RU2796896C1 - Method for manufacturing miniature copper parts for electronic microwave devices - Google Patents

Abstract

FIELD: electronic engineering.

SUBSTANCE: invention can be used in manufacturing of miniature parts made of copper, such as miniature retarding systems, vacuum microwave devices. The method includes cutting with an electroerosive wire-cutting machine with a CNC system, chemical cleaning, washing and polishing. Cleaning and polishing of parts is carried out in the following sequence: they are treated in a container with a magnetic stirrer with an etching solution to remove the defective layer of the following composition: NaOH 4-8%, H₂O₂ 8-15%, C₁₀H₁₄N₂Na₂O₈ 4-12%, tartaric acid 6-12%, water - the rest, at a temperature of 45-75°C in 1-3 minute cycles with washing in 20% hydrochloric acid and water after each cycle until visible traces of electroerosion disappear, they are treated in a container with a magnetic stirrer with a suspension solution for mechanical polishing containing 2-10% of SiC abrasive powder with a particle size distribution of less than 2 mcm for 2-6 min, then etching is carried out in cycles of 0.5-1 min in a solution for chemical polishing of the following composition: H₃PO₄ 50-70%, HNO₃ 8-12%, HCl 0.4-1%, CH₄N₂S 0.07-0.7%, water - the rest, at room temperature until a shine appears on the details, washed with water after each cycle, then the parts are washed in acetone, blown first with dry nitrogen, then with carbon monoxide.

EFFECT: manufacturing high-precision systems of very small sizes for electronic microwave devices with a high class of surface quality by the electrospark method.

1 cl, 4 dwg, 1 tbl, 1 ex

Description

The invention relates to the field of electronic engineering and can be used in the manufacture of miniature parts made of copper (for example, miniature retarding systems) of electrovacuum microwave devices.

With a decrease in the size of copper elements of periodic systems of electrovacuum microwave devices in the short-wavelength range, it is important to increase the requirements for the accuracy of manufacturing elements and the quality of their surface.

There are known methods for manufacturing copper parts for microwave products of micron sizes using various technologies, for example, LIGA technology (LIGA) - deposition of thick layers of photoresist up to 1 mm on a substrate, irradiation with synchrotron radiation at accelerators through a special photomask, subsequent etching of the photoresist and galvanic deposition of copper in formed drawing. The method is characterized by high spatial resolution and low roughness. (See, for example, the information collection "News of microwave technology", No. 5, 2020, pp. 15-20). However, the implementation of this method requires the use of special expensive photoresists, photomasks and the use of accelerators, which is very expensive. In addition, galvanized copper has a low modulus of elasticity and poor dimensional stability, which leads to a rather high percentage of rejects in the manufacture and operation of comb-type retarding systems.

There is also a method for manufacturing micron-sized copper parts using the ultraLIGA (ultraLiga) method (Information collection "Microwave Technology News", No. 5, 2020, p. 15-20). In this case, instead of synchrotron radiation, ultraviolet light sources such as DRSH lamps are used. The technology for manufacturing parts using this method is cheaper, however, the spatial resolution is much worse for structures with a thickness of 0.4-1 mm; in addition, galvanized copper has a low modulus of elasticity and poor dimensional stability.

There is also known a method for manufacturing copper parts of micron sizes on CNC machines with a special diamond cutter with a diameter of 0.08-0.12 mm and a rotation speed of up to 20-60 thousand revolutions / sec. This method is used to manufacture parts, for example, of a looping waveguide with a high surface finish from high-quality vacuum copper with a hardness of more than 100 Vickers. However, in this method, it is impossible to produce structures with a resolution of less than 0.08 mm, which is determined by the size of the cutter (Information collection "News of microwave technology", No. 5, 2020, p. 15-20).

