SMT production site design guidelines
1. Infrastructure and power resources
The design of the SMT production site must put safety in the first place. Since SMT equipment is generally installed in-line, the length of the production line is relatively long (for example, a high-speed SMT line has a total length of 25m~35m), and the load on the ground is relatively concentrated. After a single high-speed placement machine is loaded with a feeder, the total weight will exceed 6000kg, so it has higher requirements for the load-bearing capacity of the plant floor. Usually, the SMT high-speed line is installed in the factory building, it is recommended that the load-bearing capacity of the factory floor should not be less than 7.5kN/m2, or even more than 10kN/n?. If the bearing capacity of the floor is too low, after the equipment is installed and used for a period of time, the floor is prone to deformation or cracks, which affects the reliability of equipment operation and the accuracy of processing. The power supply for SMT production site should be sufficient and safe. SMT equipment generally uses compressed air and electric power as dual power, and the requirements for the cooperation of gas and electricity are relatively strict. Reflow soldering machines and wave soldering machines are all power-consuming equipment, and the impact of their startup and shutdown on other power-consuming equipment should be fully considered. The power configuration system adopts the three-phase five-wire system to be the safest. Some companies combine the protective grounding and the neutral wiring into one connection method, which has great unsafe factors. Poor quality of power supply from the power grid may cause damage to production equipment. The SMT production line may cause failures of the reflow soldering machine, multi-function placement machine, and wave soldering machine due to the abnormal power grid or sudden power outage, and even damage the electrical components. In some areas where the grid voltage fluctuates more severely, SMT equipment should be equipped with AC stabilized power supply, and attention should be paid to the balance of the three-phase power load when wiring the equipment power supply. SMT production equipment requires the use of clean and dry compressed air. As the power source, the compressed air should not only meet the technical requirements of the equipment in terms of pressure, flow and other parameters, but also filter out the water, oil, dust and other impurities contained in the gas before entering the machine. The design of any industrial plant should follow the enterprise’s people-oriented principle. Many modern enterprises have introduced the concept of “green production site” when designing SMT production sites. Some countries and regions regard the implementation of IS014001 as as important as the implementation of the 1S09000 series of standards in order to achieve the sustainable development of enterprises and society. At the installation site of SMT equipment, if the building structure space of the workshop is relatively narrow and the material with high reflection coefficient is used (the sound absorption coefficient is very small, a<0.02), the sound absorption capacity is almost no, and it is completely reflective. The indoor noise is continuously strengthened by reflections, resulting in a strong reverberation effect, causing the main component of the noise in the workshop to be mechanical noise, accompanied by some aerodynamic noise, so most of the noise can be reduced by sound insulation and sound absorption measures deal with. The use of materials with strong sound absorption capacity for the suspended ceiling of the factory building will help reduce noise reflection. Noise control standards should be implemented (GBJ 87-85 Industrial Enterprise Noise Control Design Code”, and the relevant requirements of the “Design Regulations on Occupational Safety and Health in the Machinery Industry” promulgated by the Ministry of Machinery and Electronics Industry on November 10, 1988. The noise value in some areas should be controlled within 70dB. SMT equipment will produce a certain amplitude of vibration during operation, especially when large-scale high-speed placement machines are mounted at high speeds, the vibration caused by the plant is more obvious. If you compare “GB 10070-88 Urban Area Environmental Vibration Standard”, the daytime vibration should be controlled within 70dB, and the maximum value should not exceed 80dBo. Too much vibration is not only harmful to the safety of the plant structure, but also interferes with the operation of other equipment and instruments, and also makes the operator Produce discomfort. The bright and clean workshop will help the operators to concentrate on work and ensure the quality of production. For the SMT production site, the illuminance is recommended to be no less than 3001x (Note: measured at a height of 800mm from the ground). For some work areas that require better lighting, local lighting can be installed.
2. Temperature conditions and air quality
SMT production equipment, SMT patch glue, solder paste and other auxiliary materials should be used within a certain temperature range in order to maintain their specific special performance and good manufacturability. Generally speaking, it is more appropriate to control the temperature in the workshop within the range of 18X3 ~ 26C. In the heating season in winter, or in the case of using air conditioning in summer, care must be taken to inject a certain percentage of fresh air into the plant. The necessary fresh air volume should be able to provide enough oxygen to meet the breathing requirements of indoor personnel to maintain normal physiological activities. The impact of different oxygen content in the air on human physiology is shown in Table 5.120. The human body’s oxygen requirement mainly depends on the level of energy metabolism. Each liter of oxygen breathed into the lungs provides an average of 20kJ of heat. The air exhaled from the lungs contains approximately 16.3% oxygen, 4% 002,78.7% nitrogen and other gases (mainly ammonia). It also contains 45g/m3 of water vapor (saturated vapor at 37C body temperature). Therefore, in an air-conditioned environment or in the season when heating is used, if there is not enough air exchange rate in a relatively closed workshop, the indoor air will become more and more turbid, and the symptoms of hypoxia will be very obvious. As an indicator of indoor air quality, since Pettenkofor et al. proposed a CQ concentration of 0.1% and Yaglon et al. proposed the necessary fresh air volume based on air indicators, countries have generally adopted these values as the rough standard for determining air quality. In 1970, the Japanese Building Management Law and the Building Law applied to general public building air conditioners. When the total building area is greater than 300m2, the required indoor air standards are shown in Table 5.130. The Japanese Building Management Law stipulates that the fresh air volume is 31.4m3/h per person (according to 002 Allowable gas concentration is 0.1%, CO concentration is 0.03%, human energy metabolism rate is 0.8, (202 gas exhalation volume is 0.022m3/h per person).
