Nondestructive testing method and system for thermal interface material application defects

Abstract

The invention relates to the technical field of thermal interface material defect detection, in particular to a nondestructive detection method and system for thermal interface material application defects, and the system comprises an electric displacement table, heating laser, detection laser, a photoelectric detector, an acoustic optical modulator, a lock-in amplifier, an optical element and a data processing unit; the electric displacement table is used for fixing a sample and accurately controlling the position of the sample; the sample is of a silicon-thermal interface material-substrate sandwich structure; the upper-layer silicon wafer of the sample is plated with a metal film as a transduction layer; the heating laser is used for heating the sample; the acoustic optical modulator is used for modulating the heating laser, so that the heating laser heats the sample in a sine wave form; the detection laser is used for detecting sample temperature fluctuation; the photoelectric detector is used for collecting and detecting laser reflection signals; the lock-in amplifier is used for extracting and detecting laser phase and amplitude signals. According to the invention, non-destructive rapid detection of the defects of the thermal interface material in an application scene can be realized.

Description

Technical Field

[0001] This application relates to the field of thermal interface material defect detection technology, and in particular to a non-destructive testing method and system for defects in thermal interface materials. Background Technology

[0002] Thermal interface materials (TIMs) are commonly used to fill the gaps between heat sources and heat sinks in electronic devices, such as between chips and cover plates, or between cover plates and heat sinks, providing a heat dissipation path and preventing electronic components from failing due to overheating. However, interface defects (voids, cracks, oxide layers, etc.) that may exist in TIMs during practical applications can lead to reduced heat dissipation efficiency, decreased mechanical properties, reduced long-term reliability, and degraded electrical performance. Therefore, defect detection of TIMs is crucial for their research and development and application.

[0003] Currently, commonly used methods for material defect detection mainly include: optical microscopy, scanning electron microscopy (SEM), X-ray computed tomography (X-ray CT), ultrasonic testing, focused ion beam (FIB), and thermal imaging. Optical microscopy is primarily used for larger surface defects; it is simple to operate and inexpensive, but it cannot detect defects within multilayered structures. Scanning electron microscopy offers higher resolution and can observe microscopic defects, but sample preparation is often time-consuming, requiring destructive methods to observe internal defects. X-ray computed tomography has drawbacks such as high equipment cost and resolution limited by material properties. Ultrasonic testing is the most commonly used non-destructive defect scanning method; however, it has low resolution for some micrometer-level interfaces and requires immersion in water, potentially affecting some electronic devices. Focused ion beam (FIB) requires cutting the sample to observe internal microscopic defects, is complex to operate, expensive, and can only be used for observing small areas of samples. Traditional thermal imaging can only detect surface or shallow interface defects. Summary of the Invention

[0004] This application provides a non-destructive testing method and system for defects in thermal interface materials, which can realize non-destructive and rapid detection of the working state and defects of thermal interface materials in applications. This is of great significance for understanding the performance of thermal interface materials and their application in various thermal management scenarios.

[0005] To address the aforementioned technical problems, in a first aspect, embodiments of this application provide a non-destructive testing system for defects in thermal interface materials, comprising: an electric displacement stage, a heating laser, a probe laser, a photodetector, an acousto-optic modulator, a lock-in amplifier, optical elements for laser guidance, and a data processing unit; the electric displacement stage is used to fix the sample and precisely control its position; the sample has a silicon-thermal interface material-substrate sandwich structure; a metal film is deposited on the upper silicon wafer of the sample as a transducer layer; the heating laser is used to heat the sample; the acousto-optic modulator is used to modulate the heating laser to heat the sample in a sinusoidal wave form; the probe laser is used to detect temperature fluctuations in the sample; the photodetector is used to acquire the reflection signal of the probe laser; both the electric displacement stage and the lock-in amplifier are connected to the control unit, and the lock-in amplifier is used to extract the phase and amplitude signals of the probe laser.

