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Composition and Functions of Solder Flux
Author:
Release Date:
2022-12-13
Solder paste composition: Solder paste is primarily composed of alloy solder powder and flux. We will now discuss each component in turn:
Solder paste
I. Alloy Solder Powder: Alloy solder powder is the primary constituent of solder paste. Common alloy solder powders include tin–silver, tin–copper, tin–silver–bismuth, tin–copper, tin–bismuth, tin–lead, and tin–lead–silver. The melting temperatures vary depending on the specific alloy composition; accordingly, solder pastes can be classified as high-temperature, ambient-pressure, or ultra-low-temperature types based on their melting points and the operating temperature range.
The key factors determining solder paste performance include the morphology, particle-size distribution, and high-temperature oxidation level of the alloy solder powder. Alloy solder powders are classified into amorphous and spherical types based on their shape; spherical alloy powders have a smaller surface area, lower oxidation levels, and produce solder pastes with superior printing characteristics. The typical particle-size distribution for alloy solder powders ranges from 200 to 400 mesh: a narrower distribution results in higher viscosity, while an excessively broad distribution reduces the paste’s adhesion properties; conversely, if the distribution is too fine, the increased surface area leads to higher surface oxygen content, making such a distribution undesirable as well.
Lead-based solder paste
II. Flux: Flux is an indispensable raw material in the formulation of solder paste, and it constitutes a robust system within the solder paste composition. The main components and functions of flux are as follows:
A. Activator (ACTIVATION):
This ingredient primarily functions to remove surface oxides from the PCB copper foil solder layer and from the component soldering joints, while also reducing the interfacial tension between tin and lead.
B. Thixotropic Agent:
This ingredient is typically used to adjust the viscosity of solder paste and its printability during packaging, effectively preventing issues such as tailing and adhesion during printing.
Solder paste
C. Epoxy Resins:
This ingredient primarily enhances the adhesion of solder paste and provides protection to prevent post-soldering oxidative degradation of the PCB in ambient air; moreover, it plays a critically important role in securing components in place.
D. Organic solvent (SOLVENT):
This component is an organic solvent in the two-part solder flux, playing a crucial role in ensuring uniform mixing throughout the entire solder paste formulation process and thereby influencing the service life of the solder paste. The composition of the flux has a significant impact on the solder paste’s spreadability, lubricity, slump, viscosity changes, cleanability, solder balling and spattering, as well as its shelf life.
The foregoing section has summarized the types of solder paste ingredients and the functions of fluxes. Our product lineup includes lead-free solder pastes, SMT pick-and-place solder pastes, LED solder pastes, SMT red adhesive, solder wire, lead-free solder wire, leaded solder wire, rosin-core solder wire, various grades of solder wire, and lead-free solder bars, among other manufactured products.
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