Importance of Humidity Control in PCB Assembly

Importance of Humidity Control in PCB Assembly

When working with a printed circuit board (PCB) manufacturer, you tend to focus on the latest equipment they showcase for PCB assembly. However, as a buyer, one should also check out other exciting aspects of their manufacturing facility. It is important to educate yourself about whether the less obvious areas are keeping pace with the more obvious features.

One such aspect to look for in a PCB manufacturer's equipment is humidity control. This is an area where manufacturers have to take care of two different goals. On the one hand, high humidity is required to mitigate the risk of damage to the PCB from electrostatic discharge (ESD). On the other hand, low humidity helps maximize the durability of humidity-sensitive electronics or MSDs. These factors are becoming increasingly important as the electronics industry moves towards small SMT components that are sensitive to ESD and moisture.

Dry heat can be hazardous to PCB assembly. Therefore, the facility must have a steady supply of fresh air as well as a well-developed exhaust system. Also, fresh air should be continuously humidified to maintain a relative humidity above 30%, as recommended by the IPC. This can be achieved by installing a humidity control system at the factory. Additionally, any good, safe, and static-free PCB assembly equipment should use ESD wrist and heel straps, as well as grounded floor mats and carts to eliminate electrostatic discharge.

What to look for in a PCB assembly and fabrication facility

You have to look for the following in PCB assembly and manufacturing plants:

First, see if they have a humidity control system. Warm, humid climates may not require a separate humidity system. The air conditioning system can take care of relative humidity if needed. However, in areas with dry summers or cold winters, it is necessary to use a dedicated humidity control system.

If the system shows humidity below 30%, the system is set too cold or too low to meet the facility's humidity requirements. Modern humidity control equipment includes small, high pressure atomizing systems that are small, quiet and energy efficient,

If the relative humidity remains above 30%, you need to ensure that the MSD stays dry. In particular, smaller components and ball grid arrays (BGAs) require special handling. When the MSD is not in use, it must be kept in dry storage as the MSD may come out of the dry storage for hours before soldering.

Traditionally, the MSD is sealed in a moisture barrier bag along with a moisture indicator card and desiccant. Dry cabinets are also becoming more common these days, especially in "high mix" operations. Drying cabinets store MSD tubes and reels at 0.1% humidity and provide easier access to frequently used components.