A cross-sectional EBSD sample preparation method for flexible copper-clad laminates

Abstract

The present invention relates to the technical field of test sample preparation, and in particular to a method for preparing cross-sectional EBSD samples of flexible copper-clad laminates, comprising the following steps: cutting at least two samples to be tested on the flexible copper-clad laminate; stacking and gluing the cut at least two samples to be tested; conductively mounting the stacked cross-section of the stacked and glued samples; mechanically grinding and polishing the mounted samples; after mechanical polishing, rinsing the surface of the sample to be tested until there is no polishing residue on the surface, and finally performing argon ion polishing to obtain the cross-sectional EBSD sample of the flexible copper-clad laminate. The present invention completely preserves the cross-section of the copper layer in the flexible copper-clad laminate, breaking through the high cost and small field of view limitations of preparing cross-sectional EBSD samples of the flexible copper-clad laminate using ion thinning technology. Good conductivity of the sample is ensured, image drift during the detection process is avoided, and the test efficiency is high, so that the EBSD calibration rate can be stably maintained at above 90%.

Description

Technical Field

[0001] The present invention relates to the technical field of test sample preparation, and in particular to an EBSD sample preparation method for a cross section of a flexible copper-clad laminate. Background Art

[0002] As a unique base material for electronic interconnects, flexible copper-clad laminates (FCCLs) enable flexible printed circuits (PCBs) with high wiring density, thinness, bendability, and three-dimensional assembly capabilities. This has driven the development of thinner, lighter, shorter, and smaller electronic products. The properties of the copper layer in FCLs are a key factor in determining their performance and lifespan. Therefore, studying the microstructure of the copper layer in FCLs under different processes and parameters is crucial for improving the process and developing FCLs with superior performance. In addition to the microstructure characteristics of the material surface, the microstructure characteristics of the material cross-section are equally important for evaluating the material's performance and structure.

[0003] Electron backscattered diffraction (EBSD) analysis and characterization technology can provide key information such as the thickness, uniformity, internal quality, crystal structure, and morphology of the material cross-section, making it an important means of conducting in-depth analysis of flexible copper-clad laminates. The specimens used for EBSD testing must have a smooth and flawless surface, free of oxide films and residual processing strain layers. Therefore, specimen preparation is the prerequisite and key to EBSD analysis technology. Flexible copper-clad laminates, primarily composed of a flexible polyimide insulating base film and metal copper foil, are thin, light, and flexible, making cross-sectional sample preparation difficult.

[0004] The main method for preparing cross-sectional EBSD samples of flexible copper-clad laminates is currently ion thinning technology. However, ion thinning technology requires the sample to be made into a 60-100μm thin slice, which takes a long time to prepare, and it is impossible to take an EBSD image with a large field of view at one time. It requires multiple thinning samples, and then a splicing method is used to obtain an EBSD image with a large field of view, which is extremely costly. Mechanical grinding and polishing technology is a traditional sample preparation method with low cost, but it may cause deformation of the cross section of the flexible copper-clad laminate due to the influence of material properties (such as Figure 1 Therefore, there is an urgent need to propose an improved mechanical grinding and polishing method to reduce cross-sectional deformation and obtain EBSD images with a wide field of view in one go, thereby reducing sample preparation costs. Summary of the Invention

[0005] To solve the above problems, the present invention proposes an EBSD sample preparation method for a cross-section of a flexible copper-clad laminate. This method can capture EBSD images in a large field of view at one time and has the advantages of simple sample preparation and low cost.

[0006] To achieve the above object, the present invention provides a method for preparing cross-section EBSD samples of a flexible copper-clad laminate, the steps of which include:

[0007] Step (1): cutting at least two samples to be tested on the flexible copper clad laminate;

[0008] Step (2): stacking and gluing at least two pieces of the sample to be tested cut in step (1);

[0009] Step (3): Conductively inlaying the stacked cross-section of the stacked and glued samples;

[0010] Step (4): mechanically grinding and polishing the mounted sample;

[0011] Step (5): After mechanical polishing is completed, the surface of the sample to be tested is rinsed until there is no polishing residue on the surface, and finally argon ion polishing is performed to obtain the EBSD sample of the cross section of the flexible copper clad laminate.

[0012] In step (2) of the present invention, the method of stacking more than two layers of flexible copper-clad laminates increases the area of ​​mechanical grinding and polishing, thereby improving the continuity of the copper layer.

[0013] Preferably, in step (1), the cut sample is ultrasonically cleaned.

[0014] Preferably, in step (2), the flexible copper-clad laminates are stacked in a manner of laminating copper surfaces to each other.

[0015] Preferably, in step (2), the adhesive used is a mixture of epoxy resin AB glue and copper powder. The adhesive is prepared by placing the epoxy resin AB glue in a container, adding 400-1000 mesh copper powder, and stirring and mixing thoroughly for use.

