Sintered thermoelectric (TE) nanoparticle films are known to have a high figure-of-merit ZT factor and are considered for waste hear recovery and heating and cooling applications. The conventional process of thermal sintering of TE nanoparticles requires an inert environment and long heating times, and cannot be used on polymer substrates due to the requirements of the process (e.g., heating up to 400 C). In this communication, the authors demonstrate for the first time the use of an intense flash of UV light from a Xenon lamp to sinter TE nanoparticles within milliseconds under ambient conditions on flexible polymer as well as glass substrates to create functional TE films. Photonic sintering is used to fabricate Bismuth Telluride thermoelectric films with a conductivity of 3200 S m À1 (a 5-6 orders of magnitude increase over unsintered films) and a peak power factor of 30 mW m À1 K À2 . Modeling is used to gain an insight into the physical processes occurring during photonic sintering process and identify the critical parameters controlling the process. This work opens-up an exciting possibility of extremely rapid fabrication of TE generators under ambient conditions on a variety of flexible and rigid substrates.Thermoelectric generators based on the Seebeck effect have shown a great promise for waste heat recovery in diverse applications such as automotive engines, power plants, and microelectronics. [1] Thermoelectric devices have also been considered for heating and cooling applications. [2] The efficiency of thermoelectric materials is determined by the figure-of-merit ZT which is defined by ZT ¼ α 2 σT/κ, where α, σ, κ, and Tare Seebeck coefficient, electrical conductivity, thermal conductivity, and absolute temperature, respectively. The ZT factor of TE generators can be significantly enhanced by making nanostructured TE materials using nanoparticles due to the reduction in lattice thermal conductivity. [3] High performance TE films have been demonstrated by printing nanoparticles followed by thermal sintering at around 400 C in an inert environment. [4] However, the conventional sintering methods such as thermal sintering in a furnace suffer from two major limitations. First, the process of thermal sintering can take several hours per batch and is unsuitable for rapid fabrication methods such as roll-to-roll manufacturing [5] of TE generators. Second, the conventional thermal sintering exposes both the printed film and substrate to high temperatures, which limits the type of substrate that can be used to form the films.To overcome these challenges, we demonstrate in this work the use of photonic sintering method [6,7] to create TE films from Bismuth Telluride-based nanoparticles where sintering/densification is achieved over large areas (several square inches), in extremely short periods of time (milliseconds per pulse) and using a rigid glass as well as flexible polymer substrate. Due to the high speed of sintering, this method is highly compatible with rapid roll-to-roll manufacturing of low-cost
The development of micro lens arrays has garnered much interest due to increased demand of miniaturized systems. Traditional methods for manufacturing micro lens arrays have several shortcomings. For example, they require expensive facilities and long lead time, and traditional lens materials (i.e. glass) are typically heavy, costly and difficult to manufacture. In this paper, we explore a method for manufacturing a polydimethylsiloxane (PDMS) micro lens array using a simple spin coating technique. The micro lens array, formed under an interfacial tension dominated system, and the influence of material properties and process parameters on the fabricated lens shape are examined. The lenses fabricated using this method show comparable optical properties-including surface finish and image quality-with a reduced cost and manufacturing lead time.
Nowadays microelectronic packaging has become a billion dollar business. Due to the increased material and production costs per package, manufacturing yield loss in this state-of-art business is expected to be at a bare minimum which is tough to persevere in a high volume manufacturing environment. Additionally, high performance and varied power computing needs in the electronic business demands microprocessors with different form factors and complex package designs. One of the most common joint which is extensively used in such a complicated package is the polymer to metal bonding. In the latest technology products involving high package warpage, interfacial bonding has to be strong enough to withstand the dynamic warpage and high mechanical stresses associated with it and hence the reliability of polymer to metal adhesion is critical. In this paper, fundamental mechanisms related to adhesion phenomena of polymer-metal interface are proposed. Adhesive failure modes related to polymer-metal bonding and key variables influencing the bonding of silicone based polymer material to nickel electroplated on copper in an integrated circuit heat spreader assembly are experimentally studied. Factors modulating polymer to metal bonding including interfacial chemistry, surface contamination and material roughness are evaluated.
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