At SMT production sites, customers often ask which is better, Leaded Solder Paste or lead-free Solder Paste. There is no standard answer to this question, and analysis must be combined with specific process scenarios. Leaded solder paste has a lower melting point and good fluidity, making it suitable for soldering fine-pitch components, but lead is harmful to the environment and human body. While lead-free solder paste meets the RoHS standard, it has a higher melting point and stricter requirements for the Reflow Soldering temperature profile.

We once handled a batch of defective solder joints caused by using lead-free solder paste, and found that the preheating zone's heating rate was too fast, causing the Flux to volatilize prematurely and the solder to fail to fully wet the pads. This shows that lead-free solder paste has higher requirements for the stability of the temperature profile, and requires more precise soldering parameter settings. Leaded solder paste is relatively more forgiving, but long-term use may face environmental compliance risks.

The procurement department often prioritizes cost, but neglects process adaptability. For example, using leaded solder paste for certain low-end products can indeed reduce the soldering defect rate, but it may be detained by customs during export. While lead-free solder paste is slightly more expensive, it can avoid greater losses caused by later rectification. Therefore, it is recommended to make a comprehensive judgment based on product positioning and target market.

In actual operation, we will first verify the compatibility of the solder paste with the printing machine, such as whether parameters such as squeegee angle, pressure, and speed are suitable for the type of solder paste currently used. At the same time, we pay attention to the shelf life of the solder paste. Leaded solder paste usually has a longer storage time than lead-free solder paste, but lead-free solder paste has a lower tendency to oxidize. This needs to be decided based on the workshop environment and inventory turnover.

For some precision PCBs, such as high-frequency circuits or medical equipment, we will prioritize the use of lead-free solder paste to reduce the risk of lead pollution. In industrial control equipment, leaded solder paste is still widely used because of its higher soldering reliability, especially in high-temperature environments.

The final choice of which solder paste to use depends on the production process, product requirements, and cost control. It is recommended to verify through small-batch trial production, while regularly monitoring soldering quality and adjusting process parameters in a timely manner to ensure both production efficiency and product quality.