A method for detecting defects in-situ in a bonding process by combining coarse and fine detection

Abstract

The application discloses a kind of rough-fine combination defect in-situ detection methods for bonding process, belong to chip stacking bonding process detection field.First, the ultrasonic vibration emitted by phased array ultrasonic probe is used to assist chip interlayer bonding to promote solder joint formation, and after bonding, rough detection is realized in the whole chip area by multi-element electronic scanning, and the approximate range of suspected false welding, cavity, crack defects is locked by collecting ultrasonic reflection signals;Then drive Fresnel lens and the matched ultrasonic probe to move to the target area, so that the ultrasonic is focused by Fresnel lens and accurately acts on the suspected defect position, receives high-frequency reflected sound wave and realizes high-resolution imaging by three-dimensional reconstruction image technology, judges the defect type, size and spatial position;Finally, the above steps are cycled, and the rough detection and fine detection of all areas of chip are completed in turn, and the bonding quality and defect distribution dynamic data are comprehensively obtained.The application realizes the rapid screening and accurate positioning of defects in the bonding process, and meets the real-time quality control requirements.

Description

Technical Field

[0001] This invention relates to the field of process inspection technology for multilayer chip stacking and flip bonding processes, and more specifically to an in-situ detection method for coarse-fine bonding defects in the bonding process. Background Technology

[0002] Multilayer chip stacking and bonding is a core process in advanced integrated circuit packaging. By vertically interconnecting and stacking multiple chips, it achieves the characteristics of small device size, low power consumption, and high integration, releasing stronger performance within a limited space, while reducing the stringent requirements on individual chip manufacturing processes, thus combining integration efficiency and cost advantages. However, as the number of stacked layers increases and the chip spacing decreases, the probability of defects such as cold solder joints, voids, and cracks increases significantly. Existing traditional detection methods are mostly offline operations, which suffer from long detection cycles and high equipment costs, and it is difficult to balance detection efficiency and accuracy, resulting in limited chip production yield. Therefore, there is an urgent need for a coarse-fine combined in-situ defect detection method for the bonding process, which can achieve rapid defect screening and accurate location, meeting the needs of real-time quality control during the bonding process.

[0003] In-situ inspection technology is a rapidly developing discipline closely related to sensing principles, signal processing technology, intelligent algorithms, and precision control technology. It is widely used in various fields such as defect identification in electronic devices, quality control in advanced manufacturing, and traceability of industrial production processes. Its basic principle is that objects under different conditions exhibit differences in physical or chemical properties. Without damaging the object's structure or interrupting the production process, characteristic signals (such as temperature, acoustic, and optical signals) of the target area are collected in real time by sensing devices. After analysis and processing, the internal state and defect status can be determined. Therefore, in-situ inspection technology has outstanding advantages such as non-destructive nature, online synchronization, rapid response, and complete process information. With in-depth research and development, it shows broader application prospects. For example, by optimizing the accuracy of sensing devices and signal acquisition frequency, precise capture of minute defects can be achieved; intelligent algorithms such as machine learning and deep learning can be used to complete the automatic classification and quantitative evaluation of defect types; and multimodal sensing data can be integrated to build a comprehensive inspection system, breaking through the limitations of single-signal detection and comprehensively improving the reliability and applicability of inspection in complex manufacturing scenarios.

[0004] The coarse-fine combined in-situ defect detection technology is an innovative detection solution that integrates the phased array ultrasonic detection principle, Fresnel acoustic focusing mechanism, precision mechanical control and intelligent signal processing. It is specifically applied to the rapid screening and precise location of solder joint defects during the multilayer chip stacking and bonding process. Its core design logic is as follows: Phased array ultrasonic testing is used as the "rough inspection" stage. Utilizing the multi-element electronic scanning characteristics of the phased array probe, it can quickly cover the entire area and depth of the chip stack. By leveraging the differences in the propagation and reflection of ultrasonic waves in different media, it can efficiently pinpoint the approximate range of suspected defects such as cold solder joints, voids, and cracks, achieving large-scale, high-speed initial defect screening. Fresnel lens testing is used as the "fine inspection" stage. The Fresnel lens, as the core acoustic focusing element, is composed of a series of concentric rings. Based on the principle of wave diffraction, the rings, made by etching rigid materials, form slits that gradually narrow from the inside out. When used in conjunction with an ultrasonic transducer, the ultrasonic waves diffract after passing through the slits and focus towards the center, significantly increasing the acoustic energy flux density and reducing the measurement area, greatly improving spatial resolution. This allows for precise point detection of the suspected areas identified in the rough inspection, clarifying the specific type, size, and location of the defects. This technology is typically used in real-time quality control scenarios for multi-layer chip stacking and bonding. However, it still faces some challenges, including optimizing the collaborative response speed of the coarse-fine inspection process, improving the system's equipment integration, and how to further improve the system's vertical and horizontal resolution. Summary of the Invention

[0005] The purpose of this invention is to solve the problem of lagging chip quality control and low production efficiency caused by the asynchronous packaging and fine inspection in the multilayer chip bonding process. It provides an in-situ detection method for coarse-fine bonding defects in the bonding process, which can achieve rapid screening and accurate location of defects and meet the needs of real-time quality control in the bonding process.

