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Soldering is a technique that uses meltable conductive material – called solder – to create strong, permanent, or semi-permanent electrical connections between components like sensors, motors, and microcontrollers.

This ensures that electrical connections in a circuit remain secure, even in environments with constant movement or vibration, allowing the robot to operate consistently and effectively. As an additional benefit, solder can be melted back down, allowing it to be removed and replaced as needed.

In this activity, you will learn and practice soldering for electrical repair and assembly. First, you will make practice connections to become comfortable with the technique. Then, you will perform spot repairs on a damaged circuit. Finally, you will assemble a small electronic device by soldering its components into place.

Electrical solders are metal alloys with low melting points, usually a combination of Tin, Lead, Silver, and Copper. Commercial electronics mostly use lead-free solders for long-term health and safety, while aerospace and defense applications typically favor lead-based solders because they are more resilient to environmental stresses.

Most electrical solder also contains rosin (or “resin”) flux, which removes and prevents oxidation (rust) of the surfaces being coated, makes the consistency of the melted solder easier to work with, and improves the structural strength of the solder joint when cooled. However, you can also get flux to use to clean your soldering iron for better performance.

Electrical soldering is sometimes called soft soldering because the lead originally used in electrical solder is a soft metal that allowed the solder to melt at relatively low temperatures. Low temperatures minimize risk to nearby electrical components during soldering. However, this softness means that the joints are not as mechanically strong as other types of solder.

For instance, silver-based solders are used in jewelry repair, and create joints that can be even stronger than the original jewelry. Unfortunately, melting silver solder requires temperatures nearly 100° F higher (usually applied with a blowtorch), and the joints need to be quenched in water afterward – both highly unsuitable processes for electronics repair!

Even higher temperature solders are used to create mechanically strong joints between metal pieces in plumbing and structural applications. Note that this is still soldering and not welding, because the solder is being melted to form the joint, not the two joined pieces themselves.