PCBA and SMT processing generally have two processes, one is a lead-free process and the other is a leaded process. Everyone knows that lead is harmful to humans. Therefore, the lead-free process meets the requirements of environmental protection, which is a general trend and an inevitable choice in history. . We do not think that PCBA processing plants below the scale (below 20 SMT lines) have the ability to accept both lead-free and lead-free SMT processing orders, because the distinction between materials, equipment, and processes greatly increases the cost and difficulty of management. I don’t know how easy it is to do lead-free process directly.
Below, the difference between lead process and lead-free process is briefly summarized as follows. There are some inadequacies, and I hope you can correct me.
1. The alloy composition is different: the common lead process tin-lead composition is 63/37, while the lead-free alloy composition is SAC 305, that is, Sn: 96.5%, Ag: 3%, Cu: 0.5%. The lead-free process cannot absolutely guarantee that it is completely free of lead, only contains extremely low content of lead, such as lead below 500 PPM.
2. Different melting points: the melting point of lead-tin is 180°~185°, and the working temperature is about 240°~250°. The melting point of lead-free tin is 210°~235°, and the working temperature is 245°~280°. According to experience, for every 8%-10% increase in tin content, the melting point increases by about 10 degrees, and the working temperature increases by 10-20 degrees.
3. The cost is different: the price of tin is more expensive than that of lead. When the equally important solder is replaced with tin, the cost of solder will rise sharply. Therefore, the cost of the lead-free process is much higher than that of the lead process. Statistics show that the tin bar for wave soldering and the tin wire for manual soldering, the lead-free process is 2.7 times higher than the lead process, and the solder paste for reflow soldering The cost is increased by about 1.5 times.
4. The process is different: the lead process and the lead-free process can be seen from the name. But specific to the process, the solder, components, and equipment used, such as wave soldering furnaces, solder paste printers, and soldering irons for manual soldering, are different. This is also the main reason why it is difficult to handle both leaded and lead-free processes in a small-scale PCBA processing plant.
Other differences such as process window, solderability, and environmental protection requirements are also different. The process window of the lead process is larger and the solderability will be better. However, because the lead-free process is more environmentally friendly, and the technology continues to improve, the lead-free process technology has become increasingly reliable and mature.