Aluminum nitride ceramic polishing method based on temperature flow coupling control

Abstract

The invention discloses an aluminum nitride ceramic polishing method based on temperature flow coupling control, which comprises the following steps: when an aluminum nitride ceramic workpiece and a polishing disk are in an interface lubrication state, the friction coefficient between the aluminum nitride ceramic workpiece and the polishing disk is large, a large amount of friction heat is generated, hydration reaction occurs on the surface of the aluminum nitride ceramic workpiece, and a softening layer is generated; when the temperature reaches an upper threshold value, the flow of the polishing solution is increased, the aluminum nitride ceramic workpiece and the polishing disc are converted from an interface lubrication state to a mixed lubrication state, and a softened layer on the surface of the workpiece is removed under the synergistic effect of liquid film shearing force and a rough peak; and when the temperature drops to a lower threshold value, the aluminum nitride ceramic workpiece and the polishing disc are converted into an interface lubrication state. According to the method, high-quality surface polishing of the aluminum nitride ceramic can be achieved, in the machining process, friction heat is used for increasing the temperature, a softening layer is generated, then material removal is conducted through the synergistic effect of the shearing force of a liquid film and the rough peak of a polishing disc, and high-quality surface polishing of the aluminum nitride ceramic is achieved.

Description

Technical Field

[0001] The present invention relates to the field of ultra-precision machining technology, and particularly to a method for polishing aluminum nitride ceramics based on temperature-flow coupling control. Background Art

[0002] Aluminum nitride ceramic is a covalent bond compound with a hexagonal crystal system wurtzite-type structure, and has broad application prospects in the fields of power electronics, aerospace, national defense and military, automobiles and locomotives, communications, and other industrial fields. Aluminum nitride ceramic is widely used as a heat dissipation substrate and an electronic packaging material due to its excellent thermal conductivity, thermal expansion coefficient similar to that of silicon, good mechanical strength, and chemical stability. In these application scenarios, the surface quality and machining accuracy of aluminum nitride ceramic have an important impact on the performance and service life of the device. For example, in electronic packaging, aluminum nitride ceramic with high surface quality can reduce the volume and internal resistance, and is more conducive to the heat dissipation of the chip; in the application of the heat dissipation substrate, the surface roughness of the aluminum nitride ceramic sheet should reach below 8 nm, and its surface damage layer should reach the nanoscale. Aluminum nitride ceramic belongs to a hard and brittle material, and surface defects and damages are very likely to occur during the machining process. How to achieve low-damage and high-surface-quality machining of aluminum nitride ceramic has always been a difficult point in the field of precision machining.

[0003] Chemical mechanical polishing (CMP) is an effective means to achieve global planarization of hard and brittle materials. Therefore, the current processing method for aluminum nitride ceramics still mainly relies on CMP. To improve the polishing efficiency and reduce the surface roughness, different types of new polishing fluids for AlN ceramics are disclosed in patent documents CN112521866A and CN106956212A. The polishing fluid disclosed in the former improves the material removal rate during the polishing process, and the polishing efficiency reaches 0.6 - 2.2 μm / h. The polishing fluid disclosed in the latter extends the service life of the polishing equipment and ensures the stability during the processing. In addition to CMP, the processing methods for AlN ceramics also include magnetorheological and ELID grinding. However, although the methods of the prior art have improved the material removal rate and the problem of easy surface damage in the processing of aluminum nitride ceramics, there are still problems such as difficult construction of the processing platform and expensive processing costs. Moreover, the material removal process during processing mainly relies on the collision and cutting of abrasive grains, which easily leave defects such as pits and scratches on the workpiece surface, and it is difficult to achieve damage-free processing of the workpiece surface. A non-contact polishing method for aluminum nitride ceramics is disclosed in patent document CN110328607A. However, due to the lack of abrasive grains in the polishing process, the material removal ability of the non-contact polishing method is limited, and during the processing, the critical liquid film forming conditions are harsh and the process control is difficult. Since this method will also corrode the polishing disc during the polishing process, when the rough peaks on the disc surface are removed, timely correction is required. However, the ceramic disc itself has the characteristic of high hardness, and the dressing process is difficult to complete quickly, reducing the polishing efficiency. Summary of the Invention

[0004] To overcome the deficiencies in the prior art, the present invention provides a polishing method for aluminum nitride ceramics based on temperature-flow coupling control. During the processing, the flow rate of the polishing fluid is controlled according to the temperature of the processing area, and then the contact state between the aluminum nitride ceramic workpiece and the polishing disc during the processing is controlled, so that the aluminum nitride ceramic workpiece and the polishing disc are in an interface lubrication state. The frictional heat causes the temperature of the processing area to rise, and then a hydration reaction occurs on the surface of the aluminum nitride ceramic workpiece to generate a softened layer, and then it changes to a mixed lubrication state. The material removal is carried out by the synergistic action of the liquid film shear force and the rough peaks on the disc surface. During the processing, the dressing ring sharpens the grinding disc in real time, so that the rough peaks on the disc surface are continuously exposed, solving the problems of low polishing efficiency and harsh reaction conditions in non-contact polishing, and realizing high-surface-quality polishing of aluminum nitride ceramics.

