Proper soldering with a soldering iron and hair dryer from scratch for beginners

Solder Paste Reviews

Solder paste is a substance that is used in the soldering process instead of regular rosin; it contains solder powder, flux, some kind of binder and some other components.
The main selection parameters: • its composition – solders with alloying additives, with or without lead content, and so on; • the size of individual solder particles and shape, depending on this there are different dosages; • viscosity level - the method of application depends on this - using a stencil or dispenser; • solderability - determined by the contamination of the particles and the level of their oxidation.

In addition, such pastes may not be subject to corrosion - no-clean. Rust may form in soldering areas, since water-washable pastes contain organic substances. For high-quality soldering, you need to choose a paste depending on the metal with which it will be used. There are special compositions for chrome-nickel, copper, aluminum, gold, and silver.

I bought it because of the title “solder paste” and, accordingly, I expected to receive exactly solder paste in the classical sense - a mixture consisting of flux mixed with highly crushed solder particles, which is very convenient. When I opened the jar, it became clear that this was not the same paste, but only a flux, and very similar in appearance to the bad Chinese flux RMA-223. But after trying it at work, I was pleasantly surprised. However, there are some nuances that you need to be aware of. That's all we'll talk about in the review.

Today's review will be devoted to the MECHANIC XG-50 (XG-500) solder paste, which I purchased on eBay. I had a desire to acquire soldering paste for a long time, but since my tool assortment did not include a soldering gun, this purchase was constantly pushed into the background. But after I came across a budget technical hair dryer, I decided to purchase solder paste along with it. The choice was made spontaneously, mainly based on data from the seller’s pages, and fell on MECHANIC XG-50 paste.

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Soldering parts from boards with one soldering iron

Small-sized SMD parts can be desoldered using a conical tip. Both contacts of the part heat up and it quickly comes off the board. Also, a conical tip is convenient when soldering SMD parts, since you can accurately dose the amount of solder onto the contacts.

Braided soldering

Braid consists of strands of thin copper wires.

You can use shielding insulation from the antenna as a braid. Using a braid, you can quickly and easily remove solder from a contact. It is necessary to apply flux to the braid and contact. Next, using a soldering iron, the soldering area is slowly heated and the tin is transferred to the braid. This soldering method is good for small parts and small DIP contacts. If you need to unsolder the PCI connector, then the braiding will quickly be wasted.

Vacuum syringe and needles

The vacuum syringe quickly removes massive burnt parts of solder. And with the help of DIP needles, the contacts are easily unsoldered from the board. The needle is put on the contact and heated up using a soldering iron. You need to have time to pass the needle through the board contact onto the microcircuit body while the solder is in a molten state. Or vice versa, when the contact is already warmed up, and at the same second the needle is inserted.

Such soldering methods are outdated. Modern boards are manufactured for machine assembly, so the gap between the contacts and pins of the parts is minimal. The needle is already weak, and the vacuum syringe does not have time to pick up the sharp drops of solder. It is no longer possible to desolder a regular electrolytic capacitor using a syringe. In this case, the liquid sting method will help.

Liquid sting and its advantages

The liquid tip is a drop of solder, which allows you to avoid using additional tools (braid, hair dryer, needles or syringe). The technique is the same as with the Rose alloy. The main difference is in temperatures.

The hatchet-type sting has a massive longitudinal working surface. It allows you to capture multiple contacts at once.

Apply solder to the tip.

A paste-like flux is applied to the chip to be soldered using a syringe.

The part and its contacts are heated with a sting until the tin melts, and the same must be done on the other side.

Using this technique you can also remove DIP contacts.

What is SMD and basic principles

The use of flux for soldering SMD components has its own characteristics, which make it possible to improve the connection of the surface of microcircuits and boards. General recommendation for using flux for soldering SMD is effective for chip resistors, as well as SOIC, LQFP, QFN and others. The application of the thinnest layer of material allows for production soldering without compromising quality. By the way, literally from English the meaning of SMD soldering paste is translated as “using components for surface soldering” (Surface Mounted Devices). As can be seen from the working name of the paste, it allows for sufficient assembly density of the connection compared to conventional technologies.

SMD component soldering process

Most craftsmen mistakenly believe that using SMD components is impractical at home. Most craftsmen believe that only TN technology can be needed at home, although the main problem is choosing the correct diameter of the soldering iron tip. Inexperienced craftsmen really do not know the intricacies of using SMD soldering with solder paste, since the result of the work is “staining” of SMD contacts on the printed circuit board with tin. To avoid typical mistakes, some parameters should be taken into account: capillary effect, which must have a fine structure, as well as surface tension and proper wetting of the surface being treated. Ignoring the tasks at hand will not be able to fully answer the difficult question of which flux is best for soldering SMDs at home or on an industrial scale.

