阅读说明：本技术 一种高温电涡流位移传感器的制作方法 (Manufacturing method of high-temperature eddy current displacement sensor ) 是由 翟敬宇 崔得位 刘冲 李经民 丁来钱 刘济铭 万光勋 于 2021-03-03 设计创作，主要内容包括：本发明属于传感器技术领域,公开了一种高温电涡流位移传感器的制作方法。本发明采用低温共烧陶瓷作为基体材料,介电损耗和热膨胀系数小,适宜在高温环境中使用。通过在陶瓷基体上打孔、通孔填充银浆和层压实现上下层的连接。采用干法刻蚀和湿法刻蚀技术结合制作Si模具,使用Si模具在陶瓷表面纳米压印得到导体路径的微通道,通过涂银浆、光刻和显影技术得到线圈金属导体。最后通过对齐、等静压、切割和烧结得到最终的感应探头。采用高温氧化铝陶瓷和无机高温胶对探头进行无缝隙封装,实现了探头位置的固定和避免油污等的腐蚀。本发明通过将LTCC技术和MEMS技术有机结合,制作的感应探头灵敏度更高、高温适应性更强以及品质因数更大。(The invention belongs to the technical field of sensors and discloses a manufacturing method of a high-temperature eddy current displacement sensor. The invention adopts low-temperature co-fired ceramic as a base material, has small dielectric loss and thermal expansion coefficient, and is suitable for being used in a high-temperature environment. The connection of the upper layer and the lower layer is realized by punching holes on the ceramic substrate, filling silver paste into the through holes and laminating. And (2) manufacturing a Si mold by combining dry etching and wet etching technologies, performing nano-imprinting on the surface of the ceramic by using the Si mold to obtain a micro-channel of a conductor path, and obtaining the coil metal conductor by silver paste coating, photoetching and developing technologies. And finally, obtaining the final inductive probe through alignment, isostatic pressing, cutting and sintering. The probe is subjected to seamless packaging by adopting high-temperature alumina ceramic and inorganic high-temperature glue, so that the position of the probe is fixed, and oil stain and the like are prevented from being corroded. According to the invention, the LTCC technology and the MEMS technology are organically combined, so that the manufactured inductive probe has higher sensitivity, stronger high-temperature adaptability and higher quality factor.)

1. A manufacturing method of a high-temperature eddy current displacement sensor is characterized by comprising the following steps:

step 1: pre-treating, namely pressing a porous metal polar plate with the thickness of 2-8 mm, which is the same as the size of the green ceramic chip, on the surface of the green ceramic chip, and pre-treating in a drying furnace, so that organic glue of the green ceramic chip can be discharged, shrinkage is limited, and wrinkle deformation is prevented;

step 2: punching and filling holes, namely punching through holes in specific positions of the green ceramic chips by using a laser punching technology, then coating metal slurry on the backs of the green ceramic chips, and filling the through holes with the slurry by using a vacuum negative pressure adsorption method;

and step 3: manufacturing a metal mold, namely, taking aluminum as a base material, etching a vertical side wall on the surface of the base by using a mask plate through a dry method, and then etching a groove which is narrow at the top and wide at the bottom and has a demolding inclination of 1-5 degrees by using the isotropy of wet etching;

and 4, step 4: nano-imprinting, namely nano-imprinting the prepared metal mold on a low-temperature co-fired ceramic substrate to obtain a micro-channel, and drying the surface of the micro-channel by using inert gas after deionized water treatment;

and 5: performing metal patterning, namely spin-coating photosensitive metal slurry with the thickness of 5-30 microns on the surface of low-temperature ceramic, photoetching a coil pattern on the surface by using a mask, developing and rinsing by using a developing solution, drying and cooling to obtain a coil metal conductor;

step 6: the method comprises the steps of (1) carrying out constrained pressure assisted sintering, putting a laminated multilayer substrate blank into a sintering furnace, and controlling the shrinkage rate of the sintered substrate by adopting a common sintering method of a ceramic substrate and a sacrificial layer;

and 7: surface treatment, namely plating a gold film layer on the surface of the coil by adopting a chemical plating method in order to prevent the surface of the coil from being oxidized at high temperature, and adding 2-5 layers of blank ceramic substrates on the top layer and laminating and sintering the blank ceramic substrates in order to avoid the surface of the coil from being broken due to extrusion abrasion;

and 8: the coaxial cable is connected with the electrode, the end face of the coil surface electrode connected with the high-temperature coaxial cable is polished to be flat, and the end face is fixed by adopting a mechanical compression joint method, so that the reliability at high temperature is ensured;

and step 9: the probe is packaged, a coil is fixed in a groove of the lower shell made of high-temperature ceramic, the position of the coaxial cable is fixed by a through hole of the upper shell, the upper shell and the lower shell are connected through a bolt, and inorganic high-temperature glue is filled in the shells to perform seamless packaging, so that the functions of fixing position, oxidation resistance and corrosion resistance are achieved.

