Rhodium(I) complexes of α-keto-stabilised 1,2-bis(diphenylphosphino)alkane mono ylides
Rhodium(I) complexes of the hybrid ylide-phosphine ligands, Ph2P(CH2)nPPh2(CHC(O)C6H5) (n = 1: dppm-yl, or 2: dppe-yl) have been synthesised from [Rh(μ-C1)(COD)]2 (COD = 1,5-cyclooctadiene) and characterized by NMR spectroscopic and X-ray structural methods. The dppe-yl behaves as an ambidentate ligand; it functions as a monodentate P-donor ligand with a dangling ylidic carbon in the neutral chloro complex, [(COD)Rh(Cl)(dppe-yl)] (1), whereas replacement of the chloride by a non-coordinating counter anion results in the formation of the complexes, [(COD)Rh(L-L’)]+ (L-L’ = dppe-yl (2) or dppm-yl (3)) respectively in which the ligands are bonded to the metal via the phosphorus and the ylidic carbon atoms. The 1,5-cyclooctadiene (COD), present in the Rh(I) precursor, remains intact in the products. The structures of1,2 and3 have been confirmed by X-ray crystallography.
Synthesis and structural characterization of methanide silver(I) complexes. Unprecedented co-ordination of the methanide ligand in [Ag2(PPh3)2(SPPh2CHPPh2CHCO2Me)]ClO4·4CH2Cl2
The mixed phosphine-phosphonium salt [PPh2CH2PPh2CH2CO2Me]ClO4 reacts with [Ag(acac)(PPh3)](acac = acetylacetonate), with deprotonation of the ligand, displacing acac as acetylacetone and yielding the complex [Ag(OClO3)(PPh3)(PPh2CH2PPh2CHCO2Me)], where the methanide ligand chelates the four-co-ordinate metal centre. The sulfide or oxide derivatives [XPPh2CH2PPh2R]ClO4(X = S or O; R = Me or CH2CO2Me) also react with [Ag(acac)(PPh3)] in various stoichiometries to give [Ag(PPh3)(XPPh2CHPPh2Me)]ClO4 or [Ag2(PPh3)2(XPPh2CHPPh2CHCO2Me)]ClO4; in the latter the methanide ligand co-ordinates both silver atoms through four donor centres (X, C, C, CO). Two of these derivatives have been characterized by X-ray analysis: [Ag(OClO3)(PPh3)(PPh3(CH2PPh2CHCO2Me)] crystallizes in the monoclinic space group P21/n, a= 12.448(4), b= 21.021(7), c= 19.803(7)A, β= 108.60(3)°, Z= 4, T=–100 °C; [Ag2(PPh3)2(SPPh2CHPPh2CHCO2Me)]ClO4 crystallizes in the same space group with a= 13.759(3), b= 12.074(3), c= 43.353(9)A, β= 92.62(2)°, Z= 4, T=–100 °C.
“ PARTIALLY-ACTIVATED ” FLUX RESIDUE IMPACTS ON ELECTRONIC ASSEMBLY RELIABILITIES
The reliabilities of the flux residue of electronic assemblies and semiconductor packages are attracting more and more attention with the adoption of no-clean fluxes by majority of the industry. In recent years, the concern of “partiallyactivated” flux residue and their influence on reliability have been significantly raised due to the miniaturization along with high density design trend, selective soldering process adoption, and the expanded use of pallets in wave soldering process. When flux residue becomes trapped under low stand-off devices, pallets or unsoldered areas (e.g. selective process), it may contain unevaporated solvent, “live” activators and metal complex intermediates with different chemical composition and concentration levels depending on the thermal profiles. These partially-activated residues can directly impact the corrosion, surface insulation and electrochemical migration of the final assembly. In this study, a few application tests were developed internally to understand this issue. Two traditional liquid flux and two newly developed fluxes were selected to build up the basic models. The preliminary results also provide a scientific approach to design highly reliable products with the goal to minimize the reliability risk for the complex PCB designs and assembly processes.