = 3, and the number of particles is 800; set the space boundary S = [20, 20], the small particle size r = 4, and the number of particles is 500; set the space boundary S = [20, 20], the small particle size r = 5, and the number of particles is 400; set the space boundary S = [20, 20], the small particle size r = 6, and the number of particles is 200. For details, refer to Fig.11 Four cross-sectional views of small particle size r = 1, Fig.12 is the corresponding three-dimensional diagram in the above specific embodiment 1, Fig.13 It is the density corresponding to each size in the above specific implementation example 1.

[0192] In the second specific implementation, the double-particle mixed ball: set the spatial boundary S = [20,20], the small particle size r1 = 1, the large particle size r2 = 5, that is, r1 / r2 = 0.2. The mass of small particles accounts for 0-1 of the total mass, and for every 0.1 of the mass of large particles, there are 2 large particles; set the spatial boundary S = [20,20], the small particle size r1 = 1, the large particle size r2 = 4, that is, r1 / r2 = 0.25. The mass of small particles accounts for 0-1 of the total mass, and for every 0.1 of the mass of large particles, there are 2 large particles; set the spatial boundary S = [20,20], the small particle size r1 = 1, the large particle size r2 = 2.5, that is, r1 / r2 = 0.4. The mass of small particles accounts for 0-1 of the total mass, and for every 0.1 of the mass of large particles, there are 2 large particles. For specific reference Fig.14The cross-sectional view is one of the cases where r1 / r2=0.2. Fig.15 is the corresponding three-dimensional graph in the above specific embodiment 2, Fig.16 It is a density diagram corresponding to each mass proportion under the three size ratios in the above specific implementation example 2.

[0193] In the third embodiment, the three-particle mixed ball: set the space boundary S = [40, 40], the small particle size r1 = 1, the medium particle size r2 = 4, and the large particle size r3 = 16, that is, r1 / r2 = 0.25, r2 / r3 = 0.25. For every 0.1 of the total mass of the large particles, there are 2 large particles. The mass of small particles accounts for 0 of the total mass, and the mass of medium particles accounts for 0-1 of the total mass; the mass of small particles accounts for 0.1 of the total mass, and the mass of medium particles accounts for 0-0.9 of the total mass; the mass of small particles accounts for 0.2 of the total mass, and the mass of medium particles accounts for 0-0.8 of the total mass; the mass of small particles accounts for 0.3 of the total mass, and the mass of medium particles accounts for 0-0.7 of the total mass; the mass of small particles accounts for 0.4 of the total mass, and the mass of medium particles accounts for 0-0.6 of the total mass; the mass of small particles accounts for 0.5 of the total mass, and the mass of medium particles accounts for 0-0.5 of the total mass; the mass of small particles accounts for 0.6 of the total mass, and the mass of medium particles accounts for 0-0.4 of the total mass; the mass of small particles accounts for 0.7 of the total mass, and the mass of medium particles accounts for 0-0.3 of the total mass; the mass of small particles accounts for 0.8 of the total mass, and the mass of medium particles accounts for 0-0.2 of the total mass; the mass of small particles accounts for 0.9 of the total mass, and the mass of medium particles accounts for 0-0.1 of the total mass; the mass of small particles accounts for 1 of the total mass, and the mass of medium particles accounts for 0 of the total mass. For specific reference Fig.17 is a two-dimensional cross-sectional view of a simulation in the above specific embodiment 3, Fig.18 is the corresponding three-dimensional graph in the above specific embodiment 3, Fig.19 It is a comprehensive diagram of density at various mass ratios in the above specific embodiment 3.

[0194] In the fourth embodiment, spheres and elliptical pieces are mixed: the space boundary S is set to [25, 25], the maximum tilt angle is 10°, the num_point value is 16, the sphere particle size r is 1, and the elliptical piece size a is 10, b is 8, and d is 3. The mass of the sphere particles accounts for 0-1 of the total mass. The number of elliptical pieces is fixed to 20. For details, refer to Fig. 20 is a three-dimensional graph corresponding to a certain operation in the above specific embodiment 4, Fig.21 It is a density diagram corresponding to each mass proportion in the above specific embodiment 4.

[0195] Since the dimensions of the sphere and ellipsoidal piece are actual data obtained from actual measurements, they are obtained according to the corresponding reduction ratio. Fig.21 It can be seen that when the mass ratio of the small spherical particles reaches about 0.6, the density reaches the maximum value. This is almost the same as the experimental data.

