Soldered joints

Soldered joints is one of the most popular methods of connecting metal components with the use of a low melt alloy solder.

This type of joint is used for fixed parts, i.e. located inside the enclosure of a device, or for PCB components.

Soldering is used for:

• connecting cables to sockets,
• shields,
• radiator blades,
• grips,
• other large mechanical components.

Soldering iron of appropriate power

Obviously, you’ll need a soldering device in order to do soldered joints. For small electronic components, a 10-20 W soldering iron is enough. When working with construction elements, a 40-60 W soldering iron is handy, whereas for soldering the largest components, a 100 W soldering tool should be used.

If the power of a soldering tool is insufficient, it results in the so-called cold solder joints, which are not connected to the surface. This is caused by the fact that the soldering tip cools down too fast, and the melted metal cannot dampen the surface well enough. Such a joint is vulnerable to any mechanical factors, and after some time it usually breaks.

Photograph 1. Fluxes for soldering are available in liquid, gel, paste, and even in spray form.

Correct soldering alloy and flux

Also, a soldering alloy and flux is needed for soldering. For small components, the alloy is usually in the form of a 0.5–1mm wire with the flux inside. Larger components are soldered using alloys in the form of rods or bars, and the flux is applied separately by immersion or with the use of a brush.

Soldering alloy may include lead (Sn 60% and Pb 40%), with the melting temperature of ca. 200oC, or may be lead-free, based on tin with a small addition of copper and silver – with melting temperature of ca. 225oC.

Lead alloys are gloss, whereas lead-free ones can be identified by their matt and rugged surface.

Photograph 2. Soldered connections made with the use of lead alloy (on the left) and lead-free alloy (on the right). Lead-free connection has a characteristically matt surface.

Connecting by soldering

In service works, alloys of the same type as the original joints should be used. In mass production of new devices, the use of lead-free alloys is obligatory. In singular or uncommon cases, lead alloys can be used (as for now), which ensures the best joints with handheld soldering tools.

See also:

• Crimped joints
• Welded joints
• Separable joints

Summary

Thanks to soldering, you can easily connect any metal components of copper, brass or bronze - all you need is rosin or products based on rosin, which importantly enough do not have to be washed away. Soldering zinc, aluminium or steel alloys requires the use of an aggressive flux in the form of paste or liquid, based on organic acids. They have to be removed from the surface of the connection (by washing), or the joint may start to corrode.