How to solder with a soldering iron: instructions for dummies

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The art of soldering must be learned gradually. Starting from soldering wires and moving on to printed circuit boards – each of the methods has its own subtleties, both in the selection of consumables for soldering and in technology. Today we will share with our readers the basics of soldering and basic work skills.

What is the essence of soldering

Soldering uses the ability of some metals in a molten state to effectively spread over the surface of others under the influence of gravity and moderate surface tension. The soldering connection is one-piece: the two parts to be joined are, as it were, enveloped with a layer of solder and remain motionless after it has solidified.

Since we will consider soldering in the context of metal soldering, the most important parameters will be the strength of the mechanical and the conductivity of the electrical connection. In most cases, these are directly proportional values, and if two parts are tightly grasped, then the conductivity between them will also be high. However, the solder has a resistivity higher than even that of aluminum, so its layer should be as thin as possible, and the hiding power – as high as possible.

Soldering copper wires

For soldering to be possible in principle, there are two conditions. The first and most important thing is the cleanliness of the parts at the soldering point. Solder adheres to the metal surface at the atomic level and the presence of even the slightest oxide film or contamination will make reliable adhesion impossible.

The second condition is that the melting point of the solder should be significantly lower than the temperature of the parts to be brazed. It seems obvious, but there are solders with a melting point higher than aluminum, for example. In addition, if the real difference in melting temperatures is not high enough, when the solder solidifies, the temperature shrinkage of the parts can interfere with the normal formation of the solder crystal lattice..

Fluxes and solders – how to choose the right one

For the reasons described above, the correct choice of flux and solder is almost half the success in the soldering business. Fortunately, there are quite universal brands that are suitable for most tasks. The industry of application of almost all fluxes and solders is clearly indicated on the labels, but you still need to know some aspects of their application.

Let’s start with the fluxes. They are used for etching parts, removing and dissolving the oxide film with further protection of the metal from corrosion. As long as the surface is covered with flux, you can be sure that it is clean, as well as that the molten tin will wet and spread well..

Fluxes are distinguished by the type of metals and alloys of the parts to be joined. These are mainly mixtures of metal salts, acids and alkalis, which actively react when heated with a soldering iron. Well, since there are a lot of oxide forms and impurities, a cocktail should be specially selected for a specific type of metals and alloys..

Active flux for soldering Active flux for soldering

Conventionally, soldering fluxes are divided into two types. Active fluxes are created on the basis of inorganic acids, mainly perchloric and hydrochloric. The lack of them in the need to wash off immediately after the completion of the soldering, otherwise acid residues cause a rather strong corrosion of the compound and by themselves have a sufficiently high conductivity that can cause a short circuit. But almost anything can be soldered with active fluxes..

The second type of flux is created mainly on the basis of rosin, which can be used in its pure form. Liquid flux is much more convenient to apply, it also contains alcohol and / or glycerin, which completely evaporate when heated. Rosin fluxes are the least effective when brazing steel, however, for non-ferrous metals and alloys, they or other compounds of organic chemistry are mainly used. Rosin also needs to be rinsed out because in the long term it tends to corrode and can become conductive by picking up moisture from the air..

Liquid and solid rosin Liquid and solid rosin

With solders, everything is somewhat simpler. Basically, lead-tin solders of the POS brand are used for soldering. The number after the marking indicates the tin content of the solder. The larger it is, the higher the mechanical strength and electrical conductivity of the joint and, at the same time, the lower the melting point of the solder. Lead is used to normalize the solidification process; without lead, tin can crack or become covered with needles.

Solder POS-61 with rosin inside Solder POS-61 with rosin inside

There are special types of solders, primarily lead-free (BP) and others non-toxic, in which lead is replaced by indium or zinc. The melting point of BP is higher than that of conventional ones, but the connection is stronger and more resistant to corrosion. There are also low-melting alloys, spreading already at 90–110? С. These include Wood and Rose alloys, used for soldering components that are sensitive to overheating. Special solders are mainly used in the soldering of radio equipment.

Alloy Rose Alloy Rose

Power and types of soldering irons

The main difference between the soldering tool is the type of power source. For ordinary people, the most familiar are network soldering irons powered by 220 V. They are used mainly for soldering wires and more massive parts, because it is almost impossible to overheat a copper wire, with the exception, perhaps, of melting the insulation.

Soldering iron

The advantage of network soldering irons is their high power. Due to it, high-quality and deep heating of the part is ensured, plus a bulky power supply is not required for operation. Among the shortcomings, one can single out the low convenience of work: the soldering iron is quite heavy, the tip is located far from the handle and such a tool is not suitable for fine work.

Soldering Station

Soldering stations use thermal control to maintain a stable temperature level. Such soldering irons do not have significant power, usually 40 W is already the ceiling. However, for overheating sensitive electronics and soldering small parts, this tool is best suited.

