A self-dressing freeze-dried gel grinding wheel and its preparation method and application

Abstract

The present invention discloses a self-dressing freeze-dried gel grinding wheel, its preparation method, and application. Specifically, a gel is prepared using sodium alginate, carboxymethyl chitosan, aramid powder, glass fiber powder, diamond abrasive, and water as raw materials. The gel is then vacuum-dried and freeze-dried to obtain a freeze-dried gel block for the self-dressing gel grinding wheel. This is then combined with a substrate to obtain a self-dressing freeze-dried gel grinding wheel. This invention is the first to use a freeze-dried gel block as a grinding tool, achieving the advantages of low roughness and high yield compared to existing methods for grinding diamond wafers.

Description

Technical Field

[0001] The invention belongs to grinding technology, and in particular relates to a self-dressing freeze-dried gel grinding wheel and a preparation method and application thereof. Background Art

[0002] Diamond wafers, as a representative material for third-generation semiconductors, possess numerous excellent characteristics, including ultra-high thermal conductivity and an ultra-wide bandgap, and are considered the "star material" of third-generation semiconductors. However, due to the inherently high hardness and brittleness of diamond wafers, the difficulty of processing them has limited their rapid development, and wafer processing technology has become a bottleneck restricting their development. Grinding is a crucial step in the diamond wafer processing process and a necessary step in existing wafer processing. However, due to the difficult processing of diamond wafer materials, existing traditional grinding wheels for wafer processing are extremely inefficient when processing diamond wafers. Furthermore, the processing process is prone to diamond wafer fragmentation, resulting in an extremely high scrap rate, which has become a bottleneck restricting their rapid industrialization. Summary of the Invention

[0003] For diamond processing, the present invention designs a new type of self-dressing freeze-dried gel grinding wheel. Different from traditional ceramic bond or resin bond grinding wheels, this grinding wheel tool uses biosol-gel technology to disperse the abrasive in the sol, and through gelation and freeze-drying methods, it is prepared into a grinding wheel agglomerate with certain flexibility and multiple pores. The agglomerate is then fixed on a stainless steel substrate according to the desired shape to finally prepare a grinding and polishing wheel.

[0004] The present invention adopts the following technical solutions:

[0005] A freeze-dried gel block for self-dressing gel grinding wheels is prepared by the following steps: adding mixture 2 to mixture 1, then adding mixture 3, and stirring to obtain a mixed solution; pouring the mixed solution into a mold and immersing the mold in a calcium salt solution to obtain a gel; and then sequentially subjecting the gel to vacuum drying and freeze drying to obtain a freeze-dried gel block for self-dressing gel grinding wheels.

[0006] A self-dressing freeze-dried gel grinding wheel, the preparation method of which comprises the following steps: adding mixture 2 to mixture 1, then adding mixture 3, and stirring to obtain a mixed solution; pouring the mixed solution into a mold and immersing the mold in a calcium salt solution to obtain a gel; then subjecting the gel to vacuum drying and freeze drying in sequence to obtain a freeze-dried body; and combining the freeze-dried body with a matrix to obtain a self-dressing freeze-dried gel grinding wheel.

[0007] In the present invention, sodium alginate, carboxymethyl chitosan, and water are mixed to obtain mixture 1; aramid powder is mixed with water to obtain mixture 2; and glass fiber powder and diamond abrasive are mixed with water to obtain mixture 3. Preferably, the mass ratio of sodium alginate, carboxymethyl chitosan, aramid powder, glass fiber powder, diamond abrasive, and water in the mixture is (15-25):(3-8):(80-110):(180-230):(50-100):1200, preferably (15-25):(3-8):(90-105):(190-210):(70-90):1200. The diamond abrasive is a W10-W63 diamond abrasive, and the remaining raw materials are conventional raw materials in the field of gel abrasive tools.

[0008] In the present invention, the calcium salt solution is a calcium chloride aqueous solution; the immersion time in the calcium salt solution is 100 to 150 minutes; and the calcium salt concentration in the calcium salt solution is 0.1 to 1 wt%.

[0009] In the present invention, the stirring speed is 800-1500 rpm, and the time is 1-15 hours; preferably, the stirring speed is 900-1200 rpm, and the time is 2-10 hours.

[0010] In the present invention, during vacuum drying, the vacuum degree is 500-1000 Pa, the time is 1-2 hours, and the temperature is 40-60°C. During freeze drying, the vacuum degree is 1-50 Pa, the temperature is reduced to -80--60°C over 5-7 hours, and then maintained for 20-30 hours. Preferably, during freeze drying, the vacuum degree is 1-5 Pa, the temperature is reduced to -75--65°C over 5.5-6.5 hours, and then maintained for 21-27 hours. Before freeze drying, the vacuum-dried gel is frozen at -30--10°C for 3-5 hours and then freeze dried.

