CN117473728A - Electric connector contact evaluation method considering jack closing-in amount and gold-plating layer thickness - Google Patents
Electric connector contact evaluation method considering jack closing-in amount and gold-plating layer thickness Download PDFInfo
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Abstract
The invention provides an electric connector contact evaluation method taking the jack closing-up amount and the thickness of a gold-plating layer into consideration, which comprises the steps of establishing a storage reliability model, carrying out an accelerated degradation experiment and carrying out contact storage life evaluation, wherein the establishment of the storage energy model comprises the establishment of a contact mechanical model, an accelerated degradation model of contact performance of the contact and a storage reliability statistical model of the electric connector contact; the accelerated degradation experiment comprises a test object, a test acceleration factor, a test stress level, a test sample size, a measurement time interval, test parameters and failure criteria thereof, preparation before test development, a test method and a test combination mode; and according to the obtained contact reliability life functions under each closing-in amount group, substituting the contact reliability life functions into parameters to calculate the reliability life estimated values of the contact pieces with different coating thicknesses under different closing-in amounts at the storage temperature, and evaluating the storage life of the contact pieces, thereby providing theoretical basic data for evaluating the storage life of the contact pieces of the electric connector.
Description
Technical Field
The invention relates to the technical field of electric connectors, in particular to an electric connector contact evaluation method considering jack closing-in quantity and gold-plating layer thickness.
Background
The electric connector is an important electronic component for bearing the functions of circuit connection, electric signal transmission and the like in an aerospace model system, and the reliability level of the contact serving as a key component for realizing the electric signal transmission function of the electric connector directly influences the overall reliability of the electric connector. Among the components, the contact is one of the key components affecting the reliability of the electrical connector, and its contact performance can directly affect the overall reliability level of the electrical connector.
The traditional research method generally performs various performance surveys on the whole electric connector, but with the continuous development of technology, the model specification of the electric connector is gradually increased, if the reliability evaluation of each model electric connector is to be completed through the test, a great deal of manpower, material resources and financial resources are required, the consumed time period is long, and the test is difficult to complete the whole coverage.
Because the thickness of different gold plating layers and the closing-up amount have different influence degrees on the contact performance degradation or the storage life of the contact, in order to deeply explore the influence rules of the two design parameters on the storage life of the contact of the electric connector, the influence mechanism of the closing-up amount and the thickness of the gold plating layers on the contact performance degradation of the contact under the storage condition is revealed from the aspect of failure mechanism, a contact performance degradation model considering the closing-up amount and the thickness of the gold plating layers is established, the storage life of the contact under the different closing-up amount and the plating thickness level is evaluated, and theoretical basic data is provided for the storage life evaluation of the contact of the electric connector.
Disclosure of Invention
(one) solving the technical problems
Aiming at the defects of the prior art, the invention provides an electric connector contact evaluation method considering the jack closing-in amount and the thickness of a gold-plating layer, and solves the problems in the background art.
(II) technical scheme
In order to achieve the above purpose, the invention is realized by the following technical scheme: the method for evaluating the electric connector contact by considering the jack closing-in amount and the thickness of the gold plating layer takes a slotted closing-in contact as a research object, provides a reference method and a reference basis for evaluating the service life of the slotted closing-in contact under the storage condition, and comprises the following steps:
s101: establishing a contact storage reliability model considering the closing-in amount and the thickness of the gold-plating layer, wherein the contact storage reliability model is specifically as follows:
preferably, the contact mechanics model:
insertion and extraction force F c Satisfies the following relation
Wherein N is the number of reeds of the jack; μ is the coefficient of friction between the standard pin (the test optical pin made for testing the insertion and extraction force of the jack, and having an outside diameter and surface roughness meeting the requirements) and the jack; e represents the elastic modulus of the jack reed material;representing the average closing-in amount of each reed of the jack; r as shown in FIG. 2 1 The inner diameter of the root of the reed is the inner wall radius before the reed closes; r is R 2 Is the radius of the surface of the contact pin; as shown in FIG. 3, R 3 、R 4 Respectively represents the outer radius and the inner radius of the reed; />L is the total length of the cantilever end of the reed; r is R k To simplify the radius of curvature of the back socket spring fillet at the contact area.
Preferably, the degradation trajectory model:
the degradation track model of the contact performance of the contact at the time t can be expressed as:
r＝r 0 +α c t β
wherein r is 0 Beta is a model parameter unrelated to temperature stress; a, a c Representing the contact performance degradation rate;
preferably, the contact performance of the contact accelerates the degradation equation:
degradation rate alpha c The lognormal mean expression of (2) is as follows
Wherein E (·) represents a mathematical expectation; z 1 = lnA, a is a constant independent of the gold plating thickness, the amount of shrinkage, and the temperature; z 2 ＝-βΔE/k；c＝2β；
Preferably, the storage reliability statistical model:
the time to first exceed the failure threshold is noted as the life of the contact at the corresponding stress level. Let the life value of the contact be T e The failure threshold of the contact resistor is D, and the reliability function of the contact piece is at t time;
wherein Φ {.cndot. } represents a standard normal distribution function; wherein mu α Representing the degradation rate alpha c Log-normal mean, sigma α Representing the degradation rate alpha c Is a logarithmic normal standard deviation of (c).
