Soldering alloys: classification, properties, selection criteria

POS 61

The melting point of pos 61 is 183 degrees, which is the starting point. Complete melting is achieved at a temperature of about 190 degrees, which allows you to work with it using any household soldering iron or professional soldering station. Soldering temperature is 240 degrees. This is the lowest melting point solder of the entire group of tin-lead solders.

Compound

This filler material belongs to the soft category, contains 61% tin, 38-39% lead and may contain an acceptable percentage of impurities in the form of antimony, nickel, iron, sulfur and bismuth.

Within the tin-lead group, this material is the purest solder in composition and is more suitable for electrical installation and tinning, since due to the copper content in it, it reduces the rate of dissolution of copper wires and tracks and wears out the soldering iron tip less, and the relatively low melting temperature does not harm printed circuit board.

Material characteristics

1. The melting point is 183 degrees.
2. Melt temperature 190 degrees.
3. Density 8.5 g/cm3.
4. Resistivity - 0.139 µOhm/m.
5. Tensile strength - 4.3 MPa.

Available in several varieties, which differ only in appearance:

• In the form of wire - section thickness approximately 2 mm, the most convenient and common option. Wire with flux inside can also be found. The role of a flux is played by pine rosin, which works well when soldering electrical connections, since it does not oxidize parts, unlike acid fluxes, after working with which the parts must be thoroughly washed.
• In the form of solder tape - solder in the form of a very thin long strip. Ideal for quick soldering of strands and tinning of wires. Like wire, it comes with or without flux.
• In the form of rods up to 8 mm thick and approximately 40 cm in length. These rods are convenient to use when soldering installation wires and tinning the soldering iron tip. If desired, you can make them yourself by pouring them into pre-made molds.

Use in everyday life and at work

This solder is widely used both in everyday life and in industry. The low cost of the material makes it very accessible, and its chemical composition and technical properties allow its use in solving many problems.

So, it was already said above that using POS 61 it is convenient to solder radio components, because its low melting point will not damage the printed circuit board tracks and radio components, especially microcircuits that can fail if overheated.

Also, using this material you can carry out high-quality soldering of twisted copper wires, which is actively used in electrical installations, and you can solder with both a soldering iron and a gas torch. In addition, pos 61 has very good fluidity and forms tight seams, which allows its use when welding pipes together using a gas torch.

But the low melting point also imposes some restrictions on the scope of its application - it cannot be used when working with materials that will subsequently be subject to strong heating. This can cause the weld to become distorted or even melt, ruining the entire job.

Varieties

The main type of output is wire, which is available in various diameters. The thinnest diameter is 0.5 mm. This is an excellent option for soldering wires and other small parts. For thicker workpieces, 2-3 mm wire is suitable. This is one of the most common options for home use and industry. Solder POS 40 rod 8 mm is the thickest of all varieties, while the wire has a maximum diameter of 7 mm. It is suitable for working with workpieces whose thickness is more than.

Solder POS 40 in the form of wire

In addition to wire and rods, production is made in the form of foil strips, cast flakes, and small tubes, the diameter of which reaches up to 5 mm, which already contain rosin. Sometimes there are pastes and liquid fluxes.

Solder POS 40 in the form of rods

Solder paste

Mainly used for soldering surface-mounted components (SMDs), as well as leadless chips in BGA packages.

It looks like a gray paste, consists of tiny balls of Sn62Pb36Ag2 alloy (silver 2%, lead 36%, tin 62%), and also contains no-clean flux. The fact that the flux is no-clean is indicated by two letters on the packaging: NC (No Clean). The flux containing solder balls dries in air, so the paste is stored in a closed container.

This product is used for complex cell phone repairs and for soldering microcircuits in BGA housings. Its use involves the use of additional equipment for repairing mobile phones, for example, special stencils. The paste is quite expensive because it contains silver.

Lead-free solders are now widely used in electronics production.

Solder Material Selection

One of the main criteria for choosing an alloy for creating a solder joint of metal parts is its melting point.

That is, the filler material must melt earlier than the base material. But this is not the only condition for choice.

The liquid melt should well wet the surface of the base metal. In addition, certain strength requirements are imposed on the soldered joint.

It is for this reason that when soldering any metal product, they try to use an additive based on the same metal as the metal of the product.

