Shear Stress in Devices
Advanced packaging technologies and assembly techniques are putting emphasis on shear stress on the device level. The SIRD technique is designed for inspection of substrates and wafers, hence it does not offer the required spatial resolution to work on device level. The solution is a well focused laser beam used in reflective mode called SIREX.
The reflective stress measurement is based on the physical effect that a polarized light will be depolarized, if it is transmitted through a substrate under mechanical stress. While metal layers block the light, making SIRD measurement impossible, SIREX takes advantage of the metal layers by establishing a suitable upside-down reflection arrangement.
It is used for stress evaluation throughout the realms of layer deposition, development and production as well as packaging for MEMS devices, as the increased resolution in combination with the scanning stage allows imaging of almost any device size or package geometry
The SIREX inspection includes special analysis programs. The results will be presented not only in detailed maps but also in numeric values for statistical process control applications. The analytical package allows post measurement analysis for global stress fields, localized defects, analysis of a small area and many more.