How to make a flux for soldering do it yourself

Flux is a low-melting alloy of metals, through which two materials are soldered. Flux for soldering with your own hands can be done if you know the characteristics of the connection of different materials by heat treatment.


Flux is designed for soldering metals.

With the help of solders connect the wires, radio nodes and small parts.

Flux Types

The connection of the two materials is obtained if a certain temperature is maintained in the weld zone. For different materials, this figure varies from 50ºС to 500ºС and higher. The melting point of solder should be significantly higher than the melting point of the material being processed.

Fluxes for soldering are of different types, its choice depends on the type of metal, soldering temperature.

Fluxes for soldering are of different types, its choice depends on the type of metal, soldering temperature.

The choice of flux depends on the following parameters:

  • connected materials;
  • melting points of the part and flux;
  • surface dimensions;
  • strength and corrosion resistance.

Fluxes are divided into two groups: solid with a high temperature threshold and soft with a low melting point.

Refractory solders have a melting point of more than 500ºС and create a very strong connection. The disadvantage of these solders is that their high melting point sometimes leads to undesirable consequences: overheating of the main part and its removal from the working state.

Fusible solders have a melting point of 50 ºС to 400 ºС. Their composition is dominated by 38% tin, 61% lead and 1% other impurities. This type of flux used by radio engineering for installation work.

There is a group of so-called ultrafusible solders. They are used to connect transistors. The melting temperature of such fluxes does not exceed 150ºС.

Soft solders are used to solder thin surfaces, and large-diameter wires require hard solders with a high temperature threshold.

Flux must comply with such characteristics as:

Soldering Flux Characteristics

Characteristics of fluxes for soldering.

  • good conduct current and heat;
  • strength;
  • high stretch ratio;
  • resistance to corrosive effects;
  • melting point of solder and base metal.

Solders are in the form of rods, tapes, coils of wire, tubes, filled with rosin or other flux.

The most common form of solder is a tin rod with a diameter of 1 to 5 meters.

Also, there are multichannel fluxes that have several sources of solder inflow for a strong connection. Such solders are sold in hanks, in flasks, coiled, in bobbins. For single use, it is recommended to purchase small piles of wire the size of a match.

For soldering electrical circuits using fluxes in the form of tubes filled with colophony. This resin acts as a solder. With the help of this filler material is made the connection of copper, brass, silver.

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Low melting flux for soldering

Soft flux melts at a temperature of not more than 400ºС. They create a soft, elastic and fairly strong seam.

Fusible fluxes are divided into the following categories:

Solder flux and low melting solder

Flux for soldering and low-melting solder.

  1. Lead-tin.
  2. Low in tin.
  3. Ultrafusible.
  4. Special.

Tin is considered to be the best solder, but it is rarely used in its pure form. This material is expensive, so most often tin-lead solders are used. The compounds are strong and melt at a temperature of 180-200ºС.

Tin-lead solder is designated as: POS-40, POS-60. The letters are an abbreviation for the name of the flux, and the numbers indicate the percentage of tin. These solders contain a small amount of antimony: 3-5%. These fluxes are used for non-critical compounds that are not subject to vibrations and stresses.

Lead-free flux with a low content of tin is used when soldering contacts of small electrical circuits. The process should occur at a temperature not exceeding 300 ºС.

Ultrafusible fluxes become liquid at a temperature of from 60 to 145ºС. They are used for manual soldering of very delicate parts. These compounds do not have high strength, as they are used most often for repeated process.

Special solders are prepared in special cases when it is necessary to obtain compatibility of properties with the base material. As such materials are compounds that are not amenable to soldering: nickel, aluminum, low carbon steel, cast iron.

For example, solder is used to prepare solder, which is 99% tin. For good diffusion, add small amounts of borax, zinc and cadmium to the mixture.

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Refractory flux for smelting

Solid solder

Solid solder is used to join joints exposed to shocks and stresses.

This type of solder is used to connect critical seams that are subject to shock, vibration and temperature changes. Fluxes of this group become liquid at temperatures above 400ºС.

Brazing alloys are divided into the following categories:

  • alloy of copper and zinc (up to 1000ºС);
  • phosphor-copper alloy (up to 900ºС);
  • silver flux (up to 800ºС);
  • pure copper (for high carbon steel).

A mixture of copper and zinc grades M21, M11 are not very widely used. This is due to the lack of strength of the seam and the high cost of the alloy.

This solder is successfully replaced with brass or an alloy of bronze with zinc.

Copper-phosphorus type is used to connect copper, bronze and brass parts that are not subjected to power loads. This alloy successfully replaces expensive silver solder. It is also called solder for flux-free soldering.