[0006] To achieve the above objectives, the present invention provides the following technical solution: In a first aspect, the present invention provides an in-situ detection method for coarse-to-fine bonding defects in the bonding process, comprising the following steps: An in-situ detection method for coarse-to-fine bonding defects in the bonding process, characterized in that it comprises the following steps:

[0007] Step 1, Bonding and Rough Inspection Stage: After the multilayer chip stacking is completed, the first phased array ultrasonic probe is driven to move to the preset station. The ultrasonic vibration emitted by the first phased array ultrasonic probe is used to assist the interlayer bonding of the chip and promote the formation of solder joints. After the bonding is completed, the first phased array ultrasonic probe is used to perform a rough inspection of the entire chip area, collect the ultrasonic reflection signal of the whole area and transmit it to the host computer to locate the approximate range of suspected cold solder joints, voids and cracks.

[0008] Step Two, Fine Inspection Stage: The host computer analyzes and outputs the coordinates of the suspected defect area identified in the coarse inspection stage. Coordinate analysis is mainly used after the data obtained in the coarse inspection stage is obtained and the coordinates are used in the fine inspection stage. Based on the echo data of the phased array electronic scanning in the coarse inspection stage, the transit time t of the defect echo and the corresponding beam deflection angle θ are extracted. Combined with the medium sound velocity c, the planar coordinates and depth of the defect in the probe coordinate system are calculated. The Fresnel lens fine inspection system is then driven to move to the target area, so that all Fresnel lenses, the second phased array ultrasonic probe, and the chip to be inspected area contained in the Fresnel lens fine inspection system are located on the ultrasonic transmission path. Fine inspection stage The transmitter and receiver of the ultrasonic wave are both the second phased array ultrasonic probe in the Fresnel lens precision inspection system. First, the second phased array ultrasonic probe at the transmitter end of the Fresnel lens precision inspection system emits parallel ultrasonic waves towards the Fresnel lens. After being focused by the Fresnel lens, the ultrasonic waves are precisely applied to the suspected defect location. After being reflected by the defect interface, the ultrasonic waves return along the original path. The second phased array ultrasonic probe at the receiver end receives the reflected high-frequency sound waves and converts them into electrical signals. After filtering and amplification, the signals are transmitted to the host computer. High-resolution imaging is achieved through image reconstruction technology to accurately determine the type, size, and spatial location of the defect.

[0009] Step 3, Cyclic Inspection Phase: After the detailed inspection of a single suspected area is completed, the mobile device is moved according to the inspection plan, and Steps 1 to 2 are repeated to complete the coarse and fine inspection of all areas of the chip in sequence, so as to obtain dynamic data on the bonding quality and defect distribution of the multilayer stacked chip.

[0010] Furthermore, in step one, by controlling the emission delay and phase deflection of each element of the first phased array ultrasonic probe, ultrasonic scanning coverage of the entire area and depth of the chip is achieved, and the approximate range of suspected defects is quickly located.

[0011] Furthermore, in step one, the differences in the propagation and reflection of ultrasound in different media are used to identify acoustic feature anomalies in the weld area, thereby distinguishing and locking in the approximate range of suspected incomplete welds, voids, and cracks.

[0012] Furthermore, the distinguishable acoustic and imaging characteristics of defects such as incomplete welds, voids, and cracks are as follows: incomplete welds appear as blurred boundaries and low grayscale contrast in ultrasonic imaging, and the resonant frequency of the echo signal is significantly lower than that of intact welds; voids appear as dot-shaped bright spots with high reflectivity in ultrasonic imaging, and the peak value of the echo signal is significantly higher than that of intact welds; cracks appear as continuous linear bright lines with high reflectivity in ultrasonic imaging, and the echo signal is continuously distributed along the direction of defect extension.

[0013] Furthermore, in step two, the image reconstruction technology includes three-dimensional image reconstruction technology, which is used to achieve high-resolution three-dimensional imaging and accurately determine the type, size and spatial location of defects.

