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Static Fire Stories Articles & Technical Papers Current News

Copyright (c) 1999, Desco Industries, Inc.

ESD Audits

by Ryne C. Allen
December 1999

Reproduced with Permission, EE-Evaluation Engineering, Decmber, 1999

An ESD audit is an essential part of a good ESD control program. This 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 plan 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 an Electrostatic Control Discharge Program developed and controlled by the ESD Association is the ANSI/ESD S20.20-1999[2], an excellent choice for a guiding standard.

In the audit, all facets of the program must be checked to see that they are in accordance with defined company procedures. Any discrepancies must be recorded and reported to the work area supervisor and to company management. Graphic summaries are helpful tools for presenting audit results, and will enable managers to commend personnel in areas that have improved and to detect and analyze problems in areas that are having difficulties.

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

It is highly recommended to on occasion include external auditors in the audit process to ensure a non-biased audit. External Auditors can include personnel from other work areas, location or even hired consultants.

Work Area

The audit must verify that the boundary that separates an ESD-Protected (ESDP) area from non-ESDP areas is clearly defined. Signs, directional arrows, aisle marking tape, and other methods may be used. This is a reminder to the workers in that area, of course, but also reminds visitors that they are entering or exiting a sensitive control environment.

When entering an ESDP area, it should be easily identified by the use of signs, posters or other designations to enforce the proper use of ESD controls.

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

Cleaning crews, contractor personnel, and maintenance workers must come into sensitive areas from time to time. These visiting personnel should be quizzed or trained for ESD safe practices before entering ESDP areas and asked to not touch ESD-Sensitive (ESDS) devices. If ESDS devices are stored in ESDP packaging, then this problem is minimized. Depending on their involvement with ESD sensitive devices or proximity to, their training does not need to be extensive.

Any visitor who will be in the area for an extended period should be required to wear a smock of a different color from regular workers, or should be given a different-colored badge for control purposes. 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 ESDS equipment or parts should go through an orientation to be certified or trained in ESD Safe practices according to the internal ESD control plan. A yearly refresher ESD control training program is recommended for all personnel.

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

There should be a prominently-posted self-checking procedure in the area, and the auditor must verify that each operator is aware of the procedure and follows it every day. One such procedure requires each employee to:

  • check the work area for charge generators,

  • don and test personal grounding devices,

  • check for insulators and clear them from the work area,

  • verify that sensitive devices are in ESDP packaging with proper labels,

  • make sure that there are no static generators inside ESDP packaging with ESDS items,

  • determine that the approved cleaners are on hand,

  • verify that wiring of discharge devices is grounded,

  • see that if an ionizer is used, it is positioned and working properly, and

  • make sure that non-grounded personnel stay a least a foot away from your static-safe area.

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

Each operator must wear the prescribed grounding devices at all times. A useful device is the continuous monitor, which tests the wrist strap and static mat connections continuously, and sounds an alarm when there is a problem. If each operator uses such a monitor, 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 such daily checks are part of the workstation routine.

If smocks or other ESDP outer clothing are required by the ESD control plan, the auditor must verify that that they are worn properly and checked regularly. Smocks help to minimize problems with street clothing and possibly hair. Proper donning of a smock includes securing the smock at the opening and covering of the sleeves. A further precaution is to ground the smock either connecting it to a grounded wrist strap or ground cord at the hip connection to ground when in a stationary position. Smocks also look neat, clean and increase the perception of professionalism and uniformity. Garments should be bar-coded, laundered and tested (sleeve-to-sleeve) according to ESDA Standard on Garments, ESD STM2.1.

Workbenches and Floors

The floors in an ESDP area must be checked for surface resistance, especially in the high-traffic areas. A common high-end limit for this is 1 GW per ANSI/ESD-S7.1. The audit will check this by using a megohmeter that meets both ESD S4.1 and ANSI/ESD-S7.1. Especially check for high traffic areas. ANSI/ESD S20.20 states that footwear and flooring are individual elements and for each element should be less than 1x10^9 ohms, but the total system resistance should be less than 35 Megohms. The best electrical check for a floor is surface resistance to ground (RTG) as this insures a connection to ground as well.

Each workbench must be evaluated for ESD prevention, which involves removal of non-essential insulators, such as coffee cups, radios, food wrappers, etc. or the control of essential insulators via ionization such as some tools and jigs.

The workbench should have a dissipative-grounded work surface, a common point ground or 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).

