On the Electrochemical Migration Mechanism of Gold in Electronics—Less Reliable Than Expected?

Electrochemical migration (ECM) forming dendritic short circuits is a major reliability limiting factor in microcircuits. Gold, which is a noble metal, has been regarded as a metallization that can withstand corrosion and also ECM, therefore its application in high-reliability metallization and surface finishing systems became widespread although it has a relatively high and fluctuating price. Gold electrochemical short circuits have been found only in the case of halogen (e.g., chloride containing) contaminants that can initiate the anodic dissolution of gold via complex ion formation. The experimental results of the study demonstrate that gold can form dendritic shorts even without the presence of halogen contaminants, therefore the direct anodic dissolution of gold must also be supposed. This could also be a serious reliability influencing factor even when applying gold metallization systems and must be taken into consideration. The theoretical background of the classical (contaminant-free) model of gold is also discussed in the paper.

Evidence for Au(I)…Au(I) Interactions in a Sterically Congested Environment: Two-Coordinate Gold(I) Halide Phosphine Complexes

Two-coordinate tris(2-methylphenyl)phosphine and tris(4-methylphenyl)phosphinegold(I) halide complexes, [AuP(otol)3X], [AuP(ptol)3X], where X = Cl, Br, and I, have been crystallized from dimethylformamide and characterized by single-crystal X-ray structure determinations. The P(otol)3 structures comprise an isomorphous series distinct from the previously published chloride, crystallizing with two independent molecules in the asymmetric unit in the space group Pbca, with a ≈ 20.0, b ≈ 28.0, c ≈ 14.0 Å. The molecules associate to form dimers through a back-to-back sextuple phenyl embrace (6PE). The P(ptol)3 complexes are isomorphous with the previously published chloride, crystallizing with two independent molecules in the unit cell in the space group P21/c, with a ≈ 10.0, b ≈ 22.0, c ≈ 19.5 Å, β ≈ 99°. The molecules associate through edge-to-face interactions along the direction of the a-axis. Preparation of the chloride by anodic dissolution of gold in an acetonitrile solution of the ligand and aqueous HCl yields a new polymorph, crystallizing in the space group Aba2, with a 19.738(2), b 11.813(3), c 17.645(1) Å. Despite the bulkiness of the phosphine ligand, this form of [AuP(ptol)3Cl] exhibits a short intermolecular Au…Au contact distance of 3.375(1) Å, indicative of a significant aurophilic interaction. The ranges for the Au—P, Au—Cl, Au—Br, Au—I bond lengths and P—Au—X bond angles in the series are: 2.201(3)–2.265(4), 2.255(3)–2.290(4), 2.388(2)–2.411(2), 2.542(1)–2.556(2) Å, and 173.2(2)–179.6(1)° respectively.