Due to the increasing complexity, miniaturization and higher density of components in modern devices, reliability and lifetime are important issues in electronic packaging. In modern electronic devices, the packaged structure consists of a variety of metallic, ceramic, plastic or composites components. The large differences in coefficient of thermal expansion (CTE) between ceramic substrates (such as Al2O3 and AlN) heat dissipation materials (such as Cu and Al,) and semiconductors (such as Si and GaAs) induce thermal stress and therefore possible thermal failure in solder joints or ceramic substrates. As a result, to ensure the reliability of electronic devices at increased packing and power densities, thermal management must be considered as a critical aspect in the design of multi-chip modules. There is, therefore, a strong need for the development of new designs utilising novel heat dissipation materials with low coefficients of thermal expansion and high thermal conductivities. During the last decade, the developments in material selection and thermo-mechanical modelling software have lead to design optimisation of complex devices and the prediction of their lifetime.[1,2] It is very important to study material and design parameters that would improve reliability. The challenge is determining the thermal properties of new materials such as composites, which can be very powerful materials in controlling thermal stress and, as a result, increasing the reliability of electronic packages. In this paper, thermo-mechanical modelling predicts i) stress/strain responses in the electronic device under thermal loads, and ii) the corresponding reliability (lifetime). The thermal stress and strain analyses in this study have been performed with FEMLAB multi-physics software. Furthermore, it models the couple between different materials in complex device designs.Read less <