With the development of electronic products in the direction of miniaturization and high assembly density, electronic assembly technology is also dominated by surface mount technology. Therefore, the following points of the following lead-free reflow characteristics FASTPCBA and everyone simply explain.
(1) The lead-free process has a high temperature and a higher melting point than conventional lead-based eutectic solder.
(2) The surface tension is large and the wettability is poor.
(3) The process window is small and the quality control is difficult.
(4) The lead-free solder joint has poor wettability and poor expandability.
(5) The appearance of lead-free solder joints is rough, so the traditional inspection standards and AOI must be upgraded.
(6) There are many holes (pores) in the lead-free solder joints. Especially when lead solder is mixed with lead-free solder, the lead solder on the Korean side is first melted, covering the pads, and the flux is not discharged, causing voids. In general, the holes inside the BGA do not affect the mechanical strength, but the holes in the large holes and the welding interface, especially when the holes are connected together, will affect the reliability.
(7) There are many defects. Mainly caused by poor wettability, resulting in weak self-alignment effect.
Due to the high melting point and poor wettability of lead-free solder, the reflow soldering process has a high welding temperature and a small process window, making reflow soldering easy to produce defects such as solder joints, pores, and licensing, and it is easy to cause components, Reliability problems such as PCB damage, therefore, setting the optimal temperature curve, not only to ensure the quality of the solder joints, but also to ensure that the components and PCBs are not damaged, is the fundamental problem that the lead-free reflow soldering process must be decided.