At the same time, the lower melting temperature of the solder is ensured by the additional components included in its composition.

However, it should be noted that it is never possible to equalize these characteristics when soldering. That is, during mechanical fracture tests, fracture will always occur at the joint.

In some specific types of soldering, the strength of the connection does not play a major role. For example, when soldering jewelry, the main thing is the aesthetic part of the work. Therefore, products made of gold, silver and platinum are soldered only with solders based on the same metals, and of the same standard.

Warming up

Depending on the melting point of the filler material used, different heating methods are used during soldering. In the case of soft materials containing tin, zinc, and lead, the main tool for soldering can be a regular soldering iron.

An example is the assembly and repair of electronic circuits containing components that are critical to overheating. In this situation, lead-tin materials with a low melting point and low-power electric soldering irons are usually used.

The mechanical strength of the connections plays a secondary role here; the main thing is to ensure reliable electrical contact.

When it comes to soldering with high-temperature materials, the soldering iron is powerless. In these cases, heating is carried out using gas burners and special installations using high-frequency currents.

This applies to industrial soldering in production workshops and the use of hard solders.

In some cases, when the parts to be soldered are very massive, and using conventional heating means it is not possible to achieve melting, special furnaces are used, where the workpieces are placed entirely. This is the only way to ensure reliable soldering.

General information about soldering

What is more important in a soldering job: the tool or the material? Everything is important: the soldering iron, the solder, and the flux. The variety of soldering irons is related to the object of soldering. Massive parts are heated with powerful soldering irons, and microscopic circuits of chips are heated with low-power ones. Professional soldering workers use several types of these heating tools.

Classification of soldering irons by power:

• A soldering iron with a nichrome insert with a power of 25 watts is a common household tool used by craftsmen, radio amateurs, and electronics engineers. They are still popular to this day, quite cheap, and last up to 10 years. A metal insert in the form of a copper rod, the tip of which is cut at 60 degrees. It is used in 90% of cases that arise in business situations; even many repair shops use them.
• The second type is more powerful with a 40-watt heater and a nichrome insert, twice as heavy and larger than its 25-watt counterpart. Used for more complex work. The tip is sharpened into a wedge, similar to a screwdriver, but it cannot be used for screwing screws. This sharpening is made for the convenience of soldering massive parts, for heating up to 190 C. They are used by professionals, but not recommended for home use.
• The third type is a gas soldering iron, three in one. The soldering iron itself has a copper core sharpened for a needle. The second function is a hair dryer that can heat an object up to 600 degrees. Gas burner - in this case the nozzle is changed, the tool performs the functions of a gas burner, heats the parts to a temperature of 1300 degrees.
• The fourth type is a modern ceramic soldering iron. Champion compared to all presented instruments. It has a very thin tip, capable of soldering millimeter dots, and is used to perform very precise work. Power - 100 watts. It is equipped with a soldering station with a temperature range from 200 to 480 degrees. Among specialists it is used as a universal tool.

Group of special alloys

When antimony is added to metal compositions in small quantities, the strength of seam joints significantly increases.

The material is marked “POSSU” and has a melting point from 189 ℃ (for a composition with a trace antimony content) to 270 ℃ (for a solder with an antimony content reaching 4%, in some even 6%).

Materials of the first subgroup with an additive concentration measured in hundredths of a percent are low-antimony grades.

Such solders are used in the aircraft and automotive industries, in the production of refrigeration equipment, and food utensils that are subject to subsequent tinning.

Table 1. Low antimony solders:

Metal tin-lead compositions with an antimony concentration from 1.5% to 6% are called antimony. They are recommended for use in electric lamps, tubular radiators, and tinplate.

The addition of antimony makes the tin-lead material cheaper, but soldering is more difficult. A slight change in the tin-lead composite significantly reduces the wetting properties of the melt. Only professionals can work with this consumable.

Table 2. Antimony solders

How POS stands for

Let's consider the main brands of tin-lead and tin solders, which are widely used today in soldering. To mark all solders containing lead and tin, a special abbreviation is used, consisting of Russian letters and numbers.

The letter “P” means solder, the letter “O” means tin solder, and the letter “C” means lead solder. The number at the end of the abbreviation POS means one thing - the percentage of tin content. For example, POS-61 or the so-called “Tretnik” contains 61% Sn, that is, tin.

