Cold soldering defect detection method and detection system

Abstract

The embodiment of the present application discloses a method and a detection system for detecting cold solder joint defects. The cold solder joint defect detection method detects the cold solder joint defect area in the welding layer of the test piece based on eddy current phase-locked thermal imaging technology. The AC signals of different frequencies are modulated to phase-locked eddy current to heat the test piece, effectively suppressing the influence of complex materials and inconsistent surface emissivity of the materials. The thermal imager has clearer images, greater detection depth, and wider applicability.

Description

Technical Field

[0001] The present application relates to the technical field of welding component detection, and in particular to a method and system for detecting cold weld defects. Background Art

[0002] During the laser welding process of two layers of material, the opposing surfaces of the two layers of material melt due to the laser to form a welding layer. This laser welding method carries the risk of cold weld defects within the welding layer. The connection between the two layers of material corresponding to the cold weld defect area is not firm, and poor conductivity is likely to occur after a period of use, leading to failure. For cold weld defect detection, the existing technology uses a cold weld detection finite element analysis method. This method is based on the principle of eddy current pulse thermal imaging. Through finite element analysis of the temperature change curve difference between the cold weld defect and the normal welding area during heating and cooling, the cold weld defect area is discovered. However, in actual applications, pulsed eddy current heating is uneven, the detection depth is not large, the imaging image is seriously interfered with by the eddy current background noise, and complex surfaces cannot be intuitively formed into an effective observable image, affecting the accuracy of the cold weld defect detection results. Summary of the Invention

[0003] The embodiments of the present application provide a method and system for detecting cold solder joint defects, which can solve the problems of uneven eddy current heating and shallow detection depth in existing eddy current pulse detection of cold solder joint defects, resulting in poor detection result accuracy.

[0004] The present invention provides a method for detecting a cold solder joint defect, which is used to detect a solder joint layer in a test piece. The cold solder joint defect detection method includes the following steps:

[0005] S1) providing a high-frequency alternating current, and performing amplitude modulation on the high-frequency alternating current by a low-frequency phase-locked signal to generate a periodically varying current signal;

[0006] S2) arranging an induction coil on one side of the device under test, and supplying the periodically varying current signal to the induction coil after power amplification, so that the induction coil generates a periodically varying induced magnetic field;

[0007] S3) according to the periodically varying induced magnetic field generated by the induction coil, the test piece generates a frequency-varying phase-locked eddy current to heat the test piece;

[0008] S4) collecting temperature data of a side of the test piece away from the induction coil during a supply time, wherein the supply time is a time duration for supplying the periodically varying current signal to the induction coil;

[0009] S5) processing the temperature data by Fourier transform to form an amplitude map and a phase map;

[0010] S6) comparing the amplitude map and the phase map with the amplitude map and the phase map of the normal welding area of ​​the test piece.

[0011] Optionally, in step S2), the induction coil is arranged in parallel with an adjacent surface of the test piece.

[0012] Optionally, the test piece includes a first layer and a second layer stacked together, and the first layer and the second layer are welded to form the weld layer. The supply time in step S4) is t r ,

[0013]

[0014] L r is the sum of the thicknesses of the first layer and the welding layer of the test piece, and α is the thermal diffusion coefficient of the test piece.

[0015] Optionally, in step S3), part of the phase-locked eddy current is converted into heat energy inside the test piece to heat the test piece, and the heat generated by the phase-locked eddy current inside the test piece is Q1.

[0016]

[0017] σ represents the conductivity of the test piece, J S It represents the eddy current density generated by induction, and E is the electric field strength.

[0018] Optionally, in step S4), the heat Q1 generated by the phase-locked eddy current inside the test piece is transferred from the side of the test piece close to the induction coil to the direction away from the induction coil, and the heat transferred to the side of the test piece away from the induction coil is Q2.

[0019]

[0020] In the above formula, ρ represents the material density of the test piece, C p represents the heat capacity of the test piece, represents the divergence operator, represents the gradient operator, and k represents the thermal conductivity of the test piece.

[0021] Optionally, when there is a cold solder defect area in the welding layer of the test piece, the temperature of the area of ​​the test piece away from the induction coil corresponding to the cold solder defect area is T1, and the temperature of the area of ​​the test piece away from the induction coil corresponding to the normal welding area is T2, T1<T2; when the difference between T1 and T2 reaches a maximum value, the supply of current signal to the induction coil is stopped.

