In 2006, electronic products will fully implement lead-free soldering, which raises a new topic for research and development and medium-volume production. SMT is constantly updated to meet the growing trend of thinning, miniaturization and high precision in the electronics field.
In the field of microelectronics production in the 1960s, a new English character of SMT appeared in our field of vision. Its Chinese meaning is surface mount technology. It involves a number of disciplines such as PCB substrate, electronic components, circuit design and assembly process. It is an emerging science and technology. This technology can be said to have a lot to do in scientific research and production.
--- China introduced SMT and its equipment from the middle of the year. It was introduced in large scale in the 1990s and has been in development for about 30 years. SMT was originally applied to the production of video recorders. Now it has been widely used in communications, computers, automatic control and household appliances. It is no exaggeration to say that as long as it is an electronic product, there is no need for SMT. As long as the electronics factory does not need to use SMT equipment. Functionally speaking, SMT has also evolved from the initial simple high-volume welding process to meet the needs of different levels of research and development, teaching and training, and small and medium-sized production. At present, there are about 200,000 electronics factories in Shenzhen that use reflow soldering and wave soldering. We can imagine how wide the application of SMT is.
--- In this development process, reflow soldering equipment has undergone several different stages of development. Its performance not only affects the quality of welding, but also affects the quality and reliability of the final product. Therefore, research on reflow soldering equipment and reflow soldering process is particularly important.
Development history of reflow soldering equipment
---1 Full hot air reflow soldering technology --- In the 1990s, full hot air reflow soldering technology was gradually used. It is a device that uses a convection jet nozzle or a heat-resistant fan to force the airflow to circulate, thereby achieving reflow soldering. The PCB circuit board overcomes the insufficiency of reflow soldering temperature unevenness as the chain rail moves. However, in order to ensure circulation, the airflow must have a certain pressure, which causes PCB jitter and component misalignment to some extent.
---2 Infrared heating reflow soldering technology --- In the early 1980s, infrared heating was more common, it has the characteristics of fast heating, energy saving and reliable operation. However, the PCB circuit board is in motion with the chain rail, and the radiant heat absorption rate is greatly different in different temperature zones, which causes the temperature of the PCB circuit board to be uneven, so this technical form is gradually eliminated.
---3 Infrared hot air reflow soldering technology --- In the late 1990s, infrared hot air reflow soldering technology began to appear. It is an infrared heating and hot air circulation method developed by combining the characteristics of infrared and hot air. It uses infrared heating PCB boards and hot air circulation to even out the temperature in the work area. This kind of equipment makes full use of the characteristics of strong infrared penetrating power, high thermal efficiency and power saving. It effectively overcomes the temperature unevenness and shadowing effect of infrared reflow soldering, and compensates for the bad caused by hot air reflow soldering. influences.
There is a basic requirement for the reflow soldering process temperature curve, that is, the soldering temperature of the device must meet the temperature curve required by the reflow soldering process. The reflow soldering process temperature curve is divided into the following four segments.
Preheating section -- The purpose of the preheating section is to heat the room temperature PCB as quickly as possible to reach the second specific target. In this process, the temperature is usually 1 to 3 ° C / s. Insulation section --- Insulation section refers to the process of increasing the temperature from 140 ° C to 160 ° C. The main purpose is to make the temperature of the PCB components uniform, and to ensure that the flux in the solder paste is fully melted. This stage requires 80 to 150 s. Reflow section -- The main purpose of the reflow section is to melt the solder paste quickly and solder the component to the PCB. The reflow at this stage should not be too long, usually 30 to 50 s. The temperature rate rises to 3 °C / s, the peak temperature is generally 210 ~ 230 ° C, the peak time is 10 ~ 20s. The melting temperature of different solder pastes is different, such as 63Sn/37Pb is 183 °C, and 62Sn/36Pb/2Ag is 179 °C, so the performance of solder paste should be taken into account when setting parameters. Cooling section --- Cooling down should be done as fast as possible in the cooling section, which will help to get bright solder joints. The cooling rate is 2 to 3 ° C / s, and it is generally required to cool to below 100 ° C.
Difficulties and countermeasures applied to R&D and small and medium-sized production--In the 21st century, SMT gradually penetrated into the direction of scientific research, and the cycle of electronic product renewal became shorter and shorter. In the computer field, for example, from the market to the new product to replace its cycle Usually 6 months. Therefore, it is required to have a new type of equipment that can meet the requirements of SMT process and meet the characteristics of R&D and small and medium batch production, that is, many varieties, small batch sizes, strict process requirements and short time. However, from the 1980s to the end of the 1990s, SMT equipment was introduced to meet the needs of mass production and processing. If such equipment is used in scientific research and production, there will be problems such as huge investment amount, high maintenance cost, time consuming, laborious and long production cycle, so it is impossible to meet the research needs. --
Guided by the professionalism and quality management concept, Weidake people continue to innovate with the innovative spirit of continuous focus and continuous improvement. At the end of 2002, in response to the introduction of the international electronic industry environmental protection concept, Weidake took the lead in the domestic market. A V-series lead-free wave soldering machine, followed by the TOP, RTOP series of lead-free reflow soldering, they successfully assisted many companies to achieve lead-free process and process improvement.
The function and operation of each equipment of the welding machine
● The solder paste printing station prints the solder paste onto the PCB circuit board through the metal mesh board.
● The observation magnifier is used to check the solder paste leakage and the quality of the chip and IC chip soldering.
● Solder paste preservation refrigerator is used for solder paste low temperature refrigeration.
● TOP, RTOP series lead-free reflow soldering is used to accurately place the IC chip on the PCB board printed with solder paste.
● TOP, RTOP series lead-free reflow soldering The PCB board with the IC chip placed in the work surface of the surface mount soldering machine for reflow soldering.
Technical characteristics of TOP and RTOP series lead-free reflow soldering
● Adopt advanced infrared hot air heating mode.
● Eliminate the form of the PCB transport PCB board, so that the PCB board is always in the static state to complete the reflow soldering process, avoiding the welding misalignment defects caused by the movement.
● Adopt the overall temperature control mode of the work area and use the fuzzy math control principle to make the PCB board welding temperature curve meet the welding process curve requirements, thus ensuring product quality requirements.
● Advanced display technology enables the reflow soldering process curve to be dynamically displayed through the LCD screen of the device.
● The reflow soldering process parameters can be flexibly modified according to different solder paste and PCB conditions, and finally high quality products are soldered.
● TOP, RTOP series lead-free reflow with RS232 interface and upper management software, each reflow soldering process curve, setting parameters and welding time can be recorded and stored in the PC through the PC, and can be consulted at any time. Print related process soldering data.