Conductive silicon carbide wafer aggregation discharge assisted micro-grinding method

Abstract

The application discloses a kind of electrically conductive silicon carbide wafer aggregation discharge assisted micro-grinding methods, belong to the field of precision machining, specifically including laser micro-nano machining, two processes of aggregation discharge assisted micro-grinding;The laser micro-nano machining includes wafer processing, electrode processing two steps, refers to the adoption femtosecond or picosecond pulse laser, and the sharp microstructure of small radius of curvature is processed on the surface of silicon carbide wafer and the bottom surface of graphite rod electrode;The aggregation discharge assisted micro-grinding includes circuit connection, parameter adjustment, aggregation discharge, four steps of micro-grinding, refers to the adoption direct current pulse power supply, electrochemical reaction tank and micro-grinding platform, through electrostatic induction in workpiece surface microstructure aggregation charge, guide it and the localized discharge between the bottom surface microstructure of graphite rod electrode, solve electrochemical discharge instability problem, induce workpiece processing surface to form softened layer, assist diamond micro-abrasive to carry out micro-grinding, reduce the thermal damage and discharge damage of non-processing surface.

Description

Technical Field

[0001] This invention belongs to the field of precision machining technology, specifically relating to a method for micro-grinding of conductive silicon carbide wafers assisted by focused discharge. Background Technology

[0002] With the rapid development of high-tech fields such as aerospace, electronic information, and energy metallurgy, my country's demand for silicon-based microstructure components is becoming increasingly urgent. Due to the inherent brittleness and hardness of silicon carbide, existing processing methods have achieved high-gloss finishes, but inevitably produce negative effects such as edge chipping, pitting, and cracking, severely impacting the service performance of parts made from this material. Electrochemical discharge machining, a commonly used processing method for hard, brittle, and poorly conductive materials, can improve workpiece removal efficiency when combined with micro-grinding; however, it is prone to causing unnecessary thermal and discharge damage along with non-machined surfaces during the process.

[0003] To address the aforementioned issues, it is necessary to design a conductive silicon carbide wafer aggregate discharge-assisted micro-grinding method to reduce or even eliminate these problems.

[0004] Chinese invention patent CN201711339341.1 discloses a chemically modified liquid and mechanical micro-grinding method. This invention utilizes a specific chemically modified liquid to generate a silicate layer with lower hardness through a modification reaction between the liquid and the workpiece's processed layer. This weakens the mechanical stress removed between the micro-grinding tool and the workpiece, thereby improving the surface finish of the micro-grinding process. However, it does not address the microstructure treatment of the workpiece surface and the bottom of the graphite electrode. This invention, using femtosecond or picosecond pulsed laser processing, creates sharp microstructures with small radii of curvature on the workpiece surface. This reduces mechanical stress removal while inducing localized electrochemical discharge aggregation modification, effectively reducing damage to the non-machined / subsurface surfaces of the workpiece and achieving low-defect grinding of the machined surface.

[0005] Chinese invention patent CN201711051786.8 discloses a chemical-mechanical-mechanical-chemical synergistic micro-grinding method and a composite micro-abrasive. This invention uses a two-stage composite abrasive micro-abrasive to complete roughing and finishing of a workpiece in one pass. By combining the advantages of micro-grinding, mechanical-chemical machining, and chemical-mechanical machining, it achieves high-quality and high-precision machining of parts. However, it does not utilize microstructure-based concentrated discharge to soften the workpiece, thereby reducing mechanical stress and achieving low-defect, high-precision machining. In contrast, the microstructure-based concentrated discharge-assisted micro-grinding method described in this invention effectively reduces surface defects such as burrs, cracks, and chipping on the machined surface caused by simple machining, and improves thermal damage, electrochemical damage, and discharge damage on non-machined surfaces.

[0006] Chinese invention patent CN114406375A discloses an electrochemical discharge-assisted micro-grinding method for silicon-based material micro-parts. This method achieves electrochemical discharge in the silicon-based material processing area, transforming the workpiece surface material into a modified layer with significantly reduced mechanical properties. The modified layer is then rapidly and efficiently removed using a micro-grinding tool. However, the electrochemical discharge achieved by this invention generates high temperatures, which can easily lead to high-temperature brittle fracture of the micro-grinding tool during prolonged operation. Furthermore, the electrochemical discharge itself is characterized by regional instability, easily accumulating at sharp edges of the micro-grinding tool, thus exacerbating edge damage, microcracks, and other negative effects on the processed surface. In contrast, the microstructure-accumulated discharge-assisted micro-grinding method described in this invention features a sharp microstructure array with a small radius of curvature on both the workpiece surface and the bottom of the graphite rod electrode. On the one hand, the electrochemical discharge body can be transferred from the diamond micro-grinding tool to the graphite rod electrode, relieving it of the burden of being the electrochemical discharge body and improving the service life of the grinding tool; on the other hand, through the concentrated discharge effect between the sharp microstructures on the surface of the silicon carbide wafer and the bottom surface of the graphite rod electrode, localized discharge-induced modification can be achieved on the processing surface, avoiding edge damage on the processing surface and reducing thermal and discharge damage on the non-processing surface. Summary of the Invention

