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

Abstract

This application discloses a conformal coating detection method, apparatus, electronic device, storage medium, and product, relating to the field of nondestructive testing technology. The disclosed conformal coating detection method includes: obtaining a terahertz reflection signal from a chip under test and generating 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 the ratio of the frequency-domain spectrum to the reference frequency-domain spectrum; performing a frequency-domain reconstruction operation on the transfer function using a preset autoregressive model to obtain an optimized transfer function; and calculating the characteristics of the conformal coating of the chip under test based on the optimized transfer function. This application can ensure high-precision measurement of conformal coatings.

Description

Technical Field

[0001] The present application relates to the field of nondestructive testing technology, and in particular to conformal coating detection 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, 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. These inspection technologies cannot be fully applied 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 equipment, 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 includes:

[0006] Acquire a terahertz reflection signal of the chip to be tested, and generate a time domain spectrum of the terahertz reflection signal;

[0007] 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;

[0008] Performing a frequency domain reconstruction operation on the transfer function through a preset autoregressive model to obtain an optimized transfer function;

[0009] The characteristics of the conformal coating of the chip to be tested are calculated according to the optimized transfer function.

[0010] 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:

[0011] 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;

[0012] Calculating missing components in a low-frequency region and a high-frequency region of the transfer function using a preset autoregressive model, wherein the low-frequency region is a region of the transfer function with a frequency lower than the low-frequency threshold, and the high-frequency region is a region of the transfer function with a frequency higher than the high-frequency threshold;

[0013] A frequency domain reconstruction operation is performed on the transfer function based on the missing component to obtain an optimized transfer function.

[0014] 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 method further includes:

[0015] The frequency components in the high signal-to-noise ratio region are trained using an 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.

[0016] 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:

[0017] Performing inverse Fourier transform on the optimized transfer function to obtain an impulse response function;

[0018] The characteristics of the conformal coating of the chip to be tested are calculated according to the impulse response function.

[0019] In one embodiment, the characteristic includes thickness, and the step of calculating the characteristic of the conformal coating of the chip under test according to the impulse response function includes:

[0020] 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;

[0021] The thickness of the conformal coating is calculated based on the time delay data and the refractive index of the conformal coating.

[0022] In one embodiment, the characteristic further includes uniformity, and the step of calculating the characteristic of the conformal coating of the chip under test according to the impulse response function further includes:

[0023] Calculating an average thickness of the conformal coating according to the thickness of each pixel in the conformal coating;

[0024] 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.

[0025] In addition, to achieve the above objectives, the present application also proposes a conformal coating detection device, which includes:

[0026] A time domain spectrum generation module is used to obtain the terahertz reflection signal of the chip to be tested and generate a time domain spectrum of the terahertz reflection signal;

[0027] a transfer function construction module, configured to convert the time domain spectrum into a frequency domain spectrum, and 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;

[0028] A transfer function optimization module, configured to perform a frequency domain reconstruction operation on the transfer function using a preset autoregressive model to obtain an optimized transfer function;

[0029] 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.

[0030] 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.

[0031] In addition, to achieve the above-mentioned purpose, the present application also proposes a storage medium, which is a computer-readable storage medium. 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.

[0032] In addition, to achieve the above objectives, the present application also provides a computer program product, which includes a computer program. When the computer program is executed by a processor, the steps of the conformal coating detection method as described above are implemented.

[0033] The present application proposes a conformal coating detection method. The present application obtains the terahertz reflection signal of the chip to be tested by using terahertz time-domain spectroscopy technology 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 using 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 based on the optimized transfer function.

[0034] 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, it effectively removes the noise interference in the detection process and improves the longitudinal resolution of conformal coating detection on the chip to be tested. 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. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] 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.

