ESD Protection & EPA Workstation Guide
Electrostatic discharge (ESD) is the bane of sensitive PCB components and can lead to shorted and damaged parts. Electronics manufacturers uses EPA workstations and various practices to eliminate the risk of ESD. ANSI/ESD S20.20-2014 is what is looked upon as the standard for ESD testing. The standard outlines resistance values and practices to maintain an Electrostatic Discharge Protected Area (EPA) safe workspace.
A grounded work mat is needed for working on PCBs and their components. The material that makes up an ESD work mat is generally layers of vinyl that is anti-static. These mats are made to connect to a ground for dissipation. Potential grounds that can be used are large portions of bare metal or the ground of an electric outlet with an adapter. To test the effectiveness of a workstation using ANSI/ESD S4.1 requirements, 5 lb conductive rubber electrodes are placed on top and resistance is measured point to point with the goal to have a resistance of under 1.0×109 ohms.
Working at a protected workstation generally involves either standing on an ESD mat or in a chair. Chairs can be grounded using a drag chain. This is just a conductive metal chain with a 1MEG resistor inline. The next level of protection is having ESD chair caster wheels that dissipate charge to the ground. This method of ESD protection is effective due to the chair acting as a constant medium between the sensitive components and the ground. Under the chair should either be another grounded work mat or flooring that is not insulated.
Personal ESD Protection
There are differing levels of personal grounding that a technician can use. The bare minimum is an ESD wrist strap. This band goes around the wrist and makes contact with the skin. The strap is then grounded to bare metal or to a mounted ground. Next will be foot straps; these go around the shoe and into the sock to make contact with skin. These are necessary if ESD sensitive components will be moved around by a technician. These two methods must be checked regularly for functionality and effectiveness. Through heavy use, the foot and wrist straps can wear down causing ineffective static dissipation. Testing involves a foot and wrist strap tester which will measure the resistance and give a pass fail rating to the gear. According to ANSI/ESD S20.20-2014, the required limit for wrist straps and footwear is < 3.5×107 ohms and < 1.0×109 ohm respectively.
Moving & Storage of Sensitive Components
For protection of parts or assemblies, ESD bags are made from polyethylene or static shielding materials. These are good investments along with ESD sensitive labels if a circuit board assembly is going to be shipped or moved. Parts that can be statically sensitive should be stored on a rack that is grounded and in ESD bags. Drag chains and conductive copper tape can be used to create a ground path for racks. There are also specific crates and containers that are made for storage of parts that are ESD sensitive.
Vinatronic’s strict ESD policies ensure that their customers projects are protected from damage and can be trusted upon in the field.