[0005] The technical solution of the present invention is as follows:

[0006] A method for polishing aluminum nitride ceramics based on temperature-flow coupling control, which is realized by using a single-plane polishing device; the single-plane polishing device includes a polishing disc, a carrier disc, a dressing ring, a polishing fluid supply device and a controller; grooves are distributed on the surface of the polishing disc; a temperature sensor is embedded on the carrier surface of the carrier disc, and the controller adjusts the flow rate of the polishing fluid according to the signal of the temperature sensor;

[0007] The method comprises the following steps:

[0008] Step 1: Prepare a polishing fluid with a certain viscosity that can spread rapidly on the surface of the polishing disc; fix the workpiece on the carrier surface of the carrier disc, and then place it in the processing area inside the dressing ring;

[0009] Step 2: Control the polishing fluid supply device to drip the polishing fluid onto the polishing disc, so that the workpiece and the polishing disc are in an interface lubrication state, and start processing; the rough peaks on the surface of the polishing disc and the rough peaks on the surface of the workpiece rub against each other, generating frictional heat, causing the liquid molecules adhering to the surface of the workpiece to desorb, and undergoing a hydration reaction with the surface of the workpiece to form a processing softening layer; when it is detected that the temperature in the processing area rises to the set upper threshold, the polishing fluid supply device increases the flow rate of the polishing fluid, and the lubrication state between the workpiece and the polishing disc changes to a mixed lubrication state, and material removal is carried out under the synergistic action of the liquid film shear force and the rough peaks on the surface of the polishing disc; when it is detected that the temperature in the processing area drops to the set lower threshold, the polishing fluid supply device reduces the flow rate of the polishing fluid, so that the lubrication state between the workpiece and the polishing disc changes to an interface lubrication state;

[0010] Step 3: After polishing reaches the set time, the polishing disc stops rotating, the polishing fluid supply device stops dripping the polishing fluid, and the workpiece is taken off.

[0011] Compared with the prior art, the method for polishing aluminum nitride ceramics based on temperature-flow coupling control of the present invention has the following remarkable improvements:

[0012] 1) By detecting the temperature of the machining area to control the flow rate of the polishing fluid, and further control the contact state between the aluminum nitride ceramic workpiece and the polishing disc during the machining process. In the initial stage, control the flow rate of the polishing fluid to make the aluminum nitride ceramic workpiece and the polishing disc in an interfacial lubrication state. At this time, the polishing disc and the workpiece are in contact, and the frictional heat causes the temperature of the machining area to rise. At the same time, the frictional action catalyzes the desorption of the polishing fluid on the rough peaks of the workpiece, and reacts with the rough peaks on the workpiece surface to form a softened layer. When it is detected that the temperature of the machining area reaches the set upper threshold, by increasing the flow rate of the polishing fluid, the load-bearing capacity of the liquid film on the disc surface is enhanced, so that the lubrication state between the aluminum nitride ceramic workpiece and the polishing disc changes to a mixed lubrication state. At this time, the polishing disc surface and the workpiece are in a semi-contact state. Under this lubrication state, the influence of the roughness between the rough peaks of the workpiece and the disc on the liquid film behavior is enhanced, and the fluid between the peaks shows a microchannel effect similar to that caused by the narrowing of the pipeline, the fluid velocity between the rough peaks increases, and the shear force increases sharply, realizing the material removal process under the synergistic action of the liquid film shear force and the rough peaks on the disc surface, which can weaken the surface damage caused to the workpiece by the material removal process dominated by the normal force and the damage caused to the workpiece and the polishing disc during the long-term friction process, avoid the formation of surface defects, and thus obtain a high surface quality;

[0013] 2) During the polishing process, the dressing ring sharpens the polishing disc in real time, so that new rough peaks continuously appear on the surface of the polishing disc, ensuring the machining efficiency;

[0014] 3) Construct a textured surface on the polishing disc surface, so that the polishing fluid can enter the machining area and enhance the hydrodynamic pressure during the polishing process;

