Moisture in Printed Circuit Boards: Understanding and Preventing PCB Moisture

Printed circuit boards underpin every modern electronic system, yet one of their most persistent reliability risks often goes unnoticed: PCB moisture. Whether absorbed during storage, handling or assembly, even small amounts of moisture can compromise solder joints, dielectric properties and overall performance. 

The issue is not new. Previous studies explored the thermal and mechanical effects of absorbed water, but as miniaturisation and multilayer complexity have increased, so too has the need to revisit how the industry controls and prevents PCB moisture.

At A.R.T., we train manufacturers and engineers to understand these practical risks through certified IPC programmes that turn theory into effective process control. As covered in our related blog on PCB design, material selection and environmental management play a defining role in ensuring long-term board reliability.

What Is PCB Moisture and How Does It Occur?

Moisture in a printed circuit board originates primarily from the hygroscopic nature of laminate materials. Epoxy resins, solder masks and glass reinforcements can all absorb atmospheric humidity over time, particularly under high-temperature or high-humidity conditions. Once trapped, this moisture expands rapidly during soldering, leading to delamination, blistering or microcracking.

Improper storage conditions are the most common cause. Boards stored in uncontrolled environments or opened moisture-barrier bags absorb water through resin matrices and microscopic voids. Even cleaning residues or flux solvents can act as moisture traps. The level of absorption varies by material, as shown in Table 1.

Table 1: Typical Moisture Absorption Rates by PCB Material

PCB Material	Moisture Uptake (% by Weight)	Primary Cause of Absorption	Impact on Reliability
FR-4 Epoxy Glass	0.15 – 0.30%	Capillary action in glass weave	Moderate delamination risk
Polyimide	0.40 – 0.60%	High resin permeability	May blister during reflow
PTFE Composite	0.02 – 0.05%	Minimal absorption	Highly stable in humidity
Cyanate Ester	0.10 – 0.15%	Resin–fibre interface	Excellent dielectric stability

Understanding how different substrates interact with environmental moisture is the first step in mitigating PCB moisture risk.

How PCB Moisture Affects Reliability and Performance

Absorbed moisture changes both mechanical and electrical characteristics of a board. Mechanically, it reduces the glass-transition temperature (Tg), making the laminate more prone to stress during soldering. Electrically, it alters the dielectric constant, affecting impedance and signal integrity in high-frequency designs.

When exposed to reflow soldering temperatures, trapped moisture expands into vapour. This can lead to “popcorning,” delamination or via barrel cracking. These are PCB moisture-related defects that often remain hidden until functional testing or field deployment. Over time, PCB moisture may also promote ionic migration, corroding copper features and reducing insulation resistance.

Such problems are especially critical in aerospace, automotive and defence applications where consistent performance is essential. Managing PCB moisture, therefore, requires not just post-assembly inspection but preventive control throughout storage and fabrication.

Detecting and Measuring PCB Moisture

Manufacturers employ several methods to detect and quantify moisture content before boards enter reflow. Traditional gravimetric analysis remains reliable for laboratory assessment but is destructive and slow. Modern techniques for measuring PCB moisture, such as capacitance-based sensing and infrared spectroscopy, allow rapid, non-destructive analysis and can be integrated into production environments.

Table 2: Common Methods for Detecting PCB Moisture

Method	Principle	Advantages	Limitations
Gravimetric Weighing	Measures mass change after conditioning	Accurate baseline data	Destructive and time-consuming
Capacitance Sensor	Monitors dielectric constant change	Real-time and non-destructive	Requires calibration
Infrared (IR) Spectroscopy	Detects hydroxyl bond absorption	Fast and precise	High equipment cost
Ultrasonic Scanning	Identifies delamination voids	Reveals hidden damage	Needs expert interpretation

Continuous monitoring helps track PCB moisture levels and prevents boards from entering soldering processes while still saturated.

Managing PCB Moisture in Production and Storage

Preventing PCB moisture begins long before assembly. Best practice includes storing boards in dry cabinets below 10% relative humidity and sealing them in moisture-barrier bags with desiccant packs when not in use. If exposure occurs, pre-baking the boards at 105 to 125 °C removes absorbed water before soldering.

Moisture-sensitive components and laminates should always be handled according to IPC/JEDEC J-STD-033 guidelines. Labels recording exposure time and humidity conditions help maintain traceability and reduce operator error.

Manufacturers are also adopting predictive maintenance systems that log ambient conditions in real time. This data-driven approach supports compliance with IPC standards while optimising oven profiles and material handling to minimise PCB moisture risk across multiple production lines.

Advanced Material and Process Developments

As designs become denser and operating frequencies rise, the industry is shifting toward materials with lower water absorption and higher thermal stability. Modern halogen-free resins, nano-reinforced epoxies and improved solder masks exhibit significantly reduced moisture uptake compared with legacy FR-4.

At the same time, low-temperature solder alloys are helping mitigate thermal stress during reflow, reducing the chance of trapped moisture expanding into voids. Some manufacturers now integrate inline vacuum drying or plasma cleaning as standard process stages, ensuring that even trace PCB moisture is removed before critical steps such as coating or encapsulation.

These advances demonstrate how engineering innovation continues to outpace historical limitations, providing both performance gains and higher reliability.

Practical Training and Quality Assurance

Controlling PCB moisture effectively requires a blend of technology, discipline and expertise. Even the most advanced materials will fail if stored or handled incorrectly. For this reason, A.R.T. emphasises real-world process control through IPC-certified training that combines theory with practical inspection and soldering techniques.

Training programmes teach technicians how to recognise early signs of moisture damage, including discolouration, blistering or delamination, and implement corrective actions during both assembly and rework. By understanding the physics behind PCB moisture, teams can improve first-pass yield, minimise rework and maintain consistent production quality.

Conclusion

Moisture management is not a single procedure but an integrated part of reliable electronics manufacturing. From material selection and storage conditions to reflow control and inspection, every stage influences how effectively PCB moisture is prevented or removed.

As component density and environmental demands continue to rise, the ability to combine robust design practice, informed process control and ongoing professional training remains key to ensuring that printed circuit boards deliver long-term reliability across every industry sector.