Explain the composition and characteristics of solder paste?

A.the composition of the solder paste

Solder paste is a key material in electronic soldering, mainly composed of the following three parts:

1. Tin powder, proportion: 80-90%

Composition: The main component is tin (Sn), sometimes also contains lead (Pb), silver (Ag), copper (Cu), bismuth (Bi) and other metal elements, the specific proportion of welding needs and application scenarios to adjust.

Characteristics:

Melting point: determines the soldering temperature of the solder paste, and the melting point of tin powder of different compositions is different.

Particle size: affects the printing performance and soldering effect, the smaller the particle, the higher the printing accuracy, but the risk of oxidation also increases.

Solder joints performance: solder joints thermal conductivity and electrical conductivity is only based on the alloy composition of the tin powder in the solder paste, different alloy compositions, its electrical conductivity and thermal conductivity is different.

2. Flux Percentage: 10-20 per cent

Ingredients: including resins, activators, solvents and thixotropic agents.

Function:

Resin: to provide adhesion, solder paste moulding, easy to transfer, to prevent solder powder flying when soldering.

Activator: removes solder powder and pad surface oxides, reduces alloy surface tension and enhances wettability.

Solvent: adjust the viscosity, easy to print and storage.

Thixotropic agent: improve fluidity, prevent collapse after printing and facilitate the storage of solder paste, no delamination, no cracking.

3. Additives Percentage: 1-5 per cent

Ingredients: including antioxidants, stabilisers and levelling agents, etc.

Function:

Antioxidant: delay the chemical reaction between tin powder and active agent in solder paste, prevent the oxidation of tin powder and prolong the storage time.

Stabiliser: maintains chemical stability, prevents deterioration and prolongs solder paste life.

Levelling agent: improve the surface flatness after printing.

B. the characteristics of the solder paste

Good printing performance: solder paste has moderate viscosity, suitable for stencil printing, can be accurately deposited on the pad to meet the requirements of high-precision printing.

Excellent soldering performance: flux can effectively remove metal surface oxides, to ensure that the soldering firm, improve the quality of soldering.

Storage stability: under appropriate conditions, the solder paste can maintain stable performance for a long time, not easy to deteriorate, generally require refrigerated storage environment for 6 months.

Environmental protection: lead-free solder paste gradually replace leaded solder paste, in line with environmental requirements, reduce environmental pollution.

C. Application of solder paste

Solder paste is widely used in SMT (surface mount technology) in the welding of electronic components, such as mobile phones, computers, automotive electronics and other electronic products manufacturing field.In the SMT process, solder paste is precisely printed on the circuit board pads, through the patch, reflow soldering and other process steps, the electronic components and circuit boards firmly welded together to form a reliable electrical connection.

Summary

As a key material for electronic soldering, solder paste, its composition, characteristics and application have an important impact on the manufacturing quality and performance of electronic products.With the development of electronic technology, the performance and application areas of solder paste will continue to expand and improve.