[0022] Optionally, in step S5), the supply time t is converted into r The multiple temperature data T in the data are converted from time threshold to frequency threshold to obtain amplitude response and phase response.

[0023]

[0024]

[0025]

[0026]

[0027] n is the maximum time value, ω is the angular frequency, is the phase, A(ω) is the amplitude, according to the phase of multiple temperature data T The phase map is formed, and the amplitude map is formed according to the amplitudes A(ω) of a plurality of temperature data T.

[0028] Optionally, in step S6), an infrared thermal imaging recorder is used to collect a thermal image of the second layer away from the first layer, the thermal image including a plurality of pixel temperature points, each of which corresponds to a piece of temperature data T.

[0029] At the same time, the embodiment of the present application also provides a cold soldering defect detection system for detecting the welding layer in the test piece, and the cold soldering defect detection system includes: a phase-locked signal source for generating a high-frequency alternating current and a low-frequency phase-locked signal, and the low-frequency phase-locked signal is used to perform amplitude modulation on the high-frequency alternating current to generate a periodically varying current signal; a power amplifier, the input end of the power amplifier is electrically connected to the output end of the phase-locked signal source to receive the periodically varying current signal, and the power amplifier is used to power amplify the periodically varying current signal; an induction coil is arranged opposite to one side of the test piece, and the induction coil is electrically connected to the output end of the power amplifier to receive the periodically varying current signal. The power amplifies the current signal and generates a periodically changing induced magnetic field; a thermal imager is arranged opposite to the side of the test piece away from the induction coil, and the thermal imager is used to collect the thermal image of the side of the test piece away from the induction coil; a host computer, the output end of the thermal imager is communicatively connected to the host computer to transmit the temperature data in the thermal image to the host computer, and the host computer includes a processing module and a comparison module, the processing module is used to perform Fourier transform on the temperature data to form an amplitude map and a phase map, and the comparison module is used to compare the amplitude map and phase map of the cold weld defect area with the amplitude map and phase map of the normal welding area to obtain the morphological characteristics of the cold weld defect area.

[0030] Optionally, the thermal imager is an infrared thermal imager.

[0031] The beneficial effect of the present application is to provide a method and a detection system for cold soldering defects, wherein a high-frequency alternating current is amplitude-modulated by a low-frequency phase-locked signal to form a periodically varying current signal, and the power-amplified current signal is supplied to an induction coil to form a periodically varying induced magnetic field, the induction coil is arranged on one side of the test piece, and the periodically varying induced magnetic field generates a frequency-varying phase-locked eddy current inside the test piece, and the frequency-varying phase-locked eddy current heats the test piece, and the generated heat is transferred to the side of the test piece away from the induction coil, and the thermal imager collects the temperature of the test piece away from the induction coil. The thermal image of one side of the coil is taken and temperature data is generated. An amplitude diagram and a phase diagram are formed based on the temperature data. By comparing the amplitude diagram and the phase diagram with the amplitude diagram and the phase diagram of the normal welding area, it is possible to detect whether there is a cold solder defect in the welding layer of the test piece. This application is based on eddy current phase-locked thermal imaging technology to detect the cold solder defect area in the welding layer of the test piece. The AC signals of different frequencies are modulated to phase-locked eddy currents to heat the test piece, effectively suppressing the influence of complex materials and inconsistent surface emissivity of the materials. The thermal imager has clearer images, a greater detection depth, and a wider applicability. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on these drawings without creative work.

[0033] Figure 1 1 is a flow chart of a method for detecting cold solder joint defects provided by an embodiment of the present application;

[0034] Figure 2 This is a structural diagram of a cold soldering defect detection system provided by an embodiment of the present application;

[0035] Figure 3 It is a structural diagram of the test piece.

