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January 27, 2025
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January 27, 2025FR4 is a commonly used fiberglass-reinforced epoxy laminate material, particularly in printed circuit boards (PCBs). Understanding its moisture absorption properties is crucial for determining its suitability in various environments.

Does FR4 absorb moisture?
- Moisture Absorption Rate:
Yes, FR4 absorbs moisture, but the absorption rate is relatively low compared to other materials. Typically, the moisture absorption rate of FR4 is around 0.10% to 0.20% by weight, depending on the specific grade and environmental conditions. - Impact of Humidity:
FR4 can absorb moisture when exposed to high humidity or wet environments. Prolonged exposure to humid conditions increases the likelihood of moisture uptake. - Effects of Moisture on Electrical Properties:
Absorbed moisture can affect the electrical properties of FR4, such as its dielectric constant and insulation resistance. This can lead to reduced performance in high-frequency applications or sensitive electronic circuits. - Thermal Expansion Concerns:
When moisture is absorbed and the material is subjected to high temperatures (e.g., during soldering processes), the water content can vaporize, causing delamination or warping in PCBs. - Preventive Measures:
To minimize moisture absorption, FR4 boards are typically stored in dry conditions, sealed packaging, or with desiccants. Manufacturers may also use conformal coatings to protect the material from environmental moisture. - Moisture Resistance Variants:
Enhanced grades of FR4, such as high-Tg (glass transition temperature) or low-Dk (dielectric constant) variants, offer improved resistance to moisture absorption and related performance degradation.
While FR4 does absorb some moisture, proper handling and protective measures mitigate its effects.