Metal Foil Conductivity Test Method

Abstract

The present invention provides a method for testing the conductivity of metal foil, which comprises: when the thickness of the metal foil to be tested is less than a first set value, providing a first relational expression between a first parameter and the conductivity of the metal foil; processing the metal foil to be tested to obtain a first metal foil to be tested and a second metal foil to be tested with different thicknesses, wherein the thicknesses of the first metal foil to be tested and the second metal foil to be tested are both less than the first set value; using an eddy current detection method to obtain the coil feedback voltage of the first metal foil to be tested and the second metal foil to be tested; using the thickness and the coil feedback voltage as parameters to obtain a first value; using the first value as a known value of the first parameter, and obtaining the conductivity of the metal foil to be tested according to the first relational expression. The testing method of the present invention can improve the accuracy of conductivity testing.

Description

Technical Field

[0001] The invention relates to the field of material testing, and in particular to a method for testing the electrical conductivity of a metal foil. Background Art

[0002] With the rapid development of consumer electronics and new energy industries, servers, PCBs, lithium batteries and other related equipment and devices are gradually developing in the direction of miniaturization, high-density interconnection and high precision, which provides a broad market space for ultra-thin copper foil. For example, PCB is developing in the direction of multi-layer and high integration, and the printed circuit graphics, line width and spacing are also developing towards miniaturization. Ultra-thin copper foil is increasingly used in fine circuits; for lithium battery metal foil, in order to meet the characteristics of high energy density and high safety of power batteries, the development of lithium battery metal foil towards lightness and thinness is a general trend. Conductivity, as an important performance indicator of metal foil, determines the application scenario of metal foil. The conductive properties of ultra-thin and thin metal foils produced by different manufacturers vary, so conductivity testing of metal foil is an important means to judge its performance.

[0003] At present, the commonly used methods for testing the conductivity of metal foil in industry include four-probe measurement method and eddy current technology detection.

[0004] The principle of the four-probe measurement method is to place four probes with equal spacing on the same straight line, so that the probes form ohmic contact with the sample, use a constant current source to apply current between probes 1 and 4, and at the same time use a high input impedance precision voltmeter to measure the voltage difference between probes 2 and 3. Finally, the conductivity of the sample can be obtained after correction by the thin layer principle and the thick block principle. Since there is contact resistance between the probe and the material, and the measurement system has internal resistance, this method is often used to measure materials with low conductivity, such as semiconductor materials; in addition, in the four-probe measurement method, the probe must be in contact with the specimen, which will cause damage to the surface of the specimen.

[0005] Eddy current technology is a non-destructive testing technology. When a coil with alternating current approaches the sample to be tested, eddy currents will be generated on the surface of the sample to be tested. The eddy currents will form a secondary magnetic field. This magnetic field interacts with the original magnetic field of the coil, causing the impedance of the coil to change, thereby changing the feedback voltage of the coil and obtaining the parameters to be tested, such as conductivity, magnetic permeability, etc. Its advantages are that it is suitable for high-conductivity samples, does not require contact with the sample, has loose requirements on the test environment and high detection accuracy. Therefore, eddy current sensors are widely used in aerospace and large-scale industrial production. However, because this method has strict requirements on the thickness of the material to be tested (the thickness of the material to be tested must be greater than three times the skin depth of the material), it is only suitable for conductivity testing of bulk metal materials. For ultra-thin metal foils and thin metal foils, the measurement accuracy of traditional eddy current technology is low.

[0006] Therefore, a new metal foil conductivity testing method is urgently needed to improve the accuracy of conductivity measurement of ultra-thin metal foil and thin metal foil. Summary of the invention

[0007] The technical problem to be solved by the present invention is to provide a method for testing the electrical conductivity of a metal foil, which can improve the accuracy of measuring the electrical conductivity of an ultra-thin metal foil or a thin metal foil.

[0008] In order to solve the above problems, the present invention provides a method for testing the electrical conductivity of a metal foil, which comprises: when the thickness of the metal foil to be tested is less than a first set value, providing a first relationship between a first parameter and the electrical conductivity of the metal foil; processing the metal foil to be tested to obtain a first metal foil to be tested and a second metal foil to be tested having different thicknesses, wherein the thicknesses of the first metal foil to be tested and the second metal foil to be tested are both less than the first set value; using an eddy current detection method to obtain coil feedback voltages of the first metal foil to be tested and the second metal foil to be tested; using the thickness and the coil feedback voltage as parameters to obtain a first value; using the first value as a known value of the first parameter, and obtaining the electrical conductivity of the metal foil to be tested according to the first relationship.

