Concentration discharge assisted fine grinding method for conductive silicon carbide wafer

Abstract

The invention discloses a conductive silicon carbide wafer aggregate discharge auxiliary fine grinding method, which belongs to the field of precision machining and specifically comprises two procedures of laser micro-nano machining and aggregate discharge auxiliary fine grinding. The laser micro-nano processing comprises two steps of wafer processing and electrode processing, namely, a femtosecond or picosecond pulse laser is adopted to process sharp microstructures with small curvature radiuses on the surface of the silicon carbide wafer and the bottom surface of the graphite rod electrode; the aggregated discharge assisted micro-grinding comprises four steps of circuit connection, parameter adjustment, aggregated discharge and micro-grinding, namely, charges are aggregated on a surface microstructure of a workpiece through electrostatic induction by adopting a direct-current pulse power supply, an electrochemical reaction tank and a micro-grinding platform, and localized discharge is guided to occur between the surface microstructure of the workpiece and a bottom surface microstructure of a graphite rod electrode; the problem that electrochemical discharge is unstable is solved, a workpiece machining face is induced to form a softening layer, a diamond micro-grinding tool is assisted to conduct fine grinding, and heat damage and discharge damage of a non-machining face are reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of precision machining, and in particular relates to a method for conducting silicon carbide wafer concentrated discharge assisted micro-grinding. Background Art

[0002] With the rapid development of high-tech fields such as aerospace, electronic information, energy and metallurgy, my country's demand for silicon-based micro-structure parts is becoming increasingly urgent. Due to the brittleness and hardness of silicon carbide itself, the existing processing methods have achieved high-finish processing of silicon carbide, but it inevitably produces negative effects such as edge collapse, pits, and cracks, which seriously affect the service performance of parts made of this material. Electrochemical discharge machining is a commonly used processing method for hard, brittle and difficult to conduct electricity materials. Combined processing with micro-grinding can improve the workpiece removal efficiency, but unnecessary thermal damage and discharge damage are likely to occur to the non-machined surface during the processing.

[0003] In order to solve the above problems, it is necessary to design a conductive silicon carbide wafer concentrated discharge assisted micro-grinding method to reduce or even eliminate the occurrence of the above problems.

[0004] Chinese invention patent CN201711339341.1 discloses a chemical modification liquid and mechanical micro-grinding processing method. The invention prepares a specific chemical modification liquid, utilizes the modification reaction between the modification liquid and the workpiece processing layer, produces a silicate layer with lower hardness, weakens the mechanical stress removal between the micro-grinding tool and the workpiece, thereby improving the surface processing quality of micro-grinding, but does not involve microstructural treatment of the workpiece surface and the bottom of the graphite electrode. The present invention processes a sharp microstructure with a small radius of curvature on the workpiece surface by femtosecond or picosecond pulse laser processing, reduces mechanical stress removal, and induces electrochemical discharge localized aggregation modification, effectively reducing damage to the non-processed surface / sub-surface of the workpiece, and achieving low-defect grinding of the processed surface.

[0005] Chinese invention patent CN201711051786.8 discloses a chemical mechanical-mechanical chemical synergistic micro-grinding method and a composite micro-abrasive tool. The invention uses a two-level composite abrasive micro-abrasive tool to complete the rough and fine processing of the workpiece at one time; by combining the advantages of micro-grinding, mechanical chemical processing and chemical mechanical processing, high-quality and high-precision processing of parts is achieved, but it does not involve the use of micro-structured structure to gather discharge to soften the workpiece, so as to weaken the mechanical stress removal and achieve the effect of low-defect high-precision processing. In comparison, the micro-structured aggregate discharge assisted micro-grinding described in the present invention is used for processing, which effectively reduces the surface defects such as burrs, cracks and edge collapse caused by simple mechanical processing, and improves the thermal damage, electrochemical damage and discharge damage of the non-processed surface.

