Static dissipative material
Many times static electricity is inevitable, so it is more important to safely eliminate static electricity. Many antistatic materials also have a static dissipative function when grounded or in contact with large planar conductors such as floors. Static dissipative materials have similar volumetric resistance or are covered with a conductive material, such as a table mat for a workbench. The dissipative material can limit the current of the discharge when it contacts the charged device.
According to the definition of EIA and ESDA, static dissipative materials are materials with surface resistivity of 105 ~ 1012 Ω / sq. Studies by Bossard et al. have shown that a 105Ω/sq lower limit resistor is appropriate for the protection of ESD energy sensitive devices, which can fail due to hot melt.
In addition to surface resistivity, another important property of static dissipative materials is their ability to vent static charge from objects, and the technical specification describing this characteristic is the rate of electrostatic decay. According to the isolated conductor electrostatic attenuation model, the static decay period is exponentially related to the resistance and capacitance product (RC) of the bleeder circuit:
V(t) = V0e-t/t
Where V(t) is the decayed electrostatic voltage, V0 is the pre-amplification electrostatic voltage, t is time, and t=RC is the time constant.
To study electrostatic discharge capability, the typical assumption is to attenuate the electrostatic voltage to a specific percentage, such as 1%, within a certain time, such as within 2 seconds. In addition, relative humidity is also an important factor for static dissipative materials and should be controlled and recorded during electrostatic decay testing.