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
A Comprehensive Program Is Required For Effective ESD Control
With most companies pressured by global competition, effective ESD control can be a key to improving productivity, quality, and customer satisfaction. It is a pity that many companies buy ESD protective products or equipment and then misuse them, often causing more harm than good.
Electronic components that are electrostatic discharge sensitive (ESDS) must be protected throughout the entire manufacturing cycle. According to ANSI/ESD S20.20, the ESD Association’s standard for the development of an Electrostatic Discharge Control Program, safeguards are required during activities that “manufacture, process, assemble, install, package, label, service, test, inspect or otherwise handle electrical or electronic parts, assemblies and equipment susceptible to damage by electrostatic discharges.”
If ESD latent defects occur during this manufacturing and product cycle, it can be most frustrating and costly. Latent defects in components by deﬁnition will not be detected so products will pass normal inspections. ESD damage is the hidden enemy; electrostatic charges cannot be seen, typically discharges less than 3,000 volts cannot be felt, and latent defects cannot be detected through normal quality control procedures.
Manufacturing facilities should be as diligent with their ESD control program as hospital operating rooms are in implementing sterilization procedures. Damage caused by invisible and undetectable events occurs in medicine where people can experience infection or even death from viruses or bacteria. In hospitals, the defense against this invisible threat is extensive contamination control procedures including sterilization.
To learn more about correct ESD product usage Click Here