Conformal coating detection method and device, electronic equipment, storage medium and product

Abstract

The invention discloses a conformal coating detection method and device, electronic equipment, a storage medium and a product, and relates to the technical field of nondestructive detection.The conformal coating detection method comprises the steps that a terahertz reflection signal of a chip to be detected is obtained, and a time-domain spectrum of the terahertz reflection signal is generated; the time-domain spectrum is converted into a frequency-domain spectrum, an initial transfer function is constructed based on the frequency-domain spectrum and a preset reference frequency-domain spectrum, and the initial transfer function is the ratio of the frequency-domain spectrum to the reference frequency-domain spectrum; performing frequency domain reconstruction operation on the transfer function through a preset autoregression model to obtain an optimized transfer function; and calculating the characteristics of the conformal coating of the to-be-tested chip according to the optimized transfer function. According to the invention, high-precision measurement of the conformal coating can be guaranteed.

Description

Technical Field

[0001] The present application relates to the field of nondestructive testing technology, and in particular to conformal coating testing methods, devices, electronic equipment, storage media and products. Background Art

[0002] With the rapid development of emerging industries such as big data, Internet of Things, artificial intelligence, and 5G communications, the global demand for semiconductor chips continues to grow. Conformal coating is an important means to protect semiconductor chips from physical and chemical damage, and its quality has a significant impact on the performance and reliability of semiconductor chips.

[0003] However, existing coating inspection technologies such as ultrasonic inspection, X-ray inspection, infrared inspection, eddy current inspection, etc., have shortcomings such as poor spatial resolution, the need for direct contact with the surface of the inspection sample, or are only applicable to laboratory environments. They are not fully applicable to the industrial production environment of semiconductor chips and it is difficult to ensure high-precision measurement of conformal coatings. Summary of the invention

[0004] The main purpose of this application is to provide a conformal coating detection method, device, electronic device, storage medium and product, aiming to ensure high-precision measurement of conformal coatings.

[0005] To achieve the above objectives, the present application proposes a conformal coating detection method, which comprises: Acquire a terahertz reflection signal of the chip to be tested, and generate a time domain spectrum of the terahertz reflection signal; Converting the time domain spectrum into a frequency domain spectrum, and constructing an initial transfer function based on the frequency domain spectrum and a preset reference frequency domain spectrum, wherein the initial transfer function is a ratio of the frequency domain spectrum to the reference frequency domain spectrum; Performing a frequency domain reconstruction operation on the transfer function through a preset autoregressive model to obtain an optimized transfer function; The characteristics of the conformal coating of the chip under test are calculated according to the optimized transfer function.

[0006] In one embodiment, the step of performing a frequency domain reconstruction operation on the transfer function using a preset autoregressive model to obtain an optimized transfer function includes: Performing frequency domain analysis on the transfer function to determine a low frequency threshold and a high frequency threshold in a high signal-to-noise ratio region of the transfer function; Calculate the missing components in the low-frequency region and the high-frequency region of the transfer function by using a preset autoregressive model, wherein the low-frequency region is a region in the transfer function whose frequency is lower than the low-frequency threshold, and the high-frequency region is a region in the transfer function whose frequency is higher than the high-frequency threshold; A frequency domain reconstruction operation is performed on the transfer function based on the missing component to obtain an optimized transfer function.

[0007] In one embodiment, before the step of performing a frequency domain reconstruction operation on the transfer function using a preset autoregressive model to obtain an optimized transfer function, the step further includes: The frequency components in the high signal-to-noise ratio region are trained using the initial autoregressive model through a preset modified covariance method, the optimal order of the initial autoregressive model is determined, and a trained autoregressive model is obtained.

[0008] In one embodiment, the step of calculating the characteristics of the conformal coating of the chip under test according to the optimized transfer function comprises: Performing inverse Fourier transform on the optimized transfer function to obtain an impulse response function; The characteristics of the conformal coating of the chip to be tested are calculated according to the impulse response function.

[0009] In one embodiment, the feature includes thickness, and the step of calculating the feature of the conformal coating of the chip under test according to the impulse response function includes: Determine time delay data according to the pulse response function, wherein the time delay data is the time delay between two adjacent reflection echoes from the conformal coating of the chip to be tested; The thickness of the conformal coating is calculated based on the time delay data and the refractive index of the conformal coating.

[0010] In one embodiment, the characteristic further includes uniformity, and the step of calculating the characteristic of the conformal coating of the chip to be tested according to the impulse response function further includes: Calculating an average thickness of the conformal coating according to the thickness of each pixel in the conformal coating; A variance value is calculated based on the thickness mean value, and the uniformity of the conformal coating is inversely proportional to the variance value.

[0011] In addition, to achieve the above objectives, the present application also proposes a conformal coating detection device, the conformal coating detection device comprising: A time domain spectrum generation module, used to obtain a terahertz reflection signal of the chip to be tested and generate a time domain spectrum of the terahertz reflection signal; A transfer function construction module, used for converting the time domain spectrum into a frequency domain spectrum, and constructing an initial transfer function based on the frequency domain spectrum and a preset reference frequency domain spectrum, wherein the initial transfer function is a ratio of the frequency domain spectrum to the reference frequency domain spectrum; A transfer function optimization module, used for performing a frequency domain reconstruction operation on the transfer function through a preset autoregressive model to obtain an optimized transfer function; A feature calculation module is used to calculate the features of the conformal coating of the chip to be tested according to the optimized transfer function.