[0011] The present invention discloses the use of the freeze-dried gel block for the self-dressing gel grinding wheel in preparing gel grinding tools and the use of the self-dressing freeze-dried gel grinding wheel in grinding and polishing diamond workpieces. The diamond workpiece is preferably a diamond wafer.

[0012] The prior art adopts the method of heat curing to obtain a gel with mechanical strength, which is used for processing wafers and has good flexibility. It also avoids the use of external abrasives, but has poor dimensional stability and the grinding effect needs to be improved. Due to the use of sol-gel means and drying technology, the grinding wheel prepared by the present invention has certain flexibility. At the same time, during the freeze-drying process, the water molecules inside directly sublimate to produce holes. At the same time, due to the addition of supporting materials such as glass fiber and aramid, the agglomerate has a certain strength and will not deform during the processing. Through self-dressing, the abrasive grains inside can be continuously exposed, achieving high grinding efficiency. At the same time, since the agglomerate has certain flexibility, it will not produce hard collisions with the diamond wafer during the processing, which greatly reduces the breakage rate of the diamond wafer and improves the production yield. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 This is a physical picture of the self-dressing freeze-dried gel grinding wheel of the present invention;

[0014] Figure 2 This is a diagram showing the effect of the self-dressing freeze-dried gel grinding wheel of the present invention after processing a diamond wafer;

[0015] Figure 3 This is a roughness effect diagram after the self-dressing freeze-dried gel grinding wheel of the present invention is used to process a diamond wafer;

[0016] Figure 4 This is a physical picture of the air-dried gel. DETAILED DESCRIPTION

[0017] The raw materials used in this invention are all existing products in the field and meet the general requirements of existing gel materials. The fiber powder has a particle size of 100 to 800 mesh. The invention's innovation lies in the selection of different existing raw materials, the design of a new formula, and the combination of freeze-drying technology to produce a hard gel block that can be used in diamond wafer grinding and polishing, achieving excellent processing results. The surface roughness is evaluated using a three-dimensional roughness indicator, and the instrument used is an AFM Nanoview atomic force microscope from Suzhou Feishiman Co., Ltd. The specific testing methods are conventional.

[0018] Example 1

[0019] 20 g of sodium alginate, 5 g of carboxymethyl chitosan, and 200 g of water were added to a beaker and stirred at 800 rpm for 2 h at room temperature to prepare a mixture 1;

[0020] In another beaker, 500 g of water and 100 g of aramid powder were added and stirred at 60° C. and 550 rpm for 60 min to prepare mixture 2.

[0021] In another beaker, add 500 g of water, 200 g of glass fiber powder, and 80 g of diamond abrasive (W30), and stir at 550 rpm for 30 min at room temperature to prepare mixture 3;

[0022] Add 5g of calcium chloride to 1kg of water to obtain a calcium salt solution;

[0023] At room temperature, mixture 2 was added to mixture 1, and stirred at 1000 rpm for 2 h. Then, mixture 3 was added and stirred at 1000 rpm for 8 h. After stirring, the mixture was poured into a mold, and then the mold was immersed in a calcium salt solution for 120 min and taken out to obtain a gel.

[0024] The gel was placed in a vacuum drying oven and vacuum-dried at 50°C for 1.5 hours, with a vacuum of 800 Pa. After removal, it was frozen at -18°C for 4 hours, then freeze-dried for 6 hours, cooled to -70°C, and then freeze-dried at -70°C for 24 hours. This yielded a freeze-dried gel block, which was used for self-dressing gel grinding wheels, maintaining a vacuum of 2 Pa. Unlike conventional flexible polishing pads, the freeze-dried gel block of the present invention does not contain water, whereas conventional flexible polishing pads must contain water for use. However, hydrogel flexible polishing pads are not suitable for high-speed diamond wafer processing.

[0025] The freeze-dried gel blocks prepared by the present invention will sink to the bottom when placed in water, which is different from existing aerogels. They are also elastic and will return to their original shape after being pressed down hard and released.

[0026] Example 2

[0027] Use conventional grinding wheel structural glue (such as epoxy AB glue) to glue the freeze-dried gel block to the existing stainless steel substrate, see Figure 1 The freeze-dried gel block is fixed in the tooth groove of the stainless steel base to form a self-dressing freeze-dried gel grinding wheel.

