Types of solders for soldering, their use and purpose

To create a tight, reliable connection between metal parts, soldering is most often used. The essence of the process is to bond materials when heated using an alloy - solder, the melting point of which is lower than the melting point of the substances being joined. When heated, solder, spreading between the joined areas, ensures strong adhesion (sticking) of metals to each other at the molecular level, which gives high strength and electrical conductivity of the connection. The molten solder should wet the metal well. That is, the connection between the molecules of a solid and a liquid must be more reliable than between particles of a liquid material. In this article we will tell readers of the Sam Electric website what types of solders there are for soldering, having examined the purpose and scope of each brand.

Varieties

Types of alloys intended for the soldering process, depending on the melting point, are divided into hard refractory and soft low-melting compositions. The former melt at 450 degrees and above, the latter below this value. Soldering with hard alloys is more durable. But soft types of solders are indispensable for radio installation work.

Soft or fusible

The most widespread are tin-lead solders, abbreviated as POS. The number indicated in the marking after the letter abbreviation corresponds to the percentage of tin in the composition. For example, POS-60 contains 60% tin. These types are used in the production of instruments and electronic devices.

POS-90 contains only 10% toxic lead, so this variety is used for repairing food utensils and medical instruments.

POS-40 is used for soldering brass and copper pipes, electrical equipment, and elements made of galvanized iron.

POS-30 is used for soldering zinc sheets, in the cable industry, and for soldering galvanized iron.

POS-61 is used for soldering radio components to printed circuit boards. Its melting point is 183 degrees, and complete transition to the liquid state occurs at 190 degrees, which helps to avoid overheating and prevents failure of radioelements.

There is a universal and convenient variety POS-61, which is a hollow tin-lead tube with rosin inside. This form is very convenient, since soldering is carried out without additional flux.

The next type of POS is POSSu brand solder. In addition to the lead and tin components, it contains up to 2% antimony. This material can be used to solder the windings of electrical machines, electrical equipment elements, cable products, and galvanized parts.

The table briefly presents some types of PIC and their main properties.

Currently, lead-free alloys are widely used in the manufacture of electronics. For example, lead-free solder POSu95-5. Its composition can be determined by labeling. The number 95 means the percentage of tin, 5 - antimony. The melting point is in the range of 234 - 240 degrees.

Hard or refractory

Hard types of solders for soldering create high joint strength. The disadvantage of their use is the need for intense heating above 500 degrees, which can damage some types of devices.

Among the refractory ones with a high melting point, two groups are divided: alloys of copper and silver. Copper solders, based on zinc and copper, are used in connections intended for static loads due to their brittleness. They cannot be used to solder materials subject to dynamic shock or vibration loads.

Silver types of solders are universal; they can be used to solder various materials. The disadvantage is the high cost, so the use of the composition must be economically justified. Silver alloy is used for soldering stainless steel, copper, in orthopedic dentistry, and for repairing silver jewelry.

Compositions containing silver are designated by the letters PSr. There are markings PSr-15, PSr-25, PSr-45, PSr-65, PSr-70, where the number indicates the percentage of silver.

Low temperature

The composition of POSK 50-18 includes 50% tin, 18% cadmium, 32% lead. Cadmium enhances corrosion resistance, but makes the material toxic. The purpose of solder is the installation of components sensitive to overheating. The melting point of the material is 142-145 degrees.

The melting point of the ROSE alloy ranges from 90 to 94 degrees. This species is labeled as POSV-50. The composition contains 25% tin, 25% lead, and 50% bismuth. The percentage of metals may vary slightly. The material is produced in the form of rods, granules, pigs.

The composition is used in jewelry production, for mounting electronic devices, and tinning copper tracks on printed circuit boards. It is used in electromechanics for protective fuses and fuse links. And also for dismantling radio-electronic components and connectors with plastic cases

Benefits of ROSE:

releases a minimal amount of toxic substances, as it does not contain cadmium;
easy to melt, contact with boiling water is sufficient;
can be used at home without the use of special equipment;
economical to use.

The melting point of the VUDA alloy is in the range of 65-72 degrees, which expands the scope of its application. But 10% of cadmium in its composition makes the material toxic. The remaining components of the alloy: 13% tin, 27% lead, 50% bismuth.

It applies:

in sensors of fire alarm systems;
in microcircuits;
in galvanoplasty;
in dentistry;
for the production of cast elements;
in typography for the production of fonts, matrices, cliches;
in mechanical engineering and shipbuilding;
in the aviation industry;
in the metallurgical industry.

What is solder solder

Solder is a special alloy that is applied to metals to join them together. Pure tin is recognized as the best solder. However, such solder is very expensive to use, so tin is mixed with lead to make tin-lead solder (PLS).

This solder has a low melting point, up to 200 degrees, good adhesion to metal and softness. However, when choosing solder for soldering, it is important to consider the size of the parts being joined. For thin wires, it is preferable to use soft solder, while for thick wires, a solder with a higher melting point will be needed.

Brazing solder is characterized by greater tensile strength.

Other types

There are rare solders used for special conditions. These include:

Nickel-based compounds used in parts operating at high temperatures;
gold, used for vacuum tubes;
magnesium, used in ferrous and non-ferrous metallurgy.

We will give examples of some of them, since there are a lot of them and it will not be possible to consider all types within the scope of the article.

