Structure of the solders used for low-temperature of the soldering of semiconductors, are resulted in tab. 2.

Table 2

Compositions низкотемпературных solders applicable when soldering germanium and silicon

As gumboil use alcohol and water solutions of chloride zinc and chloride ammonium or vaseline pastes (no-acid gumboils - a solution of rosin in alcohol). At the high-temperature soldering apply gumboils on a basis drills.

Diffusion processes between solder and the semiconductor promote formation of the connections increasing transitive resistance of a thermoelement, therefore time of contact of the semiconductor with solder in process covering by tin and the soldering should be extremely limited. The deviation of temperature of heating at the soldering should not exceed 2-3 °С.

III Soldering of graphite

The small density of graphite, the high heat conductivity close to heat conductivity of metals, and also higher thermostability, than at the majority of ceramic materials, have caused its application in various branches of technics. With rise in temperature up to 2000÷2500 °С durability of graphite grows; at these temperatures it has the greatest strength from all known materials.

Use of the graphite and combined designs is defined by way of their connection. Mechanical fastening, pasting, welding and the soldering is known. The soldering is the most technological and economic method of connection of the graphite materials, providing reception of high-strength, electrowire and tight connections.

Physicomechanical properties of graphite depend on a kind of initial raw material and parameters of technological process of its reception.

The capillary, contact-reactive, diffusion soldering and soldering-welding can be applied to connection of graphite.

Graphite is well moistened with refractory metals (the titan, zirconium, silicon, hafnium, vanadium, niobium, tungsten, molybdenum), metals of group of iron, aluminium, and also silicon and a bor.

The basic stage of process of the soldering of graphite with metals is its impregnation by the fused solder. The metal skeleton formed at it determines durability soldering connections.

Difficulty of connection of graphite materials with metals is caused by essential their distinction heat-physical and physicomechanical characteristics: heat conductivities, the module of elasticity, durability and especially thermal expansion.

Owing to distinction of temperature factor of linear expansion (TFLE) of metals and graphite at the soldering there are significant internal pressure. As graphite - rather fragile and sleazy a material destruction of a graphite detail in a zone of connection is possible. To lower a level of internal pressure in connection it is possible at performance of the following conditions:

· Reduction of temperature of the soldering;

· Selection of materials, it is maximum relatives on TFLE to graphite in a range of temperatures of heating;

· Application of plastic solders or intermediate layers from molybdenum, tungsten, the titan, zirconium, an alloy 29НК which limit of elasticity is lower or it is close to strength at a stretching of a graphite material;

· A choice of a design of connection at which graphite is influenced only with pressure of compression;

· Creation of a non-uniform temperature field at which graphite is influenced only with pressure of compression;

· Creation of a non-uniform temperature field at which metal details are heated up at the soldering to lower temperature, than graphite.

The soldering of graphite with steels

Steel-graphite designs have various value: units of fastening of graphite cathodes and anodes to current-carrying copper or aluminium trunks of metallurgical furnaces and electrolysis baths for melt of nonferrous metals; face condensation, подпятники, radial and persistent bearings of the devices working in the environment of liquid hydrocarbons; heat exchangers nuclear reactors; units of a joint of chambers of combustion and graphite rudders with metal armature.

At the contact-reactive soldering of alloys of iron with graphite there is a diffusion active carbide-form components of an alloy in a zone of junction to formation of the boundary layers enriched carbides of these elements.

Optimum mode of the contact-reactive soldering of graphite in density 1,6 - 1,9 g/sm3 with low-carbon steel the following: heating with a speed more than 100 °С/mines up to 1150÷1200 °С, endurance at this temperature of 1-2 mines, cooling in the furnace or on press of hot pressing at the switched - off current, pressure of compression (1,5 - 1,7) *107 Pa.

The soldering of graphite with high-carbon steels is limited to their thickness (no more than 15 mm). An optimum mode of the soldering the following: temperature of heating 1270÷1350 °С, endurance 2 - 10 mines in vacuum 13,3 - 1,33 Pa or in an atmosphere of protective gases.

Depending on purpose of products to connection of graphite and steel materials apply low or the high-temperature soldering.

Low-temperature the soldering use basically at manufacturing face condensation, подпятников, radial and persistent bearings, working which temperature of operation does not exceed 200 - 250 °С. At this soldering apply solders on the basis of tin, lead, bismuth, cadmium and antimonies. The listed solders do not moisten pure graphite, therefore they are recommended for the soldering of graphite with preliminary put covering. As coverings most frequently apply copper and nickel.

The high-temperature soldering of graphite with steel widely use at manufacturing separate units of nuclear reactors, and also for connection of graphite electrodes with current carrying elements, sealing rings and loose leaves with metal holders.

During the soldering of graphite with refractory metals especially pure environment as even the insignificant contents of oxygen, nitrogen, hydrogen is required or carbon (up to 10-4 %) is accompanied forming the rifts in refractory metal.

Wide application for connection of refractory metals with graphite have found the high-temperature soldering in furnaces with a controllable atmosphere and soldering-welding with use of an electronic beam and gas-electric arches. Prevention of saturation by carbon and frail metal is reached by preliminary drawing on connected surfaces of a covering from the plastic metals which are not forming in contact to graphite continuous fragile carbide diffusion layers, and also application of solders with a basis from plastic metals, inert in relation to graphite, and introduction in them carbide-form additives for maintenance of wet ability.