Solder pastes: how to use? DIY solder paste

Category: All about soldering, About materials and tools, Articles about everything Published 03/02/2020 · Comments: · Reading time: 2 min · Views: Post Views: 1,290

Solder paste is a mixture of solder and flux. Widely used for soldering SMD and planar chips.

It differs from conventional solder wire in its paste-like form.

The paste is soft and contains lead microballs.

Therefore, it should not be applied with your fingers. It is better to use toothpicks or spatulas. And cotton swabs are ineffective because they absorb a lot.

The paste is also sold in syringes. In this form, using a piston, you can precisely dose the amount of solder onto the board. Use a large diameter needle.

After applying the paste, be sure to close it, regardless of the time. Otherwise, the balls will harden in the dried flux, and it will lose its properties.

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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Properties

Viscosity

This is nothing more than the thickness of the solder paste substance. The paste is endowed with the ability to change the degree of its viscosity when exposed to mechanical loads. It can be determined using special instruments: Brookfield and Malcolm viscometers. As a rule, this indicator is indicated by the marking method.

Draft

Solder pastes have the ability to expand in size after the imprint is applied to the surface. The considered indicator should be at a low level, since a significant increase in the size of the solder paste print causes the formation of jumpers.

Properties saving time

This is reflected in indicators such as the longest residence time of the substance on the stencil before or after application, which does not entail degradation of properties. In most cases, the value of the first parameter is within 8-48 hours, the second - 72 hours. These indicators are recorded by the manufacturer on the packaging. Moreover, either one parameter (either of the two) or both can be specified.

Stickiness

Identifies the ability of solder paste to hold SMD components in place after installing them on the surface and before the soldering procedure. The degree of stickiness indicates the “viability” of the paste and determines its shelf life. It is calculated by implementing a special test, which uses a traditional tester capable of measuring the force required to move an element of certain weight parameters from an area of ​​a paste-like substance of certain sizes.

The presence of adhesiveness and its level depend on the type of solder paste. On average, the retention time is in the range of 4-8 hours, while the maximum value, which is typical for a number of pastes, can reach 24 hours or more.

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.

What is needed for soldering

To solder copper conductors, you will need the following devices, materials and tools:

• Electric soldering iron with a power of 80 watts or more
• Solder
• Flux
• Flux remover (neutralizer)
• Pliers
• Flux brush
• PVC electrical tape
• Heat shrink tube of suitable diameter
• Hairdryer

You can solder copper wires not only with an electric soldering iron, but also with other equipment: a propane torch for soldering copper pipes, a mini gas torch, or a gas soldering iron with a torch attachment.

A burner with a small torch is convenient in that it provides local heating of the twist without damaging the conductor insulation. Before using an electric soldering iron, its tip must be cleaned from oxides with a file or sandpaper. It is recommended to use POS-60 or analogues with a melting point of 190°C as a solder for copper.

Flux removes metal oxides, promotes better adhesion of solder and its uniform spreading over the surface. It is better to use water-based flux - it does not contain alcohol or acid, so it does not require subsequent removal. If you use orthophosphoric acid, liquid rosin or LTI-120 for this purpose, then the products must be removed from the surface after work - otherwise they will destroy copper parts over time.

Read also: Feron sen26 connection diagram

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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Storage conditions

Solder pastes require not only compliance with operating rules, but also special storage conditions, the main ones being the following:

• the temperature of the room where the substance is stored should not exceed 25°C;
• the temperature range for storing paste depends on the manufacturer and can range from 4-10°C;
• the shelf life of the paste when stored under recommended conditions for compositions with water-washable fluxes is 3-6 months, and with indelible fluxes - 6-12 months;
• Soldering with solder paste should be carried out in a room where the relative humidity is 60-80%.
• started pastes can be stored for no more than 12 hours;
• in order to reduce the degree of degradation that remained from the previous soldering process, the paste can be used in new soldering works, but only with the addition of a new one;
• jars, cartridges and syringes with soldering agent should be stored only in a vertical position, with the syringe tips down to avoid the possibility of delamination.

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.

Stencil method

It is most popular and involves applying paste to the soldering surface by pressing it through apertures in the stencil with a specially designed tool - a squeegee. In this case, the squeegee makes moving movements along the surface of the stencil in a horizontal position.

Step-by-step instructions for the stencil method:

• Step 1. Fix the soldering surface (board) in the work area.
• Step 2. Align the soldering board and the stencil with absolute precision.
• Step 3. Squeeze or apply the required amount of solder paste onto the stencil fabric.
• Step 4: Apply the paste through the stencil using a squeegee.

• Step 5. Check the quality characteristics of the soldering agent application.
• Step 6: Remove the soldering surface.
• Step 7. Clean the stencil.

