Role of Powder Production Route in Direct Write Applications
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INTRODUCTION Direct write transfer for fabrication of electronic circuits involves making an ink or a paste with powders of a variety of functional materials along with additives and a vehicle. The mixture is then transferred onto a substrate using one of several direct write techniques currently available or in development. Depending on their desired function these powders may vary from metals to oxides and other. The transferred material must consolidate on the substrate to maximize their functional characteristics and must adhere to well to the substrate. Feature Characteristic feature dimensions may vary from submicron to several hundred microns. The functions required from powders may range from dielectric properties, resistors, inductors, and capacitors to solid electrolytes for active energy supply. Most of the materials to satisfy these needs are single and multicomponent oxides, metals and alloys. Because of the small feature size, particle size is limited to less than 2-3 Rtm. The powder has to be well dispersed and incorporated with various additives, binders and a vehicle to make ink or a paste. Once the material is transferred on the substrate the vehicle and solvents have to be removed by evaporation and other chemical transformation. To achieve a dense layer of the functional material in the final feature predictable high loading of the powder in the paste or ink is necessary. A spherical particle shape is desirable to permit high loading at a given viscosity. Multimodal or broad size distributions are best attributes of the powder to achieve high loading by distribution of smaller particles between the interstices formed by larger particles. POWDER PRODUCTION ROUTES Table I is a summary of powder processes available to produce the desired oxide and metal powders. Three major routes, solid state; aerosol; and liquid precipitation are represented.
35 Mat. Res. Soc. Symp. Proc. Vol. 624 © 2000 Materials Research Society
Table 1: Powder Production Routes
Production
Applicability
Process
Particle
Shape
Size, ýtm.
Post Production
Comparative
Treatment
Cost
Primarily Inexpensive, post production processing may be expensive Value added offsets higher cost
Solid State Reaction
Single, multicomponent oxides
>5
Irregular
Calcination, size reduction
Spray Pyrolysis
Single, multicomponent oxides, metals,alloys Single oxides, metals,
0.5 - 15
Spherical
Calcination may be needed
10 nm to 1 pLm
Equi - axial, lacy
Calcination may be needed
Inexpensive in high volumes Contamination freedom and size control may be
Vapor Phase Reactor
agglomerates
nitrides,carbides
Solution Precipitation
Single, multicomponent oxides,
10 nm to several Jim
Varity of shapes possible
Calcination required
10 nm to several gm
Generally equi-axial
Calcination may not be required
expensive
hydroxides
Hydrothermal
Single, multicomponent oxides
Moderately expensive - high pressure equipment, batch processing
SOLID STATE ROUTE Solid state reactions represent the conventional technology used in produci
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