In the blog post titled "Introduction to ESD", which you can read here. It discussed the basics of electrostatic charge and discharge, the mechanisms of creating demand, materials, types of ESD damage, ESD events, and ESD sensitivity. It concluded with the following summary:
- Virtually all materials, including conductors, can be triboelectrically charged.
- The amount of charge is affected by material type, speed of contact and separation, humidity, and several other factors.
- Charged objects have electrostatic fields.
- Electrostatic discharge can damage devices, so a parameter fails immediately, or ESD damage may be a latent defect that may escape immediate detection, but may cause the device to fail prematurely.
- Electrostatic discharge can occur throughout the manufacturing, test, shipping, handling, operational processes, and field service operations.
- ESD damage can occur due to discharge to the device, from the device, or from induction to the item resulting from electrostatic fields. Tools vary significantly in their sensitivity or susceptibility to ESD.
Protecting products from the effects of ESD damage begins by understanding these fundamental concepts of electrostatic charges and discharges. An effective ESD control program requires an effective training program where all personnel involved understand the key concepts. Armed with this information, you can then begin to develop an effective ESD control program. In Part Two, we will focus on some essential ESD control and ESD control program development principles.
BASIC PRINCIPLES OF STATIC CONTROL
Controlling electrostatic discharge (ESD) in the electronics manufacturing environment is a formidable challenge. However, the task of designing and implementing ESD control programs becomes less complicated if we focus on just six basic principles of static control. In doing so, we also need to keep in mind the ESD corollary to Murphy’s law, “no matter what we do, the static charge will try to find a way to discharge.”
Design In Protection
The first principle is to design products and assemblies to be as resistant as reasonable from ESD effects. This involves such steps as using less static sensitive devices or providing appropriate input protection on tools, boards, assemblies, and equipment. For engineers and designers, the paradox is that advancing product technology requires smaller and more complex geometries that often are more susceptible to ESD. The Industry Council on ESD Target Levels and the ESD Association’s “Electrostatic Discharge (ESD) Technology Roadmap,” revised April 2010, suggest that designers will have less ability to provide the protection levels available the past. Consequently, the ESD target levels are reduced to 1000 volts for Human Body Model robustness and 250 volts for Charged-Device Model robustness, with the tendency to reduce these values further. Those target values are considered realistic and safe levels for manufacturing and handling today’s products using basic ESD control methods described in international industry standards, e.g., ANSI/ESD S20.20 or IEC 61340-5-1. When devices with lower ESD target levels must be used and handled, application-specific controls beyond the principles described here may be required. Users should refer to the most recent update by the Industry Council.
Define the Level of Control Needed in Your Environment.
What is the most sensitive or ESD susceptible (ESDS) item you are using, and what is the withstand voltage classification of the products you are manufacturing and shipping? To get an idea of what is required, it is best to know the Human-Body Model (HBM) and Charged-Device Model (CDM) sensitivity levels for all devices that will be handled in your facility. ANSI/ESD S20.20 and IEC 61350-5-1 define control program requirements for items that are sensitive to 100 volts HBM and 200 volts CDM. Both standards allow the criteria to be tailored as appropriate for specific situations with proper documentation and objective evidence.
Identify and Define the Electrostatic Protected Areas (EPA).
Per Glossary ESD ADV1.0, an ESD protected area is “A defined location with the necessary materials, tools, and equipment capable of controlling static electricity to a level that minimizes damage to ESD susceptible items.” These are the areas in which you will be handling ESDS items and the places you will need to implement the necessary ESD control procedures, including bonding or electrically connecting all conductive and dissipative materials, including personnel a known common ground.
Reduce the Electrostatic Charge Generation
If ESD sensitivity projections are correct, ESD protection measures in product design will be increasingly less effective in minimizing ESD losses. The fourth principle of control is to reduce electrostatic charge generation and accumulation in the first place. It’s fairly basic: no charge – no discharge. We begin by eliminating as many fixed costs generating processes or materials, specifically high-charging insulators such as common plastics, as possible from the EPA work environment. We keep conductive/dissipative materials at the same electrostatic potential using equipotential bonding or attaching to equipment ground. The electrostatic discharge does not occur between materials held at the same potential. In the EPA, ESD control items such as worksurface mats, flooring, smocks, etc. are to be attached to the ground to reduce charge generation and accumulation and should be used in place of more common factory products. Personnel is grounded via wrist straps or a flooring/footwear system. While the basic principle of “controlling static electricity to a level that minimizes damage” should be followed, complete removal of charge generation is not achievable.