[0028] Example 3

[0029] The self-dressing freeze-dried gel grinding wheel of Example 2 was used to grind and polish a 2-inch diamond wafer (Sa is 100 nm). The base was a Tokyo precision grinder HEG300, the speed was 1500 / 300 rpm, and the processing time was 30 min. The surface roughness Sa of the wafer after processing was 0.396 nm and Sq was 1.029 nm. The results are shown in FIG. Figure 2 and Figure 3 The thickness of the wafer before and after grinding and polishing was measured using a thickness gauge to calculate the material removal rate, which was 6.13 nm / min.

[0030] In comparison, the surface roughness of the 2-inch diamond wafer processed by the grinding and polishing method used in existing industrial production is greater than 10nm, and the processing time of existing production exceeds 5 hours; the self-dressing freeze-dried gel grinding wheel of the present invention is used to process the same workpiece, and the processing efficiency and processing quality are significantly better than the existing industrial production level.

[0031] Comparative Example 1

[0032] At room temperature, the gel of Example 1 was blown by an industrial fan. After 10 hours, no gel blocks were obtained. During the air-drying process, warping occurred due to uneven dehydration. Figure 4 .

[0033] The gel of Example 1 was placed in an oven and dried at 40° C. for 8 hours, but no gel blocks were obtained. During the drying process, dehydration occurred, resulting in stress concentration. Due to the shrinkage of the gel, cracks occurred, and the gel grinding wheel agglomerates could not be prepared.

[0034] The gel of Example 1 was placed in a vacuum dryer. After drying at 50° C. for 7 hours, the vacuum degree was 800 Pa, and no gel blocks were obtained. Shrinkage and warping occurred.

[0035] Comparative Example 2

[0036] The vacuum drying in Example 1 was omitted, and the rest remained unchanged to obtain a freeze-dried gel block. According to the methods of Example 2 and Example 3, a gel grinding wheel was prepared and used to grind and polish a 2-inch diamond wafer. The surface roughness Sa of the wafer after processing was 4.89 nm.

[0037] The freezing and freeze-drying of Example 1 were omitted (i.e., only vacuum drying was performed), and the rest remained unchanged to obtain a flexible gel block. According to the methods of Example 2 and Example 3, a gel grinding wheel was prepared and used to grind and polish a 2-inch diamond wafer. However, the processing could not be performed, and cracks appeared in the flexible gel block within a few tens of seconds after the machine was turned on.

[0038] Comparative Example 3

[0039] The glass fiber powder in Example 1 was replaced with carbon fiber powder, and the rest remained unchanged to obtain a freeze-dried gel block. According to the methods of Example 2 and Example 3, a gel grinding wheel was prepared and used to grind and polish a 2-inch diamond wafer. The surface roughness Sa of the wafer after processing was 3.32 nm.

[0040] The aramid powder in Example 1 was omitted, and the rest remained unchanged to obtain a freeze-dried gel block. According to the methods of Example 2 and Example 3, a gel grinding wheel was prepared and used to grind and polish a 2-inch diamond wafer. The surface roughness Sa of the wafer after processing was 6.28 nm.

[0041] Example 4

[0042] 17 g of sodium alginate, 7 g of carboxymethyl chitosan, and 200 g of water were added to a beaker and stirred at 600 rpm for 2 h at room temperature to prepare a mixture 1;

[0043] In another beaker, 500 g of water and 95 g of aramid powder were added and stirred at 60° C. and 650 rpm for 70 min to prepare mixture 2.

[0044] In another beaker, add 500 g of water, 200 g of glass fiber powder, and 82 g of diamond abrasive (W40), and stir at 500 rpm for 30 min at room temperature to prepare mixture 3;

[0045] Add 5g of calcium chloride to 1kg of water to obtain a calcium salt solution;

[0046] At room temperature, mixture 2 was added to mixture 1, and stirred at 1200 rpm for 2 h. Then, mixture 3 was added and stirred at 1000 rpm for 7 h. After stirring, the mixture was poured into a mold, and then the mold was immersed in a calcium salt solution for 110 min and taken out to obtain a gel.

[0047] The gel was placed in a vacuum drying oven and vacuum dried at 50°C for 80 minutes with a vacuum degree of 600Pa. After being taken out, it was frozen at -18°C for 4 hours, then freeze-dried, and then dropped to -70°C for 6 hours. It was then freeze-dried at -70°C for 25 hours to obtain freeze-dried gel blocks, which were used for self-dressing gel grinding wheels. The vacuum degree was maintained at 2Pa.

[0048] Example 5

[0049] 22 g of sodium alginate, 6 g of carboxymethyl chitosan, and 200 g of water were added to a beaker and stirred at 700 rpm for 1.5 h at room temperature to prepare a mixture 1;

[0050] In another beaker, 500 g of water and 105 g of aramid powder were added and stirred at 60° C. and 600 rpm for 60 min to prepare mixture 2.

