Bart Allaert

Improved ruthenium catalysts for the modified Friedlaender quinoline synthesis

Herein we describe an improved ruthenium catalyst for the oxidative cyclization of 2-aminobenzylalcohol with ketones, leading to quinolines via a modified Friedlaender synthesis.

Rational design and convenient synthesis of a novel family of ruthenium complexes with O,N-bidentate ligands

A two step procedure for the synthesis of a novel family of homogeneous and immobilized Ru-complexes containing Schiff bases as O,N-bidentate ligands is described. The new Ru-complexes have been structurally characterized by IR, Raman,1H-,13C-NMR spectroscopy. The Schiff bases were associated with a diversity of inorganic and organic ligands such as chloride, phosphane, arenes, various carbenes (alkylidene, vinylidene, indenylidene and allenylidene as well as N-heterocyclic carbenes) and cyclodienes. By choosing a selective range of substituents for the Schiff base, useful physical and chemical properties of the prepared Rucomplexes can be induced. This synthetic approach is promising in creating a valuable and diverse selection of Ru-complexes, valuable for future applications.

Brittle to Ductile Fracture Transition in Bulk Pb-Free Solders

The fracture toughness of bulk Sn, Sn-Cu, Sn-Ag, and Sn-Ag-Cu lead-free solders was measured as function of the temperature by means of a pendulum impact test (Charpy test). A ductile to brittle fracture transition was found, i.e., a sharp change in the fracture toughness. No transition was found for the eutectic Sn-Pb. The transition temperature of high purity Sn, Sn-0.5%Cu and Sn-0.5%Cu(Ni) alloys is around -125degC. The Ag-containing solders show a transition at higher temperatures: in the range of -78 to -45degC. The increase of the Ag content shifts the transition temperature towards higher values, which is related to the higher volume fraction of SnAg particles in the solder volume. At fixed volume fraction, smaller particle size shifts the transition temperature towards higher values. Therefore, a careful microstructure control is needed during the solder solidification after reflow in order to decrease the low temperature brittleness hazard.

Exploring new synthetic strategies in the development of a chemically activated Ru-based olefin metathesis catalyst

The objective of this work was to develop an industrially relevant olefin metathesis initiator, which circumvents the expensive, patent protected, often cumbersome preparative routes via Grubbs benzylidene complexes. Upon coordination of a Schiff base ligand to a second-generation ruthenium allenylidene complex, the formation of three catalyst isomers was observed. The major isomer was successfully isolated, and tested in a few olefin metathesis reactions. Acids such as HCl and HSiCl(3) were found to boost the metathesis reaction but the in situ formation of a neutral Ru carbyne complex restricted the catalytic capacity. Using the Lewis acid PhSiCl(3), the formation of a carbyne species was avoided, and turnover numbers up to 30,000 were reached in the ring-opening metathesis polymerisation of cycloocta-1,5-diene.

Low-Temperature Embrittlement of Lead-Free Solders in Joint Level Impact Testing

The low-temperature embrittlement of tin-based (Sn- based) lead-free (Pb-free) solder alloys has been previously reported for bulk specimens tested in impact by means of a conventional Charpy V-notch test setup. The brittle failure of Sn-based Pb-free solders at low temperatures (i.e. below -30degC) is of great concern for electronic assemblies that operate at harsh conditions, because it can lead to occurrences of early failures. A miniaturized impact test setup has been devised to perform a scaled-down version of the conventional Charpy impact test on specimens, which lie in the size range of 300 mum to 3 mm. In this work, the impact tests have been carried out in the temperature range between 23 degC and -110degC. The specimens consisted of SuperBGAreg (SBGAreg) substrates bumped with 4 different solder alloys: Sn3%Ag0.5%Cu (SAC 305), Sn4%Ag0.5%Cu (SAC 405), Sn3.5%Ag, and Sn37%Pb. The energy absorbed during the fracture of the solder joints was seen to decrease as a function of temperature for the SAC 305 and SAC 405 alloys, while for the Sn37%Pb and Sn3.5%Ag this trend was less pronounced. The ductile-to-brittle transition in the fracture behavior of Sn- based Pb-free solders was confirmed by scanning electron microscopy (SEM) investigations. These investigations showed the progressive bulk embrittlement of the Sn matrix of SAC 305 and SAC 405 solder alloys. The onset of the Sn embrittlement was observed between -40degC and -50degC leading to the complete brittle fracture of the solder joint at around -70degC.

Four-point bending cycling: The alternative for thermal cycling solder fatigue testing of electronic components

Abstract This paper deals with an alternative testing approach for quantifying the life time of board level solder joint reliability of components. This approach consists of applying a relative shear displacement between component and Printed Circuit Board (PCB) through cyclic board bending. During the cycling, the temperature is kept constant, preferably at elevated temperature in order to accelerate the creep deformation of the solder joint. This is done in a four-point bending setup which allows to apply an equal loading on all components lying between the inner bars. The scope of the paper is, firstly, to evaluate if the four point bending testing generates the same fatigue fracture as in thermal cycling; secondly, that the measured life times can be also predicted through finite element simulations; and thirdly if the technique can finally accelerate the cycling frequency to reduce the testing time.

How the mold compound thermal expansion overrules the solder composition choice in board level reliability performance

IC packages using mold compounds with low coefficient of thermal expansion (CTE) have been introduced in the last decade packages with basically no attention to its impact on board level reliability. In this study, the impact is shown for a large size QFN package. In this parameter sensitivity study, also the solder composition and the flank wettability of the QFN leads are varied. The QFNs soldered to a thick Printed Circuit Board (PCB) are tested under thermal cycling and the outcome is a Weibull failure distribution. Comparing the different results reveals which of the three parameters (mold CTE, solder composition, flank wettability) is the one dominating most the board level reliability. The work is supported by optical inspection on failed samples.

Olefin Metathesis Mediated By: - Schiff Base Ru-Alkylidenes -Ru-Alkylidenes Bearing Unsymmetrical NH Ligands

The classic Grubbs second-generation complex 2 was modified through 1. The introduction of a bidentate Schiff base ligand 2. Changes in the amino side groups of the NHC ligand Representative olefin metathesis test reactions show the effects induced by the ligand modifications and demonstrate some interesting new properties of the described catalysts. catalysts.

Towards New Generations of Metathesis Metal–Carbene Pre-catalysts

A short general introduction combined with some historical milestones in the field of olefin metathesis is presented followed by an overview of recent repre- contributions and overwhelming work invested in intelligent design and innovative synthesis in this area. Despites of recent advances there is still a great interest in the generation of new, better performing, and more environment friendly metathesis.