Dissipate and Neutralize
Because we simply can’t eliminate all generation of electrostatic charge in the EPA, our fifth principle is to dissipate or neutralize those electrostatic charges that do occur safely. Proper grounding and the use of conductive or dissipative materials play significant roles. For example, personnel starting work may have an account on their body; they can have that charge removed by attachment to a wrist strap or when they step on ESD flooring while wearing ESD control footwear. The charge goes to the ground rather than being discharged into a sensitive part. The discharge current’s magnitude can be controlled with static dissipative materials to prevent damaging a charged device.
For some objects, such as common plastics and other insulators, being non-conductors, grounding cannot remove an electrostatic charge because there is no pathway conductive enough to reduce the charge in a reasonable time. If the object cannot be eliminated from the EPA, ionization can neutralize these insulators’ charges. The ionization process generates negative and positive ions. The like-charged ions are repelled from a charged object while the oppositely charged ions are attracted to a charged object’s surface, therefore neutralizing it (see Figure 1). A balanced Ionizer, with limits outlined in Table 3 of ANSI/ESD S20.20, will effectively produce both negative and positive ions, which will result in a net charge of zero.
Protect Products
Our final ESD control principle is to prevent discharges that do occur from reaching a sensitive object’s surface and assemblies. There are various ESD control packaging and material handling products to use both inside and outside the EPA. One way is to protect ESDS items with proper grounding or shunting that will “dissipate” any discharge away from the product. A second method is to package, store, or transport ESDS items in packaging that is low charging and conductive/dissipative so it can dissipate charges when grounded. In addition to these properties, packaging used to move ESDS items outside the EPA should have the control property of “discharge shielding.” These materials should effectively shield the product from charges and discharges and reduce the generation of demand caused by any product movement within the container.
ELEMENTS OF AN EFFECTIVE ESD CONTROL PROGRAM
While these six principles may seem somewhat necessary, they can guide us in selecting appropriate materials and procedures to use in effectively controlling ESD. In most circumstances, effective programs will involve all of these principles. No single method or product will do the whole job; somewhat effective static control requires a full ESD control program.
How do we develop and maintain a program that puts these basic principles into practice? How do we start? What is the process? What do we do first? Ask a dozen experts, and you may get a dozen different answers. If you dig a little deeper, you will find that most of the solutions center on similar vital elements. You will also find that starting and maintaining an ESD control program is similar to many other business activities and projects. Although each company is unique in terms of its ESD control needs, there are at least 6 critical elements to successfully developing, implementing, and maintaining an effective ESD control program (see Figure 2).
Establish an ESD Coordinator and ESD Teams
A team approach particularly applies to ESD because of the problems, and the solutions cross various functions, departments, divisions, and suppliers in most companies. ESD team composition includes line employees as well as department heads or other management personnel. The ESD team may also cut across functions such as incoming inspection, quality, training, automation, packaging, and test. ESD teams or committees help assure various viewpoints, the availability of the needed expertise, and commitment to success. An active ESD team helps unify the ongoing effort.
Heading this ESD team effort is an ESD program coordinator (“ESD coordinator”). Ideally, this responsibility should be a full-time job. However, we seldom operate in an ideal environment, and you may have to settle for the function to be a significant responsibility of an individual. The ESD coordinator is responsible for developing, budgeting, and administering the program. The ESD coordinator also serves as the company’s internal ESD consultant to all ESD control program areas.
Assess Your Organization, Facility, Processes, and Losses
Your next step is to gain a thorough understanding of your environment and its impact on ESD. Armed with your product quality loss and ESD sensitivity data, you can evaluate your facility, looking for areas and procedures that may cause ESD problems. Be on the lookout for static generating materials, personnel handling procedures for ESDS items, and contacts of ESDS items to conductors.
Document your processes or work instructions. Observe the movement of people and materials through the areas. Note those areas that would appear to have the most significant potential for ESD problems. Remember that ESD can occur in the warehouse just as it can in the assembly areas. Then conduct a thorough facility survey or audit. Try to measure personnel, equipment, and materials to identify acceptable resistance ranges and the presence of electrostatic fields in your environment.
