CN113567744B - Method for calculating contact resistance of electric connector under storage condition - Google Patents

Abstract

The invention discloses a simulation method of an electric connector contact performance degradation process considering discrete stress, which comprises the following steps: s1, measuring the contact surface of an electric connector to obtain an initial value of a three-dimensional W-M function; s2, establishing two contact surface models based on a three-dimensional W-M function; s3, obtaining two section skeleton diagrams based on the two contact surface models; s4, respectively selecting two-dimensional curves at corresponding positions of the two profile skeleton diagrams based on preset components, and comparing the heights of the two-dimensional curves, so as to judge that the film resistance or the shrinkage resistance is generated on the contact surface; and determining the number and diameter of the contact spots and the oxide film spots; s5, repeatedly executing the step S4 until the selection of all two-dimensional curves in the X-axis interval range is completed, thereby determining the quantity of all oxide film spots and contact spots; and S6, calculating to obtain a contact resistance value based on the diameter of each contact spot and the oxide film spot and the number of all contact spots and oxide film spots.

Description

A method for calculating contact resistance of electrical connectors under storage conditions

Technical field

The invention relates to the technical field of electrical connectors, and in particular to a method for calculating contact resistance under storage conditions of an electrical connector.

Background technique

Electrical connectors are widely used components in model equipment, and their reliability is crucial. Electrical connectors are the basic components for transmitting electrical energy and signal energy. Its connection and separation functions play a vital role in certain models of equipment.

Due to some special reasons, whether the long-term storage of electrical connectors can have the same functions and effects as before storage after a long period of storage, a large amount of empirical data can be used to discover the main failures of electrical connectors under storage conditions. The form is contact failure, accounting for approximately 45.1% of the total field failures. During long-term storage, the contact performance of electrical connectors will inevitably show an irreversible gradual degradation trend.

There are many types of reasons for contact failure of electrical connectors: the increase of oxidation corrosion, stress relaxation of the contact on the reed, accumulation of contaminants, severe wear of the contact parts, etc. Under storage conditions, electrical connectors are stored in warehouses for a long time and are no longer opened, so the impact of contaminants and wear on them is negligible under this condition. Many scholars have studied that the stress relaxation of the reed has a small impact on it. , so the main cause of failure during storage can be considered to be the accumulation of oxidized corrosion products on the surface due to contact, resulting in an increase in contact resistance.

Therefore, the calculation of contact resistance under storage conditions is an important indicator for judging the reliability of electrical connectors. However, currently few people have constructed a calculation model of contact resistance through computer models. The contact resistance is mainly obtained through traditional experimental tests. the size of.

Contents of the invention

In order to overcome the deficiencies of the above technology, the present invention provides a method for simulating the formation process of contact resistance based on storage conditions of an electrical connector and creating a model to calculate the contact resistance.

The technical solution adopted by the present invention to overcome its technical problems is:

The invention proposes a method for calculating contact resistance under storage conditions of an electrical connector, which specifically includes: S1, measuring the contact surface of the electrical connector to obtain the initial parameter value of the three-dimensional W-M function; S2, determining based on the initial parameter value The three-dimensional W-M function establishes two contact surface models of the electrical connector; S3, obtains two cross-sectional skeleton diagrams based on the two contact surface models of the electrical connector; S4, selects the corresponding positions of the two cross-sectional skeleton diagrams based on the preset components Two two-dimensional curves and compare the heights of the two-dimensional curves to determine whether the contact surface produces film resistance or shrinkage resistance, and determine the number and diameter of contact spots and oxide film spots; S5, repeat step S4 until Complete the selection of all two-dimensional curves in the X-axis interval range to determine the number of all oxide film spots and contact spots on the electrical connection contact surface; S6, based on the diameter of each contact spot and oxide film spot, and all contact spots and oxide film spots Calculate the film layer resistance value and shrinkage resistance value, and then obtain the contact resistance value.

Further, the contact surface of the electrical connector is measured to obtain the initial value of the three-dimensional WM function, which specifically includes: S11. Measure the height of the contact surface to obtain the Z(x) curve of multiple sections, that is, the two-dimensional WM function. S12. Perform Fourier transformation on the two-dimensional WM function to obtain the power spectrum of the surface profile/> S13. Take the logarithm of both sides of the power spectrum to get/> S14, the fractal dimension D and the scale parameter G are calculated based on the linear relationship between lgP(ω) and lgω and the profile of the measured surface.

