SMT is the surface mount technology (short for Surface Mounted Technology) and is currently the most popular technology and process in the electronics assembly industry.

The assembly density is high, the size of the electronic product is small, and the weight is light. The volume and weight of the chip components are only about 1/10 of that of the conventional plug-in components. After the SMT is generally used, the volume of the electronic product is reduced by 40% to 60%, and the weight is reduced by 60%-80%.
High reliability and strong anti-vibration ability. The solder joint defect rate is low.
High frequency characteristics are good. Reduced electromagnetic and radio frequency interference.
Easy to automate and increase productivity. Reduce costs by 30% to 50%. Save materials, energy, equipment, manpower, time, etc.

The pursuit of miniaturization of electronic products, the previously used perforated plug-in components can not be reduced
Electronic products are more complete, and the integrated circuits (ICs) used have no perforated components, especially large-scale, highly integrated ICs, which have to use surface mount components.
Product batching, production automation, the factory must produce high-quality products at low cost and high yield to meet customer needs and strengthen market competitiveness
Development of electronic components, development of integrated circuits (ICs), multi-application of semiconductor materials
The revolution of electronic technology is imperative, chasing the international trend

Lead is a toxic heavy metal. Excessive absorption of lead in the human body can cause poisoning. Low intake of lead may affect human intelligence, nervous system and reproductive system. The global electronic assembly industry consumes about 60,000 tons per year. Solder, and it is increasing year by year, the industrial residue containing lead salt is seriously polluting the environment, so reducing the use of lead has become the focus of attention around the world. Many large companies in Europe and Japan are accelerating the development of lead-free alternative alloys. And has planned to gradually reduce the use of lead in electronic product assembly in 2002. Completely eliminated by 2004. (Traditional solder composition 63Sn/37Pb, lead is widely used in the current electronic assembly industry).

1. Price: Many manufacturers require that the price cannot be higher than 63Sn/37Pn, but at present, the finished products of lead-free substitutes are 35% higher than 63Sn/37Pb.
2. Melting point: Most manufacturers require a solid phase temperature of at least 150 ° C to meet the working requirements of electronic equipment. The liquidus temperature will depend on the specific application.
Wave soldering electrode: For successful wave soldering, the liquidus temperature should be lower than 265 °C.
Solder wire for manual soldering: The liquidus temperature should be lower than the soldering iron operating temperature of 345 °C.
Solder paste: The liquidus temperature should be below 250 °C.
3. Electrical conductivity.
4, good thermal conductivity.
5. Smaller solid-liquid coexistence range: Most experts recommend that this temperature range be controlled within 10 °C to form a good solder joint. If the alloy solidification range is too wide, solder joint cracking may occur, making electronic products premature. damage.
6, low toxicity: alloy components must be non-toxic.
7, has good wettability.
8. Good physical properties (strength, tensile, fatigue): The alloy must be able to provide the strength and reliability that Sn63/Pb37 can achieve without protruding fillet welds through the device.
9. Repeatability of production, consistency of solder joints: Since the electronic assembly process is a high-volume manufacturing process, it is required to maintain a high level of repeatability and consistency, if some alloy components cannot be in high-volume conditions. Repeated manufacturing, or its melting point in the mass production, due to changes in composition, can not be considered.
10. Appearance of solder joints: The appearance of solder joints should be close to the appearance of tin/lead solder.
11, supply capacity.
12. Compatibility with lead: Since it will not be fully transformed into a lead-free system in the short term, lead may still be used on the terminals of PCB pads and components. If solder is mixed, it may cause solder alloy. The melting point is very low and the strength is greatly reduced.