Papers by Author: Tadahiro Shibutani

Abstract: The cavity growth behavior in a polycrystalline LSI conductor is investigated on the basis of diffusion along grain boundary (GB) and interface (IF) induced by stress and electric current. The of GB and IF, which strongly affects the characteristics of the atom migration. Numerical analysis is conducted for a polycrystalline conductor with GB/IF network after a discussion on a specialized FEM for the diffusion. Results obtained are as follows. (i) In a conductor, the atom migration is eminently activated near a cavity along GBs while there is little flow without the defect. (ii) IF diffusion between the conductor and the surrounded passivation activates the atom migration along GBs inside of a conductor. This implies that the cavity grows under the interaction between GB diffusion and IF one. (iii) Under an external stress, the cavity growth is fast in the early stage while it is decelerated by the constraint of the triple junction ahead of the cavity. (iv) The complex branches of the atom migration due to electric current (EM) amplifies the stress evolution and the stress-induced atom migration (SM) takes place. The cavity grows under the interaction between EM and SM, which stems from the GB/IF network.

Abstract: In recent years, package downsizing has become one of biggest trends in packaging technologies because of miniaturization and the high integration of electronic devices. As a result, the reliability of fatigue life has been prioritized as an important concern, since the thermal expansion difference between a package and printed circuit board causes thermal fatigue. But, the reliability of thermal fatigue life may be lowered by the dispersion of design factors such as the dimensions, shapes, and material properties of package systems. Also, the fracture modes (fatigue fracture, brittle destruction in the interface, and compound destruction, and so on) will be affected by these dispersion factors. Although this dispersion should be reduced in order to improve the reliability, reducing all dispersion is inefficient and time-consuming. So, the factors that greatly contribute to thermal fatigue life have to be reduced. In this study, evaluations of the influence of various design factors on the reliability of soldered joints of a BGA (Ball Grid Array) were carried out, and got each influence. With the results, design engineers can rate each factor’s effect on reliability and assess the reliability of their design beginning at the concept design stage. Consequently, it will be possible to avoid almost all reliability problems from the beginning. Also, by rating the factors, the design period can be shortened