High-quality contact with the legs of the microcircuit of the board with SMD components occurs for one simple reason, the effect begins to be exerted by the general tension force, which forms separate independent drops of tin formation on the surface of the board.”

As can be seen from the general description, the wizard’s actions are minimized and the flux for soldering SMD components only heats the legs of the microparts used. Remember, when working with very small components and parts, seizing (unexpected connection) of technological elements to the tip of a working hot soldering iron may occur, which negatively affects the further operation of the microcircuit.

In what cases will soldering with a hairdryer not work?

A soldering gun usually reaches a power of no more than 500 W. The lower the power, the less the board area can be heated.

Using a soldering gun will not adequately desolder massive parts or computer BGA chips (bridges, CPU, GPU). A hairdryer will not be able to warm up such areas.

It's like boiling a glass of water with one match. Increasing the temperature is also not an option; this will destroy both the part itself and the board.

A massive board requires bottom heating. Most often this is a stove that heats up to 100 - 200 °C. The printed circuit board will be heated evenly. And use a hair dryer to bring the solder to melt.

You can also use a hair dryer. It has a larger nozzle and its power can be up to 3000 watts. However, a hair dryer is not a solution either. Due to the fact that only the part and a small surrounding space around it are heated, after soldering the board is deformed due to the high heating difference, thereby tearing off the leads from the pads (this is especially true for large BGA parts).

Features of technology in factory conditions

For industrial production, soldering paste for SMD components is adapted to a group system, which uses an electronic system for applying flux to the surface of the microcircuit. Fine application technology using silk-screen printing is used on the surface of contact working areas. Thus, in its technology and consistency, the material somewhat reminds us of the usual toothpaste. The substance includes solder powder, as well as flux components. The entire substance is mixed and applied to the surface of the microcircuit using a conveyor method.

Appearance of paste for SMD

An automated system carefully turns over the boards that need to be soldered, then the microcircuits are moved to a temperature cabinet, where the mass spreads, followed by solder. In the oven, under the influence of the required temperature, a conditional flow occurs around the technological contact legs of the SMD components, and as a result, a fairly strong connection is obtained. After the temperature cabinet, the chip is again moved to a natural environment, where cooling occurs.

Is it possible to solder with SMD paste yourself?

Theoretically, yes, but in practice, quite a lot of experience is needed to carry out this technological operation. For work we will need the following tools and preparations:

The flux should always be in a liquid state, this way you completely disinfect the surface of the microcircuit. In addition, the drug removes the formation of oxides on the surface of the board during operation. Remember that an alcohol solution together with rosin cannot ensure the quality of soldering, and their use is only permissible if a suitable soldering compound is not available.

Soldering iron selection

To work, you need to select a special soldering iron that has an adjustable heating range. To work with the microcircuit, a soldering iron is suitable, which has an operating heating temperature of no more than +250...+300 C. If you do not have such a soldering iron at hand, you can use a device with a power of 20 to 30 W and no more than 12-36 Volts.

A soldering iron with a voltage of 220 Volts will not be able to ensure the quality of soldering, where it is very difficult to regulate the required heating temperature of the flux.

Soldering iron for soldering SMD components

We do not recommend using a soldering iron with a cone-type tip; this will lead to damage to the surface being processed. The most optimal tip is the “microwave” type. A soldering iron with a voltage of 220 Volts not only heats up quickly, but also leads to volatilization of components during the soldering process. For efficient operation of the soldering iron, we recommend using the thinnest wire to ensure interaction between the tip, flux and solder.

But, for a microcircuit, the soldering procedure is slightly different from the above:

In some cases, it is possible to use a special soldering gun for soldering, but for this it is necessary to create appropriate working conditions. Remember that the hair dryer can only be heated to a temperature of +250 C, no more (in rare cases, up to +300 C).

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Soldering LED strip

The LED strip has the same heat capacity as a thick wire. It contains a copper substrate, which absorbs heat when heated.

We tin the contacts using rosin. We use a mini wave and very little solder. There should be some solder at the soldering area.

Next, we take the soldering iron away from us with the handle, lean the wire against the contact and on top with the tip of the soldering iron. Soldering should take no longer than a second while there is flux. This is due to the fact that the copper substrate quickly absorbs heat, and the burning flux is no longer able to assemble the solder into a single whole. Therefore, if soldering work lasts more than a second, then there will be lumps of solder on the tape with signs of cold contact. If this happens, apply flux again and correct the bad soldering with one touch.

