DIY soldering acid. Making at home

Rations. This method connecting several parts together is considered one of the most reliable and simplest.

The soldering process is a series of technological activities that result in a practical and durable connection. Such operations are possible only if special solders and fluxes are used, which serve as a binder. Thus, the quality of the connection will directly depend on the properties and characteristics of the resulting joint.

This method of connecting two or more parts was developed by the Egyptians more than 5 thousand years ago. At the same time, a list of materials that were fastened using a similar method was compiled. It is fair to note the fact that this list of metals is still widely used in production.

In addition, soldering acid is distinctive feature soldering process from the welding process. Let's look at these concepts in more detail. Welding of parts occurs by heating their edges to the melting temperature and subsequent fusion of these edges into a single whole. At the same time, soldering parts is nothing more than the usual heating of the required parts of the parts and further fusing a substance called “rosin for soldering” onto the formed heated space. In this case, the edges of the metal parts do not change their properties, but are only subjected to heating. It should be noted that an easily meltable special substance is used to join materials. Due to their excellent characteristics, products connected using the soldering process are sometimes even stronger than when welded.

Soldering acid has only one drawback: due to some features, the connections obtained in this way are non-separable. This means that replacing worn parts is impossible.

As a result of the development of plastic parts, soldering and welding connections are being used less and less in manufacturing plants and in everyday life. However, such processes are still indispensable for the repair of metal parts.

The soldering acid determined for a particular part material may differ slightly in composition. Just like solders, which are an alloy of two metals that have low and similar melting points. In technical language, such a range is called the melting zone.

All substances used to join parts are divided into three categories, thanks to which it is possible to obtain hard or soft soldering, as well as high-temperature soldering. It should be noted that the latter variety is prohibited for use in domestic conditions precisely because of the high temperatures.

Hard soldering provides connections with high strength and refractoriness. In some cases - malleability. At the same time, soft soldering (the main area where soldering acid is used) gives the material elasticity and flexibility.

Soldering acid (also called etched acid) is used in the preparation or repair of various metal objects or devices, when some parts or small parts need to be connected to each other very firmly.

Not everyone knows what soldering acid is, why it is needed, where you can get it and the principles of working with it.

In order to understand the full range of “possibilities”, you need to know the difference between two methods of joining metals: welding and soldering.

Welding is the process of heating metals to their melting point with their subsequent joining to each other through interatomic bonds of molecules.

Soldering same - a completely different process of joining metals, in which two bodies, relatively speaking, made of different “rocks” of metal, are connected to each other by laying another material, naturally molten, whose melting point is much lower.

The main thing in this matter is to provide this “lubricant” to the surfaces of both parts that need to be connected.

Necessary procedures before work

Before soldering, as before any other work, It is necessary to perform a number of procedures that contribute to a better result of the work:

The concept of soldering acid

Otherwise, this is called zinc chloride water solution. This mixture contains zinc and chlorine. The chemical formula of this solution is ZnCl2 .

The mixture is sold in ready-made packaging in stores such as “radio technicians” or others related to small parts and mechanisms, but soldering acid with your own hands can be no worse than purchased one. It will be much more difficult to prepare it than to buy it, because it is sold as freely as aspirin in a pharmacy, but the manufacturing process can be interesting. The most necessary “ingredient” is acidic saline solution. However, instead of fiddling with preparing it, it is better to use ready-made products.

We must remember how to use soldering acid. It must be used correctly and carefully, without contact with skin or other objects. Its use should occur only within the workplace, without spreading it over a large area.

Storing it in its pure form is very dangerous, and the composition of soldering acid itself is extremely harmful.

