Rao Tummala

Bio: Rao Tummala is an academic researcher from Georgia Institute of Technology. The author has contributed to research in topics: Interposer & Capacitor. The author has an hindex of 43, co-authored 623 publications receiving 11663 citations. Previous affiliations of Rao Tummala include Qualcomm & IBM.

Japan's electronic packaging technologies

Abstract: The JTEC panel found Japan to have significant leadership over the United States in the strategic area of electronic packaging. Many technologies and products once considered the 'heart and soul' of U.S. industry have been lost over the past decades to Japan and other Asian countries. The loss of consumer electronics technologies and products is the most notable of these losses, because electronics is the United States' largest employment sector and is critical for growth businesses in consumer products, computers, automobiles, aerospace, and telecommunications. In the past there was a distinction between consumer and industrial product technologies. While Japan concentrated on the consumer market, the United States dominated the industrial sector. No such distinction is anticipated in the future; the consumer-oriented technologies Japan has dominated are expected to characterize both domains. The future of U.S. competitiveness will, therefore, depend on the ability of the United States to rebuild its technological capabilities in the area of portable electronic packaging.

Multilayered Ferromagnetic Polymer Composite Structures for High-Density Power Inductors

Abstract: This paper presents the modeling, design, processing, and characterization of a new class of multilayered ferromagnetic polymer composite structures for high-density power inductor applications. The multilayered composite structures comprise high-permeability, high saturation magnetization ( $M_{s} > 0.5$ T), and low-coercivity magnetic layers stacked with ultra-thin polymer adhesives. The adhesive acts as an an insulating layer to reduce eddy current losses while also enabling high permeabilities at higher operating frequencies. Fundamental material models were used to design the composite structures to achieve a permeability of above 500 in the frequency range of 1–10 MHz. A new adhesive coating and layering process was developed to achieve thicker composite structures in a single lamination step for increasing the inductance density and power handling. The frequency-dependent effective permeability of the composite structure was estimated from the measurement and analysis of $S_{11}$ parameters from a shorted strip transmission line using a vector network analyzer. The fabricated composite structures showed a permeability of $\sim 500$ , saturation magnetization of 0.6 T, and a coercivity of 4.4 Oe at 10 MHz. Such composite structures with excellent magnetic properties can be used to design power inductors in the 1–10-MHz frequency range.

Solder paste wicking in socketable BGAs

Abstract: The trend of the electronics industry to miniaturize package design has caused the need to adopt BGA packages for a variety of applications. OEM microprocessors have conventionally used LGA designs...

An automated workcell for meniscus coating on 24-in packaging substrates

Abstract: Improved coating procedures are essential to the success of low-cost large substrate multichip module (MCM) fabrication, as existing coaters are slow and waste too much material. New coaters are needed that are able to coat large area substrates and have sufficient throughput and material savings to substantially reduce the manufacturing costs. The requirements for a large substrate coater include sufficient flexibility to coat a wide range of materials at various film thicknesses. This paper describes a meniscus coating workcell that meets these requirements. The complete coating workcell includes robotic material handling, automated sample transport, and convection drying of coated films. In-situ viscosity monitoring and in-line thickness measurements can be retrofitted into this workcell. Feasibility of a thin and uniform polymer coating with thickness on the order of a micrometer is demonstrated on a 24/spl times/24 in glass substrate using the automated coating operation. Preliminary study indicates that a throughput of /spl sim/20 substrates/h is achievable by optimizing the turnaround time of the coater heads, substrate holder, and substrate loading/unloading by the robot.

Lead-Free Solder Films Via Novel Solution Synthesis Routes

Abstract: We report two novel routes, sol-gel and electroless plating, for the synthesis of lead-free solders. Novel processes with these routes were developed and demonstrated for Sn-Ag-Cu, Sn-Ag systems to achieve thin bonding layers for assembly of fine pitch integrated circuits onto substrates. Sol-gel route can be used to accurately control the final alloy composition and incorporate additives leading to the designed thermomechanical properties. In this process, the inorganic polymer solutions were spin coated and then heat-treated in a reducing atmosphere to form thin films of lead-free solders. The presence of Ag and Cu enabled easy reduction of tin oxide to tin at 400degC that was not possible with Sn precursor. With the alternate solution reduction (electroless plating) approach, bonding layers can be deposited at almost room temperatures directly on organic substrates. With this approach, the deposition selectively occurs on the metal bonding pads, which eliminates the need for any lithography. Using this approach, electroless Sn-Ag films were demonstrated on organic laminates. These thin film synthesis routes can enable short interconnections that are critical for high density, high frequency, and embedded active component packaging.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

Microfibre–nanowire hybrid structure for energy scavenging

Abstract: Nanodevices don't use much energy, and if the little they do need can be scavenged from vibrations associated with foot steps, heart beats, noises and air flow, a whole range of applications in personal electronics, sensing and defence technologies opens up. Energy gathering of that type requires a technology that works at low frequency range (below 10 Hz), ideally based on soft, flexible materials. A group working at Georgia Institute of Technology has now come up with a system that converts low-frequency vibration/friction energy into electricity using piezoelectric zinc oxide nanowires grown radially around textile fibres. By entangling two fibres and brushing their associated nanowires together, mechanical energy is converted into electricity via a coupled piezoelectric-semiconductor process. This work shows a potential method for creating fabrics which scavenge energy from light winds and body movement. A self-powering nanosystem that harvests its operating energy from the environment is an attractive proposition for sensing, personal electronics and defence technologies1. This is in principle feasible for nanodevices owing to their extremely low power consumption2,3,4,5. Solar, thermal and mechanical (wind, friction, body movement) energies are common and may be scavenged from the environment, but the type of energy source to be chosen has to be decided on the basis of specific applications. Military sensing/surveillance node placement, for example, may involve difficult-to-reach locations, may need to be hidden, and may be in environments that are dusty, rainy, dark and/or in deep forest. In a moving vehicle or aeroplane, harvesting energy from a rotating tyre or wind blowing on the body is a possible choice to power wireless devices implanted in the surface of the vehicle. Nanowire nanogenerators built on hard substrates were demonstrated for harvesting local mechanical energy produced by high-frequency ultrasonic waves6,7. To harvest the energy from vibration or disturbance originating from footsteps, heartbeats, ambient noise and air flow, it is important to explore innovative technologies that work at low frequencies (such as <10 Hz) and that are based on flexible soft materials. Here we present a simple, low-cost approach that converts low-frequency vibration/friction energy into electricity using piezoelectric zinc oxide nanowires grown radially around textile fibres. By entangling two fibres and brushing the nanowires rooted on them with respect to each other, mechanical energy is converted into electricity owing to a coupled piezoelectric–semiconductor process8,9. This work establishes a methodology for scavenging light-wind energy and body-movement energy using fabrics.

Self-powered nanowire devices.

Abstract: The lateral and vertical integration of ZnO piezoelectric nanowires allows for voltage and power outputs sufficient to power nanowire-based sensors.