Rosin (flux) can be cleaned from the tape using alcohol (or gasoline) and a cotton pad.

Solder paste and its properties

Initially, such compositions were used only in SMT technologies. Now their area of ​​use has increased. Solder paste for SMD contains the following ingredients:

It is possible to achieve high-quality soldering only in a situation where all conditions and shelf life of the solder mass have been met. Most of the ingredients in such formulations have a shelf life of no more than six months. They should be stored at a temperature of +2…+10°C. The room should not be too cold or hot. The air humidity level should not exceed 80%. Before using the composition, it must be warmed to room temperature and only then open the jar or remove the substance from the syringe. In some cases, it takes about 5-6 hours to warm up.

It is also necessary to take into account that over time the solder mixture loses its properties. It is necessary to select materials for soldering with tin or other materials taking into account the following requirements:

In addition, solder paste materials must be easy to dispense and suitable for screen printing.

Educational program for beginners

To desolder a part from a board, you need to make sure that the contacts are heated until the solder melts (approximately 230 °C). The main mistake beginners make is to immediately heat the place where they are soldering to 300 - 350 °C.

For example, you need to desolder a microcircuit from a board using a Lukey 702 soldering station.

Many radio amateurs and electronics engineers set heating parameters above 300 °C.

At the first moment, the part is exposed to about 200 °C. The contacts and the surrounding area of ​​soldering work are at room temperature.

The heating of the part reaches 300 °C, but the contacts have not yet reached 200 °C.

The microcircuit experiences a critical temperature of 350 °C. Meanwhile, the surrounding soldering area is heated unevenly, even if the hair dryer is evenly moved across the soldering area. A noticeable temperature difference appears at the contacts of the part.

400 °C and the microcircuit begins to fry.

A little more, and it will unsolder due to the fact that the contacts have practically heated up until the solder melts. But this happens because the board has warmed up. And in this case, it happened unevenly. High temperatures lead to thermal breakdown of the microcircuit and it fails. The board bends, turns black, and bubbles appear due to boiled PCB and its components.

This soldering method is very dangerous and ineffective.

How do you solder parts without damage?

It is necessary to analyze the soldering area and equipment:

• Estimate the thickness of the board. The thicker the board, the more difficult and longer it takes to warm it up. The board consists of layers of tracks, masks, pads and many metal parts that are very heat-intensive.

• What's nearby? To avoid damaging surrounding components, they must be protected from temperature. The following will cope with this task: thermal tape, aluminum tape, radiators and coins.
• What is the ambient temperature ? If the air is cold, the board will have to be heated a little longer. Of particular importance is what is located under the board. No need to solder on a metal plate or on an empty bench. A wooden board or a set of napkins works best. And at the same time, the board must be in the same plane, without distortions.
• Equipment. Many soldering stations are sold without calibration. The difference between the temperature shown on the indicator and the actual temperature can reach either 10 °C or 50 °C.

Important Specifications

Solder mass must be selected taking into account its physical and chemical properties. These characteristics are directly dependent on the ingredients of the composition. These properties are:

In addition, no-clean pastes do not provoke the formation of corrosion, while water-washable pastes can lead to such problems at the soldering site, since they contain a number of organic substances.

Liquid flux made from rosin and alcohol

The first recipe will be useful for those who have regular solid rosin. It is cheap, environmentally friendly, but soldering with it is still a pain. You still need to get used to handling boiling rosin with the tip of a sting. It is much better and more convenient to use it in the form of liquid flux.

1. We break the rosin with a hammer or break off pieces with a knife.
2. Wrap the fragments in thick paper. We knock. We get the powder.
3. Pour it into a glass jar.
4. Pour medical alcohol there (at least 96%).
5. Proportions – 3 parts rosin powder, 7 parts alcohol.
6. Stir for a few minutes.

Rosin dissolves quickly. The resulting liquid flux can be applied with a brush.

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Useful tips Connection diagrams Principles of operation of devices Main concepts Meters from Energomer Precautions Incandescent lamps Video instructions for the master Testing with a multimeter

Making at home

Sometimes ready-made solder paste is not available, so it is useful to learn about how to make it. For this purpose, it is necessary to prepare soldering fat and a solder rod made of lead and tin. If the first material is not available, it can be replaced with Vaseline LTI-120.

The solder must be crushed using a needle file or a special drill attachment. The finished crumb should consist of small particles. It is put into a container into which Vaseline is added in a 1:1 ratio and a small amount of flux.

