Spinel ferrite polishing method

Abstract

The invention discloses a spinel ferrite polishing method, and belongs to the technical field of waveguide device materials, the method comprises the following steps: using a high hardness polyurethane polishing pad (A) to cooperate with white corundum for first round polishing; a low-hardness polishing pad (B) is matched with the polycrystalline diamond liquid for second-round polishing; the polishing method is used for solving the problems that after the spinel ferrite substrate is polished, the surface roughness is large, the surface quality is poor, orange peel exists, and the surface roughness is uneven, the production efficiency and the product consistency of the substrate are greatly improved, and the stability and the reliability of microwave devices are facilitated.

Description

Technical Field

[0001] The present invention relates to the technical field of waveguide device materials, and in particular to a spinel ferrite polishing method. Background Art

[0002] At present, the processing technology of spinel ferrites has always been a difficult point due to their high hardness and low toughness. High hardness means that the surface roughness needs to be reduced as much as possible through fine grinding before polishing, but low toughness causes the edges to be fragile during the fine grinding process, resulting in fine scratches. In the polishing stage, due to the high hardness of the substrate, the polishing effect of using white corundum with polishing pads made of non-woven fabrics, artificial leather and other materials is not good, showing a slow removal rate, large surface roughness and poor consistency after polishing, and the roughness distribution of the same batch is between 40nm and 55nm. This results in the worst processing pass rate of spinel ferrite being only 50%, and the device performance is unstable and the insertion loss is large due to the large difference in surface roughness of the same batch of materials. Chinese patent application 202010630260.2 discloses a large-size ferrite substrate and a polishing method thereof. The method is for garnet ferrites. Garnet ferrites have much lower hardness than spinel and are less difficult to polish. The same process applied to spinel will result in a low pass rate and a large roughness distribution in the same batch. Summary of the invention

[0003] The object of the present invention is to provide a spinel ferrite polishing method to solve the above problems.

[0004] In order to achieve the above object, the technical solution adopted by the present invention is as follows: a spinel ferrite polishing method, characterized in that it comprises the following steps: (A) Prepare 1.5μm~3μm white corundum polishing liquid; It should be noted that due to the D50 in the abrasive particle size distribution, the "1.5μm~3μm" mentioned above refers to the particle size model of the abrasive. The reason for choosing such a particle size range is that the larger the particle size, the faster the processing rate, and the greater the surface roughness of the substrate after processing. The processing rate and particle size do not change linearly. If the particle size is lower than 1.5μm, it will take a lot of time to polish it to a roughness below 40nm. If the particle size is higher than 3μm, the roughness of the substrate after processing will be greater than 40nm, resulting in a longer time for subsequent diamond liquid processing; (B) polishing the spinel ferrite substrate in the first round with the white corundum polishing liquid obtained in step (A) and a polyurethane polishing pad with a Shore hardness of 70 to 90 to obtain a semi-finished product with a flatness of less than 2 μm and a roughness of 35 to 40 nm; It should be noted that the higher the hardness of the polishing pad, the smaller the deformation of the polishing pad during the processing, and the better the flatness of the polishing surface. One-time polishing focuses on rapid removal and maintaining flatness, so a high-hardness polishing pad with a Shore hardness of 70 to 90 is required; Regarding the control of the flatness and roughness of the first polishing: if the removal amount of the first polishing is guaranteed to be more than 0.02mm, the roughness can be reduced to about 40nm. The use of a hard polishing pad can reduce the flatness difference caused by the collapse of the edge. The second polishing uses diamond liquid, which has a low concentration and a slow removal rate. The second polishing usually only removes less than 5μm thickness. If the flatness of the first polishing is greater than 2μm, it will cause incomplete removal of parts in the second polishing. If the roughness is greater than 40nm, it will take a lot of time for the second polishing to smooth out the processing marks of the first polishing. If it is less than 35nm, it will take a long time for the first polishing abrasive to achieve it. Even the roughness of 3μm abrasive will not be less than 40nm after processing. (C) preparing a 1.5 μm to 2.5 μm diamond liquid; the diamond liquid may be a polycrystalline or single crystal diamond liquid; (D) The semi-finished product obtained in step (B) is polished for the second time using the diamond liquid obtained in step (C) and a polyurethane polishing pad with a Shore hardness of 60 to 70.