S102: making an acceleration test scheme of the contact piece of the electric connector:
confirming the matrix material, the thickness of the gold-plated layer and the plugging force of the jack after closing up of the study object; testing an acceleration factor, taking the temperature as the acceleration factor, and accelerating the degradation rate of the contact performance of the contact piece by increasing the temperature on the premise of unchanged failure mechanism; confirming a test stress level, wherein the number of the stress levels is greater than or equal to 4, and respectively taking the lowest stress level, the highest temperature stress level and the middle stress level; confirming the test sample quantity, and taking 10 or more test samples; confirming a measurement time interval, and determining the measurement time interval under each temperature stress level according to a 10 ℃ rule; confirming test parameters and failure criteria thereof, wherein the test state of the contact is a plug and a contact, and when the contact resistance is greater than a certain value, the contact is considered to have failed; preparing before the experiment is carried out according to the experiment requirement; the method adopts the Kelvin four-wire method to measure the contact resistance of the contact as a test method; based on an orthogonal test method, an orthogonal table is prepared as a test combination mode, a closing-in contact piece is taken as a test object, and an acceleration test scheme is preliminarily formulated according to the read layer thickness and the plugging force calibration value of the contact piece.
S103: contact shelf life assessment:
preferably, the contact reliability life function for each group of closing amounts:
t R ＝exp{[σ α Φ -1 (1-R e,i )+ln(D-r 0 )-μ α,i ]/β}
and substituting the parameters to calculate the estimated reliability life values of the contact pieces with different coating thicknesses at different closing-in amounts at the storage temperature.
(III) beneficial effects
The invention provides an electric connector contact evaluation method considering jack closing-up amount and gold-plating thickness.
The beneficial effects are as follows:
1. according to the scheme, the slotted closing-in type contact is taken as a research object, a reference method and a reference basis are provided for service life assessment under the storage condition, from the failure mechanism perspective, the influence mechanism of closing-in quantity and gold-plating layer thickness on contact performance degradation of the contact under the storage condition is revealed, a contact performance degradation model considering the closing-in quantity and the gold-plating layer thickness is established, the storage service lives of the contact under different closing-in quantity and plating layer thickness levels are assessed, and theoretical basic data are provided for storage service life assessment of the contact of the electric connector.
Drawings
FIG. 1 is an overall flow chart of the present invention;
FIG. 2 is a schematic illustration of a cantilever mechanical model of the present invention;
figure 3 is a schematic cross-sectional view of a four-slot jack reed of the present invention;
FIG. 4 is a schematic diagram showing the current generation shrinkage of the conductive contact surface according to the present invention;
fig. 5 is a schematic diagram of the kelvin four-wire method of the present invention.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is apparent that the described embodiments are some embodiments of the present invention, but not all embodiments, and all other embodiments obtained by persons of ordinary skill in the art without making any inventive effort based on the embodiments of the present invention are within the scope of protection of the present invention.
The invention is described in further detail below with reference to the attached drawing figures:
the embodiment of the invention provides an electric connector contact evaluation method considering jack closing-in amount and gold plating thickness, which is used for analyzing the actual contact state of a slotted closing-in contact of an electric connector and analyzing the contact state of the contact by combining structural characteristics of the slotted closing-in contact and the inner wall of a reed.
As shown in fig. 1, the embodiment provides a method for evaluating reliability of an electrical connector contact by considering the influence of the closing-in amount of a jack and the thickness of gold plating, and in combination with the plugging characteristic of the contact, in order to facilitate calculation, the spring deformation process can be simplified into a fixed end cantilever beam mechanical model, as shown in fig. 2, the total length L of the cantilever end of the spring; the inner diameter of the root of the reed is the inner wall radius R before the reed closes 1 The method comprises the steps of carrying out a first treatment on the surface of the Pin surface radius R 2 The method comprises the steps of carrying out a first treatment on the surface of the The closing-in quantity f generated by closing-in the jack reed; the contact describing the relation between the closing-in amount and the plugging force is established by the reed corner theta and the deflection delta generated in the process of inserting the contact pin into the jackThe method comprises the steps of (1) a mechanical model, deducing a contact performance degradation track model of a contact piece considering the closing-in amount and the thickness of a gold-plated layer, establishing a storage reliability statistical model of the contact piece by combining a statistical distribution theory, and formulating a contact piece acceleration test scheme taking temperature as acceleration stress and taking the closing-in amount (plug force) and the thickness of the gold-plated layer as design variables and a contact piece storage life assessment method.
