Audits Essential to Successful ESD Control Programs

An ESD audit is an essential part of a good ESD control program. It checks all ESD-control practices and products, provides a constant reminder to personnel of their responsibilities, and gives management the necessary feedback for any corrective action.

An audit is based on an ESD control program that has been defined, approved by management, and implemented at all operating levels. Generally, such a program is based on some industry-generated standards. The new parent document for many programs is ANSI/ESD S20.20-1999, developed and controlled by the ESD Association and an excellent choice for a guiding standard.¹

In the audit, all facets of the program must be checked to ensure they agree with defined company procedures. Discrepancies must be recorded and reported to the work-area supervisor and company management.

Graphic summaries are helpful tools for presenting audit results. They also help managers to commend personnel who have improved and detect and analyze areas that are having difficulties.

Each company’s audit procedures are unique to the local control program, but certain aspects will be part of every program. The major areas to be examined are work-area integrity, operator conformance to proper procedures, and the condition of the workbench and floor.

Occasionally, it is highly recommended to include external auditors in the process to ensure a nonbiased report. External auditors can include personnel from other work areas, locations, or even outside the company.

Work Area

The audit must verify that the boundary separating an ESD-protected area from non-ESD-protected areas is clearly defined, such as with signs, directional arrows, and markings on the floors. This is a reminder to both workers and visitors that they are entering or exiting a sensitive control environment.

Supply carts that store or transport ESD-sensitive devices should have the uprights and shelves electrically connected and grounded by a drag chain to minimize tribocharging. A ground snap permanently attached to the cart is highly recommended for hard grounding the cart when docked in an ESD-protective area.

Cleaning crews, contractor personnel, and maintenance workers must come into sensitive areas from time to time. These personnel should be trained regarding ESD-safe practices before entering the areas and cautioned not to touch ESD-sensitive devices. The level of training depends on the degree of job involvement in the area and on whether the ESD-sensitive devices are stored in protective packaging. For control purposes, any visitor who will be in the area for an extended period must wear a smock of a different color or a different-colored badge from regular workers. This makes it easy to identify and monitor them for ESD safe practices.

Generally, assembly workers clean their own workbenches, and outsiders are forbidden to touch anything on the benches unless they are properly trained and protected. This should be verified by the audit.

Operators

Every operator, supervisor, material handler, or other employee that comes near ESD-sensitive equipment or parts should go through an orientation and be certified in ESD-control practices as defined by the control plan. A yearly refresher program is recommended for all personnel in these categories.

Certification records should be readily available to the auditor and area supervisors. In reality, the operators are the full-time ESD monitors, and this role must be emphasized.

There should be a prominently posted self-checking procedure in the area, and the auditor must verify that each operator knows the procedure and follows it daily. One procedure requires each employee to:

• Check the work area for charge generators.
• Don and test personal grounding devices.
• Clear any insulators from the work area.
• Verify that sensitive devices are in ESD protective packaging with proper labels.
• Determine that there are no static generators inside ESD protective packages containing sensitive items.
• Determine that the approved cleaners are available.
• Verify that wiring of discharge devices is grounded.
• Verify that the ionizer is working and positioned correctly.
• Ensure that ungrounded personnel stay at least 1 ft away from the static-safe area.

Some companies require that every person entering a sensitive area pass a grounding test and that certification be verified. The audit must validate that such a system, if implemented, is operating properly.

Each operator must wear prescribed grounding devices at all times. A useful device is the continuous monitor that tests the wrist-strap and static-mat connections continuously and sounds an alarm when a problem arises. If a monitor is used by each operator, the auditor must verify proper operation. If the continuous monitor is not used, the audit must determine that wrist straps are checked daily.

The same goes for heel straps if they are used. Part of the audit is getting assurance that daily checks are part of the workstation routine.

If smocks or other ESD-protective outer clothing is required by the ESD control plan, the auditor must verify that they are worn properly and checked regularly. Smocks help minimize any ESD generated by street clothes. Typically, the smock is grounded through a wrist strap or hip connection whenever the operator is stationary. Smocks should be bar-coded, laundered, and tested (sleeve-to-sleeve) according to the ESD Association Standard on Garments, ESD STM 2.

Workbenches and Floors

The surface resistance of floors in an ESD-protective area, especially high-traffic areas, must be checked with a megohmmeter that meets ESD S4.1 and ANSI/ESD S7.1. A common limit for this is 1 GW per ANSI/ESD S7.1.