[0015] 4) When the ceramic workpiece and the polishing disc are in a mixed lubrication state, the extrusion effect of the rough peaks causes the local pressure of the polishing fluid between the peaks to change rapidly, causing cavitation. The cavitation phenomenon prevents the entire fluid film from losing its load-bearing capacity due to the cancellation of positive and negative pressures. The collapse of the bubbles forms high temperature and high pressure, which will not cause the rapid temperature drop in the polishing area due to the loss of frictional contact. As the polishing progresses, the softened layer on the workpiece surface is removed. When it is detected that the temperature of the polishing area drops to the set lower threshold, by reducing the flow rate of the polishing fluid, the lubrication state between the ceramic workpiece and the polishing disc changes to an interfacial lubrication state, and then a softened layer that is easy to remove is regenerated on the workpiece surface. Through the continuous switching between the interfacial lubrication state and the mixed lubrication state, high-efficiency polishing is achieved.

[0016] Further, in the above-mentioned aluminum nitride ceramic polishing method based on temperature-flow coupling control, the grooves on the surface of the polishing disc are square grids, and the ratio of the side length to the depth of the square grid is 0.1 - 0.18. By controlling the ratio of the side length of the square grid of the groove on the surface of the polishing disc to the marking depth to be between 0.1 and 0.18, the resistance of the polishing liquid during spreading on the polishing disc is small, the spreading speed of the liquid film on the polishing disc is fast, and a large hydrodynamic pressure can be generated during the polishing process, so that the surface material of the aluminum nitride ceramic workpiece can be removed relatively quickly.

[0017] Further, in step one of the above-mentioned aluminum nitride ceramic polishing method based on temperature-flow coupling control, the polishing liquid composition includes polyether and water. Among them, the mixing ratio of polyether and water is 1:15 - 25. Using polyether and water to prepare the polishing liquid not only has a strong liquid film forming ability but also has good spreading performance.

[0018] Further, in step two of the above-mentioned aluminum nitride ceramic polishing method based on temperature-flow coupling control, during processing, the rotation speed of the polishing disc can be 150 - 200 rpm.

[0019] Further, in step two of the above-mentioned aluminum nitride ceramic polishing method based on temperature-flow coupling control, the chemical reaction equation for the formation of a processing softening layer on the workpiece surface is AlN + H2O → Al(OH)3 + NH3.

[0020] Further, in step two of the above-mentioned aluminum nitride ceramic polishing method based on temperature-flow coupling control, the lower threshold of the processing area temperature can be set in the range of 45 - 55 °C, and the upper threshold can be set in the range of 65 - 75 °C.

[0021] Further, in step two of the above-mentioned aluminum nitride ceramic polishing method based on temperature-flow coupling control, the polishing liquid supply device can drip the polishing liquid onto the polishing disc at a flow rate of 1 - 5 ml / min to make the workpiece and the polishing disc in an interface lubrication state; the polishing liquid supply device can drip the polishing liquid onto the polishing disc at a flow rate of 15 - 25 ml / min to make the workpiece and the polishing disc in a mixed lubrication state.

[0022] Further, in step two of the above-mentioned aluminum nitride ceramic polishing method based on temperature-flow coupling control, the workpiece can be installed on the loading surface of the loading tray through paraffin.

[0023] Further, in the above-mentioned aluminum nitride ceramic polishing method based on temperature-flow coupling control, the temperature sensor and the controller can be connected by a wireless signal. The wireless connection between the temperature sensor and the controller has the advantage of being easy to implement.

[0024] Further, in the aforementioned aluminum nitride ceramic polishing method based on temperature-flow coupling control, the polishing disc is an iron polishing disc. Using an iron polishing disc for polishing, the iron polishing disc is relatively soft, which can avoid damaging the workpiece and is conducive to ensuring the surface profile accuracy of the aluminum nitride ceramic workpiece after polishing. At the same time, the dressing ring can efficiently dress the iron polishing disc to maintain its surface profile. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is a processing schematic diagram of the aluminum nitride ceramic polishing method based on temperature-flow coupling control of the present invention;

[0026] Figure 2 is a schematic diagram of the state when the aluminum nitride ceramic workpiece and the polishing disc are in an interface lubrication state in the aluminum nitride ceramic polishing method based on temperature-flow coupling control of the present invention;

[0027] Figure 3 is a schematic diagram of the state when the dressing ring and the polishing disc are in a mixed lubrication state in the aluminum nitride ceramic polishing method based on temperature-flow coupling control of the present invention;

[0028] Figure 4 is a schematic diagram of the material removal principle of the aluminum nitride ceramic workpiece in the aluminum nitride ceramic polishing method based on temperature-flow coupling control of the present invention;

[0029] Figure 5 is a topographic map of the surface of the aluminum nitride ceramic before polishing in the embodiment;

[0030] Figure 6 is a topographic map of the surface of the polished aluminum nitride ceramic in the embodiment;

[0031] Figure 7 is a roughness detection map of the surface of the aluminum nitride ceramic polished by the aluminum nitride ceramic polishing method based on temperature-flow coupling control of the present invention using a white light interferometer.

