Soldering flux is an auxiliary substance, the use of which helps clean the surfaces of metal elements being joined from oxidation. When resorting to soldering without using flux, you should not count on high-quality work and reliable fastening of the necessary parts. Therefore, before you begin joining parts using a soldering iron, you need to select a good, high-quality flux.
Purpose
Fluxes are used primarily to remove all kinds of contaminants from the surface of the metal. Moreover, when soldering joints, they protect the heated solder from oxidation. This, in turn, promotes the spreadability of solder and, accordingly, improves the quality of soldering.
A good flux for soldering can only be selected based on the nature of the metal joints and the alloy of the solder. Residues of any fluxes, regardless of their type, must be removed from the joints after completing the work, since they themselves contaminate the metal and can lead to the development of corrosion processes.
Types of fluxes for soldering
Conventionally, fluxes are divided into two main categories - oxidizing and reducing. Also, depending on the need to perform certain tasks, fluxes are used for melting metal, welding work, electrolysis, growing single crystals, soldering non-ferrous and jewelry alloys.
In general, according to the effect that is exerted on the metal during soldering, the following fluxes are distinguished:
- active (acidic);
- acid-free;
- anti-corrosion;
- activated;
- protective.
Active fluxes
This soldering flux often contains hydrochloric acid, fluoride and chloride metals. The action of active fluxes involves the active dissolution of oxide films on the surface of metal parts. Thanks to these properties, maximum mechanical strength of the resulting joints is ensured.
Despite their wide distribution, active fluxes are not suitable for use in the installation and soldering of electrical equipment, because their residues quickly corrode the joint of parts.
Acid-free fluxes
Acid-free soldering flux, commonly known as rosin, is a substance made from alcohol, glycerin and turpentine. When the soldering iron is heated to a temperature of more than 150 o C, the use of such a flux makes it possible to dissolve the oxides of lead, copper, and tin, reliably cleaning the metal surfaces.
The main advantage of flux in the form of rosin is the absence of the effect of separation of the joined surfaces during soldering. This flux is widely used for soldering copper, bronze, and brass.
Activated fluxes
This type of flux is prepared on the basis of phosphoric or hydrochloric acid aniline, diethylamine or salicylic acid. This option is suitable for soldering a wide range of metals and alloys, such as iron, copper, steel, nickel, zinc, silver, as well as copper parts without the need for pre-cleaning.
Anti-corrosion fluxes
Based on the definition itself, it is easy to guess that anti-corrosion flux is used for soldering most often when it is necessary to connect parts that are potentially susceptible to the development of corrosion processes.
The composition of soldering flux with anti-corrosion properties includes the use of technical petroleum jelly, salicylic acid, triethanolamine and ethyl alcohol. Despite its main purpose, this type of flux requires careful removal of its residues upon completion of soldering by wiping the parts with acetone or alcohol.
Protective fluxes
Since there is no destructive chemical effect on metals during use, protective flux can be used for soldering microcircuits. Like most other types of fluxes, such substances protect previously cleaned metal surfaces from oxidation. The category of protective fluxes primarily includes petroleum jelly, wax, powdered sugar, olive oil, and other substances with weak chemical activity.
Storage
The most common alcohol-based fluxes usually have a liquid consistency. Therefore, they need to be stored in a carefully sealed, airtight container. Otherwise, there is a loss of their basic properties and even complete evaporation.
Soldering flux paste also needs to be stored in a closed container. The optimal conditions for such flux are a room with a low level. Although the paste does not absorb moisture from environment, there is a danger of moisture condensation on the walls of the container and surfaces located nearby.
It is recommended to store flux gel for soldering away from flammable substances, objects and sources of open flame, since most fluxes in this category are highly flammable. In this case, the storage temperature should be no lower than 10 and no more than 25 degrees Celsius.
Application of flux
When soldering, the joints are thoroughly cleaned, coated with flux and heated with a soldering iron. At the point of application, the flux begins to foam and smoke. At this moment, a small amount of solder must be applied to the tip of the soldering iron, which will subsequently cover the surfaces to be connected.
It’s probably not worth talking about the properties and advantages of using fluxes for soldering once again. You just need to take a soldering iron and try to connect the parts without flux. In this case, the soldering process will be truly lengthy, and the result will be frankly of poor quality, since the solder will be too unreliably fixed to the surface being soldered.
How to prepare flux for soldering yourself?