[0014] Furthermore, prior to testing, the chip orientation is adjusted to ensure alignment accuracy between multiple chip layers and eliminate the impact of chip tilt on subsequent ultrasonic signal transmission and detection results. Chip tilt causes ultrasonic incident angle shift, sound path distortion, echo energy attenuation, and focus shift, leading to inaccurate defect location, amplitude interpretation distortion, and noise interference, directly reducing detection accuracy and defect identification reliability.

[0015] Secondly, this invention provides an in-situ detection system for coarse-fine bonding defects in the bonding process, comprising: a host computer for receiving ultrasonic reflection signals from the coarse and fine inspection stages, analyzing and outputting the coordinates of suspected defect areas, controlling a drive mechanism to move the Fresnel lens fine inspection system to the target area, and generating a high-resolution three-dimensional defect image using three-dimensional reconstruction image technology; a support frame, a rigid load-bearing frame that connects and fixes various functional modules, providing a stable installation benchmark for the entire bonding, coarse inspection, and fine inspection process, and ensuring the positional accuracy of each module working collaboratively; a force sensor, mechanically connected to a first phased array ultrasonic probe, for real-time monitoring of the contact pressure between the first phased array ultrasonic probe and the chip during the bonding process, accurately feeding back pressure data to ensure the stability of pressure parameters in ultrasonic-assisted bonding; the first phased array ultrasonic probe is used to emit ultrasonic vibrations with specific parameters to assist interlayer bonding of the chip, and to achieve full-area coarse inspection of the chip through multi-element electronic scanning, quickly locating suspected defects. The system includes a bonding stage, which serves as a chip support platform to fix multi-layer stacked chips. It works with a heating module to provide the necessary temperature environment for the bonding process and acts as a reference carrier for inspection, ensuring the stability of the inspection area. The Fresnel lens precision inspection system includes a Fresnel lens and a second phased array ultrasonic probe. The Fresnel lens focuses the ultrasound onto the suspected defect area identified in the rough inspection, improving the spatial resolution of the inspection and accurately identifying the type and location of defects. A six-axis leveling mechanism, connected to the bonding stage, adjusts the chip's orientation to ensure the alignment accuracy between multi-layer chips and eliminate the influence of chip tilt on subsequent ultrasonic signal transmission and detection results. A longitudinal displacement stage, connected to the first phased array ultrasonic probe and a force sensor, moves the first phased array ultrasonic probe vertically to the desired position, achieving multi-layer chip bonding and simultaneously completing the rough inspection of the bonded product.

[0016] Furthermore, the Fresnel lens is made of metallic or non-metallic materials and consists of a series of concentric rings. Based on the principle of wave diffraction, the rings, made by etching rigid materials, form slits that gradually narrow from the inside out, and the center of the Fresnel lens is a hole.

[0017] The width W and focal length f of the Fresnel acoustic lens are designed. Based on the focal length f and the sound velocity of the Fresnel acoustic lens and the propagation medium, the radius of curvature R of the Fresnel acoustic lens is determined. The thickness d of the Fresnel acoustic lens is determined according to the process requirements, resulting in the following formula:

[0018]

[0019] in It is the radius of the nth Fresnel zone. Where f is the phased array ultrasonic wave length, f is the lens focal length, and n is the Fresnel zone number.

[0020] Furthermore, the Fresnel lens is made of pure tungsten material through a precision etching process, with a lens thickness of 0.05mm. The lens is composed of a series of concentric rings forming a slit structure that gradually narrows from the inside out. The Fresnel lens operates in the frequency range of 10MHz to 50MHz, has a nominal focal length of 10cm, a focal full width at half maximum (FWHM) of 50μm, and a numerical aperture of 0.2. Numerical aperture is a dimensionless physical quantity, defined as the product of the sine of the beam's half-aperture angle and the equivalent refractive index of the medium. Based on the principle of wave diffraction, ultrasonic waves diffract and focus towards the center after passing through the slit, increasing the acoustic energy flux density, reducing the effective measurement area, and improving the detection spatial resolution. The Fresnel lens is driven by a lens holder and moves between the coarse inspection station and the fine inspection station.

[0021] Furthermore, the first phased array ultrasonic probe has dual functions of ultrasonic-assisted bonding and coarse inspection. The ultrasonic parameters used for bonding are different from those used for inspection, and the host computer automatically switches the parameters according to the process stage. In the bonding stage, low-frequency high-power ultrasonic parameters are used, with a transmission frequency range of 5MHz to 15MHz, to output sufficient vibration energy to assist in interlayer bonding of the chip and promote solder joint formation. In the coarse inspection stage, high-frequency low-power ultrasonic parameters are used, with a transmission frequency range of 15MHz to 30MHz. The probe emits and receives reflected sound waves through multi-element electronic scanning, converts the acoustic signal into an electrical signal, and transmits it to the host computer to achieve initial screening of defects in the entire chip area.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1. Overcoming the limitations of lagging quality control and insufficient defect identification accuracy in the existing bonding-detection separation mode, a synchronized in-situ detection scheme of phased array ultrasonic-assisted bonding + coarse inspection + Fresnel lens fine inspection is proposed. Compared with the traditional single detection method, it can more efficiently achieve the coordinated advancement of bonding process and defect detection.