[0006] Chinese invention patent CN114406375A discloses a method for electrochemical discharge-enabled micro-grinding of tiny parts of silicon-based materials. Electrochemical discharge is achieved in the processing area of ​​the silicon-based material. After the surface material of the workpiece is converted into a modified layer with significantly reduced mechanical properties, the modified layer is quickly and efficiently removed by a micro-grinding tool. However, the electrochemical discharge that can be achieved by the invention will generate high temperatures, and the micro-grinding tool is prone to high-temperature brittle fracture during long-term operation; at the same time, the electrochemical discharge itself has the characteristic of regional instability, and it is easy to gather in the sharp area of ​​the edge of the micro-grinding tool, thereby aggravating the negative effects such as edge damage and microcracks on the processed surface. In comparison, the microstructure aggregation discharge assisted micro-grinding described in the present invention has a sharp microstructure array with a small curvature radius on the surface of the workpiece and the bottom of the graphite rod electrode. On the one hand, the electrochemical discharge body can be transferred from the diamond micro-abrasive tool to the graphite rod electrode, eliminating the burden of being its electrochemical discharge body and improving the service life of the abrasive tool; on the other hand, through the concentrated discharge effect between the surface of the silicon carbide wafer and the sharp microstructure of the bottom surface of the graphite rod electrode, localized discharge induction modification can be achieved on the machined surface, thereby avoiding edge damage on the machined surface and reducing thermal damage and discharge damage on the non-machined surface. Summary of the invention

[0007] The purpose of the present invention is to provide a method for conductive silicon carbide wafer micro-grinding assisted by concentrated discharge in order to overcome the shortcomings of the prior art. The electrochemical discharge and micro-grinding are combined to complement each other, and the discharge is induced by localized concentration of sharp microstructures before micro-grinding is performed, aiming to achieve low-defect, high-efficiency, high-quality processing of conductive silicon carbide wafers, and avoid unnecessary thermal, chemical and discharge damage on non-processed surfaces.

[0008] The above technical objectives of the present invention are achieved through the following technical solutions: a method for concentrated discharge assisted micro-grinding of a conductive silicon carbide wafer, characterized in that it includes two processes: laser micro-nano processing and concentrated discharge assisted micro-grinding;

[0009] S1 Laser Micro-Nano Processing: Using femtosecond or picosecond pulsed lasers, a sharp microstructure array with a small radius of curvature is processed on the surface of a conductive silicon carbide wafer and the bottom surface of a graphite rod electrode as a charge agglomerate to enhance the electrochemical discharge effect;

[0010] S2 discharge-assisted micro-grinding: Using a DC power supply, an electrochemical reaction tank and a micro-grinding platform, the charges are gathered on the sharp microstructures on the surface of the silicon carbide wafer through electrostatic induction, and electrochemical discharge is generated between the sharp microstructures on the bottom of the graphite rod electrode, inducing an oxidation reaction on the surface of the silicon carbide wafer to form a softened layer, which assists the diamond micro-abrasive tool in micro-grinding.

[0011] Specifically, the S1 laser micro-nano processing step includes the following steps:

[0012] S101 wafer processing: Prepare a conductive silicon carbide wafer with a thickness of 350-650μm, control the laser power to 4-9W, and the scanning speed to 50-100mm / s, and process a sharp microstructure array on the surface;

[0013] S102 electrode processing: prepare graphite rod electrodes with a diameter of 500-800 μm, control the laser power to 2-3 W and the scanning speed to 50-100 mm / s, and completely process a sharp microstructure array on the bottom surface.