[0036] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0037] Figure 1 A schematic diagram of a process flow provided for Example 1 of the conformal coating detection method of this application;

[0038] Figure 2 A schematic structural diagram of a reflective terahertz time-domain spectroscopy system provided in Example 1 of the conformal coating detection method of the present application;

[0039] Figure 3 A schematic diagram of the structure of the chip to be tested provided in Example 1 of the conformal coating detection method of this application;

[0040] Figure 4 A schematic diagram of the propagation path provided in Example 1 of the conformal coating detection method of this application;

[0041] Figure 5 A schematic diagram of the time domain spectrum of the terahertz reflection signal provided in Example 1 of the conformal coating detection method of the present application;

[0042] Figure 6 A schematic diagram of the time domain spectrum of the terahertz reference signal provided in Example 1 of the conformal coating detection method of the present application;

[0043] Figure 7 Schematic diagram of the impulse response function provided in Example 2 of the conformal coating detection method of this application;

[0044] 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;

[0045] Figure 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.

[0046] The purpose, features and advantages of this application will be further explained with reference to the accompanying drawings in conjunction with the embodiments. DETAILED DESCRIPTION

[0047] It should be understood that the specific embodiments described herein are merely used to explain the technical solutions of the present application and are not intended to limit the present application.

[0048] 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.

[0049] 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.

[0050] An embodiment of the present application provides a solution by acquiring the terahertz reflection signal of the chip to be tested, obtaining a time domain spectrum, and then converting the time domain spectrum into a frequency domain spectrum. Combined with the optimization of the autoregressive model, it effectively removes noise interference in the detection process and improves the longitudinal resolution of conformal coating detection on the chip to be tested. 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.

[0051] It should be noted that the execution subject of this embodiment can be an electronic device with data processing, network communication, and program execution functions, such as a computer, server, etc., or an electronic device capable of performing the above functions. The following uses a conformal coating inspection terminal as an example to illustrate this embodiment and the following embodiments.

[0052] Based on this, the embodiment of the present application 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.

[0053] In this embodiment, the conformal coating detection method includes steps S10 to S30:

[0054] Step S10, obtaining a terahertz reflection signal of the chip to be tested, and generating a time domain spectrum of the terahertz reflection signal;

[0055] Using a reflective terahertz time-domain spectroscopy system, the terahertz reflection signal is emitted from the chip under test and its reflected signal is received, thereby obtaining the response of the chip surface under test and its conformal coating to the terahertz wave, and then generating a time-domain spectrum reflecting the response characteristics. This time-domain spectrum can intuitively show the change of the terahertz reflection signal over time.

[0056] 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 terahertz pulses, and the other beam is processed by increasing the optical path for phase delay. The terahertz pulse spectrum range is 60GHz-3THz (2 -100 ), spectral resolution 0.0075THz(0.25 The generated terahertz pulse is focused by a parabolic mirror onto a pixel on the surface of the sample being measured, and a terahertz detector is used on the focal plane to collect the terahertz reflected signal. A delayed pump pulse is also directed 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 receiver to produce 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.

[0057] In a feasible embodiment, 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 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.

[0058] Figure 4 This is a schematic diagram of the propagation path of the terahertz pulse emitted to the chip under test. The reflective terahertz time-domain spectroscopy system emits a terahertz pulse to a complete conformal-coated microelectronic chip (i.e., the chip under test) and obtains the reflected light 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 as follows: Figure 5As shown, the horizontal axis Optical delay (ps) is the optical delay (picoseconds), and the vertical axis Amplitude (au) is the amplitude (arbitrary unit).

[0059] 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;

[0060] It should be noted that the reference frequency domain spectrum in this embodiment is obtained by transmitting 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.

[0061] For example, in a feasible embodiment, the time domain spectrum of the terahertz reference signal i(t) is as follows: Figure 6 As shown in the figure, 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 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 change trend of the signal.

