Written by Miles Budimir
Senior Editor, WTWH Media
Brazing and soldering are metal joining techniques that use heat as the main mechanism to bind together the two metals. Broadly speaking, there are three common techniques for joining metals together thermally: welding, brazing, and soldering.
The main characteristic of welding is that it uses high temperatures of about 1,000 ˚C or higher. It differs from brazing and soldering in that it’s the only method of the three that melts the metals for joining with a filler metal. After cooling, the metals solidify to form a strong bond.
In soldering and brazing, a metal alloy (solder) is melted and flows over the two metals to be joined, connecting them together. The main difference between the two is the temperature. In fact, the American Welding Society defines brazing as the process where the filler metal (i.e. solder) has a liquidus above 450 ˚C. This means it becomes liquid or melts at temperatures above this point and begins to solidify below that temperature.
Soldering, on the other hand, involves filler metals with a liquidus below 450 ˚C. In brazing, the most common heat source is a gas flame torch. Other methods include furnace brazing, dip brazing, electron beam, laser brazing, and others.
For soldering, the most common technique is to use a soldering iron. Other techniques, such as reflow or wave soldering, are used in high-volume manufacturing environments. Brazing and soldering use flux as a part of the process. It’s used to clean the metals to be joined, removing any oxidation and preventing any from forming. Using the right flux for the job requires ensuring that the flux is chemically compatible with the metals and the solder.
For instance, flux used in electrical soldering typically contains a rosin core while flux for brazing applications might use borax or other compounds. Soldering is typically used in electronic applications, primarily to make an electrical connection. So it’s not as mechanically strong as a brazing joint, which makes a much stronger bond between the metals to be joined. Brazing also requires the parts to have a much tighter fit than soldering to form a strong connection between the parts.