Types of Solder

Choosing the right solder for electronics

Electronic technician soldering on a circuit board
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Different types of solder are suited for a range of temperatures and applications. Choosing the right solder is vital to securing an electrical connection that will last the life of the circuit and not be a point 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 a number of diameters, with 0.02", 0.04", and 0.063" being most common. Larger diameter solders are great for big jobs such as tinning multi-stranded wires, but they are less useful for fine work such as surface mounting. Solders for electronics generally fall into one of three categories:

  • Lead alloy solders
  • Lead-free solders
  • Silver alloy solders

Lead Alloy Solders

Lead alloy solders are made from an alloy of tin and lead, sometimes with other metals as well. 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 temperature changes. This property helps reduce cold solder joints, which can 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-Free Solders

Lead alloys were the standard for solder used in electronics for decades, but due to the health issues associated with lead, manufacturers are moving away from lead-based solders. 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.

Electronic technician soldering on a circuit board
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Lead-free alloys are typically more expensive than lead alloy solders. They also melt at a higher temperature, which means they take longer to apply. Nonetheless, they 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 will leach out into the solder and cause 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, can be 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 pellets
  • Solder rings
  • Solder spheres
  • Solder rods
  • Solder ingots
  • Solder 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 by using separate irons for each type of solder.

How to Select the Right Solder

When choosing solder, you need to take into account the cost, the material being soldered, the use of flux, the size of the parts being soldered, and the potential health and safety issues.

You can 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, but 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.