[0024] 2. By using a phased array ultrasonic probe to assist bonding and perform global coarse screening, and with the help of a Fresnel lens to focus the ultrasound to the suspected defect area, the state characteristics and defect information of each layer of solder joints can be captured simultaneously during the multilayer chip bonding process. This ensures the stability of the bonding process and can also identify potential problems in real time.

[0025] 3. The combined coarse-fine inspection logic not only ensures bonding efficiency but also significantly improves the accuracy of defect identification. The dynamic inspection data during the bonding process can not only intuitively reflect the microscopic process of solder joint formation but also optimize bonding parameters and processes based on the inspection results at different stages. This not only improves the yield rate but also provides accurate process data support for the iterative upgrade of subsequent bonding processes. Attached Figure Description

[0026] The present invention will now be described in further detail with reference to the accompanying drawings and specific implementation methods.

[0027] Figure 1 This is a schematic diagram of the in-situ detection mechanism for coarse-fine bonding defects in the bonding process according to the present invention.

[0028] Figure 2 This is a flowchart of the in-situ detection method for coarse-fine bonding defects in the bonding process according to the present invention.

[0029] Explanation of reference numerals in the attached drawings: 1. Support frame; 2. Force sensor; 3. First phased array ultrasonic probe; 4. Bonding stage; 5. Fresnel lens precision inspection system; 6. Six-axis leveling mechanism; 7. Longitudinal displacement stage; 8. Second phased array ultrasonic probe. Detailed Implementation

[0030] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0031] like Figure 1 As shown, the in-situ detection system for coarse-fine bonding defects in the bonding process described in this invention includes: a support frame 1, a force sensor 2, a first phased array ultrasonic probe 3, a bonding stage 4, a Fresnel lens precision inspection system 5, a six-axis leveling mechanism 6, and a longitudinal displacement stage 7; wherein the Fresnel lens precision inspection system 5 integrates a second phased array ultrasonic probe 8.

[0032] Among them, the support frame 1 is a rigid load-bearing frame that fixes each functional module by bolt connection. It is mainly responsible for providing a stable installation benchmark for the entire process of bonding, rough inspection and fine inspection, ensuring the positional accuracy of each module working together, and adapting to the integrated layout requirements of the equipment.

[0033] Force sensor 2 is mechanically connected to the first phased array ultrasonic probe 3. It is mainly responsible for real-time monitoring of the contact pressure between the first phased array ultrasonic probe 3 and the chip during the bonding process, and accurately feeding back pressure data to ensure the stability of pressure parameters in ultrasonic-assisted bonding.

[0034] The first phased array ultrasonic probe 3 includes, but is not limited to, a multi-element phased array probe, primarily responsible for both ultrasonic-assisted bonding and coarse inspection functions: on the one hand, it emits ultrasonic vibrations with specific parameters to assist interlayer bonding of the chip and promote solder joint formation; on the other hand, it performs coarse inspection of the entire chip area through multi-element electronic scanning, quickly locating the suspected defect range, while simultaneously receiving reflected sound waves and converting them into electrical signals for transmission to the host computer. The first phased array ultrasonic probe 3 has dual functions of ultrasonic-assisted bonding and coarse inspection. The ultrasonic parameters used for bonding are different from those used for inspection, and the host computer automatically switches the parameters according to the process stage; in the bonding stage, low-frequency high-power ultrasonic parameters are used, with a transmission frequency range of 5MHz to 15MHz, outputting sufficient vibration energy to assist interlayer bonding of the chip and promote solder joint formation; in the coarse inspection stage, high-frequency low-power ultrasonic parameters are used, with a transmission frequency range of 15MHz to 30MHz, emitting and receiving reflected sound waves through multi-element electronic scanning, converting the acoustic signal into an electrical signal for transmission to the host computer, achieving initial screening of defects across the entire chip area.

[0035] The bonding stage 4 is a chip carrier platform, mainly responsible for fixing multi-layer stacked chips, providing the required temperature environment for the bonding process in conjunction with the heating module, and serving as a reference carrier for testing to ensure the stability of the testing area.