[0006] In some exemplary embodiments, the above-described nondestructive testing system further includes a temperature control stage; the temperature control stage is used to perform different temperature tests on the sample.

[0007] In some exemplary embodiments, the above-described nondestructive testing system further includes: a pressure application fixture; the pressure application fixture is used to apply pressure to the sample to achieve different pressure tests on the sample.

[0008] In some exemplary embodiments, the optical elements include: a dichroic mirror, a reflector, an objective lens, an optical isolator, and a filter.

[0009] In some exemplary embodiments, the wavelength of the heating laser is matched with the metal of the metal film, so that the transducer layer has a large absorption rate; the wavelength of the probe laser is matched with the metal of the metal film, so that the transducer layer has a large photothermal reflectance coefficient.

[0010] In some exemplary embodiments, the thickness of the metal film is 100 nm to 200 nm.

[0011] In some exemplary embodiments, the photodetector is matched to the wavelength of the probe light.

[0012] Secondly, this application also provides a non-destructive testing method for defects in thermal interface materials. Based on the non-destructive testing system for defects in thermal interface materials described in the above embodiments, the method performs non-destructive testing on defects in thermal interface materials, including the following steps:

[0013] Step 1: Fix the sample on the electric displacement stage and make the upper surface of the metal film coincide with the focal plane of the objective lens of the optical element;

[0014] Step 2: Turn on the heating laser and the detection laser and irradiate the metal film surface with the laser;

[0015] Step 3: The heating laser is modulated using an acousto-optic modulator to heat the sample surface in the form of a sinusoidal wave at a specific frequency; another stable continuous probe laser is used to hit the heating position and a photodetector is used to collect its reflected light; the control unit controls the electric displacement stage to move the sample, and the photodetector collects and simultaneously uses a lock-in amplifier to extract the amplitude and phase data of the probe laser reflection signal at each position; the data processing unit records the extracted amplitude and phase data of the probe laser reflection signal at each position.

[0016] Step 4: Use the amplitude or phase data of the probe light reflection signal recorded in Step 3 at each position of the sample to output the phase distribution map or amplitude distribution map of the scan area;

[0017] Step 5: Determine whether the interface is uniform and whether there are gaps by using the phase distribution diagram.

[0018] In some exemplary embodiments, in step five, it is determined according to formula (1) that the phase corresponds one-to-one with the sample structure; formula (1) is shown below:

[0019]

[0020] Where ω is the modulation angular frequency, The phase delay introduced to the system This is the inverse Hankel transform of the thermal response in the frequency domain.

[0021] In some exemplary embodiments, during the scanning process, the sample moves with the electric displacement stage while the positions of the two laser beams remain unchanged.

[0022] The technical solution provided in this application has at least the following advantages:

[0023] This application provides a method and system for non-destructive testing of defects in thermal interface materials. The system includes: an electric displacement stage, a heating laser, a probe laser, a photodetector, an acousto-optic modulator, a lock-in amplifier, optical elements for laser guidance, and a data processing unit. The electric displacement stage is used to fix the sample and precisely control its position. The sample has a silicon-thermal interface material-substrate sandwich structure. A metal film is deposited on the upper silicon wafer of the sample as a transducer layer. The heating laser is used to heat the sample. The acousto-optic modulator is used to modulate the heating laser to heat the sample in a sinusoidal wave form. The probe laser is used to detect temperature fluctuations in the sample. The photodetector is used to collect the reflection signal of the probe laser. The electric displacement stage and the lock-in amplifier are both connected to the control unit, and the lock-in amplifier is used to extract the phase and amplitude signals of the probe laser.

