Surface Ground Plane ESD Floors The Best Way to Protect ESD-Sensitive Components

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ESD Control is More Difficult Today than Ever Before

The development of smaller, faster and more powerful electronics, which are more sensitive to static damage, has led to an extreme demand on quality and production engineers to limit ESD events in their facility. Many of these damaging events occur as a result of the energy created during the movement of people, carts, chairs and vehicles. The best way to safely and efficiently ground mobile items and persons in the workplace remains the floor.

Over the last decade, flooring manufactures have been flooded with requests to comply with the ever advancing electronics industry and the requirements created by sensitive components for lower triboelectric effect. Tribocharging is the energy generated as a result of contact and separation and is ultimately discharged from transport equipment and people in motion. As the need for the lowest possible voltage generation continues, it has become very clear that maximizing access and contact to the conductive materials in the floor surface, while at the same time minimizing contact with insulated material or non-conductors, is the key to consistently low energy generation and discharge risk. Establishing a high-contact monolithic floor surface with a fully conductive pigment, that is directly connected to a confirmed earth ground, is key in maximizing generation related-performance. This is also known as creating a SURFACE GROUND PLANE.

Definition and History of the Ground Plane of an ESD Floor

To better understand the role of the ground plane in creating a static control floor, it is helpful to both define a grounding plane and review the history of conductive floor coating design. The ground plane is simply the layer of a floor system that is actually carrying a charge to ground. This layer could be an adhesive base coat, a grid of copper shielding tape or a conductive polymer coating.

The formal history books are weak when it comes to recording the timing and evolution of industrial polymer floor systems, but it is documented that the polymer systems used for the original floor coating designs were invented by Swiss chemists in the 1800’s. Most credit Ciba Grigy with creating the modern

Surface Ground Plane ESD Floors The Best Way to Protect ESD-Sensitive Components

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polymer resins that are used today in the 1940’s. By all accounts, these crudely conductive floor coatings first appeared in 1955. Ironically, the earliest conducting floors utilized a SURFACE GROUND PLANE by filling thermoset epoxy with carbon and graphite aggregates. It was applied as a thick black finish or final coating and grounded directly. By description, the surface could be “sparked” or hit with a charge and shown to conduct electricity. These floors were effectively used for decades in severe flammable, chemical and explosive production and handling operations. Although these coatings were soft and tracked black everywhere when exposed to traffic, they were surprisingly efficient and very functional even by today’s ESD standards. Adding to their electrical functionality was the fact that much of the footwear of the day was leather which harbored moisture and served to connect the wearer to the floor surface and generated far less charge upon contact and separation as compared to man-made materials.

ESD Polymer Flooring Evolution

Surface Ground Plane ESD Floors The Best Way to Protect ESD-Sensitive Components

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ESD Flooring - Two Steps Forward and One Step Back

In addition to the first conductive overshoes being patented in the 1960’s, conductive coatings also saw a significant improvement in physical performance during the same decade. This was accomplished by covering or topping the soft conductive layer with a polymer system that utilized conductive fiber mixed with much lower quantities of carbon or graphite fillers. This step mimicked the design of hard surface ESD flooring, such as tile, that placed preformed floor pieces made with conductive fiber into carbon-filled adhesives acting as a ground plane. This same pre-manufactured floor design is still utilized today, more than 50 years later. This transformation introduced the first laminated or encapsulated ground plane. Although more durable, the distancing from the conductive layer and reduction in contact points lowered electrical efficiency. It would be several years before awareness of this reduction would become evident. At the time this was introduced, it was considered to be a major advancement in the development of electrostatic control in the manufacturing arenas of both electronic protection and flammable ignition protection. This practice of burying the ground plane is still utilized today in the design of many floor systems created to control static. These types of ESD-control floor systems can be referred to as Facilitated Pathway ESD Flooring Systems. Here, the static charge must contact a conductive point, or points, on the surface and be transferred through the surface to the underlying ground plane where it is then carried away to ground.