Further, in step S1, the contact surface of the electrical connector is measured to obtain the initial value of the three-dimensional W-M function, which specifically includes:

S11’, measure the roughness Ra of the contact surface;

S12’ obtains the fractal dimension D and scale parameter G based on the roughness Ra, and formula (1) and formula (2) respectively,

Further, in step S2, two contact surface models of the electrical connector are established based on the three-dimensional W-M function that determines the initial parameter values, specifically including:

Two contact surface micrographs are generated based on the three-dimensional WM function determined by the initial parameter values, which is used to simulate the contact process of the electrical connection contact surface, where the three-dimensional WM function is is the sampling length, D is the fractal dimension in three dimensions, 2<D<3, G is the scale parameter, γ is the randomness and frequency of the curve phase, m is the proportion of the number of protrusions and depressions in the contact surface macrogram, n is a sequence of natural numbers, and φ _m,n is a random number uniformly distributed in the interval (0, 2π).

Further, step S3 specifically includes: cutting the two contact surface micrographs along the X-axis cross-sectional direction to obtain single line cross-sectional skeleton diagrams of the first contact surface and the second contact surface respectively.

Further, step S4 specifically includes: S41, respectively select two-dimensional curves at the same position on the X-axis of the single line cross-section skeleton diagram of the first contact surface and the second contact surface based on the preset components; S42, calculate the two curves Height difference Δz=z ₁ (x, y)-z ₂ (x, y)-λ, where z ₁ (x, y) is the height of the first curve, z ₂ (x, y) is the height of the second curve , λ is the variation error, θ is the thickness of the oxide film covering the metal surface; S43, if the height difference is less than or equal to 2θ, it is considered that the contact spots and oxidized corrosion products produce film layer resistance, if not, determine whether the height difference is greater than 0, If it is greater than 0, the part of the contact spot is considered to be shrinkage resistance, otherwise there is no contact resistance here.

Further, step S6 specifically includes: obtaining the contact resistance value based on formula (3),

Among them, R _j is the contact resistance, a _sp is the radius corresponding to the P-th contact spot; a _bk is the radius corresponding to the k-th oxide film spot, n is the number of contact spots, and m is the number of oxide film spots.

The beneficial effects of the present invention are:

1. Analyze the contact process of two conductors from the microstructure and mechanism level, use the W-M function to construct a microscopic contact surface model, convert the three-dimensional contact surface into a two-dimensional intersection curve to distinguish the resistance type, and calculate the size of the contact resistance.

2. Reduce the manpower and material resources consumed by the traditional method-actual measurement. By inputting the initial parameters of the corresponding material, the corresponding contact resistance can be obtained, realizing the process of numerically calculating the contact resistance.

3. From a practical point of view, it provides a reference for accurately evaluating the storage life of electrical connectors, optimizing the process of reliability assessment of electrical connectors, and is of great significance to extending the life of model equipment.

Description of drawings

Figure 1 is a schematic diagram of the contact surface of an electrical connector;

Figure 2 is a flow chart of a method for calculating contact resistance under storage conditions of an electrical connector according to an embodiment of the present invention;

Figure 3 shows the W-M curve under different conditions of parting parameter D;

Figure 4 shows the W-M curve under different scale parameter G conditions;

Figure 5 is a detailed diagram characterizing the contact surface of the electrical connector;

Figure 6 is a contact surface model of the contact surface 1 according to the embodiment of the present invention;

Figure 7 is a contact surface model of the contact surface 2 according to the embodiment of the present invention;

Figure 8 is a single line cross-sectional skeleton diagram of the contact surface 1 according to the embodiment of the present invention;

Figure 9 is a perspective view of a single line cross-sectional skeleton diagram of the contact surface 1 according to the embodiment of the present invention;

Figure 10 is a two-dimensional curve diagram of the contact surface according to the embodiment of the present invention;

Figure 11 is a two-dimensional curve diagram of the contact surface marked with intersection points according to the embodiment of the present invention;

Figure 12 is the contact resistance calculation flow chart;

Figure 13 is a schematic diagram of computer simulated contact resistance.

