Soldering is a joining process used to join different types of metals together. Solder is a metal alloy usually made of tin and lead which is melted using a hot iron. The iron is heated to temperatures above 600 degrees fahrenheit which then cools to create a strong bond.
This article is one of a series of TWI frequently asked questions (FAQs).
How it Works
Solder is melted by using heat from an iron connected to a temperature controller. It is heated up to temperatures beyond its melting point at around 600 degrees fahrenheit which then causes it to melt, which then cools creating the soldered joint.
As well as creating strong electrical joints solder can also be removed using a desoldering tool.
Solder is a metal alloy used to create strong permanent bonds; such as copper joining in circuit boards and copper pipe joints. It can also be supplied in two different types and diameters, lead and lead free and also can be between .032” and .062”. Inside the solder core is the flux, a material used to strengthen and improve its mechanical properties.
What Metals are Used?
Filler metals used in soldering were once lead based (lead solder), however, owing to regulations, lead-based solders are increasingly replaced with lead free solders, which may consist of antimony, bismuth, brass, copper, indium, tin or silver.
Which Flux Can be Used for Soldering?
Occasionally at the site of the joint, there are impurities such as oil, dirt or oxidation, the flux helps prevent oxidation and can sometimes chemically clean the metal. The flux used is rosin flux which helps the mechanical strength and electrical contact of electrical joints. Sometimes it is also possible to apply a ‘wetting agent’ to reduce the surface tension.
Types of Soldering
There are three types of soldering which use increasingly higher temperatures, which in turn produce progressively stronger joints:
- Soft soldering (90 °C - 450 °C) - This process has the lowest filler metal melting point of all the soldering types at less than around 400°C these filler metals are usually alloys, often containing lead with liquidus temperatures under 350°C. Because of the low temperatures used in soft soldering it thermally stresses components the least but does not make strong joints and is then therefore unsuitable for mechanical load-bearing applications. It is also not suited for high temperature use as this type of solder loses strength and melts.
- Hard (silver) soldering (>450 °C) – Brass or silver is the bonding metal used in this process, and requires a blowtorch to achieve the temperatures at which the solder metals.
- Brazing (>450 °C) – This type of soldering uses a metal with a much higher melting point than those used in hard and soft soldering. However, similarly to hard soldering, the metal being bonded is heated as opposed to being melted. Once both the materials are heated sufficiently, you can then place the soldering metal between them which melts and acts as a bonding agent.
Uses of a Soldering Iron
A soldering iron is a hand tool used to heat solder, usually from an electrical supply at high temperatures above the melting point of the metal alloy. This allows for the solder to flow between the workpieces needing to be joined.
This soldering tool is made up of an insulated handle and a heated pointed metal iron tip. Good soldering is influenced by how clean the tip of your soldering iron is. To maintain cleanliness, a user will hold the soldering iron and use a wet sponge to clean the soldering iron tip prior to soldering components or making soldered connections.
In addition to the soldering iron, solder suckers are an important part of the soldering setup. If excessive solder is applied, these small tools are used to remove the solder, leaving only that desired.
What is a Soldering Gun Used For?
Soldering guns are used for applications where more heat is required as irons use lower power. This tool is used for joining stained glass, light sheet metal and heavy electronic soldering work. When you need to solder intermittently, the soldering gun is much more practical as it cools much quicker.