What is SMT?

SMT is Surface assembly Technology (short for Surface Mounted Technology), and it is the most popular technology and process in the electronic assembly industry.

It compresses traditional electronic components into only a few tens of the volume of the device, thus realizing the assembly of electronic products of high density, high reliability, miniaturization, low cost, and production automation. This miniaturized component is called: SMY device (or SMC, chip device). The process of assembling components onto a print (or other substrate) is called the SMT process. The associated assembly equipment is called SMT equipment. At present, advanced electronic products, especially in computers and communication electronic products, have widely adopted SMT technology. The international output of SMD devices has increased year by year, while the output of traditional devices has decreased year by year, so with the passage of SMT technology will become more and more popular.

• High assembly density, small size of electronic products, light weight, the size and weight of the patch components is only about 1/10 of the traditional plug-in components, generally after the use of SMT, the volume of electronic products reduced by 40% to 60%, the weight reduced by 60% to 80%.
• High reliability, strong vibration resistance. Low defect rate of solder joint.
• Good high-frequency characteristics. Reduced electromagnetic and radio frequency interference.
• Easy to achieve automation, improve production efficiency. Reduce the cost by 30%~50%. Save materials, energy, equipment, manpower, time, etc.

• The pursuit of miniaturization of electronic products, previously used perforated plug-in components have been unable to shrink.
• Electronic products function more complete, the integrated circuit (IC) used has no perforated components, especially large-scale, highly integrated ICs, have to use surface patch components.
• Product mass, production automation, the factory to low cost and high output, produce quality products to meet customer needs and strengthen market competitiveness.
• The development of electronic components, integrated circuit (IC) development, semiconductor materials of multiple applications.
• Electronic technology revolution is imperative, chasing the international trend.

Lead is a toxic heavy metal, excessive absorption of lead by the human body will cause poisoning, intake of low amounts of lead may have an impact on human intelligence, nervous system and reproductive system, the global electronic assembly industry consumes about 60,000 tons of solder every year, and is increasing year by year, the resulting lead-salt industrial slag seriously polluted the environment. Therefore, reducing the use of lead has become the focus of worldwide attention, many large companies in Europe and Japan are vigorously accelerating the development of lead-free alternative alloys, and have planned to gradually reduce the use of lead in the assembly of electronic products in 2002. It will be completely eliminated by 2004. (The traditional solder composition of 63Sn/37Pb, in the current electronic assembly industry, lead is widely used).

1. Price: Many manufacturers require that the price cannot be higher than 63Sn/37Pn, but at present, the finished products of lead-free alternatives are 35% higher than 63Sn/37Pb.
2. The melting point: most manufacturers require a minimum solid phase temperature of 150 ° C to meet the working requirements of electronic equipment. The liquid phase temperature depends on the application.
   • Electrode for wave soldering: For successful wave soldering, the liquid phase temperature should be below 265 ° C.
   • Solder wire for manual welding: liquid phase temperature should be lower than the working temperature of the soldering iron 345℃.
   • Solder paste: liquid phase temperature should be lower than 250℃.
3. Electrical conductivity.
4. Good thermal conductivity.
5. Small solid-liquid coexistence range: most experts recommend that this temperature range be controlled within 10 ° C, in order to form a good solder joint, if the alloy solidification range is too wide, it is possible to crack the solder joint, so that electronic products premature damage.
6. Low toxicity: the alloy composition must be non-toxic.
7. With 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, and there will be no protruding fillet welds on the passing device.
9. The production of repeatability, solder joint consistency: because the electronic assembly process is a mass manufacturing process, requires its repeatability and consistency to maintain a high level, if some alloy components can not be repeated in mass conditions, or its melting point in mass production due to changes in the composition of the larger changes, it can not be considered.
10. Solder joint appearance: solder joint appearance should be close to the appearance of tin/lead solder.
11. Supply ability.
12. Compatibility with lead: due to the short term will not immediately be fully transformed into a lead-free system, so lead may still be used on the PCB pad and component terminals, such as mixing such as drilling in the solder, may make the melting point of the solder alloy drop very low, the strength is greatly reduced.