Daniel R. Gamota

Fine-line conductor manufacturing using drop-on demand PZT printing technology

An emerging selective metallization process to fabricate fine-line conductors based on drop-on-demand (DOD) ink jet printing and novel nano-particle fluid suspensions (NPFS) was studied. The suspensions consist of 1-10 nm silver or gold particulates that are homogeneously suspended in an organic carrier. A piezo-electric droplet generator driven by a bipolar voltage signal is used to dispense 50-70 /spl mu/m diameter droplets traveling at 1-3 m/s before impacting a compliant polyimide substrate. The deposit/substrate composite is subsequently processed at 300/spl deg/C for 15 min to allow for complete evaporation of the carrier and for sintering of the nano-particles, thereby yielding a finished circuit interconnect. Test vehicles created using this technique exhibit features as fine as 120 /spl mu/m wide and 1 /spl mu/m thick with resistivities on the order of 3.5/spl times/10/sup -5/ /spl Omega/cm. The circuitry performed well under environmental conditioning. As expected, repeatability of circuitry fabrication showed sensitivity to the generation of steady, satellite-free droplets. In an effort to generate droplets consistently, it is essential to develop a strong fundamental understanding of the correlation between device excitation parameters and dispensed fluid properties, and to resolve the microrheological behavior of the NPFS when flowing through the droplet generator.

Printed Organic Semiconducting Devices

Recent improvements in carrier mobility, environmental stability, and advancements in p- and n-type organic semiconductor materials have resulted in reports of device operation suitable for low-functionality, low-cost products. Deposition of solution-processable materials that enable the use of low-cost, high-speed deposition techniques such as screen printing, spin coating, and conventional graphic arts printing technologies have also recently been demonstrated. The material requirements necessary to realize these products, an organic transistor device structure that can be fabricated with these materials via printing processes, and the resulting device performance are presented and discussed. The use of standards and their impact on driving technology to commercialization are also addressed.

INK JET PROCESSING OF METALLIC NANOPARTICLE SUSPENSIONS FOR ELECTRONIC CIRCUITRY FABRICATION

A solution-processable approach in creating gold circuit electrodes with features as fine as 100 μm is demonstrated, using a piezoelectrically driven printhead to deposit metallic nanoparticle suspensions. The suspensions consist of gold particles ranging 5–20 nm in diameter suspended in a toluene solvent. The amount of gold nanoparticles present in the suspensions ranges between 30 to 50% by weight. Inductor and capacitor electrode patterns are deposited onto a glass substrate and thermally processed to drive off the solvent and allow the nanoparticles to coalesce/sinter, thereby yielding a conductive path with an electrical resistivity of O(10−7) Ωm.

The development of reflowable materials systems to integrate the reflow and underfill dispensing processes for DCA/FCOB assembly

Unique materials systems with sufficient fluxing activities to remove the metal oxides on the die and/or substrate bumps and assist in the formation of metallurgical interconnects were developed for the assembly of flip chip on board (FCOB). This materials system is referred to as a reflowable underfill. The experimental process flow was as follows: a finite volume of reflowable underfill was dispensed on the printed circuit board (PCB) at the die site, the die was aligned over the bond pads, and the die was placed into the material. Next, the FCOB assembly was transferred to a reflow furnace and subjected to a standard surface mount technology (SMT) eutectic Pb/Sn reflow profile, the solder was reflowed, interconnects were formed between the die and PCB, and the reflowable underfill was partially cured. The built FCOB assemblies were placed in liquid to liquid thermal shock and air to air temperature cycling. The assembly yields varied and continued development of systems with increased flux activity are warranted for the acceptance of this FCOB assembling technology. Promising accelerated life testing (ALT) results were obtained warranting further evaluation of the reflowable materials systems and process.

Analysis and surface energy estimation of various model polymeric surfaces using contact angle hysteresis

Wetting of hydrophobic polymer surfaces commonly employed in electronic coatings and their interaction with surfactant-laden liquids and aqueous polymer solutions are analyzed using a contact angle hysteresis (CAH) approach developed by Chibowski and co-workers. In addition, a number of low surface tension acrylic monomer liquids, as well as common probe liquids are used to estimate solid surface energy of the coatings in order to facilitate a thorough analysis of surfactant effects in adhesion. Extensive literature data on contact angle hysteresis of surfactant-laden liquids on polymeric surfaces are available and are used here to estimate solid surface energy for further understanding and comparisons with the present experimental data. In certain cases, adhesion tension plots are utilized to interpret wetting of surfaces by surfactant and polymer solutions. Wetting of an ultra-hydrophobic surface with surfactant-laden liquids is also analyzed using the contact angle hysteresis method. Finally, a detailed analysis of the effect of probe liquid molecular structure on contact angle hysteresis is given using the detailed experiments of Timmons and Zisman on a hydrophobic self-assembled monolayer (SAM) surface. Hydrophobic surfaces used in the present experiments include an acetal resin [poly(oxymethylene), POM] surface, and silane, siloxane and fluoro-acrylic coatings. Model surfaces relevant to the literature data include paraffin wax, poly(methyl methacrylate) and a nano-textured surface. Based on the results, it is suggested that for practical coating applications in which surfactant-laden and acrylic formulations are considered, a preliminary evaluation and analysis of solid surface energy can be made using surfactant-laden probe liquids to tailor and ascertain the quality of the final coating.

