Effect of static dissipative material
In many cases, the generation of static electricity is inevitable, so it is more important to safely eliminate static electricity. Many antistatic materials also have static dissipative functions when they are grounded or in contact with large flat conductors such as the floor. Static dissipative materials have similar volume resistance, or are covered with conductive materials, such as bench mats for workbenches. The dissipative material can limit the discharge current when it contacts a charged device.
According to the definition of EIA and ESDA, static dissipative materials are materials with a surface resistivity of 105 ~ 1012 Ω/sq. Research by Bossard and other scholars has shown that the lower limit resistance of 105Ω/sq is appropriate for the protection of ESD energy-sensitive devices, which may fail due to thermal fusion.
In addition to surface resistivity, another important characteristic of static dissipative materials is the ability to discharge static charges from objects, and the technical index describing this characteristic is static decay rate. According to the electrostatic attenuation model of isolated conductors, the electrostatic attenuation period is exponentially related to the product of resistance and capacitance (RC) of its discharge circuit:
V(t) = V0e-t/t
Where V(t) is the electrostatic voltage after attenuation, V0 is the electrostatic voltage before attenuation, t is time, and t=RC is the time constant.
To study the electrostatic discharge capacity, the typical assumption is that the electrostatic voltage is attenuated to a specific percentage, such as 1%, within a specific time, such as 2 seconds. In addition, relative humidity is also an important factor for static dissipative materials, which should be controlled and recorded during static decay testing.