[0009] In some specific embodiments, the first relationship between the first parameter and the conductivity of the metal foil is the relationship between the first parameter and the square of the conductivity of the metal foil:

[0010] Y=k1σ 2 +b1

[0011] Among them, Y is the first parameter, σ is the conductivity of the metal foil, and k1 and b1 are constants.

[0012] The method for obtaining constant k1 and constant b1 includes: obtaining the thickness of at least two metal foil standard samples of different thicknesses in a first standard sample group and obtaining the coil feedback voltage of the metal foil standard samples by an eddy current detection method, obtaining the thickness of at least two metal foil standard samples of different thicknesses in a second standard sample group and obtaining the coil feedback voltage of the metal foil standard samples by an eddy current detection method, the first standard sample group has a first conductivity, the second standard sample group has a second conductivity, and the thickness of the metal foil standard samples in the first standard sample group and the second standard sample group are both less than the first set value; taking the thickness of the metal foil standard samples in the first standard sample group and the coil feedback voltage as parameters to obtain the first constant, and taking the thickness of the metal foil standard samples in the second standard sample group and the coil feedback voltage as parameters to obtain the second constant; taking the first constant and the second constant as known first parameters and the first conductivity and the second conductivity as known metal foil conductivity, obtaining the constant k1 and constant b1 according to the first relationship.

[0013] In a specific implementation, the relationship between the first constant is:

[0014] C1=(ln(U A2 )-ln(U A1 )) / (ln(t A2 )-ln(t A1 ))

[0015] Among them, C1 is the first constant, U A1 is the coil feedback voltage of the first metal foil standard sample in the first standard sample group, U A2 is the coil feedback voltage of the second metal foil standard sample in the first standard sample group, t A1 is the thickness of the first metal foil standard sample in the first standard sample group, t A2 is the thickness of the second metal foil standard sample in the first standard sample group; the relationship formula of the second constant is:

[0016] C2=(ln(U B2 )-ln(U B1 )) / (ln(t B2 )-ln(t B1 ))

[0017] Among them, C2 is the second constant, U B1 is the coil feedback voltage of the third metal foil standard sample in the second standard sample group, U B2 is the coil feedback voltage of the fourth metal foil standard sample in the second standard sample group, t B1 is the thickness of the third metal foil standard sample in the second standard sample group, t B2 is the thickness of the fourth metal foil standard sample in the second standard sample group.

[0018] In one embodiment, the difference between the first conductivity and the second conductivity is greater than or equal to 30% IACS.

[0019] In a specific embodiment, the step of processing the metal foil to be tested to obtain at least two metal foils with different thicknesses includes: thickening or thinning the metal foil to be tested to obtain metal foils with different thicknesses.

[0020] In a specific implementation, the relationship between the first value is:

[0021] Y1=ln(U E2 )-ln(U E1 )) / (ln(t E2 )-ln(t E1 ))

[0022] Wherein, Y1 is the first value, U E1is the coil feedback voltage of the first metal foil to be tested, U E2 is the coil feedback voltage of the second metal foil to be tested, t E1 is the thickness of the first metal foil to be tested, t E2 is the thickness of the second metal foil to be tested.

[0023] In a specific embodiment, when the thickness of the metal foil to be measured is greater than or equal to a second set value, a second relationship between a second parameter and the electrical conductivity of the metal foil is provided, and the second set value is greater than the first set value; an eddy current detection method is used to obtain the coil feedback voltage of the metal foil to be measured; the obtained coil feedback voltage is used as the second parameter, and the electrical conductivity of the metal foil to be measured is obtained according to the second relationship.

[0024] In a specific embodiment, the second relationship between the second parameter and the conductivity of the metal foil is:

[0025] ln(U)=k2ln(σ)+b2

[0026] Wherein, U is the second parameter, σ is the conductivity of the metal foil, and k2 and b2 are constants.

[0027] In a specific embodiment, the method for obtaining constant k2 and constant b2 includes: obtaining the conductivity of two metal foil standard samples with different conductivity, the thickness of the metal foil standard samples being greater than the second preset value; using an eddy current detection method to obtain the coil feedback voltage of the two metal foil standard samples; using the conductivity and the coil feedback voltage as known parameters, obtaining the constant k2 and constant b2 according to the second relationship.

