There is the difference between lead tin solder and lead-free solder:
1, from the appearance of the tin luster:
The surface of the lead solder is bright white; lead free solder is a pale yellow.
2, from the metal alloy components:
Lead tin solder is tin and lead two kinds of main metal elements (such as: Sn50Pb50, Sn63Pb37, etc.);
Lead free solder is basically no lead (EU ROHS standard is less than 1000PPM, the Japanese standard is less than 500PPM), lead-free solder generally contain
Tin, silver or copper metal elements.
3, from the use of points:
Lead solder is used for welding of lead products, and all of the tools and components used are lead.
Lead free soldering is used for soldering of products from Europe, America and other countries. The tools and components used in this product must be lead free.
4, such as hand rub method to distinguish the words: there will be lead in the hands of a black mark left, there is a light yellow lead free traces, because lead free general contain copper metal.
Lead free solder is the main component of tin, melting point is 232 degrees Celsius, and other metals such as silver, bismuth, zinc and other components of the alloy system.
Sn-Ag system lead-free solder melting point is 221 degrees Celsius, and Sn-Pb system solder many of the situation is more close, more applications. In the Sn-Ag system, the appropriate addition of some copper, in addition to the melting point has been reduced, but also improve the reliability of the welding. As the biggest feature of Sn-Ag system lead-free solder, it is obviously better than Sn-Pb system solder. The most suitable for use in the long term reliability of the joint.
Two why do you want to use it?
Lead is a persistent pollutant, which can not be decomposed in the natural environment. Lead is harmful to most systems in the human body, especially in bone marrow hematopoietic system, nervous system and kidney. Lead levels in the blood can cause convulsions, coma, and even death when they reach high levels of lead. Low levels of lead can damage the central nervous system, kidney and blood cells. Chronic lead poisoning can cause high blood pressure and kidney damage. Therefore, many developed countries have banned the use of lead plating, according to the "European restriction of hazardous substances (RoHS) directive 2002/95/EC" provisions, tin lead solder has been prohibited to use. In the United States, the use of lead has also made a strict limit on the total amount of the connector manufacturers to allow the use of only 1/250 of the past, and each year must be published its actual annual lead usage.