On the impossibility of multi-pass equal-channel angular drawing

Experimental results and numerical calculations show that multi-pass equal-channel angular drawing (ECAD) will be of little technical use because of the important cross-sectional reduction accompanying the shear deformation imparted by the process. Continuous equal-channel deformation without section reduction can only be performed by techniques based on rolling impulsion or hydrostatic ECA pressing. (C) 2002 Published by Elsevier Science Ltd. on behalf of Acta Materialia Inc.status: publishe

Degradation of Cu6Sn5 intermetallic compound by pore formation in solid-liquid interdiffusion Cu/Sn microbump interconnects

The degradation of the Cu6Sn5 intermetallic compound layer caused by pore formation in fine pitch Cu/Sn microbump interconnects is reported in this study. Die-to-die stacking was carried out using the solid-liquid interdiffusion principle. The diameters of the microbumps on the top (Cu/Sn) and bottom die (Cu) were 15 and 25 μm, respectively. The stacking process was carried out in air atmosphere at 240 and 260 C with varying holding time at the peak temperature 10 s, 1, 2, 3, 4, 10 and 20 min. Flux and flux-containing no-flow underfill were used for stacking. Subsequent thermal storage experiments were done in N2 and in air at 240 and 260 C for 10 min, 20 min, 1, 3, 24 and 96 h. The pores start to form after 1 min bonding at the edges of Cu6Sn5 exposed to flux/underfill. These pores propagate to the center of the interconnect with longer bonding time till the complete Cu6Sn5 layer is affected (after 4 min). The possible mechanism of the pore formation is the dissolution of Sn atoms from the Cu6Sn5 matrix due to the reaction between Cu 6Sn5 and flux residues. The remaining pore layer has the composition of Cu3Sn. The results of a subsequent thermal storage show, that a complete transformation of Cu6Sn5 into Cu3Sn without further degradation is possible after the removal of the flux residues. © 2013 Published by Elsevier B.V.status: publishe

Microstructure simulation of grain growth in Cu through silicon vias using phase-field modeling

© 2015 Elsevier Ltd. A computationally-efficient 3D phase-field model for simulating grain growth in through silicon vias (TSVs) is presented. The model is capable of simulating grain growth in the cylindrical shape of a TSV. The results generated from the phase-field simulations are used in a finite element model with anisotropic elastic and isotropic plastic effects to investigate the large statistical distribution of Cu pumping (i.e. the irreversible thermal expansion of TSV) experimentally seen. The model thus allows to correlate the macroscopic plastic deformation with the grain size and grain orientations.status: publishe