A method of non-focussing testing the thickness of an organic coating
By combining non-focused testing methods with FTIR infrared microscopy, the problems of rapid, non-destructive, and accurate measurement of organic coating thickness were solved, thereby improving the stability and accuracy of organic coating thickness.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- GUANGZHOU TERMBRAY ELECTRONICS TECH CO LTD
- Filing Date
- 2023-07-31
- Publication Date
- 2026-08-04
AI Technical Summary
Existing technologies struggle to measure the thickness of organic coatings quickly, non-destructively, and accurately, especially when the thickness of the organic coating is uneven. Traditional methods are easily affected by the unevenness of the coating surface and the variation in thickness, resulting in poor measurement accuracy and stability.
A non-focused testing method was adopted, in which an infrared testing device was vertically raised a certain distance on the organic coating to increase the testing area. Infrared reflectance spectroscopy was performed using an FTIR infrared microscope to establish the correlation between the area of infrared characteristic peaks and the coating thickness. Non-destructive measurement was achieved using the Lambert-Beer law.
It enables rapid, non-destructive, and accurate measurement of organic coating thickness, improves measurement stability and accuracy, reduces errors caused by uneven coating surfaces and varying thicknesses, and enhances the reliability of test signals and results.
Smart Images
Figure CN116972759B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of testing technology, and more specifically, to a method for non-focused testing of the thickness of organic coatings. Background Technology
[0002] Organic coatings are widely used in industrial technology as functional layers such as anti-corrosion layers. Currently, methods for measuring the thickness of organic coatings include chemical dissolution quantitative methods and film thickness measurement methods. However, both of these methods inevitably have some problems when accurately measuring the thickness of organic coatings. For example, when using chemical dissolution quantitative methods, the organic coating may be damaged. Furthermore, this method assumes that the thickness of the organic coating is very uniform, and when the thickness of the organic coating is not very uniform, it is impossible to evaluate the quality of the organic coating in a specific area. On the other hand, film thickness measurement instruments on metal layers usually use methods such as magnetic attraction, eddy current, or optical rays to measure the film thickness. The measurement range for organic coating thickness is relatively narrow, especially when the organic coating thickness is small, the data error is relatively large. In addition, there are some applications that use non-destructive testing methods such as infrared spectroscopy to test the thickness of organic coatings. However, the application range of infrared spectroscopy is extremely limited when testing the thickness of organic coatings on metal layers. For example, the accuracy of the thickness test is affected by the roughness of the metal layer and the unevenness of the organic coating surface. Therefore, specifically, the traditional test method using infrared reflection spectroscopy is not suitable for detecting the thickness of OSP film (Organic Solderability Preservatives) on PCBs (Printed Circuit Boards).
[0003] The rapid development and widespread application of integrated circuits have led to a rapid expansion in the types and applications of PCBs, resulting in increasingly higher requirements for the reliability and precision of PCB manufacturing. Copper, as a major component of PCB circuit patterns, plays a crucial role in connecting the various circuit layers and conducting electrical signals. However, as an active chemical substance, copper is easily oxidized or sulfided when exposed to air, which can lead to manufacturing defects in subsequent processes, such as high-temperature soldering. This affects the mounting of components on the PCB surface and the reliability of the final PCB product. Therefore, in actual PCB manufacturing, after etching copper foil to form the outer layer circuitry, a surface treatment process is performed on the etched copper circuitry to prevent oxidation and to provide a soldering surface for component mounting on the PCB.
