Flexible printed circuit boards (FPCs) are flexible, insulated substrates that can be freely bent, coiled, and folded, making them well-suited for the trend toward high-density, miniaturized, and highly reliable electronic products.
However, FPCs also have their weaknesses, one of which is their sensitivity to humid environments.
In this article, we will take an in-depth look at common failures in flexible printed circuit boards caused by moisture, to help PCB manufacturers, PCB designers, and PCBA manufacturers better understand this issue and how to prevent it.
FPC: A Key Component of Electronic Products
An FPC is a flexible electronic circuit made from a flexible insulating substrate, typically polyimide or polyester film.
It has a wide range of applications in electronic products, including aerospace, military, mobile communications, laptops, and digital cameras. The flexibility and high performance of FPCs allow for more creative and flexible designs in electronic products.
Challenges in Humid Environments
A humid environment refers to conditions with high relative humidity, where the air contains a large amount of moisture. Under these conditions, electronic components on circuit boards are susceptible to damage from moisture.
Problems arise when moisture in the air condenses into water droplets and settles on the circuit board.
FPCs typically use SOP or SSOP surface-mount components, which have very small spacing between their pins.
When moisture condenses into droplets on the leads of these components, it creates an invisible resistance between the circuit board’s pins and can even cause a short circuit, leading to circuit board failure.
Common Types of Malfunctions
Circuit board failures caused by moisture can be broadly categorized as follows:
1. Changes in Circuit Parameters
A humid environment can cause changes in the circuit parameters within a circuit board, which can lead to circuit board malfunctions.
Under these circumstances, the performance of electronic components may be compromised—for example, resistance values may change, capacitance values may decrease, and inductance values may increase. This can have a negative impact on the overall performance of the circuit.
2. Circuit Short Circuit
The presence of moisture can cause a short circuit in the FPC. When a short circuit occurs, current cannot flow normally, resulting in board failure.
This is particularly concerning for electronic products that require a high degree of precision.
3. Signal Processing and Transmission Line Faults
In humid environments, printed circuits and signal transmission lines are highly susceptible to damage. These lines are typically very fine, so moisture intrusion can cause them to break, leading to circuit board failures.
This could cause serious problems for equipment that requires high reliability.
Prevention and Resolution
To prevent common failures caused by moisture in FPCs, there are several key measures you can take:
- Environmental Control: When using FPCs in humid environments, consider using desiccants or controlling the ambient humidity to minimize the impact of moisture on the circuit boards.
- Sealed Protection: Properly seal and protect the FPCs in electronic products to prevent moisture from entering.
- Regular Inspections: Inspect the circuit boards regularly to ensure there is no visible moisture damage. If any problems are found, take prompt action to repair them.