DIY soldering process

This process requires a little perseverance, because soldering is a small job on which you need to focus all your skills to get it done exactly as needed. And now about how to properly solder with a soldering iron with acid:

1. To begin, apply a couple of drops to perfectly clean surfaces of materials. It is best to use a bottle with a “spout”, from which the acid will be released dropwise. If you don’t have such a bottle at hand, you can replace it with any bottle of nasal drops. In order for the solder to lie evenly, the acid must cover the entire surface of the metal uniformly. The process of melting solder with a soldering iron tip and then applying it is called tinning.
2. After use required quantity acid must be carefully removed from the surface, otherwise it will begin to react with the surrounding oxygen and react in the form of rust.
3. After completing the work, you need to wipe the soldering iron tip.

Types of acids:

In general, there is not much difference which flux to choose, the only difference is the danger of working with them. However, you should adhere to some rules. The area of ​​application is determined by the intensity of the solution, but it can be diluted manually if you have something.

In general, you should pay attention to the type of product. If there is sediment at the bottom of a vessel containing flux, then it is better not to use such a product. It is also important to pay attention to the expiration date. Each acid has a certain shelf life and use. It is important to understand that you should not take such things “in reserve”, because one jar of flux can last for several months, even with intensive use.

You should also be careful when choosing a soldering iron. Available different types this tool. However, before choosing a soldering iron and rosin, you should make sure that you need soldering and not welding.

If soldering technology is followed, they allow you to obtain high-quality and durable connections for difficult-to-solder materials.

The composition of fluxes created using acids may vary depending on the area of ​​their application. Different kinds fluxes have their own characteristics that should be taken into account when soldering certain metals.

If we talk about soldering acid in general, it is a solution of acid in various substances. Acid in its pure form is practically not used for soldering, since, being an extremely aggressive chemical compound, it can have a destructive effect on various materials, including metals.

It is not recommended to use soldering acid when working with printed circuit boards, since thin connection buses and contacts of radio components are not able to withstand such aggressive influence. The best option for soldering radio circuits is fluxes created on its basis.

Types and chemical composition of soldering acids

Let's present the most common acid-based fluxes

Flux based on orthophosphoric acid

Phosphoric acid is an inorganic chemical compound of medium potency. This is a colorless substance, however, sometimes light yellow stains can be observed in it. To obtain flux, phosphoric acid can be diluted with water, ethanol, alcohol, and other solvents.

Flux based on hydrochloric acid.

Due to its high aggressiveness, hydrochloric acid in its pure form is not used for soldering. In most cases, it is diluted with water in various proportions. To improve the adhesive properties, zinc can be added to the solution. This type of soldering acid is used to create solder joints from the most difficult metals.

Sulfuric acid based flux

Sulfuric acid is an oily substance without color or odor. Sulfuric acid flux is made by diluting it in water or sulfuric anhydride in certain proportions.

Depending on the scope and technology of application, the ratio of acids and solvents in fluxes can be different - the acid content in them ranges from 25% to 85%.

Selection of acid fluxes

Before making a choice in favor of one or another soldering acid, you should determine exactly what problems will be solved with its use. Based on this, it is necessary to choose a flux with the most suitable composition.

A solution with orthophosphoric acid is optimal for soldering metals affected by corrosion. This substance effectively fights oxides, which allows you to obtain a fairly high-quality compound.

Fluxes based on hydrochloric acid are considered universal; they can be used for soldering a wide range of ferrous and non-ferrous metals, as well as alloys. For soldering large-scale parts, concentrated hydrochloric acid is used, since in such cases its aggressiveness is not critical for the safety of the metal.

In all cases, the choice of acid concentration in solutions must be correlated with the cross-section or thickness of the parts to be soldered.

An important indicator of the quality of solutions is the presence of sediment in them. In fluxes, the presence of a minimum amount of undissolved substances is acceptable, but their abundance indicates poor quality of the solution.

For specialists whose main activity is soldering, soldering acid acts as a flux. When used correctly, it can be used to increase the soldering properties of the material, which entails obtaining a high-quality connection that will last for decades.

