RU2336980C2 - Method of ceramics soldering with metals and nonmetals - Google Patents

Abstract

FIELD: technological processes.

SUBSTANCE: invention may be used in electronic, radio engineering industry and precision instrument-making for soldering of items with high requirements of vacuum density, heat resistance, moisture resistance, corrosion resistance under influence of high pressures, high temperatures and impact loads. Solder that contains titanium is installed between connected surfaces. It is heated in vacuum to the temperature of solder melting and cooled down. Compound that contains lithium pentaborate is applied onto soldered joint. Repeated heating is performed in vacuum to the temperature of at least 850°C with delay of at least 2 minutes and further cooling down to room temperature. Repeated soldering provides for tight cohesion of soldered joint, metal and ceramics. Glassy film is produced on the surface of soldered joint during cooldown.

EFFECT: protection of joint against effect of high humidity and temperature.

1 ex

Description

The invention relates to the connection of dissimilar materials, in particular to soldering, and can be used in the electronic, radio engineering industry and precision instrument engineering, where high demands are placed on products in terms of vacuum density, heat resistance, moisture resistance, corrosion resistance when exposed to high pressures, high temperatures and shock loads.

A known method of vacuum-tight connection of ceramics with metals, according to which the metallization of the ceramic product is first carried out by applying a metallized layer and its subsequent sintering (the operation is repeated twice), and then the metallized ceramic product is subjected to nickel plating, first chemical and then electrolytic, and soldering is carried out copper -silver solder (French patent No. 2217.290 “Method of joining metal and ceramic products by brazing”, published on 10/11/1974, IPC B23K 1/19).

The disadvantages of this method are the complex technology of applying a metallized coating to ceramics, the additional operation of sintering a metallized junction, as well as the use of copper-silver alloy as solder.

The closest in technical essence to the invention is a method of brazing ceramics with metals and non-metals, in which a solder foil based on copper and titanium with the addition of low-melting metals from the group of tin, lead, indium and their alloys is placed between the brazed surfaces of the parts, heating is carried out in vacuum 10 ^-3 -10 ^-1 mmHg to the melting and cooling temperature (USSR author's certificate No. 1742269, IPC V23K 1/19 "Method for brazing ceramics with metals and non-metals" published on 11/23/89). The disadvantage of this method is the use of solder with a carbide-forming metal such as titanium. The molten solder containing titanium moistens the ceramics well, however, when interacting with the latter, they form solid carbide phases, which leads to the formation of cracks in the soldered joint and, therefore, to the lack of tightness of the soldered joint. Correction of this defect can only be carried out by re-soldering, but re-soldering does not always lead to the elimination of the aforementioned defect. Another significant drawback of the use of copper-titanium solder is the low corrosion resistance in conditions of high humidity and temperature.

The problem to which the invention is directed, is to increase the tightness and corrosion resistance of a soldered seam.

The technical result achieved by using the proposed method is as follows:

- obtaining a sealed solder seam (1 · 10 ^-8 MPa · m ³ / s);

- corrosion resistance of the solder joint when exposed to high humidity, pressure and high temperatures.

To solve the problem in a known method between the joined parts, one of which is made of ceramic, place the solder and carry out heating to the melting temperature of the solder. An alloy of the eutectic composition copper-titanium with the addition of low-melting metals tin and indium was used as solder.

Heating is carried out to the temperature of formation of the eutectic copper-titanium and maintained at this temperature for at least 20 minutes. As a result, there is a mutual dissolution of titanium, tin and indium in copper and obtaining an active alloy, which will ensure that the soldered materials are wetted at the melting temperature of the active alloy. Cooling is carried out to a temperature of 700 ... 750 ° C with holding at this temperature for at least 20 minutes. Further cooling is carried out to room temperature. Soldering is carried out in a vacuum of 1 · 10 ^-3 -1 · 10 ^-4 mm RT.article The soldered assembly is removed from the working volume of the electrovacuum furnace and a soldering composition is applied to the brazed joint containing a mixture of lithium pentaborate, which provides the following content of components in the soldering composition, wt.%:

- lithium pentaborate 15

- water the rest

The resulting composition for soldering with a brush or spray is applied to the solder joint, after which this surface is dried in air until a continuous coating is formed. Then the coated unit is placed in the working volume of the electric vacuum furnace and heated to a temperature of at least 850 ° C and with exposure at this temperature for at least 2 minutes.