[0024] This application provides a measurement method and testing device for measuring interface defects in thermal interface materials, based on the detection of actual heat transfer effects. A lock-in amplifier and detector are used to achieve precise acquisition of the phase and amplitude of the detection laser. A high-precision electric displacement stage and lock-in amplifier are used in synergistic control to achieve scanning imaging of the sample. Compared to ordinary optical microscopy, it can detect internal defects below the surface. Compared to scanning electron microscopy and FIB, it is a non-destructive method. Compared to X-ray tomography, it is lower in cost and offers resolution close to or even higher. Compared to ultrasonic scanning, it has higher resolution for shallow interfaces and does not require immersion of the sample in water, which is crucial for electronic devices. Compared to traditional thermal imaging detection, it can detect deeper internal defects. Furthermore, this method is simple to operate, data consistency is easily guaranteed, and the requirements for testing personnel are reduced. Attached Figure Description

[0025] One or more embodiments are illustrated by way of example with reference to the accompanying drawings. These illustrations do not constitute a limitation on the embodiments, and unless otherwise stated, the figures in the drawings are not to be limited by scale.

[0026] Figure 1 This is a schematic diagram of the structure of a non-destructive testing system for defects in thermal interface materials provided in an embodiment of this application.

[0027] Figure 2 This is a sample scanning result diagram of Example 1 of this application.

[0028] Figure 3 This is an image showing the ultrasonic scanning results of the sample in Example 1 of this application.

[0029] Figure 4 This is an X-ray non-destructive scanning result of the sample in Example 1 of this application.

[0030] Figure 5 This is a sample scanning result diagram of Example 2 of this application.

[0031] Figure 6 This is an image showing the ultrasonic scanning results of the sample in Example 2 of this application. Detailed Implementation

[0032] As can be seen from the background art, existing traditional methods for detecting material defects, such as optical microscopy, scanning electron microscopy, X-ray tomography, ultrasonic scanning, focused ion beam, and thermal imaging, all have various problems.

[0033] To address the aforementioned technical problems, this application provides a non-destructive testing method and system for defects in thermal interface materials. The system includes: an electric displacement stage, a heating laser, a probe laser, a photodetector, an acousto-optic modulator, a lock-in amplifier, optical elements for laser guidance, and a data processing unit. The electric displacement stage is used to fix the sample and precisely control its position. The sample has a silicon-thermal interface material-substrate sandwich structure. A metal film is deposited on the upper silicon wafer of the sample as a transducer layer. The heating laser is used to heat the sample. The acousto-optic modulator is used to modulate the heating laser to heat the sample in a sinusoidal wave form. The probe laser is used to detect temperature fluctuations in the sample. The photodetector is used to collect the reflected signal of the probe laser. Both the electric displacement stage and the lock-in amplifier are connected to the control unit, and the lock-in amplifier is used to extract the phase and amplitude signals of the probe laser. This application provides a non-destructive testing method and system for defects in thermal interface materials, enabling rapid non-destructive detection of defects in thermal interface materials in application scenarios.

[0034] The embodiments of this application will now be described in detail with reference to the accompanying drawings. However, those skilled in the art will understand that many technical details have been provided in the embodiments of this application to facilitate a better understanding of the application. However, the technical solutions claimed in this application can be implemented even without these technical details and various variations and modifications based on the following embodiments.

[0035] See Figure 1 This application provides a non-destructive testing system for defects in thermal interface materials, comprising: an electric displacement stage, a heating laser, a probe laser, a photodetector, an acousto-optic modulator, a lock-in amplifier, optical elements for laser guidance, and a data processing unit; the electric displacement stage is used to fix the sample and precisely control its position; the sample has a silicon-thermal interface material-substrate sandwich structure; a metal film is deposited on the upper silicon wafer of the sample as a transducer layer; the heating laser is used to heat the sample; the acousto-optic modulator is used to modulate the heating laser to heat the sample in a sinusoidal wave form; the probe laser is used to detect temperature fluctuations in the sample; the photodetector is used to collect the reflection signal of the probe laser; the electric displacement stage and the lock-in amplifier are both connected to the control unit, and the lock-in amplifier is used to extract the phase and amplitude signals of the probe laser.

