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Solder and Its Classification

Solder is a kind of fusible metal with lower melting point than the metal being soldered, and also has certain compression capabilities with good conductivity and fast crystallization rate. When solder melts, it can wet the surface of metal being soldered and form the alloy layer on the connection to connect the metal together. It is widely used in electronic products mounting.



Solder has various categories. According to the melting point, solder can be divided into soft solder and hard solder. And the differences of composition makes solder have several solder types: tin-lead solder, sliver solder and copper solder and so on. But in solder paste printing, PCB manufacturers usually use the tin-lead solder.

Tin-lead solder is the most popular in solder paste printing and it is mainly composed of tin and lead, with some trace metal element like Sb. Tin-lead solder is widely used in radiators and soldering of electronic industry, and waving soldering dip and soldering in other industries. One of the best tin-lead solder is named eutectic solder with 61.9% tin and 38.1% lead, which enables it melt in a certain temperature but not in a temperature range. Besides, it has the lowest melting point so that it can turn into liquid from solid.

In application, solder will be processed into different sizes and shapes, like sheet, block, rod, strip, and filament, etc.

1. Filament solder with rosin core is named as rosin-cored filament solder that usually be used in manual soldering.

2. Sheet solder is commonly used in the soldering of silicon wafer and other weldments.

3. Strip solder will be commonly applied in automatic assembly line. Automatic soldering machine will punch a part of solder to do soldering in order to improve the production efficiency.

4. Solder paste is the mixture of solder and flux. It will be coated on the printed circuit board when soldering. And it has been extensively used in Surface Mount Technology (SMT).

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