[0004] OSP film is one of the main surface treatment processes on PCBs. OSP film is an organic film formed chemically on a clean bare copper surface. Due to its anti-oxidation, thermal shock resistance, and moisture resistance, OSP film can effectively protect the copper foil on the PCB surface. At the same time, OSP film is easily and quickly removed by flux in subsequent high-temperature soldering processes, and the exposed clean copper surface can immediately bond with molten solder to form a strong solder joint in a very short time. In addition, OSP film is usually made of water-based compounds, which is simple to manufacture, economical, and environmentally friendly. Furthermore, OSP film acts directly on the PCB surface, facilitating damage repair or replacement, making the PCB easy to reuse. However, in actual manufacturing, the OSP film thickness is usually small (μm level). If the film thickness is too small, the OSP film will be easily damaged during handling and storage, which will not only reduce the protection effect on the copper foil on the PCB surface, but also greatly reduce the soldering performance in the subsequent high-temperature soldering process. On the other hand, if the OSP film thickness is set too thick, it will increase the cost, and the flux will be difficult to remove the OSP film during high-temperature soldering, reducing production efficiency and affecting the subsequent soldering performance. Therefore, the thickness of the OSP film on the PCB surface must be controlled within a certain range. Controlling the thickness of the OSP film relies on accurate measurement of its thickness, preferably using a non-destructive and precise measurement method. However, since the OSP film is directly attached to the etched copper foil surface of the PCB, its uneven thickness makes it difficult to accurately test using traditional non-destructive infrared reflectance spectroscopy. Specifically, in traditional infrared reflectance spectroscopy testing methods, the emitted infrared light is usually focused on the sample before testing. The area of the sample covered by the focal point is the test area on the sample. While a smaller test area ensures measurement accuracy, it also results in a smaller feedback test signal. The characteristic peaks in the obtained infrared reflectance spectrum are easily affected by the unevenness of the coating surface and the coating thickness, causing large fluctuations and thus affecting the accuracy and stability of the measurement. Summary of the Invention
[0005] The present invention aims to overcome at least one of the defects of the prior art and provide a method for non-focused testing of organic coating thickness, which can achieve rapid, non-destructive and accurate measurement of organic coating thickness.
[0006] This technical solution provides a method for non-focused testing of organic coating thickness, including the following steps:
[0007] S1. Based on the correlation reference of a standard sample, the standard sample includes a metal substrate and a reference organic coating of known thickness disposed on the surface of the metal substrate;
[0008] The infrared reflectance spectrum of a reference organic coating formed on a standard sample was measured using a non-focusing test method.
[0009] The infrared characteristic peak area within a predetermined wavenumber range is statistically analyzed from the infrared reflectance spectrum of the reference organic coating;
[0010] Based on the thickness of the reference organic coating and the infrared reflectance spectrum of the reference organic coating, the correlation between the thickness of the organic coating and the area of the infrared characteristic peaks is determined.
[0011] S2. Testing of the sample to be tested, wherein the sample to be tested includes a metal substrate consistent with the standard sample and an organic coating to be tested disposed on the surface of the metal substrate;
[0012] The infrared reflectance spectrum of the organic coating formed on the sample under test was measured using a non-focusing test method.
[0013] The infrared characteristic peak area within a predetermined wavenumber range is statistically analyzed using the infrared reflectance spectrum of the organic coating under test.
[0014] Based on the correlation between the thickness of the organic coating and the area of the infrared characteristic peaks determined in S1, the thickness of the organic coating to be tested is calculated from the area of the infrared characteristic peaks.
[0015] The non-focused testing method is as follows: based on the focusing of the sample being tested by the infrared testing device, the sample being tested is raised vertically by a certain distance to generate a focusing error, and the infrared reflectance spectrum of the sample being tested is obtained under the state of focusing error.