In the 1980’s, a separation of ESD functionality was created and the market offered ESD floors for both ignition risk and electrical component protection. The advancement of electronics created a large demand for static control to protect components during assembly and the industry was becoming much

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more aware of the quality and performance risks associated with uncontrolled static discharge. The variation between market systems was both resin choice and filler. The anti-ignition market continued to utilize the original design and occasionally added shells such as walnut or pecan to address the mechanical spark risk. These natural fillers unfortunately carried with them a myriad of performance issues ranging from moisture absorption to biodegradation. The ignition risk mitigating systems utilized resins and designs that targeted solvent and chemical resistance rather than appearance. The newly evolving electronic component protection floor systems were able to modify their design due to the newly introduced addition of conductive fiber. ESD flooring gained a much wider range of resin choices, colors and looks that better served the market demand. This laminate design allowed elevated physical durability and improved appearance. Even though the electrical properties were diminished, they primarily fit the performance requirements of the era or at least the perception of them. Ironically, at the same time there was some overall ESD coating market erosion due the often erratic conductivity of these new systems related to installation challenges which led to performance problems. The use of pre-manufactured ESD floor materials not traditionally used in manufacturing, such as linoleum and vinyl tile, were used as an alternative despite higher maintenance cost and lower physical properties, but at least had electrical predictability. Of course, these systems were also utilizing a buried ground plane in the form of conductive adhesives.

The Rise of the Ground Plane

The late 1980’s and early 1990’s saw significant ESD polymer change. Many people credit Garland Floor Company of Ohio with developing the first particulate or conductive pigment flooring. This floor style not only afforded a more precise electrical performance based on the amount of conductor now present in the film, it moved the functional ground plane back to the surface for the first time in decades. The size and design of the conductive pigments allowed for the retention of many of the appearance benefits and all of the physical properties of the buried plane designs. Although very successful, only a limited number of manufactures were able to consistently produce this style of ESD coating. There was also a limitation of conductivity to resistance ranges between 1 million and 1 billion ohms. This resistance range had started to be referred to as static dissipative. Surface resistivity ranges that were termed “conductive” and below 1 million ohms still required the use of an embedded ground plane. However, even when used over a buried plane the benefits associated with the use of increased surface conductors were recognized. These benefits were associated with improved connection. Footwear, straps, chains and casters all displayed better performance due to the increase of available conductors to make contact with. Slowly, polymer coatings began to return to the forefront as the best overall performance solution for industrial static control because this new floor style utilized a SURFACE GROUND PLANE which was easily proven more effective. Here, entire topcoating acts as its own ground plane. A static charge immediately flows to the electrical ground without contacting individual points and travelling through conductive materials or facilitators.

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The 1990’s was also the decade that arguably produced the most dramatic improvements in the development of Electrostatic Protected Areas (EPAs). The idea of measuring and controlling the voltage generated during the contact and separation associated with personnel and equipment movement was introduced. Steve Halperin and Prostat Corporation of Illinois were the first to develop chart recorders and equipment specifically designed to test for these measurements and they remain the industry leader in this field. This technology and awareness would take more than 10 years to become part of modern standards and requirements. Today, this phenomenon referred to as Body Voltage Generation (BVG) is recognized as the true measurement of the static probability performance.

A Non ESD floor Actually Generates Static

In order to understand the value of a SURFACE GROUND PLANE, it is necessary to understand how standard industrial polymer or tile floors actually generate static. Static is generated as materials come together and then separate. There is some debate between the theory that atoms sluff or transfer to build up a potential based on their charge and position on the dielectric series and the newer theory that atoms cluster or peak creating static energy. There is no debate that vinyl, plastic and other polymers used in flooring are very likely to build a significant amount of energy when they contact and separate from other materials, even conductive materials. Almost inarguably, polymer coatings are the most cost effective, durable and aesthetic surface for heavy industrial use. However, polymer coatings can generate static at a very high level, often as high as 30,000 volts in the right tribocharging conditions. This makes mobile equipment, personnel, and movable furniture making contact with the polymer surface obvious sources for elevated static discharge risk. Because the surface of the floor bears the majority of all traffic in most production facilities, using any polymer to create a floor in a facility with static discharge risk, whether tile or coating, would be counterintuitive. And yet, most ESD flooring

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is a created with polymers as a binder and still have a well-documented conductivity and static control performance – or do they?