Depending on the variety, the composition of soldering acid may differ. This affects the scope of its application and the quality of work performed with it. The characteristics of some properties of a given substance may be repeated, regardless of its composition, but each of them has its own characteristics.

General information about acid

When choosing a soldering flux, the quality of the composition should be a priority, regardless of the type of work performed. As a rule, the solution consists directly of the substance itself and the solvent in which it is dissolved. This is due to the fact that the use of 100% concentrate is not always acceptable, since the acid solution is a rather aggressive environment and can damage the material to which it is applied.

This is especially true for radio circuits, since elements of small contacts and adjacent leading parts can be damaged and dissolved. In this regard, specialists use pine rosin for soldering such devices.

In addition to damage to small parts, negative impact Soldering acid may have an effect on human health. Basically, the solution is supplied in small containers with a volume of 10 to 20 ml. For rare works this volume will be sufficient. It is not worth purchasing large volumes of the substance for periodic soldering, since without timely use its validity period may expire. For industrial scales, it is advisable to use bulk containers. However, regardless of the amount of substance used, it is important to ensure proper storage at a given temperature to avoid its spoilage before the expiration date.

Thanks to the aggressive environment of the substance, oxide films and other types of plaque formed on the metal surface are eliminated. Certain types of flux can be used as a solution to remove rust from materials. A solution that gets on a metal surface affects all the substances that are present there. This is how the oxides are destroyed. During the cleaning process, a protective layer is formed that prevents the metal from the subsequent appearance of an oxide film. The correct production process is carried out taking into account GOST 23178-78.

Type and composition of soldering acid

Orthophosphoric acid

It is an inorganic compound that has a characteristic average strength of action. The formula of this composition can be written as H3PO4. In most cases it is colorless, less often found in the form of a solution with a light yellow tint. The main features of the substance include its ability to transform into a pyrophosphorus cyst (H4P2O7). When a substance is exposed to water, ethanol and other solvents, it dissolves. This composition contains zinc chloride in the amount of about 50%. Also acceptable is insoluble sediment in a proportion of 0.001%, and ammonia no more than 0.5%.

Sulfuric acid

The composition of sulfuric acid can be expressed in the formula H2SO4. By appearance It is a gray oily liquid that is odorless. Before soldering, the substance must be diluted with water or sulfuric anhydride SO3. The use of this dibasic substance is widespread in various fields.

The ratio of the amount of acid and the substance in which it is diluted, that is, in water, alcohol, ethanol or other material, may differ. The ratio range is between 25-85%. In some cases, if you have the appropriate materials, you can dilute everything yourself.

Hydrochloric acid

It has the simplest composition compared to similar substances. It is a compound of hydrogen chloride HCl and is a strong one-compound acid that is mainly diluted with water. Zinc can be periodically added to it to improve the properties of the material. The characteristics of a substance are determined by the concentration of the compound. In the form of a pure solution, hydrochloric acid solution is used extremely rarely, due to its causticity.

If there are iron impurities, the solution becomes yellowish. The use of a solution allows you to solder the most complex metals.

How to choose soldering acid

It is noteworthy that if in a substance in large quantities If visible sediment is present, then it can be argued that the acid used is of poor quality or old.

It is necessary to choose a flux taking into account the area of ​​its application, since this determines not only its constituent components, but also what intensity of the solution should be.

1. Orthophosphoric. Often used for rusty parts, where oxides need to be removed from the metal surface.
2. Solyanaya. Designed for any type of work, as it has a wide range of actions for processing ferrous and non-ferrous metals, as well as their alloys.
3. Sulfuric. It is quite aggressive, which is why it is used less often. It allows you to work well with parts that are difficult to solder and workpieces of large thickness, since the negative impact of the substance is not dangerous for them. Due to the high aggressiveness of sulfuric acid, it is used for parts that are difficult to solder, as well as for workpieces of large thickness, since it will not cause much harm to them.

It is necessary to select a solution taking into account the thickness and dimensions of the parts being processed. At the same time, when working with contacts and delicate elements, any acid must first be diluted.