There is also known a method (prototype) for the manufacture of copper parts for microwave products of micron size, for example, decelerating comb-type systems on electric spark machines. The minimum size of the structure is determined by the diameter of the wire and for modern machines can be 8-10-100 micrometers. This method makes it possible to manufacture parts from materials of almost any hardness and with a sufficiently high surface quality, if 4-6 consecutive cuts are used along one boundary. However, for slow-motion micron-sized systems, only one cut pass is possible, otherwise the structure will be distorted and enlarged. At the same time, the surface quality is not higher than class 7 (RF Patent No. 2411605, priority 01/11/2010, published 02/10/2011, Bull. No. 4).

The main problem in the manufacture of miniature copper parts for microwave electronic devices is to ensure not only cutting accuracy, but also a high quality class (roughness) of the surface, which affects the gain of the device (due to attenuation and scattering of the electromagnetic wave). Therefore, in the manufacture of miniature copper parts, additional procedures are required to ensure the removal of the defective surface after electric spark cutting in order to achieve the smoothest possible surface.

A known method of cleaning (RF Patent No. 2714574, priority 04/10/2019, published 02/18/2020 Bull. No. 5) parts made of steel and alloys after electric spark cutting, which includes a solution of the following composition wt. %: citric acid 5.0-7.0, tartaric acid 5.0-7.0, disodium salt of ethylenediamine-N,N,N',N'-tetraacetic acid 0.5-0.7, surfactant OP-7 0.25-0.7, distilled water - the rest. To increase the efficiency, the processing is carried out with the imposition of ultrasonic vibrations. The method ensures the removal of the defective layer from the surface after electroerosive cutting directly in mechanical shops at the part washing area, while improving the environmental friendliness of production. The disadvantage of this method is low efficiency without the use of ultrasound, which cannot be used for micron-sized parts, as they are deformed, as well as the presence of citric acid, which contributes to the etching of not only the defective layer, but also copper. An increase in cleaning time in solution leads to etching of already cleaned areas. OP-7 is used for degreasing parts, so its use is not necessary for clean parts.

There is another method of chemical cleaning using a solution for chemical polishing of copper, containing, ml:

Sulfuric acid (conc.) - 10 ml

Hydrochloric acid (conc.) - 1 ml

Saturated solution of chromic anhydride - 35 ml.

(See Grilikhes S.Ya. Electrochemical and chemical polishing: Theory and practice. Influence on the properties of metals. - 2nd ed., Revised and added. L .: Mashinostroenie, Leningrad. otd., 1987, p. 146) . Mode of chemical polishing of copper: process temperature - 20-25°C, processing time - 5-10 minutes.

The disadvantage of this method is the toxicity of the solution due to the high concentration of hexavalent chromium compounds, the high speed of the copper etching process and, as a result, poor roughness, overetching of miniature structures.

The technical result of the claimed invention is the possibility of manufacturing high-precision systems of very small sizes for microwave electronic devices with a high class of surface quality using the electrospark method.

The claimed technical result is ensured by the fact that when implementing a method for manufacturing copper parts for microwave electronic devices, including cutting with an electroerosive wire-cutting machine with a CNC system, chemical cleaning, washing and polishing, the parts are cleaned and polished in the following sequence: they are processed in a container with magnetic stirrer with an etching solution to remove the defective layer of the composition:

NaOH 4-8% _{H2O2 _} 8-15% C ₁₀ H ₁₄ N ₂ Na ₂ O ₈ 4-12% Wine acid 6-12% Water rest

at a temperature of 45-75 ° C in cycles of 1-3 minutes with washing in 20% hydrochloric acid and water after each cycle until visible traces of electroerosion disappear, treated in a container with a magnetic stirrer with a suspension solution for mechanical polishing containing 2-10% abrasive SiC powder with a granulometric composition of less than 2 microns, for 2-6 minutes, then etching is carried out in cycles of 0.5-1 minutes in a solution for chemical polishing of the composition:

_{H3PO4 _} 50-70% _HNO3 8-12% HCl 0.4-1% _{CH4N2S _} 0.07-0.7% Water rest

at room temperature until a shine appears on the parts with washing with water after each cycle, the parts are washed in acetone, blown first with dry nitrogen, then with carbon monoxide.