[0016] In this technical solution, the thickness of the organic coating is mainly tested using a non-focusing infrared testing device. Under infrared light irradiation, the compound molecules in the organic coating can absorb infrared light of a specific wavelength, thereby generating an infrared absorption spectrum or infrared reflection spectrum with corresponding infrared characteristic peaks. Since both the standard sample and the sample to be tested are organic coatings coated on a metal layer, infrared light can pass through the organic coating and be reflected by the metal layer. Therefore, the thickness of the organic coating can be accurately measured by using infrared reflection spectroscopy and based on the Lambert-Beer law. This allows the infrared testing device to perform non-destructive testing of the organic coating thickness without contact with the organic coating. Specifically, in this technical solution, the infrared reflection spectrum of the standard sample is first obtained using a non-focusing testing method, and the area of the infrared characteristic peaks within a predetermined wavenumber range is statistically analyzed. A correlation is established between the area of the infrared characteristic peaks within the predetermined wavenumber range and the thickness of the organic coating on the standard sample, forming a relationship. Based on the relationship obtained from the standard sample, the infrared reflection spectrum of the sample to be tested is obtained using a non-focusing testing method, and the area of the infrared characteristic peaks within the predetermined wavenumber range is statistically analyzed. Substituting these values into the relationship, the thickness of the organic coating on the sample to be tested can be quickly calculated. Among these methods, the non-focusing testing method yielded infrared reflectance spectra of the tested samples with better accuracy and stability. In traditional infrared spectroscopy, focusing the sample inevitably introduces slight focusing errors due to the organic coating of a certain thickness on the metal layer. These errors can significantly impact testing accuracy, especially when the focal point area is small and the test signal is weak, leading to unavoidable testing errors. The non-focusing method, however, artificially generates a sufficiently large and controllable focusing error by vertically raising the sample after focusing. This increases the area of infrared light irradiated on the sample, thus increasing the test area and consequently the area of the infrared characteristic peaks. At the same time, the predetermined wavenumber range statistically defined for the tested organic coating is correspondingly increased, which enhances the test signal, eliminates minor focusing errors during focusing, and reduces test errors. Simultaneously, the increased test area results in an infrared reflectance spectrum encompassing the test results for the entire test region. This includes the effects of uneven coating surfaces and varying coating thicknesses within the test region, reducing the variability in test data caused by these factors and improving the stability of the test results. Furthermore, it enhances the stability and reliability of establishing a correlation between the infrared characteristic peak area within the predetermined wavenumber range and the thickness of the organic coating, thereby improving the accuracy and reliability of the thickness test for the organic coating on the test sample.
[0017] Furthermore, the infrared testing device employs an FTIR (Fourier Transform Infrared Absorption Spectrometer) infrared microscope. The infrared reflectance spectrum of the tested sample is formed based on the reflectance mode test of the FTIR infrared microscope. The detection principle of FTIR is to simultaneously detect infrared light of all wavelengths using an interferometer, and then convert the detected data into an infrared spectrum through Fourier transform mathematical operations. Therefore, its detection efficiency is extremely high, and it uses fewer optical components, without gratings or prism beam splitters, reducing light loss. Moreover, the interference further increases the infrared light signal, resulting in a high radiation intensity reaching the detector and a high signal-to-noise ratio. At the same time, since FTIR collects data across the entire wavelength range, the spectrum obtained is the result of averaging multiple data acquisitions, thus having higher accuracy than traditional infrared spectrometers. By using the reflectance mode of FTIR for testing, while retaining the advantages of infrared reflectance spectroscopy in measuring the thickness of organic coatings—strong characteristic, rapid analysis, and non-destructive testing—it also improves the efficiency and accuracy of the test, thereby achieving rapid, non-destructive, and accurate testing of the thickness of organic coatings. Furthermore, by attaching a microscopic device to the FTIR, the spatial resolution of the FTIR can be improved, thereby further enhancing the accuracy of organic coating thickness testing.
[0018] Furthermore, step S1 specifically includes the following steps:
[0019] S11. Define a standard sample series, and prepare several standard samples with reference organic coatings of different thicknesses on their surfaces to form a standard sample series with thickness gradients;
[0020] S12. Standard sample series testing: The infrared reflectance spectra of the standard sample series are obtained by testing based on a non-focusing testing method, and the infrared characteristic peak areas within a predetermined wavenumber range are statistically analyzed.
[0021] S13. Correlation fitting: The reference organic coating thickness and infrared characteristic peak area of the standard sample series are fitted to calculate their correlation and form a relationship.
[0022] Preferably, in step S13, the correlation between the reference organic coating thickness of the standard sample series and the infrared characteristic peak area within a predetermined wavenumber range is not less than 0.95.