[0036] The technical problem this invention aims to solve is to provide a novel in-situ method and experimental system for detecting defects in thermal interface materials used in applications, enabling non-destructive and rapid detection of defects in thermal interface materials within application scenarios. Specifically, this experimental method starts with the distribution and changes in the thermal conductivity of thermal interface materials during application, evaluating their working state and defects—something difficult to achieve with other experimental devices or methods. Specifically, this invention employs laser-modulated heating to scan and image the thermal response of the entire application coverage surface of the thermal interface material in a sandwich structure, thereby analyzing its thermal resistance distribution and reflecting its defect distribution, thus overcoming the shortcomings of existing instruments or systems that cannot cover or involve destructive sample preparation and testing. Furthermore, the scanning and imaging of defects in thermal interface materials under different external loads, such as temperature and pressure, provides an important tool for studying changes in the working state of thermal interface materials in application scenarios.

[0037] It should be noted that the sample to be tested is a silicon wafer-thermal interface material-substrate structure, and the thickness of the top silicon wafer is less than 100 micrometers, with a metal film of 100nm to 200nm deposited on the surface. The shape and thickness of the middle thermal interface material are not limited, and the substrate material is not limited.

[0038] Specifically, both the heating laser and the detection laser utilize semiconductor single-mode lasers, which are characterized by stable power, low cost, easy maintenance, linear polarization, and good collimation. The control unit coordinates the control of the lock-in amplifier and the electric displacement stage; this application employs a lock-in amplifier and detector to achieve precise acquisition of the detection laser phase and amplitude. This application uses a high-precision electric displacement stage and lock-in amplifier in coordinated control to achieve sample scanning imaging.

[0039] The data processing unit includes a computer program for data processing and a computer for performing control program calculations; the computer program refers to a program that directly calculates the thermal resistance distribution and interface defect distribution of the thermal interface material at a specific modulation frequency.

[0040] The non-destructive testing system for thermal interface materials provided in this application measures interface defects in thermal interface materials. Compared to observation with ordinary optical microscopes, this application can detect internal defects below the surface. Compared to scanning electron microscopy and FIB, it is a non-destructive method. Compared to X-ray tomography, it is lower in cost and offers resolution close to or even higher. Compared to ultrasonic scanning, it has higher resolution for shallow interfaces and does not require immersion of the sample in water, which is crucial for electronic devices. Compared to traditional thermal imaging inspection, it can detect deeper internal defects.

[0041] In some embodiments, the above-described nondestructive testing system further includes: a temperature control stage; the temperature control stage is used to perform different temperature tests on the sample.

[0042] In some embodiments, the nondestructive testing system further includes a pressure application fixture; the pressure application fixture is used to apply pressure to the sample to achieve different pressure tests on the sample.

[0043] In some embodiments, the optical elements include: a dichroic mirror, a reflector, an objective lens, an optical isolator, and a filter.

[0044] In some embodiments, the heating laser wavelength is matched with the metal of the metal film, so that the transducer layer has a large absorption rate; the probe laser wavelength is matched with the metal of the metal film, so that the transducer layer has a large photothermal reflectance coefficient.

[0045] In some embodiments, the thickness of the metal film is 100 nm to 200 nm.

[0046] In some embodiments, the photodetector is matched to the wavelength of the probe light.

[0047] In some embodiments, the electric displacement stage controller provides an API interface for interfacing with MATLAB.

[0048] In some embodiments, the lock-in amplifier features built-in FPGA and ASIC sampling circuitry, a data transfer rate of up to 1600 times per second, a test accuracy in the 0.1 microvolt range, and provides an API interface for interfacing with MATLAB.