All components of the homemade paste are thoroughly mixed and heated in a water bath. The finished composition can be stored in a large syringe. With the help of it, a paste-like substance will be applied to the boards.

How to understand that a part is already soldered

A glare appears on the contacts. Using tweezers, gently push the chip. If it moves easily and smoothly from side to side, then it can already be removed; if not, we heat it further.

This technique must be individually adjusted for each soldering and soldering station. For example, sometimes you will have to heat the board longer, and sometimes about 240 °C will be enough. The soldering method depends on the case.

Application benefits

Solder pastes are used not only in everyday life, but also in industry. Such widespread distribution of this material is explained by its following advantages:

If there is no opportunity or desire to make the mixture yourself, you can purchase a ready-made version. But you need to remember that high-quality solder paste costs about 10 US dollars per 50 g. Cheaper options are of poor quality and may not only not provide sufficient fixation reliability, but also lead to additional problems during subsequent use of the electronic product. To avoid problems, it is better to buy such materials in certified stores or directly from manufacturers.

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Varieties

The modern market offers products from the brands ALPHA, HERAEUS, Felder, etc. All soldering pastes are classified according to the following criteria:

• according to the composition of the solder - halogen-free or halogen-containing;
• if necessary, additional washing;
• by type of solder - lead-free or lead-based;
• according to temperature indicators - high, medium, low temperature.

If the composition is not washed off, it contains rosin. In such a situation, special solvents must be used to wash the elements.

It is also necessary to take into account that an increase in the level of solderability of elements is accompanied by a decrease in the reliability of fixation. For example, compositions containing halogen are highly technological, but their reliability is low.

Solder paste for smd which is better with solder

Mikhail Nizhnik

, General Director, METTATRON Group LLC

The author summarizes information about the properties and behavior of solder pastes during soldering, based on extensive experience working with solder pastes. The article will be of interest to a technologist working on a surface mounting line.

Types of solder pastes

Pastes are classified according to the type of flux (see Fig. 1).

“Water-soluble” solder paste (flux residues after soldering are dissolved with water), which requires mandatory cleaning due to the content of active flux (see Table 1), is washed sequentially with ordinary, distilled and deionized water, and at each stage jet cleaning or ultrasound is used. For “water-soluble” pastes that do not require mandatory cleaning, the process is limited to distilled water.

Rice. 1. Classification of solder pastes

Table 1. Classification of fluxes

With pastes that require cleaning with special liquids, the situation is different. Regardless of the presence of halogens in the composition, such pastes are based on rosin fluxes, therefore, to clean them after soldering, it is recommended to use a solvent such as HCFC and a saponifying reagent. Then the cleaning liquids, in turn, are washed with distilled and then deionized water.

However, many halogen-free solder pastes are difficult to clean and leave a whitish flux residue on the surface of the boards. In this case, resistance to sediment is considered more important than washability.

Most no-clean solder pastes eliminate this process from production. The fluxes of such pastes protect the soldered joint from corrosion like varnish. Let's focus on pastes that do not require cleaning: they are the most technologically advanced.

Rice. 2. Composition of solder pastes

It is often said that no-clean pastes must be halogen-free. It must be clearly understood that if the documentation for the paste states “Requires washing,” then it must be washed, and if there is no such marking, then the issue is resolved based on additional requirements for the product: appearance, application of varnish.

In Japan, for example, halogen-containing pastes (0.2%) in processes without cleaning after soldering are much more popular than halogen-free ones. Halogen-containing solder pastes are comparatively more technologically advanced, for example, in terms of solderability, but are often inferior to halogen-free pastes in terms of reliability, which is manifested in a decrease in the insulation resistance of the finished installation. This is explained by the higher chemical activity of flux residues. Thus, solderability and reliability, in most cases, are mutually exclusive factors.

Rice. 3. Main characteristics taken into account when developing or selecting solder pastes

Ideally, for no-clean soldering you need a halogen-free paste, but with the solderability of a halogen-containing paste.

The difficulty lies in increasing the chemical activity of halogen-free no-clean pastes. In most of these pastes, organic acids are used as an activator instead of halogen-containing compounds, and the lower the molecular weight of the acid, the greater the activation ability. Since the activating effect of organic acids is much weaker than that of halogen-containing components, they try to introduce a couple of dozen relatively active organic acids into the flux system.

At the same time, such highly active organic acids absorb moisture. This is fraught: the acid remaining in the flux residues on the surface of the substrate is ionized when interacting with water, which reduces the surface insulation resistance and leads to electromigration.