At this temperature and exposure, a chemical interaction of the soldered seam, metal, ceramic with lithium pentaborate occurs. This interaction occurs due to lithium ions, which are part of lithium pentaborate. Lithium ions have a high electrostatic field. These properties of lithium ions lead to a strong fluxing effect, which allows molten lithium pentaborate to flow into the cracks of the soldered seam and seal it. In addition, lithium oxide, which is part of lithium pentaborate, has high chemical activity and the ability to form with titanium in the soldered joint, and with aluminum oxide (Al ₂ O ₃ ), which is an integral part of ceramics, lithium titanites and aluminites, which reduce re-soldering temperature and ensure strong adhesion of the brazed joint, metal and ceramic with lithium pentaborate at a lower temperature (850 ° C). And when cooled to room temperature, it forms a glassy film that protects the soldered joint from exposure to high humidity and temperature. Heating is carried out in a vacuum of 1 · 10 ^-3 -1 · 10 ^-4 mm RT.article

Example. When soldering the screen for a microwave emitter, consisting of a shell (alloy 29NK) and a ceramic part (grade VK94-1), a solder made of copper-titanium foil of eutectic composition was placed at the junction of the parts. The parts assembled for soldering are placed in the working volume of the VP-575-13-3 electric vacuum furnace.

Soldering was carried out according to the following temperature conditions:

- heating to a temperature of 700 ° C at a rate of 5 ° C / min;

- exposure at a temperature of 700 ° C for 20 minutes;

- heating to a melting point of solder 960 ± 10 ° C at a rate of 5 ° C / min;

- exposure at the melting point of the solder for 2 minutes;

- cooling to a temperature of 700 ° C at a rate of 5 ° C / min;

- exposure at a temperature of 700 ° C for 15 minutes.

Further cooling was carried out with the oven to room temperature. The temperature in the furnace was measured with a platinum-platinum-native thermocouple with an accuracy of ± 10 ° С. After that, the brazed ceramic-metal assembly was removed from the working volume of the electric vacuum furnace. The quality of the soldered seam was evaluated by tightness. The tightness of the soldered seam was 1 · 10 ^-5 m ³ Pa / s, which does not meet the requirements of the design documentation for tightness.

And after that we prepare the composition for re-soldering as follows. Taped or distilled water in a predetermined quantity is poured into a glass or metal container. The water is heated to a temperature of about 60-70 ° C and lithium pentaborate powder is added to it, which provides the following content of components in the soldering composition, wt.%:

lithium pentaborate 15

water rest

Stir the specified powder in water until it is completely dissolved. The composition for soldering is ready for use.

The resulting solution is applied to the surface of the solder joint, after which the coated surface is dried in air for 10 hours until a continuous coating is formed.

Re-soldering was carried out according to the following temperature conditions:

heating to a temperature of 850 ° C at a rate of 5 ° C / min;

exposure at a temperature of 850 ° C for 2 minutes;

cooling to a temperature of 400 ° C at a rate of 5 ° C / min.

Further cooling was carried out together with the furnace. The temperature in the furnace, as in the first case, was measured with a platinum-platinum-thermocouple with an accuracy of ± 10 ° С. The quality of the brazed joint was evaluated by tightness before and after heating to an operating temperature of 650 ° C. Before and after heating, the tightness did not change and amounted to no more than 1 · 10 ^-8 MPa · m ³ / s by leakage of helium. This method of soldering can be implemented on common electrovacuum thermal equipment and allows you to get products with high physical and mechanical characteristics.

Claims (1)

The method of brazing ceramics with metals and non-metals, including placing between the joined surfaces of the solder containing titanium, heating in vacuum to the melting point of the solder and cooling, characterized in that a composition containing lithium pentaborate is applied to the soldered seam and reheated in vacuum to a temperature not less than 850 ° С with a holding time of at least 2 min and subsequent cooling to room temperature.