The simplest option for self-cooking flux is the use of a rosin-alcohol base. To begin with, rosin powder is poured into the container, after which it is filled with an alcohol solution. After some time, the alcohol will evaporate and the flux will acquire a moderately thick consistency, convenient for applying the substance to metal parts during soldering.
As a self-prepared flux, which is suitable for tinning steel and copper surfaces, you can use acetylsalicylic acid dissolved in a small amount of water, acetone or alcohol. It is convenient to store such liquid flux in a varnish container, using a lid with a brush when applying.
How to choose the right flux?
According to avid radio amateurs who are well versed in soldering, choosing the right flux is an almost 100% guarantee of successful completion of the job. Here, first of all, you should focus on the material of the parts being connected, as well as the nature of the soldering.
For soldering radio components, copper parts and wires, it is advisable to use inactive fluxes based on rosin. Such fluxes are a modified version of ordinary rosin as a result of the addition of a number of components known as activators.
Inactive fluxes have improved antioxidant properties. Due to their paste or liquid state, such fluxes can be applied directly to circuit boards or soldering joints of metal joints. This flux is ideal for soldering aluminum. Additionally, it is worth noting their wide availability and relatively low cost.
As for medium-active fluxes, it is advisable to use them for soldering the most delicate contacts, for example during repairs mobile phones and other modern portable devices. Suitable for this purpose are fluxes that do not foam or boil during operation, have minimal corrosion, and are also easy to apply to boards.
Often, medium-active fluxes are used by craftsmen service centers digital repair mobile devices. They are usually used for soldering the smallest microcircuits. Moreover, they are suitable for use not only with lead, but also with lead-free solders.
The most versatile are gel fluxes. They can be used for almost any type of soldering. Gel-like flux is especially effective for soldering aluminum, copper, and other common materials using lead solders.
In conclusion
Correct selection of suitable consumables when performing soldering, it is a guarantee of quality work done. In addition to choosing a good flux, you need to select a solder that matches the nature of the soldering, a hair dryer attachment, a soldering iron tip, and other things.
Even if you use the most advanced soldering stations in your work, if you have the wrong flux, solder or tip, you can end up getting a completely different result than you expected. Enough water has flown under the bridge since then, when specialists actively used classic soldering irons with a power of up to 60 W with a homemade copper tip turned by a file, as well as ordinary rosin as a flux. Currently, the use of such material and technical base is extremely ineffective.
Hi all.
Today's review will be devoted to three Chinese fluxes that I purchased on eBay. They were bought after my home supplies of this soldering accessory began to run out. Since I had not ordered this type of product from China before, and had not used Chinese fluxes at all, I decided to buy several different jars at once, fortunately, they all cost mere pennies - $0.99 per piece.
All three lots were ordered in one store, so as not to rush to the post office 3 times. So the order was placed and paid, and the next day the seller gave me a track to track it. So you can see all the information about moving a parcel from China to Belarus.
So, as I already said, I ordered 3 different fluxes. 
As a test, we will try to tin and solder stranded copper wires with their help. True, the wires are terribly oxidized. I specifically looked for three pieces identical in cross-section and similar in contamination. 
The soldering object will be some kind of automotive connector, which has been lying idle in my garage for many years. It also managed to become quite oxidized and dusty. For the purity of the experiment, neither the wires nor the connector will be cleaned before starting the “procedure”. Actually, the connector itself to which we will try to solder the wires (to a metal arc): 
But before moving directly to the review, let me remind you what flux is and why it is needed. Flux - substances (usually a mixture) of organic and inorganic origin, intended to remove oxides from the surface for soldering, reducing surface tension, improving the spread of liquid solder and/or protection from the environment.
The first one is RMA 223, was ordered.
It comes as if in a syringe, however, this syringe has neither a plunger nor a needle :) But you don’t have to worry about it accidentally leaking.
Description (Google translation):
Type: RMA-223.
Good dive;
Volume: 10 ml / 10 cc;
Size: 95 x 35 x 23 mm.
RMA-223 is a high viscosity impure flux, it can be used for PCB, BGA, PGA processing, it can be used for soldering and reballing of computer and telephone chips. It is a mixture of high quality alloy powder and resinous paste flow, it can avoid the pale yellow residue, so you can clean the board easily.
This flux has a gel-like consistency, making it easy to apply. Outwardly it has a pale yellow color, but when viewed through light it is cloudy. 
When heated, it spreads perfectly and smokes :) I would like to believe that it also actively penetrates between the wire strands. 
Second - PPD PD-18, (although it says PD-10 on the jar) was ordered.