Contact resistance model of contact:
in the field of electrical contact, the contact area formed by the contact surfaces of conductive metals or metalloids constitutes a truly effective contact conductive area, and these exposed contact points of conductive metals are called "contact spots" and are lightly cold welded together as a sole conductive path as a result of external forces.
When the contact is energized, the current wire will shrink near the contact spot, increasing the path of current through the contact interface, thereby creating a local parasitic resistance-the "shrink resistance," denoted as "r s ", as shown in fig. 4. According to the quantum mechanics theory, because of the extremely thin oxide film on the surface of the contact, when electron current is conducted between the contact surfaces through the oxide film by "tunneling effect", another additional resistance, namely "film resistance", is generated, which is denoted as "r m ". The sum of the shrink resistance and the film resistance of the contact when the current is conducted is referred to as the contact "additional contact resistance".
The additional contact resistance r generated on the single leaf spring of the contact jack can be made c,i Can be recorded as
r c,i ＝r s,i +r m,i (1)
Wherein r is s,i Representing the shrinkage resistance formed when the ith reed of the jack contacts with the contact pin; r is (r) m,i Representing the film resistance formed when the ith spring leaf of the jack is contacted with the contact pin.
For slotted, necked-in contacts, the total additional contact resistance on the contact may be expressed as
Wherein r is c Representing the total additional contact resistance of the contact; n represents the number of contact jack reeds.
The contact after leaving the factory has an integral resistance, which is marked as r, due to the influence of the material characteristics of the contact v As shown in FIG. 4, the total contact resistance r of the contact is
The method for evaluating the reliability of the contact of the electric connector by considering the influence of the closing-in amount of the jack and the thickness of the gold plating comprises the following steps:
s101, establishing a contact storage reliability model considering the closing-in amount and the thickness of the gold-plating layer:
contact mechanics model:
a is a long half shaft of an elliptic contact surface, b is a short half shaft of the elliptic contact surface, R k To simplify the radius of curvature of the back jack reed fillet in the contact region, R z In order for the pin to be of a radius,to simplify the axis crossing angle of jack reed and contact pin on the rear contact area
The total volume of the distributed pressure on the semiellipsoid should theoretically be equal to the total average pressure F on the contact surface, according to the equilibrium conditions r The compressive stress distribution function is integrated to obtain:
wherein q is max Is the maximum compressive stress on the contact surface. It is known that the maximum compressive stress on the contact surface is 3/2 times the average compressive stress, and that the maximum compressive stress point occurs at the center O of the ellipse.
The moment of inertia of the section about the neutral axis can be calculated as
Wherein y is 1 Is the distance from the centroid of the reed to the circle center; a is the cross-sectional area of the reed; r is R 3 、R 4 Respectively represents the outer radius and the inner radius of the reed; from fig. 2, ρ is the half angle value of the angle between the outer rings of the reed.
The average closing-up amount of each reed of the jack isThe reed deflection may be expressed in connection with fig. 2 as reed deflection delta
The actual deflection length L of the jack reed in the contact area is combined with the actual contact state of the contact piece 0 Should be expressed as
L o ＝L-R k (7)
Where L is the total length of the cantilever end of the reed.
When the plug force is tested, the peak value of the quick rising stage of the plug force is taken as the test result of the plug force, and the plug force is the maximum plug force of the contact piece at the moment and is generated by the maximum contact pressure on the contact surface, so that the plug force F obtained by the actual test is obtained c Satisfies the following relation
Wherein E represents the elastic modulus of the jack reed material.
Because it is relatively difficult to monitor or measure the contact pressure, the contact pressure of the contact surface is usually reflected indirectly by measuring the insertion force of the contact, and the peak value of the rapid rising stage of the insertion force is used as the insertion force test result when the insertion force is tested, and the insertion force is the maximum insertion force of the contact, and is generated by the maximum contact pressure on the contact surface, so that the insertion force F obtained by the actual test c Satisfies the following relation
Wherein N is the number of reeds of the jack; μ is the coefficient of friction between the standard needle and the socket.
The formula (9) shows the mathematical relationship between the plugging force obtained by the test and the closing-in amount of the contact, under the condition that each parameter of the contact is determined, the larger the closing-in amount of the contact is, the larger the plugging force is, the size of the closing-in amount of the contact is represented by the plugging force, the plugging force is converted into the corresponding closing-in amount and then is substituted into a model for calculation, and the influence rule of different closing-in amounts on the contact performance and the storage life of the contact can be obtained.
Considering a contact performance degradation track model of the closing-in amount and the thickness of the gold-plating layer:
for the bulk resistance, summing the bulk resistance of the contact pin and the receptacle gives the overall resistance of the contact as
In the method, in the process of the invention,representing the bulk resistance of the pin; />Representing the bulk resistance of the jack.
For the contraction resistance, the contraction resistance of the single-piece reed can be expressed as if m contact spots are provided to generate the contraction resistance in the whole contact area
In the method, in the process of the invention,a pinch resistance generated at a single contact spot; ρ v Representing the resistivity of the material at standard temperature;/>the average envelope radius of the contact spot for the contact region.