[0012] In addition, to achieve the above objectives, the present application also proposes an electronic device, which includes: a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the computer program is configured to implement the steps of the conformal coating detection method as described above.

[0013] In addition, to achieve the above-mentioned purpose, the present application also proposes a storage medium, which is a computer-readable storage medium, and a computer program is stored on the storage medium. When the computer program is executed by a processor, the steps of the conformal coating detection method as described above are implemented.

[0014] In addition, to achieve the above objectives, the present application also provides a computer program product, which includes a computer program, and when the computer program is executed by a processor, the steps of the conformal coating detection method described above are implemented.

[0015] The present application proposes a conformal coating detection method, which uses terahertz time-domain spectroscopy technology to obtain the terahertz reflection signal of the chip to be tested and generates a time-domain spectrum of the terahertz reflection signal. Then, the time-domain spectrum is converted into a frequency-domain spectrum, and an initial transfer function is constructed by the frequency-domain spectrum and a preset reference frequency-domain spectrum. The initial transfer function is the ratio of the frequency-domain spectrum to the reference frequency-domain spectrum. Then, a preset autoregressive model is used to perform a frequency-domain reconstruction operation on the initial transfer function to obtain an optimized transfer function. Finally, the characteristics of the conformal coating of the chip to be tested are calculated according to the optimized transfer function.

[0016] In summary, the present application obtains the terahertz reflection signal of the chip to be tested, obtains the time domain spectrum, and then converts the time domain spectrum into the frequency domain spectrum. Combined with the optimization of the autoregressive model, the noise interference in the detection process is effectively removed, and the longitudinal resolution of conformal coating detection on the chip to be tested is improved. Compared with traditional detection methods, the present application can achieve high-precision characterization of complete conformal coatings at the micron level without peeling the conformal coating from the chip to be tested, and is suitable for the industrial production environment of chips, ensuring the accurate extraction of conformal coating characteristic parameters. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0018] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0019] Figure 1 A schematic diagram of a process flow provided for Embodiment 1 of the conformal coating detection method of the present application; Figure 2 A schematic diagram of the structure of a reflective terahertz time-domain spectroscopy system provided in Example 1 of the conformal coating detection method of the present application; Figure 3 A schematic diagram of the structure of a chip to be tested provided in Example 1 of the conformal coating detection method of the present application; Figure 4 A schematic diagram of a propagation path provided in Example 1 of the conformal coating detection method of the present application; Figure 5 A schematic diagram of a time domain spectrum of a terahertz reflection signal provided in Example 1 of the conformal coating detection method of the present application; Figure 6 A schematic diagram of a time domain spectrum of a terahertz reference signal provided in Example 1 of the conformal coating detection method of the present application; Figure 7 A schematic diagram of an impulse response function provided in Example 2 of the conformal coating detection method of the present application; Figure 8 This is a schematic diagram of the module structure of the conformal coating detection device according to an embodiment of the present application; Fig. 9 Schematic diagram of the device structure of the hardware operating environment involved in the conformal coating detection method in the embodiment of the present application.

[0020] The purpose, features and advantages of this application will be further described in conjunction with the embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0021] It should be understood that the specific embodiments described herein are only used to explain the technical solutions of the present application and are not used to limit the present application.

[0022] In order to better understand the technical solution of the present application, a detailed description will be given below in conjunction with the accompanying drawings and specific implementation methods.

[0023] Existing coating inspection technologies such as ultrasonic inspection, X-ray inspection, infrared inspection, eddy current inspection, etc., have shortcomings such as poor spatial resolution, the need for direct contact with the surface of the inspection sample, or are only applicable to laboratory environments. They cannot be fully applied to the industrial production environment of semiconductor chips, and it is difficult to ensure high-precision measurement of conformal coatings.

[0024] The embodiment of the present application provides a solution by acquiring the terahertz reflection signal of the chip to be tested, obtaining the time domain spectrum, and then converting the time domain spectrum into the frequency domain spectrum. Combined with the optimization of the autoregressive model, the noise interference in the detection process is effectively removed, and the longitudinal resolution of conformal coating detection on the chip to be tested is improved. Compared with traditional detection methods, the present application can achieve high-precision characterization of complete conformal coatings at the micron level without peeling the conformal coating from the chip to be tested, and is suitable for the industrial production environment of chips, ensuring the accurate extraction of characteristic parameters of the conformal coating.

[0025] It should be noted that the execution subject of this embodiment can be an electronic device with data processing, network communication and program running functions, such as a computer, a server, etc., or an electronic device capable of realizing the above functions, etc. The following takes the conformal coating detection terminal as an example to illustrate this embodiment and the following embodiments.

[0026] Based on this, the present application embodiment provides a conformal coating detection method, referring to Figure 1 , Figure 1 This is a flow chart of the first embodiment of the conformal coating detection method of the present application.