Unlike the first one, it comes in a metal jar, somewhat reminiscent of the “Zvezdochka” balm jars, although several times larger. If in the first case the syringe was sealed, then the iron jar turned out to be not such a reliable package. At the time of receipt, it was all covered in gumboil both inside and outside. He carefully wiped everything off and threw it on the shelf. I got it out after some time - the same story again. So you need to store it carefully, do not allow the jar to turn over, otherwise its contents may not survive until soldering - it will leak out. 
Description (Google translation):
Type: PPD PD-18;
Weight: 10 g;
Peculiarities:
Joint high intensity;
Good dive;
Neutral PH7 ± 3;
No poison no;
Good insulation;
Smooth welding surface;
There is no wear and tear.
It is thicker in consistency than the first and has a more pronounced orange color. They smell similar, but it’s hard to say what exactly they smell like. The smell is familiar, but I can’t remember what exactly it is.
The open can provides excellent access to the contents. If you want wiring, dip it in, if you want, insert a board :) 
When heated, it spreads beautifully and smokes perfectly. There seemed to be a little more smoke than in the first case and it was more acrid.
Third - XY-5 (soldering rosin), was ordered.
Like the second option, it comes in a jar, although not metal, but plastic. 
Due to its solid state, it can be easily transported and constantly stored, even in your pocket. Nothing will leak, nothing will get dirty.
In the solid state, it has a rich amber color, familiar to everyone who has worked with rosin. When heated, it melts with a profuse release of smoke that smells like resin, which is not surprising :) To be honest, my favorite option. When heated, it spreads well, but also cools quite quickly. When solid it crumbles.
Description (Google translation):
Name: Solid rosin;
Weight: 22 grams (including box).
It’s austere, but what we have is what we have :)
It may not be entirely correct to compare the first two samples with this one, but, by and large, the first, second, and third are flux and are used for the same purposes.
So let's begin.
The first wire was soldered using flux No. 2 PPD PD-18. Due to the abundance of contamination and the rather large cross-section of the wire, quite a bit of solder had to be used: (But the result was not long in coming - the wire was soldered: 
Without the use of flux, the solder on the bracket refused to adhere completely. If you look at the photo above, you will see how it flowed from it, spreading across the plastic.
The second wire was soldered using solid flux No. 3 XY-5 (or rosin). To be honest, the first attempt was not entirely successful: the wire fell off the connector bracket along with all the solder :) But you can see how all the dirt had collected on the solder, and a place appeared on the bracket without dirt: 
But on the second attempt, he finally took his place where it was required.
The last flux used was No. 1 RMA 223. The wiring was soldered without any problems and finished the exposure called “hedgehog” :) 
It's a hedgehog, but the most important thing that is required from a flux is to strengthen the joint during soldering. So the simplest thing that came to my mind to check the results is to try to tear off the soldered wires :) Result: 
As you can see, flux No. 2 worked perfectly: the solder itself remained in place, but the wire simply tore it. True, I had to pull with a fair amount of effort. Flux No. 3 (rosin) also turned out to be quite good: no matter how hard I pulled, the wire remained in place. The only thing we managed to separate was the insulation from the cores :) But flux No. 1 failed. The solder just fell off and I didn’t have to work too hard to do it :(
Conclusion: RMA 223 is not worth taking; it does not cope with its task as a flux (because it is more Vaseline, and not a flux as such). But XY-5 and PD-18 showed themselves with positive side. When choosing between them, I would give preference to solid flux only because it is more practical to store, and its smell is much more pleasant :) But everyone decides for themselves what to buy.
Yes, to improve the results, it would be possible to tin the wires and treat the bracket with orthophosphoric acid, but I wanted to know which flux would perform better under the harshest conditions :)
That's probably all. Thank you for your attention and your time.
I'm planning to buy +31 Add to favorites I liked the review +49 +86|
Physical state: Gel Used for soldering radio engineering products and mounting SMD components. Suitable for soldering almost all metals and alloys. The flux contains an activity indicator. After installation, the red flux becomes discolored, which indicates the absence of an active component at the soldering site, and therefore there is no need for cleaning. |
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Delivery and pickup Pickup from the office (m. Oktyabrskoye Pole): for free Courier delivery in Moscow: 400 rubles Delivery to Boxberry pick-up points*: From 187 rub. *delivery to Boxberry pick-up point is available only to individuals |
Specifications
TT flux gel is suitable for soldering almost all metals and alloys.
Active in the temperature range: 110 - 250°C
Does not have its own electrical resistance
Flux residues protect the soldered seam from corrosion
Toxicity:
General toxicity: Moderate.
