Main features of lead-free reflow soldering and lead-free solder joints

Lead free reflow soldering is a kind of reflow soldering. With the deepening of environmental protection, people pay more and more attention to lead-free technology (lead-free reflow soldering). The biggest change is in the material, especially in the solder. Here are the main features of lead-free reflow soldering and lead-free solder joints.

1、 Main features of lead-free reflow soldering

1. The high temperature and melting point are about 34 ℃ higher than those of traditional lead eutectic solder.

2. High surface tension and poor wettability.

3. The process window is small and the quality control is difficult.

2、 Characteristics of lead-free reflow solder joint

1. Poor infiltration and expansibility.

2. The appearance of lead-free solder joint is rough. Traditional inspection standards and AOI need to be upgraded.

3. There are many air holes in lead-free solder joints, especially when lead solder ends are mixed with lead-free solder, the lead solder on the solder ends (balls) is melted first, covering the pad, and the flux cannot be discharged, resulting in air holes. However, the porosity does not affect the mechanical strength.

4. Many defects - the self localization effect is weakened due to poor wettability.

The lead-free solder joint has rough appearance, many air holes, large wetting angle and no half moon shape. Because the appearance of the lead-free solder joint is obviously different from that of the lead solder joint, it can even be considered as unqualified if measured by the original inspection standard with lead, but it does not affect the use quality of civil electronic products with general requirements. Therefore, it is necessary to convince customers that this is caused by poor wettability of lead-free welding.