ANSI/ESD S20.20 Foreword states:
- “This standard covers … electrical or electronic parts, assemblies and equipment susceptible to damage by electrostatic discharges greater than or equal to 100 volts Human Body Model (HBM).”
- “When handling devices susceptible to less than 100 volts HBM, more stringent ESD Control
Program Technical Requirements may be required, including adjustment of program Technical
Element Recommended Ranges.”
HMB Classification Class 0 is:
Per ESD-STM5.1 Human Body Model (HBM) Table 1 Class 0 has ESD Voltage Range < 250 Volts
Basically, to control the environment to decrease the probability of ESD damage in “Class Zero”
situations, involves increasing ESD protective redundancies and periodic verifications to those ESD
Control technical elements.
- Personnel: Decrease Wrist Strap and ESD Footwear upper limit permitted (The ESD Association has test data showing charge on a person is less as the path-to-ground resistance is less) The use of continuous monitors, smocks, use / increased use of ESD flooring, sole or full coverage foot grounders (HBM & CDM)
- Worksurfaces: Dissipative (CDM) i.e. change < 10^9 to a requirement of 10^6 to 10^8 ohms
- Bonded grounds – Carts, shelves, equipment
- Conductors: Minimizing isolated conductors like devices on PC Boards (CDM)
To see examples of Wrist Straps capable of dealing with class zero environments Click Here
To see examples of Grounding Cords capable of dealing with class zero environments Click Here
Minimize Charge Generation
The best form of control is to minimize charge generation. Grounding and ionization eliminate charges once generated. Shielding protects from generated charges.
- Personnel – Low Charging floor finish
- Surfaces – Use of low charging (anti-static) topical treatments
- Eliminate as best as possible all non-process necessary insulators
- Topically treat where ever possible insulators that cannot be removed
- Consider use of ESD Chairs or treat to reduce charge generation
- Shield charges on clothing by using ESD Smocks
To continue reading ESD Control Program Considerations when Dealing with
Class Zero Items Click Here
by Ryne C. Allen and Gene Felder, Desco Industries
ESD events are the cause of maddening, difficult-to-duplicate, and intermittent product malfunctions. They consume a great deal of time, annoy all involved, and are often never resolved.
Combating the invisible enemy with an effective ESD control program can produce financial benefits. But the greatest savings come from decreasing latent defects, which are extremely difficult to detect after the component is assembled into a finished product.
Any relative contact and physical separation of materials (or flow of solids, liquids, or particle-laden gases) can generate electrostatic charges. Common sources include personnel, items made from common polymeric materials, and processing equipment. ESD can damage parts by direct contact with a charged source or by electric fields emanating from charged objects that induce a charge on ungrounded sensitive items.
To view more information on how to Develop an ESD Control Program CLICK HERE