[0049] Furthermore, this application also provides a non-destructive testing method for defects in thermal interface materials. Based on the non-destructive testing system for defects in thermal interface materials described in the above embodiments, the method performs non-destructive testing on defects in thermal interface materials, including the following steps:

[0050] Step 1: Fix the sample on the electric displacement stage and make the upper surface of the metal film coincide with the focal plane of the objective lens of the optical element;

[0051] Step 2: Turn on the heating laser and the detection laser and irradiate the metal film surface with the laser;

[0052] Step 3: The heating laser is modulated using an acousto-optic modulator to heat the sample surface in the form of a sinusoidal wave at a specific frequency; another stable continuous probe laser is used to hit the heating position and a photodetector is used to collect its reflected light; the control unit controls the electric displacement stage to move the sample, and the photodetector collects and simultaneously uses a lock-in amplifier to extract the amplitude and phase data of the probe laser reflection signal at each position; the data processing unit records the extracted amplitude and phase data of the probe laser reflection signal at each position.

[0053] Step 4: Use the amplitude or phase data of the probe light reflection signal recorded in Step 3 at each position of the sample to output the phase distribution map or amplitude distribution map of the scan area;

[0054] Step 5: Determine whether the interface is uniform and whether there are gaps by using the phase distribution diagram.

[0055] The method for measuring defects in thermal interface materials provided in this application includes the following steps: preparing a silicon-TIM-substrate sandwich structure and fixing it on a displacement stage; using a continuous-wave laser for sinusoidal modulation heating, causing the temperature of the heated area to change periodically in a sinusoidal manner at a fixed frequency (f); using another stable continuous laser beam to strike the heated position and collecting its reflected light with a photodetector; recording the difference between the phase of the reflected light and the phase of the modulated laser. The sinusoidally changing heat source generates sinusoidally changing temperature fluctuations on the sample surface, and these fluctuations are modulated at the same frequency as the heat source. Due to differences in the thermal properties of the sample, such as thermal conductivity or contact thermal resistance, the temperature fluctuations and the phase delay between the modulated heat source differ. By scanning the entire sample surface to obtain the phase distribution, the differences in thermal properties at different locations of the sample and the presence of defects can be determined.

[0056] In the experimental operation of this method, the upper silicon wafer of the sample needs to have a small thickness and roughness and be coated with a metal film of 100nm to 200nm as a transducer layer; the wavelength of the heating laser should be matched with the metal so that the transducer layer has a large absorption rate; the wavelength of the detection laser should also be matched with the metal so that the transducer layer has a large photothermal reflection coefficient.

[0057] Using the above method, when performing sample scanning tests, the sample is fixed on an electric displacement stage, and the sample position can be precisely controlled and obtained through the matching controller and computer control interface.

[0058] According to the above method, the signal generator is used to modulate the heating laser so that it heats the sample in the form of a sine wave.

[0059] Using the above method, the lock-in amplifier used to acquire amplitude and phase signals has high acquisition accuracy, reaching 1 microvolt, which is equivalent to detecting temperature fluctuations below 0.1℃, and has a high data acquisition rate of at least 1600 times per second.

[0060] Using the above method, the distribution of interface defects in the thermal interface material is finally obtained by acquiring the phase signal or amplitude signal of the probe light at each location under different modulation frequencies. The entire data processing and calculation process is completed by program control.

[0061] In some embodiments, in step three, the voltage amplitude of the sinusoidal alternating current needs to satisfy a signal-to-noise ratio greater than 40 dB for the amplitude of the probe light reflection signal.

[0062] In some embodiments, in step five, the phase corresponds one-to-one with the sample structure according to formula (1), which is shown below:

[0063]

[0064] Where ω is the modulation angular frequency, The phase delay introduced to the system This is the inverse Hankel transform of the thermal response in the frequency domain.

[0065] In some embodiments, during the scanning process, the sample moves with the electric displacement stage while the positions of the two laser beams remain unchanged.