[0014] Specifically, the S2 concentrated discharge assisted micro-grinding includes the following steps:

[0015] S201 circuit connection: Use a DC power supply, connect the ordinary graphite rod electrode to the negative pole of the power supply, connect the graphite rod electrode with a sharp microstructure to the positive pole of the power supply, and fix it at the front end of the diamond micro-abrasive tool, make the same feed movement and keep a distance of 1 to 2 mm from the workpiece;

[0016] S202 parameter adjustment: fix the workpiece in the electrochemical reaction tank of the micro-grinding platform, add sodium hydroxide solution into the electrochemical reaction tank so that it covers the bottom of the diamond micro-grinding tool by 1.8-2.2 mm, adjust the DC pulse voltage to 36-60 V and the frequency to 100-600 Hz;

[0017] S203 Concentrated discharge: Utilize the large amount of charge gathered by the sharp microstructure of the graphite rod electrode to perform electrochemical discharge on the sharp microstructure of the conductive silicon carbide wafer. The current concentration effect will release electric sparks, inducing localized modification of the processing area on the workpiece surface, while the non-processing area is not affected by the discharge.

[0018] S204 micro-grinding: Use electroplated diamond micro-grinding tools with a diameter of 500-800μm, control the feed depth to 20-50μm, the feed speed to 5-10μm / s, and the rotation speed to 6000rad / s. Grinding is performed under the softening effect of the localized modified layer of concentrated discharge to avoid thermal damage and discharge damage in the non-processing area.

[0019] Specifically, the conductive silicon carbide sheet refers to one of N-type and P-type doped silicon carbide.

[0020] Specifically, the sharp microstructure array processed by S1 laser micro-nano processing refers to one or more micro-pyramids, micro-spikes, and micro-papillary structures, with a structure length of 20 to 50 μm and a maximum tip curvature radius of 20 μm.

[0021] Specifically, the S203 concentrated discharge refers to that an ordinary graphite rod electrode and a graphite rod electrode with a sharp microstructure are both immersed in an electrolyte to form a circuit. The gas film generated by the reaction completely isolates the electrode from the electrolyte to generate electric sparks, and the localized discharge is guided by the microstructure with a small curvature radius.

[0022] Specifically, the S204 micro-grinding refers to the interaction between the surface of the conductive silicon carbide wafer and the sharp microstructure at the bottom of the graphite rod electrode, whereby concentrated localized discharge and micro-grinding occur only in the sharp microstructure area of ​​the workpiece.

[0023] Compared with the existing technology, the above-mentioned conductive silicon carbide wafer concentrated discharge assisted fine grinding method has the following beneficial effects.

[0024] ① High grinding efficiency. The sharp microstructures on the surface of the conductive silicon carbide wafer and the bottom of the graphite rod electrode are processed by femtosecond or nanosecond pulse laser, which changes the structural properties of the workpiece and the discharge electrode, reduces some mechanical removal stress, and enables the electroplated diamond micro-abrasive tool to grind quickly and efficiently; the sharp microstructure on the surface of the silicon carbide wafer is subjected to enhanced discharge by utilizing the large amount of electric charge gathered by the sharp microstructure at the bottom of the electrode. The large amount of current concentration will release electric sparks, weakening the mechanical properties of the modified area of ​​the workpiece under the physical and chemical coupling, thereby achieving high-efficiency removal.

[0025] ②Good machining surface quality. Using direct current pulse current to discharge the sharp microstructure on the workpiece surface, sufficient heat is generated to oxidize the workpiece surface to form a softened layer, weakening the mechanical force between the micro-abrasive tool and the workpiece, thereby improving the surface machining quality of micro-grinding.

[0026] ③ Less damage to non-machined surfaces. Sharp microstructures are used to gather discharge to perform localized modification on the machined surface, reducing damage defects such as edge collapse, pits, cracks, and breakage, and reducing thermal, chemical, and discharge damage to the non-machined surface.

