Method for observing microstructure of MLCC ceramic dielectric material based on scanning electron microscope and application

Abstract

The invention discloses a sample preparation and observation method for observing the microstructure of an MLCC ceramic dielectric material based on a scanning electron microscope, and the method comprises the following steps: pretreating an MLCC sample: fixedly sealing the MLCC sample in insulating resin, and exposing an inner electrode through metallographic polishing; fixing: connecting the left side and the right side of the polished surface of the MLCC with the metal sample table through conductive adhesive tapes respectively; a back scattering image is obtained through SEM shooting; and the microstructure of the dielectric material of the MLCC sample is observed in a magnetic lens and CBS mode. By adopting the method to observe the microstructure of the MLCC ceramic dielectric material, the operation process is convenient and fast, the surface structure of the MLCC is not influenced, the morphology and the size of the MLCC ceramic dielectric material can be more accurately observed, and convenient conditions are provided for subsequent microscopic analysis.

Description

Technical Field

[0001] The present invention relates to the technical field of detection and analysis of the microstructure of ceramic dielectric materials, and in particular to a method and application of observing the microstructure of MLCC ceramic dielectric materials based on a scanning electron microscope. Background Art

[0002] Ceramic capacitors are the main capacitor category, among which multilayer ceramic capacitors (MLCC) are widely used, with a market size of 93%. MLCC is used in circuits such as noise suppression, power supply voltage smoothing, filtering, etc. It has the characteristics of high voltage resistance, high temperature resistance, small size, wide capacitance range, and is suitable for surface mounting, with advantages in cost and performance.

[0003] The ceramic dielectric material of MLCC is mainly barium titanate, but the dielectric constant of pure barium titanate has a sudden change in temperature, which cannot meet the temperature stability requirements of electronic components. In order to overcome the problem of sudden changes in the dielectric constant of barium titanate near the phase transition temperature, it needs to be modified. The temperature stability and reliability of MLCC are related to the microstructure of the dielectric material.

[0004] Based on the limitations of existing analytical techniques, it is very important to develop a SEM sample preparation and characterization method for the MLCC microstructure that has no effect on the MLCC cross section. Summary of the invention

[0005] In response to the above technical problems, the present invention provides a method for statistically preparing and characterizing the microscopic morphology and size of MLCC based on backscattering scanning electron microscopy. After the MLCC device is processed, the backscattering image of the scanning electron microscope is used to observe the microscopic grain morphology.

[0006] To achieve the above object, the technical solution adopted by the present invention is:

[0007] On the one hand, the present invention provides a method for observing the microstructure of MLCC ceramic dielectric materials based on a scanning electron microscope, comprising the following steps: (1) MLCC sample pretreatment: sealing the MLCC sample in an insulating resin and exposing the inner electrode by metallographic polishing; (2) MLCC sample fixation: connecting the inner electrode to the sample stage using a conductive tape to ensure that the whole has good conductivity; (3) SEM backscatter imaging: imaging and observing the MLCC sample after the treatment in step (2) in CBS mode under a magnetic lens.

[0008] As a preferred embodiment, in step (1), the insulating resin is epoxy resin.

[0009] As a preferred embodiment, in step (1), the metallographic polishing includes sequentially rough polishing with sandpaper and mirror polishing with a polishing cloth and a diamond suspension as a metallographic polishing agent.

[0010] As a preferred embodiment, the rough sandpaper polishing is performed by sequentially using 600 mesh, 1000 mesh, 2000 mesh, 3000 mesh and 5000 mesh sandpaper.

[0011] As a preferred embodiment, the total time of the rough polishing with sandpaper is ≤10 min; and the rotation speed of the rough polishing with sandpaper is 100-150 rpm.

[0012] As a preferred embodiment, the particle size of diamond in the diamond suspension is 0.05 to 0.07 μm;

[0013] As a preferred embodiment, the mirror polishing time is 5 to 20 minutes, and the rotation speed is 100 to 150 rpm. The mirror polishing time depends on the size of the MLCC sample. The smaller the size, the shorter the polishing time.

[0014] As a preferred embodiment, the step (3) specifically involves using backscattered electron imaging to observe the dielectric layer grains of the MLCC sample processed in step (2).

[0015] On the other hand, the present invention also provides application of the above method in preparing MLCC ceramic capacitors.