[0062] Using mathematical methods such as the Fast Fourier Transform (FFT), the resulting time-domain spectrum is converted into a frequency-domain spectrum. This frequency-domain spectrum can intuitively display the signal distribution at different frequencies, facilitating in-depth analysis. Next, by comparing the frequency-domain spectrum of the chip under test with a 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 how the conformal coating of the chip under test affects the electromagnetic wave transmission characteristics.

[0063] In one possible implementation, the initial transfer function can be expressed as , where FFT stands for Fourier transform.

[0064] It is understandable that during the detection process, the reflective terahertz time-domain spectroscopy system may be affected by various 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.

[0065] Step S30, performing a frequency domain reconstruction operation on the transfer function using a preset autoregressive model to obtain an optimized transfer function;

[0066] 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.

[0067] 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.

[0068] It is understandable 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, making 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.

[0069] Step S40 , calculating the characteristics of the conformal coating of the chip to be tested according to the optimized transfer function.

[0070] Based on the optimized transfer function, the characteristics of the conformal coating of the chip to be tested are calculated and extracted. The characteristics can be thickness and uniformity. These characteristics are key indicators for evaluating the quality performance of the conformal coating.

[0071] 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, it effectively removes the noise interference in the detection process and improves the longitudinal resolution of conformal coating detection on the chip to be tested. 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.

[0072] 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 hereafter. On this basis, step S30 may include steps S301 to S303:

[0073] 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;

[0074] Frequency domain analysis technology is used to determine the low-frequency threshold (i.e., the lowest frequency point at which the signal quality begins to significantly degrade) and high-frequency threshold (i.e., the highest frequency point at which the signal quality begins to significantly degrade) of the high signal-to-noise ratio region in the transfer function. Spectral 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, thereby determining the specific values of the low-frequency threshold and the high-frequency threshold.

[0075] Step S302: Calculate missing components in a low-frequency region and a high-frequency region of the transfer function using a preset autoregressive model, wherein the low-frequency region is a region of the transfer function with a frequency lower than the low-frequency threshold, and the high-frequency region is a region of the transfer function with a frequency higher than the high-frequency threshold;

[0076] 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.

[0077] Specifically, autoregressive models can be used as predictive filters, using a forward predictive 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 forward prediction filter of the autoregressive model, 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.

[0078] Step S303: Perform a frequency domain reconstruction operation on the transfer function based on the missing component to obtain an optimized transfer function.

[0079] 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.

[0080] In a feasible embodiment, step A10 may be further included before step S30:

[0081] Step A10 , using a preset modified covariance method to train the frequency components in the high signal-to-noise ratio region using the initial autoregressive model, determining the optimal order of the initial autoregressive model, and obtaining a trained autoregressive model.

[0082] It should be noted that the modified covariance method is a technology aimed at improving the stability of model parameter estimation. By adjusting the covariance matrix in the parameter estimation process, it can reduce model errors and improve model fit and prediction accuracy.

[0083] Using statistical analysis, empirical rules, or professional judgment, determine an appropriate order for the initial autoregressive model (i.e., an untrained autoregressive model). The choice of order directly affects the model's ability to capture dependencies in time series data. Excessively high or low orders can lead to overfitting or underfitting, so the order should be carefully determined based on the characteristics of the data and the analysis objectives.

[0084] 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 indicators are achieved, thereby obtaining a trained autoregressive model.

[0085] 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:

[0086] ,

[0087] In this example, the frequency components within [0.14THz, 1.2THz] are assigned to the backward prediction filter, and the frequency components within [0.3THz, 1.5THz] are assigned to the forward prediction filter. The trained autoregressive model is used to perform extrapolation to find missing frequency components below 0.14THz (the low-frequency region) and above 1.5THz (the high-frequency region, up to 85.99THz).

[0088] In a feasible embodiment, step S40 may include steps S401 and S402:

[0089] Step S401, performing inverse Fourier transform on the optimized transfer function to obtain an impulse response function;

[0090] Step S402 : calculating the characteristics of the conformal coating of the chip to be tested according to the impulse response function.