[0023] In this technical solution, the specific steps for providing a correlation reference between the infrared characteristic peak area and the thickness of the organic coating of the sample under test based on standard samples include three steps: defining a standard sample series, testing the standard sample series, and fitting the correlation. Specifically, when defining the standard sample series, several standard samples with reference organic coatings of different thicknesses are prepared to form a standard sample series with a thickness gradient. The thickness gradient range of the standard sample series should be designed to be sufficiently wide to cover the thickness of the organic coating on the sample under test, ensuring that the subsequently calculated correlation and relationship between the infrared characteristic peak area and the thickness of the organic coating are applicable to measuring the thickness of the organic coating under test. Simultaneously, the spacing of the thickness gradient of the standard sample series around the thickness of the organic coating under test should also be reasonably dense, thereby ensuring the accuracy and reliability of the subsequently calculated correlation and relationship between the infrared characteristic peak area and the thickness of the organic coating. After defining and fabricating a series of standard samples with reasonable ranges and spacing, the infrared reflectance spectra of the standard sample series are obtained based on the same focusing error test. The infrared characteristic peak areas within a predetermined wavenumber range are then statistically analyzed. The reference organic coating thickness and the infrared characteristic peak areas within the predetermined wavenumber range of the standard sample series are then fitted together, and their correlation is calculated to form a relationship. Preferably, in the calculation, a correlation of not less than 0.95 between the reference organic coating thickness and the infrared characteristic peak areas within the predetermined wavenumber range is considered significant. This relationship can then be used in subsequent calculations to obtain the thickness of the organic coating on the test sample by substituting the infrared characteristic peak areas within the predetermined wavenumber range of the test sample into the relationship.
[0024] Furthermore, the predetermined wavenumber range corresponds to the range of reflection peaks of the main components in the reference organic coating.
[0025] In this technical solution, the frequency unit in the spectroscopy of atoms, molecules, etc., is often the wavenumber, which is the reciprocal of the wavelength. It is used to characterize the number of light waves per unit length in the direction of light propagation. Since the compound molecules in the reference organic coating can absorb infrared light of a specific wavelength and generate infrared reflection characteristic peaks in a specific wavelength range in the infrared reflection spectrum, the predetermined wavenumber range in this technical solution corresponds to the range of reflection peaks in the infrared reflection spectrum generated by the main components in the organic coating under infrared light excitation.
[0026] Furthermore, in the non-focused testing method, there is an optimal vertical ascent distance for the tested sample. Under the optimal ascent distance, the infrared reflectance spectrum of the tested sample has the largest infrared characteristic peak area and the smallest coefficient of variation of the peak area within a predetermined wavenumber range.
[0027] Specifically, before step S12, the following step S111 is also included:
[0028] S111. Determine the optimal ascent distance. Based on the standard sample series, test the infrared reflectance spectra of the standard sample series at several different vertical ascent distances, and statistically analyze the infrared characteristic peak areas in a predetermined wavenumber range at different vertical ascent distances to form an ascent distance gradient. The optimal ascent distance is the vertical ascent distance at which the measured infrared reflectance spectra of the standard sample series have the largest infrared characteristic peak area in the predetermined wavenumber range and the smallest coefficient of variation of the peak area.
[0029] In this technical solution, a non-focused testing method is achieved by vertically raising the sample to be tested by a certain distance. While simply raising the sample increases the test area, excessively large raising distances can cause infrared signals to be reflected outside the detector's receiving range, resulting in a weaker signal. Furthermore, due to errors such as focusing, uneven coating surfaces, and coating thickness variations, changes in the test area also affect the stability of the test results, causing stability to initially increase and then decrease. Therefore, there exists an optimal raising distance to maximize the test area and achieve the best stability. Specifically, this manifests as the maximum area of the infrared characteristic peaks in the infrared reflectance spectrum within a predetermined wavenumber range, with the minimum coefficient of variation for the peak area. Therefore, after defining and fabricating a series of standard samples with reasonable ranges and spacing, the optimal raising distance is determined using this series of standard samples, thus providing a data basis for subsequent non-focused testing of standard samples and the sample to be tested. Specifically, to test the infrared reflectance spectra of a series of standard samples at several different vertical ascent distances, an ascent distance gradient is formed, and the infrared characteristic peak areas within a predetermined wavenumber range at different vertical ascent distances are statistically analyzed. The optimal ascent distance is the vertical ascent distance at which the measured infrared reflectance spectra of the series of standard samples have the largest infrared characteristic peak area within the predetermined wavenumber range and the smallest peak area variation coefficient.