1. Security
In the process of SMT production, it is necessary to use solvents such as absolute ethanol, flux and other flammable materials. It is necessary to design the production area and warehouse for fire safety. The design, construction and implementation of large-scale technical renovation projects of the factory buildings should all be reviewed by the fire department. The importance of electrostatic safety protection has been recognized by more and more people. Strictly speaking, the entire SMT production site should be designed in accordance with the standards of electrostatic safe working areas. Electrostatic protection is a systematic project, which should be regarded as a part of total quality management, which has attracted the attention of all employees of the enterprise. The production area should not only be equipped with all necessary electrostatic protection equipment, but also educate relevant personnel on electrostatic protection knowledge and consciously implement the electrostatic protection process regulations. Production and work sites should be designed with a good grounding system (for example, the resistance to ground should be less than 40), and the ground of the workshop should have anti-static performance, or be covered with anti-static floor mats.
2. Pollution protection
SMT production site air pollution sources mainly come from the smoke and dust generated by wave soldering, reflow soldering and manual soldering (the main components are lead, tin vapor, oxychloride, ozone and carbon monoxide and other harmful gases). The lead vapor contained in it is harmful to people. The health hazards are the most serious, and effective measures must be taken to purify the air in the workshop. The exhaust gas emission system designed and installed in the production area should have sufficient emissions, and the emission standards and emission requirements should comply with the regulations of the local environmental protection department. Smoke filters can be installed in some stations to absorb and filter out harmful gases. In the environmental design of the SMT production site, the following relevant evaluation standards should not be followed:
(1) (GBJ4-73 Industrial’, “Three Wastes” Emission Trial Standard”, hazardous substances: lead emission concentration <34mg/nm3);
(2) (TJ36-90 Design Sanitation Standard for Industrial Enterprises”, the maximum allowable concentration of lead smoke in the air of the workshop: 0.03mg/m3);
(3) (GB7355-87 Hygienic Standard for Lead and Its Inorganic Compounds in the Air”, the daily average maximum allowable concentration of lead and its inorganic compounds: 0.0015mg/m3) o
The national environmental protection department is drafting more stringent air protection regulations. When the new regulations are promulgated and implemented, they will put forward more scientific requirements for the design of SMT production sites. Lead and its compounds are toxic substances. Long-term use will bring greater harm to human living environment and safety. A large amount of lead vapor escapes during production, which will seriously affect the health of operators. The disposal of waste generated in production activities and waste is an important link. Chemical products, such as waste gasoline, engine oil, alcohol, and waste solder paste, patch glue, flux, solder slag, etc., are recommended to be collected in a centralized manner. They should be disposed of by units that have such garbage disposal capabilities and comply with national environmental protection requirements. They should not be arbitrarily throw away. Other recyclable waste generated, such as packaging materials for SMD components, should be stored separately and handed over to the garbage disposal station for disposal. Electromagnetic radiation has been recognized as the fourth largest source of pollution after water pollution, air pollution, and noise pollution. Excessive electromagnetic radiation will endanger the health of operators. Therefore, when selecting and purchasing SMT production equipment, the electromagnetic radiation that may be generated by the equipment should be required to ensure the personal safety of the operators. In recent years, the environmental issue of protecting the ozone layer has aroused great attention from countries all over the world. In view of the time limit for the complete cessation of use and production of Freon is approaching, it is necessary to actively develop and promote the use of no-clean welding materials. The success of EMS (Environmental Management System) implementation depends on the participation of all employees of the company. Therefore, operators must have a good environmental awareness, a high sense of responsibility, and a full understanding of their job responsibilities and environmental factors.
3. Management Guarantee
The modernization of process technology and scientific management are important signs of the modernization of industrial enterprises. It is necessary to use modern management ideas, methods and means to rationally configure the elements of productivity (people, materials, process methods, environment, information) to achieve the optimal combination, and implement effective planning, organization and control of the entire production process. The process layout of the SMT production site should be efficient and orderly, and the logistics route should be reasonable and consistent with the process flow. The logistics route should be as short as possible to improve the efficiency of production and management. The various items involved in the production shall be classified into categories and fixed management shall be implemented. All work areas and storage areas for various items must be clearly marked. Items not related to the production site should be removed from the site resolutely to completely eliminate the dirty, messy, and poor state of the production site. The production site with advanced design should be able to reflect the management characteristics of “equal production, orderly production, scientific process layout, reasonable labor organization, clear job responsibilities, and elimination of invalid labor”.
