Different types of solder are suited for a range of temperatures and applications. The right solder secures an electrical connection that lasts the life of the circuit and avoids points of failure.
Information in this article applies broadly to different solder types. Check the solder packaging to make sure it is safe to use with electronics.
Types of Solder
Solder is available in several diameters, with 0.02-inch, 0.04-inch, and 0.063-inch being most common. Larger diameter solders are great for big jobs such as tinning multi-stranded wires. These are less useful for fine work such as surface mounting. Solders for electronics generally fall into one of three categories:Lead alloy soldersLead-free soldersSilver alloy solders
Lead Alloy Solders
Lead alloy solders are made from an alloy of tin and lead, sometimes with other metals. The combination of the metals results in an alloy with a low melting temperature.
Lead alloy solder is often referenced by its alloy ratio, such as 60/40 or 63/37, with the first number being the tin by weight and the second number being the amount of lead by weight. Both of these common alloys are suitable for common electronics, but 63/37 is a eutectic alloy, which means that it has a sharp transition between liquid and solid states as the temperature changes. This property helps reduce cold solder joints, which occur when a part moves as the solder is cooling.
Wash your hands thoroughly after handling lead solder. The residue can be harmful if ingested, especially for children.
Lead alloys were the standard for solder used in electronics for decades. Manufacturers are moving away from lead-based solders because of the health risks associated with lead. One of the most popular lead-free alloys is a 96.5/3/0.5 alloy with 96.5% tin, 3% silver, and 0.5% copper.bucky_za / E+ / Getty Images
Lead-free alloys are typically more expensive than lead alloy solders. Lead-free alloys also melt at a higher temperature, which means this type of alloy takes longer to apply. Nonetheless, lead-free alloys are safer and more environmentally friendly.
Silver Alloy Solders
Silver alloy solder can be either lead-free or combined with lead. Silver was originally added to lead alloy solder to prevent an effect known as silver migration. With typical lead alloy solders, the silver in a silver plating leaches into the solder, which causes the joints to become brittle and prone to breaking. Lead alloy solders with silver—such as 62/36/2 solder with 2% silver, 62% tin, and 36% lead—are expensive, and the benefits aren't always worth the extra cost.
Forms of Solder
Solder typically comes in spools of wire, but there are also other forms of solder, including:Solder pelletsSolder ringsSolder spheresSolder rodsSolder ingotsSolder strips
You can also find washers coded in solder for automated soldering. Some lead-free alloys are only available as solder paste.
Avoid mixing lead alloys and lead-free solders. Use separate irons for each type of solder.
How to Select the Right Solder
When choosing solder, consider the cost, the material being soldered, the use of flux, the size of the parts being soldered, and the potential health and safety risks.
Find solder with one or more rosin (flux) cores that run through the center of the solder wire. This embedded solder flux helps the solder flow and bond to the parts being soldered. However, this type of solder isn't ideal for all jobs. For example, acid-flux solders that are commonly used in plumbing should never be used on electronics.