Disclosure of the essence of the invention. In the manufacture of copper parts for microwave products of micron sizes on electric spark machines, only one cut pass is possible, while the surface quality is not higher than class 7.

To obtain a good surface quality in the manufacture of copper parts for microwave electronic devices, including cutting with a CNC wire EDM, chemical cleaning, washing and polishing, the following sequence of actions is used.

The defective layer on the parts after electroerosion is removed with an etching solution at a temperature of 45-75 ° C and stirring the solution with a magnetic stirrer in cycles, followed by washing in 20% hydrochloric acid and distilled water after each cycle until visible traces of electroerosion disappear, quality control of the removal of the defective layer is carried out under a microscope .

The optimal temperature of the solution is 45-75°C. At a lower temperature, the process is too slow, at a higher temperature, hydrogen peroxide begins to decompose intensively, the volume of the solution increases, the temperature and the rate of copper etching increase. The use of sodium alkali in the specified amount contributes to the effective loosening of the defective layer, and the combined effect of temperature and hydrogen peroxide - the transition of the grout into solution. Increasing or decreasing the amount of caustic soda leads either to an undesirable increase in the etching rate, or to a long, more than an hour, processing. Hydrogen peroxide promotes the interaction of sodium alkali and Trilon B with a defective layer, in addition, the decomposition of hydrogen peroxide at a moderate rate contributes to the mechanical separation of the loose layer from the base. With an increase in its concentration above the specified value, intensive decomposition begins, which is undesirable, since the volume of the solution increases and the temperature rises (peroxide decomposition is an exothermic reaction).

Processed in a container with a magnetic stirrer at a certain speed. The solution must move at such a speed that it flows in the form of laminar flows through the slots of the fabricated structure and over the surface of the part. In this case, uniform etching over the entire cut surface will be achieved. At high speeds, the solution will move over the surface of the part without penetrating into fine structures; at low speeds or in the absence of stirring, the etching rate will be determined by the diffusion rate of the ions of the solution. As a result, the ends of, for example, a columnar structure will be etched faster (sharpen, shorten), and the bases (with a slot width of 10–20 μm) will be etched at a much lower rate, since ion diffusion is difficult.

The advantage of chemical cleaning in an alkaline solution of the inventive composition is the minimum (less than 1 μm) etching of pure copper, low cost of reagents, low viscosity and high permeability of the solution into slot structures.

At the same time, the processes of etching the defective layer are carried out in cycles lasting 1-3 minutes, followed by washing in a solution of 20% hydrochloric acid and running water, and visual control of the cleaning quality is carried out.

The use of a polishing suspension with silicon carbide powder contributes to the gentle smoothing of sharp edges and irregularities, the removal of a defective layer and burrs. The item is processed in an aqueous solution-suspension containing 2-10% silicon carbide polishing powder SiC with a particle size distribution of less than 2 μm and using a magnetic stirrer for 1-3 minutes, followed by washing in running water.

The use of 2-10% silicon carbide polishing powder in an aqueous or water-alcohol solution with a granulometric composition of less than 2 microns is justified by the fact that at lower concentrations, polishing is slow, and at concentrations of more than 10%, the solution will not penetrate into gap structures less than 15 microns. With a granule size of more than 2 microns, the powder can get stuck in the fine structures of parts, the polishing effect decreases or disappears. The number of revolutions of the magnetic stirrer sets the speed of movement of the polishing solution. At lower speeds, the polishing effect disappears, since the kinetic energy of the powder granules is insufficient for polishing, and at high speeds, the aqueous suspension of the powder will move over the surface of the part without penetrating into the slot structures.

The final cleaning of the part is carried out within 0.5-1 min in a chemical polishing aqueous solution of the following composition: phosphoric acid, nitric acid, hydrochloric acid, thiourea in the indicated concentrations. The main contribution to the etching rate is made by nitric acid, phosphoric acid contributes to the appearance of gloss, hydrochloric acid brings copper nitrates into solution, and thiourea promotes glossy etching. The indicated concentrations are optimal, since at lower concentrations the process takes too long, and at high concentrations due to the presence of strong acids it is too fast.