Solder paste

Soldering microcircuits, installing SMD components on printed circuit boards, and complex repairs of mobile phones can be carried out using soldering paste consisting of no-clean flux and Sn62Pb36Ag2 alloy. The composition contains 62% tin, 36% lead and 2% silver.

The paste meets the basic requirements imposed on it by surface mount technologies (SMD components) in the electronics industry.

For aluminum

Lucas-Milhaupt Filalu 1192 NC solder has good fluidity and high adhesion to aluminum. They can be used to solder refrigeration equipment, car radiators, and air conditioners. Soldering aluminum to aluminum will not cause any difficulties even for non-professionals. Available in the form of a rod with flux inside. Melting point 577 degrees.

Composition structure: Si-11.94%, Fe-0.18%, Cu-0.01%, Mn-0.03%, Mg < 0.01%, Zn-0.01%, Al-rest, Flux – 32%

For copper

Almost any type of copper, both soft and hard, is suitable for soldering copper. For example, you can use solders made of tin, lead, zinc, and silver.

Flux for soldering with a soldering iron

An auxiliary substance that promotes the spreading of soldering materials over the surface of the parts being soldered is flux. High-quality connections are created by solders and fluxes ; without one of the components, soldering is impossible. A common type of flux is rosin, made from hard coniferous trees. Softening occurs at 50 °C, and when the temperature reaches 250 °C, the process begins to boil the composition.

Flux for soldering aluminum

Due to the hydrolysis provided for in the manufacture of rosin, the material is not resistant to atmospheric influences. After soldering, it is necessary to remove flux residues, because... the compound may undergo an oxidation process. By absorbing moisture from the atmosphere, rosin can disrupt the operation of radio components.

Popular fluxes for soldering with an electric soldering iron

Soldering of metal joints occurs using various substances. Fluxes are divided into three main categories, differing in their area of application and method of preparation. The process of preparing elements for work may vary; after soldering, it is necessary to remove residues in the manner described in the instructions.

Inactive rosin fluxes are used for soldering copper and other types of soft metals. There is a light rosin that is ready for use and does not include additional substances. Alcohol-rosin solution is made from components with a concentration of 1 to 5. It is used for soldering in hard-to-reach places, it is produced in powder form, and must be mixed with alcohol before use. Glycerin - rosin materials are used when a hermetic connection is necessary.
Active fluxes suitable for soldering precious and non-ferrous metals include zinc chloride, alcohol or petroleum jelly. The last parameter differs in its composition, when used in a liquid or paste state. It is more convenient to work with flux as a paste; it is possible to apply it directly to the product in the required amount.
Acid-active flux is divided into zinc chloride and phosphoric acid. It is performed in the form of liquid solutions or paste, using rosin, zinc chloride, alcohol or petroleum jelly.

Orthophosphoric acid

Orthophosphoric acid consists of water, ethyl alcohol and the acid itself with a density of 1.7. It is used for soldering stainless materials, copper, and silver. Alcohol-based fluxes must be stored in airtight containers. A convenient container for storage is a nail polish jar, the brush does not react to the active medium, and the lid allows you to tightly close the container, avoiding evaporation of the components.

Tinol soldering pastes for soldering

Among the substances offered, there are solder pastes that are produced with a mixed type of flux. It is used when installing open-frame elements in hard-to-reach places. Application occurs with a special spatula, then heating with an electric tool. The result is a reliable, high-quality connection, which is actively used by novice craftsmen in the absence of appropriate experience.

Tinol pasta

It is possible to prepare an alloy for soldering with your own hands; for this you will need the solder required by the element. Using a medium-grain file, tin for soldering in the form of wire is crushed to the state of metal chips. A flux selected from the above in a liquid state is added to the composition, after which the elements are mixed. The composition must be prepared in a small container, the shelf life is limited to 6 months, after which the metal oxidizes in an acidic environment.

Bottom line

A great variety of solders for soldering various products are produced; listing them in the scope of one article is simply not realistic. But to summarize what has been said above, we note:

To install radio-electronic components, radio amateurs use the relatively low-melting POS-61; parts on lead-free solder are soldered by preliminary tinning with ROSE alloy to reduce the melting point; subsequently the parts are easily dismantled. Hard-melting grades are used for pipes and refrigeration equipment.
The alloy composition should not contain toxic substances in excess of the established norm. Work should only be carried out in a ventilated area, observing safety precautions.

Low-melting solders for radio components

Ultra-low-melting solders can also be included in a separate category, which in their composition, in addition to tin and lead, contain substances such as cadmium and bismuth. The heating temperature of these solders is less than 100 degrees. These are very soft solders that are unable to provide greater mechanical strength to the metal connection.

Ultra-low-melting solders are used where it is important not to overheat radio components, for example, when soldering transistors. For example, Wood's solder has a melting point of only 75 degrees. It is widely used by radio amateurs for soldering transistors and microcircuits at home.

Solder pastes

Thanks to the development of new technologies and the increasing scale of growth in the production of electronic circuit boards, solder pastes began to be used as a soldering element. The paste is made from several components: powdered solder, flux and a binder. This fine mixture is used in manual and screen soldering.

For soldering radio electronics, pastes contain tin and alloying components to improve the quality of the connection. The properties of ductile solder are significantly affected by particle size. The most common pastes are those with particle sizes in the range of 25-45 microns. Since this technology is used more for stencil soldering than for hand soldering, pastes must meet established requirements for reliable mating of elements.