[0027] In this embodiment, the conformal coating detection method includes steps S10 to S30: Step S10, obtaining a terahertz reflection signal of the chip to be tested, and generating a time domain spectrum of the terahertz reflection signal; Using the reflective terahertz time-domain spectroscopy system, the terahertz reflection signal reflected by the chip under test is emitted and received, so as to obtain the response of the surface of the chip under test and its conformal coating to the terahertz wave, and then generate a time domain spectrum reflecting the response characteristics. The time domain spectrum can intuitively show the change of the terahertz reflection signal over time.

[0028] It should be noted that the specific structure of the reflective terahertz time-domain spectroscopy system used in this embodiment is as follows: Figure 2 As shown. The laser generated by the 780nm femtosecond pulse laser is split into two beams by a beam splitter. One beam acts on the photoconductive antenna to generate a terahertz pulse, and the other beam is processed by increasing the optical path for phase delay. The terahertz pulse spectrum ranges from 60GHz to 3THz (2 -100 ), spectral resolution 0.0075THz (0.25 ). The generated terahertz pulse is focused by a parabolic mirror and acts on a certain pixel point on the surface of the sample under test. The terahertz reflected signal is collected by a terahertz detector on the focal plane. The delayed pump pulse is also guided to the detector to change the optical delay difference between the incoming terahertz pulse and the detection laser pulse at the receiving electrode. A bias is also applied between the transmitter and the receiver to generate a time-gated output signal. By sampling the terahertz pulse carrying the sample information, the time domain waveform of the terahertz pulse electric field intensity is obtained.

[0029] In a feasible implementation, a reflective terahertz time-domain spectroscopy system is used to transmit a terahertz pulse nearly vertically (~3°) to a complete conformal-coated microelectronic chip (i.e., the chip to be tested) to obtain a time-domain spectrum of the terahertz reflection signal r(t). For example, the structure of the chip to be tested is as follows: Figure 3 As shown, the chip to be tested includes a PCB, , serpentine metal film, conformal coating, solder joints and socket connectors, wherein the conformal coating covers the surface of the chip to be tested, and the thickness of the conformal coating ranges from 39-45μm. During measurement, the chip to be tested is fixed on a displacement device to achieve relative movement of the chip and the reflective terahertz time-domain spectroscopy system.

[0030] Figure 4 Schematic diagram of the propagation path of the terahertz pulse emitted to the chip to be tested. The reflective terahertz time-domain spectroscopy system emits a terahertz pulse to a complete conformal-coated microelectronic chip (i.e., the chip to be tested) and obtains the reflected terahertz pulse from the interface between the air and the conformal coating. Echo and conformal coating and serpentine copper film interface The echo is the terahertz reflection signal r(t), and the time domain spectrum of the terahertz reflection signal r(t) is shown in Figure 5 As shown, the horizontal axis Optical delay (ps) is the optical delay (picoseconds), and the vertical axis Amplitude (au) is the amplitude (arbitrary unit).

[0031] Step S20, converting the time domain spectrum into a frequency domain spectrum, and constructing an initial transfer function based on the frequency domain spectrum and a preset reference frequency domain spectrum, wherein the initial transfer function is a ratio of the frequency domain spectrum to the reference frequency domain spectrum; It should be noted that the reference frequency domain spectrum in this embodiment is obtained by emitting a terahertz pulse nearly vertically (~3°) to the metal plate through a reflective terahertz time-domain spectroscopy system, collecting the time domain spectrum of the terahertz reference signal i(t), and then converting the time domain spectrum of i(t) into a frequency domain spectrum, which is the reference frequency domain spectrum.

[0032] For example, in a feasible implementation, the time domain spectrum of the terahertz reference signal i(t) is as follows: Figure 6 As shown, the horizontal axis Optical delay (ps) is the optical delay (picoseconds), the vertical axis Amplitude (au) is the amplitude (arbitrary unit), the illustration in the upper right corner of the figure is the power spectrum (i.e., frequency domain spectrum) corresponding to the terahertz reference signal i(t), the horizontal axis Frequency [Thz] is the frequency [terahertz], and the vertical axis Log (ThzPower) [au] is the logarithm of the terahertz frequency band power with a certain base (such as 10 or e), which is used to analyze the signal power in the terahertz band to reveal the dynamic range and changing trend of the signal.

[0033] Using mathematical methods such as Fast Fourier Transform (FFT), the obtained time domain spectrum is converted into a frequency domain spectrum, which can intuitively display the distribution of the signal at different frequencies, facilitating in-depth analysis. Then, by comparing the frequency domain spectrum of the chip under test with the preset reference frequency domain spectrum, an initial transfer function is constructed. This initial transfer function is essentially the ratio of the frequency domain spectrum to the reference frequency domain spectrum, reflecting the change of the conformal coating of the chip under test on the electromagnetic wave transmission characteristics.

[0034] In one possible implementation, the initial transfer function can be expressed as , where FFT stands for Fourier transform.

[0035] It is understandable that during the detection process, the reflective terahertz time-domain spectroscopy system may be affected by many factors, such as the alignment of optical components, the response characteristics of the detector, optical delay, etc., which may lead to errors in the detection results. By pre-collecting the reference signal on the metal plate, these errors can be identified and eliminated, thereby improving the accuracy of the measurement results. Therefore, constructing a transfer function based on the frequency domain spectrum and the reference frequency domain spectrum can ensure the accuracy and reliability of the measurement results.