Detailed ways

In order to facilitate those in the art to better understand the present invention, the present invention will be further described in detail below with reference to the drawings and specific embodiments. The following are only exemplary and do not limit the scope of the present invention.

First, the terms involved in the embodiments of this application are introduced:

Shrinkage resistance: refers to the fact that the contact surface cannot remain completely flat from a microscopic point of view during the processing process. During the contact process, there is actually contact between a small number of convex hills as shown in Figure 1, resulting in the current flowing. Convergence, when the current converges, the resistance produced is called shrinkage resistance. In the embodiment of the present invention, the prerequisites for calculating shrinkage resistance are as follows:

1) It is considered that the conductive spot is circular, and its size should be much smaller than the apparent area of the contact area, which can be regarded as "long contraction".

2) The materials of the two contact surfaces are consistent and their resistivities are the same.

3) Ignore the effect of temperature on resistivity.

4) The electric potential on the entire surface is consistent.

Thus, the shrinkage resistance of the contact surface and the shrinkage resistance of the contact surface on the other side are obtained. Among them, ρ is the resistivity; a is the contact spot radius, and the shrinkage resistance of the contact element can be expressed as:/> If there are n contact spots on the contact surface, the radius of the contact spot can be written as a _sp , and the shrinkage resistance can be expressed as/>

Film layer resistance: For some electrical contact surfaces, because they are exposed to the air, a layer of metal oxide, stains, dust, etc. will be produced on the surface. However, usually metal oxides are semiconductors and their resistance is large, so when calculating the film When measuring layer resistance, more attention is often paid to the resistance of metal oxides. For contact spots covered with a layer of metal oxide on the surface, from the perspective of classical physics, current cannot pass through the film no matter how thick it is. However, according to quantum mechanics theory, electrons, as a wave, can penetrate The film conducts electricity. This effect is called the tunnel effect. From the Schrödinger equation, we can know that the tunnel resistivity of the film is Among them, U is the potential between the contact surfaces; J is the current density flowing through the film; therefore, the film resistance generated by passing through the conductive surface with radius r can be calculated as:/> If there are n conductive spots on the contact surface, the radius of each film spot can be written as a _bk , and the total film resistance can be written as:

Contact resistance: R _j includes shrinkage resistance Rs and film resistance R _b , R _j =R _s + R _b . The essence of contact resistance is that the two conductors generate _heat during the contact process. The reason is that there is a gap in the contact caused by resistance. In the embodiment of the present application, two contact surfaces are brought into contact to simulate the contact process in real situations, thereby calculating the contact resistance.

Two-dimensional Weierstrass-Mandelbrot function: referred to as W-M function, has the special property of being continuous everywhere but not differentiable everywhere, and can be used to express random phenomena in nature. What is expressed in formula (1) is a commonly used two-dimensional W-M function.

In the embodiment of the present application, Z(x) is the contour height, G is the scale parameter, and D is the fractal parameter, where for the two-dimensional case 1<D<2, γ ⁿ represents the spatial phase and randomness of the contour, Generally, γ = 1.5 is used when the surface profile is normally distributed.

As shown in Figure 2, the flow chart of a method for calculating contact resistance under storage conditions of an electrical connector according to this embodiment specifically includes:

S1, measure the contact surface of the electrical connector to obtain the initial parameter values of the three-dimensional W-M function;

S2, establish two contact surface models of the electrical connector based on the three-dimensional W-M function determined by the initial parameter values;

S3, two cross-sectional skeleton diagrams are obtained based on the two contact surface models of the electrical connector;

S4, based on the preset components, select the corresponding two-dimensional curves at a certain position on the X axis of the two cross-sectional skeleton diagrams, and compare the heights of the two-dimensional curves to determine whether the contact surface produces film resistance or shrinkage resistance, and, Determine the number and diameter of contact spots and oxide film spots;

S5, repeat step S4 until the selection of all two-dimensional curves in the X-axis interval range is completed, thereby determining the number of all oxide film spots and contact spots on the electrical connection contact surface;

S6, calculate the film layer resistance value and shrinkage resistance value based on the diameter of each contact spot and oxide film spot, and the number of all contact spots and oxide film spots, thereby obtaining the contact resistance value.