[0028] In a specific embodiment, when the thickness of the metal foil to be tested is less than the second set value and greater than the first set value, the metal foil to be tested is thickened to make the thickness greater than the second set value, and the conductivity test is performed on the thickened metal foil to be tested.

[0029] In a specific embodiment, the method of thickening the metal foil to be tested includes stacking multiple layers of the metal foil to be tested.

[0030] In a specific implementation, the thickness of the metal foil to be measured is obtained, and the relationship between the thickness of the metal foil to be measured and the first set value and the second set value is determined.

[0031] In a specific embodiment, the first setting value is less than one time of the skin depth, and the second setting value is greater than three times of the skin depth.

[0032] The metal foil conductivity testing method of the present invention establishes the relationship between coil feedback voltage, thickness and conductivity based on the eddy current principle, and calculates and inversely infers the conductivity of the metal foil to be tested by testing the coil feedback voltage and thickness of the metal foil to be tested. The method has the advantages of non-destructiveness and high test accuracy (error less than 2%) of the traditional eddy current technology, and the eddy current technology detection is no longer limited by the thickness of the material to be tested, and is suitable for metal foils with a thickness less than one skin depth, such as metal foils with a thickness less than 100 microns. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a schematic diagram of the steps of a method for testing the electrical conductivity of a metal foil provided by a specific embodiment of the present invention;

[0034] Figure 2 This is a flow chart of a method for testing the electrical conductivity of a metal foil provided by a specific embodiment of the present invention.

[0035] Figure 3 It is a schematic diagram of the linear relationship of ln(t)-ln(U) when the conductivity of metal foil is different;

[0036] Figure 4 is the relationship between the first parameter and the square of the conductivity of the metal foil;

[0037] Figure 5 It is a theoretical error diagram of the metal foil conductivity testing method of the present invention;

[0038] Figure 6 This is a graph showing the relationship between the number of metal foil layers and electrical conductivity. DETAILED DESCRIPTION

[0039] The specific implementation of the metal foil conductivity testing method provided by the present invention is described in detail below with reference to the accompanying drawings.

[0040] Figure 1 1 is a schematic diagram of the steps of a method for testing the electrical conductivity of a metal foil provided by a specific embodiment of the present invention. Figure 2 This is a flow chart of a method for testing the conductivity of a metal foil provided by a specific embodiment of the present invention. Figure 1 and Figure 2 , the method comprising:

[0041] Step S10: When the thickness of the metal foil to be measured is less than a first set value, a first relationship between a first parameter and the conductivity of the metal foil is provided.

[0042] Before performing the step, in this specific embodiment, the following steps are further included: measuring the thickness of the metal foil to be measured, and determining whether the thickness of the metal foil to be measured is greater than or equal to a first set value. If the thickness of the metal foil to be measured is less than the first set value, step S10 is executed. Optionally, if the thickness of the metal foil to be measured is greater than or equal to the first set value, step S20 is executed.

[0043] Further, the first set value is less than one skin depth. In this specific embodiment, the first set value is taken as 100 microns. It can be understood that in other specific embodiments, the first set value can also be other values as long as it is less than one skin depth.

[0044] In this specific embodiment, the first relationship between the first parameter and the metal foil conductivity is the relationship between the first parameter and the square of the metal foil conductivity. The relationship between the first parameter and the square of the metal foil conductivity is as shown in Equation (1).

[0045] Y = k1σ 2 + b1 (1)

[0046] where Y is the first parameter, σ is the metal foil conductivity, and k1 and b1 are constants.

[0047] The present invention also provides a method for obtaining the constant k1 and the constant b1. The method includes the following steps:

[0048] Obtaining the thicknesses of at least two metal foil standard specimens with different thicknesses in the first standard specimen group and the coil feedback voltages of the metal foil standard specimens obtained by using the eddy current detection method, obtaining the thicknesses of at least two metal foil standard specimens with different thicknesses in the second standard specimen group and the coil feedback voltages of the metal foil standard specimens obtained by using the eddy current detection method. The first standard specimen group has a first conductivity, the second standard specimen group has a second conductivity, and the thicknesses of the metal foil standard specimens in the first standard specimen group and the second standard specimen group are all less than the first set value.

[0049] For example, in this specific embodiment, the first metal foil standard specimen A1 and the second metal foil standard specimen A2 in the first standard specimen group, and the third metal foil standard specimen B1 and the fourth metal foil standard specimen B2 in the second standard specimen group are provided.