ANSI/ESD S20.20 states that footwear and flooring are individual elements and each element should be less than 1 × 10⁹ W, but the total system resistance should be less than 35 MW. The best electrical check for a floor is surface resistance to ground (RTG) because this ensures a connection to ground as well.

Each workbench must be evaluated for ESD prevention, which means removing nonessential insulators such as coffee cups or radios and controlling essential insulators such as tools and jigs by ionization. The workbench should have a dissipative-grounded worksurface, a common-point ground, or a continuous monitor with banana jacks for grounding wrist straps and a ground cord to power ground (connected to the common-point ground or continuous monitor).

It is a good practice to use a conformity sticker located in the same place on every bench to indicate that it meets all ESD control requirements. If an infraction occurs or if the bench is moved, the sticker must be removed.

The positioning of equipment that generates static must be monitored carefully in relation to ESD-sensitive devices. Some companies have a 1-ft rule, and others require a 3-ft separation.

The PC monitor, a well-known static generator, is necessary on many production benches. ESD can be controlled by using a well-grounded protective screen or a topical antistatic-dissipative treatment.

If ionizers are used on or above workbenches, the audit must include verification that each ionizer is working properly. The checking procedure should be defined in an ESD control program, and the audit should verify that each operator can and does follow that procedure.

An auditor should check trash holders to verify that they are ESD-protective containers. Documents stored at the bench should be in dissipative holders or binders. Packaging or general-purpose tapes found at the bench should be verified with a field meter as ESD safe (antistatic and or dissipative).

Other Audit Concerns

Evaluate the types of cleaning materials and the practices for the work area. Cleaners should not contain insulators such as silicon, soap, lanolin, free-salts, or mineral oil.

All sensitive components must be protected as they arrive and leave an ESD-sensitive area. The audit must verify that this procedure is followed rigorously. Equipment to be shipped is especially vulnerable because the manufacturer cannot control the environment in transit. Consequently, those goods must be packed to withstand the worst possible ESD environment.

Report to Management and Others

As each audit is completed, the auditor must review it with the supervisor in charge of the area and present it to plant management. Corrective recommendations will be a part of the report, and the net result will be an improved or well-run ESD control program. This is the reason for and the discipline of an ESD audit.

Test Schedule for ESD Control Products

An ESD coordinator or another person responsible for the static-control program should test other ESD control products periodically to ensure that they are functioning properly. Table 1 (see below) presents information on how often ESD-control products should be tested.²

Checklists

MIL-HDBK-263, Section K, includes a checklist to use in performing an ESD audit.³ It provides more than 500 specific questions on several subjects: management, training, engineering, procurement, receiving area, storage area, work areas, shipping area, intraplant and interplant movements, ESD-protected workstations, and quality functions. The checklist should be tailored to reflect the requirements of the ESD control program.

Standards

With the introduction of ANSI/ESD S20.20-1999, there now exists a collection of the ESD Association’s recommended constraints on product performance. Designing an ESD control program around the ESD-sensitive devices and complying with ANSI/ESD S20.20 make it easy to audit the program.

Conclusion

The ESD audit is the feedback channel to assure company management and customers that an ESD control program is working. As one industry expert summed it up, “The auditing process is the binding force behind the entire ESD control program.”⁴

Auditing is easy. The hard part is making the results bear fruit through improved ESD control. An ESD auditor must persevere until all the right things have been recognized and rewarded and all the wrong things have been corrected.

References

1. ANSI/ESD S20.20-1999, Electrostatic Discharge Control Program, ESD Association.
2. ANSI/EIA-625, Requirements for Handling Electrostatic-Discharge-Sensitive (ESDS) Devices, Electronics Industries Association, 1994.
3. MIL-HDBK-263B, ESD Control Handbook for Protection of Electrical and Electronic Parts, Assemblies, and Equipment, Appendix K, ESD Damage Prevention Checklist, Department of Defense, Dec. 31, 1992.
4. Dangelmayer, T., ESD Program Management, 2nd Edition, 1999.

About the Author

Ryne C. Allen is the technical manager at ESD Systems, a division of Desco Industries. Previously, he was chief engineer and laboratory manager at the Plasma Science and Microelectronics Research Laboratory at Northeastern University. Mr. Allen is a NARTE-certified ESD control engineer, author of 27 published papers and articles, and a member of the ESD Association. He graduated from Northeastern University with B.S.E.E., M.S.E.E., and M.B.A. degrees. ESD Systems, 19 Brigham St., Unit 9, Marlboro, MA 01752-3170, (508) 485-7390, e-mail: [email protected].

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December 1999