Characterization of thin films and intermetallic compounds in solder joint

Abstract

Numerical simulation such as finite element methods have been widespread in structure designs and analyses in IC industry and researches. Only if the inputs of material properties are correct, can the outcome be referable to its applications. Thin-film materials have been widely used in many applications. The mechanical properties of thin films may be markedly distinct with different processes and processing conditions. To study the mechanical behaviour of thin films, thin films on substrates are adopted most often [Jie-Hua Zhao, Yong Du, Michael Morgen, and Paul S. Ho, [200]]. The most commonly used material for substrate is silicon, which has low coefficient of thermal expansion (CTE) and is a prevalent semiconductor material. The theoretical values of Young's moduli of silicon were usually applied. However, the values might be different in practice. Before further study of thin-films, the actual mechanical properties of silicon substrates should be cautiously investigated first. Intermetallic compounds (IMC) are formed when interconnections in IC packages are jointed with solder. Though IMC just comes into a small amount, it usually dominates the reliability of the interconnections because of its characteristic material properties. Individual mechanical properties of a solder/IMC/UBM layered structure are required for simulation and analyses of the interconnection reliability, but always difficult to obtain because the thickness of each layer is on micrometer order. Further, it is impossible to separate each thin layer and apply commercially available testing machines to test it.