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|"Green" Nanocomposites for Electronic Packaging|
|Keywords: Green materials, Nanomaterials, Electronic Packaging|
|In recent years significant progress has been achieved in the development of environmentally friendly semiconductor packaging technology using various green materials. This trend is driven by demand for low cost, large area; lead free, halogen free and RoHS compliant devices. For these purposes, Green organic and polymeric materials have been widely pursued since they offer numerous advantages for easy low temperature processing, compatibility with organic substrates, and great opportunities for structural modifications. Nanocomposites provide the greatest potential benefit for high density, high speed, miniaturized electronic packaging. The small dimensions, strength and the remarkable physical and electrical properties of these structures make them a very unique material with a whole range of promising applications. Several Nanocomposites have been reported for advanced packaging applications. Although several nanocomposites are available for the advance of semiconductor packaging technology, the authors believe that there is potential room for improvement of the existing materials, so that low processing temperature, environmentally friendly and cost effective processes/ materials can be developed for large scale production. An effort in this direction is presented in the paper. In this work we report novel green nanocomposites that have the potential to surpass conventional composites to produce materials, structures, manufacturing and circuit applications compatible with laminated organic substrates. Specifically we discuss the electronic applications of green nanocomposites such as adhesives (both conductive and non-conductive), interlayer dielectrics (low-k, low loss dielectrics), embedded passives (capacitors, resistors), circuits, etc. We are also investigating green magnetically active and optically active nanocomposites for fabrication of devices such as inductors, embedded lasers etc. Here we have used halogen free (HF) epoxy as the typical polymer matrix and a range of metal /ceramic fillers with particle size ranging from 10 nm to 10 microns. Addition of different fillers into the polymer matrix controls the overall electrical properties of the composites. For example, addition of zinc oxide nano particles into polymer show laser like behavior upon optical pumping and addition of barium titanate (BaTiO3) nanoparticle results in high capacitance. Halogen free materials having advantages in terms of manufacturability, processing temperatures, low moisture absorption, high Tg, and versatility make it quite promising for advanced packaging. However, homogeneous dispersions of ceramic particles in the polymer matrix is a critical step in order to achieve uniform property films. Green Nanocomposites were processed on Cu substrate by coating processes. The content of metal/ceramic filler in the composites ranged from 40% to 90% by weight, depending on the application. The effects of polymer, particle size, and loading parameters on the observed electrical performance are presented. Network, Impedance Analyzer and a Keithley micro-ohmmeter were used for electrical characterization. 90 degree peel and tensile strength were measured using an Instron (Model 1122) and MTS tensile tester, respectively. Rheology and CTE of materials with different loading was measured using a MELVERN C-VOR Rheometer and Q400 TMA, respectively. Heat of reaction of nanocomposites was studied using a differential scanning calorimeter (DSC). Nanocomposites can provide high capacitance densities, ranging from 10nF/inch2 to 50 nF/inch2, depending on composition, particle size and thickness of the coating. Polymer mixed with ceramics can also produce low loss and low k dielectrics. The electrical properties of nanocomposites fabricated from silica/glass/zinc borate showed a stable dielectric constant over a wide frequency ranging from 100 MHz to 5000 MHz. Composites also show low coefficient of thermal expansion (26-30 ppm/ °C). A variety of discrete resistors with different sheet resistances have been fabricated. Low resistivity nanocomposites with volume resistivity in the range of 10-4 ohm-cm to 10-6 ohm-cm depending on composition, particle size, and loading can be used as conductive joints for high frequency and high density interconnect applications. Similarly, highly resistive nanocomposites such as copper filled halogen free materials can be used as non-conducting hole fill materials. Reliability of the nanocomposites will be ascertained by IR-reflow, thermal cycling, pressure cooker test (PCT), and solder shock.|
|Mark D. Poliks , R&D Director
Endicott Interconnect Technologies,Inc.