[0050] The first metal foil standard specimen A1 and the first metal foil standard specimen A2 have the same conductivity, both being the first conductivity σ A ; the third metal foil standard specimen B1 and the fourth metal foil standard specimen B2 have the same conductivity, both being the second conductivity σ BThat is, the electrical conductivities of the first metal foil standard sample A1, the second metal foil standard sample A2, the third metal foil standard sample B1, and the fourth metal foil standard sample B2 are known numbers.

[0051] In a specific embodiment, the first metal foil standard sample A1 and the first metal foil standard sample A2 are selected according to the first conductivity σ A With the second conductivity σ B The difference is greater than or equal to 30% IACS. Since the first relation is an approximate relation, if the first conductivity σ A With the second conductivity σ B The difference between them is not big. Within the test range, the deviation of the first relation may be large. Therefore, in order to improve the accuracy of the first relation, that is, to improve the accuracy of the test, the first conductivity σ A With the second conductivity σ B The difference is greater than or equal to 30% IACS.

[0052] Further, in a specific embodiment of the present invention, limited by the test range of the test method of the present invention, the first conductivity σ A With the second conductivity σ B The difference needs to be less than or equal to the difference between the maximum and minimum values ​​of the conductivity test range of the present application. For example, in this specific embodiment, when the excitation frequency is 500kHz, the conductivity test range of the present invention is 50-110%IACS, then the conductivity of the first metal foil standard sample A1 and the first metal foil standard sample A2 can only be selected within this range, that is, the first conductivity σ A With the second conductivity σ B The difference needs to be less than or equal to 60% IACS.

[0053] The thickness t of the first metal foil standard sample A1, the second metal foil standard sample A2, the third metal foil standard sample B1 and the fourth metal foil standard sample B2 is measured. A1 ,t A2 ,t B1 ,t B2 The thicknesses of the first metal foil standard sample A1, the second metal foil standard sample A2, the third metal foil standard sample B1 and the fourth metal foil standard sample B2 are all less than the first set value. In other specific embodiments of the present invention, the thicknesses t of the first metal foil standard sample A1, the second metal foil standard sample A2, the third metal foil standard sample B1 and the fourth metal foil standard sample B2 can also be obtained according to the pre-stored records. A1 ,t A2 ,t B1 ,t B2That is, the thickness t of the first metal foil standard sample A1, the second metal foil standard sample A2, the third metal foil standard sample B1 and the fourth metal foil standard sample B2 is A1 ,t A2 ,t B1 ,t B2 Is a known number.

[0054] The coil feedback voltages of the first metal foil standard sample A1, the second metal foil standard sample A2, the third metal foil standard sample B1 and the fourth metal foil standard sample B2 are obtained by using an eddy current detection method. Specifically, the probe of the eddy current detection device is connected to an impedance analyzer and placed above the first standard sample group and the second standard sample group, respectively, to measure the coil feedback voltages U of the first metal foil standard sample A1, the second metal foil standard sample A2, the third metal foil standard sample B1 and the fourth metal foil standard sample B2. A1 , U A2 , U B1 , U B2 .

[0055] The first constant is obtained by taking the thickness of the metal foil standard sample in the first standard sample group and the coil feedback voltage as parameters, and the second constant is obtained by taking the thickness of the metal foil standard sample in the second standard sample group and the coil feedback voltage as parameters.

[0056] For example, in this specific embodiment, the thickness t of the first metal foil standard sample A1 and the second metal foil standard sample A2 is A1 ,t A2 The logarithm of the coil feedback voltage U A1 , U A2 The logarithm of is a variable, forming a point M1(ln(t A1 ), ln(U A1 ))、M2(ln(t A2 ), ln(U A2 )) and obtain the linear relationship of ln(t)-ln(U), the slope of which is the first constant C1. The calculation formula of the first constant C1 is as follows:

[0057] C1=(ln(U A2 )-ln(U A1 )) / (ln(t A2 )-ln(t A1 ))

[0058] For another example, in this specific embodiment, the computer collects and analyzes the thickness t of the third metal foil standard sample B1 and the fourth metal foil standard sample B2. B1 ,t B2 And coil feedback voltage U B1 , UB2 As parameters, point N1(ln(t B1 ), ln(U B1 ))、N2(ln(t B2 ), ln(U B2 )) and obtain the linear relationship of ln(t)-ln(U), the slope of which is the second constant C2. The calculation formula of the second constant C2 is as follows:

[0059] C2=(ln(U B2 )-ln(U B1 )) / (ln(t B2 )-ln(t B1 ))

[0060] Figure 3 It is a linear relationship diagram of ln(t)-ln(U) when the conductivity of metal foil is different. When the excitation frequency is 500kHz, the conductivity test range of the present invention is 50%-110% IACS. IACS (International Annealed Copper Standard) means the international annealed copper standard, which is used to characterize the conductivity of metals or alloys (referenced to standard annealed pure copper). The conductivity of standard annealed pure copper is generally defined as 100% IACS. For example, please refer to Figure 3 , the electrical conductivity of metal foil is 60% IACS means that the electrical conductivity of metal foil under this standard is 60%.

[0061] The skin depth calculation formula is as follows:

[0062] δ=1000(1 / μ0πfσ)

[0063] Where: δ is the skin depth (mm); μ0 is the magnetic permeability of the conductor in a vacuum; f is the frequency (Hz); σ is the electrical conductivity of the conductor (S / m). The skin depth of the metal foil can be calculated according to this formula, thereby determining the first set value.

[0064] Please continue reading Figure 3 As an example, the slope of the linear relationship corresponding to the metal foil conductivity of 60% IACS is the first constant C1, and the slope of the linear relationship corresponding to the metal foil conductivity of 80% IACS is the second constant C2. Figure 3 It can also be seen that under the same metal foil conductivity, ln(t)-ln(U) is in a linear relationship.

[0065] The first constant and the second constant are used as the known first parameters and the first conductivity and the second conductivity are used as the known conductivity of the metal foil, and the constant k1 and the constant b1 are obtained according to the first relationship.

[0066] For example, the first constant C1 and the second constant C2 are used as the known first parameter Y and the first conductivity σ A and the second conductivity σ B As the conductivity of the metal foil is known, the constant k1 and the constant b1 are obtained according to formula (1), as shown in the following formula.

[0067] C1=k1σ A 2 +b1

[0068] C2=k1σ B 2 +b1

[0069] Among them, the first constant C1, the second constant C2, the first conductivity σ A and the second conductivity σ B It is known that constants k1 and b1 can be obtained.

[0070] Please continue reading Figure 1 and Figure 2 Step S11, processing the metal foil to be tested to obtain a first metal foil to be tested and a second metal foil to be tested with different thicknesses, wherein the thicknesses of the first metal foil to be tested and the second metal foil to be tested are both less than the first set value. In this step, the thickness t of the first metal foil to be tested is obtained. E1 and the thickness t of the second metal foil to be tested E2 .

[0071] In this step, the metal foil to be tested may be thickened or thinned to obtain metal foils with different thicknesses. The thickening method includes stacking multiple layers of the metal foil to be tested, and the thinning method includes mechanically polishing the metal foil to be tested. Wherein, when stacking multiple layers of the metal foil to be tested, the number of stacked layers of the metal foil to be tested is less than or equal to 5 layers to avoid affecting the conductivity of the metal foil to be tested due to too many stacked layers.

[0072] In some specific embodiments of the present invention, the original metal foil to be tested is thickened or thinned to obtain the first metal foil to be tested and the second metal foil to be tested, and in this specific embodiment, the original metal foil to be tested is used as the first metal foil to be tested, and the original metal foil to be tested is thinned to obtain the second metal foil to be tested, and in other specific embodiments of the present invention, the original metal foil to be tested may also be thickened to obtain the second metal foil to be tested. It is understood that, whether the metal foil to be tested is thickened or thinned, its thickness is less than the first set value.

[0073] Please continue reading Figure 1 and Figure 2 , step S12, using an eddy current detection method to obtain the coil feedback voltage of the first metal foil to be tested and the second metal foil to be tested.

[0074] Specifically, the probe of the eddy current detection device is connected to the impedance analyzer and placed above the first metal foil to be tested and the second metal foil to be tested, respectively, to measure the coil feedback voltage U of the first metal foil to be tested and the second metal foil to be tested. E1 , U E2 .

[0075] Please continue reading Figure 1 and Figure 2 , step S13, taking the thickness and the coil feedback voltage as parameters, obtaining a first value. In this step, the relationship between the first value Y1 is:

[0076] Y1=ln(U E2 )-ln(U E1 )) / (ln(t E2 )-ln(t E1 ))

[0077] Please continue reading Figure 1 and Figure 2 Step S14: Taking the first value Y1 as the known value of the first parameter, the conductivity of the metal foil to be tested is obtained according to the first relationship. That is, taking the first value Y1 as the known first parameter, substituting it into the formula (1), the conductivity σ of the metal foil to be tested is obtained.