[0036] Description of reference numerals:

[0037] 100. Cold soldering defect detection system, 110. Phase-locked signal source, 120. Power amplifier, 130. Induction coil, 140. Thermal imager, 150. Host computer, 151. Analysis module, 152. Comparison module;

[0038] 200 , test piece; 201 , first surface; 202 , second surface; 210 , first layer; 220 , second layer; 230 , welding layer; 231 , cold soldering defect area; 232 , normal welding area. DETAILED DESCRIPTION

[0039] The following will provide a clear and complete description of the technical solutions in the embodiments of this application, in conjunction with the accompanying drawings. Obviously, the described embodiments are only some of the embodiments of this application, and not all of them. Based on the embodiments of this application, all other embodiments obtained by persons skilled in the art without inventive effort are within the scope of protection of this application. Furthermore, it should be understood that the specific embodiments described herein are intended only to illustrate and explain this application and are not intended to limit this application. In this application, unless otherwise indicated, directional terms such as "upper" and "lower" generally refer to the upper and lower sides of the device in actual use or operation, specifically the directions in the drawings; whereas "inner" and "outer" refer to the outline of the device. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed to indicate or imply relative importance or to implicitly specify the number of the technical features indicated. Therefore, features designated "first" or "second" may explicitly or implicitly include one or more of the designated features.

[0040] The embodiments of the present application provide a method and system for detecting cold soldering defects, which modulate the amplitude of a high-frequency alternating current through a low-frequency phase-locked signal to form a periodically changing current signal, and supply the power-amplified current signal to an induction coil to form a periodically changing induced magnetic field. The induction coil is arranged on one side of the piece to be tested, and the periodically changing induced magnetic field generates a frequency-changing phase-locked eddy current inside the piece to be tested. The frequency-changing phase-locked eddy current heats the piece to be tested, and the generated heat is transferred to the side of the piece to be tested away from the induction coil. The thermal imager collects a thermal image of the side of the piece to be tested away from the induction coil and generates temperature data. An amplitude diagram and a phase diagram are formed based on the temperature data. By comparing the amplitude diagram and the phase diagram with the amplitude diagram and the phase diagram of the normal welding area, it can be detected whether there is a defect in the welding layer of the piece to be tested. In the case of cold solder joint defects, the present application detects the cold solder joint defect area in the welding layer of the test piece based on eddy current phase-locked thermal imaging technology, and modulates the phase-locked eddy current to heat the test piece with AC signals of different frequencies, effectively suppressing the influence of complex materials and inconsistent surface emissivity of materials. The thermal imager has clearer imaging, greater detection depth and wider applicability. As a typical application, the cold solder joint defect detection method and detection system can be used to detect cold solder joint defects in the welding of two layers of materials, and are particularly suitable for detecting cold solder joint defects in the welding layer between two layers of conductive metal materials, such as the welding layer between a nickel material layer and an aluminum material layer, the welding layer between a nickel material layer and a nickel material layer, the welding layer between a nickel material layer and a copper material layer, the welding layer between two layers of nickel-aluminum alloy, and the welding layer between two layers of nickel-copper alloy.

[0041] In one embodiment of the present application, a method for detecting a cold solder joint defect is provided. Figures 1 to 3The method for detecting a cold solder joint defect is used to detect a cold solder joint defect in the welding layer 230 of the test piece 200. Figure 3 The test piece 200 includes a first layer 210 and a second layer 220 that are stacked. The opposite surfaces of the first layer 210 and the second layer 220 are welded to form a welding layer 230. The side of the first layer 210 away from the second layer 220 is the first surface 201 of the test piece 200, and the side of the second layer 220 away from the first layer 210 is the second surface 202 of the test piece 200. The first surface 201 and the second surface 202 are arranged opposite to each other.

[0042] Reference Figure 1 The cold soldering defect detection method comprises the following steps:

[0043] S1) provides a high-frequency alternating current, and modulates the amplitude of the high-frequency alternating current through a low-frequency phase-locked signal to generate a periodically changing current signal;

[0044] S2) Arranging the induction coil 130 in parallel with one side of the first layer 210 of the device under test 200, amplifying the power of the periodically varying current signal and supplying it to the induction coil 130, so that the induction coil 130 generates a periodically varying induced magnetic field;

[0045] S3) According to the periodically varying induced magnetic field generated by the induction coil 130, the test piece 200 generates a frequency-varying phase-locked eddy current to heat the test piece 200;

[0046] S4) collecting temperature data of the second surface 202 of the test piece 200 during a supply time, wherein the supply time is a time duration for supplying a periodically varying current signal to the induction coil 130;

[0047] S5) processing the temperature data by Fourier transform to form an amplitude map and a phase map;

[0048] S6) comparing the amplitude map and the phase map with the amplitude map and the phase map of the normal welding area of ​​the test piece 200.