[0016] The method of using epoxy resin to bond the copper surface of the flexible copper clad laminate can resist the damage of external forces to the copper layer during mechanical grinding and polishing, improve the continuity of the copper layer, and reduce the bending deformation of the copper layer; adding appropriate copper powder to the epoxy resin improves the conductivity of the flexible copper clad laminate, reduces image drift, and increases the EBSD calibration rate.

[0017] Preferably, in step (3), the conductive inlay is performed by cold inlay.

[0018] Preferably, the hot-pressed mounting material is graphite-type, and the cold-mounted mounting material is epoxy resin-type.

[0019] Preferably, in step (4), the pressure value of the mechanical grinding and polishing treatment is set to 1-3N, the grinding and polishing head speed is set to 50-80r / min, and the grinding and polishing disc speed is set to 150-240r / min.

[0020] Preferably, in step (4), the mechanical grinding and polishing process comprises the following steps:

[0021] The conductive embedded EBSD sample to be tested was ground on silica sandpaper, and the sandpaper grinding sequence was from 400 mesh, 600 mesh, 800 mesh, 1000 mesh, 1200 mesh, 1500 mesh, 2000 mesh to 2500 mesh; the polishing agents used were 1.5 μm diamond polishing agent and 0.02 μm silica suspension, and the polishing time was 5 min and 20 min, respectively.

[0022] Preferably, in step (5), the argon ion polishing time is 15-30 minutes.

[0023] Preferably, in the step (3), before the conductive inlay, the following step is further included: fixing the opposite sides of the stacked sample with metal blocks, and exposing the stacked cross section to the outside after fixing.

[0024] Preferably, the metal block is a conductive metal.

[0025] The method of using metal blocks to fix the stacked cross-section of the flexible copper clad laminate can fix the flexible copper clad laminate during the process of inlaying and mechanical grinding and polishing, thereby reducing the bending deformation of the flexible copper clad laminate.

[0026] Preferably, the method further includes the following steps: after rinsing the surface of the sample to be detected by EBSD until there is no polishing residue on the surface, the sample to be detected by EBSD is subjected to argon ion polishing and EBSD testing to obtain a cross-sectional grain feature image and an EBSD calibration rate.

[0027] The method of the present invention has the following significant effects:

[0028] The sample preparation method of the present invention utilizes at least two layers of flexible copper-clad laminate (FCCL) stacked and glued together to increase the area for mechanical grinding and polishing, improve the continuity of the copper layer, and fully preserve the cross-section of the copper layer in the FCL. This overcomes the high cost and small field of view limitations of ion thinning technology for preparing EBSD samples of FCL cross-sections. While meeting the requirements of high surface flatness, low stress values, and retaining the original surface stress distribution of the sample to be tested, the sample also ensures good conductivity, avoids image drift during testing, and achieves high testing efficiency, maintaining an EBSD calibration rate consistently above 90%. This significantly reduces the cost of preparing EBSD samples for FCL cross-sections and has high practical and promotional value in practical engineering applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a cross-sectional micrograph of a flexible copper-clad laminate prepared by an unimproved mechanical grinding and polishing method.

[0030] Figure 2 This is a flow chart of the present invention for preparing EBSD samples of cross sections of flexible copper clad laminates.

[0031] Figure 3 This is a sample diagram of the present invention in which a stainless steel clamp is used to clamp the copper metal block after the copper metal block is fixedly stacked and glued to the flexible copper clad laminate.

[0032] Figure 4 This is an EBSD sample image after conductive cold mounting of the present invention.

[0033] Figure 5 This is a cross-sectional microscope image of the stacked and bonded multi-layer flexible copper clad laminate prepared by the present invention.

[0034] Figure 6 This is a SEM image of the cross section of the flexible copper clad laminate prepared in the present invention.

[0035] Figure 7 This is an EBSD calibration rate diagram of the cross section of the flexible copper clad laminate prepared by the present invention.

[0036] Figure 8 This is an EBSD analysis diagram of the cross section of the flexible copper clad laminate prepared by the present invention. DETAILED DESCRIPTION

[0037] For a better understanding of the present invention, the following examples are provided to further illustrate the present invention, but the present invention is not limited to the following examples.

[0038] Example

[0039] A cross-sectional EBSD sample preparation method for flexible copper clad laminates, the flow chart is as follows Figure 2 As shown, the following steps are included:

[0040] First, cut at least two samples of suitable size for EBSD testing from the flexible copper clad laminate.

[0041] Put epoxy resin AB glue in a container, add an appropriate amount of 800 mesh copper powder, stir and mix thoroughly, and then evenly apply it on the copper surface of the obtained flexible copper clad laminate. Then, bond the copper surfaces of two flexible copper clad laminates coated with the mixed glue to each other.

[0042] Then use copper metal blocks to fix the stacked and glued flexible copper clad laminates, and clamp the copper metal blocks with stainless steel clips, such as Figure 3 shown.