[0030] Furthermore, this technical solution can be used to test the thickness of OSP film on PCB, wherein the metal substrate of the standard sample and the sample to be tested is copper, and the reference organic coating on the standard sample and the test organic coating on the sample to be tested are both OSP films formed on the outer copper circuit pattern of the PCB.
[0031] In one embodiment of this technical solution, when non-focusing the thickness of the OSP film on the PCB, based on the focused sample being tested, the sample is vertically raised by 0.4 mm to generate a focusing error; when calculating the infrared characteristic peaks within a predetermined wavenumber range in the infrared reflectance spectrum under non-focusing testing, the predetermined wavenumber range is 2937-2880 cm⁻¹. -1 ;
[0032] The relationship between the thickness of the OSP film to be tested and the area of the infrared characteristic peak in the predetermined wavenumber range under non-focused testing, obtained by fitting with standard samples, is: thickness of OSP film to be tested = 0.70309 × (area of infrared characteristic peak in the predetermined wavenumber range under non-focused testing) - 0.0491 (μm), and its correlation is 0.9827.
[0033] Compared with the prior art, the beneficial effects of the present invention are as follows:
[0034] 1. The infrared testing device performs non-focused testing on the sample to generate the corresponding infrared reflection spectrum and achieves accurate measurement of the thickness of the organic coating according to the Lambert-Beer law. This allows the infrared testing device to achieve rapid and non-destructive testing of the thickness of the organic coating without contact with it.
[0035] 2. By employing a non-focusing testing method, a more accurate and stable infrared reflectance spectrum was obtained. By vertically raising the sample after focusing, a sufficiently large and controllable focusing error was artificially generated, increasing the area of infrared light irradiated on the sample, thus increasing the test area, enhancing the test signal, eliminating minor focusing errors during focusing, and reducing test errors. Simultaneously, the increased test area resulted in an infrared reflectance spectrum encompassing the test results for the entire test region, dispersing the influence of uneven coating surfaces and varying coating thicknesses within the test area, reducing the coefficient of variation in the test data, and improving the stability of the test results. This, in turn, improved the stability and reliability of establishing a correlation between the area of infrared characteristic peaks within the predetermined wavenumber range and the thickness of the organic coating, thereby enhancing the accuracy and reliability of testing the thickness of the organic coating on the test sample. Attached Figure Description
[0036] Figure 1 This is a flowchart of a non-focused method for testing the thickness of organic coatings according to the present invention.
[0037] Figure 2 This is a flowchart illustrating the correlation and optimal ascent distance reference based on a series of standard samples in this invention.
[0038] Figure 3 This is a schematic diagram of the optical path of the non-focused testing method in this invention.
[0039] Figure 4 This is a schematic diagram comparing the peak area and peak area variation coefficient of the sample after it rises by 0.4 mm in Example 2 of the present invention with those in focused mode. Detailed Implementation
[0040] The accompanying drawings are for illustrative purposes only and should not be construed as limiting the invention. To better illustrate the following embodiments, some parts in the drawings may be omitted, enlarged, or reduced, and do not represent the actual product dimensions; it is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.
[0041] Example 1
[0042] like Figures 1-3 As shown, this technical solution provides a method for non-focused testing of organic coating thickness, including the following steps:
[0043] S1. Based on the correlation reference of a standard sample, the standard sample includes a metal substrate and a reference organic coating of known thickness disposed on the surface of the metal substrate;
[0044] The infrared reflectance spectrum of a reference organic coating formed on a standard sample was measured using a non-focusing test method.
[0045] The infrared characteristic peak area within a predetermined wavenumber range is statistically analyzed from the infrared reflectance spectrum of the reference organic coating;
[0046] Based on the thickness of the reference organic coating and the infrared reflectance spectrum of the reference organic coating, the correlation between the thickness of the organic coating and the area of the infrared characteristic peaks is determined.
[0047] S2. Testing of the sample to be tested, wherein the sample to be tested includes a metal substrate consistent with the standard sample and an organic coating to be tested disposed on the surface of the metal substrate;
[0048] The infrared reflectance spectrum of the organic coating formed on the sample under test was measured using a non-focusing test method.