[0036] Step S30, performing a frequency domain reconstruction operation on the transfer function through a preset autoregressive model to obtain an optimized transfer function; It should be noted that the autoregressive model can reduce noise interference and smooth data fluctuations based on the autocorrelation of the data through an iterative optimization algorithm, thereby obtaining a more accurate and smooth optimization transfer function.

[0037] In order to further improve the accuracy and stability of the transfer function, a preset autoregressive model is used to reconstruct the transfer function in the frequency domain to obtain the optimized transfer function.

[0038] It can be understood that when the terahertz time-domain spectroscopy system is used for non-contact, non-invasive and non-destructive characterization of the surface structure of the semiconductor chip, the collected terahertz echo signal not only contains the faint features of the conformal coating reflected from the surface of the semiconductor chip, but also carries a large amount of invalid redundant features and noise and other invalid information, which makes it difficult to accurately decouple the thickness information and uniformity information of the conformal coating from the terahertz echo signal, affecting the detection accuracy of the conformal coating. Therefore, step S30 can identify and eliminate redundant features and noise, thereby improving measurement accuracy and reliability.

[0039] Step S40, calculating the characteristics of the conformal coating of the chip to be tested according to the optimized transfer function.

[0040] According to the optimized transfer function, the characteristics of the conformal coating of the chip to be tested are calculated and extracted. The characteristics may be thickness and uniformity, which are key indicators for evaluating the quality performance of the conformal coating.

[0041] In summary, the embodiment of the present application obtains the terahertz reflection signal of the chip to be tested to obtain the time domain spectrum, and then converts the time domain spectrum into the frequency domain spectrum. Combined with the optimization of the autoregressive model, the noise interference in the detection process is effectively removed, and the longitudinal resolution of the conformal coating detection on the chip to be tested is improved. Compared with traditional detection methods, the present application can achieve high-precision characterization of complete conformal coatings at the micron level without peeling the conformal coating from the chip to be tested, and is suitable for the industrial production environment of chips, ensuring the accurate extraction of characteristic parameters of the conformal coating.

[0042] Based on the first embodiment of the present application, in the second embodiment of the present application, the same or similar contents as those in the above-mentioned embodiment 1 can be referred to the above introduction, and will not be repeated later. On this basis, step S30 can include steps S301~S303: Step S301, performing frequency domain analysis on the transfer function to determine a low frequency threshold and a high frequency threshold in a high signal-to-noise ratio region of the transfer function; Through frequency domain analysis technology, the low-frequency threshold (i.e., the lowest frequency point where the signal quality begins to significantly decrease) and high-frequency threshold (i.e., the highest frequency point where the signal quality begins to significantly decrease) of the high signal-to-noise ratio region in the transfer function are determined. Specifically, spectrum analysis tools such as power spectral density (PSD) graphs or spectrum response graphs can be used to identify the boundaries of frequency bands where the signal-to-noise ratio of the transfer function is relatively high, that is, to determine the specific values ​​of the low-frequency threshold and the high-frequency threshold.

[0043] Step S302, calculating missing components in a low-frequency region and a high-frequency region in the transfer function by using a preset autoregressive model, wherein the low-frequency region is a region in the transfer function whose frequency is lower than the low-frequency threshold, and the high-frequency region is a region in the transfer function whose frequency is higher than the high-frequency threshold; Based on the preset autoregressive model, the missing components of the transfer function in the low-frequency region (frequency below the low-frequency threshold) and the high-frequency region (frequency above the high-frequency threshold) are calculated.

[0044] Specifically, the autoregressive model can be used as a prediction filter, using a forward prediction filter to find i> The missing component , use the backward prediction filter to find i< The missing component , where i represents the frequency, represents the low frequency threshold, represents the high frequency threshold, represents the missing component, p is the order of the AR process (autoregressive process), are the coefficients of the autoregressive model forward prediction filter, is the coefficient of the backward prediction filter of the autoregressive model, and H is the frequency component of the high signal-to-noise ratio area.

[0045] Step S303: performing a frequency domain reconstruction operation on the transfer function based on the missing component to obtain an optimized transfer function.

[0046] The transfer function is reconstructed in the frequency domain using the calculated missing components in the low-frequency and high-frequency regions to improve its performance in the entire frequency range. Specifically, the missing components in the low-frequency and high-frequency regions can be combined with the frequency components of the original transfer function in the high signal-to-noise ratio region to obtain an optimized transfer function. In this way, the performance of the transfer function in a certain frequency range can be effectively improved.

[0047] In a feasible embodiment, step A10 may be further included before step S30: Step A10, training the frequency components in the high signal-to-noise ratio region using the initial autoregressive model by using a preset modified covariance method, determining the optimal order of the initial autoregressive model, and obtaining a trained autoregressive model.

[0048] It should be noted that the modified covariance method is a technology that aims to improve the stability of model parameter estimation. It reduces model errors and improves model fit and prediction accuracy by adjusting the covariance matrix in the parameter estimation process.

