10 research outputs found
Silver oxalate-based solders: New materials for high thermal conductivity microjoining
Micrometric oxalate powders can be decomposed starting from temperatures as low as 90°C, leading to the formation of temporary nanometric grains of metallic silver with a high propensity for sintering. The decomposition being highly exothermic, this additional energy favours the sintering, i.e. the soldering, process. Solders processed at 300°C and very low pressure (<0.5 MPa) displayed a thermal conductivity close to 100 W m-1 K-1, making silver oxalate very promising for safe, moderate temperature and very low pressure bonding
Developing new joining materials for low-temperature electronics assembly
International audienceThe present work focuses on a new kind of lead-free joining method for surface-mount technology based on precursor chemistry. The interest of metal oxalates as new soldering materials for die attachment (1st level packaging) was previously demonstrated with silver oxalate. The thermal decomposition of metal oxalates under controlled atmosphere can be used to produce small metal particles below their melting point. These particles are found to be in a highly active particulate form. First experimental studies are focusing on several metal oxalates (tin oxalate and bismuth oxalate) to assess their suitability for low-temperature metal particle production. The main work is dealing with controlled chemical precipitation synthesis and characterization of the compounds as well as study of the properties of decomposition solid products (powder X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy and thermal analyses under different atmospheres)
Matériaux innovants sans plomb pour l'assemblage de composants électroniques à basse température
Dans le cadre du dĂ©veloppement de nouveaux matĂ©riaux dâassemblage sans plomb, les premiers rĂ©sultats de synthĂšse et de caractĂ©risations physicochimiques dâoxalate de bismuth sont prĂ©sentĂ©s. Par une mĂ©thode de dĂ©composition thermique de prĂ©curseurs mĂ©tal-organiques, la possibilitĂ© de produire des particules mĂ©talliques en dessous de la tempĂ©rature de
fusion du bismuth massif (271°C) est discutĂ©e ici. LâĂ©tude du comportement en tempĂ©rature de lâoxalate de bismuth montre lâinfluence de lâatmosphĂšre (air ou azote) sur la
nature des produits de dĂ©composition (oxyde ou mĂ©tal). Sous une atmosphĂšre inerte contrĂŽlĂ©e, les Ă©chantillons dâoxalate prĂ©parĂ©s se dĂ©composent en bismuth mĂ©tallique entre 210 et 250°C
Bi2(C2O4)3·7H2O and Bi(C2O4)OH Oxalates Thermal Decomposition Revisited. Formation of Nanoparticles with a Lower Melting Point than Bulk Bismuth
Two bismuth oxalates, namely, Bi2(C2O4)3·7H2O and Bi(C2O4)OH, were studied in terms of synthesis, structural characterization, particle morphology, and thermal behavior under several atmospheres. The oxalate powders were produced by chemical precipitation from bismuth nitrate and oxalic acid solutions under controlled pH, then characterized by X-ray diffraction (XRD), temperature-dependent XRD, IR spectroscopy, scanning electron microscopy, and thermogravimetric differential thermal analyses. New results on the thermal decomposition of bismuth oxalates under inert or reducing atmospheres are provided. On heating in nitrogen, both studied compounds decompose into small bismuth particles. Thermal properties of the metallic products were investigated. The Bi(C2O4)OH decomposition leads to a BiâBi2O3 metalâoxide composite product in which bismuth is confined in a nanometric size, due to surface oxidation. The melting point of such bismuth particles is strongly related to their crystallite size. The nanometric bismuth melting has thus been evidenced âŒ40 °C lower than for bulk bismuth. These results should contribute to the development of the oxalate precursor route for low-temperature soldering applications
Paramagnetic behaviour of silver nanoparticles generated by decomposition of silver oxalate
International audienceSilver oxalate Ag2C2O4, was already proposed for soldering applications, due to the formation when it is decomposed by a heat treatment, of highly sinterable silver nanoparticles. When slowly decomposed at low temperature (125 °C), the oxalate leads however to silver nanoparticles isolated from each other. As soon as these nanoparticles are formed, the magnetic susceptibility at room temperature increases from -3.14 10-7 emu.Oe-1.g-1 (silver oxalate) up to -1.92 10-7 emu.Oe-1.g-1 (metallic silver). At the end of the oxalate decomposition, the conventional diamagnetic behaviour of bulk silver, is observed from room temperature to 80 K. A diamagnetic-paramagnetic transition is however revealed below 80 K leading at 2 K, to silver nanoparticles with a positive magnetic susceptibility. This original behaviour, compared to the one of bulk silver, can be ascribed to the nanometric size of the metallic particles
Tuberculosis control in refugee settlements
Tuberculosis and its management in refugees and other displaced persons in temporary settlements poses a challenge to organisations coordinating and providing care in refugee emergencies. This paper offers a consensus of the co-sponsoring agencies on practical recommendations for implementing measures aimed at both interrupting transmission of tuberculosis and treatment of individual patients. © 1989
Bi<sub>2</sub>(C<sub>2</sub>O<sub>4</sub>)<sub>3</sub>·7H<sub>2</sub>O and Bi(C<sub>2</sub>O<sub>4</sub>)OH Oxalates Thermal Decomposition Revisited. Formation of Nanoparticles with a Lower Melting Point than Bulk Bismuth
Two bismuth oxalates,
namely, Bi<sub>2</sub>(C<sub>2</sub>O<sub>4</sub>)<sub>3</sub>·7H<sub>2</sub>O and BiÂ(C<sub>2</sub>O<sub>4</sub>)ÂOH, were studied in terms
of synthesis, structural characterization, particle morphology, and
thermal behavior under several atmospheres. The oxalate powders were
produced by chemical precipitation from bismuth nitrate and oxalic
acid solutions under controlled pH, then characterized by X-ray diffraction
(XRD), temperature-dependent XRD, IR spectroscopy, scanning electron
microscopy, and thermogravimetric differential thermal analyses. New
results on the thermal decomposition of bismuth oxalates under inert
or reducing atmospheres are provided. On heating in nitrogen, both
studied compounds decompose into small bismuth particles. Thermal
properties of the metallic products were investigated. The BiÂ(C<sub>2</sub>O<sub>4</sub>)ÂOH decomposition leads to a BiâBi<sub>2</sub>O<sub>3</sub> metalâoxide composite product in which
bismuth is confined in a nanometric size, due to surface oxidation.
The melting point of such bismuth particles is strongly related to
their crystallite size. The nanometric bismuth melting has thus been
evidenced âŒ40 °C lower than for bulk bismuth. These results
should contribute to the development of the oxalate precursor route
for low-temperature soldering applications