ESD Floors with a Split Personality / If the Shoe Fits

If it appears the ESD floor coating is both the problem (polymer) and the solution (conductive material), why does testing show that many of them have an acceptable surface resistance level? The best answer is because most of the testing equipment used (megohmeters) efficiently focus on the conductive portion of the floor. Measuring surface resistance using these meters highlights the effectiveness of the portion of the floor this is made of conductive materials. When a laminate or below SURFACE GROUND PLANE is used, the meter will use the conductive materials and their associated connection to the ground plane to transfer a charge to the ground plane. Not tested when measuring simple surface resistance in this manner is the portion or percentage of the floor surface that is insulated polymer. The insulated portion of the surface will still tribocharge or generate voltage upon contact and separation even though it is in proximity to conductive discharge points. The fewer points, the greater the voltage generation will be. To measure this generation, more sophisticated testing is needed. Field meters and charge plate monitors will capture and measure this voltage so it can be recorded. Therefore the level of voltage generated will directly reflect both the percentage of the floor surface that is insulated. The

Surface Ground Plane ESD Floors The Best Way to Protect ESD-Sensitive Components

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result is the higher the percentage of insulators making contact at the surface, the higher the risk of discharge related damage will be. It must be recognized that understanding the performance of an ESD floor starts with recognizing the actual requirements of the components the floor is protecting. The acceptable voltage generation number can vary greatly, but has been sharply trending lower over the last few years as higher performance and higher speed microelectronics continue to evolve. It is clear that lower voltage generation is the present and the future.

Take Me to the Top Floor

In understanding this relationship between conductive and insulated materials in the surface and voltage generation, a conclusion is drawn regarding the location of the ground plane location. Regardless of location, the ground plane must possess a maximum conductive content to function effectively. In the early versions, this was carbon and graphite and this is often still the case today when a ground plane is buried or fully encapsulated. Many manufactures still design ESD flooring using carbon ground planes and lower percentages of conductive fillers and fibers. This is a low cost, simple method for establishing conductivity. Unfortunately, encapsulating a ground plane with coatings only designed to assist in making a connection to the ground plane greatly increase the amount of that surface that will be made up of insulated materials. More body voltage will be generated.

Surface Ground Plane ESD Floors The Best Way to Protect ESD-Sensitive Components

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SURFACE GROUND PLANE designs are capable of functioning as both a ground plane and surface wear course and contain a maximum percentage of conductive pigment. When combined with footwear that utilizes maximum conductor contact such as ESD shoes, full overshoes and sole straps, a minimum amount of voltage will be produced and the highest performance electrostatic protected area will be created.

Helpful Links for Your Next ESD Flooring Project:

PIP Blog:

ESD FLOORING BLOG

SingleSource Program Overview:

PIP’s Industrial Flooring Self-Assessment Tool: Our Industrial Flooring Self-Assessment Will Change The Way You Think About Flooring Needs

Surface Ground Plane ESD Floors The Best Way to Protect ESD-Sensitive Components

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Patrick Scudder

President Protective Industrial Polymers

Patrick Scudder is the President of Protective Industrial Polymers, a company that manufactures high-performance resinous floor coatings for industrial manufacturing environments. It has a keen focus on developing unique solutions for managing electrostatic, microbial, chemical, explosion and safety risk concerns. He has been in the protective coatings industry for over 25 years and is a leading advisor for manufacturers with unique environmental challenges. Patrick is a SH&A Level I Certified ESD Plant Auditor. You can follow Pat on LinkedIn, or contact Protective Industrial Polymers at 866-361-3331.

PIP’s certified ESD Plant Auditors obtain a thorough understanding of the fundamentals of ESD. Additionally, our

auditing team members have been trained on how to properly perform ESD Control Measurements as required by

ANSI/ESD S20.20 and IEC 61340-5-1 ESD Program standards including:

Work Surfaces - Floors - Chairs - Mobile Equipment - Garments - Personnel Grounding (footwear, wrist straps etc…) - Ionizers - - Hand Tools - ESD Ground Verification - Packaging