Sting selection and care

Soldering iron tips are distinguished by shape and material. With the shape, everything is simple: the most primitive and at the same time universal is the subulate sting. Variations are possible in the form of a spatula, a cone with a blunt end, with a bevel and others. The main task when choosing a shape is to achieve the maximum area of ​​contact with a specific type of soldered parts, so that the heating is powerful and at the same time short-lived.

Copper Soldering Iron Tips Copper Soldering Iron Tips

In terms of material, almost all stings are copper, but they can be coated or uncoated. Copper tips are coated with chromium and nickel to increase heat resistance and eliminate oxidation of the copper surface. Coated tips are very durable, but slightly less wetted with solder and require careful handling. To clean them, use brass shavings and viscose sponges..

Nickel plated blades Nickel plated blades

Uncoated tips can rightfully be attributed to soldering consumables. During operation, such a sting is periodically covered with a layer of oxides and the solder ceases to stick to it. The working edge must be cleaned and tinned again, therefore, with intensive use, the sting is grinded off quickly enough. To slow down the burning of the sting, it is recommended to first forge it, and then grind it to give the desired shape.

Soldering iron with copper tip

Soldering wires

The wires are the easiest to solder. The ends of the veins are dipped in a flux solution and carried along them with a soldering iron, the tip of which is abundantly moistened in the flux. In the process of tinning, it is advisable to shake off excess molten solder. After applying half a twist, a twist is formed from the wires, and then it is carefully heated with a small amount of solder, filling the free space between the veins.

Soldering stranded wires

Another method is also possible, when, before twisting, the wires are simply thoroughly moistened with flux and soldered without preliminary tinning. This method is especially popular when soldering stranded conductors and small diameter wires. If the flux is of high quality, and the soldering iron provides a sufficiently strong heating, even twisting of 3-4 “fluffy” cores of 1.5 mm2 well impregnated with tin and will be reliably soldered.

Soldering stranded wires

Please note that in electrical wiring, that is, inside junction boxes, it is not customary to solder the wiring. First of all, due to the inseparability of the connection, plus the whole, the spike has a significant transition resistance and there is always a high risk of its corrosion. The wires are soldered exclusively when making connections inside electrical appliances or for tinning the ends of stranded conductors before tightening them with screw terminals.

Working with electronic components

Soldering electronics is the most extensive and complex topic, requiring experience, skills and special equipment. However, an amateur can also replace a faulty element on a printed circuit board, even if there is only one network soldering iron..

The output elements (which are with legs) are the easiest to solder. They are preliminarily fixed (with plasticine, wax) with leads in the holes of the board. Then, on the reverse side, the soldering iron is tightly pressed against the tail to warm it up, after which a solder wire containing flux is inserted into the soldering point. Too much tin is not needed, enough for it to flow into the hole from all sides and form a kind of elongated cap.

Soldering electronic components

If the outlet element dangles and needs to be held by hands, then the soldering point is first moistened with flux. It needs a very small amount, here it is optimal to use bottles of nail polish, pre-washed with acetone. With this soldering technique, tin is collected on a soldering iron in a small amount and its droplet is gently brought to the element output 1–2 mm from the board surface. The solder flows down the leg, evenly filling the hole, after which the soldering iron can be removed.

High quality soldered connection

It is very important that the parts to be joined remain stationary until the solder has completely cooled. Even the slightest violation of the shape of tin during crystallization leads to the so-called cold soldering – crushing the entire mass of the solder into many small crystals. A characteristic sign of this phenomenon is a sharp turbidity of the solder. It needs to be reheated and wait for uniform cooling in complete immobility.

Cold soldering Poor quality, cold soldering

To maintain the tin in a liquid state, it is enough for the soldering iron to contact the tinned surface of the tip with any point of the wetted area. If the soldering iron literally sticks to the parts to be soldered, this indicates a lack of power for heating. For soldering heat-sensitive semiconductor elements and microcircuits, ordinary solder can be mixed with low-melting.

Soldering solid parts

Finally, let’s briefly talk about soldering parts with a high heat capacity, such as cable glands, pots or utensils. The requirement for the immobility of the connection is most important here, large parts are pre-connected with clamps, small parts – with lumps of plasticine, before soldering the connection, it is grabbed pointwise in several places and the clips are removed.

Solid parts are soldered as usual – first half a day at the joint, then filling the seam with liquid solder. However, a special solder is used for this purpose, usually refractory and capable of maintaining high tightness, as well as withstanding partial heating well..

Soldering aluminum

With this kind of soldering, it is extremely important to keep the parts well heated. For these purposes, the solder seam is heated with a gas torch directly in front of the soldering point, and instead of a conventional electric soldering iron, a massive copper hatchet is used. It is also constantly heated in a burner flame, simultaneously wetting it with solder, and then filling the joint, partially melting the previous seam by a few millimeters.

A similar heated soldering technique can also be used when working with a conventional soldering iron, for example, when soldering thick cable cores. The sting in this case acts only as an operational tool for careful distribution of tin, and the main source of heating is a gas burner.

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