A good practice is to use a conformity sticker (always located in the same spot for each workstation) indicating that the bench meets all ESD control requirements. If a sticker is missing, it denotes that an infraction had occurred and not to use the bench. If the bench is ever moved then the sticker should be removed until re-inspected.

The positioning of equipment that generates static must be monitored carefully in relation to ESD-sensitive devices. Some companies have a one-foot rule, and others require a three-foot separation. The PC monitor, a well-known static generator, is necessary on many production benches. The static generation from this device can be made acceptable by use of a well-grounded protective screen or a topical antistatic-dissipative treatment.

If ionizers are used on or above workbenches, then the audit must include a verification that each ionizer is working properly. The checking procedure should be defined in the 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 ESDP containers.

Documents stored at the bench should be in dissipative holders and or binders.

Packaging or general purpose tapes found at the ESDP bench should be verified that they are ESD safe (antistatic and or dissipative) with a field meter.

Other Audit Concerns

The auditor must evaluate the types of cleaning materials and the cleaning practices for the work area. Cleaners should not contain insulators such as silicon, soap, lanolin, free-salts, mineral oil, etc.

All sensitive components must be protected both as they arrive and as they leave the ESD Sensitive area. The audit must verify that proper care is taken. Equipment to be shipped is especially vulnerable, because the manufacturer cannot control the environment in transit. Therefore those goods must be packed for the worst possible ESD environment.

Report to Management and Others

If there are any discrepancies, then the archived test records should be consulted to verify that the control devices in question have been historically tested and comply to internal specs. Also, whether the discrepancy is corrected or not on the spot, it needs to be recorded on the audit form as an infraction.

As each audit is completed, the auditor must go over it with the supervisor in charge of the area, and must 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, chairman or another person responsible for your static control program should regularly test the ESD Control products to ensure that they are functioning properly.

See below for a "laundry list" of how often your ESD control products should be tested, according to the Electronics Industry Association, Standard ANSI/EIA-625 [3], and general practices of major corporations. Each test referenced also explains the methodology used to perform the test.

ESD Protective Item Checks [3]

Frequency

Items

Daily

Wrist straps, Footwear, Smocks (properly worn)

Weekly

Workstations, Floor mats, ESD ground connections

Monthly

Static surveys of ESDP areas and workstations, Smocks (electrical tests)

Quarterly

RTG of work surface, RTG of floor, Wrist strap monitor check, ESD ground continuity

Semi-annually

Ionizer balance and charge decay

Annually

ESD system compliance to the ESD control program plan

 

Checklists

The MIL-HDBK-263, section K, has a suggested checklist to use in performing an ESD audit which encompasses over 500 specific questions in several subjects: Management; Training; Engineering; Procurement; Receiving area; Storage area; Work areas; Shipping area; Intra-plan and inter-plant movement; ESDS protected work stations; and Quality functions. The checklist should be tailored to reflect the requirements of the ESD control program as well as complement the program plan.

Standards

With the introduction of ANSI/ESD S20.20-1999, we now have a collective source for ESDA recommended constraints on product performance. Designing your ESD Control program around your ESDS devices and complying with ANSI/ESD S20.20 makes it easy to audit your ESD control program.

The ANSI/ESD S20.20 will be used extensively for ESD auditing by most companies and organizations.

Conclusion

The ESD audit is the feedback channel to assure company management and the customer that the ESD Control Program is working. Dangelmayer [1] notes, "The auditing process is the binding force behind the entire ESD control program".

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.

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 and the author of 29 published papers and articles. He is a member of the ESD Association, involved with several standards working groups as well as the Northeast Chapter 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.

References

1. ESD Program Management, 2nd Edition, T. Dangelmayer, Kluwer Academic Publishers, 1999.

2. ANSI/ESD S20.20-1999, Electrostatic Discharge Control Program, The ESD Association, 7900 Turin Road, Bldg. 3, Suite 2, Rome, NY 13440-2069.

3. ANSI/EIA-625, Requirements for Handling Electrostatic-Discharge-Sensitive (ESDS) Devices, Electronics Industries Association, Global Engineering Documents, Washington D.C., 1994

4. MIL-HDBK-263B, ESD Control Handbook for Protection of Electrical and Electronic Parts, Assemblies, and Equipment, Appendix K, ESD Damage Prevention Checklist. DoD, Defense Printing Service Detachment Office, Philadelphia, PA, 31 December 1992.

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