Electroless Ni-W-P alloys as barrier coatings for liquid solder interconnects

The control of the interfacial reaction rate is of great importance for liquid solder interconnects for high temperature electronic assemblies. Conventional electroless Ni-P barrier metallizations have been found to be inadequate for providing long term protection of the underlying metallization from the attack of molten solders. In this paper, binary Ni-P was modified with the co-deposition of a refractory alloying element, tungsten (W), from its soluble metal salt added to the plating bath. Critical parameters for the deposition of ternary Ni-W-P were identified. The long term reaction between Ni-W-P and molten Sn-Bi solder at 200 degC was studied. The results indicated that Ni-W-P barrier coatings with higher W contents have much longer service lifetime as a barrier than normal Ni-P coatings. A mechanism for the reaction between Ni-W-P and molten Sn-Bi solder, and a failure mechanism for the Ni-W-P layer, are also propose

A comparative study of the interfacial reaction between electroless Ni-P coatings and molten tin

A comparative study of the reaction characteristics between molten tin and both as-plated and heat-treated Ni-P coatings was carried out, with a specific focus on the stability of the Ni3P intermetallic layer and its effects on the subsequent reaction. It was found that a continuous layer of Ni3P may be formed on both types of Ni-P during the interfacial reaction, despite the fact that heat-treated Ni-P is a two-phase mixture of Ni3P and Ni. The Ni3P formed on the heat-treated Ni-P was thinner than that on as-plated Ni-P. A mass conservation analysis of P revealed that no or limited P was lost into the molten tin when the Ni3P layer was thin, whereas a significant loss of P took place as the Ni3P thickness increased. It is proposed that the Ni3P phase is stable and it may not undergo chemical decomposition during the interfacial reaction. The loss of P to the molten tin observed in the present study is most likely due to the crumbling of Ni3P particles into the liquid phase, as a result of the enhanced mass transport due to use of thin copper wire substrates rather than a planar surface. Finally, the results show that the Ni3P phase cannot act 2 as an effective barrier layer to the attack of molten tin toward the substrate. Defects in the Ni3P were found to allow localised penetration of molten tin

Interactions between liquid Sn-Bi based solders and contact metals for high temperature applications

Liquid solder interconnects are promising as an alternative approach to conventional high melting point solder interconnects for applications where the operating temperature is likely to exceed 125°C. In order to ensure that a liquid solder interconnect remains in contact with the terminations on the component and the substrate, and that electrical contact between them remains unbroken, there must be some growth of an intermetallic compound (IMC) at the interfaces between the solder and the contact metallizations. However, given that IMC growth is generally much faster when the solder is liquid, the growing IMC must act as a strong diffusion barrier to suppress further IMC growth. This paper presents preliminary studies of liquid-phase Sn-Bi based solders that result in stable interfaces between the solders and three common contact metallizations, consisting of electroless Ni(P)/Au, of Cu and of Ti-W. Small quantities (1 or 2 %) of an additional element, including Cr, Si, Zn, Ag, Au, Al and Cu, have been alloyed with the eutectic Sn-Bi composition to find an effective inhibitor additive that can achieve a strong IMC diffusion barrier. IMCs and their growth rates, as well as the consumption rates of the three contact metallizations in contact with the molten solders, were investigated. Storage temperatures of 200°C and 240°C were used, with storage times ranging between two hours and one month. Results to date show that suitable additives can significantly reduce IMC growth rates for both the Ni(P)-Au and Cu contact metallizations, while no appreciable IMC growth is observed for Ti-W in contact with both the original and the various alloyed Sn-Bi based solders. Based on the current results, criteria to further assist the design of feasible molten liquid solder – contact metallization systems have been deduced

Visualization 2.mp4

Stable spectrum operation of coexistence of dissipative soliton and stretched pulse with fixed pump strength

Visualization 1.mp4

Self-start evolution of coexistence of dissipative soliton and stretched pulse as pump stretgth increases

Effects of cation charges on the binding of stabilizers with human telomere and TERRA G-quadruplexes

