Perceived susceptibility of microcontrollers

Failure within a microcontroller based circuit has often been attributed to the microcontroller itself, with many questions being asked about its immunity to fast transients. Many criticisms have been based upon comparisons of microcontrollers placed in similar circumstances. One production parameter that can have changed and is often overlooked is the PCB. Examinations of the variations in performance between PCBs of different construction techniques have been performed and show the effects on the perceived immunity performance of microcontrollers. Simulation of a test circuit has been carried out through the use of an electromagnetic modeller and SPICE based simulator. The performance of two and four layer PCBs have been simulated and close correlation between simulated and measured results obtained. This has been extended to show how variations in the PCB substrate material can further affect immunity performance