[0032] The reference numerals in the drawings are: 1 - aluminum nitride ceramic workpiece; 2 - dressing ring; 3 - polishing disc; 4 - temperature sensor; 5 - polishing liquid supply device; 6 - carrier plate. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0033] The present invention will be further described below in conjunction with the drawings and embodiments, but it shall not be used as a basis for the present invention. The workpieces in the present invention all refer to aluminum nitride ceramics. The content not described in detail in the following embodiments is all common technical knowledge in the art or conventional technical means in the art.

[0034] Embodiment (see Figure 1-7 )

[0035] In an embodiment, the aluminum nitride ceramic polishing method based on temperature-flow coupling control of the present invention is implemented on a single-plane polishing device; the single-plane polishing device includes a polishing disc 3, a carrier disc 6, a dressing ring 2, a polishing liquid supply device 5 and a controller; the polishing disc 2 is an iron polishing disc, and its surface is distributed with fine grid-shaped grooves formed by a laser marking machine, and the ratio of the side length of the grid to the marking depth is 0.15; a temperature sensor 4 is embedded on the carrier surface of the carrier disc 6, and the probe of the temperature sensor 4 directly contacts the back surface of the aluminum nitride ceramic workpiece 1, and temperature data is collected in real time during polishing and wirelessly transmitted to the controller; during operation, the controller can adjust the flow rate of the polishing liquid according to the signal of the temperature sensor 4.

[0036] In an embodiment, the aluminum nitride ceramic polishing method based on temperature-flow coupling control of the present invention includes the following steps:

[0037] Step 1: Prepare a polishing liquid by mixing polyether and water, and the mass fraction of polyether is 5%; fix the workpiece 1 on the carrier surface of the carrier disc 6 with paraffin, and then place it in the processing area inside the dressing ring 2 (the position of the dressing ring 2 is fixed by an arc-shaped retaining arm); when implementing the present invention, it is not necessarily necessary to use polyether to prepare the polishing liquid, and other materials with similar properties can also be used to prepare the polishing liquid.

[0038] Step 2: Control the polishing liquid supply device 5 to drip the polishing liquid onto the polishing disc 3 to control the polishing area, and control the flow rate to be 2 ml / min, so that the workpiece 1 and the polishing disc 3 are in an interface lubrication state, and start processing (the polishing disc rotates at 200 rpm); the rough peaks on the surface of the polishing disc 3 and the rough peaks on the surface of the workpiece 1 rub against each other to generate frictional heat, causing the liquid molecules adhering to the surface of the workpiece 1 to desorb and undergo a hydration reaction with the surface of the workpiece 1 to form a processing softening layer, and the reaction equation is AlN + H2O → Al(OH)3 + NH3; when it is detected that the temperature in the processing area rises to the set upper threshold (70 °C), the polishing liquid supply device 5 increases the flow rate of the polishing liquid (20 ml / min), and the lubrication state between the workpiece 1 and the polishing disc 3 changes to a mixed lubrication state, and material removal is carried out under the synergistic action of the liquid film shear force and the rough peaks on the surface of the polishing disc; when it is detected that the temperature in the processing area drops to the set lower threshold (50 °C), the polishing liquid supply device 5 reduces the flow rate of the polishing liquid, so that the lubrication state between the workpiece 1 and the polishing disc 3 changes to an interface lubrication state;

[0039] Step 3: After polishing reaches the set time (30 min), the polishing disc 3 stops rotating, the polishing liquid supply device 5 stops dripping the polishing liquid, and the workpiece 1 is taken off.

[0040] In the embodiment, during the polishing process, the dressing ring 2 is always in direct contact with the polishing pad 3 to achieve real-time dressing of the polishing pad surface during the machining process. The polishing pad 3 with a disk diameter of 200 mm is used to polish the workpiece 1 (aluminum nitride ceramic), and the initial surface roughness S of the workpiece 1 a value is 430 nm.

[0041] As Figure 7 shown, after polishing for 30 minutes, the surface roughness S of the aluminum nitride ceramic is measured by a white light interferometer a value is 16.62 nm.