[0007] The purpose of this invention is to address the shortcomings of existing technologies by providing a method for micro-grinding of conductive silicon carbide wafers assisted by focused discharge. This method combines electrochemical discharge and micro-grinding, leveraging their respective strengths to compensate for each other's weaknesses. Micro-grinding is performed after localized focused discharge induced by sharp microstructures, aiming to achieve low-defect, high-efficiency, and high-quality processing of conductive silicon carbide wafers while avoiding unnecessary thermal, chemical, and discharge damage to non-processed surfaces.

[0008] The above-mentioned technical objective of the present invention is achieved through the following technical solution: a method for focused discharge-assisted micro-grinding of conductive silicon carbide wafers, characterized in that it includes two processes: laser micro-nano processing and focused discharge-assisted micro-grinding;

[0009] S1. Laser micro-nano processing: Using femtosecond or picosecond pulsed lasers, sharp microstructure arrays with small radii of curvature are processed on the surface of conductive silicon carbide wafers and the bottom surface of graphite rod electrodes, serving as charge aggregates to enhance the electrochemical discharge effect;

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

[0011] Specifically, the S1 laser micro / nano fabrication process 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 be 4-9W and the scanning speed to be 50-100mm / s, and process a sharp microstructure array on the surface.

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

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

[0015] S201. Circuit connection: A DC power supply is used. The ordinary graphite rod electrode is connected to the negative terminal of the power supply, and the graphite rod electrode with sharp microstructure is connected to the positive terminal of the power supply. It is fixed at the front end of the diamond micro-grinding tool and makes the same feed motion while maintaining a distance of 1-2 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 to the electrochemical reaction tank so that it covers the bottom of the diamond micro-grinding tool by 1.8 to 2.2 mm, and adjust the DC pulse voltage to 36 to 60V and the frequency to 100 to 600Hz.

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

[0018] S204, Micro Grinding: Using electroplated diamond micro abrasives with a diameter of 500-800μm, the feed depth is controlled at 20-50μm, the feed speed at 5-10μm / s, and the rotation speed at 6000rad / s. Grinding is performed under the softening effect of the concentrated discharge localized modification layer to avoid thermal damage and discharge damage in the non-machining area.

[0019] Specifically, the conductive silicon carbide wafer refers to either N-type or P-type doped silicon carbide.

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

[0021] Specifically, S203, or aggregated discharge, refers to the process where both a regular graphite rod electrode and a graphite rod electrode with a sharp microstructure are immersed in the electrolyte to form a circuit. The gas film generated by the reaction completely isolates the electrode from the electrolyte, producing an electric spark, which is then guided by the aggregation of microstructures with a small radius of curvature to form a localized discharge.

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

[0023] The above-mentioned conductive silicon carbide wafer focusing discharge-assisted micro-grinding method has the following advantages compared with existing technologies.

[0024] ① High grinding efficiency. Femtosecond or nanosecond pulsed lasers are used to process sharp microstructures on the surface of conductive silicon carbide wafers and the bottom of graphite rod electrodes, which changes the structural properties of the workpiece and the discharge electrode, reduces some of the mechanical removal stress, and enables electroplated diamond micro-grinding tools to grind quickly and efficiently. The large amount of charge accumulated in the sharp microstructures at the bottom of the electrode is used to enhance the discharge of sharp microstructures on the surface of silicon carbide wafers. The large amount of current concentrated will release electric sparks, which weaken the mechanical properties of the modified area of ​​the workpiece under the physical and chemical coupling effect, thereby achieving high-efficiency removal.

[0025] ②Good surface finish. By using DC pulsed current, a concentrated discharge is applied to the sharp microstructures on the workpiece surface, generating sufficient heat to oxidize the workpiece surface and form a softening layer. This weakens the mechanical force between the micro-grinding tool and the workpiece, thereby improving the surface finish of micro-grinding.

[0026] ③ Less damage to non-machined surfaces. Sharp microstructures are used to concentrate discharge and perform localized modification on machined surfaces, reducing defects such as chipping, pitting, cracking, and breakage, while also mitigating thermal, chemical, and discharge damage to non-machined surfaces.