[0049] At the same time, in this embodiment, a cold soldering defect detection system 100 is also provided. The cold soldering defect detection system 100 adopts Figure 1 The method for detecting a cold solder joint defect is to detect a cold solder joint defect in the solder layer 230 of the test piece 200. Figure 2The cold solder joint defect detection system 100 includes: a phase-locked signal source 110, a power amplifier 120, an induction coil 130, a thermal imager 140, and a host computer 150. The output end of the phase-locked signal source 110 is electrically connected to the input end of the power amplifier 120, the output end of the power amplifier 120 is electrically connected to the input end of the induction coil 130, the output end of the thermal imager 140 is in communication connection with the host computer 150, and the thermal imager 140 and the induction coil 130 are arranged opposite each other.

[0050] During use, the test piece 200 is placed between the induction coil 130 and the thermal imager 140 , the induction coil 130 is arranged parallel to and spaced apart from the first surface 201 of the test piece 200 , and the image acquisition end of the thermal imager 140 faces the second surface 202 of the test piece 200 .

[0051] The phase-locked signal source 110 is used to generate the high-frequency alternating current and the low-frequency phase-locked signal in step S1). The low-frequency phase-locked signal is used to amplitude-modulate the high-frequency alternating current to form a periodically varying current signal. In this embodiment, the frequency range of the high-frequency alternating current is: 100 kHz to 300 kHz, and the frequency range of the low-frequency phase-locked signal is: 0.1 Hz to 1 Hz. The frequency range of the periodically varying current signal obtained after the high-frequency alternating current is amplitude-modulated (amplitude modulated) by the low-frequency phase-locked signal is: 10 kHz to 300 kHz. The output end of the phase-locked signal source 110 outputs the periodically varying current signal. The period variation of the current signal is consistent with the frequency variation of the current signal, that is, the period of the current signal varies according to the frequency variation of the current signal.

[0052] The input end of the power amplifier 120 is electrically connected to the output end of the phase-locked signal source 110 to receive a periodically varying current signal. Since the periodically varying current signal is a low voltage, the power is usually a few watts or less than a few tenths of a watt, which cannot achieve heating of the test piece 200. Therefore, it is necessary to amplify the power of the periodically varying current signal, that is, the power amplification in step S2). The power amplifier 120 amplifies the power of the periodically varying current signal to 1KW~2KW to achieve a rapid heating effect on the test piece 200.

[0053] The input end of the induction coil 130 is electrically connected to the output end of the power amplifier 120 to receive a periodically varying current signal with a power amplified to 1 kW to 2 kW. The induction coil 130 generates a periodically varying induced magnetic field based on the periodically varying current signal, i.e., the periodically varying induced magnetic field generated by the induction coil 130 as described in step S2). The induction coil 130 is arranged on one side of the first layer 210 of the device under test 200. The periodically varying induced magnetic field generated by the induction coil 130 causes frequency-varying phase-locked eddy currents to be generated within the first surface 201 and / or the first layer 210 of the device under test 200. The phase-locked eddy currents are converted from electrical energy into thermal energy within the device under test 200 to heat the device under test 200. The closer the induction coil 130 is to the first surface 201 of the test piece 200, the stronger the induction effect and the faster the heating response. However, the induction coil 130 cannot contact the first surface 201, as contact would cause heat conduction. Therefore, in this embodiment, the distance between the induction coil 130 and the first surface 201 of the test piece 200 is 1 mm to 5 mm.

[0054] If a conventional eddy current is used to heat the test piece 200, only a portion of the test piece 200 will be heated, resulting in concentrated heat, obstructing observation and interfering with the identification of cold solder joints. However, this embodiment uses a frequency-variable phase-locked eddy current to heat the test piece 200, resulting in a uniform heat distribution within the test piece 200, facilitating observation and identification of cold solder joints.

[0055] In step S3), the supply time of the periodically changing current signal to the induction coil 130 is t r ,

[0056]

[0057] L r is the sum of the thickness of the first layer 210 and the thickness of the welding layer 230 of the test piece 200, and α is the thermal diffusion coefficient of the test piece 200. For example, if the thickness of the first layer 210 is 0.08 mm, the thickness of the second layer 220 is 0.08 mm, and the thickness of the welding layer 230 formed by laser welding is 0.01 mm to 0.02 mm, then L r It is 0.09mm~0.1mm.

