ESD (Electrostaic Discharge) Soft Failure Risk Assessment For a Thin Display Metal Back Cover

摘要

Most of the connected electronic devices such as smart phone, tablet and laptop has LCD (liquid crystal display) with metal back plate as a part of system stack up. The metal back plate of the display helps in grounding the system ingredients and FPC (Flexible Printed Circuits) into the chassis/ system ground which helps to prevent the ESD (Electrostatic Discharge) soft failures and its thickness is around 0.5mm. But as the devices are trending towards more and more thin designs the thickness of the display metal back cover becomes a problem. The paper provides an ESD soft failure risk assessment where the thick display metal back cover is replaced with a less than 0.05mm thin metal sheet and its effect on ESD soft failure is studied. The paper covers following key topics: a) creation of an ESD pass and fail case for a given issue, b) identification of correct measurement parameters in simulation to distinguish between pass and fail case, c) validation of an ESD simulation setup with the help of Z parameter correlation and d) assessment of ESD soft failure using a thick display metal back cover and using a thin metal sheet. The ESD soft failure risk assessment is performed using 3D EM simulation and identified surface current on the system ground as a critical part of soft failure mechanism.