Coating processes – Particles – flakes – or granules coated or encapsulated
Reexamination Certificate
2000-06-21
2003-09-02
Kiliman, Leszek (Department: 1773)
Coating processes
Particles, flakes, or granules coated or encapsulated
C427S213000, C427S215000, C427S216000, C427S218000, C428S402000, C428S403000, C428S404000
Reexamination Certificate
active
06613383
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to particles having ultrathin coatings on their surfaces and to methods for making and using such coated particles.
Ceramics and metals are used in particulate form in a variety of industrial settings, such as in the electronics and structural advanced materials industries. It is often desirable to alter the surface properties of these particles while maintaining their bulk properties.
For example, in some cases the particles have reactive surfaces that can be attacked by the surrounding environment or which otherwise engage in undesirable reactions. In these cases, it is often desirable to passivate the reactive surfaces to inhibit these reactions from occurring.
Conversely, it is desirable in other situations to activate the particle surfaces for various reasons, such as to improve coupling to other materials (or between particles) or to promote desired chemical reactions. In this manner, it would be desired to provide for improved coupling at ceramic/polymeric, ceramic/metallic (cermet), or ceramic/ceramic (monolithic or composite) particulate interfaces. For example, boron nitride (BN) and aluminum nitride (AlN) particles have been developed as fillers for electronics packaging applications. These materials significantly enhance the thermal conductivity of polymer based composite packages, while maintaining good electrical insulation. These properties are becoming increasingly important as faster and denser integrated circuits are being developed by the microelectronics industry. The high thermal conductivity of BN and AlN make them attractive candidates for filler materials. However, the surfaces of BN and AlN particles are relatively nonreactive and do not adhere well to the coupling agents commonly used with these epoxy polymers. This incompatibility with the polymer makes it difficult to load these materials at levels sufficient for use with newer, high-density integrated circuits. Thus, it is desirable to find a way to improve the adhesion of these particles to the polymer matrix and to incorporate more of these nitride particles into the packaging material without significantly decreasing the thermal conductivity of the particles.
Another example of the desire to modify surface properties of materials comes from the ceramics industry. The development of sintering methods has enabled the widespread use of advanced ceramic materials for various applications. Densification of a ceramic material through sintering can be achieved by several methods that involve heating constituent particles either with pressure (such as hot-pressing, hot isostatic pressing, or gas pressure assisted sintering) or without pressure (such as pressureless sintering). Pressureless sintering is a preferred method due to its low cost. However, it requires the development of specialized processing formulations that usually involve liquid phase sintering. It is important to be able to control the surface properties of the constituent particles during pressureless sintering densification. In addition, it is desirable in these sintering applications to obtain a uniform dispersion of sintering aids, and to disperse the sintering aid as finely as possible.
Thus, it would be desirable to provide a method by which the surface properties of particulate materials can be modified without significantly changing the bulk properties of the particulate material.
SUMMARY OF THE INVENTION
In one aspect, this invention is a material in the form of particles having an average diameter of up to about 500 microns wherein the particles have an ultrathin, conformal coating on the surface thereof
In another aspect, this invention is a method for depositing an ultrathin conformal coating on particles, comprising conducting a sequence of two or more self-limiting reactions at the surface of said particles to form an ultrathin conformal coating bonded to the surface of said particles.
In a third aspect, this invention is a resin matrix filled with particles of an inorganic material, wherein the particles have an ultrathin conformal coating on their surfaces.
In a fourth aspect, this invention is a method of making a cermet part, comprising forming a shaped mass from a plurality of particles of a sinterable inorganic material that have an ultrathin conformal metal coating on their surfaces, and then exposing said shaped mass to conditions sufficient to sinter the particles to form a shaped part.
In a fifth aspect, this invention is a method of making a ceramic part, comprising forming a shaped mass from a plurality of particles of a sinterable inorganic material that have an ultrathin conformal coating of a sintering aid on their surfaces, and then exposing said shaped mass to conditions sufficient to sinter the particles to form a shaped part.
In a sixth aspect, this invention is a method of catalyzing a chemical reaction, comprising conducting said chemical reaction in the presence of particles having an average diameter of less than 500 microns and having on their surfaces an ultrathin conformal coating of a metal which is a catalyst for said chemical reaction.
DETAILED DESCRIPTION OF THE INVENTION
In this invention, ultrathin conformal coatings are provided onto the surfaces of various particulate materials. The size of the particles will depend somewhat on the particular material and the particular application. Suitable particle sizes range up to about 500 &mgr;m, with preferred particle sizes ranging from the nanometer range (e.g. about 0.001 &mgr;m) to about 100&mgr;m, more preferred particle sizes ranging from 0.005 to about 50 &mgr;m, even more preferred particle sizes ranging from about 0.1 to 10 &mgr;m and most preferred particle sizes ranging from about 0.4 to about 10 &mgr;m. Particle size can also be expressed in terms of the surface area of the particles. Preferred particulate materials have surface areas in the range of about 0.1 to 200 m
2
/g or more.
A wide variety of particulate materials can be used, with the composition of the base particle and that of the coating typically being selected together so that the surface characteristics of the particle are modified in a way that is desirable for a particular application. The base particles preferably have some functional group on the surface that can participate in a reaction sequence that creates the ultrathin coating. Examples of such functional groups include hydroxyl groups, amino groups and metal-hydrogen bonds, which can serve as a site of further reaction to allow formation of the ultrathin coating. If necessary, the surface of the particle can be treated to introduce such functional groups. Depending on the particular base particle, techniques such as water plasma treatment, ozone treatment, ammonia treatment and hydrogen treatment are among the useful methods of introducing functional groups.
Inorganic materials are of particular interest as the base particle. Several types that are of particular interest are those which (1) are sinterable with the use of a sintering aid to form a ceramic part, (2) are useful as high thermal conductivity fillers, such as for electronic packaging applications, (3) have reactive surfaces that are desirably passivated for certain applications, (4) are useful in making cermet (ceramic metallic) composite materials or (5) are useful supports for other materials, such as catalyst supports. It will be recognized that many materials are useful for more than one of these applications.
Examples of inorganic materials that can be sintered to form ceramic parts include, for example various nitrides, carbides, borides and other nonoxide ceramic materials.
Inorganic materials that are useful as high thermal conductivity fillers for electronics packaging applications preferably have bulk thermal conductivities of greater than about 3 W/mK, preferably greater than 5 W/mK, more preferably greater than 10 W/mK, even more preferably greater than about 15 W/mK and most preferably greater than about 200 W/mK. Suitable such materials include, for example, silicon dioxide, alumina, nitr
Ferguson John D.
George Steven M.
Weimer Alan W.
Cohn PLLC Gary C
Kiliman Leszek
Regents of the University of Colorado
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