[0027] ④ Long service life of micro-grinding tools. By separating electrochemical discharge and micro-grinding into two parts, graphite rod electrodes are used for focused discharge, while diamond micro-grinding tools are used for micro-grinding. This eliminates the burden of discharge, reduces the risk of high-temperature fatigue damage to micro-grinding tools, improves service life, ensures the integrity of micro-grinding tools during processing, and reduces processing costs. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the microstructure aggregated discharge-assisted micro-grinding process in this invention;

[0029] Figure 2 This is a flowchart of the microstructure aggregated discharge-assisted micro-grinding process in this invention;

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

[0031] Figure 4 and Figure 5 These are schematic diagrams showing the morphology of the side and bottom microstructures of the graphite rod electrode in this invention.

[0032] Figure 6 This is a schematic diagram illustrating the principle of microstructure aggregated discharge-assisted micro-grinding in this invention;

[0033] Figure 7 This is a surface morphology diagram of the sharp microstructures on the surface of the conductive silicon carbide wafer in this invention;

[0034] Figure 8 This is a surface morphology diagram of the conductive silicon carbide wafer microstructure aggregated discharge assisted grinding in this invention. Detailed Implementation

[0035] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, the specific embodiments of this application are described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of this application. However, this application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of this application. Therefore, this application is not limited to the specific embodiments disclosed below.

[0036] This invention addresses the challenges of machining hard, brittle, and difficult-to-machine silicon-based materials, specifically conductive silicon carbide wafers, which inevitably suffer from chipping, pitting, and cracking during micro-grinding, severely impacting the performance of parts made from this material. While electrochemical discharge machining (EDM) is a commonly used method for machining hard, brittle, and poorly conductive materials, it is prone to causing unnecessary thermal and discharge damage to both the machined and unmachined surfaces. This invention combines the advantages of both methods, leveraging the strengths of both: it achieves high-efficiency, high-quality, and low-defect precision machining of hard, brittle silicon-based materials by inducing discharge through localized aggregation of sharp microstructures followed by micro-grinding.

[0037] The aforementioned conductive silicon carbide wafer focused discharge-assisted micro-grinding method, such as... Figure 1 and Figure 2 As shown, the feature is that it includes two processes: laser micro / nano processing and focused discharge-assisted micro-grinding.

[0038] S1. Laser micro-nano processing: Using femtosecond or picosecond pulsed lasers, sharp microstructure arrays with small radii of curvature are processed on the surface of conductive silicon carbide wafers and the bottom surface of graphite rod electrodes, serving as charge aggregates to enhance the electrochemical discharge effect;

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

[0040] Furthermore, the S1 laser micro / nano fabrication process includes the following steps:

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

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

[0043] Furthermore, S2, the focused discharge-assisted micro-grinding, includes the following steps:

[0044] S201. Circuit connection: A DC power supply is used. The ordinary graphite rod electrode is connected to the negative terminal of the power supply, and the graphite rod electrode with sharp microstructure is connected to the positive terminal of the power supply. It is fixed at the front end of the diamond micro-grinding tool and makes the same feed motion while maintaining a distance of 1-2 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 to the electrochemical reaction tank so that it covers the bottom of the diamond micro-grinding tool by 1.8 to 2.2 mm, and adjust the DC pulse voltage to 36 to 60 V and the frequency to 100 to 600 Hz.

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

[0047] S204 micro-grinding: Employs electroplated diamond micro-grinding tools with a diameter of 500–800 μm, controlling the feed depth to be 20–50 μm, the feed speed to be 5–10 μm / s, and the rotational speed to be 6000 rad / s. Grinding is performed under the softening effect of the concentrated discharge localized modification layer, avoiding thermal damage and discharge damage in the non-machining area.

[0048] Furthermore, the conductive silicon carbide wafer refers to either N-type or P-type doped silicon carbide.

[0049] Furthermore, the S1, the laser-fabricated sharp microstructure array, such as... Figure 3 As shown, it refers to one or more micropyramid, microspiky, and micropapillary structures, with a structural length of 20-50 μm and a maximum tip curvature radius of 20 μm.

[0050] Furthermore, S203, focusing discharge, refers to ordinary graphite rod electrodes and graphite rod electrodes with sharp microstructures (see...). Figure 4 and Figure 5 All electrodes are immersed in the electrolyte to form a circuit. The gas film generated by the reaction completely isolates the electrodes from the electrolyte, generating an electric spark. The microstructures with small curvature radii aggregate to guide localized discharge.

[0051] Furthermore, S204, micro-grinding, refers to the interaction between the sharp microstructures on the surface of a conductive silicon carbide wafer and the bottom of a graphite rod electrode, resulting in concentrated localized discharge and micro-grinding only in the sharp microstructure region of the workpiece.