[0049] Through statistical analysis, empirical rules or professional judgment, set a suitable order for the initial autoregressive model (i.e., the untrained autoregressive model). The choice of order directly affects the model's ability to capture dependencies in time series data. Too high or too low an order may lead to overfitting or underfitting of the model, so it needs to be carefully determined based on the characteristics of the data and the analysis objectives.

[0050] The model is trained using the preset modified covariance method. In this step, by setting a suitable training data set, the model parameters are iteratively optimized using the modified covariance algorithm until the preset convergence conditions are met or the optimal model performance evaluation index is achieved, thereby obtaining a trained autoregressive model.

[0051] For example, in one possible implementation, the modified covariance method (MCM) is used to solve the autoregressive model coefficients, and the optimal coefficients are obtained by minimizing the squared error between the model and the available data. Get, square error The calculation formula is: , In this example, the frequency components in [0.14THz, 1.2THz] are assigned to the backward prediction filter, and the frequency components in [0.3THz, 1.5THz] are assigned to the forward prediction filter. The trained autoregressive model is used to extrapolate and find the missing frequency components below 0.14THz (i.e., low-frequency region) and above 1.5THz (i.e., high-frequency region, up to 85.99THz).

[0052] In a feasible embodiment, step S40 may include steps S401-S402: Step S401, performing inverse Fourier transform on the optimized transfer function to obtain an impulse response function; Step S402: calculating the characteristics of the conformal coating of the chip to be tested according to the impulse response function.

[0053] The optimized transfer function is processed by inverse Fourier transform to convert the information in the frequency domain back to the time domain, thereby obtaining the impulse response function, which intuitively reflects the response of the conformal coating of the chip under test to the input pulse signal and is the basis for the subsequent analysis of the conformal coating structural characteristics. By analyzing the impulse response function, the characteristics of the conformal coating of the chip under test are calculated.

[0054] For example, in a feasible implementation, the impulse response function is as follows: Figure 7 As shown, the horizontal axis Optical delay (ps) is optical delay (picoseconds), and the vertical axis Amplitude (au) is amplitude (arbitrary unit), which describes the change of the amplitude of the optimized terahertz echo over time in the time domain. By analyzing the amplitude and phase of the pulse response function, the thickness and uniformity characteristics of the conformal coating of the chip to be tested can be determined.

[0055] In a feasible embodiment, step S402 may include steps S4021-S4022: Step S4021, determining time delay data according to the impulse response function, wherein the time delay data is the time delay between two adjacent reflection echoes from the conformal coating of the chip to be tested; By analyzing the pulse response function, the time delay between two adjacent echoes reflected by the conformal coating of the chip to be tested is identified and recorded. The time delay data is directly related to the physical properties of the coating, especially its thickness information.

[0056] Step S4022: Calculate the thickness of the conformal coating according to the time delay data and the refractive index of the conformal coating.

[0057] Using the acquired time delay data and the known refractive index of the conformal coating, the specific thickness of the coating is calculated using the formula: , where c is the speed of light in air, is the time delay between two adjacent reflected echoes from the conformal coating, is the refractive index of the conformal coating.

[0058] Exemplarily, the conformal coating in this embodiment is acrylic fiber. According to literature review, the refractive index of acrylic fiber in the terahertz band is n≈1.6, so it can be calculated that the thickness of the acrylic fiber at this position is 36 μm.

[0059] In a feasible embodiment, step S402 may further include steps S4023-S4024: Step S4023, calculating the average thickness of the conformal coating according to the thickness of each pixel in the conformal coating; By statistically analyzing the thickness of each pixel (or smaller analysis unit) in the conformal coating, the average thickness of the conformal coating is calculated.

[0060] Step S4024, calculating a variance value according to the thickness mean value, wherein the uniformity of the conformal coating is inversely proportional to the variance value.

[0061] Based on the mean thickness, the variance between the thickness of all pixels and the mean is further calculated. The size of the variance directly reflects the fluctuation of the coating thickness, that is, the uniformity of the coating. The smaller the variance, the more uniform the coating; conversely, it indicates that there is a large thickness difference in the coating.

[0062] For example, after obtaining the thickness information of the conformal coating at different positions, the uniformity of the conformal coating can be determined by the mean μ and the variance σ 2 express: , , in, is the thickness of the conformal coating calculated from the terahertz results at different locations, N is the number of data sampling points, and in this example, the mean value µ of the acrylic conformal coating is 38.4µm, and the standard deviation σ is 1.3µm after the root mean square of the variance.

[0063] In summary, in this embodiment, a reflective terahertz time-domain spectroscopy system is used to emit terahertz pulses to a metal plate and a chip to be tested coated with a conformal coating to collect a time domain spectrum. Then, a terahertz super-resolution imaging strategy based on an autoregressive model is constructed to analyze the thickness and uniformity of the conformal coating from the complex terahertz echo signal, thereby effectively improving the detection accuracy and efficiency of the conformal coating quality of semiconductor chips.

[0064] It should be noted that the above examples are only used to understand the present application and do not constitute a limitation on the conformal coating detection method of the present application. More simple transformations based on this technical concept are all within the scope of protection of the present application.