Then the part is washed in distilled water, visual control is carried out for the absence of overetching and the presence of gloss. If necessary, the polishing process is repeated. Upon completion of chemical polishing, the part is washed in acetone, blown with dry nitrogen and carbon monoxide to protect the copper part from oxidation during assembly and storage). Since pure copper quickly oxidizes, which increases the attenuation of the signal, washing in acetone helps to quickly remove water. Dry nitrogen removes water and acetone residues. Gaseous carbon monoxide reacts with active sites on the copper surface, preventing interaction with atmospheric oxygen and water vapor.

The invention is illustrated by drawings. Figures 1,2,3,4 show the stages of manufacturing one of the types of copper retarding system, according to the proposed method. In FIG. 1 shows the initial state of the slowing system after the manufacture of longitudinal rows on an electric spark machine. In Fig.2. shows the state of the part after treatment in an etching solution to remove the defective layer. The pictures were taken with an optical microscope. In FIG. Figure 3 shows a view of the slowing system with longitudinal and transverse cuts (cut on an electric spark machine) after etching in an etching solution to remove the defective layer. In FIG. 4 (a, b) shows a view of the retarding system manufactured by the claimed method. The pictures were taken with a scanning electron microscope.

An example of using the claimed method. A typical pin retarding system for submillimeter waves has several rows of pins with a cross section of 10x10 µm-15x15 µm and a height of 40-100 µm. After manufacturing the longitudinal rows on an electric spark machine, the part with the longitudinal rows is processed in an etching solution. After that, transverse rows are cut on an electric spark machine, and the finished part is sent for sequential processing in solutions - an etching solution to remove a defective layer, a solution-suspension for mechanical polishing, a solution for chemical polishing.

The results of the manufacture and processing of one of the types of copper retarding system, according to the proposed method, with average values of the components of the solutions are presented in figures 1-4.

It is not possible to quantify the quality of the surface of parts obtained by the proposed method by a direct method due to their smallness, therefore, in order to assess the roughness and gloss of the surface on copper parts manufactured by the proposed method, special instruments were used (profilometer 296 and gloss meter BF5-60/60 ). Cuts were made on an electroerosive machine of copper blanks measuring 24x30x4 mm. The workpiece and the cut surface (4x30 mm) were processed according to the claimed method (sample No. 2). For comparison, when processing other workpieces, other compositions were used, for example, for finishing polishing: the known solution with chromic anhydride (sample No. 1) and the proposed solution with a 1.5-fold increase in the concentration of nitric acid (control sample). After that, with the help of special instruments, an assessment was made of the roughness and gloss of the surface.

The results of surface treatment of copper blanks after EDM cutting are presented in Table 1.

As can be seen from the presented data, copper parts manufactured by the claimed method have a higher surface quality, which confirms the achievement of the claimed technical result.

Claims (5)

A method for manufacturing copper parts for microwave electronic devices, including cutting with an electroerosive wire-cutting machine with a CNC system, chemical cleaning, washing and polishing, characterized in that the parts are cleaned and polished in the following sequence: they are treated in a container with a magnetic stirrer with an etching solution for removal of the defective layer of the composition NaOH 4-8% _{H2O2 _} 8-15% C ₁₀ H ₁₄ N ₂ Na ₂ O ₈ 4-12% wine acid 6-12% water rest, at a temperature of 45-75 ° C in cycles of 1-3 minutes with washing in 20% hydrochloric acid and water after each cycle until visible traces of electroerosion disappear, treated in a container with a magnetic stirrer with a suspension solution for mechanical polishing containing 2-10% abrasive SiC powder with a particle size distribution of less than 2 microns, for 2-6 minutes, then etching is carried out in cycles of 0.5-1 minutes in a solution for chemical polishing of the composition H ₃ RO ₄ 50-70% _HNO3 8-12% HCl 0.4-1% _{CH4N2S _} 0.07-0.7% water rest, at room temperature until a shine appears on the parts with washing with water after each cycle, the parts are washed in acetone, blown first with dry nitrogen, then with carbon monoxide.

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