The surface contact pressure is generated on the surface of the contact member due to the external pressure. The relation between the contact pressure and the microscopic contact spot area is satisfied
Wherein ζ is a pressure factor; h is the contact hardness of the contact surface.
Substituting formula (12) into the contraction resistance expression (11) can obtain the contraction resistance of the single-piece reed as follows:
the sheet resistance on a single leaf spring can be expressed as:
in the method, in the process of the invention,is the average tunnel resistivity of the surface film layer.
At oxide film thickness less than 3nm, its average tunnel resistivityAnd average film thickness->The following relation is satisfied:
wherein k is 1 And c is a constant.
The rate at which oxide volumes are formed at the individual pores satisfies the following relationship:
wherein V is t Generating a volume of oxide; k is the chemical reaction rate and is related to the temperature T.
Λ is a frequency factor; ΔE is activation energy (eV); k is Boltzmann constant (8.617 ×10) -5 eV/K); t is the temperature in degrees Celsius (C.).
Assuming that all of the oxide formed is uniformly covered on the contact surface, the average thickness of the oxide film layer on the contact surface is as follows:
wherein ε d Is a coefficient to be determined; d is the thickness of the gold plating layer; ζ is a parameter related to the plating process, the material, and the like.
The external average pressure on the contact surface is generated by elastic deformation of the jack cantilever reed, and the film resistance generated at the position of the single reed can be obtained after finishing is as follows:
in summary of the above derivation, the overall mathematical expression for the contact resistance of the contact is obtained by the arrangement:
in the above formula, since the calculated parameters of the bulk resistance and the shrinkage resistance are mainly determined by the parameters of the material itself, the structure and the process parameters thereof, they can be regarded as constant values, and they are denoted as r 0 . Since the contact resistance increase is mainly affected by the film resistance, a degradation track model of the contact performance of the contact is obtained, which is expressed as follows:
r＝r 0 +α c t β (20)
in the method, in the process of the invention,is a model parameter which is irrelevant to temperature stress;
representing the contact performance degradation rate.
Accelerated degradation model of contact performance of a contact:
when the temperature stress is taken as an acceleration factor, the deduced degradation track model can be arranged to obtain a relational expression between the contact performance degradation rate and the temperature of the contact element, namely
In the method, in the process of the invention,expressed as a temperature independent coefficient; />Is constant independent of the thickness, the closing-up amount and the temperature of the gold plating layer.
Analysis of the above features shows that when the logarithm is taken on the left and right sides of the expression, the right side of the expressionContains more random coefficients, which can be considered to be approximately subject to a normal distribution, i.e.>Obeying the lognormal distribution, the degradation rate alpha c Also obeys the lognormal distribution, i.e. +.>Wherein mu α Representing the degradation rate alpha c Log-normal mean, sigma α Representing degradation rateα c Is a logarithmic normal standard deviation of (c).
Will lnα c Is arranged and substituted into the mathematical expectation degradation rate alpha of each coefficient c The lognormal mean expression of (c) is as follows:
wherein E (·) represents a mathematical expectation; z 1 ＝lnA；z 2 ＝-βΔE/k；c＝2β；Storage reliability statistical model of electrical connector contacts:
the time to first exceed the failure threshold is noted as the life of the contact at the corresponding stress level. If the failure threshold value of the contact resistance of the contact is set as D, in the storage state, the contact resistance of the contact at a certain time t gradually increases along with the extension of time, and the degradation rate of the contact performance of the known contact is subject to lognormal distribution, and the service life distribution function of the contact can be expressed by combining with a statistical distribution theory:
wherein T is e Indicating the life of the contact; Φ {.cndot. } represents a standard normal distribution function.
At time t, the reliability function of the contact is:
s102, making an acceleration test scheme of the contact of the electric connector, which comprises the following steps:
(1) Test subjects
The patent research object is a 3.5mm aperture slotted closing-in contact of a certain type of electric connector, wherein the jack matrix material is tin bronze. Directly plating gold on the copper surface of the contact substrate to divide the thickness of the gold plating layer into four grades of 0.8 mu m, 1.0 mu m, 1.2 mu m and 1.4 mu m; the end part of the jack reed adopts a closing-up process, so that the plug force of the jack after closing-up is divided into four grades of 3.2N, 3.4N, 3.6N and 3.8N.
(2) Test acceleration factor
The temperature is taken as an acceleration factor, and the degradation rate of the contact performance of the contact piece is accelerated by increasing the temperature on the premise of unchanged failure mechanism.