Hard solders are not used for soldering low carbon steel and cast iron. This is due to the fact that when iron is heated with copper and phosphorus, brittle elements are formed - iron phosphides, which destroy the integrity of the weld.

For iron, silver is the best solder. This solder is expensive, but it will provide a solid connection of materials.

A silver solder connects wires and complex boards made up of silver components.

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Other types of solder

There are alternative types of solders:

Silver Solder Characteristics

Characteristics of silver solders.

  1. Fluxes with enhanced anti-corrosion properties. This composition is made on the basis of acid, phosphorus and solvent. They are advantageous in that after the soldering process it is not necessary to use additional cleaners.
  2. Liquid fluxes based on salicylic acid, petroleum jelly, gold and ethyl alcohol. They are used for soldering radiators and electrical wires. In this case, very neat and clean seams are obtained.
  3. The connection of rosin with air. This flux is called neutral and is used for high-precision electrical devices: switches, relays, mobile phone circuits. Rosin is inactive, so it should be used on metals, pre-cleaned and tinned. For high-quality cleaning of diamond contacts you can use a laser.
  4. Mixture of borax with rosin. They are used to connect water copper pipes. This flux is highly active and does not require thorough stripping of metals. The borax melts at a temperature of 70ºС, without emitting harmful evaporations.
  5. For soldering compounds that are subject to power loads and shocks, you can prepare the activated flux yourself. For this, it is necessary to take rosin, aniline, anhydride, salicylic acid, diethylamine in certain proportions and mix.
  6. A mixture of rosin with alcohol - active flux, which has recently been the most popular solder. The disadvantage of this flux is that at high temperatures not only metal oxide is removed, but also the metal itself. In addition, cleaning the board after soldering requires a lot of work.
Lead free solder types

Types of lead-free solders.

Flux residues are not only unaesthetic, but also harmful. In electrical circuits with small gaps between the wires possible circuit caused by galvanic processes on the uncleaned surface.

For soldering with the help of tubes filled with colophony, it is necessary:

  1. Carefully clean the mating surfaces from dirt and oxides.
  2. Heat the component at the weld site to a temperature that exceeds the melting point of the flux.
  3. Perform the soldering process.

This method is not suitable for large surfaces with good thermal conductivity, as the power of the soldering iron may not be enough to sufficiently heat the metal.

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How to make flux for soldering yourself

For soldering radio wires you can use solders in the form of thin rods with a diameter of 2 mm. They can be made independently.

To do this, take a vessel and make a hole at the bottom. Then take the molten tin-lead solder and pour it into this hole. In this case, the vessel should be above the metal plate or sheet of tin. When the rods are hardened, they should be cut into pieces of the desired length.

This mixture can also be poured into special forms: tin trough, duralumin, gypsum. Cooking technology is as follows:

DIY flux

You can make the flux yourself by pouring molten metal into a jar with a hole.

  1. On scales weigh tin and lead in necessary quantities.
  2. The metals are melted in a metal crucible over a gas burner, mixing the mixture with a steel rod.
  3. A steel plate removes a thin film from the molten surface.
  4. Pour the liquid alloy into the form.

Finished soldering, regardless of the type of flux, must be wiped with a cloth moistened with acetone or rectified spirit. The seam can be cleaned with a stiff brush dipped in solvent.

So-called run-off fluxes are now produced in the form of a liquid or gel. Their advantages:

  • they do not contain components that cause corrosion, oxidation;
  • these fluxes do not conduct electrical current;
  • do not require cleaning after the soldering process.

Liquid flux in this category must be applied with a brush or cotton swab. And you can make yourself a device for applying this fluid.

This will require: a disposable medical syringe, a piece of silicone hose with a diameter of 5-6 mm. The syringe is cut into two parts and inserted on both sides of the rubber pipe. The needle should be slightly shortened and slightly bent.

Now it is necessary to fill the hose with liquid. Lightly pressing on the structure, extrude flux droplets on the parts to be joined.

If the process is repeated, then this design can be saved. So that the needle cavity does not dry, a thin wire is inserted into it.

This construction can be used if gel or paste is used as a flux.

The advantages of joining metals by soldering are:

  • excellent strength;
  • tightness;
  • resistance to oxidation and corrosion;
  • the simplicity of the process, which requires a minimum of time and professional skills, compared with welding.

In the process of soldering, harmful gases are emitted that cause damage to the body, so you should use protective gloves, goggles and an apron made of thick fabric. The use of professional mixtures of famous brands will significantly reduce the risk of poisoning by harmful fumes.

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