[0051] In another beaker, add 500 g of water, 205 g of glass fiber powder, and 78 g of diamond abrasive (W20), and stir at 600 rpm for 45 min at room temperature to prepare mixture 3.

[0052] Add 5g of calcium chloride to 1kg of water to obtain a calcium salt solution;

[0053] At room temperature, mixture 2 was added to mixture 1, and stirred at 1100 rpm for 2 h. Then, mixture 3 was added and stirred at 1100 rpm for 9 h. After stirring, the mixture was poured into a mold, and then the mold was immersed in a calcium salt solution for 90 min and taken out to obtain a gel.

[0054] The gel was placed in a vacuum drying oven and vacuum dried at 50°C for 100 minutes with a vacuum degree of 700Pa; after being taken out, it was frozen at -18°C for 5 hours, then freeze-dried, and then dropped to -70°C for 6 hours, and then freeze-dried at -70°C for 23 hours to obtain freeze-dried gel blocks, which were used for self-dressing gel grinding wheels, and the vacuum degree was maintained at 2Pa.

[0055] Example 6

[0056] According to Example 2, Example 4 and Example 5 were made into grinding wheels respectively, and the same grinding and polishing test as Example 3 was carried out, and the processing roughnesses of 0.755 nm and 0.925 nm were obtained respectively.

Claims

1. A freeze-dried gel block for self-dressing gel grinding wheels, characterized in that: The preparation method comprises the following steps: adding mixture 2 to mixture 1, and then adding mixture 3, and stirring to obtain a mixed solution; pouring the mixed solution into a mold and immersing the mold in a calcium salt solution to obtain a gel; then subjecting the gel to vacuum drying and freeze drying in sequence to obtain a freeze-dried gel block for a self-dressing gel grinding wheel; mixing sodium alginate, carboxymethyl chitosan, and water to obtain mixture 1; mixing aramid powder with water to obtain mixture 2; and mixing glass fiber powder and diamond abrasive with water to obtain mixture 3; in the mixed solution, the mass ratio of sodium alginate, carboxymethyl chitosan, aramid powder, glass fiber powder, diamond abrasive, and water is (15-25): (3-8): (80-110): (180-230): (50-100): 1200; during vacuum drying, the vacuum degree is 500-1000 Pa, the time is 1-2 hours, and the temperature is 40-60°C; during freeze drying, the vacuum degree is 1-50 Pa, drop to -80~-60℃ in 5~7 hours, and then maintain it for 20~30 hours.

2. The freeze-dried gel block for self-dressing gel grinding wheels according to claim 1, characterized in that: In the mixed solution, the mass ratio of sodium alginate, carboxymethyl chitosan, aramid powder, glass fiber powder, diamond abrasive and water is (15-25): (3-8): (90-105): (190-210): (70-90): 1200.

3. The method for preparing the freeze-dried gel block for self-dressing gel grinding wheel according to claim 1, characterized in that: Mixture 2 is added to mixture 1, and then mixture 3 is added and stirred to obtain a mixed liquid; the mixed liquid is poured into a mold and then immersed in a calcium salt solution to obtain a gel; the gel is then vacuum dried and freeze-dried in sequence to obtain a freeze-dried gel block for a self-dressing gel grinding wheel; sodium alginate, carboxymethyl chitosan, and water are mixed to obtain mixture 1; aramid powder is mixed with water to obtain mixture 2; and glass fiber powder, diamond abrasive, and water are mixed to obtain mixture 3.

4. The method for preparing the freeze-dried gel block for self-dressing gel grinding wheel according to claim 3, characterized in that: The stirring speed is 800 to 1500 rpm, and the stirring time is 1 to 15 hours.

5. A self-dressing freeze-dried gel grinding wheel, characterized in that: The preparation method comprises the following steps: combining the freeze-dried gel block for the self-dressing gel grinding wheel according to claim 1 with a matrix to obtain the self-dressing freeze-dried gel grinding wheel.

6. The method for preparing the self-dressing freeze-dried gel grinding wheel according to claim 5, characterized in that: The freeze-dried gel block for the self-dressing gel grinding wheel according to claim 1 is combined with a matrix to obtain a self-dressing freeze-dried gel grinding wheel.

7. Use of the freeze-dried gel block for self-dressing gel grinding wheel according to claim 1 in preparing gel grinding tools.

8. Use of the self-dressing freeze-dried gel grinding wheel according to claim 5 in grinding diamond workpieces.

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