PROTECTION AGAINST UNCONTROLLED ELECTRIC DISCHARGE (ESD)

Electrostatic discharge (ESD) is a transfer of electric charge between bodies of different electric potential in proximity or through direct contact.

ESD can damage electronic components and cause failures and disturbances in electronic devices.

Packaging requirements of ESD-sensitive devices depend on the durability of the device. The requirements are provided in the standards IEC 61340-5-3 and ANSI/ESD S541. Generally, transportation of sensitive products outside of an ESD Protected Area (EPA) shall require packaging that provides both dissipative or conductive materials for intimate contact and a structure that provides electrostatic discharge shielding.

According to IEC 61340-5-1:2016, an organization shall qualify all ESD control items selected for use as part of the ESD control program. You may use data sheets if the test methods and conditions are referred to and if the limits comply with the limits set for the item. You can use independent laboratory services or perform your own laboratory tests in controlled conditions and following the standard test methods.

Your personnel should be grounded or equipotentially bonded when handling electrostatically sensitive devices. When personnel are seated at ESD protective workstations, they can be connected to the ground via a wrist strap system. For standing operations, personnel can be grounded via a wrist strap system or by a footwear-flooring system.

Depending on the ESD control program, optional ESD control items such as garments and hand tools may also be required.

If you are looking for static dissipative material, the question arises of why you have defined the limits so tightly. When the lower limit has been set too high, this might cause additional costs or overkill. For example, CDM risk does not require such a high resistance level.

If you want to study this subject in more detail, please check our technical paper “Electrostatic discharge characteristics of conductive polymers” ESD Association Symposium 2017 from IEEE’s Xplore digital library.

Practical tips and pitfalls related to resistance and resistivity measurements can also be found in our blog article “Practical insights into resistivity measurements.”

This depends on what kind of resistivity range and properties you are looking for. Transparent or translucent dissipative plastics are normally based on either migrating, non-permanent antistatic additives or permanent dissipative polymers. The important question is whether you are looking for permanent or non-permanent properties.

The permanent static dissipative plastics are compounds that are a mixture of inherently dissipative polymers (IDP) and carrier polymers. The transparency of the compounds depends on, not only the base polymer but also the IDP type. Typically, PET-based materials are the most transparent alternatives to IDP compounds. Typically with IDP compounds, the lowest surface resistance values are around E8.

Materials with antistatic treatments (e.g. coating, spray, “antistatic batch”) or additives are typically more transparent. It must be remembered, however, that these materials do not fulfill the ESD standard’s definition for static dissipative materials.

Carbon black based conductive compounds do not fulfill FDA, since their carbon black content exceeds the maximum limit of 2.5%.

Highly conductive compounds are typically based on metallic conductive fillers. Some of them carry also food approval status, but that has to be checked case by case.

Electric conductivity 0.1 S/m equals the resistivity of 10 Ω·m (1000 Ω·cm) that can be achieved with electrically conductive carbon black compounds. Whether this kind of material can be used as a conductor or not depends on the requirements of an application.

Generally, metallic conductivity cannot be replaced with conductive plastics. However, in certain applications, for example, in sensor technology, higher resistance may be useful as low-current applications. Higher-current applications may suffer from high power consumption and undesired heating.

There are no general guidelines for EMI-shielding materials. Frequency and attenuation requirements depend on the application. Some carbon black compounds with lower resistance might provide adequate shielding. The material’s electrical properties, as well as the product construction, have an effect on the product performance. A thicker layer provides better shielding.

When carbon black is compounded to the polymer matrix, it has a significant impact on the polymer’s mechanical properties; both hardness and flexural modulus will be increased, whereas elongation and tensile strength will decrease. Special modifying agents will therefore be used in electrically conductive compounds in order to maintain the mechanical properties of the base polymer also after carbon black addition. The level of modification depends on the application and the requirements set for the end product.

One has to also keep in mind that the surface resistance of the end product is highly dependent on the processing parameters used in extrusion or injection molding. The carbon black network is very sensitive to shear forces; high shear will lead to the degrading of the carbon black network and higher resistance levels.

Carbon black based conductive plastics cannot be colored. They are always black. Carbon fiber based compounds can be colored in darker shades. The brightest colors can be reached by using static dissipative plastics. They are naturally creamy and can be colored in different colors. One has to remember anyhow that typically the lowest surface resistance values reached with dissipative polymers are around E8.

Resistance and resistivity describe the material’s or the object’s ability to impede the flow of current passing through it.

Resistivity relates to the material’s electric properties. It is a characteristic of the material and is not dependent on the dimensions of the measured material sample. The SI-unit for volume resistivity is [Ω·m] or [Ω·cm] and for surface resistivity [Ω].

Resistance (R) describes an object’s ability to resist electrical current in a measurement circuit. Resistance is dependent on the dimensions of the object and measurement electrode. The SI-unit for resistance is [Ω] which describes the ratio of voltage across the object to the current through the object (R=U/I=[V/A]).