[0058] The heat generated by the phase-locked eddy current in the test piece 200 from converting electrical energy into thermal energy is Q1.

[0059]

[0060] σ represents the conductivity of the test piece 200, J S It represents the eddy current density generated by induction, and E is the electric field strength.

[0061] The calculation formula of electric field intensity E is:

[0062]

[0063] In the above formula, r is the distance between the induction coil 130 and the first surface 201 of the test object 200, which in this embodiment is 1 mm to 5 mm, preferably 1 mm to 2 mm, Q is the charge per unit time I / f, K is the electrostatic constant, I is the current on the induction coil 130, and f is the phase-locked frequency (i.e., the frequency of the periodically changing current signal: 10 kHz to 300 kHz).

[0064] Phase-locked eddy currents of different frequencies generate thermal energy of different frequencies. The heat Q1 generated by the thermal energy is transferred inside the DUT 200 toward the second layer 220 to form heat conduction, and the heat conducted to the second surface 202 of the DUT 200 is Q2.

[0065]

[0066] In the above formula, ρ represents the material density of the test piece, C p represents the specific heat capacity of the test piece, represents the divergence operator, represents the gradient operator, and k represents the thermal conductivity of the test piece.

[0067] The first layer 210 and the second layer 220 of the test piece 200 are both made of conductive metal materials. The welding layer 230 formed by welding the opposing surfaces of the first layer 210 and the second layer 220 is an alloy material layer formed by melting the conductive metal material constituting the first layer 210 and the conductive metal material constituting the second layer 220. For example, if the first layer 210 is a nickel material layer and the second layer 220 is an aluminum material layer, the welding layer 230 is a nickel-aluminum alloy layer.

[0068] When the materials of the first layer 210 and the second layer 220 of the test piece 200 are the same, for example, the first layer 210 and the second layer 220 are both nickel material layers, the electrical conductivity σ of the test piece 200 is the electrical conductivity of nickel, the material density ρ of the test piece 200 is the material density of nickel, and the specific heat capacity C of the test piece is p is the heat capacity of nickel, and the thermal conductivity k of the test piece is the thermal conductivity of nickel;

[0069] When the materials of the first layer 210 and the second layer 220 of the test piece 200 are different, for example, the first layer 210 is a nickel material layer and the second layer 220 is an aluminum material layer, then the electrical conductivity σ of the test piece 200 is the sum of the electrical conductivity of nickel and the electrical conductivity of aluminum, the material density ρ of the test piece 200 is the sum of the material density of nickel and the material density of aluminum, and the specific heat capacity C of the test piece is pThat is, the sum of the heat capacity of nickel and the heat capacity of aluminum. The calculation formula of the thermal conductivity k of the test piece is as follows: k=K1*K2 / (K1+K2), K1 is the thermal conductivity coefficient of nickel in the first layer 210, and K2 is the thermal conductivity coefficient of aluminum in the second layer 220.

[0070] In addition, copper can also be selected as the material of the first layer 210 and the material of the second layer 220 according to actual needs. Specifically, the properties of nickel, aluminum, and copper are shown in Table 1.

[0071] Table 1

[0072] nickel aluminum copper <![CDATA[Conductivity σ (10 6 S / m)]]> 14.62 22.53 60.09 <![CDATA[Thermal diffusivity α (10 -6 m 2 / s)]]> 22.9 73 112 100kHz skin depth / mm 0.042 0.335 0.205 Thermal wave input depth at 0.1s / mm 3.03 5.40 6.71 <![CDATA[Density ρ (g / cm 3 )]]> 8.9 2.7 8.9 <![CDATA[Specific heat capacity C at (20 °C) p (kJ / kg·°C)]]> 0.46 0.88 0.39 (20℃) thermal conductivity k (w / m·k) 71.4 273 397

[0073] When the cold solder joint defect area 231 exists, there is air in the cold solder joint defect area 231, and the density of the air is 1.29*10 -6 g / cm 3 , specific heat capacity C at 20℃ p The thermal conductivity k at 20°C is 1.004 kJ / kg·c and 0.26273 w / m·k.

