Meets Standards MIL-B-81705 B Type – 2
For Protecting Electronic Components that are Sensitive to Static Electricity
Static electricity is a very familiar phenomenon, yet not well understood, that affects all branches of industry and on a variety of environments. It is something like a ghost – impossible to see it, touch it or smell it. But, the effects of an accumulated amount of static electricity can definitely be detected. These effects include an electric shock that can be dangerous and can cause a reduction in productivity, defects in machinery, fire and explosions. Electrical charges can also cause severe damage to sensitive electronic components leading to expensive reprocessing and/or on-site repairs
Electrical charging is a result of the contact (the exchange of electrons) between two materials that come into contact with each other and are then separated. An excess amount of negative ions accumulate on one of the materials and an excess of positive ions on the other. The static charge is caused by one of two processes: either the contact between two surfaces (contact induced charge) or by being near an electrostatic field (electrostatic induction).
Whenever two materials are charged by contact, electrons are passed from the surface of one of the materials to the surface of the other material (see illustrations 1 and 2). When the two surfaces are separated from each other, one surface loses electrons and becomes positively charged while the other gains electrons and becomes negatively charged
Contact, pressure and separation are the primary causes of industrial static electricity. There is a direct correlation: the greater the amount of pressure, or the faster the contact and separation between the materials, the greater the static charge (the level of tension) that accumulates. Materials that move quickly can develop charges exceeding 25,000 V.
The object or material can also be charged if it is surrounded by an electrostatic field. Even an isolated conductor or an object that is not grounded will become charged. This creates the opportunity for the discharge of static electricity to the other conducting object that can create enough energy to ignite flammable materials or destroy sensitive electronic components.
Conductors and Insulators
The materials are divided into two basic groups: conductors and insulators. Within conductors, electrons move freely throughout the entire material. Therefore, when conductors are not grounded, the entire volume of the conducting body is charged with the same polarity. Charged conductors can be neutralized by grounding.
A charged insulator can remained charged for hours.
A conductor can be simultaneously charged with opposite polarities.
The charge does not move within insulators.
Grounding of insulators does not remove or prevent surface level charges.
A charge with one polarity cannot remain for an extended period of time in a conductor since it is isolated from the ground.
Insulators and conductors have different surface level charges and different grounding abilities. An insulator reacts very differently to static electricity and its charge cannot be neutralized by simple grounding techniques (see illustration 3). The flow of electrons inside an insulator is very limited, and as a result, an insulator can maintain a number of static charges with varying polarities and different levels of potential at various points along its surface level. For this reason, certain areas of a material can stick together while others are likely to repel each other. Contrary to conducting materials, connecting an insulator to the ground does not cause an exchange of electrons. Therefore, other means are required in order to neutralize static electricity. The diagram of the triboelectric series (see illustration 4) illustrates the relative positive or negative charge of each of the different materials.
Diagram of the triboelectric series illustrating the relative positive or negative charge of each of the different materials