Manufacture of Microelectronic Circuitry by Drop-on-Demand Dispensing of Nano-particle Liquid Suspensions
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I. INTRODUCTION Over the past 15 years integrated circuit feature dimensions and pitches have seen a dramatic reduction in size. An excellent indicator of this trend is the wireless communications market. Cellular manufacturers are continuously striving to improve capital utilization, reduce downtime associated with changeover and obtain higher yields and output of their products. Recently, interest has increased in the rapid prototyping capabilities of Direct Write Technologies (DWT), propelling the development of a number of candidate deposition systems for the fabrication of micro-electronic components. For example, Bharathan and Yang [11 have successfully created an electro-luminescent device using inkjet technology and light-emitting polymers. In response to this growing interest in DWT, a preliminary investigation has been conducted to determine whether it is possible to use DOD inkjet technology and recent developments in nano-particle suspension technology as a means to fabricate horizontal, fine line circuitry for electronic assemblies. A common method of fabricating fine-line conductor formations or printed wiring boards (PWB) involves the selective metallization of non-conductive substrates using a subtractive etching process [2]. Traditional selective metallization processes use non-conducting substrates that have one or both surfaces electroless-deposited with a metal coat only to have the majority of the deposited metal etched away. Such practice not only wastes material but also generates substantial amounts of chemical pollutants. Furthermore, this method of producing a PWB does not lend itself to rapid translation due to the need of masks and rather lengthy substrate processing steps. An advantage of using DOD inkjet technology in circuit interconnect manufacturing is that the process is additive. Material is only deposited in desired locations, thereby reducing the amount of chemical and material waste. In addition, the ability of DOD to produce entire circuit patterns that are simply drawn using computer graphics software makes it a very powerful rapid prototyping technology. To demonstrate the feasibility of DOD to fabricate fine-line conductors on conformal substrates, two test vehicles having different pattern geometries were created.
23 Mat. Res. Soc. Symp. Proc. Vol. 624 © 2000 Materials Research Society
H. EXPERIMENT A. MaterialSystem One of the major setbacks to using DOD inkjet technology for circuit interconnect fabrication is the stringent requirement of the conductive inks' physicochemical properties [3]. Most commercially available conductive inks possess too high of a viscosity and surface tension to allow droplet formations of micron size. However, recent developments in nano-particle suspension technology have created a new category of low viscosity conductive inks suitable for use with DOD. The particular material used in this study, shown in Figure 1, consists of silver (Ag) nano-particles on the order of 10 nm in diameter. Suspensions containing gold nano-particles have also
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