A novel approach to deprocess highly sensitive multi-layered IC device using polyimide protective films without damaging active circuitry

Recent advancement in chip design which made it possible to achieve more functionality in a smaller package means that the silicon die design needs to be compact and multi layered. One particular case which often caused difficulty to failure analysts was the Common Mode Filter (CMF) devices packed in the multi-leads, XDFN package. The device comes with an integrated ESD protection. Differential signaling I/O´s can now have both common mode filtering and ESD protection in one package which makes the device a favorite in application for protecting systems using high-speed differential ports such as USB 3.0. Sometimes, due to assembly/wafer process mis-processing, the device will fail for high resistance between the internal/external connection pins. After exhaustive experimentations in which four techniques were evaluated to deprocess the devices in order to expose the silicon die, and wires, this paper aims to explore the best method to preserve the silicon die´s active circuitry which consists of an intricate copper coil interconnects, and protective polyimide films which is very critical for a successful identification of the failure mechanism that will explain the reason why the devices failed in the first place. The chosed method in the end allowed the analyst to pin point the cause of high resistance failure which was contributed by micro-gap between the upper and lower layer of copper metal interconnects.