[0005] The main innovation of the present invention is that the polishing of pure aluminum oxide abrasives takes a long time for low-grain processing and has a large roughness distribution after processing due to the low hardness of aluminum oxide. The roughness after high-grain processing cannot reach below 30nm. In addition, aluminum oxide cannot process spinel to 10nm, while diamond can process spinel to 10nm, but its abrasive particle concentration is low, the removal rate is slow, the price is high, it cannot be recycled, and the cost of removing the substrate thickness is high. The present invention combines the advantages of both, uses aluminum oxide for one polishing, quickly and at low cost to obtain a substrate that tends to be a mirror surface, and then uses diamond processing to achieve an ultra-low roughness mirror surface. Moreover, the present invention is also unique in that the diamond liquid used in the ceramic and sapphire processing industries is applied to ferrite polishing.

[0006] As a preferred technical solution, in step (A), the white corundum polishing liquid uses white corundum, water, and polyvinyl alcohol as raw materials, and the mass ratio of the white corundum, water, and polyvinyl alcohol is 15-25:100:1-2. The white corundum is preferably made of aluminum oxide with a purity of 99wt%, which is obtained by sintering and crushing.

[0007] The proportion of white corundum in the above-mentioned white corundum polishing liquid mainly affects the filtering effect. When the proportion of white corundum to the abrasive is less than 15%, the abrasive removal rate will be very slow; if it is higher than 25%, the abrasive is easy to agglomerate and will clog the filter screen during the abrasive circulation process, resulting in poor actual use effect, so 15-25% is preferred.

[0008] As a preferred technical solution, in step (A), the particle size of the white corundum polishing liquid is 1.5 μm. The surface roughness after processing is different for different particle sizes, 1.5 μm is 30 nm to 40 nm, 2 μm is 35 to 40 nm, and 3 μm is 40 to 45 nm. The use of 1.5 μm white corundum polishing liquid can reduce the amount of removal required for secondary polishing, because the polishing liquid for secondary polishing does not use circulating feeding and is expensive, so two-stage polishing can reduce the time of secondary polishing, thereby saving costs.

[0009] As a preferred technical solution, in step (C), the diamond liquid uses diamond powder, water, calcium carbonate and ethylene glycol as raw materials, and the mass ratio of the diamond powder, water, calcium carbonate and ethylene glycol is 0.5-1:100:1:30.

[0010] The above-mentioned diamond liquid concentration formula is because the price of diamond abrasive is very high. From a cost perspective, it is not advisable to use a high concentration; however, if the concentration is too low, the polishing liquid has almost no removal ability. Considering the cost and effect comprehensively, the preferred abrasive ratio is 0.5% to 1%.

[0011] As a preferred technical solution, in step (C), the particle size of the diamond liquid is 1.5 μm.

[0012] As a preferred technical solution, in step (B) or step (D), the polyurethane polishing pad is grooved with a grid size of 20 mm*20 mm. The groove can be used as a flow channel for the polishing liquid, thereby controlling the distribution of the polishing liquid and making it more evenly distributed.

[0013] Compared with the prior art, the advantages of the present invention are: by adopting the polishing method of the present invention, a spinel ferrite substrate with a surface roughness of 10nm and a whole-surface roughness deviation of 2nm can be obtained; while achieving high surface quality, the polishing time can be greatly shortened. Compared with the traditional one-time polishing, the processing time is shortened from 5 to 6 hours to less than 4.5 hours, thereby improving the polishing efficiency; the polishing method of the present invention solves the problems of large surface roughness of the spinel ferrite substrate after polishing, poor surface quality with orange peel, and uneven surface roughness after polishing, thereby greatly improving the production efficiency and product consistency of the substrate, and being beneficial to the stability and reliability of microwave devices. DETAILED DESCRIPTION

[0014] The present invention will be further described below in conjunction with embodiments.

[0015] Embodiment 1: A spinel ferrite substrate polishing method comprises the following steps: (A) Prepare white corundum polishing liquid by mixing 1.5 μm white corundum, water and polyvinyl alcohol in a mass ratio of 20:100:1; (B) The substrate was finely ground to a thickness of 0.42 mm, a polyurethane polishing pad with a Shore hardness of 90 was attached to the polishing machine and leveled, a fixture was placed, a workpiece was placed, and the polishing liquid obtained in step (A) was added in a circulating feeding manner to start polishing. After 3 hours, the workpiece was taken out to obtain a product with a thickness of 0.4 mm, a flatness of less than 2 μm, and a roughness of about 40 nm; (C) preparing a polishing liquid by mixing 1.5 μm polycrystalline diamond powder, water, calcium carbonate and ethylene glycol in a mass ratio of 1:100:1:30, and adding boric acid and sodium soap to adjust the pH to neutral; wherein the sodium soap, also known as hard soap, is a sodium salt of a higher fatty acid, and its function in the present invention is to fine-tune the pH value of the polishing liquid; (D) A polyurethane polishing pad with a Shore hardness of 70 was placed on the polishing machine and leveled. The fixture was placed, and the spinel ferrite substrate obtained in step (B) was placed. The polishing liquid obtained in step (C) was added by titration to start polishing. After 1.5 hours, the workpiece was taken out to obtain a spinel ferrite substrate with a surface roughness of 10 nm and a whole surface roughness deviation of 2 nm (see Table 1).