The calculation method of contact resistance under storage conditions of electrical connectors will be described below with reference to specific embodiments;

S1, measure the contact surface of the electrical connector to obtain the initial parameter values of the three-dimensional W-M function;

As shown in Figure 3, it is the W-M curve corresponding to different parting parameters D. It can be seen from Figure 3 that as D increases, the W-M curve will increase more fluctuations in the flat area. The larger D, the greater the The W-M function has more details.

Adjusting the size of the fractal parameter D by fixing other parameters can be seen as shown in Figure 1. It can be seen from Figure 1 that as D increases, the W-M curve will add more fluctuations in the flat area. The larger D, the more details the W-M function will have.

As shown in Figure 4, it is the W-M curve corresponding to different parting parameters G. It can be seen from Figure 4 that the amplitude of the W-M curve decreases as G decreases. The smaller G, the smaller the peak value.

Therefore, the line shape of the W-M curve can be changed by adjusting the fractal dimension D and the scale parameter G to achieve a true simulation of rough surface roughness.

However, two dimensions can only express local features and cannot clearly characterize the characteristics of a region. A three-dimensional W-M function model is introduced. The representation of the three-dimensional W-M function is as shown in formula (2):

Among them, L-represents the sampling length; D-the fractal dimension in the three-dimensional case, its value has one more dimension than in the two-dimensional condition, 2<D<3, and the complexity of the curve fluctuates with D increases with the increase in value; G-scale parameter is used to adjust the amplitude of the curve; γ-represents the randomness and frequency of the curve phase; m-is selected so that the number of bulges and depressions in the generated three-dimensional image is proportional , the smaller m is, the smaller the proportion will be; n - natural sequence; φ _m,n - is a random number that obeys uniform distribution in the (0, 2π) interval; Figure 5 uses the WM three-dimensional surface to represent the electrical connector contact surface Detailed situation diagram.

In embodiments of the present invention, by measuring the contact surface of the electrical connector, the initial parameter values of the three-dimensional W-M function are obtained, that is, the fractal dimension D and the scale parameter G are obtained.

In some embodiments, a power spectrum algorithm is used. First, use a pressure sensor to measure the height of the measured contact surface to obtain the Z(x) curve under several sections, which is the W-M function in two dimensions. You can perform Fourier transformation on equation (1) to obtain the power under the real surface profile. Spectrum, such as formula (3), take the logarithm of both sides to obtain formula (4).

lgP(ω) and lgω have a linear relationship, and the fractal dimension D and scale parameter G are calculated from the obtained contour of the measured surface.

In some embodiments, the roughness value Ra of the measured surface is measured by a roughness meter, and the fractal dimension and scale parameters are obtained through formula (5) and formula (6), thereby obtaining the W-M function curve.

S2, establish two contact surface models of the electrical connector based on the three-dimensional W-M function determined by the initial parameter values;

Based on the three-dimensional W-M function that determines the fractal dimension and scale parameters, the contact surface model of contact surface 1 and the contact surface model of contact surface 2 are generated as shown in Figures 6 and 7 respectively, and the contact process of the contact pair is simulated through the two models.

In one embodiment of the present application, the initial parameter values are set to L=3, G=10^(-7), D=2.2, Y=1.5, M=9, nmax=20, where the contact surface model X and The coordinate axis of the Y axis is selected to avoid the 0 point. In the embodiment of the present application, the positions of the X-axis and the Y-axis are in the interval (1, 2), and the graduation interval is 0.05. And the units of the coordinate axes in the X, Y, and Z directions are all microns um.

In the embodiment of the present invention, it is assumed that the roughness of the rough surfaces of the jack and the pin is the same, and there are only slight differences, so the initial parameters can be kept unchanged. In addition, because the φ _{m, n} phase set by equation (2) is a random number obeying a uniform distribution on (0, 2π), the randomness of the phase can express the randomness of the details.