[0036] The Fresnel lens precision inspection system 5 includes a Fresnel lens and a second phased array ultrasonic probe 8. The Fresnel lens is made of metal or non-metal materials and is fixed by mechanical cooperation. It is mainly responsible for focusing the ultrasound to the suspected defect area locked by the rough inspection, improving the spatial resolution of the inspection, and accurately identifying the type and location of defects. Specifically, the Fresnel lens is made of pure tungsten material through a precision etching process, with a lens thickness of 0.05mm. The lens is composed of a series of concentric rings forming a slit structure that gradually narrows from the inside out. The Fresnel lens operates in the frequency range of 10MHz to 50MHz, has a nominal focal length of 10cm, a focal full width at half maximum (FWHM) of 50μm, and a numerical aperture of 0.2. Numerical aperture is a dimensionless physical quantity, defined as the product of the sine of the beam's half-aperture angle and the equivalent refractive index of the medium. Based on the principle of wave diffraction, ultrasonic waves diffract and focus towards the center after passing through the slits, increasing the acoustic energy flux density, reducing the effective measurement area, and improving the detection spatial resolution. The Fresnel lens is driven by a lens holder and moves between the coarse inspection station and the fine inspection station.

[0037] The six-axis leveling mechanism 6 is connected to the bonding stage 4 by bolts. It is mainly responsible for adjusting the orientation of the chip to ensure the alignment accuracy between layers, while eliminating the influence of chip tilt on ultrasonic signal transmission and detection results.

[0038] The longitudinal displacement stage 7 is connected to the first phased array ultrasonic probe 3 and the force sensor 2 through the drive mechanism. It is mainly responsible for driving the system to move in the vertical direction, so that the first phased array ultrasonic probe 3 can move to the expected position, realize the bonding of multi-layer chips, and at the same time complete the rough inspection of the bonded product.

[0039] like Figure 2 As shown, the present invention provides an in-situ detection method for coarse-fine bonding defects in the bonding process, mainly comprising the following steps: Step 1: After multilayer chip stacking is completed, the heating stage at the bottom of the bonding stage 4 is activated for heating. Simultaneously, the drive motor drives the longitudinal displacement stage 7 to move through the transmission mechanism. The longitudinal displacement stage 7 synchronously moves the force sensor 2 and the first phased array ultrasonic probe 3 to a preset position. The first phased array ultrasonic probe 3 emits ultrasonic waves with specific parameters, using ultrasonic vibration to assist interlayer bonding of the chip and promote solder joint formation. After bonding is completed, a coarse inspection of the entire chip area is achieved through multi-element electronic scanning of the first phased array ultrasonic probe 3, collecting ultrasonic reflection signals across the entire area and transmitting them to the host computer to quickly pinpoint the approximate range of suspected defects such as cold solder joints, voids, and cracks.

[0040] In this step, the first phased array ultrasonic probe 3 serves a dual function of bonding assistance and coarse inspection. During the bonding stage, ultrasonic vibration acts on the interlayer interface of the chip supported by the bonding stage 4, promoting the flow and formation of solder joint material and effectively improving solder joint quality. The bonding stage employs low-frequency, high-power ultrasonic parameters, with a transmission frequency range of 5MHz to 15MHz, outputting sufficient vibration energy to assist in interlayer bonding and promote solder joint formation. The coarse inspection stage employs high-frequency, low-power ultrasonic parameters, with a transmission frequency range of 15MHz to 30MHz, with the host computer automatically switching parameters according to the process stage. During the coarse inspection stage, utilizing the multi-element electronic scanning characteristics of the first phased array ultrasonic probe 3, a focused beam is formed by controlling the transmission delay and phase of each element, which can quickly cover the entire area and depth of the chip stack, achieving large-scale initial defect screening. Ultrasonic waves have different propagation speeds and reflection characteristics in different media (intact solder joints and defective areas). By analyzing parameters such as amplitude, phase, and transit time of the global reflection signal, it is possible to effectively distinguish between intact solder joint areas and defective areas such as cold solder joints, voids, and cracks, thereby pinpointing the approximate range of suspected defects. Specifically, cold solder joint defects appear as blurred boundaries and low grayscale contrast in ultrasonic imaging, and the resonant frequency of the echo signal is significantly lower than that of intact solder joints; void defects appear as bright spot-like spots with high reflection amplitude in ultrasonic imaging, and the peak value of the echo signal is significantly higher than that of intact solder joint areas; crack defects appear as continuous bright line-like patterns with high reflection amplitude in ultrasonic imaging, and the echo signal is continuously distributed along the direction of defect extension. The chip is placed on the bonding stage 4, and the six-axis leveling mechanism 6 pre-levels the chip's attitude to eliminate the interference of chip tilt on the ultrasonic signal transmission and rough inspection results of the first phased array ultrasonic probe 3. Chip tilting can cause deviations in the ultrasonic incident angle, distortion of the sound path, attenuation of echo energy, and shift in focus, leading to inaccurate defect location, distortion of amplitude interpretation, and noise interference, directly reducing detection accuracy and reliability of defect identification.

