Mechanical reliability of plastic packages for integrated circuit devices is significantly affected by the moisture adsorption property of the polymer material, primarily epoxy compound, used in the package. Numerous research efforts have been focused on the different parameters controlling the kinetics or ultimate moisture uptake inside plastic packages. However, they are mostly concern with the bulk diffusion inside the epoxy compound. When compared with bulk diffusion, there is very little effort in assessing the role of interfacial diffusion. There is some concern to understand moisture diffusion at material interface at fundamental level, especially when the package size shrinks. Most of the mathematical models based on Fick’s Laws are not fitted for describing interfacial moisture...[ Read more ]

Mechanical reliability of plastic packages for integrated circuit devices is significantly affected by the moisture adsorption property of the polymer material, primarily epoxy compound, used in the package. Numerous research efforts have been focused on the different parameters controlling the kinetics or ultimate moisture uptake inside plastic packages. However, they are mostly concern with the bulk diffusion inside the epoxy compound. When compared with bulk diffusion, there is very little effort in assessing the role of interfacial diffusion. There is some concern to understand moisture diffusion at material interface at fundamental level, especially when the package size shrinks. Most of the mathematical models based on Fick’s Laws are not fitted for describing interfacial moisture diffusion or seepage. In this study, a new concept describing interfacial diffusion was introduced based on the concept of interfacial layer model. Interfacial characterization is important in forming a model to describe the interfacial moisture diffusion process. Experimental measurements of the interfacial moisture content at the epoxy / copper interface was characterized by using Fourier transform infrared (FTIR) spectroscopy. It was found that the interface has the different absorption behavior against bulk epoxy

Higher moisture diffusion rate at the edge region was found by FTIR and leads to faster rate of moisture diffusion which in turn increases the rate of interfacial degradation. Crack initiation will take place once the degradation is serious and exceed critical interfacial bonding energy. The higher and faster interfacial moisture diffusion at the edge therefore will lead to delamination and pop-corning along the interface. Even the cuprous oxide will help with the adhesion at low moisture concentration, the continuous moisture diffusion into the samples will eventually fails the package.

The thesis has conducted a preliminary investigation on the mechanism of interfacial moisture diffusion. It is concluded the interfacial moisture diffusion is a dominant factor when compare with the traditional bulk moisture diffusion model. A new model for interfacial moisture diffusion is proposed.