What is solder paste and what is it for?
Features of the solder paste composition
Solder paste is a mixture of the following components: solder, flux and other binders. Pastes are necessary for soldering together various parts, and the work itself is very thin, almost jewelry. They are applied in a thin layer of a predetermined thickness using automated means.
If you answer the question “what is solder paste for”, then we will analyze the answer to it further. It has its advantages and disadvantages.
Any solder paste must meet the requirements on which, in fact, the quality of this product depends:
- Lack of spreading from the place of its application;
- The predominance of adhesive properties;
- Absence of splashing under the action of a heating source;
- Lack of delamination, as well as oxidation;
- Must be able to deform over time;
- No residue after soldering;
- Should not adversely affect the technical characteristics of the board;
- Should lose its properties in solvents (wash off).
- The predominance of adhesive properties;
- Absence of splashing under the action of a heating source;
- Lack of delamination, as well as oxidation;
- Must be able to deform over time;
- No residue after soldering;
- Should not adversely affect the technical characteristics of the board;
- Should lose its properties in solvents (wash off).
The paste used for dosing and for stenciling should be different in viscosity. The quality depends on the size of the solder particles - if the particles are too large, then the viscosity and the ability to deform deteriorate, and if the number of particles with small sizes predominates, then the fluidity of the paste deteriorates. Find more info about solder paste and how to use it at our website - https://electronicshacks.com. The shape of the particles also plays a role. If the particles are scaly or just a large amount of irregular shape, then such a paste will clog the stencil or syringe through which it will be fed. However, there is still an application for them - they are fed into the dispenser by means of a stencil.
The solderability of the paste, which is its main characteristic, depends on the particles of the solder and on the degree of its oxidation. An important role is played by the amount of oxygen that reacts with the flux and with the base metal. The regulations say that the oxygen content should not exceed 0.6%. In addition, the carbon that remains on the surface of the powder has a negative effect. From this we can conclude that the interaction of powder, carbon and oxygen must be strictly controlled throughout the entire duration of work, from the very beginning of manufacture to the very process of soldering.
In solder powder, binders are necessarily present in an amount of 5 to 15%. They are responsible for the consistency, protect the paste from spreading, cracking, delamination, and provide adhesive ability. When exposed to temperature, the binder evaporates, but when normal storage occurs, nothing terrible can happen, no effect on the solder is produced, and therefore its qualities remain at the same level. Such substances can be both resins and their mixtures.
Varieties of solder pastesThe choice of solder paste depends on the properties of the metal for which it is planned to use it. For example, for a nickel-chromium alloy, pastes are suitable, one of the components of which is either nickel or chromium. Such alloys are hard and the best place for their alloy is vacuum, argon.
For copper parts, copper-silver pastes are used, and to lower the melting point, they can be alloyed with lead or tin. For parts made of aluminum, "tin-zinc" solders are used, for silver and gold - a standard paste with a base of silver, where copper or zinc can be added.
In the event that you need to cover a large area with solder paste, then you can use a soldering dryer , which will prevent the product from warping and will contribute to uniform heating. If the connection is local, then a soldering iron will help.
Varieties of solder pastes can differ in flux components: there are three types in total:
- Rosin - compositions differ in activity: activated compositions, moderately activated and non-activated. The latter are active in the smallest amount. The most common are the components with the activity of the average value. They diverge well on the surface, wet the elements well, and also clean the surfaces. But since there is one minus - they can cause corrosion, the work surface must be washed with aqueous solutions or solvents. Highly active components are used for oxidized parts and after work they immediately clean the workplace.
- Water- washable - based on organic acids. When using such components, a good seam is obtained, but they must be washed with hot water.
- No- wash - made from natural resins and does not require rinsing. Even if some residual parts are present on the product, it will not bring any harm. These residues will not conduct current, will not oxidize, but if you want, you can wash it off with hot water.
- Water- washable - based on organic acids. When using such components, a good seam is obtained, but they must be washed with hot water.
- No- wash - made from natural resins and does not require rinsing. Even if some residual parts are present on the product, it will not bring any harm. These residues will not conduct current, will not oxidize, but if you want, you can wash it off with hot water.
Solder Paste Recommendations
It is very important that the area where the work will be carried out is clean and free from accumulation of dirt, debris or other contaminants. In order to ensure protection during work, gloves must be used for hands and goggles for the eyes . To wash the already applied paste from any element, it is necessary to use alcohol-containing compounds or another solvent.
Before the package with solder paste is opened, it must be placed in a room with a room temperature of 23-28 degrees, the humidity in the room should be from 30 to 60%. Before opening the package, it must stay in this room for at least two hours. Under no circumstances should artificial heating methods be used to accelerate. When the package is opened and work with the soldering agent has begun, it is advisable not to forget that the paste must be stirred periodically.
The application of solder paste is quite simple: you need to apply some solder paste to the stencil web. As you use the paste is added in small portions. In the event that the work is nearing completion, and the paste has not been used up, then it should never be mixed with a new paste. It should be stored in the refrigerator in a specially designated place.
In the event that the work has not yet been completed, you can continue to use the started paste or paste from the new package, but you need to mix the old paste with the new one and stir well. Then work must be started as soon as possible so that the properties of the paste remain the same.
Perhaps due to some unforeseen circumstances, the work should be interrupted for some short time, and the paste has already been applied to the stencil. In this case, it is necessary to place this paste in a container and close it tightly. Every 40 minutes, clean the stencil cloth.
In order to perform high-quality work with the help of solder pastes, you need to clearly understand how they work, understand the compositions. The substance that serves to bind the particles evaporates when the degrees are raised, and the composition remaining on the surface melts and connects the surfaces.
To speed up drying, you can use weak heating from below. The melting temperature of solder paste is 40-50 degrees, the activation process starts at 180-300 degrees.
When the binder evaporates, the heating temperature will increase. It is necessary to strictly follow the passport data and prevent either underheating or overheating, since underheating will reduce strength, and overheating can simply destroy the adhesion of parts with which you have already worked.
Since all these operations require precise execution, it may be better to try such activities on trial materials. When the job is done, you need to clean up, although this may not be necessary, as this depends on the choice of paste you have made.
The use of paste is very convenient - this is reflected not only in the application, but also in the fact that the board remains clean, and due to the spot application, the material is consumed economically and rationally. But there is still one drawback - this is a short shelf life, which is only a few months, after which the paste can simply exfoliate and be unusable.