MPC: 2.5 mg/m³
Allergen: Hypoallergenic.
Compatibility with materials in contact with food and skin: No data.
General toxicity after heat treatment at 160°C: Low
Directions for use:
Apply TT flux gel to the area intended for soldering.
Solder with solder (POS 10-90, Rose, Wood alloy)
For SMD:
Apply TT flux gel to the area intended for planting components, with a layer of 0.5-0.9 mm.
Place components.
Treat with a hot air gun at 170-250°C
If necessary, flux residues are removed with alcohol or white spirit.
Product form:
Jars of 20 and 500 ml.
OKP code: 17 1800, not subject to mandatory certification.
Passport:
Flux-gel TT
TU 1718-001-30663583-2011
No. Name of indicators
1. Appearance Paste, dark to light red in color.
2. Content of mechanical impurities - Absence
3. Reaction of the medium (pH of aqueous extract) - 2-4
4. Mass fraction of nitrogen,% - 0.15-0.25
5. Specific volume resistivity, after heat treatment at 210°C, 10 min. With a layer of 0.5 mm., Ohm *cm- Absent.
Note:
1. Thickener - Vaseline.
2. MPC in air 2.5 mg/m^2
Guaranteed shelf life 1 year.
Of course, you can make your own flux for soldering. To do this, the resin collected from coniferous trees in the forest must be melted in a tin can over low heat, stirring occasionally, and then simply poured into containers. When the mixture hardens, you will get rosin. But let’s not engage in amateur activities, it’s not worth it, but it’s better to consider different types fluxes, which can be purchased at any electronics store.
Requirements for fluxes used in soldering work
- The melting point of the flux must be lower than the melting temperature of the solder.
- The flux must be completely molten and have good fluidity during the soldering process.
- It should quickly and completely dissolve the oxides of the metal being soldered.
- Should not form chemical compounds with metal or solder.
- It should evenly cover the surface of the metal at the soldering site, preventing it from oxidizing during the soldering process.
- It should not quickly evaporate during soldering, and its decomposition products should be displaced by solder and easily washed off after soldering without causing corrosion of the soldering area
Gel fluxes are, in principle, ordinary rosin, but in a gel state. They are best used for delicate soldering of radio components and repair of mobile phones, laptops, smartphones, etc. Their main feature is that they are very easy to wash off with Flux-Plus, acetone or gasoline; you can also use alcohol.
Currently, two types of gel fluxes can be found on sale: Flux-Plus and its cheap Chinese analogue RMA-223
Flux-Plus is considered the best among gel products. Even a complete guy can solder with it. But its price of 20 green pieces of paper is not at all pleasing. So before you buy, think about whether it is worth the money? If you are a repairer of smartphones or tablets, then it will definitely pay for itself, but for ordinary fans of soldering, I would recommend its Chinese counterpart.
Gel soldering flux RMA-223 is a Chinese counterfeit of the branded Flux-Plus. The cheapest place to order it is from Chinese internet stores During soldering work, it also spreads well and envelops the solder. I advise everyone to use it and you won’t go wrong.
To prepare it at home and with our own hands, we will need the following ingredients: medical or industrial alcohol to dissolve the rosin, a hammer or something similar to grind the rosin, and a container for storing the resulting liquid composition. Then we crush the pieces of rosin with a hammer, I advise you to wrap them in a bandage or any piece of cloth before doing this. Pour the resulting powder into a bottle and fill it with alcohol (I’ll answer your question right away: “Vodka will not work”), after a few days of settling, the product will serve perfectly for soldering operations.
Why can't you solder with rosin? It’s possible, but it’s not very convenient since you have to very quickly bring the evaporating rosin to the place and you still have to spread it a little with a soldering iron on all the surfaces to be soldered.
It is used for soldering work as a liquid agent for oxidized copper, ferrous metal and stainless steel. Can also be used to remove rust. After use, it forms on the treated surface. protective film which prevents the corrosion process
Used for soldering carbon and low-alloy steels, nickel and alloys. The liquid is active at a temperature of 290-350 °C. After using a special product, the surfaces must be washed with a solution of soda ash
Made on a Vaseline base, suitable for soldering highly oxidized metals from ferrous and non-ferrous metals
The active agent is used for radio installation of electronic components and printed circuit boards. After use, rinse with water or alcohol is necessary.
This liquid can be purchased at a regular pharmacy, it costs much less than alcohol, and the effect is the same, although it contains 90% ethyl alcohol.