[0074] When a cold solder joint defect exists in the soldering layer 230, the soldering layer 230 includes a cold solder joint defect region 231 and a normal solder joint region 232. The cold solder joint defect region 231 is a weld void region formed in the soldering layer 230 where the first layer 210 and the second layer 220 are not welded to form a nickel-aluminum alloy. In the cold solder joint defect region 231, there is air instead of alloy, resulting in a cold solder joint. The thermal resistance of the cold solder joint defect region 231 is higher than that of the normal solder joint region 232. The cold solder joint defect region 231 hinders heat conduction more than the normal solder joint region 232 does. As a result, the amount of heat Q2 conducted to the second surface 202 via the cold solder joint defect region 231 is lower than the amount of heat Q2 conducted to the second surface 202 via the normal solder joint region 232. In other words, the temperature T1 of the second surface 202 corresponding to the cold solder joint defect region 231 is lower than the temperature T2 of the second surface 202 corresponding to the normal solder joint region 232, where T1 is less than T2, and there is a difference between T1 and T2.

[0075] The thermal imager 140 is used to collect the supply time t rThe heat Q2 conducted to the second surface 202 forms a thermal image, which is composed of a number of temperature pixels, each of which constitutes a temperature data T. The temperature data T includes the temperature T1 of the second surface 202 corresponding to the defective area 231 of the cold solder joint, and the temperature T2 of the second surface 202 corresponding to the normal solder joint area 232. When the difference between T1 and T2 reaches the maximum value, the supply of the periodically changing current signal to the induction coil 130 is stopped, and the best thermal image can be obtained. The time t1 required to reach the maximum difference between T1 and T2 is equal to the supply time t r Basically the same, that is, t1 and t r The absolute value of the difference between them is less than or equal to 1. The thermal imager 140 is an infrared thermal imager.

[0076] The thermal imager 140 transmits the temperature data T to the host computer 150. The host computer 150 includes an analysis module 151 and a comparison module 152. The analysis module 151 receives the temperature data T and converts the supply time t into the supply time t by performing Fourier transform according to the following formula: r The multiple temperature data T in the data are converted from time threshold to frequency threshold to obtain amplitude response and phase response.

[0077]

[0078]

[0079]

[0080]

[0081] n is the maximum time value, ω is the angular frequency, is the phase, A(ω) is the amplitude, according to the phase of multiple temperature data T The phase diagram is formed, and the amplitude diagram is formed according to the amplitudes A(ω) of the plurality of temperature data T. The host computer 150 is further connected to the phase-locked signal source 110 for controlling the phase-locked signal source 110 .

[0082] Since the temperature data T includes the temperature T1 of the second surface 202 corresponding to the cold solder defect area 231 and the temperature T2 of the second surface 202 corresponding to the normal soldering area 232, there will be a difference between the amplitude map and phase map formed by the temperature T1 of the cold solder defect area 231 and the amplitude map and phase map formed by the temperature T2 of the normal soldering area 232. By comparing this difference, the comparison module 152 can obtain the morphological characteristics of the cold solder defect area 231. The host computer 150 is a PC.

[0083] The above is a detailed introduction to a method and system for detecting cold solder joint defects provided in the embodiments of the present application. Specific examples are used herein to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only used to help understand the method and core idea of ​​the present application. At the same time, for those skilled in the art, based on the ideas of the present application, there may be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as a limitation on the present application.

Claims

1. A method for detecting a cold solder joint defect, for detecting a solder joint layer in a test piece, characterized in that: The cold soldering defect detection method comprises the following steps: S1) providing a high-frequency alternating current, and performing amplitude modulation on the high-frequency alternating current by a low-frequency phase-locked signal to generate a periodically varying current signal; S2) arranging an induction coil on a side of the first surface of the test piece facing away from the second surface, and supplying the periodically varying current signal to the induction coil after power amplification, so that the induction coil generates a periodically varying induced magnetic field; S3) according to the periodically varying induced magnetic field generated by the induction coil, the test piece generates a frequency-varying phase-locked eddy current to heat the test piece; Part of the phase-locked eddy current is converted into heat energy inside the test piece to heat the test piece. The heat generated by the phase-locked eddy current inside the test piece is Q1. S4) collecting temperature data of a side of the test piece away from the induction coil during a supply time, wherein the supply time is a time duration for supplying the periodically varying current signal to the induction coil; When a cold solder joint defect area exists in the welding layer of the test piece, the temperature of the area of ​​the test piece away from the induction coil corresponding to the cold solder joint defect area is T1, and the temperature of the area of ​​the test piece away from the induction coil corresponding to the normal welding area is T2, and T1<T2; When the difference between T1 and T2 reaches a maximum value, stopping supplying the current signal to the induction coil; The heat Q1 generated by the phase-locked eddy current inside the test piece is transferred from the side of the test piece close to the induction coil to the direction away from the induction coil, and the heat Q2 transferred to the side of the test piece away from the induction coil; The test piece includes a first layer and a second layer stacked together, and the opposite surfaces of the first layer and the second layer are welded to form the welding layer. The supply time is t r , L r is the sum of the thicknesses of the first layer and the welding layer of the test piece, and α is the thermal diffusion coefficient of the test piece; S5) processing the temperature data by Fourier transform to form an amplitude map and a phase map; S6) comparing the amplitude map and the phase map with the amplitude map and the phase map of the normal welding area of ​​the test piece.

