1. Master the principle and working process of welding.

2. Master the selection and use of solder and flux.

3. Master the classification and usage of electric soldering iron.

4. Master the welding process: the difference between component forming and bending and SMT welding process, and improve the welding process in the actual process.

Second, the content of welding practice: the classification of brazing is mainly divided into three categories: fusion welding, contact welding and brazing.

1. fusion welding: fusion welding refers to the method of heating the welded joint to a molten state during the welding process and completing the welding without external pressure. Such as arc welding, gas welding, etc.

2. Contact welding: Contact welding refers to a method in which pressure (heating or not) must be applied to the weldment to complete welding. Such as ultrasonic welding, pulse welding and friction welding.

3. Brazing: Brazing refers to heating the weldment and solder to a temperature higher than the melting point of the solder but lower than the melting point of the welded object, wetting the welded object with liquid solder, and diffusing with the welded object to realize the connection.

4. Welding mechanism: Welding is to heat the solder and the welded metal to the optimal temperature at the same time. The solder melts into the gap between the welded metal materials, and the surfaces of different metals penetrate and diffuse with each other, eventually forming an alloy layer, so that the welded metals are permanently and firmly combined.

Third, the choice and use of solder and flux.

(1) Definition of solder: a fusible metal or alloy that can fuse two or more metals into a whole.

Classification: according to components: tin-lead solder, silver solder, copper solder, etc. According to temperature resistance: high temperature solder, low temperature solder and low melting point solder.

1. Characteristics of tin:

1. Soft, low melting point, melting point temperature 2320C；;

2. Pure tin is expensive, fragile and has poor mechanical properties;

3. At room temperature, it has strong oxidation resistance.

2. Lead (Pb) characteristics:

1. Light blue soft metal with melting point of 3270°C；;

2. Poor mechanical properties, good plasticity, high oxidation resistance and corrosion resistance;

3. Harmful to human body (heavy metal).

3. Tin-lead alloy (commonly known as "solder") is an alloy solder made of lead and tin in different proportions. In the installation of electronic products, the proportion of tin and lead in common tin-lead alloy solder is 63% and 37%, also known as "* * * crystal solder" * * crystal solder features:

1. Low melting point, melting point temperature 1830C, to prevent damage to components;

No semi-liquid, which can make the solder joint solidify quickly and avoid virtual welding;

3. The surface tension is low, the solder has strong fluidity, and it has a good wetting effect on the welded object, thus improving the welding quality;

4. Strong oxidation resistance;

5. Good mechanical properties.

(2) Flux function: remove the oxide layer and impurities between the surfaces of the welded metals during the welding process.

1. Inorganic flux: type: sulfuric acid, hydrochloric acid, hydrofluoric acid, salts (ZnCl, NH4Cl, SnCl2) and other characteristics: it has the strongest activity and can remove the oxide film on the metal surface at room temperature. Easy to damage metals and solder joints, generally not used; Commonly known as "welding oil": a paste-like substance emulsified with engine oil, which can be cleaned with solvent.

2. Organic solvent: type: organic acid (stearic acid, lactic acid, oleic acid, amino acid, etc. ), organic halogen (aniline hydrochloride), amine (urea, ethylenediamine, etc. ). Features: It has certain corrosiveness; Not easy to clean

3. Rosin-based flux:

Type: rosin flux, active perfume, hydrogenated rosin.

For more information, please check Baidu Library.