Recent Advances in Oxide Glass Fiber Science
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Recent Advances in Oxide Glass Fiber Science Ernest L. Lawton1, Frederick T. Wallenberger2, and Hong Li2 PPG Industries, Fiber Glass Science and Technology 1 ESM Science and Technology Center Lexington, NC 27293-0949, U.S.A. 2 Fundamental Science and Technology, Glass Technology Center Pittsburgh, PA 15230-2844, U.S.A.
ABSTRACT The predominate substrate for multilayer printed wiring boards is laminate constructed from epoxy resin reinforced with fiber glass fabrics. This combination of materials dominates the segment of the electronics market where dimensional stability of the substrate is critical. The rapid development of high speed digital and analog electronic systems has challenged the predominance of fiber glass as the reinforcement of choice. As systems move to the GHz frequency range, there is a need for lower dielectric constant of the substrate to insure integrity and speed of signals. A lower dissipation factor of the substrate is desired for the wireless communication applications of printed wiring boards. A review is presented of materials competing as substrates for the high speed application of the printed wiring board market. INTRODUCTION The printed wiring board (PWB) is the platform for mounting electronic components such as integrated circuit chips and for interconnecting components. Printed wiring board technology originated in the mid-1930’s. The use of a laminated composite of fiber glass fabric and epoxy resin emerged in the 1950’s and has grown to the predominate substrate for mounting and interconnecting the complex electronic components used in computers and a host of electronic applications. In this context, the present paper bridges recent advances in the disciplines of inorganic fibers [1], composite reinforcing fibers [2, 3], and fiber glass reinforcements [4]. BACKGROUND Fiber glass fabrics, as a reinforcement, has a dominant position in the PWB applications. Several key characteristics of fiber glass attribute to its commercial successes. First of all, oxide fiber glasses are good electrical insulators under normal operation conditions for PWB applications. They have dielectric properties, dielectric constant and dissipation factor, compatible with PWB operating frequencies into the lower GHz range, plus the glass dielectric strength exceeding the PWB application need. The specific modulus and strength of fiber glass provide adequate mechanical stability or reinforcement to resin component of laminates. Because of its very low thermal expansion coefficient, the use of fiber fabrics significantly retards thermal expansion of the laminates during processing, which in turn insure a consistency of product quality due to predictability of laminate dimensional change due to thermal expansion. Fiber glass is nonflammable and U5.2.1
resistant to corrosion of the chemicals used in processing PWB. Low moisture absorption by fiber glass is another attractive property for PWB processing and uses. Fiber glass fabrics are available in thickness from 0.024 to 0.20 mm, which provide flexibility in
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