Technical Field

The invention belongs to the technical field of sensors, and discloses a manufacturing method of a high-temperature eddy current displacement sensor used in a severe environment.

Background

The eddy current sensor has good sensitivity, linearity and dynamic characteristics, strong anti-interference capability and is not influenced by mediums such as oil stains, and the like, so the eddy current sensor is widely applied to the nondestructive detection fields of electric power, metallurgy, machinery and the like. However, in some severe environments, such as the measurement of gaps of air preheaters in power plants and the measurement of turbine rotating speed of aero-engines, the temperature is very high and the corrosivity is strong, the general sensor cannot meet the temperature requirement, and the traditional eddy current sensor has the problems of poor coil size uniformity, ferrite failure at high temperature, large thermal deformation, large electromagnetic loss and the like. Therefore, the use temperature of the eddy current sensor does not exceed 200 ℃ generally, and the research on the eddy current sensor is very little.

Disclosure of Invention

The invention aims to provide a high-temperature eddy current sensor and a manufacturing method thereof, which are used for solving the problems of poor size uniformity of an eddy current sensor coil, failure of a high-temperature ferrite magnet, large thermal deformation, large electromagnetic loss and the like in the prior art.

The technical scheme of the invention is as follows:

a ceramic-based high-temperature eddy current sensor comprises a probe assembly, a shell assembly and a high-temperature coaxial cable assembly. The probe assembly comprises an induction coil 3 and a low-temperature co-fired ceramic substrate 2, wherein the coil 3 is obtained by manufacturing metal conductors on the surface and in the ceramic substrate 2 and laminating and sintering multilayer ceramics. The shell component comprises an upper shell 6 and a lower shell 1 which are connected through bolts, and high-temperature insulating cement is filled in the shells to form a closed environment. The high-temperature coaxial cable 5 is connected with the surface electrode 4 of the probe assembly in a crimping mode and is fixed in position through the high-temperature glue and the through hole of the upper shell 6.

A manufacturing method of a high-temperature eddy current displacement sensor comprises the following steps:

step 1: and (3) preprocessing, namely pressing a porous metal polar plate with the thickness of 2-8 mm, which is the same as the size of the green ceramic chip, on the surface of the green ceramic chip, and preprocessing in a drying furnace, so that organic glue of the green ceramic chip can be discharged, and the phenomenon that the precision of key processes such as punching, metal patterning and the like is influenced due to larger deformation in the subsequent process is avoided.

Step 2: and (5) punching the green ceramic chip. Punching holes in the appointed positions of the green ceramic chips according to a pre-designed pattern, wherein the hole diameter and the position precision directly influence the wiring density and the substrate quality, and the punching mode can be ultraviolet laser punching and CO₂And (5) laser drilling.

And step 3: and filling the through hole. Preparing metal slurry with a certain concentration, fully coating the back of the green ceramic chip, and filling the slurry in the through hole by setting parameters such as pressure, time and the like and using a vacuum negative pressure adsorption method. The negative pressure adsorption method may be a micro-hole injection method and a screen printing method.

And 4, step 4: and (5) manufacturing a metal mold. The method comprises the steps of taking a metal aluminum (Al) sheet as a base material, manufacturing a mask according to a designed pattern, covering the surface of the base body with the mask to etch a vertical side wall by dry etching, and then etching a groove which is narrow at the top and wide at the bottom and has a demoulding inclination of 1-5 degrees by utilizing the isotropy of wet etching. The wet etching method may be immersion and spray.

And 5: and nano-imprinting, namely nano-imprinting the prepared metal mold on a low-temperature co-fired ceramic substrate to obtain a micro-channel, and drying the surface of the micro-channel by using inert gas after deionized water treatment. Nanoimprint techniques may be thermal and microcontact printing.

Step 6: and (3) metal patterning, namely spin-coating photosensitive metal slurry with the thickness of 5-30 microns on the surface of the low-temperature ceramic, photoetching a coil pattern on the surface by using a mask, developing and rinsing by using a developing solution, drying and cooling to obtain the coil metal conductor. The metal paste may be a photosensitive silver paste or a gold paste.

And 7: lamination and lamination. The green ceramic chips with the metallized patterns and the formed interconnected through holes are put into a laminating machine, aligned and stacked together according to the designed sequence, and sent into a laminating machine for isostatic pressing after vacuum packaging, so that the green ceramic chips become a tightly bonded multilayer substrate blank.