[0052] like Figure 6 As shown, the working principle of this invention is to fabricate sharp microstructures such as micro-pyramids, micro-spiky structures, and micro-papillary structures on the surface of conductive silicon carbide and the bottom of the graphite rod electrode (see...). Figure 7 In this process, graphite rod electrodes are immersed in the electrolyte to form a circuit. The gas film generated by the reaction completely isolates the electrodes from the electrolyte, producing an electric spark. The distribution of conductive silicon carbide on the conductor surface in the electric field depends on its shape. Charge is accumulated in the small curvature region of the sharp microstructure on the surface, inducing localized release of electric sparks to assist in micro-grinding. This induces the formation of a softening layer on the oxidized workpiece surface, which is then assisted by diamond micro-grinding tools for high-efficiency removal. This avoids thermal, chemical, and discharge damage to non-machined surfaces, while also freeing the diamond micro-grinding tools from discharge constraints, thus extending their service life. Figure 8 As shown, by using a sharp microstructure localized focusing discharge method, the conductive silicon carbide wafer experiences less edge damage on the processed surface during micro-grinding, and no thermal, chemical, or discharge damage occurs on the non-processed surface, thus improving the processing quality.

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

Claims

1. A method for micro-grinding conductive silicon carbide wafers assisted by focused discharge, characterized in that, It includes two processes: laser micro / nano processing and focused discharge assisted micro-grinding. S1. Laser micro-nano processing: Using femtosecond or picosecond pulsed lasers, sharp microstructure arrays with small radii of curvature are processed on the surface of conductive silicon carbide wafers and the bottom surface of graphite rod electrodes, serving as charge aggregates to enhance the electrochemical discharge effect; S2. Focused Discharge Assisted Micro-grinding: Using a DC power supply, an electrochemical reaction tank, and a micro-grinding platform, charges are accumulated on the sharp microstructures on the surface of the silicon carbide wafer through electrostatic induction. Electrochemical localized discharge is generated between the charge and the sharp microstructures on the bottom surface of the graphite rod electrode, inducing an oxidation reaction on the surface of the silicon carbide wafer to form a softening layer, which assists the diamond micro-grinding tool in micro-grinding. The specific steps include: S201. Circuit connection: A DC power supply is used. The ordinary graphite rod electrode is connected to the negative terminal of the power supply, and the graphite rod electrode with sharp microstructure is connected to the positive terminal of the power supply. It is fixed at the front end of the diamond micro-grinding tool and makes the same feed motion while maintaining a distance of 1-2 mm from the workpiece. S202. Parameter adjustment: Fix the workpiece in the electrochemical reaction tank of the micro-grinding platform, add sodium hydroxide solution to the electrochemical reaction tank so that it covers the bottom of the diamond micro-grinding tool by 1.8 to 2.2 mm, and adjust the DC pulse voltage to 36 to 60 V and the frequency to 100 to 600 Hz. S203, Concentrated Discharge: Utilizing the large amount of charge accumulated in the sharp microstructure of the graphite rod electrode, electrochemical discharge is performed on the sharp microstructure of the conductive silicon carbide wafer. The current concentration effect will release electric sparks, inducing localized modification of the processed area on the workpiece surface, while the non-processed area is unaffected by the discharge. Both ordinary graphite rod electrodes and graphite rod electrodes with sharp microstructures are immersed in the electrolyte to form a circuit. The gas film generated by the reaction completely isolates the electrode from the electrolyte, generating electric sparks, and the localized discharge is guided by the accumulation of microstructures with small curvature radius. S204, Micro Grinding: Using electroplated diamond micro-grinding tools with a diameter of 500-800μm, the feed depth is controlled at 20-50μm, the feed speed at 5-10μm / s, and the rotational speed at 6000rad / s. Grinding is performed under the softening effect of the localized discharge modification layer, avoiding thermal and discharge damage in non-processing areas. Based on the interaction between the sharp microstructures on the surface of the conductive silicon carbide wafer and the bottom of the graphite rod electrode, localized discharge and micro-grinding only occur in the sharp microstructure areas of the workpiece.

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

3. The method for micro-grinding of conductive silicon carbide wafers assisted by focused discharge according to claim 1, characterized in that, The conductive silicon carbide wafer refers to either N-type or P-type doped silicon carbide.

4. The method for micro-grinding of conductive silicon carbide wafers assisted by focused discharge as described in claim 1, characterized in that, The aforementioned S1, the laser micro-nano fabrication of sharp microstructure array, refers to one or more micro pyramids, micro spikes, and micro papillae structures, with a structural length of 20–50 μm and a maximum tip curvature radius of 20 μm.

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