[0066] In the technical solution of this invention, the sample to be tested is fixed on an electric displacement stage, and an acousto-optic modulator is used to modulate a heating laser to generate a sinusoidally changing periodic heat source. Another unmodulated laser beam is used to detect temperature changes at different positions during sample movement. A high-response photodetector is used to acquire the phase and amplitude signals at each position of the sample at the corresponding modulation frequency, and a high-speed, high-precision lock-in amplifier is used to extract these signals. A data processing program is used to record the amplitude and phase data of the laser reflection signal at each extracted position.

[0067] In the experimental operation of this invention, when a sinusoidal periodic heat source is applied, the temperature of the heated area of ​​the sample fluctuates periodically at the same frequency. The heat is transferred from the gold transducer layer to the bottom and is finally completely absorbed by the sample, that is, the heat flux density of the lower surface is 0. By solving the heat transfer matrix and Hankel transformation, the relationship between the thermal properties of the sample and the temperature of the upper surface can be obtained, and the relationship between the thermal properties of the sample and the phase of the probe light can be obtained, reflecting the interface defects of the thermal interface material.

[0068] In the technical solution of this invention, the derivation process of formula (1) is as follows:

[0069] The heat conduction differential equation is as follows:

[0070]

[0071] κ in equation (2) r and κ z These are the radial thermal conductivity and the axial thermal conductivity, respectively.

[0072] Applying the Hankel transformation to equation (2), we get:

[0073]

[0074] The above equation is a second-order linear differential equation with constant coefficients, and its general solution is:

[0075]

[0076] Depend on Equation (5) can be transformed into:

[0077]

[0078] Substituting equation (6) into Fourier's law, we get:

[0079]

[0080] For any two points z1 and z2, the following holds:

[0081]

[0082] Considering the cases where z1 = 0 and z2 = l, we have:

[0083]

[0084] Substituting, we get:

[0085]

[0086] The intermediate matrix is ​​the heat transfer matrix within a certain medium, which can be simplified as follows:

[0087]

[0088] Since the heat flux density at the bottom is 0, we can obtain:

[0089]

[0090] The temperature distribution on the real space surface can be obtained as follows:

[0091]

[0092] The intensity distribution of Gaussian light in Hankel space is known to be:

[0093]

[0094] The known reflectance is:

[0095] R(r,t,0)=C th T(r,t,0)+R0 (19)

[0096] Where C th R0 is the photothermal reflectance coefficient of the transducer metal, and R0 is the reflectance at room temperature.

[0097] The intensity of the reflected light is a weighted value of the intensity distribution of the probe light and the reflectivity, as follows:

[0098]

[0099] Substituting into formulas (16) and (19) and simplifying, we get:

[0100]

[0101] By extracting only the frequency signal and introducing the transfer function (output signal / input signal), we can obtain:

[0102]

[0103] Finally, the phase difference formula can be obtained:

[0104]

[0105] The following detailed description of the non-destructive testing method and system for defects in thermal interface materials provided in this application is based on specific embodiments.

[0106] Example 1: Interface defect scanning of metallic indium

[0107] Specifically, the following steps are included:

[0108] Step 1: Sample Preparation. In this specific embodiment of the invention, the sample is a sandwich structure of a gold-plated silicon wafer and an indium wafer. First, a 3mm thick silicon wafer is heated to 158°C. Then, while maintaining the heat, an indium wafer is placed on the silicon wafer and allowed to melt. Next, a 65μm thick gold-plated silicon wafer is placed on top and pressure is applied until it adheres. Heating is stopped, and the sample is allowed to cool. The sample is then fixed on an electric displacement stage, and its position is adjusted until the upper surface of the gold plating layer coincides with the focal plane of the objective lens.

[0109] Step Two: Conduct Testing. Deploy all components, turn on all equipment, open the lock-in amplifier and motorized stage control software, and set all scanning parameters. Select a 2000Hz sinusoidal signal output modulation frequency to illuminate the area to be scanned with two laser beams. Begin scanning, and extract and record the phase and amplitude signals of the probe light at each position using the lock-in amplifier and data processing program.