[0049] The infrared characteristic peak area within a predetermined wavenumber range is statistically analyzed using the infrared reflectance spectrum of the organic coating under test.
[0050] Based on the correlation between the thickness of the organic coating and the area of the infrared characteristic peaks determined in S1, the thickness of the organic coating to be tested is calculated from the area of the infrared characteristic peaks.
[0051] The specific method of non-focusing testing is as follows: Based on the focused infrared testing device, the sample is vertically raised a certain distance to generate a focusing error. Under this focusing error, the infrared reflectance spectrum of the sample is obtained. This non-focusing method artificially generates a sufficiently large and controllable focusing error by vertically raising the sample after focusing, thus increasing the testing area, eliminating focusing errors, and reducing testing errors. Simultaneously, the increased testing area encompasses the test results for the entire testing area in the resulting infrared reflectance spectrum. Therefore, it also includes the effects of uneven coating surfaces and varying coating thicknesses within the testing area, reducing the variation in test data caused by uneven coating surfaces and varying coating thicknesses during testing, and improving the stability of the test results.
[0052] Preferably, the infrared testing device can employ an FTIR infrared microscope, and the obtained infrared reflectance spectrum is formed based on the reflectance mode test of the FTIR infrared microscope. The FTIR infrared microscope increases the infrared light signal by using an interferometer to simultaneously detect infrared light of all wavelengths, resulting in high radiation intensity and high signal-to-noise ratio. Then, the detected data is converted into an infrared spectrum through Fourier transform mathematical operations, resulting in extremely high detection efficiency. Furthermore, the spatial resolution of the testing device is improved through full-band detection and additional microscopic devices, thereby improving the accuracy of organic coating thickness testing.
[0053] Furthermore, step S1 specifically includes the following steps:
[0054] S11. Define a standard sample series. Prepare several standard samples with reference organic coatings of different thicknesses on their surfaces to form a standard sample series with a thickness gradient. Specifically, the thickness gradient range of the standard sample series should be designed to be wide enough to cover the thickness of the organic coating on the sample to be tested, so as to ensure that the correlation and relationship between the infrared characteristic peak area and the thickness of the organic coating calculated later are applicable to the measurement of the thickness of the organic coating. At the same time, the spacing of the thickness gradient of the standard sample series around the thickness of the organic coating to be tested should also be reasonably dense, so as to ensure the accuracy and reliability of the correlation and relationship between the infrared characteristic peak area and the thickness of the organic coating calculated later.
[0055] S12. Standard sample series testing: The infrared reflectance spectra of the standard sample series are obtained by testing based on a non-focusing testing method, and the infrared characteristic peak areas within a predetermined wavenumber range are statistically analyzed.
[0056] S13. Correlation fitting: The reference organic coating thickness and infrared characteristic peak area of the standard sample series are fitted to calculate their correlation and form a relationship.
[0057] Preferably, in step S13, a correlation of not less than 0.95 between the reference organic coating thickness and the infrared characteristic peak area within a predetermined wavenumber range is considered significant. The thickness of the organic coating on the sample to be tested can be calculated by substituting the infrared characteristic peak area within the predetermined wavenumber range of the sample into the relational formula.
[0058] Furthermore, the range of the predetermined wavenumber is determined by corresponding to the range of reflection peaks of the main components in the reference organic coating.
[0059] Furthermore, in non-focused testing methods, the test area increases with the vertical rise of the sample. However, if the rise distance is too large, the infrared signal will be reflected outside the detector's receiving range, and the detector will not receive the signal, resulting in a weaker signal intensity. At the same time, due to errors such as focusing error, uneven coating surface, and coating thickness differences, the change in test area will also affect the stability of the test results, causing the stability to show a trend of first increasing and then decreasing. Therefore, there is an optimal rise distance when the sample is raised to increase the test area, which maximizes the test area of the tested sample and provides the best stability. Specifically, this means that the infrared characteristic peak area of the infrared reflectance spectrum of the tested sample is maximized and the coefficient of variation is minimized within the predetermined wavenumber range.
