Aging effects of Epoxy Moulding Compound on the long-term stability of plastic package

The typical approach to investigate the reliability of plastic packages is based on material characterizations. Thereby the material characterization is carried out using standard methods like Dynamic Mechanical Analysis (DMA) and Thermo-Mechanical Analysis (TMA). Based on these results the change of Epoxy Moulding Compounds (EMC) thermo-mechanical properties is used to predict long-term stress changes in the plastic package. Using this approach the effects of certain reactions, which occur when EMCs age in contact with other materials, are not considered in the prediction. In this work by using the bi-material specimens composed of EMC and copper, the way how these effects lead to a huge stress change in transfer moulded plastic packages is shown. EMC material has been characterized before and after thermal aging by means of DMA and TMA. The aging-induced warpage changes of the bimaterial specimens have been experimentally investigated. Using the warpage curves over temperatures, the impacts of these reaction effects on the second glass transition temperature of the aged EMC have been investigated. Since the investigated EMC shows two glass transition temperatures after thermal aging. The thermal storage of EMCs at certain high temperature leads to semi-carbonization of the EMC surfaces. The dependency of the thickness of the semi-carbonized layer on storage time has been carried out and the way how this layer impacts EMC warpage is shown. It has been shown, that not only the aged material properties but also the effects of these reactions must be taken into account during simulations to predict stress changes in plastic packages accurately.