[0091] The optimized transfer function is then subjected to an inverse Fourier transform to convert the frequency domain information back to the time domain, resulting in an impulse response function. This impulse response function intuitively reflects the response of the conformal coating of the chip under test to the input pulse signal and forms the basis for subsequent analysis of the conformal coating's structural characteristics. By analyzing the impulse response function, the characteristics of the conformal coating of the chip under test can be calculated.

[0092] For example, in a feasible implementation, the impulse response function is as follows: Figure 7 As shown, the horizontal axis Optical delay (ps) is the optical delay (picoseconds), and the vertical axis Amplitude (au) is the amplitude (arbitrary unit). It 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.

[0093] In a feasible embodiment, step S402 may include steps S4021 and S4022:

[0094] 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;

[0095] By analyzing the pulse response function, the time delay between two adjacent echoes reflected by the conformal coating of the chip under test is identified and recorded. This time delay data is directly related to the physical properties of the coating, especially its thickness information.

[0096] Step S4022: Calculate the thickness of the conformal coating according to the time delay data and the refractive index of the conformal coating.

[0097] Using the obtained time delay data and the known refractive index of the conformal coating, the specific thickness of the coating is calculated. The thickness calculation formula is: , where c is the speed of light in air, is the time delay between two adjacent reflection echoes from the conformal coating, is the refractive index of the conformal coating.

[0098] For example, the conformal coating in this embodiment is acrylic fiber. According to literature review, the refractive index n≈1.6 of acrylic fiber in the terahertz band. Therefore, it can be calculated that the thickness of the acrylic fiber at this position is 36 μm.

[0099] In a feasible embodiment, step S402 may further include steps S4023 and S4024:

[0100] Step S4023, calculating the average thickness of the conformal coating according to the thickness of each pixel in the conformal coating;

[0101] The thickness of each pixel (or smaller analysis unit) in the conformal coating is statistically analyzed to calculate the average thickness of the conformal coating.

[0102] Step S4024: Calculate a variance value based on the thickness mean value, wherein the uniformity of the conformal coating is inversely proportional to the variance value.

[0103] Based on the mean thickness, the variance of the thickness of all pixels relative to the mean is 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 difference in the coating thickness.

[0104] 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 variance σ 2 express:

[0105] ,

[0106] ,

[0107] in, is the conformal coating thickness at different locations calculated from the terahertz results, and N is the number of data sampling points. In this example, the mean µ of the acrylic conformal coating is 38.4 µm, and the standard deviation σ obtained by root square of the variance is 1.3 µm.

[0108] In summary, in this embodiment, a reflective terahertz time-domain spectroscopy system is used to emit terahertz pulses to a metal plate and a conformal-coated chip to be tested, and a time-domain spectrum is collected. 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.

[0109] 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.

[0110] The present application also provides a conformal coating detection device, please refer to Figure 8 , conformal coating detection device includes:

[0111] 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;

[0112] a transfer function construction module 20, configured to convert the time domain spectrum into a frequency domain spectrum, and 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;

[0113] A transfer function optimization module 30 is configured to perform a frequency domain reconstruction operation on the transfer function using a preset autoregressive model to obtain an optimized transfer function;

[0114] The feature calculation module 40 is configured to calculate the features of the conformal coating of the chip to be tested according to the optimized transfer function.

[0115] Optionally, the transfer function optimization module 30 is further configured to:

[0116] 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;

[0117] Calculating missing components in a low-frequency region and a high-frequency region of the transfer function using a preset autoregressive model, wherein the low-frequency region is a region of the transfer function with a frequency lower than the low-frequency threshold, and the high-frequency region is a region of the transfer function with a frequency higher than the high-frequency threshold;

[0118] A frequency domain reconstruction operation is performed on the transfer function based on the missing component to obtain an optimized transfer function.

