Part 2: Principles of ESD Control

Fundamentals of Electrostatic Discharge
Part Two – Principles of ESD Control – ESD Control Program Development
© 2013, ESD Association, Rome, NY

In Part One of this series, Introduction to ESD, we discussed the basics of electrostatic charge and discharge, the mechanisms of creating charge, materials, types of ESD damage, ESD events, and ESD sensitivity. We concluded our discussion with the following summary:

1. Virtually all materials, including conductors, can be triboelectrically charged.

2. The amount of charge is affected by material type, speed of contact and separation, humidity, and several other factors.

3. Charged objects have electrostatic fields.

4. Electrostatic discharge can damage devices so a parameter fails immediately, or ESD damage may be a latent defect that may escape mediate detection, but may cause the device to fail prematurely.

5. Electrostatic discharge can occur throughout the manufacturing, test, shipping, handling, or operational processes, and during field service operations.

6. ESD damage can occur as the result of a discharge to the device, from the device, or from charge transfers resulting from electrostatic fields. Devices vary significantly in their sensitivity or susceptibility to ESD.

Protecting products from the effects of ESD damage begins by understanding these key 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 basic principles of ESD control and ESD control program development.
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 complex 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, static charge will try to find a way to discharge.”

1. Design In Protection

The first principle is to design products and assemblies to be as resistant as reasonable from the effects of ESD. This involves such steps as using less static sensitive devices or providing appropriate input protection on devices, 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 that were available in the past. Consequently, the ESD target levels are reduced to 1000 volts for Human Body Model robustness and 250 volts for robustness against the Charged Device Model, with tendency to reduce these values further. Those target values are considered to be realistic and safe levels for manufacturing and handling of today’s products using basic ESD control methods as described in international industry standards as 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.

2. Define the Level of Control Needed in Your Environment.

What is the most sensitive or ESD susceptible ESDS you are using and what is the classification of withstand voltage of the products that you are manufacturing and shipping? In order 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 the manufacturing environment. ANSI/ESD S20.20 and IEC 61350-5-1, both published in 2007,  define control program requirements for items that are sensitive to 100 volts HBM; future version of those standards will most likely address also items that are sensitive to 200 volts CDM.  With documentation, both standards allows requirements to be tailored as appropriate for specific situations.

3.  Identify and Ddefine 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 ESD sensitive items and the areas in which you will need to implement the basic ESD control procedures including bonding or electrically connecting all conductive and dissipative materials, including personnel, to a known common ground.

4.  Reduce Electrostatic Charge Generation

If projections of ESD sensitivity 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 static charge 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. Electrostatic discharge does not occur between materials kept at the same potential. In the EPA, ESD control items should be used in place of more common factory products such as worksurface mats, flooring, smocks, etc. which are to be attached to ground to reduce charge generation and accumulation. Personnel are 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.

product within the container.

Elements of an Effective ESD Control Program

While these six principles may seem rather basic, they can guide us in the selection of appropriate materials and procedures to use in effectively controlling ESD. In most circumstances, effective programs will involve all of these principles. No single procedure or product will do the whole job; rather effective static control requires a full ESD control program.

How to 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. But, if you dig a little deeper, you will find that most of the answers center on similar key 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).

For Additional Information

• ANSI/ESD S20.20-2007 – Standard for the Development of Electrostatic Discharge Control Program, ESD Association, Rome, NY.

• Dangelmayer, Theodore, ESD Program Management: A Realistic Approach to Continuous, Measurable Improvement in Static Control, 1999, Kluwer Academic Publishers, Boston, MA

• ESD TR20.20, ESD Control Handbook, ESD Association, Rome, NY.

• ESD TR53-01-06, Compliance Verification of ESD Protective Equipment and Materials, ESD Association, Rome, NY.

• Industry Council on ESD Target Levels, White Paper I: “A Case for Lowering Component Level HBM/MM ESD Specifications and Requirements”, Revision 2.0, October 2010.

• Industry Council on ESD Target Levels, White Paper II: “A Case for Lowering Component

• Level CDM ESD Specifications and Requirements”, Revision 2.0, April 2010.

• ESDA Technology Roadmap,  March 2013

• IEC 61340-5-1, ed. 1.0, “Electrostatics – Part 5.1: Protection of electronic devices from electrostatic phenomena – General requirements”, IEC, Geneva, Switzerland, 2007-08.

• Terry Welsher, The “Real” Cost of ESD Damage, InCompliance, May 01, 2010.

Figure 1: Prinziple of neutralization of a charged object by an ionizer that generates negative and positive ions. The like charged ions are repelled from a charged object while the opposite charged ions are attracted to the surface of a charged object, neutralizing the object