[0016] Compared with the prior art, the technical solution of the present invention has the following advantages or beneficial effects:

[0017] The present invention processes the MLCC ceramic capacitor and uses a scanning electron microscope to truly reflect the microstructure and grain morphology of the dielectric material. The operation process is convenient and quick, and corrosion treatment of the MLCC ceramic capacitor is avoided. The obtained microstructure is clearer and the details of the microstructure are clearer, which provides convenient conditions for subsequent morphology analysis and defect analysis. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] One or more embodiments are exemplarily described by pictures in the corresponding drawings, and these exemplifications do not constitute limitations on the embodiments. Unless otherwise stated, the pictures in the drawings do not constitute proportional limitations.

[0019] Figure 1 This is the schematic diagram of the backscattering of a scanning electron microscope;

[0020] Figure 2 This is a SEM image of the MLCC sample after metallographic polishing in step (1) of Example 1 of the present invention;

[0021] Figure 3Schematic diagram of the fixing method in step (2) of Example 1 of the present invention;

[0022] Figure 4 This is a backscattered SEM image of the MLCC sample in step (3) of Example 1 of the present invention;

[0023] Figure 5 This is a SEM image of the MLCC sample in Comparative Example 1 of the present invention;

[0024] Figure 6 This is a SEM image of the MLCC sample in Comparative Example 2 of the present invention;

[0025] Figure 7 This is the TEM image of the MLCC sample in Comparative Example 3 of the present invention. DETAILED DESCRIPTION

[0026] The inventors found that the conventional method for preparing and observing the microstructure of MLCC samples is to obtain a flat cross section of the MLCC by mechanical destruction or grinding, distinguish the grains and grain boundaries by polishing and corroding the cross section, and then directly observe using a scanning electron microscope (SEM). This method is intuitive and efficient, but it must go through a corrosion process. The metal electrodes and ceramic grains of the MLCC may be affected under corrosion conditions, and it is impossible to obtain information such as the true device grain morphology and size. Compared with characterization methods such as transmission electron microscopy (TEM), SEM scanning is more convenient and has advantages in observing the surface morphology and size statistics of grains.

[0027] On the one hand, the present invention provides a method for observing the microstructure of MLCC ceramic dielectric materials based on a scanning electron microscope, comprising the following steps: (1) MLCC sample pretreatment: sealing the MLCC sample in an insulating resin and exposing the inner electrode by metallographic polishing; (2) MLCC sample fixation: connecting the inner electrode to the sample stage using a conductive tape to ensure that the whole has good conductivity; (3) SEM backscatter imaging: imaging and observing the MLCC sample after the treatment in step (2) in CBS mode under a magnetic lens.

[0028] On the other hand, the present invention also provides application of the above method in preparing MLCC ceramic capacitors.

[0029] The following embodiments are only some embodiments of the present invention, rather than all embodiments. Therefore, the detailed description in the embodiments of the present invention provided below is not intended to limit the scope of the present invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making creative work belong to the protection scope of the present invention.

[0030] In the present invention, unless otherwise specified, all equipment and raw materials can be purchased from the market or are commonly used in the industry. The methods in the following embodiments are all conventional methods in the art unless otherwise specified.

[0031] Example 1

[0032] The method for observing the microstructure of MLCC ceramic dielectric material based on scanning electron microscopy in this embodiment includes the following steps:

[0033] (1) MLCC sample pretreatment: The MLCC sample was sealed in epoxy resin along the long axis, and metallographic polishing was performed using 600 mesh, 1000 mesh, 2000 mesh, 3000 mesh and 5000 mesh sandpaper in sequence. The total polishing time was 10 min. During the polishing process, the speed of the polishing machine was 150 rpm. Then, a diamond suspension polishing liquid with a particle size of 0.05 mm was used to polish for 15 min at the same speed until the mirror surface was exposed, exposing the internal electrode.

[0034] (2) Cut the conductive tape into 3 cm*1 cm strips and stick them to the left and right sides of the MLCC sample after treatment in step (1), and then connect the conductive tape to the metal surface of the sample stage to meet the conductivity requirements for shooting backscattered SEM;

[0035] (3) SEM photography: Use a ThermoFisher Apero2 SEM field emission microscope, set the electron beam voltage to 10.00 kV, the current to 1.6 nA, WD = 10 mm, and HFW = 5 μm; adjust the electron microscope to CBS mode (which can simultaneously image, observe component contrast, and obtain morphological information), add a backscatter detector, turn on the magnetic lens, adjust the center position, focal length, and astigmatism to make appropriate observations, and then perform observations. The schematic diagram of the backscattering principle of the scanning electron microscope is shown in the figure. Figure 1 shown.

[0036] In step (1) of this embodiment, the SEM image of the MLCC after polishing is as follows: Figure 2 shown.

[0037] In step (2) of this embodiment, the sample stage after the MLCC is fixed is as follows Figure 3 shown.

