Kiichiro Yamanobe

A new systematic method of characterization for the strength of thin films on substrates—evaluation of mechanical properties by means of ‘film projection’

Abstract The strength of a thin film deposited on a substrate should be recognized as the strength of a materials system which is made of a film, a substrate and an interface. The macroscopic fracture of this system should be controlled by the strength of the film and the interface, as well as the residual stress and elastic properties in/of the film. We have developed a systematic method of measurement for all these properties by means of a specimen with ‘film projection’. By applying external load to the film projecting a little out of the edge of the substrate, cracks can be introduced exclusively in the film or along the interface. The strength of film and interface is independently evaluated in terms of toughness on the basis of crack extension resistance. Deformation of the film projection gives its Youngs modulus, and the buckling behavior is used to estimate the residual stress. As an application example of the method, those properties mentioned above were evaluated for the case of a diamond film deposited on a cobalt-cemented tungsten carbide cutting tool.

Analysis of Solderless Press-Fit Interconnections During the Assembly Process

This paper deals with typical mechanical problems that are encountered in a solderless press-fit assembly process. First, the elastic-plastic properties of two types of press-fit pins and the friction coefficients of the pins in thin plated through holes are determined both experimentally and by three-dimensional finite element analysis. The elastic-plastic properties of the press-fit pins are determined by small-scale testing under three-point bending. The coefficients of friction of the pins in the through holes are successfully determined from the load-displacement relationships of the pins during press-fit assembly processes. The validity of the parameters that are determined is clarified by inserting the press-fit pins into holes of different diameters. By comparing the damaged areas of the printed circuit boards after assembly and the numerically obtained stress distributions, the failure stress of the boards is determined. Finally, both the retention force of the pins and the degree of damage to the printed circuit boards after assembly are predicted by numerical analysis.

Quantitative evaluation of bonding energy for the interfaces in Cu metallization systems

The toughness of two different interfaces in Cu metallization systems (Cu∕barrier metals and Cu∕cap layer) was evaluated by developed techniques. To establish the measurement technique at first, the effect of Cu film thickness on the evaluated toughness of the interface between Cu and barrier metal was examined. A small-scale yielding condition was realized even with ductile thin-film systems, and the toughness obtained was almost independent of the film thickness. The difference in the interface toughness among different Cu deposition techniques (sputtered and vacuum evaporated) was also quantitatively discussed. The method was then expanded to the Cu films as thin as those in the commercial integrated circuit. Finally, the toughness of interfaces between nanometer-scale cap layer materials and Cu was also evaluated by using a modified configuration of the specimens.