This grant provides funding for a multi-institution, multi-disciplinary project to understand the processing-structure-property relationships of composite nanoheater-joining-material structures. The focus is on joining applications at the microscale level where spatial and temporal control of temperature profiles is important in complex geometries and heterogeneous devices with temperature sensitive parts. This research aims to understand (1) the fabrication of nanoheater composites of nanoheaters and joining materials, including the effect of mixing on proper distribution of heat output; (2) the deposition of the nanoheater-joining material composite onto flexible substrates; (3) the controlled, non-contact ignition of the nanoheaters; and (4) the functionality and reliability of the joining/interconnects. Both metal-based structures and polymer adhesives will be investigated. Fabrication and deposition of the composite joining system will be done by both ultrasonic powder consolidation and printing or direct electrospinning/electrospraying. Ignition experiments and modeling of self-ignition will be conducted. Finally, joint quality and robustness will be characterized.
If successful, this research will enable new ways of joining materials in conventional applications that increase productivity, reduce energy and material usage, lower costs, and broaden the range of products. This research is anticipated to lead to new ways to build microscale devices such as Lab-On-Chips, flexible electronics, micro-optical devices, sensors, medical devices, and energy and information storage devices. The project will also contribute to human resource development (especially women and minorities) and increased public understanding of STEM through collaborations with the Urban Massachusetts Louis Stokes Alliance for Minority Participation (UMLSAMP), local K-12 schools, the Museum of Science, and international partners (University of Cyprus).
The main objective of this collaborative project is to fabricate nanoheater structures and study their processing-structure-property relationships to enable microscale joining applications. Nanoheater structures are fabricated from constituent powders by ultrasonic powder consolidation (UPC), a new rapid powder consolidation technique that can consolidate reactive powder mixtures without causing premature reactions among the reactive constituents in the powder compact. Bimetallic Al-Ni nanoheaters and hybrid bimetallic-thermite 2Al-Fe2O3-x(Al-Ni), 2Al-3CuO-x(Al-Ni) nanoheaters are fabricated from ball-milled nano-thick flakes and commercially available nano-powders of metal oxides. These nanoheater structures possess full potential for reactions among the constituents and can be ignited in a controlled manner to generate defined, localized exotherms. The hybrid bimetallic-thermite 2Al-Fe2O3-x(Al-Ni), 2Al-3CuO-x(Al-Ni) nanoheaters, Figure 1, combine the good ignitability of bimetallic nanoheaters with the high heat output of thermites, Figure 2. These nanoheater structures, in combination with the low melting point solder nanoparticles that have been synthesized at UMass Lowell and consolidated by the UPC method (see Figure 3), provides a promising platform for micro-scale joining with localized and minimum amount of heat. Intellectual Merit: These nanoheaters provide heat sources for joining at the microscale level where spatial and temporal control of temperature profiles is important in complex geometries and heterogeneous devices with temperature sensitive parts. Figure 4 shows a schematic of an experiment to join copper sheets to solder layer using a hybrid nanoheater as the heat source and a cross section of the resultant joint. Figure 5 shows the feasibility of copper-copper (Cu-Cu) joining with the tin/indium (Sn/In) nanosolder particles and the cross-section structure and intermetallic formation. Microscale curing of polymers in which spatial and/or temporal control is required is another area of application. Other advantages of the proposed structures/systems include a fewer processing steps and greater processability, higher material utilization, higher energy efficiency and on-demand heat delivery, and applicability to non-flat surfaces. Broader impact: The outcomes of this research may lead to new ways to build or operate microscale devices such as Lab-On-Chips, micro-optical components, advanced sensors, medical devices, and energy and information storage devices. Student participants (5 graduate students and 5 REU undergraduate students) are trained on various materials fabrication and characterization techniques through the interdisciplinary joint project conducted at the three domestic participating institutions (UMass Lowell, Northeastern University and Tufts University) and an international collaborator – University of Cyprus. The joint project has yielded 7 journal papers (5 published, 2 in preparation), 2 conference papers and 21 conference presentations.
