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A Class 3 OEM found high correlation between audits and follow-through.

As result of the unprecedented exponential rate of devices with less than 100V ESD sensitivities^1-2, the now constantly changing and tightening of a facility’s ESD controls makes for interesting challenges with regard to operator discipline to the new controls and procedures. A goal of any ESD training effort is to educate personnel on how to use a facility’s ESD controls. As important, results need to be monitored on a constant basis to ensure full compliance. If procedures aren’t followed, the training program must be able to change the behavior. We have found that a combination of auditing and training functions is needed to change behavior patterns and allow quick acceptance of rapidly changing ESD controls. Historically, some considered it acceptable to allow personnel a year or more for full compliance to ESD policies, as the policies would be in place for many years. Today, however, many facilities change their ESD controls each year.

Program Components

The current General Dynamics Advanced Information Systems (GDAIS) ESD auditing and training components work in unison to achieve the desired discipline at the facility. (Auditing feedback is critical to track the discipline resulting from the training.) They include:

Online training. Once annually, all operators are required to complete an online training course. The course was developed in-house and describes the GDAIS program’s dos and don’ts. It includes the basics: general ESD theory, ESD failure modes (HBM, CDM, etc.), clothing requirements, grounding devices, ESD workstation requirements, transportation techniques, packaging materials and all operator requirements. Experience concluded that commercially available online presentations do not achieve the same level of subsequent discipline as custom training based on the facility’s exact mode of operation. We also found that discipline improvements are traceable to the introduction of more pictures – and less text – in the presentations. It is important to show the exact materials found throughout the facility: It has a noticeable impact on resulting discipline. Both internal and external (independent) audit results are continually analyzed, and appropriate changes to the online presentation are made as needed, if a lingering discipline issue exists. Most important, when a training course change is made, subsequent internal audits are inspected to determine whether the discipline issue has been eliminated. If not, additional changes are made to the presentations and subsequent audits conducted. This closed-loop system keeps budding discipline issues from becoming widespread. As in the advanced course (described below), the online course includes a final quiz.

Advanced training. All operators are required to attend a one-hour, advanced, instructor-led ESD course every other year. This course is custom-designed for the facility and describes the “why” of the program. Although some program requirements are reviewed, this course focuses on:

• Where the industry is going.
• How the packaging lapses actually can cause product damage.
• Why the new controls were implemented.
• How the ionizers actually work.

Course contents change dramatically each time operators are trained, thanks to the frequent changes of so many static-related items. Internal and external audit feedback is incorporated regularly into this training. Classes are available on a four-month interval so that newcomers get trained in a timely fashion. Tests are administered in the advanced training courses. In all training venues, operating personnel are instructed and encouraged to police their own areas and bring potential violations to the attention of their supervisors immediately. This is a hallmark of GDAIS’s training efforts. The training programs are geared to instruct the operators to catch ESD violations when they occur, and we’ve been successful in many cases.

Target training. There are instances when special, “targeted” ESD training classes are held (instructor-led) – many times for specific new product lines – when new, special ESD precautions have been determined to be necessary. In these cases, time is of the essence, and special custom training classes are developed and delivered. As in all training venues at the facility, audit results are inspected to verify the needed discipline is in fact occurring.

External audits. On a four-month basis, GDAIS is audited fully to ESDA S20.20 requirements. A host of internal specifications by an independent, outside auditor, is an important factor in achieving fine results. No matter how rigorous the internal effort, an outside and independent organization is more likely to conduct impartial auditing. Internal audits are monitored for accuracy as a result of the external audits, and internal auditors check the findings of outside auditors. Checks and balances ensure better results all around. This is almost impossible to achieve with internal staff alone.

As part of the outside S20.20 audit, all ESD controls, including ESD work surfaces, wrist strap constant monitors, flooring, carts, shelves, ionizers, soldering irons, grounding receptacles, etc. are electrically checked and certified with dated calibration stickers attached to audited items. Operator discipline is closely observed and recorded. At each workstation, more than 40 potential ESD discipline issues are inspected for compliance. Out-of-compliance issues such as hardware problems and discipline issues are noted and incorporated into a complete, formal audit report. The ESD team and appropriate line supervisors and managers review this report in its entirety on the final day of the audit, and corrective actions are put into place immediately so that product damage is avoided. The outside auditor incorporates any new training focus issues generated from the previous audit. Discipline lapses are reported to the training functions, completing the closed loop functions. At GDAIS, the outside auditor also presents the advanced training classes. Firsthand knowledge of each function aides the other.

Internal audits. In-house production personnel conduct “self-audits” of the facility between the external, four-month interval full audits. We have observed a direct correlation between internal self-audits and subsequent ESD discipline. Management tracks and reviews internal audit results. As one discipline issue is corrected, often another one will arise from the new procedures initiated to correct the former. The key to a successful program is continuous monitoring.

Documented Discipline Improvements

There are many well-documented discipline-based ESD damage modes in electronics manufacturing.³ Maintaining rigorous ESD discipline is critical to avoiding those damage modes. For seven years, GDAIS has documented operator progress toward ESD discipline. We have selected a few examples of such improvement that illustrate the effectiveness of the closed-loop, audit-feedback training program.

