RU2609583C2 - Solder for flux-free soldering and method for its manufacture - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention can be used to produce permanent joints of dissimilar materials by soldering diffusion-hardening solders on gallium base. Upon receipt of the solder, indium is introduced into the gallium melt and the resulting melt is introduced with a filler in the form of copper powder with a particle size of 25-40 microns. Before introduction into the melt, the copper powder is treated with hydrochloric acid (counter-etched), and its particles are covered with a layer of silver. The content of components is selected from the conditions of solder obtaining of the following composition, wt %: gallium 50-60, indium 10-15, copper powder being the rest.

EFFECT: invention allows to solder powerful electronic components, particularly crystals of monolithic integrated circuits, onto the heat-removing bases at room temperature and contact pressure.

2 cl

Description

The invention relates to brazing by diffusion-hardening gallium-based solders and can be used to obtain permanent joints of dissimilar materials, in particular, for low-temperature flux-free brazing of high-power electro-radio products on heat-removing bases.

A known method of diffusion soldering [1] solder containing equal parts of gallium, tin and metal filler.

The disadvantages of this solder are the high soldering temperature (the solder and parts must have a temperature of at least 70 ° C), the high viscosity of the composition and the complex technology of its preparation and use, requiring the creation of a vacuum of up to 10 ^-5 -10 ^-6 mm. Hg followed by inert gas inlet.

Known solder for flux-free brazing [2], containing, mass. %:

Gallium 45-50 Copper silver alloy 8-12 Copper-Tin Alloy Rest

The disadvantage of this solder is the high viscosity of the solder and the need for constant heating of tools and materials (gallium melting temperature 30 ° C), which causes inconvenience in operation.

Known solder for flux-free soldering of dissimilar materials [3], containing, mass. %:

Gallium 32-45 Copper silver alloy 8-12 Aluminium oxide 0.5-3 Zinc 3-7 Brass Rest

The disadvantage of this solder is also the need to heat up the solder and the parts to be joined, the high viscosity of the composition and the need to work using pressure, which is not possible when installing powerful electrical radio products (for example, open-frame monolithic integrated circuits).

The closest set of features to the claimed is a method using solder for flux-free brazing, including gallium, copper with a particle size of 25-45 microns and tin [4] in the following ratio of components, mass. %:

Gallium 54-66.5 Copper 30-40 Tin 3,5-7

The disadvantages of the prototype include:

- inconvenience of application and low wetting ability of solder at room temperature (the melting point of the eutectic mixture of gallium + tin is 20 ° C [5]);

- high viscosity of solder, large thickness of the soldered seam;

- short solder pot life (curing begins after 15 minutes) and high viscosity, which makes it difficult to work with it when installing high-power radio products.

The objective of the invention is to create a composition of solder and a method for its manufacture, which allows for the soldering of high-power radio products (in particular, crystals of monolithic integrated circuits) on heat sinks at room temperature (15-35 ° C) and contact pressure.

The technical result is to increase the viability of the solder and the mechanical strength of the connection, reducing the curing time of the solder.

The technical result is achieved by the fact that when receiving solder for flux-free soldering of dissimilar materials, indium is introduced into the gallium melt, after which copper powder with a particle size of 25-40 microns is introduced, and the content of the components is selected from the conditions for obtaining solder of the following composition, wt.%:

Gallium 50-60; Indium 10-15; Copper Rest

Copper powder before being introduced into the composition of the solder is subjected to processing (decapitation) with a solution of hydrochloric acid.

After decapitation, the particles of copper powder are coated with a thin layer of silver.

At the first stage, gallium is placed in a fluoroplastic glass, heated to a temperature of 40-60 ° C, and indium is introduced with mechanical stirring. The introduction of indium into the gallium melt lowers the melting point to 15 ° C and allows further work with the composition at room temperature. At the second stage, copper powder is introduced into the obtained melt and mechanically mixed until a homogeneous mass is obtained. The resulting composition remains viable for 2 hours. The composition wetts the surfaces of the parts to be joined and, using a film mask, form a layer of the composition 100-150 μm thick on one of the surfaces, after which the surfaces are combined. The curing of the composition is carried out without applying pressure in one of the modes:

at a temperature of 80 ° C for 18 hours, or

at 120 ° C for 4 hours, or

at a temperature of 150 ° C for 1 hour.

This (claimed) solder for diffusion soldering has the following properties:

the strength of the soldered seam at separation (on titanium bars 10 × 10 × 30 mm coated NZ.ZlZ) not less than 80 kgf / cm volumetric electrical resistance of cured solder 1.2⋅10 ^-5 Ohm⋅cm thermal conductivity of cured solder (calculated) 92 W / m⋅K

The impact of climatic factors does not impair the strength and electrical characteristics of the solder.

During experimental work with solders for diffusion soldering, some instability of the pot life and curing time of compositions containing copper powder was revealed. It was found that this phenomenon manifests itself only during prolonged storage of the powder and is due to the presence of an oxide film on the surface of copper particles. One way to solve this problem is to treat the copper powder (decapitation) with a solution of hydrochloric acid, followed by washing with distilled water and drying.

If you need long-term storage of copper powder used for the preparation of solders, it is possible to coat particles of copper powder with a thin layer of silver. To do this, the copper powder is placed in a solution containing 26-52 g / l AgNO ₃ , 60-240 g / l citric acid and 40-80 g / l thiourea, and mixed at room temperature for 10-20 minutes. Then the copper powder is separated (by sedimentation or filtration), washed with distilled water and dried. This technology of processing metal filler allows to reduce the curing time of solder up to 1.5 hours compared with the claimed composition and to increase the strength of the adhesive bonding at separation from 80 kgf / cm ² to 100-120 kgf / cm ² .

The use of gallium and indium in the indicated ratio and filler - copper powder with the specified particle size provides the possibility of soldering at room temperature, low viscosity of the composition, which allows the soldering of powerful electrical products without the application of pressure (at contact pressure), high mechanical strength, minimum thickness and high thermal conductivity soldered seam.

Bibliography

1. Patent of the Russian Federation: RU 2053063 from 01/27/1996, IPC ⁶ B23K 1/00 - “Method for soldering parts with diffusion hardening solders”.

2. RF patent: RU 2317882 dated 02.27.2008, IPC ⁸ B23K 35/26 - “Solder for flux-free soldering”.

3. RF patent: RU 2432242 dated 10.27.2011, IPC ⁸ B23K 35/28 - “Solder for flux-free soldering”.

4. RF patent: RU 2498889 dated 11/20/2013, IPC ⁸ B23K 35/26 - “Solder for flux-free soldering”.

5. State diagrams of double metal systems: Reference: In 3 t.: T. 2 / Under the general. ed. N.P. Lyakisheva. - M.: Mechanical Engineering, 1997 .-- 1024 p.

Claims (4)

1. A method of producing solder for flux-free soldering of dissimilar materials, comprising introducing indium into the gallium melt and then introducing into the obtained melt a filler in the form of a copper powder with a particle size of 25-40 microns, wherein the copper powder is treated with a hydrochloric acid solution before being introduced into the melt and particles are coated with a layer of silver, and the content of the components is selected from the conditions for obtaining solder of the following composition, wt.%: Gallium 50-60 Indium 10-15 Copper powder Rest 2. Solder for flux-free soldering of dissimilar materials containing gallium and indium, as well as a filler in the form of copper powder, the particles of which are pre-treated with a solution of hydrochloric acid and coated with a layer of silver and have a size of 25-40 microns, with the following content of solder components, wt.% : Gallium 50-60 Indium 10-15 Copper powder Rest