Lara-Rodríguez, Yareni P.

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    Stability of silver colloid by process control of the synthesis using design of experiments
    (2013) Lara-Rodríguez, Yareni P.; Quintero, Pedro O.; College of Engineering; Valentín, Ricky; Cabrera, Mauricio; Department of Mechanical Engineering; Ramírez Vick, Jaime
    Extensive resources have been utilized to develop SiC (silicon carbide) semiconductor devices, there has been relatively little effort into the development of adequate, environmentally benign electronic packaging materials and methods to provide functional modules that will enable and take full advantage of the capabilities of these SiC devices. A critical requirement for any metallic interconnection within an electronic package is that the joint cannot re-melt during the operation. This condition implies a rule in which the attach material has to be selected as such, that its melting temperature (Tm) must be higher than the application temperature (Ta). Therefore a novel alternative will have to result in a high melting attach material that can be processed at a low enough temperature to avoid excessive residual stresses. An alternative, and possible solution is the use Ag nanoparticles, these particles can be used as an attach material owing to its excellent thermal and electrical properties in addition to its high melting point (962°C). Theoretically the driving force (DF) for the sintering mechanism is a function of the applied pressure (P) and a geometrical factor (K) which is inversely proportional to the particle size (K α 1/s). Increasing the densification rate is crucial in a sintering process, therefore to achieve this densification it is desired to apply a low pressure for the minimum possible time. Thus, to provide a large driving force, without increasing the detrimental externally applied pressure, we proposed to take advantage of the size effect of Ag nanoparticles. In this work a methodology for the manufacture of stable silver nanoparticles (NP´s) was proposed together with a prediction model for these parameters. To reach the aims of this work, Ag nanoparticles were produced by chemical reduction method. During the preparation, reducing agent directly reduced Ag+ ions to generate metallic Ag atoms and the borohydride from NaBH4(reducer agent) were absorbed on the surface of the Ag atoms giving a electrostatic mechanism effect in order to avoid early agglomeration. A factorial design of experiments 23 with three replicates (24 runs) plus a center point with three replicates (27 trials in total) were proposed with the objective to explore the feasible area of elaboration of nanoparticles with stability. The factors were the concentration rate [R=NaBH4/AgNO3](1, 12.5 and 26), stirrer time (50% , 100% and 150%) and temperature (0°C, 7.5 °C and 15°C). The synthesis was elaborated with DI water 17MΩ at room temperature. The size and size slope of the NP´s was characterized via X-ray diffraction (XRD), UV-Vis and DLS. The results showed that was possible to find stabilization in a feasible area of synthesis when the concentration rate (R) was 12.5 and the stirrer time was 100%, in addition, low level of temperature also helped to reach the stabilization of NP´s. The statistical model for the prediction of size and slope of was obtained.