Soldering is an essential part of assembling electronics. To join the selected pieces together so they connect faultlessly, you firstly need the right equipment, and secondly the right soldering technique. Find out all you need to know about soldering here, in our special feature.
The origins of soldering
The Cambridge Dictionary defines soldering as “joining pieces of metal together using solder”. Solder is a filler material containing one or more alloys to create a stable and robust joint structure. Additionally, soldering filler materials melt at a distinctively lower temperature than the adjoining metal components, thus preventing damage to heat-sensitive electronic components.
The precise origins of soldering are not clear, but the technique in its basics has been in use for millennia; over 5000 years ago, Old Egyptians melted gold and silver together to create pieces of jewellery. The next step in innovation occurred approximately 4000 years ago, when tin was used as a low-temperature solder filler. This basic principle of metal joining has then been honed and refined for thousands of years. To this day, in many houses the copper heating pipes are commonly soldered.
The first electrical soldering tools
One of the pioneers of mechanized soldering was Ernst Sachs. Having patented the first electrically-operated soldering iron in 1921, he soon started the serial production of the tool, thus introducing it to the electric engineering industry. His company, ERSA, was called after the first letters of his fore- and family names.
Another pioneer, Carl E. Weller, was granted the first patent for a handheld solder gun in 1941, and started to mass manufacture his invention near the city of Philadelphia, USA, in 1945. In 1959, Weller went on to manufacture soldering tools in Besigheim, Germany, with his company becoming one of the leading players in the industry. In 1968, Weller developed the first wave soldering machines for the mass-production printed circuit boards. The company also introduced further innovations to soldering by hand: the first temperature-controlled irons and work stations (Magnastat) in 1976, followed by the first Weller soldering station with a digital temperature controller. In 1992, the company presented their first comprehensive fume extraction system, Zero Smog.
ERSA have been continuously advancing their soldering equipment. Since 1993, the company has been offering the reflow soldering technology (Hotflow) for printed circuit boards with SMD components and hybrid integrated circuits. In this process, fine solder particles and flux are mixed into a sticky paste and applied directly to the circuit board. Second, the SMD components are placed onto the paste. Finally, the entire assembly is subjected to controlled heat, which melts the solder paste and connects the joint permanently.
Soldering tools for electronics
In order to solder items together the solder filler has to be heated up with the tip of the soldering iron. The tip is typically heated electrically but can be sometimes heated externally as well.
Externally heated portable soldering tools are usually heated by a gas flame. Such gas torches are equipped with a small gas tank, filled with white gas or butane. The flame is either activated with a lighter or with a piezo igniter. Controlling the temperature of a gas torch requires some practice and, depending on the make, temperatures can reach between 200-400°C, and sometimes even up to 580°C. Some gas torches can be additionally equipped with hot-air-nozzles, enabling temperatures of up to 1300°C for non-soldering applications.
Hot-air soldering stations
Standalone soldering stations can also accommodate electrically-operated hot-air heads, which are often used for soldering operations on heat-sensitive SMD components. Due to microelectronics, the electrical hot-air tools can be temperature controlled in a tighter manner than gas-powered tools. On the downside, hot-air stations need an additional pump to create the airflow.
Electrically-operated irons heat up their usually interchangeable tips either internally or externally. Simple soldering irons do not offer temperature control. More advanced tools use the temperature dependency of their heating element’s resistance to control and indicate temperature.
The most useful are soldering tools controlled electronically with a temperature sensor placed near the tip, offering preset temperature regulation. This is why many modern soldering stations are equipped with a digital temperature display for the preset temperature and a second indicator for the actual temperature. At the same time, the microelectronics ensure steady adjustment to the preset value. As a general rule: the smaller the heat capacity of the tip, the better the continuous temperature accuracy and stability. This is why the finer tips are the best choice for small electronic operations.
Soldering guns (pistol-shaped models of soldering tools) are becoming increasingly rare nowadays. The guns are usually equipped with a loop-shaped heating coil at the tip. The coil is powered directly by current; alas very high current with very low voltage is required in most cases. Soldering guns have a rapid heat-up time ranging in seconds. This is why the power has to be switched on temporarily with a trigger and then released. Soldering guns are not particularly useful for smaller electronic projects.