Why Must High-End PCBA Factories Step Up Dehumidification in Their Production Facilities During the Summer?

Introduction

In the PCBA manufacturing industry, many customers focus more on core equipment such as SMT machines, AOI, X-ray, and reflow soldering machines, yet they often overlook a fundamental factor that has a significant impact on quality: humidity control in the production facility. Especially as summer sets in, air humidity rises rapidly, in some coastal regions, workshop humidity can even exceed 75% RH for extended periods. If the dehumidification system fails to maintain proper control, solder paste, PCBs, components, and the electrostatic environment will all be significantly affected. For high-reliability PCBA manufacturing projects, uncontrolled humidity is not merely an environmental issue—it is a process risk that directly impacts soldering yield and long-term stability.

High-humidity environments accelerate moisture absorption by PCBs

During the PCBA manufacturing process, PCBs themselves are not completely sealed materials. FR-4 boards, solder mask layers, and certain filling structures slowly absorb moisture from the air. When a workshop is exposed to high humidity over an extended period, the moisture content inside the PCBs continues to rise.
This change is not noticeable at room temperature, but once the board enters the high-temperature phase of the reflow soldering process, the internal moisture rapidly vaporizes and expands, creating localized vapor pressure. In mild cases, this results in bubbling and delamination on the board surface; in severe cases, it can even lead to pad cracking, CAF failure, and damage to the inner layer structure.
Therefore, high-end PCBA manufacturing facilities significantly intensify dehumidification in their workshops during the summer, with one of the core objectives being to reduce the risk of PCB moisture absorption.

Components are prone to the “popcorn effect” when exposed to moisture

In addition to PCBs, IC devices with higher MSL ratings are even more sensitive to humidity. In PCBA manufacturing facilities, if BGA, QFN, or large-sized packaged devices are exposed to high-humidity air for extended periods, the packaging materials will gradually absorb moisture. Upon entering the reflow oven soldering process, the internal moisture expands due to heat, creating immense internal pressure in a very short time. This phenomenon is commonly referred to in the industry as the “popcorn effect” .
Consequences include package delamination, chip cracking, and damage to solder ball structures. Many of these issues cannot even be detected directly by AOI equipment but are gradually revealed during subsequent thermal cycling stages. Therefore, humidity management in the summer affects not only the production environment but also directly impacts the long-term reliability of components.

Solder paste performance fluctuates with changes in humidity

In the SMT process of PCBA manufacturing, solder paste is also highly sensitive to ambient humidity. High-humidity environments alter the evaporation rate of flux and increase the risk of moisture from the air being drawn into the paste. When solder paste absorbs excessive moisture, printing stability decreases significantly. Common issues include edge collapse, tip formation, an increase in solder balls, and a higher risk of bridging in fine-pitch areas.
Some PCBA production lines frequently experience situations where “the morning runs normally but the afternoon has issues” during the summer; the root cause is that workshop humidity fluctuates constantly with temperature changes. Therefore, high-end factories not only control temperature but also maintain humidity at a stable level between 40% and 60% RH to ensure consistent solder paste rheological properties.

High Humidity Amplifies the Risk of Uncontrolled Static Electricity

Many people mistakenly believe that “static electricity is more likely to occur in dry environments.” In reality, humidity management at PCBA manufacturing sites is far more complex than simply preventing static electricity. While the risk of static electricity does indeed increase when humidity is too low, excessively high humidity can similarly affect the stability of ESD systems.
For example, in high-humidity environments, the surface resistance of anti-static flooring, ionization equipment, and ESD materials may drift, leading to abnormal static discharge paths. For precision chips used in high-end PCBA manufacturing, this instability increases the risk of potential ESD damage. Therefore, high-end factories typically do not aim for “the drier, the better,” but rather maintain a stable balance through constant temperature and humidity control systems.

High-Humidity Environments Also Affect the Stability of AOI and Optical Inspection

In modern PCBA production lines, a large number of inspection devices rely on high-definition optical systems. If workshop humidity remains persistently high, a thin layer of moisture is more likely to form on lenses, light sources, and PCB surfaces. Although these changes are not visible to the naked eye, they directly affect image contrast and recognition stability. Particularly in areas with high-density solder joints, the AOI false positive rate may increase significantly. Some high-end PCBA manufacturers implement enhanced dehumidification specifically in inspection areas during the summer to ensure consistent image capture.

Humidity control has become a key metric in high-reliability PCBA manufacturing.

In the past, many factories viewed dehumidification as a matter of “environmental comfort management,” but today, high-reliability PCBA manufacturing has incorporated humidity as a core process parameter. For products such as automotive electronics, medical devices, servers, and industrial control products, customers typically review workshop temperature and humidity records during audits.
Some projects even require the MES system to simultaneously record humidity fluctuations during production for subsequent quality traceability. This means that humidity control is no longer merely a supplementary management measure but an integral part of the PCBA manufacturing reliability system.

Truly stable PCBA manufacturing requires more than just advanced equipment.

Many PCBA quality issues stem not from insufficient equipment precision but from long-term instability in environmental conditions. Even with the same reflow profile, the same solder paste, and the same placement program, the final yield can vary significantly under different humidity conditions. The reason high-end PCBA factories intensify dehumidification during the summer is essentially to reduce uncertainty throughout the entire manufacturing process. Only when the environment is stable can soldering, testing, and material performance be truly consistent.
In the PCBA manufacturing process, humidity is never merely a simple environmental parameter; it is a critical variable that affects the reliability of PCBs, components, solder paste, and solder joints. Especially in the summer, the hidden risks posed by high-humidity air can permeate the entire SMT process.

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