[0078] The metal foil conductivity testing method of the present invention establishes the relationship between coil feedback voltage, thickness and conductivity based on the eddy current principle, and calculates and inversely infers the conductivity of the metal foil to be tested by testing the coil feedback voltage and thickness of the metal foil to be tested. The method has the advantages of non-destructiveness and high test accuracy (error less than 2%) of the traditional eddy current technology, and the eddy current technology detection is no longer limited by the thickness of the material to be tested, and is suitable for metal foils with a thickness less than one skin depth, such as metal foils with a thickness less than 100 microns.

[0079] Figure 4 The first parameter Y and the square of the metal foil conductivity σ are shown. 2 The relationship diagram from Figure 4 It can be seen that the original data points are highly consistent with the fitting straight line (such as the dotted line in the figure), and the fitting determination coefficient R 2 is 0.99992, which means that the first parameter Y is related to the square of the metal foil conductivity σ 2 It is a nearly linear relationship, that is, in the test method of this application, the first relationship can be determined by two standard samples. Among them, the original data point refers to the corresponding metal foil conductivity square σ obtained by finite element analysis 2 The first parameter Y under the condition is the fitting line, which is obtained by least squares fitting based on the original data points.

[0080] Figure 5 1 is a theoretical error diagram of the test results when the present invention selects a metal foil with a conductivity of 50% IACS as the first standard sample group and a metal foil with a conductivity of 110% IACS as the second standard sample group, wherein the solid line is the standard line, that is, when the true conductivity of the material is equal to the test conductivity, the data point will be located on the standard line, and the square points represent the data points obtained by the test method of the present invention. For example, in the figure, the conductivity of the sample with a true conductivity of 60% IACS obtained by the test method of the present invention is slightly less than 60% IACS, from Figure 5 It can be seen that the overall theoretical error is within 2% IACS, and the test method of the present invention greatly improves the accuracy of the conductivity test.

[0081] Please continue reading Figure 1 and Figure 2 Optionally, in this specific embodiment, the metal foil conductivity testing method of the present invention also includes measuring the thickness of the metal foil to be tested, and determining the relationship between the thickness of the metal foil to be tested and a first set value. If the thickness of the metal foil to be tested is greater than or equal to the first set value, step S20 is executed. Step S20 includes: determining whether the thickness of the metal foil to be tested is greater than or equal to a second set value. If so, step S21 is executed; if not, step S30 is executed.

[0082] Step S21, when the thickness of the metal foil to be measured is greater than or equal to a second set value, providing a second relationship between a second parameter and the conductivity of the metal foil, wherein the second set value is greater than the first set value.

[0083] In some specific embodiments of the present invention, the second set value is greater than three times the skin depth to improve the accuracy of the conductivity measurement. For example, in this specific embodiment, the second set value is 400 microns. It can be understood that in other specific embodiments, the second set value can also be other values ​​as long as it is greater than three times the skin depth.

[0084] In this specific implementation, the second relationship between the second parameter and the conductivity of the metal foil is:

[0085] ln(U)=k2ln(σ)+b2 (2)

[0086] Wherein, U is the second parameter, σ is the conductivity of the metal foil, and k2 and b2 are constants.

[0087] The present invention also provides a method for obtaining constant k2 and constant b2. The method comprises:

[0088] The electrical conductivities of two metal foil standard samples with different thicknesses are obtained, wherein the thicknesses of the metal foil standard samples are greater than the second preset value.

[0089] The coil feedback voltage of the two metal foil standard samples is obtained by using the eddy current detection method. For example, in this specific embodiment, the probe of the eddy current detection device is connected to the impedance analyzer and placed above the two metal foil standard samples respectively to measure the coil feedback voltage U A , U B .

[0090] The conductivity and the coil feedback voltage are used as known parameters, and the constant k2 and the constant b2 are obtained according to the second relational expression. For example, in this specific embodiment, the conductivity and the coil feedback voltage are not directly used as variables of the second relational expression, but the conductivity and the logarithm of the coil feedback voltage are used as variables of the second relational expression. Specifically, two points M(ln(σ A ), ln(U A ))、N(ln(σ B ), ln(U B )), ln(σ A ) and ln(U A ), ln(σ B ) and ln(U B ) into formula (2) to obtain the values ​​of constants k2 and b2.