[0110] Step 3: Data Processing. Use a data processing program to draw the phase distribution map of the scanned area (e.g., ...). Figure 2 As shown in the image, the defective region (white area) exhibits a significantly different phase. Ultrasonic scans of the same sample (e.g.) Figure 3 (as shown) and X-ray non-destructive imaging (such as...) Figure 4 The same defect was found in the test (as shown).

[0111] Example 2: Interface defect scanning of thermally conductive gel

[0112] Specifically, the following steps are included:

[0113] Step 1: Sample Preparation. In this specific embodiment of the invention, the thermally conductive gel sample is a sandwich structure sample consisting of a gold-plated silicon wafer, thermally conductive gel, and another silicon wafer. An appropriate amount of thermally conductive gel is applied to a 3mm thick silicon wafer. A circular stainless steel pad with a thickness of 10 micrometers and a radius of 1.5 millimeters is then placed on top. A thin gold-plated silicon wafer with a thickness of 65μm is then placed on top and appropriate pressure is applied until it adheres to the substrate. The sample is then dried in a 125℃ oven for 2 hours until the thermally conductive gel solidifies. After cooling, the sample is fixed on an electric displacement stage, and its position is adjusted until the upper surface of the gold plating layer coincides with the focal plane of the objective lens.

[0114] Step Two: Conduct Testing. Deploy all components, turn on all equipment, open the lock-in amplifier and motorized stage control software, and set all scanning parameters. Select a 2500Hz sinusoidal signal output modulation frequency to illuminate the area to be scanned with two laser beams. Begin scanning, and extract and record the phase and amplitude signals of the probe light at each position using the lock-in amplifier and data processing program.

[0115] Step 3: Data Processing. Use a data processing program to draw the phase distribution map of the scanned area (e.g., ...). Figure 5 (as shown), Figure 6 The image shows the ultrasonic scanning results of the sample in Example 2. The area with the gasket (white part) has a significantly different phase and shows the outline of the stainless steel gasket.

[0116] Based on the above technical solutions, this application provides a method and system for non-destructive testing of defects in thermal interface materials. The system includes: an electric displacement stage, a heating laser, a probe laser, a photodetector, an acousto-optic modulator, a lock-in amplifier, optical elements for laser guidance, and a data processing unit. The electric displacement stage is used to fix the sample and precisely control its position. The sample has a silicon-thermal interface material-substrate sandwich structure. A metal film is deposited on the upper silicon wafer of the sample as a transducer layer. The heating laser is used to heat the sample. The acousto-optic modulator is used to modulate the heating laser to heat the sample in a sinusoidal wave form. The probe laser is used to detect temperature fluctuations in the sample. The photodetector is used to collect the reflection signal of the probe laser. The electric displacement stage and the lock-in amplifier are both connected to the control unit, and the lock-in amplifier is used to extract the phase and amplitude signals of the probe laser.

[0117] This application provides a measurement method and testing device for measuring interface defects in thermal interface materials, based on the detection of actual heat transfer effects. A lock-in amplifier and detector are used to achieve precise acquisition of the phase and amplitude of the detection laser. A high-precision electric displacement stage and lock-in amplifier are used in synergistic control to achieve scanning imaging of the sample. Compared to ordinary optical microscopy, it can detect internal defects below the surface. Compared to scanning electron microscopy and FIB, it is a non-destructive method. Compared to X-ray tomography, it is lower in cost and offers resolution close to or even higher. Compared to ultrasonic scanning, it has higher resolution for shallow interfaces and does not require immersion of the sample in water, which is crucial for electronic devices. Compared to traditional thermal imaging detection, it can detect deeper internal defects. Furthermore, this method is simple to operate, data consistency is easily guaranteed, and the requirements for testing personnel are reduced.

[0118] Those skilled in the art will understand that the above embodiments are specific examples of implementing this application, and in practical applications, various changes in form and detail can be made without departing from the spirit and scope of this application. Any person skilled in the art can make their own modifications and alterations without departing from the spirit and scope of this application; therefore, the scope of protection of this application should be determined by the scope defined in the claims.

