Some thermal mismatch problems in electronic devices
Date of Issue2009
School of Mechanical and Aerospace Engineering
Electronic devices consist of multiple layers of different materials having different coefficient of thermal expansion (CTE). During processing, the high operating temperature induces thermal stress on the interface of the different layer as well as thermally-induced bending of the structure due to the mismatch in CTE of the materials. If the magnitude of stress is high enough, failure of the structure may occur. Hence, this project aimed to investigate the effects of temperature changes on thermal stress in these devices. Three cases were studied in this project: (1) Investigation of thermal stress during thermal oxidation of silicon, (2) Investigation of thermally-induced crack propagation during die attach and (3) Popcorn cracking in plastic IC devices. Parametric analyses of the factors that may affect the reliability of the devices during these processing operations were performed using the commercial Finite Element software, Ansys. Results indicated that factors that can increase the magnitude of thermal stress during thermal oxidation include higher CTE mismatch and higher substrate thickness and modulus. In addition, a shorter crack length and lower CTE mismatch are some of the conditions that can lower the likelihood of crack propagation in a silicon die during the die attach operation. Finally, it was found out that a higher vapor pressure loading and crack length can increase the probability of popcorn cracking. The results in this study have indicated the importance of processing temperature, device geometry and material properties on the effect of thermal stress and crack propagation during processing. Hence, it is paramount for manufacturers to take these factors into consideration in order to improve the reliability of these devices.
Final Year Project (FYP)
Nanyang Technological University