Activation systems in solder pastes (here the author relies on technical data on pastes) use less hygroscopic organic acids and a specially developed non-ionic activator. This special system does not dissociate into ions, its electrical properties are stable, and its activating ability is not inferior to halogens. Due to the high activation temperature, the non-ionic activator in combination with carefully selected organic acids makes the activation at the reflow stage longer. As a result, solderability is improved without sacrificing reliability.

Here are examples of popular types of pastes:

Composition of solder pastes

Solder pastes consist of solder and flux (see Fig. 2). When choosing a solder + flux complex for solder paste, take into account the characteristics shown in Fig. 3.

Gas and centrifugal atomization methods are used to produce solder powder. Features of the gas atomization method:

— obtaining small particles;

— ease of control of the process of formation of an oxide film on the surface of particles;

— low level of oxidation of solder particles.

The resulting solder powder particles range in size from 1 to 100 microns. The size distribution of solder particles and their diameter are influenced by solder feed speed, spindle speed and oxygen content.

Rice. 4. Obtaining solder powder by gas atomization

The powder is obtained in a container about 5 m high and 3 m in diameter, which is filled with nitrogen and oxygen of very low density (see Fig. 4). The solder ingots are melted in a crucible located at the top of the tank. Molten solder drips down onto the spindle, which rotates at high speed. When drops of solder hit the spindle, the solder splashes towards the walls of the reservoir, causing the solder to become spherical and solidify before the particles reach the wall of the reservoir.

Rice. 5. The degree of oxidation of solder particles depending on their size

The solder powder then goes to the sorting screen, where it is best to use the double sorting method of solder powder. At the first stage, the powder is sorted by a stream of nitrogen from a blower. In this case, particles with sizes smaller than the required size are eliminated. Then the powder goes to a sieve, where particles with sizes exceeding the specified values ​​are retained.

Solder pastes with a particle size of 20–38 microns are used for mounting printed circuit boards with a stencil aperture pitch of up to 0.4 mm, and with a particle size of 20–50 microns for pitches of 0.5 mm.

The quality of powders is influenced by two factors.

Particle size distribution affects solder paste rheology, printability, flow, stencil release behavior, and paste slump performance. The minimum size of the stencil apertures depends on the minimum size of the pads on the printed circuit board, with the maximum size of the aperture being less than or equal to the size of the pad. Select the required particle size on the basis that at least 5 particles of solder should be guaranteed to fit into the smallest aperture of the stencil, as shown in Fig. 12.

The second component of solder paste is flux. The role of flux in solder pastes is the same as in wave soldering, or selective soldering. The flux should:

— remove the oxide film and prevent re-oxidation during the soldering process. Metal surfaces at high temperatures during melting quickly oxidize. At these temperatures, the solid components of the flux soften and turn into a liquid state, covering and protecting the soldered surfaces from re-oxidation. Flux restores metal and removes oxide film from the surface of contacts of electronic components, the final coating of the printed circuit board and the surface of the solder powder;

- remove dirt. However, flux will not cope with a large number of sweat and grease marks, so it is better to handle the board with gloves;

— ensure the stability of the paste viscosity required during printing and reflow.

The main fluxing components and their role are indicated in Table 3.

Table 3. Main fluxing components and their role

Let us now consider the factors affecting print quality.

Rice. 6. Factors affecting print quality

Paste technology

Before soldering SMD elements using solder paste, you need to study the technology of working with this composition. You need to use it as follows:

• First you need to clean, degrease and dry the board;
• after this, the board must be securely fixed in a horizontal position;
• paste is applied evenly at the marked connection points;
• small parts are installed on the surface of the board;
• sometimes additional treatment with the composition of the legs of conductive microcircuits is required;
• You can warm up the installed SMD components with a hairdryer;
• when the solder has completely evaporated, the melting temperature can be increased;
• soldering must be done carefully, observing all necessary safety requirements;
• After work, the board must be cooled and washed.

To install microcircuits, soldering irons with temperatures ranging from +250...+300°C are used. It is not advisable to use devices with cone-shaped nozzles for such work. To achieve maximum efficiency, you should use a thin wire to contact the paste with the soldering tip.

SMD components can also be soldered using the following scheme:

• parts are installed on the site;
• solder paste is applied to the legs;
• under the influence of a soldering iron, the paste-like substance spreads evenly over the contact area;
• the elements cool down and are cleaned.

To solder cables, the paste is applied to them in the connection area. After this, a soldering tip is applied to the mass.