And 8: there is a confining pressure to assist sintering. Carrying out hot cutting on the laminated multilayer green ceramic chips according to the designed size to form a monomer substrate, then putting the monomer substrate into a sintering furnace, and controlling the shrinkage rate of the sintered substrate by adopting a common sintering method of the ceramic substrate and the sacrificial layer;

and step 9: and (6) surface treatment. In order to prevent the surface of the coil from being oxidized at high temperature, a chemical plating method is adopted to plate a gold film layer on the surface of the coil, and in order to avoid the surface of the coil from being broken due to extrusion abrasion, 2-5 layers of blank ceramic substrates are added on the top layer and are laminated and sintered.

Step 10: the coaxial cable is connected with the electrode. The end face of the coil surface electrode connected with the high-temperature coaxial cable is polished to be flat and fixed by adopting a mechanical compression joint method, so that the reliability at high temperature is ensured;

step 11: and (6) packaging the probe. The coil is fixed in the groove of the lower shell made of high-temperature ceramic, the position of the coaxial cable is fixed in the through hole of the upper shell, the upper shell and the lower shell are connected through the bolt, and inorganic high-temperature glue is filled in the shells to perform seamless packaging, so that the effects of fixing position, oxidation resistance and corrosion resistance are achieved.

The invention has the beneficial effects that:

1. the common sensor adopts a ferrite magnet as a magnetic core, and the magnetism fails at high temperature, so that the electromagnetic loss is increased, and unknown errors and drift are brought; when the air core is adopted as the coil magnetic core, the problem of high-temperature failure can be avoided, and the inductance value can be increased by the planar multi-turn coil structure, so that the linear measurement range is enlarged.

2. Manufacturing a metal mold: the metal mold is manufactured by a method combining dry etching and wet etching, the process controllability is good, the aluminum (Al) mold is high in heat conductivity coefficient and strong in wear resistance, and the deformation amount is small during imprinting. The mold is of a structure with a narrow top and a wide bottom, so that demolding and subsequent microchannel formation are facilitated.

3. Nanoimprint to obtain microchannels: the metal mould is used for carrying out nano imprinting on the surface of the low-temperature co-fired ceramic to form the micro-channel, so that the micro-channel has higher resolution, the diffraction phenomenon in optical exposure and the scattering phenomenon in electron beam exposure cannot occur, and the designed pattern is almost indiscriminately transferred to a substrate. Due to the existence of the micro-channel, the thickness of the coil conductor is increased, the resistance is reduced, and the quality factor of the sensor is improved.

4. And (3) constrained pressure assisted sintering: by adopting the co-sintering method of the ceramic thin plate and the sacrificial layer, the shrinkage rate of the sintered substrate can be controlled, and the shape precision and the position precision of the conductor pattern and the through hole are ensured. The substrate with small shrinkage rate has extremely high mechanical strength, impact resistance and good heat dissipation, and can meet the requirements of severe environments.

Drawings

FIG. 1 is a schematic view of the overall structure of the sensor of the present invention;

FIG. 2 is a schematic view of a metal mold of the present invention;

FIG. 3 is a schematic view of a green ceramic chip nanoimprint of the present invention;

fig. 4 is a schematic diagram of the top layer structure of the induction coil of the present invention.

Detailed Description

The following further describes a specific embodiment of the present invention with reference to the drawings and technical solutions.

Step 1: and (4) preprocessing. And (3) putting the green ceramic chips into a drying furnace in a purification room for pretreatment, wherein the drying condition is 80-100 ℃, and the time is 20-30 min. And covering a porous stainless steel plate with the thickness of 5mm on the surface of the green ceramic chip during drying, so as to avoid the green ceramic chip from generating large deformation during rubber discharge and shrinkage, thereby influencing the precision of key processes such as subsequent punching, printing and the like.

Step 2: and (5) punching the green ceramic chip. And forming through holes by adopting mechanical stamping, drilling or laser drilling technology so as to connect all layers of LTCC substrates and form a conductor loop. When the diameter of the through holes is more than 100 mu m and the batch is not high, laser drilling is adopted, the laser power and the moving speed are adjusted, and the focused laser beams are utilized to evaporate the materials on the green ceramic tape layer by layer to form the through holes. The method is simple to operate, high in efficiency, good in economy and suitable for small-batch punching. When the diameter of the through hole is less than 100 mu m and the batch size is larger, mechanical punching is adopted to manufacture a punch and a die matched with the diameter of the through hole.

