The Control of Light and Moisture In PCB Factory

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Why PCB Environmental Control is Critical

Printed circuit boards (PCBs) are the backbone of modern electronics, found in everything from smartphones to medical devices to aerospace systems. The reliability and performance of these PCBs is directly impacted by the manufacturing environment. Proper control of light, moisture, temperature, and other environmental factors in the PCB factory is critical to producing high-quality boards.

The Impact of Light on PCB Manufacturing

Exposure to certain wavelengths of light, particularly in the ultraviolet (UV) spectrum, can cause problems during the PCB manufacturing process:

  • UV light can prematurely cure photoresist coatings and solder masks
  • Bright visible light can overexpose photoresist during imaging
  • Stray light causes uneven curing of coatings

To control light levels, PCB factories often use:

Method Description
Yellow lighting Eliminates UV wavelengths
Light-blocking curtains Prevents stray light between areas
Light meters Monitor lux levels in critical processes

Keeping light exposure within specified limits, typically under 100 lux, helps ensure proper photoresist patterning and solder mask curing for optimal PCB Quality.

Moisture Control in the PCB Factory Environment

Moisture is another environmental factor that must be tightly controlled in PCB manufacturing. Excess humidity can cause multiple issues:

  1. Oxidation and corrosion of copper conductors
  2. Reduced photoresist adhesion
  3. Delamination of board layers
  4. Moisture absorption into the laminate
  5. Solder Defects during assembly

The acceptable relative humidity range depends on the specific processes and materials but is typically maintained between 30-60% RH.

Humidity Control Techniques Used in PCB Factories

PCB factories employ several methods to regulate moisture levels:

Technique Principle
Dehumidification Removes moisture from makeup air
Localized dry air Provides low-humidity zones as needed
Moisture barriers Isolates areas of differing humidity
Humidity sensors Continuously monitor RH levels

Along with temperature control, keeping humidity in the optimal range promotes consistently high PCB quality. Insufficient humidity control is a common cause of manufacturing defects.

Clean Room Standards for PCB Factories

PCB manufacturing is increasingly moving to clean room environments, especially for high-reliability applications like medical, military, and aerospace. Clean rooms provide the ultimate control over environmental contaminants.

Clean Room Classifications for PCB Manufacturing

The ISO 14644-1 standard defines clean room classifications based on the allowable concentration of airborne particles. The most common classes for PCB manufacturing are:

ISO Class Maximum Particles ≥0.5 μm/m³ Typical Applications
6 1,000,000 Consumer electronics
7 352,000 Automotive, telecom
8 35,200 Medical, military

Higher-grade clean rooms, such as ISO Class 5 (3,520 particles/m³), may be used for specialised PCB Fabrication processes.

Clean Room Design and Operation

Key aspects of clean room design for PCB factories include:

  • HEPA filtration to remove airborne particles
  • Positive air pressure to prevent unfiltered influx
  • Personnel gowning procedures to minimize contamination
  • Strict material control and cleaning protocols

Effective clean room operation requires ongoing monitoring of particulate levels and rigorous adherence to contamination control procedures by all personnel.

Environmental Monitoring in PCB Factories

Continuous monitoring of light, moisture, and other environmental parameters is necessary to maintain optimal conditions for PCB manufacturing.

Environmental Monitoring Systems

Modern PCB factories use sophisticated environmental monitoring systems (EMS) that typically include:

  • Networks of distributed sensors for temperature, humidity, light, etc.
  • Central monitoring stations with data logging and alarms
  • Integration with building management systems for automated control

EMS provides real-time visibility of conditions throughout the factory and enables rapid response to any deviations from specifications.

Data Analysis and Trending

The data collected by EMS is valuable for optimizing PCB manufacturing processes:

  • Identifying patterns and correlations between environmental factors and PCB defects
  • Determining optimal set points for temperature, humidity, light levels, etc.
  • Enabling predictive maintenance of HVAC and humidity control systems

Advanced data analytics, including machine learning techniques, can extract actionable insights from EMS data to drive continuous improvement in PCB quality and yield.


Controlling light, moisture, and other environmental factors is essential for producing reliable, high-performance PCBs. By implementing effective control strategies, monitoring systems, and clean room technologies, PCB factories can ensure the consistency and quality of their products. As electronics continue to advance, the importance of tight environmental control in PCB manufacturing will only increase.

Frequently Asked Questions

What is the ideal humidity level for PCB manufacturing?

The optimal humidity range for PCB manufacturing depends on the specific processes and materials used, but is typically maintained between 30-60% relative humidity (RH). Excessive humidity can cause oxidation, delamination, and other defects, while insufficient humidity can lead to static damage and brittle materials.

Why are clean rooms used for PCB manufacturing?

Clean rooms provide the highest level of control over environmental contaminants like dust, airborne particles, and chemical vapors. By maintaining an ultra-clean environment, PCB factories can minimize the risk of defects caused by contamination, which is especially critical for high-reliability applications like aerospace, medical devices, and military systems.

How does light affect the PCB manufacturing process?

Exposure to ultraviolet (UV) and bright visible light can interfere with photoresist patterning and solder mask curing during PCB manufacturing. UV light can cause premature curing of these light-sensitive materials, while excessive visible light can result in overexposure and loss of pattern fidelity. Proper control of light levels, typically below 100 lux, is necessary to ensure optimal results.

What environmental monitoring is needed in a PCB factory?

PCB factories require continuous monitoring of key environmental parameters including temperature, humidity, light levels, and airborne particulates. This is typically achieved using networks of sensors integrated with a central monitoring system that provides real-time data logging, alarms, and control capabilities. Environmental monitoring helps ensure consistent conditions for PCB manufacturing and enables rapid troubleshooting of any issues that arise.

How can data from environmental monitoring systems be used to improve PCB manufacturing?

The data collected by environmental monitoring systems (EMS) in PCB factories is a valuable resource for optimizing manufacturing processes. By analyzing trends and correlations in the data, engineers can identify patterns that may be causing defects, determine the optimal set points for parameters like temperature and humidity, and implement predictive maintenance on HVAC and other systems. Advanced analytics and machine learning techniques can help uncover deeper insights to drive continuous improvement.