Pb-Free SAC305 solder paste and its application in PCB reflow process

In modern electronic manufacturing, lead-free (Pb-Free) solder paste has become the mainstream, especially with the continuous strengthening of environmental protection requirements and regulations, such as the EU Restriction of Hazardous Substances Directive (RoHS). Among them, SAC305 solder paste is one of the most commonly used Pb-free solder pastes, and is popular for its excellent performance and wide applicability. This article will introduce the composition, advantages and application of SAC305 solder paste in PCB (printed circuit board) reflow process.

1. What is SAC305 solder paste?

SAC305 solder paste is also known as SAC305 paste, it is a typical pb-free solder paste, and its main components are tin (Sn), silver (Ag), and copper (Cu). Among them, the ratio of SAC305 is 96.5% tin, 3.0% silver and 0.5% copper. This ratio gives SAC305 paste excellent soldering performance and good mechanical strength, making it the first choice among lead-free solder paste for PCB assembly. It’s generally used as reflow paste for SMT soldering process, and making it possible for soldering of small electronics or PCB components. It is available in both type 3 and type 4 powder size, depending on the requirements of your PCB SMT soldering projects.

2. Advantages of SAC305 solder paste

Environmental protection: Pb-Free solder paste means that it does not contain harmful lead elements and meets environmental regulations such as RoHS and WEEE directives. SAC305 PCB paste is therefore widely used in the production of electronic products, especially for export.

Good soldering strength: The silver component in SAC solder paste increases the mechanical strength and conductivity of the solder joints, thereby ensuring the reliability of electronic devices, especially under high temperature and high stress environments.

Excellent wettability: Although the wettability of lead-free solder is generally slightly worse than that of lead-containing solder, SAC305 can still provide better wetting performance through its reasonable metal ratio, which helps to improve the quality of soldering when comparing to other SAC solder paste.

Good thermal fatigue performance: Adding Copper is to improve resistance to thermal cycle fatigue, and improves wetting properties of the solder paste. Under long-term high temperature working conditions, SAC305 solder paste shows strong resistance to thermal fatigue, which can reduce cracks or failures caused by temperature fluctuations in solder joints.

3. Application of SAC305 solder paste in PCB reflow soldering process

Reflow soldering is one of the most commonly used soldering processes in large-scale electronic product production. During PCB assembly, PCB paste is often used to fix electronic components on the board, and the solder paste is melted by heating to form stable solder joints.

1. Printing stage

In the first step of the reflow soldering process, SAC solder paste is accurately deposited on the pads of the PCB by screen printing or dispensing machine. The viscosity and wettability of the solder paste are important factors in determining the printing quality. SAC305 ensures the stability of the solder paste during the printing process through optimized particle size and flux formula.

2. Mounting stage

After the solder paste is printed, the components are mounted on the PCB. Since the viscosity of SAC305 reflow paste is large enough, it can effectively support lighter electronic components and ensure that they do not shift during heating.

3. Reflow heating stage

When the PCB passes through the reflow oven, the temperature gradually increases until the pb free solder paste melts. The melting point of SAC305 is about 217℃. This relatively high temperature requires precise control of process parameters to avoid excessively high or low temperatures that affect the soldering quality.

4. Cooling and solidification stage

After the solder paste is melted, as the PCB cools, the solder paste begins to solidify and form electrical and mechanical connections. The cooling rate of SAC305 PCB paste is directly related to its mechanical properties, so the cooling curve needs to be strictly controlled to prevent cracks in the solder joints.

IV. Challenges of SAC305 solder paste

Although SAC305 solder paste has many advantages, there are also some challenges in practical applications. For example, due to its high melting point, the energy consumption of the equipment is also increased accordingly. In addition, lead-free solder paste is generally slightly worse than lead-containing solder paste in wettability, which requires more precise process parameters and higher technical level.

V. Summary

As the leader of lead-free solder paste, SAC305 solder paste has become a common material in PCB reflow soldering process due to its environmental protection, excellent mechanical properties and good wettability. With the continuous improvement of environmental protection requirements and the increasing complexity of electronic products, SAC305 solder paste will continue to play an important role in electronic manufacturing.

By optimizing the process flow and reasonably controlling the temperature curve, SAC305 solder paste can ensure soldering quality and extend the service life of electronic products.

If you are looking for the SAC305 Pb Free Solder Paste for PCB SMT soldering, please contact us. Email: xfsolder@gmail.com or xfsolder@163.com ; WhatsApp/Wechat 008613450770997