And step 3: and filling the through hole. The LTCC substrate through-hole filling method includes two methods, and when the diameter of the through-hole is larger than 0.3mm, a screen printing method is generally used, which is a process of manufacturing a screen having a certain mesh number so that the metal paste is uniformly deposited in the through-hole through the mesh under the action of the squeegee. However, when the diameter of the through hole is less than 0.3mm, the screen printing cannot meet the requirements well, and a micropore filling machine is required to complete through hole filling. By arranging a special injection tool, setting parameters such as injection pressure, injection time, slurry viscosity and alignment condition of a filling hole, and adopting a negative pressure suction method, gold, silver or platinum slurry with certain viscosity is filled into the through hole. And drying the filled green ceramic chip to solidify metal in the hole, wherein the drying condition is 60 ℃ and the drying time is 20-30 min. And flattening by a flattening machine after drying.

And 4, step 4: and (5) manufacturing a metal mold. Dry etching: and (3) taking a metal (Al) sheet as a base material, spin-coating photoresist on the surface, obtaining a photoresist masking layer through photoetching and developing, and etching a groove with the side wall vertical to the substrate in a dry etching machine. Wet etching: preparing a mixed solution of phosphoric acid, nitric acid, acetic acid and deionized water in a certain proportion, heating the solution to 60 ℃, spraying the solution on the surface of a substrate to start to corrode Al, and processing to obtain a groove with a narrow upper part and a wide lower part and a 4-degree demoulding inclination.

And 5: and (4) nanoimprinting. And hot-pressing the prepared metal die on a ceramic substrate to print a micro-channel, wherein the technological parameters are temperature of 60 ℃, pressure of 100MPa and pressure maintaining time of 5 minutes. Treating the microchannel with deionized water, drying the surface with nitrogen,

step 6: the coil conductor is patterned. Coating metal slurry on the surface of a ceramic substrate, then putting the ceramic substrate into a step spin coater, drying and standing after a film layer is uniform to 20 mu m. And then, the substrate is put into a photoetching machine for photoetching, so that the position accuracy of the conductor channel of the mask is ensured to improve the reliability of the circuit. And developing the substrate after photoetching, placing the green ceramic chip in a rotary machine, spraying a developing solution on the surface of the green ceramic chip, and developing in a static state, wherein after developing, rinsing, drying and cooling are required.

And 7: lamination and lamination. And placing the green ceramic chips with the metallized patterns and the formed interconnection through holes into a laminating machine, aligning and stacking the green ceramic chips with the positioning reference according to the designed sequence, and tightly bonding the green ceramic chips and the positioning reference at a certain temperature and pressure to form a complete multilayer substrate blank. In addition to the exact design sequence, pressure, temperature and positional accuracy are also ensured during lamination to ensure the accuracy of the pattern between the layers. And (3) carrying out vacuum packaging on the laminated green ceramic chip, and then sending the green ceramic chip into a laminating machine for isostatic pressing, wherein the hot pressing temperature and pressure are determined according to the area and the number of layers of the substrate. In order to avoid the phenomena of delamination, blistering, cracking and the like during sintering, the green body hot pressing process should be carried out in a vacuum environment, which is beneficial to gas elimination and adhesion strength improvement. The hot pressing pressure is uniform and consistent, and the hot pressing pressure has great influence on the shrinkage rate of the green body during sintering. The larger the pressure, the smaller the shrinkage. The pressure is too small, the green body is not pressed well, delamination can occur, the shrinkage rate is large, and the shrinkage rate consistency is poor; if the hot pressure is too high, the adhesive may foam and delaminate when being discharged. Vacuum packaging, and isostatic pressing in a laminator to obtain a tightly bonded multi-layer substrate blank

And 8: there is a constraint to assist sintering. The LTCC stack is incubated in the organic dispensing zone (the zone between 200 and 500 ℃) for at least 60min and then co-fired to a peak temperature (typically 850 ℃) within 5-15 min. By adopting the method of co-sintering the ceramic thin plate and the green sheet stack, the ceramic thin plate and the green sheet stack do not need to be removed after sintering, and the worry of restraining residue does not exist. The method can realize zero shrinkage of the sintered LTCC substrate, avoid generation of micro and macro defects, remove the polymer binder in the sintering process and ensure the antioxidation of the conductor material.

And step 9: the coaxial cable is connected with the electrode, the end face of the coil surface electrode connected with the high-temperature coaxial cable is polished to be flat, and the end face is fixed by adopting a mechanical compression joint method, so that the reliability at high temperature is ensured;

step 10: the probe is packaged, a coil is fixed in a groove of the lower shell made of high-temperature ceramic, the position of the coaxial cable is fixed by a through hole of the upper shell, the upper shell and the lower shell are connected through a bolt, and inorganic high-temperature glue is filled in the shells to perform seamless packaging, so that the functions of fixing position, oxidation resistance and corrosion resistance are achieved.