CS214623B1 - Lead or tin-based low melting solder - Google Patents

Abstract

The invention relates to the field of low-melting lead-based or tin-based solders, e.g. Pbln3, PbSn60, SnAg3,5, etc., which are used for soldering various elements in electrical engineering. The invention solves the problem of saving precious metals, since the previous solders used for soldering structural elements in electrical engineering necessarily assumed silvering or golding of the soldered structural elements, which had to be carried out after their coppering and nickeling in order to create a layer with a perfectly clean metal surface on the soldered element, which wets the solders well and thus ensures the creation of a perfect connection and reliable, perfect function. The invention consists in the fact that the solder contains a lithium additive in an amount of 0.001 to 0.1% by weight. The addition of lithium will perfectly clean the connecting surfaces of the structural elements from a thin oxide film, so there is no need to galvanically silver or gold-plate them, while lithium will also positively affect the fluidity, run-in and wettability of solders and thus significantly improve the overall solderability of the components. The invention can be used in a wide range of production of soldered components for electrotechnical purposes, especially for soldering contacts, connectors, bushings, transistors, etc. Its use is possible in all enterprises of the Tesla General Directorate, etc.

Description

The invention relates to low-melting lead or tin based solders, e.g. Pbln3, PbSn60, SnAg3,5, PblnlSZn and solves the problem of soldering or hot-dipping of components in electrical engineering and their semi-finished products, especially contacts, connectors, bushings, transistors and transistor systems , without galvanic silvering or gold plating of contact surfaces.

Various electrical components and their semi-finished products are soldered or hot-dip coated by low-melting solders. The condition for perfect bonding or hot-dip coating and reliable long-term function is perfect wetting of the bonded or metallized parts by solder, which is achieved by two basic procedures:

- the use of solder - rosin-based fluxes or various scientific chloride solutions. The flux acts to remove the oxide film, thereby. perfect cleaning of the cleaned surface with solder. However, this method cannot be used if it is not possible to efficiently clean the joint from the flux residues after soldering and eventually. passivation,

- electroplating of surfaces to be joined without using aggressive fluxes. This electroplating consists of several operations, namely copper, nickel and silvering or gilding. A thin layer of precious metals creates a perfectly clean metal surface that wets the solders well. The disadvantage of this method is the necessity of using precious metals.

These disadvantages are overcome by a low-melting lead-or tin-based solder for soldering without silvering or gilding, suitable for joining and hot-dipping components and their semi-finished products in electrical engineering, according to the invention, characterized in that the solder contains 0.1% by weight. Addition of lithium on contact with the bonded or hot-dipped spot will perfectly clean the bonded surfaces from the thin oxide film, so that there is no need to silver or gold the parts. In addition to the wettability, the addition of lithium also positively affects the flowability and the wettability of the solders, thus significantly improving the overall solderability of the components. When using a lithium additive solder according to the invention, the components are only treated with copper and bright nickel plating or are hot-dipped and further soldered without further operations.

Example 1 ·

The feet of some silicon power transistors are still manufactured from complete leads coated with galvanic copper, nickel and gold plating. Standard solder Pbln3 is used for soldering. The contacting of the transistors is performed by ultrasound by contacting the leads of aluminum wires 0 0.4 mm to the system, i.

emitter wires and 1 base wires. Pofom is done by spot welding contact of all wires to the cylindrical surface of the foot feed.

According to the invention, the complete feeds were surface treated with copper to a thickness of 4 to 7 μα and, after ignition in a hydrogen furnace, a shiny nickel plating of 6 to 9 μm. The complete feeds treated in this way were soldered to the nickel-plated base with Pbln3 solder, alloyed with 0.01% lithium by weight without gilding. The contacting of the aluminum wires with the leads was performed by ultrasound directly to the front circular surface of the lead. The connection was perfect, without defects. The function and quality of the transistors produced remain unaffected.

Example 2

In another series of tests, Pbln3 solders containing 0.0008 and 0.15 wt% lithium were used. It was found that part of the transistor feet when using a solder with a lithium content of 0.0008% by weight, i.e. a low lithium content, showed a vacuum leak in 15% of the cases. As a result, it has been found that the lower limit of the lithium content must not be less than 0.001% by weight for the integrity of the joint. In the case of a lithium content of 0.15% by weight, a long-term tropicization corrosion resistance test resulted in the formation of an off-white whitish film along the grain boundaries of the Pbln matrix. This limited the lithium content to 0.1% by weight as the maximum.

Claims (1)

Low-flux solder based on lead or tin, suitable for joining or hot-dipping electrical components and their components BACKGROUND OF THE INVENTION, characterized in that it contains lithium in an amount of 0.001 to 0.1% by weight.