Timothy J. Singler

High-resolution inkjet printing of electrically conducting lines of silver nanoparticles by edge-enhanced twin-line deposition

We report a process for inkjet printing electrically continuous micron-wide lines of silver nanoparticles by exploiting edge-enhanced evaporation commonly associated with the coffee-stain effect. In situ and real-time flow observation confirmed preferential nanoparticle deposition at the contact line of printed rivulets. The resulting twin-pair of parallel continuous lines showed characteristic width (2–8 μm), height (100–300 nm), and pair spacing (100–600 μm) that depended on substrate and printing conditions in a theoretically predictable way. Thermally sintered lines were used to form rectilinear grids showing ∼5 Ω/◻ effective sheet resistance. The robustness of the deposition process was investigated, and line pathologies were found to depend on substrate surface wettability.

Electroless Copper Plating of Inkjet-Printed Polydopamine Nanoparticles: a Facile Method to Fabricate Highly Conductive Patterns at Near Room Temperature

Aqueous dispersions of artificially synthesized, mussel-inspired poly(dopamine) nanoparticles were inkjet printed on flexible polyethylene terephthalate (PET) substrates. Narrow line patterns (4 μm in width) of poly(dopamine) resulted due to evaporatively driven transport (coffee ring effect). The printed patterns were metallized via a site-selective Cu electroless plating process at a controlled temperature (30 °C) for varied bath times. The lowest electrical resistivity value of the plated Cu lines was about 6 times greater than the bulk resistivity of Cu. This process presents an industrially viable way to fabricate Cu conductive fine patterns for flexible electronics at low temperature, low cost, and without need of sophisticated equipment.

Reactive wetting in metal–metal systems

Wetting and spreading in high temperature reactive metal-metal systems is of significant importance in many joining processes. An overview of reactive wetting is presented outlining the principal differences between inert and reactive wetting. New experimental evidence is presented that identifies an early time regime in reactive wetting in which spreading occurs without macroscopic morphological change of the solid-liquid interface. This regime precedes the heavily studied reactive wetting regime. Additional new experimental evidence is presented of kinetic roughening in a high temperature reactive system. Quantitative characterization of this roughening reveals similarities with room temperature systems. These new data provide evidence that supports the existence of several sequential time regimes in the reactive wetting process in which different physicochemical phenomena are dominant.

Highly conductive lines by plasma-induced conversion of inkjet-printed silver nitrate traces

We report a rapid process of argon plasma conversion of inkjet printed lines of silver nitrate to yield final electrical resistivities comparable to that of bulk silver. The plasma processing produces a layer of silver with electrical and thickness properties dependent on plasma power and process time. Final line morphology is shown to be determined by the evaporatively driven process of silver nitrate crystallization during printing. This technique holds significant potential for rapid and low-cost additive fabrication of metallization patterns for electronic circuits.

A hybrid perturbation–Galerkin solution to a problem in selective withdrawal

A model of selective withdrawal is considered in which a source is located above a gas–liquid interface in a gravitational field. The effects of surface tension are included, and the flow is assumed to be incompressible, inviscid, and irrotational. A perturbation solution is obtained for both the interfacial position and the velocity potential, and then improved using a Galerkin technique. The distortion of the interface by the source is found to be localized and nonmonotonic, and weakly modified by surface tension. An estimate for the stability of the interface is derived from the perturbation solution for the case of zero surface tension.

Uniform asymptotic solutions for small and large sessile drops

SummaryThe problem of determining the equilibrium shape of either a small or large sessile drop is studied. By the correspondence principle, the problem of approximating the static meniscus in a vertical right circular cylinder is also solved. A parameter ε is introduced which is ratio of the physical length scale to the capillary length scale. Perturbation solutions, which are uniformly valid over the entire surface of the drop, are obtained for either small or large values of ε using the method of successive substitutions. Comparisons of the results with solutions obtained by other approximate methods are presented and discussed. The solutions for small and large values of ε are then combined using an ad hoc, but straightforward, technique, resulting in an approximate solution which is valid for all positive values of the parameter ε.

Effect of solder joint geometry on the predicted fatigue life of BGA solder joints

A general computational approach to determine the effect of solder joint shape on the fatigue life is presented. Using the integrated matrix creep failure metric, a number of cases are considered wherein the solder volume, standoff height, or both, are varied and the joint life computed. Both volumetric and interface averaging of the matrix creep are considered. For non-mask defined pads, the greater the solder volume, the higher the life; for mask defined pads, the reverse trend was observed.

Transport processes associated with inkjet printing of colloidal drops for printable electronics fabrication

This paper presents an experimental investigation of deposition dynamics of inkjet-printed colloidal drops on glass and PET substrates. Using fluorescent particles and confocal microscopy, the evaporatively-driven and thermal Marangoni flows inside a colloidal drop, as well as the particle self-assembly and deposition on the substrate are directly observed. In addition, Ar plasma treatment is used to modify the substrate surfaces. Wetting properties (i.e., advancing /receding contact angle and contact angle hysteresis) of colloidal drops on different substrates, substrate surface roughness, and final particle deposition morphologies are characterized using goniometer, AFM, and SEM. A correlation between the substrate surface roughness, static receding contact angle, contact line pinning/de-wetting, and final particle deposition morphology is explored. This study seeks to provide design guidelines for substrate surfaces that will improve the resolution and edge definition of printable electronics fabrication.

AN EXAMINATION OF FLOW REGIMES ASSOCIATED WITH INKJET - PRINTED COLLOIDAL DROPS

An experimental study of the evaporation dynamics for an inkjet-printed drop on a solid substrate has been attempted. Using fluorescent spherical colloids, the internal flow of an evaporating drop has been observed directly. During the initial stages of the process, a novel inward radial flow carries the particles as a single group towards the center of the drop. Once the particles have converged near the center, a significantly slower outward radial flow proceeds. These flow regimes are qualitatively analyzed and their relationship to a possible thermal Marangoni flow is discussed.Copyright

The Wetting of Metallic Substrates by Low Melting Point Alloys

The behavior of Sn (liquid) spreading on Au (solid) was evaluated experimentally using the sessile drop technique. The experiments performed over a temperature range of 250 to 428 °C. At 250 °C, spreading results were compared with those from the Bi-Sn and Cu-Sn systems. In the temperature range 290 < T < 413 ° C, the Au-Sn system exhibits rapid spreading and rapid formation of a transient solid phase which eventually re-liquefies.