ESD Modeling

The obvious question is, “Why do I need to model ESD?” Modeling describes a physical process in mathematical terms. The equations describing the physical processes are used to simulate its response to external stimulus. Through this mathematical simulation we can study the physical processes and understand their behavior with regard to changes in the stimulus or in the equations comprising the model. The goal in any model is to perfectly represent in a mathematical form what occurs in the physical form, but achieving this goal can be elusive. The simulation space where a model is valid is often just a subset of the total operational space. As an example, the behavior of a spring can be described as a simple linear relationship between the distance traveled and the force exerted (F=k•x; where F=force, x=distance; k=spring ratio) provided the spring is not allowed to stretch beyond its elastic limit. Figure6-1 shows the stress-strain (force-distance) curve for a spring. The elastic region is the linear portion at the beginning of the curve. In this region the spring will return to its original shape after the force is removed. Once the spring crosses over to the plastic region structural changes in the spring have occurred. The spring will not behave the same as it once did. The simplified model only covers the linear region. The equations governing the entire space up to the point where the spring fails are more complicated and difficult to model.