ESD audits are an essential part of a proper ESD control programme. Audits check all ESD control practices and products, identify problem areas and faulty equipment, provide a reminder to personnel of their responsibilities and indicate areas that require correct action.
The compliance of all aspects of the ESD equipment, procedures and training must be checked at regular intervals, otherwise gradual deterioration can be expected. Equipment will fail over time and materials and equipment will become non-compliant. Static awareness and correct use of procedures will tend to gradually fade unless reinforced by refresher training.
An audit is based on an ESD control document that has been defined, approved by management and implemented at all operating levels. In the audit, all facets of the ESD programme must be checked to see that they are in accordance with the ESD control document. Discrepancies must be recorded and reported to supervisors and to company management as soon as possible. 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 programme.
Work area compliance
The audit must verify that the boundary that separates an ESD protection area (EPA) from non-EPA 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 EPA, 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 minimise tribocharging.
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 safety practices before entering EPAs and instructed to not touch ESD-sensitive components.
Any visitor who will be in the area for an extended period should be required to wear a coat of a different colour from regular workers, or should be given a different coloured badge for control purposes. This makes it easy to identify and monitor them for ESD practices.
Employee audit
Every operator, supervisor, material handler or other employee that comes near sensitive equipment or parts should go through an orientation to be certified or trained in ESD practices. A yearly refresher ESD control training programme is recommended for all personnel. Certification records should be readily available to the auditor and to area supervisors.
There should be a self-check procedure in the area, and the auditor must verify that each operator is aware of the procedure and follows it every day. Self-check shall ensure that the employee performs the following:
* Check the work area for charge generators.
* Wear and test personal grounding devices.
* Check for ESD insulators and remove them from the work area.
* Check that ESD sensitive equipment is in proper packaging with labels.
* Ensure that approved cleaners are on hand.
* Check that wiring of discharge devices is grounded.
* Ensure that ioniser is positioned and working properly.
* Ensure that non-grounded personnel stay at least a foot away from static-safe areas.
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 continuous monitor tests the wrist strap and static mat connections continuously and sounds an alarm when there is a problem. If an operator uses a monitor, the auditor must verify proper operation. If the monitor is not used, the auditor must determine that wrist straps and heel straps are checked daily.
Work benches and floor covering
The floors in an EPA must be checked for surface resistance, especially in the high-traffic areas.
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 ionisation (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).
The positioning of equipment that generates static must be monitored carefully in relation to ESD sensitive equipment. 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 ionisers are used on or above workbenches, then the audit must include a verification that each ioniser is working properly. The checking procedure should be defined in the ESD document and the audit should verify that each operator can and does follow that procedure.
Documents stored at the bench should be in dissipative holders and/or binders. Packaging or general purpose tapes found at the work bench should be verified that they are ESD safe (antistatic and or dissipative) with a field meter.
Cleaning materials and packaging
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 EPA. The auditor must verify that proper care is taken. Equipment to be shipped is especially vulnerable, because the manufacturer cannot control the environment in transit. Those goods must be packed for the worst possible ESD environment.
Reporting discrepancies
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 with specifications. The discrepancy must be recorded on the audit form as an infraction.
ESD test schedule
An ESD coordinator, supervisor or other person responsible for the static control programme should regularly test all ESD control products to ensure that they are functioning properly. Table 1 describes the test intervals recommended by the Electronics Industry Association, in accordance with standard ANSI/EIA-625.
Actum Electronics offers comprehensive ESD advice and audits.
| Tel: | +27 11 608 3001 |
| Email: | [email protected] |
| www: | www.actum.co.za |
| Articles: | More information and articles about Actum Electronics |
© Technews Publishing (Pty) Ltd | All Rights Reserved
printer friendly version