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Near-surface voids and pores are generated in metal processing operations as diverse as additive manufacturing and powder processing, but their effect on indentation hardness has not been explored outside homogenized frameworks. Here we model the micromechanics of near-surface void deformation up to closure in a wedge-indentation field in ductile metal, and reveal the considerable softening effect of voids on the indentation hardness. Both symmetrically and eccentrically located voids, at various depths below the free surface, are studied. Notably, the extent of apparent reduction in the elastic modulus due to a void is much smaller than its effect on apparent hardness, e.g. 6.5% against 55% for the same void. Critical to the simulations is an adaptive remeshing finite element (FE) framework that allows accurate capture of processes like void closure and void-wall self-contact. The simulations reveal the subsurface plastic strain, strain-rate, and velocity fields with high fidelity, and their radical differences from the radial indentation field in a void-free specimen. These differences include the presence of localized pockets of high and low strain, and the initial accommodation of material displaced by the indenter by a corresponding reduction in void area. Unlike voids under uniform compression, the void-area evolution in indentation shows a characteristic sigmoidal pattern of reduction with indentation depth for all but the smallest voids. Interestingly, the indented surface profile can exhibit a one-sided pile-up feature which is diagnostic of the presence of an eccentrically located sub-surface void. Our remeshing scheme is versatile, as exemplified by its ability to model the extreme deformation associated with two nearly closed-spaced voids under an indenter. Our work shows that void-closure simulations in related applications like forming could benefit from the adoption of a remeshing framework. • First study of sub-surface void mechanics in an indentation field. • Quantification of softening effect of voids on indentation hardness. • Diagnostic changes to indented surface due to subsurface voids identified. • Void area evolution under wedge indenter is characteristically sigmoidal. • Remeshing-based simulations critical for accurate capture of void closure. [ABSTRACT FROM AUTHOR]

This paper reports results of a study on copper voids seen in a back end of line (BEOL) module. The experiment was designed to study the effect of multiple parameters that can influence the occurrence of voids and their process margins. This work also reports the effect of changes in copper seed thickness on the product’s lifetime and reliability. [ABSTRACT FROM AUTHOR]

Since the introduction of lead-free solder alloys, the impact of voids in solder joints has rapidly gained in importance. Particularly in power electronics, voids in solder joints can reduce their reliability due to less heat dissipation and a significant reduction of the cross-sectional area. While void formation in the printed circuit board (PCB) technology has been the focus of many research projects, the increasing application of molded interconnect devices (MIDs) demands a vivid understanding of void formation and its impact on reliability. This report will show that those processes specific to MID technology do not significantly influence the void formation in SAC305 solder deposits. The processed different roughness levels on Vectra, Vestamid, and FR4 substrate materials show no significant impact on void formation. The surface finish metallization was detected as the most important factor. Especially, the chemical-Sn (iSn) surface finish is inclined to having more voids compared to a nickel–phosphor–gold (NiP-Au) finish. Furthermore, three solder processes were investigated: convection, condensation, and vacuum-condensation soldering. The vacuum-condensation processes significantly reduced the voids in the Sn–3.0Ag–0.5Cu (simplified as SAC305) solder joints of CR0805, MLF20, and switches on all the investigated substrates. An accelerated thermal cycling test of these components according to JESD22-A104D demonstrates no significant effect of the void content of <19% on the solder joints’ reliability. Finally, the result of accelerated thermal cycling shows the possibility to achieve an equivalent lifetime of the solder joints on Vectra in comparison to the FR4 substrate. [ABSTRACT FROM PUBLISHER]

Molecular dynamics simulations were conducted to elucidate dislocation mechanisms of the void growth and coalescence in single crystal and nanotwinned nickels subjected to uniaxial tension. The simulation results reveal that twin boundary is capable of decreasing the critical stress, suppressing the emission of dislocations and reducing the overall stiffness of the crystal. A size-scale dependence of critical stress is definitely illustrated through stress–strain response, where the larger void size leads to the lower critical stress and strain. It is the successive emissions of leading partials and the subsequent trailing partials that cause the atoms on the void surfaces to escape from the void surfaces continually, and consequently the voids grow to be larger and larger with increasing strain. The voids in the nanotwinned nickel coalesce earlier than those in the single crystal nickel even though the initiation of dislocations in the former is later than that in the latter. Void fraction remains a constant during elastic deformation, while it presents a linear increase with increasing strain during plastic deformation. Evolution of void fraction during void growth and coalescence is independent on void size. [ABSTRACT FROM PUBLISHER]

Electromigration (EM) is a growing concern in on-chip interconnects, particularly in the computing and automotive domains. EM can cause wire resistances in a circuit to increase, which may result in circuit performance failure within the lifetime of a product. Classical circuit-level EM models have two drawbacks: first, they do not accurately capture the physics of degradation in modern copper dual-damascene (Cu DD) metallization and second, they fail to model the inherent resilience in a circuit that may allow it to continue to function even after some wires fail. This paper overcomes both limitations, and develops a method to analyze the effect of EM on the resistance of wires in a circuit. For a single wire, our probabilistic analysis encapsulates known realities about Cu DD wires, e.g., that some regions of these wires are more susceptible to EM than others, and that void evolution shows statistical behavior. We develop a new criterion for identifying mortal wires based on this analysis. One part of the criterion incorporates the achievement of steady state and provides a result that is slightly tighter than the traditional Blech criterion, while another part is tied to the lifetime of the system. We apply these ideas to the analysis of on-chip power grids and demonstrate the inherent robustness of these grids that maintains supply integrity under some EM failures. [ABSTRACT FROM PUBLISHER]

This is the first of three overviews on failure of metals. Here, brittle and ductile failure under monotonic loadings are addressed within the context of the local approach to fracture . In this approach, focus is on linking microstructure, physical mechanisms and overall fracture properties. The part on brittle fracture focuses on cleavage and also covers intergranular fracture of ferritic steels. The analysis of cleavage concerns both BCC metals and HCP metals with emphasis laid on the former. After a recollection of the Beremin model, particular attention is given to multiple barrier extensions and the crossing of grain boundaries. The part on ductile fracture encompasses the two modes of failure by void coalescence or plastic instability. Although a universal theory of ductile fracture is still lacking, this part contains a comprehensive coverage of the topic balancing phenomenology and mechanisms on one hand and microstructure-based modeling and simulation on the other hand, with application examples provided. [ABSTRACT FROM AUTHOR]