[0196] The present invention further provides a system for preparing solder paste, which adopts the method for preparing solder paste described in any one of the above embodiments, comprising:

[0197] Acquisition and measurement module: used to acquire metal particles of different shapes and measure the characteristic dimensions of metal particles of different shapes;

[0198] Calculation module: used to calculate the corresponding density based on the characteristic size of metal particles of different shapes and the mass ratio between metal particles of different shapes. The calculation method of density includes:

[0199] Mix and add metal particles of different shapes, or combine metal particles of different shapes in a preset ratio;

[0200] Setting basic parameters of metal particles; the basic parameters include: three-dimensional space boundary, particle characteristic size, preset step length, target movement direction and number of particles;

[0201] Based on the sum of the Z-axis coordinate of the highest point of the existing particles and the preset distance, generate the three-dimensional coordinates of the target particles on the current height plane where the sum of the Z-axis coordinate of the highest point and the preset distance is located;

[0202] Within the three-dimensional space boundary, the target particle is moved along the target movement direction with a preset step length, the three-dimensional coordinates of the target particle are updated, and the target particle and the existing particles are judged according to preset conditions until all the target particles to be placed are placed, and then the density is calculated by using the Monte Carlo method to solve pi;

[0203] Selection module: used to select the mass ratio corresponding to the maximum density from the calculated density to configure metal particles of different shapes when configuring solder paste;

[0204] Preparation module: used to evenly mix the configured mixed metal particles with the preset solvent to prepare solder paste.

[0205] The present invention also provides an electronic device, comprising: a processor, a memory and a bus, wherein the memory stores machine-readable instructions executable by the processor, and when the electronic device is running, the processor and the memory communicate through the bus, and the machine-readable instructions are executed by the processor to execute the steps of the method for preparing the solder paste as described in any of the above embodiments.

[0206] The present invention further provides a computer-readable storage medium, on which a computer program is stored. When the computer program is executed by a processor, the steps of the method for preparing solder paste as described in any of the above embodiments are executed.

[0207] In summary, the solder paste preparation method and system provided by the present invention can improve the computational simulation efficiency of stacking and construct a model of multimodal non-spherical particles when preparing multimodal silver / copper solder paste, and can quickly and effectively obtain the density of multimodal non-spherical particles, thereby providing theoretical guidance for the development of high-performance multimodal silver / copper solder paste and accelerating the research progress of new materials.

[0208] Those skilled in the art will appreciate that the embodiments of the present application may be provided as methods, systems, or computer program products. Therefore, the present application may adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the present application may adopt the form of a computer program product implemented in one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) that include computer-usable program code.

[0209] The present application is described with reference to flowcharts and / or block diagrams of methods according to embodiments of the present application.

[0210] Obviously, the above embodiments are merely examples for clear explanation and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from these are still within the protection scope of the invention.

Claims

1. A method for preparing a solder paste, characterized in that: include: Step 1: Obtain metal particles of different shapes and measure the characteristic sizes of metal particles of different shapes; Step 2: According to the characteristic size of metal particles of different shapes and the mass ratio between metal particles of different shapes obtained by measurement, the corresponding density is calculated. The density calculation method includes: Mix and add metal particles of different shapes, or combine metal particles of different shapes in a preset ratio; Setting basic parameters of metal particles; the basic parameters include: three-dimensional space boundary, particle characteristic size, preset step length, target movement direction and number of particles; Based on the sum of the Z-axis coordinate of the highest point of the existing particles and the preset distance, generate the three-dimensional coordinates of the target particles on the current height plane where the sum of the Z-axis coordinate of the highest point and the preset distance is located; Within the three-dimensional space boundary, the target particle is moved along the target movement direction with a preset step length, the three-dimensional coordinates of the target particle are updated, and the target particle and the existing particles are judged according to preset conditions until all the target particles to be placed are placed, and then the density is calculated by using the Monte Carlo method to solve pi; Step 3: When configuring solder paste, select the mass ratio corresponding to the maximum density from the calculated density to configure metal particles of different shapes; Step 4: Evenly mix the prepared mixed metal particles with a preset solvent to obtain solder paste.

2. The method for preparing solder paste according to claim 1, characterized in that: Performing preset condition judgment on the target particles and the existing particles includes: Determine whether the target particle overlaps with the existing particle; if not, determine the particle stability; If the particle meets the stability condition, the target particle is added to the existing particle sequence, and it is determined whether all the target particles to be placed have been placed; if all have been placed, the cycle ends and density calculation is performed.