Claims

1. A non-destructive testing system for defects in thermal interface materials, characterized in that, include: Electric displacement stage, heating laser, detection laser, photodetector, acousto-optic modulator, lock-in amplifier, optical components for laser guidance, and data processing unit; The electric displacement stage is used to fix the sample and precisely control its position; the sample has a silicon-thermal interface material-substrate sandwich structure; a metal film is deposited on the upper silicon wafer of the sample as a transducer layer; The heating laser is used to heat the sample; the acousto-optic modulator is used to modulate the heating laser so that it heats the sample in a sinusoidal form; The detection laser is used to detect temperature fluctuations in the sample; the photodetector is used to collect the reflected signal of the detection laser. Both the electric displacement stage and the lock-in amplifier are connected to the control unit. The lock-in amplifier is used to extract the phase and amplitude signals of the probe laser.

2. The non-destructive testing system for defects in thermal interface materials according to claim 1, characterized in that, Also includes: Temperature control stage; the temperature control stage is used to perform different temperature tests on samples.

3. The non-destructive testing system for defects in thermal interface materials according to claim 1, characterized in that, Also includes: A pressure application fixture; the pressure application fixture is used to apply pressure to the sample to achieve different pressure tests on the sample.

4. The non-destructive testing system for defects in thermal interface materials according to claim 1, characterized in that, The optical components include: a dichroic mirror, a reflecting mirror, an objective lens, an optical isolator, and a filter.

5. The non-destructive testing system for defects in thermal interface materials according to claim 1, characterized in that, The wavelength of the heating laser is matched with the metal of the metal film, so that the transducer layer has a large absorption rate; the wavelength of the probe laser is matched with the metal of the metal film, so that the transducer layer has a large photothermal reflection coefficient.

6. The non-destructive testing system for defects in thermal interface materials according to claim 1, characterized in that, The thickness of the metal film is 100nm to 200nm.

7. The non-destructive testing system for defects in thermal interface materials according to claim 1, characterized in that, The photodetector is matched with the wavelength of the probe light.

8. A method for non-destructive testing of defects in thermal interface materials, comprising non-destructive testing of defects in thermal interface materials based on the non-destructive testing system for defects in thermal interface materials as described in any one of claims 1 to 7, characterized in that, Includes the following steps: Step 1: Fix the sample on the electric displacement stage and make the upper surface of the metal film coincide with the focal plane of the objective lens of the optical element; Step 2: Turn on the heating laser and the detection laser and irradiate the metal film surface with the laser; Step 3: Modulate the heating laser using an acousto-optic modulator to heat the sample surface in the form of a sine wave of a specific frequency; use another stable continuous probe laser to hit the heating position and use a photodetector to collect its reflected light; The control unit controls the electric displacement stage to move the sample, and uses a photodetector to collect the amplitude and phase data of the laser reflection signal at each position, while using a lock-in amplifier to extract the amplitude and phase data of the laser reflection signal at each position; the data processing unit records the extracted amplitude and phase data of the laser reflection signal at each position. Step 4: Use the amplitude or phase data of the probe light reflection signal recorded in Step 3 at each position of the sample to output the phase distribution map or amplitude distribution map of the scan area; Step 5: Determine whether the interface is uniform and whether there are gaps by using the phase distribution diagram.

9. The non-destructive testing method for defects in thermal interface materials according to claim 8, characterized in that, In step five, according to formula (1), the phase corresponds one-to-one with the sample structure; formula (1) is shown below: Where ω is the modulation angular frequency, The phase delay introduced to the system This is the inverse Hankel transform of the thermal response in the frequency domain.

10. The non-destructive testing method for defects in thermal interface materials according to claim 8, characterized in that, During the scanning process, the sample moves with the electric displacement stage, while the positions of the two laser beams remain unchanged.

Images