<p>Both telomere and telomeric repeat-containing RNAs (TERRA) can fold into G-quadruplexes (G4) in eukaryotic cells. Given their key roles in the regulation of telomere length and translation, telomere and TERRA G4 are interesting targets of novel drug development strategies. It is known that the cation charge of a stabilizer is crucial to the binding of G4 and stabilizer. However, the quantitative relationship between the cation charge of a stabilizer and the binding strengths with telomere and TERRA G4 remain unclear. In the current study, by substituting positive charged TMPyP4 with neutral and negative charged groups, the effects of cation charges on the binding conformation and binding strength of porphyrin stabilizers are investigated via molecular docking and molecular dynamic (MD) simulations. The results show that all TMPyP4 analogs form stable binding complexes with telomere and TERRA G4 and that, stabilizer charges have limited effects on binding conformation and can hardly lead to any special conformational alternations of G4. Our hydrogen bond analysis shows that all stabilizers can hardly form stable intermolecular hydrogen bonds with G4. Regarding binding strength levels, a linear correlation is found between the binding free energies and cation charges of stabilizers in all G4‒stabilizer complexes, revealing the pivotal role of electrostatic interactions. The present work is the first to reveal a quantitative correlation between the charges and binding strengths of stabilizers in their binding with human telomere and TERRA G4, which will prove pivotal for G4 targeted drug design and development.</p

Selective Silylation of Nitriles with an NHC-Stabilized Silylene to 1,2-Disilylimines and Subsequent Synthesis of Silaaziridines

The highly regioselective synthesis of <i>trans</i>-1,2-disilylimines have been achieved by the bis-silylation of nitriles with the NHC-stabilized silylene NHC-Si­(NArSiMe₃)Cl (<b>1</b>; Ar = 2,6-<i>i</i>Pr₂C₆H₃, NHC = 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene). The bis-silylation involves the migration of the SiMe₃ group on the nitrogen atom in the silylene to the carbon atom of the nitrile functionality. The 1,2-disilylimine products feature an NHC-stabilized silaimine moiety and could undergo nucleophilic attack by phenyllithium reagents to yield novel silaaziridines with an NHC-stabilized exocyclic SiN double bond

Axial Mn–C_CN Bonds of Cyano Manganese(II) Porphyrin Complexes: Flexible and Weak?

Three five-coordinate high-spin (cyano)­manganese­(II) complexes, utilized tetraphenylporphyrin (TPP), tetratolylporphyrin (TTP), and tetramesitylporphyrin (TMP) as ligands, are prepared and studied by single-crystal X-ray, FT-IR, UV–vis, and EPR spectroscopies. The crystal structure studies revealed noteworthy structural features including unexpectedly wide tilting angles of the axial Mn–C_CN bonds, which is contrasted to the isoelectronic Fe­(III)–C_CN bonds. Solid-state EPR measurements (90 K) and simulations are applied to obtain the ZFS parameters (<i>D</i>, <i>E</i>, and <i>E</i>/<i>D</i> (λ)), which are compared to Mn­(II) porphyrin analogues of hemes to understand the ligand field of the cyanide. The solution EPR studies gave new insights into the chemical equilibrium of four- and five-coordinate species, which has been monitored by UV–vis spectroscopy

Synthesis of 1,2-Borazaronaphthalenes from Imines by Base-Promoted Borylation of C–H bond

A new route from benzylic imines permits the synthesis of 1,2-borazaronaphthalenes in good yields. The reaction involves formation of the enamidyl dibromoborane, which undergoes base-promoted borylation of the nearby aromatic C–H bond. Electrophilic attack of the boron species onto the benzylic arene is supported by the slow borylation of arenes substituted with electron-withdrawing groups. The resultant boron bromides can be easily substituted with lithium reagents to provide a range of products. The electronic properties of these 1,2-borazaronaphthalene derivatives have been investigated by UV–vis and fluorescence spectroscopy

Cyclopentadienyl Yttrium Ene-Diamido Complexes: Coupling of the Ene-Diamido Ligand with Isocyanate

The yttrium ene-diamido complexes supported by Cp (C₅H₅) and Cp* (C₅Me₅) ligands have been synthesized and characterized. The reactions of the Cp* derivative with the isocyanate ArNCO (Ar = 2,6-<i>i</i>Pr₂C₆H₃) led to the C–C coupling of the ene-diamido ligand with ArNCO, while reaction of the Cp derivative resulted in not only the same C–C coupling but also the C–N coupling of the C–C coupling product with another molecule of ArNCO, demonstrating the unique reactivity of ene-diamido ligands in rare-earth chemistry. The products have been characterized by X-ray single-crystal analysis