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.

Soldering procedure

Soldering copper wires is technologically simple; copper can be processed well without losing its conductive properties, while the joints are strong. Soldering of copper wires located in the junction box occurs in the following sequence.

1. The wires in the junction box are cut to the required length - 20–25 cm and correctly distributed by color: yellow-green is grounding, blue is zero, white (brown, red or black) is phase. Using special pullers, the insulation is removed from them, leaving bare ends 4.5–5 cm long.
2. Connect the wires crosswise - this is necessary to ensure that the twisting is uniform and tight. To make the twist correctly, one wire is placed on top of the other; to connect three conductors, the first is placed on top of the other two. They twist it, then crimp it using pliers, cut off the excess tails and crimp it again.
3. Before soldering, the twist is generously moistened with flux or placed in it.
4. To solder the wires correctly, the twist is heated with a soldering iron or torch until the flux begins to boil. As soon as the flux begins to boil, solder is placed on top of the twist. For soldering copper, use POS-60 solder or analogues. When using a soldering iron to connect wires, its tip is located at the bottom of the twist.
5. When the solder melts, it will spread under the action of tension forces and fill the twist, forming a reliable connection. The reddish copper color of the wires will take on a silver tint.
6. The last step is to isolate the junction. To do this, the soldered area is wrapped with PVC electrical tape, starting from the insulation that has not been removed. The adhesive layer of the electrical tape dries out over time, and the tape itself can unwind. Therefore, a heat-shrinkable tube of suitable diameter is put on top of it, which is heated with a hairdryer until it shrinks in size. It presses the electrical tape tightly and provides additional insulation.
7. Further soldering of wires in the distribution box - phase and neutral - is carried out in the same way.
8. After soldering and insulating the twists, the wires are carefully placed in the junction box and closed.

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.

General information

Solder paste is a pasty mass that consists of many small particles of spherical solder, flux and various additives. Why is it needed and what to do with it?

Solder pastes are used for surface mounting of electronic components by soldering on printed circuit boards, hybrid integrated circuits, and ceramic substrates. After application to the surface, the composition remains active for several hours. Scope of application: industry.

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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What is compound and how to remove it from the board

The compound is a resin that increases the strength of the board and reduces the operating temperature of the microcircuits. Also saves the board when exposed to moisture

If you need to resolder the chip, the compound will have to be removed. It is applied in different ways. Manufacturers can coat the edges of contacts with SMD parts. Or they can fill it completely.

How to remove resin from a board

Can be removed mechanically. To do this, heat the board with a hairdryer to 150 °C and use a toothpick or metal tweezers to remove pieces of the compound from the board. It's not always possible to do this.

You can also try chemical solvents. Typically sold at mobile phone parts stores.

And in order to desolder a microcircuit that has a compound under the contacts, you need cutting tweezers. The soldering procedure is similar to the usual one, but this time you need to cut off the compound.

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

Soldering process with an electric soldering iron

The entire technology of soldering wires with a soldering iron can be divided into several successive stages. All of them are repeated in a certain sequence:

• Training of conductors. When soldering wires, they are freed from insulation. After this, the oxide film is removed from them mechanically. You can use a small piece of fine-grit sandpaper. The metal should shine and be light.
• Tinning. Heat the soldering iron to the melting temperature of the rosin (it begins to actively melt when touched). Take a conductor, bring it to a piece of rosin, heat it with a soldering iron so that the entire stripped part of the wire is immersed in rosin. Then take a drop of solder onto the soldering iron tip and spread it over the treated part of the conductor. The solder spreads quickly, covering the wire with a thin layer. To make it distributed faster and more evenly, the wire is turned slightly. After tinning, copper conductors lose their redness and become silvery. This is how all wires that need to be soldered are processed.

That's all. In the same way, you can solder two or more wires, you can solder a wire to some contact pad (for example, when soldering headphones, you can solder the wire to a plug or to a pad on a headphone), etc.

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After you have finished soldering the wires with a soldering iron and they have cooled down, the connection must be insulated. You can wrap electrical tape, put it on, and then heat up the heat shrink tube. When it comes to electrical wiring, it is usually recommended to first screw on a few turns of electrical tape, and then put a heat-shrinkable tube on top, which is heated.

Differences in technology when using flux

If active flux is used rather than rosin, the tinning process changes. The cleaned conductor is lubricated with the compound, and then heated with a soldering iron with a small amount of solder. Further everything is as described.

Soldering twists with flux - faster and easier

There are also differences when soldering twists with flux. In this case, you can not tin each wire, but twist it, then treat it with flux and immediately start soldering. The conductors don’t even need to be cleaned—the active compounds corrode the oxide film. But instead, you will have to wipe the soldering areas with alcohol to wash away the remnants of chemically aggressive substances.