[0060] Specifically, in order to define the optimal rise distance of the tested sample, before starting the non-focusing test on the standard sample series in step S12, the following step S111 is also included:
[0061] S111. Determine the optimal ascent distance. Based on the standard sample series, test the infrared reflectance spectra of the standard sample series at several different vertical ascent distances, and statistically analyze the infrared characteristic peak areas in the predetermined wavenumber range at different vertical ascent distances to form an ascent distance gradient. The optimal ascent distance is the vertical ascent distance at which the measured infrared reflectance spectra of the standard sample series have the largest infrared characteristic peak area in the predetermined wavenumber range and the smallest coefficient of variation.
[0062] Example 2
[0063] This embodiment uses FTIR infrared microscopy to test the thickness of the OSP film on the PCB. Specifically, the test is performed using the reflectance mode of the FTIR microscope with a clean gold mirror as the test background. The background scan is 32 scans, the sample scan is 64 scans, and the resolution is 4 cm. -1 The integration mode is G, and the characteristic peak wavenumber range of the integral is 2937-2880 cm⁻¹. -1 ;
[0064] The specific testing process is as follows:
[0065] S11. A series of standard PCB test boards with copper foil surfaces covered with OSP films of thicknesses of 0.09μm, 0.12μm, 0.13μm, 0.14μm, 0.21μm, and 0.34μm;
[0066] S111. Using a series of standard PCB test boards, the infrared reflectance spectra of the standard PCB test boards were measured in focusing mode at vertical rise distances of 0.1mm, 0.2mm, 0.3mm, 0.4mm, 0.5mm, and 0.6mm, and the wavenumber range of 2937-2880cm⁻¹ was statistically analyzed. -1 The infrared characteristic peak area, the result is as follows Figure 4 As shown, with the increase of the vertical ascent distance of the sample, the area of the FTIR characteristic peak first gradually increases and then gradually decreases. The average area of the FTIR characteristic peak is the largest and the coefficient of variation is the smallest when the vertical ascent distance is 0.4 mm. Therefore, the infrared reflectance spectra of the PCB standard test board series in the wavenumber range of 2937-2880 cm⁻¹ are used. -1 The optimal rise distance is 0.4 mm, which has the largest infrared characteristic peak area and the smallest coefficient of variation.
[0067] S12. The test was conducted using the reflectance mode of an FTIR infrared microscope. Based on FTIR focusing, the sample was raised by 0.4 mm by elevating the test platform. The thickness of the OSP film and its corresponding wavenumber range for the PCB standard test board series were statistically analyzed to be 2937-2880 cm⁻¹. -1 The areas of the infrared characteristic peaks are shown in the table below:
[0068] 0.0861 0.2138 0.1203 0.2260 0.1269 0.2322 0.1434 0.2596 0.2129 0.3394 0.3402 0.5412
[0069] S13. The thickness of the OSP film corresponding to the fitted PCB standard test board series and its corresponding wavenumber range is 2937-2880 cm⁻¹. -1 The infrared characteristic peak area was calculated, and its data correlation was found to be 0.9827, forming the following relationship: Thickness of the OSP film under test = 0.70309 × (wavenumber range under non-focused testing: 2937-2880 cm⁻¹) -1 The infrared characteristic peak area is -0.0491 (μm);
[0070] S2. Using the reflection mode of an FTIR infrared microscope, and based on FTIR focusing, the OSP film under test was raised by 0.4 mm by raising the test platform, and the OSP film under test was tested and statistically analyzed in the wavenumber range of 2937-2880 cm⁻¹. -1 The infrared characteristic peak area of the OSP film to be tested is substituted into the relationship obtained in S13 to calculate the thickness of the OSP film to be tested.
[0071] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the technical solution of the present invention, and are not intended to limit the specific implementation of the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the claims of the present invention should be included within the protection scope of the claims of the present invention.