Anticipatory Standards and the Commercialization of Nanotechnology

Standardization will play an increasing role in creating a smooth transition from the laboratory to the marketplace as products based on nanotechnology are developed and move into broad use. Traditionally, standards have evolved out of a need to achieve interoperability among existing products, create order in markets, simplify production and ensure safety. This view does not account for the escalating trend in standardization, especially in emerging technology sectors, in which standards working groups anticipate the evolution of a technology and facilitate its rapid development and entrée to the market place. It is important that the nanotechnology community views standards as a vital tool to promote progress along the nanotechnology value chain – from nanoscale materials that form the building blocks for components and devices to the integration of these devices into functional systems.This paper describes the need for and benefits derived from developing consensus standards in nanotechnology, and how standards are created. Anticipatory standards can nurture the growth of nanotechnology by drawing on the lessons learned from a standards effort that has and continues to revolutionize the telecommunications industry. Also, a brief review is presented on current efforts in the US to create nanotechnology standards.

Encapsulant materials systems for flip‐chip‐on‐board assemblies: addressing manufacturing issues

Encapsulant materials for flip‐chip‐on‐board (FCOB) were developed to address issues that have been observed during assembly of consumer electronic products on a high volume manufacturing FCOB/SMT line. The viscosity, surface tension, and filler particle sizes of several encapsulants were studied in an attempt to correlate these properties to their recorded underfill times and to observe their flow properties under the gap. Materials characterization studies were performed to determine their glass transition temperatures (Tg), tensile elastic and loss moduli (E′ and E′′), coefficients of thermal expansion (CTE), and apparent strengths of adhesion (ASA). In addition, reliability tests were conducted, and several promising materials were identified. The ASA of the encapsulant to the die passivation and the printed circuit board (PCB) is critical to the robustness of the assembly. Studies were conducted to observe the ASA as a function of FCOB assembly conditioning prior to underfilling and the degradation o...

Evolutionary Path Planning With Subpath Constraints

We develop an evolutionary method of planning paths that are subject to subpath constraints. These constraints can include subpaths that must be incorporated into the solution path, path intersection restrictions, and obstacle avoidance. Our method involves two stages. In the first stage, a global solution is found without consideration of any obstacles. In the second stage, local planning is performed to modify the global path to avoid obstacles. Stage one involves a fixed-length chromosome formulation of a genetic algorithm that utilizes existing operators and a new subpath reversal operator. Stage two involves a graph search process. Our algorithm is applicable to the field of printed electronics where continuous-spray processes are used to deposit electrically functional material onto flexible substrates. These processes give rise to the kinds of subpath constraints we have investigated. We evaluate our algorithm by applying it to a representative problem in the printed electronics field.

Ink Jet Processing of Metallic Nanoparticle Suspensions for Electronic Circuitry Fabrication

A novel approach in creating circuit electrodes with features as fine as 100 μm is demonstrated using a single 38 μm diameter orifice, piezoelectrically driven print head to deposit metallic nanoparticle suspensions. The suspensions consist of gold particles of ∼20 nm diameter suspended in toluene solvent. The amount of gold nanoparticles present in the suspension is 30% wt. Inductor and capacitor electrode patterns are deposited onto a glass substrate and thermally processed at 300°C for 15 minutes to drive off the solvent and allow the nanoparticles to sinter, thereby yielding a conductive path with a resistivity of O(10−7 ) Ω m.Copyright

Use of Contact Angle Hysteresis in Estimating Thin Polymer Film Surface Energy and Wettability

A recent surface energy estimation method [1] interpreting contact angle hysteresis measurements was used to estimate surface energy of various commercially important polymer films including UV radiation cross-linked acrylic based monomer systems. The validity of the method was tested on highly hydrophobic non-polar amorphous fluoro-polymers using a number of polar and low surface tension liquids. Contact angle hysteresis was present on these surfaces even though surface morphology of the solution processed fluoro-polymers is close to ideal. Estimated surface energies using such probe liquids were consistent varying slightly with the probe liquid type. On such highly ordered and non-polar polymer surfaces use of polar and low surface tension liquids results in accurate surface energy estimation. However, use of polar probe liquids commonly employed in surface energy estimation methods, such as, Harmonic mean (HM), Geometric mean (GM) or Lewis Acid-Base method (LWAB) on polar surfaces such as polyester resulted in inconsistent surface energy values. To strengthen this observation, the ASTM surface energy estimation procedure (ASTM D2578 04a) developed for polyethylene and polypropylene surfaces (both non-polar) was employed on a sample polar polyester surface using the ASTM probe liquids. Results showed inconsistent surface energy values supporting the conclusion that care must be exercised during use of polar probe liquids in estimating surface energy on polar polymers with the contact angle hysteresis method. Finally, UV radiation cross-linkable acrylic polymer surface energies were estimated with the hysteresis method. Surface energy results were consistent based on five different probe liquids. It was observed that surface energy of the cross-linked monomer networks decreased slightly with increasing UV curing time.Copyright