1. Welding Basics

Manual soldering: refers to the process of soldering/or desoldering the solder and the soldered parts (such as component pin soldering ends, pads, wires, etc.) by manual operation with the soldering iron head as the main heat source and other manual equipment. /Operation. It is the basic and effective assembly method for manufacturing electronic products.

1. Wetting: The molten solder expands on the surface of the base metal to be welded to form an adhesion layer.

There are many examples of this in nature. For example, drop a drop of water on a clean glass plate, and the water droplet can be completely spread on the glass plate. At this time, it can be said that the water completely wets the glass plate; if the drip is A drop of oil, the oil drop will form a ball, which will spread to a limited extent. At this time, it can be said that the oil drop can be wetted on the glass plate; if a drop of mercury is dropped, the mercury will form a sphere and roll on the glass plate. Explain that mercury does not wet glass. The same is true for the wetting and spreading of the base metal by the solder. When the solder melts on the pad without flux, the solder rolls on the pad in a spherical shape, that is, the cohesion of the solder is greater than the adhesion of the solder to the pad. At this time, the solder does not wet the pad; when the flux is added, the solder will spread on the pad, which means that the cohesion of the solder is less than the adhesion of the solder to the pad, so the solder can be wet on the pad. Wet and spread.

2. Wetting angle: refers to the angle between the interface between the solder and the base metal and the tangent to the surface of the solder after the solder is melted, also known as the contact angle

3. Diffusion: With the progress of wetting, the mutual diffusion between the solder and the metal atoms of the base metal begins to occur. Usually atoms are in a thermal vibrational state in a lattice lattice, once the temperature is raised. The intensified atomic activity causes the atoms in the molten solder and the base metal to cross the contact surface and enter the lattice lattice of each other. The moving speed and number of atoms are determined by the heating temperature and time.

Second, the role of flux

The word FLUX comes from the Latin for "Flow in Soldering".

The main functions of flux are:

1. remove oxides

To achieve a good solder joint, the object to be soldered must have a completely oxide-free surface, but once the metal is exposed to air, an oxide layer will regenerate, which cannot be cleaned with traditional solvents, and must rely on flux. It has a chemical effect with the oxide layer. After the oxide layer is removed by the flux, the clean surface of the soldered object can be combined with the solder.

There are several chemical screenings of fluxes and oxides:

a, chemical interaction to form a third substance;

b. The oxide is directly peeled off by the flux;

c. The above two reactions coexist.

2. prevent re-oxidation

When the flux removes the oxide reaction, it must also form a protective film to prevent the surface of the solder from re-oxidizing until it contacts the solder. Therefore, the flux must be able to withstand high temperatures, and will not decompose or evaporate at the temperature of the soldering operation. If it decomposes, it will form solvent-insoluble substances, which are difficult to clean with solvents.

3. Reduce the surface tension of the welded material

During the soldering process, the solder is basically in a liquid state, while the component pins or pads are in a solid state. When the two substances are in contact, the surface tension of the liquid substances will directly reduce the contact interface between the two substances. Our superficial generalization of this phenomenon is "poor tin fluidity" or "low expansion rate", the existence of which affects the area, volume or shape of alloy formation. What is needed at this time is the role of "surfactant" in the flux. "Surfactant" usually refers to a substance that can significantly reduce the surface tension of other substances at very low concentrations. A group structure, one end is hydrophilic and oleophobic and the other end is lipophilic and hydrophobic. It can be seen from its external performance that it is composed of solvent-soluble and solvent-insoluble parts, which are located at the two ends of the molecule, forming a combined The asymmetric structure, the reason why it can significantly reduce the surface tension is determined by this special structure.

The amount of surfactant added in the flux is very small, but its role is very important. It reduces the "surface tension of the material to be welded", which shows a strong wetting effect, which can ensure that the tin liquid is in the soldered object. Smooth surface expansion, flow, wetting, etc. Usually, the bad conditions of solder joints such as balling, false soldering, and tipping are related to insufficient surface activity. The reason for this is not necessarily that the amount of "surfactant" added in the flux is too small, but it may also be caused by the production process. Caused its composition decomposition, failure, etc., thus greatly weakening the surface activity.

Third, the structure of the soldering iron

(1) Handle (2) Electric heater (3) Soldering iron tip (4) Temperature control system

The role of each part:

Soldering Iron Handle - Provides the operator with a handle that is comfortable and safe to use.

Electric heater - electric heat conversion, providing heat energy for the tip of the soldering iron.

Soldering iron tip - accepts and stores thermal energy, and transfers the thermal energy or temperature required for soldering to the required soldering place quickly and efficiently.

Temperature control system - to control the soldering iron tip to reach the required soldering temperature and maintain its stability.

Characteristics and parameters of electric soldering iron

1. Input electric power (power consumption) 6. Soldering iron tip leakage voltage

2. Electrothermal conversion rate 7. Electrical insulation resistance

3. Heat capacity 8. Service life

4. Maximum welding temperature 9. Operation and maintainability

5. Reheat rate 10. Price

Basic principles of soldering iron tip selection

1. The thickness or quality (ie weight) of the soldering iron tip should match the heat capacity or soldering temperature required at the place to be soldered.

2. The geometry of the soldering iron head (especially its head) should be suitable for the spatial orientation of the soldering iron.

3. The geometry of the head of the soldering iron head should maximize the contact area with the soldered part.

4. The handle of the soldering iron head should match the body of the soldering iron used (that is, the inner diameter or outer diameter of the handle should match the body of the soldering iron properly without loosening).

5. The soldering iron tip should have a long service life (such as high temperature resistance, corrosion resistance, not easy to wear, etc.) and the price should be suitable.