[0027] ④ The micro-abrasive tool has a long service life. The electrochemical discharge and micro-grinding are divided into two parts, using graphite rod electrodes for concentrated discharge and diamond micro-abrasive tool for micro-grinding, which eliminates the burden of discharge, reduces the risk of high-temperature fatigue damage of micro-abrasive tool, increases service life, ensures the integrity of micro-abrasive tool during processing, and reduces processing costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Schematic diagram of microstructure aggregation discharge-assisted micro-grinding in the present invention;

[0029] Figure 2 It is a processing flow chart of microstructure aggregation discharge assisted micro grinding in the present invention;

[0030] Figure 3It is a schematic diagram of laser processing of sharp microstructures on the surface of a conductive silicon carbide wafer in the present invention;

[0031] Figure 4 and Figure 5 They are schematic diagrams of the morphology of the microstructures on the side and bottom of the graphite rod electrode in the present invention;

[0032] Figure 6 It is a schematic diagram of the principle of microstructure aggregation discharge assisted micro-grinding in the present invention;

[0033] Figure 7 It is a surface topography of a sharp microstructure on the surface of a conductive silicon carbide wafer in the present invention;

[0034] Figure 8 It is a surface morphology diagram of the conductive silicon carbide wafer microstructure aggregate discharge assisted grinding in the present invention. DETAILED DESCRIPTION

[0035] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are described in detail below in conjunction with the accompanying drawings. In the following description, many specific details are set forth to facilitate a full understanding of the present application. However, the present application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present application, so the present application is not limited by the specific embodiments disclosed below.

[0036] The problem of hard and brittle silicon-based materials that are difficult to process is solved, specifically a conductive silicon carbide wafer that inevitably produces negative effects such as edge collapse, pits, and cracks during micro-grinding, which seriously affects the performance of the material parts. Electrochemical discharge machining is a commonly used processing method for hard and brittle materials that are difficult to conduct electricity, but it is easy for unnecessary thermal damage and discharge damage to occur on the non-processed surfaces during the processing. The present invention combines the two, taking advantage of their strengths and making up for their weaknesses, and then micro-grinding is performed after inducing discharge through localized aggregation of sharp microstructures, so as to achieve high-efficiency, high-quality, and low-defect precision processing of hard and brittle silicon-based materials.

[0037] The conductive silicon carbide wafer aggregate discharge assisted micro-grinding method is as follows: Figure 1 and Figure 2 As shown, it is characterized by including two processes: laser micro-nano processing and concentrated discharge assisted micro-grinding:

[0038] S1 Laser Micro-Nano Processing: Using femtosecond or picosecond pulsed lasers, a sharp microstructure array with a small radius of curvature is processed on the surface of a conductive silicon carbide wafer and the bottom surface of a graphite rod electrode as a charge agglomerate to enhance the electrochemical discharge effect;

[0039] S2 discharge-assisted micro-grinding: Using a DC power supply, an electrochemical reaction tank and a micro-grinding platform, the charges are gathered on the sharp microstructures on the surface of the silicon carbide wafer through electrostatic induction, and electrochemical discharge is generated between the sharp microstructures on the bottom of the graphite rod electrode, inducing an oxidation reaction on the surface of the silicon carbide wafer to form a softened layer, which assists the diamond micro-abrasive tool in micro-grinding.

[0040] Furthermore, the S1 laser micro-nano processing step comprises the following steps:

[0041] S101 wafer processing: Prepare a conductive silicon carbide wafer with a thickness of 350-650μm, control the laser power to 4-9W, and the scanning speed to 50-100mm / s, and process a sharp microstructure array on the surface;

[0042] S102 electrode processing: prepare graphite rod electrodes with a diameter of 500-800 μm, control the laser power to 2-3 W and the scanning speed to 50-100 mm / s, and completely process a sharp microstructure array on the bottom surface.

[0043] Furthermore, the S2 concentrated discharge assisted micro-grinding comprises the following steps:

[0044] S201 circuit connection: Use a DC power supply, connect the ordinary graphite rod electrode to the negative pole of the power supply, connect the graphite rod electrode with a sharp microstructure to the positive pole of the power supply, and fix it at the front end of the diamond micro-abrasive tool, make the same feed movement and keep a distance of 1 to 2 mm from the workpiece;

[0045] S202 parameter adjustment: fix the workpiece in the electrochemical reaction tank of the micro-grinding platform, add sodium hydroxide solution into the electrochemical reaction tank so that it covers the bottom of the diamond micro-grinding tool by 1.8-2.2 mm, adjust the DC pulse voltage to 36-60 V and the frequency to 100-600 Hz;

[0046] S203 Concentrated discharge: Utilize the large amount of charge gathered by the sharp microstructure of the graphite rod electrode to perform electrochemical discharge on the sharp microstructure of the conductive silicon carbide wafer. The current concentration effect will release electric sparks, inducing localized modification of the processing area on the workpiece surface, while the non-processing area is not affected by the discharge.

