Soldering - an old method of joining

Welding of two metal parts

As far back as five thousand years BC, soldering was a very popular technique for joining materials. Archaeology knows of many instances of artefacts made of precious metals using this technique. Nowadays, brazing is the most popular method of joining material parts next to welding. This technique consists of joining components by means of solder, which is a metallic bonding agent. Its melting point is lower than that of the components to be soldered. To perform brazing correctly, the solder must be soldered at a temperature above the melting point, but not above the melting point of the materials to be joined. Brazing is used for metals and non-metals (glass, ceramics, graphite). It is possible to join not only homogeneous materials, but also materials that differ in structure. The biggest difference between brazing and welding is that welding produces very high temperatures, which melt the additional material and the edges of the parts to be joined. A permanent connection is ensured by the creation of a adhesion and diffusion. In order to form a soldered joint, there must be a metallic bond between the solder and the components. To achieve this, the liquid solder must wet the materials to be soldered. Soldering is divided according to the melting temperature of the solder into: 

  • high-temperature brazing (from 900°C upwards) 
  • brazing (above 450°C) 
  • soft soldering (below 450°C) 

Solder, also known as solder, is the material used for joining, and the tool for soldering is a soldering iron or torch. Special ovens can also be used in this process.

Desoldering 

In order to reverse the soldering, the following are used desoldering. This is a reverse process and is used to repair or replace soldered components. It is an essential activity for repairing equipment. To desolder we can use a soldering iron or a desoldering iron, usually together with a tin extractor. To remove the tin, a soldering iron or desoldering tape is used. When it is difficult to disconnect components and there is a risk of damaging one of them, specialised tooling should be used. 

Soldering in industry 

Industrial mass soldering of components created by the through-hole assembly technique is carried out using the so-called "wave" method. This involves moving the printed circuit when all the necessary components are already inserted. A transverse hump is formed on the surface of the solder, which is placed in the solder receptacle. This is how a wave is formed, the top of which contacts the underside of the moving PCB and the parts made of metal are covered by the molten solder. Once the solder has cooled down, it forms a very good quality connection. Non-contact soldering involves heating components with warm air or infrared. It is used for printed circuits. In this situation, the flux and solder are applied in paste form to various areas of the circuit. When everything is in place, the board and other components are heated up with the aforementioned hot air or so-called infrared heat. infrared heater. Later, the circuit is cooled, the solder coagulates, the joints cool down and the process ends. Modern soldering stations that use hot air are called hot air. In them, a pump generates an airflow, which is then heated to a specific temperature. Everything is supervised by a microprocessor, whose tasks are to regulate the temperature, air flow and operating time. To regulate the air flow as desired, nozzles are used. 

Lead-free soldering 

Disconnection process

This type of soldering is carried out with a lead-free alloy. On 1 July 2006, the European Union introduced a restriction on the use of hazardous substances, including, for example, lead in solders. Developments in technology have necessitated a change in the parameters of equipment or its complete replacement in order to comply with the new requirements. In lead-free technology, there are some obstacles that hinder the whole process, such as: 

  • the chance of so-called tin blight occurring at low temperatures, 
  • the presence of tin whiskers, which lead to short circuits and various types of damage, 
  • increased solder flow temperature. 

There is a risk of capillary beads forming on resistors and capacitors, which can vary in size depending on how they were formed. The causes of this phenomenon are: 

  • hot slip, 
  • too little flowability, 
  • flux wettability. 

For this type of soldering to take place, temperatures in the range of 215- 220°C. Due to the matt and granular surface of lead-free solder, it is difficult to detect a bad connection or so-called cold solder.  

Soldering under the influence of nitrogen 

This type of process involves introducing nitrogen where the solder melts. This improves the performance of the joint. Nitrogen atmosphere brazing is used in mass production as well as in manual work. 

Soft soldering 

This type of soldering takes place at a temperature that does not exceed 450°C (usually around 320). It involves joining a metal with a lower melting point than that of the metals being joined together. This technique is used at low operating temperatures, that is, for example, in electronic circuits, electronic wires, sheet metal, etc.  

The most common metals used in soft soldering are steel, brass, zinc or copper. Soft solder melts at a temperature of 183- 280°C. They can be found in the form of wire, plates, powder or sticks. The most common alloys used in brazing are tin, bismuth, cadmium and antimony. Flux is used to lower the melting point of the solder, stop it oxidising and improve penetration into hard-to-reach metal structures. Fluxes are very often encountered in the form of various caustic liquids, a special paste or in solid form. 

Brazing 

Connected soldering iron

The type of soldering taking place at temperatures above 450°C. Hard solders are used in its manufacture. By means of brazing carbon, tungsten, molybdenum or nickel steels are combined. In addition, they are used with gold, silver or copper. The brazing process uses acetylene-oxygen burner or a soldering lamp. It is also possible to solder inductively with an electric current or on a smithing fire. It is very important to use the right fluxes, which serve to dissolve the metal oxides, making it easier for the solder to dissolve and penetrate more thoroughly into all crevices. In addition, they prevent oxidation of the entire process. 

Difference between soldering and welding 

During the welding process, both metals melt through the heat generated. This is due to the formation of an atomic bond, which greatly improves the bonding effect. Soldering, on the other hand, does not create this kind of bond, which means that a third metal, called solder, is needed to join the parts together. After welding, a thick and ugly-looking seam is left which has to be masked later. Solder, on the other hand, provides a better and less conspicuous effect. Soldering also takes less time than welding, which is definitely in its favour.