[0041] Step Two: After the coarse inspection is completed, the host computer analyzes and outputs the coordinates of the suspected defect area. The coordinate analysis is mainly for the data obtained in the coarse inspection stage, and the coordinates are used for the fine inspection stage. Based on the echo data of the phased array electronic scanning in the coarse inspection stage, the transit time t of the defect echo and the corresponding beam deflection angle θ are extracted. Combined with the medium sound velocity c, the planar coordinates and depth of the defect in the probe coordinate system are calculated. The drive motor is started, and the Fresnel lens fine inspection system 5 is moved to the target area through the lens bracket. The ultrasound is focused by the Fresnel lens inside the Fresnel lens fine inspection system 5 and accurately falls on the suspected defect position, starting the fine inspection test. At this time, the second phased array ultrasonic probe 8 in the Fresnel lens fine inspection system 5 receives the focused high-frequency reflected sound wave, converts it into an electrical signal and transmits it to the host computer. High-resolution three-dimensional imaging is achieved using technologies including but not limited to three-dimensional reconstruction image technology to accurately determine the defect type, size and spatial location.

[0042] In this step, the Fresnel lens within the Fresnel lens precision inspection system 5 serves as the core acoustic focusing element. It consists of a series of concentric rings, formed by etching from a rigid material to create slits that gradually narrow from the inside out, based on the principle of wave diffraction. Specifically, the Fresnel lens is made of pure tungsten material using a precision etching process, with a lens thickness of 0.05 mm. The Fresnel lens operates in the frequency range of 10 MHz to 50 MHz, has a nominal focal length of 10 cm, a focal full width at half maximum (FWHM) of 50 μm, and a numerical aperture of 0.2. Numerical aperture is a dimensionless physical quantity, defined as the product of the sine of the beam's half-aperture angle and the equivalent refractive index of the medium. The width W and focal length f of the Fresnel acoustic lens are designed. Based on the focal length f and the sound velocity of the Fresnel acoustic lens and the propagation medium, the radius of curvature R of the Fresnel acoustic lens is determined. The thickness d of the Fresnel acoustic lens is determined according to process requirements. The radius of the nth Fresnel zone is determined by the ultrasonic wave length, the lens focal length f, and the number of Fresnel zones n. The Fresnel lens is driven by a lens holder and moves between the coarse inspection station and the fine inspection station. After passing through the slit, the ultrasonic wave diffracts and focuses towards the center, significantly increasing the acoustic energy flux density and reducing the measurement area, thus greatly improving the spatial resolution. The focused ultrasonic energy is concentrated in the suspected defect area identified in the coarse inspection. Combined with the second phased array ultrasonic probe 8 in the Fresnel lens fine inspection system 5 to receive the echo signal, a detection sensitivity and spatial resolution far exceeding that of the coarse inspection stage can be obtained. The host computer processes and performs imaging operations on the received high-frequency echo signals, generating high-resolution 3D defect images through 3D reconstruction imaging technology. This accurately determines the specific type (such as poor weld, void, crack), size, and spatial location of the defects, providing data support for precise evaluation of bonding quality. The entire Fresnel lens precision inspection system 5, the first phased array ultrasonic probe 3, the force sensor 2, the bonding stage 4, and the six-axis leveling mechanism 6 are all mounted on the support frame 1. The support frame 1 provides a unified installation reference, ensuring the positional accuracy of the coarse and fine inspection stations.

[0043] Step 3: After the fine inspection of a single suspected area is completed, the drive motor controls the longitudinal displacement stage 7 and the Fresnel lens fine inspection system 5 to move the equipment synchronously according to the inspection plan. Steps 1 and 2 are repeated to complete the coarse inspection of all areas of the chip by the first phased array ultrasonic probe 3 and the fine inspection by the second phased array ultrasonic probe 8 in the Fresnel lens fine inspection system 5 in sequence, so as to comprehensively obtain the bonding quality and defect distribution dynamic data of the multilayer stacked chips on the bonding stage 4.