[0065] The present application also provides a conformal coating detection device, please refer to Figure 8 , the conformal coating detection device includes: A time domain spectrum generating module 10 is used to obtain a terahertz reflection signal of the chip to be tested and generate a time domain spectrum of the terahertz reflection signal; A transfer function construction module 20, configured to convert the time domain spectrum into a frequency domain spectrum, and to construct an initial transfer function based on the frequency domain spectrum and a preset reference frequency domain spectrum, wherein the initial transfer function is a ratio of the frequency domain spectrum to the reference frequency domain spectrum; The transfer function optimization module 30 is used to perform a frequency domain reconstruction operation on the transfer function through a preset autoregressive model to obtain an optimized transfer function; The feature calculation module 40 is used to calculate the features of the conformal coating of the chip to be tested according to the optimized transfer function.

[0066] Optionally, the transfer function optimization module 30 is further used for: Performing frequency domain analysis on the transfer function to determine a low frequency threshold and a high frequency threshold in a high signal-to-noise ratio region of the transfer function; Calculate the missing components in the low-frequency region and the high-frequency region of the transfer function through a preset autoregressive model, wherein the low-frequency region is a region in the transfer function whose frequency is lower than the low-frequency threshold, and the high-frequency region is a region in the transfer function whose frequency is higher than the high-frequency threshold; A frequency domain reconstruction operation is performed on the transfer function based on the missing component to obtain an optimized transfer function.

[0067] Optionally, the conformal coating detection device further includes a model training module (not shown), and the model training module is used to: The frequency components in the high signal-to-noise ratio region are trained using the initial autoregressive model through a preset modified covariance method, the optimal order of the initial autoregressive model is determined, and a trained autoregressive model is obtained.

[0068] Optionally, the feature calculation module 40 is further used for: Performing inverse Fourier transform on the optimized transfer function to obtain an impulse response function; The characteristics of the conformal coating of the chip to be tested are calculated according to the impulse response function.

[0069] Optionally, the feature calculation module 40 is further used for: Determine time delay data according to the pulse response function, wherein the time delay data is the time delay between two adjacent reflection echoes from the conformal coating of the chip to be tested; The thickness of the conformal coating is calculated based on the time delay data and the refractive index of the conformal coating.

[0070] Optionally, the feature calculation module 40 is further used for: Calculating an average thickness of the conformal coating according to the thickness of each pixel in the conformal coating; A variance value is calculated based on the thickness mean value, and the uniformity of the conformal coating is inversely proportional to the variance value.

[0071] The conformal coating detection device provided in the embodiment of the present application adopts the conformal coating detection method in the above embodiment, which can ensure high-precision measurement of the conformal coating. Compared with the prior art, the beneficial effects of the conformal coating detection device provided in the embodiment of the present application are the same as the beneficial effects of the conformal coating detection method provided in the above embodiment, and other technical features in the conformal coating detection device are the same as the features disclosed in the conformal coating detection method in the above embodiment, which will not be repeated here.

[0072] An embodiment of the present application provides an electronic device, which includes: at least one processor; and a memory communicatively connected to the at least one processor; wherein the memory stores instructions executable by the at least one processor, and the instructions are executed by the at least one processor so that the at least one processor can execute the conformal coating detection method in the above-mentioned embodiment 1.

[0073] Reference below Fig. 9, which shows a schematic diagram of the structure of an electronic device suitable for implementing the embodiments of the present application. The electronic devices in the embodiments of the present application may include but are not limited to mobile terminals such as laptop computers, digital broadcast receivers, PDAs (Personal Digital Assistants), PADs (Portable Application Descriptions), PMPs (Portable Media Players), etc., and fixed terminals such as digital TVs, desktop computers, etc. Fig. 9 The electronic device shown is merely an example and should not bring any limitation to the functions and scope of use of the embodiments of the present application.

[0074] like Fig. 9 As shown, the electronic device may include a processing device 1001 (e.g., a central processing unit, a graphics processor, etc.), which can perform various appropriate actions and processes according to a program stored in a read-only memory (ROM: Read Only Memory) 1002 or a program loaded from a storage device 1003 to a random access memory (RAM: Random Access Memory) 1004. In RAM1004, various programs and data required for the operation of the electronic device are also stored. The processing device 1001, ROM1002, and RAM1004 are connected to each other through a bus 1005. An input / output (I / O) interface 1006 is also connected to the bus. Generally, the following systems can be connected to the I / O interface 1006: an input device 1007 including, for example, a touch screen, a touch pad, a keyboard, a mouse, an image sensor, a microphone, an accelerometer, a gyroscope, etc.; an output device 1008 including, for example, a liquid crystal display (LCD: Liquid Crystal Display), a speaker, a vibrator, etc.; a storage device 1003 including, for example, a magnetic tape, a hard disk, etc.; and a communication device 1009. The communication device 1009 can allow the electronic device to communicate with other devices wirelessly or by wire to exchange data. Although the figure shows an electronic device with various systems, it should be understood that it is not required to implement or have all the systems shown. More or fewer systems can be implemented or have alternatively.