Video “Making soldering acid with your own hands”

All existing metals, as well as their alloys, can be connected to each other using two different technological processes. We are talking about welding and soldering. Welding of metals means short-term heating of two metal surfaces at the point of contact to the maximum high temperatures. At these temperatures, the surfaces to be joined undergo complete melting. As a result, a connection of two metals occurs at the level of interatomic bonds of the crystal lattice. The consequence of this process is a monolithic welding seam, whose strength sometimes even exceeds the strength of the metal products being welded themselves.

Soldering is a completely different process. It does not affect the internal structure of the metal in any way. It occurs exclusively on the surface of the materials being soldered. No monolithic connections at the atomic level are formed during soldering.

To perform soldering, the presence of a third, lower-melting metal, which is called solder, is necessary. With the help of solder, the soldering process occurs directly. Pure tin or its various alloys are most often used as solder. The task of any soldering is to melt the solder and ensure its good spreading over the surface of the metals being soldered. As the solder hardens, it changes from its liquid molten state to a solid state and provides reliable connection two metal products.

In practice, everything turns out to be a little different. The fact is that all metals, without exception, have a fairly hard and chemically inert oxide film on their surface. The strength of this film varies among different metals. The most durable oxide film is formed on the surface of aluminum. This film, as well as all kinds of mechanical impurities that are always present on the surface of any metal, lead to the fact that the solder does not want to spread over the metal.

That is, in professional terms, Tinning of the metal does not occur. Instead, the solder becomes a moving ball that rolls around the metal surface without connecting to it in any way. This suggests that the surface tension of the molten solder is much higher than the adhesion (sticking) of this solder to the metal surface. To enhance the adhesion of solder and ensure reliable soldering of two metals, so-called fluxes are used.

Acid fluxes

Why are fluxes used? The task of any flux is to:

• Dissolve the surface oxide film on the metal.
• Clean the surface from mechanical contamination.
• Prevent oxidation and the formation of a new oxide film.
• Reduce the surface tension of the molten solder, thereby facilitating its free flow over the metal.

Rosin

Among radio technicians, the most common flux is rosin. It's essentially resin coniferous trees, from which the turpentine was removed by an evaporation process. It is widely used due to its low cost, ease of storage and chemical inertness. Rosin is used as a flux for soldering products made of copper, brass, silver, and nickel. That is, those metals on the surface of which the oxide film is not very strong and is quite easily destroyed by the weak influence of molten rosin.

But when it comes to metals such as aluminum, cast iron, all kinds of steel alloys or iron, rosin stops working and its use in these cases turns out to be extremely ineffective. The rosin needs to be replaced and the flux made more aggressive to make the soldering process easier.

Soldering acid

It is for these purposes that the so-called chemically active acid fluxes. There are several types of acid fluxes due to the fact that different metals form oxide compounds of different strengths on their surface.

The so-called soldering acid can be easily purchased at a specialized store and is inexpensive. But there is a small problem. Most often, manufacturers do not indicate the exact composition chemical substance, which they sell under the name "soldering acid". But, as you know, soldering different metals requires acid fluxes of different compositions. Therefore, sometimes it will be much more rational to make one or another flux for a specific metal at home than to buy a pig in a poke.

Zinc chloride flux

For soldering, so-called pickling acid is used. This is one of the most common acid fluxes. This is the same soldering acid that is most often sold in specialized stores. This flux is mainly used for soldering iron. For example, pure hydrochloric acid can be used to solder roofing iron. Usually this is a solution of zinc in hydrochloric acid, in other words, zinc chloride.

All the necessary reagents for this reaction can be freely purchased at a chemical store, namely: granulated zinc and chemically pure hydrochloric acid. This is the composition of soldering acid.

The proportions are as follows:

• Concentrated HCl: 1000 ml.
• Pure zinc: 400 gr.