The 6" rule policy. Most facilities have incorporated a “set distance” rule whereby charge-generating materials must be kept a minimum distance from ESD-sensitive items (components, PCBs, final systems when a side of the panel is removed, etc.) during handling and other assembly operations. Most often, a 6" or 12" rule is called out in company specifications. GDAIS has a 6" requirement. (S20.20 permits generating materials under 2 Kv to be within 12" of vulnerable ESDS items. GDAIS’s position is to exclude all charge generators within 6" to ensure superior compliance.)

There are two common ways to implement the 6" rule. One works well; one does not. The most common method is also the least effective, as observed by interaction with more than 2,000 different facilities since 1986. Specifically, a facility implements ESD mats (or laminates) on work surfaces and instructs operating personnel to keep all charge-generating materials at least 6" from ESDS (ESD-sensitive) items (the 6" rule “by decree”). Operator discipline is usually very poor, however.

Perhaps 2% of facilities use the more effective technique to maintain a 6" inch rule. In this technique, an additional, smaller and different colored ESD mat is placed on top of the existing ESD mat or laminate at the workstation. The purpose of these “No Man’s Land” (NML) mats is to designate the exclusive area where ESDS items can be placed. These additional mats (light blue at GDAIS, Figure 1) are kept absolutely clear of all materials, except for ESDS items. The NML mats are sized to provide a natural 6" or 12" clear area border when the ESDS item is placed in the center of the mat. Operators have a number of NML mats at their workstation, for use with different-sized ESDS items. The NML mat can be placed anywhere on the ESD work surface. The NML mat mates electrically with the work surface mat or laminate – no additional ground cord is needed – and the 6" or 12" border is inherently maintained. It is quite simple and obvious to monitor the 6" or 12" rule in this manner, as the mats are highly visible and nothing but the ESDS item should be on them.

To improve discipline, GDAIS in 2000 switched from the 6" rule by decree to the NML mat technique. Initial training was conducted and the first audit revealed more than 150 NML mat rule violations. The training functions received feedback and focus was renewed. By maintaining this closed loop system, NML mat violations observed per external audit have fallen to typically less than five in more than 600 workstations; during the past three years, no 6" rule violation has been observed during audits.

Self-testing constant monitors. Another discipline improvement is the requirement for operators to test their wrist strap constant monitors at the beginning of each shift. GDAIS employs wrist strap constant monitors at all locations where ESDS items are handled. During external audits and certifications, constant monitor equipment failures typically totaled 10 per audit. The training/auditing closed loop system was used to educate operators to perform simple tests each shift to ensure the constant monitor was working correctly. Operators were instructed to perform an additional “fail” condition. During seven external audits between June 2004 and June 2006, the number of constant monitors failing calibration tests fell (Table 1).

Identifying expired calibration stickers. Operators have been trained to routinely check calibration stickers on all sorts of items and equipment where they work. In numerous cases, the calibration sticker on ESD controls was out of date or missing. These now are caught routinely by operators and corrected immediately.

Soldering iron violations. Similarly, the closed loop training/auditing system was used to improve discipline on soldering irons testing and the use of calibration stickers. GDAIS operators are required to perform monthly calibration checks on their soldering irons, and upon completion, to put calibration stickers on the units. Again, from external audit records between October 2002 and June 2006 – 12 consecutive audits – the number of soldering irons failing either the soldering iron calibration test or missing a calibration sticker fell dramatically (Table 2).

Overall audit scores. A grading system has been implemented and monitored constantly to quantify overall improvements and benchmark against other leading facilities. The grading system is consistent with many other electronics manufacturing facilities. It is very stringent, and our outside auditor has used it exclusively at hundreds of facilities since 1986. During that timeframe, only 10 to 15 companies were successful at routinely (three quarters in a row) scoring above 95 overall (100 is perfect). “World-class” ESD control programs maintain a score of 95 or above. Since 2000, GDAIS has steadily improved the overall external full audit scores from 92 to more than 98. Documented, external audit scores from June 2004 to 2006 rose substantially (Table 3). This improvement has been a direct result of the training and auditing system in place.

Other issues. Similar training focus and improvement has been provided on a number of ESD discipline issues as detected during auditing, including operator discipline for connecting ESD carts to ground when using them as an extension of their work surface; placing ESD cloth shielding covers over open product at a workstation before leaving the area; covering product completely with blue cloth shielding covers employed to shield large boards and systems during transportation; and correctly pointing the ionizers. Some previous discipline issues have virtually been eliminated, such as completely closing static shielding bags and lids on conductive totes during transportation. Those two packaging issues have been thoroughly covered in the training courses and audit feedback loop over the years. Consequently, no audit violation of either requirement has been observed in the past six years.

GDAIS encourages team-based continuous improvement whereby processes are measured and nonconformances evaluated for root cause. The program now in place benefits from “closed-loop,” feedback-driven auditing and training functions designed to incorporate the operating personnel in the discipline improvement process. The system has led to documented progress and improved discipline to the ESD policies at the facility.
 

References

1. G. T. Dangelmayer and Terry L. Welsher, “Class 0 ESD Trends: Implications for Back and Front End Processes,” A2C2 Magazine, May 2005.
2. International Sematech, “International Technology Roadmap for Semiconductors,” 2003.
3. R. J. Peirce, “The Most Common Causes of ESD Damage,” Evaluation Engineering Magazine, November 2002. 

Jim Colnar is a principal engineer and ESD program coordinator at General Dynamics Advanced Information Systems (generaldynamics.com). Roger J. Peirce is director of technical services at Simco (simcoion.biz); rpeirce@esimco.com.

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