In the production process of printed circuit boards (PCBs), tiny dust particles can cause quality problems such as short circuits and open circuits, seriously affecting product performance and reliability. Therefore, the design and construction of PCB cleanrooms have become a key link in ensuring product quality. A clean room that meets standards can not only effectively control pollutants such as dust and microorganisms in the air, but also stabilize environmental parameters such as temperature, humidity, and airflow, providing an ideal environment for high-precision PCB production. The following will provide a detailed introduction to the design and construction of PCB cleanrooms from aspects such as design planning, construction points, and environmental monitoring.
Table of Contents
1、 PCB cleanroom design and planning
（1） Determination of Cleanliness Level
Determine the cleanliness level of the cleanroom based on the precision requirements and production process of PCB products. For example, cleanrooms used for producing high-end PCBs such as high-density interconnect (HDI) boards and semiconductor packaging substrates typically require ISO Class 5 (equivalent to Class 100) or higher standards, with no more than 100 dust particles of ≥ 0.5 μ m per cubic meter of air; For ordinary PCB production, ISO 7 level (Class 10000) is sufficient to meet basic requirements.
When determining the cleanliness level, it is also necessary to refer to international standards (such as ISO 14644) and industry standards (such as China’s “Code for Design of Cleanrooms” GB 50073).
（2） Functional area division
Reasonable division of functional areas can improve production efficiency and reduce cross contamination. Cleanrooms are generally divided into production areas, auxiliary areas, and equipment areas. The production area is the core area, which includes processes such as drilling, electroplating, photolithography, and assembly; The auxiliary area is used for material storage, personnel changing and disinfection, etc; The equipment area is equipped with air conditioning units, purification equipment, electrical control cabinets, etc. Each area is isolated by facilities such as buffer rooms and transfer windows to prevent external pollutants from entering the production area. For example, materials need to undergo ultraviolet disinfection or dust removal through the transfer window before entering the production area.
（3） Airflow organization design
The form of airflow organization determines the purification effect of the cleanroom. The common air flow organization includes unidirectional flow and non unidirectional flow (turbulent flow). The airflow in a unidirectional clean room follows a parallel streamline, flowing in a straight line from the supply air outlet to the return air outlet, which can effectively discharge pollutants and is suitable for high cleanliness areas; The airflow in a non unidirectional clean room is irregular and relies on dilution to reduce dust concentration. It is cost-effective and suitable for areas with relatively low cleanliness requirements. In practical design, mixed airflow organization is often used, with unidirectional flow in key process areas (such as photolithography) and non unidirectional flow in other areas, balancing effectiveness and cost.
（4） Temperature, humidity, and pressure control
PCB production is extremely sensitive to temperature and humidity. For example, the photolithography process requires temperature control at 22 ± 1 ℃ and humidity maintenance at 45% ± 5% RH to ensure stable performance of the photoresist and accurate pattern transfer; The electroplating process requires high humidity to prevent the solution from evaporating. In terms of pressure control, the clean room needs to maintain positive pressure to prevent external pollutants from infiltrating. Reasonable pressure differentials (usually 5-10 Pa) should also be set between different functional areas to ensure that airflow flows from areas with higher cleanliness levels to areas with lower cleanliness levels.
2、 Key points for PCB cleanroom construction
（1） Construction of building structures
The building structure of the cleanroom needs to have good air tightness and insulation. The walls and ceilings are usually made of sandwich color steel plates, and the core material can be selected from rock wool (with good fire resistance) or polyurethane (with strong insulation). The boards are spliced with tongue and groove joints and sealed with sealant. The ground is generally paved with epoxy resin self leveling flooring or PVC anti-static flooring.
The former has good wear resistance and is easy to clean, while the latter has outstanding anti-static performance and can effectively protect PCB components from static damage. During construction, it is necessary to ensure that the ground flatness error does not exceed 2mm/m to avoid affecting equipment installation and personnel access.
（2） Purification equipment installation
Purification equipment is the core of a clean room, mainly including air filters, air conditioning units, fan filtration units (FFUs), etc. HEPA (High Efficiency Particulate Air) and ULPA (Ultra High Efficiency Particulate Air) filters are crucial and must be installed strictly in accordance with operating procedures to ensure that there are no gaps between the filter and the installation frame, preventing unfiltered air leakage. The selection of air conditioning units should be based on the heat and humidity load of the clean room to ensure stable temperature and humidity; FFU is commonly used in one-way flow clean rooms, and its installation density and wind speed need to be precisely adjusted according to the cleanliness level requirements.
（3） Installation of Electrical and Automation Systems
The electrical system must meet the explosion-proof and anti-static requirements of the clean room. All electrical equipment should be of explosion-proof or sealed type, and wires and cables should be laid in conduit and properly grounded. The self-control system is used to monitor and control the environmental parameters of the clean room, including the installation and commissioning of temperature and humidity sensors, dust particle counters, pressure differential sensors, and other equipment. These sensors need to be distributed in key locations in the clean room to collect real-time data and provide feedback to the control system. Once the parameters exceed the standard, the system will automatically alarm and start adjusting the equipment.
（4） Construction of pipelines and ventilation systems
Ventilation ducts should be made of materials that are not prone to dust accumulation and are corrosion-resistant, such as stainless steel plates or galvanized steel plates. The inner walls of the ducts should be smooth and flat to reduce airflow resistance and dust adhesion. The pipeline connection adopts welding or flange connection, and undergoes strict sealing treatment. After the completion of the ventilation system construction, it is necessary to conduct an air leakage test to ensure that the system’s airtightness meets the requirements. In addition, it is necessary to install an exhaust system to promptly remove harmful gases and exhaust gases generated during the production process.
3、 Cleanroom acceptance and daily maintenance
（1） Engineering acceptance
After the construction is completed, a comprehensive inspection of the cleanroom must be carried out in accordance with relevant standards. The acceptance content includes cleanliness testing (using a dust particle counter to measure the concentration of dust particles of different sizes), temperature and humidity testing, wind speed and volume testing, static pressure difference testing, lighting intensity testing, etc. Only when all indicators meet the design requirements can the clean room be put into use. For example, cleanliness testing needs to be conducted in two states: static (equipment idling, no personnel) and dynamic (normal production) to ensure environmental quality under different working conditions.
（2） Daily maintenance
The daily maintenance of the cleanroom is the key to ensuring its long-term stable operation. Regular replacement of air filters is a key maintenance focus, and the replacement cycle for high-efficiency filters is generally 1-2 years, which needs to be determined based on actual usage and testing data. At the same time, it is necessary to regularly clean the floor, walls, and equipment of the cleanroom, using specialized dust-free cloths and cleaning agents to avoid secondary pollution. Calibration and maintenance of the self-control system are also necessary to ensure the accuracy of environmental parameter monitoring. In addition, strict personnel management systems need to be established, and personnel entering the clean room must wear protective equipment such as dust-free clothing, masks, gloves, etc., and pass through the air shower room for dust removal.
The design and construction of PCB cleanrooms is a systematic project, from early planning to construction, and then to later acceptance and maintenance, each link is crucial. Only by strictly following relevant standards and specifications, combined with the characteristics of PCB production technology, can we create an efficient, stable, and reliable dust-free production environment, providing a solid guarantee for the manufacturing of high-quality PCB products. With the development of PCB technology towards higher precision and integration, the design and construction of clean rooms will continue to be optimized and upgraded to meet the new needs of the industry.
The above article comprehensively introduces the key points of PCB cleanroom design and construction. If you would like to further understand certain aspects, such as the selection of specific purification equipment or energy-saving design of cleanrooms, please feel free to contact us at any time.
