Multi-scale modeling of moisture transfer in electronic packaging

Interfacial delamination is one of the primary concerns in electronic package design. Pop-corning in plasticencapsulated IC packages is a defect frequently occurring during the solder reflow due to moisture penetration into the packages. Moisture absorption has a detrimental effect on the EMC/Cu interfacial adhesion and drastically reduces the reliability of the encapsulated package. To obtain good reliability and to prevent interfacial delamination, it is important to understand the mechanism of moisture transport to the epoxy/copper interface at a fundamental level. The object of this paper is an investigation of moisture transport in electronic packaging by using multi-scale approach. Three kinds of models containing SAM1, SAM2 and a mixture of SAM1 and SAM2, have been used to evaluate wettability of SAM coated Cu substrate in this study. In each model, SAM1 or SAM2 or mixture of SAM1 and SAM2 chains were aligned on the copper substrate. MD simulations were performed at a given temperature using the constant-volume and temperature ensemble (NVT). Nonbond interactions cut-off distance of 1.25 nm with a smooth switching function was used in all simulations. The simulations were performed with an interval of 1 femto second (fs) in each MD simulation step. A CFD model with a mixture of air and water was built to study hydrophobicity of different SAM coated interface. The interfacial wettability derived from MD simulations is assigned to the CFD model. Water distribution in the model can be predicted, which can be used to demonstrate optimization of SAM for a hydrophobic interface. This study shows that an efficient tool for optimization of SAM to create a hydrophobic interface, which can provide useful pointers of reliable interface design.