(3) Test stress level
In GB2689.1-1981 general rules of constant stress life test and accelerated life test methods, it is specified that the number of stress levels in a complete accelerated test is not less than four. The stress level m=4 was taken for this test. The minimum stress level should be as close as possible to the actual storage environment temperature. However, if the minimum temperature stress is set too low, the test period will be longer, taking the minimum stress level T 1 =105℃. The maximum temperature stress level T of the test is controlled strictly within a known safe range 4 =158℃. The intermediate stress level can be selected according to the principle of equal interval, and the intermediate stress level T is obtained after the intermediate stress level T is further rounded for the convenience of test temperature setting 2 =120 ℃ and T 3 ＝140℃。
(4) Test sample size
According to the requirements of GB2689.1-1981, the test sample size should be no less than 10 at each stress level, and the accelerated test will deliver an additional 5 pairs of contacts (i.e. 15 pairs of contacts in each test group) in each test group.
(5) Measuring time interval
During the experimental test, contact resistance tests are typically performed using equally spaced time measurements. With reference to previous study experience, according to the rule of 10 ℃, the measurement time interval at each temperature stress level is determined by
Stress levels were tested at 158 ℃ groups every 12 hours;
stress levels were tested at 140 ℃ groups every 24 hours;
stress levels were tested at 120 ℃ groups every 72 hours;
stress levels were tested at 105 ℃ groups every 120 hours.
The subsequent test time interval can be properly adjusted according to the actual test conditions.
(6) Test parameters and failure criteria thereof
According to the specification of a certain rectangular separation drop-off electric connector and a product design manual, the contact failure criterion of the contact element in the test research is determined as follows: the contact test state is a 3.5mm aperture contact of a plug and a single-layer socket, and when the contact resistance is greater than 1.0mΩ, the contact is considered to have failed.
(7) Test requirements
Before the test is carried out, the contact sample is assembled according to the test scheme; welding wires at two ends of the contact piece respectively for measuring contact resistance; the contact resistance of the contact element is measured at constant room temperature; and (3) checking whether the electric contact is firm or not and whether the resistance is stable or not by testing the initial value of the contact resistance of each contact, and replacing the contact with abnormal contact resistance data.
(8) Test method
The contact resistance of the contact element is measured by adopting the Kelvin four-wire method, the testing working principle is shown in figure 5, R 1 、R 2 、R 3 、R 4 The resistance of the lead; i v The current is the loop current of the voltmeter; I. is the ammeter loop current.
(9) Test combination mode
The method has the advantages of uniform test dispersion, neat and comparable level and the like based on an orthogonal test method, and L is selected 16 (4 5 ) The orthogonal table was used as a test combination.
Taking a slotted closing-in contact with the aperture of 3.5mm as a test object, and preliminarily making an acceleration test scheme according to the thickness of a delivery coating of the contact and a calibration value of a plugging force, wherein the acceleration test scheme comprises the following steps:
s103, evaluating the storage life of the contact, wherein the method specifically comprises the following steps of:
according to formula (22), wherein z 1 lnA is a constant independent of stress levels, z 2 The = -beta delta E/k is a variable related to the activation energy delta E, the contact pressure is increased due to the increase of the closing-in amount of the contact piece, so that the reaction activation energy is increased, and beta is a coefficient unrelated to the temperature stress level, namely z is the same when the plugging force is the same 2 The same can be obtained by fitting the z under different plugging force levels 1 、z 2 And (5) preliminary estimation value.
Record q ljkhi (l＝1,2,…,4；j＝1,2,…,4；k＝1,2,…,4；h＝1,2,…,m ljk ；i＝1,2,…,n ljk ) Represents the contact resistance value epsilon measured by the ith time of the h contact piece of the thickness of the k plating layer of the j group of plugging forces under the temperature stress of the first group ljkh (t) represents the test error generated by the h contact piece of the thickness of the k plating layer of the j group under the temperature stress of the first group at the time t, which is generally considered to be subjected to normal distribution, namelyα ljkh Representing the degradation rate of the h contact piece of the thickness of the k plating layer of the j group of plugging forces under the temperature stress of the first group; m is m ljk The number of the contact pieces representing the thickness of the k-th plating layer of the j-th plugging force under the temperature stress of the first group, and n ljk The number of times of measuring the thickness of the coating of the kth group of plug force and the kth group of coating of the jth group of plug force under the temperature stress of the first group is shown; r is (r) ljkh0 And the contact resistance value of the ith measurement of the contact resistance of the h-th contact piece of the k-th plating thickness of the j-th group of plug force under the temperature stress of the first group is shown.