In some embodiments, Figures 6 and 7 are generated through the plot3 program in MATLAB, which can be regarded as a combination of generating two-dimensional W-M function curves at each x-axis spacing as a skeleton, and sweeping the skeleton. Finally, the contact surface model shown in Figure 6 and Figure 7 is obtained. The sweeping process makes the peak point in the skeleton the highest point in the three-dimensional image. The swept model will generally be lower than the peak position in the original image.

S3, respectively, cut the three-dimensional images in Figures 6 and 7 along the X-axis section to obtain a single line section skeleton diagram as shown in Figure 8. Figure 9 is a three-dimensional view of the single line section skeleton diagram.

S4, as shown in Figure 10, after contacting the contact surfaces of contact surface 1 and contact surface 2 according to the required contact size, select a two-dimensional curve of the contact surface at a certain point on the X-axis component. The solid line in the figure is contact surface 1, and the dotted line is contact surface 2.

In one embodiment of the present application, there are processing errors during the contact and mating process of the two contact planes, and the contact cannot be completely made according to the original size, so a variation error amount λ = 0.1um is set. As shown in Figure 10 Seeing that some parts of the dotted line have surpassed the solid line, it is considered that the two contact surfaces have come into contact. From a microscopic perspective, the convex hills intersect.

During the long-term storage and placement of electrical connectors, the surface of the contact piece is fully exposed to oxygen, which will produce an oxide film. The thickness of the oxide film on a single contact surface will also change over time. The volume growth of the oxide film is a change over time. function, as shown in formula (7).

In formula (7), A and B are parameters related to the material. Depending on the material, a>1 for the material that promotes the oxide film, a<1 for the material that inhibits the production of the oxide film, and a=1 under normal circumstances.

In one embodiment of the present application, it is considered that the oxide film grows uniformly on the contact surface of the metal, so the volume of the oxide film can be calculated according to equation (7), and the volume of the oxide film covering the metal can be calculated through equation (8). Surface thickness.

Oxidation corrosion products uniformly cover the metal surface, covering the surface area like a thin film layer. The thickness θ of the corrosion products is calculated by formula (8). X=1.2 in Figure 10

In one embodiment of the present application, θ=0.1um is calculated. .

As shown in Figure 11, it is a schematic diagram of two-dimensional line contact between two contact surfaces. The two endpoints of the contact part are marked in the figure.

In the process of judging the contact spots, it is necessary to consider whether the oxide film is worn away during the contact between the two contact pairs, and then whether the resistance generated somewhere is film resistance or shrinkage resistance.

According to formula (1), the height of the entire three-dimensional contact surface can be expressed by z(x,y). Therefore, the height difference of the contact surface after contact can be expressed by formula (9),

Δz＝z ₁ (x,y)-z ₂ (x,y)-λ (9)

In one embodiment of the present invention, because the contact surface is covered with an oxide film, if the height difference between the two points is less than 2θ = 0.2um, it is considered that the oxide film here has not broken during the contact process. At this time, the contact spot And oxidation corrosion products produce film layer resistance. On the contrary, it is considered that the oxide film has been broken, and the contact between the contact surfaces produces shrinkage resistance.

After judging whether the intersection is shrinkage resistance or film resistance, the contact surface at the intersection is considered to be circular, so find and determine the size of the contact spot and its diameter.

S5: Repeat step S4 until the number of all oxide film spots and the number of contact spots on the electrically connected contact surface are determined.

S6, Figure 12 is a contact resistance calculation flow chart. In the figure, Xi represents a two-dimensional W-M curve represented on the Head.

Figure 13 shows a schematic diagram of the computer program simulating film resistance and shrinkage resistance. The black spots are represented as oxide film spots, and the hollow spots are contact spots. Finally, calculate the radius of each spot and put it into formula (10) to calculate the contact resistance under the unit square of the contact surface, where R _j is the contact resistance and a _sp is the radius corresponding to the Pth contact spot. ;a _bk is the radius corresponding to the kth oxide film spot, n is the number of contact spots, and m is the number of oxide film spots.

The above only describes the basic principles and preferred embodiments of the present invention. Those skilled in the art can make many changes and improvements based on the above description, and these changes and improvements should fall within the protection scope of the present invention.