[0091] After executing step S21, execute step S22, which includes: using an eddy current detection method to obtain the coil feedback voltage of the metal foil to be tested. Specifically, in this specific embodiment, the probe of the eddy current detection device is connected to an impedance analyzer and placed above the metal foil to be tested, and the coil feedback voltage U of the metal foil to be tested is measured. T .

[0092] Step S23, the obtained coil feedback voltage is used as the second parameter, and the conductivity of the metal foil to be tested is obtained according to the second relationship. Specifically, the coil feedback voltage U of the metal foil to be tested is used as the second parameter. T Substituting into formula (2), we can get the conductivity σ of the sample to be tested. T .

[0093] Furthermore, in this specific embodiment, the method further includes: step S30, if the thickness of the metal foil is less than the second set value and greater than the first set value, thickening the metal foil to be tested so that the thickness of the metal foil to be tested is greater than the second set value, and then executing step S21.

[0094] Further, in this specific embodiment, the method of thickening the metal foil to be tested includes stacking multiple layers of the metal foil to be tested, for example, stacking 2 to 4 layers of the metal foil to be tested, so that the thickness thereof is greater than a second set value.

[0095] The metal foil conductivity testing method provided in the specific embodiment of the present invention can adopt different testing methods according to the thickness of the metal foil, thereby greatly improving the accuracy of the metal foil conductivity testing.

[0096] When the thickness of the metal foil to be tested is greater than three times the skin depth, the effect of the change in the thickness of the metal foil to be tested on the coil feedback voltage is almost negligible. Therefore, when the maximum thickness requirement is met, the effect of the thickness of the metal foil to be tested on the test results can be ignored, and accurate conductivity test results can be obtained.

[0097] When the thickness of the metal foil to be measured is between three times the skin depth and one time the skin depth, the thickness of the metal foil to be measured can be increased to more than three times the skin depth by stacking 2-4 layers, so that accurate measurement of conductivity can be achieved. Figure 6 is the relationship between the number of metal foil layers and electrical conductivity. Figure 6 It can be seen that when the number of metal foil layers is four or less, the effect on conductivity is very small.

[0098] When the thickness of the metal foil to be tested is less than one times the skin depth, the double logarithm of the coil feedback voltage and the thickness is in a linear relationship. Based on the eddy current principle, the relationship between the coil feedback voltage, thickness and conductivity is established. By testing the coil feedback voltage and thickness of the metal foil to be tested, the conductivity of the metal foil to be tested is calculated and inferred. This method has the advantages of traditional eddy current technology such as non-destructiveness and high test accuracy (error less than 2%), and eddy current technology detection is no longer limited by the thickness of the material to be tested, greatly improving the test accuracy.

[0099] The above is only a preferred embodiment of the present invention. It should be pointed out that ordinary technicians in this technical field can make several improvements and modifications without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for testing the electrical conductivity of a metal foil, characterized in that: include: When the thickness of the metal foil to be measured is less than the first set value, a first relationship between the first parameter and the conductivity of the metal foil is provided, the first set value is less than one skin depth, and the first relationship between the first parameter and the conductivity of the metal foil is the relationship between the first parameter and the square of the conductivity of the metal foil: Y=k1σ 2 +b1 Among them, Y is the first parameter, σ is the conductivity of the metal foil, k1 and b1 are constants; Processing the metal foil to be tested to obtain a first metal foil to be tested and a second metal foil to be tested having different thicknesses, wherein the thicknesses of the first metal foil to be tested and the second metal foil to be tested are both less than the first set value; The coil feedback voltage of the first metal foil to be tested and the second metal foil to be tested is obtained by using an eddy current detection method; the first value is obtained by using the thickness and the coil feedback voltage as parameters, and the relationship between the first value is: Y1=ln(U E2 )-ln(U E1 )) / (ln(t E2 )-ln(t E1 )) Wherein, Y1 is the first value, U E1 is the coil feedback voltage of the first metal foil to be tested, U E2 is the coil feedback voltage of the second metal foil to be tested, t E1 is the thickness of the first metal foil to be tested, t E2 is the thickness of the second metal foil to be tested; The first numerical value is used as the known value of the first parameter, and the conductivity of the metal foil to be tested is obtained according to the first relationship.