According to the test errorRate of degeneration->Assuming that contact resistances of different groups of contact pieces are independently distributed in the same way, establishing a log likelihood function
Wherein,
based on the basic principle of maximum likelihood estimation, the method can be performed by solving a set of parameters (σ ε ,β,σα,z 1 ,z 2 ) So that the measured value q of the contact resistance ljkhi The probability of occurrence is maximized, i.e., a set of solutions is found that minimizes-lnL. Then in sigma ε ,β,σ α ,z 1 ,z 2 To optimize the variables, the optimization objective function is
f(σ ε ,β,σ α ,z 1 ,z 2 )＝-lnL(σ ε ,β,σ α ,z 1 ,z 2 |q ljkhi ) (26)
By MATLAB programming, using the fminesearch function with the least squares estimation result as the initial value, a set of parameters is found to be minf (σ ε ,β,σ α ,z 1 ,z 2 ) Unconstrained optimal solution of (a). The parameter beta and the parameter sigma are irrelevant to the stress level, and the estimated values under the same closing-in quantity are supposed to be the same, but the average value is taken as a parameter estimation result due to errors in experimental tests or parameter estimation. And substituting the estimated parameters into the formula (9) respectively, carrying out the contact structural parameters, converting the plugging force into the closing-in amount respectively, obtaining the maximum likelihood estimated value of the model parameters, substituting the estimated parameters into the formula (22) respectively, and obtaining the accelerating equation calculation expression under each closing-in amount group.
Substituting the thickness of the gold-plating layer and the storage environment temperature into the obtained acceleration equation calculation expression to obtain the logarithmic average value of degradation rate of different thickness of the gold-plating layer under each closing-in amount group. Combining (24) can obtain the contact reliability function under each closing-in amount group:
and (3) converting the reliability function into a reliability service life function shown in a formula (28), and substituting the reliability service life function into parameters to calculate reliability service life estimated values of the contact pieces with different coating thicknesses at different closing-in amounts at storage temperatures.
t R ＝exp{[σ α Φ -1 (1-R e,i )+ln(D-r 0 )-μ α,i ]/β} (28)
Although embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made therein without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.
Claims (7)
1. The method for evaluating the electric connector contact piece by considering the jack closing-in amount and the thickness of the gold plating layer is characterized by comprising the following steps:
s101: establishing a storage reliability model, wherein the establishment of the storage reliability model comprises the establishment of a contact mechanics model, an accelerated degradation model of contact performance of a contact piece and a storage reliability statistical model of the contact piece of the electric connector;
s102: the method comprises the steps of performing an accelerated degradation experiment, wherein the accelerated degradation experiment comprises a confirmation test object, a test acceleration factor, a test stress level, a test sample size, a measurement time interval, a test parameter and a failure criterion thereof, a preparation before test development, a confirmation test method and a test combination mode;
s103: and (3) carrying out storage life evaluation of the contact, and respectively substituting the obtained contact reliability life functions under each closing-in amount group into parameters to calculate the reliability life estimated values of the contact with different coating thicknesses under different closing-in amounts at the storage temperature.
2. The method for evaluating the electrical connector contact taking account of the jack closing-in amount and the gold plating thickness according to claim 1, wherein S101 specifically comprises:
contact mechanics model
S1011: according to the planeThe overall volume of the pressure distribution on the semiellipsoid should theoretically be equal to the total average pressure F on the contact surface r By integrating the compressive stress distribution function
Wherein q is max For the maximum compressive stress on the contact surface, the maximum compressive stress on the contact surface is 3/2 times of the average compressive stress, and the maximum compressive stress point appears at the center O of the ellipse;
s1012: calculating the moment of inertia of the section about the neutral axis as
Wherein y is 1 The distance from the centroid of the reed to the circle center is A, and the cross-sectional area of the reed is A; r is R 3 、R 4 Respectively represents the outer radius and the inner radius of the reed;
s1013: the average closing-up amount of each reed of the jack isExpressed reed deflection as reed deflection delta
The actual deflection length L of the jack reed in the contact area is combined with the actual contact state of the contact piece 0 Should be expressed as
L o ＝L-R k
Wherein L is the total length of the cantilever end of the reed;
s1014: the peak value of the rapid rising stage of the plugging force is used as the testing result of the plugging force, and the plugging force is the maximum plugging force of the contact piece at the moment and is generated by the maximum contact pressure on the contact surface, so that the plugging force F obtained by the actual test c Satisfies the following relation
Wherein E represents the elastic modulus of the jack reed material;
s1015: the contact pressure of the contact surface is indirectly reflected by measuring the plug force of the contact, the peak value of the quick rising stage of the plug force is used as the test result of the plug force, the plug force is the maximum plug force of the contact, and the maximum contact pressure on the contact surface generates the plug force F obtained by the actual test c Satisfies the following relation
Wherein N is the number of reeds of the jack; μ is the friction coefficient between the standard needle and the jack, the mathematical relationship between the plugging force obtained by the test and the closing-in amount of the contact element is expressed, and under the condition that each parameter of the contact element is determined, the larger the closing-in amount of the contact element is, the larger the plugging force is;
contact performance degradation track model considering necking quantity and gold-plating layer thickness
S1016: for the bulk resistance, summing the bulk resistance of the contact pin and the receptacle gives the overall resistance of the contact as
In the method, in the process of the invention,representing the bulk resistance of the pin; />Representing the volume resistance of the jack, a shrinkage resistor meter of a single reed is provided that m contact spots generate shrinkage resistance in the whole contact area with respect to the shrinkage resistanceShown as