Specifications

Solder for soldering POS 61 is quite common in our country. It is widely used both at the industrial level and in domestic conditions. Its distinctive feature is that due to the high percentage of tin in the chemical composition, its temperature point at which the material begins to melt is very low. It is worth noting that this solder can be classified as one of the most fusible consumables for soldering. This category includes all filler materials whose melting point is less than 450 degrees Celsius. POS 61 melts at temperatures below 200 degrees Celsius. This model is produced in our country in strict accordance with government standards.

Due to the properties described above, the filler material of this model has increased fluidity. In some cases, this property is considered a disadvantage, but not in this case. Due to the low melting point and high fluidity of solder, you can work with it with almost any equipment, from an ordinary household soldering iron to professional specialized units. During the soldering process, solder is able to penetrate even the smallest cracks and recesses, which, of course, allows you to raise the level of quality of the final result of the connection, in particular its strength.

The filler material also interacts well with water. Due to good wetting, soldering using solder of this model does not cause any difficulties during operation. All chemical, physical and mechanical properties of a consumable material are determined by its chemical composition, or rather by a certain ratio of elements in it. Even if you change this value by just one percent, all the characteristics of the material can change dramatically. In addition to the main elements in the composition, additional substances can be added to its structure, which can improve one or another specific characteristic of the solder.

This filler material can be used when working with microcircuits, since the low melting point will not cause technical problems, and most importantly, it minimizes the risk of damage to the thin surface. Unlike other solder models, which work with high temperatures, which can damage the condition of the working surface, using POS 61, with the proper skill and equipment, is absolutely safe even for the thinnest metal.

The low temperature point at which the material begins to melt helps achieve another important property of the material. It lies in the fact that in addition to its main use as a consumable for soldering, it can be used as a substance for tinning a soldering iron and working surface

There is a characteristic feature, the essence of which is that the less lead is present in the chemical composition of the solder, the more various additional elements there are. The rarest element, which is found quite rarely in alternative models, is antimony. Its presence makes it possible to obtain connections with the maximum level of tightness, which significantly improves the quality of the final result of the connection as a whole.

Solder POS 61 GOST 21931 76 is very often used in the process of repairing pipelines and other products whose working activities are carried out in constant contact with water and other various liquids. The high level of popularity is due to the ease of use of this material model.

Classification

All criteria for classifying solders represent a rather broad area, which, perhaps, can only be done by highly specialized specialists. Therefore, to simplify the selection, specific brands are made for specific purposes - soldering aluminum, jewelry, copper wire, radio components, etc. The main thing you should pay attention to is the temperature parameter. Since, for example, soldering a microcircuit cannot be done with the same brand of PIC as the connection of cable cores, since the sensitive component may burn out and fail.

Solders for soldering are classified according to the following criteria:

• according to the method of supplying flux - flux-free and self-fluxing, for the former the flux is supplied separately, for the latter they contain it in their composition;

Rice. 1. Self-fluxing and with flux feed

• according to the main soldering element - tin solders, nickel, cobalt, manganese, titanium, silver, zirconium, vanadium, mixed, etc.
• according to the method of production - they are ready-made or formed directly during soldering;
• according to the solubility of components - there are completely melted and partially melted;
• by release form - tin wire, rod, ingots, sheet, granules, paste;

Solder release form

• by melting point - there are those that turn into a liquid state at low and high temperatures.

When choosing tin-lead solder, the most important criterion is the last one, so we will dwell on it in more detail.

Low-melting (soft).

Low-melting solders include those compositions that turn into a liquid state at temperatures from 145 to 400°C. But, at the same time, they provide relatively low strength; for low-melting alloys, the tensile strength is no more than 7 kg/mm2. The most common are tin-lead. Most often, soft solders are used in electronics for printed circuit boards or parts.

Refractory (hard).

Hard solders have significantly greater mechanical strength, but their melting point is more than 400°C, which is unacceptable for most radio components, since they can be damaged even if touched by a heated soldering iron tip. The two largest groups in this category are copper and silver compounds. Copper alloys are generally combined with zinc, but are too brittle and are therefore suitable for carbide alloys that only experience static loading. Silver solders are universal and can be used for soldering any connection points, however, the cost of these brands is also quite high.

Solder pastes.