Before seeking solutions to your problems, you will need to determine the extent of your product quality losses to ESD. These losses may be reflected in receiving reports, Quality Assurance and Quality Control records, customer returns, in-plant yields, failure analysis reports, and other data that you may already have or need to gather. This information identifies the magnitude of the problem and helps pinpoint and prioritize areas that need attention. Where available, the potential for future issues resulting from technology roadmaps and internal product evolution should be considered. Document your actual and potential ESD losses regarding defective components, rework, customer returns, and failures during the final test and inspection. Use data from outside sources or the results of your pilot program for additional support. Develop estimates of the savings to be realized from implementing an ESD control program.
You will also want to identify those items (components, assemblies, and finished products) that are the most sensitive to ESD, noting the classification or withstand voltage. Note that two functionally identical items from two different suppliers may not have similar ESD ratings.
Establish and Document Your ESD Control Program Plan
After completing your assessment, you can begin to develop and document your ESD control program plan. The plan should cover the program’s scope and include the tasks, activities, and procedures necessary to protect the ESDS items at or above the ESD sensitivity level chosen for the plan. Prepare and distribute written designs and specifications so that all departments have a clear understanding of what is to be done. Fully documented procedures will help you meet the administrative and technical elements of ANSI/ESD S20.20 or IEC 61340-5-1 and help you with ISO 9000 certification as well.
Build Justification to Get the Top Management Support
To be successful, an ESD program requires your top management’s support, at the highest level possible. What level of commitment is needed? To obtain commitment, you will need to build justification for the plan. You will need to emphasize quality and reliability, the costs of ESD damage, and ESD’s impact on customer service and product performance. It may be useful to conduct a pilot program if other companies’ experience is not sufficient, and you expect that you can show meaningful results in the pilot.
Prepare a short corporate policy statement on ESD control. Have top management co-sign it with the ESD coordinator. Periodically reaffirm the policy statement and management’s commitment to it. Published articles such as The “Real” Cost of ESD Damage by Terry Welsher should be provided to top management.
Develop and Implement a Training Plan
Train and retrain your personnel in ESD control and your company’s ESD control program and procedures. Training should include testing or other methods to verify comprehension. Proper training for line personnel is especially important. They are often the ones who have to live with the procedures on a day-to-day basis. A sustained commitment and mindset among all employees that ESD prevention is a valuable, ongoing effort by everyone are one of the primary training goals. Please be aware that it might be necessary to tailor the ESD training to the trainees’ education.
ANSI/ESD S20.20 requires a written training plan; however, your company has the flexibility to determine how best to design the project.
Develop and Implement a Compliance Verification Plan
Developing and implementing the program itself is evident. What might not be so obvious is the need to continually review, audit, analyze, obtain feedback, and improve. Auditing is essential to ensure that the ESD control program is successful. You will be asked to continually identify the return on investment of the program and justify the savings realized. Technological changes will dictate improvements and modifications. Feedback to employees and top management is essential. Management commitment will need reinforcement.
Include both reporting and feedback to management, the ESD team, and other employees as part of your plan. Management will want to know that their investment in time and money yields a return in quality, reliability, and profits. ESD team members need a pat on the back for a job well done. Other employees will want to know that the procedures you have asked them to follow are right, worthwhile. It helps integrate the process improvement process into the overall quality system and use the existing quality tools such as root cause analysis and corrective action reports. As you find areas that need work, be sure to make the necessary adjustments to keep the program on track.
Conduct periodic evaluations of your program and audits of your facility. You will find out if your plan is booming and is giving you the expected return. You will spot weaknesses in the program and shore them up. You will discover whether the procedures are being followed.
ANSI/ESD S20.20 and IEC 61340-5-1 require a written compliance verification plan. However, your company has the flexibility to determine how best to design the project. Test procedures are described in ESD TR53, which is available as a complimentary download from www.ESDA.org. The objective is to identify if significant changes in ESD equipment and materials performance have occurred over time. Each user will need to develop their own set of test frequencies based on the critical nature of those ESDS items handled and the risk of failure for the ESD protective equipment and materials.
Finally,
The six basic principles of static control are:
- Design in protection
- Define the level of control needed in your environment
- Identify and define the electrostatic protected areas (EPA)
- Reduce electrostatic charge generation
- Dissipate and neutralize
- Protect products
Six critical elements to ESD control program development and implementation are:
- Establish an ESD Coordinator and ESD teams
- Assess your organization, facility, processes, and losses
- Establish and document your ESD control program plan
- Build justification to get the top management support
- Develop and implement a training plan
- Develop and implement a compliance verification plan
As always, you can find our huge range of ESD products and materials to help your ESD program here.