Features of soldering stranded wires

The soldering technology described above is suitable for monocores. If the wire is multi-core, there are nuances: before tinning, the wires are untwisted so that everything can be dipped in rosin. When applying solder, you need to make sure that each wire is covered with a thin layer of solder. After cooling, the wires are twisted into one bundle again, then you can solder with a soldering iron as described above - dipping the tip into solder, heating the soldering area and applying tin.

When tinning, multi-core wires must be “fluffed”

Is it possible to solder copper wire to aluminum

Aluminum cannot be combined directly with other chemically active metals. Since copper is a chemically active material, copper and aluminum are not joined or soldered. The point is too different thermal conductivity and different current conductivity. When current passes, aluminum heats up more and expands more. Copper heats up and expands much less. Constant expansion/constriction to varying degrees leads to the fact that even the best contact is broken, a non-conducting film is formed, and everything stops working. That's why copper and aluminum are not soldered.

If there is such a need to connect copper and aluminum conductors, make a bolted connection. Take a bolt with a suitable nut and three washers. At the ends of the connected wires, rings are formed according to the size of the bolt. Take a bolt, put on one washer, then a conductor, another washer - the next conductor, a third washer on top and secure everything with a nut.

Aluminum and copper conductors cannot be soldered

There are several other ways to connect aluminum and copper lines, but soldering is not one of them. You can read about other methods here, but bolted is the simplest and most reliable.

Connecting wires is a necessary operation when carrying out electrical work. Each method of connecting electrical wiring (crimping, twisting, soldering) has its own conditions for use. Soldering copper wires and soldering aluminum wires is the most reliable method of contact connection; in terms of strength, it competes only with welding.

BGA soldering of a processor using the example of a tablet

The tablet booted every other time. When pressure is applied to the processor, the loading screen goes through, but the charging percentage is 0%. Changing the battery and trying to flash the device did not lead to anything. Engineer mode is also not available.

There is a lot of loose debris near the processor; it is better to cover it with thick aluminum tape so as not to accidentally blow it away.

Processor desoldering

Be sure to take a photo of the soldering area so that there are no problems determining which side the key is located. First, the soldering area is heated to 100 - 150 °C at maximum air flow. After about a minute, gradually increase the temperature. 200 °C, 250 °C and ceiling 310 °C - 320 °C. At temperatures above 250, we try to gently rock the processor with tweezers. If it stands still, then wait some more (or increase the temperature, but not more than 320 °C). When the processor wobbles from one touch of tweezers, then it’s time to remove it. In this case, everything is protected with foil, so the risk of touching the crumbs is minimal, so you can use tweezers to fold it onto the board.

Removing the solder

It is better not to use braid to avoid damaging the mask. Using a soldering iron and a little solder on the tip (to dilute the solder with what is on the board), we move along the pads with light and not sudden movements. Naturally, before this we apply flux to the board. The same procedure applies to the processor itself. It is important not to overheat it and not rip off the coin.

By the way, after desoldering it was discovered that on several contacts there was a detachment of the processor from the board. Since the copper layer was intact on the processor, we were able to re-tin the broken contacts with the balls.

CPU reballing

Reballing is the resoldering of a microcircuit. This is not replacing the old one with a new one; in fact, the balls on the chip are updated for better contact with the board.

Using solder paste and a stencil, we apply new balls to the processor.

Soldering temperature is much lower. 180 °C - 200 °C. We fix the processor to the stencil using the same aluminum tape.

After the stencil, clean the processor and apply a little flux. Then we heat it again so that the balls fall into place more accurately and melt better. Clean after this procedure.

Then, before installation, apply flux to the board in an even layer. Using spatulas or toothpicks, distribute it evenly so that all contacts are well soldered and the processor does not float.

We place the processor according to the key and position its edges. Since there is a lot of tape around, this won’t be too difficult. After this, we also first heat the board at 100 - 150 °C, then increase it to 200 °C - 230 °C and carefully try to touch it with tweezers to make sure whether the solder has melted or not. If you do this abruptly, you will have to repeat everything again because... the balls stick together.

After soldering, remove the tape and it is best not to clean the board at all. There is very little air under the BGA chips, and therefore, once the cleaning agent gets there, it is very difficult to completely remove it. Of course, you can try to “evaporate” the flux at 100 °C, but if you have a good and no-clean flux, then there is no need to worry.

The tablet started to turn on without any pressure on the processor, but after booting it turned off at 0%. Only now can you enter engineer mode and try to reset the tablet. After the reset, the device turned on normally and shows the charging process, the remainder and stopped turning off.

Now you need to carefully check all its functions. Camera, sound, microphone, Wi-Fi, touchscreen.