No laundering. If desired, wipe off excess liquid with a rag. In addition to soldering, aluminum can be used for soldering stainless steels, nickel, copper and other metals.
Rosin, in its properties and characteristics, fully satisfies the requirements for fluxes; it just needs to be able to solder.
The specific gravity and melting point of rosin are lower than those of solder
It melts completely and has good fluidity at the correct soldering temperature. At the same time, there is a small advantage compared to standard fluxes, namely, the molten rosin does not “leak out” from the soldering site
Rosin completely dissolves oxides, and this reaction occurs at a temperature that is several degrees lower than the melting temperature of solder
Rosin is always neutral, it does not react and does not form chemical compounds with solder and the base metal.
It evenly covers the surface of the soldered metal, creating protection against oxidation.
Rosin does not burn out at soldering temperature, while the solder completely expels all its decomposition products
After the soldering process, the remaining rosin remaining on printed circuit board, easy to wash
It is a clear glassy resin, light yellow in color, hard but brittle. It is obtained from the resin of trees of various coniferous species. Rosin is essentially a mixture consisting of resin acids (their chemical formula is C 20 H 30 O 2), various types fatty acids and small amounts of oxidized and neutral substances. The basis for high-quality rosin is abietic acid.
Rosin dissolves well in alcohol, ether, turpentine, and worse - in kerosene and gasoline. Completely insoluble in ordinary water.
According to the method of obtaining rosin, there are:gum– obtained from the resin of coniferous trees. Mostly pine trees. This type of rosin has virtually no fatty acids in its composition.
extraction– obtained by extracting crushed coniferous wood with gasoline. This type of rosin is darker, has a lower softening point and has a fairly high fatty acid content.
tallow rosin- It is a by-product of cellulose sulfate production in the manufacture of soap.
Rosin soldering technique
Soldering with rosin is quite easy. Before starting soldering, it is necessary to tin the parts. For this purpose, heated to operating temperature A soldering iron with a clean tip is dipped into rosin.
Then you need to coat it with solder and apply it to the surface to be soldered. After which the parts are fixed and at the point of contact they are briefly touched with a sting. Solder spreading over the surface as a thin film after cooling will create good connection. After soldering is completed, the remaining rosin is washed off with alcohol or solvent.
It is common knowledge that fluxes are used to remove solder residues and contaminants, as well as to protect against oxidation.
A variety of fluxes are used chemical compositions: rosin, orthophosphoric acid, soldering acid and active soldering fat, Borax, TAGS glycerin flux, etc. Today we will talk about another type of flux - gel fluxes.
Gel fluxes are the same rosin, only in gel form. They are used for primary and re-soldering of critical components, at the household level when repairing laptops or smartphones. Their important advantage is that they are easily washed off or do not require rinsing at all.
You can often read on forums that the best flux gel is FluxPlus, but there is also its Chinese analogue RMA-223. This big mistake! Of course, there is a Chinese analogue, but RMA-223 is a high-quality flux made in America by Amtech.
What to do with Chinese counterfeits? After all, the market is large, there is demand, and there are counterfeits. Of course, you can spend a long time sorting out the numbers that should be indicated on the labeling, lot numbers, etc. Or you can simply purchase fluxes from trusted suppliers. For example, our Amtech fluxes are purchased only from the official Amtech representative in Russia.
Today, the most popular brands of Amtech fluxes are two: RMA-223 and LF-4300.
LF-4300 is a water-washable flux of medium viscosity, it does not require cleaning and is used with both lead and lead-free alloys. It is convenient to use for installing solder balls, BGA pins and reballing. This flux gel is widely used in the installation of all types of Flip Chip and CSP.
The flux is water-washable, but in most cases, residues can be left on the boards. If the boards undergo cleaning, it can be removed using deionized water at a temperature of 40-60 degrees.
RMA-223- This is a rosin flux, it is recommended only for lead-free soldering. It has excellent spreadability and wettability. Like the LF-4300, it is used to work with components in BGA/PGA packages. The flux has weak activity, so its remains must be washed off.
Both flux gels are marked at the end with the letters -TF. This stands for Tacky Paste Fluxes, i.e. sticky, viscous fluxes. They are often compared to honey because they are supposed to have the viscous consistency of honey and the same yellow-amber color. It is their stickiness and ductility that make it easy to work with solder balls during BGA soldering.
Amtech gel fluxes are supplied in a syringe, which allows you to accurately dose the flux and apply it only to those areas where it is needed, without contaminating adjacent surfaces.
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