Prediction of electrostatic discharge soft failure issue in case of a six layer PCB of a tablet using SIwave tool

Abstract

ESD (Electrostatic Discharge) is a natural phenomenon which occurs when a charged carrier comes in contact with a conductive material and discharges upon it. ESD has measurable impact on electronic devices. Due to size reduction of the electronic components, the component and thus the system, both becomes more susceptible to ESD effect. To protect the system from ESD failure the I/O terminals are provided with ESD protection, but in some cases the ESD current can enter through the shield of external port e.g. USB OR HDMI shield. In such particular cases the majority of the current directly reaches to the PCB ground thus providing the ESD protection circuitry at the I/O terminal may not help at all. In such cases the ESD can affect the proper functioning of an IC and may result into issues such as system reboot, display freeze, system hang all together called as soft failure and in worst cases it may cause permanent damage to the system called as hard failure. Hard failure of a system is easy to detect because due to permanent damage the failure location is easy to track, but in case of soft failure, it is difficult to determine the exact ESD sensitive location as the system regains its proper functioning after restart. This paper focuses on ESD soft failure issues which has occurred in the case of a particular tablet. The focus of this paper is to coin a new way to debug the ESD soft failure using mechanical model file, board file and using 2.5D EM tool to perform the near field simulation. The paper gives an idea about the possibility that the board level EM simulation of a system as complex as tablet is possible and using the simulation results we can predict the susceptible areas.