[0047] S204 micro-grinding: Use electroplated diamond micro-grinding tools with a diameter of 500-800μm, control the feed depth to 20-50μm, the feed speed to 5-10μm / s, and the rotation speed to 6000rad / s. Grinding is performed under the softening effect of the localized modified layer of concentrated discharge to avoid thermal damage and discharge damage in the non-processing area.

[0048] Furthermore, the conductive silicon carbide sheet refers to one of N-type and P-type doped silicon carbide.

[0049] Furthermore, the S1 laser micro-nano processed sharp microstructure array, such as Figure 3 As shown, it refers to one or more of micro-pyramid, micro-spike, and micro-papillary structures, with a structure length of 20 to 50 μm and a maximum tip curvature radius of 20 μm.

[0050] Further, the S203 aggregate discharge refers to the common graphite rod electrode and the graphite rod electrode with sharp microstructure (see Figure 4 and Figure 5 ) are immersed in the electrolyte to form a circuit. The gas film generated by the reaction completely isolates the electrode from the electrolyte to produce electric sparks, and the localized discharge is guided by the microstructure with a small curvature radius.

[0051] Furthermore, the S204 micro-grinding refers to the interaction between the surface of the conductive silicon carbide wafer and the sharp microstructure at the bottom of the graphite rod electrode, where concentrated localized discharge and micro-grinding occur only in the sharp microstructure area of ​​the workpiece.

[0052] like Figure 6 As shown, the working principle of the present invention is to process sharp microstructures such as micro-pyramids, micro-spikes, and micro-papillary structures on the surface of conductive silicon carbide and the bottom of the graphite rod electrode (see Figure 7 ), the graphite rod electrodes are immersed in the electrolyte to form a circuit, and the gas film generated by the reaction completely isolates the electrode from the electrolyte to produce electric sparks, and the distribution of conductive silicon carbide in the electric field on the surface of the conductor depends on the shape; the small curvature radius area of ​​the sharp microstructure on the surface is used to gather charges, induce localized release of electric sparks to assist micro-grinding, induce the formation of a softened layer on the surface of the oxidized workpiece, and then assist the diamond micro-abrasive tool to remove it efficiently, avoiding thermal, chemical and discharge damage to the non-processed surface. At the same time, the diamond micro-abrasive tool is not restricted by discharge and its service life is extended. Figure 8 As shown, through the sharp microstructure localized concentrated discharge method, when micro-grinding the groove, the edge damage of the machined surface of the conductive silicon carbide wafer is less, and there is no thermal, chemical and discharge damage on the non-machined surface, and the processing quality is improved.

[0053] The contents explained in the above embodiments should be understood as these embodiments are only used to more clearly illustrate the present invention, and are not used to limit the scope of the present invention. After reading the present invention, various equivalent forms of modifications to the present invention by those skilled in the art all fall within the scope defined by the claims attached to this application.

Claims

1. A method for fine grinding of conductive silicon carbide wafers by concentrated discharge assistance, characterized in that: It includes two processes: laser micro-nano processing and concentrated discharge assisted micro-grinding; S1 Laser Micro-Nano Processing: Using femtosecond or picosecond pulsed lasers, a sharp microstructure array with a small radius of curvature is processed on the surface of a conductive silicon carbide wafer and the bottom surface of a graphite rod electrode as a charge agglomerate to enhance the electrochemical discharge effect; S2 concentrated discharge assisted micro-grinding: Using a DC power supply, an electrochemical reaction tank and a micro-grinding platform, the charges are gathered on the sharp microstructures on the surface of the silicon carbide wafer through electrostatic induction, and electrochemical localized discharge is generated between the sharp microstructures on the bottom of the graphite rod electrode, inducing an oxidation reaction on the surface of the silicon carbide wafer to form a softened layer, which assists the diamond micro-abrasive tool in micro-grinding.