[0044] In this step, the entire inspection process is automatically executed in a loop according to the preset inspection plan, completing the coarse and fine inspection of the entire chip carried by the bonding stage 4 area by area. After the Fresnel lens fine inspection system 5 completes the fine inspection of each area, the inspection results are automatically summarized into the defect distribution database of the host computer, and finally a complete bonding quality inspection report covering all stacked chip layers is generated, including dynamic data such as defect type statistics, size distribution, and spatial location distribution, which provides accurate process data support for the iterative optimization of bonding process parameters and the continuous improvement of the production process. The support frame 1 provides stable rigid support for all functional components such as the longitudinal displacement stage 7, the six-axis leveling mechanism 6, and the Fresnel lens fine inspection system 5 throughout the process, ensuring the repeatability and positioning accuracy of multiple rounds of coarse and fine joint inspection.

[0045] The above are embodiments of this application and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made to the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A method for in-situ detection of coarse-fine bonding defects in the bonding process, characterized in that, Includes the following steps: Step 1, Bonding and Rough Inspection Stage: After the multilayer chip stacking is completed, the first phased array ultrasonic probe (3) is driven to move to the preset station. The ultrasonic vibration emitted by the first phased array ultrasonic probe (3) is used to assist the interlayer bonding of the chip and promote the formation of solder joints. After the bonding is completed, the first phased array ultrasonic probe (3) is used to perform a rough inspection of the entire chip area, collect the ultrasonic reflection signal of the whole area and transmit it to the host computer to lock the approximate range of suspected cold solder joints, voids and cracks. Step 2, Fine Inspection Stage: The host computer analyzes and outputs the coordinates of the suspected defect area locked in the coarse inspection stage, driving the Fresnel lens fine inspection system (5) to move to the target area, so that the Fresnel lens in the Fresnel lens fine inspection system (5), the second phased array ultrasonic probe (8), and the chip to be inspected are all located on the ultrasonic transmission path; in the fine inspection stage, the ultrasonic source and receiver are both the second phased array ultrasonic probe (8) in the Fresnel lens fine inspection system (5). First, the second phased array ultrasonic probe (8) located at the transmitting end in the Fresnel lens fine inspection system (5) emits parallel ultrasonic waves towards the Fresnel lens. The ultrasonic waves pass through the Fresnel lens... After the Niel lens is focused, it is precisely applied to the suspected defect location; the ultrasonic wave is reflected by the defect interface and returns along the original path. The high-frequency sound wave reflected back is received by the second phased array ultrasonic probe (8) located at the receiving end and converted into an electrical signal. After filtering and amplification, it is transmitted to the host computer. High-resolution imaging is achieved through image reconstruction technology to accurately determine the type, size and spatial location of the defect; Step 3, Cyclic Detection Stage: After the fine inspection of a single suspected area is completed, the mobile device is moved according to the detection plan, and Step 1 to Step 2 are repeated to complete the coarse inspection and fine inspection of all areas of the chip in sequence, and to fully obtain the bonding quality and defect distribution dynamic data of the multilayer stacked chip; Step 3, Cyclic Inspection Phase: After the detailed inspection of a single suspected area is completed, the mobile device is moved according to the inspection plan, and Steps 1 to 2 are repeated to complete the coarse and fine inspection of all areas of the chip in sequence, so as to obtain dynamic data on the bonding quality and defect distribution of the multilayer stacked chip.

2. The in-situ detection method for coarse-fine bonding defects in the bonding process according to claim 1, characterized in that, In step one, by controlling the emission delay and phase deflection of each element of the first phased array ultrasonic probe (3), ultrasonic scanning coverage of the entire area and depth of the chip is achieved, and the approximate range of suspected defects is quickly located.

3. The in-situ detection method for coarse-fine bonding defects in the bonding process according to claim 1, characterized in that, In step one, the differences in the propagation and reflection of ultrasound in different media are used to identify acoustic anomalies in the weld area, thereby distinguishing and locking in the approximate range of suspected cold welds, voids, and cracks.

4. The in-situ detection method for coarse-fine bonding defects in the bonding process according to claim 3, characterized in that, The distinguishable acoustic and imaging characteristics of defects such as incomplete welds, voids, and cracks are as follows: In ultrasonic imaging, cold solder joint defects are characterized by blurred boundaries, low grayscale contrast, and a significant decrease in the resonant frequency of the echo signal compared to intact solder joints. In ultrasonic imaging, void defects appear as bright spot-like spots with high reflectivity, and the peak value of the echo signal is significantly higher than that of intact solder joints. Crack defects appear as continuous linear bright lines with high reflectivity in ultrasonic imaging, and the echo signal is continuously distributed along the direction of defect extension.

5. The in-situ detection method for coarse-fine bonding defects in the bonding process according to claim 1, characterized in that, In step two, the image reconstruction technology includes three-dimensional image reconstruction technology, which is used to achieve high-resolution three-dimensional imaging and accurately determine the type, size and spatial location of defects.