2. The method for testing the electrical conductivity of metal foil according to claim 1, characterized in that: Methods for obtaining constant k1 and constant b1 include: Obtaining the thickness of at least two metal foil standard samples of different thicknesses in a first standard sample group and obtaining the coil feedback voltage of the metal foil standard samples by using an eddy current detection method, obtaining the thickness of at least two metal foil standard samples of different thicknesses in a second standard sample group and obtaining the coil feedback voltage of the metal foil standard samples by using an eddy current detection method, the first standard sample group has a first conductivity, the second standard sample group has a second conductivity, and the thickness of the metal foil standard samples in the first standard sample group and the second standard sample group are both less than the first set value; The first constant is obtained by taking the thickness of the metal foil standard sample in the first standard sample group and the coil feedback voltage as parameters, and the second constant is obtained by taking the thickness of the metal foil standard sample in the second standard sample group and the coil feedback voltage as parameters; The first constant and the second constant are used as the known first parameters and the first conductivity and the second conductivity are used as the known conductivity of the metal foil, and the constant k1 and the constant b1 are obtained according to the first relationship.

3. The method for testing the electrical conductivity of metal foil according to claim 2, characterized in that: The relationship of the first constant is: C1=(ln(U A2 )-ln(U A1 )) / (ln(t A2 )-ln(t A1 )) Among them, C1 is the first constant, U A1 is the coil feedback voltage of the first metal foil standard sample in the first standard sample group, U A2 is the coil feedback voltage of the second metal foil standard sample in the first standard sample group, t A1 is the thickness of the first metal foil standard sample in the first standard sample group, t A2 is the thickness of the second metal foil standard sample in the first standard sample group; The relationship of the second constant is: C2=(ln(U B2 )-ln(U B1 )) / (ln(t B2 )-ln(t B1 )) Among them, C2 is the second constant, U B1 is the coil feedback voltage of the third metal foil standard sample in the second standard sample group, U B2 is the coil feedback voltage of the fourth metal foil standard sample in the second standard sample group, t B1 is the thickness of the third metal foil standard sample in the second standard sample group, t B2 is the thickness of the fourth metal foil standard sample in the second standard sample group.

4. The method for testing the electrical conductivity of metal foil according to claim 2, characterized in that: The difference between the first conductivity and the second conductivity is greater than or equal to 30% IACS.

5. The method for testing the electrical conductivity of metal foil according to claim 1, characterized in that: The step of processing the metal foil to be tested to obtain at least two metal foils with different thicknesses includes: thickening or thinning the metal foil to be tested to obtain metal foils with different thicknesses.

6. The method for testing the electrical conductivity of metal foil according to claim 1, characterized in that: When the thickness of the metal foil to be measured is greater than or equal to the second set value, a second relationship between the second parameter and the conductivity of the metal foil is provided, the second set value is greater than the first set value, the second set value is greater than three times the skin depth, and the second relationship between the second parameter and the conductivity of the metal foil is: ln(U)=k2ln(σ)+b2 Wherein, U is the second parameter, σ is the conductivity of the metal foil, and k2 and b2 are constants; Using an eddy current detection method to obtain the coil feedback voltage of the metal foil to be tested; The obtained coil feedback voltage is used as the second parameter, and the conductivity of the metal foil to be measured is obtained according to the second relationship.

7. The method for testing the electrical conductivity of metal foil according to claim 6, characterized in that: Methods for obtaining constant k2 and constant b2 include: Obtaining the electrical conductivity of two metal foil standard samples with different electrical conductivities, wherein the thickness of the metal foil standard samples is greater than the second set value; Using an eddy current detection method to obtain coil feedback voltages of two metal foil standard samples; The conductivity and the coil feedback voltage are used as known parameters, and the constant k2 and the constant b2 are obtained according to the second relationship.

8. The method for testing the electrical conductivity of metal foil according to claim 6, characterized in that: When the thickness of the metal foil to be tested is less than the second set value and greater than the first set value, the metal foil to be tested is thickened to make the thickness of the metal foil to be tested greater than the second set value, and the conductivity test is performed on the thickened metal foil to be tested.

9. The method for testing the electrical conductivity of metal foil according to claim 8, characterized in that: The method of thickening the metal foil to be tested includes stacking multiple layers of the metal foil to be tested.

10. The method for testing the electrical conductivity of metal foil according to claim 6, characterized in that: Also includes: The thickness of the metal foil to be measured is obtained, and the relationship between the thickness of the metal foil to be measured and the first set value and the second set value is determined.

Images