Solder pastes are also a component for soldering radio components, but they are used for small elements made of low-melting metal. The paste composition contains crushed pieces of solder in a solution of liquid flux. They are used in those boards or devices where exposure to high temperatures can harm the equipment. Pastes are typically soldered with a hairdryer without an electric soldering iron, or can simply be applied as a conductive adhesive.

The soldering mixture is applied to the point where the leads are attached in batches and can be done using a special stencil, syringe or drop-jet cartridge.

Fig 3. Applying solder paste with a printer, syringe, stencil

However, the use of soldering paste imposes a number of requirements that must be met:

• before opening the container, be sure to keep it at room temperature for at least 2 hours; using means of forced solder heating for this is prohibited;
• after opening, the mixture must be mixed until a homogeneous substance is obtained, since during storage the flux can separate from the solder;

Rice. 4. Stir until a homogeneous mixture

• before application, the surface must be cleaned of possible impurities and contaminants; during long-term soldering, the procedure is repeated every 45 minutes;
• installation of electronic components in the applied paste must be carried out within 60 minutes, otherwise it will begin to lose its properties;
• after soldering, the remains and excess paste are washed off, there are those that can be washed off with plain water, others require a solvent, some may not be washed off.

The functional characteristics of such solder are extremely negatively affected by placement in an environment with high or low temperatures, as well as exposure to moisture.

Lead-free solders.

Initially, the reason for creating lead-free solder was the need to eliminate harmful effects on the environment and the human body. Such solders are widely used for soldering aluminum or steel in the food industry, for drinking water supply pipes, laboratory equipment and tools.

In total, there are three most common groups of lead-free solders:

• tin with copper - used for high-temperature soldering, refers to refractory solders, well suited for working on copper products;
• tin and silver - suitable for low-temperature soldering, provide better contact than lead solders, but they are expensive.
• tin with both copper and silver is also a soft option, which has a lower cost than the previous one and is practically in no way inferior to it in the quality of connections.
• tin with bismuth and silver - can be used for soldering copper at low temperatures;
• tin with zinc and bismuth is a cheaper version of the previous one, but has a number of difficulties in use.

Composition and characteristics

Chemical components

It was previously mentioned that PIC solder consists of an alloy of tin and lead. Tin has a lower melting point than lead, so by varying the percentage of these two components, you can select certain temperature characteristics. POS 60 has the following chemical compounds in its composition:

• Tin. The share is 59–60.5% of the total mass.
• Lead. The percentage content ranges from 39 to 40.5% by weight of POS.
• Impurities. They are represented by various elements such as copper, iron, antimony, nickel, zinc and others. Their mass fraction is no more than 0.3% of the total mass of the alloy.

Chemical composition of POS61 solder

Other metals also influence the technical properties of the solder alloy.

Physical properties

The large amount of tin contained in this brand of solder directly affects its temperature characteristics and physical properties. Thus, POS 60 has the following properties:

• Melting point 183-190 degrees Celsius.
• Density 8.5 grams per cubic centimeter.
• The resistivity is 0.137 ohms per meter, which is 9–15% of the conductivity of copper.
• The tensile strength corresponds to the limit for soft solders and is equal to 50–70 MPa.
• The Brinell hardness is 14.9 PV.
• Thermal conductivity is 0.117 W/(m×k). Tensile strength is 4.3 kg/mm.

Physical properties of POS 60 and other solders

It is worth noting that tin and lead are identical in both softness and viscosity. Both of these metals have a characteristic of 1.5 on the Moss scale, so their percentage does not affect the physical properties of the solder.

Basic properties of solders

When choosing a specific brand of solder for soldering copper wires or aluminum alloys, you must be guided by their technical characteristics.

However, for all compositions a list of basic properties can be identified:

• wettability - shows how well the solder envelops and sticks to the parts being soldered;
• strength - determines the ability to withstand mechanical forces and loads; for this, boron, iron, nickel, zinc or cobalt can be added to the composition;
• plasticity - the ability to deform, achieved through additives from manganese, bismuth, lithium, etc.;
• resistance to high temperatures - important for soldering with hard alloys that are found in boiler rooms, furnaces, pipelines, heating devices, the property is achieved by adding tungsten, zirconium, vanadium, hafnium, niobium, etc.
• resistance to corrosion destruction - increases by alloying with copper or nickel.