[0119] Optionally, the conformal coating detection device further includes a model training module (not shown), which is configured to:

[0120] The frequency components in the high signal-to-noise ratio region are trained using an 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.

[0121] Optionally, the feature calculation module 40 is further configured to:

[0122] Performing inverse Fourier transform on the optimized transfer function to obtain an impulse response function;

[0123] The characteristics of the conformal coating of the chip to be tested are calculated according to the impulse response function.

[0124] Optionally, the feature calculation module 40 is further configured to:

[0125] 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;

[0126] The thickness of the conformal coating is calculated based on the time delay data and the refractive index of the conformal coating.

[0127] Optionally, the feature calculation module 40 is further configured to:

[0128] Calculating an average thickness of the conformal coating according to the thickness of each pixel in the conformal coating;

[0129] 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.

[0130] The conformal coating detection device provided in the embodiments of the present application utilizes the conformal coating detection method described in the above-mentioned embodiments to ensure high-precision measurement of conformal coatings. Compared to the prior art, the conformal coating detection device provided in the embodiments of the present application has the same beneficial effects as the conformal coating detection method described in the above-mentioned embodiments. Other technical features of the conformal coating detection device are the same as those disclosed in the conformal coating detection method described in the above-mentioned embodiments and are not further elaborated here.

[0131] An embodiment of the present application provides an electronic device, comprising: 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 to enable the at least one processor to perform the conformal coating detection method of the above-mentioned embodiment 1.

[0132] Reference below Figure 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), and fixed terminals such as digital TVs and desktop computers. Figure 9 The electronic device shown is merely an example and should not limit the functions and scope of use of the embodiments of the present application.

[0133] like Figure 9 As shown, the electronic device may include a processing device 1001 (e.g., a central processing unit, a graphics processing unit, etc.), which can perform various appropriate actions and processes based on programs stored in a read-only memory (ROM) 1002 or programs loaded from a storage device 1003 into a random access memory (RAM) 1004. RAM 1004 also stores various programs and data required for the operation of the electronic device. Processing device 1001, ROM 1002, and RAM 1004 are interconnected via a bus 1005. An input / output (I / O) interface 1006 is also connected to the bus. Typically, the following systems may be connected to I / O interface 1006: input devices 1007, such as a touchscreen, touchpad, keyboard, mouse, image sensor, microphone, accelerometer, gyroscope, etc.; output devices 1008, such as a liquid crystal display (LCD), speaker, vibrator, etc.; storage device 1003, such as a magnetic tape or hard disk; and 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 instead.

[0134] In particular, according to the embodiments disclosed in the present application, the processes described above with reference to the flowcharts can be implemented as computer software programs. For example, the embodiments disclosed in the present application include a computer program product comprising a computer program carried on a computer-readable medium, the computer program comprising 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 via 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.

[0135] The electronic device provided in the embodiments of the present application utilizes the conformal coating detection method of the above-described embodiments to ensure high-precision measurement of conformal coatings. Compared to the prior art, the electronic device provided in the embodiments of the present application achieves the same beneficial effects as the conformal coating detection method provided in the above-described embodiments. Other technical features of the electronic device are the same as those disclosed in the conformal coating detection method of the above-described embodiments and are not further described here.

[0136] It should be understood that the various parts disclosed in the embodiments of the present application can be implemented using 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 appropriate manner in any one or more embodiments or examples.

[0137] The above are only specific embodiments of the present application, but the scope of protection of this application is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in this application should be included in the scope of protection of this application. Therefore, the scope of protection of this application should be based on the scope of protection of the claims.

[0138] An embodiment of the present application provides a computer-readable storage medium having computer-readable program instructions (ie, a computer program) stored thereon, wherein the computer-readable program instructions are used to execute the conformal coating detection method in the above embodiment.