In the method, in the process of the invention,shrink resistance, ρ, generated at a single contact spot v Represents the material resistivity at standard temperature, +.>For the average envelope radius of the contact spots of the contact area, the surface contact pressure is generated on the surface of the contact element under the action of external pressure, and the relation between the contact pressure and the area of the microscopic contact spots is satisfied
Wherein ζ is a pressure factor, and H is contact hardness of the surface of the contact;
s1017: substituting the relationship between the contact pressure and the microscopic contact spot area in S1016 into the contraction resistance expression of the single-sheet reed to obtain the contraction resistance of the single-sheet reed as,
the resistance of the membrane layer on the individual leaf springs is shown as,
in the method, in the process of the invention,the average tunnel resistivity of the surface film layer is +.about.H when the thickness of the oxide film layer is less than 3nm>And average film thickness->The following relation is satisfied,
wherein k is 1 And c is a constant, and the rate of oxide volume formation at a single pore satisfies the following relationship:
wherein V is t Generating a volume of oxide; k is the chemical reaction rate, which is related to the temperature T, Λ is the frequency factor, ΔE is the activation energy eV, and K is the Boltzmann constant 8.617 ×10 -5 eV/K, T is the temperature degree centigrade;
s1018: assuming that all of the oxide formed is uniformly covered on the contact surface, the average thickness of the oxide film layer on the contact surface is related to time t,
wherein ε d Is a coefficient to be determined; d is the thickness of the gold plating layer; and xi is a parameter related to a plating process, a material and the like, and because the external average pressure on a contact surface is generated by elastic deformation of the jack cantilever reed, the film resistance generated at the position of the single reed after finishing is as follows:
s1019: the overall mathematical expression for the contact resistance of the contact is sorted according to the above derivation,
in the above formula, the calculated parameters of the bulk resistance and the shrinkage resistance are mainly determined by the parameters of the material, the structure, the technological parameters thereof and the like, and are regarded as constant values and are marked as r 0 . Since the contact resistance increase is mainly affected by the film resistance, a degradation track model of the contact performance of the contact is obtained, expressed as,
r＝r 0 +α c t β
where beta is a model parameter independent of temperature stress,
wherein alpha is c Representing the contact performance degradation rate.
3. The method for evaluating the electrical connector contact taking account of the jack closing-in amount and the gold plating thickness according to claim 1, wherein S101 specifically comprises:
accelerated degradation model for contact performance of contact element
S10110: when the temperature stress is taken as an acceleration factor, the degradation track model is arranged to obtain a relational expression between the degradation rate of the contact performance of the contact element and the temperature, namely
In the method, in the process of the invention,expressed as a temperature independent coefficient, +.>Analysis of the above formula characteristics for constants independent of the thickness, the amount of shrinkage, and the temperature of the gold plating layer shows that when the logarithm is taken on both the left and right sides of the expression, the right side of the expressionContains more random coefficients, which are considered to be approximately subject to normal distribution according to the central limit theorem, i.e. +.>Obeying the lognormal distribution, the degradation rate alpha c Also obeys the lognormal distribution, i.e. +.>Wherein mu α Representing the degradation rate alpha c Log-normal mean, sigma α Representing the degradation rate alpha c Is used for the logarithmic normal standard deviation of (c),
will lnα c Is arranged and substituted into the mathematical expected degradation rate alpha of each coefficient c The log-normal mean expression of (c) is as follows,
wherein E (·) represents the mathematical expectation, z 1 ＝lnA，z 2 ＝-βΔE/k，c＝2β，
4. The method for evaluating the electrical connector contact taking account of the jack closing-in amount and the gold plating thickness according to claim 1, wherein S101 specifically comprises:
storage reliability statistical model of electric connector contact
S10111: the time when the failure threshold value is exceeded for the first time is the service life of the contact under the corresponding stress level, the failure threshold value of the contact resistance of the contact is set as D, then in the storage state, the contact resistance of the contact is gradually increased along with the time extension at a certain moment t, the contact performance degradation rate of the contact is known to obey the lognormal distribution, and the service life distribution function of the contact is obtained by combining the statistical distribution theory and is expressed as,
wherein T is e Indicating the life of the contact; phi {.cndot }, represents a standard normal distribution function, and at time t, the reliability function of the contact is,
5. the method for evaluating an electrical connector contact according to claim 1, wherein S102 specifically comprises:
s1021: confirming the matrix material, the thickness of the gold-plated layer and the plugging force of the jack after closing up of the study object;
s1022: testing an acceleration factor, taking the temperature as the acceleration factor, and accelerating the degradation rate of the contact performance of the contact piece by increasing the temperature on the premise of unchanged failure mechanism;
s1023: confirming a test stress level, wherein the number of the stress levels is greater than or equal to 4, and respectively taking the lowest stress level, the highest temperature stress level and the middle stress level;
s1024: confirming the test sample quantity, and taking 10 or more test samples;
s1025: confirming a measurement time interval, and determining the measurement time interval under each temperature stress level according to a 10 ℃ rule;
s1026: confirming test parameters and failure criteria thereof, wherein the test state of the contact is a plug and a contact, and when the contact resistance is greater than a certain value, the contact is considered to have failed;
s1027: preparing before the experiment is carried out according to the experiment requirement;
s1028: the method adopts the Kelvin four-wire method to measure the contact resistance of the contact as a test method;
s1029: based on an orthogonal test method, an orthogonal table is prepared as a test combination mode, a closing-in contact piece is taken as a test object, and an acceleration test scheme is preliminarily formulated according to the read layer thickness and the plugging force calibration value of the contact piece.