3. The method for preparing solder paste according to claim 2, characterized in that: If it is determined that the target particle overlaps with the existing particle, the target particle is discarded, and the three-dimensional coordinates of a new target particle are generated on the current height plane based on the sum of the Z-axis coordinate of the highest point of the existing particle and the preset distance.

4. The method for preparing solder paste according to claim 2, characterized in that: The operation of determining overlap includes: When the target particle and the existing particle are both spheres, calculating the distance between the center of the moving sphere and the existing sphere; When the particles are a mixture of non-spherical and spherical particles, there are three cases: The first case is: when judging the overlap between spheres, the distance between the center of the moving sphere and the existing sphere is calculated; The second case is: when judging the overlap between the sphere and the elliptical sheet, the target particle is transformed into a new three-dimensional coordinate system using the oblique ellipse in space through the spatial coordinate conversion formula, and other particles are transformed into the new three-dimensional coordinate system for judgment: in the new three-dimensional coordinate system x'O'y' plane, the circle is circumscribed to the ellipse, and the center trajectory forms an envelope; by judging whether the center of the sphere projected on the new three-dimensional coordinate system x'O'y' plane falls inside the outer ellipse, it is preliminarily judged whether the sphere and the elliptical sheet overlap; the relationship between the sphere center Z' and the half thickness of the elliptical sheet is used for target judgment, and the specific formula is: The third situation is: when judging the overlap between elliptical slices, the target particle is transformed into a new three-dimensional coordinate system with an oblique ellipse in space through a spatial coordinate conversion formula, and other particles are transformed into the new three-dimensional coordinate system for judgment. When judging, the outer surface operation of the elliptical slice is described by multiple scattered points; and whether an overlap occurs is judged by judging whether the scattered points fall into other elliptical slices, wherein the oblique ellipse is an elliptical slice tilted in three-dimensional space.

5. The method for preparing solder paste according to claim 2, characterized in that: The stability conditions include: The number of contact points between any spherical particle and other particles or boundaries is not less than three; When the elliptical piece moves, it does not participate in the collision, and only the gravity effect is considered; When the elliptical sheet is stable, a displacement of a target length is applied to the elliptical sheet along a preset direction so that the elliptical sheet reaches a relative lowest potential energy position.

6. The method for preparing solder paste according to claim 2, characterized in that: If it is determined that the particle does not meet the stability condition, a force analysis is performed on the target particle, the target movement direction is updated, and the target particle is returned to be moved along the target movement direction with a preset step length.

7. According to the method for preparing solder paste as claimed in claim 4, if the center of the projection of the sphere on the new system x′O′y′ plane falls between the outer ellipse and the central ellipse, the direction of the force on the sphere is along the negative direction of the thickness of the elliptical sheet; if the center of the projection falls inside the central ellipse, the direction of the force on the sphere is along the major axis, the minor axis and the direction, and obliquely downward.

8. The method for preparing solder paste according to claim 3, characterized in that: If all the current particles are not placed, the three-dimensional coordinates of the new target particles are generated on the current height plane based on the sum of the Z-axis coordinates of the highest point of the existing particles and the preset distance.

9. The method for preparing solder paste according to claim 3, characterized in that: The preset solvent is any one of ethylene glycol, polyethylene glycol 200, polyethylene glycol 300, glycerol, and diethylene glycol.

10. A system for preparing solder paste, using the method for preparing solder paste according to any one of claims 1 to 9, characterized in that: include: Acquisition and measurement module: used to acquire metal particles of different shapes and measure the characteristic dimensions of metal particles of different shapes; Calculation module: used to calculate the corresponding density based on the characteristic size of metal particles of different shapes and the mass ratio between metal particles of different shapes. The calculation method of density includes: Mix and add metal particles of different shapes, or combine metal particles of different shapes in a preset ratio; Setting basic parameters of metal particles; the basic parameters include: three-dimensional space boundary, particle characteristic size, preset step length, target movement direction and number of particles; Based on the sum of the Z-axis coordinate of the highest point of the existing particles and the preset distance, generate the three-dimensional coordinates of the target particles on the current height plane where the sum of the Z-axis coordinate of the highest point and the preset distance is located; Within the three-dimensional space boundary, the target particle is moved along the target movement direction with a preset step length, the three-dimensional coordinates of the target particle are updated, and the target particle and the existing particles are judged according to preset conditions until all the target particles to be placed are placed, and then the density is calculated by using the Monte Carlo method to solve pi; Selection module: used to select the mass ratio corresponding to the maximum density from the calculated density to configure metal particles of different shapes when configuring solder paste; Preparation module: used to evenly mix the configured mixed metal particles with the preset solvent to prepare solder paste.

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