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Research and production of lead-free reflow

In the 1960s, production in the field of microelectronics, SMT a new English characters appear in our field of vision, its Chinese meaning is a surface mount technology. Related to PCB board, electronic components, circuit design and device-linking process, and many other disciplines, is an emerging science and technology, research and production in this technology can be described as much to offer a wide range of applications.
--- China from the mid-year and the beginning of the introduction of SMT equipment, large-scale introduction of the 1990s, to the current development course of about 30 years. SMT original recorders used in production, is now widely used in communications, computer, automatic control and household appliances and many other areas, it is no exaggeration to say, as long as electronic products, there is no need to SMT's. As long as there is no need to SMT electronic factory equipment. Functionally, SMT also in large quantities by simply welding the initial development to be able to meet the research and development, education and training of small batch production needs of different levels. Currently, there are about 200,000 Shenzhen electronics factory reflow soldering, wave soldering of these devices, we can imagine, SMT range of applications is how extensive.
--- In this development process, reflow soldering equipment through several different stages of development. It not only affects the performance of the merits of the quality of welding, but also affect the final product quality and reliability, the study of reflow soldering equipment and reflow soldering process is particularly important.
Development of reflow soldering equipment --- 1 all hot air reflow soldering --- 90s, all hot air reflow soldering technique gradually started. It is a spray nozzle or by convection heat fan to force air circulation in order to achieve reflow soldering equipment, PCB circuit board with the movement when the caterpillar to overcome the reflow soldering temperature uneven deficiencies. However, to ensure cycle gas stream must have a certain pressure, which causes the displacement element and the PCB jitter to some extent. --- 2 infrared heating reflow soldering --- In the early 1980s, the use of infrared heating is more common, it has a fast heating, energy-saving and reliable features. However, PCB board with caterpillar in motion, in different temperature region are very different thermal radiation absorption rate, which resulted in a temperature of PCB board is uneven, so this form of technology is phased out.
--- 3 --- infrared hot air reflow soldering technique to the late 1990s, infrared hot air reflow soldering technology began to appear, it is a combination of infrared and hot air developed their own characteristics of infrared heating and hot air circulation. It uses infrared heat PCB board and the temperature of the hot air circulation to the work area evenly. Such devices take advantage of the characteristics of infrared penetrating power, high thermal efficiency and energy-saving, effectively overcome when using infrared reflow soldering temperature unevenness and shadowing effects, and to make up for bad hot air reflow soldering airflow caused by excessive requirements influences.
Reflow soldering temperature profile there is a basic requirement is that the device during welding, soldering temperature must meet the requirements of the reflow soldering process temperature curve. Reflow soldering temperature profile is divided into 4 sections.
   --- Object of the preheating zone to the preheating temperature of the PCB is heated quickly to achieve the second specific goals, this process is typically in the rate of temperature 1 ~ 3 ℃ / s. Thermal insulation segment --- segment refers to the temperature rises from 140 ℃ to 160 ℃ process, the main purpose is to make the temperature of the PCB component tends to be uniform, and to ensure that the solder paste flux sufficiently melted, this stage requires 80 ~ 150s. The main purpose of the regeneration section --- reflux segment is to rapidly melt the solder paste, and soldering components on the PCB board, refluxed at this stage can not be too long, when the temperature is generally 30 ~ 50s. Rate of temperature rose to 3 ℃ / s, the peak temperature is generally 210 ~ 230 ℃, time to reach peak is 10 ~ 20s. Different solder melting temperature is different, such 63Sn / 37Pb is 183 ℃, and 62Sn / 36Pb / 2Ag of 179 ℃, so when setting parameters to take into account the performance of the solder paste. --- In the cooling section cooling section should be as fast as possible to cool the cooling, which would contribute to a bright solder joints. Cooling rate of 2 ~ 3 ℃ / s, generally require less cooling to 100 ℃.
   Difficulties and Countermeasures used in research and development and small and medium volume when --- 21st century, SMT gradually penetrate to the direction of scientific research, electronic product update cycles are getting shorter, computer art, for example, a new product from the market to replace its cycle typically 6 months. Therefore requires a new type of device can not only meet the requirements of SMT technology R & D and small batch production to meet the characteristics of that breed category, small batch, process demanding and time is short. But China from the 1980s to the late 1990s, SMT equipment to meet the high-volume processing and introduction. If such equipment for research and production will be a huge amount of investment, high maintenance costs and long time-consuming, laborious and production cycle problems, so can not meet research needs.

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