Commercial Practices Standard Set to Replace MIL-STD 1686

In 1992, as part of the Military Standardization Reform Act, numerous military standards were targeted for replacement with equivalent commercial standards. MIL-STD 1686, the ESD Program Standard for the Department of Defense, was among those listed. The military conducted a search to find a relevant commercial practices standard to replace 1686, but no suitable standard existed.

As a result, the Department of Defense contacted the ESD Association (ESDA)—the cognizant American National Standards Institute (ANSI) standards development group in the field of electrostatics—to ask if the Association would write a commercial practices standard to replace MIL-STD 1686. The ESDA accepted the mission and formed a task group under the Association's Standards Committee. The task group comprised members of the military, military contractors, industry experts, and ESDA directors.

After six years and more than 20 drafts, a final document was released for industry review in late 1998. The final document was approved by the ESDA's Standards Committee in June and is ready for release as ESDA Standard for the Development of an Electrostatic Discharge Control Program for Protection of Electrical and Electronic Parts, Assemblies, and Equipment (Excluding Electrically Initiated Explosive Devices). In addition, the document is undergoing a parallel review by ANSI, which intends to make the final standard available as ANSI/ESD S20.20 this September.

The new document should be available for free on ESDA's Web site once the review work and final editing are completed. The document should also be available at the 1999 EOS/ESD Symposium in Orlando, FL. A paper copy of the standard will be available for a nominal fee that covers printing and handling.

One unique feature of the 20.20 document is its layout. All military documents contain requirements that form the essence of the standard. Many times the explanation of the requirement is listed in an appendix to the document. In 20.20, a requirement paragraph is followed immediately by a guidance section that explains or provides methods to help meet the requirement. All of the requirements, relevant guidance information, and references are also listed in a convenient table (highlights are shown in Table I). Many experienced users of military standards have commented on how easy ESD S20.20 is to use.

ESD S20.20 has simple requirements based on three fundamental principles of static control:

ESD S20.20 is intended to include finished-component handling (as in circuit card assembly) up through and including field service or repair activities. The scope was harmonized with the Electronic Industry Alliance committee rewriting EIA 625–Requirements for Handling Electrostatic-Discharge-Sensitive (ESDS) Devices. In addition, because of the ESDA's position as Technical Advisory Group to the International Electrotechnical Commission (IEC) Technical Committee 101 on Electrostatics, the review of draft 20.20 included members of TC 101. Specifically, members of TC 101 Working Group 5 were chosen to review the draft because they had experience preparing a broad-based handling practices document, IEC TR 61340-5-1/2. There is only a bit of philosophical, and perhaps political, difference that does not lead to complete harmonization of all the handling practices documents, but knowledgeable people will be able to make them work together.

ESD S20.20 has both administrative and technical elements that may be tailored for a specific application or activity requirement. The administrative elements include requiring the user organization to develop an ESD Control Program Plan, a Training Plan, and a Compliance Verification Plan (routine audits).

The ESD S20.20 technical elements have only a few "hard" requirements, with many options for compliance. This allows users to develop a plan for their applications that is cost-
effective and technically adequate. For example, grounding of personnel is an obvious requirement in any facility handling ESD-sensitive items. How the personnel are actually grounded, however, is left open by the plan. The common methods of grounding include wrist straps and ESD control floor–ESD control footwear systems. In this area, the only hard requirement in ESD S20.20 applies to seated operators. The standard calls for the operators to wear wrist straps rather than rely on the floor–footwear system that may be in place because a seated operator rarely, if ever, has both feet planted firmly on the floor.

The use of special chairs, garments, tools, fixtures, and other common ESD control items are options included in the technical plan. In the specialty area, ionization becomes a requirement if there are numerous and necessary nonconductors in the work area. ESD S20.20 includes a requirement to maintain the electric field on necessary nonconductors to less than a specified value if they are within 12 in. of sensitive items. A reading of 2000 volts (usually at 1 in.) from an item (this is field strength, not voltage in the normal sense) requires that the item be kept at least 12 in. away from 100-V human body model (HBM)–susceptible items. The value of 2000 volts at 1 in. for field strength was determined by empirical testing and has a safety margin of about a factor of two for 100-volt HBM devices.

Two appendices provide information on device and system ESD susceptibility testing and a list of important and useful references related to ESD control.

Several major military contractors have already adopted ESD S20.20, with several more set to follow suit. In addition, many electronics manufacturing companies are using 20.20 or are considering using it. A key to the implementation of ESD S20.20 by the Department of Defense is for at least one of the branches of the military to adopt it. When this occurs (which is expected to happen soon), ESD S20.20 will appear in contracts instead of MIL-STD 1686. Although it may take some time for 20.20 to completely displace 1686, it is anticipated that ESD S20.20 will become the most important document in the ESD control area in North America and, ultimately, have an impact worldwide.