The use of
solder paste is inseparable from the SMT chip processing technology. Solder paste is a slurry or paste made of uniformly mixed alloy solder powder and paste flux. Solder paste is an indispensable soldering material in the SMT process. It is widely used in reflow soldering and is one of the more important electronic accessories in the electronics industry.
Composition of solder paste: Solder paste is mainly composed of alloy solder powder and flux. Let's introduce them separately:
1. Alloy solder powder: Alloy solder powder is the main component of solder paste. Commonly used alloy solder powders include tin, silver-copper, tin-silver-bismuth, tin-copper, tin-bismuth, tin-lead, tin-lead-silver, etc. The different alloy ratios are Different melting temperatures can be divided into high-temperature solder paste, medium-temperature solder paste, and low-temperature solder paste according to the melting point temperature.
The main factors that determine the performance of solder paste are the shape, particle size and surface oxidation degree of alloy solder powder. The spherical alloy powder has a small surface area and a low degree of oxidation, and the solder paste made has good printing performance. The particle size of the alloy solder powder is generally 200-400 mesh, the smaller the particle size , the greater the viscosity, the larger the particle size, the poorer the bonding performance of the solder paste will be. If the particle size is too fine, the oxygen content on the surface will increase due to the increase in the surface area, so it is not suitable for use.
2. Flux: Flux is an essential raw material in the manufacture of solder paste. Flux is also a powerful system in the composition of solder paste. The main components of flux and their functions:
A. Activator (ACTIVATION):
This ingredient mainly plays the role of removing the oxidized substances on the surface layer of the PCB copper film pad and the welding parts of the parts.
B. Thixotropic agent (THIXOTROPIC):
This ingredient is mainly to adjust the viscosity and printing performance of the solder paste, and to prevent tailing and adhesion during printing;
C. Resin (RESINS):
This ingredient is mainly used to increase the adhesion of solder paste, and to protect and prevent the re-oxidation of PCB after soldering; this ingredient plays an important role in fixing parts;
D. Solvent (SOLVENT):
This component is the solvent of the flux component, which plays a role in adjusting the uniformity during the stirring process of the solder paste, and has a certain influence on the life of the solder paste; the composition of the flux has a great influence on the expansion, wettability, collapse and viscosity of the solder paste Changes, cleaning properties, bead splash and storage life all have a greater impact.
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