For mixing, you must have an appropriate glass, porcelain or ceramic container.

• The zinc is first placed in the container, and only then hydrochloric acid is slowly added to the zinc in a thin stream.
• In no case should you do the opposite and add zinc to hydrochloric acid. This can lead to very sad consequences, namely the splashing of acid in all directions.
• During chemical reaction hydrogen will be released. This gas, when combined with oxygen in the air, forms an extremely dangerous gas mixture called detonating gas. This gas explodes at any opportunity. Therefore, before you start dissolving zinc in hydrochloric acid, think about good ventilation. It would be ideal to carry out the reaction outside, in the fresh air.

Olein flux

The basis of this flux is oleic acid, which is contained in olive oil or in any fat. To prepare the flux, technical olein is used, which is mixed with lithium iodide.

Suitable for both pure and aluminum-based alloys. This is the only flux that can dissolve the extremely durable aluminum oxide film, while the protective flux layer remains until the end of the soldering process.

It is impossible to make oleic flux at home. Yes, this is not necessary. It is freely sold and inexpensive.

Orthophosphoric acid

The chemical formula is H3PO4. For soldering alloys based on chromium or nickel, flux is prepared in the following proportion:

• Ethyl alcohol: 62%;
• Phosphoric acid H3PO4: 32%;
• Rosin: 6%.

Sometimes the acid is mixed with zinc chloride in a 50/50 ratio to prepare a flux for soldering iron products.

The composition consisting of H3PO4 25% and diethylamine hydrochloride 75% is called active flux F-38N, which is used for soldering copper alloys, as well as medium-carbon and low-carbon steel. Solders pure copper well, as well as iron, steel and nickel-containing alloys.

Based on this acid, you can make any fluxes for soldering almost all types of metals, except aluminum, at home. The only problem is that acquiring pure acid is quite problematic.

Salicylic acid

Or the well-known aspirin. Purchased in tablet form at your nearest pharmacy. It costs a penny.

It belongs to the so-called inactive fluxes, that is, after soldering is completed, salicylic acid does not affect the contact point in any way and therefore no additional treatment is required after soldering to remove flux residues. Moreover, after hardening, salicylic flux protects the soldering area from corrosion.

You can solder with pure acid using it in powder form or as a whole aspirin tablet. But it is much more effective to use aspirin as part of a multicomponent flux, which is called VTS.

VTS flux is used for soldering copper conductors, as well as products made of silver and platinum. The flux contains technical petroleum jelly as a filler, ethyl alcohol and acetylsalicylic acid.

This flux can be used to solder almost any metal, with the exception of aluminum.

The only disadvantage of aspirin: during soldering, extremely caustic smoke is released, which can damage the respiratory tract with frequent contact. Therefore, good exhaust is a prerequisite for productive work with this flux.

How to solder correctly

How to use soldering acid? The key to successful soldering is not only the correctly selected flux, but also the correct preparation for soldering. To do this you need to know the following:

• Before soldering, metal surfaces must be cleaned of rust and other contaminants using a file and sandpaper.
• All liquid fluxes are best applied to the surface using a special brush. In this case, maximum application accuracy and uniformity of distribution are achieved.
• The acid flux should cover the surfaces to be soldered with an even, uniform layer, without gaps. Otherwise, uniform distribution of solder over the metal surface will not be achieved.
• The tip of a well-heated soldering iron picks up a small amount of solder and transfers it to the metal surface pre-treated with flux. The solder is distributed in an even layer over the entire surface of the metal. This is called "tinning". The second metal surface is tinned in the same way. After this, both tinned surfaces are soldered.
• After completing the soldering process, it is necessary to remove any remaining acid solder. Otherwise, the acid will begin to destroy the metal and a corrosion center will arise, which can lead to destruction of the soldering area.
• Acid is neutralized by alkali. As the latter, it is best to use baking soda. The soldering area is sprinkled with soda and then washed with water.