Processes taking place in the polymer free volume are very important in the initiation phase of electrical trees under ac stress. Electrons injected from the electrode are accelerated in the free volume (between 10 and 100 nm) and bombard the free volume wall to produce free radicals and break polymer chains. The type of gas in the free volume has a large effect on ac tree initiation. Under O2‐rich conditions, free radicals react with O2 and autoxidation begins. Autoxidation, a chain reaction with low activation energy, creates a large cavity in a short time, where discharge can occur. He or Ar atoms in the free volume are excited to metastable level by electron impact. Metastable atoms collide with the free volume wall and break polymer bonds with high efficiency, creating a cavity in a short time. © 1998 Scripta Technica, Electr Eng Jpn, 124(2): 8–15, 1998

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In order to evaluate the robustness of automotive ECU's against electrostatic discharge, a conventional method where electrostatic discharge pulses are applied to connector parts on a printed circuit board is commonly used. However, until now quantitative redesigning principles to improve the static electricity tolerance that fully utilize the test data shown below have not been made clear because the propagation mechanism of static electricity on a circuit board was not clear. This paper describes the ESD current measurement technique which detects the near magnetic field generated by ESD currents. We developed a technique to measure the ESD currents using a new loop antenna on the circuit board. The ESD current, was generated with the static electricity applied to a model circuit pattern in conformity with IEC and ISO standards and measured using the antenna. It was also possible to visualize how static electricity energy would propagate through the circuit board. We concluded that ESD current measurement via the near magnetic field and using a small shielded loop antenna was effective