[0075] In particular, according to the embodiments disclosed in the present application, the process described above with reference to the flowchart can be implemented as a computer software program. For example, the embodiments disclosed in the present application include a computer program product, which includes a computer program carried on a computer-readable medium, and the computer program includes a program code for executing the method shown in the flowchart. In such an embodiment, the computer program can be downloaded and installed from a network through a communication device, or installed from a storage device 1003, or installed from a ROM 1002. When the computer program is executed by the processing device 1001, the above-mentioned functions defined in the method of the embodiment disclosed in the present application are executed.

[0076] The electronic device provided in the embodiment of the present application adopts the conformal coating detection method in the above embodiment to ensure high-precision measurement of the conformal coating. Compared with the prior art, the beneficial effects of the electronic device provided in the embodiment of the present application are the same as the beneficial effects of the conformal coating detection method provided in the above embodiment, and other technical features in the electronic device are the same as the features disclosed in the conformal coating detection method in the previous embodiment, which will not be repeated here.

[0077] It should be understood that the various parts disclosed in the embodiments of the present application can be implemented by hardware, software, firmware or a combination thereof. In the description of the above embodiments, specific features, structures, materials or characteristics can be combined in any one or more embodiments or examples in a suitable manner.

[0078] The above are only specific implementations of the present application, but the protection scope of the present application is not limited thereto. Any technician familiar with the technical field can easily think of changes or substitutions within the technical scope disclosed in the present application, which should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

[0079] An embodiment of the present application provides a computer-readable storage medium having computer-readable program instructions (ie, a computer program) stored thereon, and the computer-readable program instructions are used to execute the conformal coating detection method in the above-mentioned embodiment.

[0080] The computer-readable storage medium provided in the embodiment of the present application may be, for example, a USB flash drive, but is not limited to electrical, magnetic, optical, electromagnetic, infrared, or semiconductor systems or devices, or any combination of the above. More specific examples of computer-readable storage media may include, but are not limited to: an electrical connection with one or more wires, a portable computer disk, a hard disk, a random access memory (RAM: Random Access Memory), a read-only memory (ROM: Read Only Memory), an erasable programmable read-only memory (EPROM: Erasable Programmable Read Only Memory or flash memory), an optical fiber, a portable compact disk read-only memory (CD-ROM: CD-Read Only Memory), an optical storage device, a magnetic storage device, or any suitable combination of the above. In this embodiment, the computer-readable storage medium may be any tangible medium containing or storing a program that can be used by or in combination with an instruction execution system or device. The program code contained on the computer-readable storage medium can be transmitted using any appropriate medium, including but not limited to: wires, optical cables, RF (Radio Frequency: Radio Frequency), etc., or any suitable combination of the above.

[0081] The computer-readable storage medium may be included in the electronic device, or may exist independently without being installed in the electronic device.

[0082] The computer-readable storage medium carries one or more programs. When the one or more programs are executed by an electronic device, the electronic device: obtains a terahertz reflection signal of the chip to be tested, and generates a time domain spectrum of the terahertz reflection signal; converts the time domain spectrum into a frequency domain spectrum, and constructs an initial transfer function based on the frequency domain spectrum and a preset reference frequency domain spectrum, wherein the initial transfer function is a ratio of the frequency domain spectrum to the reference frequency domain spectrum; performs a frequency domain reconstruction operation on the transfer function through a preset autoregressive model to obtain an optimized transfer function; and calculates the characteristics of the conformal coating of the chip to be tested according to the optimized transfer function.

[0083] The computer program code for performing the operation of the embodiment of the present application can be written in one or more programming languages ​​or a combination thereof, including object-oriented programming languages ​​such as Java, Smalltalk, C++, and conventional procedural programming languages ​​such as "C" language or similar programming languages. The program code can be executed entirely on the user's computer, partially on the user's computer, as an independent software package, partially on the user's computer and partially on the remote computer, or completely on the remote computer or server. In the case of a remote computer, the remote computer can be connected to the user's computer through any type of network, including a local area network (LAN) or a wide area network (WAN), or can be connected to an external computer (for example, using an Internet service provider to connect through the Internet).

[0084] The flow chart and block diagram in the accompanying drawings illustrate the possible architecture, function and operation of the system, method and computer program product according to various embodiments of the present application. In this regard, each square box in the flow chart or block diagram can represent a module, a program segment or a part of a code, and the module, the program segment or a part of the code contains one or more executable instructions for realizing the specified logical function. It should also be noted that in some alternative implementations, the functions marked in the square box can also occur in a sequence different from that marked in the accompanying drawings. For example, two square boxes represented in succession can actually be executed substantially in parallel, and they can sometimes be executed in the opposite order, depending on the functions involved. It should also be noted that each square box in the block diagram and / or flow chart, and the combination of the square boxes in the block diagram and / or flow chart can be implemented with a dedicated hardware-based system that performs a specified function or operation, or can be implemented with a combination of dedicated hardware and computer instructions.

[0085] The modules involved in the embodiments described in this application may be implemented by software or hardware, wherein the name of the module does not constitute a limitation on the unit itself in some cases.