6. The in-situ detection method for coarse-fine bonding defects in the bonding process according to claim 1, characterized in that, Before testing, the chip orientation is adjusted to ensure the alignment accuracy between the multi-layer chips and to eliminate the impact of chip tilt on subsequent ultrasonic signal transmission and signal detection results.

7. A system for in-situ detection of coarse-fine bonding defects in the bonding process, characterized in that, include: The host computer is used to receive ultrasonic reflection signals from the coarse inspection stage and the fine inspection stage, analyze and output the coordinates of the suspected defect area, control the drive mechanism to move the Fresnel lens fine inspection system (5) to the target area, and use three-dimensional reconstruction image technology to generate a high-resolution three-dimensional defect image. The support frame (1) is a rigid load-bearing frame that connects and fixes each functional module, providing a stable installation benchmark for the entire process of bonding, rough inspection and fine inspection, and ensuring the positional accuracy of each module working together. Force sensor (2) is mechanically connected to the first phased array ultrasonic probe (3) to monitor the contact pressure between the first phased array ultrasonic probe (3) and the chip in real time during the bonding process, and accurately feed back pressure data to ensure the stability of pressure parameters in ultrasonic-assisted bonding; The first phased array ultrasonic probe (3) is used to emit ultrasonic vibrations with specific parameters to assist chip interlayer bonding, and to perform coarse inspection of the entire chip area through multi-element electronic scanning, quickly locking the range of suspected defects, while receiving reflected sound waves and converting them into electrical signals to be transmitted to the host computer. The bonding stage (4) is a chip carrier platform used to fix multi-layer stacked chips, and together with the heating module, it provides the required temperature environment for the bonding process and serves as a reference carrier for detection to ensure the stability of the detection area. The Fresnel lens precision inspection system (5) includes a Fresnel lens and a second phased array ultrasonic probe (8). The Fresnel lens is used to focus the ultrasound onto the suspected defect area locked by the coarse inspection, improve the detection spatial resolution, and accurately identify the defect type and location. The six-axis leveling mechanism (6) is connected to the bonding stage (4) to adjust the orientation of the chip, ensure the alignment accuracy between the layers of the multilayer chip, and eliminate the influence of chip tilt on subsequent ultrasonic signal transmission and signal detection results. The longitudinal displacement stage (7) is connected to the first phased array ultrasonic probe (3) and the force sensor (2) to drive the first phased array ultrasonic probe (3) to move in the vertical direction, so that the first phased array ultrasonic probe (3) moves to the expected position, realizes the bonding of multilayer chips, and at the same time completes the rough inspection of the bonded product.

8. The in-situ detection system for coarse-fine bonding defects in the bonding process according to claim 7, characterized in that, The Fresnel lens is made of metallic or non-metallic materials and consists of a series of concentric rings. Based on the principle of wave diffraction, the rings, made by etching rigid materials, form slits that gradually narrow from the inside out. The center of the Fresnel lens is a hole.

9. The in-situ detection system for coarse-fine bonding defects in the bonding process according to claim 8, characterized in that, The Fresnel lens is made of pure tungsten material through a precision etching process. The lens thickness is 0.05mm. The entire lens is composed of a series of concentric rings, forming a slit structure that gradually narrows from the inside out. The Fresnel lens has a working frequency range of 10MHz to 50MHz, a nominal focal length of 10cm, a focal full width at half maximum (FWHM) of 50μm, and a numerical aperture of 0.

2. Based on the principle of wave diffraction, the ultrasonic wave diffracts and focuses towards the center after passing through the slit, thereby increasing the acoustic energy flux density, reducing the effective measurement area, and improving the detection spatial resolution. The Fresnel lens is driven by a drive mechanism through a lens bracket and moves between the coarse inspection station and the fine inspection station.

10. The in-situ detection system for coarse-fine bonding defects in the bonding process according to claim 7, characterized in that, The first phased array ultrasonic probe (3) has dual functions of ultrasonic-assisted bonding and rough inspection. The ultrasonic parameters used for bonding are different from those used for inspection. The host computer automatically switches the parameters according to the process stage. The bonding stage uses low-frequency high-power ultrasonic parameters with a transmission frequency range of 5MHz to 15MHz to output sufficient vibration energy to assist the bonding between chip layers and promote the formation of solder joints. The rough inspection stage uses high-frequency low-power ultrasonic parameters with a transmission frequency range of 15MHz to 30MHz. The probe emits and receives reflected sound waves through multi-element electronic scanning, converts the sound signal into an electrical signal and transmits it to the host computer to achieve initial screening of defects in the entire chip area.

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