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.
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.
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