[0016] Table 1 Surface roughness test data of Example 1 Surface roughness range (nm) 10-20 20 and above Proportion 100% 0% The pass rate is reflected in the roughness distribution. Customers require the roughness to be less than 40nm. The old process will result in excessive roughness, resulting in failure.

[0017] Comparative Example 1: A spinel ferrite substrate polishing method comprises the following steps: (A) Prepare white corundum polishing liquid by mixing 0.8 μm white corundum, water and polyvinyl alcohol in a mass ratio of 20:100:1; (B) The substrate was finely ground to a thickness of 0.42 mm, a Shore hardness 70 compressed fiber polishing pad was attached to the polishing machine and leveled, the fixture was placed, the workpiece was placed, and the polishing liquid obtained in step (A) was added in a circulating feeding manner to start polishing. After 5 hours, the workpiece was taken out and tested (Table 2). Compared with Example 1, this comparative example uses finer white corundum for polishing, and on the other hand, the hardness of the polishing pad used is lower. Tests show that after the same round of processing, only some substrates have a roughness less than 40nm, and the roughness of the remaining substrates is up to 62nm. The roughness distribution is very large, and even if diamond liquid polishing is used later, the processing time needs to be increased.

[0018] Table 2 Surface roughness test data of comparative example 1 Surface roughness range (nm) 35-40 40-65 Proportion 40% 60% Comparative Example 2: A spinel ferrite substrate polishing method comprises the following steps: (A) A polishing liquid is prepared by mixing 1.5 μm polycrystalline diamond powder, water, calcium carbonate, and ethylene glycol in a mass ratio of 1:100:1:30, and boric acid and sodium soap are added to adjust the pH to neutral; (B) Put a polyurethane polishing pad with a Shore hardness of 70 on the polishing machine and flatten it. Put the fixture in place, grind the substrate to a thickness of 0.42 mm and place it on the equipment. Add the polishing liquid obtained in step (A) by titration and start polishing. Take it out every 1 hour to test the roughness (Table 3). Compared with Example 1, since the substrate after fine grinding is not polished once, the amount of removal required for diamond liquid polishing is very large, the processing time is greatly increased, resulting in a large increase in diamond liquid consumption and very high costs.

[0019] Table 3 Variation of roughness of substrate processed by diamond liquid with processing time Processing time Roughness (nm) 1h 300 2h 250 3h 220 4h 170 5h 130 6h 95 7h 35 8h 13

[0020] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A spinel ferrite polishing method, characterized in that: The following steps are involved: (A) Prepare 1.5μm~3μm white corundum polishing liquid; (B) polishing the spinel ferrite substrate in the first round using the white corundum polishing liquid obtained in step (A) and a polyurethane polishing pad with a Shore hardness of 70 to 90 to obtain a semi-finished product with a flatness of less than 2 μm and a roughness of about 40 to 45 nm; (C) Prepare 1.5μm to 2.5μm diamond liquid; (D) The semi-finished product obtained in step (B) is polished for a second time using the diamond liquid obtained in step (C) and a polyurethane polishing pad having a Shore hardness of 60 to 70 to obtain the target product.

2. The spinel ferrite polishing method according to claim 1, characterized in that: In step (A), the white corundum polishing liquid uses white corundum, water and polyvinyl alcohol as raw materials, and the mass ratio of the white corundum, water and polyvinyl alcohol is 15-25:100:1-2.

3. The spinel ferrite polishing method according to claim 1, characterized in that: In step (A), the particle size of the white corundum polishing liquid is 1.5 μm.

4. The spinel ferrite polishing method according to claim 1, characterized in that: In step (C), the diamond liquid uses diamond powder, water, calcium carbonate and ethylene glycol as raw materials, and the mass ratio of the diamond powder, water, calcium carbonate and ethylene glycol is 0.5-1:100:1:

30.

5. The spinel ferrite polishing method according to claim 1, characterized in that: In step (C), the particle size of the diamond liquid is 1.5 μm.

6. The spinel ferrite polishing method according to claim 1, characterized in that: In step (B) or step (D), the polyurethane polishing pad is grooved, and the grid size is 20 mm*20 mm.