6. The method for evaluating an electrical connector contact taking into account the jack shrinkage and the gold plating thickness according to claim 5, wherein S1027 specifically comprises:
s10271: assembling the contact sample according to a test scheme;
s10272: welding wires at two ends of the contact piece respectively for measuring contact resistance;
s10273: the contact resistance of the contact element is measured at constant room temperature;
s10274: checking whether the electric contact is firm or not and whether the resistance is stable or not by carrying out initial value test of contact resistance on each contact piece;
s10275: and replacing the contact with abnormal contact resistance data.
7. The method for evaluating an electrical connector contact according to claim 1, wherein S103 specifically comprises:
s1031: according to the degradation rate alpha c Is a lognormal mean expression of (2), wherein z 1 lnA is a constant independent of stress levels, z 2 The = -beta delta E/k is a variable related to the activation energy delta E, the contact pressure is increased due to the increase of the closing-in amount of the contact piece, so that the reaction activation energy is increased, and beta is a coefficient independent of the temperature stress level, namely when the plugging force is increasedWhen the two are identical, then z 2 The z under different plugging force levels is obtained by fitting 1 、z 2 A preliminary estimated value;
s1032: record q ljkhi Represents the contact resistance value epsilon measured by the ith time of the h contact piece of the thickness of the k plating layer of the j group of plugging forces under the temperature stress of the first group ljkh (t) represents the test error generated by the h contact piece of the thickness of the k plating layer of the j group under the temperature stress of the first group at the time t, which is generally considered to be subjected to normal distribution, namely
α ljkh Represents the degradation rate, m, of the h contact piece of the thickness of the k plating layer of the j group of plugging force under the temperature stress of the first group ljk The number of the contact pieces representing the thickness of the k-th plating layer of the j-th plugging force under the temperature stress of the first group, and n ljk The number of times of measuring the thickness of the coating of the kth group of plug force and the kth group of coating under the temperature stress of the first group is expressed, and r ljkh0 The contact resistance value measured for the ith time of the contact resistance of the h-th contact piece of the k-th plating thickness of the j-th group of plugging force under the temperature stress of the first group is represented;
s1033: according to the test errorRate of degeneration->Assuming that contact resistances of different groups of contact pieces are independently distributed in the same way, establishing a log likelihood function
Wherein,based on the basic principle of maximum likelihood estimation, the method is performed by solving a set of parameters (sigma ε ,β,σα,z 1 ,z 2 ) So that the measured value q of the contact resistance ljkhi The probability of occurrence is maximized, i.e., a set of solutions is solved to minimize-lnL, then σ ε ,β,σ α ,z 1 ,z 2 To optimize the variables, the optimization objective function is
f(σ ε ,β,σ α ,z 1 ,z 2 )＝-lnL(σ ε ,β,σ α ,z 1 ,z 2 |q ljkhi )；
S1034: by MATLAB programming, using the fminesearch function with the least squares estimation result as the initial value, a set of parameters is found to be minf (σ ε ,β,σ α ,z 1 ,z 2 ) The unconstrained optimal solution of (1), wherein the parameter beta and sigma are irrelevant to the stress level, and the estimated values under the same closing-in amount are supposed to be the same, but because of errors in experimental tests or parameter estimation, the average value is taken as a parameter estimation result;
s1035: substituting the estimated parameters into the plugging force F c Relational expression, substituting structural parameters of the contact, respectively converting the plugging force into the closing-in amount to obtain maximum likelihood estimated values of model parameters, and respectively substituting the estimated parameters into degradation rate alpha c Obtaining the acceleration equation calculation expression under each closing-up quantity group;
s1036: substituting the thickness of the gold-plated layer and the storage environment temperature into an obtained acceleration equation calculation expression to obtain the average value of degradation rate pairs of different thickness of the gold-plated layer under each closing-up amount group, and combining the reliability function of the contact piece under the t moment to obtain the contact reliability function under each closing-up amount group:
s1037: converting the reliability function into a reliability life function shown in the following formula, and substituting the reliability life function into parameters to calculate reliability life estimated values of different coating thickness contact pieces at different closing-in amounts at storage temperatures
t R ＝exp{[σ α Φ -1 (1-R e,i )+ln(D-r 0 )-μ α,i ]/β}。
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