[0086] The readable storage medium provided in the embodiment of the present application is a computer-readable storage medium, which stores computer-readable program instructions (i.e., computer programs) for executing the above-mentioned conformal coating detection method, and can ensure high-precision measurement of the conformal coating. Compared with the prior art, the beneficial effects of the computer-readable storage medium provided in the embodiment of the present application are the same as the beneficial effects of the conformal coating detection method provided in the above-mentioned embodiment, and will not be repeated here.

[0087] The present application also provides a computer program product, comprising a computer program, which implements the steps of the above-mentioned conformal coating detection method when executed by a processor.

[0088] The computer program product provided in this application can solve the technical problem of conformal coating detection. Compared with the prior art, the beneficial effects of the computer program product provided in this application are the same as the beneficial effects of the conformal coating detection method provided in the above embodiment, which will not be repeated here.

[0089] The above are only some embodiments of the present application, and are not intended to limit the patent scope of the present application. All equivalent structural changes made using the contents of the present application specification and drawings under the technical concept of the present application, or direct / indirect application in other related technical fields are included in the patent protection scope of the present application.

Claims

1. A conformal coating detection method, characterized in that: The method comprises: Acquire a terahertz reflection signal of the chip to be tested, and generate a time domain spectrum of the terahertz reflection signal; Converting the time domain spectrum into a frequency domain spectrum, and constructing an initial transfer function based on the frequency domain spectrum and a preset reference frequency domain spectrum, wherein the initial transfer function is a ratio of the frequency domain spectrum to the reference frequency domain spectrum; Performing a frequency domain reconstruction operation on the transfer function through a preset autoregressive model to obtain an optimized transfer function; The characteristics of the conformal coating of the chip under test are calculated according to the optimized transfer function.

2. The conformal coating detection method according to claim 1, characterized in that: The step of performing a frequency domain reconstruction operation on the transfer function through a preset autoregressive model to obtain an optimized transfer function comprises: Performing frequency domain analysis on the transfer function to determine a low frequency threshold and a high frequency threshold in a high signal-to-noise ratio region of the transfer function; Calculate the missing components in the low-frequency region and the high-frequency region of the transfer function by using a preset autoregressive model, wherein the low-frequency region is a region in the transfer function whose frequency is lower than the low-frequency threshold, and the high-frequency region is a region in the transfer function whose frequency is higher than the high-frequency threshold; A frequency domain reconstruction operation is performed on the transfer function based on the missing component to obtain an optimized transfer function.

3. The conformal coating detection method according to claim 1, characterized in that: Before the step of performing frequency domain reconstruction operation on the transfer function by using a preset autoregressive model to obtain an optimized transfer function, the method further includes: The frequency components in the high signal-to-noise ratio region are trained using the initial autoregressive model through a preset modified covariance method, the optimal order of the initial autoregressive model is determined, and a trained autoregressive model is obtained.

4. The conformal coating detection method according to claim 1, characterized in that: The step of calculating the characteristics of the conformal coating of the chip to be tested according to the optimized transfer function comprises: Performing inverse Fourier transform on the optimized transfer function to obtain an impulse response function; The characteristics of the conformal coating of the chip to be tested are calculated according to the impulse response function.

5. The conformal coating detection method according to claim 4, characterized in that: The feature includes thickness, and the step of calculating the feature of the conformal coating of the chip to be tested according to the impulse response function includes: Determine time delay data according to the pulse response function, wherein the time delay data is the time delay between two adjacent reflection echoes from the conformal coating of the chip to be tested; The thickness of the conformal coating is calculated based on the time delay data and the refractive index of the conformal coating.

6. The conformal coating detection method according to claim 5, characterized in that: The characteristic also includes uniformity, and the step of calculating the characteristic of the conformal coating of the chip to be tested according to the impulse response function also includes: Calculating an average thickness of the conformal coating according to the thickness of each pixel in the conformal coating; A variance value is calculated based on the thickness mean value, and the uniformity of the conformal coating is inversely proportional to the variance value.

7. A conformal coating detection device, characterized in that: The device comprises: A time domain spectrum generation module, used to obtain a terahertz reflection signal of the chip to be tested and generate a time domain spectrum of the terahertz reflection signal; A transfer function construction module, used for converting the time domain spectrum into a frequency domain spectrum, and constructing an initial transfer function based on the frequency domain spectrum and a preset reference frequency domain spectrum, wherein the initial transfer function is a ratio of the frequency domain spectrum to the reference frequency domain spectrum; A transfer function optimization module, used for performing a frequency domain reconstruction operation on the transfer function through a preset autoregressive model to obtain an optimized transfer function; A feature calculation module is used to calculate the features of the conformal coating of the chip to be tested according to the optimized transfer function.

8. An electronic device, characterized in that: The device comprises: a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the computer program is configured to implement the steps of the conformal coating detection method according to any one of claims 1 to 6.

9. A storage medium, characterized in that: The storage medium is a computer-readable storage medium, on which a computer program is stored. When the computer program is executed by a processor, the steps of the conformal coating detection method according to any one of claims 1 to 6 are implemented.

10. A computer program product, characterized in that The computer program product comprises a computer program, and when the computer program is executed by a processor, the steps of the conformal coating detection method according to any one of claims 1 to 6 are implemented.

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