The production of printed control boards (PCB) requires that the surrounding environment is safe from electrostatic discharges (ESD) as much as possible. An ESD of as little as 30 volts has been known to cause to damage to electronic components in a PCB during its production, storage, and/or shipping stages. When you consider that the average ESD you feel when walking across a carpet contains about 3000 volts, it doesn’t take much to hurt a circuit board. This is why it’s imperative that the clean room where the PCBs are made is an ESD-safe working environment. Here is an overview of what it means to have an ESD-safe production environment and how it is accomplished.
ESD- Resistant Flooring
The working space needs to be free of things that can cause ESD releases to occur. This means the flooring has to be ESD-safe. Any carpeting needs to be removed and replaced with anti-static materials like static dissipative tiles (SDT) for the floor. The tiles typically have a 4-layered structure. The base layer is made with a static dissipative adhesive to affix the tile to the sub-flooring. On top of the base layer, is another one made of conductive metals like copper strips. The third layer of the SDT is typically made out of plastic because of its conductive ability. Some tiles have added bits of carbon graphite, aluminum flakes, carbon fiber, and other conductive materials to increase the conductivity of the tiles. The fourth layer is often an anti-static acrylic floor polish to cover the tiles. This flooring system takes an electrical charge that gets created by something or someone moving over the floor. Since an electrical charge will follow the path of least resistant, it will flow from the top of the floor down through the adhesive where it gets grounded and dissipates.
If flooring mats are used to help workers standing at workstations, it’s imperative that the matting has a material like conductive carbon fibers to disperse the electrical charge from the mat to the SDT tiles under it.
Provide Protective Clothing
The clothing people wear in a clean room where printed circuit boards are made is important to regulate in order to keep the room ESD-safe. Workers should be wearing shoes with static dissipating soles that meet the ESD-compliance guidelines. The letters SD are required to be put on the side of the shoe so you can tell whether it is compliant or not.
Regular clothing often builds-up electricity that can lead to an ESD. Those entering a clean room should be dressed or covered in clothing made with electrically conductive textiles. The clothing incorporates metal strands mixed with other materials like cotton to make cloth for the clothing. Protecting hands with ESD-safe gloves is also important to minimize the risk of discharge.
A worker should also be “grounded” when working in a clean room. This is achieved by having the workers wear grounding wristbands. The wristband moves an electrical charge from the person to the ground where it dissipates.
Use ESD-free Tools
Tools used in the clean room should have a double-layered grip made out of a material like polyethylene that minimizes the movement of an electrical charge from a worker to the electronic device she is working on. All electrical tools should be plugged into a properly grounded outlet before using as well.
Control the Atmosphere
Controlling the atmospheric conditions in the clean room is also important to reduce the chances of an ESD event. Ionization machines are typically used to control the electrical charges in the atmosphere. The machine uses a fan to pull the air in the clean room into it. As the air passes through the ionizer, it electrically charges the positive and negative ions connected to the air molecules. The ions spread out into the room and bond to their positive and negative ion counterparts on workbenches, clothing, and other things to provide an electronically-charged balanced workspace that minimizes the probability an ESD event will occur.
If you have any questions about ESD and how Hallmark maintains an ESD-Safe environment to protect the printed circuit boards we make, just give us a call. We have seasoned personnel who can answer any questions you may have about printed circuit boards and our ESD-Safe environment.