Solder joint failures under thermo-mechanical loading conditions – a review

Solder joints play a critical role in electronic devices by providing electrical, mechanical and thermal interconnections. These miniature joints are also the weakest links in an electronic device. Under severe thermal and mechanical loadings, solder joints could fail in ‘tensile fracture’ due to stress overloading, ‘fatigue failure’ because of the application of cyclical stress and ‘creep failure’ due to a permanent long-term load. This paper reviews the literature on solder joint failures under thermo-mechanical loading conditions, with a particular emphasis on fatigue and creep failures. Literature reviews mainly focused on commonly used lead-free Sn-Ag-Cu (SAC) solders. Based on the literature in experimental and simulation studies on solder joints, it was found that fatigue failures are widely induced by accelerated thermal cycling (ATC). During ATC, the mismatch in coefficients of thermal expansion (CTE) between different elements of electronics assembly contributes significantly to induce thermal stresses on solder joints. The fatigue life of solder joints is predicted based on phenomenological fatigue models that utilise materials properties as inputs. A comparative study of 14 different fatigue life prediction models is presented with their relative advantages, scope and limitations. Creep failures in solder joints, on the other hand, are commonly induced through isothermal ageing. A critical review of various creep models is presented. Many of these strain rate-based creep models are routed to a very well-known Anand Model of inelastic strain rate. Finally, the paper outlined the combined effect of creep and fatigue on solder joint failure.N/

Amidation of silyl enol ethers and cholesteryl acetates with chiral ruthenium(II) schiff-base catalysts: catalytic and enantioselective studies.

Chiral ruthenium(II)-salen complexes [RuII(salen)(PPh3)2] catalyse asymmetric aziridination of alkenes with up to 83% ees, asymmetric amidation of silyl enol ethers with up to 97% ees, and allylic amidation of cholesteryl acetates with good regioselectivity.link_to_subscribed_fulltex

Polymer-supported ruthenium porphyrins: Versatile and robust epoxidation catalysts with unusual selectivity

Carbonyl ruthenium(II) 5,10,15-tris(4-R-phenyl)-20-(4- hydroxyphenyl)porphyrins (R = Cl, Me) covalently attached to Merrifield's peptide resin were prepared. The catalyst with R = Cl was found to efficiently catalyze Cl 2pyNO epoxidation of a wide variety of alkenes, including aromatic and aliphatic terminal alkenes, cis- and trans-stilbene, cyclohexene and cyclooctene, α,β-unsaturated ketones, conjugated enyne, glycal, and protected α-amino alkene. Unusual selectivities were observed for the epoxidations of 1,5-cyclooctadiene, cis-1-phenyl-3-penten-1-yne (9), 3,4,6-tri-O-acetyl-D-glucal (11), and 2-(Boc-amino)-1-phenylbut-3-ene (13), which feature a complete bisepoxide selectivity (1,5-cyclooctadiene), unprecedentedly high cis:trans ratio (9), and complete diastereoselectivity (11 and 13). The new heterogenized metalloporphyrin epoxidation catalysts are of high stability and reusability.link_to_subscribed_fulltex

Amidation of saturated C-H bonds catalyzed by electron-deficient ruthenium and manganese porphyrins. A highly catalytic nitrogen atom transfer process

(equation presented) Amidation of a variety of hydrocarbons with PhI=NTs catalyzed by ruthenium and manganese meso-tetrakis(pentafluorophenyl)porphyrins 1 and 2 afforded N-substituted amides in up to 92% yields with good to excellent substrate conversions. By employing catalyst 2, exceptionally high turnovers (up to 2600) were achieved, and the amidations can be effected by directly using PhI(OAc)2/NH2R as amidating reagents; in the case of R = COCF3 a direct amination was realized in up to 90% yield.link_to_subscribed_fulltex

Asymmetric amidation of saturated C-H bonds catalysed by chiral ruthenium and manganese porphyrins

Chiral ruthenium(II) and manganese(III) porphyrins catalyse the asymmetric amidation of saturated C-H bonds of ethylbenzene and ethylnaphthalenes to form the corresponding amides in up to 85% yield with 45-58% ee.link_to_subscribed_fulltex

Binaphthyl Schiff base complexes of palladium(II). Structures and reactivities toward alkene epoxidation

Palladium(II) binaphthyl Schiff base complexes [PdII(L)](1: H2L =(racemic or fl)-2,2′-bis(3,5-dichloro-2-hydroxybenzylideneamino)-l, 1′-binaphthyl(H2L2);2: H2L =(A)-2,2′-bis(3,5-dichloro-2-hydroxylbenzylideneamino)-5,5′,6, 6′,7,7′,8,8′-octahydro-l,1′-binaphthyl(H 2L3)) were prepared from sequential reactions of H2L with sodium methoxide and palladium(II) acetate in methanol in about 70% yields. Both complexes 1 and 2 have been characterised by X-ray crystallography as well as 1H NMR, IR, UV/VIS and MS spectroscopy. The structures of 1 and 2 feature a pseudo planar N2O2 arrangement with the Schiff base ligands adopting a stepped conformation, in contrast to the non-planar N2O2 geometry usually observed for this type of Schiff base bound to various metal ions. The catalytic behaviour of complexes 1 and 2 toward asymmetric epoxidation of styrènes was investigated. With 2 as a catalyst, a 71% ee was obtained for the epoxidation of p-fiuorostyrene by 1BuOOH. © The Royal Society of Chemistry 2000.link_to_subscribed_fulltex

Asymmetric epoxidation of alkenes catalysed by chromium binaphthyl Schiff base complex supported on MCM-41

A chromium(III) binaphthyl Schiff base complex immobilised on modified MCM-41 is an effective catalyst for asymmetric epoxidation of unfunctionalised alkenes and gave significantly higher ee than the free complex.link_to_subscribed_fulltex

Characterization of InAs quantum dots on lattice-matched InAlGaAs/InP superlattice structures

Self-assembled InAs quantum dots (QDs) in an InAlGaAs matrix, lattice-matched to InP substrate, have been grown by molecular beam epitaxy (MBE). Transmission electron microscopy (TEM), double-crystal X-ray diffraction (DCXRD) and photoluminescence (PL) are used to study their structural and optical properties. In InAs/InAlGaAs/ InP system, we propose that when the thickness of InAs layer deposited is small, the random strain distribution of the matrix layer results in the formation of tadpole-shaped QDs with tails towards random directions, while the QDs begin to turn into dome-shaped and then coalesce to form islands with larger size and lower density to release the increasing misfit strain with the continuous deposition of InAs. XRD rocking curves showing the reduced strain with increasing thickness of InAs layer may also support our notion. The results of PL measurements are in well agreement with that of TEM images. (C) 2004 Elsevier B.V. All rights reserved