Flexible Circuit Boards Handle Moisture and Humidity
Most devices and equipment we use today are outfitted with printed circuit boards (PCBs), which are laminated structures of conductive insulated layers that host electronic components like resistors, capacitors, microcontrollers, interfaces, etc. These elements are connected via traces and planes, which are typically chemically etched onto thin layers of copper that have been laminated on sheets of non-conductive substrates such as polyimide.
While PCBs are incredibly useful in a wide array of applications and industries, they must be properly cared for to ensure their optimal performance. As such, the environment in which PCBs are stored or exposed has a major impact on their durability and reliability. In particular, moisture and humidity must be controlled to protect against degradation and damage.
Humidity and moisture can cause a variety of issues with a flexible circuit board, from corrosion to electrical failures. Moisture can interfere with the electrical conductivity of a circuit by reducing the glass transition temperature and causing conductive filament formation. Additionally, it can slow circuit speeds and cause delays in the activation of the corresponding functions in the device.
How Do Flexible Circuit Boards Handle Moisture and Humidity?
PCBs are often exposed to moisture and humidity during production, assembly, or shipping. One of the most common ways that moisture can enter the enclosure of a PCB is through water particulates in the air that land on the surface and diffuse into the board itself. Another way is through the process of baking, where moisture is forced out of the board through heating. Unfortunately, moisture can actually swell within the board during this process, which opens the doors for further diffusion and damage.
In addition to the potential for contamination from moisture, a PCB can be damaged by mechanical force. This can occur when a PCB is dropped, crushed, or subjected to vibration and movement. Fortunately, flexible PCBs are much more durable than their rigid counterparts. However, they still need to be properly secured in an appropriate enclosure to avoid exposure to physical force.
The best way to keep moisture and humidity out of a flexible circuit board is to use proper coatings. The type of coating will depend on the application and environment, but some commonly used options include acrylic, silicone, and polyimide. Silicone is a very versatile option that is resistant to high temperatures, abrasion, and corrosion, and has good flexibility. Polyimide, on the other hand, is a very durable and chemical-resistant material that can be used in aerospace and down-hole electronics.
Keeping moisture and humidity out of a flexible circuit will improve its resistance to corrosion, reduce testing time, rejections, and rework costs, and ultimately help the device perform more reliably in a harsh working environment. To prevent these problems, it is important to thoroughly inspect the PCB for areas where the coating may have been compromised or worn away. This can be done by using optical magnification to look for thin spots, cracks, and pinholes. Once these areas have been identified, they should be repaired and re-coated with the appropriate waterproofing material.