[0042] The above general description of the invention involved in this application and the description of its specific implementation manners should not be construed as limiting the technical solution of the invention. Those skilled in the art can, based on the disclosure of this application, without departing from the constituent elements of the invention involved, add, subtract, or combine the disclosed technical features in the above general description or / and specific implementation manners (including embodiments) to form other technical solutions that fall within the protection scope of this application.

Claims

1. A method for polishing aluminum nitride ceramics based on temperature-flow coupling control, the method being implemented using a single-plane polishing device; the single-plane polishing device comprising a polishing plate (3), a carrier plate (6), a dressing ring (2), a polishing liquid supply device (5) and a controller; the method being characterized in that: The polishing disc (3) has grooves distributed on its surface; a temperature sensor (4) is embedded on the loading surface of the loading disc (6), and the controller adjusts the flow rate of the polishing liquid according to a signal from the temperature sensor (4); The method comprises the following steps: Step 1: prepare a polishing liquid with a certain viscosity that can be quickly spread on the surface of the polishing disc (3); fix the workpiece (1) on the loading surface of the loading disc (6), and then place it in the processing area inside the dressing ring (2); Step 2: Control the polishing liquid supply device (5) to drip polishing liquid onto the polishing disk (3), so that the workpiece (1) and the polishing disk (3) are in an interface lubrication state, and processing begins; the rough peaks on the surface of the polishing disk (3) rub against the rough peaks on the surface of the workpiece (1), generating friction heat, causing the liquid molecules adhering to the surface of the workpiece (1) to desorb, and a hydration reaction occurs with the surface of the workpiece (1) to generate a processing softening layer; when it is detected that the temperature of the processing area rises to a set upper threshold, the polishing liquid supply device (5) increases the flow rate of the polishing liquid, and the lubrication state between the workpiece (1) and the polishing disk (3) is converted into a mixed lubrication state, and material removal is performed under the synergistic effect of the liquid film shear force and the rough peaks on the surface of the polishing disk; when it is detected that the temperature of the processing area drops to a set lower threshold, the polishing liquid supply device (5) reduces the flow rate of the polishing liquid, so that the lubrication state between the workpiece (1) and the polishing disk (3) is converted into an interface lubrication state; Step 3: After the polishing reaches the set time, the polishing disc (3) stops rotating, the polishing liquid supply device (5) stops dripping the polishing liquid, and the workpiece (1) is removed.

2. The aluminum nitride ceramic polishing method based on temperature-flow coupling control according to claim 1 is characterized in that: The grooves on the surface of the polishing disc (3) are in a grid shape, and the ratio of the side length to the depth of the grid is 0.1 to 0.

18.

3. The aluminum nitride ceramic polishing method based on temperature-flow coupling control according to claim 1 is characterized in that: In step 1, the polishing liquid comprises polyether and water, wherein the mixing ratio of polyether to water is 1:15-25.

4. The aluminum nitride ceramic polishing method based on temperature-flow coupling control according to claim 1 is characterized in that: In step 2, during processing, the rotation speed of the polishing disc (3) is 150 to 200 rpm.

5. The aluminum nitride ceramic polishing method based on temperature-flow coupling control according to claim 1 is characterized in that: In step 2, the chemical reaction equation for forming a processing softened layer on the surface of the workpiece (1) is AlN+H2O→Al(OH)3+NH3.

6. The aluminum nitride ceramic polishing method based on temperature-flow coupling control according to claim 1 is characterized in that: In step 2, the lower threshold of the temperature in the processing area is 45-55°C, and the upper threshold is 65-75°C.

7. The aluminum nitride ceramic polishing method based on temperature-flow coupling control according to claim 1, characterized in that: In step 2, the polishing liquid supply device (5) drips polishing liquid onto the polishing disc (3) at a flow rate of 1 to 5 ml / min, so that the workpiece (1) and the polishing disc (3) are in an interface lubrication state; the polishing liquid supply device (5) drips polishing liquid onto the polishing disc (3) at a flow rate of 15 to 25 ml / min, so that the workpiece (1) and the polishing disc (3) are in a mixed lubrication state.

8. The aluminum nitride ceramic polishing method based on temperature-flow coupling control according to claim 1 is characterized in that: In step 2, the workpiece (1) is mounted on the bottom of the carrier plate (6) by means of paraffin.

9. The aluminum nitride ceramic polishing method based on temperature-flow coupling control according to claim 1, characterized in that: The temperature sensor is connected to the controller via a wireless signal.

10. The aluminum nitride ceramic polishing method based on temperature-flow coupling control according to any one of claims 1 to 9, characterized in that: The polishing disc (3) is an iron polishing disc.

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