Briefly describe the classification characteristics of welding materials in PCB smt patch processing

Briefly describe the classification characteristics of welding materials in PCB smt patch processing

Commonly used solder matching examples are as follows:

1. Tin 60%, lead 40%, melting point 182℃;

2. Tin 50%, lead 32%, cadmium 18%, melting point 150℃;

3. Tin 55%, lead 42%, bismuth 23%, melting point 150℃.

There are several types of solder, such as wafer, ribbon, ball, and solder wire. The commonly used solder wire has a solid flux rosin sandwiched in it. There are many types of solder wire diameter, commonly used are 4mm, 3mm, 2mm, 1.5mm and so on.

According to its component parts, solder in smt chip processing can be divided into tin-lead solder, silver solder and copper solder. According to the ambient humidity of use, it can be divided into high temperature solder (solder used at high temperature) and low temperature solder (solder used in low temperature environment). In order to ensure the quality of soldering in the patch processing, it is important to choose different solders depending on the different objects to be soldered. In the assembly of electronic products, tin-lead solders are generally used, also known as solder.

Solder has the following characteristics:

1. Has good electrical conductivity: Since tin and lead solders are good conductors, their resistance is very small.

2. Strong adhesion to component leads and other wires, not easy to fall off.

3. Low melting point: it can be melted at 180℃, and it can be soldered using 25W external heating type or 20W internal heating type soldering iron.

4. It has a certain mechanical strength: the strength of tin-lead alloy is higher than that of pure tin and pure lead. Due to the light weight of electronic components, the strength of solder joints in smt patch is not very high, so it can meet the strength requirements of its solder joints.

5. Good anti-corrosion performance: The soldered printed circuit board can resist atmospheric corrosion without applying any protective layer, thereby reducing the process flow and cost.

Among tin-lead solders, those with melting points below 450°C are called soft solders. Anti-oxidation solder is solder used in automated production lines in industrial production, such as wave soldering. When this liquid solder is exposed to the atmosphere, the solder is easily oxidized, which will cause virtual soldering, which will affect the soldering quality. Therefore, adding a small amount of active metal to the tin-lead solder can form a covering layer to protect the solder from further oxidation, thereby improving the soldering quality.

Because tin-lead solder is composed of two or more metals in different proportions. Therefore, the performance of tin-lead alloys must change with the tin-lead ratio. Due to different manufacturers, the proportion of tin-lead solder is very different. In order to make the solder ratio meet the needs of soldering, it is very important to choose the appropriate ratio of tin-lead solder.