2. A conductive silicon carbide wafer concentrated discharge assisted micro-grinding method according to claim 1, characterized in that: The S1 laser micro-nano processing step comprises the following steps: S101 wafer processing: Prepare a conductive silicon carbide wafer with a thickness of 350-650μm, control the laser power to 4-9W, and the scanning speed to 50-100mm / s, and process a sharp microstructure array on the surface; S102 electrode processing: prepare graphite rod electrodes with a diameter of 500-800 μm, control the laser power to 2-3 W and the scanning speed to 50-100 mm / s, and completely process a sharp microstructure array on the bottom surface.

3. The method for conductive silicon carbide wafer micro-grinding assisted by concentrated discharge according to claim 1, characterized in that: The S2 concentrated discharge assisted micro-grinding comprises the following steps: S201 circuit connection: Use a DC power supply, connect the ordinary graphite rod electrode to the negative pole of the power supply, connect the graphite rod electrode with a sharp microstructure to the positive pole of the power supply, and fix it at the front end of the diamond micro-abrasive tool, make the same feed movement and keep a distance of 1 to 2 mm from the workpiece; S202 parameter adjustment: fix the workpiece in the electrochemical reaction tank of the micro-grinding platform, add sodium hydroxide solution into the electrochemical reaction tank so that it covers the bottom of the diamond micro-grinding tool by 1.8-2.2 mm, adjust the DC pulse voltage to 36-60 V and the frequency to 100-600 Hz; S203 Concentrated discharge: Utilize the large amount of charge gathered by the sharp microstructure of the graphite rod electrode to perform electrochemical discharge on the sharp microstructure of the conductive silicon carbide wafer. The current concentration effect will release electric sparks, inducing localized modification of the processing area on the workpiece surface, while the non-processing area is not affected by the discharge. S204 micro-grinding: Use electroplated diamond micro-grinding tools with a diameter of 500-800μm, control the feed depth to 20-50μm, the feed speed to 5-10μm / s, and the rotation speed to 6000rad / s. Grinding is performed under the softening effect of the localized modified layer of concentrated discharge to avoid thermal damage and discharge damage in the non-processing area.

4. A method for fine grinding of conductive silicon carbide wafers assisted by concentrated discharge according to claim 1, characterized in that: The conductive silicon carbide sheet refers to one of N-type and P-type doped silicon carbide.

5. A method for conductive silicon carbide wafer concentrated discharge assisted micro-grinding according to claim 1, characterized in that: The sharp microstructure array processed by S1 laser micro-nano processing refers to one or more micro-pyramids, micro-spikes, and micro-papillary structures, with a structure length of 20 to 50 μm and a maximum tip curvature radius of 20 μm.

6. A method for conductive silicon carbide wafer concentrated discharge assisted micro-grinding according to claim 1, characterized in that: The S203 concentrated discharge refers to that an ordinary graphite rod electrode and a graphite rod electrode with a sharp microstructure are both immersed in an electrolyte to form a circuit. The gas film generated by the reaction completely isolates the electrode from the electrolyte to generate electric sparks, and the localized discharge is guided by the microstructure with a small curvature radius.

7. A method for conductive silicon carbide wafer concentrated discharge assisted micro-grinding according to claim 1, characterized in that: The S204 micro-grinding refers to the interaction between the surface of the conductive silicon carbide wafer and the sharp microstructure at the bottom of the graphite rod electrode, whereby concentrated localized discharge and micro-grinding occur only in the sharp microstructure area of ​​the workpiece.

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