[0038] The backscattered SEM image obtained in step (3) of this embodiment is as follows: Figure 4 As shown, the microscopic morphology and grain structure of the dielectric layer material can be clearly seen from the figure, and the holes in the sample can be observed.

[0039] Comparative Example 1

[0040] The sample preparation method in this comparative example is the same as that in Example 1, except that in step (1), after grinding and polishing, the MLCC sample is hot-etched in air at 950°C for 30 minutes to distinguish grain boundaries and grains. In step (3), backscatter imaging is not used, but secondary electron imaging is used. The SEM image obtained is as follows: Figure 5 As shown. Figure 5 It can be seen that the microscopic morphology in this comparative example has changed significantly, the grain size has slightly increased, the holes have disappeared and cannot be observed, and the electrode layer has expanded significantly. This comparative example shows that the thermal corrosion process has an impact on both the MLCC dielectric material and the electrode material, and the obtained microstructure and grain morphology are not realistic enough.

[0041] Comparative Example 2

[0042] The sample preparation method in this comparative example is the same as that in Example 1, except that in step (1), after grinding and polishing, the MLCC sample is etched for 10 seconds under HF-H2SO4 to distinguish grain boundaries and grains. In step (3), backscatter imaging is not used, but secondary electron imaging is used. The SEM image obtained is as follows: Figure 6 As shown. Figure 6 It can be seen that the microstructure in this comparative example is destroyed, the dielectric material grains are deformed, and the electrode material is obviously corroded. This comparative example shows that the acid corrosion process has a significant impact on both the MLCC dielectric material and the electrode material, and the obtained microstructure and grain morphology are not realistic enough.

[0043] Comparative Example 3

[0044] The sample preparation method in this comparative example is the same as that in Example 1, except that in step (2), the MLCC sample is subjected to ion thinning (Focused Ion Beam, FIB cutting) by a dual-beam focused ion beam system: in this process, the ion beam starts cutting from the surface of the sample and gradually penetrates the sample to form a thin slice with a thickness of about 1 mm; the slice is captured by a nanomanipulator and transferred to the FIB semi-divided grid, and through further fine processing, a cut sample with a thickness of 50 nm is finally obtained, which meets the requirements for high-resolution TEM shooting. The TEM bright field image of the MLCC sample taken in step (3) is as follows: Figure 7 Shown from Figure 7It can be seen that the microstructure and grain morphology of the MLCC sample under TEM are similar to those in Example 1, and the details of the holes in the sample can be observed. Due to the use of TEM, the field of view of this comparative example is narrow, and it can only locally reflect the microstructure and grain morphology information of the MLCC sample; compared with Example 1, the characterization operation is also more complicated.

[0045] In summary, the method provided by the present invention for observing the microstructure and grain morphology of MLCC ceramic dielectric materials based on scanning electron microscope backscattered electron imaging successfully prepares samples that do not undergo a corrosion process and are suitable for backscattered SEM imaging, providing a method for non-destructive characterization of microstructure and grain morphology.

[0046] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for observing the microstructure of MLCC ceramic dielectric materials based on a scanning electron microscope, characterized in that: The following steps are involved: (1) MLCC sample pretreatment: The MLCC sample is sealed in insulating resin and the internal electrodes are exposed by metallographic polishing; (2) MLCC sample preparation and fixation: Use conductive tape to connect the inner electrode to the sample stage to ensure good overall conductivity; (3) SEM backscattering image: The MLCC sample treated in step (2) is imaged and observed in CBS mode under a magnetic lens.

2. The method according to claim 1, characterized in that In step (1), the insulating resin is epoxy resin.

3. The method according to claim 1, characterized in that In step (1), the metallographic polishing includes rough polishing with sandpaper and mirror polishing with polishing cloth and diamond suspension as metallographic polishing agent.

4. The method according to claim 3, characterized in that The rough sandpaper polishing is performed by sequentially using 600 mesh, 1000 mesh, 2000 mesh, 3000 mesh and 5000 mesh sandpapers.

5. The method according to claim 3, characterized in that: The total time of the rough polishing with sandpaper is ≤10min; the rotation speed of the rough polishing with sandpaper is 100-150rpm.

6. The method according to claim 3, characterized in that The particle size of the diamond in the diamond suspension is 0.05-0.07 μm.

7. The method according to claim 3, characterized in that The mirror polishing time is 5 to 20 minutes, and the rotation speed is 100 to 150 rpm.

8. The method according to claim 1, characterized in that The step (3) specifically involves using backscattered electron imaging to observe the dielectric layer grains of the MLCC sample processed in step (2).

9. Use of the method according to any one of claims 1 to 8 in preparing MLCC ceramic capacitors.

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