Generally, there are two kinds of SMT processes, one is lead-free process and the other is lead-containing process. Everyone knows that lead is harmful to people, so lead-free process meets the requirements of environmental protection and is the general trend. Shenzhen Yingcheng Electronic SMT SMD foundry adopts lead-free technology.
The difference between lead-containing process and lead-free process is briefly summarized as follows:
1. different alloy compositions: the composition of tin and lead in the common lead process is 63/37, while the composition of lead-free alloy is SAC305, i.e. sn: 96.5%, ag: 3% and Cu: 0.5%. The lead-free process can’t absolutely guarantee that it doesn’t contain lead at all, but only contains extremely low content of lead, such as lead below 500PPM.
2. Different melting points: the melting point of lead and 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, when the tin content increases by 8%-10%, its melting point increases by about 10 degrees and its working temperature increases by 10-20 degrees.
3. Cost difference: The price of tin is more expensive than that of lead. When the equally important solder replaces lead with tin, the cost of solder goes up greatly. Therefore, the cost of lead-free process is much higher than that of lead-free process. Statistics show that the cost of solder paste for wave soldering and manual soldering is 2.7 times higher than that of lead-free process and 1.5 times higher than that of solder paste for reflow soldering.
4. Different processes: There are lead process and lead-free process, which can be seen from the name. But when it comes to technology, the solder, components and equipment used are different, such as wave soldering furnace, solder paste printer, soldering iron for manual soldering, etc.
Other differences such as process window, weldability and environmental protection requirements are also different. The process window with lead process is larger, the solderability is better, and the lead-free process is more in line with the environmental protection requirements. With the continuous progress of technology, the lead-free process technology has become increasingly reliable and mature.