[0139] The computer-readable storage medium provided in the embodiments 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 thereof. 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, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), optical fiber, portable compact disk read-only memory (CD-ROM), optical storage device, magnetic storage device, or any suitable combination thereof. In this embodiment, the computer-readable storage medium may be any tangible medium that contains or stores a program that can be used by or in conjunction with an instruction execution system or device. The program code contained on the computer-readable storage medium can be transmitted using any suitable medium, including but not limited to: wires, optical cables, RF (Radio Frequency), etc., or any suitable combination thereof.

[0140] The computer-readable storage medium may be included in the electronic device, or may exist independently without being incorporated into the electronic device.

[0141] 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 the 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 the 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 based on the optimized transfer function.

[0142] The computer program code for performing the operations of the embodiments 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" or similar programming languages. The program code can be executed entirely on the user's computer, partially on the user's computer, as a separate software package, partially on the user's computer and partially on a remote computer, or entirely on a 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, through the Internet using an Internet service provider).

[0143] The flow charts and block diagrams in the accompanying drawings illustrate the possible architecture, functions and operations of the systems, methods and computer program products according to various embodiments of the present application. In this regard, each box in the flow chart or block diagram can represent a module, program segment or a part of code, and the module, program segment or a part of 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 box can also occur in a different order than that marked in the accompanying drawings. For example, two 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 box in the block diagram and / or flow chart, and the combination of the boxes in the block diagram and / or flow chart can be implemented by a dedicated hardware-based system that performs the specified function or operation, or can be implemented by a combination of dedicated hardware and computer instructions.

[0144] The modules described in the embodiments of the present application may be implemented in software or hardware, wherein the name of a module does not necessarily limit the unit itself.

[0145] The computer-readable storage medium provided in the embodiments of this application is a computer-readable storage medium. The computer-readable storage medium stores computer-readable program instructions (i.e., a computer program) for executing the aforementioned conformal coating detection method, thereby ensuring high-precision conformal coating measurement. Compared to the prior art, the computer-readable storage medium provided in the embodiments of this application has the same beneficial effects as the conformal coating detection method provided in the aforementioned embodiments, and therefore is not further elaborated here.

[0146] 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.

[0147] 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.

[0148] 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 transformations 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; Calculating the characteristics of the conformal coating of the chip to be tested according to the optimized transfer function; 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; Calculating missing components in a low-frequency region and a high-frequency region of the transfer function using a preset autoregressive model, wherein the low-frequency region is a region of the transfer function with a frequency lower than the low-frequency threshold, and the high-frequency region is a region of the transfer function with a frequency 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.

2. The conformal coating detection method according to claim 1, wherein: 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 method further includes: The frequency components in the high signal-to-noise ratio region are trained using an 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.

3. The conformal coating detection method according to claim 1, wherein: 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.

4. The conformal coating detection method according to claim 3, wherein: The characteristic includes thickness, and the step of calculating the characteristic of the conformal coating of the chip to be tested according to the impulse response function includes: 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; The thickness of the conformal coating is calculated based on the time delay data and the refractive index of the conformal coating.

5. The conformal coating detection method according to claim 4, wherein: 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.

6. A conformal coating detection device, characterized in that: The device comprises: A time domain spectrum generation module is used to obtain the 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, configured to convert the time domain spectrum into a frequency domain spectrum, and 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; A transfer function optimization module, configured to perform a frequency domain reconstruction operation on the transfer function using a preset autoregressive model to obtain an optimized transfer function; a feature calculation module, configured to calculate the features of the conformal coating of the chip to be tested according to the optimized transfer function; The transfer function optimization module is further used to: 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; Calculating missing components in a low-frequency region and a high-frequency region of the transfer function using a preset autoregressive model, wherein the low-frequency region is a region of the transfer function with a frequency lower than the low-frequency threshold, and the high-frequency region is a region of the transfer function with a frequency 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.

7. 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 5.

8. A storage medium, characterized in that: The storage medium 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 according to any one of claims 1 to 5 are implemented.

9. 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 5 are implemented.

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