Claims
1. A method for non-focused testing of organic coating thickness, characterized in that, Includes the following steps: S1. Based on the correlation reference of a standard sample, the standard sample includes a metal substrate and a reference organic coating of known thickness disposed on the surface of the metal substrate; The infrared reflectance spectrum of a reference organic coating formed on a standard sample was measured using a non-focusing test method. The infrared characteristic peak area within a predetermined wavenumber range is statistically analyzed from the infrared reflectance spectrum of the reference organic coating; Based on the thickness of the reference organic coating and the infrared reflectance spectrum of the reference organic coating, the correlation between the thickness of the organic coating and the area of the infrared characteristic peaks is determined. S2. Testing of the sample to be tested, wherein the sample to be tested includes a metal substrate consistent with the standard sample and an organic coating to be tested disposed on the surface of the metal substrate; The infrared reflectance spectrum of the organic coating formed on the sample under test was measured using a non-focusing test method. The infrared characteristic peak area within a predetermined wavenumber range is statistically analyzed using the infrared reflectance spectrum of the organic coating under test. Based on the correlation between the thickness of the organic coating and the area of the infrared characteristic peaks determined in S1, the thickness of the organic coating to be tested is calculated from the area of the infrared characteristic peaks. The non-focused testing method is as follows: based on the focusing of the sample being tested by the infrared testing device, the sample being tested is raised vertically by a certain distance to generate a focusing error, and the infrared reflectance spectrum of the sample being tested is obtained under the state of focusing error.
2. The method of testing the thickness of an organic coating layer without focusing according to claim 1, characterized in that, The infrared testing device employs an FTIR infrared microscope, and the infrared reflectance spectrum is formed based on the reflectance mode test of the FTIR infrared microscope.
3. The method of testing the thickness of an organic coating layer without focusing according to claim 1, characterized in that, Step S1 specifically includes the following steps: S11. Define a standard sample series, and prepare several standard samples with reference organic coatings of different thicknesses on their surfaces to form a standard sample series with thickness gradients; S12. Standard sample series testing: The infrared reflectance spectra of the standard sample series are obtained by testing based on a non-focusing testing method, and the infrared characteristic peak areas within a predetermined wavenumber range are statistically analyzed. S13. Correlation fitting: The reference organic coating thickness and infrared characteristic peak area of the standard sample series are fitted to calculate their correlation and form a relationship.
4. The method of testing the thickness of an organic coating layer without focusing according to claim 3, characterized in that, In step S13, the correlation between the reference organic coating thickness of the standard sample series and the infrared characteristic peak area within a predetermined wavenumber range is not less than 0.
95.
5. The method of testing the thickness of an organic coating layer without focusing according to claim 1, characterized in that, The range of the predetermined wavenumbers corresponds to the range of reflection peaks of the main components in the reference organic coating.
6. The method of testing the thickness of an organic coating layer without focusing according to any one of claims 1 to 5, characterized in that, In the non-focused testing method, there is an optimal vertical ascent distance for the tested sample. At the optimal ascent distance, the infrared reflectance spectrum of the tested sample has the largest infrared characteristic peak area and the smallest coefficient of variation of the peak area within a predetermined wavenumber range.
7. The method of testing the thickness of an organic coating layer without focusing according to claim 6, characterized in that, Before step S12, the following step S111 is also included: S111. Determine the optimal ascent distance. Based on the standard sample series, test the infrared reflectance spectra of the standard sample series at several different vertical ascent distances, and statistically analyze the infrared characteristic peak areas in a predetermined wavenumber range at different vertical ascent distances to form an ascent distance gradient. The optimal ascent distance is the vertical ascent distance at which the measured infrared reflectance spectra of the standard sample series have the largest infrared characteristic peak area in the predetermined wavenumber range and the smallest coefficient of variation of the peak area.
8. The method for non-focused testing of organic coating thickness according to any one of claims 1-7, characterized in that, The test is used to test the thickness of the OSP film on a PCB. The metal substrate is copper, and both the reference organic coating and the organic coating to be tested are OSP films formed on the outer copper circuit pattern of the PCB.
9. The method of testing the thickness of an organic coating layer without focusing according to claim 8, characterized in that, When testing the thickness of the OSP film on a PCB using a non-focused method, the sample is raised vertically a distance of 0.4 mm.
10. The method of testing the thickness of an organic coating layer without focusing according to claim 9, characterized in that, the predetermined wave number range is 2937-2880 cm -1 ; The thickness of the OSP film to be tested is 0.70309 × (area of infrared characteristic peaks in the predetermined wavenumber range under non-focused testing) - 0.0491, with a correlation of 0.9827.