Modeling ion transport through molding compounds and its relation to product reliability

Abstract

Nowadays highly filled epoxy molding compounds are used as material for encapsulation of microelectronic devices. These molding compounds always contain a very low concentration of ionic impurity. In addition ionic species can originate from chemical processes inside the encapsulation. In the presence of an electrical field ions will migrate through the encapsulation, which might eventually result in failures, such as corrosion or dendrite growth. Although these failures are well-known they still lack a knowledge based description of their failure mechanism. Therefore a model describing the transport of ions might be useful to give more insight into these failures. However, calculating the transport of ions is numerically very challenging since it requires a multi-physics model on a multi-time and length-scale. Besides, the notion of a maximum ion concentration due to volume constraints opposed by the molding compound increases the complexity of the mathematical framework even further and results in a model that is very difficult to solve. In this paper we discuss several simplified models for the transport of ionic species that might be used to model their corresponding failure mechanisms. Further, we show the conductivity of molding compounds as a function of temperature and discuss how this accelerates the transport of ions.