An overview of the technical policy developed by Renault to manage ESD risks in airbags

In this paper, we present the technical policy developed at Renault in order to manage electrostatic discharges (ESD) hazards leading to airbag inadvertent deployment or airbag electronic control unit (ECU) failures. A wide set of experiments is presented in order to characterize ESD sources in an automotive environment. We show that the worst case is an induction charging mechanism, which corresponds to a "0 Ω" discharge, with an energy of 2 mJ transmitted to the pyrotechnic system. Hence, usual requirements, like human body model (HBM) discharges with a serial resistance of 150 Ω or above, do not cover our most critical cases. Alternatively, the "0 Ω" discharges described in the machine model (MM) are more representative of induction charging mechanisms. We demonstrate that, for qualification tests, the serial resistance of the ESD generator has a great influence on the energy transmitted to the squib or to the ECU. This phenomenon makes almost impossible to specify a voltage level. Therefore, we define an energy level requirement of 9 mJ for the airbag and 2 mJ for each line of the airbag ECU instead. The discharge characteristics are specified in our requirement: capacitance of 330 pF, circuit impulse resistance (measured during ESD) below 30 Ω in order to avoid the un-physical "0 Ω" criterion, and pulse duration between 1 μs and 100 μs to take electrical oscillations into account. Both the test methodology and the detailed procedure are given in the paper. At last, an ESD aging profile representative of the vehicle lifetime is proposed.