Claims (7)

1. A method for calculating the contact resistance of an electrical connector under storage conditions, which is characterized by specifically including: S1, measure the contact surface of the electrical connector to obtain the initial parameter values of the three-dimensional W-M function; S2, establish two contact surface models of the electrical connector based on the three-dimensional W-M function determined by the initial parameter values; S3, two cross-sectional skeleton diagrams are obtained based on the two contact surface models of the electrical connector; S4, select two two-dimensional curves at the corresponding positions of the two cross-sectional skeleton diagrams based on the preset components, and compare the heights of the two-dimensional curves to determine whether the contact surface produces film resistance or shrinkage resistance, and determine the contact spots. The number and diameter of oxide film spots; S5, repeat step S4 until the selection of all two-dimensional curves in the X-axis interval range is completed, thereby determining the number of all oxide film spots and contact spots on the electrical connection contact surface; S6, calculate the film layer resistance value and shrinkage resistance value based on the diameter of each contact spot and oxide film spot, and the number of all contact spots and oxide film spots, thereby obtaining the contact resistance value. 2. The method for calculating contact resistance under storage conditions of an electrical connector according to claim 1, characterized in that in step S1, the contact surface of the electrical connector is measured to obtain the initial value of the three-dimensional W-M function, which specifically includes: S11. Measure the height of the contact surface to obtain the Z(x) curve of multiple sections, that is, the two-dimensional WM function S12. Perform Fourier transformation on the two-dimensional WM function to obtain the power spectrum of the surface profile. S13. Take the logarithm of both sides of the power spectrum to get S14. Based on the linear relationship between lgP(ω) and lgω and the profile of the measured surface, the fractal dimension D and scale parameter G are calculated as the initial value of the three-dimensional W-M function. 3. The method for calculating contact resistance under storage conditions of an electrical connector according to claim 1, characterized in that, in step S1, the contact surface of the electrical connector is measured to obtain the initial value of the three-dimensional W-M function, which specifically includes: S11’, measure the roughness Ra of the contact surface; S12’, based on the roughness Ra, formula (1) and formula (2) respectively obtain the fractal dimension D and scale parameter G, 4. The method for calculating contact resistance under storage conditions of an electrical connector according to any one of claims 2 or 3, characterized in that, in step S2, two parameters of the electrical connector are established based on the three-dimensional W-M function that determines the initial parameter value. Contact surface model, including: Two contact surface micrographs are generated based on the three-dimensional W-M function determined by the initial parameter values, which is used to simulate the contact process of the electrically connected contact surface, where the three-dimensional W-M function is L is the sampling length, D is the fractal dimension in three dimensions, 2<D<3, G is the scale parameter, γ is the randomness and frequency of the curve phase, m is the number ratio of convexities and depressions in the contact surface macrogram, n is a sequence of natural numbers, φ _m,n is a random number uniformly distributed in the (0, 2π) interval. 5. The method for calculating contact resistance under storage conditions of an electrical connector according to claim 4, characterized in that step S3 specifically includes: cutting the two contact surface micrographs along the X-axis cross-sectional direction to obtain the first first contact surface. Single line section skeleton diagram of the contact surface and the second contact surface. 6. The method for calculating contact resistance under storage conditions of an electrical connector according to claim 4, wherein step S4 specifically includes: S41. Select two-dimensional curves at the same position on the X-axis of the single line section skeleton diagram of the first contact surface and the second contact surface based on the preset components; S42, calculate the height difference Δz of the two curves=z ₁ (x, y)-z ₂ (x, y)-λ, where z ₁ (x, y) is the height of the first curve, z ₂ (x, y) ) is the height of the second curve, λ is the variation error, and θ is the thickness of the oxide film covering the metal surface; S43, if the height difference is less than or equal to 2θ, it is considered that the contact spot and the oxidized corrosion product produce film resistance. If not, it is judged whether the height difference is greater than 0. If it is greater than 0, the part of the contact spot is considered to be shrinkage resistance. Otherwise, there is nothing here. Contact resistance. 7. The method for calculating contact resistance under storage conditions of an electrical connector according to claim 6: step S6 specifically includes: obtaining the contact resistance value based on formula (3), Among them, R _j is the contact resistance, a _sp is the radius corresponding to the P-th contact spot; a _bk is the radius corresponding to the k-th oxide film spot, n is the number of contact spots, and m is the number of oxide film spots.