(3) Observation of Three-dimensional Structures in Adhesive Layer by X-ray Imaging

Inner structures in adhesive layer affect strength of adhesion and it was not so easy to visualize them. X-ray imaging is one of the methods to observe opaque objects and it was widely used for clinical examinations and industrial inspections. However, because of weak contrast and worse spatial resolution, it was difficult to distinguish individual structures consisting of light elements like adhesive layer with such X-ray imaging system. In this article, three-dimensional observation of an adhesive layer by using X-ray microscopy is described. The microscope employs long wavelength X-rays and its sensitivity is about 10 times higher than that of conventional systems. Computed tomography technique is also applied and a sample is sliced into 0.95um thick cross sections in any direction non-destructively. Adhesive agent, voids and organic particles in the adhesive layer are clearly observed on tomograms. It is found that distribution of voids and organic particles is not uniform. Therefore, in some regions, thickness of adhesive agent is about half of width of adhesive layer. Such X-ray imaging system will help understanding of complex adhesion and speed up research and development.