[0043] Then, the sample stack sections fixed with the copper metal block were cold mounted using epoxy resin conductive mounting material, such as Figure 4 shown.

[0044] The embedded EBSD sample to be tested is mechanically ground and polished. The main purpose of this step is to perform mechanical grinding and polishing to obtain a smooth surface to be tested. Mechanical grinding and polishing are performed using a Huayin MP-3S-2 automatic grinding and polishing machine, with the pressure value set to 2N, the grinding and polishing head speed set to 50r / min, and the grinding and polishing disc speed set to 150r / min. The specific operating steps are: Grind the conductive embedded EBSD sample to be tested on silica sandpaper, and the sandpaper grinding sequence is from 400 mesh, 600 mesh, 800 mesh, 1000 mesh, 1200 mesh, 1500 mesh, 2000 mesh to 2500 mesh; the polishing agents used are 1.5μm diamond polishing agent and 0.02μm silica suspension, and the polishing time is 5min and 20min respectively.

[0045] After mechanical polishing is completed, rinse the surface of the specimen until no polishing liquid remains on the surface.

[0046] Argon ion polishing is performed on the mechanically polished sample to be analyzed for EBSD. The primary purpose of this step is to remove residual stress introduced during the mechanical polishing process. The argon ion polishing time is 25 minutes. If the polishing time is too short, the residual stress generated by the mechanical polishing process cannot be eliminated. However, if the polishing time is too long, pits will form on the sample surface, affecting subsequent EBSD analysis.

[0047] The cross-section EBSD sample of the flexible copper clad laminate prepared by the present invention completely preserves the cross-section of the copper layer in the flexible copper clad laminate, and the cross-section protection effect is good. Figure 5 and 6 As shown; At the same time, it ensures good conductivity of the sample, avoids image drift during the detection process, and has high calibration accuracy, such as Figure 7 As shown in the figure, the red area is the EBSD calibration area, and the final calibration rate reaches more than 90%; the EBSD detection and analysis effect is good, such as Figure 8 shown.

[0048] The above description is only a preferred embodiment of the present invention, which certainly cannot be used to limit the scope of rights of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and changes can be made without departing from the principles of the present invention. These improvements and changes are also considered to be within the scope of protection of the present invention.

Claims

1. A method for preparing cross-section EBSD samples of flexible copper-clad laminates, characterized in that: The following steps are involved: Step (1): Cut at least two pieces of samples to be tested on the flexible copper clad laminate; Step (2): stacking and gluing at least two pieces of the sample to be tested cut in step (1); Step (3): Conductively inlaying the stacked cross-section of the stacked and glued samples; Step (4): Mechanically grind and polish the mounted sample; Step (5): After mechanical polishing is completed, the surface of the sample to be tested is rinsed until there is no polishing residue on the surface, and finally argon ion polishing is performed to obtain the EBSD sample of the cross section of the flexible copper clad laminate.

2. The EBSD sample preparation method for a cross section of a flexible copper clad laminate according to claim 1, wherein: In the step (2), the samples to be tested are stacked in a manner of copper surface to copper surface bonding.

3. The EBSD sample preparation method for a cross section of a flexible copper clad laminate according to claim 1, wherein: In the step (2), the adhesive used is a mixture of epoxy resin AB glue and copper powder.

4. The EBSD sample preparation method for a cross section of a flexible copper clad laminate according to claim 1, wherein: In the step (3), the inlay is performed by conductive hot pressing or cold inlay.

5. The EBSD sample preparation method for a cross section of a flexible copper clad laminate according to claim 4, wherein: The hot pressing mounting material used is graphite type, and the cold mounting material used is epoxy resin type.

6. The EBSD sample preparation method for a cross section of a flexible copper clad laminate according to claim 1, wherein In the step (4), the pressure value of the mechanical grinding and polishing treatment is set to 1-3N, the speed of the grinding and polishing head is set to 50-80 r / min, and the speed of the grinding and polishing disc is set to 150-240 r / min.

7. The EBSD sample preparation method for a cross section of a flexible copper clad laminate according to claim 1, wherein: In step (4), the mechanical grinding and polishing process includes the following steps: The conductively mounted EBSD sample to be tested was ground on silica sandpaper, and the sandpaper grinding was sequentially from 400 mesh, 600 mesh, 800 mesh, 1000 mesh, 1200 mesh, 1500 mesh, 2000 mesh to 2500 mesh; the polishing agents used were 1.5 μm diamond polishing agent and 0.02 μm silica suspension, and the polishing time was 5 min and 20 min, respectively.

8. The EBSD sample preparation method for a cross section of a flexible copper clad laminate according to claim 1, wherein: In the step (3), before the conductive inlay, the following steps are also included: using metal blocks to fix the opposite sides of the stacked sample, and after fixing, the stacked cross section is exposed to the outside.

9. The EBSD sample preparation method for a cross section of a flexible copper clad laminate according to claim 1, wherein: The metal block is a conductive metal.

Images