2. The method for detecting cold solder joint defects according to claim 1, wherein: In step S2), the induction coil is arranged in parallel with the adjacent surface of the test piece.

3. The method for detecting cold solder joint defects according to claim 1, wherein: In step S3), σ represents the conductivity of the test piece, J S It represents the eddy current density generated by induction, and E is the electric field strength.

4. The method for detecting cold solder joint defects according to claim 1, wherein: In step S4), In the above formula, ρ represents the material density of the test piece, C p represents the heat capacity of the test piece, represents the divergence operator, represents the gradient operator, and k represents the thermal conductivity of the test piece.

5. The method for detecting cold solder joint defects according to claim 1, wherein: In step S5), Fourier transform is performed according to the following formula to convert the supply time t r The multiple temperature data T in the data are converted from time threshold to frequency threshold to obtain amplitude response and phase response. n is the maximum time value, ω is the angular frequency, is the phase, A(ω) is the amplitude, according to the phase of multiple temperature data T The phase map is formed, and the amplitude map is formed according to the amplitudes A(ω) of a plurality of temperature data T.

6. The method for detecting cold solder joint defects according to claim 5, wherein: In step S6), an infrared thermal imaging recorder is used to collect a thermal image of the second layer on a side away from the first layer, wherein the thermal image includes a plurality of pixel temperature points, and each pixel temperature point corresponds to a piece of temperature data T.

7. A cold solder joint defect detection system for detecting the solder joint layer in a test piece, characterized in that: The cold soldering defect detection system comprises: a phase-locked signal source for generating a high-frequency alternating current and a low-frequency phase-locked signal, wherein the low-frequency phase-locked signal is used to amplitude-modulate the high-frequency alternating current to generate a periodically varying current signal; a power amplifier, wherein an input end of the power amplifier is electrically connected to an output end of the phase-locked signal source to receive the periodically varying current signal, and the power amplifier is used to amplify the power of the periodically varying current signal; an induction coil, arranged opposite to one side of the test piece, the induction coil being electrically connected to the output end of the power amplifier to receive the power-amplified current signal and generate a periodically varying induced magnetic field; a thermal imager, arranged opposite to a side of the test piece away from the induction coil, and configured to capture a thermal image of the side of the test piece away from the induction coil within a supply time; When a cold solder joint defect area exists in the welding layer of the test piece, the temperature of the area of ​​the test piece away from the induction coil corresponding to the cold solder joint defect area is T1, and the temperature of the area of ​​the test piece away from the induction coil corresponding to the normal welding area is T2, and T1<T2; When the difference between T1 and T2 reaches a maximum value, stopping supplying the current signal to the induction coil; The test piece includes a first layer and a second layer stacked together, and the opposite surfaces of the first layer and the second layer are welded to form the welding layer. The supply time is t r , L r is the sum of the thicknesses of the first layer and the welding layer of the test piece, and α is the thermal diffusion coefficient of the test piece; A host computer, wherein the output end of the thermal imager is communicatively connected to the host computer to transmit the temperature data in the thermal image to the host computer, and the host computer includes a processing module and a comparison module. The processing module is used to perform Fourier transform on the temperature data to form an amplitude map and a phase map. The comparison module is used to compare the amplitude map and the phase map of the cold weld defect area with the amplitude map and the phase map of the normal weld area to obtain the morphological characteristics of the cold weld defect area.

8. The cold soldering defect detection system according to claim 7, wherein: The thermal imager is an infrared thermal imager.

Images